Climatology of Water Vapor Fluxes and Precipitation in the Northeastern United States

A climatology of water vapor fluxes and resultant precipitation in the mid-Atlantic and northeastern United States is developed in this research. Given the changes in precipitation observed in the study region, understanding the water vapor fluxes producing precipitation is becoming increasingly necessary. The importance of this knowledge is amplified when considering the high impact of extreme precipitation. Therefore, investigation into the sources and mechanisms of heavy precipitation through analysis of the initial moisture fluxes provides greater insight into the changes in precipitation observed in the region. The development of a baseline climatology of regional water vapor fluxes provides a point from which deviations, such as those associated with recently observed extreme precipitation, can be measured. Presently, no such climatology has been developed. This research fills this need by developing a baseline climatology of water vapor fluxes in the northeastern United States and associating that climatology of water vapor fluxes to regional precipitation. In this research, moisture transport patterns are identified using integrated vapor transport (IVT) calculated from daily eastward and northward vertically integrated vapor fluxes from ERA-Interim Reanalysis for 1986—2016 at a spatial resolution of 0.75° × 0.75°. The study region is bounded by 30°N—50°N and 90°W—60°W to include the source region for moisture entering the northern portion of the eastern United States. A self-organizing map (SOM) methodology is employed with the daily IVT data to produce a set of IVT maps identifying recurrent moisture transport patterns intersecting the northeastern US. While some map nodes show little water vapor flux likely to produce precipitation, other nodes show narrow bands of enhanced vapor transport suggesting the influence of atmospheric rivers on the regional hydroclimatic regime. The IVT dataset is extended through 1900 through the incorporation of IVT, calculated identically as in ERA-Interim, in ERA-20C. An overlap period of 6 years is used to train the classification of ERA-20C IVT into the patterns identified in the ERA-Interim. The annual and seasonal frequency of the patterns are analyzed from 1900-2016. Precipitation observations from the mid-Atlantic and northeastern United States are related to the water vapor flux patterns to determine the characteristics of precipitation produced under each flux pattern. Results from this study indicate that atmospheric rivers play a non-negligible role in the climatology of water vapor fluxes and resultant precipitation in the northeastern United States.