副极地海洋锋区海温异常影响厄尔尼诺的机制研究

基于1979—2021年的ERA5再分析资料,研究了副极地海洋锋区(Subarctic Frontal Zone, SAFZ)海温(Sea Surface Temperature, SST)异常相关的冬季海气相互作用过程及其影响次年冬季厄尔尼诺(El Niño)的机制。研究表明,冬季SAFZ的特征海气异常表现为大尺度的SST暖异常与偶极型的大气环流异常。在SAFZ海气相互作用过程中,海洋首先通过直接的非绝热加热影响低层大气斜压性,随后通过间接的瞬变涡旋反馈使相当正压的位势高度异常在整个冬季内维持。其中,南部的气旋式环流异常通过减弱副热带的平均信风激发太平洋经向模态(Pacific Meridional Mode, PMM)与风—蒸发—SST (Wind-Evaporation-SST, WES)反馈,从而使中纬度SST暖异常南传至热带太平洋中部,随后导致El Niño发生。然而,并非所有的SAFZ暖异常事件都能激发次年冬季的El Niño,中纬度海气耦合异常的初始配置及同期热带太平洋的表现情况将对中纬度信号南传至热带的过程产生较大的影响。     

Simulation by CMIP5 models of the atlantic multidecadal oscillation and its climate impacts

This study focuses on the climatic impacts of the Atlantic Multidecadal Oscillation (AMO) as a mode of internal variability. Given the difficulties involved in excluding the effects of external forcing from internal variation, i.e., owing to the short record length of instrumental observations and historical simulations, we assess and compare the AMO and its related climatic impacts both in observations and in the “Pre-industrial” experiments of models participating in CMIP5. First, we evaluate the skill of the 25 CMIP5 models’ “Historical” simulations in simulating the observational AMO, and find there is generally a considerable range of skill among them in this regard. Six of the models with higher skill relative to the other models are selected to investigate the AMO-related climate impacts, and it is found that their “Pre-industrial” simulations capture the essential features of the AMO. A positive AMO favors warmer surface temperature around the North Atlantic, and the Atlantic ITCZ shifts northward leading to more rainfall in the Sahel and less rainfall in Brazil. Furthermore, the results confirm the existence of a teleconnection between the AMO and East Asian surface temperature, as well as the late withdrawal of the Indian summer monsoon, during positive AMO phases. These connections could be mainly caused by internal climate variability. Opposite patterns are true for the negative phase of the AMO.     

从2011/2012和2015/2016年冬季大气环流异常看北极海冰以及前期夏季北极大气环流异常的作用

利用美国NCEP/NCAR、欧洲中心ERA-Interim再分析资料,以及英国哈得来中心海冰密集度资料,通过诊断分析和数值模拟试验,研究了2011/2012和2015/2016年两个冬季大气环流异常的主要特征和可能原因。结果表明,尽管热带太平洋海温背景截然不同（分别为弱的拉尼娜事件和强厄尔尼诺事件）,但这两个冬季西伯利亚高压均异常偏强,自1979年以来其强度分别排第1和第5位。前期秋季北极海冰异常偏少是导致这两个冬季西伯利亚高压偏强的主要原因。更为重要的是,前期夏季北冰洋表面反气旋风场,以及其上空对流层中、低层平均气温偏高,加强了北极海冰偏少对冬季大气变率的负反馈,进一步促进了西伯利亚高压的加强,从而有利于东亚地区冬季阶段性强严寒的出现。因此,夏季北极大气环流的动力和热力状态不仅影响夏、秋季北极海冰,而且对海冰偏少影响亚洲冬季气候变率有重要调节作用。2015/2016年冬季强厄尔尼诺事件并不能掩盖来自北极海冰和大气环流的影响。      

Heterozoan carbonates from the equatorial rocky reefs of the Galápagos Archipelago

Strongly influenced by seasonal and interannual (i.e. El Niño‐Southern Oscillation) upwelling, the equatorial setting of the Galápagos Archipelago is divided into well‐defined temperature, nutrient and calcium carbonate saturation (Ω_aragonite) regions. To understand the relationship between oceanographic properties and sediment grain associations, grain size, carbonate content and components from sea floor surface samples were analysed, representing the main geographical regions of the Galápagos Archipelago. The shallow‐water rocky reefs of the Galápagos Archipelago are characterized by mixed carbonate–siliciclastic slightly gravelly sands. Despite minor differences in carbonate content, major differences exist in the distribution and composition of key carbonate producing biota. Halimeda is absent and benthic foraminifera occur in extremely low abundance. The western side of the Galápagos Archipelago is strongly influenced by nutrient‐rich, low‐Ω_aragonite, subtropical water, which generates a heterozoan carbonate biofacies in a tropical realm resembling cold‐water counterparts (i.e. serpulid, echinoderm, gastropod, barnacle and bryozoan‐rich facies). The Central East region is composed of a transitional‐heterozoan biofacies. Biofacies observed in the northern region have an increased occurrence of tropical corals, albeit with a minor overall contribution to the carbonate components. Although the temperature gradient would allow for a broader distribution of photozoan biofacies, the increased nutrient concentration and related reduced light penetration from the upwelled waters favour heterozoan carbonate factories, mimicking cool‐water, deeper or higher latitude environments. The recent sedimentary record of the Galápagos Archipelago presents a range of tropical heterozoan carbonate communities, responding to more than simply latitude or temperature but a much more complex mixture of physical, evolutionary and geological processes.     

