Radio and the 1999 UK Total Solar Eclipse [EPA]

http://arxiv.org/abs/1703.01491

On the morning of the August 11th 1999, a total eclipse of the sun plunged Cornwall and parts of Devon into darkness. The event of the eclipse was bound to attract a great deal of scientific and media attention. Realizing that the differences in day-time/night-time propagation of VLF/LF/MF to HF bands would also apply during the darkness of the eclipse, the eclipse offered a rare PR opportunity to promote radio to the general public. At the same time the specific nature of the disturbance to the upper atmosphere and the effect on radio propagation could be examined in detail using scientific instruments at minimum cost since most instruments would not have to be moved. This would allow prediction models to be tested in a controlled fashion. Contained within this report are the details and results of the radio and ionospheric experiments conducted by the Rutherford Appleton Laboratory during the 1999 total solar eclipse. The promoting of the radio experiments with the general public produced nearly 60 appearances on local and national TV, newspapers and periodicals. Close to 1700 people responded to the general public medium wave experiment and 16 million people looked in on the general eclipse web site (part funded by RA) that included the details of the radio experiments. A large database of systematic observations across VLF to HF was collected from radio amateurs and from the RA Regional Offices allowing comparisons to be made with ITU estimates. There is a brief look at the scientific results and a forward look as to how the analysis of this disturbance might have impact on the use of ionospheric models for Space Weather tools in the future.

Read this paper on arXiv…

R. Bamford
Tue, 7 Mar 17
16/66

Comments: 41 pages, 33 Figures, government funded research final report, unclassified

Advertisement

Topological Origin of Geophysical Waves [CL]

http://arxiv.org/abs/1702.07583

Symmetries and topology are central to an understanding of physics. Topology explains the precise quantization of the Hall effect and the protection of surface states in topological insulators against scattering by non-magnetic impurities or bumps. Subsequent to the discovery of the quantum spin Hall effect, states of matter with different topological properties were classified according to the discrete symmetries of the system. Recently topologically protected edge excitations have been found in artificial lattice structures that support classical waves of various types. The interplay between discrete symmetries and the topology of fluid waves has so far played no role in the study of the dynamics of oceans and atmospheres. Here we show that, as a consequence of the rotation of the Earth that breaks time reversal symmetry, equatorially trapped Kelvin and Yanai waves have a topological origin, manifesting as equatorial edge modes in the rotating shallow water model. These unidirectional edge modes are guaranteed to exist by the non-trivial global structure of the bulk Poincar\’e modes encoded through the first Chern number of value $\pm2$, in agreement with the correspondence between behavior deep in the bulk and edge excitations of a physical system. Thus the oceans and atmospheres of Earth and other rotating planets naturally share fundamental properties with topological insulators, despite the absence of an underlying lattice. As equatorially trapped Kelvin waves are an important component of El Ni\~no Southern Oscillation, and Madden-Julian Oscillation, our results demonstrate the topology plays an unexpected role in Earth’s climate system. These and other geophysical waves of topological origin are protected against static perturbations by time scale separation from other modes that inhibits scattering.

Read this paper on arXiv…

P. Delplace, J. Marston and A. Venaille
Mon, 27 Feb 17
16/49

Comments: N/A

The theory of transmission spectra revisited: a fast method for analyzing WFC3 data and an unresolved challenge [EPA]

http://arxiv.org/abs/1702.02051

The computation of transmission spectra is a central ingredient in the study of exoplanetary atmospheres. First, we revisit the theory of transmission spectra, unifying ideas from several workers in the literature. Transmission spectra lack an absolute normalization due to the a priori unknown value of a reference transit radius, which is tied to an unknown reference pressure. We show that there is a degeneracy between the uncertainty in the transit radius, the assumed value of the reference pressure (typically set to 10 bar) and the inferred value of the water abundance when interpreting a WFC3 transmission spectrum. Second, we demonstrate that transmission spectra may be assumed to be isobaric, which simplifies the data analysis. We validate the isothermal, isobaric analytical formula for the transmission spectrum against full numerical calculations and show that the typical errors are $\sim 0.1\%$ ($\sim 10$ ppm) within the WFC3 range of wavelengths. Third, we generalize the previous formula for the transit radius to include a small temperature gradient. Finally, we analyze the measured WFC3 transmission spectrum of WASP-12b and demonstrate that we obtain consistent results with the retrieval approach of Kreidberg et al. (2015) if the reference transit radius and reference pressure are fixed to assumed values. The unknown functional relationship between the reference transit radius and reference pressure implies that it is the product of the water abundance and reference pressure that is being retrieved from the data, and not just the water abundance alone. This degeneracy leads to a fundamental limitation on how accurately we may extract molecular abundances from transmission spectra. We suggest an approximate expression for this relationship.

Read this paper on arXiv…

K. Heng and D. Kitzmann
Wed, 8 Feb 17
61/65

Comments: 9 pages, 6 figures, 2 tables

Room temperature line lists for CO\2 symmetric isotopologues with \textit{ab initio} computed intensities [EPA]

http://arxiv.org/abs/1701.08267

Remote sensing experiments require high-accuracy, preferably sub-percent, line intensities and in response to this need we present computed room temperature line lists for six symmetric isotopologues of carbon dioxide: $^{13}$C$^{16}$O$_2$, $^{14}$C$^{16}$O$_2$, $^{12}$C$^{17}$O$_2$, $^{12}$C$^{18}$O$_2$, $^{13}$C$^{17}$O$_2$ and $^{13}$C$^{18}$O$_2$, covering the range 0-8000 \cm. Our calculation scheme is based on variational nuclear motion calculations and on a reliability analysis of the generated line intensities. Rotation-vibration wavefunctions and energy levels are computed using the DVR3D software suite and a high quality semi-empirical potential energy surface (PES), followed by computation of intensities using an \abinitio\ dipole moment surface (DMS). Four line lists are computed for each isotopologue to quantify sensitivity to minor distortions of the PES/DMS. Reliable lines are benchmarked against recent state-of-the-art measurements and against the HITRAN2012 database, supporting the claim that the majority of line intensities for strong bands are predicted with sub-percent accuracy. Accurate line positions are generated using an effective Hamiltonian. We recommend the use of these line lists for future remote sensing studies and their inclusion in databases.

Read this paper on arXiv…

E. Zak, J. Tennyson, O. Polyansky, et. al.
Tue, 31 Jan 17
21/58

Comments: N/A

Forecasting surface layer atmospheric parameters at the LBT site [IMA]

http://arxiv.org/abs/1701.07341

In this paper we quantify the performances of an automated weather forecast system implemented on the Large Binocular Telescope (LBT) site at Mt. Graham (Arizona) in forecasting the main atmospheric parameters close to the ground. The system employs a mesoscale non-hydrostatic numerical model (Meso-Nh). To validate the model we compare the forecasts of wind speed, wind direction, temperature and relative humidity close to the ground with the respective values measured by instrumentation installed on the telescope dome. The study is performed over a large sample of nights uniformly distributed over two years. The quantitative analysis is done using classical statistical operators (bias, RMSE and $\sigma$) and contingency tables, which allows to extract complementary key information, such as the percentage of correct detection (PC) and the probability to obtain a correct detection within a defined interval of values (POD). Results of our study indicate that the model performances in forecasting the atmospheric parameters we have just cited are very good, in some cases excellent: RMSE for temperature is below 1{\deg} C, for relative humidity is 14%, for the wind speed is around 2.5m/s. The relative error of the RMSE for wind direction varies from 9% to 17% depending on the wind speed conditions. This work is performed in the context of ALTA (Advanced LBT Turbulence and Atmosphere) Center project, which final goal is to provide forecasts of all the atmospheric parameters and the optical turbulence to support LBT observations, adaptive optics facilities and interferometric facilities.

Read this paper on arXiv…

A. Turchi, E. Masciadri and L. Fini
Thu, 26 Jan 17
53/68

Comments: this http URL 22 pages, 16 figures, 21 tables

A Condensation-Coalescence Cloud Model for Exoplanetary Atmospheres: Formulation and Test Applications to Terrestrial and Jovian Clouds [EPA]

http://arxiv.org/abs/1701.00917

A number of transiting exoplanets have featureless transmission spectra that might suggest the presence of clouds at high altitudes. A realistic cloud model is necessary to understand the atmospheric conditions under which such high-altitude clouds can form. In this study, we present a new cloud model that takes into account the microphysics of both condensation and coalescence. Our model provides the vertical profiles of the size and density of cloud and rain particles in an updraft for a given set of physical parameters, including the updraft velocity and the number density of cloud condensation nuclei (CCN). We test our model by comparing with observations of trade-wind cumuli on the Earth and ammonia ice clouds in Jupiter. For trade-wind cumuli, the model including both condensation and coalescence gives predictions that are consistent with observations, while the model including only condensation overestimates the mass density of cloud droplets by up to an order of magnitude. For Jovian ammonia clouds, the condensation-coalescence model simultaneously reproduces the effective particle radius, cloud optical thickness, and cloud geometric thickness inferred from Voyager observations if the updraft velocity and CCN number density are taken to be consistent with the results of moist convection simulations and Galileo probe measurements, respectively. These results suggest that the coalescence of condensate particles is important not only in terrestrial water clouds but also in Jovian ice clouds. Our model will be useful to understand how the dynamics, compositions, and nucleation processes in exoplanetary atmospheresaffects the vertical extent and optical thickness of exoplanetary clouds via cloud microphysics.

