HR: 0800h
AN: SM41A-0325 [WITHDRAWN]    [Abstracts]
TI: Modeling Ionospheric HF/VHF Radio-Wave Absorption due to Solar Energetic Proton Events
AU: * Sauer, H H
EM: Herbert.H.Sauer@noaa.gov
AF: NOAA National Geophysical Data Center, E/GC2 325 Broadway, Boulder, CO 80305, United States
AU: Wilkinson, D C
EM: Daniel.C.Wilkinson@noaa.gov
AF: NOAA National Geophysical Data Center, E/GC2 325 Broadway, Boulder, CO 80305, United States
AB: Abstract Simple, one-parameter, algorithms have been applied to the observed energetic proton flux as provided by the GOES series of satellites to yield estimates of the high latitude HF and VHF radio-wave absorption for both day and night respectively. The twilight response is obtained as a bi-linear function of the solar zenith angle at the observation positions, and the latitude dependence of the absorption region near the edge of the absorbing region (the polar caps) are estimated from extant models of geomagnetic cut-offs and their dependence on geomagnetic activity. The approximate inverse square frequency dependence of ionospheric absorption is used to translate across the HF/VHF range and predictions of the minimum duration of events are determined. Calculations of the polar cap absorption of HF radio waves have been performed for eleven larger Solar Energetic Proton (SEP) events during the period from 1992 through 2002 and the results compared to observations of 30 MHz Riometers operated by the AFGL and located at Thule, Greenland. While discrepancies between the estimated and observed absorption using these procedures occur, especially at low absorption levels, this model has operational value in view of its simplicity and its being the only extant model, to our knowledge, which treats solar-illumination, geomagnetic cutoff variation, and frequency effects, at least to first order. Specimen graphical representations of the north and south polar caps illustrate the output of the model for the peak of the 12 December 2006 solar proton event. Given sufficient interest, improvements to the methodology used here are practicable and could be expected to achieve accuracies to the order of 25% or better.
DE: 2447 Modeling and forecasting
DE: 2475 Polar cap ionosphere
DE: 2479 Solar radiation and cosmic ray effects
DE: 6964 Radio wave propagation
SC: SPA-Magnetospheric Physics [SM]
MN: 2007 Fall Meeting