THE INTENSITY VARIATION OF THE SUMMER INTERTROPICAL CONVERGENCE ZONE IN WESTERN NORTH PACIFIC AND ITS IMPACT ON TROPICAL CYCLONES

Based on the satellite data from the National Oceanic and Atmospheric Administration and the NCEP/NCAR reanalysis data, the variation of the intensity of convection over the Intertropical Convergence Zone （ITCZ） in summer and its impacts on tropical cyclones are studied. In this paper, an intensity index of the ITCZ is proposed according to Outgoing Longwave Radiation （OLR） in the region of （5°-20°N, 120°-150°E） in the western North Pacific （WNP）. Then strong and weak ITCZ years are classified and different variables during the strong/weak ITCZ years are analyzed. The composite results show that the ITCZ anomaly is connected to the general atmospheric circulation and SST distribution. In the strong ITCZ years, the subtropical anticyclone weakens and shifts northward. Besides, there is salient cyclonic anomaly at the low level and anticyclonic anomaly at the high level. SST patterns in the preceding winter resemble to those of La Nifia. It could persist into the succeeding summer. However, it is opposite in the weak ITCZ years. The impact of the ITCZ anomaly on the tropical cyclone （TC） formation and track is also discussed. There are more TCs over the WNP （5°-20°N, 120°-150°E） in the strong ITCZ years and there is a significant increase in the northward recurving TCs. In the weak ITCZ years, fewer TCs occur and the frequency of the northwestward track is higher.

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.

南海ITCZ异常变化及其对非移入性南海热带气旋(TC)活动的可能影响

利用美国NOAA提供的向外长波辐射(OLR)资料、NCEP/NCAR再分析资料以及上海台风所提供的热带气旋(TC)资料等,通过定义一个描写南海范围内(5°N^20°N,105°E^120°E)的热带辐合带(Intertropical Convergence Zone,简称ITCZ)强度指数,研究了南海ITCZ年际和年代际异常变化特征及其对非移入性南海TC[South China Sea–generated tropical cyclone(SCS-G TC)]活动的可能影响,并从异常强、弱南海ITCZ年份的大气环流背景和海表温度等变化特征来尝试揭示南海TC的活动规律。结果表明:在年际和年代际时间尺度上,南海ITCZ强度指数与南海TC的生成频数存在显著的负相关关系,长期趋势变化间的关系存在不同。南海ITCZ的强、弱显著地影响到南海TC的生成频数。强南海ITCZ年,南海TC频数偏多;弱南海ITCZ年,南海ITCZ频数偏少。强、弱南海ITCZ年对于南海TC的生成源地、TC的维持时间以及路径和强度的影响不显著。进一步分析表明,动力和环境条件方面,强、弱南海ITCZ年可能差异较大。异常偏强年,对流层低层出现气旋性环流,上层出现反气旋性环流;季风槽在南海区域偏强、位置偏南。与OLR表示的深对流区相配合,存在暖的海表温度和低层强烈的正涡度和强辐合,在高层存在相应的强的气流辐散,形成了极有利于南海TC发生发展的条件。弱南海ITCZ年则相反。另外,ITCZ强年,太平洋异常SST(Sea Surface Temperature)出现为La Ni?a特征,南海ITCZ区对流活跃,强度偏强。反之,ITCZ弱年则表现为El Ni?o特征,南海ITCZ关键区的对流强度偏弱。这些结果可为深刻认识南海TC的生成规律以及对南海TC的预报提供线索。

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。

2—4月北极涛动对中西太平洋ITCZ活动的可能影响

利用1979—2008年逐日向外长波辐射(OLR)资料以及北极涛动(AO)指数,从日尺度上分析了中西太平洋上赤道辐合带(ITCZ)的类型及活跃程度,并研究其与AO的关系。结果表明:在日尺度上ITCZ存在不同的强对流中心,依据中心位置可以划分为北、南、赤道、双、全和弱等六种型态,其中北、南和弱型ITCZ在日尺度上频次最高,分别占总天数的30.98%、31.11%和24.05%,而赤道、双和全型ITCZ出现频次较少。AO与西北太平洋ITCZ活动的相关分析表明,2—4月AO指数与北型ITCZ频次存在显著正相关,相关系数达到0.49,而与弱型ITCZ频次存在显著负相关,相关系数为-0.42。当AO处于正(负)位相时,从同期至8—10月北型ITCZ活跃程度偏强(弱),而弱型ITCZ偏弱(强),在滞后1～2个月时相关达到最高。此外低层环流场以及SST也存在显著变化。当AO为正位相时,中西太平洋上赤道至15°N范围内存在异常西风气流,SST异常偏暖。这也加大了南北向SST梯度,导致赤道以北辐合加强,对流活跃,北型ITCZ频次增多。这表明AO可能是通过风场和SST来影响北型ITCZ的活动,这种海气相互作用产生的影响具有较长的持续性。

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.

