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1.
Teleconnections between equatorial African climate and the surrounding circulation are examined using a convective index over the Congo River Basin in March to May (MAM) and July to September (JAS) seasons. Its influence on the wider region is determined through lag correlation and cross-wavelet analysis. During seasons of deeper convection, easterly winds weaken over the tropical Atlantic (anomalous flow toward Africa), whilst upper westerly winds weaken over southern Africa (in JAS). We view this as zonal overturning with ascent over the equatorial African lowlands and Congo River Basin that spreads moisture to the North African Sahel, with influence from the Pacific El Niño. Another facet of our study is the relationship between East African highlands rainfall and the Indian Ocean circulation. We find coupling between the Indian Ocean Rossby wave, a thermocline oscillation and Walker cell over the Indian Ocean that induces shifts in rainfall, particularly in the October to December season. 相似文献
2.
印度季风的年际变化与高原夏季旱涝 总被引：11，自引：6，他引：5
根据NCEP／NCAR再分析资料和海表面温度距平资料,分析了西藏高原夏季降水5个多、少雨年春、夏季印度洋850hPa、200hPa合成风场和合成海温场,发现多、少雨年前期与同期印度洋高、低空风场和海温场均存在明显差异,主要表现为高原夏季降水偏多(少)年印度夏季风偏强(弱),在850hPa合成风场上印度半岛维持西(东)风距平,西印度洋—东非沿岸为南(北)风距平,夏季阿拉伯海区和孟加拉湾出现反气旋(气旋)距平环流;200hPa合成风场上印度半岛维持东(西)风距平,南亚高压偏强(弱),索马里沿岸为南(北)风距平。印度夏季风异常与夏季印度洋海温距平的纬向分布型有密切联系。当夏季海温场出现西冷(暖)东暖(冷)的分布型时,季风偏强(弱),高原降水普遍偏多(少)。相关分析指出,索马里赤道海区的风场异常与高原夏季降水的关系最为密切,在此基础上我们定义了一个索马里急流越赤道气流指数,用它识别高原夏季旱涝的能力较之目前普遍使用的印度季风指数有了明显的提高。 相似文献
3.
P. P. Sreekala S. V. Bhaskara Rao M. S. Arunachalam C. Harikiran 《Theoretical and Applied Climatology》2014,118(1-2):107-114
Using the NCEP/NCAR reanalysis wind and temperature data (1948–2011) and India Meteorological Department (IMD) rainfall data, a long-term trend in the tropical easterly jet stream and its effect on Indian summer monsoon rainfall has been explained in the present study. A decreasing trend in zonal wind speed at 100 mb (maximum decrease), 150 mb, and 200 mb (minimum) is observed. The upper-level (100, 150, and 200 mb) zonal wind speed has been correlated with the surface air temperature anomaly index (ATAI) in the month of May, which is taken as the difference in temperature anomaly over land (22.5°N–27.5°N, 80°E–90°E) and Ocean (5°S–0°S, 75°E–85°E). Significant high correlation is observed between May ATAI and tropical easterly jet stream (TEJ) which suggests that the decreasing land–sea temperature contrast could be one major reason behind the decreasing trend in TEJ. The analysis of spatial distribution of rainfall over India shows a decreasing trend in rainfall over Jammu and Kashmir, Arunachal Pradesh, central Indian region, and western coast of India. Increasing trend in rainfall is observed over south peninsular and northeastern part of India. From the spatial correlation analysis of zonal wind with gridded rainfall, it is observed that the correlation of rainfall is found to be high with the TEJ speed over the regions where the decreasing trend in rainfall is observed. Similarly, from the analysis of spatial correlation between rainfall and May ATAI, positive spatial correlation is observed between May ATAI and summer monsoon rainfall over the regions such as south peninsular India where the rainfall trend is positive, and negative correlation is observed over the places such as Jammu and Kashmir where negative rainfall trend is observed. The decreased land–sea temperature contrast in the pre-monsoon month could be one major reason behind the decreased trend in TEJ as well as the observed spatial variation in the summer monsoon rainfall trend. Thus, the study explained the long-term trend in TEJ and its relation with May month temperature over the Indian Ocean and land region and its effect on the trend and spatial distribution of Indian summer monsoon rainfall. 相似文献
4.
