| Sea breeze front is the front part of sea breeze propagating inland.It is one of the important systems that trigger small and medium scale local convective weather.It is the key and difficult point of forecast in coastal areas at home and abroad.Therefore,in this paper,the mesoscale high-resolution numerical model WRF-ARW（V4.0）is used to simulate sea breeze fronts in clear skies and cloudy skies over Hainan Island.The horizontal and vertical structures of sea breeze fronts and their evolution characteristics are discussed in detail.Finally,the sensitivity test and control test of forest degradation were designed to compare,and the influence of forest underlying surface on sea breeze front of Hainan Island in clear sky and cloudy weather were respectively discussed,and the possible reasons for the influence of forest underlying surface on sea breeze front were analyzed.The results show that:（1）The influence period of sea breeze front under clear sky is 11:00～21:00,and that under cloudy weather is 13:00～22:00.In both cases,sea breeze front experienced four periods of birth,development,strength and decline.In clear skies and cloudy skies,the maximum distance of the sea breeze front advancing inland is 68 km and 78 km,respectively.In the course of the sea breeze front,the sea breeze and land breeze converge in the eastern coastal area of Hainan Island,forming an obvious front area.In strong times,the near-surface wind speed is greater than 4 m·s-1.The sea breeze circulation thickness is about 0.7 km for most of the period,and can exceed 1 km for some periods,with the strongest rise velocity in front of the front exceeding 1.5 m·s-1.（2）The forest cushion has an obvious blocking effect on the sea breeze,which will reduce the inland advancing speed of the sea breeze front,weaken the sea breeze intensity,and affect the sea breeze front’s propagation to a certain extent.After forest degradation,surface roughness decreased significantly in the former forest area,and near-surface wind speed increased by 1.0～5.0 m·s-1,which was related to forest degradation degree and weather conditions.The 10 m wind speed difference between forested and non-forested areas also increased,with the largest increment of about 1.6 m·s-1 at 18:00.（3）The underlying forest surface has a significant effect on the thermal structure of the sea breeze front.After forest degradation in clear sky,the surface temperature of the original forest area at 12:00 decreased by about 1℃.However,with the development of the sea breeze front,the surface temperature increased significantly at 18:00,with a temperature rise of more than 3℃.At the same time,forest degradation can also lead to a decrease in the difference of near-surface temperature between forest and non-forest areas,and the difference of temperature at 2 m before and after 19:00 decreases by about 1.5℃.Under cloudy weather,after forest degradation,the temperature near the ground increased by more than 4.5℃at 19:00,which was slightly larger than the condition of clear sky.By analyzing the surface radiation flux on the underlying surface,the possible reason for the change of sea breeze front after forest degradation is that the friction velocity decreases,the surface net radiation flux and latent heat flux decrease significantly,and the near-surface temperature increases significantly,thus affecting the thermal dynamic structure of sea breeze front. |
PDF Full Text Request