The Analysis Study On Characteristics Of Sea/Land Breeze Over The Hainan Island

In this study, based on the hourly observational data from 19 regular stations and 5 island stations in Hainan Island, with the radiosonde data over Haikou station, the temporal and spatial characteristics of sea breeze over Hainan Island in 2012 are analyzed, and the development characteristics of sea breeze under different weather conditions are also discussed. In addition, the temporal and spatial characteristics of near-surface wind over the coastal areas over the Hainan Island during 2012 are analyzed, and the daily change of wind speed are also discussed. Conclusions are as follows:Firstly, sea breeze tends to occur in spring (40%) and autumn (33%), with the minimum frequency (19%) in winter, especially in January, frequencies of most stations are less than 10%. In summer, sea breeze appears earlier, and compared to the northern area, the sea breezes over southern coastal area have longer duration, but in winter sea breezes represent the opposite characteristics. The sea breezes last for about 10 hours in average. The speed of sea breezes in coastal stations is about 3-6 m/s, and the maximum speed appears in spring. Except Qiongshan and Haikou stations, the largest sea breezes strength appears in spring or summer. Among inland stations, a higher frequency of sea breezes is present in stations that centered by mountains due to the enhancement effect of the mountain-valley breeze, with earlier onset time, stronger speed and longer lasting time. The sea breezes can spread to the inland about 70 km far away at least.Secondly, depending to the weather condition, the sea breezes days are classified into several tapes, and the characeteristics under different weather condition are analyzed, the main conclusions are as follows:Most sea breezes occur during overcast days, followed by cloudy, few under clear-sky conditions; compared to inland stations, sea breeze tends to occure in cloudy days over coastal areas, especially, the frequency of sea breeze under rainy days over inland stations is less than 20%; sea breezes start earlier during days with precipitaition than clear-sky days; the intensity of sear breezes show strongest during clear-sky condions, followed by cloudy days, with weakest under cloudy days.Finally, the yearly mean wind speed over coastal areas is about 1.8-5.7m/s, and the strongest wind speed appears in Sanya, and especially in winter, the wind speed could reach 6.5 m/s. Generally speaking, the highest wind velocity usually appears in winter or spring over most coastal stations, with the weakest wind in summer, and the wind velocity is higher in southern and west coastal areas. The diurnal evolution of wind speed exhibits the canonical pattern, with the higher velocity in daytime than nighttime, and the daily maxima appears in 15h afternoon and daily minima appears at night, but Sanya exhibits the opposite pattern as a result of its unique topography and vegetation. In summer, the dominant wind direction is SW and in winter is NE, which similar to the pattern of South China Sea Monsoon. As the season changes, the prevailing wind over southern coastal areas shows significant variability, followed by eastern and western regions, and wind directions over northern coastal areas represents little changes.