Local meteorology in a northern Himalayan valley near Mount Everest and its response to seasonal transitions

摘要

An automatic weather station (AWS) has been installed at the Qomolangma Station of the China Academy of Sciences (QOMS) since 2005,in a northern Himalayan valley near Mount Everest,with an altitude of 4,270 m a.s.l..Nine years of meteorological records (2006-2014) from the automatic weather station (AWS) were analyzed in this study,aiming to understand the response of local weather to the seasonal transition on the northern slopes of Mount Everest,with consideration of the movement of the subtropical jet (ST J) and the onset of the Indian Summer Monsoon (ISM).We found:(1) Both the synoptic circulation and the orography have a profound influence on the local weather,especially the local circulation.(2) Southwesterly (SW) and southeasterly (SE) winds prevail alternately at QOMS in the afternoon through the year.The SW wind was driven by the STJ during the non-monsoon months,while the SE was induced by the trans-Himalayan flow through the Arun Valley,a major valley to the east of Mount Everest,under a background of weak westerly winds aloft.(3) The response of air temperature (T) and specific humidity (q) to the monsoon onset is not as marked as that of the nearsurface winds.The q increases gradually and reaches a maximum in July when the rainy period begins.(4) The alternation between the SW wind at QOMS and the afternoon SE wind in the pre-monsoon season signals the northward shift of the STJ and imminent monsoon onset.The average interval between these two events is 14 days.