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OBSERVING EARTH'S OCEAN WAVE CLIMATE WITH MICROSEIMS OBSERVING EARTH'S OCEAN WAVE CLIMATE WITH MICROSEISMS
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Seismic stations worldwide record an incessant excitation of seismic waves stimulated by ocean wave activity, the microseism. This signal has two principal components, a primary near 16 s period resulting from the coastal energy transfer of breaking and shoaling waves, and a (stronger) secondary, near 8 s period, arising from standing wave components of the ocean wave field, such as are created by incoming swell interfering its coastal reflection. Here, the incidence of winter microseism intensity extremes (uppermost fifth percentile microseism events from large, wave-generating storms) at GSN stations is depicted as the number of hours per year exceeding (red) or less than (blue) the long-term averages in these extremes at each station. The quiet year in 2001 is associated with a notable 2000–2002 La Niña-El Niño transition, illustrating a remarkably widespread influence of the El Niño-southern oscillation on extremal wave climate. Microseism data are currently available in digital form since the early 1970s, and recent efforts suggest that, by digitizing and processing older analog records, wave climate can be synoptically studied back to the early 20th century, providing important new information in regions lacking buoy or other data. (After Aster et al., 2010. Global trends in extremal microseism intensity. Geophysical Research Letters, 37, l14303, doi:10.1029/2010gl043472.)</p>

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