Different Configurations of Interannual Variability of the Western North Pacific Subtropical High and East Asian Westerly Jet in Summer

This study investigates the circulation and precipitation anomalies associated with different configurations of the western North Pacific subtropical high(WNPSH)and the East Asian westerly jet(EAJ)in summer on interannual timescales.The in-phase configuration of the WNPSH and EAJ is characterized by the westward(eastward)extension of the WNPSH and the southward(northward)shift of the EAJ,which is consistent with the general correspondence between their variations.The out-of-phase configuration includes the residual cases.We find that the in-phase configuration manifests itself as a typical meridional teleconnection.For instance,there is an anticyclonic(cyclonic)anomaly over the tropical western North Pacific and a cyclonic(anticyclonic)anomaly over the mid-latitudes of East Asia in the lower troposphere.These circulation anomalies are more conducive to rainfall anomalies over the Yangtze River basin and south Japan than are the individual WNPSH or EAJ.By contrast,for the out-of-phase configuration,the mid-latitude cyclonic(anticyclonic)anomaly is absent,and the lower-tropospheric circulation anomalies feature an anticyclonic(cyclonic)anomaly with a large meridional extension.Correspondingly,significant rainfall anomalies move northward to North China and the northern Korean Peninsula.Further results indicate that the out-of-phase configuration is associated with the developing phase of ENSO,with strong and significant sea surface temperature(SST)anomalies in the tropical central and eastern Pacific which occur simultaneously during summer and persist into the following winter.This is sharply different from the in-phase configuration,for which the tropical SSTs are not a necessity.

DISTRIBUTION OF LOW FREQUENCY WAVES IN NORTH PACIFIC AND INTRASEASONAL ABNORMALITY OF THE WESTERN PACIFIC SUBTROPICAL HIGH

By using ECMWF (2. 5°×2. 5°) grid data, analyzing correlation for the summer (June-August) of 1980 (the West Pacific Subtropical High (WPSH) anomalously more to the south), 1988 (the WPSH anomalously more to the north), 1981 (normal) in the west Pacific area, distribution characteristics of the low frequency waves are discussed. The relationship between distribution of the low frequency waves and intraseasonal abnormality of the west subtropical high is also analyzed. There is some discussions:(1)If the WPSH acts anomalously in summer, there is a distinct zonal wave series in the subtropical zone of the north Pacific.(2) One of the important characteristics of the WPSH abnormality is that there are low frequency geopotential high centres from east Pacific and northeast Asia, being combined in the west Pacific area.For different circulation, the combination areas are different, which define the WSPH anomalously more to the north or south.

Decadal Change in the Influence of the Western North Pacific Subtropical High on Summer Rainfall over the Yangtze River Basin in the Late 1970s

It is well known that on the interannual timescale,the westward extension of the western North Pacific subtropical high(WNPSH)results in enhanced rainfall over the Yangtze River basin(YRB)in summer,and vice versa.This study identifies that this correspondence experiences a decadal change in the late 1970s.That is,the WNPSH significantly affects YRB precipitation(YRBP)after the late 1970s(P2)but not before the late 1970s(P1).It is found that enhanced interannual variability of the WNPSH favors its effect on YRB rainfall in P2.On the other hand,after removing the strong WNPSH cases in P2 and making the WNPSH variability equivalent to that in P1,the WNPSH can still significantly affect YRB rainfall,suggesting that the WNPSH variability is not the only factor that affects the WNPSH-YRBP relationship.Further results indicate that the change in basic state of thermal conditions in the tropical WNP provides a favorable background for the enhanced WNPSH-YRBP relationship.In P2,the lower-tropospheric atmosphere in the tropical WNP gets warmer and wetter,and thus the meridional gradient of climatological equivalent potential temperature over the YRB is enhanced.As a result,the WNPSH-related circulation anomalies can more effectively induce YRB rainfall anomalies through affecting the meridional gradient of equivalent potential temperature over the YRB.

