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1.
Most, if not all forests in the Caribbean are subject to occasional disturbances from hurricanes. If current general circulation model (GCM) predictions are correct, with doubled atmospheric CO2 (2 × CO2), the tropical Atlantic will be between 1 °C and 4 °C warmer than it is today. With such a warming, more than twice as many hurricanes per year could be expected in the Caribbean. Furthermore, Emanuael (1987) indicates that in a warmed world the destructive potential of Atlantic hurricanes could be increased by 40% to 60%. While speculative, these increases would dramatically change the disturbance regimes affecting tropical forests in the region and might alter forest structure and composition. Global warming impacts through increased hurricane damage on Caribbean forests are presented.An individual tree, gap dynamics forest ecosystem model was used to simulate the range of possible hurricane disturbance regimes which could affect the Luquillo Experimental Forest in Puerto Rico. Model storm frequency ranged from no storms at all up to one storm per year; model storm intensity varied from no damage up to 100% mortality of trees. The model does not consider the effects of changing temperature and rainfall patterns on the forest. Simulation results indicate that with the different hurricane regimes a range of forest types are possible, ranging from mature forest with large trees, to an area in which forest trees are never allowed to reach maturity.  相似文献   

2.
Caribbean hurricanes: changes of intensity and track prediction   总被引：1，自引：0，他引：1  
The meteorological conditions of hurricanes passing near Puerto Rico (18N, 68W) are analyzed using composite daily reanalysis and satellite data. When an intense hurricane is present, the regional circulation is dominated by upper easterly flow over the Caribbean and central Atlantic and a surge of low-level westerly anomalies across the tropics. Warm SST anomalies extend along the coast of Venezuela, doubling the convective energy available to Caribbean hurricanes. Intensifying hurricanes tend to propagate westward with an atmospheric ridge over the Gulf Stream, in an environment with aerosol optical depth <0.6. Hurricanes form and strengthen in the east-shear phase of the Madden Julian Oscillation. Sinking motions and dry air appear in an anti-cyclonic gyre behind intensifying hurricanes. Numerical model 48-h forecasts of Caribbean hurricane tracks are analyzed over the period 2000–2010. A “slow right” bias is found east of Puerto Rico in comparison with observed.  相似文献   

3.
Recent intense hurricane response to global climate change   总被引：1，自引：0，他引：1  
An Anthropogenic Climate Change Index (ACCI) is developed and used to investigate the potential global warming contribution to current tropical cyclone activity. The ACCI is defined as the difference between the means of ensembles of climate simulations with and without anthropogenic gases and aerosols. This index indicates that the bulk of the current anthropogenic warming has occurred in the past four decades, which enables improved confidence in assessing hurricane changes as it removes many of the data issues from previous eras. We find no anthropogenic signal in annual global tropical cyclone or hurricane frequencies. But a strong signal is found in proportions of both weaker and stronger hurricanes: the proportion of Category 4 and 5 hurricanes has increased at a rate of ~25–30 % per °C of global warming after accounting for analysis and observing system changes. This has been balanced by a similar decrease in Category 1 and 2 hurricane proportions, leading to development of a distinctly bimodal intensity distribution, with the secondary maximum at Category 4 hurricanes. This global signal is reproduced in all ocean basins. The observed increase in Category 4–5 hurricanes may not continue at the same rate with future global warming. The analysis suggests that following an initial climate increase in intense hurricane proportions a saturation level will be reached beyond which any further global warming will have little effect.  相似文献   

4.
Belmadani  Ali  Dalphinet  Alice  Chauvin  Fabrice  Pilon  Romain  Palany  Philippe 《Climate Dynamics》2021,56(11):3687-3708

