热带大西洋对东亚气候的影响

运用Hadley中心资料,对1980—2015年间热带大西洋平均海温进行EOF分析。通过对其第一模态空间分布和时间系数图的分析,运用NCEP/NCAR再分析资料做出对应正相关年与负相关年的东亚地区500 hPa位势高度场距平与800 hPa年平均环流场图。通过2个高度正/负相关年环流场差值分析,研究热带大西洋地区海温异常与东亚地区上空环流场之间的关系。结果表明,热带大西洋海温异常对东亚大气环流影响存在一定因素,热带大西洋海温异常可能对东亚地区部分气旋移动产生影响,具体表现为热带大西洋海温变化影响着东亚区域季风推进。

2008年1月乌拉尔阻塞高压异常活动的分析研究

不少研究已经表明,乌拉尔阻塞高压的持续活动对2008年1月中国南方雨雪冰冻灾害的发生有重要作用。本文针对2008年1月乌拉尔阻塞高压的异常,利用NCEP再分析逐日环流资料、哈德莱中心的海温资料等,从对流层北极涛动(AO)、平流层极涡(PV)以及海温异常等几方面,对2008年1月乌拉尔阻塞高压异常产生的原因进行了分析研究。结果显示,虽然从以往多年情况来看,前期AO及平流层极涡的异常很可能会导致其后乌拉尔阻塞高压发生异常,然而就2008年1月的情况而言,2007～2008年冬季对流层AO和平流层极涡的异常都不能成为异常乌拉尔阻塞高压产生和偏强的原因,因为它们的关系与多年存在的长期关系相反。进一步的分析研究则显示,2007年12月和2008年1月赤道太平洋的LaNin～a事件也对乌拉尔阻塞高压的活动没有明显影响;而北大西洋海温正异常,尤其是北大西洋副热带海温正异常的存在,是2008年1月乌拉尔阻塞高压持续的重要外强迫因素。

Enhanced correlation between ENSO and western North Pacific monsoon during boreal summer around the 1990s

The correlation between summertime Nino3.4 index and western North Pacific(WNP)summer monsoon index has strikingly enhanced since the early 1990 s,with nonsignificant correlation before the early1990 s but significant correlation afterward.This observed interdecadal change around the 1990 s may be associated with more frequent occurrences of central Pacific(CP)El Nino and the interdecadal changes in ENSO-associated SST anomalies.During the post-1990 s period(the pre-1990 s period),highly noticeable tropical Atlantic(Indian)Ocean SST anomalies tend to co-occur with the summertime Nino3.4 SST anomalies.The concurrent tropical Atlantic(Indian)Ocean SST anomalies could constructively reinforce(destructively mitigate)the WNP monsoon circulation anomalies induced by the summertime Nino3.4 SST,thus boosting(muting)the correlation between summertime Nino3.4 SST and WNP monsoon.In addition,the faster decaying pace of preceding-winter El Nino after the 1990 s,which may have been mainly induced by the influences from the spring tropical North Atlantic SST anomalies,could also have contributed to the enhanced correlation between the summertime Nino3.4 index and WNP monsoon.These results suggest that the enhanced influences from the tropical Atlantic SST may have triggered the intensified correlation between summertime ENSO and WNP monsoon since the early 1990 s.

Sea surface temperature anomaly in the tropical North Atlantic during El Nino decaying years

Based on reanalysis data from 1979 to 2016,this study focuses on the sea surface temperature(SST)anomaly of the tropical North Atlantic(TNA)in El Nino decaying years.The TNA SST exhibits a clear warm trend during this period.The composite result for 10 El Nino events shows that the TNA SST anomaly reaches its maximum in spring after the peak of an El Nino event and persists until summer.In general,the anomaly is associated with three factors-namely,El Nino,the North Atlantic Oscillation(NAO),and a long-term trend,leading to an increase in local SST up to 0.4℃,0.3℃,and 0.35℃,respectively.A comparison between 1983 and 2005 indicates that the TNA SST in spring is affected by El Niño,as well as the local SST in the preceding winter,which may involve a long-term trend signal.In addition,the lead-lag correlation shows that the NAO leads the TNA SST by 2-3 months.By comparing two years with an opposite phase of the NAO in winter(i.e.,1992 and 2010),the authors further demonstrate that the NAO is another important factor in regulating the TNA SST anomaly.A negative phase of the NAO in winter will reinforce the El Nino forcing substantially,and vise versa.In other words,the TNA SST anomaly in the decaying years is more evident if the NAO is negative with El Nino.Therefore,the combined effects of El Nino and the NAO must be considered in order to fully understand the TNA SST variability along with a long-term trend.