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基于IAP AGCM4的青藏高原积雪初始化对我国东部夏季降水预测的影响

Impact of Snow Initialization over the Tibetan Plateau on Seasonal Prediction of Summer Rainfall in Eastern China based on IAP AGCM4 Model

  • 摘要: 利用IAP AGCM4气候模式,首先采用基于标准化异常的积雪初始化方案,获取青藏高原区域相对“真实”的积雪初值。然后通过两组集合后报试验,考察青藏高原积雪初值对我国东部夏季降水可预报性的影响,以检验初始化方案的有效性。结果表明:考虑“真实”的青藏高原区域初始积雪异常作用后,春季高原雪深模拟能力相比于常规后报试验有明显改进,特别是高原中西部地区改进显著;对夏季环流场可预报性的分析表明,考虑较真实的青藏高原积雪初值后,欧亚中高纬度环流场的可预报性有明显提高,东亚夏季风环流的预报技巧也有所改善,这些都有利于我国夏季降水预报技巧的改进;考虑积雪初值作用能提高模式对我国东部夏季降水的预报技巧,尤其是积雪显著异常年份。就东部分区而言,江淮区域降水预报技巧的改进最明显,36年平均的空间相关评分由0.02提高到0.11;最后通过个例分析进一步检验积雪初始化方案的有效性,结果表明,引入积雪初始化方案后,青藏高原积雪预报技巧得以改进,改进后的高原积雪通过影响东亚季风环流场,最终使我国东部夏季降水预报技巧得以改善。以上结果表明基于标准化异常的积雪初始化方案对提高我国短期气候的预测水平是有效的,可应用于实时预测中。

     

    Abstract: A snow initialization scheme based on anomaly rescaling has been introduced into IAP AGCM4 (Institute of Atmospheric Physics Atmospheric General Circulation Model 4) to obtain realistic initial snow conditions over the Tibetan Plateau (TP). Two suites of seasonal ensemble hindcasts with and without snow initialization were implemented, and the predictability skills of large-scale atmospheric circulations and precipitation over East China were estimated. The results show that the potential predictability of spring snow depth over the TP increased greatly when more realistic snow initial anomalies were applied, especially in the western part of TP. Furthermore, the results indicate that the potential predictability for the large-scale atmospheric circulation at middle-high latitude Eurasia was enhanced. The predictive skill also showed some improvement for the East Asian summer monsoon. These results are favorable for the improved prediction of rainfall anomalies in China. Hence, the results of the present study indicate that seasonal prediction for summer rainfall anomalies over eastern China is improved by using more realistic initial snow states over the TP, especially in the years with pronounced snow anomalies. Large improvement can be found for the Yangtze River valley with an anomaly correction coefficient from 0.02 without snow initialization to 0.11 with snow initialization for the 36-year average. Finally, the effectiveness of this snow initialization was validated through a case study. The results of the case study show that the atmospheric circulation responds to the improved snow anomalies over the TP with snow initialization and then impacts the predictability of rainfall anomalies over eastern China. Thus, it is suggested that snow initialization based on anomaly rescaling is effective for improving the predictive skill of rainfall anomalies over China, and this snow initialization scheme can be used in real-time predictions.

     

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