基于CLM4.5的高寒草地辐射收支和水热交换的数值模拟研究

利用那曲高寒气候环境观测研究站本部BJ观测点2014年6-8月的近地层观测资料,结合CLM4.5陆面模型,探究空气动力学粗糙长度、叶面积指数、植被覆盖度和热力学粗糙长度参数化方案的改变对陆面能水平衡的模拟结果产生的影响,并且探讨了粗糙度及植被状态指数影响陆面能水平衡模拟性能的机制。结果表明:(1)CLM4.5默认的热力学粗糙长度方案Z98高估了感热通量,并且低估了地表温度,Z12方案和B82方案能够很大程度上减小感热模拟的正偏差与地表温度模拟的负偏差。(2)基于不同类型数据计算了两组空气动力学粗糙长度的月均值,在替换模式中原有值后,明显减小了地表通量的模拟偏差。(3)叶面积指数的增加(减少),使感热减小(增大),潜热增大(减小),反射辐射和地面长波辐射通量降低(增加),并且土壤温湿度也有所下降(上升)。(4)随着植被覆盖度的增加(减少),潜热通量降低(升高),感热、反射短波辐射以及地面长波辐射增强(减弱),地面土壤温、湿度有所增加(降低)。本研究为选择最优参数及参数化方案,进而更合理地模拟出整个高原地区的地表能水平衡提供了参考依据。

A Simulation Study on Radiation Budget and Water-Heat Exchange over Alpine Grassland Based on CLM4.5

Forced by observations from 1 June to 31 August 2014,which are provided by Naqu station of Plateau Climate and Environment in northern Qinghai-Xizang Plateau,CLM4.5 is used to evaluate the influence on simulated results of both radiation balance and exchange of water-heat after some surface parameters and parameterization schemes including LAI、vegetation coverage and roughness length have changed.The reason for these changes are also discussed in this article.The results suggested that(1)Compared with the results produced by default scheme Z98,those of schemes named Z12 and B82 perform better in decreasing the positive bias of latent heat fluxes and negative bias of sensible heat fluxes.(2)aerodynamic roughness length calculated by revised Massman model and a method named“Chen”are respectively used to replace the default value,the outcomes produced by CLM approach the observations further.(3)With leaf area index increasing,sensible heat fluxes and reflected radiation and surface long-wave radiation decrease a lot,while latent heat fluxes are on the increase.(4)As the vegetation cover increases,latent fluxes decreases,while sensible heat fluxes and reflected radiation and surface long-wave radiation rise,meanwhile soil temperature and moisture also rise.The aim of this study is to provide a basis for future ambition to simulate the balance of ground surface water and heat over the whole Plateau.