Analysis of South Asian Monsoons within the Context of Increasing Regional Black Carbon Aerosols

South Asian monsoons were analyzed within the context of increasing emissions of black carbon(BC) aerosols using a global atmospheric general circulation model.The BC aerosols were allowed to increase only over the south Asian domain to analyze the impacts of regional black carbon over the climatological patterns of monsoons.The black carbon significantly absorbed the incoming short wave radiation in the atmosphere,a result that is consistent with previous studies.Pre-monsoon(March-April-May) rainfall showed positive anomalies,particularly for some coastal regions of India.The summer(June-July-August) rainfall anomalies were negative over the northern Himalayas,Myanmar,southern China,and most of the regions below 20°N due to the decrease in temperature gradients induced by the absorption of radiation by BC aerosols.The vertical wind speed anomalies indicated that these regions experienced less convection,which reduces the precipitation efficiency of the monsoon system in South Asia.

THE MONSOON INFLUENCED BY BASIC FLOW AND SHEAR FLOW IN SOUTH ASIA

Using the equatorial balanced model and the low-corder spectral method to consider the effect of the basic flow, the primary and secondary shear flows, the nonlinear equation describing the winter and summer monsoon in south Asia is derived. The stress is on the influence of the flows on the formation,transformation and intensity of the monsoon in south Asia. The results show that the influence on the monsoon in south Asia is significantly different among the primary shear flow, the basic flow and the secondary shear flow.

TYPICAL STRONG AND WEAK SOUTH ASIAN SUMMER MONSOON YEARS AND SEA SURFACE TEMPERATURE OF ARABIAN SEA

The South Asian Summer Monsoon （SASM） is an important member of the monsoon system for Asia. It is made up of low-level subsystems of the Mascarene high in the Southern Hemisphere, cross-equatorial Somali jet stream, 850-hPa westerly jet over the Arabian Sea, Indian monsoon trough north of the Bay of Bengal through west India and upper-level tropical easterly jet centered at 5°N and South Asia high centered at 30°N. During the summer monsoon, convection is intense in South Asia, with large scale and in association with abundant amount of latent heat release from condensation. Its anomalies affect not only the industrial and agricultural production and people＇s life in South Asia, but also the southwestern part of China. SASM is therefore drawing attention from quite a number of meteorologists from home and abroad. For instance, in their search for indicators of the summer monsoon in the region, Parthasarathy et al. Webster et al. and Goswami et al. defined a number of indexes based on precipitation and circulation. Wang et al.studied existing, widely-used indexes and came up with different regional indexes for the circulation and convection of SASM. Hahn et al.worked on the effect of topography on SASM. With wind field data, Wang et al. divided the years by the intensity of SASM and analyzed the characteristics of interannual variation and circulation for strong and weak years of monsoon. They found that the SASM intensified and weakened as a whole and there were four types of monsoon, being wholly strong and weak, stronger in the west than in the east and weaker in the west than in the east. Yan et al.discow,＇red sharp differences in individual members of the SASM at upper and lower levels over middle and lowe,r latitudes in both strong and weak years of the monsoon. Using, the dynamics method, Zhu et al. took the South Asia winter and summer monsoons as two stable equilibrium states and discussed the formation mechanism from the viewpoint of non-linear equilibrium theory. Their result further shows that in addition to thermal difference between land and sea, the topographic effect of South Asia also has significant restraints and influence on the formation and activity of the monsoon

IMPACT OF THE HEATING OVER SOUTH ASIA UPON THE SUBTROPICAL HIGH OVER WEST-PACIFIC

A case is reported, during which the Subtropical High over the Western Pacific (hereafter, SHWP in abbreviation) shifted northwestward and met-yu at Chaniiang River valley ended. Several numerical experiments onSHWP activity influenced by the heating over south Asia monsoon area are carried out, and the statistic significance of the results is checked. The results indicate that the enhancement of positive heating over South Asia willmotivate a wave-like series of anomaly centers, which propagate northeastward from the maximum heating center.so that a strong positive potential height anomaly center will set up from North China to Japan at Day X resultingin the enhancement of SHWP. Comparison of the influence upon SHWP by the heating over south Asia monsoonarea with that over ITCZ area south to SHWP is also carried out. It is pointed out that the heating over South Asiamonsoon area tends to favor SHWP north\vard movement while the heating over ITCZ area tends to thvor SHWPwestward stretching. As for the time to begin to influence on SHWP, the heating over south Asia monsoon areafavors the enhancement of SHWP atter Day 3 while that over ITCZ south to SHWP effects atter Day 5.

