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1.
Using a high-resolution precipitation dataset,the present study detected that the mountainous area of central China(MACA)is a hotspot of ENSO’s impact on the summer rainfall variability.Further analysis suggests that both ENSO and atmospheric forcing make contributions to the summer rainfall variability in MACA.The dominant rainfall-related SST mode features as a seasonal transition from an El Niño-like warming in the preceding winter to a La Nina-like cooling in the following autumn,and it explains about 29%of the total variance of the rainfall during 1951–2018.It indicates that ENSO with a rapid phase transition is responsible for inducing summer rainfall anomalies in MACA.Besides,an upperlevel circumglobal wave mode in the Northern Hemisphere during summer also explains about 29%of the summer rainfall variance.Contributions of both the SST and the atmospheric modes have experienced interdecadal changes.The influence of the SST mode gradually increases and plays a dominant role in the recent decades,suggesting that ENSO with a rapid phase transition becomes more important for rainfall prediction in MACA. 相似文献
2.
Annalisa Bracco Fred Kucharski Franco Molteni Wilco Hazeleger Camiel Severijns 《Climate Dynamics》2007,28(5):441-460
This study investigates how accurately the interannual variability over the Indian Ocean basin and the relationship between the Indian summer monsoon and the El Niño Southern Oscillation (ENSO) can be simulated by different modelling strategies. With a hierarchy of models, from an atmospherical general circulation model (AGCM) forced by observed SST, to a coupled model with the ocean component limited to the tropical Pacific and Indian Oceans, the role of heat fluxes and of interactive coupling is analyzed. Whenever sea surface temperature anomalies in the Indian basin are created by the coupled model, the inverse relationship between the ENSO index and the Indian summer monsoon rainfall is recovered, and it is preserved if the atmospherical model is forced by the SSTs created by the coupled model. If the ocean model domain is limited to the Indian Ocean, changes in the Walker circulation over the Pacific during El-Niño years induce a decrease of rainfall over the Indian subcontinent. However, the observed correlation between ENSO and the Indian Ocean zonal mode (IOZM) is not properly modelled and the two indices are not significantly correlated, independently on season. Whenever the ocean domain extends to the Pacific, and ENSO can impact both the atmospheric circulation and the ocean subsurface in the equatorial Eastern Indian Ocean, modelled precipitation patterns associated both to ENSO and to the IOZM closely resemble the observations. 相似文献
3.
Relationships between intraseasonal rainfall variability of coastal Tanzania and ENSO 总被引：1，自引：0，他引：1
Summary The influence of ENSO on intraseasonal variability over the Tanzanian coast during the short (OND) and long (MAM) rainy seasons is examined. In particular, variability in the rainfall onset, peak and end dates as well as dry spells are considered. In general, El Niño appears to be associated with above average rainfall while La Niña is associated with below average rainfall over the northern Tanzanian coast during OND, and to lesser extent MAM. Over the southern coast, the ENSO impacts are less coherent and this region appears to be a transition zone between the opposite signed impacts over equatorial East and southern Africa. The increased north coast rainfall during El Niño years is generally due to a longer than normal rainfall season associated with early onset while reduced rainfall during La Niña years tends to be associated with a late onset, and thus a shorter than average rainfall season. Wet conditions during El Niño years were associated with enhanced convection and low-level easterly anomalies over the equatorial western Indian Ocean implying enhanced advection of moisture from the Indian Ocean while the reverse is true for La Niña years. Hovmöller plots for OLR and zonal wind at 850 hPa and 200 hPa show eastward, westward propagating and stationary features over the Indian Ocean. It was observed that the propagating features were absent during strong El Niño years. Based on the Hovmöller results, it is observed that the convective oscillations over the Tanzanian coast have some of the characteristic features of intraseasonal oscillations occurring elsewhere in the tropics. 相似文献
4.
