珠穆朗玛峰北坡绒布冰川表面辐射特征观测研究

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

中文关键词:  珠穆朗玛峰, 冰川, 辐射特征, 观测研究

英文关键词:Mt. Qomolangma, Glacier, Radiation feature, Experimental study

中文摘要:

      在资料比较稀少的偏远山地冰川进行地面综合气象观测对于研究冰川变化极其重要。珠穆朗玛峰（27.98°N,86.92°E,海拔8844.43 m）地区位于青藏高原南部边缘喜马拉雅山脉中段，自然地理条件独特，环境脆弱，是气候变化和环境变迁的敏感区，同时也是现代冰川作用中心。2005年5—7月和2007年10月—2008年1月在珠穆朗玛峰北坡东绒布冰川积累区（28°01′N, 86°57′E，海拔6560 m）开展了综合气象观测研究。分析表明，在东绒布冰川积累区春末夏初月平均气温从5月的-11.3 ℃上升到7月的-3.4 ℃，秋冬季月平均气温则从10月的-11.3 ℃下降到次年1月的-19.0 ℃。秋冬季主要受西风气流影响，盛行西风或西北风，而且风速较大，1月最大风速达到35 m/s；而在印度季风爆发后主要以南风或西南风为主，风速相对较小。由于海拔高、冰雪面与云之间的多重反射以及复杂地形影响导致地面总辐射较大。春末夏初和秋冬季总辐射平均值分别达到635和502 W/ m2。尤其造成5—6月正午前后10 min短波辐射平均值发生超太阳常数的现象比较频繁，最长持续时间接近3 h。晴天由于周围地形作用可使地面总辐射增加140—310 W/ m2，约占短波辐射的10%—23%。春末夏初和秋冬季平均反射率分别为0.72和0.69。云和空气湿度对大气长波辐射的影响比较显著，导致大气长波辐射同样具有日变化特征。在地表辐射平衡中云对地面净辐射起负效应。除在秋冬季阴天日平均净辐射为负值外，其余时间均为正值，说明净辐射是地表能量的主要来源。

英文摘要:

      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.