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1.
The differences in tropical Pacific sea surface temperature (SST) expressions of El Niño-Southern Oscillation (ENSO) events of the same phase have been linked with different global atmospheric circulation patterns. This study examines the dynamical forcing of precipitation during October–December (OND) and March–May (MAM) over East Africa and during December–March (DJFM) over Central-Southwest Asia for 1950–2010 associated with four tropical Pacific SST patterns characteristic of La Niña events, the cold phase of ENSO. The self-organizing map method along with a statistical distinguishability test was used to isolate La Niña events, and seasonal precipitation forcing was investigated in terms of the tropical overturning circulation and thermodynamic and moisture budgets. Recent La Niña events with strong opposing SST anomalies between the central and western Pacific Ocean (phases 3 and 4), force the strongest global circulation modifications and drought over the Northwest Indian Ocean Rim. Over East Africa during MAM and OND, subsidence is forced by an enhanced tropical overturning circulation and precipitation reductions are exacerbated by increases in moisture flux divergence. Over Central-Southwest Asia during DJFM, the thermodynamic forcing of subsidence is primarily responsible for precipitation reductions, with moisture flux divergence acting as a secondary mechanism to reduce precipitation. Eastern Pacific La Niña events in the absence of west Pacific SST anomalies (phases 1 and 2), are associated with weaker global teleconnections, particularly over the Indian Ocean Rim. The weak regional teleconnections result in statistically insignificant precipitation modifications over East Africa and Central-Southwest Asia.  相似文献   

2.
Severe droughts in the middle-12th and late-13th centuries appear to have affected Anasazi (pre-Columbian Native American) populations. During the first drought most of the great houses in the central San Juan Basin were vacated; the second drought resulted in the abandonment of the Four Corners region. During the first drought, villages may not have been completely abandoned. The multi-year drought periods probably were characterized by reductions in both winter and summer precipitation. Maize is dependent on winter precipitation for its germination and initial growth and on summer (monsoonal) precipitation for its continued growth. Reductions in precipitation are hypothesized to have resulted in low yields of maize, the dietary staple of the Anasazi. A comparison of historic climate data and tree-ring-based reconstructions of precipitation in the Four Corners region with tree-ring-based reconstructions of the Pacific Decadal Oscillation (PDO) and the Atlantic Multidecadal Oscillation (AMO) indicate that severe and persistent drought in the Four Corners region occurs when the PDO is negative and the AMO is positive. Historic climate data from the greater San Juan Basin indicate that a negative PDO is characterized by reductions in both water-year and summer precipitation, reinforcing the concept that at least some multi-year droughts involved weakening of the summer monsoon with attendant decreases in the yields of maize.  相似文献   

3.
We developed the first tree-ring chronology, based on 73 cores from 29 Pinus tabulaeformis trees, for the Xiaolong Mountain area of central China, a region at the boundary of the Asian summer monsoon. This chronology exhibits significant (at 0.01 level) positive correlations with precipitation in May and June, and negative correlations with temperature in May, June and July. Highest linear correlation is observed between tree growth and the seasonalized (April–July) precipitation, suggesting that tree rings tend to integrate the monthly precipitation signals. Accordingly, the April–July total precipitation was reconstructed back to 1629 using these tree rings, explaining 44.7?% of the instrumental variance. A severe drought occurred in the area during the 1630s–1640s, which may be related to the weakened Asian summer monsoon caused by a low land-sea thermal gradient. The dry epoch during the 1920s–1930s and since the late 1970s may be explained by the strengthened Hadley circulation in a warmer climate. The dry (wet) epochs of the 1920s–1930s (the 1750s and 1950s) occurred during the warm (cold) phases of the El Ni?o-Southern Oscillation and the Pacific Decadal Oscillation that are often associated with weakened (strengthened) East Asian summer monsoon. These relationships indicate significant teleconnections operating over the past centuries in central China related to large-scale synoptic features.  相似文献   

