Physics
Scientific paper
Dec 2010
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2010agufmsa33b1780w&link_type=abstract
American Geophysical Union, Fall Meeting 2010, abstract #SA33B-1780
Physics
[2435] Ionosphere / Ionospheric Disturbances, [2479] Ionosphere / Solar Radiation And Cosmic Ray Effects, [6929] Radio Science / Ionospheric Physics, [6969] Radio Science / Remote Sensing
Scientific paper
It is well known that subionospherically-propagating very low frequency (VLF) signals are sensitive to the ionospheric effects of solar flares. It has been documented since the 1960's that the typical X-ray flare affects the phase of the VLF signal (known as a sudden phase anomaly, or SPA), but a sudden change in both the amplitude and the phase of the narrowband VLF signal may be produced during a C-class or stronger emission. Previous research has studied event onset times, growth rates, and recovery times, for example. In January 2010, the ELF/VLF radiometer at Arrival Heights (which was installed in 1984) was upgraded to continually record both the extremely low frequency (ELF) and the very low frequency (VLF) bands. This upgrade additionally provided the first real-time signal processing of narrowband VLF transmitter signals at Arrival Heights. Since that time, near-real-time amplitude and phase summary charts of subionospherically-propagating narrowband VLF signals recorded at Arrival Heights have been posted to the Internet, updated once per minute. Observations of sudden amplitude and phase anomalies were observed in this data stream on 12 June 2010 and on 7 August 2010, and the full resolution broadband data sets were downloaded at that time, demonstrating the scientific utility of the receiver upgrade providing near-real-time data access. In this paper, we demonstrate a new spread-spectrum analysis technique to analyze the sudden anomalies observed at Arrival Heights as a function of frequency. The 200-Hz bandwidth of the narrowband VLF signal is fully utilized to analyze the effect of these events on VLF propagation as a function of frequency within the band. Events were observed at Arrival Heights using the NAA (24.0 kHz, Cutler, Maine) and NLK (24.8 kHz, Jim Creek, Washington) transmitter signals, and to our knowledge, these are the first narrowband VLF events recorded at Arrival Heights to be analyzed.
Fraser-Smith Antony C.
Moore Robert C.
Wang Tower
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