HR: 0800h
AN: SA31A-1116    [Abstracts]
TI: Short range VLF sky wave observations of lightning-induced ionospheric effects
AU: * Cotts, B R
EM: bcotts@stanford.edu
AF: Stanford University, 350 Serra Mall #037, Stanford, CA 94305 United States
AU: Inan, U S
EM: inan@nova.stanford.edu
AF: Stanford University, 350 Serra Mall #037, Stanford, CA 94305 United States
AB: At locations close (~100-km) to a VLF transmitter, observation of the sky wave signal from the transmitter is possible by aligning a proximate magnetic loop antenna to null the ground signal. Previous observations using this arrangement [e.g., Rodriguez et al. 1992], and [Pasko et al., 2002] show a very high degree of temporal variability in received signal amplitude. Consideration of Early/Fast and Lightning-induced Electron Precipitation (LEP) events under these constraints show an unusual number of remarkably large events. For example, we have observed Early/Fast events with positive amplitude changes up to ~8 dB and negative amplitude changes as high as ~19 dB. In addition we have observed possible LEP events with positive amplitude changes of ~5 dB and onset duration of 15 seconds. The recovery signatures of these events are also very unusual, often with non-exponential recovery, or no recovery at all. Combining the data from previous campaigns with a recent data set (August 2004) of observations at Arecibo, Puerto Rico we analyze three separate instances in which a magnetic loop antenna is deployed with the intent of observing the sky wave. In this paper we report the results of the analysis of this data to quantitatively determine whether the anomalous nature of these findings is primarily due to the high inherent variability of the observed amplitude signal or the close proximity of the receiver to the disturbed ionospheric region, which must necessarily be nearly overhead the receiver and/or transmitter.
DE: 6900 RADIO SCIENCE
DE: 6929 Ionospheric physics (2409)
DE: 2487 Wave propagation (6934)
SC: SPA-Aeronomy [SA]
MN: 2004 AGU Fall Meeting