How will precipitation change in extratropical cyclones as the planet warms?

Vineel Yettella (1), Jennifer Kay (1)

Abstract
A significant amount of midlatitude precipitation occurs in extratropical cyclones. The purpose of this study is to understand how and why precipitation changes in these cyclones due to global warming. Daily fields from the Community Earth System Model (CESM) Large Ensemble Project are used for this purpose. Extratropical cyclone centers during two periods (2006 – 2015 and 2061 – 2070) are identified using a filtering algorithm based on pressure gradients typical of extratropical cyclone centers. For each cyclone center, the surrounding precipitation field is interpolated from the CESM grid onto a radial cap centered on the cyclone center. Average precipitation fields are calculated for the two periods to obtain “cyclone composites”. In agreement with the warm conveyor belt model, the cyclone composites for both periods have a comma-shaped precipitation band with maximum precipitation close to the cyclone center. The precipitation composites for the two periods are compared to identify locations of significant change (at 95 % confidence).As the climate warms, precipitation in the comma-shaped band increases, especially near the cyclone center. This result agrees with the hypothesis that, with constant relative humidity, moisture convergence increases in a warmer climate. Future work will extend the cyclone compositing approach for studying other variables (e.g., near-surface air temperature, wind speed and radiative fluxes), and to investigate land-ocean and hemispheric differences in cyclone characteristics.