10.1 Influence of Large-Scale Dynamics on the Duration of Midlatitude Precipitation Extremes in Different Climates

Wednesday, 28 June 2017: 3:30 PM
Salon F (Marriott Portland Downtown Waterfront)
Paul A. O'Gorman, Massachusetts Institute of Technology, Cambridge, MA; and J. G. Dwyer

Precipitation extremes intensify with climate warming in observations and simulations, but changes in their duration or spatial extent are not well understood. Here we investigate the influence of large-scale dynamics on the duration of midlatitude precipitation extremes in idealized and comprehensive climate model simulations. We use an advective time scale to link the duration to the mean zonal wind speed and the zonal length of the precipitation extremes.

In simulations with an idealized general circulation model, a stronger meridional temperature gradient leads to a decrease in the duration. The decrease in duration can be understood through the advective time scale, and it occurs despite an increase in the zonal length of the precipitation events. The zonal wind speed increases linearly with the meridional temperature gradient (following thermal wind balance), whereas the zonal length increases more weakly as the square root of the meridional temperature gradient (following the scaling of the Rossby deformation radius).

For climate change over the 21st century, most comprehensive climate models project a decrease in duration. The advective time scale helps to explain the decrease in duration, but the changes in zonal length of the precipitation extremes are not easily understood in this case. The magnitude of the projected decrease in duration is less than 1%/K in the multi-model mean which is relatively small compared to the increase in intensity of the precipitation extremes.

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