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| Titel |
Detection of Gravity Waves and Infrasound Signals at the USArray |
| VerfasserIn |
Catherine De Groot-Hedlin, Michael Hedlin |
| Konferenz |
EGU General Assembly 2015
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 17 (2015) |
| Datensatznummer |
250108327
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| Publikation (Nr.) |
 EGU/EGU2015-8077.pdf |
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| Zusammenfassung |
| The USArray Transportable Array (TA) is a 400-station network that has been deployed in
the continental United States since 2004. The network, which at its height spanned 2,000,000
km2, has gradually moved east across the country via station re-deployments. Although
originally conceived as a seismic-only network, a suite of atmospheric pressure sensors added
to each station starting in early 2010 allows for enhanced observations of pressure variations
at the Earth’s surface associated with infrasound and other atmospheric phenomena. We
present novel techniques that make use of the close spacing of stations within the TA
to detect and track the progress of pressure disturbances across the network. The
method has been applied to the detection of both atmospheric gravity waves having
periods from 40 minutes to 8 hours, and 1-3 Hz infrasound energy generated by
meteoroids.
The TA is sufficiently dense that gravity waves with wavelengths from tens to hundreds of
kilometers are coherent between neighboring stations, but is too large for coherence across
the entire network. To examine the characteristics of gravity waves propagating across the
network, the TA is divided into a large number of elemental, triangular, sub-arrays consisting
of three neighboring stations. Coherent analysis of the data at each triad provides a
robust estimate of the signal’s direction and speed. The results from all triads are
combined to follow the progress of a gravity wave as it propagates across the TA. This
method allows for observation of fine-scale variations in the speed, direction and
amplitude of long period signals across the TA, as well as the statistics of these
waves.
The method has been applied to TA data collected over the eastern half of the continental
United States over a 5-year timespan beginning on January 1, 2010. The network has detected
particularly large and long-lived gravity waves such as from a tornadic storm system in the
American south in April, 2011. In addition to studying the characteristics of singular events,
we have used the data to study the statistics of gravity wave activity across the study area. We
observe clear variations across the study region – most notably a persistent and active
region in the vicinity of the Great Lakes. This high coincides with elevated activity
seen in images of gravity wave activity in the stratosphere observed with satellite
data.
The method described above has been modified to detect pressure disturbances with
wavelengths much less than the inter-station spacing. In this case, the waveform data is
appropriately bandpassed and an STA/LTA filter is applied to form envelopes of the data.
Coherent analysis is performed on the data envelopes at each triad rather than the
waveforms; in other respects the analysis is similar to that described above. This method
has been applied to infrasound generated by the terminal burst of meteors in order
to infer the trajectory of several small bolides, and the location of their terminal
burst. |
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