Characteristics of the air temperature and humidity on the north slope of Mt Qomolangma.

Weather and climatic conditions over the Himalaya regions are of great interest to the scientific community at large. The objective of this study is to present spatial and temporal variations of air temperatures and the relative humidity on the north slope of Mt Qomolangma. Both the hourly air temperature and relative humidity were measured at the seven automatic weather stations (AWS) from 5207 to 7028 m a.s.l. from May 2007 through September 2008. The preliminary results show that the elevational variation of the mean annual air temperature is non-linear, which decreases from 0.2℃ at elevations of 5207 m to -4.4℃ at 5792 m, and -5.4℃ at 5955 m. The maxima are 14.6℃, 9.1℃, and 18.6℃, and the minima are -24.2℃, -28.8℃, and -29.3℃ at the three elevations, respectively. The relative humidity does not change significantly with increasing elevation except over the glacier ice, but the mixing ratio decreases due to the decrease in air temperature. The mean diurnal ranges of air temperature and relative humidity decrease with increasing elevation. The daily maximum air temperature occurs significantly later at the high elevation site than that at the low elevation site because the air temperature at the high elevation site is affected to a large extent by the downward mixing of warm air near the ablation zone of the glacier during daytime. The air moisture content reflects the pronounced alternation of the wet and dry seasons, and the highest water vapor content is associated with the southwesterly Indian monsoon. The mean annual lapse rate of surface air temperature is 0.72±0.01℃/100 m, and also shows a pronounced seasonal signature. Moreover, the reason of the Rongbuk Glacier retreat is also discussed based on the long-term (1959-2007) air temperature and precipitation data from Dingri meteorological station.