Observational Analysis of Tidal Effect on Sea Breeze

The tidal effect on a sea breeze is examined using a 4-year 30-min database of wind-speed profiles obtained from a 300-m tower at a coastal site in Boseong, South Korea, facing a bay with tidal flats. We consider sea-breeze days during the warm season from May to September of each year from 2014 to 2017. A sea-breeze day is defined as a day with both onset and cessation of a sea breeze within 24 h. Sea-breeze days are divided into four groups depending on the tidal state and ambient flow direction. The tidal effect on the sea breeze is tested at a significance level of 5% using a two-sample t-test for onshore and offshore flows. The results indicate that there is a significant difference due to tidal state in the onset time of the sea breeze only for offshore flow, showing earlier arrival for the high-tide group in the morning than the low-tide group in the morning. This could be explained by the shorter distance to the sea due to the movement of the water boundary towards the station as well as larger sea–land temperature difference during high tide. For offshore flows, the tidal effect on wind-speed profiles is examined, with results showing that the tide state influences the time at which the sea-breeze speed increases but not the daily maximum speed of the sea breeze.