Temporal And Spatial Characteristics Of Sea Breeze And The Response To Urban Heat Island In Tianjin

In this paper, the temporal and spatial characteristics of sea breeze, and the influence of urban heat island to it in Tianjin area during the year of2008are analyzed by using observation data of14automatic weather stations, and data from the6-hourly general surface meteorological stations. The main conclusions are summarized as follows:(1) In four seasons, the frequency and intensity of sea breeze are different in different stations. Throughout the year, sea breeze is most frequent in the spring and summer months, especially in Dagang station, the annual frequency of sea breeze days is about31.0%, with the station to the coast distance increase, the frequency of sea breeze days gradually decrease. The spatial distribution of sea breeze strength shows offshore stations greater than inland stations, suburban stations stronger than urban station, and the strongest in spring, weaker in autumn and winter.(2) There is significant variation in starting and ending time, wind speed and wind direction of sea breeze in standard stations for four seasons. Sea breeze starting time and duration are the greatest for standard stations in summer, and it is prevalent between12:00to20:00. The most frequency of wind speed is3m/s in spring and summer at Dagang and Hanggu stations, compared with2m/s in autumn and winter. In Tanggu station, the wind speed of sea breeze is focus on3m/s, except autumn. The main distribute of wind direction is between East and ESE in Tanggu and Dagang stations, SE to SSE in Hangu.(3) The frequency of sea-land breeze is very low in weak or strong Urban Heat Island conditions, and the strong heat island intensity has effect of blocking penetration of the sea breeze. In all ground stations, the highest frequency of maximum wind speed of sea breeze is concentrated in weak heat island condition, and to the east of city station, Jinnan has the highest frequency.(4) Urban Heat Island delays the starting time of sea breeze in suburban stations, and makes the duration shorter. When the sea breeze spreads to the city station or farther areas, there almost isn’t heat island effection, if the sea breeze extends to Jinnan, Dongli or Ninghe station, the heat island intensity will increase during the period prevalence of sea breeze and result in the sea breeze spreads to the center of city or westward, increasing surface-layer wind flow at the same time.