青藏高原东南缘攀枝花市降水特征及其成因初探

为更好地认识青藏高原东南缘地形复杂区降水特征及其成因,利用位于青藏高原东南缘的攀枝花市2015—2020年72个国家、区域气象观测站资料和欧洲中心0.25°×0.25°分辨率的ERA5再分析资料,对攀枝花降水特征及成因进行分析。结果表明:(1)攀枝花降水具有地形作用突出、北多南少的特点,降水日数是造成降水空间分布差异的主要原因之一。(2)攀枝花夜雨特征显著,呈单峰型,降水峰值出现在03时(北京时),因攀枝花位于干热河谷区,日间湿度小、夜间湿度大,夜间较饱和的大气更容易凝结,触发降水,湿度的日变化是攀枝花易发生夜雨的原因之一。(3)攀枝花干湿季分明,6—10月为攀枝花湿季,11月至次年5月为攀枝花干季,6月和10月是干湿转换的过渡期。6月孟加拉湾西南季风爆发,攀枝花雨季开始,干季逐渐结束;10月干燥的高原南支西风气流加强,雨季趋于结束,干季开始。

季风吹拂的土地:东南亚生态电影与全球南方主义

全球生态美学的表述与实践大多源于全球北方,但全球南方呈现出独特的美学特征与认识论模式,蕴含着比全球北方更具批判性的政治潜能。从以东南亚为代表的全球南方的角度来看待人类世的新兴生态电影美学,主要呈现为幽灵影像、季风影像和盖娅影像三个方面。当生态已经成为超越国族疆界而逐渐走向去政治化的生物区域主义的时候,东南亚电影将生态问题置入全球南方框架下,进而变得再政治化了。同时,它们启示我们必须成为生态电影类型学中的行动者,即从批判实践走向社会行动,以此书写自己的地球奥德赛。

THE ESTABLISHMENT OF THE SOUTH CHINA SEA SUMMER MONSOON IN 1998:THE NORTHWARD JUMP OF SOUTH ASIA ANTICYCLONE AND ITS EFFECT ON THE ONSET OF SOUTH CHINA SEA SUMMER MONSOON

By using the NCEP/NCAR reanalysis data,the activities of the 200 hPa South Asia Anticyclone (SAA) and its effect on the onset of South China Sea (SCS) summer monsoon in May 1998 are studied.The results show that:(1)During the pre-onset period the reversal of the mid- upper troposphere meridional horizontal temperature gradient over South Asia to the east of 90°E was caused mainly by warm horizonal thermal advections over this area.About 36 h after the reversal,the SCS summer monsoon bursts.(2)The variation of thermal wind circulation caused by the reversal of temperature gradient gave rise to the 200 hPa center of the SAA to jump from 15°N to 21°N within 12 hours.(3)The northward jump of the SAA and the intrusion eastward of the SAA under the effect of the warm horizonal thermal advections resulted in the rapid development of a trough over the South China coast.This induced the West Pacific Subtropical Anticyclone ridge,which originally controlled the South China Sea,to weaken rapidly and retreat eastward.Subsequently,the SCS summer monsoon built.(4)The superimposition in phase of the anticyclone ridge moving eastward over the middle-latitudes of China with the SAA has a rather important influence on the development of the trough over the South China coast.

