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1.
Ingo Heinrich Kathrin Weidner Gerhard Helle Heinz Vos Janette Lindesay John C. G. Banks 《Climate Dynamics》2009,33(1):63-73
Australian climate-proxy reconstructions based on tree rings from tropical and subtropical forests have not been achieved so far due to the rarity of species producing anatomically distinct annual growth rings. Our study identifies the Australian Red Cedar (Toona ciliata) as one of the most promising tree species for tree-ring research in Australasia because this species exhibits distinct annual tree rings, a prerequisite for high quality tropical dendroclimatology. Based on these preliminary studies, we were able, for the first time in subtropical and tropical Australia, to develop a statistically robust, precisely dated and annually resolved chronology back to AD1854. We show that the variability in ring widths of T. ciliata is mainly dependent on annual precipitation. The developed proxy data series contains both high- and low-frequency climate signals which can be associated with the El Niño Southern Oscillation (ENSO) and the Interdecadal Pacific Oscillation (IPO). A comparison of different data sets (Brisbane precipitation, tree rings, coral luminescence record from the Great Barrier Reef, ENSO and IPO) revealed non-stationary correlation patterns throughout the twentieth century but little instability between the new tree-ring chronology and Brisbane precipitation. 相似文献
2.
Rainfall in New South Wales (NSW), located in the southeast of the Australian continent, is known to be influenced by four major climate drivers: the El Niño/Southern Oscillation (ENSO), the Interdecadal Pacific Oscillation (IPO), the Southern Annular Mode (SAM) and the Indian Ocean Dipole (IOD). Many studies have shown the influences of ENSO, IPO modulation, SAM and IOD on rainfall in Australia and on southeast Australia in particular. However, only limited work has been undertaken using a multiple regression framework to examine the extent of the combined effect of these climate drivers on rainfall. This paper analysed the role of these combined climate drivers and their interaction on the rainfall in NSW using Bayesian Model Averaging (BMA) to account for model uncertainty by considering each of the linear models across the whole model space which is equal to the set of all possible combinations of predictors to find the model posterior probabilities and their expected predictor coefficients. Using BMA for linear regression models, we are able to corroborate and confirm the results from many previous studies. In addition, the method gives the ranking order of importance and the probability of the association of each of the climate drivers and their interaction on the rainfall at a site. The ability to quantify the relative contribution of the climate drivers offers the key to understand the complex interaction of drivers on rainfall, or lack of rainfall in a region, such as the three big droughts in southeastern Australia which have been the subject of discussion and debate recently on their causes. 相似文献
3.
M. J. Salinger 《Climatic change》2013,119(1):23-35
Climatic variability has profound effects on the distribution, abundance and catch of oceanic fish species around the world. The major modes of this climate variability include the El Niño-Southern Oscillation (ENSO) events, the Pacific Decadal Oscillation (PDO) also referred to as the Interdecadal Pacific Oscillation (IPO), the Indian Ocean Dipole (IOD), the Southern Annular Mode (SAM) and the North Atlantic Oscillation (NAO). Other modes of climate variability include the North Pacific Gyre Oscillation (NPGO), the Atlantic Multidecadal Oscillation (AMO) and the Arctic Oscillation (AO). ENSO events are the principle source of interannual global climate variability, centred in the ocean–atmosphere circulations of the tropical Pacific Ocean and operating on seasonal to interannual time scales. ENSO and the strength of its climate teleconnections are modulated on decadal timescales by the IPO. The time scale of the IOD is seasonal to interannual. The SAM in the mid to high latitudes of the Southern Hemisphere operates in the range of 50–60 days. A prominent teleconnection pattern throughout the year in the Northern Hemisphere is the North Atlantic Oscillation (NAO) which modulates the strength of the westerlies across the North Atlantic in winter, has an impact on the catches of marine fisheries. ENSO events affect the distribution of tuna species in the equatorial Pacific, especially skipjack tuna as well as the abundance and distribution of fish along the western coasts of the Americas. The IOD modulates the distribution of tuna populations and catches in the Indian Ocean, whilst the NAO affects cod stocks heavily exploited in the Atlantic Ocean. The SAM, and its effects on sea surface temperatures influence krill biomass and fisheries catches in the Southern Ocean. The response of oceanic fish stocks to these sources of climatic variability can be used as a guide to the likely effects of climate change on these valuable resources. 相似文献
4.
5.
