Observational Analysis of Seasonal and Diurnal Variations in Water Vapor Flux in the Eastern United States and its Application to Model Evaluation

The seasonal and diurnal climatology of water vapor flux in the eastern United States is examined using high temporal resolution observation data. Vertical profiles of water vapor flux are computed at 15-minute time interval for the period of 2007-2012 from Global Positioning System precipitable water observations, radiosonde profiles of water vapor density at 00 UTC and 12 UTC, and Velocity-Azimuth Display wind profiles derived from the Sterling, VA WSR-88D. The vertically integrated water vapor flux shows a clear seasonal variation, in which its zonal component reaches a maximum in summer and a minimum in winter. A seasonal transition of the meridional water vapor flux from spring to summer is observed. Water vapor flux exhibits pronounced seasonal contrasts in its diurnal cycle. In spring, strong (weak) southwesterly water vapor flux is observed in the nighttime (in the daytime). In summer, while the water vapor flux is southwesterly from afternoon until around midnight, it becomes northwesterly after midnight and reaches its maximum in the early morning. These results are generally consistent with results using the North American Regional Reanalysis (NARR) data. However, the magnitude of water vapor flux derived from the NARR data at 3-hour interval is found to be much smaller than observed one particularly for the meridional component. A case study is carried out using the Weather Research and Forecast model, and the performance of the model is evaluated against the observational and reanalysis datasets.