MESOSCALE MOTIONS IN OCEANIC STRATUS AS REVEALED BY SATELLITE DATA

Abstract

Over maritime areas, meteorological satellite data generally have been used only in the study of synoptic scale systems. However, TIROS 7 pictures of summertime stratus over the northern Pacific, when rectified and combined with mesoscale radiation analyses, give valuable clues regarding the mesoscale dynamics of the lower atmosphere. Radiation data distinguish stratus from middle level cloud layers. Stratus bands, averaging 15 km. wide and oriented 16° to the left of the geostrophic wind, are thought to be related to horizontal roll vortices. Reflectance cross sections cross these bands indicate sharp variations in the thickness of the stratus. Precisely gridded photographs show the relation of marked clear areas in the stratus to the topography of the Aleutian Islands. Only when execeding a critical size do isolated mountainous islands produce clear wakes. One island appears to be shedding a possible vortex street. A derived model for the flow of the stable air over long mountain ridges in the Alentians includes such phenomena as upstream blocking, windward slope bolster eddies, and extreme turbulent mixing on the Ice slopes causing clear areas to extend over 100 km. domnstream. Radiosonde data indicate that the mixed layer downstream is approximately the depth of the obstructing ridge.