THE RELATIONSHIP OF THE SOUTH CHINA SEA MONSOON WITH THE SOUTH ASIA HIGH AND ITS CHARACTERISTICS OF SEASONAL OR INTERANNUAL VARIATIONS

By using NCEP/NCAR daily data of the wind,the vapour and the temperature from 1958 to 1997 as well as the monthly geopotential height and the vertical velocity data,the evolution characteristics of the potential vorticity before and after the onset of the South China Sea (SCS) monsoon are studied.An intensity index is developed by using potential vorticity.In the meantime,the relationship between the intensity index and the position as well as the intensity of the South Asia High (SAH) is analyzed.The results show that,the seasonal and interannual variations of the SCS monsoon are remarkable,the anomaly of the summer monsoon is obvious before 1978.The intensity of the SCS monsoon has a close relation with the position of the SAH. When the position of the SAH inclines to west in the previous December,the SAH will incline to north in May and the intensity of the SCS summer monsoon will much enhance.Conversely,the SAH inclines to south,then the intensity of the SCS summer monsoon will be weaker.

Red Palaeosols Development in Response to the Enhanced East Asia Summer Monsoon since the Mid-Pleistocene in South China: Evidence Derived from Magnetic Properties and Molecular Fossil Records

Although Pleistocene red paleosols are widely distributed in South China, paleoenviron-mental interpretation has proved difficult because of intense weathering. Here we combine data from molecular fossil and magnetic properties to reconstruct a record of changes in pedogenic intensity for red paleosols in Southeast China. Depth distribution pattern of magnetic properties indicates that lower （higher） χ but higher （lower） values of HIRM （hard isothermal remanent magnetization） and SIRM （saturation isothermal remanent magnetization）/χ has tight relationship with the intensity of pedogenesis,especially the occurrence of well-developed net-like veins, which is absolutely responsible for the presence of anti-ferromagnetic minerals at the cost of fine-grained SP （superparamagnetic）/SD （single domain） ferrimagnetic minerals. The carbon distribution pattern of n-alkanes, n-alkanols, and n-alkanoic acids reflects the predominant contributions of microorganisms to the organic matter during pedogenesis, which provide direct evidence for strong microbial activities in response to theextremely hot-humid condition while white coarse net-like veins occurrence. Our results demonstrate that the presence of the enhanced East Asia summer monsoon has played a key role in the oxide-dominated weathering regime, and pedogenesis, and microbial activities. Changes in molecular ratios and magnetic properties are used to show that red paleosols have undergone three stages of soil formation in striking response to the evolution of the East Asia summer monsoon： （1） the most effective since the Middle Pleistocene; （2） moderately effective since 270 ka or so; （3） least effective since the last glacial. Our research provides important evidence to understand how red paleosols espond to global change since the Middle Pleistocene.

Differences in Atmospheric Heat Source between the Tibetan Plateau–South Asia Region and the Southern Indian Ocean and Their Impacts on the Indian Summer Monsoon Outbreak

In this paper, the NCEP-NCAR daily reanalysis data are used to investigate the characteristics of the atmospheric heat source/sink （AHSS） over South Asia （SA） and southern Indian Ocean （SIO）. The thermal differences between these two regions and their influence on the outbreak of the Indian summer monsoon （ISM） are explored. Composite analysis and correlation analysis are applied. The results indicate that the intraseasonal variability of AHSS is signi- ficant in SA but insignificant in the SIO. Large inland areas in the Northern Hemisphere still behave as a heat sink in March, similar to the situation in winter. Significant differences are found in the distribution of AHSS between the ocean and land, with distinct land-ocean thermal contrast in April, and the pattern presents in the transitional period right before the ISM onset. In May, strong heat centers appear over the areas from the Indochina Peninsula to the Bay of Bengal and south of the Tibetan Plateau （TP）, which is a typical pattern of AHSS distribution during the monsoon season. The timing of SA-SIO thermal difference turning positive is about 15 pentads in advance of the onset of the ISM. Then, after the thermal differences have turned positive, a pre-monsoon meridional circulation cell develops due to the near-surface heat center and the negative thermal contrast center, after which the meridional circulation of the ISM gradually establishes. In years of early （late） conversion of the SASIO thermal difference turning from neg- ative to positive, the AHSS at all levels over the TP and SIO converts later （earlier） than normal and the establish- ment of the ascending and descending branches of the ISM＇s meridional circulation is later （earlier） too. Meanwhile, the establishment of the South Asian high over the TP is later （earlier） than normal and the conversion of the Mas- carene high from winter to summer mode occurs anomalously late （early）. As a result, the onset of the ISM is later （earlier） than normal. However, the difference in vorticity between early and late conversion only shows in the changes of strong vorticity centers＇ location in the upper and lower troposphere.