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.

Primary Reasoning behind the Double ITCZ Phenomenon in a Coupled Ocean-Atmosphere General Circulation Model

This paper investigates the processes behind the double ITCZ phenomenon, a common problem in Coupled ocean-atmosphere General Circulation Models (CGCMs), using a CGCM—FGCM-0 (Flexible General Circulation Model, version 0). The double ITCZ mode develops rapidly during the ?rst two years of the integration and becomes a perennial phenomenon afterwards in the model. By way of Singular Value Decomposition (SVD) for SST, sea surface pressure, and sea surface wind, some air-sea interactions are analyzed. These interactions prompt the anomalous signals that appear at the beginning of the coupling to develop rapidly. There are two possible reasons, proved by sensitivity experiments: (1) the overestimated east-west gradient of SST in the equatorial Paci?c in the ocean spin-up process, and (2) the underestimated amount of low-level stratus over the Peruvian coast in CCM3 (the Community Climate Model, Version Three). The overestimated east-west gradient of SST brings the anomalous equatorial easterly. The anomalous easterly, a?ected by the Coriolis force in the Southern Hemisphere, turns into an anomalous westerly in a broad area south of the equator and is enhanced by atmospheric anomalous circulation due to the underestimated amount of low-level stratus over the Peruvian coast simulated by CCM3. The anomalous westerly leads to anomalous warm advection that makes the SST warm in the southeast Paci?c. The double ITCZ phenomenon in the CGCM is a result of a series of nonlocal and nonlinear adjustment processes in the coupled system, which can be traced to the uncoupled models, oceanic component, and atmospheric component. The zonal gradient of the equatorial SST is too large in the ocean component and the amount of low-level stratus over the Peruvian coast is too low in the atmosphere component.

POSSIBLE INFLUENCE OF FEBRUARY-APRIL ARCTIC OSCILLATION ON THE ITCZ ACTIVITY OF WESTERN-CENTRAL PACIFIC

The daily patterns and activity of Intertropical Convergence Zone(ITCZ) in the Western-Central Pacific Ocean are analyzed using NOAA interpolated Outgoing Longwave Radiation dataset during the period from 1979 to 2008, and the relationships between ITCZ patterns and Arctic Oscillation(AO) is investigated in this paper. In accordance with the central activity region the daily ITCZ can be divided into six patterns—north, south, equator, double, full and weak pattern, respectively. The statistic result shows that the north(accounting for 30.98% of the total observations), south(31.11%) and weak(24.05%) ITCZ patterns are the most active daily patterns within a 30-year period, while the other three ITCZ patterns occur infrequently. Results show that the February-April AO index has a significant positive(negative) correlation with the frequency of the north(weak) ITCZ pattern from March-May to August-October, with the strongest correlation in April-June(March-May). At the same time, the lower tropospheric atmosphere circulation(850-hPa wind field) and SST anomalies corresponding to the AO change significantly in the tropical Pacific. When AO is in the positive phase, there is an anomalous westerly from the equator to 15°N and warmer SST in the critical north ITCZ active region, while there is an anomalous easterly and insignificant change of SST from the equator to 15°S. The wind and SST anomalies share the same characteristics of the equatorial asymmetry and thus enlarge the gradient between the south and north of equator, which would help reinforce convection in the north of equator and result in more frequent occurrence of the northern type of ITCZ.

