A Numerical Simulation of Thermal Belt on an Ideal Mountain Using Local-scale Climate Model
1997 Volume 53 Issue 3 Pages 217-225
Details
1997 Volume 53 Issue 3 Pages 217-225
Using a three-dimensional local-scale climate model developed in the Applied Meteorological Division, Japan Meteorological Agency, a numerical simulation of thermal belt is carried out. Numerical simulations are made using a personal computer with an ideal mountain. Simulated temperature field qualitatively represents several features of observed thermal belt in some literature. Computed surface temperature difference between on the slope and on flat surface is about 2°C in maximum and a center of the thermal belt appears at about 100m level on the mountain slope.
The formation mechanism obtained through analyses of calculated results is as follows.
Though the lower atmosphere is cooled on the mountain slope, as well as on the flat surface, due to turbulent heat transfer to more cooled ground surface just after sunset, cooled air subsides and it forms a circulation of mountain breeze which carries relatively warm air to the lower air layer. In the analysis of calculated cooling rate upon the slope, advective warming by a system of mountain breeze compensates turbulent transfer (cooling), so that, the air in not cooled strongly through the night. On the other hand, the air upon the flat surface where mountain breeze does not penetrate is constantly cooled by both processes of turbulent transfer and radiative cooling. The temperature difference between slope and flat surface makes thermal belt. Wind speed of the mountain breeze has a maximum during a few hours after sunset and is becoming to be weaker through night time. Because the breeze circulation on the lower part of the slope diminishes relatively, decrease in advective warming cause upper slightly of thermal belt.
Intensity of the thermal belt, defined by a difference between maximum temperature on the slope and minimum temperature on the flat surface, and height of the thermal belt depend on horizontal and vertical size of mountain. The narrower mountain seems to make the more intense thermal belt.
