Passive Microwave Measurments of Water Vapor Fields and Rain for Locating Fronts in Cyclonic Storms

摘要

The report describes some basic research techniques and algorithms developed to diagnose fronts in cyclonic storms over the ocean with passive microwave data. The need for this research stems from the limited availability of reliable weather reports over the ocean, and the occasional disruption of weather map transmissions. In earlier work we found that strong gradients in integrated atmospheric water vapor are good indicators of surface locations of fronts in midlatitude cyclones over the oceans. A second significant indicator of frontal activity is precipitation. Therefore, we have developed methods for flagging strong gradients in integrated atmospheric water vapor (WVG-flag) and the presence of rain by using data from the Scanning Multichannel Microwave Radiometer (SMMR) aboard polar-orbiting Seasat and Nimbus-7 satellites. The data were not received in real time, but were analyzed from archived tapes. Examination of 65 frontal systems showed the water vapor gradient flag to catch 86% of the fronts while the precipitation flagged 90%. Each flag emphasizes different portions of the cyclone and are therefore complimentary. Ultimately these techniques are intended for operational use with data from the Special Sensor Microwave Imager (SSM/I) which was launched in June 1987 on a satellite in the Defense Meteorological Satellite Program (DMSP). Such data can be received in real time directly by ships at sea. (RH)