Impact of sea breeze penetration over urban areas on midsummer temperature distributions in the Tokyo Metropolitan area

Abstract

We investigate the relationship between sea breeze penetration and anomalously high summer daytime temperatures in the inland suburbs of Tokyo, with consideration of the relative position of sea breeze fronts. We use data from the high‐density temperature observation network (Extended‐METROS) established by our research group to clarify in detail the mechanisms creating these high‐temperature areas.We conducted case and composite analyses of the temperature and wind distributions when typical sea breeze fronts developed. The observations showed that the highest temperatures were near Kawagoe City in the early afternoon, which is 40 km leeward of central Tokyo, on all days analysed, and that the high‐temperature inland areas were located leeward of Tokyo. The high temperatures near Kawagoe City were not observed by the Automated Meteorological Data Acquisition System (AMeDAS). From the case and composite analyses, there was a 2‐h time lag between the sea breeze front penetrating the area leeward of Tokyo and extreme high temperatures being observed around Kawagoe City. Significant divergence was also observed during this time, and a decrease in the dew point temperature was also observed around Kawagoe City on the case study day; these conditions persisted for approximately 2 h. These results suggest the existence of a subsidence flow near Kawagoe City, and the resulting adiabatic compression heating contributed to the observed extreme high temperatures. In the late evening, a high‐temperature band was observed leeward of the northern suburbs of Tokyo, even though southerly sea breezes were recorded over the entire Kanto Plain, and cold advection dominated at that time. However, the cold advection in this high‐temperature band was less notable than in the periphery. Thus, temperature declines were small in this area, and overall temperatures remained relatively high.