Tropical cyclones are a major hazard for numerous countries surrounding the tropical-to-subtropical North Atlantic sub-basin including the Caribbean Sea and Gulf of Mexico. Their intense winds, which can exceed 300 km h−1, can cause serious damage, particularly along coastlines where the combined action of waves, currents and low atmospheric pressure leads to storm surge and coastal flooding. This work presents future projections of North Atlantic tropical cyclone-related wave climate. A new configuration of the ARPEGE-Climat global atmospheric model on a stretched grid reaching ~ 14 km resolution to the north-east of the eastern Caribbean is able to reproduce the distribution of tropical cyclone winds, including Category 5 hurricanes. Historical (1984–2013, 5 members) and future (2051–2080, 5 members) simulations with the IPCC RCP8.5 scenario are used to drive the MFWAM (Météo-France Wave Action Model) spectral wave model over the Atlantic basin during the hurricane season. An intermediate 50-km resolution grid is used to propagate mid-latitude swells into a higher 10-km resolution grid over the tropical cyclone main development region. Wave model performance is evaluated over the historical period with the ERA5 reanalysis and satellite altimetry data. Future projections exhibit a modest but widespread reduction in seasonal mean wave heights in response to weakening subtropical anticyclone, yet marked increases in tropical cyclone-related wind sea and extreme wave heights within a large region extending from the African coasts to the North American continent.

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5.
The atmospheric circulation response to decadal fluctuations of the Atlantic meridional overturning circulation (MOC) in the IPSL climate model is investigated using the associated sea surface temperature signature. A SST anomaly is prescribed in sensitivity experiments with the atmospheric component of the IPSL model coupled to a slab ocean. The prescribed SST anomaly in the North Atlantic is the surface signature of the MOC influence on the atmosphere detected in the coupled simulation. It follows a maximum of the MOC by a few years and resembles the model Atlantic multidecadal oscillation. It is mainly characterized by a warming of the North Atlantic south of Iceland, and a cooling of the Nordic Seas. There are substantial seasonal variations in the geopotential height response to the prescribed SST anomaly, with an East Atlantic Pattern-like response in summer and a North Atlantic oscillation-like signal in winter. In summer, the response of the atmosphere is global in scale, resembling the climatic impact detected in the coupled simulation, albeit with a weaker amplitude. The zonally asymmetric or eddy part of the response is characterized by a trough over warm SST associated with changes in the stationary waves. A diagnostic analysis with daily data emphasizes the role of transient-eddy forcing in shaping and maintaining the equilibrium response. We show that in response to an intensified MOC, the North Atlantic storm tracks are enhanced and shifted northward during summer, consistent with a strengthening of the westerlies. However the anomalous response is weak, which suggests a statistically significant but rather modest influence of the extratropical SST on the atmosphere. The winter response to the MOC-induced North Atlantic warming is an intensification of the subtropical jet and a southward shift of the Atlantic storm track activity, resulting in an equatorward shift of the polar jet. Although the SST anomaly is only prescribed in the Atlantic ocean, significant impacts are found globally, indicating that the Atlantic ocean can drive a large scale atmospheric variability at decadal timescales. The atmospheric response is highly non-linear in both seasons and is consistent with the strong interaction between transient eddies and the mean flow. This study emphasizes that decadal fluctuations of the MOC can affect the storm tracks in both seasons and lead to weak but significant dynamical changes in the atmosphere.  相似文献   

6.
北大西洋年代际振荡（AMO）气候影响的研究评述   总被引：6，自引：0，他引：6  
北大西洋年代际振荡（theAtlantic Multidecadal Oscillation,AMO）是发生在北大西洋区域空间上具有海盆尺度、时间上具有多十年尺度的海表温度（sea surface temperature,SST）准周期性暖冷异常变化。它具有65～80a周期,振幅为0.4℃。AMO的形成与热盐环流的准周期性振荡有关,它是气候系统的一种自然变率。诸多研究表明,AMO在北大西洋局地气候及全球其他区域气候演变中发挥了重要影响。欧亚大陆的表面气温,美国大陆、巴西东北部、西非以及南亚的降水,北大西洋飓风等都与之密切相关。AMO对东亚季风气候的年代际变化有显著的调制作用,暖位相AMO增强东亚夏季风,减弱冬季风,冷位相则相反。本文总结了这方面的研究进展,讨论了AMO对未来气候预测的意义,认为最近20多年来我国冬季的显著增暖与AMO处于暖位相有关,是人类温室气体强迫与暖位相AMO（自然因子）两种增暖影响相叠加的结果。随着AMO逐渐转入冷位相,我国冬季变暖趋势将放慢,并有望于21世纪20年代中期逆转。  相似文献   

