Rain-induced Dissipation in Hurricanes

Hurricanes originate from a potent mix of atmospheric and oceanic conditions, and manifest intensely swirling winds and torrential rains. The drag forces on the falling raindrops act to dissipate energy, which, in the context of global precipitation, has been shown to play a key role in global atmospheric circulation. And yet, the role of rain-induced dissipation in the energetics of a hurricane remains uncharted. In this study we investigate this topic. Using dimensional analysis and satellite data assimilated from the Tropical Rainfall Measuring Mission (TRMM), we propose a simple model of rain-induced dissipation in the eyewall of a hurricane. We modify Emanuel's idealized heat engine model of axisymmetric hurricanes by incorporating our model of the rain-induced dissipation. The Emanuel model predicts the maximum intensity a hurricane can achieve for a given set of atmospheric and oceanic conditions. We find that modified model reduces the predicted maximum intensity and pulls the model predictions closer to the observed data. Further, we use the modified model to predict inter-annual trends in various metrics of hurricane activity in the North Atlantic basin and show that the model predictions compare well with the observed trends. We conclude that rain-induced dissipation plays a significant role in the energetics of hurricanes and should be incorporated in global climate models.