5.
印度洋海温异常年际变率模态对中国东部地区夏季降水影响机制的数值试验 总被引：3，自引：2，他引：1
利用ECHAM5全球大气环流模式研究了印度洋海温异常年际变率模态从冬至夏的演变对我国东部地区夏季降水影响的机制。观测资料研究表明:对于正的印度洋海温异常年际变率模态,春、夏季热带印度洋和澳大利亚以西洋面(东极子)均为水汽的异常源区,向马达加斯加以东南洋面(西极子)及印度洋邻近大陆提供水汽。夏季,印度洋地区南极涛动、马斯克林高压加强;而印度季风低压和南亚高压均减弱,对应于印度夏季风减弱。夏季印度洋地区正压性的纬向风异常经向遥相关使热带印度洋地区出现西风异常,导致海洋性大陆地区对流活动减弱,而菲律宾海地区对流活动加强,进而导致西太平洋副热带高压偏弱、位置偏东北。对于负的印度洋海温异常年际变率模态,则反之。模式结果基本支持了已有的观测资料诊断结果。 相似文献
6.
Summary Teleconnections between the seasonal rainfall anomalies of March through May (“long-rains”) over eastern Africa (Uganda,
Kenya and Tanzania) and the lower equatorial stratospheric (30-mb) zonal winds for the 32-year period 1964–1995 are examined
using statistical methods. The analysis is based on the application of the simple correlation method and QBO/rainfall composite
analysis. A statistical study of spatial correlation patterns is made in an effort to understand the climatic associations
between the equatorial stratospheric zonal wind and regional rainfall at the interannual scale. The aim of this analysis is
to establish whether this global signal can be employed as predictor variable in the long-range forecasts. The study is part
of an ongoing investigation, which aims at designing a comprehensive and objective, multi-variate-forecast system of seasonal
rainfall over eastern Africa. The correlation parameters include simultaneous (zero lag), and the non-zero lag correlations.
The statistical significance of the correlation coefficient [r] is tested based on the Monte Carlo t-statistical method, and
the standard correlation tables.
Our results indicate significant positive simultaneous and non-zero lag correlations between rainfall over parts of East Africa
and lower equatorial stratospheric zonal wind during the months of March–May and June–August. Significantly high correlations
are concentrated over the western regions of eastern Africa with peak values of (+ 0.8) observed over these areas. These associations
have been observed to be more prominent during lag than in the simultaneous correlations. Strong month to month lag coherence
is observed after June prior to the onset of the March to May seasonal rainfall and persists for more than 4 months. Correlation
indices for the eight homogeneous rainfall regions over eastern Africa which are derived from our Empirical Orthogonal Function/Cluster
analysis shows a clear annual cycle with significant relationships between QBO and seasonal rainfall occurring during boreal
summer (June–August). The season with the weakest relationship is December–February. It is however, noted that although the
coherence between QBO-Index and rainfall during the long-rains is significantly high, there are some wet/dry years for which
the relationship between the long rains and the lower equatorial zonal wind are not significant (for example in 1966, 1973
and 1983). These years have been associated with strong and prolonged ENSO events. Preliminary comparison of the QBO-Index
and the newly found Indian Ocean dipole mode index (DMI) indicates that the two climate variables may be significantly related.
Of the six high dipole mode events in the Indian Ocean that were observed in 1961, 1967, 1972, 1982, 1994 and 1997, all except
1967 coincided with the easterly phase of the QBO-Index and below normal rainfall over western highlands of eastern Africa.
Contingency analyses indicate 60 percent likelihood for the occurrence of above normal rainfall during the westerly phase
of the QBO and 63 percent likelihood of below normal rainfall during the east phase of the QBO. Our correlation analysis results
indicate that about 36 percent of the variability of the long-rains season over eastern Africa are associated with the QBO-Index.
Our results further show that the tendency of the lower equatorial stratosphe ric zonal wind prior to the season is a good
indicator of the performance of the long rains of eastern Africa. A positive OND minus JJA QBO trend is a good indicator for
the non-occurrence of drought over eastern Africa. Similarly, a negative trend is a good indicator for the non-occurrence
of high rainfall over the region. The identified characteristics and domain of influence of the QBO signal in different regions
of East Africa suggests that this global oscillator may offer useful input to objective multi-variate rainfall prediction
models for eastern Africa.
