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

Abstract:

The majority 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 precipitation fields from the Community Earth System Model (CESM) Large Ensemble Project are used for this purpose. Extratropical cyclone centers during three periods (1986 - 2005, 2016 - 2035 and 2081 - 2100 representing the present day, the near future and the far future respectively) 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 three periods to obtain "cyclone composites".

In agreement with the warm conveyor belt model, the cyclone composites for the three periods have a comma-shaped precipitation band with maximum precipitation close to the cyclone center. The near future and the far future composites are compared with the present day composite to identify locations of significant change (at 95% confidence). Statistically significant precipitation increases are found both for the near future and the far future, especially near the cyclone center. To identify the processes contributing to these changes, we decompose precipitation change into two parts - one part that is due to changes in dynamics (mean cyclone wind speed) and another part that is due to changes in thermodynamics (mean cyclone water vapor path). We find that precipitation increases occur primarily due to changes in thermodynamics.

We will also present ongoing work to investigate changes in cyclone location and density in a warming climate and also investigate land-ocean and hemispheric differences in cyclone charactersitics.