7.
The occurrence of first hurricane in early summer signifies the onset of an active Atlantic hurricane season. The interannual variation of this hurricane onset date is examined for the period 1979-2013. It is found that the onset date has a marked interannual variation. The standard deviation of the interannual variation of the onset day is 17.5 days, with the climatological mean onset happening on July 23.A diagnosis of tropical cyclone (TC) genesis potential index (GPI) indicates that the major difference between an early and a late onset group lies in the maximum potential intensity (MPI). A further diagnosis of the MPI shows that it is primarily controlled by the local SST anomaly (SSTA). Besides the SSTA, vertical shear and mid-tropospheric relative humidity anomalies also contribute significantly to the GPI difference between the early and late onset groups.It is found that the anomalous warm (cold) SST over the tropical Atlantic, while uncorrelated with the Niño3 index, persists from the preceding winter to concurrent summer in the early (late) onset group. The net surface heat flux anomaly always tends to damp the SSTA, which suggests that ocean dynamics may play a role in maintaining the SSTA in the tropical Atlantic. The SSTA pattern with a maximum center in northeastern tropical Atlantic appears responsible for generating the observed wind and moisture anomalies over the main TC development region. A further study is needed to understand the initiation mechanism of the SSTA in the Atlantic.  相似文献   

8.
Prediction of the Pacific sea surface temperature (SST) anomaly in the coming decades is a challenge as the SST anomaly changes over time due to natural and anthropogenic climate forcing. The climate changes in the mid-1970s and late-1990s were related to the decadal Pacific SST variability. The changes in the mid-1970s were associated with the positive phase of decadal El Niño-Southern Oscillation (ENSO)-like SST variation, and the changes in the late-1990s were related to its negative phase. However, it is not clear whether this decadal SST variability is related to any external forcing. Here, we show that the effective solar radiation (ESR), which includes the net solar radiation and the effects of volcanic eruption, has modulated this decadal ENSO-like oscillation. The eastern Pacific warming (cooling) associated with this decadal ENSO-like oscillation over the past 139 years is significantly related to weak (strong) ESR. The weak ESR with strong volcanic eruption is found to strengthen the El Niño, resulting in an El Niño-like SST anomaly on the decadal time scale. The strong eruptions of the El Chicho’n (1982) and Pinatubo (1991) volcanoes reduced the ESR during the 1980s and 1990s, respectively. The radiation reduction weakened the Walker circulation due to the “ocean thermostat” mechanism that generates eastern Pacific warming associated with a decadal El Niño-like SST anomaly. This mechanism has been confirmed by the millennium run of ECHO-G model, in which the positive eastward gradient of SST over the equatorial Pacific was simulated under the weak ESR forcing on the decadal time scale. We now experience a reversal of the trend in the ESR. The strong solar radiation and lack of strong volcanic eruptions over the past 15 years have resulted in strong ESR, which should enhance the Walker circulation, leading to a La Niña-like SST anomaly.  相似文献   

