![]() It includes very high resolution surface meteorological stations and several surface-based remote sensing stations (Park et al. Recently, an urban meteorological observation system in the SMA (UMS-Seoul) was installed by the weather information service engine (WISE) and Korea Meteorological Administration. Additionally, like in the case of sea breeze, there have been very few studies on the features of land breeze in the area. Although the penetration distance of sea breeze has been reported to have a wide range, there have been few observation-based studies in the SMA. However, maximum penetration distance of sea breeze has been reported with a variable range from 24 km (Jeong et al. 2008 Pokhrel and Lee 2011 Ryu and Baik 2013). There have been model-based studies on sea breezes in SMA (Jeong et al. Thus, local circulations are expected to be very complicated. The Seoul Metropolitan Area (SMA), noted in 2015 as the world’s fifth largest urban area in terms of population, has a very complex geography, topography, and land cover distribution (Demographia 2015 Park et al. The detailed features of sea breeze are regarded as specific to the geographical location and conditions. The height of the sea-breeze head grows to 1300 m or so, and an overhead returning flow is often observed (Nakane and Sasano 1986 Banta 1995 Tijm et al. The sea-breeze penetration has a wide range, from 15 km in Alaska to 300 km in Australia at around 1500–1900 LST (Atkinson 1981 Kozo 1982 Simpson 1994 Tijm et al. ![]() A sea-breeze front at the landward edge of circulation advances inland at a rate of 5–16 km h −1, accompanied by an increase in relative humidity, a decrease in temperature, and an abrupt change in wind direction and speed (Nakane and Sasano 1986 Yoshikado and Kondo 1989 Abb and Physick 1992 Miller et al. ![]() Many observational features about the sea breezes have been broadly reported (Changnon et al. Furthermore, the sea breeze is accelerated or decelerated depending on the urbanward convergent flow induced by the urban heat island. It is well known that the inland penetration of sea breezes is retarded because of the increased surface roughness of cities (Thompson et al. Sea–land breezes or mountain–valley breezes sometimes interact with urban–rural breezes, complicating detailed local meteorological features (Bornstein and Tompson 1981 Freitas et al. The thermal internal boundary layer is formed over land with different diffusive characteristics below and above the layer, affecting the air quality along the coastal region (Gaza 1998 Luhar et al. For instance, the nighttime drainage wind, accompanied by a mountain breeze, has been observed over mountainous regions, often causing vegetation frostbite (Mahrt and Larsen 1982 Hootman and Blumen 1983 Wang et al. They play an important role on the local weather and air quality in a number of ways. Local circulations (e.g., sea–land breezes, mountain–valley breezes, and urban–rural breezes) are driven by thermal differences between two different land covers (Simpson 1987). The returning (easterly) flow at 1.5–1.6 km was clearly observed over the sea-breeze cells. The time–height cross section of wind indicated that the top of sea (land) breeze reached a maximum height of 1.5 km (0.8 km) with maximum winds 0.4 km (0.3–0.4 km) high in the late afternoon (early morning). The sea-breeze front was identified by a steep horizontal temperature gradient, and its passage was accompanied by an abrupt temperature drop as well as vapor pressure and wind increases. The land breeze occurred within 50 km of the shoreline until noon. The resulting sea breeze began at the shoreline at 1200 local standard time (LST), moved landward at a rate of about 10 km h −1, and reached 60 km from the shoreline at 1800 LST. This induced sea–land-breeze circulation. The 6-day average diurnal variations of surface meteorological variables revealed temperature differences between land and sea, driving the pressure differences between the two. These data were obtained from high-resolution surface meteorological stations and three wind lidar stations for 6 consecutive days (17–) with very weak synoptic winds and low cloud covers. In this study, detailed surface meteorological and vertical profile features about sea and land breezes in the Seoul Metropolitan Area (SMA) were investigated using the data from urban meteorological observation system in SMA (UMS-Seoul). Local circulation plays an important role in producing high-resolution meteorological and air quality information.
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