4.
This study examines the sensitivity of a mid-size basin’s temperature and precipitation response to different global and regional climate circulation patterns. The implication of the North Atlantic Oscillation (NAO), El Ni?o Southern Oscillation (ENSO), Indian Monsoon and ten other teleconnection patterns of the Northern Hemisphere are investigated. A methodology to generate a basin-scale, long-term monthly surface temperature and precipitation time series has been established using different statistical tests. The Litani River Basin is the focus of this study. It is located in Lebanon, east of the Mediterranean Basin, which is known to have diverse geophysical and environmental characteristics. It was selected to explore the influence of the diverse physical and topographical features on its hydroclimatological response to global and regional climate patterns. We also examine the opportunity of conducting related studies in areas with limited long-term measured climate and/or hydrological data. Litani's monthly precipitation and temperature data have been collected and statistically extrapolated using remotely sensed data products from satellites and as well as in situ gauges. Correlations between 13 different teleconnection indices and the basin’s precipitation and temperature series are investigated. The study shows that some of the annual and seasonal temperature and precipitation variance can be partially associated with many atmospheric circulation patterns. This would give the opportunity to relate the natural climate variability with the watershed’s hydroclimatology performance and thus differentiate it from other anthropogenic induced climate change outcomes.  相似文献   

5.
利用1961-2017年松花江流域31个气象站初夏降水资料、NCEP/NCAR再分析资料,采用多种统计方法,讨论了松花江流域初夏降水时空分布及影响环流特征。结果表明：松花江流域初夏降水具有全流域一致型、西北-东南反位相型和东北-西南反位相型3个主要分布模态。影响3个分布型的主要环流特征分别为贝加尔湖以东低值系统-鄂霍茨克海阻塞高压（西南低-东北高）、乌拉尔山脊-西西伯利亚槽-外兴安岭脊（两脊一槽型）、渤海/华北低值系统及其东北部高压,东部局地高压或阻塞形势对松花江流域初夏降水的3个模态起到非常重要的作用。东亚-太平洋型和极地-欧亚型是对第一模态降水分布起重要作用的遥相关型。  相似文献   

6.
T. Mavromatis 《Climatic change》2012,110(1-2):249-267
The aim of the present study is, primarily, to compare the frequencies of exceptional hydrological and meteorological weekly events, employing the self-calibrated versions of Palmer’s drought indices (PDSI and PHDI, respectively), from 17 stations across Greece in the decade 1997–2006 with these of 1961–1990; on second level, to identify the trends and define the time lags between these two indices for the study period 1961–2006. The changes in the spatial distribution of exceptional weekly event frequencies between the most recent decade and the baseline period were similar for both drought indices. When 1997–2006 was compared with 1961–1990, the number of stations with a frequency of exceptionally dry weekly events >93rd percentile, increased by seven stations (41%) for PDSI and nine (53%) for PHDI, at the expense of exceptionally moist weekly spells. PDSI was found to lead PHDI by three to 20?weeks. If exceptional weekly events continue to be more frequent in the future, major implications for natural water resources are expected.  相似文献   

7.
El-Niño/Southern Oscillation (ENSO) variability and its relationship with precipitation in the tropics and subtropics are analysed using the ARPEGE-OPA ocean-atmosphere coupled model. Three 150-year simulations are considered, differing by greenhouse gases (GHG) and aerosols concentrations. The first one has constant (1950 level) concentrations, and the two others follow observed values till 1999, then the SRES B2 scenario until 2099. The model is able to reproduce most present-day features characteristic of ENSO in the Pacific. It also displays ENSO as the leading mode of sea-surface temperature (SST) variability, with spatial patterns and explained variance both quite similar to the observation. A detailed analysis of its teleconnections with rainfall variability is carried out on a seasonal basis. Patterns for the last part of the twentieth century compare favourably with the observation, with the notable exception of parts of the Atlantic sector. The overall strong rainfall response arises from the strong interannual variability of simulated ENSO, and also suggests an ability to simulate atmospheric dynamics in a realistic way. In the future climate, the model does not exhibit major changes in the ENSO/rainfall teleconnections. However, on a regional basis, there is some evidence of strengthening (e.g., in parts of Southern Africa) and weakening (e.g., East Africa) in the course of the twenty-first century. In most cases, decadal swings in the correlations suggest that these alterations may partly reflect natural changes in the teleconnections with ENSO, long-term correlation trends (possibly GHG-induced) being comparatively weaker.  相似文献   

