A Comparison of Saturation Pressure Differences and GOES VAS Estimates to Surface Observations of Cloudiness

Abstract

Saturation pressure differences are calculated from upper-air soundings and compared to manual surface observations of cloudiness. The mean saturation pressure difference between 1000 and 700, 700 and 400, and 400 and 300 mb is calculated and compared to the observed composite cloudiness for those layers. Results indicate that as the absolute value of saturation pressure difference decreases toward zero, the resulting ground observed composite cloud amount increases. However, the mean saturation pressure difference for high clouds ranges from 64 mb under clear skies to 16 mb for overcast conditions. This corresponds to relative humidities between 25% and 76%. Most previous studies do not indicate such large cloud amounts at these humidities. Three empirical relationships that define low, middle, and high clouds are developed based on one year of comparisons. These relationships are then tested on an independent dataset that include a wide variety of cloud cover conditions. Qualitative comparisons are made to manual observations of cloudiness and indicate that the relationships overall slightly overestimate the frequency of cloudiness. Cloudiness derived from the Visible-Infrared Spin Scan Radiometer Atmospheric Sounder onboard the Geostationary Environmental Operational Satellite 7 using the CO{sub 2} slicing technique is also compared to surface observations. Results indicate thatmore » the satellite-derived cloudiness overestimates cloudiness compared with surface observations but is also very similar to the saturation pressure difference estimates. 12 refs., 13 figs., 3 tabs.« less