Summary Separate predictive models are created for the Caribbean early wet season (May–June–July) and late wet season (August–September–October). Simple correlations are used to select predictors for a Caribbean rainfall index and predictive equations are formulated using multiple linear regression. The process is repeated after long term trends are removed from the Caribbean rainfall index and the models validated using a number of statistical methods. Four variables are confirmed as predictors for the early season: Caribbean sea surface temperature anomalies, tropical North Atlantic sea level pressure anomalies, vertical shear anomalies in the equatorial Atlantic, and the size of the Atlantic portion of the Western Hemisphere Warm Pool. Only the first two are retained in the late season model. On the interannual time-scale, equatorial Pacific sea surface temperature anomalies become significant in both seasons. The NINO3 index is retained among the predictors for the early season, and zonal gradients of sea surface temperature between the equatorial Pacific and tropical Atlantic are retained for the late season. The results also indicate spatial variation in the importance of the seasonal predictors. 相似文献
5.
Trevor C. Hall Andrea M. Sealy Tannecia S. Stephenson Shoji Kusunoki Michael A. Taylor A. Anthony Chen Akio Kitoh 《Theoretical and Applied Climatology》2013,113(1-2):271-287
Present-day (1979–2003) and future (2075–2099) simulations of mean and extreme rainfall and temperature are examined using data from the Meteorological Research Institute super-high-resolution atmospheric general circulation model. Analyses are performed over the 20-km model grid for (1) a main Caribbean basin, (2) sub-regional zones, and (3) specific Caribbean islands. Though the model’s topography underestimates heights over the eastern Caribbean, it captures well the present-day spatial and temporal variations of seasonal and annual climates. Temperature underestimations range from 0.1 °C to 2 °C with respect to the Japanese Reanalysis and the Climatic Research Unit datasets. The model also captures fairly well sub-regional scale variations in the rainfall climatology. End-of-century projections under the Intergovernmental Panel on Climate Change SRES A1B scenario indicate declines in rainfall amounts by 10–20 % for most of the Caribbean during the early (May–July) and late (August–October) rainy seasons relative to the 1979–2003 baselines. The early dry season (November–January) is also projected to get wetter in the far north and south Caribbean by approximately 10 %. The model also projects a warming of 2–3 °C over the Caribbean region. Analysis of future climate extremes indicate a 5–10 % decrease in the simple daily precipitation intensity but no significant change in the number of consecutive dry days for Cuba, Jamaica, southern Bahamas, and Haiti. There is also indication that the number of hot days and nights will significantly increase over the main Caribbean basin. 相似文献
6.
Caribbean Sea rainfall variability during the rainy season and relationship to the equatorial Pacific and tropical Atlantic SST 总被引：1，自引：1，他引：0
The present study investigates the Caribbean Sea rainfall variability during the early and late rainy seasons and its association with sea surface temperature (SST) and air?Csea interaction based on observational estimates, the NCEP Climate Forecast System (CFS) and Global Forecast System (GFS) simulations, and the CFS retrospective forecasts. Analysis of the observational estimates indicates that air?Csea interaction is important over the Caribbean Sea, whereas the atmospheric forcing of SST dominates over the Gulf of Mexico. The CFS simulation captures the basic elements of this observed air?Csea relationship. The GFS simulation produces spurious SST forcing of the atmosphere over the Gulf of Mexico largely due to prescribing SST. The CFS forecasts capture the air?Csea relationship in the late rainy season (August?COctober), but cannot reproduce the SST forcing of atmosphere over the Caribbean Sea in the early rainy season (May?CJuly). An empirical orthogonal function (EOF) analysis indicates that the leading modes of percent anomalies of the rainy season precipitation have the largest loading in the southern Caribbean Sea in observations. The model simulations and forecasts skillfully reproduce the spatial pattern, but not the temporal evolution. The Caribbean Sea rainfall variability in the early rainy season is mainly due to the tropical North Atlantic (TNA) SST anomalies in observations, is contributed by both the TNA and eastern equatorial Pacific (EEP) SST anomalies in the CFS simulation, and has an overly large impact from the EEP SST anomalies in the GFS simulation and the CFS forecasts. The observed Caribbean Sea rainfall variability in the late rainy season has a leading impact from the EEP SST anomalies, with a secondary contribution from the TNA SST anomalies. In comparison, the model simulations and forecasts overestimate the impacts of the EEP SST anomalies due to an earlier development and longer duration of the El Ni?o-Southern Oscillation in the CFS compared to observations. 相似文献
7.
