Satellite derived gap jet characteristics in the lee of the Philippine Archipelago
Michael J. Caruso1, Michelle M. Gierach1 and Hans C. Graber1
1
Center for Southeastern Tropical Advanced Remote Sensing, University of Miami, Miami, Florida,
33177, USA. mcaruso@rsmas.miami.edu
Understanding small scale oceanographic processes in coastal areas requires high resolution
measurements of atmospheric and oceanographic variables. Although atmospheric and oceanographic
models produce realistic features, the results are highly dependent on the accuracy of in situ
measurements. Coastal buoys provide accurate measurements with high temporal resolution, but have
limited spatial resolution. Scatterometers are capable of measuring winds with high spatial resolution, but
the swath sampling produces spatial and temporal gaps. Measuring winds in coastal areas using satellite
scatterometers is difficult. Near the coast, partial backscatter returns from land can contaminate wind
speed estimates. Scatterometer processing techniques have been developed to compensate for these
contaminations and produce wind fields within 25 km of the coast. Synthetic Aperture Radars are capable
of measuring winds higher spatial resolution than scatterometers and within 1 km of the coast. However,
these wind fields derived from synthetic aperture radars are not produced globally and have limited
availability.
We investigate winds in regions of strong orography since these regions provide clear examples of linear
wakes, kármán vortex streets and lee waves at scales down to about 100m. Characteristic scales of jets
and the respective power laws describing jet variation have been well documented in theoretical literature
and experimental studies. In the lee of the Philippine Archipelago, wind jets are common during the
winter monsoon (November-March) season as a result of steady northeasterly winds that interact with
volcanic topography. The scales/power laws respective to the Philippine mountain gap jets were derived,
and compared to the held scales/power laws. Previous studies describe the flow within mountain gaps,
flow over the ocean, and/or examined the jet-induced ocean response (i.e., SST cooling, chlorophyll-a
enhancement, and eddy generation). None characterized or quantified gap jet scales, such as jet spreading
rate, velocity decay rate, and length at which the gap flow becomes fully developed or self-preserving.
Such scales and power laws are applied to scattterometer and synthetic aperture radar winds to assess the
validity of the held scales/laws in Philippine Island wind jets and to determine the spatial scale
requirements of future coastal wind measurement systems.