Atmospheric Precipitable Water and its Correlation with Clear Sky Infrared Temperature Observations

Abstract. Total precipitable water (TPW) in the atmosphere is the vertically integrated amount of atmospheric water in all of its phases. TPW is a valuable predictor for weather forecasting, and it is routinely measured using radiosondes, ground-based global positioning systems (GPS), sun photometers, or microwave radiometers. The use of these sophisticated instruments limits the number of TPW measurement sites, which affects the accuracy of forecast models in regards to storm formation, strength, and the potential for precipitation. We have analyzed this relationship for the much drier climate zone found in the Desert Southwest, specifically over Socorro, New Mexico (34° N, 107° W). Daily measurements of the ground and zenith sky temperatures have been made at Socorro for two complete annual cycles using infrared thermal sensors. Radiosonde TPW measurements from National Weather Service stations located in nearby Albuquerque, and Santa Theresa, New Mexico, are input into our dataset and analysed via a newly developed computational tool. Our results show that an exponential relationship between TPW and zenith sky temperature also holds for the Desert Southwest, but with parameters that are different than those obtained for the Gulf Coast. Model simulations can accurately reproduce the observed relationship between TPW and temperature, and the results suggest that half of the signal in temperature is directly related to direct changes in opacity due to changes in TPW, while the other half is due to changes in air temperature that usually accompany changes in TPW.