Simulation of the western North Pacific subtropical high in El Ni?o decaying summers by CMIP5 AGCMs

The performances of CMIP5 atmospheric general circulation models （AGCMs） in simulating the western North Pacific subtropical high （WNPSH） in El Nino decaying summers are examined in this study. Results show that most models can reproduce the spatial pattern of both climatological and anomalous circulation associated with the WNPSH in El Nino decaying summers. Most CMIP5 AGCMs can capture the westward shift of the WNPSH in El Nino decaying summers compared with the climatological location. With respect to the sub-seasonal variation of the WNPSH, the performances of these AGCMs in reproducing the northward jump of the WNPSH are better than simulating the eastward retreat of the WNPSH from July to August. Twenty-one out of twenty-two （20 out of 22） models can reasonably reproduce the northward jump of the WNPSH in El Nino decaying summers （climatology）, while only 7 out of 22 （8 out of 22） AGCMs can reasonably reproduce the eastward retreat of the WNPSH in El Nino decaying summers （climatology）. In addition, there is a close connection between the climatological WNPSH location bias and that in El Nino decaying summers.

Interdecadal Change in the Interannual Variation of the Western Edge of the Western North Pacific Subtropical High During Early Summer and the Influence of Tropical Sea Surface Temperature

This study reveals that the interannual variability of the western edge of the western North Pacific(WNP)subtropical high(WNPSH)in early summer experienced an interdecadal decrease around 1990.Correspondingly,the zonal movement of the WNPSH and the zonal extension of the high-pressure anomaly over the WNP(WNPHA)in abnormal years possess smaller ranges after 1990.The different influences of the tropical SSTAs are important for this interdecadal change,which exhibit slow El Nino decaying pattern before 1990 while rapid transformation from El Nino to La Nina after 1990.The early summer tropical SSTAs and the relevant atmospheric circulation anomalies present obvious interdecadal differences.Before 1990,the warm SSTAs over the northern Indian Ocean and southern South China Sea favor the WNPHA through eastward-propagating Kelvin wave and meridional-vertical circulation,respectively.Meanwhile,the warm SSTA over the tropical central Pacific induces anomalous ascent to its northwest through the Gill response,which could strengthen the anomalous descent over the WNP through meridional-vertical circulation and further favor the eastward extension of the WNPHA to central Pacific.After 1990,the warm SSTAs over the Maritime Continent and northern Indian Ocean cause the WNPHA through meridional-vertical and zonal-vertical circulation,respectively.Overall,the anomalous warm SSTs and ascent and the resultant anomalous descent over the WNP are located more westward and southward after 1990 than before 1990.Consequently,the WNPHA features narrower zonal range and less eastward extension after 1990,corresponding to the interdecadal decease in the interannual variability of the western edge of the WNPSH.On the other hand,the dominant oscillation period of ENSO experienced an interdecadal reduction around 1990,contributing to the change of the El Nino SSTA associated with the anomalous WNPSH from slow decaying type to rapid transformation type.

Projected changes in the western North Pacific subtropical high under six global warming targets

The summer western North Pacific subtropical high(WNPSH) has large influences on the East Asian summer climate. Many studies have focused on the projected changes in the WNPSH, but little is known about the changes under different global warming targets, such as 1.5℃ and 2.0℃. This study investigates the changes in the WNPSH under six global warming targets(1.5℃, 2.0℃, 2.5℃,3.0℃, 3.5℃, and 4.0℃) in both the mid-and lower troposphere, using the outputs of CMIP5 model in historical simulations and under Representative Concentration Pathway 8.5. The projected changes in the WNPSH, which is measured by multiple variables, show that it changes little under the 1.5℃ target in the mid-troposphere, but weakens and retreats approximately 2.5° in longitude under the 2.0℃ target. It tends to linearly weaken with warming greater than 2.5℃ and shifts eastward by approximately 6.0° in longitude by the 4.0℃ target. Meanwhile, the WNPSH intensifies and extends westward under the 1.5℃ target in the lower troposphere, but changes little with warming rising from 1.5℃ to 2.0℃. It is projected to extend westward by approximately2.0° in longitude by the 4.0℃ target.