Read this paper on arXiv…

K. Ohno and S. Okuzumi
Thu, 5 Jan 17
58/58

Comments: 11 pages, 7 figures, accepted for publication in ApJ

Evaluating the wind-induced mechanical noise on the InSight seismometers [CL]

http://arxiv.org/abs/1612.04308

The SEIS (Seismic Experiment for Interior Structures) instrument onboard the InSight mission to Mars is the critical instrument for determining the interior structure of Mars, the current level of tectonic activity and the meteorite flux. Meeting the performance requirements of the SEIS instrument is vital to successfully achieve these mission objectives. Here we analyse in-situ wind measurements from previous Mars space missions to understand the wind environment that we are likely to encounter on Mars, and then we use an elastic ground deformation model to evaluate the mechanical noise contributions on the SEIS instrument due to the interaction between the Martian winds and the InSight lander. Lander mechanical noise maps that will be used to select the best deployment site for SEIS once the InSight lander arrives on Mars are also presented. We find the lander mechanical noise may be a detectable signal on the InSight seismometers. However, for the baseline SEIS deployment position, the noise is expected to be below the total noise requirement >97% of the time and is, therefore, not expected to endanger the InSight mission objectives.

Read this paper on arXiv…

N. Murdoch, D. Mimoun, R. Garcia, et. al.
Wed, 14 Dec 16
63/67

Comments: 32 pages, 16 figures

Optical turbulence forecast: ready for an operational application [IMA]

http://arxiv.org/abs/1612.00711

One of the main goals of the feasibility study MOSE (MOdellig ESO Sites) is to evaluate the performances of a method conceived to forecast the optical turbulence above the ESO sites of the Very Large Telescope and the European-Extremely Large Telescope in Chile. The method implied the use of a dedicated code conceived for the optical turbulence (OT) called Astro-Meso-Nh. In this paper we present results we obtained at conclusion of this project concerning the performances of this method in forecasting the most relevant parameters related to the optical turbulence (CN2, seeing , isoplanatic angle theta_0 and wavefront coherence time tau_0). Numerical predictions related to a very rich statistical sample of nights uniformly distributed along a solar year and belonging to different years have been compared to observations and different statistical operators have been analyzed such as classical bias, RMSE and and more sophisticated statistical operators derived by the contingency tables that are able to quantify the score of success of a predictive method such as the percentage of correct detection (PC) and the probability to detect a parameter within a specific range of values (POD). The main conclusions of the study tell us that the Astro-Meso-Nh model provides performances that are already very good to definitely guarantee a not negligible positive impact on the Service Mode of top-class telescopes and ELTs. A demonstrator for an automatic and operational version of the Astro-Meso-Nh model will be soon implemented on the sites of VLT and E-ELT.

Read this paper on arXiv…

E. Masciadri, F. Lascaux, A. Turchi, et. al.
Mon, 5 Dec 16
5/61

Comments: This is a pre-copyedited, author-produced PDF of an article accepted for publication in MNRAS following peer review. The version of record [doi: 10.1093/mnras/stw3111] is available online at: this http URL&ijkey=te4TKA10zzdydVK. 13 figures

An Optical Atmospheric Phenomenon Observed in 1670 over the City of Astrakhan Was not a Mid-Latitude Aurora [CL]

http://arxiv.org/abs/1612.00705

It has been recently claimed (Zolotova and Ponyavin, Solar Phys., 291, 2869, 2016, ZP16 henceforth) that a mid-latitude optical phenomenon, which took place over the city of Astrakhan in July 1670, according to Russian chronicles, was a strong aurora borealis. If this was true, it would imply a very strong or even severe geomagnetic storm during the quietest part of the Maunder minimum. However, as we argue in this article, this conclusion is erroneous and caused by a misinterpretation of the chronicle record. As a result of a thorough analysis of the chronicle text, we show that the described phenomenon occurred during the daylight period of the day (“the last morning hour”), in the south direction (“towards noon”), and its description does not match that of an aurora. The date of the event was also incorrectly interpreted. We conclude that this phenomenon was not a mid-latitude aurora but an atmospheric phenomenon, the so-called sundog (or parhelion) which is a particular type of solar halo. Accordingly, the claim about a strong mid-latitude aurora during the deep Maunder minimum is not correct and should be dismissed.

Read this paper on arXiv…

I. Usoskin, G. Kovaltsov, L. Mishina, et. al.
Mon, 5 Dec 16
28/61

Comments: accepted to Solar Physics

Pressure-dependent water absorption cross sections for exoplanets and other atmospheres [EPA]

http://arxiv.org/abs/1610.09008

Many atmospheres (cool stars, brown dwarfs, giant planets, extrasolar planets) are predominately composed of molecular hydrogen and helium. H$_2{}^{16}$O is one of the best measured molecules in extrasolar planetary atmospheres to date and a major compound in the atmospheres of brown-dwarfs and oxygen-rich cool stars, yet the scope of experimental and theoretical studies on the pressure broadening of water vapour lines by collision with hydrogen and helium remains limited.
Theoretical H$_2$- and He-broadening parameters of water vapour lines (rotational quantum number $J$ up to 50) are obtained for temperatures in the range 300 – 2000 K. Two approaches for calculation of line widths were used: (i) the averaged energy difference method and (ii) the empirical expression for $J$\p $J$\pp-dependence.
Voigt profiles based on these widths and the BT2 line list are used to generate high resolution ($\Delta \tilde{\nu}$ = 0.01 \cm) pressure broadened cross sections for a fixed range of temperatures and pressures between 300 – 2000 K and 0.001 – 10 bar. An interpolation procedure which can be used to determine cross sections at intermediate temperature and pressure is described. Pressure broadening parameters and cross sections are presented in new ExoMol format.

Read this paper on arXiv…

E. Barton, C. Hill, S. Yurchenko, et. al.
Mon, 31 Oct 16
44/49

Comments: 40 pages, 5 Figures, 6 Tables JQSRT, in press

HELIOS-Retrieval: An Open-source, Nested Sampling Atmospheric Retrieval Code, Application to the HR 8799 Exoplanets and Inferred Constraints for Planet Formation [EPA]

http://arxiv.org/abs/1610.03216

We present an open-source retrieval code named HELIOS-Retrieval (hereafter HELIOS-R), designed to obtain chemical abundances and temperature-pressure profiles from inverting the measured spectra of exoplanetary atmospheres. In the current implementation, we use an exact solution of the radiative transfer equation, in the pure absorption limit, in our forward model, which allows us to analytically integrate over all of the outgoing rays (instead of performing Gaussian quadrature). Two chemistry models are considered: unconstrained chemistry (where the mixing ratios are treated as free parameters) and equilibrium chemistry (enforced via analytical formulae, where only the elemental abundances are free parameters). The nested sampling algorithm allows us to formally implement Occam’s Razor based on a comparison of the Bayesian evidence between models. We perform a retrieval analysis on the measured spectra of the HR 8799b, c, d and e directly imaged exoplanets. Chemical equilibrium is disfavored by the Bayesian evidence for HR 8799b, c and d. We find supersolar C/O, C/H and O/H values for the outer HR 8799b and c exoplanets, while the inner HR 8799d and e exoplanets have substellar C/O, substellar C/H and superstellar O/H values. If these retrieved properties are representative of the bulk compositions of the exoplanets, then they are inconsistent with formation via gravitational instability (without late-time accretion) and consistent with a core accretion scenario in which late-time accretion of ices occurred differently for the inner and outer exoplanets. For HR 8799e, we find that spectroscopy in the K band is crucial for constraining C/O and C/H. HELIOS-R is publicly available as part of the Exoclimes Simulation Platform (ESP; http://www.exoclime.org).

Read this paper on arXiv…

B. Lavie, J. Mendonca, C. Mordasini, et. al.
Wed, 12 Oct 16
3/64

Comments: 25 pages, 20 figures, 3 tables

On the astronomical origin of the Hallstatt oscillation found in radiocarbon and climate records throughout the Holocene [CL]

http://arxiv.org/abs/1610.03096

An oscillation with a period of about 2100-2500 years, the Hallstatt cycle, is found in cosmogenic radioisotopes (C-14 and Be-10) and in paleoclimate records throughout the Holocene. Herein we demonstrate the astronomical origin of this cycle. Namely, this oscillation is coherent to the major stable resonance involving the four Jovian planets – Jupiter, Saturn, Uranus and Neptune – whose period is p=2318 yr. The Hallstatt cycle could derive from the rhythmic variation of the circularity of the solar system disk assuming that this dynamics could eventually modulate the solar wind and, consequently, the incoming cosmic ray flux and/or the interplanetary/cosmic dust concentration around the Earth-Moon system. The orbit of the planetary mass center (PMC) relative to the Sun is used as a proxy. We analyzed how the instantaneous eccentricity vector of this virtual orbit varies from 13,000 B. C. to 17,000 A. D.. We found that it undergoes kind of pulsations as it clearly presents rhythmic contraction and expansion patterns with a 2318 yr period together with a number of already known faster oscillations associated to the planetary orbital stable resonances. We found that a fast expansion of the Sun-PMC orbit followed by a slow contraction appears to prevent cosmic rays to enter within the system inner region while a slow expansion followed by a fast contraction favors it. Similarly, the same dynamics could modulate the amount of interplanetary/cosmic dust falling on Earth. These would then cause both the radionucleotide production and climate change by means of a cloud/albedo modulation. Other stable orbital resonance frequencies (e.g. at periods of 20 yr, 45 yr, 60 yr, 85 yr, 159-171-185 yr, etc.) are found in radionucleotide, solar, aurora and climate records, as determined in the scientific literature. Thus, the result supports a planetary theory of solar and/or climate variation.

