Characteristic of Fog after Weir Construction around the Nakdong River in the Korean Peninsula

Weirs were constructed near the Nakdong River in Korean Peninsula for the purpose of water resource securement and weather disaster prevention of the area near the river. Therefore, it is necessary to perform the local meteorological impact assessment by the change of water area. In order to analyze the impact on visibility by water surface, visibility meters were installed around the Gangjeong–Goryeong Weir in Nakdong River. Seasonal variation of the bad visibility was distinctive from late autumn (November) to winter. It is noticeable that diurnal variation of bad visibility peaks from midnight to early morning. Bad visibility was mainly observed when humidity was over 90% or water temperature was higher than air temperature. It seems that contribute to make bad visibility due to water vapor in the air. Fog formation (visibility <1 km) was observed using a transmissometer around Gangjeong-Goryeong Weir over the Nakdong River along with air temperature, relative humidity, surface temperature, and wind speed and direction. In addition, visibility at Deagu Weather Station (DWS) and water temperature at Gangjeong-Goryeong Weir data were used. The meteorological characteristics at the Weir were observed as follows: summer (winter) temperature was higher (lower) than normal year; humidity was higher than that at DWS; and soil temperature was lower than water temperature that at Gangjeong-Goryeong Weir; and soil temperature at DWS. Fog formation at the Wier was most frequently observed in the fall - generally during dawn or morning. When the fog occurs, wind direction was Southwest and soil temperature was lower than air temperature. Evaporation fog was the main type out of four fog types (radiation, advection, evaporation, and front) considered.