Circulation patterns of summer monsoon corresponding to two kinds of indices over the South China Sea     

Sun?JilinEmail author  Wang?Dongxiao 《中国海洋大学学报(英文版)》2002,1(2):125-129

The characteristics of circulation corresponding to two kinds of indices of summer monsoon onset over the South China Sea (SCS) have been discussed using the reanalysis data of the National Centers for Environmental Prediction-National Center for Atmospheric Research. It is found that there are two patterns of deep convection that occur at different locations and influence the summer monsoon onset over the SCS. One is over the Asia continent and the western Pacific corresponding to the southwesterly of summer monsoon prevailing over the northern and central part of the SCS, while the other is near the Philippines that affects the westerly summer monsoon as prevailing over the central and southern southern part of the SCS. Since these two kinds of convection affecting the summer monsoon onset do not always occur together, thus the summer monsoon onset time is different when determined by various indices.  相似文献   

Onset of aridity in southern Western Australia—a preliminary palaeomagnetic appraisal     

Hongbo Zheng  Karl-Heinz Wyrwoll  Zhengxiang Li  Chris McA Powell 《Global and Planetary Change》1998,18(3-4)

The timing of the onset of full arid conditions in southern Western Australia during the late Cenozoic remains uncertain. The playas and associated sedimentary sequences preserved as part of the Tertiary palaeodrainage networks, which are widely developed in Western Australia, provide the stratigraphic evidence necessary to resolve this issue. Lake Lefroy forms part of a chain of playas that occur in the eastern Yilgarn Craton. These lake chains are the remnants of a once external palaeodrainage system, developed in pre-Eocene times. Eocene non-marine to marginal marine sequences were deposited in the palaeodrainage as channel infills. The low relief area of the palaeodrainage featured a permanent to semi-permanent lacustrine environment during post-Eocene times, and fine-grained red–brown clastic clay up to 10 m in thickness was deposited over an extensive area. A significant hydrological transition, as inferred by the litho-sedimentary change from freshwater clay to evaporitic gypsum-dominated sedimentation, took place in the late Cenozoic. The extensive freshwater system changed to the saline/deflation playas that characterises this landscape today. A detailed palaeomagnetic study was carried out on the lacustrine clay unit and the overlying evaporitic gypsum unit in Lake Lefroy. Results from drill core and pit wall exposures have provided the first time constraints for these sequences. Age estimates, based on extrapolation from the Brunhes/Matuyama geomagnetic boundary, suggest that the gypsum-dominated sedimentation and by inference, full arid conditions in Lake Lefroy, commenced within the Brunhes Normal Polarity Chron, probably within the last 500 Ka. This age is considerably younger than previously thought, but appears to bear some correspondence to similar claims to the age of the onset of aridity in southeast and central Australia. Evidence emerging from the inland dune field to the surrounding oceans suggests a trend of increasing aridity during the Quaternary in Australia. The onset of full aridity may well indicate that the impact of global glacial–interglacial cycles on Australian climate, especially the large scale glacial ‘dryness' resulted from the 100 Ka astronomic variations reached beyond its threshold.  相似文献   

厄尔尼诺现象对北半球大气环流和中国降水的影响   总被引：48，自引：7，他引：48  

赵振国 《大气科学》1996,20(4):422-428

本文主要讨论了厄尔尼诺现象对北半球大气环流和中国季风降水的影响。研究表明，在厄尔尼诺开始年的春夏季，对流层上部位势高度和副热带高压都处在由弱到强的转变状态，我国东部地区大范围少雨；秋季发生明显的趋势转折，秋季到次年夏季，对流层上部位势高度升高，副高增强西伸，除次年2、3月份全国大范围少雨外，其余月份大都为南多北少的分布型，这种分布形态在开始年秋季最典型。厄尔尼诺开始年、次年，长江中下游入梅期偏晚。  相似文献   

Seasonal　Transition　of　Summer　Rainy　Season　over　Indochina　and　Adjacent　Monsoon　Region   总被引：10，自引：0，他引：10  

Jun MatsumotoDepartment of Geography  University of Tokyo --  Hongo  Bunkyo-ku  Tokyo  Japan 《大气科学进展》1997,(2)