Analysis of More Tropical Cyclone Genesis over the Western North Pacific in 2016

Tropical cyclone (TC) is the most catastrophic weather system characterized by strong winds and heavy rains, and is therefore the main research object of tropical meteorology. Based on National Oceanic and Atmospheric Administration (NOAA) Sea Surface Temperature (SST), Outgoing Long wave Radiation (OLR) and National Centers for Environmental Prediction (NCEP) monthly reanalysis data and Regional Specialized Meteorological Center (RSMC) Tokyo best track data and China Meteorological Administration (CMA) tropical cyclone during 1979-2016, we analyze the feathers of tropical cyclones and causes of more tropical cyclones (TCs) over the western north Pacific(including the South China Sea) (WNP) in 2016. The results show that compared the number of tropical cyclone genesis was higher, the originated time was later and concentrated in autumn, the region of more cyclones formed in north and east, and the number of landing TCs was higher. Negative sea surface temperature anomaly in the equatorial eastern Pacific and a westward deviation of the ascending branch of Walker circulation can strengthen the intensity of convection activity based on an existing lead-lag correlation during the period of TC activity (from August to September).The West Pacific subtropical high (WPSH) was exceptionally stronger than in other years and its west ridge point appreciably stretched westward and northward from August to September in 2016, which is favorable to TC genesis. At the same time, ω positive anomaly located in northward which was favorable for more TC genesis in WNP. In addition, the anomalous distribution of environmental factors such as low vorticity, OLR and vertical wind shear may also be the cause of the formation of tropical cyclones in the West North Pacific in 2016.

“23·7”华北极端暴雨精细特征和天气学成因分析

2023年7月29日至8月1日,华北京津冀地区遭受极端特大暴雨袭击,导致区域性洪涝灾害,造成重大经济损失和人员伤亡。为探明此次“23·7”华北极端降水过程的基本特征和形成原因,基于地面自动气象站分钟级降水资料、风廓线雷达和雨滴谱仪观测资料及ERA5再分析数据,揭示了“23·7”华北极端暴雨的精细特征和天气学成因。结果表明:(1)此次降水过程持续时间长、累计雨量极大,特大暴雨落区、突破降水量历史极值的国家级观测站站点密集分布在京津冀太行山近山地区,降水呈现显著极端性、区域性差异和阶段性变化。河北和北京太行山东侧迎风坡地区出现持续性、强度相对稳定的强降水过程,雨滴谱分布偏向于高雨滴数密度、小雨滴直径的海洋型对流降水;京津冀平原地区过程雨量明显小于山区,但中尺度对流雨带活跃,降水阵性、对流性特征明显。(2)在“杜苏芮”台风残涡、西太平洋副热带高压、大陆高压等天气系统协同作用下,中层位势高度场出现罕见的“北高南低”+“西低东高”的稳定天气形势。北上台风“杜苏芮”残涡在高压坝以及太行山、燕山地形影响下移动缓慢,残涡中心北侧的地形障碍流与低空东南风之间形成稳定倒槽,京津冀地区出现持续性低层辐合,同时配合来自南海季风和东部洋面台风“卡努”的双路水汽输送,导致京津冀地区出现长历时、区域性极端暴雨过程。(3)在阶段性降水发展过程中,与台风残涡相关的倒槽、暖切变线、低空急流等精细结构调控了中尺度对流系统的组织和发展特征,7月31日早晨至上午京津冀地区出现超过22 m/s的超低空东南风急流,配合对流和地形抬升等因素影响,降水强度明显增强,北京西部山前出现超100 mm/h的极端雨强。此次极端降水事件中的地形影响、中小尺度特征以及极端暴雨可预报性等问题尚待更深入研究。

