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1.
Summary This paper is to promote a further understanding of the interdecadal mode of the South Pacific. With this focus, we will specifically aim at better understanding the difference between interannual and interdecadal SSTA modes over South Pacific. We define the difference of the normalization area-averaged SSTA in the southern extratropical Pacific (160° W–110° W, 40° S–25° S) and the south subpolar Pacific (150° W–110° W, 60° S–45° S) as the South Pacific interdecadal index (I spd). It is found that the interannual mode is more coherent than the interdecadal mode in the central and eastern tropical Pacific, and the interdecadal mode is significant only during boreal winter (DJF). The interdecadal variation of SSTA firstly occurring in the extratropic South Pacific propagates to the western boundary of the South Pacific, then moves northeast to cross the equator, and finally reaches the central tropic Pacific. It takes about 8 years to propagate from southeast subtropical Pacific to the north hemisphere. The previous studies have suggested the mechanism of waves in the subsurface in the South Pacific. Our study also highlights the Rossby waves play important roles in linkage between the extratropics-tropics South Pacific SSTA on interdecadal time scales. Moreover, the paper shows that the interdecadal variability originated in the extrotropic southeast Pacific is mainly induced by interannual variability in the tropic Pacific.  相似文献   

2.
Summary One of the greatest challenges in tropical weather forecasting is the rapid intensification (RI) of the tropical cyclone (TC), during which its one-minute maximum sustained wind speed increases at least 30 knots per 24 hours. Here we identify and elucidate the climatic conditions that are critical to the frequency and location of the RI on annual, intraseasonal, and interannual time scales. Whereas RI and formation share common environmental preferences, we found that the percentage of TCs with RI varies annually and from year to year. In August, only 30% of TC actually experiences RI, in contrast to the annual maximum of 47% in November. The proportion of RI in July–September is higher during El Ni?o years (53%) than the corresponding one in the La Ni?a years (37%). Three climate factors may contribute to the increase in the proportion of RI: the southward shift in the monthly or seasonal mean location of the TC formation, the increase in the low-level westerly meridional shear vorticity, and the decrease in northerly vertical shear. When the mean latitude of TC formation increases, the mixed-layer heat content decreases while TC’s inertial stability increases; both are more detrimental to the RI than to TC formation because the RI requires large amount of latent heat energy being extracted efficiently from the ocean mixed layer and requires accelerated low-level radial inflow that carries latent heat reaching the inner core region. We further demonstrate that the RI frequency in the Philippine Sea and South China Sea can be predicted 10 to 30 days in advance based on the convective anomalies in the equatorial western Pacific (5° S–5° N, 130°–150° E) on intraseasonal time scale. The Ni?o 3.4 SSTA in June is a potential predictor for the peak TC season (July–September) RI activity in the southeast quadrant of the western North Pacific (0–20° N, 140–180° E). The RI is an essential characteristic of category 4 and 5 hurricanes and super typhoons because all category 4 and 5 hurricanes in the Atlantic basin and 90% of the super typhoons in the western North Pacific experience at least one RI process in their life cycles. Over the past 40 years, the annual total of RI in the western North Pacific shows pronounced interdecadal variation but no significant trend. This result suggests that the number of supper typhoons has no upward trend in the past 40 years. Our results also suggest that when the mean latitude, where the tropical storms form, shifts southward (either seasonally or from year to year) the proportion of super typhoon or major hurricane will likely increase. This shift is determined by large scale circulation change rather than local SST effects. This idea differs from the current notion that increasing SST can lead to more frequent occurrence of category 4 or 5 hurricanes through local thermodynamics. Corresponding author’s address: Bin Wang, Department of Meteorology, University of Hawaii, 2525 Correa Rd., Honolulu, Hawaii 96822, USA (also visiting professor at the Ocean University of China)  相似文献   

