东亚夏季风环流和雨带的季节内变化

基于常规气象要素资料及变差度方法, 分析了东亚夏季风环流的演变特征, 发现东亚地区在夏季期间存在两次明显的次季节突变, 主要表现为西太平洋副热带高压 (副高) 的两次东退北跳, 第一次是在6月中旬, 第二次是在7月下旬。由于副高与雨带密切相关, 雨带在演进过程中也呈现出两次明显的突跳, 分别对应于江淮流域至日本一带梅雨期以及中国华北和东北雨季的开始。较第一次北跳而言, 副高的第二次北跳更为明显。副高的第一次北跳主要受南海地区对流活动加强的影响, 而第二次北跳则是暖池对流活动与高纬地区环流共同作用的结果。暖池地区向东北方向传播的Rossby波列以及高纬地区东传的Rossby波通过锁相作用使得副高强烈北跳。此外, 副高与其西部边缘凝结潜热的相互作用导致副高发生季节内的低频振荡。 风场变差度的分析表明, 高纬地区对流层中低层环流的调整随着夏季季节进程逐渐减弱, 这与中高纬地区温差的变化有关。而高纬地区高层环流的调整在夏季后半期随着高度的增加却逐渐增强, 这与高层环流从夏到冬的季节变化有关。从风场相似度的变化上还可以看到, 副高第二次北跳后东亚地区呈现出明显不同的环流状态。 南半球环流对于南海及暖池地区对流活动的增强有重要影响。6月中旬, 南海与暖池地区对流活动的增强是由于南海西边界西风加强并向东扩展造成的, 这与马斯克林高压 (马高) 的加强密切相关。而在7月中旬, 澳大利亚高压 (澳高) 的增强使其东北部的越赤道气流加强, 南半球大量冷空气侵入到暖池地区, 加强了暖池地区的不稳定性以及低层的辐合, 从而使暖池地区的对流活动增强。但在夏季前半期, 暖池对流活动也可调制澳高强度与其东北部越赤道气流强弱的关系, 使得二者呈现出相反的变化趋势。南半球冬季期间, 澳高在振荡中减弱, 这与澳洲大陆下垫面温度及上游马高的能量频散有关, 前者影响澳高的变化趋势 (减弱), 而后者影响澳高的低频振荡。     

7月东亚高空西风急流变化对我国雨带的影响

分析了7月东亚高空西风急流北跳和急流中心西移时我国雨带的变化特征,发现急流北跳与长江中下游梅雨结束有很好的对应关系;急流中心西移则与长江中下游梅雨结束无对应关系,但急流中心西移相对于急流北跳发生的早晚对雨带北移过程有重要影响:在急流中心西移晚于急流北跳发生年份,雨带北移依次为长江中下游地区—淮河流域—黄淮地区逐渐北推,其他年份雨带则从长江流域直接北跳至黄淮地区。进一步分析表明:(1)急流北跳和急流中心西移引起中纬度大气环流发生显著变化,从而引起西太平洋水汽输送发生显著变化,孟加拉湾水汽输送无变化。(2)急流北跳和急流中心西移时大气环流调整不同,导致来自西太平洋的水汽输送变化不同,进而对雨带北移产生不同的影响。急流中心西移相对于急流北跳发生时间早晚不同,大气环流调整过程和水汽输送调整过程也不同,使得雨带北推进程不同。     

近百年中国汛期雨带类型气侯变化

利用近百年中国夏季雨带类型资料，统计得其10年际变化趋势，并用马尔科夫概型分析的方法计算实际各状态间的转移概率及其优势成分、各状态间的可置换性和持续性，探讨了近百年雨带类型的气候变化规律及成因。     

