Cassini radio occultations of Saturn's ionosphere: Model comparisons using a constant water flux

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/94688/1/grl22099.pd

Saturn's atmospheric response to the large influx of ring material inferred from Cassini INMS measurements

During the Grand Finale stage of the Cassini mission, organic-rich ring material was discovered to be flowing into Saturn's equatorial upper atmosphere at a surprisingly large rate. Through a series of photochemical models, we have examined the consequences of this ring material on the chemistry of Saturn's neutral and ionized atmosphere. We find that if a substantial fraction of this material enters the atmosphere as vapor or becomes vaporized as the solid ring particles ablate upon atmospheric entry, then the ring-derived vapor would strongly affect the composition of Saturn's ionosphere and neutral stratosphere. Our surveys of Cassini infrared and ultraviolet remote-sensing data from the final few years of the mission, however, reveal none of these predicted chemical consequences. We therefore conclude that either (1) the inferred ring influx represents an anomalous, transient situation that was triggered by some recent dynamical event in the ring system that occurred a few months to a few tens of years before the 2017 end of the Cassini mission, or (2) a large fraction of the incoming material must have been entering the atmosphere as small dust particles less than ~100 nm in radius, rather than as vapor or as large particles that are likely to ablate. Future observations or upper limits for stratospheric neutral species such as HC$_3$N, HCN, and CO$_2$ at infrared wavelengths could shed light on the origin, timing, magnitude, and nature of a possible vapor-rich ring-inflow event.Comment: accepted in Icaru

The dynamics of the Venusian mesosphere and thermosphere

We present the first circulation model of Venus' atmosphere to couple the super-rotating cloud tops and upper thermosphere. To drive these simulations, we formulate the first continuous semi-empirical model of atmospheric structure between 60-250 km. Our model hydrostatically links the VIRA and VTS3 models. Our approach is validated by comparisons with observations where we find a good agreement with data. We base our dynamic model on the Müller-Wodarg et al. [2003] general circulation model (GCM) of Titan's thermosphere. Our simulations solve the full non-linear Navier-Stokes momentum equation assuming a realistic thermal structure and lower boundary super-rotation. We find our derived winds are consistent with much of the data between 70-120 km. Solving the full momentum equation we find dynamics below 80km are predominately cyclostrophic. Near 75km we find a good agreement between our GCM, cyclostrophic and cloud tracked winds between 45-85⁰ latitude. Equatorward of 30⁰ cyclostrophic winds decrease steeply with latitude. This is not seen in our GCM winds, which are sustained by an equatorward transport of momentum, neglected in the cyclostrophic approximation. Above 80km we find a balance of advection and pressure gradients replaces cyclostrophic balance poleward of (50-60⁰). Above 75km a pole-to-equator temperature gradient drives equatorward winds with peak speeds of 100ms⁻1 near 95 km, and zonal winds decrease with height. Zonal forcing above 90km drives a reversal in dayside meridional winds and accelerates a subsolar-to-antisolar flow. We find the winds between 90-150km are not characterised by a simple balance of accelerations. Above 150km we find a symmetric subsolar-to-antisolar flow, characterised by a balance of horizontal pressure gradients and viscosity with 200 ms⁻1 cross terminator winds. Our simulations address the origin of the thermospheric super-rotation. We find the cloud top super-rotation does not propagate above 100 km, nor is a super-rotation above 150km driven in situ by our pressure gradients.EThOS - Electronic Theses Online ServiceScience and Technology Facilities CouncilGBUnited Kingdo

Titan: interior, surface, atmosphere, and space environment

This comprehensive reference and guide examines the processes that shape the atmosphere and surface of Titan, Saturn's largest moon

Atmospheric Structure and Composition

International audienc

The thermal structure of the Venus atmosphere: Intercomparison of Venus Express and ground based observations of vertical temperature and density profiles✰