3.
ENSO多样性研究进展   总被引：2，自引：0，他引：2  
El Ni?o是热带中东太平洋异常偏暖的现象,发展过程具有显著的季节锁相特征。近年来,新形态事件更频繁发生引起了科学界广泛关注。学者们根据空间分布形态或爆发时间将ENSO事件分为两类,虽然选取标准不同,分类结果却有诸多相似点:中太平洋(Dateline、Modoki、CP、WP及SU型)El Ni?o事件发展至成熟时,正SSTA中心位于赤道太平洋中部;东太平洋(传统、EP、CT及SP型)El Ni?o发展至成熟时,正SSTA中心位于赤道东太平洋,低层西风异常更强,向东传输的距离也更远。研究结果显示,东太平洋El Ni?o比中太平洋El Ni?o持续时间更长,强度也更强;两类事件对全球气候的影响模态有很大的差异。近几十年,中太平洋El Ni?o出现频率有所增加,但其原因尚未清楚。关于两类事件生成发展和位相转换的动力原因,目前科学界普遍认为东太平洋El Ni?o是一个海盆尺度的海气耦合过程,其生消过程与温跃层的变化有紧密联系,但对中太平洋El Ni?o的动力机制尚未有统一的认识。   相似文献   

4.
Interannual variations of the Bay of Bengal summer monsoon (BOBSM) onset in association with El Ni?o?Southern Oscillation (ENSO) are reexamined using NCEP1, JRA-55 and ERA20C atmospheric and Hadley sea surface temperature (SST) reanalysis datasets over the period 1900?2017. Decadal changes exist in the dependence of the BOBSM onset on ENSO, varying with the Pacific Decadal Oscillation (PDO). A higher correlation between the BOBSM onset and ENSO arises during the warm PDO epochs, with distinct late (early) onsets following El Ni?o (La Ni?a) events. In contrast, less significant correlations occur during the cold PDO epochs. The mechanism for the PDO modulating the ENSO?BOBSM onset relationship is through the variations in SST anomaly (SSTA) patterns. During the warm PDO epochs, the superimpositions of the PDO-related and ENSO-related SSTAs lead to the SSTA distribution of an El Ni?o (La Ni?a) event exhibiting significant positive (negative) SSTAs over the tropical central?eastern Pacific and Indian Ocean along with negative (positive) SSTAs, especially over the tropical western Pacific (TWP), forming a strong zonal interoceanic SSTA gradient between the TWP and tropical Indian Ocean. Significant anomalous lower tropospheric easterlies (westerlies) together with upper-tropospheric westerlies (easterlies) are thus induced over the BOB, favoring an abnormally late (early) BOBSM onset. During the cold PDO epochs, however, the superimpositions of PDO-related SSTAs with El Ni?o-related (La Ni?a-related) SSTAs lead to insignificant SSTAs over the TWP and a weak zonal SSTA gradient, without distinct circulation anomalies over the BOB favoring early or late BOBSM onsets.  相似文献   

5.
Summary This paper investigates the warming trend and interannual variability of surface air temperatures in the Malaysian region during the period 1961–2002. The trend analyses show that most regions in Malaysia experience warming over the period at comparable rates to those in regions surrounding the Bay of Bengal. The regions of Peninsular Malaysia and northern Borneo experience warming rates of between 2.7–4.0 °C/100 years. However, the warming rates are lower in the south-western region of Borneo. The interannual variability of Malaysian temperature is largely dominated by the El Ni?o-Southern Oscillation (ENSO). Regardless of the warming trends, all regions in Malaysia experience uniform warming during an El Ni?o event, particularly during the October–November–December (OND) and the January–February–March (JFM) periods. This uniform warming is associated with the latent heat released from the central eastern Pacific region and forced adiabatic subsidence in the Maritime Continent during an El Ni?o event. During its early development period i.e. during the July–August–September (JAS) season, the El Ni?o’s impact on the Malaysian temperatures is relatively weak compare to its influence during the OND and JFM seasons. However, the warming continues to the April–May–June (AMJ) season although during this period the anomalous conditions in the eastern central Pacific have begun or have returned to normal. The Indian Ocean Dipole (IOD) mode exerts an influence on Malaysian temperatures. When it co-occurs with ENSO, it tends to weaken the ENSO influence particularly during an OND period. However, it appears to have an appreciable influence only during an AMJ period when it occurs in the absence of an ENSO event. Despite the strong influence of the ENSO, the warming rates during the 42-year period appears to be least affected by interannual variability.  相似文献   