Abstract Teleconnections between sea surface temperature (SST) anomalies over the Pacific and the dominant patterns of wintertime Northern Hemisphere 500‐hPa height are examined by applying statistical techniques such as rotated principal component analysis and composite analysis. It is shown that the Pacific/North American (PNA) patterns in December through March are correlated most significantly with the ENSO‐related SST anomalies in the previous October, while the western Pacific (WP) patterns in December through February are most closely linked to the ENSO‐related SST anomalies in the same season. In addition, the PNA response to the ENSO signal during La Niña events is more significant than that during El Niño events, while the WP response is stronger during El Niño events than during La Niña events. A composite analysis shows that in the El Niño winters the North Pacific centre of the PNA pattern is located about 10 degrees east of its normal position, leading to a less significant correlation between the ENSO signal and the PNA pattern in these winters. The ENSO‐related SST anomalies include a large centre of action over the tropical Pacific and an oppositely signed anomaly centre over the North Pacific. The North Pacific centre appears to the west of the dateline in September and October. This ENSO‐related seed of SST anomalies slowly moves eastward in the following months, gradually cutting off its connection with SST anomalies over the tropical Pacific and being coupled with the PNA pattern. It is pointed out that, although the wintertime SST anomaly over the North Pacific may appear as a mode linearly independent of the ENSO signal in the same season, it is partially related to the ENSO signal in the preceding autumn. Possible dynamical explanations of the above results are discussed. It is suggested that the WP pattern can be linked to the tropical Pacific heat source via advection of vorticity by the upper‐tropospheric divergent/convergent flow, and the intensification of vorticity gradients associated with a stronger east Asian jet is likely to be responsible for a more significant WP pattern response to the ENSO signal in the El Niño winters. On the other hand, the ENSO‐related PNA pattern could be considered a manifestation of the eastward extension (El Niño) or westward withdrawal (La Niña) of the east Asian jet stream due to the local Hadley cell over the Pacific. In addition, the ENSO‐related seed of extratropical SST anomaly over the western Pacific in autumn may also play an important role in the development of the PNA pattern in the following winter. 相似文献
8.
Raphael Neukom David J. Nash Georgina H. Endfield Stefan W. Grab Craig A. Grove Clare Kelso Coleen H. Vogel Jens Zinke 《Climate Dynamics》2014,42(9-10):2713-2726
This study presents the first consolidation of palaeoclimate proxy records from multiple archives to develop statistical rainfall reconstructions for southern Africa covering the last two centuries. State-of-the-art ensemble reconstructions reveal multi-decadal rainfall variability in the summer and winter rainfall zones. A decrease in precipitation amount over time is identified in the summer rainfall zone. No significant change in precipitation amount occurred in the winter rainfall zone, but rainfall variability has increased over time. Generally synchronous rainfall fluctuations between the two zones are identified on decadal scales, with common wet (dry) periods reconstructed around 1890 (1930). A strong relationship between seasonal rainfall and sea surface temperatures (SSTs) in the surrounding oceans is confirmed. Coherence among decadal-scale fluctuations of southern African rainfall, regional SST, SSTs in the Pacific Ocean and rainfall in south-eastern Australia suggest SST-rainfall teleconnections across the southern hemisphere. Temporal breakdowns of the SST-rainfall relationship in the southern African regions and the connection between the two rainfall zones are observed, for example during the 1950s. Our results confirm the complex interplay between large-scale teleconnections, regional SSTs and local effects in modulating multi-decadal southern African rainfall variability over long timescales. 相似文献
9.
ENSO事件对我国季节降水和温度的影响 总被引：82，自引：11，他引：82
对近40年来ENSO当年和次年我国季节降水和温度异常进行了合成分析和信度检验。结果表明，ENSO当年我国以少雨、低温为主，次年则相反。降水和温度异常季节变化也基本呈相反趋势。长江中下游地区显著降水异常并不发生在夏季，而在ENSO当年春、秋季和次年春季；东北地区最显著的低温也不在夏季，而在ENSO当年秋季至次年春季。根据本文结果对目前ENSO影响研究中的有关问题提出了看法。 相似文献
10.