The Key Oceanic Regions Responsible for the Interannual Variability of the Western North Pacific Subtropical High and Associated Mechanisms

The western North Pacific subtropical high （WNPSH） is an important circulation system that impacts the East Asian summer climate. The interannual variability of the WNPSH is modulated by tropical air-sea interaction. In order to make it clear which oceanic regions are crucial to the interannual variability of the WNPSH, the research progresses in this regard in the past decade are reviewed. Based on the review, it is recognized that five oceanic regions are responsible for the interannual variability of the WNPSH in summer, including the equatorial central-eastern Pacific Ocean, tropical Indian Ocean, subtropical western North Pacific, the vicinity of the maritime continent, and the tropical Atlantic Ocean. The mechanisms how the sea surface temperature anomalies （SSTAs） in these regions affect the WNPSH are elaborated. The formation mechanisms for the SSTAs in these five regions are discussed. Strengths and weaknesses of the climate models in simulating and predicting the WNPSH are also documented. Finally, key scientific problems deserving further studies are proposed.

Impacts of Two Types of Northward Jumps of the East Asian Upper-tropospheric Jet Stream in Midsummer on Rainfall in Eastern China

The East Asian upper-tropospheric jet stream （EAJS） typically jumps north of 45~N in midsummer. These annual northward jumps are mostly classified into two dominant types： the first type corresponds to the enhanced westerly to the north of the EAJS＇s axis （type A）, while the second type is related to the weakened westerly within the EAJS＇s axis （type B）. In this study, the impacts of these two types of northward jumps on rainfall in eastern China are investigated. Our results show that rainfall significantly increases in northern Northeast China and decreases in the Yellow River-Huaihe River valleys, as well as in North China, during the type A jump. As a result of the type B jump, rainfall is enhanced in North China and suppressed in the Yangtze River valley. The changes in rainfall in eastern China during these two types of northward jumps are mainly caused by the northward shifts of the ascending air flow that is directly related to the EAJS. Concurrent with the type A （B） jump, the EAJS-related ascending branch moves from the Yangtze-Huai River valley to northern Northeast （North） China when the EAJS＇s axis jumps from 40~N to 55~N （50~N）. Meanwhile, the type A jump also strengthens the Northeast Asian low in the lower troposphere, leading to more moisture transport to northern Northeast China. The type B jump, however, induces a northwestward extension of the lower-tropospheric western North Pacific subtropical high and more moisture transport to North China.

Prediction of the Western North Pacific Subtropical High in Summer without Strong ENSO Forcing

The western North Pacific subtropical high(WNPSH) is one of the deterministic predictors of the East Asian summer climate, and a better prediction of the WNPSH favors more reasonable forecast of the East Asian summer climate. This study focuses on seasonal prediction of the WNPSH during neutral summers without strong El Ni?o–Southern Oscillation(ENSO) forcing, and explores the associated predictable sources, using the one-month lead time retrospective forecasts from the Ensembles-Based Predictions of Climate Changes and Their Impacts(ENSEMBLES) project during 1960–2005. The results indicate that the ENSEMBLES atmosphere–ocean–land coupled models exhibit considerable prediction skill for the WNPSH during neutral summers, with successful reproduction of the WNPSH in the majority of neutral summers. The anomalous WNPSH in neutral summers, which corresponds to cyclonic/anticyclonic anomalies in the lower troposphere, is highly correlated with an east–west dipole local sea surface temperature(SST) distribution over the tropical WNP, suggesting an intimate local air–sea coupling. Further diagnosis of the local SST–rainfall relationship and surface heat flux indicates that the anomalous local SST plays an active role in modulating the variation of the WNPSH during neutral summers, rather than passively responding to the atmospheric change. The local SST anomalies and relevant air–sea coupling over the tropical WNP are reasonably well reproduced in the model predictions, and could act as primary predictable sources of the WNPSH in neutral summers. This could aid in forecasting of the East Asian rainband and associated disaster mitigation planning.