8.
The atmospheric low frequency variability at a regional or global scale is represented by teleconnection. Using monthly dataset of the Climatic Research Unit (CRU) for the period 1971–2016, the impacts of four large-scale teleconnection patterns on the climate variability over Southwest Asia are investigated. The large-scale features include the El Niño-Southern Oscillation (ENSO), the North Atlantic Oscillation (NAO) and the East Atlantic (EA) teleconnection patterns, as well as western tropical Indian Ocean (WTIO) sea surface temperature anomaly index. Results indicate that ENSO and EA are the first leading modes that explain variation of Southwest Asian precipitation, with positive (negative) anomalies during El Niño (La Niña) and the negative (positive) phase of EA. Variation of Southwest Asian near-surface temperature is most strongly related to WTIO index, with above-average (below-average) temperature during the positive (negative) phase of WTIO index, although the negative (positive) phase of NAO also favours the above-average (below-average) temperature. On the other hand, temperature (precipitation) over Southwest Asia shows the least response to ENSO (WTIO). ENSO and EA individually explain 13 percent annual variance of precipitation, while WTIO index explains 36 percent annual variance of near-surface temperature over Southwest Asia. Analysis of the European Centre for Medium-Range Weather Forecasts (ECMWF) reanalysis Interim (ERA-Interim) data indicated establishments of negative (positive) geopotential height anomalies in the middle troposphere over Southwest Asia during El Niño (La Niña) or the negative (positive) phase of NAO, EA and WTIO. The response of precipitation variability over Southwest Asia to NAO is opposite to that expected from the geopotential height anomalies, but the correlation between precipitation and NAO is not statistically significant. Due to predictability of large-scale teleconnections, results of this study are encouraging for improvement of the state-of-the-art seasonal prediction of the climate over Southwest Asia.  相似文献   

9.
Theoretical and Applied Climatology - In this study, multiscale variability of monthly precipitation in Yangtze River Basin (YRB) and subregional precipitation teleconnections with climate indices...  相似文献   

10.

A long-term (1948 to 2012) trend of precipitation (annual, pre-monsoon, monsoon, and post-monsoon seasons) in Bangladesh was analyzed in different regions using both parametric and nonparametric approaches. Moreover, the possible teleconnections of precipitation (annual and monsoon) variability with El Niño/Southern Oscillation (ENSO) episode and Indian Ocean Dipole (IOD) were investigated using both average and individual (both positive and negative) values of ENSO index and IOD. Our findings suggested that for annual precipitation, a significant increasing monotonic trend was found in whole Bangladesh (4.87 mm/year), its western region (5.82 mm/year) including Rangpur (9.41 mm/year) and Khulna (4.95 mm/year), and Sylhet (10.12 mm/year) and Barisal (6.94 mm/year) from eastern region. In pre-monsoon, only Rangpur (2.88 mm/year) showed significant increasing trend, while in monsoon, whole Bangladesh (3.04 mm/year), Sylhet (7.17 mm/year), and Barisal (6.94 mm/year) showed similar trend. In post-monsoon, there was no significant trend. Our results also revealed that the precipitation (annual or monsoon) of whole Bangladesh and almost all of the spatial regions did not show any significant correlation with ENSO events, whereas the average IOD values showed significant correlation only in monsoon precipitation of western region. The individual positive IODs showed significant correlation in whole Bangladesh, western region, and its two divisions (Rajshahi and Khulna). So, in the context of Bangladesh climate, IOD has the more teleconnection to precipitation than that of ENSO. Our findings indicate that the co-occurrence of ENSO and IOD events may suppress their influence on each other.

