Martian Thermospheric Warming Associated With the Planet Encircling Dust Event of 2018

We report the first observations of Martian thermospheric warming associated with the Planet Encircling Dust Event (PEDE) of 2018. We used dayglow observations made by the Imaging Ultraviolet Spectrograph instrument aboard the MAVEN spacecraft to retrieve the upper atmosphere temperature structures. Our analysis shows that the two‐cell meridional circulation pattern may be operating before the PEDE‐2018, which resulted in the cooling of lower/middle latitudes and warming at higher latitudes. However, after the onset, the existing circulation pattern gets dampened, resulted in a weaker latitudinal temperature structure. We saw that mean temperatures rose by about 20 K for the same local time after the onset of the dust storm. Our 3‐D Mars General Ionosphere Thermosphere Model calculations were able to reproduce the temperatures during the predust and early dust storm but failed to fully capture the temperature trend during the growth phase of the PEDE of 2018.Key PointsThe IUVS Observations show potential thermospheric warming associated with a global dust stormOur analysis shows active two-cell meridional circulation in the Martian thermosphere before the PEDE-2018Temperature observations show breakdown of nominal circulation during the dust stormPeer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/154332/1/grl60064.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/154332/2/grl60064_am.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/154332/3/grl60064-sup-0002-Table_SI-S01.pd

MAVEN IUVS observations of the aftermath of the Comet Siding Spring meteor shower on Mars

We report the detection of intense emission from magnesium and iron in Mars' atmosphere caused by a meteor shower following Comet Siding Spring's close encounter with Mars. The observations were made with the Imaging Ultraviolet Spectrograph, a remote sensing instrument on the Mars Atmosphere and Volatile EvolutioN spacecraft orbiting Mars. Ionized magnesium caused the brightest emission from the planet's atmosphere for many hours, resulting from resonant scattering of solar ultraviolet light. Modeling suggests a substantial fluence of low-density dust particles 1-100μm in size, with the large amount and small size contrary to predictions. The event created a temporary planet-wide ionospheric layer below Mars' main dayside ionosphere. The dramatic meteor shower response at Mars is starkly different from the case at Earth, where a steady state metal layer is always observable but perturbations caused by even the strongest meteor showers are challenging to detect

Advancing Our Understanding of Martian Proton Aurora through a Coordinated Multi-Model Comparison Campaign

Proton aurora are the most commonly observed yet least studied type of aurora at Mars. In order to better understand the physics and driving processes of Martian proton aurora, we undertake a multi-model comparison campaign. We compare results from four different proton/hydrogen precipitation models with unique abilities to represent Martian proton aurora: Jolitz model (3-D Monte Carlo), Kallio model (3-D Monte Carlo), Bisikalo/Shematovich et al. model (1-D kinetic Monte Carlo), and Gronoff et al. model (1-D kinetic). This campaign is divided into two steps: an inter-model comparison and a data-model comparison. The inter-model comparison entails modeling five different representative cases using similar constraints in order to better understand the capabilities and limitations of each of the models. Through this step we find that the two primary variables affecting proton aurora are the incident solar wind particle flux and velocity. In the data-model comparison, we assess the robustness of each model based on its ability to reproduce a MAVEN/IUVS proton aurora observation. All models are able to effectively simulate the data. Variations in modeled intensity and peak altitude can be attributed to differences in model capabilities/solving techniques and input assumptions (e.g., cross sections, 3-D versus 1-D solvers, and implementation of the relevant physics and processes). The good match between the observations and multiple models gives a measure of confidence that the appropriate physical processes and their associated parameters have been correctly identified and provides insight into the key physics that should be incorporated in future models

The cost effectiveness of REACH-HF and home-based cardiac rehabilitation compared with the usual medical care for heart failure with reduced ejection fraction:a decision model-based analysis

This is the final version. Available from Sage Publications via the DOI in this record.Background The REACH-HF (Rehabilitation EnAblement in CHronic Heart Failure) trial found that the REACH-HF home-based cardiac rehabilitation intervention resulted in a clinically meaningful improvement in disease-specific health-related quality of life in patients with reduced ejection fraction heart failure (HFrEF). The aims of this study were to assess the long-term cost-effectiveness of the addition of REACH-HF intervention or home-based cardiac rehabilitation to usual care compared with usual care alone in patients with HFrEF. Design and methods A Markov model was developed using a patient lifetime horizon and integrating evidence from the REACH-HF trial, a systematic review/meta-analysis of randomised trials, estimates of mortality and hospital admission and UK costs at 2015/2016 prices. Taking a UK National Health and Personal Social Services perspective we report the incremental cost per quality-adjusted life-year (QALY) gained, assessing uncertainty using probabilistic and deterministic sensitivity analyses. Results In base case analysis, the REACH-HF intervention was associated with per patient mean QALY gain of 0.23 and an increased mean cost of £400 compared with usual care, resulting in a cost per QALY gained of £1720. Probabilistic sensitivity analysis indicated a 78% probability that REACH-HF is cost effective versus usual care at a threshold of £20,000 per QALY gained. Results were similar for home-based cardiac rehabilitation versus usual care. Sensitivity analyses indicate the findings to be robust to changes in model assumptions and parameters. Conclusions Our cost-utility analyses indicate that the addition of the REACH-HF intervention and home-based cardiac rehabilitation programmes are likely to be cost-effective treatment options versus usual care alone in patients with HFrEF.National Institute for Health Research (NIHR

Enhanced Conformational Sampling using Replica Exchange with Collective-Variable Tempering

The computational study of conformational transitions in RNA and proteins with atomistic molecular dynamics often requires suitable enhanced sampling techniques. We here introduce a novel method where concurrent metadynamics are integrated in a Hamiltonian replica-exchange scheme. The ladder of replicas is built with different strength of the bias potential exploiting the tunability of well-tempered metadynamics. Using this method, free-energy barriers of individual collective variables are significantly reduced compared with simple force-field scaling. The introduced methodology is flexible and allows adaptive bias potentials to be self-consistently constructed for a large number of simple collective variables, such as distances and dihedral angles. The method is tested on alanine dipeptide and applied to the difficult problem of conformational sampling in a tetranucleotide

Diffusion and thermal escape of H 2 from Titan's atmosphere: Monte Carlo simulations

a b s t r a c t The Direct Simulation Monte Carlo (DSMC) technique is used here to describe the transition region in Titan's atmosphere where the gas flow goes from being collisional to collisionless. We expand on our previous study (Tucker, O.J., Johnson, R.E. [2009]. Planet. Space Sci. 57, 1889-1894) by including H 2 in addition to CH 4 and N 2 . We again find that thermal escape of CH 4 is Jeans-like, contrary to what has been suggested by some fluid/continuum models. However, we also show that the temperature of molecular hydrogen separates from the background gas well below the exobase, and its escape cools the background gas. This results in a non-isothermal CH 4 density profile without requiring an upward CH 4 flux and, therefore, fits using the diffusion equation can overestimate the escape flux. These simulations also reproduce the Cassini H 2 density versus altitude data averaged over flybys for which Titan is orbiting in Saturn's plasma sheet, but with a somewhat different escape rate than suggested by the diffusion equation. However, for flybys for which Titan is not in Saturn's plasma sheet our simulations result in H 2 densities that diffusively separate from the N 2 densities at lower altitudes than typically indicated by the Cassini data. By tracking ballistic transport in the H 2 corona we show that a global, as well as temporal description of the exobase region is required. Published by Elsevier Inc