Use of radio occultation to probe the high-latitude ionosphere

Abstract

Abstract.We have explored the use of COSMIC data to provide valuable scientific information on the ionospheric impacts of energetic particle precipitation during geomagnetic storms. Ionospheric electron density in the E region, and hence ionospheric conductivity, is significantly altered by precipitating particles from the magnetosphere. This has global impacts on the thermosphere-ionosphere because of the important role of conductivity on high-latitude Joule heating. Two high-speed stream (HSS) and two coronal mass ejection (CME) storms are examined with the COSMIC data. We find clear correlation between geomagnetic activity and electron density retrievals from COSMIC. At nighttime local times, the number of profiles with maximum electron densities in the E layer (below 200 km altitude) is well correlated with geomagnetic activity. We interpret this to mean that electron density increases due to precipitation are captured by the COSMIC profiles. These "E-layer-dominant ionosphere" (ELDI) profiles have geomagnetic latitudes that are consistent with climatological models of the auroral location. For the two HSS storms that occurred in May of 2011 and 2012, a strong hemispheric asymmetry is observed, with nearly all the ELDI profiles found in the Southern, less sunlit, Hemisphere. Stronger aurora and precipitation have been observed before in winter hemispheres, but the degree of asymmetry deserves further study. For the two CME storms, occurring in July and November of 2012, large increases in the number of ELDI profiles are found starting in the storm's main phase but continuing for several days into the recovery phase. Analysis of the COSMIC profiles was extended to all local times for the July 2012 CME storm by relaxing the ELDI criterion and instead visually inspecting all profiles above 50 • magnetic latitude for signatures of precipitation in the E region. For 9 days during the July 2012 period, we find a signature of precipitation occurs nearly uniformly in local time, although the magnitude of electron density increase may vary with local time. The latitudinal extent of the precipitation layers is generally consistent with auroral climatology. However, after the storm main phase on 14 July 2012 the precipitation tended to be somewhat more equatorward than the climatology (by about 5-10 • latitude) and equatorward of the auroral boundary data acquired from the SSUSI sensor onboard the F18 DMSP satellite. We conclude that, if analyzed appropriately, high-latitude COSMIC profiles have the potential to contribute to our understanding of MI coupling processes and extend and improve existing models of the auroral region.

Evaluation of E Layer Dominated Ionosphere Events Using COSMIC/FORMOSAT-3 and CHAMP Ionospheric Radio Occultation Data

“…In examining the influence of geomagnetic storms, we found an increase in the number of ELDI events during storm times, accompanied by a slight shift of the auroral ELDI distributions towards lower latitudes. Our results confirm and extend the findings of Mayer and Jakowski [4], Cai et al [6], and Mannucci et al [7]. Compared to previous work, we did all our analyses utilizing an IRO database that covers a very long period and includes a large amount of electron density profiles, which were obtained from two different satellite missions.…”

“…The results indicate that the number of ELDI events increased around the main phase of the storms, i.e., around the Dst minimum. This result correlates with the findings of Mannucci et al [7],…”

“…The results indicate that the number of ELDI events increased around the main phase of the storms, i.e., around the Dst minimum. This result correlates with the findings of Mannucci et al [7], who have also found an increase in the number of ELDI events during geomagnetic storms. A possible reason for the observed variation of %ELDI could be that geomagnetic storms are induced by CMEs or HSSs from the Sun, which are accompanied by an increase in the flow of solar charged particles.…”

“…Mannucci et al [7] investigated energetic particle precipitation associated with geomagnetic storms. For this purpose, they analyzed electron density profiles that were retrieved for both hemispheres during four geomagnetic storms.…”

“…By evaluating IRO data for the entire high latitude regions of both hemispheres, we would like to confirm the diurnal and the seasonal variation of ELDI events and put their analysis on a broader basis. Through the evaluation of individual years and the examination of selected storm events, Mayer and Jakowski [4] and Mannucci et al [7] have found a correlation between ELDI occurrence and geomagnetic activity. In this context, they observed an increase in the size and width of the elliptic concentration of ELDI events at times of increased geomagnetic activity.…”