Identifying and Attributing Changes in the Ratio of Locally and Synoptically Forced Midlatitude Precipitation Events

Unpredictability of precipitation over land is a major forecasting challenge, particularly when it is predominantly driven by convective precipitation. In this study, we introduce a novel application of the quasigeostrophic (QG) Omega approximation for vertical wind speeds in a classification of precipitation type. Using NASA’s Modern-Era Retrospective Research and Application Version 2 (MERRA-2) reanalysis as input, our objective is to identify regions in which convective precipitation frequency is relatively high and/or has exhibited large variability since 1980. We then test our hypothesis that changes in a region’s convective precipitation regime are a proxy for changes in the region’s land-atmosphere coupling regime. The analysis hinges on the strength of the two relationships. First, the correlation between Omega and precipitation type. Second, the correlation between precipitation type frequency and land-atmosphere coupling strength. Initial results reveal regional variations in the correlation between precipitation type and Omega within the midlatitudes. However, most locations have a strong negative Omega during the time of stratiform dominant precipitation events, which indicates stratiform events will be well captured by this approach. QG Omega and convective precipitation correlation is weak and motivates our search for additional environmental fields to improve the classification of this precipitation type. We plan to analyze the long-term changes to the seasonality of convective and stratiform precipitation events and their relative contribution to total precipitation in global hot spots of land-atmosphere interaction.