6.
In this paper we seek to identify inter-annual sea surface temperature anomalies (SSTA) patterns outside the tropical Pacific that may influence El Niño/Southern Oscillation (ENSO) through atmospheric teleconnections. We assume that a linear ENSO hindcast based on tropical Pacific warm water volume and Niño3.4 SSTA indices captures tropical Pacific intrinsic predictability inherent to recharge oscillator dynamics. This simple hindcast model displays statistically significant skill at the 95 % confidence level at leads of up to seven seasons ahead of the ENSO peak. Our results reveal that ENSO-independent equatorial wind stress anomalies only significantly improve the skill of that linear hindcast at the 95 % level in boreal spring and summer before the ENSO peak and in boreal fall, five seasons ahead of the ENSO peak. At those seasons, the robust large-scale SST patterns that provide a statistically significant enhancement of ENSO predictability are related to the Atlantic meridional mode and south Pacific subtropical dipole mode in spring, the Indian Ocean Dipole and the south Atlantic subtropical dipole mode in fall. While the first two regions display significant simultaneous correlations with western equatorial Pacific wind stress in three reanalyses (ERA-I, NCEP and NCEP2), the Indian Ocean Dipole and south Atlantic subtropical dipole mode correlation with Pacific winds is less robust amongst re-analyses. We discuss our results in view of other studies that suggest a remote influence of various regions on ENSO. Although modest, the sensitivity of our results to the dataset and to details of the analysis method illustrates that finding regions that influence ENSO from the statistical analysis of observations is a difficult task.  相似文献   

7.
石世玮  智海  林鹏飞  陈涛 《大气科学》2020,44(5):1057-1075
海洋盐度变化为研究气候变化的机制提供了一个新的视角。本文通过对比1997/1998年、2015/2016年两次强厄尔尼诺（El Ni?o）事件和2014/2015年特殊El Ni?o事件,对盐度变化及其影响海表面温度异常（SSTA）的物理过程进行了比较分析。研究表明,El Ni?o和南方涛动（El Ni?o–Southern Oscillation, ENSO）发展的强弱与热带西太平洋大范围海表层盐度异常（SSSA）及其向东扩散的差异有明显关联。1997/1998、2015/2016年赤道东太平洋SSTA的增暖,对应两次强El Ni?o事件,在发生年4月,中西太平洋海域出现了明显的负SSSA,之后东移至日期变更线以西,SSSA引发的混合层深度（MLD）变浅、障碍层厚度（BLT）变厚,导致热带中—西太平洋表层升温增强,促使了赤道中太平洋的早期变暖;2014/2015年弱El Ni?o事件虽然在发生年4月,位于赤道中西太平洋出现了负SSSA,但没有发展东移,导致BLT的增厚过程减弱,对表层温度的调制作用减弱甚至消失。三次事件对应的盐度变化过程中,水平平流和淡水通量（FWF）引起的表层强迫是影响盐度收支的主要因子,水平平流影响盐度异常的前期变化,触发事件的发生;热带太平洋西部降水引起的FWF负异常的影响最为显著,对ENSO异常信号出现后SSSA的维持起决定性作用。相比较两次强El Ni?o事件,2014/2015年El Ni?o对应的早期FWF负异常没有发展和东移,并且之后迅速减弱,导致中西太平洋盐度负趋势减缓,MLD加深,BLT变薄,促使上表层海水冷却,抑制了赤道东太平洋的早期变暖和ENSO发展。研究结果表明,盐度变化与ENSO密切相关,热带中西太平洋海域早期表层盐度变化可能可以作为SSTA的指数。特别地,SSSA在调节SSTA时,不仅影响它的强度,而且可以作为判断ENSO是否发展及其强弱的前兆因子。  相似文献   