Received June 4, 1999 Revised November 25, 1999 相似文献
7.
全球热带海气耦合距平模式及其数值模拟 总被引：1，自引：1，他引：1
用观测海温距平对一个中等分辨率的细网格大气模式和观测 FSU假风应力对全球热带三大洋距平海洋模式分别进行强迫试验。结果表明 :无论是大气模式还是海洋模式均在一定程度上较好地模拟了观测事实 ,热带大西洋的模拟效果好于热带印度洋。对大气模式而言 ,经向风距平的模拟要好于纬向风距平 ,热带大西洋西部好于东部 ,热带印度洋东部好于西部 ,赤道南侧好于北侧。对海洋模式而言 ,热带大西洋模拟最好的区域是赤道中东部 ,对赤道东印度洋的暖事件及偶极子事件年际变率模拟也较好。在此基础上 ,用和海气耦合模式同样的耦合方式将两者耦合起来 ,构成了一个中等复杂程度的全球热带海气耦合模式 ,这是进一步研究全球热带海气相互作用的基础 相似文献
8.
Several studies demonstrate that North Atlantic Oscillation influences variability of climate over Middle East. We use the centers of action approach for the study of winter rainfall variability over Middle East, taking into account variations in the components of the North Atlantic Oscillation, the Azores High and the Icelandic Low pressure systems. The results show there is a negative relation between the interannual variations of winter rainfall over Middle East and Azores High pressure. The east–west shifts of Indian Ocean high pressure has also impact on precipitation over Middle East, there being more precipitation when the Indian Ocean High shifts eastward versus when it is westward. We present a regression model for Middle East precipitation in which the Azores High pressure and the Indian Ocean High longitude are independent variables and it explains 40 % of the variance of precipitation during 1952–2002. Furthermore, the ongoing decrease in winter precipitation over the Middle East is attributed to the increasing pressure of the Azores High over the same period. 相似文献
9.
对近百年观测资料的分析表明赤道印度洋海温(SST)确实存在着偶极子型振荡的变化特征,它在9～11月最强,而在1～4月最弱;年际变化(4～5年周期)和年代际变化(主要为20～25年周期)也十分清楚.这个偶极子主要有正位相型(海温西高东低)和负位相型(海温东高西低);一般正位相型的振幅强于负位相型.尽管在极个别年赤道印度洋海温偶极子似乎与太平洋ENSO无关,但总体而论,赤道印度洋海温偶极子与赤道太平洋海温偶极子(类似ENSO)有很好负相关.它们的联系主要是赤道大气纬向(Walker)环流.资料分析表明,赤道印度洋海温偶极子与亚洲南部流场、青藏高压和西太平洋副高都有明显关系,表明它对亚洲季风活动有重要影响. 相似文献
10.
冬季和春季印度洋海温异常年际变率模态对中国东部夏季降水的可能影响过程 总被引：11，自引：4，他引：7
印度洋热力状况是影响全球气候变化和亚洲季风变异的一个重要的因素,但以往研究更多关注热带印度洋海温的变化,对南印度洋中高纬地区海温变化关注不够,由此限制了我们对印度洋的全面认识.本文研究了年际尺度上整个印度洋海温异常主导模态的特征及其对我国东部地区夏季降水的可能影响过程,以期望为气候变异研究及预测提供理论依据.研究结果表明:全印度洋海温异常年际变率的主导模态特征是在南印度洋副热带地区海温异常呈现西南—东北反向变化的偶极子模态,西极子位于马达加斯加以东南洋面,东极子位于澳大利亚以西洋面;同时,热带印度洋海温异常与东极子一致.当西极子为正的海温异常,东极子、热带印度洋为负异常时定义为正的印度洋海温异常年际变率模态;反之,则为负的印度洋海温异常年际变率模态.从冬至春,印度洋海温异常年际变率模态具有较好的季节持续性;与我国长江中游地区夏季降水显著负相关,而与我国华南地区夏季降水显著正相关.其可能的影响过程为:对于正的冬、春季印度洋海温异常年际变率模态事件,印度洋地区异常纬向风的经向大气遥相关使得热带印度洋盛行西风异常,导致春、夏季海洋性大陆对流减弱,使夏季西太平洋副热带高压强度偏弱、位置偏东偏北,造成华南地区夏季降水增多,长江中游地区降水减少;反之亦然.同时,印度洋海温异常年际变率模态可通过改变印度洋和孟加拉湾向长江中游地区的水汽输送而影响其夏季降水. 相似文献
11.
