Observational Study of Surface Wind Regime on the North Slope of Mount Qomolangma (Mount Everest)

From May 2007 to September 2008, six automatic weather stations (AWS) were installed along the traditional mountaineering line on the north slope of Mount Qomolangma. The elevations of the stations ranged between 5207 and 6560 m above sea level (a.s.l.). Some sounding data were also measured at Base Camp (5207 m a.s.l.) in late April and early May of 2007 and 2008. The spatial arrangement of the stations and temporal duration of the measurements, as well as the sounding data, generated a data set enabling the analysis of the wind regime in this region. The wind directions and speeds show change at different elevations because of the complicated terrain, the glacier-moraine-rock transition underlying surface, and the synoptic-scale wind. The katabatic wind dominates at low-elevation areas in the Rongbuk Valley, and the depth and frequency of it are about 800 m and 59% during the observational period. The up-valley wind always erodes the katabatic wind, and causes the lowest directional constancy in summer. With the elevation ascending, the katabatic wind weakens due to the smaller fetch and temperature contrast, as well as the relatively open landscape of the valley and smaller glacier area. At site 3 (5792 m a.s.l.), the frequency of the katabatic wind is only 25%, whereas the frequency of the up-valley wind is 47%, and especially in winter, the up-valley wind (82%) predominates all day. Moreover, the synoptic-scale wind also plays an important role in the surface wind regime on the north slope of Mount Qomolangma. From November to March, the active westerly troughs always intrude into the bottom of the Rongbuk Valley and could maintain the strong katabatic wind, and the maximum wind speed reaches 43.1 m s⁻¹ at site 1 (5207 m a.s.l.). At high-elevation areas, the westerlies can penetrates more easily, and dominate the wind regime. The wind speed can reach as high as 57.1 m s⁻¹ at site 3 in winter.