9.
Summary The objective of this study is to describe spatial and temporal patterns of sea-surface temperature (SST) variability in the Atlantic and Indian Oceans. The analysis domain extends from 40°S to 25°N and 50°W to 80°E, hence the tropical and most of the South Atlantic and central and western Indian Oceans. The investigation, covering the years 1948 to 1979, utilizes the COADS marine data set. Empirical orthogonal functions and spectral analysis are used to analyze SST fields.A major finding of this investigation is that SSTs vary coherently throughout most of the analysis domain. The greatest coherence is evident from 10°N to 30°S in the Atlantic and from 20°N to 35°S in the western Indian Ocean. Spectral analysis of regional time series shows that throughout this region the time scale of 5–6 years is the dominant one in the fluctuations; this is also the case for the Southern Oscillation and for equatorial rainfall. SST variations are roughly in-phase within each ocean and the two oceans are roughly in-phase with each other, i.e., the lags which exist are much smaller than the dominant time scale of the fluctuations. The SST anomalies appear to propagate eastward from NE Brazil; the eastern Atlantic lags the western by two to six months and the Indian Ocean lags the western Atlantic by four to eight months.With 15 Figures  相似文献   

10.
Spring rainfall secular variability is studied using observations, reanalysis, and model simulations. The joint coherent spatio-temporal secular variability of gridded monthly gauge rainfall over Ethiopia, ERA-Interim atmospheric variables and sea surface temperature (SST) from Hadley Centre Sea Ice and SST (HadISST) data set is extracted using multi-taper method singular value decomposition (MTM-SVD). The contemporaneous associations are further examined using partial Granger causality to determine presence of causal linkage between any of the climate variables. This analysis reveals that only the northwestern Indian Ocean secular SST anomaly has direct causal links with spring rainfall over Ethiopia and mean sea level pressure (MSLP) over Africa inspite of the strong secular covariance of spring rainfall, SST in parts of subtropical Pacific, Atlantic, Indian Ocean and MSLP. High secular rainfall variance and statistically significant linear trend show consistently that there is a massive decline in spring rain over southern Ethiopia. This happened concurrently with significant buildup of MSLP over East Africa, northeastern Africa including parts of the Arabian Peninsula, some parts of central Africa and SST warming over all ocean basins with the exception of the ENSO regions. The east-west pressure gradient in response to the Indian Ocean warming led to secular southeasterly winds over the Arabian Sea, easterly over central Africa and equatorial Atlantic. These flows weakened climatological northeasterly flow over the Arabian Sea and southwesterly flow over equatorial Atlantic and Congo basins which supply moisture into the eastern Africa regions in spring. The secular divergent flow at low level is concurrent with upper level convergence due to the easterly secular anomalous flow. The mechanisms through which the northwestern Indian Ocean secular SST anomaly modulates rainfall are further explored in the context of East Africa using a simplified atmospheric general circulation model (AGCM) coupled to mixed-layer oceanic model. The rainfall anomaly (with respect to control simulation), forced by the northwestern Indian Ocean secular SST anomaly and averaged over the 30-year period, exhibits prevalence of dry conditions over East and equatorial Africa in agreement with observation. The atmospheric response to secular SST warming anomaly led to divergent flow at low levels and subsidence at the upper troposphere over regions north of 5° S on the continent and vice versa over the Indian Ocean. This surface difluence over East Africa, in addition to its role in suppressing convective activity, deprives the region of moisture supply from the Indian Ocean as well as the Atlantic and Congo basins.  相似文献   

11.
Offshore wind-energy development is planned for regions where hurricanes commonly occur, such as the USA Atlantic Coast. Even the most robust wind-turbine design (IEC Class I) may be unable to withstand a Category-2 hurricane (hub-height wind speeds >50 m s\(^{-1}\)). Characteristics of the hurricane boundary layer that affect the structural integrity of turbines, especially in major hurricanes, are poorly understood, primarily due to a lack of adequate observations that span typical turbine heights (<200 m above sea level). To provide these data, we use large-eddy simulations to produce wind profiles of an idealized Category-5 hurricane at high spatial (10 m) and temporal (0.1 s) resolution. By comparison with unique flight-level observations from a field project, we find that a relatively simple configuration of the Cloud Model I model accurately represents the properties of Hurricane Isabel (2003) in terms of mean wind speeds, wind-speed variances, and power spectra. Comparisons of power spectra and coherence curves derived from our hurricane simulations to those used in current turbine design standards suggest that adjustments to these standards may be needed to capture characteristics of turbulence seen within the simulated hurricane boundary layer. To enable improved design standards for wind turbines to withstand hurricanes, we suggest modifications to account for shifts in peak power to higher frequencies and greater spectral coherence at large separations.  相似文献   

