Evaluation of Reanalysis Products with in situ GPS Sounding Observations in the Eastern Himalayas

Previous studies have shown that reanalysis products contain large uncertainties in the Tibetan Plateau(TP),and the biases are location dependent.Therefore,these products must be evaluated with in situ observations prior to their applications.In this study,the authors compare the results of several reanalysis projects with independent sounding observations recorded in the Yarlung Tsangpo River valley in the Eastern Himalayas in June 2010.These reanalysis projects include Climate Forecast System Reanalysis(CFSR),Interim European Centre for Medium Range Weather Forecasts Reanalysis(ERA- Interim),Japanese 25-year Reanalysis(JRA-25),Modern Era Retrospective Analysis for Research and Applications(MERRA),National Center for Environmental Prediction and the Department of Energy Reanalysis 2(NCEP-R2),and NCEP Final Analysis(FNL).Statistical quantities such as average,mean bias(MB),root-mean-square difference(RMSD),and correlation coefficient(R) of temperature,specific humidity,u-wind,and v-wind between 100 hPa and 650 hPa were calculated.The authors determined that the performance of each product differed with variables at different levels.The average profiles of the variables were captured by the reanalysis products,with large biases appearing at lower levels.ERA-Interim and NCEP-R2 showed the best and worst performances,respectively,for all variables.This study suggests that users should select appropriate reanalysis products according to their specific purposes for TP research.

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.

The Observed Low CO_2 Concentration in the Rongbuk Valley on the Northern Slope of Mt. Everest

In the summers of 2006 and 2007, the atmospheric CO 2 concentration and the wind speed in the Rongbuk Valley on the northern slope of Mt. Everest were measured by an ultrasonic anemometer with an Li-7500 CO 2 /H 2 O gas analyzer. The average CO 2 concentration was 370.23±0.59 and 367.45±1.91 ppm in June of 2006 and 2007, respectively. The values are much lower than those at sites with similar latitudes and altitudes worldwide. The observed atmospheric CO 2 concentration in Rongbuk Valley can be affected by the transportation of prevailing down-valley winds from the up-valley direction to the observation site. Our results suggest that the Mt. Everest region could be ideal for background atmospheric and environmental studies.

考虑侧向变形影响的黄土路基沉降模型试验研究

受荷土体发生的侧向变形是引起黄土路基产生沉降的原因之一,明确侧向位移条件下黄土路基的沉降变形规律成为其科学合理利用的关键。因此,在明确侧向位移对黄土路基沉降影响的基础上,依据黄土路基土体受力形式,为研究侧向位移对压实黄土路基的影响,通过自行设计加工的一种对土体施加不同约束条件的试验装置,研究了同种压实度的土单元在不同约束条件下的加载压缩试验特性。结果表明:受力控制条件下的压缩试验,土单元抵抗变形的能力随着侧面约束数目的增多而逐渐增强;对于侧向预留一定距离的试样而言,土样的竖向压缩应变和侧面预留距离有很大关系。土单元在不同约束条件下的试验成果说明土体的侧向变形是路基产生沉降的重要因素,为黄土在公路工程中的应用提供了重要依据。