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。

Seasonal Variation of the Sea Surface Temperature Growth Rate of ENSO

El Ni?o–Southern Oscillation(ENSO) exhibits a distinctive phase-locking characteristic, first expressed during its onset in boreal spring, developing during summer and autumn, reaching its peak towards winter, and decaying over the next spring. Several studies have demonstrated that this feature arises as a result of seasonal variation in the growth rate of ENSO as expressed by the sea surface temperature(SST). The bias towards simulating the phase locking of ENSO by many state-of-the-art climate models is also attributed to the unrealistic depiction of the growth rate. In this study, the seasonal variation of SST growth rate in the Ni?o-3.4 region(5°S–5°N, 120°–170°W) is estimated in detail based on the mixed layer heat budget equation and recharge oscillator model during 1981–2020. It is suggested that the consideration of a variable mixed layer depth is essential to its diagnostic process. The estimated growth rate has a remarkable seasonal cycle with minimum rates occurring in spring and maximum rates evident in autumn. More specifically, the growth rate derived from the meridional advection(surface heat flux) is positive(negative) throughout the year. Vertical diffusion generally makes a negative contribution to the evolution of growth rate and the magnitude of vertical entrainment represents the smallest contributor. Analysis indicates that the zonal advective feedback is regulated by the meridional immigration of the intertropical convergence zone, which approaches its southernmost extent in February and progresses to its northernmost location in September, and dominates the seasonal variation of the SST growth rate.

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．

2015年西北太平洋热带气旋活动特征及强El Nio现象对其影响的初步分析

通过统计分析,本文研究了强El Nio年西北太平洋及南海热带气旋(TC)的活动特征并详细分析了造成2015年TC活动的大气环流特征。强El Nio年上半年TC生成偏多,台风活跃季(6—10月)TC生成偏少,登陆我国TC偏少,TC的生成位置较偏东南,并且台风路径多发生向东北的偏转。2015年生成的TC符合这一规律。El Nio成熟前赤道西太平洋存在大面积的西风异常,同时El Nio使得西北太平洋地区对流活动受到抑制,而副热带高压位置偏南,导致热带辐合带(ITCZ)位置偏南,这些因素综合作用导致了2015年台风季TC数量偏少。强El Nio年台风不但整体强度偏强,个体台风的强度也偏强,这是由于强El Nio年的副热带高压面积和强度偏小,有利于TC活动的加强。强El Nio年西北太平洋东南部生成的TC偏多,并且强度偏大;东北部生成的TC偏少。2015年的TC活动特征符合上述规律,生成于我国南海的TC个数少、强度偏小。从路径上来看,2015年台风路径多呈抛物线型,发生了向东北方向的转向,进入我国南海的TC明显偏少,这与副热带高压西伸脊点偏东,西北太平洋上空500 hPa异常的西北气流有关。

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 .

热带辐合带的季节内振荡及其与热带气旋发生阶段性的关系

利用中国气象局提供的热带气旋资料和NCEP/NCAR再分析等资料,研究了热带辐合带(Intertropical Convergence Zone,简称ITCZ)上对流强度的季节内振荡特征及其与热带气旋生成频数阶段性变化的关系,并进一步研究了它与越赤道气流、赤道西风和ITCZ北侧偏东风季节内振荡的关系。研究发现:(1)ITCZ对流强度的变化有明显的30~60d振荡,西太平洋(5°N^20°N,120°E^150°E)范围内的热带气旋约有2/3发生在30~60d振荡的活跃位相。(2)ITCZ季节内振荡在热带地区表现为向东传播的特征,而在副热带地区(25°N^35°N)表现出清晰的西传特征。在ITCZ季节内振荡较强年,振荡在由赤道传播至15°N左右时,与北面向南传播的振荡在该纬度附近汇合,对流强度增强,使热带气旋在此期间频繁发生。而在弱年,振荡由赤道一直向北传播至30°N附近,15°N附近的ITCZ对流较弱,热带气旋生成偏少。(3)赤道西风、105°E^110°E越赤道气流和ITCZ北侧的偏东风气流本身也存在30~60d振荡。这三支气流的30~60d振荡与ITCZ的季节内强弱变化密切相关。然而,相比之下偏东风气流的30~60d振荡和ITCZ对流强弱的30~60d振荡对应关系略差。

