An Observational Study of a Thermal Belt on Hillsides

Abstract

A thermal belt or a warm zone on a hillside, developing under calm weather conditions during the night, is one of the well-known local climatic phenomena. Although many models describing its fundamental concept have been constructed, very little observational data exists to support the models directly.The difficulty in studying local climatic phenomena lies mainly in collecting data. In the present study, an infrared radiation thermometer installed on the roof of a high building was used to obtain data for analyzing the air temperature structure in complex terrain. The altitude data set (Digital National Land Information, Japan) also was utilized to examine the dependence of air temperature on topography by applying multiple regression analysis.It is confirmed by observation that a thermal belt on a hillside is produced by nocturnal drainage winds and by a cold-air lake which is formed over the basin by the drainage wind and radiative cooling. The height and intensity of a thermal belt are subject to local and temporal variations due to topographical environments and weather conditions, and can vary from hill to hill, even in situations where they are located face to face. These results show that a thermal belt is a phenomenon produced dynamically by the movement of cold air.

Modeling Seasonal Changes in the Temperature Lapse Rate in a Northern Thailand Mountainous Area

“…Positive DT min values (i.e., higher T min values at higher elevation) have been reported in many earlier studies (e.g., Horst and Doran 1986;Barr and Orgill 1989;Kobayashi et al 1994;Mori et al 1995;Kondo 2000). Background mechanisms of this phenomenon are understood fairly well (e.g., Kondo et al 1989;Kondo 2000;Whiteman 2000).…”

Observational Study of the Thermal Belt on the Slope of Mt. Tsukuba

“…Furthermore, zonally non-uniform temperature structure, obtained by thermography, indicates a possible presence of terrain-related cold air drainage along the slope. Kobayashi et al (1994) has revealed that the thermal belt is closely linked with dynamic motion relevant to the cold air drainage. In addition to this, it is still uncertain whether the warmest region appears centered on the western side of the mountain, especially the Sakayori region, where the orange farms are concentrated.…”

Recent Studies of Local-scale Climate in Japan

“…They also found that the top of the inversion was at a height of about 100-200m above the foot of the slope, and that this height corresponded to that of the inver sion layer observed at the aerological station located on the edge of the plain near this slope. While studying the mechanism of a thermal belt on a hillside, Kobayashi et al (1994) clarified that the movement of cold air on the slopes and over the basin produced thermal belts dynamically in a small valley in the north ern part of Kyushu, using an IR radiation ther mometer and tethered balloons.…”