The Time Change of Cloud Features in Hurricane Anna, 1961, from the Easterly Wave Stage to Hurricane Dissipation

摘要

Development of the basic easterly wave that produced Hurricane Anna of 1961 is followed from the time the wave first give indications of intensifying until the subsequent hurricane dissipated. Using radiation and photographic data obtained from TIROS III during the period from July 16, 1961 to July 25, 1961, combined with standard observations taken from radiosonde stations in the path of the storm, a representative picture of storm behavior is obtained. The cloud activity was originally in two adjacent areas with the major cloud activity in the southern portion of the wave and a small cloud area just east of the wave crest. Both are believed to have trailed the wave axis or circulation center. The wave itself developed under a tropical anticyclone with a local anticyclone intensifying over the storm. Three major cloud bands became apparent almost simultaneously with the formation of the cirrus shield, one of which included the northern or crest cloud. Hurricane intensity was reached within 30 hours of the obscuration of the apparent circulation center and band formation. At maximum intensity the cirrus shield covered the major rain bands leaving an isolated hurricane system as viewed from the satellite. There were also indications of strong convection regions imbedded within the remnant cirrus shield. A clear region was apparent in front of the storm shield but lay well behind the outer shear line. It is believed that the clear band is more the result of dry air advection than subsidence at the cirrus rim. Although the storm dissipated at the surface, a cirrus cover remained over the depression. (Author)