Read this paper on arXiv…

N. Scafetta, F. Milani, A. Bianchini, et. al.
Wed, 12 Oct 16
52/64

Comments: 36 pages, 14 figures, 1 table

Atmospheric Refraction [CL]

http://arxiv.org/abs/1609.08921

Calculations of atmospheric refraction are generally based on a simplified model of atmospheric density in the troposphere which assumes that the temperature decreases at a constant lapse rate from sea level up to a height equal to eleven km, and that afterwards it remains constant. In this model, the temperature divided by the lapse rate determines the length scale in the calculations for altitudes less than this height. But daily balloon measurements across the U.S.A. reveal that in some cases the air temperature actually increases from sea level up to a height of about one km, and only after reaching a plateau, it decreases at an approximately constant lapse rate. Moreover, in three examples considered here, the temperature does not remain constant at eleven km , but continues to decreases to a minimum at about sixteen kilometers , and then increases at higher altitudes at a lower rate. Calculations of atmospheric refraction based on this atmospheric data is compared with the results of simplified models.

Read this paper on arXiv…

M. Nauenberg
Thu, 29 Sep 16
15/76

Comments: 12 pages, 5 figures

Exploring the Venus global super-rotation using a comprehensive General Circulation Model [EPA]

http://arxiv.org/abs/1609.06549

The atmospheric circulation in Venus is well known to exhibit strong super-rotation. However, the atmospheric mechanisms responsible for the formation of this super-rotation are still not fully understood. In this work, we developed a new Venus general circulation model to study the most likely mechanisms driving the atmosphere to the current observed circulation. Our model includes a new radiative transfer, convection and suitably adapted boundary layer schemes and a dynamical core that takes into account the dependence of the heat capacity at constant pressure with temperature.
The new Venus model is able to simulate a super-rotation phenomenon in the cloud region quantitatively similar to the one observed. The mechanisms maintaining the strong winds in the cloud region were found in the model results to be a combination of zonal mean circulation, thermal tides and transient waves. In this process, the semi-diurnal tide excited in the upper clouds has a key contribution in transporting axial angular momentum mainly from the upper atmosphere towards the cloud region. The magnitude of the super-rotation in the cloud region is sensitive to various radiative parameters such as the amount of solar radiative energy absorbed by the surface, which controls the static stability near the surface. In this work, we also discuss the main difficulties in representing the flow below the cloud base in Venus atmospheric models.
Our new radiative scheme is more suitable for 3D Venus climate models than those used in previous work due to its easy adaptability to different atmospheric conditions. This flexibility of the model was crucial to explore the uncertainties in the lower atmospheric conditions and may also be used in the future to explore, for example, dynamical-radiative-microphysical feedbacks.

Read this paper on arXiv…

J. Mendonca and P. Read
Thu, 22 Sep 16
31/62

Comments: Accepted for publication in Planet. Space Sci

A statistical state dynamics based theory for the formation and equilibration of Saturn's North Polar Jet [CL]

http://arxiv.org/abs/1609.06170

Coherent jets containing most of the kinetic energy of the flow are a common feature in observations of atmospheric turbulence. In the gaseous planets these jets are maintained by incoherent turbulence excited by small scale convection. Large scale coherent waves are sometimes observed to coexist with the jets; a prominent example being Saturns hexagonal north polar jet (NPJ). Observations of the large scale jet/wave coexistence regime raises the question of identifying the mechanism responsible for forming and maintaining this turbulent state. The coherent planetary scale component of the turbulence arises and is maintained by interaction with the incoherent small-scale turbulence component. It follows that theoretical understanding of the dynamics of the jet/wave/turbulence coexistence regime is facilitated by employing a statistical state dynamics (SSD) model in which the interaction between coherent and incoherent components is explicitly represented. In this work a second order closure implementation of a two-layer beta-plane SSD is used to develop a theory that accounts for the structure and dynamics of the NPJ. Analysis with this model of the jet/wave/turbulence regime dynamics reveals that jet formation is controlled by the effective value of $\beta$ and the required value of this parameter for correspondence with observation is obtained. As this is a robust prediction it is taken as an indirect observation of a deep poleward sloping stable layer beneath the NPJ. The slope required is obtained from observations of NPJ structure as is the small scale turbulence excitation required to maintain the jet. The observed jet structure is then predicted by the theory as is the wave six disturbance. This wave, which is identified with the least stable mode of the equilibrated jet, is shown to be primarily responsible for equilibrating the jet with the observed structure and amplitude.

Read this paper on arXiv…

B. Farrell and P. Ioannou
Wed, 21 Sep 16
46/53

Comments: submitted to Phys. Rev. Fluids

The new world atlas of artificial night sky brightness [IMA]

http://arxiv.org/abs/1609.01041

Artificial lights raise night sky luminance, creating the most visible effect of light pollution-artificial skyglow. Despite the increasing interest among scientists in fields such as ecology, astronomy, health care, and land-use planning, light pollution lacks a current quantification of its magnitude on a global scale. To overcome this, we present the world atlas of artificial sky luminance, computed with our light pollution propagation software using new high-resolution satellite data and new precision sky brightness measurements. This atlas shows that more than 80% of the world and more than 99% of the U.S. and European populations live under light-polluted skies. The Milky Way is hidden from more than one-third of humanity, including 60% of Europeans and nearly 80% of North Americans. Moreover, 23% of the world’s land surfaces between 75{\deg}N and 60{\deg}S, 88% of Europe, and almost half of the United States experience light-polluted nights.

Read this paper on arXiv…

F. Falchi, P. Cinzano, D. Duriscoe, et. al.
Tue, 6 Sep 16
15/74

Comments: 26 pages, 19 figures, 3 tables

Role of gravity waves in vertical coupling during sudden stratospheric warmings [CL]

http://arxiv.org/abs/1609.00734

Gravity waves are primarily generated in the lower atmosphere, and can reach thermospheric heights in the course of their propagation. This paper reviews the recent progress in understanding the role of gravity waves in vertical coupling during sudden stratospheric warmings. Modeling of gravity wave effects is briefly reviewed, and the recent developments in the field are presented. Then, the impact of these waves on the general circulation of the upper atmosphere is outlined. Finally, the role of gravity waves in vertical coupling between the lower and the upper atmosphere is discussed in the context of sudden stratospheric warmings.

Read this paper on arXiv…

E. Yigit and A. Medvedev
Tue, 6 Sep 16
64/74

Comments: Accepted for publication in Geoscience Letters

Forecasts of the atmospherical parameters close to the ground at the LBT site in the context of the ALTA project [IMA]

http://arxiv.org/abs/1609.00237

In this paper we study the abilities of an atmospherical mesoscale model in forecasting the classical atmospherical parameters relevant for astronomical applications at the surface layer (wind speed, wind direction, temperature, relative humidity) on the Large Binocular Telescope (LBT) site – Mount Graham, Arizona. The study is carried out in the framework of the ALTA project aiming at implementing an automated system for the forecasts of atmospherical parameters (Meso-Nh code) and the optical turbulence (Astro-Meso-Nh code) for the service-mode operation of the LBT. The final goal of such an operational tool is to provide predictions with high time frequency of atmospheric and optical parameters for an optimized planning of the telescope operation (dome thermalization, wind-dependent dome orientation, observation planning based on predicted seeing, adaptive optics optimization, etc…). Numerical simulations are carried out with the Meso-Nh and Astro-Meso-Nh codes, which were proven to give excellent results in previous studies focused on the two ESO sites of Cerro Paranal and Cerro Armazones (MOSE Project). In this paper we will focus our attention on the comparison of atmospherical parameters forescasted by the model close to the ground with measurements taken by the observatory instrumentations and stored in the LBT telemetry in order to validate the numerical predictions. As previously done for Cerro Paranal (Lascaux et al., 2015), we will also present an analysis of the model performances based on the method of the contingency tables, that allows us to provide complementary key information with the respect to the bias and RMSE (systematic and statistical errors), such as the percentage of correct detection and the probability to obtain a correct detection inside a defined interval of values.

Read this paper on arXiv…

A. Turchi, E. Masciadri and L. Fini
Fri, 2 Sep 16
45/49

Comments: 13 pages, 11 figures, Proc. SPIE 9909 “Adaptive Optics Systems V”, 990938, 2016

Plasma-screening effects in the atrophysically relevant He-like and Li-like Mg and Fe ions [CL]

http://arxiv.org/abs/1608.07919

The effect of plasma environment on the atomic energy levels of He-like and Li-like Mg and Fe ions have been studied using Debye model. The equation-of-motion coupled-cluster (EOMCC) and Fock-space coupled-cluster (FSCC) formalisms in the relativistic frame work have been adopted to describe the atomic states and the energy levels of the above plasma embedded ions. Salient features of these methods have been described to account the two electron screening effects through the Debye potentials. The two-body screening potential has been derived in the multipole expansion form to evaluate the reduced matrix elements in solving the equation of motion. Using this extended model, we have also predicted that quasi-degeneracy among the energy states having same principal quantum number ($n$) but different angular momentum ($l$) is slacken, whereas fine structure splitting is unaffected with increasing plasma strength. These knowledge are useful in estimatingradiative opacity, photoionization cross sections, line intensities, etc of the aforementioned astrophysical plasmas.

