Preliminary Study of the Feasibility of Detecting Long-Term Trends in Atmospheric Humidity

摘要

Humidiy data at the surface and at 850, 700 and 500 mb pressure surfaces at Brownsville, Texas, and Great Falls, Montana, have been examined for the interval 1958 to 1980. Adjustments have been applied to the data prior to 1966 because at this earlier time dry observations (motorboating) were not reported. The adjustment is based on the assumption that all missing observations had a relative humidity of 20%. In general, the relative humidity at these two stations decreased between 1958 and about 1970 and has increased since, similar to the variation in Northern Hemisphere surface temperature. Mixing ratio and precipitable water have varied in an analogous fashion. At these two stations mixed signals have been obtained with regard to the relation between long-term variations in temperature, relative humidity, and mixing ratio, but on the seasonal and yearly time scale, the relative humidity has tended to be out-of-phase with temperature, and the mixing ratio in-phase with temperature. The correlation between Northern Hemisphere precipitable water and surface-500 mb precipitable water at Brownsville and Great Falls has been 0.87 and 0.66, respectively, with a correlation of about 0.50 between these precipitable water estimates and Northern Hemisphere surface temperature. (ERA citation 09:017222)