Surface Cooling Due to Precipitation in the Tropics
Gomes Martins Ramos, Camila
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Precipitation is an important component of the global hydrological cycle. It affects the upper ocean salinity by adding freshwater to the ocean. In addition, precipitation plays a role in cooling the ocean and land surfaces, when the temperature of the raindrops is lower than the temperature of the surface. However, the surface cooling due to precipitation (QP) remains an overlooked feature and is not included in the Intergovernmental Panel on Climate Change (IPCC) models. One might expect that heavy precipitation events may lead to large QP, which can impact the surface temperature, surface energy balance, and local- to regional-scale circulations. The maximum QP values are found following the annual march of the Intertropical Convergence Zone (ITCZ) and in the Indian Monsoon region. The mean QP from 30°N to 30°S, for precipitating days is 1.33 W m-2, with an annual variation of 1.0 - 1.7 W m-2. Relatively higher QP values are concentrated in the Bay of Bengal and Indo-Pacific Warm Pool regions. QP values for above average rain can exceed 50% of the surface turbulent sensible heat (QSH) close to the tropics, and. For rain values above the 95th percentile, QP can exceed 14 W m-2 and have the same magnitude as the QSH. To explore the role of QP, this term was included in the Weather Research and Forecasting (WRF) model, which was coupled to an ocean model. The simulation with QP had significant impact on the upper ocean dynamics and thermodynamics, and also on the atmosphere. As QP lowers the surface temperature, it tends to reduce the atmospheric convection. Latent and sensible heat also decrease over the ocean. QP was also included into the land surface model within the WRF to explore its role on the land surface and subsequent atmospheric circulations over the Maritime Continent during the passage of a Madden-Julian Oscillation (MJO) event. During the day, QP has a cooling effect since the land surface is warmer than the air. But for precipitation during night, it can have the opposite effect in the presence of warmer air above the surface, causing surface warming and an increase in rain. The results indicate that QP should be included in model simulations over the deep convective regions of the tropics.