The diurnal variation of the evaporation duct height and its relationship with environmental variables in the South China Sea

Based on data from the European Centre for Medium-Range Weather Forecasts (ECMWF) ECWMF ERA5 Reanalysis (ERA-5) and the National Centers for Environmental Prediction (NCEP) Climate Forecast System Reanalysis (CFSR) datasets, the diurnal variation of the evaporation duct height (EDH) in the South China Sea (SCS) and its relationship with environmental variables using the Naval Postgraduate School (NPS) model are analyzed, discussed, and presented. The findings are given as follows. First, the EDH diurnal variations are primarily influenced by the sea-land thermal contrast, with the major influencing variables being the relative humidity (RH) and the near-surface wind speed (WS), followed by the air-sea temperature difference (ASTD). Secondly, the areas where the EDH and the RH are highly correlated are mostly in northern SCS, and the two variables are negatively correlated. Besides, in southeastern SCS, the EDH has a greater and positive correlation with the WS. Seasonal changes can be found in areas where the EDH is highly correlated with the ASTD, primarily to the northwest of Luzon Island in winter and the east coast of Vietnam in summer. Finally, the spatial patterns of the EDH first mode in the SCS present a monopolar structure with the strong loading in northern SCS.