AIRBORNE SYNTHETIC APERTURE RADAR IMAGERY OF ATMOSPHERIC GRAVITY-WAVES

We analyze the oceanic "imprints" of atmospheric internal gravity waves detected in airborne synthetic aperture radar (SAR) images collected off the west coast of Vancouver Island, British Columbia, in June 1990. A sequence of SAR images taken over a period of 2.5 hours reveals that the waves traveled with group velocities of 3-6 m s-1 toward the northwest, counter to the 10 m s-1 surface winds. Wave crests were oriented normal to the coast and had lateral extents of several tens of kilometers, Observed wavelengths ranged from 1.2 to 2.3 km, while calculated wave periods ranged from 3 to 8 min. A comparison of the observed wave properties with values derived from a simple three-layer density model of the troposphere suggest that the waves were low-mode oscillations trapped within a 0.75-km-thick temperature inversion overlying a 1-km-thick weakly stratified marine boundary layer. Wave propagation was counter to the wind shear within the inversion layer. Generation of the internal wave groups appears to have occurred near the southern boundary of the stable marine air mass, where it bordered a convectively active air mass that was intruding northward along the coast.