Predictability of the Western North Pacific Subtropical High Associated with Different ENSO Phases in GloSea5

The western North Pacific subtropical high(WNPSH) dominates the summer climate over East Asia. The intensity,position, and shape of WNPSH influence the spatiotemporal distributions of precipitation, temperature, and tropical cyclone activities in this region. This paper intends to investigate the performance of the UK Met Office Global Seasonal forecast system version 5(GloSea5) in simulation/prediction of the WNPSH based on a hindcast dataset. Analyses of the hindcast data show a systematic bias in the mean circulation over West Pacific, with negative geopotential height anomalies over the western North Pacific(WNP) and cyclonic anomalies in the 850-hPa winds and water vapor transport, indicating a weakening and eastward shift of the WNPSH. Despite the model’s bias in the climatology, it well captured the interannual variability of the monthly and seasonal-mean intensity of the WNPSH and the position of its ridge line in boreal summer from 1993 to 2015. The seasonal hindcasts indicate that there is significant prediction skill at up to three-month lead time for both the intensity and position of the WNPSH ridge line. The relationship between the WNPSH and different phases of the El Nino–Southern Oscillation(ENSO) in both the observational data and GloSea5 hindcasts was then investigated. The model captured the summer WNPSH anomalies well during most of the ENSO phases, except in the La Nina decaying and neutral summers. The intensity of the anticyclone in the WNP is weak in the decaying phase of El Nino in the GloSea5 hindcasts compared with the reanalysis data. GloSea5 is capable of representing the lagged teleconnection between El Nino events in the previous winter and the intensity of the WNPSH in the following summer. Regression analysis reveals weakened negative sea surface temperature anomalies(SSTAs) over the WNP in GloSea5, which reduced the gradient between the tropical western Pacific and the tropical Indian Ocean, resulting in a weaker easterly anomaly and stronger westerly anomaly, contributing to the weak anomalous anticyclone over the WNP and the weakened WNPSH relative to the reanalysis data.

Unprecedented East Asian warming in spring 2018 linked to the North Atlantic tripole SST mode

An unusually warm East Asia in spring 2018,when exceptionally high surface air temperatures were recorded in large areas of Asia,such as northern China,southern China,and Japan,was investigated based on the ERA-Interim reanalysis.The East Asian warming anomalies were primarily attributed to a tripole mode of North Atlantic SST anomalies,which could have triggered anomalous Rossby wave trains over the North Atlantic and Eurasia through modulating the North Atlantic baroclinic instability.Atlantic-forced Rossby waves tend to propagate eastward and induce anomalously high pressure and anticyclonic activity over East Asia,leading to a northward displacement of the Pacific subtropical high.As a result,descending motion,reduced precipitation,and increased surface solar radiation due to less cloud cover appear over East Asia,accompanied by remarkably warm advection from the ocean to southern China,northern China,and Japan.The transportation of anomalously warm advection and the feedbacks between soil moisture and surface temperature were both favorable for the recordbreaking warmth in East Asia during spring 2018.The seasonal‘memory’of the North Atlantic tripole SST mode from the previous winter to the following spring may provide useful implications for the seasonal prediction of East Asian weather and climate.

