Large-scale moisture flux analysis for the United States

The seasonal and annual United States moisture budget (precipitation minus evaporation, P-E) is calculated using monthly NCEP/NCAR reanalysis data. Statistical methodologies, primarily Rotated Principal Component Analysis (RPCA), are used to evaluate the variability in the moisture budget. RPCA was performed on monthly moisture budget data and each pattern identifies an individual region of the data domain exhibiting unique variability characteristics. Time series of the RPC patterns are correlated and compared to station precipitation records, and composites of atmospheric circulation fields are obtained during sets of years when extreme values of RPC scores occur.; RPCA was performed on the annual mean values of total P-E in to examine the inter-annual and inter-decadal variability of the moisture budget changes. The seasonal RPCA analyses of P-E fields revealed patterns with similar characteristics. For example, the first principal component was centered over the continental interior, indicating high seasonal P-E variation in that area, while subsequent patterns are located near coastal areas including the Gulf of Mexico.; The RPC scores were correlated to atmospheric and oceanic teleconnection indices and the links between the teleconnections and the P-E patterns were further evaluated. In winter, for example, the Pacific/North American teleconnection is best linked to continental interior moisture flux. The study indicates the possibility of detecting Great Plains low-level jet events in the NCEP/NCAR reanalysis by using spatial patterns of wind speed, locations of vertical maximum winds and the nocturnal characteristics of the low-level wind maximum. RPCA was performed on the monthly April-May-June P-E data in order to evaluate the low-level jet's role in U.S. moisture flux. One RPC pattern in particular seems associated with low-level jet events in the central United States, having an association to drought and flood events in the Midwest and central United States.