Influence of tidal state on air temperature through penetrating sea breeze front in Seoul in summer

We examine the influence of tidal flats on the daily maximum air temperature in Seoul related to the penetration of sea-breeze front (SBF) using meteorological station data of summer over 10 years (2010–2019). The penetration of SBF at Seoul is detected using an objective SBF detection algorithm. 491 (53%) of the 920 days are classified as those with SBF passage on the coast. The SBF arrives in Seoul on 87% of sea breeze days on the coast. The passage time of the SBF in Seoul peaks between 1400 and 1600 LST, while the traveling time of SBF from the coast to Seoul peaks between 3 and 4 h. The cooling effect of sea breeze in Seoul is examined using the sea-breeze cooling capacity. We divide the sea-breeze days in Seoul into three groups in terms of the arrival time of the SBF in Seoul: before 1200 LST, between 1200 and 1500 LST, and after 1500 LST. All three groups show the cooling effect of sea breeze, which is greatest in the group where the SBF arrives before 1200 LST. The relationship between the tidal state and daily maximum temperature in Seoul is examined. Summer days are divided into four groups depending on the tidal state in the morning (0800–1200 LST) and ambient flow direction. The tidal effect on the daily maximum temperature in Seoul is tested at a significant level of 10% using a two-sample t test for onshore and offshore flows. A significant difference (p = 0.086) is observed for offshore flows, showing a higher daily maximum temperature in the low-tide group in the morning (LTM) than in the high-tide group in the morning (HTM). The passage rate of the SBF at Seoul in the LTM is less than that in the HTM for offshore flows. A weaker sea-breeze forcing and longer distance between the water boundary and Seoul in the LTM could prevent the inland penetration of the SBF, increasing the daily maximum temperature in Seoul.