ENSO与影响福建省热带气旋数量和强度关系研究

利用1949~2013年的热带气旋最佳路径和Nino3.4指数资料,探讨了影响福建省的热带气旋数量和强度与ENSO之间的关系.结果表明,影响福建省的热带气旋数目在拉尼娜年要比厄尔尼诺年略偏多.但对于强台风和超强台风级别的热带气旋而言,反而是在厄尔尼诺年偏多,其频数是拉尼娜年的1.5倍.另外,热带气旋发生的高峰期,在拉尼娜年为7~9月,在厄尔尼诺年则为7~10月,即厄尔尼诺年中的高峰期相对较长;同时,在拉尼娜年中,强台风和超强台风的发生时间较厄尔尼诺年的6~9月要迟延1个月左右,为7~10月.     

ENSO循环与黄河上游径流的丰枯

1IntroductionScholarsoftheinternationalmeteorologicalandoceanographicalcirclesgenerallythinkElNinoeventhasoccurredwhenthepositivedeparturesofmeansea-surfacetemperature(SST)atEquatorialEastPacificOceanArea(lyingbetween0o-10oS,180o-90oW)occurcontinuallywith0.5oCexteedingthelong-rangemeanandcontinualperiodlastinghalfayear.TheyalsothinkLaNinaeventhasoccurredwhenthestrongernegativedeparturesoccur.SouthernOscillationoccurringsynchronouslywithElNinoindicatesitisaneventwithalternativeoccurrence…     

Relation of Summer Asian-Pacific Oscillation to Tropical Cyclone Activities over the Coastal Waters of China

Using the Joint Typhoon Warning Center (JTWC) optimal typhoon tracks data and the NCEP/NCAR reanalysis,an investigation is made on the summer Asian-Pacific Oscillation (APO) in relation to synchronous air circulation from the coastal waters of East Asia to western North Pacific (WNP),along with a further exploration on the relationship between the APO and the tropical cyclone (TC) activities over the coastal waters of China.The results show that there exists a strong correlation between the APO intensity an...     

Snow in Lebanon: a preliminary study of snow cover over Mount Lebanon and a simple snowmelt model / Etude préliminaire du couvert neigeux et modèle de fonte des neige pour le Mont Liban

Abstract

The physical properties of snow, including apparent density, snow cover distribution and snowmelt in the Nahr El Kelb basin (Mount Lebanon), were studied in order to design a simple empirical snowmelt model. In February 2001, snow covered an area of 1600 km² on Mount Lebanon, representing a water equivalent of 1.1 x 10⁹ m³. The snow surface area was calculated by combining TM5 images with a digital elevation model, and field observations made every three days, from 1400 to 2300 m altitude. The depletion of snow cover was measured from the end of December 2000 to the end of June 2001. The snowmelt was measured from surface depletion on a degree-day basis. A simple model relating the daily snowmelt to the product of wind speed and average positive daily air temperature, is presented and discussed. For Mount Lebanon, this model gave a better approximation of snowmelt than a simple degree-day model.     

基于MF-DFA的西安昼夜复合高温事件变化特征及影响因素

采用随机重排去趋势波动分析(MF-DFA)和极点对称模态分解法(ESMD),对1955—2019年西安市昼夜复合高温事件变化特征进行分析.结果表明:(1)气象站点迁移,造成对西安市极端高温变化趋势低估.其中,最高温原始数据与订正序列阈值相同;订正后,最低温阈值相对偏低0.2～0.5℃.(2)MF-DFA、90.0％和9...     

中全新世和末次盛冰期北大西洋涛动变化及其与亚洲降水的联系:基于MPI-ESM模拟试验

本文利用古气候模式比较计划第三阶段(PMIP3)中MPI-ESM模式模拟输出,采用主分量分析、回归分析、多窗谱分析等方法,探讨了中全新世(MH)和末次盛冰期(LGM)北大西洋涛动(NAO)变化及其与亚洲降水的关系.结果表明:MH冬季NAO较现代有轻微增大,南部高压中心东移;而LGM冬季NAO明显减弱,南北气压活动中心转为西南-东北走向.MH冬季强NAO信号可通过海洋记忆效应持续至夏季,并以准静止Rossby波形式传至东亚地区,导致乌拉尔山和鄂霍次克海阻高增强、贝加尔湖低压加深,这种倒“Ω”流场增强有利于冷空气南下,并通过热成风原理使得副热带西风急流增强,急流南侧产生上升异常,有利于该区降水产生;而LGM时NAO减弱引起夏季倒“Ω”流场减弱,冷空气南下弱于现代,使得副热带西风急流减弱,其南侧产生下沉异常,最终抑制降水.因此,MH和LGM两阶段的NAO引起大气环流的变化可能对亚洲夏季降水产生影响.