By modulating the moisture flux from ocean to adjacent land, the North Atlantic subtropical high (NASH) western ridge significantly influences summer-season total precipitation over the conterminous United States (CONUS). However, its influence on the frequency and intensity of daily rainfall events over the CONUS remains unclear. Here we introduce a Bayesian statistical model to investigate the impacts of the NASH western ridge position on key statistics of daily scale summer precipitation, including the intensity of rainfall events, the probability of precipitation occurrence, and the probability of extreme values. These statistical quantities play a key role in characterizing both the impact of wet extremes (e.g., the probability of floods) and dry extremes. By applying this model to historical rain gauge records (1948-2019) covering the entire CONUS, we find that the western ridge of the NASH influences the frequency of rainfall as well as the distribution of rainfall intensities over extended areas of the CONUS. In particular, we find that the NASH ridge also modulates the frequency of extreme rainfall, especially that over part of the Southeast and Upper Midwest. Our analysis underlines the importance of including the NASH western ridge position as a predictor for key statistical rainfall properties to be used for hydrological applications. This result is especially relevant for projecting future changes in daily rainfall regimes over the CONUS based on the predicted strengthening of the NASH in a warming climate. SIGNIFICANCE STATEMENT: The purpose of this work is studying how the position of the North Atlantic subtropical high (NASH) western ridge modulates summer daily precipitation statistics over the conterminous United States (CONUS). We introduce a Bayesian statistical model describing daily precipitation frequency, intensity, and probability of extremes. We find that the NASH is an important predictor for daily rainfall statistics over large areas of the CONUS, in particular over the Southeast and Midwest. Since the NASH is predicted to strengthen in future climate conditions, our results are particularly relevant for understanding the corresponding shift in the probability distribution and occurrence of daily precipitation.
All Science Journal Classification (ASJC) codes
- Atmospheric Science