水汽输送对雅鲁藏布大峡谷地区陆—气间水热交换的影响研究

The Impacts of Vapor Transport on Land-atmospheric Water&Heat Exchanges over the Yarlung Zangbo Grand Canyon Area

藏东南地区的雅鲁藏布大峡谷地区(以下简称大峡谷地区)是印度洋暖湿气流输送至青藏高原的重要通道,在高原水分与能量循环过程中具有重要地位。为了揭示不同水汽输送对陆-气间水热交换通量的影响,本文利用欧洲中期天气预报中心第五代再分析数据产品,根据大气中总水汽含量和水汽水平输送通量将大峡谷地区2013年5月20日至7月9日的水汽强度划分为强/弱/极弱三种级别。并利用第五代公用陆面模式(Community Land Model version 5.0,CLM5.0)模拟了水汽输送对大峡谷-大气间水热交换的影响。研究表明:大峡谷地区的南(东)边界为水汽主要的输入(输出)边界,大峡谷南侧河谷存在水汽强输送带。CLM5.0模拟的大峡谷-大气间水热交换通量与实际相比误差较大,通过优选热力学粗糙度参数化方案和土壤属性替代数据集,提高了CLM5.0模拟大峡谷-大气间水热交换通量的精度。其中Zeng and Dickinson(1998)的方案(以下简称Z98方案)效果最优,较CLM5.0默认参数化方案下模拟的小麦站和草地站近地面感热通量均方根误差分别下降18.2%和10.9%。区域模拟结果显示:大峡谷地区近地面潜热通量区域模拟总体分布为东南高而西北低,近地面感热通量则相反,随水汽水平输送强度的减弱,潜热通量大值区向西北延伸面增大,而感热通量大值区则向东南延伸面增大。冰雪覆盖的高海拔地区近地面感热通量维持低值,而潜热通量则相反。整个试验阶段,大峡谷地区降水时长达59%,不同水汽输送条件下近地面有效能量主要以潜热的方式向大气输送,其中在强水汽水平输送条件下的水汽强输送带的近地面感热输送最弱,Z98方案下的感热通量日均值仅为-1.80 W·m^(-2),潜热通量则大于70.0 W·m^(-2)。对于大峡谷地区,当水汽维持高值范围时,近地面净辐射降低,但近地面净辐射主要被潜热消化,水汽保温大气的效应使得地-气温差降低,近地面感热输送抑制显著。本研究结果对认识雅鲁藏布大峡谷地区陆面过程及其对水汽水平输送的响应有一定的参考价值。

The Yarlung Zangbo Grand Canyon region(referred to as the YGC),located in the southeast Qinghai-Xizang Plateau,is the main channel of the warm and humid air transported from the India Ocean to the Qinghai-Xizang Plateau(referred to as the QXP),and it plays an important role in the water and energy cycle of the QXP.In order to explore the influences of the different horizontal water vapor transport on the water&heat exchanges flux,the water vapor intensity over the YGC from May 20,to July 9,2013,was divided into three levels:strong,weak,and very weak based on the ECMWF Re-Analyses version5 data.And the fifth-generation public land model(Community Land Model version 5.0,CLM5.0)was deployed to simulate the impact of the horizontal water vapor transport on the YGC-atmospheric water and heat exchanges.The results show that the south(east)boundary of the YGC is the main input(output)boundary of water vapor,and the YGC valley over the south of the YGC is a strong water vapor transport belt.The YGC-atmospheric water&heat exchanges fluxes simulated by CLM5.0 has large errors compared to the actual measurements,the CLM5.0 simulated near-surface water&heat exchanges fluxes over the YGC have a high accuracy by optimizing the thermal roughness length(Z_(0h))parameterization schemes replacing the default soil attribute data-set.Compared with the simulations by using the CLM5.0 default parameterization scheme,the one developed by Zeng and Dickinson(1998).(Z98 scheme for short)has the lowest errors,the root mean square error of the near-surface sensible heat flux at the wheat station and the grassland station decreased by 18.2%and 10.9%,respectively.The results of regional simulation show that the general distribution of the near-surface latent heat flux(LE)over the YGC is high in the southeast and low in the northwest,while the near-surface sensible heat flux(H)is the opposite.As the water vapor transport intensity decreasing,the area with high near-surface latent heat flux extends to the northwest,while the near-surface sensible heat flux(H)is the opposite.The H in the high-altitude ice and snow-covered area maintains a low value,while the LE is the opposite.During the entire experimental period,the precipitation was as high as 59%over the YGC,which is abundant precipitation.The near-surface effective energy is mainly transported to the atmosphere in a form of latent heat under different horizontal water vapor transport conditions.The near-surface sensible heat transport is the weakest in the strong water vapor transport belt under the condition of strong horizontal water vapor transport.The regional daily average value of the H is only-1.80 W∙m^(-2)by using the Z98 scheme,while the LE is greater than 70.0 W∙m^(-2).When the water vapor maintains a high-value range over the Grand Canyon area,the near-surface net radiation decreases,but the near-surface net radiation is still mainly consumed by the latent heat.The warming effect of the water vapor on the local atmosphere resulted in the difference of ground-atmospheric temperature decreases,and the near-surface sensible heat is significantly inhibited.The results of this study have a certain reference value for understanding the land surface process over the YGC and its response to horizontal water vapor transport.