近40年我国东部降水持续时间和雨带移动的年代际变化

利用我国地面观测站降水资料以及欧洲中期数值预报中心 (ECMWF) 的月平均再分析资料, 研究了在全球平均表面气温偏冷和偏暖阶段, 我国东部降水开始和结束时间以及雨带南北移动的变化, 并分析了与东部降水变化相关联的大气环流特征。结果表明:近40年, 20世纪60—70年代全球平均表面气温处于一个相对偏冷时期, 而80—90年代处于偏暖时期; 在这样的变暖背景下, 我国东部地区年总降水量呈现出“南涝北旱”异常特征, 与冷位相比较, 在暖位相阶段长江流域年总降水量明显增加, 而华北地区降水量减少, 其中长江流域降水的增加主要是由夏季降水增加引起的, 3月长江中下游降水增加也很重要, 北方的降水减少主要是由从盛夏到初秋的降水减少引起的。平均而言, 暖位相阶段我国南方强降水开始时间较早、结束较晚, 持续时间较长, 而北方强降水开始较晚, 持续时间较短。从春末到夏季, 冷位相时我国东部强降水带表现出从华南、经过长江流域向华北移动的特征, 而在暖位相时强降水主要集中在长江流域, 从华南向华北移动的特征不明显。雨带的这种异常变化与东亚大气环流有关, 在暖位相时夏季东亚大陆低压比冷位相时弱, 而鄂霍次克海高压偏强, 西太平洋副热带高压位置偏南, 使夏季东亚副热带地区的西南风减弱, 梅雨锋加强, 导致雨带滞留在长江流域, 使长江流域降水增加、北方降水减少。     

东亚季风和我国夏季雨带的关系

利用１９５１－１９９４年每月平均平面气压资料，计算了东亚地区季风强度指数。分别表明：东亚夏季风强弱与我国夏季雨带类型之间有着一定的关系。当夏季风强的年份，主要雨带分布在我国北方，而夏季风弱的年份，主要雨带分布在我国南方；夏季风为正常的年份，雨带分布一般在我国中部。分析发现：夏季季风的强弱与夏季风来临迟早还存在着联系。当夏季风来临早的年份，则夏季季风强度以偏强为主；反之夏季风来临迟的年份，则夏季季风     

近千年中国东部夏季雨带位置的变化

提出一个把中国东部夏季雨带位置划分为8类的方案：内蒙古、华北、黄河下游、淮河、长江、江南北部、江南南部、华南。建立了1470-2005年8类雨带的档案。8类雨带又可归并为4类：华北、黄淮、长江、江南。建立了1000 -1999年4类雨带的档案。这两份档案显示气候温暖时雨带在长江的频次高,而气候寒冷时雨带在黄淮的频次高。     

近千年中国东部夏季雨带位置的变化

Based on the variations of geographical locations, the summer rain belts over eastern China were classified in this study into eight types: Inner Mongolia, North China, the Yellow River, the Huaihe River, the Yangtze River, the northern and southern parts of Jiangnan ( to the south of the lower Yangtze River valley), and South China. The file of 8-type rain belts was compiled from 1470 to 2005, and in order to extend the file of rain belts, it was further merged into a file of 4-type rain belts and also completed during the last millennium from 1000 to 1999. At last, the two files show that summer rain belts frequently occur in the Yangtze River valley in warm climate periods, but in the Yellow River or the Huaihe River valley in cold periods.     

南亚高压中部型与我国雨带分布

本文通过对1981—1984年6—8月100毫巴资料的分析,提出南亚高压中心位于95°—105°E区域的中部型是高原大气的一个重要环流系统。在此流型控制下,我国主要雨带特征与西部型和东部型有着明显的不同。     

我国大陆上空平均水汽含量及其季节变化

本文根据105个探空站资料计算了我国1960—1969年各月地面—200毫巴和600—200毫巴气柱内的平均水汽含量,综述了我国大陆上空水汽含量的分布特点,详细讨论了水汽含量的季节变化与东亚低层大气环流的关系。这些结果对研究水资源、降水成因、气侯形成等问题是十分有益的。     

我国东部夏季雨带的气候分类及其环流特征

利用主分量分析和Ｋ－均值聚类分析的方法，对我国东部夏季雨带进行客观的气候分类。分析表明：当聚类因子（Ｎ＝４），聚类数（Ｋ＝２）时，第２主分量成分是在所有聚类因子中起决定性的因素，它不仅反映出两类不同雨带类型及其强弱的变化，而且在环流特征上具有显著性的差异。     

Seasonal variation of rain-belts over China

Decadal rainfall data of 228 stations in 1951–1970 and upper-wind records in 1960–1969 published by the Central Meteorological Bureau and relevant provincial organizations are employed in the analysis. It is found that the characteristic features of seasonal variation of the main rain-belts over eastern China to the east of 105°F are quite different from those to the west, over the Qinghai-Xizhang (Tibetan) Plateau. The eastern rain-belts are closely related to the low level flow convergence lines and significantly influenced by the south Asian high and the western Pacific subtropical high.     