春季厄尔尼诺快速衰减对华北夏季降水的影响

利用再分析的陆地降水、环流和辐射数据,以及表征大气波动的指数,对比了1951—2020年期间El Nino春季快速衰减年和缓慢衰减年的东亚环流和华北夏季降水异常情况,并从大气波动强度的角度探讨了为何El Nino在一些年份的春季会发生快速衰减。结果表明,相较于其他不发生El Nino衰减的年份,El Nino春季快速衰减年华北7、8月的降水量显著偏多,尤其是8月;而El Nino缓慢衰减年夏季,华北降水相较其他年份偏多不明显。El Nino春季快速衰减年6—8月850 hPa上菲律宾到南海存在异常反气旋,其强度强于El Nino缓慢衰减年;El Nino春季快速衰减年8月500 hPa西太平洋副热带高压(西太副高)显著偏北,而缓慢衰减年西太副高偏北的特征不明显,而是以偏西为主;200 hPa副热带西风急流在El Nino春季快速衰减年8月显著偏北,而在El Nino缓慢衰减年中反而略偏南;El Nino春季快速衰减年6—8月沃克环流显著偏强,相比之下El Nino缓慢衰减年沃克环流偏强的特征要弱很多。上述环流异常特征为El Nino春季快速衰减年华北7—8月降水异常偏多提供了有利条件。通过近地面风场合成分析发现,春季El Nino快速衰减月前后,赤道中西太平洋异常东风爆发非常明显,而El Nino缓慢衰减年的异常东风信号较弱。春季El Nino快速衰减前印度洋对流活动非常强盛,并向海洋性大陆传播,这种对流可能通过不断激发大气波动,继而引发近地面东风爆发,最终导致El Nino出现快速衰减。

北太平洋海温与广西前汛期降水的联系

利用1979—2019年全国160站逐月降水资料、Hadley中心海温资料、NOAA以及NCEP/NCAR再分析资料,结合相关分析、信息流以及合成分析方法,分析了北太平洋海温异常与广西前汛期降水的同期联系,并初步探讨了前者对后者的影响及可能机制,结果表明:北太平洋关键区海温是广西前汛期降水的显著影响源,海温正位相(负位相)的异常分布在一定程度上导致了广西前汛期降水增多(减少).北太平洋关键区海温变化可以独立于赤道中东太平洋影响前汛期降水,而赤道中东太平洋海温变化可以起到调制作用,增强两者联系.北太平洋为正位相海温异常时,大气为“+-+”的经向三极型位势高度异常响应.与此同时,海温异常激发了向下游中高纬传播的Rossby波列,引起东亚沿岸位势高度正异常和反气旋环流异常.在上述机制下,贝加尔湖高压脊和东亚大槽均显著增强,使得中高纬冷空气更易南下.赤道中东太平洋海温的调制作用体现在对中低纬环流的影响.关键区海温正位相对应于赤道中东太平洋海温偏暖,后者引起局地异常上升运动,减弱Walker环流进而导致赤道西太平洋出现下沉异常,抑制了对流活动,在西北太平洋强迫出异常反气旋,使得副高加强西伸.副高的增强西伸增强了暖湿气流输送,这一方面有利于广西一带的水汽输送,水汽通量辐合增强;另一方面有利于冷暖空气在广西交汇,对流不稳定增强,促进上升运动,最终导致降水增多.北太平洋为负位相时上述异常形势相反,导致降水减少.

北太平洋副热带高压年际变异与ENSO循环之间的选择性相互作用

利用NCEP/NCAR大气再分析资料以及Hadley中心海表温度资料,针对北太平洋副热带高压(简称副高)的完整系统,通过分析超前于ENSO事件的海平面副高年际异常特征及其对ENSO事件的触发作用以及ENSO事件对500 hPa副高和海平面副高的滞后影响,结果表明了北太平洋副热带高压年际变异和ENSO循环之间存在选择性相互作用.即在大多数情况下,一方面,前期海平面副高减弱会导致热带西太平洋表面西风异常,通过海洋平流过程触发El Nino事件在夏季发生发展,在秋冬季成熟;而另一方面,El Nino事件在秋冬季发展成熟后,增强了赤道中太平洋的对流性热源,通过对异常热源的动力响应,同期和次年夏季500 hPa副高增强,又通过增强的Hadley环流作用,副热带地区下沉运动增强,从而使得次年夏季海平面副高增强,增强的海平面副高又有利于触发下一个La Nina事件.副高年际变异和ENSO循环之间相互作用的选择性主要取决于副高异常是否接近于赤道以及ENSO事件本身的持续性.这种相互作用有利于在热带太平洋海气系统产生准两年振荡.

