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马潇祎, 范可. 2023. 近几十年中国西北夏秋季干湿年代际变化及成因初步分析[J]. 大气科学, 47(4): 943−956. doi: 10.3878/j.issn.1006-9895.2112.21115
引用本文: 马潇祎, 范可. 2023. 近几十年中国西北夏秋季干湿年代际变化及成因初步分析[J]. 大气科学, 47(4): 943−956. doi: 10.3878/j.issn.1006-9895.2112.21115
MA Xiaoyi, FAN Ke. 2023. Initial Examination of Interdecadal Shifts and Causes of Summer and Autumn Dryness and Wetness in Northwest China over Recent Decades [J]. Chinese Journal of Atmospheric Sciences (in Chinese), 47(4): 943−956. doi: 10.3878/j.issn.1006-9895.2112.21115
Citation: MA Xiaoyi, FAN Ke. 2023. Initial Examination of Interdecadal Shifts and Causes of Summer and Autumn Dryness and Wetness in Northwest China over Recent Decades [J]. Chinese Journal of Atmospheric Sciences (in Chinese), 47(4): 943−956. doi: 10.3878/j.issn.1006-9895.2112.21115

近几十年中国西北夏秋季干湿年代际变化及成因初步分析

Initial Examination of Interdecadal Shifts and Causes of Summer and Autumn Dryness and Wetness in Northwest China over Recent Decades

  • 摘要: 本文利用观测和再分析资料,分析了1961~2014年中国西北地区(35°N~50°N,75°E~95°E)夏秋季节干湿线性变化趋势特征,定量计算了蒸散量和降水量对干湿变化趋势的贡献,同时分析了其年代际变化特征及其相关的大尺度环流和水汽收支变化。结果表明,西北夏季和秋季干旱变率在四季中最大,是干旱最易发生季节。西北地区在1961~2014年夏秋季显著变湿,其中蒸散和降水在西北地区的线性变湿趋势中占主要作用,降水量的增加和蒸散量的减少对西北变湿都有正贡献,二者趋势总贡献率夏季为93.4%,秋季为67.5%。夏秋季西北干湿变化的年代际转折在1987年前后,自1987年后,夏季西北年代际变湿,主要受到蒸散量和降水量变化影响,地面风速减小所造成的蒸散量降低有利于该地区年代际变湿;西北地区水汽输送通量异常辐合导致其降水量增加。水汽诊断分析进一步表明,夏季降水量的增加主要来自于局地蒸发的增强,贡献率达到约80%,表明局地蒸发是降水的重要水汽源。此外,夏季水汽平流项为正值(即水汽通量辐合加强),有利于降水量增加,该贡献主要由与风速有关的动力学分量引起。而秋季,1987年后西北地区的净辐射通量和地面风速减小共同导致该地区蒸散量降低,进而造成西北地区的年代际变湿。

     

    Abstract: Using observational and reanalysis data from 1961 to 2014, the spatial and temporal characteristics of dry and wet changes during summer and autumn in Northwest China (35°N–50°N, 75°E–95°E) were investigated. The authors examined the contributions of evapotranspiration and precipitation to the linear trend of dryness and wetness, and the large-scale atmospheric circulations and water vapor budget associated with interdecadal dryness and wetness patterns were also investigated. Results indicate that drought variability in summer and autumn in Northwest China was the most significant across all four seasons, with the highest probability of drought occurring during these two seasons. However, a remarkable increasing trend in wetness was observed in Northwest China from 1961 to 2014, with evapotranspiration and precipitation playing crucial roles in the region’ s rising humidity. Both increasing precipitation and decreasing evapotranspiration positively contributed to the wetness trend in Northwest China. The combined contribution rate of these two trends was 93.4% in summer and 67.5% in autumn. An interdecadal shift from dry to wet conditions occurred in summer and autumn around 1987 over Northwest China. Since then, interdecadal humidification has been primarily influenced by changes in evapotranspiration, driven by reduced surface wind speed, which positively contributed to the area’s humidification. The anomalous convergence of water vapor transport flux resulted in increased precipitation in Northwest China. Water vapor diagnostic analysis further revealed that the increase in precipitation primarily originated from enhanced local evaporation, with an 80% contribution rate, signifying that local evaporation is a critical water vapor source for precipitation. Additionally, the summer water vapor advection term was positive, indicating strengthened water vapor flux convergence, which positively contributed to the increase in precipitation. This contribution was mainly due to the dynamic component related to wind speed. In contrast, after 1987, the decline in net radiation flux and surface wind speed together led to reduced evapotranspiration in Northwest China during autumn, causing interdecadal humidification in the region.

     

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