We present the first tree-ring based reconstruction of rainfall for the Lake Tay region of southern Western Australia. We examined the response of Callitris columellaris to rainfall, the southern oscillation index (SOI), the southern annular mode (SAM) and surface sea temperature (SST) anomalies in the southern Indian Ocean. The 350-year chronology was most strongly correlated with rainfall averaged over the autumn-winter period (March–September; r = ?0.70, P < 0.05) and SOI values averaged over June–August (r = 0.25, P < 0.05). The chronology was not correlated with SAM or SSTs. We reconstructed autumn-winter rainfall back to 1655, where current and previous year tree-ring indices explained 54% of variation in rainfall over the 1902–2005 calibration period. Some variability in rainfall was lost during the reconstruction: variability of actual rainfall (expressed as normalized values) over the calibration period was 0.78, while variability of the normalized reconstructed values over the same period was 0.44. Nevertheless, the reconstruction, combined with spectral analysis, revealed that rainfall naturally varies from relatively dry periods lasting to 20–30 years to 15-year long periods of above average rainfall. This variability in rainfall may reflect low-frequency variation in the El Niño-Southern Oscillation rather than the effect of SAM or SSTs. 相似文献
6.
Rainfall on the subtropical east coast of Australia has declined at up to 50?mm per decade since 1970. Wavelet analysis is used to investigate eight station and four station-averaged rainfall distributions along Australia??s subtropical east coast with respect to the El Ni?o-Southern Oscillation (ENSO), the inter-decadal Pacific oscillation (IPO) and the southern annular mode (SAM). The relationships are examined further using composite atmospheric circulation anomalies. Here we show that the greatest rainfall variability occurs in the 15?C30?year periodicity of the 1948?C1975 or ??cool?? phase of the IPO when the subtropical ridge is located sufficiently poleward for anomalous moist onshore airflow to occur together with high ENSO rainfall variability and high, negative phase, SAM variability. Thus, the mid-latitude westerlies are located at their most equatorward position in the Australian region. This maximizes tropospheric interaction of warm, moist tropical air with enhanced local baroclinicity over the east coast, and hence rainfall. 相似文献
7.
Global hydroclimatic changes from 1950 to 2018 are analyzed using updated data of land precipitation, streamflow, and an improved form of the Palmer Drought Severity Index. The historical changes are then compared with climate model-simulated response to external forcing to determine how much of the recent change is forced response. It is found that precipitation has increased from 1950 to 2018 over mid-high latitude Eurasia, most North America, Southeast South America, and Northwest Australia, while it has decreased over most Africa, eastern Australia, the Mediterranean region, the Middle East, and parts of East Asia, central South America, and the Pacific coasts of Canada. Streamflow records largely confirm these precipitation changes. The wetting trend over Northwest Australia and Southeast South America is most pronounced in austral summer while the drying over Africa and wetting trend over mid-high latitude Eurasia are seen in all seasons. Coupled with the drying caused by rising surface temperatures, these precipitation changes have greatly increased the risk of drought over Africa, southern Europe, East Asia, eastern Australia, Northwest Canada, and southern Brazil. Global land precipitation and continental freshwater discharge show large interannual and inter-decadal variations, with negative anomalies during El Niño and following major volcanic eruptions in 1963, 1982, and 1991; whereas their decadal variations are correlated with the Interdecadal Pacific Oscillation (IPO) with IPO’s warm phase associated with low land precipitation and continental discharge. The IPO and Atlantic multidecadal variability also dominate multidecadal variations in land aridity, accounting for 90 % of the multidecadal variance. CMIP5 multi-model ensemble mean shows decreased precipitation and runoff and increased risk of drought during 1950–2018 over Southwest North America, Central America, northern and central South America (including the Amazon), southern and West Africa, the Mediterranean region, and Southeast Asia; while the northern mid-high latitudes, Southeast South America, and Northwest Australia see increased precipitation and runoff. The consistent spatial patterns between the observed changes and the model-simulated response suggest that many of the observed drying and wetting trends since 1950 may have resulted at least partly from historical external forcing. However, the drying over Southeast Asia and wetting over Northwest Australia are absent in the 21st century projections.
相似文献8.
