The effects of the intertropical convergence zone on the easterly jet stream during Northern summer

In this paper, a strong 1TCZ process and an 1TCZ - absent process during FGGE in 1979 were selected for comparison to explore how they were subject to the influence of the evolution of the upper easterly jets.

西北太平洋TC高频源地与GMS-SST暖水区及ITCZ的匹配关系

利用GMS高精度遥感海表温度(SST)反演资料、外逸长波辐射(OLR)反演资料和西北太平洋热带气旋(TC)源地及频数数据,分析了GMS-SST、赤道辐合带(ITCZ)、TC源地及频数的时空分布特征。研究发现:TC源地、发生频数以及强度的时空分布和变化均具有趋暖性。GMS-SST大于等于28℃的阈值条件为西北太平洋TC发生和维持的必要条件。并且存在10°N高频收缩轴,其与由GMS-SST大于等于28℃所定义的西北太平洋暖水区,GMS-OLR小于等于240 W.m-2定义的ITCZ的时空分布及变化有很好的相关性,即存在TC高频源地—GMS-SST暖水区—ITCZ三者间的匹配相关。

西北太平洋SST暖水区·ITCZ对东北冷涡及副热带高压的影响

利用1958～1997年NCAR/NCEP再分析月平均500hPa位势高度格点资料,分析了东北冷涡与西太平洋副热带高压的关系,研究了海表温度(SST)和射出长波辐射(OLR)对东北冷涡及副热带高压的影响。结果表明,在夏季,东北冷涡与副热带高压是正相关关系,GMS-SST=28℃阈值特征线与东北冷涡高度指数、副热带高压高度指数都是反位相关系,随着GMS-SST=28℃阈值特征线的逐渐北移,副热带高压减弱,东北冷涡增多、加强。

The Influence of SST Warm-water Region and ITCZ in the North-West Pacific Ocean on the Northeast Cold Vortex and the Subtropical High

By using the monthly mean grid data of NCAR/NCEP reanalysis at 500 hPa geopotential height from 1958 to 1997,the relationship between the Northeast cold vortex and the western Pacific subtropical high was analyzed.The influence of the sea surface temperature(SST) and outgoing longwave radiation(OLR) on the Northeast cold vortex and subtropical high was studied.As was shown in the results,in summer,there was a positive correlation between the Northeast cold vortex and the subtropical high,and an anti-phase relationship existed between the threshold characteristic line of GMS-SST=28 ℃ and the height index of the Northeast cold vortex and the subtropical high.With the gradual northward moving of the threshold characteristic line,the subtropical high was weakening,and the Northeast cold vortex was increasing and strengthening.

Modulation of Western North Pacific Tropical Cyclone Genesis by Intraseasonal Oscillation of the ITCZ:A Statistical Analysis

The present study investigates modulation of western North Pacific （WNP） tropical cyclone （TC） genesis in relation to different phases of the intraseasonal oscillation （ISO） of ITCZ convection during May to October in the period 1979 2008. The phases of the ITCZ ISO were determined based on 30-80-day filtered OLR anomalies averaged over the region （5°20′N, 120°150′E）. The number of TCs during the active phases was nearly three times more than during the inactive phases. The active （inactive） phases of ISO were characterized by low-level cyclonic （anticyclonic） circulation anomalies, higher （lower） midlevel relative humidity anomalies, and larger （smaller） vertical gradient anomalies of relative vorticity associated with enhanced （weakened） ITCZ convection anomalies. During the active phases, TCs tended to form in the center of the ITCZ region. Barotropic conversion from the low-level mean flow is suggested to be the major energy source for TC formation. The energy conversion mainly depended on the zonal and meridional gradients of the zonal flow during the active phases. However, barotropic conversion weakened greatly during the inactive phases. The relationship between the meridional gradient of absolute vorticity and low-level zonal flow indicates that the sign of the absolute vorticity gradient tends to be reversed during the two phases, whereas the same sign between zonal flow and the absolute vortieity gradient is more easily satisfied in the active phases. Thus, the barotropie instability of low-level zonal flow might be an important mechanism for TC formation over the WNP during the active phases of ISO.