西风带和南亚季风对三江源雨季水汽输送及降水的影响

为了进一步明确西风带和南亚季风对三江源流域的水汽输送作用及对流域降水的影响,利用ERA-20C再分析数据集对三江源流域1948—2010年雨季水汽通量场进行经验正交函数(Empirical Orthogonal Function,EOF)分解,得到可表征西风带和南亚季风水汽输送在三江源流域强弱关系的经验正交函数模态及指标,揭示当西风带和南亚季风分别控制流域时的水汽输送和降水分布规律。结果表明:西风带控制流域水汽输送时,流域内部水汽输送方向为由西北向东南,西风带和南亚季风在流域南边界附近汇集,流域东部及南部(澜沧江源区大部,黄河源区东部)降水显著增加;南亚季风控制流域水汽输送时,流域内部水汽输送方向为由南向北,两支水汽输送路径在流域以北汇集,流域北部(长江源区大部,黄河源区偏北部)降水显著增加。西风带和南亚季风的水汽输送均对三江源流域具有重要作用,两支水汽输送路径分别控制流域时可引起流域内部不同区域降水的显著增加。

云南丽江树轮δ^(18)O记录的大气环流变化信息

通过对云南玉龙雪山丽江冷杉年轮晚材纤维素氧同位素(δ18O)的分析,建立了1902-2004时段年分辨率的树轮δ18O序列。将所得序列与相邻的丽江市气象站记录的气候资料对比,分析了树轮δ18O对气候要素的响应。结果表明,丽江冷杉年轮晚材中的δ18O与其生长季气候因子密切相关。主要与季风期(8-10月)的降水和相对湿度、6-10月总云量、5-6月平均温度显著相关,尤其和总云量相关性最高(r=-0.45,P=0.01)。同时,树轮δ18O年际变化与南亚季风指数、东亚夏季风指数呈反相关关系,并与1-5月南方涛动指数负相关显著,在一定程度上反映了大尺度的大气环流影响。

大气环流的季节突变与季风的建立I·基本理论方法和气候场分析

将曾庆存等提出的大气环流的季节划分和计算季风的理论方法作了改进,使之更便于研究季风的建立过程.该理论方法将环流突变和季风建立时段,其'变差度'和与其前和其后场的'相似度'等由空间场的泛函随时间的变化(即数学名词上的'流'[flow])一起求出来.研究Ⅰ先分析气候平均场,Ⅱ分析各个别年份的情况及年际变化.研究Ⅰ的结果表明:(1)该方法可以客观定量地定出'突变'时段的关键日期;与季风建立过程联系,即是季风建立的'预兆日期',它比人们用天气-气候学方法(甚至用别的气象要素)定出的可以明显感觉到的或有明显实用价值的'季风来临日期'要早2至4天.(2)在北半球亚澳季风系统区域,夏季风的来临在许多关键地区伴有明显的环流突变,建立和推进者很快,但也有许多区域不表现为当地环流的突变,推进速度也慢.(3)北半球亚澳季风系统低空的热带季风分支,在6月中以前可明确区分为3个子系统,(a)西太平洋暖池和邻近低纬区域,4月中下旬建立;(b)热带东北印度洋(北界与孟加拉湾相邻,但不包括其在内)及索马里东边海洋,4月末至5月初建立;和(c)南海区域,5月上旬从南到5月下旬到北部.南海夏季风向北推进最快,于5月末候即可达北回归线附近,然后与暖池西北区域风场的突变一起,于6月中旬影响到东亚30°N区域;印度洋季风于6月初到达印度半岛东南端,然后逐渐推向印-巴次大陆.7月中以后,热带季风才连成一片,由非洲东岸直至长江下游和菲律宾附近.副热带季风分支于6月中旬可以感到其影响,于7、8月盛行于东亚和西太平洋区域,且结构和演变都比较复杂;6～7月间只表现为在(5～20°N,120～150°E)区域有强的环流突变(与副高增强并北移对应),7月中至8月底,则在上述区域和沿30°N的长江下游和日本以南的洋面上有3个强的环流突变中心(对应于副高又一次增强北移和西伸).这里暂不讨论温寒带季风分支.(4)季风具有鲜明的三度空间斜压结构,尤其是在低空季风'爆发'之前,平流层早已有强的环流突变,季节调整完成,然后突变向下延伸(虽然强度大减),跟着就有当地的低空季风'爆发'(建立).平流层和对流层环流的相互作用及其与季风建立的关系很值得进一步研究.

