Lifecycle-Type Matters for Extratropical Cyclone Precipitation Production

Abstract

In the midlatitudes, extratropical cyclones produce the majority of winter precipitation. Precipitation rates and accumulation depend strongly on both the cyclone intensity and the environmental moisture amount. Using 5 years of the Integrated Multi-satellitE Retrievals for Global Precipitation Measurement (IMERG) product, cyclone-centered composites of surface precipitation rates are compared between cyclones that occlude and those that do not. Occluding cyclones produce greater surface precipitation because they tend to be more intense. When the non-occluding cyclones are selected such that they collectively have similar intensity and moisture amount distributions as the occluding cyclones, precipitation rates at peak intensity are still larger for occluding cyclones. This is because a particular type of forced, frontal-scale, ascent in the occluded thermal ridge, unique to occluded cyclones by virtue of their thermal structure, favors more precipitation. The results demonstrate that life-cycle type (i.e., achieving occlusion vs. not) matters for precipitation production in extratropical cyclones.