HR: 11:20h
AN: SA42A-05 INVITED     [Abstracts]
TI: The Thermospheric Response to Solar Irradiance Variation
AU: * Solomon, S C
EM: stans@ucar.edu
AF: High Altitude Observatory National Center for Atmospheric Research, 1850 Table Mesa Dr., Boulder, CO 80307, United States
AU: Qian, L
EM: lqian@ucar.edu
AF: High Altitude Observatory National Center for Atmospheric Research, 1850 Table Mesa Dr., Boulder, CO 80307, United States
AB: The basic structure and variation of density and composition in the thermosphere has been well-characterized since the beginning of the space age, due to the need for quantifying the effect of atmospheric drag on satellites in low-Earth orbit, and the data obtained from measuring the changes in those orbits. Empirical models constructed using satellite drag, mass-spectrometer, radar, occultation, and other techniques, have carried this forward to a highly developed state, but are still dependent on the indices used to drive them, and are known to be less reliable during periods of significant geomagnetic disturbance. In the case of solar ultraviolet irradiance variation on solar-cycle, solar-rotational, and shorter time scales, the effect on thermospheric density and composition is in principle better understood, but the proxy index approach still has limitations, including systematic solar-cycle non-linearities at lower solar activity, and poorer short-term correlations at high solar activity. Recent work has shown that using measured solar irradiances in empirical and theoretical models can improve the validity of these models in comparison with observed density fluctuations. An additional challenge is to bring theoretical models to a degree of fidelity that could make them competitive with empirical models for near-real-time description or even short-term forecasting of thermospheric density, composition, and temperature, including geomagnetic as well as solar irradiance effects. In this presentation, we briefly review the history and state of the field, and demonstrate use of the NCAR Thermosphere-Ionosphere General Circulation Model, using measured solar ultraviolet irradiance as an input, to simulate the thermospheric density distribution. These simulations are compared with empirical models and with density measurements obtained from satellite drag analyses. We show that when seasonal effects are fully accounted for, this theoretical modeling approach can be an improvement over the empirical approach for describing the density of the thermosphere.
DE: 0355 Thermosphere: composition and chemistry
DE: 0358 Thermosphere: energy deposition (3369)
DE: 2447 Modeling and forecasting
SC: SPA-Aeronomy [SA]
MN: 2007 Joint Assembly