中国东部水汽低频振荡的季节变化特征

利用NCEP多年日平均可降水量资料,进行EOF、小波分析和EEOF等分析,得到以下结论,在分布上,我国东部水汽低频振荡受水汽源地影响主要有着三种不同的地理分布形势:一是我国东部水汽低频振荡约以长江为界,南北具有相反的变化形势;二是不同的正负形势由北向南间隔分布,出现正负正或者负正负的形势;三是我国东部水汽振荡在空间上具有整体的一致性,绝大部分都是正异常或者负异常,各种形势随时间相互替换。在强度上,华南、东海、长江中下游地区强度比较大而且振荡活跃,夏季的振幅最大,振荡最明显,能量也最大,春秋次之,冬季的振荡能量最小,振荡最弱。在周期上,水汽低频振荡在春、秋和冬季都具有64天左右的振荡周期,而在夏季只有24天左右的振荡周期。     

Detecting the origins of moisture over southeast China: Seasonal variation and heavy rainfall

To examine the ability of the Hybrid Single-Particle Lagrangian Integrated Trajectory(HYSPLIT) model to detect the origins and paths of moisture supplied to Southeast China, trajectories of air particles released over Southeast China were traced backward during 1 April 2012 to 31 March 2013 and three typical regional persistent heavy rainfall events. The HYSPLIT model provides more insightful information than water vapor flux. Analysis of the specific humidity along the trajectories revealed the origins of moisture and their contributions to the moisture supply in Southeast China. In the boreal summer half year, four key moisture transport paths from the eastern Indian Ocean, central Indian Ocean, South China Sea(SCS), and western North Pacific(WNP) contribute 10%, 20%, 31%, and 16% of the moisture to Southeast China,respectively. In the winter half year, the contributions of the paths from the WNP and North China double. Examination of heavy rainfall events showed that under tropical storm conditions, all moisture transport routines are rotated cyclonically before reaching Southeast China. The invasion of cold air can trigger heavy rainfall in both the summer and winter half years but plays different roles: it does not contribute to the moisture supply but plays a key role in converging and uplifting the moisture in the summer half year, while it supplies a great amount of moisture in the winter half year as it absorbs abundant moisture in crossing the WNP.     

Seasonal variation of PM10-bound PAHs in the atmosphere of Xiamen, China

PM₁₀ samples from a garden site (site A), an industrial-traffic intersection (site B), a residential site (site C) and an island site (site D) were collected at December 21–29, 2004; March 18–22, 2005; July 4–13, 2005 and October 24–28, 2005 in Xiamen. 15 priority PAHs compounds were analyzed by using a gas chromatograph/mass spectrometer (GC/MS). The abundance and origin of PAHs are discussed to reveal seasonal variations in Xiamen air quality. Average concentrations of Σ15PAHs were 17.5 ng/m³, 3.7 ng/m³, 32.6 ng/m³ and 10.5 ng/m³ from spring to winter with the highest value in autumn. The dominant PAHs components in every season were low and middle molecular weight PAHs including phenanthrene, pyrene, fluoranthene and chrysene. Diagnostic ratios and PCA analysis identified the main sources of particle bound PAHs: mainly from both gasoline and diesel vehicles exhaust, with some contribution from coal combustion, industry emission and cooking sources.     

Seasonal variation of particulate polycyclic aromatic hydrocarbons associated with PM10 in Guangzhou, China

Polycyclic aromatic hydrocarbons (PAHs) are ubiquitous pollutants in the urban atmosphere. An investigation on seasonal variation of PAHs in the urban atmosphere of Guangzhou, China was conducted in this study. 112 PM10 (particulate matter with aerodynamic diameter < 10 μm) samples were collected at two sites between June 2002 and June 2003. PAHs were analyzed with GC–MS (gas chromatography–mass spectrometry). The result showed that PAHs exhibit distinct seasonal variation. The seasonal concentration for the ∑PAHs ranged from 8.11 to 106.26 ng m^− 3. The average ∑PAHs measured were highest in winter and lowest in summer. The PAHs distribution patterns were similar within each season at two sites. 5–6 ring PAHs were the abundant compounds, which accounted for 65–90% of ∑PAHs and benzo [b + k] fluoranthene dominated in four seasons. The PAHs concentration and distribution pattern fluctuated greatly in winter for the cold air current. Based on the different temperature in winter, the samples were split into two groups. PM10 and the abundance of the PAHs in winter-1 (temperature, 12–22 °C) were much greater than in winter-2 (temperature, 8–12 °C). In winter-1 benzo [b + k] fluoranthene and Indeno [1, 2, 3] pyrene dominated while chrysene and benzo [b + k] fluoranthene dominated in winter-2. Meteorological conditions such as wind speed and temperature had a strong influence on the seasonal variation. Potential sources of PAHs were identified using the molecular diagnostic ratios between PAHs. Results showed fossil fuel combustion may be the major source of PAHs at the two sites.     

