Influences of two types of El Ni?o event on the Northwest Pacific and tropical Indian Ocean SST anomalies

Based on the Had ISST1 and NCEP datasets,we investigated the influences of the central Pacific El Ni?o event(CP-EL)and eastern Pacific El Ni?o event(EP-EL)on the Sea Surface Temperature(SST)anomalies of the Tropical Indian Ocean.Considering the remote ef fect of Indian Ocean warming,we also discussed the anticyclone anomalies over the Northwest Pacific,which is very important for the South China precipitation and East Asian climate.Results show that during the El Ni?o developing year of EP-EL,cold SST anomalies appear and intensify in the east of tropical Indian Ocean.At the end of that autumn,all the cold SST anomaly events lead to the Indian Ocean Dipole(IOD)events.Basin uniform warm SST anomalies exist in the Indian Ocean in the whole summer of EL decaying year for both CP-and EP-ELs.However,considering the statistical significance,more significant warm SST anomalies only appear in the North Indian Ocean among the June and August of EP-EL decaying year.For further research,EP-EL accompany with Indian Ocean Basin Warming(EPI-EL)and CP El Ni?o accompany with Indian Ocean Basin Warming(CPI-EL)events are classified.With the remote ef fects of Indian Ocean SST anomalies,the EPI-and CPI-ELs contribute quite differently to the Northwest Pacific.For the EPI-EL developing year,large-scale warm SST anomalies arise in the North Indian Ocean in May,and persist to the autumn of the El Ni?o decaying year.However,for the CPI-EL,weak warm SST anomalies in the North Indian Ocean maintain to the El Ni?o decaying spring.Because of these different SST anomalies in the North Indian Ocean,distinct zonal SST gradient,atmospheric anticyclone and precipitation anomalies emerge over the Northwest Pacific in the El Ni?o decaying years.Specifically,the large-scale North Indian Ocean warm SST anomalies during the EPI-EL decaying years,can persist to summer and force anomalous updrafts and rainfall over the North Indian Ocean.The atmospheric heating caused by this precipitation anomaly emulates atmospheric Kelvin waves accompanied by low level easterly anomalies over the Northwest Pacific.As a result,a zonal SST gradient with a warm anomaly in the west and a cold anomaly in the east of Northwest Pacific is generated locally.Furthermore,the atmospheric anticyclone and precipitation anomalies over the Northwest Pacific are strengthened again in the decaying summer of EPI-EL.Af fected by the local WindEvaporation-SST(WES)positive feedback,the suppressed East Asian summer rainfall then persists to the late autumn during EPI-EL decaying year,which is much longer than that of CPI-EL.

赤道印度洋纬向海温梯度模及其气候影响

赤道印度洋纬向海温差异对气候的影响是有关印度洋地区海气相互作用研究的焦点。作者进一步分析了印度洋纬向海温差异的特征,提出了赤道印度洋纬向海温梯度模的概念,并在此基础上利用中国科学院大气物理研究所的九层大气环流模式模拟研究了赤道印度洋海温梯度变化对气候的影响。分析结果表明赤道印度洋纬向海温梯度的变化及其对气候的影响比较复杂,由于海温梯度分别产生于暖海温或冷海温两种不同的大尺度背景场,因此它对气候的影响不仅与海温梯度的变化有关,还与其产生的大尺度背景场(暖海温或冷海温)有很直接的关系。在太平洋地区海温不变的情况下,由于赤道东西印度洋大范围海温的升高或降低,有可能在整个印度洋和太平洋之间产生一个海温梯度(简称印-太海温梯度),这一海温梯度对亚洲季风区的降水分布和季风活动起着十分重要的作用,而赤道印度洋纬向海温梯度与印-太海温梯度的叠加,不仅加强或减弱了印-太海温梯度引起的大范围大气辐合、辐散,同时也使得辐合及辐散区的位置发生移动,进而影响了小范围地区的气候异常,特别是赤道东印度洋地区的降水分布和风场变化。与赤道印度洋地区纬向海温梯度的作用相比,赤道印度洋偶极子对气候的影响相对比较单纯,引起的降水异常和风场变化主要与海温偶极子的变化有关。

影响2021年西北太平洋副热带高压的春季环境因子的特征分析

对2021年春季影响西太副高的3种春季环境因子(热带印度洋与西北太平洋海域海表面温度异常(SSTA)的差值、赤道中太平洋5月与3月SSTA的差值、北大西洋涛动指数)的特征进行了分析。结果显示:2021年春季热带印度洋与西北太平洋海域SSTA的差值表现为负异常(-0.32℃)、赤道中太平洋5月与3月的SSTA差值表现为弱的正异常(0.02℃)、北大西洋涛动指数则出现负异常(-0.79)。利用3个春季环境因子构建的预报方程对2021年夏季西太副高指数的预报值为-0.44,这与2021年夏季西太副高指数的实测值(0.28)存在一些偏差。春季热带印度洋与西北太平洋的SSTA差值在3个环境因子中对2021年西太副高的预报结果有着最大的贡献,西北太平洋海域SSTA的暖异常可能是引起2021年夏季西太副高预报强度偏弱的重要原因。通过对比2021年夏季各月的西太副高指数观测值发现,8月与7月的西太副高指数存在较大差异,夏季各月之间差异的增大可能是导致预报结果不理想的原因。在西太副高的预报方面,需要进一步针对夏季各月之间差异较大的情况改进预报方法。

Positive feedback of winter ocean-atmosphere interaction in Northwest Pacific

Using monthly mean atmospheric re- analysis data and oceanic assimilation data product,the winter ocean-atmosphere interaction in middle and high latitude in Northwest Pacific was studied. Key regions were chosen to study the variations of Aleutian Low,the 500hPa westerly,the meriodional sea surface temperature (SST) gradient with three indices defined as Aleutian Low index,zonal index and meridional SST gradient between Kuroshio- influenced region and Oyashio-influenced region. The results show that when there is a deeper Aleu- tian Low accompanied by a stronger northerly wind in the western part of the Aleutian Low,the subpolar gyre of North Pacific is strengthened,the SST in the Oyashio-influenced region is decreased and the me- ridional SST gradient between Kuroshio-influ- enced region and Oyashio-influenced region is increased,which,in turn,will enhance the westerly jet in the upper troposphere due to thermal-wind relation. The strengthened westerly jet makes a favorable condi- tion for the deeper Aleutian Low over North Pacific beneath the left part of the jet exit region. Conse- quently,a positive feedback forms there.