12.
A severe drought occurred in East China (EC) from August to October 2019 against a background of long-term significant warming and caused widespread impacts on agriculture and society, emphasizing the urgent need to understand the mechanism responsible for this drought and its linkage to global warming. Our results show that the warm central equatorial Pacific (CEP) sea surface temperature (SST) and anthropogenic warming were possibly responsible for this drought event. The warm CEP SST anomaly resulted in an anomalous cyclone over the western North Pacific, where enhanced northerly winds in the northwestern sector led to decreased water vapor transport from the South China Sea and enhanced descending air motion, preventing local convection and favoring a precipitation deficiency over EC. Model simulations in the Community Earth System Model Large Ensemble Project confirmed the physical connection between the warm CEP SST anomaly and the drought in EC. The extremely warm CEP SST from August to October 2019, which was largely the result of natural internal variability, played a crucial role in the simultaneous severe drought in EC. The model simulations showed that anthropogenic warming has greatly increased the frequency of extreme droughts in EC. They indicated an approximate twofold increase in extremely low rainfall events, high temperature events, and concurrently dry and hot events analogous to the event in 2019. Therefore, the persistent severe drought over EC in 2019 can be attributed to the combined impacts of warm CEP SST and anthropogenic warming.  相似文献   

13.
利用1979—2012年西北太平洋热带气旋最佳路径资料,Hadley中心的海温资料和NCEP/NCAR再分析资料等,研究了夏季(6—10月)热带北大西洋海温异常与西北太平洋热带气旋(Tropical Cyclone,TC)生成的关系及其可能机制。结果表明,夏季热带北大西洋海温异常与同期西北太平洋TC生成频次之间存在显著的负相关关系。热带北大西洋海温的异常增暖可产生一对东—西向分布的偶极型低层异常环流,其中气旋性异常环流位于北大西洋/东太平洋地区,反气旋异常环流位于西北太平洋地区。该反气旋环流异常使得TC主要生成区的对流活动受到抑制、低层涡度正异常、中低层相对湿度负异常、中层下沉气流异常,这些动力/热力条件均不利于TC生成。此外,西北太平洋地区低层涡旋动能负异常,同时来自大尺度环流的涡旋动能的正压转换也受到抑制,不能为TC的生成和发展提供额外能量源。反之亦然。  相似文献   

14.
Abstract

The relationship between sea surface temperature (SST) and rainfall index anomalies over sub‐Saharan Africa for the 15‐year period, 1970–84, has been examined. The objectively analysed monthly mean SST data were used for the global oceans between 40°S and 60°N. The rainfall data consist of annual mean rainfall indices for the Sahel and Soudan belts over north Africa.

An Empirical Orthogonal Function analysis of the SST data has been carried out for the Atlantic, Indian and global ocean regions. The results show that the most dominant eigenmode, EOF1, is characterized by warming over the central eastern Pacific, cooling over the eastern mid‐latitude Pacific and warming over the entire Atlantic and Indian ocean basins. The second EOF for the Atlantic Ocean SST analysis shows a dipole (north‐south see‐saw) pattern. The third EOF for the Atlantic SST analysis has the same sign over the entire Atlantic basin. Global SST EOF2 and EOF3 correspondió Atlantic SST EOF3 and EOF2, respectively.

