Gaoyuan qixiang (Jun 2023)
The Impacts of Vapor Transport on Land-atmospheric Water & Heat Exchanges over the Yarlung Zangbo Grand Canyon Area
Abstract
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 （Z0h） 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.
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