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    Surprising Decrease in the Martian He Bulge During PEDE-2018 and Changes in Upper Atmospheric Circulation
    (Wiley, 2023-07-12) Elrod, Meredith K.; Bougher, Stephen; Roeten, Kali; Arnold, Kenneth
    Using the Neutral Gas and Ion Mass Spectrometer (NGIMS) on the Mars Atmosphere Volatile and Evolution spacecraft (MAVEN), we analyzed data from Mars Year (MY) 32, 34, and 35 to examine the He bulge during the northern winter solstice (Ls ∼ 180–240), specifically focusing on the effects from the planet encircling dust event (PEDE-2018). He collects on the dawn/nightside winter polar hemisphere of Mars. The seasonal migration of the He bulge has been observed and modeled (M. Elrod et al., 2017, https://doi.org/10.1002/2016JA023482; Gupta et al., 2021, https://doi.org/10.1029/2021JE006976). The MAVEN orbit precesses around Mars allowing for a variety of latitude and local time observations throughout the Martian year. MY 32, 34, and 35 had the best possible opportunities to observe the He bulge during northern winter (Ls ∼ 180–240). NGIMS observations during MY 32 and MY 35 revealed a He bulge from the nightside to dawn in alignment with modeling and previous publications. However, in MY 34, during the PEDE, the He bulge was not present, indicating that the PEDE directly impacted upper atmospheric circulation. Updates in modeling indicate changes in circulation and winds can cause He to shift further north than MAVEN was able to observe. While adding a simple static version of gravity waves to the Mars Global Ionosphere Thermosphere Model model may account for some of the variations in the global circulation during the dust event, other studies (e.g., Yiğit, 2023, https://doi.org/10.1038/s41561-022-01118-7) have posited that the gravity waves during the dust storm were more variable than the initial parameters we have included.
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    Spectral Dependent Degradation of the Solar Diffuser on Suomi-NPP VIIRS Due to Surface Roughness-Induced Rayleigh Scattering
    (MDPI, 2016-06-17) Shao, Xi; Cao, Changyong; Liu, Tung-Chang
    The Visible Infrared Imaging Radiometer Suite (VIIRS) onboard Suomi National Polar Orbiting Partnership (SNPP) uses a solar diffuser (SD) as its radiometric calibrator for the reflective solar band calibration. The SD is made of Spectralon™ (one type of fluoropolymer) and was chosen because of its controlled reflectance in the Visible/Near-Infrared/Shortwave-Infrared region and its near-Lambertian reflectance property. On-orbit changes in VIIRS SD reflectance as monitored by the Solar Diffuser Stability Monitor showed faster degradation of SD reflectance for 0.4 to 0.6 µm channels than the longer wavelength channels. Analysis of VIIRS SD reflectance data show that the spectral dependent degradation of SD reflectance in short wavelength can be explained with a SD Surface Roughness (length scale << wavelength) based Rayleigh Scattering (SRRS) model due to exposure to solar UV radiation and energetic particles. The characteristic length parameter of the SD surface roughness is derived from the long term reflectance data of the VIIRS SD and it changes at approximately the tens of nanometers level over the operational period of VIIRS. This estimated roughness length scale is consistent with the experimental result from radiation exposure of a fluoropolymer sample and validates the applicability of the Rayleigh scattering-based model. The model is also applicable to explaining the spectral dependent degradation of the SDs on other satellites. This novel approach allows us to better understand the physical processes of the SD degradation, and is complementary to previous mathematics based models.
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    Unveiling the Origin of the Fermi Bubbles
    (MDPI, 2018-02-28) Yang, H.-Y. Karen; Ruszkowski, Mateusz; Zweibel, Ellen G.
    The Fermi bubbles, two giant structures above and below the Galactic center (GC), are among the most important discoveries of the Fermi Gamma-ray Space Telescope. Studying their physical origin has been providing valuable insights into cosmic-ray transport, the Galactic magnetic field, and past activity at the GC in the Milky Way galaxy. Despite their importance, the formation mechanism of the bubbles is still elusive. Over the past few years, there have been numerous efforts, both observational and theoretical, to uncover the nature of the bubbles. In this article, we present an overview of the current status of our understanding of the bubbles’ origin, and discuss possible future directions that will help to distinguish different scenarios of bubble formation.
