The Long-term Trend And Interannaul Variability Of Latent Heat Flux In Western Pacific And South China Sea

Using the monthly latent heat flux and relevant meteorological variables datasets from 1958 to 2014 supported by the Objectively Analyzed Air-Sea Fluxes data(OAFlux)of the Woods Hole Oceanographic Institution,as well as the surface pressure data from the National Centers for Environmental Prediction and the National Center for Atmospheric Research(NCEP-NCAR)reanalysis.we investigate the long-term trend and interannual variability of latent heat flux of Western Pacific-South China Sea(WP-SCS),in which process we use the method of Trend-EOF.In addition,we assess the latent heat simulations of eight state-of-the-art ocean-atmosphere coupled models.The latent heat flux in the western Pacific-South China Sea(WP-SCS)has a strong upward trend in spring,autumn and winter,and the Kuroshio and its extension areas have the strongest upward trend in winter.But in winter,the southern part of the SCS in some areas show a downward trend,the northern part of the SCS show a rising trend in stark contrast.The latent heat increase of the Kuroshio and its extended area in winter is due to the increase of air-sea humidity difference,and further analysis shows that the root cause is the increase of sea surface temperature.The cause of the increase trend of latent heat flux in Philippine Sea and northern SCS is primarily the increase of air-sea humidity difference.The decrease trend of latent heat flux in south-western SCS is resulted from the decease of air-sea humidity difference,while in south-eastern SCS is the decrease of wind speed.Air-sea humidity difference together with wind speed leads to the north-south contrasting long-term trend.Further analysis shows that the trend of wind speed in the SCS is closely related to the change of the surface pressure,while the change trend of the air-sea humidity difference is mainly depends on the change trend of the sea surface temperature.The interannual variability of latent heat flux in the WP-SCS has a maximum at the Kuroshio and its extended regions,and the regional average time series has a significant cycle of 2-5 years.The results show that the effects of East Asian winter monsoon and ENSO on winter latent heat flux in the WP-SCS are relatively independent.The East Asian winter monsoon mainly affects Kuroshio and its extension area,while ENSO mainly affects the South China Sea and the Philippine Sea area.East Asian winter monsoon mainly affects the latent heat flux of Kuroshio and its extended area by affecting sea surface wind speed and sea surface air humidity.ENSO mainly affects the latent heat flux in the SCS and the Philippine Sea region through anomalous anti-cyclones over the Philippines,and its effect is opposite in the southern and northern SCS.In addition,it is found that the latent heat flux near Kuroshio and its extension area is highly correlated with the temperature of upper and middle subtropical Pacific.In this paper,the result of eight ocean-atmosphere coupled models in CMIP5 is evaluated in simulating the latent heat flux in WP-SCS.On the whole,the model simulates the distribution of climatology and interannual variability of latent heat flux in winter very well,but the climatology is overestimated and the interannual variation is underestimated.None of the eight models evaluated can simulate the long-term uptrend of latent heat flux near Kuroshio and its extension.In addition,the multi-model assemble can simulate the relationship between the East Asian winter monsoon and the latent heat flux near the Kuroshio and its extended area,but the difference between the models is large.