High-Altitude Thermal Inversion in the Southern Slope Area of Mt. Yatsugatake, Central Japan

Abstract

We examined a hydrothermal structure of the atmosphere on the mountain slope during clear calm nights at southern slope area of Mt. Yatsugatake, central Japan. An observation was carried out in November, 1993 using various meteorological observation methods such as ground surface observations with thermometers and a thermography, and kite-balloon observations. The results showed the frequent appearance of high-altitude thermal inversion on the mountain slope.In the vertical profile of temperature, the local maximum formed by this inversion appeared approximately at around 1400 m or 1700 m a.s.l. (700 m or 1000 m from the surface). Both its appearance altitude and difference in elevation are much higher than those of the general thermal belt, which were reported in previous studies. Successive images of thermography showed the horizontal zone of this upper inversion clearly. This horizontal zone of high temperature, which is called the high-temperature layer on the slope, is sharply isolated from the lower levels near the surface, the zone of lower temperature. The high-temperature layer is characterized by a warm and dry air mass. Conversely, it is relatively cool and moist below the high-temperature layer. These characteristics are simultaneously found at the same altitude in aerological observations at Tateno and Wajima (aerological stations of the Japan Meteorological Agency). The high-temperature layer appears when anticyclones cover central Japan.Frequently, the high-temperature layer moved vertically during the night. Whereas both in the upward and the downward case, the formation process of the high-temperature layer is different from that of the general thermal belt, which goes only upward. The main factor of the high-temperature layer formation is attributed to adiabatic warming by subsidence flow in the anticyclone.