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    Astrophotonic Spectrographs
    (MDPI, 2019-01-15) Gatkine, Pradip; Veilleux, Sylvain; Dagenais, Mario
    Astrophotonics is the application of photonic technologies to channel, manipulate, and disperse light from one or more telescopes to achieve scientific objectives in astronomy in an efficient and cost-effective way. Utilizing photonic advantage for astronomical spectroscopy is a promising approach to miniaturizing the next generation of spectrometers for large telescopes. It can be primarily attained by leveraging the two-dimensional nature of photonic structures on a chip or a set of fibers, thus reducing the size of spectroscopic instrumentation to a few centimeters and the weight to a few hundred grams. A wide variety of astrophotonic spectrometers is currently being developed, including arrayed waveguide gratings (AWGs), photonic echelle gratings (PEGs), and Fourier-transform spectrometer (FTS). These astrophotonic devices are flexible, cheaper to mass produce, easier to control, and much less susceptible to vibrations and flexure than conventional astronomical spectrographs. The applications of these spectrographs range from astronomy to biomedical analysis. This paper provides a brief review of this new class of astronomical spectrographs.
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    Questions Related to the Equation of State of High-Density Matter
    (MDPI, 2019-04-30) Miller, M. Coleman
    Astronomical data about neutron stars can be combined with laboratory nuclear data to give us a strong base from which to infer the equation of state of cold catalyzed matter beyond nuclear density. However, the nuclear and astrophysical communities are largely distinct; each has their own methods, which means that there is often imperfect communication between the communities regarding caveats about claimed measurements and constraints. Here we present a brief summary from one astronomer’s perspective of relevant observations of neutron stars, with warnings as appropriate, followed by a set of questions that are intended to help enhance the dialog between nuclear physicists and astrophysicists.
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    Orbital Characterization of the Composition and Distribution of Spinels Across the Crisium Region: Insight From Luna 20 Samples
    (Wiley, 2023-04-28) Moriarty, D. P. III; Simon, S. B.; Shearer, C. K.; Haggerty, S. E.; Petro, N.; Li, Shuai
    Spinels represent a small fraction of lunar surface materials but provide important insights into the petrological evolution of the lunar crust and mantle. Previous remote sensing analyses of highlands spinel-bearing lithologies have focused on pure Mg-Al spinels, which are rare in the lunar sample collection. Using Moon Mineralogy Mapper data, we develop and test an approach for detecting spectral signatures of spinel across a wider range of Mg, Al, Fe, Cr, Ti-bearing compositions than have been addressed in previous studies, including within mafic-bearing assemblages. This approach is validated through integration with laboratory-measured spinel spectra and petrographic observations of samples returned by the Luna 20 mission from the Hilly and Furrowed Terrain surrounding the Crisium Basin. Applying this approach to data from the Crisium region, small abundances of spinel (<∼5 vol%) with a range of Mg, Al, Fe, Cr, and Ti content and petrologic origin (inferred from Luna 20 samples) were found to be widespread within highlands soils across the Crisium region. This result diverges from previous remote sensing analyses, which only reported small, isolated exposures of pure Mg-Al spinel (as well as a possible detection of Fe, Cr-bearing spinels localized within pyroclastic materials at Sinus Aestuum). Geologic associations of candidate spinel detections across this region are consistent with a shallow crustal origin rather than excavation from depth during the Crisium-forming impact. These spinels are detectible in near-infrared spectroscopic data, particularly in areas of low optical maturity and may influence the spectral continuum of highlands soils.
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    Soft X-Ray Imaging of Earth's Dayside Magnetosheath and Cusps Using Hybrid Simulations
    (Wiley, 2023-05-11) Ng, J.; Walsh, B.M.; Chen, L.-J.; Omelchenko, Y.