中东太平洋ITCZ对两类厄尔尼诺SST异常的敏感性试验

利用MPAS-A(The Model for Prediction Across Scales-Atmosphere)模式设计了中东太平洋热带辐合带CEP-ITCZ(Intertropical Convergence Zone over Central and Eastern Pacific)对两类厄尔尼诺SST(Sea Surface Temperature)异常的敏感性试验,通过试验结果与两类厄尔尼诺年实际大气异常的对比,初步解释了CEP-ITCZ在两类厄尔尼诺年产生不同异常的可能原因。通过CP-EL试验发现,热带太平洋SST异常的第一模态会使中东太平洋低层风场辐合增强,但对辐合带的位置影响不大,与中部型厄尔尼诺对CEP-ITCZ的影响基本一致。通过EP-EL试验发现,热带太平洋SST异常的第二模态会使中东太平洋低层风场产生较大异常,辐合带中心向南移动,辐合带明显减弱增宽,与东部型厄尔尼诺对CEP-ITCZ的影响基本一致。

卫星云参数处理方法和1991年的云气候特征分析

参考国际卫星云气候计划和目前出现的几种云参数处理方法￣（［１］［２］），设计了一种适用于东亚和热带海洋地区的云参数处理方法，并着重进行了总云量的反演．处理的资料取自ＧＭＳ－４的Ｓ·ＶＩＳＳＲ资料￣［３］，覆盖范围为５０°Ｎ－３０°Ｓ，８０°－１７５°Ｅ．时间为１９９１年的１、４、７、１０四个月．使用上述方法对卫星资料计算得到了日、旬、月的平均云量，通过与其它资料和处理结果的对比分析，对处理方法和处理结果的真实性进行了初步检验。利用１９９１年４个典型月份的处理结果，研究了大范围云的季节变化，如赤道辐合带云系和副热带高压少云区的纬向移动，季风云系的爆发等；研究了一些局地区域云的季节分布；并对处理区域内云量的日变化进行了研究．

东北地区旱涝的OLR特征分析

该文选取了东北地区 4个典型多雨年和 4个典型少雨年 ,利用 OLR资料对该地区旱涝年 OL R场的时空分布规律及其低频振荡的传播特征进行了合成对比分析 .结果表明 ,东北旱涝与低纬 OLR的分布及其变化密切相关 ,特别是西北太平洋副热带高压、西太平洋 ITCZ和印度 ITCZ的位置和强度以及赤道中东太平洋 OL R的距平在旱涝年均有显著差别 ,并且热带和副热带 OLR低频振荡的向北传播对东北地区夏季降水也有至关重要的影响 .

全球变暖不同阶段热带辐合带的移动及其与大气能量输送的关系

基于第五次国际间耦合模式比较计划(The phase 5 of the Coupled Model Intercomparison Project,CMIP5)中在4.5 W/m^2的典型浓度路径(Representative Concentration Pathway,RCP4.5)试验结果,本文通过能量框架分析方法研究了全球变暖不同阶段热带辐合带(Intertropical Convergence Zone,ITCZ)的南北移动及其主要机制,发现在温室气体持续增加的海洋快响应和温室气体达到稳定后的海洋慢响应两个阶段,ITCZ的移动都和跨赤道的大气能量输送(Atmosphere Heat Transport,AHT)变化显著相关,但两者变化的原因在两个阶段中是不同的。在快响应阶段,ITCZ位置的移动以及跨赤道AHT受大气层顶(Top of the Atmosphere,TOA)的能量变化驱动,主要与南大洋云短波辐射响应、北半球中高纬度云和地表的短波辐射响应有关,气溶胶减少引起的辐射响应变化使得ITCZ在大多数模式中表现出向北移动的特征。在慢响应下辐射强迫保持稳定,ITCZ在大多数模式中表现出向南移动的特征。这一时期ITCZ的移动由大气表面能量通量变化驱动,主要与潜热通量变化的南北半球差异有关。全球变暖不同阶段ITCZ移动与大气能量输送变化的关系差异反映了海洋对于气候变化的重要调控作用。

有孔虫初房特征变化在珠江三角洲晚全新世东亚夏季风降雨研究中的应用

研究中国降雨格局变化对理解东亚夏季风演化意义重大。本文分析了珠江三角洲柱状样ZJK03-Z中浅水底栖有孔虫常见种Rotalidium annectens的平均初房大小、微球型/显球型比值和壳体δ18O值,以及底栖有孔虫组合中瓷质壳的百分含量,探讨它们对由夏季风降雨引起的河口水体盐度变化的响应,得到了珠江三角洲3114—1260a BP季风降雨的强度变化,识别出了这期间14次季风降雨减少的偏干期。与南美洲Cariaco海盆的钛含量记录对比,二者一致的结果表明,珠江三角洲晚全新世的东亚夏季风降雨与热带辐合带(ITCZ)的南北移动密切相关:夏季风降雨减少,对应于ITCZ纬度位置的南移。