Summary An investigation of the relationships between New South Wales (NSW) seasonal rainfalls and fluctuations of geopotential height at four Australian radiosonde stations is presented. The connection between the Southern Oscillation Index (SOI) and the geopotential height was explored up to the mid-troposphere. The study determined that the 800 and 600 hPa heights at Woomera show stronger and more consistent correlations with winter and spring rainfalls respectively, than occur between SOI and rainfall. The 900 hPa height at Brisbane is also strongly correlated with autumn rainfall for much of coastal NSW. These correlations are found to be stable during high and low phases of the SO cycle. It was found that the effects of the considered geopotential data on rainfall are independent of the influence of the SO phenomenon. The study also found that the fluctuations of geopotential heights at Woomera are related to rainfall variability over a wide region of southern Australia. At Darwin the 800 hPa surface appears to be the highest altitude at which there is any influence from the Southern Oscillation during winter. Furthermore, airmass movement over inland NSW is quite strongly related to SOI but coastal airmass movement is only weakly related to SOI. A mechanism for the influence of the Southern Oscillation on NSW rainfall is suggested.With 9 Figures 相似文献
9.
本文探究了不同海表温度（SST）模态对6—8月和12月—次年2月全球陆地降水的趋势以及年代际变化的相对贡献。首先对热带地区陆地降水和SST进行SVD分析,得到影响陆地降水的趋势和年代际变化主要的海洋模态为：海洋中的全球变暖（Global Warming,GW）、大西洋多年代际振荡（Atlantic Multidecadal Oscillation,AMO）和太平洋多年代际振荡（Interdecadal Pacific Oscillation,IPO）。其次利用多元线性回归模型进一步定量评估了全球变暖、AMO和IPO对不同地区陆地降水的相对贡献大小。结果表明,全球变暖对陆地降水变化的贡献在冬夏季都是最大的,AMO在6—8月的贡献次之。IPO在12月—次年2月的贡献次之。不同纬度带,三者的贡献不同。GW的贡献在6—8月期间对10°N以北地区较大,南半球受GW的贡献相对较小,GW在12月—次年2月对40°N以北降水贡献异常显著;AMO主要在6—8月对10°～40°S和50°～60°S纬度带上的降水变化的贡献比较大;而IPO主要在12月—次年2月对北半球中纬度降水变化的贡献比较大。GW对许多地区降水变化的方差贡献都是最大的,例如6—8月期间,对北美洲东北部和亚洲降水变化贡献最大,12月—次年2月期间,对欧洲降水变化贡献最大。AMO对6—8月降水变化的方差贡献最大的区域为非洲萨赫勒、西伯利亚和南美洲。12月—次年2月期间,IPO对美国西南部的降水变化贡献最大,此外,北美洲东北部、南美洲西北部、非洲南部、澳大利亚东部、南亚季风区和我国北部的降水在12月—次年2月期间同样受IPO影响显著。进一步利用信息流的方法,探究了GW、AMO和IPO与陆地降水变化之间的因果关系,验证了上述结论。 相似文献
10.
Wavelet Analysis of Solar-ENSO Imprints in Tree Ring Data from Southern Brazil in the Last Century 总被引：2，自引：0，他引：2
In order to study the imprint of solar and ENSO signals on terrestrial archives, the wavelet spectrum analysis was applied to solar-geophysical indices and tree ring data. Time series of Sunspot Number (SSN), southern oscillation index (SOI) and tree-ring indices from Southern Brazil, for the period 1876–1991, were used in this work. The 11-year solar cycle was present during the whole period in tree ring data, being more intense during 1930–1980, in agreement with an earlier study that was performed for thesame region but a different time range (1836–1996). ENSO effects on treering data from Southern Brazil were studied by the first time in this work using wavelet analysis. Short-term variations, between 2–5 years, arealso present in tree ring data. This represents the signature of ENSO events and was also observed in the SOI, as expected. The cross-wavelet spectrum analysis shows that both solar and climatic factors are recorded in tree ring data. 相似文献
11.
Guobao Xu Xiaohong Liu Dahe Qin Tuo Chen Weizhen Sun Wenling An Wenzhi Wang Guoju Wu Xiaomin Zeng Jiawen Ren 《Theoretical and Applied Climatology》2014,116(3-4):385-401
Annual tree ring δ 18O and δ 13C chronologies from 1790 to 2008 were established using Tianshan spruce (Picea schrenkiana) in the central Tianshan Mountains of northwestern China. Temperature has a positive effect on tree ring δ 18O and δ 13C in the study area, while precipitation and relative humidity have negative effects. The standardized precipitation–evapotranspiration index (SPEI) considered all of these effects and was significantly negatively correlated with tree ring δ 18O and δ 13C. We combined the tree ring δ 18O and δ 13C series to reconstruct the past 192 years of SPEI, which accounted for about 46 % of the total variance of SPEI from 1950 to 2006. The reconstruction showed good spatial agreement with gridded data in Palmer Drought Severity Index and precipitation and an inverse relationship with temperature. Our SPEI reconstruction reveals several wet and dry periods over the past 192 years and has good agreement with other drought records. Wavelet analysis showed quasi-periodic 10-, 20-, 30-, and 70-year fluctuations in the reconstruction. The 10-, 20-, and 30-year periodicities may reflect the potential influence of North Atlantic Oscillation (NAO). Overall, this study indicates that the SPEI is a potential drought index, and the winter NAO affects regional moisture conditions in the long term. 相似文献
12.