Read this paper on arXiv…

B. Sahoo and M. Das
Tue, 30 Aug 16
30/78

Comments: 10 pages, 5 tables and 4 figures

Tutorial models of the climate and habitability of Proxima Centauri b: a thin atmosphere is sufficient to distribute heat given low stellar flux [EPA]

http://arxiv.org/abs/1608.07263

Proxima Centauri b, an Earth-size planet in the habitable zone of our nearest stellar neighbour, has just been discovered. A theoretical framework of synchronously rotating planets, in which the risk of a runaway greenhouse on the sunlight side and atmospheric collapse on the reverse side are mutually ameliorated via heat transport is discussed. This is developed via simple (tutorial) models of the climate. These show that lower incident stellar flux means that less heat transport, so less atmospheric mass, is required. The incident stellar flux at Proxima Centauri b is indeed low, which may help enhance habitability if it has suffered some atmospheric loss or began with a low volatile inventory.

Read this paper on arXiv…

C. Goldblatt
Fri, 26 Aug 16
31/47

Comments: 7 pages, 3 figures. Submitted to ApJ Lett

Towards an automatic system for monitoring of CN2 and wind speed profiles with GeMS [IMA]

http://arxiv.org/abs/1608.06489

Wide Field Adaptive Optics (WFAO) systems represent the more sophisticated AO systems available today at large telescopes. A critical aspect for these WFAO systems in order to deliver an optimised performance is the knowledge of the vertical spatiotemporal distribution of the CN2 and the wind speed. Previous studies (Cortes et al., 2012) already proved the ability of GeMS (the Gemini Multi-Conjugated AO system) in retrieving CN2 and wind vertical stratification using the telemetry data. To assess the reliability of the GeMS wind speed estimates a preliminary study (Neichel et al., 2014) compared wind speed retrieved from GeMS with that obtained with the atmospherical model Meso-Nh on a small sample of nights providing promising results. The latter technique is very reliable for the wind speed vertical stratification. The model outputs gave, indeed, an excellent agreement with a large sample of radiosoundings (~ 50) both in statistical terms and on individual flights (Masciadri et al., 2013). Such a tool can therefore be used as a valuable reference in this exercise of cross calibrating GeMS on-sky wind estimates with model predictions. In this contribution we achieved a two-fold results: (1) we extended analysis on a much richer statistical sample (~ 43 nights), we confirmed the preliminary results and we found an even better correlation between GeMS observations and the atmospherical model with basically no cases of not-negligible uncertainties; (2) we evaluate the possibility to use, as an input for GeMS, the Meso-Nh estimates of the wind speed stratification in an operational configuration. Under this configuration these estimates can be provided many hours in advanced with respect to the observations and with a very high temporal frequency (order of 2 minutes or less).

Read this paper on arXiv…

E. Masciadri, B. Neichel, A. Guesalaga, et. al.
Wed, 24 Aug 16
28/52

Comments: 12 pages, 7 figures, Proc. SPIE 9909 “Adaptive Optics Systems V”, 99093B, 2016

Buoyancy driven turbulence and distributed chaos [CL]

http://arxiv.org/abs/1608.00489

It is shown, using results of recent direct numerical simulations, laboratory experiments and atmospheric measurements, that buoyancy driven turbulence exhibits a broad diversity of the types of distributed chaos with its stretched exponential spectrum $\exp(-k/k_{\beta})^{\beta}$. The distributed chaos with $\beta = 1/3$ (determined by the helicity correlation integral) is the most common feature of the stably stratified turbulence (due to the strong helical waves presence). These waves mostly dominate spectral properties of the vertical component of velocity field, while the horizontal component is dominated by the diffusive processes both for the weak and strong stable stratification ($\beta =2/3$). For the last case influence of the low boundary can overcome the wave effects and result in $\beta =1/2$ for the vertical component of the velocity field (the spontaneous breaking of the space translational symmetry – homogeneity). For the unstably stratified turbulence in the Rayleigh-Taylor mixing zone the diffusive processes ($\beta =2/3$) are the most common dominating processes in the anisotropic chaotic mixing of the two fluids under buoyancy forces. The distributed chaos in Rayleigh-B\'{e}nard turbulent convection in an upright cell is determined by the strong confinement conditions. That is: the spontaneous breaking of the space translational symmetry (homogeneity) by the finite boundaries ($\beta = 1/2$) or by the non-perfect orientation of the cell along the buoyancy direction ($\beta =4/7$). In all types of turbulence appearance of an inertial range of scales results in deformation of the distributed chaos and $\beta =3/5$.

Read this paper on arXiv…

A. Bershadskii
Wed, 24 Aug 16
38/52

Comments: N/A

Operational optical turbulence forecast for the Service Mode of top-class ground based telescopes [IMA]

http://arxiv.org/abs/1608.06506

In this contribution we present the most relevant results obtained in the context of a feasibility study (MOSE) undertaken for ESO. The principal aim of the project was to quantify the performances of a mesoscale model (Astro-Meso-NH code) in forecasting all the main atmospherical parameters relevant for the ground-based astronomical observations and the optical turbulence (CN2 and associated integrated astroclimatic parameters) above Cerro Paranal (site of the VLT) and Cerro Armazones (site of the E-ELT). A detailed analysis on the score of success of the predictive capacities of the system have been carried out for all the astroclimatic as well as for the atmospherical parameters. Considering the excellent results that we obtained, this study proved the opportunity to implement on these two sites an automatic system to be run nightly in an operational configuration to support the scheduling of scientific programs as well as of astronomical facilities (particularly those supported by AO systems) of the VLT and the E-ELT. At the end of 2016 a new project for the implementation of a demonstrator of an operational system to be run on the two ESO’s sites will start. Our team is also responsible for the implementation of a similar automatic system at Mt.Graham, site of the LBT (ALTA Project). Our system/method will permit therefore to make a step ahead in the framework of the Service Mode for new generation telescopes. Among the most exciting achieved results we cite the fact that we proved to be able to forecast CN2 profiles with a vertical resolution as high as 150 m. Such a feature is particularly crucial for all WFAO systems that require such detailed information on the OT vertical stratification on the whole 20 km above the ground. This important achievement tells us that all the WFAO systems can rely on automatic systems that are able to support their optimized use.

Read this paper on arXiv…

E. Masciadri, F. Lascaux, A. Turchi, et. al.
Wed, 24 Aug 16
50/52

Comments: 11 pages, 8 figures, Proc. SPIE 9909 “Adaptive Optics Systems V”, 99090I, 2016

Turbulent thermal diffusion in strongly stratified turbulence: theory and experiments [CL]

http://arxiv.org/abs/1608.05030

Turbulent thermal diffusion is a combined effect of the temperature stratified turbulence and inertia of small particles. It causes the appearance of a non-diffusive turbulent flux of particles in the direction of the turbulent heat flux. This non-diffusive turbulent flux of particles is proportional to the product of the mean particle number density and the effective velocity of inertial particles. The theory of this effect has been previously developed only for small temperature gradients and small Stokes numbers (Phys. Rev. Lett. {\bf 76}, 224, 1996). In this study a generalized theory of turbulent thermal diffusion for arbitrary temperature gradients and Stokes numbers has been developed. The laboratory experiments in the oscillating grid turbulence and in the multi-fan produced turbulence have been performed to validate the theory of turbulent thermal diffusion in strongly stratified turbulent flows. It has been shown that the ratio of the effective velocity of inertial particles to the characteristic vertical turbulent velocity for large Reynolds numbers is less than 1. The effective velocity of inertial particles as well as the effective coefficient of turbulent thermal diffusion increase with Stokes numbers reaching the maximum at small Stokes numbers and decreases for larger Stokes numbers. The effective coefficient of turbulent thermal diffusion also decreases with the mean temperature gradient. It has been demonstrated that the developed theory is in a good agreement with the results of the laboratory experiments.

Read this paper on arXiv…

G. Amir, N. Bar, A. Eidelman, et. al.
Thu, 18 Aug 16
24/51

Comments: 10 pages, 6 figures, REVTEX4-1

Jets or vortices – what flows are generated by an inverse turbulent cascade? [CL]

http://arxiv.org/abs/1608.04628

An inverse cascade – energy transfer to progressively larger scales – is a salient feature of two-dimensional turbulence. If the cascade reaches the system scale, it creates a coherent flow expected to have the largest available scale and conform with the symmetries of the domain. In a doubly periodic rectangle, the mean flow with zero total momentum was therefore believed to be unidirectional, with two jets along the short side; while for an aspect ratio close to unity, a vortex dipole was expected. Using direct numerical simulations, we show that in fact neither the box symmetry is respected nor the largest scale is realized: the flow is never purely unidirectional since the inverse cascade produces coherent vortices, whose number and relative motion are determined by the aspect ratio. This spontaneous symmetry breaking is closely related to the hierarchy of averaging times. Long-time averaging restores translational invariance due to vortex wandering along one direction, and gives jets whose profile, however, can be deduced neither from the largest-available-scale argument, nor from the often employed maximum-entropy principle or quasi-linear approximation.