8.
Summary The authors examine relationships between the East Asian winter monsoon and the ENSO, particularly on the interdecadal timescales. Based on the analyses of SLP data from 1899 to 1997, the East-Asian winter monsoon index (WMI) is defined as the zonal difference of SLP between ∼120° E and ∼160° E. It is found that 18 out of 28 strong winter monsoon years are either before the development of an El Ni?o or during the decaying La Ni?a event, 12 out of 28 weak winter monsoon are before the development of a La Ni?a or during the decaying El Ni?o event. There is a significant positive correlation coefficient value of about 0.49 between the normalized 11-yr running mean of WMI and ENSO index, however, the WMI-ENSO relationship is not consistently highly correlated. The temporal evolution of correlation between WMI and ENSO indices in both 11-yr and 21-yr moving window shows that the WMI-ENSO relationship clearly undergo low-frequency oscillation. Obviously, both observational and IPSL air-sea coupled modeling WMI index has a near-decadal peak with PDO timescales and internal peaks with ENSO timescales by applying the Multitaper method. Moreover, the cross wavelet and wavelet coherence analysis of WMI/ENSO indicate that there is a larger significant sections with an in phase behavior between WMI and ENSO at period of 20–30 yrs, suggesting that the interdecadal variation of the WMI-ENSO relationship might exist.  相似文献   

9.
Summary The dominant climatic mode responsible for seasonal rainfall variability across central southern Africa has been well-established as ENSO. Hence, the El Ni?o signal of the equatorial Pacific has been used extensively to predict droughts in this sub-region. Although this paper acknowledges that El Ni?o influences rainfall deficits over eastern southern Africa, an earlier signal of extreme positive sea level pressure (SLP) anomalies at Darwin for the averaged March to June period (MAMJ Darwin) has proved to have a superior remote connection to droughts in the sub-region. Simple linear statistical tools including composite techniques and correlation methods have been employed on century long data sets (1901–2000) to identify the emerging paramount connection between MAMJ Darwin SLP anomalies and southern African rainfall. Both MAMJ Darwin SLP anomalies and the Zimbabwe seasonal rainfall time series are significantly correlated (above the 95% significant level) with sea surface temperature anomalies. These represent the Indian Ocean Dipole mode in the tropical Indian Ocean and ENSO in the tropical Pacific for the averaged September to December period. ‘Pure’ MAMJ Darwin (that occur in the absence of El Ni?o in the Pacific) coincide with droughts more significantly (83% hit rate) than ‘pure’ El Ni?o events (not preceded by a high MAMJ Darwin) (38% hit rate). Co-occurrences (MAMJ Darwin preceded by El Ni?o) do not only have the highest hit rate of 93% but subsequent droughts are noticeably more severe. The ‘pure’ El Ni?os however, are not only poorly related to Zimbabwe seasonal rainfall deficits, but are apparently not connected to extreme droughts of the 20th century. Thus, MAMJ Darwin is a good simple predictor of droughts associated with or without ENSO in the Pacific. The high prediction skill of these results, especially the inherent longer lead-time than ENSO, makes MAMJ Darwin SLP anomalies an ideal additional input candidate for sub-regional drought monitoring and forecasting schemes. In this way, drought early warning and disaster preparedness activities can be enhanced over the sub-region. Authors’ addresses: D. Manatsa, W. Chingombe, H. Matsikwa, Faculty of Science, Bindura University of Science Education, P. Bag 1020, Bindura, Zimbabwe; C. H. Matarira, Department of Geography and Environmental Science, National University of Lesotho, Roma 180, Lesotho.  相似文献   

10.
Results from multiple model simulations are used to understand the tropical sea surface temperature (SST) response to the reduced greenhouse gas concentrations and large continental ice sheets of the last glacial maximum (LGM). We present LGM simulations from the Paleoclimate Modelling Intercomparison Project, Phase 2 (PMIP2) and compare these simulations to proxy data collated and harmonized within the Multiproxy Approach for the Reconstruction of the Glacial Ocean Surface Project (MARGO). Five atmosphere–ocean coupled climate models (AOGCMs) and one coupled model of intermediate complexity have PMIP2 ocean results available for LGM. The models give a range of tropical (defined for this paper as 15°S–15°N) SST cooling of 1.0–2.4°C, comparable to the MARGO estimate of annual cooling of 1.7 ± 1°C. The models simulate greater SST cooling in the tropical Atlantic than tropical Pacific, but interbasin and intrabasin variations of cooling are much smaller than those found in the MARGO reconstruction. The simulated tropical coolings are relatively insensitive to season, a feature also present in the MARGO transferred-based estimates calculated from planktonic foraminiferal assemblages for the Indian and Pacific Oceans. These assemblages indicate seasonality in cooling in the Atlantic basin, with greater cooling in northern summer than northern winter, not captured by the model simulations. Biases in the simulations of the tropical upwelling and thermocline found in the preindustrial control simulations remain for the LGM simulations and are partly responsible for the more homogeneous spatial and temporal LGM tropical cooling simulated by the models. The PMIP2 LGM simulations give estimates for the climate sensitivity parameter of 0.67°–0.83°C per Wm−2, which translates to equilibrium climate sensitivity for doubling of atmospheric CO2 of 2.6–3.1°C.  相似文献   