    Interactions between solar wind ions and neutral hydrogen atoms in Earth's exosphere can lead to the emission of soft X-rays. Upcoming missions such as SMILE and LEXI aim to use soft X-ray imaging to study the global structure of the magnetosphere. Although the magnetosheath and dayside magnetopause can often be driven by kinetic physics, it has typically been omitted from fluid simulations used to predict X-ray emissions. We study the possible results of soft X-ray imaging using hybrid simulations under quasi-radial interplanetary magnetic fields, where ion-ion instabilities drive ultra-low frequency foreshock waves, leading to turbulence in the magnetosheath, affecting the dynamics of the cusp and magnetopause. We simulate soft X-ray emission to determine what may be seen by missions such as LEXI, and evaluate the possibility of identifying kinetic structures. While kinetic structures are visible in high-cadence imaging, current instruments may not have the time resolution to discern kinetic signals.
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    Temporal, Spatial, and Velocity-Space Variations of Electron Phase Space Density Measurements at the Magnetopause
    (Wiley, 2023-03-21) Shuster, J. R.; Gershman, D. J.; Giles, B. L.; Bessho, N.; Sharma, A. S.; Dorelli, J. C.; Uritsky, V.; Schwartz, S. J.; Cassak, P. A.; Denton, R. E.; Chen, L.-J.; Gurram, H.; Ng, J.; Burch, J.; Webster, J.; Torbert, R.; Paterson, W. R.; Schiff, C.; Viñas, A. F.; Avanov, L. A.; Stawarz, J.; Li, T. C.; Liu, Y.-H.; Argall, M. R.; Afshari, A.; Payne, D. S.; Farrugia, C.J.; Verniero, J.; Wilder, F.; Genestreti, K.; da Silva, D. E.
    Temporal, spatial, and velocity-space variations of electron phase space density are measured observationally and compared for the first time using the four magnetospheric multiscale (MMS) spacecraft at Earth's magnetopause. Equipped with these unprecedented spatiotemporal measurements offered by the MMS tetrahedron, we compute each term of the electron Vlasov equation that governs the evolution of collisionless plasmas found throughout the universe. We demonstrate how to use single spacecraft measurements to improve the resolution of the electron pressure gradient that supports nonideal parallel electric fields, and we develop a model to intuit the types of kinetic velocity-space signatures that are observed in the Vlasov equation terms. Furthermore, we discuss how the gradient in velocity-space sheds light on plasma energy conversion mechanisms and wave-particle interactions that occur in fundamental physical processes such as magnetic reconnection and turbulence.
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    Hybrid Simulations of the Cusp and Dayside Magnetosheath Dynamics Under Quasi-Radial Interplanetary Magnetic Fields
    (Wiley, 2022-10-17) Ng, J.; Chen, L.-J.; Omelchenko, Y.; Zou, Y.; Lavraud, B.
    Under quasi-radial interplanetary magnetic fields (IMF), foreshock turbulence can have an impact on the magnetosheath and cusps depending on the location of the quasi-parallel shock. We perform three-dimensional simulations of Earth's dayside magnetosphere using the hybrid code HYPERS, and compare northward and southward quasi-radial IMF configurations. We study the magnetic field configuration, fluctuations in the magnetosheath and the plasma in the regions around the northern cusp. Under northward IMF with Earthward Bx, there is a time-varying plasma depletion layer immediately outside the northern cusp. In the southward IMF case, the impact of foreshock turbulence and high-speed jets, together with magnetopause reconnection, can lead to strong density enhancements in the cusp.
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    Whistler Waves Associated With Electron Beams in Magnetopause Reconnection Diffusion Regions
    (Wiley, 2022-09-12) Wang, Shan; Bessho, Naoki; Graham, Daniel B.; Le Contel, Olivier; Wilder, Frederick D.; Khotyaintsev, Yuri V.; Genestreti, Kevin J.; Lavraud, Benoit; Choi, Seung; Burch, James L.
    Whistler waves are often observed in magnetopause reconnection associated with electron beams. We analyze seven MMS crossings surrounding the electron diffusion region (EDR) to study the role of electron beams in whistler excitation. Waves have two major types: (a) Narrow-band waves with high ellipticities and (b) broad-band waves that are more electrostatic with significant variations in ellipticities and wave normal angles. While both types of waves are associated with electron beams, the key difference is the anisotropy of the background population, with perpendicular and parallel anisotropies, respectively. The linear instability analysis suggests that the first type of wave is mainly due to the background anisotropy, with the beam contributing additional cyclotron resonance to enhance the wave growth. The second type of broadband waves are excited via Landau resonance, and as seen in one event, the beam anisotropy induces an additional cyclotron mode. The results are supported by particle-in-cell simulations. We infer that the first type occurs downstream of the central EDR, where background electrons experience Betatron acceleration to form the perpendicular anisotropy; the second type occurs in the central EDR of guide field reconnection. A parametric study is conducted with linear instability analysis. A beam anisotropy alone of above ∼3 likely excites the cyclotron mode waves. Large beam drifts cause Doppler shifts and may lead to left-hand polarizations in the ion frame. Future studies are needed to determine whether the observation covers a broader parameter regime and to understand the competition between whistler and other instabilities.
