Abstract
Ocean variability plays an essential role in the climate system at different time scales through air–sea interactions. Recent studies have addressed the importance of the ocean mixed layer in cooling feedback to tropical cyclones (TCs). However, using constant sea surface temperature (SST) in short-range weather forecasts remains common, especially in high-resolution regional models. This study investigates the role of subsurface ocean mixing in the short-range forecast of non-TC extreme rainfall with the Weather Research and Forecast (WRF) model. In the simulations of 26 heavy rainfall cases, we found that using a one-dimensional mixed layer model leads to a 15% enhancement (reduction) of rainfall maximum in six (two) cases compared to using constant SST. When the initial depth of the mixed layer model is perturbed by the amount of daily variability, 13 cases exhibit larger than 15% increases or decreases. A detailed analysis of one case suggests that the radiative process dominates the overall response of SST. The warming and moistening of boundary layer air cause significant strengthening of updrafts in convection. Although the SST change in most cases due to varying mixed layer model setups is less than 0.5 K, convective motions in some cases are surprisingly sensitive to small changes.
Highlights
Our study focuses on the South China coast and the pre-summer season, during which more than 50% of annual rainfall occurs but with rarely active tropical cyclones (TCs) [13]
Sea interaction in TCs has been addressed in previous studies [9,10,38,39]
Our investigation here suggests that in the short-range forecast of non-TC precipitation events, a significant number of them are sensitive to ocean mixing processes, which improves the representation of short-term variability in sea surface temperature (SST) compared with prescribing persistent SST conditions
Summary
Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations. Physical processes in the ocean play critical roles in modulating the Earth’s climate, for the energy transport that determines the mean climate and for climate variability at different time scales, such as the El Niño-Southern Oscillation, the East. Asia Monsoon, and the Madden-Julian oscillation [1,2,3,4]. For the short-term evolution of weather systems, the importance of ocean processes other than the sea surface temperature (SST) was not well appreciated until recently. To date, it is still common to prescribe persistent SST from observation or global model data in regional simulations, especially those for a short-range forecast and at high resolutions [5,6]
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