Alternative Forms of Humidity Information in Global Data Assimilation

Abstract

Global data analysis procedures were developed to perform data assimilation for observed geopotential heights wind components, and relative humidity. These procedures were implemented in conjunction with a global spectral forecast model (GSM) and normal mode initialization procedure to produce global analyses at six-hour intervals. A set of five-day experiments were conducted to assess the impact of several alternative sources of humidity analysis procedure. Satellite moisture retrievals, surface weather observations, and Air Force Global Weather Central 3-D nephanalysis cloud amounts were used as sources of upper-air relative humidity as to permit their use in data assimilation. The 3-D nephanalysis-inferred humidities, and to a lesser extent the surface weather observation-inferred humidities, were found to have a beneficial impact on the analyses. When used in a manner to maximize their impact, their inclusion in the analysis resulted in an analysis that agreed better with withheld radiosonde relative humidity than did the uncorrected first guess.