The correlation between the sub‐Saharan annual rainfall index, which mainly represents the summer season rainfall from June to September, and SST EOFs shows that EOF1 has statistically significant monthly correlations for the Sahel and Soudan regions and that the warm El Niño‐like phases of SST EOF1 correspond to drought conditions. This result suggests that the large‐scale SST anomalies may be responsible for a significant component of the observed vacillation of sub‐Saharan rainfall. Some preliminary GLA GCM simulation results that support the above findings are also presented.  相似文献   

15.
An atmospheric general circulation model, the NCAR CCM, has been used to investigate the possible effects that reduced Gulf of Mexico sea surface temperatures (SST) could have on regional and hemispheric climates. 18O records and terrestrial evidence indicate at least two major glacial meltwater discharges into the Gulf of Mexico subsequent to the last glacial maximum. It is probable that these discharges reduced Gulf of Mexico SST. We have conducted three numerical experiments, with imposed gulf-wide SST coolings of 3°C, 6°C, and 12°C, and find in all three experiments significant reductions in the North Atlantic storm-track intensity, along with a strong decrease in transient eddy water vapor transport out of the Gulf of Mexico. Surface pressures are higher over the North Atlantic, indicating a reduction of the climatological Icelandic low. The region is generally cooler and drier, with a reduction in precipitation that agrees well with evidence from Greenland ice cores. Other statistically significant changes occur across the Northern Hemisphere, but vary between the three experiments. In particular, warmer, wetter conditions are found over Europe for both the 6°C and 12°C SST reductions, but cooler conditions are found for the 3°C reduction. This indicates a dependence, in both the sign and magnitude of the model response, on the magnitude of the imposed SST anomaly. The results suggest that the present-day North Atlantic storm track is dependent on warm Gulf of Mexico SST for much of its intensity. They also suggest that meltwater-induced coolings may help account, in part, for some of the climatic oscillations that occurred during the last glacial/interglacial transition.  相似文献   

16.
Long-term trends of temperature variations across the southern Andes (37–55° S) are examined using a combination of instrumental and tree-ring records. A critical appraisal of surface air temperature from station records is presented for southern South America during the 20th century. For the interval 1930–1990, three major patterns in temperature trends are identified. Stations along the Pacific coast between 37 and 43° S are characterized by negative trends in mean annual temperature with a marked cooling period from 1950 to the mid-1970s. A clear warming trend is observed in the southern stations (south of 46°S), which intensifies at higher latitudes. No temperature trends are detected for the stations on the Atlantic coast north of 45° S. In contrast to higher latitudes in the Northern Hemisphere where annual changes in temperature are dominated by winter trends, both positive and negative trends in southern South America are due to mostly changes in summer (December to February) temperatures. Changes in the Pacific Decadal Oscillation (PDO) around 1976 are felt in summer temperatures at most stations in the Pacific domain, starting a period with increased temperature across the southern Andes and at higher latitudes.Tree-ring records from upper-treeline were used to reconstruct past temperature fluctuations for the two dominant patterns over the southern Andes. These reconstructions extend back to 1640 and are based on composite tree-ring chronologies that were processed to retain as much low-frequency variance as possible. The resulting reconstructions for the northern and southern sectors of the southern Andes explain 55% and 45% ofthe temperature variance over the interval 1930–1989, respectively. Cross-spectral analysis of actual and reconstructed temperatures over the common interval 1930–1989, indicates that most of the explained varianceis at periods >10 years in length. At periods >15 years, the squaredcoherency between actual and reconstructed temperatures ranges between 0.6 and 0.95 for both reconstructions. Consequently, these reconstructions are especially useful for studying multi-decennial temperature variations in the South American sector of the Southern Hemisphere over the past 360 years. As a result, it is possible to show that the temperatures during the 20thcentury have been anomalously warm across the southern Andes. The mean annual temperatures for the northern and southern sectors during the interval 1900–1990 are 0.53 °C and 0.86 °C above the1640–1899 means, respectively. These findings placed the current warming in a longer historical perspective, and add new support for the existence of unprecedented 20th century warming over much of the globe. The rate of temperature increase from 1850 to 1920 was the highest over the past 360 years, a common feature observed in several proxy records from higher latitudes in the Northern Hemisphere.Local temperature regimes are affected by changes in planetary circulation, with in turn are linked to global sea surface temperature (SST) anomalies. Therefore, we explored how temperature variations in the southern Andes since 1856 are related to large-scale SSTs on the South Pacific and South Atlantic Oceans. Spatial correlation patterns between the reconstructions and SSTs show that temperature variations in the northern sector of the southern Andes are strongly connected with SST anomalies in the tropical and subtropical Pacific. This spatial correlation pattern resembles the spatial signature of the PDO mode of SST variability over the South Pacific and is connected with the Pacific-South American (PSA) atmospheric pattern in the Southern Hemisphere. In contrast, temperature variations in the southern sector of the southern Andes are significantly correlated with SST anomalies over most of the South Atlantic, and in less degree, over the subtropical Pacific. This spatial correlation field regressed against SST resembles the `Global Warming' mode of SST variability, which in turn, is linked to the leading mode of circulation in the Southern Hemisphere. Certainly, part of the temperature signal present in the reconstructions can be expressed as a linear combination of four orthogonal modes of SST variability. Rotated empirical orthogonal function analysis, performed on SST across the South Pacific and South Atlantic Oceans, indicate that four discrete modes of SST variability explain a third, approximately, of total variance in temperature fluctuations across the southern Andes.  相似文献   

