Aerial Video of Smoke-Marked Wind Shifts Caused by Ocean Internal Waves

摘要

On August 25, 1998, an experiment was conducted off the coast of Oregon for the211u001epurpose of corroborating previously measured wind shifts at the ocean surface 211u001ecaused by the passage of solitary, ocean internal waves (IWs) in the same general 211u001earea (Otto, et.al., 1998). In the 1998 experiment, smoke floats were dropped onto 211u001ethe surface in the field of the internal waves from a low flying, Coast Guard 211u001eHelicopter based at Astoria, OR. Video was simultaneously taken through a belly 211u001ewindow of a Cessna 177 flying at 3000 m above the surface. A total of four smoke 211u001efloats were dropped and approximately 10 minutes of useful video was obtained. 211u001eDuring the video, an offshore rock remains within the video field of view. This 211u001eallowed absolute positions and surface velocities of the floats to be established 211u001efrom the video. This, in turn, allowed us to estimate the absolute phase speeds 211u001eand surface currents of the internal waves. As a result we were able to confirm 211u001ethat the observed directional shifts of the smoke were not due to apparent wind 211u001eshifts caused by the surface motion of the floats. The smoke trails revealed 211u001erelative wind shifts ranging up to 30 degrees, consistent with the earlier 1995 211u001eobservations.