HR: 1340h
AN: SA13A-1063    [Abstracts]
TI: Seasonal and temporal variability of the equatorial ionosphere with radio occultation electron density profiles from CHAMP
AU: * Cahoy, K
EM: kerri.cahoy@gmail.com
AF: Stanford University, Dept. of Electrical Engineering 350 Serra Mall #325, Stanford, CA 94305, United States
AB: This work summarizes a portion of the more than two hundred thousand electron density profiles captured by the Challenging Mini-Satellite Payload for Geophysical Research (CHAMP, GFZ) from 2002-2006. The electron density profiles used in this work were processed by the Cosmic Data Analysis and Archival Center (CDAAC, UCAR) and released in July 2007. This recent release includes data not previously distributed by CDAAC, and nearly doubles the number of electron density profiles available through CDAAC. The local time of the electron density profiles varies throughout the solar day due to the geometry of the experiment (one ~400 km altitude near-polar orbiter with a ~90 minute period receives GPS signals until occulted by Earth). For a majority of the profiles, sampling occurs at two local times each day, separated by 12 hours, such that roughly every 120 days, the sampling local time repeats. The progression of local time with day of year for the CHAMP electron density profiles drives the selection of data subsets used in this multi-year study of electron density. The data are divided into local time windows from 06:00-10:00 (four hours before noon) and 22:00-02:00 (four hours near midnight). For the years 2002-2006, this yields twelve 60-day before-noon data subsets, and thirteen 60-day near-midnight data subsets. Each subset consists of roughly two thousand profiles. For each of these 25 data subsets, the electron density profiles are interpolated onto a global map with latitude and longitude, from 150-400 km altitude. The data are summarized both in terms of bulk trends as well as with focus on zonal structure. For example, the seasonal and interannual variability of the zonal mean equatorial electron density are presented, as well as a wave decomposition of the observed equatorial zonal structure at fixed altitudes, such that the possible effects of non-migrating tides on the ionosphere can be considered. The retrieved electron density profiles are sometimes also biased by steep horizontal electron density gradients in the ionosphere, and negative biases can be detected at lower altitudes in these data. The magnitude and geographical distribution of these biases at lower ionospheric altitudes is also assessed.
DE: 0300 ATMOSPHERIC COMPOSITION AND STRUCTURE
DE: 2400 IONOSPHERE (6929)
DE: 2415 Equatorial ionosphere
DE: 2427 Ionosphere/atmosphere interactions (0335)
SC: SPA-Aeronomy [SA]
MN: 2007 Fall Meeting