17.
Lu Dong  Tianjun Zhou  Bo Wu 《Climate Dynamics》2014,42(1-2):203-217
The mechanism responsible for Indian Ocean Sea surface temperature (SST) basin-wide warming trend during 1958–2004 is studied based on both observational data analysis and numerical experiments with a climate system model FGOALS-gl. To quantitatively estimate the relative contributions of external forcing (anthropogenic and natural forcing) and internal variability, three sets of numerical experiments are conducted, viz. an all forcing run forced by both anthropogenic forcing (greenhouse gases and sulfate aerosols) and natural forcing (solar constant and volcanic aerosols), a natural forcing run driven by only natural forcing, and a pre-industrial control run. The model results are compared to the observations. The results show that the observed warming trend during 1958–2004 (0.5 K (47-year)?1) is largely attributed to the external forcing (more than 90 % of the total trend), while the residual is attributed to the internal variability. Model results indicate that the anthropogenic forcing accounts for approximately 98.8 % contribution of the external forcing trend. Heat budget analysis shows that the surface latent heat flux due to atmosphere and surface longwave radiation, which are mainly associated with anthropogenic forcing, are in favor of the basin-wide warming trend. The basin-wide warming is not spatially uniform, but with an equatorial IOD-like pattern in climate model. The atmospheric processes, oceanic processes and climatological latent heat flux together form an equatorial IOD-like warming pattern, and the oceanic process is the most important in forming the zonal dipole pattern. Both the anthropogenic forcing and natural forcing result in easterly wind anomalies over the equator, which reduce the wind speed, thereby lead to less evaporation and warmer SST in the equatorial western basin. Based on Bjerknes feedback, the easterly wind anomalies uplift the thermocline, which is unfavorable to SST warming in the eastern basin, and contribute to SST warming via deeper thermocline in the western basin. The easterly anomalies also drive westward anomalous equatorial currents, against the eastward climatology currents, which is in favor of the SST warming in the western basin via anomalous warm advection. Therefore, both the atmospheric and oceanic processes are in favor of the IOD-like warming pattern formation over the equator.  相似文献   