A. G. Marshall D. Hudson M. C. Wheeler O. Alves H. H. Hendon M. J. Pook J. S. Risbey 《Climate Dynamics》2014,43(7-8):1915-1937
We assess the occurrence and probability of extreme heat over Australia in association with the Southern Annular Mode (SAM), persistent anticyclones over the Tasman Sea, and the Madden–Julian Oscillation (MJO), which have previously been shown to be key drivers of intra-seasonal variations of Australian climate. In this study, extreme heat events are defined as occurring when weekly-mean maximum temperature anomalies exceed the 90th percentile. The observed probability of exceedance is reduced during the positive phase of the SAM and enhanced during the negative phase of the SAM over most of Australia. Persistent anticyclones over the Tasman Sea are described in terms of (1) split-flow blocking at 160°E and (2) high pressure systems located in the vicinity of the subtropical ridge (STRHs), about 10° north of the split-flow blocking region, for which we devise a simple index. Split-flow blocks and STRHs have contrasting impacts on the occurrence of extreme heat over Australia, with STRHs showing enhanced probability of upper decile heat events over southern Australia in all seasons. The observed probability of an upper decile heat event varies according to MJO phase and time of year, with the greatest impact of the MJO on extreme heat occurring over southern Australia (including the Mallee agricultural region) in spring during phases 2–3. We show that this modulation of the probability of extreme heat by the SAM, persistent anticyclones over the Tasman Sea, and the MJO is well simulated in the Bureau of Meteorology dynamical intra-seasonal/seasonal forecast model POAMA-2 at lead times of 2–3 weeks. We further show that predictability of heat extremes increases in association with the negative SAM phase, STRH and MJO, thus providing a basis for skilful intra-seasonal prediction of heat extremes. 相似文献
13.
M. James Salinger 《Climatic change》2005,70(1-2):9-29
Prior to the 20th century Northern Hemisphere average surface air temperatures have varied in the order of 0.5 °C back to AD 1000. Various climate reconstructions indicate that slow cooling took place until the beginning of the 20th century. Subsequently, global-average surface air temperature increased by about 0.6 °C with the 1990s being the warmest decade on record. The pattern of warming has been greatest over mid-latitude northern continents in the latter part of the century. At the same time the frequency of air frosts has decreased over many land areas, and there has been a drying in the tropics and sub-tropics. The late 20th century changes have been attributed to global warming because of increases in atmospheric greenhouse gas concentrations due to human activities. Underneath these trends is that of decadal scale variability in the Pacific basin at least induced by the Interdecadal Pacific Oscillation (IPO), which causes decadal changes in climate averages. On interannnual timescales El Niño/Southern Oscillation (ENSO) causes much variability throughout many tropical and subtropical regions and some mid-latitude areas. The North Atlantic Oscillation (NAO) provides climate perturbations over Europe and northern Africa. During the course of the 21st century global-average surface temperatures are very likely to increase by 2 to 4.5 °C as greenhouse gas concentrations in the atmosphere increase. At the same time there will be changes in precipitation, and climate extremes such as hot days, heavy rainfall and drought are expected to increase in many areas. The combination of global warming, superimposed on decadal climate variability (IPO) and interannual fluctuations (ENSO, NAO) are expected lead to a century of increasing climate variability and change that will be unprecedented in the history of human settlement. Although the changes of the past and present have stressed food and fibre production at times, the 21st century changes will be extremely challenging to agriculture and forestry. 相似文献
14.
M. L. Shrestha 《Meteorology and Atmospheric Physics》2000,75(1-2):21-28
Summary ?Nepal, lying in the southern periphery of the Tibetan Plateau receives about 80% of the total annual rainfall during summer
monsoon (June–September). Rainfall analysis shows that summer monsoon is more active in the southern part of Nepal but in
the high Himalayas and Trans-Himalayan region other weather systems like western disturbances are also as effective as monsoon
in giving rainfall.