ＳｅａｓｏｎａｌＴｒａｎｓｉｔｉｏｎｏｆＳｕｍｍｅｒＲａｉｎｙＳｅａｓｏｎｏｖｅｒＩｎｄｏｃｈｉｎａａｎｄＡｄｊａｃｅｎｔＭｏｎｓｏｏｎＲｅｇｉｏｎＪｕｎＭａｔｓｕｍｏｔｏＤｅｐａｒｔｍｅｎｔｏｆＧｅｏｇｒａｐｈｙ，ＵｎｉｖｅｒｓｉｔｙｏｆＴｏｋｙｏ...  相似文献   

赤道涡旋与南海夏季风爆发   总被引：10，自引：0，他引：10  

谢安  刘霞  YeQian 《气象学报》1997,55(5):611-619

文中应用１９７９－１９９５年共１７ａ的８５０ｈＰａ风场资料和ＮＯＡＡ卫星的ＯＬＲ资料，分析了南海夏季风爆发的特征。证实南海夏季风爆发，落后于同纬度的中南半岛和菲律宾岛屿地区。但在南海的东部和西部，季风爆发几乎是同时的，具有某种驻波的特征。文中还证实，大多数年份的４，５月间在１０５°Ｅ附近有赤道涡旋形成，这个涡旋引导它上游的赤道西风或南半球西风进入南海南部，为南海的季风爆发创造有利条件。这种涡旋不活跃的年份，季风爆发往往偏晚。它们之间可能存在某种联系。４月中旬，这个涡旋的形成和１０５°Ｅ越赤道气流的初步建立是同时的。进入５月份，这支越赤道气流逐渐加强。南海夏季风的活动与这支气流可能关系密切。如果称位于１０５°Ｅ附近的赤道涡旋为东亚的爆发涡旋，它显然与南亚季风的情况有较大差别。南亚的爆发涡旋与季风爆发的关系是直接的，而在东亚，则是间接的，这也说明了东亚季风比南亚季风更具有复杂性。  相似文献   

太平洋次表层海温与南海夏季风建立关系初探   总被引：6，自引：1，他引：6  

高辉  何金海  张芳华 《南京气象学院学报》2002,25(3):351-357

通过合成分析和相关分析对南海夏季风爆发异常年份前期 0～ 40 0 m深度次表层海温的异常分布进行了讨论 ,发现北太平洋 (1 50°E～ 1 50°W,3 5～ 50°N)区域对季风爆发时间的早晚有着较为持续的影响 ,前冬 1 2 0～ 3 0 0 m深度尤其显著 ,具体表现为当前冬该海域海温偏低时 ,季风爆发偏晚 ,反之偏早 ;并通过定义一个北太平洋热力参数以表征该区域的热力作用 ,指出这一作用可能通过遥相关过程得以实现  相似文献   

THE CLIMATIC CHARACTERISTICS OF SUMMER MONSOON ONSET OVER THE SOUTH CHINA SEA I.40-YEAR AVERAGE     

冯瑞权  王安宇  吴池胜  林建恒  古志明  林文实  谭志文 《热带气象学报(英文版)》2002,8(1):10-19

By using 40-year NCEP reanalysis daily data (1958-1997), we have analyzed the climatic characteristics of summer monsoon onset in the South China Sea (105°E ~ 120°E, 5°N ~ 20°N, to be simplified as SCS in the text followed) pentad by pentad (5 days). According to our new definition, in the monsoon area of the SCS two of the following conditions should be satisfied: 1) At 850hPa, the southwest winds should be greater than 2m/s. 2) At 850 hPa, θ_se should be greater than 335°K. The new definition means that the summer monsoon is the southwest winds with high temperature and high moisture. The onset of the SCS summer monsoon is defined to start when one half of the SCS area (105°E ~ 120°E,5°N ~ 20°N) is controlled by the summer monsoon. The analyzed results revealed the following: 1) The summer monsoon in the SCS starts to build up abruptly in the 4th pentad in May. 2) The summer monsoon onset in the SCS is resulted from the development and intensification of southwesterly monsoon in the Bay of Bengal. 3) The onset of the summer monsoon and establishment of the summer monsoon rainfall season in the SCS occur simultaneously. 4) During the summer monsoon onset in the SCS, troughs deepen and widen quickly in the lower troposphere of the India; the subtropical high in the Western Pacific moves eastward off the SCS in the middle troposphere; the easterly advances northward over the SCS in the upper troposphere.  相似文献   

