Seasonal characteristics of surface radiative fluxes on the East Rongbuk Glacier in the north slope of Mt. Qomolangma (Mt. Everest) region

Ground-based measurements are essential for understanding alpine glacier dynamics, especially in remote regions where insitumeasurements are extremely limited. The Mt. Qomolangma (27.98°N, 86.92°E, 8844.43 m) region locates on the south margin of the QinghaiTibetan plateau. The south and north area are controlled with Indian monsoon and westerlies respectively. Due to its high elevation and unique topographic characteristics, the region provides favorable conditions for glacier development. Surface radiation as well as meteorological variables were measured over the accumulation area on the East Rongbuk Glacier, Mt. Qomolangma at an elevation of 6,560 m. Measurements were conducted using an automatic weather station (AWS) from May 1 through July 22, 2005 (springsummer period) and from October 2, 2007 through January 20, 2008 (autumn-winter period). At the AWS site on the East Rongbuk Glacier, mean monthly air temperature ranged from-11.3℃ in May to -3.4 ℃ in July, 2005 and from -11.3 ℃ in October, 2007 to -19.0℃ in January, 2008. North or northwest winds prevailed with higher wind speed (up to 35 m/s in January) in winter and 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 its high elevation, multiple reflections between the snow/ice surface and convective or broken clouds and high reflective surrounding surface. The mean incoming shortwave radiation was 635 W/ m2 and 502 W/ m2during springsummer and autumnwinter period, respectively. These also caused the observed 10 minute mean solar radiation fluxes around local noon were frequently higher than the solar constant from May through July, 2005, and the longest duration up to 3 hours. The incoming shortwave radiation can increase about 140-310 W/ m2 (10%-23% of the incoming shortwave radiation) due to around terrain reflection. The mean surface albedo ranged from 0.72 during the springsummer period and 0.69 during the autumnwinter period. High surface albedo occurred on days with high atmospheric water content, cloudy sky conditions, and fresh snow on the surface, while relative lower surface albedo occurred during the clear sky days on the firn surface. The atmospheric incoming longwave radiation was strongly controlled by cloud conditions and atmospheric moisture content. The atmospheric incoming longwave radiation increased from about 170 W/ m2 in May to 282 W/ m2 in July, 2005, and decreased from about 151 W/ m2 in October to about 118 W/ m2 in December, 2007. The outgoing longwave radiation also showed some changes but the magnitude was smaller. The net longwave radiation increased from -83.8 W/ m2 in May to -14.2 W/m2 in July, 2005, and decreased slightly from -95.2 W/ m2 in October to -109.0 W/ m2 in December, 2007. 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 cloudy days. Net all wave radiation decreased from 132.8 W/ m2 in May to 97.8 W/ m2 in July, 2005, and decreased from 73.3 W/ m2 in October, 2007 to 52.2 W/ m2 in January, 2008. Overall impact of clouds on net allwave radiation balance was negative in the north slope of Mt. Qomolangma region.