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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 precip- itation rates may exceed 250 mm day21, the pressure equivalent of the precipitation mass sink is not negligible (;25 hPa day21). 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. The importance of the precipitation mass sink is investigated for the case of Hurricane Lili (2002) through the computation of mass and potential vorticity (PV) budgets and numerical sensitivity experiments. The pre- cipitation mass reaching the surface within 100 km of the storm center is of the same order as the mass loss needed to explain the area-averaged pressure decrease during the intensification stage of Lili. The PV is altered by precipitation mass flux divergence across isentropic layers. A volume-integrated PV budget reveals that the mass sink term is small in comparison to the latent heating term, although the latter exhibits large cancellation. Comparison of a control simulation from the Eta Model to an experimental simulation in which the precipitation mass sink effect is included demonstrates that the mass sink mechanism contributes to lower pressure, stronger wind speeds, and heavier precipitation. The sea level pressure near the storm center in the mass sink simulation is generally 2-5 hPa deeper relative to the control simulation, with 10-m wind speed differences of 5 to 15 kt. The mass sink simulation exhibits a stronger cyclonic PV tower, especially above the melting level, and a stronger troposphere-deep cyclonic circulation relative to the control simulation. The analysis presented indicates that the precipitation mass sink mechanism, though not dominant, is not negligible for tropical cyclones.

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