Read this paper on arXiv…

A. Frishman, J. Laurie and G. Falkovich
Wed, 17 Aug 16
6/48

Comments: N/A

Dynamics of atmospheres with a non-dilute condensible component [EPA]

http://arxiv.org/abs/1608.03294

The diversity of characteristics for the host of recently discovered exoplanets opens up a great deal of fertile new territory for geophysical fluid dynamics, particularly when the fluid flow is coupled to novel thermodynamics, radiative transfer or chemistry. In this paper, we survey one of these new areas-the climate dynamics of atmospheres with a non-dilute condensible component, defined as the situation in which a condensible component of the atmosphere makes up a substantial fraction of the atmospheric mass within some layer. Non-dilute dynamics can occur for a wide range of condensibles, generically applying near both the inner and the outer edges of the conventional habitable zone and in connection with runaway greenhouse phenomena. It also applies in a wide variety of other planetary circumstances. We first present a number of analytical results developing some key features of non-dilute atmospheres, and then show how some of these features are manifest in simulations with a general circulation model adapted to handle non-dilute atmospheres. We find that non-dilute atmospheres have weak horizontal temperature gradients even for rapidly rotating planets, and that their circulations are largely barotropic. The relative humidity of the condensible component tends towards 100% as the atmosphere becomes more non-dilute, which has important implications for runaway greenhouse thresholds. Non-dilute atmospheres exhibit a number of interesting organized convection features, for which there is not yet any adequate theoretical understanding.

Read this paper on arXiv…

R. Pierrehumbert and F. Ding
Fri, 12 Aug 16
8/38

Comments: Accepted for publication in Proc. R. Soc. A

Convection in Condensible-rich Atmospheres [EPA]

http://arxiv.org/abs/1608.03216

Condensible substances are nearly ubiquitous in planetary atmospheres. For the most familiar case-water vapor in Earth’s present climate-the condensible gas is dilute, in the sense that its concentration is everywhere small relative to the noncondensible background gases. A wide variety of important planetary climate problems involve nondilute condensible substances. These include planets near or undergoing a water vapor runaway and planets near the outer edge of the conventional habitable zone, for which CO2 is the condensible. Standard representations of convection in climate models rely on several approximations appropriate only to the dilute limit, while nondilute convection differs in fundamental ways from dilute convection. In this paper, a simple parameterization of convection valid in the nondilute as well as dilute limits is derived and used to discuss the basic character of nondilute convection. The energy conservation properties of the scheme are discussed in detail and are verified in radiative-convective simulations. As a further illustration of the behavior of the scheme, results for a runaway greenhouse atmosphere for both steady instellation and seasonally varying instellation corresponding to a highly eccentric orbit are presented. The latter case illustrates that the high thermal inertia associated with latent heat in nondilute atmospheres can damp out the effects of even extreme seasonal forcing.

Read this paper on arXiv…

F. Ding and R. Pierrehumbert
Thu, 11 Aug 16
31/51

Comments: Accepted for publication in ApJ with minor revisions

Geostrophic wind induced by latitudinal variation in gravitational acceleration on oblate planets [EPA]

http://arxiv.org/abs/1608.02536

The population of known extrasolar planets includes giant and terrestrial planets that closely orbit their host star. Such planets experience significant tidal distortions that can force the planet into synchronous rotation. The combined effects of tidal deformation and centripetal acceleration induces significant asphericity in the shape of these planets, compared to the mild oblateness of Earth, with maximum gravitational acceleration at the poles. Here we show that this latitudinal variation in gravitational acceleration is relevant for modeling the climate of oblate planets including Jovian planets within the solar system, closely-orbiting hot Jupiters, and planets within the habitable zone of white dwarfs. We compare first- and third-order approximations for gravitational acceleration on an oblate spheroid and calculate the geostrophic wind that would result from this asphericity on a range of solar system planets and exoplanets. Third-order variations in gravitational acceleration are negligible for Earth but become significant for Jupiter, Saturn, and Jovian exoplanets. This latitudinal variation in gravitational acceleration can be measured remotely, and the formalism presented here can be implemented for use in general circulation climate modeling studies of exoplanet atmospheres.

Read this paper on arXiv…

J. Haqq-Misra, P. Saxena, E. Wolf, et. al.
Tue, 9 Aug 2016
3/71

Comments: Submitted to Monthly Notices of the Royal Astronomical Society

Polarized Scattering and Biosignatures in Exoplanetary Atmospheres [EPA]

http://arxiv.org/abs/1607.06874

Polarized scattering in planetary atmospheres is computed in the context of exoplanets. The problem of polarized radiative transfer is solved for a general case of absorption and scattering, while Rayleigh and Mie polarized scattering are considered as most relevant examples. We show that (1) relative contributions of single and multiple scattering depend on the stellar irradiation and opacities in the planetary atmosphere; (2) cloud (particle) physical parameters can be deduced from the wavelength-dependent measurements of the continuum polarization and from a differential analysis of molecular band absorption; (3) polarized scattering in molecular bands increases the reliability of their detections in exoplanets; (4) photosynthetic life can be detected on other planets in visible polarized spectra with high sensitivity. These examples demonstrate the power of spectropolarimetry for exoplanetary research and for searching for life in the universe.

Read this paper on arXiv…

S. Berdyugina
Tue, 26 Jul 16
11/75

Comments: JQSRT, accepted, 12 pages

THOR: A New and Flexible Global Circulation Model to Explore Planetary Atmospheres [EPA]

http://arxiv.org/abs/1607.05535

We have designed and developed, from scratch, a global circulation model named THOR that solves the three-dimensional non-hydrostatic Euler equations. Our general approach lifts the commonly used assumptions of a shallow atmosphere and hydrostatic equilibrium. We solve the “pole problem” (where converging meridians on a sphere lead to increasingly smaller time steps near the poles) by implementing an icosahedral grid. Irregularities in the grid, which lead to grid imprinting, are smoothed using the “spring dynamics” technique. We validate our implementation of spring dynamics by examining calculations of the divergence and gradient of test functions. To prevent the computational time step from being bottlenecked by having to resolve sound waves, we implement a split-explicit method together with a horizontally explicit and vertically implicit integration. We validate our global circulation model by reproducing the Earth and also the hot Jupiter-like benchmark tests. THOR was designed to run on Graphics Processing Units (GPUs), which allows for physics modules (radiative transfer, clouds, chemistry) to be added in the future, and is part of the open-source Exoclimes Simulation Platform (ESP; http://www.exoclime.org).

Read this paper on arXiv…

J. Mendonca, S. Grimm, L. Grosheintz, et. al.
Wed, 20 Jul 16
28/66

Comments: Accepted for publication in ApJ

Lightning climatology of exoplanets and brown dwarfs guided by Solar System data [EPA]

http://arxiv.org/abs/1606.09172

Clouds form on extrasolar planets and brown dwarfs where lightning could occur. Lightning is a tracer of atmospheric convection, cloud formation and ionization processes as known from the Solar System, and may be significant for the formation of prebiotic molecules. We study lightning climatology for the different atmospheric environments of Earth, Venus, Jupiter and Saturn. We present lightning distribution maps for Earth, Jupiter and Saturn, and flash densities for these planets and Venus, based on optical and/or radio measurements from the WWLLN and STARNET radio networks, the LIS/OTD satellite instruments, the Galileo, Cassini, New Horizons and Venus Express spacecraft. We also present flash densities calculated for several phases of two volcano eruptions, Eyjafjallaj\”okull’s (2010) and Mt Redoubt’s (2009). We estimate lightning rates for sample, transiting and directly imaged extrasolar planets and brown dwarfs. Based on the large variety of exoplanets, six categories are suggested for which we use the lightning occurrence information from the Solar System. We examine lightning energy distributions for Earth, Jupiter and Saturn. We discuss how strong stellar activity may support lightning activity. We provide a lower limit of the total number of flashes that might occur on transiting planets during their full transit as input for future studies. We find that volcanically very active planets might show the largest lightning flash densities. When applying flash densities of the large Saturnian storm from 2010/11, we find that the exoplanet HD 189733b would produce high lightning occurrence even during its short transit.

Read this paper on arXiv…

G. Hodosan, C. Helling, R. Asensio-Torres, et. al.
Thu, 30 Jun 16
36/59

Comments: 24 pages, 7 figures, 7 tables, accepted for publication in MNRAS

Reply to comment by K.A. Duderstadt et al. on "Atmospheric ionization by high-fluence, hard spectrum solar proton events and their probable appearance in the ice core archive" [CL]

http://arxiv.org/abs/1606.08792

Duderstadt et al. [2016b] comment that the Melott et al. [2016] study of nitrate formation by solar proton events (SPEs) and comparison with the ice core archive is “fundamentally flawed,” because it does not include pre-existing HNO3 in the stratosphere. We show that they exaggerate both the enhancement predicted by our findings and pre-industrial HNO3 levels in their model, and fail to prove this assertion. Our feasibility study matched expected SPE nitrate production with ground truth measurements. It is not clear that their approach is more realistic and absence of a detailed mechanism does not disprove our results. Models can be no better than the information they are provided and in this case there continue to be significant unknowns and uncertainties, especially in the role of polar stratospheric clouds (PSCs) and possible interactions with cosmic rays that constitute lower boundary conditions. Duderstadt et al. [2014; 2016a] used incomplete, poorly-constrained and incorrect initial and boundary conditions, and they continue to advocate on the basis of uncertain results. Meanwhile, Smart et al. [2014] identified a series of ice core nitrate spikes that have since been confirmed in 10Be by McCracken and Beer [2015]. Melott et al. [2016] computationally reproduced the ionization profile of the only major balloon measurements to date. We show that our calculated nitrate enhancement is consistent with measured results, given current levels of uncertainty, and that extreme SPEs can potentially produce occasional nitrate spikes with hundreds of percent increases. Instead of repeating old arguments to dismiss nitrates as proxies of SPEs, it is past time for a dedicated, fine-resolution, multi-parameter, replicate ice core field campaign to resolve this debate.

