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2018年东亚夏季气候异常及其成因
作者:朱志伟               发布时间:2019/9/11 13:54:17              浏览量:239

2018年的夏季,东亚地区经历了最弱的东亚夏季风、最热的华北、最弱的梅雨以及最诡异的台风。我院朱志伟和李天明教授,以及东京气候中心Shimpo博士在美国气象学会期刊《Bulletin of the American Meteorological Society》的2018年气候报告《State of the Climate in 2018》上专门撰写了关于2018年东亚夏季气候异常的短评论文。

论文指出:根据东亚地区850hPa纬向风切变定义的东亚夏季风指数,2018年东亚夏季风为过去40年中最弱(若根据业务部门季风雨带北推定义则为40年中最强)(图a);弱的夏季风对应着异常显著的西北太平洋低层气旋性环流和异常活跃对流,气旋性环流异常的东北侧的东南风引导台风向北向西移动,导致上海在短短1个月时间遭受三连台袭击(图c),而在1949-2017年的69年中,登陆上海的热带气旋数仅为6个;气旋性环流异常的北边缘受强大的东风偏北风异常控制,不利于西南季风水汽输送,导致长江中下游梅雨异常偏少(图b);此外,气旋性环流异常的北面表现为对流层整层深厚的反气旋环流(高压)异常,高压异常使得射向地面的太阳辐射增多,从而导致华北地区异常高温热浪天气(图d),中央气象台史无前例的连续33天发布高温预警,华北多个观测站打破历史最高温记录。

通常而言,夏季西北太平洋低层反气旋/气旋性环流是热带印度洋和太平洋海温异常共同驱动的结果,而高层为反气旋性环流异常,表现为斜压性特征。而2018年夏季西北太平洋气旋性环流却是一个深厚气旋(低压)系统,与北面深厚反气旋(高压)系统共存(图d)。此反气旋高压系统是中东太平洋对流异常所激发的准定常波列的一部分,此波列被命令为PNE(太平洋-北美-欧亚型)遥相关。以往有关ENSO影响东亚气候异常的机理多从海温强迫对流层低层环流来解释,而PNE遥相关能够从中高层环流异常来理解ENSO对于东北亚地区春夏降水的影响(详见Chen et al., IJOC. 2019),这对ENSO影响东亚气候机理是一个补充。

 

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Time series of (a) normalized EASM index (bars, defined by JJA averaged areal-mean 850-hPa zonal wind contrast between 22.5°–32.5°N, 110°–140°E and 5°–15°N, 90°–130°E) and (b) normalized Meiyu rainfall (MYR) index (bars, defined by JJA areal-mean precipitation over 27°–32.5°N, 107°–118°E) and the normalized North China surface air temperature (NCT) index [dashed line, defined by JJA areal-mean precipitation over (33°–49°N, 110°–130°E)]. Blue cross indicates the year 2018. (c) Precipitation (shading, mm day-1), 850-hPa wind (vector, m s-1, only winds exceeding 1 m s-1 are shown) anomalies in JJA 2018. Red dots (purple lines) denote the genesis location (moving tracks) of the three tropical cyclones (Ampil, Jongdari, and Rumbia) that made landfall in Shanghai proper (d) SST anomalies (shading over ocean, °C) and surface air temperature anomalies (shading over land, °C), negative OLR anomalies (contour in green, W m-2), 200-hPa wind (vector, m s-1, only winds exceeding 3 m s- 1 are shown) and geopotential height anomalies (red and blue contours) in JJA 2018. The purple dashed line with arrows denotes the pathway of the mid-high latitudes Rossby wave-train. Letter A (C) denotes the center of anticyclonic (cyclonic) anomaly. Base period: 1981–2010. 


论文信息:

Zhu Z., T. Li, A. Shimpo. 2019: The weakest East Asian Summer monsoon during the past 40 years [in “State of the Climate in 2018”]. Bull. Amer. Meteor. Soc., 100(9), S238-239. doi:10.1175/2019BAMSStateoftheClimate.1.

链接: https://www.ametsoc.org/ams/index.cfm/publications/bulletin-of-the-american-meteorological-society-bams/state-of-the-climate/

Chen S., Z. Zhu, Z. Ge, Z. Kang, J. He. 2019: The diversity in La Niña decay and the corresponding spring and summer precipitation anomalies over eastern China. Int. J. Climato., 39(7), 3396-3411. doi: 10.1002/joc.6100.

链接: https://rmets.onlinelibrary.wiley.com/doi/10.1002/joc.6100