Research On The Temporal And Spatial Distribution Of Sea-Land Breeze And Its Influencing Factors At Representative Stations Along The Coast Of Chinese Mainland

Sea-land breeze is mainly a thermal circulation unique to coastal areas,which is caused by the thermal contrast between sea and land,and its occurrence and development can affect the air quality,weather and climate systems in coastal areas.Most of the previous studies on sea-land breeze observations are limited to individual case analysis in individual regions,being lack of a complete and unified analysis of sea-land breeze along the coast of Chinese Mainland,especially a systematic study of different types of sea breeze.In this thesis,we use 5 years（2016-2020）of the automatic weather stations observation data,coastal anchor buoy data,wind profile radar data and ERA-5 reanalysis data to statistically analyze the occurrence frequency,wind speed evolution,start and end time and other basic characteristics of three types of sea breeze at typical representative stations along the coast of Chinese Mainland.Furthermore,the differences between different types of sea breeze in different maritime space and the atmospheric circulation patterns are compared.The main conclusions are as follows:（1）The objective determination method of three types of sea breeze is proposed,including pure sea breeze,corkscrew sea breeze and backdoor sea breeze.The wind direction range of different sea breezes is divided based on the angle of the 10 m wind direction above ground at Qingdao station relative to the coastline.According to the wind direction evolution characteristics of Qingdao station with time relative to the coastline,three types of sea breeze are clearly and intuitively defined by using the disk method,including pure sea breeze（PSB）,corkscrew sea breeze（CSB）and backdoor sea breeze（BSB）.Pure sea breeze means that the 10 m wind changes from west（land）to east（sea）and the wind direction is perpendicular to the coastline.Corkscrew sea breeze means that the 10 m wind gradually shifts from southwest（land）to southeast（sea）and the wind direction rotates counterclockwise.Backdoor sea breeze means that the 10 m wind gradually shifts from the northwest（land）to the northeast（sea）and a clockwise rotation of the wind direction occurs.（2）Using multiple observations to reveal the spatial and temporal variation characteristics of three types of sea breeze at Qingdao station and the influencing factors.The three types of sea breeze shows clear seasonal differences:the period of high frequency of sea breeze is in April to September,with wind speed concentrated at 3.00-5.00 m s^-1,the frequency of sea breeze occurrence is the highest during1200-1600 LST（local standard time）.In winter,there are relatively few sea breeze occurrences,and the duration is discontinuous,and the wind speed intensity is low.Land-sea thermal contrast and the sunrise and sunset time of sea breeze days are all the potential reasons for seasonal differences in the frequency and duration of sea breeze:a positive land-sea thermal contrast and prolonged sunlight effect are more conducive to the formation and development of sea breeze.In terms of atmospheric stability,the BSB tends to occur in weakly stable atmospheric conditions.In contrast,PSB tends to occur in conditions of high atmospheric stability.（3）The spatial and temporal characteristics of three types of sea breeze at typical representative stations along the coast of Chinese Mainland were analyzed.The number of sea breeze days occurrence at representative stations along the mainland coast presents a spatial distribution of‘more in the south and less in the north’.From the perspective of sea breeze classification,PSB mainly occur in the north,while BSB mostly occur in the south.Differences in the spatial and temporal evolution of sea breeze in different seas,in the Bohai Sea the strongest sea breeze intensity occurs in Spring,with significant increases in wind speed during the 1000-1400 LST period,and few sea breezes occur in winter.The sea breeze in the Yellow Sea has a good continuity of occurrence,associated with most of the sea breeze maintaining from sunrise to sunset and changes in the wind speed gently and in low intensity.The frequency of sea breeze in spring and summer has a significant difference of‘low in the morning and high in the afternoon’.In winter,the frequency of most sea breezes is low,and the changes are not significant.Compared with other sea areas,the frequency of sea breeze occurrence in the East China Sea is the highest.The frequency of sea breeze occurrence in the South China Sea is the lowest among the four sea areas,which mainly occurs in spring,summer,and autumn,with significant changes and obvious fluctuation in the monthly variations of sea breeze wind speed.Time of occurrence of different sea breezes,the BSB has the earliest formation time,the latest end time,and the longest duration.With the latitude decreasing,the start and end time of the sea breeze gradually delays.The start time and end time of CSB are earlier than PSB.Due to the superposition of large-scale circulation wind fields and the latitude differences in solar radiation,the high incidence seasons of sea breeze in the four seas are generally in spring and summer,and infrequently in winter.The superimposed effects of summer monsoon and land-sea thermal contrast can promote the development of sea breezes.Conversely,strong cold air in winter weakens the development of sea breezes.The average start of the sea breezes is about 3-5 hours after sunrise.The sea breezes start earliest and last longest in summer,which is due to the earliest sunrise time and strong solar radiation in summer,which can reach the thermal contrast conditions required for the formation of sea breezes in advance,and the long time of sunlight contributes to the development of sea breezes.