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| Author: | Joydeep Bhattacharyya |
| Institution: | SAIC, 1300 N. 17th St., Suite 1450, Arlington, VA 22209 |
| Email: | joydeep.bhattacharyya@saic.com |
| Authors: | Joydeep Bhattacharyya, Claus Hetzer, Milton Garces, Victoria Oancea |
Abstract Title:
"Description and Analysis of Infrasound Signals Recorded from the North Pacific Event of February 22, 2003" |
Abstract:
Description and Analysis of Infrasound Signals Recorded from the North Pacific event of February 22, 2003
Joydeep Bhattacharyya1, Claus Hetzer2, Milton Garcés2, Victoria Oancea1
Science Applications International Corporation1; University of Hawaii, Manoa2
Sponsored by the DoD Nuclear Arms Control Technology Program
under
Contract DASG60-03-C-0009, U.S. Army Space and Missile Defense Command
The International Data Centre (IDC) Reviewed Event Bulletin (REB) for February 22, 2003 reported an event in the North Pacific formed using observations from three IMS infrasound stations. Such events are rare because infrasound signals are usually observed at regional distances (< 2000 km), making it difficult for the sparse, incomplete IMS network to locate an event with only infrasound arrivals. In this study we investigate the signals reported in the IDC REB, analyze additional infrasound data from stations that detected this event, and propose a source for the event.
The February 22, 2003 REB infrasound event was built using observations from I59US, I34MN, and I10CA. We analyze data from I10CA, I34MN, I53US, I57US and I59US but do not find any impulsive signals corresponding to the reported event. With the exception of I59US, there is very little coherent energy at frequencies above 0.6 Hz that would correspond to the arrivals in the REB. A transient signal at I59US is roughly consistent with the features of the REB arrival. However, all five of the stations contain relatively low-frequency signals (0.1-0.6 Hz), which persist over a long period of time (e.g., hours). Thus, this event was likely built using these low frequency signals. We note that the REB did not provide information about the frequency content of the arrivals.
We hypothesize that microbarom energy from storms in the North Pacific is the most likely source of the REB event. This hypothesis is based on the following observations: a) coherent signals are observed in the 0.1 - 0.7 Hz frequency band on all five arrays corresponding to the time of the REB event; b) back-azimuths estimated from the coherent signals point to one or both of the two separate storms present in the North Pacific during the time of the REB event; and c) the characteristics of the infrasound signals (e.g., correlation across array, back-azimuth estimates, frequency content) persist for several hours both before and after the time of the REB event. Though the location of the REB event corresponds closely to the larger of the two storms, our analysis suggests that one or more stations may detect signals from both storms. Amplitude predictions using realistic propagation models are consistent with the low SNR of the observed signals. We recommend that in the future, the frequency content of infrasonic arrivals be reported in the REB to facilitate corroboration of events.
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| Keywords: | infrasound, detection, microbarom, storm, reviewed event bulletin |
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