  相似文献   

11.
基于1961~2016年四川盆地101个地面观测站逐日降水资料,计算综合气象干旱指数（CI）,应用气候倾向率、经验正交函数分解和小波分析等统计诊断方法,分析四川盆地春旱强度和天数的时空变化特征。结果表明:四川盆地西南部春旱强度高于其它地区,而盆地中部春旱天数较多,尤其是内江以北地区更为突出;近56a四川盆地春旱强度和天数的长期变化呈显著负相关,春旱天数呈减少趋势,春旱强度呈增加趋势;四川盆地春旱强度和天数的EOF第一模态方差贡献率分别为42.99%和44.24%,均反映出空间变化的整体一致性;四川盆地春旱强度和天数均存在1~4a、5~12a及14~28a的振荡周期。   相似文献   

12.
Summary The similarities in time series recorded at sites which are distant from each other are called teleconnections. In this paper, the loss of such correlations with inter-site distance was investigated for both climatic and dendrochronological data sets, with 70 tree-ring chronologies. A dense network of weather stations was studied in the southeastern French Alps, covering complex climatic gradients over three departments. 78 sites with precipitation data (with a total of 48 756 monthly values), and 48 stations that recorded temperature (with 20 722 monthly mean values) were analysed. In the same area, four coniferous species (mountain pine and stone pine, European larch and Norway spruce) provided 37 ring-width chronologies for high elevation sites near the timberline. Both silver fir and Norway spruce provided a second tree-ring chronology network for 33 different sites at lower elevations. The teleconnections between precipitation series were found to be higher than those observed for temperature over short distances, but the maximum threshold distance was lower (193 km) compared to a positive correlation distance that exceeds 500 km for temperature. The maximum temperatures had stronger teleconnections than minimum values (522 km versus 476 km), since the latter are linked more with other site factors, such as slope, exposure and local topography. As expected, the tree-ring chronologies showed weaker teleconnections than the climatic series, with a threshold distance of 374 km obtained for all high elevation forests. The coniferous species with high intra-specific teleconnections over large distances were, in decreasing importance, Pinus uncinata (> 500 km), Picea abies (477 km), Pinus cembra (over 254 km) and Larix decidua (over 189 km only). The two former species showed the highest intra-specific correlations (with mean correlation R=0.625 and 0.666). The dendrochronological teleconnections were found to have a extent lesser for trees species that depend on rainfall (such as larch, and stone pine). They are enhanced, however, for temperature sensitive species such as spruce and mountain pine (a drought resistant tree). Therefore, these two latter conifers appear to be especially suitable for climatic reconstruction over large distances in mountainous areas. However, teleconnections within silver fir (Abies alba) and spruce chronologies were sharply reduced (over 131 km and 135 km) in lower elevation forests, underlining the interest of timberline forests for dendroclimatology. A better knowledge of the spatial correlations in climatic series and ring-width data may enable the optimisation of weather station networks. It may also permit a better choice of weather stations used for dendroclimatology, either for tree-ring and climate relationship calibration or for climate reconstructions. In dendrochronology, wood dating also requires the knowledge of to what extent remote ring-width chronologies can be used. Received September 11, 2000 Revised March 26, 2001  相似文献   

13.
Summary The physical coupling between the occurrence of winter heavy precipitation in Europe and the surface large-scale circulation is studied by isolating their coupled modes with a singular value decomposition technique. The leading mode is a clear manifestation of the North Atlantic Oscillation forcing. The second mode reflects the influence of a centre-of-action in the pressure field westward of the British Isles. The Hadley Centre Coupled Model (3rd generation) is skilful in reproducing these two modes and an eastward extension of the North Atlantic Oscillation towards the Mediterranean Basin is projected under two future climatic scenarios. This extension yields an increase in the North Atlantic Oscillation forcing over the occurrence of heavy precipitation in several regions of Southern Europe, which is corroborated by the changes in the coupling of the daily precipitation. A combination of the first six coupled modes of the daily precipitation revealed that its amounts in some parts of Western Europe and the Mediterranean are effectively governed by the large-scale circulation. The model is still reasonably skilful in reproducing this large-scale coupling. The projected modifications, both in the strength and in the patterns of the coupled modes, explain important fractions of the projected changes in variance, which ultimately have implications in the occurrence of heavy precipitation in several European areas. Therefore, the ability of a model in reproducing the large-scale forcing over the daily precipitation is important for the reliability of its projections of the occurrence of heavy precipitation in Europe.  相似文献   

