Computer Science – Sound
Scientific paper
Dec 2009
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2009agufmsm44a..05s&link_type=abstract
American Geophysical Union, Fall Meeting 2009, abstract #SM44A-05
Computer Science
Sound
[2403] Ionosphere / Active Experiments, [6964] Radio Science / Radio Wave Propagation, [6969] Radio Science / Remote Sensing, [6984] Radio Science / Waves In Plasma
Scientific paper
This paper presents observations of whistler mode (WM) echoes on the IMAGE satellite at altitudes less than Rflhmax~2,000 km, where Rflhmax is the altitude at which lower hybrid frequency (flh) along the geomagnetic field line (B) passing through the satellite attains a local maximum value. Previous observations of WM echoes were typically above Rflhmax altitude [ Sonwalkar et al., URSI XXIX General Assembly, Chicago, 2008]. Three types of WM echoes are observed: magnetospherically reflected (MR), normally incident specularly reflected (NISR), and obliquely incident specularly reflected (OISR) whistler mode echoes. MR-WM echoes reflect at an altitude where flh~f, where f is the transmitted frequency, and NISR- and OISR-WM reflect near ~90 km. All three types of echoes frequently show spread in time delays indicative of multipath propagation or scattering due to field aligned irregularities. WM echo observations reported here possess the following new features:(1) MR-WM echoes reported here reflect at an altitude above the satellite and below Rflhmax, whereas those reported previously reflect at an altitude below the satellite and above Rflhmax. (2) First simultaneous observation of NISR- and OISR-WM echoes. (3) First observation of an SR echo reflecting from the hemisphere opposite to that of the satellite. Assuming that the magnetospheric plasma can be described by a diffusive equilibrium model, dispersion of MR- and SR-WM echoes allow determination of electron density and ion composition (H+, He+, O+) between Rflhmax and ~90 km along B. WM sounding observations from 21 June 2004 (Altitude =1280 km, λm=62°, MLT=6) are used to illustrate how the observed dispersion of MR- and SR-WM echoes combined with ray tracing simulations leads to the determination of electron density and ion composition along B between Rflhmax~2,070 km and ~90 km. The density model determined has an O+/H+ transition height at 1,820 km and F2 peak electron density of 2.6×105el-cm-3 at ~240 km, in general consistent with past observations. Analysis of WM echo observations reported here provides a better understanding of lightning-generated subprotonospheric (SP) whistlers. In general, the significance of WM echo observations on IMAGE lies in its potential for probing the low altitude region that is important for understanding ionosphere-magnetosphere coupling.
Carpenter Donald L.
Hazra S.
Mayank K.
Reddy Akula Aneesh
Reinisch Bodo. W.
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