The influence of Southern Oscillation (SO) in Nepal monsoon rainfall is found to be very significant. The years with significant
negative (positive) Southern Oscillation Index (SOI) have less (more) rainfall in most of the cases during the 32-year period.
This relationship is also found to vary with time. The years with deficient rainfall are associated most of the times with
negative departure of SOI and the composite chart during these occasions shows about 95% area of Nepal experiencing below
normal rainfall. Likewise at the time of positive departure of SOI, most of the region (94%) experienced above normal rainfall.
There is a good relation between SOI and rainfall over Nepal during monsoon. The correlation coefficient between Nepal monsoon
rainfall and monthly SOI shows a statistically significant in-phase relationship during and after monsoon but poor relation
during the months prior to monsoon season. These results suggest that monsoon plays an active and effective role on the interannual
variability including SOI.
Received December 28, 1999/Revised May 22, 2000 相似文献
15.
H. Evangelista D. Godiva A. Sifeddine Z. M. A. N. Leão N. R. Rigozo B. Segal T. Ambrizzi M. Kampel R. K. P. Kikuchi F. Le Cornec 《Climate Dynamics》2007,29(7-8):869-880
Physical and biological changes in the marine environment, induced by oceanic-atmospheric processes, can be imprinted in massive coral skeletons. Herein, we present an evidence of potential El Niño impacts at the Southwestern South Atlantic Ocean (SWSA) inferred from the sclerochronology of the reef coral Favia leptophylla. The application of spectral analysis (wavelet decomposition and the iterative regression) to coral growth length and to meteorological-oceanographic parameters (air temperature, sea surface temperature and precipitation) as well as to Southern Oscillation Index (SOI) and solar irradiation indicated a major significant inverse relationship between SOI and coral growth length at the 4–8 years frequency band. We propose here that coral growth length from the SWSA could be affected by El Niño Southern Oscillation (ENSO) events through an “atmospheric bridge”, in contrast to its direct effect at the Pacific Ocean, related to the increase in sea surface temperature. 相似文献
16.
Cold-air mesocyclones remain a forecasting challenge in the southern hemisphere middle and higher latitudes, where conventional observations are lacking. One way to improve mesocyclone predictability is to determine their larger-scale circulation environments and associations with teleconnection patterns. To help realize this objective, reanalysis datasets on atmospheric and upper-ocean synoptic variables important in mesocyclone development are composited and compared to previously published mesocyclone spatial inventories. These analyses demonstrate a consistent association between higher frequencies of mesocyclones, greater sea ice extent and large positive differences in the SST minus low-altitude air temperature fields, coinciding with enhanced westerly low-level winds having a southerly component. Composites in the 1979–2001 period also were formed for opposite phases of El Niño Southern Oscillation (ENSO), the Southern Annular Mode (SAM) and the Trans-Polar Index (TPI). Regions likely to be favorable for mesocyclone development relative to climatology were identified. The largest (smallest) variations in meso-cyclogenesis occur in the South Pacific (South Indian Ocean, south of Australia), and are dominated by ENSO. The SAM and TPI are of secondary importance, yet still influential, and exhibit strong regional-scale variations. 相似文献
17.
Site-aspect influence on climate sensitivity over time of a high-altitude Pinus cembra tree-ring network 总被引：1，自引：0，他引：1
Giovanni Leonelli Manuela Pelfini Giovanna Battipaglia Paolo Cherubini 《Climatic change》2009,96(1-2):185-201
Recently a divergence between tree-ring parameters from temperature-limited environments and temperature records has been observed worldwide but comprehensive explanations are still lacking. From a dendroclimatic analysis performed on a high-altitude tree-ring network of Pinus cembra (L.) in the Central Italian Alps we found that site aspect influences non-stationary growth-climate relationships over time. A general increasing divergence between ring width and the summer temperature record (J–A) has been observed especially for chronologies from SW-facing slopes, whereas chronologies from N-facing sites showed stable relationships over time. The monthly analysis revealed that the decrease in sensitivity was mostly accounted for by the changes in the relationships with June temperature (decreasing correlations especially for S- and W-facing site chronologies), whereas trees from N-facing sites showed an increasing sensitivity to July temperatures. Our data suggest that at high altitudes, low temperatures at the beginning of the growing season no longer limit growth. We also found that our temperature-sensitive trees did not linearly respond in radial growth to the extreme heat event of summer 2003, and formed an annual ring of average width, resulting in a strong divergence from the temperature record. Our findings underline the importance of site ecology for tree-ring based climate reconstructions using temperature-sensitive ring-width chronologies, and may help in solving the ‘divergence problem’. 相似文献
18.