2014年8月西北太平洋和南海无TC生成之原因分析

利用常规气象观测资料、NCEP/NCAR 1°×1°的月平均再分析资料、NOAA卫星观测的OLR资料和中国气象局台风年鉴资料,对2014年8月西北太平洋和南海无TC生成的原因进行了诊断分析,结果表明:极地冷空气南侵,造成8月上中旬副热带高压偏东偏南,下旬冷空气减弱,副热带高压偏西偏南,致使副热带高压南侧偏东信风与赤道西风的汇合区位置异常偏南;马斯克林高压偏弱,导致索马里急流和东印度洋越赤道气流也弱,印度半岛中低层季风低压或季风槽极其不活跃。澳大利亚高压路径偏东或偏西和势力偏弱,则南海南部越赤道气流亦弱。8月上中旬台风主要源地的海表温度明显偏低,不能酿成低层高温高湿的大气;月内西北太平洋和南海大气的对流活动很弱,层结较稳定、风速垂直切变大,均不利于TC发生发展。在南海到菲律宾以东洋面低层为弱的正涡度区和负散度区,有辐合上升运动,但垂直速度很小,不能满足TC尺度的环流发生和发展;南亚高压和副高南侧东风扰动造成对流层高层为弱上升区,不能形成高空辐散机制,不利于上升气流维持和加强。故此,8月在异常偏南的ITCZ中生成的4个热带扰动最终均未能发展成台风。

A Review of the Asian-Pacific Monsoon

Research on the Asian-Pacific monsoon has a long history. This paper starts by summarizing field experiments investigating the Asian-Pacific monsoon. Since the 1960s, a number of international and regional monsoon projects and field experiments have been carried out, and substantial progress regarding research on the Asian-Pacific monsoon has been made. Second, the onset and the seasonal march of the Asian summer monsoon and the annual cycle of active and break periods of the monsoon, which are characterized by precipitation maxima and minima, are studied. Since the inter-tropical convergence zone (ITCZ or TCZ) is the dominating weather system and is the major birthplace of typhoons and tropical convective systems, the monsoonal rainfall and ITCZ are analyzed after the onset of the Asian mon- soon. Finally, because the ITCZ has a close relationship with tropical convective systems and rainfall events in monsoon regions, analyses of the developments of deep convection and rainfall events are briefly introduced.

中东太平洋热带辐合带降水统计特征及其与厄尔尼诺的相关性

利用GPCP(Global Precipitation Climatology Project)与CMAP(CPC Merged Analysis of Precipitation)降水资料以及欧洲天气预报中心月平均SST(Sea Surface Temperature)资料,统计分析了中东太平洋热带辐合带(Centre and Eastern Pacific ITCZ,CEP-ITCZ)降水在两类厄尔尼诺年的基本特征及其与两类厄尔尼诺的相关性.结果表明:在普通年份,CEP-ITCZ平均位置约为7.6°N,强度7.25mm/day,东部型厄尔尼诺年位置偏南约2.9°,强度增强1.9mm/day;而中部型厄尔尼诺年位置偏南仅有0.2°,强度增强1.7 mm/day.不同Nio海区对CEPITCZ位置与强度的影响具有显著差异,与CEP-ITCZ位置相关性最大的海区为超前一个月的Nio 3海区,而与CEP-ITCZ强度相关性最大的海区则为超前一个月的Nio 3.4(8月—次年2月)或Nio 4(3—7月)海区,影响CEP-ITCZ位置的海区主要为东太平洋,影响CEP-ITCZ强度的海区则为中太平洋.此外,CEP-ITCZ位置和强度的异常对SST异常的敏感性均在4月份达到最强,11月份达到最弱.

Relationships between Earth’s Rotation or Revolution and Geographical Extent of the Global Surface Monsoons

Monsoon seasons, occasionally also known as wet seasons or trade-wind littoral seasons, are found in the regions where there is a complete seasonal reversal of the prevailing surface winds. Accompanying these shifts in the prevailing surface winds are modulations in rainfall activity. Given the fact that our knowledge of the monsoons is mainly based on the interpretation of the mean values of precipitation, cloudiness and winds;relationships between earth’s rotation or revolution and geographical extent of the global surface monsoons deserve to be highlighted. In the abundant literary and audiovisual production devoted to monsoons worldwide and despite the fact that everyone agrees with physical law which shows that Coriolis force acts to the right in the northern hemisphere (to the left in the southern hemisphere), there is no reference to the relationship between Coriolis force (due to earth’s rotation) effects on troposphere general circulation and geographical extent of the global surface monsoons. Furthermore knowing that the ITCZ oscillations on either side of the equators (due to earth’s revolution) determine the seasons (mainly winter and summer), it is clear that earth’s revolution also plays a crucial role in the seasonal reversal of the prevailing surface winds observed in the regions where monsoons are found. Our main objective is to provide a rational answer to the question: what is a monsoon?