11.
利用逐月台站观测降水、HadISST1.1海温和ERA5大气再分析资料,研究了前冬印度洋海盆一致模（Indian Ocean Basin,IOB）对华南春季降水（SCSR）与ENSO关系的影响,并分析了IOB通过调控ENSO环流异常进而影响SCSR的可能机制。结果表明:当前冬El Ni?o（La Ni?a）与IOB暖（冷）位相同时发生时,SCSR显著增多（减少）;而当El Ni?o或La Ni?a单独发生而IOB处于中性时,SCSR并无明显多寡倾向。其原因在于,当El Ni?o与IOB暖相位并存时,前冬热带印度洋和赤道中东太平洋均为正海温异常（Sea-Surface Temperature Anomaly,SSTA）,且印度洋SSTA强度可一直维持至春季。在对流层低层,春季赤道中东太平洋的正SSTA激发出异常西北太平洋反气旋（Western North Pacific Anticyclone,WNPAC）。而热带印度洋的正SSTA在副热带印度洋激发出赤道南北反对称环流,赤道以北的东风异常有利于异常WNPAC西伸;赤道以南的西风异常与来自赤道西太平洋的东风异常在东印度洋辐合上升,气流至西北太平洋下沉,形成经向垂直环流,有利于春季WNPAC维持。在对流层高层,印度洋的正SSTA在热带印度洋上空激发出位势高度正异常,随之形成的气压经向梯度加强了东亚高空副热带西风急流,进而在华南上空形成异常辐散环流。WNPAC的西伸和加强可为华南提供充足的水汽,同时高空辐散在华南引发水汽上升运动,共同导致SCSR正异常。而若El Ni?o发生时IOB处于中性状态,El Ni?o相关的SSTA衰减较快,春季WNPAC不显著,SCSR无明显多寡趋势。   相似文献   

12.
Summary ?The variability of El Ni?o-Southern Oscillation (ENSO) on all time scales, ranging from months to decades, has been studied from the perspective of sea-surface temperature anomaly (SSTA), sea-level pressure anomaly (SLPA), and surface wind anomaly (SWA) fields using a statistical tool called cyclostationary empirical orthogonal function (CSEOF) analysis. The analysis indicates that a significant fraction of variability in the tropical Pacific can be explained in terms of an irregular interplay of two dominant modes: the low-frequency mode and the biennial mode. These modes, and in particular the biennial mode, are well defined coupled modes of the tropical ocean-atmospheric circulation system, as suggested by strong correlation (> 0.9) in the evolution of the different physical variables. The low-frequency mode and its PC time series are very similar to the so-called “interdecadal” mode identified by earlier investigators. The corresponding PC time series of the low-frequency mode has a broad spectral peak at 5.3 yrs. The biennial mode represents the oscillation pattern of El Ni?o and La Ni?a and has a clear biennial cycle, the amplitude of which varies on a longer time scale. There is a broad spectral peak also at 5.3 yrs in the principal component (PC) time series of this mode. Unlike in earlier studies, this biennial mode is clearly separable from the low-frequency mode, since these two modes have different physical evolution patterns. Results of the present study also indicate that the biennial component, having a clear phase-locking tendency, is not as variable as has been suggested in some previous investigations. It is shown that much of the inter-El Ni?o variability can be explained in terms of an irregular interplay between the biennial mode and the low-frequency mode. Finally, the role of the low-frequency mode in the tropical Pacific seems to be more important than has been suggested previously. Specifically, recent warming events since 1975 are shown to be associated with the low-frequency mode rather than with the biennial mode. Received August 15, 2001; revised March 6, 2002  相似文献   