Using observations of rainfall and SST analysis it is shown that there is a robust relationship with two-season lag between the austral summer (December–January–February [DJF]) Equatorial Amazon (EA) rainfall and the following boreal summer season (June–July–August [JJA]) Intra-Americas Seas (IAS) Sea Surface Temperature Anomalies (SSTA). It is observed that in wetter than normal austral summer seasons over EA, the SSTA in the IAS are cooler than normal in the following JJA season. This teleconnection also manifests in the ocean heat content of the IAS region. Our analysis indicates that the net surface heat flux into the ocean (particularly the surface longwave and the shortwave radiative fluxes) dictates the strongest influence on the JJA Caribbean SSTA, the core region of the IAS where the observed teleconnection with EA rainfall is strongest. This study also finds that this teleconnection is in fact a manifestation of the remote ENSO forcing on the Caribbean SSTA through its modulation of the EA rainfall anomalies. In a wet DJF year over EA, the Atlantic Inter-Tropical Convergence Zone (ITCZ) moves further southward than climatology. This causes the dry limb of the associated overturning circulation of the Atlantic ITCZ to reside over the Caribbean Sea region in the subsequent March–April–May and JJA seasons. As a result of this large-scale descent in the wet DJF year over EA, there is a net decrease in the heat flux into the ocean from increased emission of surface longwave radiation in the presence of anomalously dry atmosphere. In a dry DJF year over EA the Atlantic ITCZ is nearly co-located in the core region of the IAS, which is northward than the climatological location, resulting in the descending limb of the overturning location to be located further south of the Caribbean Sea leading to warmer SSTA. 相似文献
11.
An Atlantic influence on Amazon rainfall 总被引：2，自引：2，他引：0
Rainfall variability over the Amazon basin has often been linked to variations in Pacific sea surface temperature (SST), and in particular, to the El Niño/Southern Oscillation (ENSO). However, only a fraction of Amazon rainfall variability can be explained by ENSO. Building upon the recent work of Zeng (Environ Res Lett 3:014002, 2008), here we provide further evidence for an influence on Amazon rainfall from the tropical Atlantic Ocean. The strength of the North Atlantic influence is found to be comparable to the better-known Pacific ENSO connection. The tropical South Atlantic Ocean also shows some influence during the wet-to-dry season transition period. The Atlantic influence is through changes in the north-south divergent circulation and the movement of the ITCZ following warm SST. Therefore, it is strongest in the southern part of the Amazon basin during the Amazon’s dry season (July–October). In contrast, the ENSO related teleconnection is through anomalous east-west Walker circulation with largely concentrated in the eastern (lower) Amazon. This ENSO connection is seasonally locked to boreal winter. A complication due to the influence of ENSO on Atlantic SST causes an apparent North Atlantic SST lag of Amazon rainfall. Removing ENSO from North Atlantic SST via linear regression resolves this causality problem in that the residual Atlantic variability correlates well and is in phase with the Amazon rainfall. A strong Atlantic influence during boreal summer and autumn is particularly significant in terms of the impact on the hydro-ecosystem which is most vulnerable during the dry season, as highlighted by the severe 2005 Amazon drought. Such findings have implications for both seasonal-interannual climate prediction and understanding the longer-term changes of the Amazon rainforest. 相似文献
12.
我国四季极端雨日数时空变化及其与海表温度异常的关系 总被引：3，自引：0，他引：3
利用1960—2004年我国586个气象站的逐日降水观测资料,对每个季节和每个站点,以雨日降水量升序排列的第90个百分位值定义极端日降水阈值,分析揭示了我国四季极端雨日数的时空变化特征、与海表温度异常的关系以及相联系的大气环流异常型。结果表明,我国长江流域极端雨日数在冬季和夏季呈显著增加趋势,华北地区极端雨日数在冬季显著增加、而在夏季显著减少,华南地区极端雨日数在春季显著增加,东北地区极端雨日数在冬季和春季显著增加,而西北地区极端雨日数在四季均显著增加。各季极端雨日数在线性趋势变化之上表现年际和年代际变化特征,并且其典型异常型明显不同,春、秋季表现为长江以南与以北地区反位相的"偶极型"变化,夏季表现为长江流域与华南、华北地区反位相的"三极型"变化,冬季表现为全国大部分地区同位相的"单极型"变化。我国季节极端雨日数与印度洋-太平洋海表温度异常的关系主要表现为与ENSO的关系,而ENSO影响我国极端降水异常是通过相应的大气环流异常型来实现的。 相似文献
13.
