HEST2007珠峰北坡风廓线观测研究

为了研究青藏高原南部喜马拉雅山区局地大气环流系统,继2006年HEST2006大气科学实验之后,2007年中国科学院大气物理研究所和中国科学院青藏高原研究所在珠穆朗玛峰北坡实施HEST2007综合观测.本文使用该观测实验中LAP-3000风廓线仪获得的绒布河谷内三维风场观测资料,并结合地面辐射资料,分析研究了该地区观测期间局地大气环流的日变化和逐日变化过程.研究表明,该地区局地环流系统,特别是沿河谷的轴向风,与其上空西风环流间存在非常紧密的联系,这种联系似乎与不同天气条件下喜马拉雅山区的大气辐射状况有关,即高层西风环流较强的阶段,地面辐射较强,激发出的局地环流也较强,反之亦然.     

珠穆朗玛峰北坡冰川表面不同季节气象特征分析

在极端高海拔地区获取定点的气象观测资料对于研究山地冰川与气候变化的关系极为重要。2005年5月1日-7月22日（春末夏初）和2007年10月2日-2008年1月19日（秋冬）在珠峰地区海拔6560m的东绒布冰川积累区进行了包括气温、湿度、风向风速和气压在内的气象要素观测。对观测资料的分析表明,气温和湿度与附近较低海拔定日气象站的变化趋势基本一致,证明了在极端环境下获得的气象观测资料的合理性。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℃。在春末夏初受印度季风影响,湿度呈持续增加趋势,月平均湿度混合比从5月的1．4g／kg增加到7月的5．4g／kg;而在西风环流控制下的秋冬季湿度呈缓慢降低,月平均湿度混合比从10月的1．4g／kg降低到次年1月的0．5g/kg。春末夏初主要以阴天为主,秋冬季则是晴天占据主导地位。西风环流控制时东绒布冰川盛行西北风,风速较大,极端最大风速可达35m／s。而受印度季风影响时东绒布冰川以南风为主,风速相对较小。     

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.Prom 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...     

Rare earth elements in an ice core from Mt. Everest: Seasonal variations and potential sources

Rare earth element (REE) concentrations in ice samples from the upper 8.4 m of a Mt. Everest ice core retrieved from the col of the East Rongbuk Glacier (28.03°N, 86.96°E, 6518 m a.s.l.) on the northeast ridge of Mt. Everest in September 2002 are presented. REEs display large seasonal variations, with high concentrations in the non-monsoon season and low concentrations in the summer monsoon season. This seasonality is useful for ice core dating. When normalized to a shale standard, the Mt. Everest REEs exhibit a consistent shale-like pattern with a slight enrichment of middle REEs during both seasons. However, individual monsoon REE patterns display differences, possibly resulting from diversified sources. Non-monsoon REE patterns are stable and are associated with the westerlies. Investigation of potential sources for the Everest REEs suggests an absence of anthropogenic contributions and minimal input from local provenances. REEs in Mt. Everest samples are most likely representative of a stable well-mixed REE background of the upper troposphere consisting of a mixture of aerosols transported by the atmospheric circulation from the west windward arid regions such as the Thar Desert, West Asia, the Sahara Desert and other uncertain provenances.     

Quantitative Estimation of Air Mass Exchange by Along-Valley Wind in the Rongbuk Valley

For a better understanding of the air mass exchange processes between the surface and free atmos-phere in the Himalayas,a Himalayan exchange between the surface and troposphere 2007 (HEST2007) campaign was carried out in the Rongbuk Valley,on the northern slope of Mt.Qomolangma,in June 2007.The wind,tem-perature and radiation conditions were measured during the campaign.Using these observation data,together with the National Centers for Environmental Prediction/the National Center for Atmospheric Research (NCEP/NCAR) reanalysis data,the air mass exchange between the inside of the valley and the outside of the valley is quantitatively estimated,based on a closed-valley method.The air mass is strongly injected into the Rongbuk Valley in the after-noon,which dominates the diurnal cycle,by a strong downward along-valley wind,with a maximum down-ward transfer rate of 9.4 cm s?1.The total air volume flux injected into the valley was 2.6×1011 m3 d?1 in 24 hours in June 2007,which is 15 times the total volume of the val-ley.The air mass transfer into the valley also exhibited a clear daily variation during the HEST2007 campaign,which can be affected by the synoptic situations through the adjustment of local radiation conditions.     

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.     

Vertical Air Mass Exchange Driven by the Local Circulation on the Northern Slope of Mount Everest

To better understand vertical air mass exchange driven by local circulation in the Himalayas, the volume flux of air mass is estimated in the Rongbuk Valley on the northern slope of Mount Everest, based on a volume closure method and wind-profiler measurements during the HEST2006 campaign in June 2006. Vertical air mass exchange was found to be dominated by a strong downward mass transfer from the late morning to late night. The average vertical air volume flux was 0.09 m s-1, which could be equivalent to a daily ventilation of 30 times the enclosed valley volume. This vertical air mass exchange process was greatly affected by the evolution of the South Asian summer monsoon (SASM), with a strong downward transfer during the SASM break stage, and a weak transfer during the SASM active stage.     

Preliminary estimation of the moisture exchange in Rongbuk Valley on the northern slope of Mt. Everest

Using observed wind and water vapor data from June 2006,water vapor exchange between the Rongbuk Valley and its above atmosphere is estimated for the first time.The water vapor level shows a high value from 23-29 June and a low from 12-21 June,which co-incide with the South Asian summer monsoon (SASM) active and break stages,respectively.The water vapor can be strongly injected into the closed region of the Rongbuk Valley from the outside atmosphere,with an average strength of 0.4 g s-1 m-2 in June 2006,given that no evaporation occurred.The air moisture exchange proc-esses can be greatly affected by the SASM evolution through changes in local radiation forcing.     

瓦里关山大气二氧化碳浓度变化及地表排放影响的研究

利用非色散红外气体分析方法，在不受人为污染直接影响的瓦里关山进行了大气CO2的连续测量，给出了我国内陆高原大气CO2本底浓度的变化特征，观测表明内陆大气CO2随陆地植被的生长而有明显的日变化及季节的周期变化，其季节变化规律与全球大气CO2本底值的地理分布相一致。瓦里关山大气CO2的年增长率在1993年明显偏低，1994年又有较快的“回升”。地表CO2排放的观测研究还给出了冬季高原草甸土壤的排放特征，测量表明在冬季陆地植被光合作用基本停滞的情况下，土壤CO2的排放率相对增强，其最大排放量可达170 mg/m2·h以上。     

珠峰绒布河谷近地面层气象要素及湍流通量变化

利用2006年5～6月和2007年5～6月中国科学院HEST大气科学实验在珠峰绒布寺河谷野外观测期间获得的观测资料,分析了珠峰地区河谷近地层风向、风速、温度、湿度和CO2的日变化特征,讨论了珠峰北坡冰川风和山谷风的特点以及高原地表辐射、地表反照率和近地层湍流通量的变化特征.结果表明:在复杂地形和特殊下垫面影响下,珠峰绒布河谷地区近地面层各个气象要素和湍流通量日变化特征显著,并且明显存在冰川风和山谷风复合的局地环流,冰川风对该地区地气间物质能量交换起着重要作用.