Invariance in the Seasonal Median Dates for Mono-Modal Monsoonal Rainfall Distribution over the Semi-Arid Ecotone of Sub-Saharan West Africa

Seasonal distribution of mono-modal, monsoonal rainfall across the semi-arid ecotone of sub-Saharan of West Africa is highly variable and unpredictable. The ever-present risk of drought and crop failure in this environment often results in food shortages that are met by emergency food aid. Humanitarian assistance planners would be better prepared for such interventions in a timely manner if they have reliable indicators that forewarn the impending failure of the rains. A good indicator would be a characteristic of the seasonal rainfall distribution that can be shown to be reasonably invariant over time and space. The objective of this study is to investigate whether such invariance existed for the seasonal median date (meaning the date when 50% of the seasonal total occurs). Such invariance is expected since the sun’s cyclic declination forces the advance and retreat of the Inter-tropical Front over West Africa. We examined the statistical properties of the seasonal median date for 1349 station-years of rainfall records for 30 rainfall stations in Burkina Faso and Niger with coordinates ranging from 9.88° to 18.5° north latitude and -4.77° to 13.2° longitude. The results showed that the median date was quite narrowly distributed over years with rather weak dependence on geographical coordinates. It can therefore be used as a reasonable ex-ante indicator of the success or failure of the rains as the rainy season progress.

Influence of Sea Level Pressure on Inter-Annual Rainfall Variability in Northern Senegal in the Context of Climate Change

This study examines the inter-annual variability of rainfall and Mean Sea Level Pressure (MSLP) over west Africa based on analysis of the Global Precipitation Climatology Project (GPCP) and National Center for Environmental Prediction/National Center for Atmospheric Research (NCEP/NCAR) Reanalysis respectively. An interconnection is found in this region, between Mean Sea Level Pressure (MSLP) anomaly (over Azores and St. Helena High) and monthly mean precipitation during summer (June to September: JJAS). We also found that over northern Senegal (15°N - 17°N;17°W - 13°W) the SLP to the north is strong;the wind converges at 200 hPa corresponding to the position of the African Easterly Jet (AEJ) the rotational wind 700 hPa (corresponding to the position of the African Easterly Jet (AEJ) coming from the north-east is negative. In this region, the precipitation is related to the SLP to the north with the opposite sign. The Empirical Orthogonal Functions (EOF) of SLP is also presented, including the mean spectrum of precipitation and pressures to the north (15°N - 40°N and 50°W - 25°W) and south (40°S - 10°S and 40°W - 0°E). The dominant EOF of Sea Level Pressures north and south of the Atlantic Ocean for GPCP represents about 62.2% and 69.4% of the variance, respectively. The second and third EOFs of the pressure to the north account for 24.0% and 6.5% respectively. The second and third EOFs of the pressure to the south represent 12.5% and 8.9% respectively. Wet years in the north of Senegal were associated with anomalous low-pressure areas over the north Atlantic Ocean as opposed to the dry years which exhibited an anomalous high-pressure area in the same region. On the other hand, over the South Atlantic, an opposition is noted. The wavelet analysis method is applied to the SLP showings to the north, south and precipitation in our study area. The indices prove to be very consistent, especially during intervals of high variance.

赤道东太平洋海温的季节波动

本文以海温月波动值为指标，从经向时－空变化、纬向时－空变化以及水平分布等方面，论述了赤道东太平洋（0°－10°S、180°－90°W）海温波动的基本特征。这一海域，特别是150°W以东，海温季节变化明显，冬半年增温，夏半年降温。自10°S向北，逐渐过渡到10°N，则转为冬半年降温、夏半年增温。海温波动的水平分布表明，1月为增温期，7月为降温期，4月和10月是过渡季节。最大月增温值为1．8℃，出现于1月和2月，最大月降温值为—1．7℃，出现于7月。增温期，海温逐月升高，累计增温峰值可达6．2℃。文中指出，赤道东太平洋海温的波动与热带辐合带（ITCZ）的活动有关。

Advances in Research on the ITCZ:Mean Position,Model Bias,and Anthropogenic Aerosol Influences

