Using radiosonde observations at five stations in the tropical western Pacific and reanalysis data for the 15 years from 2005 to 2019, we report an extremely negative anomaly in atmospheric water vapor during the super El Niño winter of 2015/16 and compare the anomaly with that in the other three El Niño winters of the period. A strong specific humidity anomaly is concentrated below 8 km of the troposphere with a peak at 2.5–3.5 km, and a column-integrated water vapor mass anomaly over the five radiosonde sites has a large negative correlation coefficient of −0.63 with the oceanic Niño3.4 index but with a lag of about 2–3 months. In general, the tropical circulation anomaly in the El Niño winter is characterized by divergence (convergence) in the lower troposphere over the tropical western (eastern) Pacific; thus, the water vapor decreases over the tropical western Pacific as upward motion is suppressed. The variability of the Hadley circulation is quite small and has little influence on the observed water vapor anomaly. The anomaly of the Walker circulation makes a considerable contribution to the total anomaly in all four El Niño winters, especially in the 2006/07 and 2015/16 eastern Pacific (EP) El Niño events. The monsoon circulation shows a remarkable change from one event to another, and its anomaly is large in the 2009/10 and 2018/19 central Pacific (CP) El Niño winters and small in the two EP El Niño winters. The observed water vapor anomaly is caused mainly by the Walker circulation anomaly in the super EP event of 2015/16 but is caused by the monsoon circulation anomaly in the strong CP event of 2009/10. The roles of the Hadley, Walker, and monsoon circulations in the EP and CP events are confirmed by the composite EP and CP El Niños based on the reanalysis data for 41 years. Owing to the anomalous decrease in upward transport of water vapor during the El Niño winter, lower cloud amounts and more outgoing longwave radiation over the five stations are clearly presented in satellite observation. In addition, a detailed comparison of water vapor in the reanalysis, radiosonde, and satellite data shows a fine confidence level for the datasets; nevertheless, the reanalysis seems to slightly underestimate the water vapor over the five stations in the 2009/10 winter.

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来自无线电探空仪和卫星观测以及ERA5再分析数据的厄尔尼诺冬季热带西太平洋水汽异常

利用热带西太平洋五个台站的无线电探空仪观测资料和 2005 年至 2019 年 15 年的再分析资料，我们报告了 2015/16 年超级厄尔尼诺冬季期间大气水汽的极负异常，并将异常与这一时期的其他三个厄尔尼诺冬季。一个强烈的比湿度异常集中在对流层 8 公里以下，峰值在 2.5-3.5 公里，五个无线电探空仪站点上的柱状积分水汽质量异常具有很大的负相关系数-0.63 与海洋 Niño3.4 指数，但滞后约 2-3 个月。总体而言，厄尔尼诺冬季热带环流异常以热带西（东）太平洋对流层低层辐散（辐合）为特征；因此，随着向上运动的抑制，热带西太平洋上空的水汽减少。哈德利环流的变异性非常小，对观测到的水汽异常影响不大。沃克环流的异常对所有四个厄尔尼诺冬季的总异常做出了相当大的贡献，特别是在 2006/07 和 2015/16 东太平洋（EP）厄尔尼诺事件中。季风环流显示出从一个事件到另一个事件的显着变化，其异常在 2009/10 和 2018/19 中太平洋（CP）厄尔尼诺冬季异常大，在两个 EP 厄尔尼诺冬季异常小。观测到的水汽异常主要是由2015/16年超EP事件中的Walker环流异常引起的，而2009/10年强CP事件中的季风环流异常引起的。Hadley、Walker 和季风环流在 EP 和 CP 事件中的作用由 EP 和 CP 的复合厄尔尼诺现象基于 41 年的再分析数据证实。由于厄尔尼诺冬季期间水汽向上输送的异常减少，卫星观测清楚地显示了五个站点的云量减少和出射长波辐射增加。此外，再分析中水汽的详细比较，无线电探空仪，卫星数据显示了数据集的良好置信水平；尽管如此，再分析似乎略微低估了 2009/10 冬季五个站点的水汽。