18.
Liguang Wu  Li Tao 《Climate Dynamics》2011,36(9-10):1851-1864
Although previous studies reported upward trends in the basin-wide average lifetime, annual frequency, proportion of intense hurricanes and annual accumulated power dissipation index of Atlantic tropical cyclones (TCs) over the past 30?years, the basin-wide intensity did not increase significantly with the rising sea surface temperature (SST). Observational analysis and numerical simulation conducted in this study suggest that Sahel rainfall is the key to understanding of the long-term change of Atlantic TC intensity. The long-term changes of the basin-wide TC intensity are generally associated with variations in Sahara air layer (SAL) activity and vertical wind shear in the main development region (MDR), both of which are highly correlated with Sahel rainfall. The drying Sahel corresponds to an equatorward shift in the African easterly jet and African easterly wave activity, introducing the SAL to lower latitudes and increasing the MDR vertical wind shear. As a result, Atlantic TCs are more vulnerable to the suppressing effects of the SAL and vertical wind shear. Since the SST warming, especially in the tropical Indian Ocean, is a dominant factor for the Sahel drying that occurred over the past 30?years, it is suggested that the remote effect of SST warming is important for the long-term change of Atlantic TC intensity. Although influence of the AMO warm phase that started in the early 1990s alone can provide a favorable condition for TC intensification, its influence may have been offset by the influence of the ongoing SST warming, particularly in the Indian Ocean. As a result, there was no significant trend observed in the basin-wide average and peak intensity of Atlantic TCs.  相似文献   

19.
Summary  The growth rates of amplifying mid-tropospheric perturbations in tropical North Africa is known to reduce with increased vertical shear in the troposphere. This phenomenon leads to a reduction in the frequency of generation of squall lines – the main rain-producing mechanism in tropical North Africa – because squalls are initiated by amplifying modes of African Easterly Waves (AEW). Ultimately, therefore, tropical North Africa experiences a shortfall, with respect to long-term averages, in annual rainfall. Weakening of AEW intensity is shown to be linked with the warming up to the sea-surface temperatures (SST) of the South Atlantic, Pacific and Indian Oceans. These findings are consistent with the observed reduction in the incidence of intense hurricanes along the entire westem Atlantic in Sahelian dry years. It is shown that the frequency of occurrence of Atlantic tropical storms and hurricanes is unaffected by the dryness or otherwise in the Sahel, but the paths of the storms are determined by the zonal exit point, from the African continental land mass to the Atlantic, of West African disturbance lines. These results have applications, and implications, in the level of preparedness for the economic impacts of Atlantic storms and hurricanes. Received June 8, 1996 Revised June 8, 2000  相似文献   

20.
Atlantic Basin Hurricanes: Indices of Climatic Changes   总被引：7，自引：0，他引：7  
Accurate records of basinwide Atlantic and U.S. landfalling hurricanes extend back to the mid 1940s and the turn of the century, respectively, as a result of aircraft reconnaissance and instrumented weather stations along the U.S. coasts. Such long-term records are not exceeded elsewhere in the tropics. The Atlantic hurricanes, U.S. landfalling hurricanes and U.S. normalized damage time series are examined for interannual trends and multidecadal variability. It is found that only weak linear trends can be ascribed to the hurricane activity and that multidecadal variability is more characteristic of the region. Various environmental factors including Caribbean sea level pressures and 200mb zonal winds, the stratospheric Quasi-Biennial Oscillation, the El Niño-Southern Oscillation, African West Sahel rainfall and Atlantic sea surface temperatures, are analyzed for interannual links to the Atlantic hurricane activity. All show significant, concurrent relationships to the frequency, intensity and duration of Atlantic hurricanes. Additionally, variations in the El Niño-Southern Oscillation are significantly linked to changes in U.S. tropical cyclone-caused damages. Finally, much of the multidecadal hurricane activity can be linked to the Atlantic Multidecadal Mode - an empirical orthogonal function pattern derived from a global sea surface temperature record. Such linkages may allow for prediction of Atlantic hurricane activity on a multidecadal basis. These results are placed into the context of climate change and natural hazards policy.  相似文献   

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