夏季MJO持续异常及其对ENSO的激发与促进作用

发布时间：2018-03-01 19:40

本文关键词： 季节内振荡 MJO ENSO 大西洋海温　出处：《云南大学》2016年博士论文　论文类型：学位论文

【摘要】：本文使用了CPC提供的MJO指数资料、澳大利亚气象台提供的RMM指数资料、NECP再分析资料(包括风场、温压场等)、NOAA提供的GODAS次表层海温资料、CMAP降水资料、全国776站点降水资料等数据。分析了MJO持续异常的周期特征和环流特征,定义出描述MJO持续异常特征的Iip指数；在发现MJO持续异常与ENSO极强相关关系的同时,通过个例年分析和合成分析探讨了MJO持续异常激发太平洋海温异常增强的内在机制：对MJO持续异常与前期海温之间存在的关系进行了讨论,提出了夏季MJO持续异常特征发生的主要原因。结果表明,(1)我们发现夏季MJO持续异常具有非常显著的特征,即在赤道太平洋持续活跃或在赤道印度洋持续活跃。在这两种情况下,MJO的东传停滞,活跃中心持续出现在太平洋或印度洋。持续异常情况下的MJO振荡周期也出现变化,表现为周期缩短或变弱。我们由此定义出Iip指数来描述6-8月MJO在印度洋或者太平洋的这种异常活跃情况。(2)我们发现夏季MJO持续异常会造成同期环流场的显著异常：当MJO在印度洋持续活跃的时候太平洋的MJO活动则是持续偏弱；而MJO在太平洋活跃的时候印度洋的MJO活动则持续偏弱。MJO的持续异常会造成大气环流的显著改变。太平洋MJO持续异常活跃时低纬沃克环流减弱,西太平洋哈德来环流增强,西太平洋副高位置偏北。与此相配合,OLR的活跃区和200hPa速度势辐散区位于赤道西太平洋160°E-160°W区域,热带海洋性大陆以及整个赤道印度洋为对流抑制区。赤道印度洋MJO持续异常活跃时大气环流情况相反。(3)在MJO持续异常情况下,夏季环流形势的异常导致了季风和降雨的差异。Iip高值年夏季索马里急流长期被北风距平控制,热带印度洋季风偏弱,导致了相应区域的降水偏少；而110°E越赤道南风气流与西太平洋西风共同加强了热带太平洋季风,使得热带西太平洋区域降水偏多。反之Iip低值年索马里急流偏强,夏季热带印度季风较强,相应热带地区降雨偏多,且影响副热带地区降雨也偏多；而热带西太平洋季风较弱,热带西太平洋降水偏少。(4)夏季的MJO的持续异常强度和秋冬季节的赤道东太平洋海温具有显著相关,由此,我们可以将MJO的持续异常作为ENSO发生与否的预测信号。如果夏季MJO在太平洋异常活跃持续,则可促进冬季El Nino事件的形成；反之,若夏季MJO在印度洋持续活跃,而在西太平洋MJO异常不活跃,则可促进冬季La Nina事件的形成。这能为相关的短期气候预测业务提供前期预测依据。(5)MJO影响ENSO发生过程的内在机制如下：当夏季MJO在太平洋持续异常时,热带对流区持续在太平洋出现,导致赤道沃克环流的减弱；热带太平洋低层为西风控制,产生了海表面风应力正距平持续。正的风应力异常激发出海洋暖性Kelvin波,将次表层暖海水从西太平洋带往东太平洋,导致了秋冬季节热带东太平洋海温偏暖。最终暖海水在东太平洋的堆积,促进了El Nino事件的形成。当夏季MJO在印度洋持续异常,热带对流区持续在热带印度洋东部出现,导致赤道太平洋沃克环流的增强；热带太平洋低层为东风控制,产生了海表面风应力负距平持续。负的风应力异常激发出海洋冷性Kelvin波,将次表层冷海水从西太平洋带往东太平洋,导致了秋冬季节热带东太平洋海温偏冷。最终冷海水在东太平洋的堆积,促进了La Nina事件的形成。(6)在讨论了春季大西洋海温异常与夏季MJO持续异常之间的关系后,我们发现：春季大西洋海温偏高会导致夏季MJO在印度洋持续异常,而春季大西洋海温偏低则会导致夏季MJO在太平洋持续异常。之后提出了春季大西洋海温影响夏季MJO持续异常可能的机制。这种海气相互作用的影响可能有两种路径：一种是通过海温激发出的气旋、反气旋,影响了赤道垂直环流。这种环流形势在夏季造成了沃克环流的加强或减弱,使得赤道的异常上升气流出现在印度洋或东太平洋地区。另一种路径是北大西洋的三极型海温可能会激发出北半球的CGT波列,影响印度洋地区对流活动。(7)我们的研究发现,春季热带大西洋海面温度的异常首先影响夏季MMJO的持续异常,导致了夏季MJO在西太平洋的异常活跃／不活跃,进一步削弱／增强了太平洋上空沃克环流,使得低层异常西风／东风显著出现,进而产生向东／向西的风应力异常,激发东、西太平洋次表层水团反向趋势的温度变化,最终导致赤道太平洋东部SST异常偏暖／偏冷,对秋冬季节ENSO的形成产生影响。因此,春季大西洋关键区海温异常可以作为秋冬ENSO发生的判断依据。
[Abstract]:This paper uses the MJO index data provided by CPC, the RMM index data Australia weather stations, NECP reanalysis data (including wind field, temperature field etc.), NOAA provides GODAS subsurface temperature data, precipitation data of CMAP, the 776 station precipitation data. Analysis of the periodic characteristics and circulation characteristics of abnormal MJO the definition of MJO Iip described the persistent anomalous features found in the index; the correlation between MJO and ENSO abnormal strong at the same time, through the example of years analysis and composite analysis, discusses the inherent mechanism of MJO anomaly excited Pacific SST anomaly enhancement: the relationship between MJO and abnormal SST are discussed, the main the reason of summer MJO sustained abnormal characteristics occurred is presented. The results show that (1) we found that the summer MJO has very significant characteristics of persistent anomaly in the equatorial Pacific, which continued to be active or In the equatorial India ocean continued to be active. In these two cases, MJO eastward stagnation, active center continues to appear in the Pacific and India ocean. The MJO oscillation cycle lasts under abnormal conditions also change, performance for the period shortened or weak. Thus we define the Iip index to describe this 6-8 month MJO in India the Pacific Ocean or unusually active. (2) we found that MJO can cause persistent anomalies of summer period circulation significantly abnormal: when MJO in India continued to be active in the Pacific Ocean when MJO activity is significantly changed and continued weak; persistent anomalies will cause the atmospheric circulation in the Pacific MJO active when India ocean MJO continues to weak.MJO. Pacific MJO sustained abnormal active Walker low latitude circulation weakened, the Western Pacific Hadley circulation increased, the Western Pacific subtropical high northward. Matched with the OLR, the active region And the 200hPa velocity potential divergence zone is located in the western equatorial Pacific 160 degrees E-160 degrees W region, tropical marine, and the equatorial India ocean for convective inhibition zone. Equatorial India ocean MJO continued active atmospheric circulation on the contrary. (3) in