Summary A general circulation model is used to study the response of the atmosphere to an idealised sea surface temperature (SST) anomaly pattern (warm throughout the southern midlatitudes, cool in the tropics) in the South Indian Ocean region. The anomaly imposed on monthly SST climatology captures the essence of patterns observed in the South Indian Ocean during both ENSO events and multidecadal epochs, and facilitates diagnosis of the model response. A previous study with this anomaly imposed in the model examined differences in the response between that on the seasonal scale (favours enhancement of the original SST anomaly) and that on the decadal scale (favours damping of the anomaly). The current study extends that work firstly by comparing the response on the intraseasonal, seasonal and interannual scales, and secondly, by assessing the changes in the circulation and rainfall over the adjoining African landmass.It is found that the atmospheric response is favourable for enhancement of the original SST anomaly on scales up to, and including, annual. However, as the scale becomes interannual (i.e., 15–21 months after imposition of the anomaly), the model response suggests that damping of the original SST anomaly becomes likely. Compared to the shorter scale response, the perturbation pressure and wind distribution on the interannual scale is shifted poleward, and is more reminiscent of the decadal response. Winds are now stronger over the warm anomaly in the southern midlatitudes suggesting enhanced surface fluxes, upper ocean mixing, and consequently, a damping of the anomaly.Examination of the circulation and rainfall patterns indicates that there are significant anomalies over large parts of southern Africa during the spring, summer and autumn seasons for both short (intraseasonal to interannual) and decadal scales. It appears that rainfall anomalies are associated with changes in the advection of moist tropical air from the Indian Ocean and its related convergence over southern Africa. Over eastern equatorial Africa, the austral autumn season (the main wet season) showed rainfall increases on all time scales, while parts of central to eastern subtropical southern Africa were dry. The signals during summer were more varied. Spring showed generally dry conditions over the eastern half of southern Africa on both short and decadal time scales, with wet areas confined to the west. In all cases, the magnitude of the rainfall anomalies accumulated over a 90 day season were of the order of 90–180 mm, and therefore represent a significant fraction of the annual total of many areas. It appears that relatively modest SST anomalies in the South Indian Ocean can lead to sizeable rainfall anomalies in the model. Although precipitation in general circulation models tends to be less accurately simulated than many other variables, the model results, together with previous observational work, emphasize the need for ongoing monitoring of SST in this region.With 14 Figures 相似文献
14.
Seasonal persistence and propagation of intraseasonal patterns over the Indian monsoon region 总被引：1，自引：0，他引：1
The space-time evolution of convection over the monsoon region containing the Indian subcontinent, the Indian Ocean and the West Pacific has been studied. A multi-channel singular spectrum analysis of the daily outgoing longwave radiation has yielded two intraseasonal oscillatory patterns and two large-scale standing patterns as the most dominant modes of intraseasonal variability. The oscillatory modes vary on time scales of about 45 and 28 days and their average cycles of variability are shown to correspond to the life cycles of active and break periods of monsoon rainfall over India. During an active (break) cycle, a convection (dry) anomaly zone first appears in the equatorial Indian Ocean, subsequently expands to cover the Indian subcontinent and finally contracts to disappear in the northern part of India. Some eastward and northward movements are found to be associated with both oscillatory modes, while westward movement may also be associated with the 28-day mode. The oscillatory modes are shown to have a large spatial scale extending to the West Pacific. One of the standing modes has anomalies of uniform sign covering the entire region and is related to El Niño and southern oscillation (ENSO) pattern. The other standing mode has a dipole structure in the equatorial Indian Ocean associated with large-scale anomalies over India with the same sign as those over the western part of the dipole. These two standing modes persist throughout the monsoon season, each maintaining its respective pattern. The seasonal mean monsoon is mainly determined by the two standing patterns, without much contribution from the oscillatory modes. The relative role of the standing patterns (ENSO mode and dipole mode) seems to be important in determining the seasonal mean during certain years. 相似文献
15.