2015年夏季气候异常特征及其成因简析 总被引：3，自引：2，他引：1
2015年夏季,全国平均降水量297.6 mm,较常年同期偏少8.5%,空间分布呈“北少南多”的显著特征,长江中下游及江淮地区降水显著偏多,梅雨雨季持续时间长,雨量偏多。进一步研究表明,2015年5月以来热带印度洋海温一致偏暖模态正位相发展,激发出西升东降的局地异常纬向环流,有利于西太平洋副热带高压强度偏强,位置偏西。加强西伸的西太平洋副热带高压造成我国东南部地区西南低空急流频发,强度偏强。低空急流将来自南海的水汽向江淮等地输送,并激发不稳定能量释放,有利于对流活动的发展和降水的产生,导致梅雨雨季持续时间长,雨量偏多。 相似文献
12.
The summer monsoon of 1988 总被引：1，自引：0，他引：1
Dr. T. N. Krishnamurti H. S. Bedi M. Subramaniam 《Meteorology and Atmospheric Physics》1990,42(1):19-37
Summary Time averaged, monthly mean fields of a number of climate parameters such as sea surface temperature anomalies, outgoing longwave radiation anomalies, 200 mb velocity potential field, streamfunction anomaly at the lower and the upper troposphere and percentage rainfall amounts are presented, for the summer of 1988 over the regions of Asian summer monsoon. Above normal rainfall occurred over most of the Indian subcontinent, southeast Asia and eastern China during 1988. In comparison, 1987 was a drought year. This paper presents a comparison of some of the salient aforementioned parameters. The evolution of the planetary scale divergent motions and the streamfunction anomaly exhibit prominent differences during the life cycle of the monsoon in these two years. The velocity potential field exhibits a pronounced planetary scale geometry with the divergent outflows emanating from the monsoon region during 1988. The descending branches of these time averaged circulations are found over the Atlantic ocean to the west and over the eastern Pacific and North America to the east. The immense size of this circulation is indicative of an above normal monsoon activity. During 1987, the outflow center was located much further to the southeast over the western Pacific ocean. The longitudinal extent of the monsoonal divergent circulations were much smaller in 1987.The positive sea surface temperature anomaly of the El Nino year 1987 is seen to move westwards to the western Pacific in 1988, a warm anomaly also appears over the eastern equatorial Indian ocean and the Bay of Bengal at this time. The latter contributes to the supply of moisutre during the active monsoon season of 1988. The outgoing long wave radiation anomalies evolve with a westward propagation of strong positive anomalies from the central Pacific ocean consistent with the evolution of divergent circulation. The streamfunction anomalies basically show westerly zonal wind anomalies being replaced by easterly anomalies during 1988 over the upper troposphere of the monsoon region.The lower tropospheric streamfunction anomaly during the drought year 1987 showed a pronounced counter monsoon circulation. That feature was absent in 1988.With 11 Figures 相似文献
13.
利用NCEP/NCAR再分析资料、全球海温海冰GISST 2.3b资料, 用EOF技术分析了热带太平洋海表温度的年际异常 (SSTA) 变化特征表明:可用Ni?o3指数表示热带太平洋SSTA, 并用该指数来讨论热带太平洋、热带印度洋SSTA间的关系。分季节分析表明:冬季Ni?o3指数与热带印度洋SSTA间的关系表现为热带印度洋整体相关系数为正的单极形态, 且1976年以后两者的关系减弱, 其原因是冬季为ENSO事件的盛期, 另外, 冬季西太平洋暖水区东移导致太平洋Walker环流上升支强盛处的东移, 造成两洋的垂直纬向环流耦合减弱。夏季两者关系表现为偶极形态 (热带西印度洋与Ni?o3指数同相变化, 热带东印度洋则相反), 但1976年以后两者的关系有所加强, 是因为夏季为偶极子盛期, 也是ENSO事件的发展期, 同时夏季西太平洋暖水区东移并未引起太平洋Walker环流上升支强盛处的明显东移, 且印度洋季风环流、太平洋Walker环流的上升支强盛处的强度增大了, 造成两洋的垂直纬向环流耦合更强烈。即1976年以后, 冬季热带两洋SSTA间的关系减弱了, 而夏季两者关系则变得更密切。 相似文献
14.
