【作者】 王遵娅；

【导师】 丁一汇；

【作者基本信息】 中国科学院研究生院 ， 气象学， 2007， 博士

【摘要】 本论文主要利用1951～2004年中国740站点的逐日降水资料,并配合其他要素场和环流场资料,采用多种统计分析方法,研究了中国夏季降水季节内、年际和年代际的多时间尺度变率。首先对中国雨季的进退过程、阶段性和区域性特征进行了分析;以后,依次对中国夏季降水的气候季节内振荡、准两年振荡和年代际三个不同时间尺度波动的周期特征、时空分布、环流背景、外强迫因子的影响等进行了详细分析,并提出了这三种变率产生的可能机制;最后对三种尺度波动的相互关系进行了讨论。主要得到的结论如下所示:(1)通过对中国雨季的定义,发现中国的主雨季最早爆发于华南中部,最晚结束于华西地区,能持续4到14候不等,雨量能占年总降水的30%～60%。主雨季在东部为季风雨季,自南向北推进;在西部雨季有较强的局地性,北方略早于南方,主要受到西风带系统的影响。中国雨季表现出了显著的阶段性和区域性特征。(2)通过对中国4～9月降水气候季节内振荡的研究,发现10～30天振荡在华北和华南最明显,而30～60天振荡在长江中下游最显著。30～60天振荡在4～9月经历了三次明显的自南向北传播:第一次始于4月初,与春雨的发生有关;第二次最强,从6月初至8月中,低频中心分别与华南前汛期、江淮梅雨和华北雨季相对应;第三次发生于8月初,与长江及其以南地区的秋雨有关。气候季节内振荡对中国各主要雨季的强度、活跃和中断均有显著的调制作用。30～60天振荡在100。E以东有较明显的西传特征。10～30天振荡的传播特征较不明显。中国夏季降水季节内振荡维持和传播的可能机制为:低纬热源的季节内振荡激发出EAP遥相关波列,波列的低频气旋和反气旋之间形成经向排列的辐合辐散带,由于气流的上升和下沉造成自东亚到北太平洋的低频雨带。低纬热源季节内振荡的维持和北传导致包括中国东部低频雨带在内的东亚到北太平洋低频雨带维持和北传。(3)通过对中国夏季降水准两年振荡特征及其可能机制的研究,发现中国75%以上站点的夏季降水序列中都存在显著的准两年振荡,该振荡能解释中国夏季降水35%,甚至55%以上的年际变化方差。强准两年振荡地区主要分布在内蒙中部,从甘肃和陕西到淮河流域和长江中下游一带。中国夏季降水准两年振荡的可能机制是:太平洋-亚澳季风系统的准两年振荡会影响赤道西太平洋热力状况发生TBO,由异常热源激发EAP和EU波列,同时对低纬和中高纬环流产生影响,造成暖湿气流和冷空气异常而引起中国降水的TBO。赤道太平洋暖池区的异常热源性质,强度和位置是决定中国夏季降水准两年模态的主要因素,而该异常热源的特征与太平洋-亚澳季风系统TBO的强度和状态等密切相关。(4)通过对中国东部夏季降水年代际变率和可能原因的分析,发现其主要有准10年,30～40年和准80年周期,并在70年代末出现了突变。另外,华北和华南夏季降水还各在60年代中期和90年代初有一突变点。中国东部夏季降水在20世纪70年代末发生了从“北旱南涝”到“南涝北旱”转型,其可能机制是:一方面,青藏高原冬春季积雪由20世纪70年代末以前的偏少突变为偏多,造成东亚大陆的夏季热力作用偏弱;另一方面,赤道中东太平洋春夏季海温分别在20世纪60年代中期、70年代末和90年代初各出现了一次显著升高,使得低纬海洋的热力作用偏强。海陆热力差异的年代际减弱造成亚洲夏季风环流偏弱,从而中国的东部雨带偏南。另外,青藏高原积雪对中国东部夏季降水年代际变化的影响总体上比赤道中太平洋海温显著,赤道中太平洋海温在20世纪90年代初的突变增强与中国华南夏季降水在同期的年代际增多有密切关系。(5)通过对中国夏季降水三种尺度波动相互关系的分析,发现在年际和年代际偏涝的背景下,长江中下游季节内振荡周期偏长,以30～60天振荡;而偏旱背景下周期偏短,以10～30天为主。偏旱背景下季节内振荡的北传比偏涝背景下强。中国雨带和东亚东部环流的季节内循环模态不受旱涝背景影响,但偏涝背景下的季节内降水和环流强度都强于偏旱背景。中国东部夏季降水由多变少时振荡强度由强变弱,反之。年代际异常是年际异常的集中反映,而年代际变率为年际变化提供了背景,即:在年代际异常的调制下,年际变化具有总是出现某种(正或负)异常的趋向性。20世纪70年代末,华南和华北的3～7年周期显著增强而长江中下游的2～3年周期显著增强。年代际背景对中国夏季降水年际空间模态的影响不明显。更多还原