14.
利用1981—2013年NCEP/NCAR逐日再分析资料及OISST海温月资料,对长江中下游地区2011年冬春连旱及2013年夏季高温、干旱事件的形成机制进行对比分析。结果发现两次干旱事件:（1）均受偏强东亚季风影响,导致冷暖气流无法交汇于长江流域;（2）赤道太平洋海温距平均呈现“西正东负”,加强Walker环流的同时引发局地Hadley环流异常,致使长江流域上空长期受异常下沉气流控制;（3）均与大西洋的Rossby波有关:2011年冬春,受NAULEA遥相关型影响,Rossby波能量向东频散至亚欧大陆东部及太平洋地区堆积,使东亚大槽长期维持在120 °E附近,加强东亚冬季风;2013年夏季,受同为负位相的“silk road”及EAP遥相关型共同作用,源自北大西洋的Rossby波能量能够影响到东亚-太平洋地区,致使西太副高异常西伸,加强东亚夏季风。   相似文献   

15.
基于赣江流域39个气象站点逐月降水和气温数据,计算不同时间尺度标准化降水蒸散发指数(SPEI),采用Mann-Kendall突变检验、主成分分析(PCA)等方法,分析了赣江流域1960—2018年干旱时空变化特征.研究表明:不同时间尺度SPEI均有微弱升高的趋势,干旱形势有所缓解,SPEI能够较好地表征赣江流域旱涝情况.赣江流域中部的轻旱和特旱发生频率要高于其他地区,中旱主要高发地区主要分布在南部和西部区域,重旱主要集中在东部和北部.赣江流域干旱的空间分布具有较好的一致性,旱涝变化整体保持一致,南部与北部旱涝状态存在相反的纵向差异,且中部与南部、北部旱状况涝存在空间差异.  相似文献   

16.
马德栗  刘敏  鞠英芹 《气象科技》2016,44(4):622-630
选取长江流域沿线及三峡库区12个代表站,根据中国500年旱涝图集等级和各站建站以来5—9月降水量资料,按照旱涝等级标准,分别得到长江全流域、上游流域、中游流域、下游流域及其三峡库区1470—2011年旱涝等级序列。结果表明:长江各流域及其三峡库区均呈现较为明显的旱涝交替阶段,20世纪偏旱频率强烈增加,19世纪和20世纪偏涝频率明显增加。长江流域和三峡库区偏旱以上等级具有准160年周期震荡,全流域偏涝以上存在准140年的周期震荡,但20世纪后有所减弱,三峡库区偏涝以上等级存在准百年的周期震荡。三峡建坝蓄水前后库区降水EOF时空分布呈一致减少趋势,与此同时长江上游降水呈下降趋势,反映了长江上游流域及三峡库区气候趋旱;M-K突变检验显示水库蓄水前后流域上游和库区降水均未发生显著变化。在全球气候变化的背景下,三峡库区旱涝演变并不是孤立事件,而是与长江上游乃至整个长江流域旱涝背景密不可分。  相似文献   

17.
Summary Groundnut production strongly contributes to Senegal’s economy. Interannual variations of groundnut yield for the country as a whole, and their relationship with rainfall amounts, are examined for the 31-yr period 1960–1990. It is shown that on that scale, and after removing decadal trends, almost half of the variance is explained by rainfall variability, especially that of the early part of the rainy season (July–August). Given the high spatial coherence of seasonal rainfall in the region, teleconnections with global- and regional-scale climate dynamics, including sea-surface temperatures, are assessed. Though some features are similar to the rest of the Sahel, others are more specific, such as the higher sensitivity to ENSO (El-Ni?o Southern Oscillation) and to coupled ocean-atmosphere climate anomalies over the nearby Tropical North Atlantic Ocean, which are associated to the latitudinal location of the ITCZ over the ocean. Lag-correlations with pre-season SST are also discussed. Some of these teleconnections are used to define preliminary empirical models for rainfall and groundnut yield prediction for Senegal. Received March 23, 1998 Revised January 11, 1999  相似文献   