Soon-Il An 《Theoretical and Applied Climatology》2004,78(4):203-215
Summary The interannual variability of sea surface temperature (SST) anomalies in the tropical Indian Ocean is dominated mainly by a basin-scale mode (BM) and partly by an east–west contrast mode (zonal mode, ZM). The BM reflects the basin-scale warming or cooling and is highly correlated with El Nino with 3- to 6-month lags, while the ZM is marginally correlated with El Nino with 9-month lags.During an El Nino, large-scale anomalous subsidence over the maritime continent occurs as a result of an eastward shift in the rising branch of the Walker circulation suppresses convection over the eastern Indian Ocean, allowing more solar radiation over the eastern Indian Ocean. At the same time, the anomalous southeasterly wind over the equatorial Indian Ocean forces the thermocline over the western Indian Ocean to deepen, especially in the southern part. As a result, SST over the whole basin increases. As El Nino decays, the subsidence over the maritime continent ceases and so does the anomalous southeasterly wind. However, the thermocline perturbation does not quickly shoal back to normal because of inertia and it disperses as Rossby waves. These Rossby waves are reflected back as an equatorial Kelvin wave, causing deepening of the thermocline in the eastern Indian Ocean, and preventing SSTs from cooling in that region. Moreover, the weaker wind speed of the monsoon circulation results in less latent heat loss, and thus warms the eastern Indian Ocean. These two processes therefore help to maintain warm SSTs over the eastern Indian Ocean until fall. During the fall, the warm SST over the eastern Indian Ocean and the cold SST over the western Indian Ocean are enhanced by air–sea interaction and the ZM returns. The ZM dissipates through the seasonal reversal of the monsoon atmospheric circulation and the boundary-reflected Kelvin wave. In the same manner, a basin-scale cooling in the tropical Indian Ocean can induce the ZM warming in the west and cooling in the east. 相似文献
15.
Summary Variability of Indian summer monsoon rainfall is examined with respect to variability of surface wind stresses over Indian
Ocean. The Indian Ocean region extending from 40°–120° E, and 30° S–25° N, has been divided into 8 homogeneous subregions,
viz (1) Arabian Sea (AS), (2) Bay of Bengal (BB), (3) West-equatorial Indian Ocean (WEIO), (4) Central-equatorial Indian Ocean
(CEIO), (5) East-equatorial Indian Ocean (EEIO), (6) South-west Indian Ocean (SWIO), (7) South-central Indian Ocean (SCIO),
and (8) South-east Indian Ocean (SEIO). The period of study extends for 13 years from 1982–1994. Monthly NCEP surface wind
stress data of five months – May through September, have been used in the study. The spatial variability of seasonal and monthly
surface wind stresses shows very low values over CEIO and EEIO and very high values over AS, SWIO, and SEIO regions. On the
seasonal scale, all India summer monsoon rainfall (AISMR) shows concurrent positive relationships with the surface wind stresses
over AS, BB, WEIO, SWIO and SCIO and negative relationships with the surface wind stresses over EEIO and SEIO. The relationships
of AISMR with the surface wind stresses over AS and WEIO are significant at 5% level. The concurrent relationships between
monthly surface wind stresses over these 8 oceanic sub-regions and monthly subdivisional rainfalls over 29 sub-divisions have
been studied. The rainfalls over the subdivisions in the central India and on the west coast of India are found to be significantly
related with surface wind stresses over AS, SWIO, SCIO. Monthly subdivisional rainfalls of four subdivisions in the peninsular
India show negative relationship with BB surface wind stresses. May surface wind stresses over AS, BB, WEIO, CEIO and SWIO
have been found to be positively related with ensuing AISMR. The relationship with AS wind stresses is significant at 5% level
and hence may be considered as a potential predictor of AISMR.