西藏两个小湖高分辨率的花粉记录

西藏东南部封闭湖泊高分辨率的花粉记录反映，在１６ ｋａ ＢＰ以前花粉组合以藜科（Ｃｈｅｎｏｐｏｄｉａｃｅａｅ） 和蒿属（Ａｒｔｅｍｉｓｉａ） 为主，花粉浓度很低，应为荒漠草原植被。当时气候寒冷干燥，１ 、７ 月份和年均温分别低于现在当地７ ～１０ ℃，０．５～１．５ ℃和４～６ ℃。年降水量仅２５０ ｍｍ 是现今当地年降水量的４０ ％ ；１２ ｋａ ＢＰ以后气温和降水逐渐增加，出现木本植物花粉，桦属（ Ｂｅｔｕｌａ） 和松属（ Ｐｉｎｕｓ）等，在９ ．２～５ ｋａ ＢＰ发育森林或森林草甸；８～６ ｋａ ＢＰ是研究区气候最适宜期，１、７ 月份气温均高于现在２～３ ℃，年降水量比现在当地高１００ ｍｍ 左右；５．５ ｋａ ＢＰ以后气温和降水呈非线性下降，主要发育草原植被。

华南前汛期持续暴雨环流分型初步研究

采用1961—2010年NCEP/NCAR逐日再分析资料和台站观测降水量资料,按一定标准选取了华南前汛期24个持续暴雨过程;并且按基本判据确定逐年华南夏季风降水开始日期。然后依据南亚高压环流型和相对于该年夏季风降水开始的早晚,将这些暴雨过程划分为夏季风降水前、后南亚高压东部型,夏季风降水后南亚高压带状、西部型共4个类型;其中,夏季风后南亚高压西部型次数最多、平均持续时间最长。所有类型持续暴雨的相同点是:广东东北部附近均为暴雨频率和雨量高值区;暴雨期间华南150 h Pa位势高度增加、500 h Pa位势高度减少;华南处在150 h Pa偏西风急流南侧辐散区中;850 h Pa华南沿海有明显的西南气流,低层辐合在华南东北部最明显;两广沿海为可降水量大值区;华南的整层水汽输送主要呈现西南向。不同点是:夏季风后南亚高压西部型平均雨量较小,夏季风后南亚高压带状型与西部型在印度洋上存在明显的偏东风高空急流;夏季风后南亚高压类型在两广沿海的可降水量数值较大。

南亚季风区加热影响副高的数值试验

就一次出梅时西太平洋副热带高压的北进过程，从加热场角度用数值试验的方法研究了南亚季风区对副高活动的影响，并利用统计方法进行了显著性检验。结果表明：南亚季风区正的加热增强将激发出一支自最大加热中心向东北方向传播的波列，至第3天将在日本到华北建立一强正区平中心，从而有利副高增强。此外，还比较了南亚季风区加热与副高南侧热带辐会带加热对副高影响的差异。结果认为：南亚季风区正加热更有利于副高北进，而副高南侧热带辐合带正加热更有利于副高西伸；从影响副高的时间来看，南亚季风区正加热在第3天便使副高增强，而副高南侧热带辐合带正加热的作用偏晚，在第5天影响才明显起来。

