HR: 11:05h
AN: SM32A-04    [Abstracts]
TI: Observations of Magnetospherically Reflected (MR), Specularly Reflected (SR), and Back Scattered (BS) Whistler Mode (WM) Echoes Observed by Radio Plasma Imager (RPI) on IMAGE: Diagnostics of Electron Density, Density Structure, and Ion Composition
AU: * Sonwalkar, V S
EM: ffvss@uaf.edu
AF: University of Alaska Fairbanks, POB 755915, Electrical and Computer Engineering Department, University of Alaska Fairbanks, Fairbanks, AK 99775, United States
AU: Reddy, A
EM: ftar1@uaf.edu
AF: University of Alaska Fairbanks, POB 755915, Electrical and Computer Engineering Department, University of Alaska Fairbanks, Fairbanks, AK 99775, United States
AU: Carpenter, D L
EM: dlc@nova.stanford.edu
AF: Stanford University, Electrical Engineering Department, STAR Laboratory, Stanford University, Stanford, CA 94305, United States
AU: Reinisch, B
EM: bodo_reinisch@uml.edu
AF: University of Massachusetts Lowell, Department of Environmental, Earth & Atmospheric Sciences, University of Massachusetts Lowell, Lowell, MA 01845, United States
AB: At low altitude (<5,000-10,000 km) RPI on IMAGE has observed a variety whistler mode (WM) echoes at all latitudes at frequencies up to 300 kHz. A survey of WM echoes observed in 2004-2005 during 3.2 ms pulse transmissions in the 6-63 kHz frequency range, with a step frequency of 0.3 kHz, has revealed several new features of WM echoes and helped in their interpretation. Based on the reflection mechanism WM echoes can be classified as: magnetospherically reflected (MR), or specularly (SR) reflected, or back scattered (BS). Furthermore, based on the characteristic spectral form WM echoes can be classified as discrete, or multipath, or diffuse echoes. The MR echoes are reflected at the altitude (>1,000 km) where the local lower hybrid frequency (f_lh) is equal to the transmitted pulse frequency f. The SR echoes are reflected at the Earth-ionosphere boundary (altitude ~90 km). The BS echoes are the result of diffuse reflections from small scale plasma density irregularities close to IMAGE. The discrete WM echoes with relatively small spreading in time delays (<5-10 ms) at each frequency occur under relatively smooth plasma density variation along the geomagnetic field (B₀) passing through IMAGE. The multipath echoes with medium spreading in time delays (~ 10-30 ms) at each frequency occur when large scale (~1-10 km) field aligned irregularities (FAI) are present near (B₀). The diffuse echoes with large spreading in time delays (>30-40 ms) occur when small scale (~10 m - 100 m) field aligned irregularities (FAI) are present near (B₀). We distinguish diffuse SR and MR echoes from BS echoes. The first two undergo reflections at the Earth-ionosphere boundary and MR reflection, respectively, whereas the third one does not. Though most of the WM echoes observed in a typical RPI plasmagram can be classified as above, a significant number of echoes display characteristics of one type of echo at certain frequencies and that of other type at certain other frequencies. We provide examples of the variety of echoes (discrete, multipath, and diffuse SRWM; discrete, multipath, and diffuse MRWM; BS) observed and explain their generation mechanisms. With the help of two case studies we illustrate how observed dispersion of MRWM and SRWM echoes combined with ray tracing simulations leads to the determination of electron density, density irregularities, and ion composition along the field line passing through IMAGE.
DE: 2403 Active experiments
DE: 2439 Ionospheric irregularities
DE: 2481 Topside ionosphere
DE: 2487 Wave propagation (0689, 3285, 4275, 4455, 6934)
DE: 2768 Plasmasphere
SC: SPA-Magnetospheric Physics [SM]
MN: 2007 Fall Meeting