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    Electron-Scale Reconnection in Three-Dimensional Shock Turbulence
    (Wiley, 2022-08-11) Ng, J.; Chen, L.-J.; Bessho, N.; Shuster, J.; Burkholder, B.; Yoo, J.
    Magnetic reconnection has been observed in the transition region of quasi-parallel shocks. In this work, the particle-in-cell method is used to simulate three-dimensional reconnection in a quasi-parallel shock. The shock transition region is turbulent, leading to the formation of reconnecting current sheets with various orientations. Two reconnection sites with weak and strong guide fields are studied, and it is shown that reconnection is fast and transient. Reconnection sites are characterized using diagnostics including electron flows and magnetic flux transport. In contrast to two-dimensional simulations, weak guide field reconnection is realized. Furthermore, the current sheets in these events form in a direction almost perpendicular to those found in two-dimensional simulations, where the reconnection geometry is constrained.
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    Variability of Hydration Across the Southern Hemisphere of the Moon as Observed by Deep Impact
    (Wiley, 2022-07-11) Laferriere, K. L.; Sunshine, J. M.; Feaga, L. M.
    Measurements of the 3 μm absorption feature, associated with the presence of hydroxyl and potentially molecular water, were first observed in 2009 by three separate spacecraft’ observations. Subsequent observations have revealed widespread but variable hydration over the sunlit regions of the Moon. The variability can help to disentangle the individual contributions of OH and H2O to the 3 μm absorption feature and provide insight into the mechanism of production and loss of OH/H2O on the lunar surface. We investigate the spatial and diurnal variations of hydration on the southern hemisphere of the Moon as observed by the Deep Impact spacecraft during the lunar flybys in 2009 at spatial scales of 30–70 km/pixel. For a subset of observations of across the lunar south polar region (∼2% of the lunar surface), repeat coverage includes three different times spanning half a lunar day, allowing for exploration of diurnal variability. We determine that OH/H2O is widespread but variable across the lunar south pole. At all but the lowest temperatures observed, highland regions have stronger hydration absorption features than the maria. Changes in band strength demonstrate variable loss rates controlled by surface temperatures with H2O lost quicker at higher temperatures. Observed variability in the band shape strongly suggests higher H2O abundance at low temperatures. These observations are strong evidence that the unique shape of the 3 μm band is due to both OH and H2O. The rapid diurnal evolution of the absorption feature implies that migration of these constituents occurs locally over short distances driven by temperature changes.
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    Lower-Hybrid Wave Structures and Interactions With Electrons Observed in Magnetotail Reconnection Diffusion Regions
    (Wiley, 2022-04-22) Wang, Shan; Chen, Li-Jen; Bessho, Naoki; Ng, Jonathan; Hesse, Michael; Graham, Daniel B.; Le Contel, Olivia; Gershman, Daniel; Giles, Barbara
    We investigate waves close to the lower-hybrid frequency in 12 magnetotail reconnection electron diffusion region (EDR) events with guide field levels of near-zero to 30%. In about half of the events, the wave vector has a small component along the current sheet normal, consistent with known lower-hybrid drift wave properties, but the perpendicular magnetic field fluctuations can be comparable or greater than the parallel component, a feature unique to the waves inside and adjacent to EDRs. Another new wave property is that the wave vector has a significant component along the current sheet normal in some events and completely along the normal for one event. In 1/4 of the events, the 𝐴𝐴∇⋅𝑷𝑷𝑒𝑒 term has a significant contribution to the wave electric field, possibly a feature of lower-hybrid waves more likely to exist in the diffusion region than further away from the X-line. Electron temperature variations are correlated with the wave potential, due to wave electric field acceleration and crossings at the corrugated separatrix region with different amounts of mixing between reconnection inflowing and outflowing populations. The latter also leads to the anti-correlation between parallel and perpendicular temperature components. Using four-spacecraft measurements, the magnetic field line twisting is demonstrated by the correlated fluctuations in 𝐴𝐴(∇×𝑽𝑽𝐸𝐸×𝐵𝐵)|| and 𝐴𝐴(∇×𝐁𝐁)||. The lower-hybrid wave in the EDR of weak guide field reconnection may be generated near separatrices and penetrate to the mid-plane or locally generated, and the latter possibility is beyond the prediction of previous reconnection simulations.
