Upscale influence of mesoscale heating in extratropical cyclones

We previously used regional modeling experiments to show that the intensity of individual extratropical cyclones and their aggregate behavior in the North Atlantic stormtrack are strongly sensitive to horizontal resolution. Current GCM resolutions are inadequate for representing mesoscale condensational heating, which plays an important role in cyclogenesis. This resolution sensitivity is exacerbated in a warmer atmosphere with more water vapor. Here we show upscale effects of the GCM resolution deficiency and the implications for modeling stormtrack response to warming. We use the Weather Research and Forecast (WRF) model configured globally with high-resolution 2-way nests over the Northern Hemisphere midlatitude stormtracks. The 2-way nested configuration mitigates a primary limitation of traditional downscaling experiments by allowing the better-resolved cyclones to feed back on regions outside of the nests. We simulate 20 DJFM winters with and without the nests. Differences in cyclone dynamics appear when mesoscale precipitation is more accurately resolved, and the climatological stormtracks are strengthened in some regions with both increased resolution and warming, consistent with our limited-area experiments. We also find upscale sensitivity of the general circulation in terms of the Lorenz energy cycle. Our results allow for better understanding of potential biases in projections of stormtrack behavior and the contribution of extratropical cyclones to the general circulation under global warming.