During the Indian Ocean Experiment (INDOEX) experiment (January-March 1999), mesoscale solitary waves have been observed and tracked over the North Indian Ocean on a series of Meteosat-5 satellite images. These solitary waves have a horizontal wavelength of 10-15 km and propagate westward at low level at a speed of 10-18 m/s. Unlike similar wave phenomena observed mainly over land, they have a long lifetime, which can exceed 48 h. A key element explaining the existence and longevity of the solitary waves is the presence of an inversion layer, acting as a waveguide and separating the boundary layer into two sublayers: a lower layer over the ocean (marine boundary layer) and an upper layer originating from the Indian subcontinent (land plume layer). Profiles from radiosondes launched from the Ron Brown and from dropsondes from the Hercules C-130 airplane helped to determine this waveguide structure. A suggested mechanism leading to the generation of solitary waves is a collision between the sea breeze in the vicinity of the West Indian coast and the easterly/northeasterly winter monsoon winds, with a possible contribution of convection reinforced by topography (Western Ghats range), during the local afternoon. Another phenomenon related to sea breeze and local convection in this coastal area, the injection of "bubbles" of moisture into the drier upper boundary layer, has also been identified on European Centre for Medium-Range Weather Forecasts analyses. These bubbles form daily during the afternoon and drift westward over the North Indian Ocean at latitudes around 12N and progressively subside and dissipate or become integrated into larger air masses. Copyright 2011 by the American Geophysical Union.

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