Use of radio occultation to probe the high-latitude ionosphere

[摘要] We have explored the use of COSMIC data to provide valuable scientificinformation on the ionospheric impacts of energetic particle precipitationduring geomagnetic storms. Ionospheric electron density in the E region, andhence ionospheric conductivity, is significantly altered by precipitatingparticles from the magnetosphere. This has global impacts on thethermosphere–ionosphere because of the important role of conductivity onhigh-latitude Joule heating. Two high-speed stream (HSS) and two coronalmass ejection (CME) storms are examined with the COSMIC data. We find clearcorrelation between geomagnetic activity and electron density retrievalsfrom COSMIC. At nighttime local times, the number of profiles with maximumelectron densities in the E layer (below 200 km altitude) is well correlatedwith geomagnetic activity. We interpret this to mean that electron densityincreases due to precipitation are captured by the COSMIC profiles. These"E-layer-dominant ionosphere" (ELDI) profiles have geomagnetic latitudesthat are consistent with climatological models of the auroral location. Forthe two HSS storms that occurred in May of 2011 and 2012, a stronghemispheric asymmetry is observed, with nearly all the ELDI profiles foundin the Southern, less sunlit, Hemisphere. Stronger aurora and precipitationhave been observed before in winter hemispheres, but the degree of asymmetrydeserves further study. For the two CME storms, occurring in July andNovember of 2012, large increases in the number of ELDI profiles are foundstarting in the storm's main phase but continuing for several days into therecovery phase. Analysis of the COSMIC profiles was extended to all localtimes for the July 2012 CME storm by relaxing the ELDI criterion and insteadvisually inspecting all profiles above 50° magnetic latitude forsignatures of precipitation in the E region. For 9 days during the July2012 period, we find a signature of precipitation occurs nearly uniformly inlocal time, although the magnitude of electron density increase may varywith local time. The latitudinal extent of the precipitation layers isgenerally consistent with auroral climatology. However, after the storm mainphase on 14 July 2012 the precipitation tended to be somewhat moreequatorward than the climatology (by about 5–10°latitude) and equatorward of the auroral boundary data acquired from theSSUSI sensor onboard the F18 DMSP satellite. We conclude that, if analyzedappropriately, high-latitude COSMIC profiles have the potential tocontribute to our understanding of MI coupling processes and extend andimprove existing models of the auroral region.

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