scostep 2010 (stp12) - Leibniz-Institut für Atmosphärenphysik an der ...

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STP12 Abstracts Berlin, 12 - 16 July 2010 SCOSTEP Symposium 2010 Non-Migrating Tidal Effects in the Ionosphere as simulated by TIME-GCM Maute Astrid 1 , Hagan Maura 1 , Richmond Arthur 1 , Roble Raymond 1 , Zhang Xiaoli 2 , Forbes Jeffrey 2 1 NCAR / HAO, 2 University of Colorado at Boulder The ionosphere and the electrodynamics of the atmosphere are closely intertwined. Although the ionosphere is ionized mainly by solar radiation it is also influenced from below. Spaceborne observations of ionospheric densities and derived ExB/B^2 drift at low and mid latitude show longitudinal variations even during geomagnetic quiet times. Studies have confirmed that many of these variations can be connected to the propagation of non-migrating tides which are excited in the troposphere. The National Center for Atmospheric Research (NCAR) Thermosphere-Ionosphere- Mesosphere-Electrodynamics General Circulation model (TIME-GCM) can reproduce part of the longitudinal variation if forced with the Global Scale Wave Model (GSWM) at the lower boundary (ca. 30 km). We will use an updated GSWM-09 tidal climatology to force TIME- GCM from below in order to examine the tidal effects in the ionosphere. We will focus on geomagnetic quiescent conditions and report on the seasonal variability of the electrodynamic effects of the tides. Comparisons with space-borne observations can show how realistic these effects might be. Model studies like this can help to understand if certain tides are more effective in varying the ionosphere.
STP12 Abstracts Berlin, 12 - 16 July 2010 SCOSTEP Symposium 2010 Gravity waves and their effects in the thermosphere during low and high solar activity Yigit Erdal 1 , Medvedev Alexander 2 1 University of Michigan, 2 Max Planck Institute for Solar System Research Propagation of internal gravity waves (GWs) from the lower atmosphere into the upper thermosphere, and their dynamical and thermal effects have been studied under low and high solar activity described by the F10.7 cm parameter. A nonlinear spectral parameterization accounting for different dissipation mechanisms of GW harmonics in the thermosphere has been used in offline calculations with typical wind and temperature distributions from the HWM and MSISE-90 models, and in simulations with the University College London Coupled Middle Atmosphere-Thermosphere-2 (CMAT2) general circulation model (GCM) under solstice conditions. GW harmonics with horizontal phase speeds less than 100 m s -1 have been utilized with an appropriate distribution of initial wave momentum fluxes at the source level (15 km). GW drag and wave-induced heating/cooling turned out to be smaller below ~170 km at high solar activity, and larger above, compared to the low solar activity case. The maxima of GW momentum deposition occur much higher in the upper thermosphere, but their peaks are half as strong in the winter hemisphere when the solar insolation is large. Instead of strong net cooling in the upper thermosphere, GWs produce a weak heating at high solar activity created by fast, high-frequency waves that are less affected by attenuation. Molecular viscosity increases with solar activity at fixed pressure levels, but seen in the Cartesian altitude coordinates it can either increase or decrease in the lower thermosphere, depending on the height. Therefore, in pressure coordinates, in which most GCMs operate, the influence of larger temperatures on GWs can be viewed as a competition between the enhanced dissipation and vertical expansion of the atmosphere.
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scostep 2010 (stp12) - Leibniz-Institut für Atmosphärenphysik an der ...

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