Read this paper on arXiv…

C. Laird, A. Melott, B. Thomas, et. al.
Wed, 29 Jun 16
44/60

Comments: Invited reply, submitted to JGR-Atmospheres

In Situ and Ex Situ Formation Models of Kepler 11 Planets [EPA]

http://arxiv.org/abs/1606.08088

We present formation simulations of the six Kepler 11 planets. Models assume either in situ or ex situ assembly, the latter with migration, and are evolved to the estimated age of the system, 8 Gyr. Models combine detailed calculations of both the gaseous envelope and the condensed core structures, including accretion of gas and solids, of the disk’s viscous and thermal evolution, including photo-evaporation and disk-planet interactions, and of the planets’ evaporative mass loss after disk dispersal. Planet-planet interactions are neglected. Both sets of simulations successfully reproduce measured radii, masses, and orbital distances of the planets, except for the radius of Kepler 11b, which loses its entire gaseous envelope shortly after formation. Gaseous (H+He) envelopes account for < 18% of the planet masses, and between 35 and 60% of the planet radii. In situ models predict a very massive inner disk, whose solids’ surface density (sigma_Z) varies from over 1e4 to 1e3 g/cm2 at stellocentric distances 0.1 < r < 0.5 AU. Initial gas densities would be in excess of 1e5 g/cm2 if solids formed locally. Given the high disk temperatures (> 1000 K), planetary interiors can only be composed of metals and highly refractory materials. Sequestration of hydrogen by the core and subsequent outgassing is required to account for the observed radius of Kepler 11b. Ex situ models predict a relatively low-mass disk, whose initial sigma_Z varies from 10 to 5 g/cm2 at 0.5 < r < 7 AU and whose initial gas density ranges from 1e3 to 100 g/cm2. All planetary interiors are expected to be rich in H2O, as core assembly mostly occurs exterior to the ice condensation front. Kepler 11b is expected to have a steam atmosphere, and H2O is likely mixed with H+He in the envelopes of the other planets. Results indicate that Kepler 11g may not be more massive than Kepler 11e.

Read this paper on arXiv…

G. DAngelo and P. Bodenheimer
Tue, 28 Jun 16
17/58

Comments: 34 pages, 19 figures, 8 tables. Accepted for publication in The Astrophysical Journal

Comment on "Atmospheric ionization by high-fluence, hard spectrum solar proton events and their probable appearance in the ice core archive" by A.L. Melott et al [CL]

http://arxiv.org/abs/1606.07471

Melott et al. [2016] suggest that individual solar proton events (SPEs) are detectable as nitrate ion spikes in ice cores. They use the high fluence, high energy (hard spectrum) SPE of 23 February 1956 to calculate an enhancement of HNO3 from the surface to 46 km that is equivalent to a ~120 ng cm-2 nitrate ion spike observed in the GISP2H ice core. The Melott et al. [2016] approach is fundamentally flawed, since it considers only the absolute column burden of SPE-produced nitrate and not the pre-existing nitrate in the stratosphere. Modeling studies supported by extensive observations [Duderstadt et al., 2014, 2016, and this comment] show background HNO3 in the lower and middle stratosphere equivalent to 2000 to 3000 ng cm-2 nitrate. These high levels of background nitrate must also be included when estimating SPE enhancements to the deposition of nitrate ions that might eventually be preserved in an ice core. The 1956 SPE results in less than a 5% increase in the column burden of atmospheric HNO3, not large enough to explain the nitrate spike seen in the GISP2H ice core. Even extreme SPE enhancements cannot explain nitrate peaks (typically hundreds of percent increases) observed in the ice record [Duderstadt et al., 2016]. Realistic mechanisms linking nitrate ions in ice cores to SPEs have not been established. It is time to move the search for indicators of SPEs away from nitrate ions: Nitrate ions cannot be used as proxies for individual SPEs in the ice core record.

Read this paper on arXiv…

K. Duderstadt, J. Dibb, C. Jackman, et. al.
Mon, 27 Jun 16
29/43

Comments: 17 pages, 3 figures

A Cloudiness Index for Transiting Exoplanets Based on the Sodium and Potassium Lines: Tentative Evidence for Hotter Atmospheres Being Less Cloudy at Visible Wavelengths [EPA]

http://arxiv.org/abs/1606.07218

We present a dimensionless index that quantifies the degree of cloudiness of the atmosphere of a transiting exoplanet. Our cloudiness index is based on measuring the transit radii associated with the line center and wing of the sodium or potassium line. In deriving this index, we revisited the algebraic formulae for inferring the isothermal pressure scale height from transit measurements. We demonstrate that the formulae of Lecavelier et al. and Benneke & Seager are identical: the former is inferring the temperature while assuming a value for the mean molecular mass and the latter is inferring the mean molecular mass while assuming a value for the temperature. More importantly, these formulae cannot be used to distinguish between cloudy and cloudfree atmospheres. We derive values of our cloudiness index for a small sample of 7 hot Saturns/Jupiters taken from Sing et al. We show that WASP-17b, WASP-31b and HAT-P-1b are nearly cloudfree at visible wavelengths. We find the tentative trend that more irradiated atmospheres tend to have less clouds consisting of sub-micron-sized particles. We also derive absolute sodium and/or potassium abundances $\sim 10^2$ cm$^{-3}$ for WASP-17b, WASP-31b and HAT-P-1b (and upper limits for the other objects). Higher-resolution measurements of both the sodium and potassium lines, for a larger sample of exoplanetary atmospheres, are needed to confirm or refute this trend.

Read this paper on arXiv…

K. Heng
Fri, 24 Jun 16
27/47

Comments: Accepted by ApJL. 6 pages, 1 figure, 2 tables

HELIOS: An Open-Source, GPU-Accelerated Radiative Transfer Code For Self-Consistent Exoplanetary Atmospheres [EPA]

http://arxiv.org/abs/1606.05474

We present the open-source radiative transfer code named HELIOS, which is constructed for studying exoplanetary atmospheres. In its initial version, the model atmospheres of HELIOS are one-dimensional and plane-parallel, and the equation of radiative transfer is solved in the two-stream approximation with non-isotropic scattering. The opacities are computed with the opacity calculator HELIOS-K and converted to k-distribution tables by weighing the molecular abundances with analytical chemistry formulae. We validate HELIOS by comparing a model of GJ 1214b to that computed using COOLTLUSTY and from the work of Miller-Ricci & Fortney, and by performing several tests, where we find: model atmospheres with single-temperature layers struggle to converge to radiative equilibrium; k-distribution tables constructed with < 0.01 cm-1 resolution in the opacity function (< 1000 points per wavenumber bin) may result in errors > 1-10% in the synthetic spectra; and a diffusivity factor of 2 approximates well the exact radiative transfer solution in the limit of pure absorption. We construct “null-hypothesis” models (chemical equilibrium, radiative equilibrium and solar element abundances) for 6 hot Jupiters. We find that the dayside emission spectra of HD 189733b and WASP-43b are consistent with the null hypothesis, while it consistently under-predicts the observed fluxes of WASP-8b, WASP-12b, WASP-14b and WASP-33b. We demonstrate that our results are somewhat insensitive to the choice of stellar models (blackbody, Kurucz or PHOENIX) and metallicity, but are strongly affected by higher carbon-to-oxygen ratios. The code is publicly available as part of the Exoclimes Simulation Platform (ESP; http://www.exoclime.net).

Read this paper on arXiv…

M. Malik, L. Grosheintz, J. Mendonca, et. al.
Mon, 20 Jun 16
26/41

Comments: 23 pages, 15 figures

Do planetary seasons play a fundamental role in attaining habitable climates? [EPA]

http://arxiv.org/abs/1605.08471

A simple phenomenological account for planetary climate instabilities is presented. The description is based on the standard model where the balance of incoming stellar radiation and outward thermal radiation is described by the effective planet temperature. It is often found to have three different points, or temperatures, where the influx of radiation is balanced with the out-flux, even with conserved boundary conditions. Two of these points are relatively long-term stable, namely the point corresponding to a frozen-climate and the point corresponding to a hot-climate. The thesis promoted in this paper is the possibility that it is the intermediate third point that is the basis for habitable-climates. I.e. that this initially unstable point is made relatively stable over a long period by the presence of seasonal climate variations. This points to an origination of stability in the axial inclination and perhaps in the presence of an amount of orbital eccentricity. Without planetary seasons a habitable climate would therefore be less likely.

