THE ANALYSIS OF MECHANISM OF IMPACT OF AEROSOLS ON EAST ASIAN SUMMER MONSOON INDEX AND ONSET     

沈新勇  黄文彦  陈宏波 《热带气象学报(英文版)》2017,23(4):357-367

RegCM4.3, a high-resolution regional climate model, which includes five kinds of aerosols(dust, sea salt,sulfate, black carbon and organic carbon), is employed to simulate the East Asian summer monsoon(EASM) from 1995 to 2010 and the simulation data are used to study the possible impact of natural and anthropogenic aerosols on EASM.The results show that the regional climate model can well simulate the EASM and the spatial and temporal distribution of aerosols. The EASM index is reduced by about 5% by the natural and anthropogenic aerosols and the monsoon onset time is also delayed by about a pentad except for Southeast China. The aerosols heat the middle atmosphere through absorbing solar radiation and the air column expands in Southeast China and its offshore areas. As a result, the geopotential height decreases and a cyclonic circulation anomaly is generated in the lower atmosphere. Northerly wind located in the west of cyclonic circulation weakens the low-level southerly wind in the EASM region. Negative surface radiative forcing due to aerosols causes downward motion and an indirect meridional circulation is formed with the low-level northerly wind and high-level southerly wind anomaly in the north of 25° N in the monsoon area, which weakens the vertical circulation of EASM. The summer precipitation of the monsoon region is significantly reduced,especially in North and Southwest China where the value of moisture flux divergence increases.  相似文献   

Local meteorology in a northern Himalayan valley near Mount Everest and its response to seasonal transitions     

FangLin Sun  YaoMing Ma  ZeYong Hu 《寒旱区科学》2018,10(6):493-501

An automatic weather station(AWS) has been installed at the Qomolangma Station of the China Academy of Sciences(QOMS) since 2005, in a northern Himalayan valley near Mount Everest, with an altitude of 4,270 m a.s.l.. Nine years of meteorological records(2006–2014) from the automatic weather station(AWS) were analyzed in this study, aiming to understand the response of local weather to the seasonal transition on the northern slopes of Mount Everest, with consideration of the movement of the subtropical jet(STJ) and the onset of the Indian Summer Monsoon(ISM). We found:(1) Both the synoptic circulation and the orography have a profound influence on the local weather, especially the local circulation.(2) Southwesterly(SW) and southeasterly(SE) winds prevail alternately at QOMS in the afternoon through the year. The SW wind was driven by the STJ during the non-monsoon months, while the SE was induced by the trans-Himalayan flow through the Arun Valley, a major valley to the east of Mount Everest, under a background of weak westerly winds aloft.(3) The response of air temperature(T) and specific humidity(q) to the monsoon onset is not as marked as that of the nearsurface winds. The q increases gradually and reaches a maximum in July when the rainy period begins.(4) The alternation between the SW wind at QOMS and the afternoon SE wind in the pre-monsoon season signals the northward shift of the STJ and imminent monsoon onset. The average interval between these two events is 14 days.  相似文献   

基于新监测指标的江南入梅早晚的气候特征及影响系统分析   总被引：3，自引：0，他引：3  

赵俊虎  陈丽娟  熊开国 《气象学报》2018,76(5):680-698

利用中国气象局2014年发布的《梅雨监测业务规定》中的入梅日期资料、NCEP/NCAR再分析资料及NOAA海温资料等,重点研究了1951—2015年江南入梅早、晚的气候特征,及其与同期(5—6月)大气环流及前期海表温度变化的关系。结果表明,近65年来江南入梅日具有显著的年际变化特征,入梅平均日期为6月8日,最早和最晚相差47 d。入梅日主要出现在6月,占80.0%。江南入梅偏早和偏晚年,对流层高层至低层的同期大尺度环流存在明显的差异。入梅偏早年,高层南亚高压和东亚副热带西风急流(西风急流)的建立较早,强度较强,南亚高压北移到青藏高原上空亦偏早,西风急流北跳偏早; 中层中高纬度经向环流较强,而西北太平洋副热带高压(副高)第1次北跳偏早; 低层索马里越赤道气流建立较早,强度较强,西太平洋为反气旋式距平环流; 入梅偏晚年上述环流系统演变特征则基本相反。冬、春季海表温度的异常是影响入梅早、晚的重要的外部强迫因子,也是重要的前期预测信号:当冬季东太平洋海表温度为负距平、澳大利亚东部海表温度偶极子为正位相及春季北大西洋三极子处于正位相时,江南入梅偏早; 上一年12月澳大利亚东侧海表温度偶极子和当年3月北大西洋三极子与江南入梅早、晚关系最为密切,当12月澳大利亚东部海表温度偶极子为正位相时,副高第1次北跳偏早,当3月北大西洋三极子为正位相时,6月西风急流偏强、偏北,有利于江南入梅偏早。   相似文献   

