Mountain-Valley Wind System in the Khumbu Himal, East Nepal

[摘要] The mountain-valley wind system in a large valley in Khumbu Himal, East Nepal was investigated on the basis of winds and other meteorological observations carried out mainly at 4, 420m above m.s.l. during about a whole year in 1975. The characteristics of this wind system revealed by the observations are as follows. The daytime valley wind is observed at a frequency of more than 90% in all seasons which means that this wind system is very stable throughout the year. The wind system in the dry season (Jan.-May, Oct.-Dec.) showed the typical mountain-valley wind circulations, while the valley wind in the wet summer monsoon season continued until 04:00 LST throughout the night. This nighttime valley wind is thought to be due to latent heat release from cloud formation and preicpitation. The annual trends of the daytime average wind speed showed maximum in May-June at 8.5m/sec and minimum in Oct. at 5.0m/sec.During the observation period, there were 45 days when the valley wind was abnormal.They were classified into three types of abnormality. The causes for them were the existence of snow cover, middle and high level clouds and the invasion of strong upper wind into valley. Most remarkable change was seen in the effect of snow cover. After the snowfall, the value of daytime wind speed decreased to 30 to 90% of the value before the snowfall. This decrease in wind speed was much remarkable when the air temperature was above 0°C.

[学科分类] 大气科学