树木生长对气候变化的响应研究不仅能为全球变化背景下森林生态系统的响应提供关键参数，也是树轮气候学研究的基础。本文利用位于新疆西北部萨吾尔山南坡的西伯利亚落叶松树木年轮宽度资料，建立了不同海拔高度的4个树轮宽度年表，采用相关分析和冗余分析法分析了树轮年表特征及其对气候的响应特征。结果表明：（1）不同海拔西伯利亚落叶松树轮宽度年表均具有较高的敏感度和一致性，可能包含较为丰富的气候信息。树轮年表参数有较一致的规律性：平均敏感度、标准差和信噪比随海拔高度降低逐渐增大；反映树轮对环境要素响应滞后效应的一阶自相关系数随海拔高度降低而减小。（2）随着海拔高度的降低，树轮宽度年表与生长季温度（5—9月）的正相关逐渐减弱，直至变为负相关；与反映水分状况的气象要素（降水量、相对湿度和水汽压）由不显著相关变为显著正相关（P<0.01）。萨吾尔山南坡海拔2000~2100m是西伯利亚落叶松树轮宽度对气候响应关系发生转折的关键高度。（3）位于下树线区域西伯利亚落叶松树轮宽度受年降水量（上年7月至当年6月）和当年生长季（5—7月）最高气温共同影响，具备开展区域干旱指数重建的潜力。 相似文献
19.
Global mean surface temperature (GMST) during 1910–2012 experienced four alternated rapid warming and warming hiatus phases. Such a temporal variation is primarily determined by global mean sea surface temperature (SST) component. The relative roles of ocean dynamic and thermodynamic processes in causing such global mean SST variations are investigated, using two methods. The first method is ocean mixed layer heat budget analysis. The budget diagnosis result shows that the thermodynamic processes dominate in the rapid warming phases, while the ocean dynamics dominate during the hiatus phases. The second method relies on the diagnosis of a simple equilibrium state model. This model captures well the horizontal distribution of SST difference between two warmer and cooler equilibrium states during either the rapid warming or hiatus phases. It is found that the SST difference during the rapid warming phases is primarily controlled by the increase of downward longwave radiation as both column integrated water vapor and CO2 increase during the phases. During the hiatus phases, the water vapor induced greenhouse effect offsets the CO2 effect, and the SST cooling tendency is primarily determined by the ocean dynamics over the Southern Ocean and tropical Pacific. The SST pattern associated with the Interdecadal Pacific Oscillation (IPO) might be responsible for the remote and local ocean dynamic responses through induced wind change. 相似文献
20.
Analysis of 149 raingauge series (1946–1988) shows a weak positive correlation between late summer rainfalls (January–March) in tropical southern Africa and the Southern Oscillation Index (SOI). The correlation coefficients have been unstable since World War II. They were close to zero before 1970 and significant thereafter. Before 1970, southern African late summer rainfalls were more specifically correlated with regional patterns of sea surface temperature (SST), mainly over the southwestern Indian Ocean. After 1970, teleconnections with near global SST anomaly patterns, i.e. over the central Pacific and Indian oceans, dominate the regional connections. The increase in the sensitivity of the southern African rainfall to the global SO-related circulation anomalies is simultaneous with the correlation between SOI and more extensive SST anomalies, particularly over the southern Indian Ocean. This feature is part of longer term (decadal), global SST variability, as inferred from statistical analyses. Numerical experiments, using the Météo-France general circulation model ARPEGE-Climat, are performed to test the impact of the observed SST warming in the southern Indian and extratropical oceans during El Niño Southern Oscillation (ENSO) events on southern African rainfall. Simulated results show that ENSO events, which occurred in the relatively cold background of the pre-1970 period in the southern oceans, had a little effect on southern Africa climatic conditions and atmospheric circulation. By contrast, more recent ENSO events, with warmer SST over the southern oceans, lead to a climatic bipolar pattern between continental southern African and the western Indian Ocean, which is characterized by reduced (enhanced) deep convection and rainfall over the subcontinent (the western Indian Ocean). A weaker subtropical high-pressure belt in the southwestern Indian Ocean is also simulated, along with a reduced penetration of the moist southern Indian Ocean trade winds over the southern African plateau. These results are consistent with the strong droughts observed over all southern Africa during ENSO events since 1970. 相似文献