Temporal Variations of Water Vapor Concentrations from the Goes-8 Sounder

This study presents the temporal variations of water vapor over the central and eastern U.S. using a thickness technique. Two sounder channels have spectral response functions lying in the water vapor absorption band. These channels are centered at 7.02um and 7.43um, with levels of maximum contribution occurring at approximately 500mb and 700mb respectively. An equivalent pressure can be defined for each channel using local profiles from radiosondes and the Eta model. This equivalent pressure is the pressure surface at which the brightness temperature equals the air temperature. The difference between the derived equivalent pressures is referred to as a thickness. In the middle to upper troposphere an increase in the relative humidity will correspond to a greater thickness. While in the lower troposphere and boundary layer, an increase in relative humidity will correspond to a reduction in the thickness. Hourly GOES sounder data is used to produce the thickness. The observed thickness changes are then related to vertical motions, as well as instabilities forming in clear air regions. Strong gradients of differential warming or cooling cause the greatest observed changes in thickness. Larger and more intense dynamic features on the synoptic scale also create these gradients. Examples of observable features include vertical motions due to jet maxima, large-scale gravity waves from mesoscale convective systems, and a diurnal pattern of vertical temperature change. Relative magnitudes of subsidence, drying, and advection of water vapor are compared using this technique.