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    Example code and data for "SOFIA FEEDBACK Survey: The Pillars of Creation in [C II] and Molecular Lines"
    (2023-09-07) Karim, Ramsey; Pound, Marc W.; Wolfire, Mark G.; Mundy, Lee; Tielens, Alexander G. G. M.
    We present here the original observations used in the manuscript "SOFIA FEEDBACK Survey: The Pillars of Creation in [C II] and Molecular Lines" (Karim et al., Astronomical Journal, 2023). The data consist of FITS format images and datacubes of the rotational transitions of molecular lines CO, 13CO, C18O, CS, HCN, HCO+, and N2H+ in the 3mm spectral window, and the atomic spectral lines [C II] 158 micron and [O I] 63 micron. We also present a snapshot copy of the scoby (Spectra from Catalogs of OB Stars) software repository, some model data necessary for it, and some examples of how to run it.
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    Example code and data for "Identifying physical structures in our Galaxy with Gaussian Mixture Models: An unsupervised machine learning technique"
    (2023) Tiwari, Maitraiyee; Kievit, Rens; Kabanovic, Slawa; Bonne, Lars; Falasca, F.; Guevara, Cristian; Higgins, Ronan; Justen, M.; Karim, Ramsey; Pabst, Cornelia; Pound, Marc W.; Schneider, Nicola; Simon, R.; Stutzki, Jurgen; Wolfire, Mark; Tielens, Alexander G. G. M.
    We present a python software repository implementing the PyGMMis (Melchior & Goudling 2018) method to astronomical data cubes of velocity resolved line observations. This implementation is described extensively in Tiwari et al. 2023, ApJ. An example is included in /example/ containing the SOFIA data of RCW120 used in Tiwari et al. 2023, ApJ, along with example scripts describing the full implementation of our code. The majority of parameter tweaking can be performed within 'rcw120-params.txt' which is continuously called during the procedure. A full description of the code and how to use it is in README.md (markdown file).
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    The PhotoDissociation Region Toolbox: Software and Models for Astrophysical Analysis
    (The Astronomical Journal, 2023-01-15) Pound, Marc W.; Wolfire, Mark G.
    The PhotoDissociation Region Toolbox provides comprehensive, easy-to-use, public software tools and models that enable an understanding of the interaction of the light of young, luminous, massive stars with the gas and dust in the Milky Way and in other galaxies. It consists of an open-source Python toolkit and photodissociation region (PDR) models for analysis of infrared and millimeter/submillimeter line and continuum observations obtained by ground-based and suborbital telescopes, and astrophysics space missions. PDRs include all of the neutral gas in the interstellar medium where far-ultraviolet photons dominate the chemistry and/or heating. In regions of massive star formation, PDRs are created at the boundaries between the H II regions and neutral molecular cloud, as photons with energies 6 eV < hν < 13.6 eV photodissociate molecules and photoionize metals. The gas is heated by photoelectrons from small grains and large molecules and cools mostly through far-infrared (FIR) fine-structure lines like [O I] and [C II]. The models are created from state-of-the art PDR codes that include molecular freezeout; recent collision, chemical, and photorates; new chemical pathways, such as oxygen chemistry; and allow for both clumpy and uniform media. The models predict the emergent intensities of many spectral lines and FIR continuum. The tools find the best-fit models to the observations and provide insight into the physical conditions and chemical makeup of the gas and dust. The PDR Toolbox enables novel analysis of data from telescopes such as the Infrared Space Observatory, Spitzer, Herschel, the Stratospheric Terahertz Observatory, the Stratospheric Observatory for Infrared Astronomy, the Submillimeter Wave Astronomy Satellite, the Atacama Pathfinder Experiment, the Atacama Large Millimeter/submillimeter Array, and the JWST.