Received May 21, 2001 Revised October 8, 2001 相似文献
16.
The first two leading modes of interannual variability of sea surface temperature in the Tropical Indian Ocean (TIO) are governed by El Niño Southern Oscillation and Indian Ocean Dipole (IOD) respectively. TIO subsurface however does not co-vary with the surface. The patterns of the first mode of TIO subsurface temperature variability and their vertical structure are found to closely resemble the patterns of IOD and El Niño co-occurrence years. These co-occurrence years are characterized by a north–south subsurface dipole rather than a conventional IOD forced east–west dipole. This subsurface dipole is forced by wind stress curl anomalies, driven mainly by meridional shear in the zonal wind anomalies. A new subsurface dipole index (SDI) has been defined in this study to quantify the intensity of the north–south dipole mode. The SDI peaks during December to February (DJF), a season after the dipole mode index peaks. It is found that this subsurface north–south dipole is a manifestation of the internal mode of variability of the Indian Ocean forced by IOD but modulated by Pacific forcing. The seasonal evolution of thermocline, subsurface temperature and the corresponding leading modes of variability further support this hypothesis. Positive wind stress curl anomalies in the south and negative wind stress curl anomalies in the north of 5°S force (or intensify) downwelling and upwelling waves respectively during DJF. These waves induce strong subsurface warming in the south and cooling in the north (especially during DJF) and assist the formation and/or maintenance of the north–south subsurface dipole. A thick barrier layer forms in the southern TIO, supporting the long persistence of anomalous subsurface warming. To the best of our knowledge the existence of such north–south subsurface dipole in TIO is being reported for the first time. 相似文献
17.
The evolution of sea surface temperature (SST) and thermocline (represented by 20 °C isotherm depth, D20) in the east equatorial Indian Ocean (EIO) associated with the Indian Ocean Dipole (IOD) years is studied for the period of 50 years from 1958 to 2007. A new IOD index based on combined anomalies of surface winds, D20 and SST over the equatorial Indian Ocean is defined to identify strong and weak IOD events. It is found that the evolution of strong IOD events is driven by ocean dynamics in the form of thermocline–SST coupling and is strongly interactive with the atmosphere, whereas the weak IOD events are mere response to surface winds without such dynamical coupling. The easterly wind anomalies extend up to the western equatorial Indian Ocean (WIO) during strong IOD years and support enhanced EIO air–sea interactions. On the other hand, the evolution of zonal wind anomalies is weak during the weak IOD years. Thermocline–SST coupling is robust in both EIO and WIO during strong IOD years, which is primarily responsible for the enhanced SST gradient, strong enough to establish anomalous Walker circulation within the Indian Ocean. The strong convection over the WIO associated with the Indian Ocean Walker cell triggers a secondary cell with subsidence over the African landmass. This double cell structure over the equatorial Indian Ocean is not reported before. Such double cell structure is not evident in weak IOD years and instead the convection over WIO extends up to African landmass. These are well supported by the spatial pattern of anomalous precipitable water during strong and weak IOD years. Strengthening of monsoon flow and local Hadley cell associated with strong IOD events enhances precipitation over the Indian subcontinent, whereas weak IOD years have less impact on the Indian summer monsoon circulation and rainfall. Analysis reveals that the EIO thermocline index and combined index could be potential predictors for the central Indian rainfall during summer. 相似文献
18.
