Lower Atmosphere Effects on Thermospheric and Ionospheric Variability

Details Lower Atmosphere Effects on Thermospheric and Ionospheric Variability Lower Atmosphere Effects on Thermospheric and Ionospheric Variability

May 2006

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2006agusmsa22a..05t&link_type=abstract

American Geophysical Union, Fall Meeting 2007, abstract #SA22A-05

Physics

3369 Thermospheric Dynamics (0358), 3389 Tides And Planetary Waves, 2437 Ionospheric Dynamics, 3332 Mesospheric Dynamics

Scientific paper

The Ionosphere-Thermosphere-Mesosphere (ITM) region is highly variable and has a complex system of drivers including variable solar radiation, geomagnetic activity, and forcing from the lower atmosphere. Waves that originate in the troposphere grow in amplitude as they travel upwards into decreasing density at higher altitudes where they become the most prominent dynamical features of the ITM. Planetary and gravity waves modify the zonal mean temperature and winds through dissipation and momentum deposition. The effects of these waves on the ITM are expected to depend on the level of solar activity. For all types of waves, how high they penetrate into the thermosphere depends on the temperature, wind, and viscosity profiles. Current observations have shown signatures of both gravity waves and planetary waves in upper atmospheric measurements of winds, temperature, and ion density. The momentum deposition from upward propagating waves is thought to generate the quasibiennial oscillation (QBO) and semiannual oscillation (SAO) in the zonal circulation of the stratosphere and mesosphere. These zonal wind oscillations, in turn, modulate the waves as they propagate upwards, including the migrating and nonmigrating tides. Understanding the behavior of the tides is not only crucial to characterizing mesopause variability but also transport in the region. Momentum deposition by the diurnal tide at low latitudes in the lower thermosphere produces indirect circulations that will transport neutral and ionized constituents both vertically and horizontally to higher latitudes. While magnetospheric forcing dominates the variability at high latitudes in the ionosphere and thermosphere, photochemistry and neutral dynamics play dominant roles in the ITM structure and variability at mid and low latitudes. The wind-driven E-region dynamo generates large-scale electric fields, causing upward plasma drifts that combine with pressure forces and gravity to form the equatorial ionization anomaly in electron density. As a result, variability in E-region winds could translate upwards into the low-latitude ionosphere. The dominant dynamical feature in the E-region is the diurnal tide, and its seasonal, interannual, and daily variability are important factors in understanding the behavior of the ionosphere. Recent global observations of the low latitude neutral atmospheric and ionospheric structure revealed by TIMED/SABER, TIMED/GUVI, TOPEX, JASON, and DMSP allow us to investigate the interplay between the neutral, plasma, and background fields. In this talk we examine the relationship between the variability observed in mesospheric and lower thermospheric dynamical fields to variations observed in the low latitude ionosphere using these long-term global satellite observations.

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