The Venus International Reference Atmosphere (VIRA) model contains tabulated values of temperature and number densities obtained by the experiments on the Venera entry probes, Pioneer Venus Orbiter and multi-probe missions in the 1980s. The instruments on the recent Venus Express orbiter mission generated a significant amount of new observational data on the vertical and horizontal structure of the Venus atmosphere from 40 km to about 180 km altitude from April 2006 to November 2014. Many ground based experiments have provided data on the upper atmosphere (90-130 km) temperature structure since the publication of VIRA in 1985. The "Thermal Structure of the Venus Atmosphere" Team was supported by the International Space Studies Institute (ISSI), Bern, Switzerland, from 2013 to 2015 in order to combine and compare the ground-based observations and the VEx observations of the thermal structure as a first step towards generating an updated VIRA model. Results of this comparison are presented in five latitude bins and three local time bins by assuming hemispheric symmetry. The intercomparison of the ground-based and VEx results provides for the first time a consistent picture of the temperature and density structure in the 40 km-180 km altitude range. The Venus Express observations have considerably increased our knowledge of the Venus atmospheric thermal structure above ∼40 km and provided new information above 100 km. There are, however, still observational gaps in latitude and local time above certain regions. Considerable variability in the temperatures and densities is seen above 100 km but certain features appear to be systematically present, such as a succession of warm and cool layers. Preliminary modeling studies support the existence of such layers in agreement with a global scale circulation. The intercomparison focuses on average profiles but some VEx experiments provide sufficient global coverage to identify solar thermal tidal components. The differences between the VEx temperature profiles and the VIRA below 0.1 mbar/95 km are small. There is, however, a clear discrepancy at high latitudes in the 10-30 mbar (70-80 km) range. The VEx observations will also allow the improvement of the empirical models (VTS3 by Hedin et al., 1983 and VIRA by Keating et al., 1985) above 0.03 mbar/100 km, in particular the 100-150 km region where a sufficient observational coverage was previously missing. The next steps in order to define the updated VIRA temperature structure up to 150 km altitude are (1) define the grid on which this database may be provided, (2) fill what is possible with the results of the data intercomparison, and (3) fill the observational gaps. An interpolation between the datasets may be performed by using available General Circulation Models as guidelines. An improved spatial coverage of observations is still necessary at all altitudes, in latitude-longitude and at all local solar times for a complete description of the atmospheric thermal structure, in particular on the dayside above 100 km. New in-situ observations in the atmosphere below 40 km are missing, an altitude region that cannot be accessed by occultation experiments. All these questions need to be addressed by future missions

Jupiter Science Enabled by ESA's Jupiter Icy Moons Explorer

ESA's Jupiter Icy Moons Explorer (JUICE) will provide a detailed investigation of the Jovian system in the 2030s, combining a suite of state-of-the-art instruments with an orbital tour tailored to maximise observing opportunities. We review the Jupiter science enabled by the JUICE mission, building on the legacy of discoveries from the Galileo, Cassini, and Juno missions, alongside ground- and space-based observatories. We focus on remote sensing of the climate, meteorology, and chemistry of the atmosphere and auroras from the cloud-forming weather layer, through the upper troposphere, into the stratosphere and ionosphere. The Jupiter orbital tour provides a wealth of opportunities for atmospheric and auroral science: global perspectives with its near-equatorial and inclined phases, sampling all phase angles from dayside to nightside, and investigating phenomena evolving on timescales from minutes to months. The remote sensing payload spans far-UV spectroscopy (50-210 nm), visible imaging (340-1080 nm), visible/near-infrared spectroscopy (0.49-5.56 $μ$m), and sub-millimetre sounding (near 530-625\,GHz and 1067-1275\,GHz). This is coupled to radio, stellar, and solar occultation opportunities to explore the atmosphere at high vertical resolution; and radio and plasma wave measurements of electric discharges in the Jovian atmosphere and auroras. Cross-disciplinary scientific investigations enable JUICE to explore coupling processes in giant planet atmospheres, to show how the atmosphere is connected to (i) the deep circulation and composition of the hydrogen-dominated interior; and (ii) to the currents and charged particle environments of the external magnetosphere. JUICE will provide a comprehensive characterisation of the atmosphere and auroras of this archetypal giant planet