R. H. Kripalani J.-H. Oh J.-H. Kang S. S. Sabade A. Kulkarni 《Theoretical and Applied Climatology》2005,82(1-2):81-94
Summary The influence of the Indian Ocean Zonal Mode on the extreme summer monsoon rainfall over East Asia (China, Korea, Japan) has been investigated applying simple statistical techniques of correlation and composite analysis. While the observed rainfall data are used as a measure of rainfall activity, the NCEP-NCAR Reanalysis data are used to examine the circulation features associated with the extreme monsoon phases and the dynamics of the zonal mode – monsoon variability connections. The data used covers the period 1960 to 2000.The equatorial Indian Ocean is dominated by westerly winds blowing towards Indonesia. However, during the positive phase of the zonal mode, an anomalous, intensified easterly flow prevails, consistent with the positive (negative) sea surface temperature anomalies over the western (southeastern) equatorial Indian Ocean. This positive phase of the zonal mode enhances summer monsoon activity over China, but suppresses the monsoon activity over the Korea-Japan sector, 3 to 4 seasons later. The relationship is more consistent and stronger over the Korea-Japan region than over China.The Indian Ocean influences the monsoon variability over East Asia via the northern hemisphere mid-latitudes or via the eastern Indian Ocean/west Pacific route. The monsoon-desert mechanism induces strong subsidence northwest of India due to the anomalous convection over the Indian Ocean region associated with the positive phase of the zonal mode. This induces a zonal wave pattern over the mid-latitudes of Asia propagating eastwards and displacing the north Pacific subtropical high over East Asia. The warming over the eastern Indian Ocean/west Pacific inhibits the westward extension of the north Pacific sub-tropical high. The location and shape of this high plays a dominant role in the monsoon variability over East Asia. The memory for delayed impact, three to four seasons later, could be carried by the surface boundary conditions of Eurasian snow cover via the northern channel or the equatorial SSTs near the Indonesian Through Flow via the southern channel. 相似文献
19.
Summary Climatic determinants of summer (Nov-Mar) rainfall over southern Africa are investigated through analysis of sea surface temperatures (SST), outgoing longwage radiation (OLR) and tropospheric wind with respect to the Southern Oscillation Index (SOI) and the stratospheric quasi-biennial oscillation (QBO). Index-to-field correlation maps are presented at various lags for the austral spring and summer seasons to establish the spatial dependence and evolution of coherent, statistically significant features. The SOI signal is reflected in upper-level zonal wind anomalies over the equatorial Atlantic Ocean during spring. SSTs in the central Indian Ocean are significantly negatively correlated with the SOI in summer. On the other hand, OLR correlations are weak over southern Africa in the summer, implying that the SOI signal may not dominate interannual convective variability.QBO correlations with SST are relatively weak, but with 200 hPa zonal winds over the western equatorial Ocean, positive correlations are noted. A standing wave pattern is described in the sub-tropics. The OLR correlation pattern represents a dipole with increased convection over eastern and southern Africa in contrast to reduced convection over Madagascar when the QBO is in west phase.Contingency analyses indicate that the global indices are unreliable predictors in isolation. However the characteristics and domain of influence of SOI and QBO signals are identified and may offer useful inputs to objective multivariate models for different modes of southern African rainfall variability.With 12 Figures 相似文献
20.
南亚高压与西太平洋副热带高压经纬向位置配置对中国东部夏季降水的影响 总被引：3，自引：2，他引：3
利用1951—2016年逐月中国160站降水资料、NCEP/NCAR全球大气再分析资料和NOAA_ERSST_V4海表温度资料,分析了南亚高压与西太平洋副热带高压(西太平洋副高)经、纬向位置的关系及其位置配置对中国东部夏季降水的影响,结果表明:(1)南亚高压与西太平洋副高在纬向上的东西进退存在明显的反相关系,在经向上主要存在一致变化的特征,并依此定义了纬向、经向位置指数。纬向位置指数大(小)表示南亚高压与西太平洋副高纬向上距离远(近),经向位置指数大(小)表示两高压经向位置均趋于偏北(南);(2)纬向位置指数与我国华北、华南沿海地区降水呈显著正相关,而与长江中下游、东北北部地区降水呈显著负相关;经向位置指数与我国华北、东北南部地区降水呈显著正相关,而与我国江南、华南地区降水呈显著负相关;(3)南亚高压与西太平洋副高的经向、纬向位置指数与关键海区的前期春季、同期夏季海表温度均有显著的相关,热带太平洋-印度洋、北印度洋、中东太平洋前期春季、同期夏季海表温度与南亚高压东脊点呈显著正相关,与南亚高压脊线及西太平洋副高西脊点均呈显著负相关,而北太平洋海表温度主要与西太平洋副高脊线呈显著正相关。 相似文献