Abstract
ᅟThe study used a 5 km-resolution regional climate model, the Advanced Research Weather Research and Forecasting Model, to quantify the potential impact of sea surface temperature (SST) west of the Philippines on summer monsoon rainfall on the northwestern coast of the country. A set of control simulations (CTL) driven by ERA-Interim reanalysis data and the monthly National Oceanic and Atmospheric Administration Optimum Interpolation SST dataset was performed for the months of June to August of 1982–2012. A second set of simulations driven by climatological SST values was performed for the same period. The difference between these two simulation sets is analyzed to determine the sensitivity of rainfall to interannual variations in local SST, not remote SST, via a regional climate model. The CTL simulations represented spatial and temporal variations in rainfall well, yielding realistic climatological rainfall values with high spatial correlations with observations. The interannual correlation of monthly rainfall over the northwestern region of the Philippines was also high when compared to observations. The results showed that positive SST anomalies west of the Philippines induced positive rainfall anomalies in the northwestern Philippines via an increase in latent heat flux from the sea surface, implying that summer monsoon rainfall in the northwestern Philippines is modulated by interannual variations in SST west of the Philippines. The impact of SST on latent heat flux and rainfall were 20–40%, greatly exceeding the 7% approximation from the Clausius–Clapeyron equation, which can be explained by the enhancement of low-level winds and a weak warming of surface air temperature over the ocean.
Highlights
The Philippines is located in an area primarily affected by the Asian summer monsoon
Evaluation of control simulations (CTL) simulations First, we evaluated the performance of the simulated regional climate over the northwestern Philippines
The simulated 850 hPa horizontal winds in domain 2 were compared with Japanese 55-year Reanalysis (JRA55), which differed from the ERA-Interim boundary forcing data
Summary
The Philippines is located in an area primarily affected by the Asian summer monsoon. The northwestern side of the country is affected by this system, which is known locally as the southwest monsoon (SWM). The SWM is part of the western North Pacific Monsoon within the Asian-Pacific summer monsoon system (Wang and LinHo 2002). The subsystems within the Asian summer monsoon are known to interact with each other. The monsoon onset of regions to the west of the Philippines, Indochina Peninsula and South China Sea (SCS), is associated with the development in the circulation and convective features in the tropical East Indian Ocean (Ding and Chan 2005). The Asian monsoon is a complex system, but the past decade have seen significant advances in understanding climate
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