Sensitivity of high-temperature weather to initial soil moisture: a case study using the WRF model
Sensitivity of high-temperature weather to initial soil moisture: a case study using the WRF model
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高温天气对初始土壤湿度的敏感性：使用 WRF 模型的案例研究
DOI：
10.5194/acp-14-9623-2014
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发表时间：
2014-09
影响因子：
6.3
通讯作者：
Wang, G.
中科院分区：
文献类型：
--
作者：
Huang, X.;Zheng, Y.;Chen, C.;Wang, G.
抽象。利用WRF模式（Weather Research and Forecasting Model）的24 h数值模拟，研究了2003年7月下旬发生在华东地区的一次短时高温天气过程对初始土壤湿度的敏感性。诺亚陆面方案中的初始土壤湿度（SMOIS）被调整（相对于控制运行CTL）为四组模拟：DRY25（-25%），DRY50（-50%），WET25（+25%）和WET50（+50%）。每组进行10次24 h积分。我们重点分析了06：00 UTC（大约14：00 LT）2 m地面气温（SAT）大于35 ° C（中国"高温"事件的阈值）的高温事件的发生。10天平均结果表明，06：00 UTC SAT（SAT 06）对SMOIS变化较为敏感;具体地说，随着SMOIS的降低，SAT 06表现出明显的增加（如与CTL相比，DRY25通常导致华东地区地表SAT06升高1 ° C），SAT06高于35 ° C的地区受影响最大，模拟结果对SMOIS的减小比对SMOIS的增大更为敏感，这表明在低土壤湿度条件下，高温天气会被放大。关于极端高SAT 06的机制，显热通量被证明直接加热低层大气，潜热通量被发现对SMOIS的变化更敏感，导致由于温室效应增加而导致地面净辐射的总体增加（例如，随着SMOIS从DRY25增加到CTL，10天平均净辐射增加了5 W m − 2）。此外，由于西太平洋副热带高压的独特性和动态性，区域大气环流与低层气温之间存在负反馈，而对流层中层则存在正反馈。利用基于相似温度关系的方法，详细分析了5组模拟的物理过程，结果表明，对于SAT变化，SMOIS变化对西太平洋副热带高压非绝热过程（如地面通量）的影响大于绝热沉降过程。有趣的是，尽管非绝热过程分别在白天和夜间主导沉降，但它们不一定在24小时期间占主导地位（例如，它们仅在WET和CTL模拟中占主导地位）。此外，随着SMOIS的减少，SAT 06增加，这主要是由于非绝热过程的冷却效应减少，而不是下沉的变暖效应。与以往的研究在气候时间尺度上的热浪事件，本文提出了模拟短期高温天气初始土壤水分的敏感性，并强调适当的土壤水分初始化模拟高温天气时的重要性。
Abstract. Using a succession of 24 h Weather Research and Forecasting model (WRF) simulations, we investigate the sensitivity to initial soil moisture of a short-range high-temperature weather event that occurred in late July 2003 in East China. The initial soil moisture (SMOIS) in the Noah land surface scheme is adjusted (relative to the control run, CTL) for four groups of simulations: DRY25 (−25%), DRY50 (−50%), WET25 (+25%) and WET50 (+50%). Ten 24 h integrations are performed in each group. We focus on 2 m surface air temperature (SAT) greater than 35 °C (the threshold of "high-temperature" events in China) at 06:00 UTC (roughly 14:00 LT in the study domain) to analyse the occurrence of the high-temperature event. The 10-day mean results show that the 06:00 UTC SAT (SAT06) is sensitive to the SMOIS change; specifically, SAT06 exhibits an apparent increase with the SMOIS decrease (e.g. compared with CTL, DRY25 generally results in a 1 °C SAT06 increase over the land surface of East China), areas with 35 °C or higher SAT06 are the most affected, and the simulations are more sensitive to the SMOIS decrease than to the SMOIS increase, which suggests that hot weather can be amplified under low soil moisture conditions. Regarding the mechanism underlying the extremely high SAT06, sensible heat flux has been shown to directly heat the lower atmosphere, and latent heat flux has been found to be more sensitive to the SMOIS change, resulting in an overall increase in surface net radiation due to the increased greenhouse effect (e.g. with the SMOIS increase from DRY25 to CTL, the 10-day mean net radiation increases by 5 W m−2). Additionally, due to the unique and dynamic nature of the western Pacific subtropical high, negative feedback occurs between the regional atmospheric circulation and the air temperature in the lower atmosphere while positive feedback occurs in the mid-troposphere. Using a method based on an analogous temperature relationship, a detailed analysis of the physical processes shows that for the SAT change, the SMOIS change affects diabatic processes (e.g. surface fluxes) more strongly than the adiabatic process of subsidence in the western Pacific subtropical high in the five groups of simulations. Interestingly, although diabatic processes dominate subsidence during the daytime and night-time separately, they do not necessarily dominate during the 24 h periods (e.g. they are dominant in the WET and CTL simulations only). Further, as the SMOIS decreases, the SAT06 increases, which is largely due to the reduced cooling effect of the diabatic processes, rather than the warming effect of subsidence. Unlike previous studies on heatwave events at climate timescales, this paper presents the sensitivity of simulated short-term hot weather to initial soil moisture and emphasises the importance of appropriate soil moisture initialization when simulating hot weather.
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