18.
The relationship between five teleconnection patterns (North Atlantic Oscillation (NAO), Arctic Oscillation (AO), East Atlantic/Western Russian (EAWR) pattern, Scandinavian (SCAND) pattern, and El Niño Southern Oscillation (ENSO)) and the frequency of occurrence of days (per month) with extreme precipitation in the Euro-Mediterranean region is investigated with National Centers for Environmental Prediction–National Center for Atmospheric Research reanalysis data. To quantify the teleconnection–precipitation relationships over the Euro-Mediterranean region, linear correlations are calculated between the monthly teleconnection indices for the five patterns and time series at each grid point of the monthly frequency of days with extreme precipitation, focusing on daily precipitation amounts that exceed a particular threshold value (a 90 % threshold is used). To evaluate dynamical processes, the teleconnection indices are also correlated with the frequencies of days with extreme values of dynamic tropopause pressure and precipitable water. The former quantity is used as a proxy for potential vorticity intrusions and the latter to identify regions of enhanced moisture. The results of this analysis indicates positive, statistically significant correlations between the NAO, AO, and SCAND indices and the frequency of extreme precipitation in the western Mediterranean; positive (negative) correlations between the EAWR index and the extreme precipitation frequency in the eastern (western) Mediterranean; and a positive correlation between the Niño3.4 index and the extreme precipitation frequency over the Iberian Peninsula and the Middle East. For all of the teleconnection patterns other than ENSO, the dynamic tropopause pressure correlation patterns resemble those for the precipitation. In contrast, similar precipitation and precipitable water correlation patterns are observed only for ENSO. These findings suggest that the teleconnections affect the interannual variation of the frequency of days with extreme precipitation over a large part of the Euro-Mediterranean region through their impact on the spatial distribution of regions with enhanced potential vorticity and air moisture.  相似文献   

19.
This paper analyses the role played by the North Atlantic Oscillation (NAO) in the creation of drought conditions in a semi-arid region of north-east Spain (the middle Ebro valley), from 1600 to the year 2000. The study used documents from ecclesiastical archives for the seventeenth, eighteenth and nineteenth centuries. For the twentieth century, instrumental precipitation records were used as well. A December–August drought index from 1600 to 1900 was compiled from the historical documentary sources (rogation ceremonies). The index was validated by means of precipitation records between 1858 and 1900 and independent precipitation data from 1600 reconstructed by means of dendrochronological records. Using instrumental data a drought index was also calculated (Standardized Precipitation Index, SPI) for the 1958–2000 period. We found that the NAO was important in explaining the droughts identified in the study area from documents and instrumental data. Positive values of the winter NAO index are prone to cause droughts in the middle Ebro valley. This finding has been verified since 1600 by means of two independent reconstructions of the winter NAO index. The same behaviour has been observed during the nineteenth and twentieth centuries by means of instrumental records. The climatic and geographic factors that explain the high influence of North Atlantic Oscillation on droughts in this region are discussed in depth.  相似文献   

20.
A gridded monthly precipitable water (PW) data for 1979?C2007 from the NCEP/NCAR reanalysis are used to investigate summertime interannual PW variability over Europe and its relation to the key climate parameters in the region. During summer season the first EOF mode of PW, explaining 27?C41% of its total variance, demonstrates significant month-to-month changes in its structure, thus, implying its essential non-stationarity. The second EOF mode of PW is also non-stationary during the summer season. In contrast to precipitation, both leading modes of PW are not associated with the North Atlantic Oscillation (NAO), as well as with other regional teleconnections, suggesting relatively minor role of the atmospheric dynamics in atmospheric moisture variability over Europe during summer season. Analysis of links between leading EOF modes of regional PW and air temperature (AT) has revealed a strong link between PW and AT over Europe, persisting during entire summer season. Locally, these links imply that positive (negative) AT anomalies result in enhanced (decreased) PW over particular region. Revealed links between leading modes of PW and AT highlight important role of thermodynamics in summertime PW variability over Europe. Detected relatively weak and unstable links between leading modes of PW and precipitation over Europe were somewhat expected since in contrast to atmospheric moisture, regional precipitation variability is largely driven by the atmospheric dynamics (particularly, the NAO).  相似文献   

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