夏季西北太平洋热带辐合带的强度变化特征及其对热带气旋的影响

利用卫星资料和再分析资料讨论夏季6—8月平均热带辐合带(Intertropical Convergence Zone,简称ITCZ)的强度变化特征及其对热带气旋的影响。首先利用120～150°E,5～20°N区域平均的对外长波辐射(Outgoing Long-wave Radiation,简称OLR)定义一个夏季ITCZ强度指数,再根据这个指数划分ITCZ强弱年并进行合成分析和相关分析。结果表明:ITCZ强弱的变化与高中低层大气环流和前冬海温场有显著的关系,ITCZ强年往往伴随有副热带高压的偏北、偏弱,对流层低层出现气旋性距平风场,高层出现反气旋性距平风场,同时整个太平洋前冬的SST的分布呈现类似La Ni a的海温分布,而弱年正好相反。另一方面,ITCZ的对流强弱对热带气旋(Tropical Cyclone,简称TC)的发生和路径均有重要影响,在ITCZ强年,相应区域上的TC个数增多,同时TC路径更易于打转;而ITCZ弱年,TC个数减少,TC路径更易于向西北行。

2006年夏季西太平洋热带气旋活动的初步研究

2006年夏季西太平洋热带气旋活动主要有如下特征：1）生成时间具有明显的阶段性,且强度强,登陆中国数偏多。2）登陆热带气旋有其各自特点。例如“碧利斯”影响范围大、降水强度大、持续时间长;“桑美”风速大,登陆后迅速减弱。作者针对上述2个特点进行了初步分析。研究发现：1）2006年6月27日-8月31日,来自印度洋的热带西风增强并东推延伸及115-140°E的越赤道气流的加强都有利于热带气旋的生成,并在西太平洋副热带高压北移、季节内振荡（Madden-Julian Oscillation,简称MJO）的湿位相、高低层纬向风切变弱和菲律宾以东地区热带辐合带（Intertropical Convengence Zone,简称ITCZ）对流活跃等背景条件配合下,使热带气旋在这一阶段频发。2）2006年夏季水汽含量与供给对登陆热带气旋的影响显著。“碧利斯”和“桑美”的水汽来源不同是造成这两个登陆热带气旋明显差异的重要原因。

全新世事件3与古文化变迁

全新世事件3是1997年由Bond等提出的、指的是发生在4.2 ka BP左右的冷事件。此后,冰心、海洋沉积物、湖泊沉积物、石笋和泥炭等各种地质载体被广泛用于全新世事件3的研究当中。此次事件在全球范围内普遍存在,在北半球中、低纬度大部分地区以冷干的气候条件为主,而在北半球高纬度地区和南半球部分地区则以冷湿的气候条件为主。同时,这次冷干或者冷湿的气候波动对于当时世界范围内的古文化变迁产生了重要的影响,是造成非洲尼罗河流域古埃及文明、两河流域美索不达米亚古阿卡德帝国、印度河流域哈拉帕文明以及中国新石器文化的衰落的主要原因。而全新世事件3的主要成因很可能是当时太阳活动减弱,一方面导致北大西洋表层浮冰增加,表层海水温度降低,减弱了温盐循环,使海陆温差减小,季风减弱;另一方面使热带幅合带南移,在北半球中、低纬度大部分地区形成干旱降温事件。

末次盛冰期太平洋赤道辐合带对暖池外热带海表温度变化的敏感性

利用美国NCAR-CAM3大气环流模式,分析了末次盛冰期(LGM)两个不同的热带海表温度重建方案中,北半球冬季热带中、西太平洋对流活动及大气环流对暖池外(赤道东太平洋和热带大西洋)热带SST异常的敏感性。结果表明:1)SST异常首先引起大气环流的改变。赤道东太平洋对流层下沉增强,而作为经向补偿,副热带东太平洋上升运动增强,其中南半球尤为明显,同时南半球热带中、西太平洋上升运动增强,加剧了该区纬向逆时针环流,说明冰期热带海气耦合过程受气候背景场(如SST)影响很大;2)大气环流格局改变引起热带中西太平洋的大气加热、对流活动、表层风场及降雨的巨大变化。140°E以西的婆罗洲和菲律宾区域,总的大气加热减少是由于对流与辐射加热减少所致,对应于该区风场辐散和降雨减少;而140°E以东的南半球热带中、西太平洋,大气吸收热量增加,对流与辐射加热均增强,总降雨量也随之增加,反映该区赤道辐合带南移并增强。该项研究为探索热带太平洋在冰期/间冰期旋回中的古海洋学变化提供了新的数据支撑。此外,不同重建SST对赤道辐合带的影响比较大,因此利用重建SST进行数值模拟或者利用耦合模式研究LGM热带海气相互作用时,应该十分重视全球热带SST分布特征。