2002—2018年叶尔羌河流域积雪时空变化研究     

易颖  刘时银  朱钰  吴坤鹏 《干旱区地理》2021,44(1):15-26

积雪是冰冻圈中较为活跃的因子,对气候环境变化敏感,其变化影响着全球气候和水文的变化。积雪覆盖日数(SCD)、降雪开始时间(SCOD)和融雪开始时间(SCMD)是影响地表物质和能量平衡的主要因素。使用MODIS无云积雪产品提取了叶尔羌河流域2002年7月-2018年6月逐日积雪覆盖率(SCP),基于像元计算了SCD、SCOD和SCMD,系统地分析了其空间分布与变化特征,并探讨了其变化的原因及积雪面积的异常变化与ENSO的联系。结果表明:(1)研究时段内,流域的积雪覆盖面积呈微弱减少趋势,与气温呈显著负相关,与降水呈显著正相关;2002-2018年,SCP随海拔的升高呈明显的线性增加趋势(R2=0.92、P<0.01));各海拔高度带最大SCP出现的月份大致随海拔的上升往后推迟,最小SCP出现月份无显著变化(集中在8月),海拔4000 m以下,春季的SCP小于冬季,海拔4000 m以上,春季的SCP大于冬季。(2)SCD、SCOD和SCMD有明显的海拔梯度,在流域内,从东北至西南,呈现出SCD增加,SCOD提前,SCMD推迟的特征;变化趋势上,流域91.9%的区域SCD表现为减少,65.6%的区域SCOD有往后推迟的趋势,77.4%的区域SCMD表现出提前的趋势。(3)2006、2008年和2017年积雪覆盖面积异常偏大,而在2010年则异常偏小,其原因可能是ENSO影响了积雪的变化。(4)以喀喇昆仑为主的高海拔地区,包括帕米尔高原东部的部分地区,其SCD、SCOD和SCMD分别表现出增加、提前和推迟的趋势,这种变化与其春秋温度的持续走低以及降水量的增加有关。  相似文献   

宁夏近44 a霜冻的气候变化特征   总被引：4，自引：1，他引：4  

唐晶  张文煜  赵光平  白庆梅  王建英  张智 《干旱气象》2007,23(3):39-43

对宁夏1961~2004年间霜冻发生次数、霜期的变化特征进行了分析,结果表明:宁夏霜冻发生主要集中在4月和10月,出现次数4月中旬最多,春季霜冻明显多于秋季;发生次数南北差异较大,宁南山区发生频率较高,年平均发生次数达8.7~10.8次。同心出现次数最少,年平均只有2.1次;霜冻发生次数阶段性变化呈"1升1降"和"1升2降"分布,总体呈下降趋势,其中6月、秋季下降趋势明显。霜冻年发生次数的跃变点是1984年,跃变年以后霜冻发生次数明显减少;3个区域的气候变化趋势均为初霜日逐渐推迟,终霜日逐渐提前,无霜期逐渐延长。  相似文献   

A unified criterion for initiation of sediment motion and inception of sheet flow under water waves   总被引：1，自引：0，他引：1  

ZAI-JIN YOU  †  BAOSHU YIN† 《Sedimentology》2006,53(5):1181-1190

A unified criterion is developed for initiation of non‐cohesive sediment motion and inception of sheet flow under water waves over a horizontal bed of sediment based on presently available experimental data. The unified threshold criterion is of the single form, U_o = 2πC[1 + 5(T_R/T)²]^?1/4, where U_o is the onset velocity of sediment motion or sheet flow, T is wave period, and C and T_R are the coefficients. It is found that for a given sediment, U_o initially increases sharply with wave period, then gradually approaches the maximum onset velocity U_o = 2πC and becomes independent of T when T is larger. The unified criterion can also be extended to define sediment initial motion and sheet flow under irregular waves provided the significant wave orbital velocity and period of irregular waves are introduced in this unified criterion.  相似文献