Three Dimensional Analysis of a Precipitation-Free, Sea-Breeze Front by Radar, Tiros, Visual, and Mesosynoptic Data

摘要

Two precipitation-free radar thin bands, viewed at Miami on October 23 and 24, 1963, while hurricane Ginny was off the northeast coast of Florida, were relatively unique in that they were almost stationary for many hours in the immediate vicinity. These lines existed only in the lowest 1000 ft on the radarscope, and many field observations taken on both sides of the line indicate that they cannot be attributed to birds, insects, or other particulate matter in the atmosphere. The lines were from 30 to 55 miles long and oriented so that major portions were found over the ocean at nearly right angles to the coast. It has been shown that they were precipitation-free and at least one of them was the combined result of a seabreeze front and the hurricane Ginny circulation. Both the Tiros VII cloud pictures and the radar composites of the hurricane Ginny precipitation pattern confirmed a connection between the thin band and an apparent spiral band tail in the later stages of the thin band's lifetime. Considering the high radar signal strength received from the thin band and the radar refractive geometry for the two radars which viewed the thin band simultaneously but from different sites, it seems most realistic to consider that these were actually ground targets detected at abnormal ranges due to superrefraction. Although the extremely low-level nature of this type of thin band has been established at the University of Miami many times, it has not yet been possible to obtain the horizontal and vertical refractive index changes within the lowest 1000 ft of the atmosphere in the immediate vicinity. (Author)