The Importance of the Precipitation Mass Sink in Tropical Cyclones and Other Heavily Precipitating Systems

When water vapor is converted to cloud and precipitation and subsequently removed to the surface via precipitation, there is a corresponding hydrostatic pressure decrease due to the reduction of mass in the overlying column. Pressure changes resulting from the addition or removal of water vapor are currently neglected in most meteorological applications. However, in heavily precipitating systems such as tropical cyclones, where precipitation rates may exceed 250 mm day 1 , the pressure equivalent of the precipitation mass sink is not negligible (25 hPa day 1 ). Pressure decreases due to this mechanism are most pronounced in the lower troposphere, particularly below the melting level. The resulting unbalanced pressure-gradient force can enhance convergence, which precludes full realization of the pressure decrease but may contribute to vorticity generation and moisture convergence.