ASPECTS OF HURRICANE STRUCTURE: NEW MODEL CONSIDERATIONS SUGGESTED BY TIROS AND PROJECT MERCURY OBSERVATIONS

Abstract

Satellite photographs of hurricanes reveal the complete storm in relationship to its environment. In many instances ?outer convective bands? or ?pre-hurricane squall lnes? appear to partially ?ring? the storm. These bands are usually separated from the rim of the high cloud shield by a relatively clear channel, visible and distinct for long distances along the circumference. This channel may be formed through the action of a major subsiding branch of the hurricane's circulation. Many photographs also reveal extensive areas of convective, cirrus-producing cloudiness in the wake of the storm. This cloudiness appears to be intimately associated with that of the hurricane, and strongly influenced by outflow effects. Time cross-section analyses of hurricanes Carla and Anna suggest peripheral subsidence. The area of possible subsidence, in both instances, occurred under an upper shear line, where air diverging in the outflow layer from the hurricane converged with air emanating from the subtropical High. A jet stream, in the case of hurricane Carla, appeared in the region of the subsident annular zone, at the edge of the high cloud shield. This high speed current curved anticyclonically along the northern quadrants of the storm?then, on being directed southward, split into two main branches. The eastern branch curved cyclonically into a trailing vortex, apparent as a cold Low at 200 mb. The western branch continued southward, in alignment with the curvature of cloud streaks forming the cirrus ?tail? of hurricane Carla. These features appear to be typical of many hurricanes in certain stages of development. Model considerations, employing these features, with a discussion of ramifications, are suggested in this paper.