CIRRUS CANOPIES IN TROPICAL STORMS

Abstract

An analysis is made of the generation, advection, and dissipation processes of the cirrus canopy in tropical storms with particular emphasis on the formation of sharp edges. Although subsidence and accompanying evaporation may be factors, this formation is closely tied with the wind flow pattern near the edges. The stronger the radial wind velocity in the vicinity of the edges, the greater is the rate of subsidence required to evaporate the cloud over a distance sufficiently short so that the edge may be considered sharp. Analyses of the wind fields in typical hurricanes indicate that cirrus generated at the eye wall and advected outward could produce in 12 to 18 hr. a canopy similar to those observed by meteorological satellites. If, in addition, generation occurs in the spiral arms, these times are shortened somewhat. Sharp edges would occur in regions where the radial outflow becomes small, probably less than 1 m. sec.?1, and where the tangential velocity is at a relative maximum.