B. Scian J. C. Labraga W. Reimers O. Frumento 《Theoretical and Applied Climatology》2006,85(1-2):89-106
Summary There is a widely held view that the Pampa region (PR) dry and wet periods are predominantly a consecuence of the El Ni?o-Southern
oscillation (ENSO) phenomenom. The current paper focuses on non-ENSO rainfall anomalies for the period 1948–2000, the more
recent of which have had catastrophic consequences throughout the region. We analyze horizontal water vapor transport, pressure
and circulation anomalies occurring in Southern South America (SSA) during this type of event. Positive and negative (wet
and dry) extreme events during the rainy and dry seasons in the region were registered. Based on NCEP reanalysis data it was
established that under rainfall deficit, anomalies of similar intensity occurred simultaneously in the PR and in central Chile,
whereas under excess rainfall the anomalies were mostly confined to the PR. The existence of a cyclone-anticyclone pair in
the anomalous circulation pattern over mid latitudes of the Atlantic and Pacific oceans and straddling the southern portion
of the continent maintains an intense and extense meridional circulation over the continental plains, which leads to the abnormal
values in moisture transport and rainfall rate. The atmospheric water balance equation calculated for the PR indicates that
anomalous water vapor is carried in from the continental equatorial region and from the subtropical Atlantic, its magnitude
varying in accordance with the season and the sign of the anomaly. Furthermore, evidence of the important role of transient
terms corroborates their contribution to the anomalous total moisture flux divergence under rainfall deficit during the dry
season. The mean sea-level pressure anomaly fields of the extreme cases were further examined by principal component analysis
to discern those circulation features directly linked to rainfall deviations. 相似文献
16.
A westward extension of the warm pool leads to a westward extension of the Walker circulation, drying eastern Africa 总被引：6，自引：2，他引：4
Observations and simulations link anthropogenic greenhouse and aerosol emissions with rapidly increasing Indian Ocean sea surface temperatures (SSTs). Over the past 60?years, the Indian Ocean warmed two to three times faster than the central tropical Pacific, extending the tropical warm pool to the west by ~40° longitude (>4,000?km). This propensity toward rapid warming in the Indian Ocean has been the dominant mode of interannual variability among SSTs throughout the tropical Indian and Pacific Oceans (55°E?C140°W) since at least 1948, explaining more variance than anomalies associated with the El Ni?o-Southern Oscillation (ENSO). In the atmosphere, the primary mode of variability has been a corresponding trend toward greatly increased convection and precipitation over the tropical Indian Ocean. The temperature and rainfall increases in this region have produced a westward extension of the western, ascending branch of the atmospheric Walker circulation. Diabatic heating due to increased mid-tropospheric water vapor condensation elicits a westward atmospheric response that sends an easterly flow of dry air aloft toward eastern Africa. In recent decades (1980?C2009), this response has suppressed convection over tropical eastern Africa, decreasing precipitation during the ??long-rains?? season of March?CJune. This trend toward drought contrasts with projections of increased rainfall in eastern Africa and more ??El Ni?o-like?? conditions globally by the Intergovernmental Panel on Climate Change. Increased Indian Ocean SSTs appear likely to continue to strongly modulate the Warm Pool circulation, reducing precipitation in eastern Africa, regardless of whether the projected trend in ENSO is realized. These results have important food security implications, informing agricultural development, environmental conservation, and water resource planning. 相似文献
17.
Chang-Hoi Ho Woosuk Choi Jinwon Kim Maeng-Ki Kim Hee-Dong Yoo 《Asia-Pacific Journal of Atmospheric Sciences》2016,52(4):395-403
A number of studies in the past two decades have attempted to find the relationship between the precipitation in Korea and the El Niño-Southern Oscillation (ENSO) on various time scales. Comprehensive analyses of station precipitation data in Korea for the 61-year period, 1954-2014, in this study show that the effects of ENSO on the seasonal precipitation in Korea are practically negligible. The correlation between summer precipitation and ENSO is insignificant regardless of the intensity, type (e.g., eastern-Pacific or central-Pacific), and stage (e.g., developing, mature, or decaying) of ENSO. Somewhat meaningful correlation between ENSO and precipitation in Korea occurs only in the ENSO-developing fall. Because summer rainfall accounts for over half of the annual total and fall is a dry season in Korea, the overall effects of ENSO on precipitation in Korea are practically nonexistent. 相似文献
18.