An Abrupt Change in Tropospheric Temperature Gradient and Moisture Transport Over East Asia in the Late 1990s     

B.H. Vaid  X. San Liang 《大气与海洋》2018,56(4):268-276

ABSTRACT

Previous studies have shown that the recent summer climate (precipitation in particular) over East Asia is varying significantly. Here we extend the study to April, May, and June (AMJ) or the seasonal transition period associated with the onset of the summer monsoon. It is found that the average 1000–400?hPa AMJ tropospheric temperature (TT) experienced a sudden change at the end of the twentieth century. The change has a dipolar modal structure, with one pole over countries in Central Asia (Pakistan, Afghanistan, Uzbekistan, Kazakhstan, Kyrgyzstan, and Tajikistan.) and the other over the Tibetan Plateau. The difference in the TT between the centres of the two poles (?TT), which characterizes the zonal gradient of the TT over Asia, has seen a significant reduction since 1999. The causal relations of ?TT with the local circulation, outgoing longwave radiation (OLR), surface shortwave flux (SSWF), precipitation, etc. have been investigated using a newly developed rigorous causality analysis, which unambiguously reveals a one-way causality from ?TT to each of OLR, SSWF, and precipitation.  相似文献   

2016年我国梅雨异常特征及成因分析   总被引：1，自引：0，他引：1  

赵俊虎  陈丽娟  王东阡 《大气科学》2018,42(5):1055-1066

利用国家气候中心梅雨监测资料和NCEP再分析资料,对2016年我国梅雨异常特征及其大尺度环流成因进行了分析。结果表明:（1）2016年我国梅雨有明显的区域特征,其中江南区入梅偏早14天,与1995年并列成为1951年以来入梅最早的年份,出梅偏晚11天,梅雨期（量）偏长（多）,但梅雨期日平均降水量偏少;长江区入梅和出梅均偏晚,梅雨期接近常年,但梅雨量偏多一倍以上,梅雨量和梅雨期日平均降水量分别为1951年以来历史同期第三和第二高值;江淮区入梅、出梅及梅雨期接近常年,但梅雨量偏多。（2）对流层高、中、低层环流系统冬夏季节性调整和转变显著提前的共同作用,导致了2016年江南区入梅显著偏早;东亚副热带西风急流、西太平洋副热带高压（副高）和东亚夏季风涌在7月中旬阶段性地南落导致了江南区和长江区出梅偏晚。（3）受到前冬超强厄尔尼诺衰减和春、夏季热带印度洋全区一致海温模态偏暖的影响,梅雨期副高异常偏强,副高西南侧转向的水汽输送异常偏强,并在长江区和江淮区与北方弱冷空气辐合,造成梅雨量异常偏多。  相似文献   

深度神经网络拾取地震P和S波到时   总被引：8，自引：0，他引：8       下载免费PDF全文

于子叶  储日升  盛敏汉 《地球物理学报》2018,61(12):4873-4886

从地震波形数据中快速准确地提取各个震相的到时是地震学中的基础问题.本文针对上述问题提出了利用深度神经网络拾取到时的新方法,建立了用于地震到时提取的17层Inception深度网络模型,在对原始三分量数据进行高通滤波和归一化处理后输入网络直接输出到时信息.整个过程基于神经网络自适应提取波形特征,自动输出结果.通过对100组加了不同强度的噪声数据进行了可靠性检验,相比于其他方法神经网络方法对于噪声具有较高的容忍度以及稳定性,并且与地震目录数据有较高的相似性.相比于AR-AIC+STA/LTA,深度神经网络虽然运算速度稍慢,但整个过程不需设定时窗与阈值,同时具有更高的可用性,并且可以迭代升级以提高精度.此方法作为人工智能方法,为波形到时拾取提供了新思路.  相似文献   

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   总被引：10，自引：0，他引：10  

曾庆存  张东凌  张铭  左瑞亭  何卷雄 《气候与环境研究》2005,10(3):285-302

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.  相似文献   

The effects of asymmetric potential vorticity forcing on the instability of South Asia High and Indian summer monsoon onset   总被引：1，自引：0，他引：1  

