Fog observation in Tsuyama basin

Tsuyama basin is the largest basin in the Chugoku District, and dense fog appears frequently in autumn/winter. The fog is considered as "radiation fog", mainly induced by radiation cooling and topographical effect as the basin, including "cold air lake". The mechanism of the fog was not studied based on field measurements. Some statistical analyses are found in the literature. So we made intensive observation of the radiation fog mainly focusing on space and time distribution for the fog appearance and disappearance. The field measurement included tethered sonde observation, mobile observation and multi-point visual observations in October, 1999 and November, 2000. According to the observation, the appearance of the fog was identified both feom visual observation and upper air sounding data. The top of the fog layer was clearly found as temperature/humidity singularities. Additionally, it is successfully confirmed the usefulness of the upward looking radiation thermometer in the fog detection.