Layered Precipitable Water from the Infrared VAS Sounder during a Return-Flow Event over the Gulf of Mexico

Abstract

Spatial and temporal changes in the vertical distribution of atmospheric water vapor are investigated during a period following the intrusion of cold continental air over the Gulf of Mexico, during the Gulf of Mexico Experiment (GUFMEX) in February-March 1988. Infrared satellite measurements from the GOES (Geostationary Operational Environmental Satellite) VISSR (Visible-Infrared Spin Scan Radiometer) Atmospheric Sounder (VAS) are used to augment the sparse coverage of rawinsonde sites in the vicinity of the Gulf of Mexico. Precipitable water from two vertical layers, surface-850 and 850?250 mb, are estimated from the VAS and compared to those from rawinsonde observations. The accuracy of precipitable-water estimates in each vertical layer is less than that for the total precipitable water. However, improvements in the estimate of precipitable water for each layer are observed with respect to the profiles used in initializing the retrieval process. A consistent horizontal and temporal pattern of the vertical partition of water vapor between the lower and middle to upper troposphere is obtained from the analysis in both layers. A band of moist air that develops with return to southerly flow is common to both layers; however, the width of the band is more extensive in the lower layer. Drying to the rear of the band predominates in the upper layer while the lower layer remains quite moist.