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    PIC simulation data for "Magnetic reconnection and instabilities in the Earth's quasi-parallel bow shock": foreshock region
    (2022) Bessho, Naoki
    Simulation data for a study of magnetic reconnection in foreshock waves, supported by a NASA grant 80NSSC20K1312, "Magnetic reconnection and instabilities in the Earth's quasi-parallel bow shock". Please see the data description file about details for the data.
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    Example code listings for the PhotoDissociation Region Toolbox
    (2022-08-31) Pound, Marc; Wolfire, Mark
    These are example code listings for the PhotoDissociation Region Toolbox (https://dustem.astro.umd.edu), and companion to the manuscript "The PhotoDissociation Region Toolbox: Software and Models for Astrophysical Analysis", by Pound & Wolfire (2022). These code snippets show typical ways to use the Toolbox and reproduce most of the figures in the manuscript. The code is written in Python 3 and demonstrate the pdrtpy Python package (https://pdrtpy.readthedocs.io).
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    Patchy Nightside Clouds on Ultra-hot Jupiters: General Circulation Model Simulations with Radiatively Active Cloud Tracers
    (AAS Journals, 2022-07-20) Komacek, Thaddeus; Tan, Xianyu; Gao, Peter; Lee, Elspeth
    The atmospheres of ultra-hot Jupiters have been characterized in detail through recent phase curve and low- and high-resolution emission and transmission spectroscopic observations. Previous numerical studies have analyzed the effect of the localized recombination of hydrogen on the atmospheric dynamics and heat transport of ultra-hot Jupiters, finding that hydrogen dissociation and recombination lead to a reduction in the day-to-night contrasts of ultra-hot Jupiters relative to previous expectations. In this work, we add to previous efforts by also considering the localized condensation of clouds in the atmospheres of ultra-hot Jupiters, their resulting transport by the atmospheric circulation, and the radiative feedback of clouds on the atmospheric dynamics. To do so, we include radiatively active cloud tracers into the existing MITgcm framework for simulating the atmospheric dynamics of ultra-hot Jupiters. We take cloud condensate properties appropriate for the high-temperature condensate corundum from CARMA cloud microphysics models. We conduct a suite of general circulation model (GCM) simulations with varying cloud microphysical and radiative properties, and we find that partial cloud coverage is a ubiquitous outcome of our simulations. This patchy cloud distribution is inherently set by atmospheric dynamics in addition to equilibrium cloud condensation, and causes a cloud greenhouse effect that warms the atmosphere below the cloud deck. Nightside clouds are further sequestered at depth due to a dynamically induced high-altitude thermal inversion. We post-process our GCMs with the Monte Carlo radiative transfer code gCMCRT and find that the patchy clouds on ultra-hot Jupiters do not significantly impact transmission spectra but can affect their phase-dependent emission spectra.
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    Dataset for "Stratigraphic Evidence for Early Martian Explosive Volcanism in Arabia Terra"
    (2021) Richardson, Jacob; Whelley, Patrick; Matiella Novak, Alexandra
    Seven Digital Elevation Models (DEMs) in the Arabia Terra region, Mars, were created using spatially overlapping images (i.e., "stereo images") from the Context Camera (CTX) aboard the Mars Reconnaissance Orbiter (MRO). Each DEM location was selected to spatially overlap hyperspectral data acquired by the Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) also aboard MRO. Elevation data from these DEMs were used to identify and measure geologic units that preserve minerals indicative of altered volcanic deposits. Stereophotogrammetry was performed using the Ames Stereo Pipeline toolkit v 2.6.0 and USGS ISIS Version 3.4.12.6662. Each DEM was aligned to the martian aeroid with Mars Orbiter Laser Altimeter Precision Experiment Data Records within the spatial footprint of the CTX DEM. DEM files are in the GeoTIFF raster format. Each raster has a sinusoidal projection coordinate system with a central longitude corresponding to the individual raster's center. For each CTX DEM, an ortho-rectified image was also produced. For naming conventions, references, and descriptions of each DEM site, see the enclosed readme.