Kaori Terada

Comparison of the Martian thermospheric density and temperature from IUVS/MAVEN data and general circulation modeling

IUVS/MAVEN data are archived in the Planetary Atmospheres Node of the Planetary Data System (http://pds-atmospheres.nmsu.edu). Modeling data supporting the figures are available upon request from A.S.M. (medvedev@mps.mpg.de). The work was partially supported by German Science Foundation (DFG) grant ME2752/3-1. E.Y. was partially supported by NASA grant NNX13AO36G.

Global Distribution and Parameter Dependences of Gravity Wave Activity in the Martian Upper Thermosphere Derived from MAVEN NGIMS Observations

Wavelike perturbations in the Martian upper thermosphere observed by the Neutral Gas Ion Mass Spectrometer (NGIMS) onboard the Mars Atmosphere and Volatile EvolutioN (MAVEN) spacecraft have been analyzed. The amplitudes of small-scale perturbations with apparent wavelengths between ~100 and ~500 km in the Ar density around the exobase show a clear dependence on temperature (T0) of the upper thermosphere. The average amplitude of the perturbations is ~10% on the dayside and ~20% on the nightside, which is about 2 and 10 times larger than those observed in the Venusian upper thermosphere and in the low-latitude region of Earths upper thermosphere, respectively. The amplitudes are inversely proportional to T0, suggesting saturation due to convective instability in the Martian upper thermosphere. After removing the dependence on T0, dependences of the average amplitude on the geographic latitude and longitude and solar wind parameters are found to be not larger than a few percent. These results suggest that the amplitudes of small-scale perturbations are mainly determined by convective breaking/saturation in the upper thermosphere on Mars, unlike those on Venus and Earth.

Polar cap ionosphere and thermosphere during the solar minimum period: EISCAT Svalbard radar observations and GCM simulations

The IPY long-run data were obtained from the European Incoherent Scatter Svalbard radar (ESR) observations during March 2007 and February 2008. Since the solar and geomagnetic activities were quite low during the period, this data set is extremely helpful for describing the basic states (ground states) of the thermosphere and ionosphere in the polar cap region. The monthly-averaged ion temperatures for 12 months show similar local time (or UT) variations to each other. The ion temperatures also show significant seasonal variations. The amplitudes of the local time and seasonal variations observed are much larger than the ones predicted by the IRI-2007 model. In addition, we performed numerical simulations with a general circulation model (GCM), which covers all the atmospheric regions, to investigate variations of the neutrals in the polar thermosphere. The GCM simulations show significant variations of the neutral temperature in the polar region in comparison with the NRLMSISE-00 empirical model. These results indicate that both the ions and neutrals would show larger variations than those described by the empirical models, suggesting significant heat sources in the polar cap region even under solar minimum and geomagnetically quiet conditions.

Comparison of the Martian thermospheric density and temperature from IUVS/MAVEN data and general circulation modeling: IUVS-MGCM COMPARISON

1.Planetary Atmosphere Physics Laboratory, Department of Geophysics, Graduate School of Science, Tohoku University, 2.Graduate School of Science, University of Tokyo, 3.Max Plank Institute for Solar System Reserach, Gottingen, Germany, 4.Laboratory for Atmospheric and Space Physics, University of Colorado Boulder, 5.Computational Physics, Inc., 6.Lunar and Planetary Laboratory, University of Arizona

Characteristics of Temperature and Density Structures in the Equatorial Thermosphere Simulated by a Whole Atmosphere GCM

Numerical simulations of the thermospheric temperature and mass density variations have been performed with a whole atmosphere general circulation model (GCM) which includes all the atmospheric regions: troposphere, stratosphere, mesosphere, and thermosphere. The GCM simulations represent hour-to-hour variations of the thermosphere due to effects from the lower atmosphere. The GCM also reproduces some characteristics of the thermospheric temperature and density structures: e.g., the midnight temperature maximum (MTM) and midnight density maximum (MDM) in the equatorial upper thermosphere. The MTMs and MDMs simulated here have the maximum amplitudes of 73 K and 19%, respectively, which are consistent with previous observations. The MTMs and MDMs simulated by the GCM also vary from hour to hour. The amplitude and location of the MTM depend on UT or longitude. In the dayside of the low-latitude region, the double-hump structure of the mass density is also seen in the GCM results. The lower atmospheric effects on the thermosphere would be important for generation of the mass density structure.