Seasonal Characteristics of Surface Radiation Fluxes on the East Rongbuk Glacier in the Mt. Everest Region

Ground-based measurements are essential for understanding alpine glacier dynamics, especially in remote regions where in-situ measurements are extremely limited. From 1 May to 22 July 2005 (the spring-summer period), and from 2 October 2007 to 20 January 2008 (the autumn-winter period), surface radiation as well as meteorological variables were measured over the accumulation zone on the East Rongbuk Glacier of Mt. Qomolangma/Everest at an elevation of 6560 m a.s.l. by using an automatic weather station (AWS). The results show that surface meteorological and radiative characteristics were controlled by two major synoptic circulation regimes: the southwesterly Indian monsoon regime in summer and the westerlies in winter. At the AWS site on the East Rongbuk Glacier, north or northwest winds prevailed with high wind speed (up to 35 m s-1 in January) in winter while south or southeast winds predominated after the onset of the southwesterly Indian monsoon with relatively low wind speed in summer. Intensity of incoming shortwave radiation was extremely high due to the high elevation, multiple reflections between the snow/ice surface and clouds, and the high reflective surrounding surface. These factors also caused the observed 10-min mean solar radiation fluxes around local noon to be frequently higher than the solar constant from May to July 2005. The mean surface albedo ranged from 0.72 during the spring-summer period to 0.69 during the autumn-winter period. The atmospheric incoming longwave radiation was greatly affected by the cloud condition and atmospheric moisture content. The overall impact of clouds on the net all-wave radiation balance was negative in the Mt. Qomolangma region. The daily mean net all-wave radiation was positive during the entire spring-summer period and mostly positive during the autumn-winter period except for a few overcast days. On monthly basis, the net all-wave radiation was always positive.