Read this paper on arXiv…

K. Olsen and J. Bohr
Mon, 30 May 16
21/36

Comments: 6 pages

Limit cycles can reduce the width of the habitable zone [EPA]

http://arxiv.org/abs/1605.07130

The liquid water habitable zone (HZ) describes the orbital distance at which a terrestrial planet can maintain above-freezing conditions through regulation by the carbonate-silicate cycle. Recent calculations have suggested that planets in the outer regions of the habitable zone cannot maintain stable, warm climates, but rather should oscillate between long, globally glaciated states and shorter periods of climatic warmth. Such conditions, similar to ‘Snowball Earth’ episodes experienced on Earth, would be inimical to the development of complex land life, including intelligent life. Here, we build upon previous studies with an updated an energy balance climate model to calculate this ‘limit cycle’ region of the habitable zone where such cycling would occur. We argue that an abiotic Earth would have a greater CO$_2$ partial pressure than today because plants and other biota help to enhance the storage of CO$_2$ in soil. When we tune our abiotic model accordingly, we find that limit cycles can occur but that previous calculations have overestimated their importance. For G stars like the Sun, limit cycles occur only for planets with CO$_2$ outgassing rates less than that on modern Earth. For K and M star planets, limit cycles should not occur; however, M-star planets may be inhospitable to life for other reasons. Planets orbiting late G-type and early K-type stars retain the greatest potential for maintaining warm, stable conditions. Our results suggest that host star type, planetary volcanic activity, and seafloor weathering are all important factors in determining whether planets will be prone to limit cycling.

Read this paper on arXiv…

J. Haqq-Misra, R. Kopparapu, N. Batalha, et. al.
Tue, 24 May 16
60/73

Comments: Accepted for publication in The Astrophysical Journal. 25 pages, 5 figures

Orbit-spin coupling and the circulation of the Martian atmosphere [EPA]

http://arxiv.org/abs/1605.02707

The physical origins of the observed interannual variability of weather and climate on Mars are poorly understood. In this paper we introduce a deterministic physical mechanism that may account for much of the variability of the circulation of the Mars atmosphere on seasonal and longer timescales. We derive a coupling expression linking orbital and rotational motions that produces an acceleration field varying with position and with time on and within a subject body. The spatially and temporally varying accelerations may interfere constructively or destructively with large-scale flows of geophysical fluids that are established and maintained by other means. The hypothesis predicts cycles of intensification and relaxation of circulatory flows of atmospheres on seasonal and longer timescales that are largely independent of solar forcing. The predictions of the hypothesis may be tested through numerical modeling. Examples from investigations of the atmospheric circulation of Mars are provided to illustrate qualitative features and quantitative aspects of the mechanism proposed. We briefly discuss the implications and applicability of the orbit-spin coupling hypothesis for planets other than Mars.

Read this paper on arXiv…

J. Shirley
Tue, 10 May 16
42/85

Comments: 59 pages, 6 figures, 3 appendices

Orbit-spin coupling and the interannual variability of global-scale dust storm occurrence on Mars [CL]

http://arxiv.org/abs/1605.01452

A new physical hypothesis predicts that a weak coupling of the orbital and rotational motions of extended bodies may give rise to a modulation of circulatory flows within their atmospheres. Driven cycles of intensification and relaxation of large-scale circulatory flows are predicted, with the phasing of these changes linked directly to the rate of change of the orbital angular momentum with respect to inertial frames. We test the hypothesis that global-scale dust storms (GDS) on Mars may occur when periods of circulatory intensification (associated with positive and negative extrema of the waveform) coincide with the southern summer dust storm season on Mars. The orbit-spin coupling hypothesis additionally predicts that the intervening transitional periods, which are characterized by the disappearance and subsequent sign change of this waveform, may be unfavorable for the occurrence of GDS, when they occur during the southern summer dust storm season. These hypotheses are confirmed through comparisons between calculated dynamical time series of the time rate of change of orbital angular momentum and historic observations. All of the nine known global-scale dust storms on Mars took place during Mars years when circulatory intensification during the dust storm season is predicted under the orbit-spin coupling hypothesis. No historic global-scale dust storms were recorded during transitional intervals. Orbit-spin coupling accelerations evidently contribute to the interannual variability of the Mars atmosphere.

Read this paper on arXiv…

J. Shirley and M. Mischna
Fri, 6 May 16
43/60

Comments: 44 pages, 7 figures

Comparison of VLT/X-shooter OH and O2 rotational temperatures with consideration of TIMED/SABER emission and temperature profiles [EPA]

http://arxiv.org/abs/1604.03961

Rotational temperatures Trot derived from lines of the same OH band are an important method to study the mesopause region near 87 km. To measure realistic temperatures, the rotational level populations have to be in local thermodynamic equilibrium (LTE). However, this might not be fulfilled, especially at high emission altitudes. In order to quantify possible non-LTE contributions to the OH Trot as a function of the upper vibrational level v’, we studied a sample of 343 echelle spectra taken with the X-shooter spectrograph at the Very Large Telescope at Cerro Paranal in Chile. These data allowed us to analyse 25 OH bands in each spectrum. Moreover, we could measure lines of O2b(0-1), which peaks at 94 to 95 km, and O2a(0-0) with an emission peak at about 90 km. Since the radiative lifetimes are relatively long, the derived O2 Trot are not significantly affected by non-LTE contributions. For a comparison with OH, the differences in the emission profiles were corrected by using OH emission, O2a(0-0) emission, and CO2-based temperature profile data from the multi-channel radiometer SABER on the TIMED satellite. For a reference profile at 90 km, we found a good agreement of the O2 with the SABER-related temperatures, whereas the OH temperatures, especially for the high and even v’, showed significant excesses with a maximum of more than 10 K for v’ = 8. We could also find a nocturnal trend towards higher non-LTE effects, particularly for high v’.

Read this paper on arXiv…

S. Noll, W. Kausch, S. Kimeswenger, et. al.
Fri, 15 Apr 16
32/51

Comments: 22 pages, 18 figures, accepted for publication in Atmos. Chem. Phys

Ionisation and discharge in cloud-forming atmospheres of brown dwarfs and extrasolar planets [EPA]

http://arxiv.org/abs/1604.03369

Brown dwarfs and giant gas extrasolar planets have cold atmospheres with a rich chemical compositions from which mineral cloud particles form. Their properties, like particle sizes and material composition, vary with height, and the mineral cloud particles are charged due to triboelectric processes in such dynamic atmospheres. The dynamics of the atmospheric gas is driven by the irradiating host star and/or by the rotation of the objects that changes during its lifetime. Thermal gas ionisation in these ultra-cool but dense atmospheres allows electrostatic interactions and magnetic coupling of a substantial atmosphere volume. Combined with a strong magnetic field $\gg B_{\rm Earth}$, a chromosphere and aurorae might form as suggested by radio and X-ray observations of brown dwarfs. Non-equilibrium processes like cosmic ray ionisation and discharge processes in clouds will increase the local pool of free electrons in the gas. Cosmic rays and lighting discharges also alter the composition of the local atmospheric gas such that tracer molecules might be identified. Cosmic rays affect the atmosphere through air showers which was modelled with a 3D Monte Carlo radiative transfer code to be able to visualise their spacial extent. Given a certain degree of thermal ionisation of the atmospheric gas, we suggest that electron attachment to charge mineral cloud particles is too inefficient to cause an electrostatic disruption of the cloud particles. Cloud particles will therefore not be destroyed by Coulomb explosion for the local temperature in the collisional dominated brown dwarf and giant gas planet atmospheres. However, the cloud particles are destroyed electrostatically in regions with strong gas ionisation. The potential size of such cloud holes would, however, be too small and might occur too far inside the cloud to mimic the effect of, e.g., magnetic field induced star spots.

Read this paper on arXiv…

C. Helling, P. Rimmer, I. Rodriguez-Barrera, et. al.
Wed, 13 Apr 16
59/60

Comments: (9 pages, accepted for publication by Plasma Physics and Controlled Fusion, IoP)

Solar irradiance changes and phytoplankton productivity in Earth's ocean following astrophysical ionizing radiation events [EPA]

http://arxiv.org/abs/1604.01816

Two atmospheric responses to simulated astrophysical ionizing radiation events significant to life on Earth are production of odd-nitrogen species, especially NO2, and subsequent depletion of stratospheric ozone. Ozone depletion increases incident short-wavelength ultraviolet radiation (UVB, 280-315 nm) and longer ( > 600 nm) wavelengths of photosynthetically available radiation (PAR, 400 -700 nm). On the other hand, the NO2 haze decreases atmospheric transmission in the long-wavelength UVA (315-400 nm) and short wavelength PAR. Here we use the results of previous simulations of incident spectral irradiance following an ionizing radiation event to predict changes in Terran productivity focusing on photosynthesis of marine phytoplankton. The prediction is based on a spectral model of photosynthetic response developed for the dominant genera in central regions of the ocean (Synechococcus and Prochlorococcus), and remote-sensing based observations of spectral water transparency, temperature, wind speed and mixed layer depth. Predicted productivity declined after a simulated ionizing event, but the effect integrated over the water column was small. For integrations taking into account the full depth range of PAR transmission (down to 0.1% of utilizable PAR), the decrease was at most 2-3% (depending on strain), with larger effects (5-7%) for integrations just to the depth of the surface mixed layer. The deeper integrations were most affected by the decreased utilizable PAR at depth due to the NO2 haze, whereas shallower integrations were most affected by the increased surface UV.