青藏高原和亚洲夏季风动力学研究的新进展

亚洲夏季风环流受海陆和伊朗高原—青藏高原大地形的热力作用调控。亚洲季风所释放的巨大潜热又对大气环流形成反馈。这种相互反馈过程十分复杂,揭示其物理过程对理解气候变化格局的形成和变化以及提高天气预报及气候预测的准确率十分重要。夏季北半球副热带对流层上层环流的主要特征是存在庞大的南亚高压(SAH)以及强大的对流层上层温度暖中心(UTTM)。本文介绍了温度—加热垂直梯度(T–QZ)理论的发展,并用以揭示SAH和UTTM的形成机制。指出沿副热带欧亚大陆东部的季风对流潜热加热及其中西部的表面感热加热和高层长波辐射冷却是导致SAH和UTTM在南亚上空发展的原因。文中还介绍了Gill模型用于上部对流层研究的局限性及解决的办法。

云南雨季开始期的时空变化特征及其与季风的关系

利用197l-2007年云南124站逐日降水资料计算雨季开始期,采用EOF(经验正交函数)分解和最大熵谱分析方法,研究云南雨季开始期的空间分布、时间演变及周期变化特征,并初步分析云南雨季开始期不同分布型与季风的关系,以期为指导春季农业生产提供依据。结果表明,全省雨季开始期一致偏早或偏晚为云南雨季开始期的最主要空间分布特征,其次为滇中及以东地区与滇西北及滇西南地区雨季开始期反向变化的空间分布型;雨季开始期全省一致分布型存在3～5a的显著周期变化,滇中及以东地区与滇西北及滇西南地区雨季开始期反向变化的空间分布型存在3～4a的显著周期变化;云南雨季开始期与同年5月孟加拉湾地区和南海地区OLR有显著的相关关系(P<0.05);南亚季风与南海季风强度指数对云南雨季开始期有重要的指示性意义。

南亚地区黑碳气溶胶对亚洲夏季风的影响

利用NCAR的全球大气模式CAM3,模拟了南亚地区黑碳气溶胶对亚洲夏季风的影响。结果表明:晚春时期,南亚地区黑碳气溶胶强烈吸收太阳辐射,加热低层大气,造成孟加拉湾及沿岸地区雨季的提前,可能导致南亚夏季风提前爆发。夏季,被加热的大气沿青藏高原南坡爬升,在高空形成一个稳定的加热层。高空的持续加热,引起局地的深对流活动,使得印度洋和南亚大陆之间产生一个北升南降的经圈环流,导致印度洋洋面上的向北运动加强,从而使南亚夏季风的强度增大。但是,南亚地区黑碳气溶胶通过影响表面气压、垂直运动、降水和850 hPa风场等减弱了东亚夏季风,且导致西太平洋副热带高压北移西伸,使我国梅雨带位置向东北方向移动。

热带地区100hPa东风气流的气候效应(Ⅱ):与华北夏季降水的关系

利用1954—1998年NCAR/NCEP再分析资料及同期我国160个测站月降水资料,分析了热带地区100hPa东风与华北夏季降水之间的关系。结果表明:(1)从春季到夏季,东风强度与华北夏季降水具有显著而稳定的正相关关系。(2)弱东风年夏季,印度洋及印度次大陆表面温度均为正异常,然而赤道印度洋地区的正异常明显强于其南北两侧。海温异常的这一分布特征,一方面使得100hPa东风减弱;另一方面使得南亚地区海陆热力对比减弱,导致南亚夏季风偏弱,进而造成由该季风区向华北地区的水汽输送减少,华北地区干旱。