空间非均匀加热对副热带高压形成和变异的影响II:陆面感热与东太平洋副高

在文献［４］尺度分析的基础上，通过对 Ｎ Ｃ Ｅ Ｐ／ Ｎ Ｃ Ａ Ｒ 月平均资料的分析，并利用 Ｉ Ａ Ｐ／ Ｌ Ａ Ｓ Ｇ Ｇ Ｏ Ａ Ｌ Ｓ全球气候模式进行模拟和试验，研究了东太平洋北美地区副热带高压主体的形成及变化规律。基于全型垂直涡度方程的诊断分析指出，北美陆地的表面感热通量是决定该地区副热带高压中心位置及其季节变化的关键因素。数值模拟和敏感性试验进一步表明，夏半年陆面感热加热是导致１０００ ｈ Ｐａ 太平洋副热带高压及５００ ｈ Ｐａ 北美副热带高压形成和变化的最重要原因。

北太平洋海平面气压场变化与海温的关系

利用SVD(singular value decomposition)方法分析了1948年1月—2002年12月北太平洋海平面气压场与海温的关系。结果表明,SVD第1对异类相关分布型反映出,当东北太平洋副热带高压加强(减弱)时,Namias海区海温升高(降低),而加利福尼亚海流区海温降低(升高)。SVD第2对异类相关分布型表明,当阿留申低压加深、北太平洋副热带地区气压升高时,黑潮暖流区海温升高,而北太平洋高、低纬海温降低;反之亦然。时滞相关表明,北太平洋大气环流异常超前海温1个月的相关最好,海温变化对大气环流异常分布型具有维持作用。NCAR CCSM3模拟结果很好地验证了上述结论,即在海气相互作用过程中,东北太平洋副热带高压和NPO(North Pacific Oscillation)与北太平洋海温存在密切联系。

副高北进过程的个例数值研究

就一次出梅时西太平洋副热带高压北进过程，用数值试验的方法，对副高北进的原因进行了分析研究，重点分析了非绝热过程在副高北进过程中所起的作用。结果表明：１）对应出梅时的环流形势，大气内部的动力调整过程具有使副高增强北进的趋势，是副高北进的主导因子。２）在３～５天时间尺度上，非绝热过程的作用不可忽视，其总效应使副高减弱。就各非绝热因子而言，净辐射过程的总效应使副高减弱，不利副高北进；降水凝结潜热释放有利副高的维持和增强，有利副高北进。就地区而言，南亚季风区加热具有同副高南侧热带辐合带加热相同的作用，正的加热增强有利副高增强北进。

夏季西太平洋副热带高压南北位置变动特征及其影响

使用ECMWF再分析数据集资料中的位势高度场、三维风场、温度场、相对湿度场、海温场以及中国气象局730站地面降水资料和日最高温度资料,对比分析研究了7月份西太平洋副高位置偏南和偏北过程(持续满足南、北位置指标6天以上定义为一次南、北部型过程)所对应的动态气候特征及其演变。分析首先揭示出了西太平洋副高的南北位置变化存在季节内振荡特征;从西太平洋副高偏南、偏北位置所对应的各层环流特征、中国东部降水分布、中国日最高温度的分布,研究了西太平洋副高南北位置对东亚及西北太平洋地区天气气候的影响。结果表明,尽管同在7月份,西太平洋副高南北位置的不同对大气环流和天气气候的影响却有显著的差异,需要从大气系统变化的角度研究和认识某时期的天气气候特征。针对两类过程的演变,分析了西太平洋副高南、北位相过程开始的前兆气候特征,过程中的变化特征以及过程结束后的后延影响,揭示出了一些以前研究所忽略的气候演变特征及其差异。