Read this paper on arXiv…

P. Neale and B. Thomas
Fri, 8 Apr 16
32/54

Comments: in Astrobiology, Vol. 16, Num. 4, 2016

Cumulus Parameterization: Those Who Can Remember the Past Are Condemned to Repeat It [EPA]

http://arxiv.org/abs/1603.07424

Moist convection plays a leading role in the dynamics and energy budget of Earth’s tropics and influences the sensitivity of Earth’s climate to greenhouse gas increases. Because individual convective cells are much smaller than the gridboxes of 3-dimensional global climate models (GCMs), these models parameterize the effects of an ensemble of moist convective updrafts and downdrafts on the environment. Cumulus parameterization has been a focus of the terrestrial meteorology community for half a century. Only in past decade, however, have GCMs with moist convective physics been applied to other planets. Given our lack of detailed knowledge about convective clouds except on Earth, planetary GCMs are often designed with very simple approaches to cumulus parameterization, adopted from the earliest generations of terrestrial GCMs. These parameterizations were based on breakthroughs in understanding of convection in their time. However, at the same time that planetary GCMs have begun to emerge, a quiet revolution in how we think about terrestrial convection has started to influence the design of terrestrial GCMs. In this paper we review how some of the assumptions in the classical cumulus parameterizations used in planetary GCMs (and still in some terrestrial GCMs) have given way in recent years to a deeper understanding of how convection operates and why it matters for atmospheric dynamics and climate – on any planet.

Read this paper on arXiv…

A. Genio
Fri, 25 Mar 16
37/50

Comments: 4 pages, 2 figures, to be published in Comparative Climatology of Terrestrial Planets II, NASA Conference Proceeding technical No. TBD

Analytical Models of Exoplanetary Atmospheres. III. Gaseous C-H-O-N Chemistry with 9 Molecules [EPA]

http://arxiv.org/abs/1603.05418

We present novel, analytical, equilibrium-chemistry formulae for the abundances of molecules in hot exoplanetary atmospheres that include the carbon, oxygen and nitrogen networks. Our hydrogen-dominated solutions involve acetylene (C$_2$H$_2$), ammonia (NH$_3$), carbon dioxide (CO$_2$), carbon monoxide (CO), ethylene (C$_2$H$_4$), hydrogen cyanide (HCN), methane (CH$_4$), molecular nitrogen (N$_2$) and water (H$_2$O). By considering only the gaseous phase, we prove that the mixing ratio of carbon monoxide is governed by a decic equation (polynomial equation of degree 10). We validate our solutions against numerical calculations of equilibrium chemistry that perform Gibbs free energy minimization and demonstrate that they are accurate for temperatures from 500–3000 K. In hydrogen-dominated atmospheres, the ratio of abundances of HCN to CH$_4$ is nearly constant across a wide range of carbon-to-oxygen ratios, which makes it a robust diagnostic of the metallicity in the gas phase. Our validated formulae allow for the convenient benchmarking of chemical kinetics codes and provide an efficient way of enforcing chemical equilibrium in atmospheric retrieval calculations.

Read this paper on arXiv…

K. Heng and S. Tsai
Fri, 18 Mar 16
45/53

Comments: 6 pages, 4 figures

Equatorial superrotation in Held & Suarez-like flows with weak equator-to-pole surface temperature gradient [CL]

http://arxiv.org/abs/1603.04218

Equatorial superrotation under zonally-symmetric thermal forcing is investigated in a setup close to that of the classic Held & Suarez (1994) setup. In contrast to the behaviour in the classic setup, a transition to equatorial superrotation occurs when the equator-to-pole surface equilibrium entropy gradient is weakened. Two factors contribute to this transition: 1) the reduction of breaking Rossby waves from the mid-latitude that decelerate the equatorial flow and 2) the presence of barotropic instability in the equatorial region, providing stirring to accelerate the equatorial flow. In the latter, Kelvin waves excited by instability near the equator generate and maintain the superrotation. However, the superrotation is unphysically enhanced if simulations are under-resolved and/or over-dissipated.

Read this paper on arXiv…

I. Polichtchouk and J. Cho
Tue, 15 Mar 16
5/77

Comments: 15 pages, 14 figures, accepted for publication in QJRMS

The mineral clouds on HD 209458b and HD189733b [EPA]

http://arxiv.org/abs/1603.04022

3D atmosphere model results are used to comparatively study the kinetic, non-equilibrium cloud formation in the atmospheres of two example planets guided by the giant gas planets HD209458b and HD189733b. Rather independently of hydrodynamic model differences, our cloud modelling suggests that both planets are covered in mineral clouds throughout the entire modelling domain. Both planets harbour chemically complex clouds that are made of mineral particles that have a height-dependent material composition and size. The remaining gas-phase element abundances strongly effects the molecular abundances of the atmosphere in the cloud forming regions. Hydrocarbon and cyanopolyyne molecules can be rather abundant in the inner, dense part of the atmospheres of HD189733b and HD209458b. No one value for metallicity and the C/O ratio can be used to describe an extrasolar planet. Our results concerning the presence and location of water in relation to the clouds explain some of the observed discrepancies between the two planets. In HD189733b, strong water features have been reported while such features are not as clear for HD209458b. By considering the location of the clouds in the two atmospheres, we see that obscuring clouds exist high in the atmosphere of HD209458b, but much deeper in HD189733b. We further conclude that the (self-imposed) degeneracy of cloud parameters in retrieval methods can only be lifted if the cloud formation processes are accurately modelled in contrast to prescribing them by independent parameters.

Read this paper on arXiv…

C. Helling, G. Lee, I. Dobbs-Dixon, et. al.
Tue, 15 Mar 16
24/77

Comments: 32 pages, accepted for publication in MNRAS

The inhabitance paradox: how habitability and inhabitancy are inseparable [EPA]

http://arxiv.org/abs/1603.00950

The dominant paradigm in assigning “habitability”‘ to terrestrial planets is to define a circumstellar habitable zone: the locus of orbital radii in which the planet is neither too hot nor too cold for life as we know it. One dimensional climate models have identified theoretically impressive boundaries for this zone: a runaway greenhouse or water loss at the inner edge (Venus), and low-latitude glaciation followed by formation of CO2 clouds at the outer edge. A cottage industry now exists to “refine” the definition of these boundaries each year to the third decimal place of an AU. Using the same class of climate model, I show that the different climate states can overlap very substantially and that “snowball Earth”, moist temperate climate, hot moist climate and a post-runaway dry climate can all be stable under the same solar flux. The radial extent of the temperate climate band is very narrow for pure water atmospheres, but can be widened with di-nitrogen and carbon dioxide. The width of the habitable zone is thus determined by the atmospheric inventories of these gases. Yet Earth teaches us that these abundances are very heavily influenced (perhaps even controlled) by biology. This is paradoxical: the habitable zone seeks to define the region a planet should be capable of harbouring life; yet whether the planet is inhabited will determine whether the climate may be habitable at any given distance from the star. This matters, because future life detection missions may use habitable zone boundaries in mission design.

Read this paper on arXiv…

C. Goldblatt
Fri, 4 Mar 16
20/61

Comments: 4 pages, accepted in NASA Conference Proceedings from Comparative Climatology of Terrestrial Planets meeting, 2015

Atmospheric ionization by high-fluence, hard spectrum solar proton events and their probable appearance in the ice core archive [CL]

http://arxiv.org/abs/1602.08462

Solar energetic particles ionize the atmosphere, leading to production of nitrogen oxides. It has been suggested that some such events are visible as layers of nitrate in ice cores, yielding archives of energetic, high fluence solar proton events (SPEs). There has been controversy, due to slowness of transport for these species down from the upper stratosphere; past numerical simulations based on an analytic calculation have shown very little ionization below the mid stratosphere. These simulations suffer from deficiencies: they consider only soft SPEs and narrow energy ranges; spectral fits are poorly chosen; with few exceptions secondary particles in air showers are ignored. Using improved simulations that follow development of the proton-induced air shower, we find consistency with recent experiments showing substantial excess ionization down to 5 km. We compute nitrate available from the 23 February 1956 SPE, which had a high fluence, hard spectrum, and well-resolved associated nitrate peak in a Greenland ice core. For the first time, we find this event can account for ice core data with timely (~ 2 months) transport downward between 46 km and the surface, thus indicating an archive of high fluence, hard spectrum SPE covering the last several millennia. We discuss interpretations of this result, as well as the lack of a clearly-defined nitrate spike associated with the soft-spectrum 3-4 August 1972 SPE. We suggest that hard-spectrum SPEs, especially in the 6 months of polar winter, are detectable in ice cores, and that more work needs to be done to investigate this.

Read this paper on arXiv…

A. Melott, B. Thomas, C. Laird, et. al.
Mon, 29 Feb 16
11/46

Comments: JGR Atmospheres, in press

The Generalized Quasilinear Approximation: Application to Zonal Jets [CL]

http://arxiv.org/abs/1601.06720

Quasilinear theory is often utilized to approximate the dynamics of fluids exhibiting significant interactions between mean flows and eddies. In this paper we present a generalization of quasilinear theory to include dynamic mode interactions on the large scales. This generalized quasilinear (GQL) approximation is achieved by separating the state variables into large and small zonal scales via a spectral filter rather than by a decomposition into a formal mean and fluctuations. Nonlinear interactions involving only small zonal scales are then removed. The approximation is conservative and allows for scattering of energy between small-scale modes via the large scale (through non-local spectral interactions). We evaluate GQL for the paradigmatic problems of the driving of large-scale jets on a spherical surface and on the beta-plane and show that it is accurate even for a small number of large-scale modes. As this approximation is formally linear in the small zonal scales it allows for the closure of the system and can be utilized in direct statistical simulation schemes that have proved an attractive alternative to direct numerical simulation for many geophysical and astrophysical problems.

Read this paper on arXiv…

J. Marston, G. Chini and S. Tobias
Tue, 26 Jan 16
25/57

Comments: 5 pages and 5 figures