13.
 The predictability of atmospheric responses to global sea surface temperature (SST) anomalies is evaluated using ensemble simulations of two general circulation models (GCMs): the GENESIS version 1.5 (GEN) and the ECMWF cycle 36 (ECM). The integrations incorporate observed SST variations but start from different initial land and atmospheric states. Five GEN 1980–1992 and six ECM 1980–1988 realizations are compared with observations to distinguish predictable SST forced climate signals from internal variability. To facilitate the study, correlation analysis and significance evaluation techniques are developed on the basis of time series permutations. It is found that the annual mean global area with realistic signals is variable dependent and ranges from 3 to 20% in GEN and 6 to 28% in ECM. More than 95% of these signal areas occur between 35 °S–35 °N. Due to the existence of model biases, robust responses, which are independent of initial condition, are identified over broader areas. Both GCMs demonstrate that the sensitivity to initial conditions decreases and the predictability of SST forced responses increases, in order, from 850 hPa zonal wind, outgoing longwave radiation, 200 hPa zonal wind, sea-level pressure to 500 hPa height. The predictable signals are concentrated in the tropical and subtropical Pacific Ocean and are identified with typical El Ni?o/ Southern Oscillation phenomena that occur in response to SST and diabatic heating anomalies over the equatorial central Pacific. ECM is less sensitive to initial conditions and better predicts SST forced climate changes. This results from (1) a more realistic basic climatology, especially of the upper-level wind circulation, that produces more realistic interactions between the mean flow, stationary waves and tropical forcing; (2) a more vigorous hydrologic cycle that amplifies the tropical forcing signals, which can exceed internal variability and be more efficiently transported from the forcing region. Differences between the models and observations are identified. For GEN during El Ni?o, the convection does not carry energy to a sufficiently high altitude, while the spread of the tropospheric warming along the equator is slower and the anomaly magnitude smaller than observed. This impacts model ability to simulate realistic responses over Eurasia and the Indian Ocean. Similar biases exist in the ECM responses. In addition, the relationships between upper and lower tropospheric wind responses to SST forcing are not well reproduced by either model. The identification of these model biases leads to the conclusion that improvements in convective heat and momentum transport parametrizations and basic climate simulations could substantially increase predictive skill. Received: 25 April 1996 / Accepted: 9 December 1996  相似文献   

14.
The study has shown that the shear component of the vertical integrated kinetic energy (Ks) over the box (40oE–100oE, 0o–20oN) can be used as a measure of the intensity of the South Asian summer monsoon (SASM). Based on its value averaged between June and August, the SASM can be divided into strong and weak monsoon episodes. Between 1958 and 2018, there existed 16 (16) strong (weak) monsoon episodes. Based on the calendar year, the relationship between the SASM and the ENSO episodes can be grouped into six patterns: weak monsoon - El Ni?o (WM-EN), normal monsoon - El Ni?o (NM-EN), weak monsoon - non ENSO (WM-NE), strong monsoon - La Ni?a (SM-LN), normal monsoon - La Ni?a (NM-LN) and strong monsoon - non ENSO (SM-NE). Previous studies have suggested that the WM-EN and SM-LN patterns reflect the correlated relationship between the SASM and El Ni?o/Southern Oscillation (ENSO) events. Therefore, we name these two strongly coupled categories WM-EN and SM-LN as the resonance effect. Two important circulations, Walker circulation (WC) and zonal Asian monsoon circulation (MC), in the vertical plane are found to be not always correlated. MC is controlled by thermal gradients between the Asian landmass and the tropical Indian Ocean, while the WC associated with the ENSO event is primarily the east-west thermal gradient between the tropical South Pacific and the tropical Indian Ocean. Furthermore, the gradient directions caused by different surface thermal conditions are different. The main factor for the resonance effect is the phenomenon that the symbols of SSTA in the tropical Indian Ocean and the equatorial eastern Pacific are the same, but are opposite to that of the SSTA near the maritime continent.  相似文献   

15.
Summary  The year 1997 witnessed one of the most severe El-Ni?o events of the century. However, the All-India Summer Monsoon Rainfall (AISMR) was 102% of its long period average. In view of recent studies (Tourre and White, 1995, 1997) of detection of ENSO signal over Indian Ocean, the Sea-Surface Temperature (SST) variation over Indian Ocean (20° N–10° S/50° E–100° E), concurrent to El-Ni?o event of 1997 is examined. It is observed that during the developing, mature and decaying stages of El-Ni?o, the North Indian Ocean was abnormally warm. This anomalous warming may be one of the factors responsible for anomalous precipitation over India during October to December of 1997. Received August 24, 1999/Revised February 15, 2000  相似文献   

