How do gravity waves determine the global distributions of winds, temperature, density and turbulence within a planetary

1. ITM Science Questions How do gravity waves determine the global distributions of winds, temperature, density and turbulence within a planetary atmosphere? What is the fundamental physics, and what are the practical consequences, of plasma-neutral coupling in the presence of a magnetic field? What are the density, temperature and wind structures in Mars’ atmosphere, and what are the fundamental processes determining these structures and their variability? What is the nature and extent of upper atmosphere chemical modifications due to energetic particle precipitation, what is the role of transport, and what are the short- and long-term consequences? What is the response of the ionosphere and thermosphere to solar activity and magnetic storms, what are the relative roles of winds, plasma-neutral coupling, and electric fields in determining the response, and what are the consequences for society?

2. How do gravity waves determine the global distributions of winds, temperature, density and turbulence within a planetary atmosphere? • GWs represent an important mechanism for redistributing energy and momentum within a planetary atmosphere. • On Earth, major modifications in wind and temperature structures are known to occur due to dissipation of GW. • The physics of gravity wave forcing (i.e., convection, shear instability, topography, Joule heating, JxB) and the spatial-temporal distributions of forcing mechanisms are poorly known. • The basics physics of wave instabilities; wave-wave, wave-mean flow, and wave-turbulence interactions; and wave dissipation are poorly known. • Parameterizations of GW effects differ widely in their basic physical formulations, and in results produced in GCM simulations. • Similar problems exist both on Earth and Mars, and probably other planetary atmospheres. • It makes sense to first comprehensively address many of the above problems on Earth, and utilize this knowledge to advance our understanding and modeling capability of Mars’ atmosphere.

3. What is the fundamental physics, and what are the practical consequences, of plasma-neutral coupling in the presence of a magnetic field? • Plasma-neutral coupling in the presence of a magnetic field is fundamental to our understanding of magnetosphere-ionosphere coupling, the disturbance and Sq wind dynamos, and the F-region dynamo in Earth’s atmosphere. • Magnetosphere-ionosphere coupling includes 3-D closure of currents, Joule heating, transfer of momentum to the neutral atmosphere by convection-driven ion drifts, and the so-called flywheel effect whereby the spun-up neutral circulation drives the magnetosphere after convection has subsided. • All of the above processes affect the variability of the global ionospheric state, including the development of instabilities and consequent small-scale plasma structures. • Similar physics is potentially important for solar wind interactions with the upper atmosphere of Mars, in particular plasma-neutral interactions in the presence of magnetic anomalies of crustal origin and the solar wind/IMF. • The physics of solar wind-magnetoplasma-neutral interactions at Mars is not well understood, but may be critical to the scavenging process and hence the current and past evolution of Mars atmosphere. • Plasma-neutral interactions may have been considerable more important in the past, when Mars’ atmosphere may have been more dense, and the solar wind/IMF more intense, perhaps in the presence of a greater intrinsic magnetic field than now exists at Mars.

4. What are the density, temperature and wind structures in Mars’ atmosphere, and what are the fundamental processes determining these structures and their variability? • The mean state and variability of Mars upper atmosphere (UA) is strongly driven by upward-propagating solar-driven thermal tides excited in the lower atmosphere, solar radiative forcing, CO2 cooling, and during some seasons, dust storms. Upper atmosphere variability below 200 km due to solar wind effects is small. • In the above sense, Mars’ upper atmosphere is driven by the same processes as Earth’s upper atmosphere during solar minimum, when geomagnetic forcing is at a minimum. The effects of large-scale waves on Mars upper atmosphere is in fact considerably larger than that on Earth. • Many key aspects of UA dynamics on both Earth and Mars are poorly understood, such as wave-wave coupling, wave-turbulence coupling, wave-mean flow interactions, the effects of radiative cooling on waves, etc. A comparative planetary study of these processes on Earth and Mars is scientifically synergistic, and will also lead to improved understanding of similar processes on Venus and the outer planets. • Measurements of density, temperature and wind structures in Mars’ UA (i.e., 25-200 km) are required in order to adequately define and ultimately predict the aerobraking and aerocapture environments for manned exploration of Mars. Such measurements will be used to (a) construct empirical models; (b) constrain Mars GCMs; and (c) form a database for data assimilation efforts. • At present, there are no wind measurements in Mars UA, no satellite-based temperature measurements above 50 km, and no density measurements, except for a few entry probes and accelerometer data between 100-150 km from MGS and Odyssey. All of the available data are extremely limited in season, latitude and local time.

5. What is the response of the ionosphere and thermosphere to solar activity and magnetic storms, what are the relative roles of winds, plasma-neutral coupling, and electric fields in determining the response, and what are the consequences for society? Priorities Determine the effects of long- and short-term variability of the Sun on the global-scale behavior of the ionospheric electron density. Determine the solar and geospace causes of small-scale ionospheric density irregularities in the 100 to 1000 km altitude range. Determine the effects of solar and geospace variability on the atmosphere enabling an improved specification of the neutral density in the thermosphere. Understand how solar variability and the geospace response determine the distribution of electric currents that connect the magnetosphere to the ionosphere. • Primary Questions • What is the contribution of solar EUV to ionospheric variability? • How does the middle- and low-latitude I-T system respond to geomagnetic storms (positive storm phases)? • How do negative ionospheric storms develop, evolve, and recover? • How are ionospheric irregularities produced, especially at mid-latitudes? • What is the variability of the thermosphere attributable to solar EUV spectral irradiance, and to magnetospheric coupling?