Climate Prediction: ENSO, MJO and Teleconnections
Abstract

Abstract Author: Emily Becker

Abstract Title: Variability of daily precipitation over the United States

Abstract: The mechanisms that affect the distribution of daily precipitation are examined using the North American Regional Reanalysis, including several precipitation-related forcing fields such as moisture flux convergence (MFC) and precipitable water. Regions of the U.S. where the seasonal mean precipitation is dominated by extremes or by more consistent, lighter events are identified. Then, the effect of ENSO on the distribution of daily precipitation is studied.

In winter, most areas of the country with high precipitation means have a strong contribution from extreme events, particularly the West and Gulf Coasts. However, the Pacific Northwest, with the greatest winter mean precipitation, has a large contribution from moderate events. The West and Gulf Coasts see consistent moderate daily values of precipitable water, but more extremes in the MFC daily values. In summer, both the wettest and the driest areas (Florida and the west, respectively) are dominated by more frequent light and moderate rainfall days; both of these areas have consistent precipitable water and MFC values. The high summer precipitation mean in the central Plains is dominated by variable rains and more extreme events; this area shows consistent precipitable water and variable MFC values.

Changes in winter mean precipitation between the phases of ENSO are largely attributable to changes in the heavy and extreme events. Areas showing increased mean precipitation during the warm phase, such as California and the Great Plains, show an even greater increase in extremes. Mean precipitable water shows little change between the phases, but during the warm phase there are fewer extremes and more consistent moderate daily values of precipitable water over the West and Southwest, areas that exhibit little change in the precipitation distribution between ENSO phases. Extreme values of MFC are more sensitive to ENSO phase than is the mean, similar to precipitation.