Observational analysis of influence of sea-land breeze on diurnal characteristics of urban heat island in Tianjin during summer

Based on the hourly observations of 14automatic weather stations in Tianjin,the Beijing radiosounding data,and the 6-hourly surface conventional observation data in Tianjin during summer 2008,this paper studies the relationship between the sea-land breeze and the diurnal characteristics of urban heat island in Tianjin.Results show that,under the atmospheric stable stratification condition,the diurnal variation of urban heat island intensity in Tianjin increases on the sealand breeze days compared to the non sea-land breeze days.The sea breeze can cool the city,reduce the urban heat island intensity,and delay the appearance of the urban heat island in the nighttime,while the land breeze can significantly enhance the urban heat island intensity at night.We also find that the urban heat island intensity is closely related to the distance of sea breeze propagating.On the sea breeze days,when the synoptic scale geostrophic winds are in the same direction with the offshore wind,the sea breeze can only spread short distance;when the synoptic scale geostrophic winds are in the same direction with the onshore wind,the sea breeze can propagate farther;when the sea breeze can only reach Jinnan,Dongli or Ninghe stations,the urban heat island intensity in Tianjin has the maximum increase;with the increasing of sea breeze propagating distance,the overall increase rate of urban heat island intensity decreases.