Seasonal variation and physical properties of the cloud system over southeastern China derived from CloudSat products

Based on the National Centers for Environmental Prediction(NCEP) and Climate Prediction Center(CPC) Merged Analysis of Precipitation(CMAP) data and Cloud Sat products, the seasonal variations of the cloud properties, vertical occurrence frequency, and ice water content of clouds over southeastern China were investigated in this study. In the Cloud Sat data, a significant alternation in high or low cloud patterns was observed from winter to summer over southeastern China. It was found that the East Asian Summer Monsoon(EASM) circulation and its transport of moisture leads to a conditional instability, which benefits the local upward motion in summer, and thereby results in an increased amount of high cloud. The deep convective cloud centers were found to coincide well with the northward march of the EASM, while cirrus lagged slightly behind the convection center and coincided well with the outflow and meridional wind divergence of the EASM. Analysis of the radiative heating rates revealed that both the plentiful summer moisture and higher clouds are effective in destabilizing the atmosphere. Moreover, clouds heat the mid-troposphere and the cloud radiative heating is balanced by adiabatic cooling through upward motion, which causes meridional wind by the Sverdrup balance. The cloud heating–forced circulation was observed to coincide well with the EASM circulation, serving as a positive effect on EASM circulation.     

Seasonal variation of lightning activity over the Indian subcontinent

The seasonal variation of lightning flash activity over the Indian subcontinent (0°N–35°N and 60°E–100°E) is studied using the quality checked monthly lightning flash data obtained from lightning imaging sensor on board the Tropical Rainfall Measuring Mission satellite. This paper presents results of spatio-temporal variability of lightning activity over the Indian subcontinent. The study of seasonal total lightning flashes indicates that the lightning flash density values are in qualitative agreement with the convective activity observed over this region. Maximum seasonal total flash counts are observed during the monsoon season. The propagation of the inter-tropical convergence zone over this region is also confirmed. Synoptic conditions responsible for variation of lightning activity are also investigated with the help of an observed dataset. The mean monthly flash counts show a peak in the month of May, which is the month of maximum temperatures over this region. Maximum flash density (40.2 km^?2 season^?1) is observed during the pre-monsoon season at 25.2°N/91.6°E and the annual maximum flash density of 28.2 km^?2 year^?1 is observed at 33.2°N/74.6°E. The study of the inter-annual variability of flash counts exhibits bimodal nature with the first maximum in April/May and second maximum in August/September.     

中国近20 a卫星遥感土壤湿度的季节变化及其验证

分析了欧洲空间局最近基于多颗卫星微波资料研发的ECV土壤湿度产品的季节性干湿变化,并与国家气象局提供的站点资料做了对比验证。研究发现:主动与被动遥感土壤湿度的干湿季节变化在中国东部季风区有显著的不一致性。在中国东部季风区,被动遥感土壤湿度的干湿季变化和站点观测一致,均表现出夏季是干季、冬季是湿季的特征;而主动遥感的数据则存在较大的空间差异,华北地区与被动遥感数据较为一致,华南地区则呈现夏季为湿季、冬季为干季的反位相特征。两者的不一致性说明,针对欧洲空间局开发ECV土壤湿度产品的过程,融合主动遥感和被动遥感资料,研制长序列土壤湿度产品的思路在中国东部季风区不可行。     

南亚高压的季节变化与趋暖性

利用NCEP／NCAR再分析资料，分析了南亚高压的季节变化，讨论了对流层中高层温度、整层大气视热源和非绝热加热率的时空变化对南亚高压季节变化的影响。结果表明，南亚高压存在两个季节平衡态，即夏半年的大陆高压和冬半年的海洋高压，大陆高压又可分为青藏高压和伊郎高压。加热场对南亚高压的季节变化有重要作用，南亚高压是一个暖性高压，其中心有“趋热性”，通常位于或趋于加热率的相对大值区。南亚高压的年循环过程，主要受南亚地区潜热和感热季节变化的支配。夏季北方地区和高压地区的强烈短波辐射加热对高压中心北移和维持也有作用，长波辐射的冷却作用则是高压减弱的重要原因。