Abstract:

Sea-land breezes (SLB) are a mesoscale atmospheric circulation phenomenon driven by thermal differences between land and ocean during the day and night, resulting in obvious diurnal variations in wind direction in coastal areas. It is one of the most prominent mesoscale atmospheric circulations in coastal regions. The intensity of the SLB influences the atmospheric boundary layer height, atmospheric chemical processes, air quality, and radiation balance in coastal areas. As a direct thermal condition affecting the SLB, the diurnal variation of sea surface temperature (SST) is influenced by multiple factors, including solar radiation, ocean heat capacity, wind speed, and cloud cover. However, the impact of SST diurnal variation on the occurrence and development of SLB in coastal areas remains unclear. This study utilizes high-resolution SST simulation data combined with the Weather Research and Forecasting (WRF) model to analyze the characteristics of SST diurnal variation and its impact on the SLB in typical coastal areas of China. The results show that the average SST in China’ s coastal regions decreases from south to north, with the Bohai Sea having the lowest annual mean SST of 10.78 ℃, the East China Sea exhibiting a 94.6% higher annual mean SST than the Bohai Sea, and the South China Sea having the highest annual mean SST of 25.19 ℃. The diurnal variation of SST in the Bohai Sea exhibits the greatest annual fluctuation, reaching up to 0.55 ℃, with a minimum of only 0.03 ℃ and an average of 0.25 ℃. The diurnal SST variation in the East China Sea fluctuates moderately, with an annual average diurnal temperature difference of 0.20 ℃. The maximum SST diurnal variation during the study period was 0.45 ℃, about 82.0% of the Bohai Sea’ s extreme value and more than 33% higher than the South China Sea. Comparing scenarios that consider diurnal SST variation with the traditional assumption of constant SST in models, the results indicate that diurnal SST variation can lead to an increase in the number of SLB days in typical coastal areas of China. The number of SLB days in the South China Sea coastal region increased by 14 days annually, with a growth rate of approximately 56.0%, while the number of SLB days in the northern Bohai Sea coastal region increased by 7 days annually, with a growth rate of 20.0%. Seasonally, the diurnal SST variation increased the number of SLB days in winter and decreased them in summer, with little effect on the spring and fall. This results in a reduction in the seasonal difference of SLB days along China’ s coastline.

Key words: global change, sea surface temperature diurnal, sea land breeze, numeric simulations