Rainfall during the warm season (June 15–October 15) is the most important of the year in terms of flood generation and erosion in rivers of the southern Colorado Plateau. Fluvial erosion of the plateau decreased substantially in the 1930s to early 1940s, although the cause of this change has not been linked to variation of warm-season rainfall. This study shows that a decrease of warmseason rainfall frequency was coincident with and probably caused the decreased erosion by reducing the probability of large floods. Warm-season rainfall results from isolated thunderstorms associated with the Southwestern monsoon and from dissipating tropical cyclones and (or) cutoff low-pressure systems that produce widespread, general rainfall. Warm-season rainfall is typically normal to above normal during warm El Niño-Southern Oscillation (ENSO) conditions. A network of 24 long-term precipitation gages was used to develop an index of standardized rainfall anomalies for the southern Colorado Plateau for the period 1900–85. The index shows that the occurrence of anomalously dry years increased and the occurrence of anomalously wet years decreased after the early 1930s, although 1939–41, 1972, and 1980–84 were anomalously wet. The decrease in warm-season rainfall after the early 1930s is related to a decrease in rainfall from dissipating tropical cyclones, shifts in the incidence of meridional circulation in the upper atmosphere, and variability of ENSO conditions. 相似文献
19.
Present-day and future Amazonian precipitation in global climate models: CMIP5 versus CMIP3 总被引：2，自引：1，他引：1
The present study aims at evaluating and comparing precipitation over the Amazon in two sets of historical and future climate simulations based on phase 3 (CMIP3) and 5 (CMIP5) of the Coupled Model Intercomparison Project. Thirteen models have been selected in order to discuss (1) potential improvements in the simulation of present-day climate and (2) the potential reduction in the uncertainties of the model response to increasing concentrations of greenhouse gases. While several features of present-day precipitation—including annual cycle, spatial distribution and co variability with tropical sea surface temperature (SST)—have been improved, strong uncertainties remain in the climate projections. A closer comparison between CMIP5 and CMIP3 highlights a weaker consensus on increased precipitation during the wet season, but a stronger consensus on a drying and lengthening of the dry season. The latter response is related to a northward shift of the boreal summer intertropical convergence zone in CMIP5, in line with a more asymmetric warming between the northern and southern hemispheres. The large uncertainties that persist in the rainfall response arise from contrasted anomalies in both moisture convergence and evapotranspiration. They might be related to the diverse response of tropical SST and ENSO (El Niño Southern Oscillation) variability, as well as to spurious behaviours among the models that show the most extreme response. Model improvements of present-day climate do not necessarily translate into more reliable projections and further efforts are needed for constraining the pattern of the SST response and the soil moisture feedback in global climate scenarios. 相似文献
20.
ENSO及其组合模态对中国东部各季节降水的影响 总被引：7，自引：1，他引：6
近期的研究发现,热带太平洋低层大气存在两种主要模态,即经向对称ENSO模态和ENSO与海表温度(SST)年循环相互作用产生的经向反对称组合模态。主要探讨了这两种不同ENSO模态对中国东部各季节降水的影响。结果表明,厄尔尼诺年秋季,中国西南、长江及华南大部分区域呈现显著正降水异常;冬季,正降水异常范围扩大,覆盖华南、华东及华北东南部地区。这两个季节的异常降水都主要受ENSO模态的影响。与ENSO模态相关的正异常海温局地强迫导致120°E以西出现反气旋性环流,其西北侧增强的西南暖湿气流使得中国东部地区降水增多。次年春季,从中国华南延伸到东北出现正的异常降水,主要是ENSO组合模态的贡献。因为次年春季热带太平洋地区ENSO模态信号只局限于赤道地区,并没有对中国东部降水有显著的影响,而ENSO与海温年循环相互作用的组合模态使得与ENSO相关的赤道大气异常可以扩展到赤道以外地区。ENSO组合模态对中国降水异常有重要影响,在今后的研究和短期预测中需引起重视。 相似文献