MJO abnormal condition, the summer circulation anomalies lead to the difference of the monsoon and the high.Iip value of rainfall in summer Somali jet has long been the north wind anomaly control, tropical India Ocean monsoon is weak, resulting in the corresponding regional rainfall; and 110 degrees E the equator and the Western Pacific westerly to strengthen the tropical Pacific monsoon, the tropical western Pacific region more precipitation. Whereas the low Iip value in the Somali jet is strong, the summer monsoon strong tropical India, corresponding tropical rainfall, and rainfall in subtropical areas are normal; and the tropical West Pacific monsoon is weak, the tropical western Pacific Less rainfall in summer (4). MJO anomaly intensity and fall and winter SST in the eastern equatorial Pacific has significant correlation, therefore, we can use the MJO anomaly as ENSO occurrence prediction signal. If the summer MJO in the Pacific active continuously, can promote the formation of winter El Nino event; on the contrary, if the summer MJO in India ocean and continued to be active, in the Western Pacific MJO anomaly is not active, can promote the formation of La in the winter of Nina events. It can provide the basis for early prediction of short-term climate prediction related business. (5) the inherent mechanism of MJO effect of ENSO occurred during the summer in the Pacific: when MJO sustained abnormal when the last appeared in the Pacific tropical convection zone, weaken the equatorial Walker circulation in the tropical Pacific Ocean; low level westerly wind control, has the sea surface wind stress anomaly is sustained. The positive wind stress anomalies excited at sea Warm ocean Kelvin wave, sub surface warm water from the Western Pacific to the East Pacific, resulting in the autumn season, the eastern tropical Pacific SST warmer. The final warm waters in the eastern Pacific Ocean accumulation, promoted the formation of El Nino events. When summer MJO in India ocean anomaly and continued to appear in the Eastern tropical India ocean tropical convection zone. To enhance the equatorial Pacific Walker circulation in the tropical Pacific Ocean; low level wind control, the sea surface wind stress and negative anomalies. Continuous negative wind stress anomalies excited by Kelvin wave of cold ocean, sub surface cold water from the Western Pacific with the East Pacific, resulting in the autumn season, the eastern tropical Pacific SST is cold cold water in the eastern Pacific. Eventually the accumulation, promoted the formation of La Nina events. (6) in the discussion of the relationship between the the Atlantic spring SST anomaly and summer MJO anomalies, we found: Spring The Atlantic will lead to higher SST in summer MJO in India ocean and the the Atlantic spring SST anomaly and low will lead to the summer MJO in the Pacific. After the proposed mechanism of persistent anomaly of the Atlantic in Spring Summer SST anomalies may continue MJO. The effect of air sea interaction may have two ways: one is through the SST generated by cyclone effect of the equatorial anticyclone, and vertical circulation. The circulation situation caused by the Walker circulation strengthened or weakened in the summer, the equatorial anomalous updraft appeared in India or the East Pacific Ocean. Another route is the North Atlantic SST triode may inspire the northern hemisphere CGT wave, effects of convective activities in India ocean area. (7) we found that the spring tropical sea surface temperature anomaly in the Atlantic first summer MMJO anomaly and led to the summer MJO in the west too Pingyang unusually active / inactive, further weakening / enhanced Walker circulation over the Pacific Ocean, the low-level westerly anomalies appear and produce significant / East, East / west wind stress anomaly, excitation temperature change East, West Pacific subsurface water reverse trend, resulting in the eastern equatorial Pacific SST anomaly warm / cold, have an impact on the formation of the autumn season of ENSO. Therefore, on the basis of judgment in spring SST anomalies can be used as key areas of the Atlantic and ENSO.

【学位授予单位】：云南大学
【学位级别】：博士
【学位授予年份】：2016
【分类号】：P732

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