Relationships between soil moisture and summer precipitation over the Great Plains and the Southwest - art. no. 8610

摘要

The relationships between evaporation ( E) and summer precipitation ( P) over the United States are examined using the observed precipitation data set, the National Centers for Environmental Prediction-National Center for Atmospheric Research (NCEP-NCAR) reanalysis and the NCEP regional spectral model (RSM) simulations. The composites of P anomalies based on soil moisture and E anomalies indicate that the relationships between E and P are regionally dependent. The E anomalies over the Great Plains are associated with large P anomalies located north of the E anomalies and areas downstream along the path of the Great Plains low-level jet (GPLLJ). The impact of E anomalies on P over the Southwest is small and is only recognized during the strong moisture surge events from the Gulf of California. The vertically integrated meridional moisture fluxes [qv] associated with the GPLLJ are stronger and more persistent than the fluxes associated with the low-level jet from the Gulf of California to the Southwest (GCLLJ). The E anomalies over the Great Plains are stronger and more persistent than the E anomalies over the Southwest. Therefore the E anomalies over the Great Plains have a better chance for the local feedback and for the changes in moisture flux convergence to take effect. The impact of E anomalies on P over the Southwest is small and only recognized during strong moisture surge events from the Gulf of California. Both the surge events and E anomalies over the Southwest persist for less than one week. The time window for the large E anomalies to occur during surge events is narrow. Therefore the net impact is small. [References: 47]