【Abstract】 Climate variability of summer rainfalls in China on multiple-time-scale, including climatic intra-seasonal oscillation (CISO), interannual variation and inter-decadal variation, is studied in this paper via various statistical analysis methods mainly based on 740 stations daily rainfall datasets in China from 1951 to 2004. Firstly, the staggered and regional advance and retreat of rainy seasons in China are analyzed. Secondly, the periodicity, temporal and spacial distribution, relating circulation and impacting external forcing factors of the CISO, interannual and interdecadal variations of summer rainfalls in China are studied, respectively. Finally, relationships among the aforementioned three variations are further discussed. The major conclusions are as follows:(1) On the basis of the definition of starting and ending dates of rainy seasons in China, it is found that the major rainy season breaks out earliest in middle South China and ends latest in the northern part of Sichuan province and the southern part of Gansu and Shanxi provinces. The duration of rainy seasons span from 4 to 14 pentads, while the amounts of which account for 30%～60% of the annual total amounts. The major rainy season in the eastern part of China, mainly affected by the East Asian monsoon, advances from the south to the north, while in the western part, it is some earlier in the north than in the south, with strong local features due to impacts of the westerlies. The spring and autumn rainy seasons are also prominent in China.(2) The 10~30-day period is much significant in South China and North China, while the 30~60-day period is more obvious in the middle and lower reaches of the Yangtze River valley. Three significant propagations of the 30~60-day oscillation from the south to the north are observed from April to September, with the first one beginning in early April and being related to the start and maintenance of the spring rainfalls in China. The second propagation begins in early June and ends in middle August, with three strong oscillation centers corresponding well to the pro-flooding rainy season in South China, the Meiyu in the middle and lower reaches of the Yangtze River valley and the rainy season in North and Northeast China, respectively. And the last one starts from early August and has close relationship with the autumn rainfalls in areas to the south of the Yangtze River. The CISO modulates significantly the intensity, activity and break of rainy seasons in China. The 30~60-day oscillation also shows obvious westward propagation in areas to the east of 100。E. However, the propagation of the 10~30-day oscillations is not significant. The possible mechanism of the maintenance and propagation of the CISO of summer rainfalls in China lies in that the strong CISO in the low-latitude inspires the EAP (East Asia - Pacific) wave train, whose anomalous cyclones and anti-cyclones form longitudinal anomalous convergence and divergence belts, resulting in the corresponding anomalous rainy belts from East Asian to North Pacific for the convergence causes the ascending airflow, while the divergence causes the descending airflow. Then, the maintenance and propagations of the CISO of the anomalous heating sources in the low-latitude may control the persistence and northward propagation of anomalous rainy belts from East Asia to North Pacific.(3) Significant TBO is observed in summer rainfalls in over 75% of stations in China. And it can account for over 35%, even 55% of the total interannual variance. Regions where summer rainfalls show strongest TBO in China are mainly located in middle Inner Mongolia and from Gansu and Shanxi provinces to the Yangtze and Huaihe River valley. The TBO in summer rainfalls of China is caused possibly by the TBO in the Pacific-Asian and Australian monsoon system through affecting the anomalous thermal situation in the western tropical Pacific. As the TBO of the anomalous heating resource there inspires the EAP and the EU wave trains, impacting the circulation at both the low and mid-high latitude and then causing the anomalies of the warm-wet airflow and the cold-dry airflow simultaneously, summer rainfalls in China oscillate on the biennial period. Moreover, the character, intensity and location of the anomalous heating resource of the warm pool in the tropical Pacific are key factors controlling the major mode of the TBO of summer rainfalls in China.(4) The quasi-10-year, 30~40-year and quasi-80-year periods are observed in summer rainfalls of East China, with the abrupt change in late 1970s. Additionally, other abrupt change points are observed in North China in middle 1960s and in South China in early 1990s. In late 1970s, summer rainfalls in East China changed from the so-called flooding in the south and drought in the north mode to the opposite one. On one hand, the winter and spring snow depth on the Tibet Plateau changed abruptly at late 1970s and began to increase from then on, resulting in the weakening of the heating force of the East Asian continent. On the other hand, the SST of the middle and eastern tropical Pacific in springs and summers shows three abrupt increases in middle 1960s, late 1970s and early 1990s, respectively, causing the strengthening of the heating force of the oceans. Then, the heating contrast between the continent and ocean in East Asia weakened on inter-decadal scale. Accordingly, the Asian summer monsoon weakened. The weakening of the Asian summer monsoon circulation directly results in the southward shift of the rainy belts in East China on inter-decadal scale. And the research further shows that the snow depth on Tibet Plateau has more important impact on the inter-decadal variation of summer rainfalls in East China than the SST in the middle and eastern tropical Pacific wholly, while the abrupt increase of the SST at early 1990s is closely related to the abrupt increase of summer rainfalls in South China during the same period.(5) By discussing the interactions among three aforementioned variations of summer rainfalls in China on multiple-time-scale, it is found that the intensity of the intraseasonal oscillation has significant positive correlation with rainfall amounts. And, in both the flooding year and the flooding decade, the period of intraseasonal oscillation is relatively longer, with the 30~60-day dominating, while it is relatively shorter under a drought climatic background, mainly being 10~30-day. A more significant northward propagation can be observed under a drought background than a flooding one. However, the anomalous rainfalls and circulations on the intraseasonal scale are stronger under the flooding background than the drought background, with both modes of anomalous rainfalls and circulations being similar. As the decrease of summer rainfalls in East China, the intraseasonal oscillation weakens, and vise versa. The integrated interannual variations compose the interdecadal variation, and the interdecadal anomaly is the climatic background of the interannual variation. That is, with the modulation of the interdecadal variation, the interannual variation always shows some trend of being positive or negative anomaly. After late 1970s, the 3~7-year period of summer rainfalls in South China and North China, as well as the 2~3-year period in the middle and lower reaches of the Yangtze River valley, became more significant. But the interdecadal background has few impacts on the temporal and spacial modes of summer rainfalls in China on the interannual scale.更多还原