Physics
Scientific paper
Dec 2011
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2011agufmsm13d2117r&link_type=abstract
American Geophysical Union, Fall Meeting 2011, abstract #SM13D-2117
Physics
[6939] Radio Science / Magnetospheric Physics, [6969] Radio Science / Remote Sensing, [6984] Radio Science / Waves In Plasma, [7954] Space Weather / Magnetic Storms
Scientific paper
This paper presents the variation of electron density and ion effective mass (meff) as a function of geomagnetic activity. The study is based on the (1) analysis of whistler mode echoes observed by RPI/IMAGE, (2) DMSP electron and ion density measurements at 840 km, and (3) ground transmitter signals spectral broadening observed by RPI/IMAGE during both quiet (Kp<2-3 and -20 nT < Dst < 20 nT) and disturbed periods in Aug-Dec 2005. A disturbed period includes one or more geomagnetic storms (Kp >5 and Dst <-50 nT), their onset and recovery periods. From Aug-Dec 2005, there was one disturbed period (Aug 23-Sep 24), which includes three major (Dst < -100 nT) and two moderate (< -50 nT) geomagnetic storms. During this period magnetospherically reflected (MR) and specularly reflected (SR) whistler mode (WM) echoes have been observed on IMAGE [Sonwalkar et al., 2011]. Most often SR echoes are patchy, i.e. at few frequencies echoes are absent. A study of patchy echoes indicated that large scale irregularities, believed to be responsible for the absence of echoes, are present during both quiet and disturbed periods. The ground transmitter signals showed evidence of spectral broadening during both quiet and disturbed periods. The analysis of MR and SR echoes observed during this disturbed period allow us to study the variations in electron density and ion effective mass as a function of storm onset, main phase, and recovery period. We selected six cases of WM radio sounding at L~2.0 at similar MLTs, one case before the first storm onset, one case during the main phase of the third storm, two cases during the subsequent recovery period of the second storm, and two cases at the end of the recovery period of the last storm. Raytracing analysis of these cases revealed that: (1) Compared to the preceding quiet time of the storm there was an increase in the electron density and then a decrease during the recovery period. ( 2) Compared to the quiet conditions before and after the storm, there was an increase in meff at altitudes below ~ 1500 km during the recovery period. The meff during the main phase of the storm is comparable to those calculated before the onset of the storm. An increase in meff during the recovery period of the storm indicates an increase in the oxygen ion density and thus an increase in the O+- H+ transition height. (3) The transition height before the onset of the storm is ~1150 km, during the recovery period of the storm it increased to ~ 1600 km and at the end of the recovery period it again decreased to ~840 km. The results obtained from this analysis are in general agreement with those measured by the DMSP satellite at ~ 840 km. We believe that our work will shed light on understanding the response of the inner magnetosphere to geomagnetic storms.
Reddy Akula Aneesh
Sonwalkar Vikas S.
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