ZHANG YaNi  WU GuoXiong  LIU YiMin  GUAN Yue 《中国科学:地球科学(英文版)》2014,57(2):337-350

Based on the theory of potential vorticity(PV),the unstable development of the South Asia High(SAH)due to diabatic heating and its impacts on the Indian Summer Monsoon(ISM)onset are studied via a case diagnosis of 1998.The Indian Summer Monsoon onset in 1998 is related to the rapidly strengthening and northward moving of a tropical cyclone originally located in the south of Arabian Sea.It is demonstrated that the rapid enhancement of the cyclone is a consequence of a baroclinic development characterized by the phase-lock of high PV systems in the upper and lower troposphere.Both the intensification of the SAH and the development of the zonal asymmetric PV forcing are forced by the rapidly increasing latent heat released from the heavy rainfall in East Asia and South East Asia after the onsets of the Bay of Bengal(BOB)monsoon and the South China Sea(SCS)monsoon.High PV moves southwards along the intensified northerlies on the eastern side of the SAH and travels westwards on its south side,which can reach its northwest.Such a series of high PV eddies are transported to the west of the SAH continuously,which is the main source of PV anomalies in the upper troposphere over the Arabian Sea from late spring to early summer.A cyclonic curvature on the southwest of the SAH associated with increasing divergence,which forms a strong upper tropospheric pumping,is generated by the anomalous positive PV over the Arabian Sea on 355 K.The cyclone in the lower troposphere moves northwards from low latitudes of the Arabian Sea,and the upper-layer high PV extends downwards and southwards.Baroclinic development thus occurs and the tropical low-pressure system develops into an explosive vortex of the ISM,which leads to the onset of the ISM.In addition,evolution of subtropical anticyclone over the Arabian Peninsula is another important factor contributing to the onset of the ISM.Before the onset,the surface sensible heating on the Arabian Peninsula is very strong.Consequently the subtropical anticyclone which dominated the Arabian Sea in spring retreats westwards to the Arabian Peninsula and intensifies rapidly.The zonal asymmetric PV forcing develops gradually with high PV eddies moving southwards along northerlies on the eastern side of the anticyclone,and a high PV trough is formed in the middle troposphere over the Arabian Sea,which is favorable to the explosive barotropic development of the tropical cyclone into the vortex.Results from this study demonstrate that the ISM onset,which is different from the BOB and the SCS monsoon onset,is a special dynamical as well as thermodynamic process occurring under the condition of fully coupling of the upper,middle,and lower tropospheric circulations.  相似文献   

Study of initial vorticity forcing for block onset by a 4-dimensional variational approach     

QIAO Fangli  ZHANG Shaoqing  YIN Xunqiang 《大气科学进展》2005,22(2):246-259

With the aid of a global barotropic model, the role of the interaction of the synoptic-scale disturbance and the planetary flow in block onset is examined by a 4-dimensional variational approach. A cost function is defined to measure the squared errors of the forecasted stream functions during block onset period (day 4 and day 5 in this study) over a selected blocking domain. The sensitivity of block onset with respect to the initial synoptic-scale disturbance is studied by examining the gradient of the defined cost function with respect to the initial (during the first 24 hours) vorticity forcing, which is evaluated by the adjoint integration. Furthermore, the calculated cost function and gradient are connected with the limited-memory quasi-Newton optimization algorithm for solving the optimal initial vorticity forcing for block onset. For two studied cases of block onset (northern Atlantic and northern Pacific) introducing the optimal initial vorticity forcing, the nonlinear barotropic advection process mostly reconstructs these blocking onset processes. The results show that the formation of blocking can be correctly described by a barotropic nonlinear advection process, in which the wave- (synoptic-scale) flow (planetary-scale) interaction plays a very important role. On an appropriate planetary-scale flow, a certain synoptic-scale disturbance can cause the blocking onset by the interaction between the synoptic scale perturbations and the planetary scale basic flows. The extended forecasts show that the introduction of the optimal initial vorticity forcing can predict the blocking process up to the 7th or 8th day in this simple model case. The experimental results in this study show that the 4-dimensional variational approach has a good potential to be applied to study the dynamics of the medium-range weather processes. This simple model case study is only an initial trial. Applying the framework in this study to a complex model will further our understanding of the mechanism of the atmospheric/oceanic processes and improve their prediction.  相似文献   

降水变差度与南亚夏季风建立的关系     

朱敏  张东凌  张铭 《气候与环境研究》2005,10(3):315-322

利用多年南亚夏季风建立前后的降水量资料计算和分析了全球和印度次大陆的气候降水变差度.在4～6月份全球该变差度先增加再减少,5月份达到峰值,这具体反映了由冬到夏的季节转换过程,5月份处于明显的季节转换之中.印度次大陆东岸和孟加拉国该变差度增幅剧烈是南亚夏季风建立的预兆.南亚夏季风与索马里急流和80～90°E的越赤道气流密不可分,该夏季风的建立与一周左右南半球高纬流场的失稳也有密切关系.该变差度可客观定量的诊断季节变化和夏季风建立的时间,是一个好用的气候诊断工具.  相似文献