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CAS ESM2模式对青藏高原积雪的模拟性能评估

Performance Evaluation of the CAS ESM2 Model in Simulating Snow Conditions over the Qinghai-Xizang Plateau

  • 摘要: 利用中国科学院地球系统模式CAS ESM2的AMIP试验结果及多种观测资料,评估该模式对青藏高原积雪的模拟性能。结果表明,模式对冬春季青藏高原东西两侧积雪多、腹地稀少的空间分布有一定的模拟能力,总体而言高估了高原区域的积雪,这与模式模拟的降水较观测偏多、气温较观测偏低有关;模式对青藏高原积雪的季节循环具有较好再现能力,特别是积雪覆盖率,但由于模拟高原区域气温总体偏低,导致模拟的高原积雪融化偏晚。冬春季青藏高原东部雪深总体呈现下降趋势,2000年以后基本偏少,模式能模拟出高原积雪的下降趋势,对年际变化有一定的模拟能力,春季的模拟技巧要优于冬季。高原东部积雪与大气变量的相关分析表明,冬季积雪与降水和气温关系密切,而春季积雪主要与气温关系密切,模式对气温预报技巧要好于降水,一定程度上导致了春季雪深年际变化模拟技巧好于冬季;进一步分析表明,冬季高原东部雪深年际变化与北极涛动(Arctic Oscillation, AO)及高原附近位势高度场密切相关,春季雪深则与高原附近位势高度场密切相关,模式对冬季AO和高原位势高度场模拟效果不够理想,而对春季高原位势高度场模拟技巧比较显著,因此可能导致了模式对春季高原区域雪深年际变化的模拟效果好于冬季。

     

    Abstract: The AMIP simulation results of the Chinese Academy of Sciences Earth System Model (CAS ESM2) were compared with various observational datasets, and the performance of CAS ESM2 simulated snow conditions over the Qinghai-Xizang Plateau was evaluated. The model successfully reproduced the spatial distribution of the Plateau snow cover in winter and spring, such as the abundant snow cover in the eastern and western parts of the Qinghai-Xizang Plateau and sparse snow cover in the hinterland, but it overestimated the snow cover over the Plateau in relation to the negative temperature and positive precipitation biases compared with observations. The model successfully simulated the seasonal cycle of snow conditions over the Qinghai-Xizang Plateau, especially the snow cover fraction. However, simulated snow melting over the Plateau occurred later than that observed because the simulated temperature was lower than the overall observations. The snow depth on the eastern part of the Qinghai-Xizang Plateau has shown a general decreasing trend in winter and spring, with below-normal snow after 2000, which was successfully reproduced by CAS ESM2. For the inter-annual variations of snow depth on the eastern part of the Qinghai-Xizang Plateau, the model simulation skill was better in spring than in winter. A diagnostic analysis showed that the Plateau snow cover was closely related to precipitation and near-surface air temperature (TAS) in winter and primarily related to TAS in spring. The model performed better on TAS than precipitation, which may have led to its superior snow depth simulation in spring than in winter to a certain extent. Further investigations of inter-annual variations revealed that snow cover on the eastern part of the Qinghai-Xizang Plateau in winter was closely correlated with the Arctic Oscillation (AO) and geopotential height near the Plateau, while snow cover in spring was mainly impacted by the geopotential height near the Plateau. The model simulation skill for winter AO and geopotential height near the Plateau was not ideal, but it was statistically significant for the geopotential height near the Plateau in spring, which may have resulted in the superior snow depth skill in spring compared to winter.

     

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