The zonal-mean position of the intertropical convergence zone(ITCZ)and its shift in the meridional direction significantly influence both the tropical and even global climate.This work reviews three aspects of the progress in ITCZ-relevant research:1)the mechanism behind the asymmetry of the ITCZ annual-and zonal-mean positions relative to the equator;2)causes of the double-ITCZ problem(pervasive in climate models)and the efforts to solve it;and 3)the physical mechanisms by which anthropogenic aerosols affect the location of the zonal-mean ITCZ.According to recent studies,the north-of-the-equator location of the annual-and zonal-mean ITCZ is mainly driven by the cross-equatorial energy transports in the ocean,induced by the Atlantic overturning circulation.A quantitative relationship between the ITCZ shift and the anomalous cross-equatorial energy transport in the atmosphere has been found.Presently,the double-ITCZ problem is still the most common and pronounced bias in tropical precipitation simulations with climate models.Recently,some studies have found that simply correcting the biases in hemispheric energy contrast does not improve the simulation of the ITCZ with climate models;whereas others have found that improving model resolutions and convective parameterizations in climate models,such as entrainment rate,raindroplet re-evaporation,and convection triggering function,can alleviate the double-ITCZ bias.Therefore,it seems that the double-ITCZ problem in climate models is rooted in the complex physics of the models,which is not yet well-understood.In addition,anthropogenic aerosols are suggested to be able to induce meridional shifts of the ITCZ,but through various physical mechanisms.Absorbing aerosols like black carbon influence the ITCZ position basically via instantaneous absorption of shortwave radiation in the atmosphere,whereas scattering aerosols like sulfate affect the location of the ITCZ through the cloud lifetime effect and the subsequent response of surface evaporation.

Late Quaternary glacial cycle and precessional period of clay mineral assemblages in the Western Pacific Warm Pool

Variability of clay mineral assemblages in the Western Pacific Warm Pool(WPWP) over the past 370 ka shows the prominent glacial-interglacial cyclicity.Smectite(62%-91%) is the dominant clay mineral,with decreased contents during interglacials while increased in glacials.In contrast,variations in chlorite(4%-21%),illite(4%-12%),and kaolinite(2%-10%) share a similar pattern with higher contents during interglacials than glacials,mirroring to that of smectite.The results indicate that the smectite-dominated clay minerals derive mainly from the river detrital inputs of New Guinea.The glacial-interglacial cycle of clay mineral assemblages well correspond to the fluctuation of sea level.When the sea level was low,the river materials can travel more easily across the narrow shelf off the island of New Guinea,inject directly into the subsurface currents flowing westwards,then merge into the Equatorial Undercurrent(EUC),and eventually deposit on the central part of WPWP.Precessional periods of the smectite content indicate the intensity of mechanical erosion in its provenance of New Guinea,responding to the river runoff and precipitation,and this could also be linked to the meridional migration of the Intertropical Convergence Zone(ITCZ).

Variations in monsoon precipitation over southwest China during the last 1500 years and possible driving forces

Understanding hydroclimatic patterns and their possible driving mechanisms during distinct climate periods over the last 1500 years—such as the Medieval Warm Period(MWP),the Little Ice Age(LIA),and the Current Warm Period—is crucial for predicting future changes to monsoon precipitation in southwest China under global warming scenarios.In this study,based on ^(210)Pb and ^(137)Cs dating of surface sediments and AMS ^(14)C dating of terrestrial plant residues,we establish a robust age model that covers the last~1500 years(AD 439–2012)at Lake Yihai in southwest China.We use analyses of multiple geochemical proxy indices,including loss on ignition at 550℃,total organic carbon,total nitrogen,C/N ratios,and stable carbon isotopes of organic matter to reconstruct changes in summer monsoon precipitation at Lake Yihai during the last~1500 years.The results show that,over southwest China,warm and dry climate conditions prevailed during the MWP(AD 1000–1400)and the past 200 years,whereas conditions during the LIA(AD 1400–1800)were cold and wet.This is consistent with evidence from other geological records over southwest China,such as stalagmite and lake sediment data.Similar hydroclimatic patterns have occurred over the last 1500 years in adjacent tropical/subtropical monsoon regions where the climate is similarly dominated by the Indian summer monsoon(e.g.,South China,the South China Sea,Southeast Asia,Northeast India).We suggest that the meridional migration of the mean position of the Inter-tropical Convergence Zone,and El Niño/Southern Oscillation conditions which are linked to tropical Pacific sea surface temperature,are responsible for centennial-scale hydroclimatic patterns over southwest China and adjacent areas during the last 1500 years.