16.
利用NCEP/NCAR再分析资料、全球海温海冰GISST 2.3b资料, 用EOF技术分析了热带太平洋海表温度的年际异常 (SSTA) 变化特征表明:可用Ni?o3指数表示热带太平洋SSTA, 并用该指数来讨论热带太平洋、热带印度洋SSTA间的关系。分季节分析表明:冬季Ni?o3指数与热带印度洋SSTA间的关系表现为热带印度洋整体相关系数为正的单极形态, 且1976年以后两者的关系减弱, 其原因是冬季为ENSO事件的盛期, 另外, 冬季西太平洋暖水区东移导致太平洋Walker环流上升支强盛处的东移, 造成两洋的垂直纬向环流耦合减弱。夏季两者关系表现为偶极形态 (热带西印度洋与Ni?o3指数同相变化, 热带东印度洋则相反), 但1976年以后两者的关系有所加强, 是因为夏季为偶极子盛期, 也是ENSO事件的发展期, 同时夏季西太平洋暖水区东移并未引起太平洋Walker环流上升支强盛处的明显东移, 且印度洋季风环流、太平洋Walker环流的上升支强盛处的强度增大了, 造成两洋的垂直纬向环流耦合更强烈。即1976年以后, 冬季热带两洋SSTA间的关系减弱了, 而夏季两者关系则变得更密切。  相似文献   

17.
Many previous studies have demonstrated that the boreal winters of super El Nino events are usually accompanied by severely suppressed Madden-Julian oscillation(MJO) activity over the western Pacific due to strong descending motion associated with a weakened Walker Circulation. However, the boreal winter of the 2015/16 super El Nino event is concurrent with enhanced MJO activity over the western Pacific despite its sea surface temperature anomaly(SSTA)magnitude over the Nino 3.4 region being comparable to the SSTA magnitudes of the two former super El Nino events(i.e.,1982/83 and 1997/98). This study suggests that the MJO enhanced over western Pacific during the 2015/16 super El Nino event is mainly related to its distinctive SSTA structure and associated background thermodynamic conditions. In comparison with the previous super El Nino events, the warming SSTA center of the 2015/16 super El Nino is located further westward, and a strong cold SSTA is not detected in the western Pacific. Accordingly, the low-level moisture and air temperature(as well as the moist static energy, MSE) tend to increase in the central-western Pacific. In contrast, the low-level moisture and MSE show negative anomalies over the western Pacific during the previous super El Nino events.As the MJO-related horizontal wind anomalies contribute to the further westward warm SST-induced positive moisture and MSE anomalies over the western tropical Pacific in the boreal winter of 2015/16, stronger moisture convergence and MSE advection are generated over the western Pacific and lead to the enhancement of MJO convection.  相似文献   

18.
 Monthly sea surface temperature anomalies (SSTA) at near-global scale (60 °N–40 °S) and May to October rainfall amounts in West Africa (16 °N–5 °N; 16 °W–16 °E) are first used to investigate the seasonal and interannual evolutions of their relationship. It is shown that West African rainfall variability is associated with two types of oceanic changes: (1) a large-scale evolution involving the two largest SSTA leading eigenmodes (16% of the total variance with stronger loadings in the equatorial and southern oceans) related to the long-term (multiannual) component of rainfall variability mainly expressed in the Sudan–Sahel region; and (2) a regional and seasonally coupled evolution of the meridional thermal gradient in the tropical Atlantic due to the linear combination of the two largest SSTA modes in the Atlantic (11% with strong inverse loadings over the northern and southern tropics) which is associated with the interannual and quasi-decadal components of regional rainfall in West Africa. Linear regression and discriminant analyses provide evidence that the main July–September rainfall anomalies in Sudan–Sahel can be detected with rather good skills using the leading (April–June) or synchronous (July–September) values of the four main oceanic modes. In particular, the driest conditions over Sahel, more marked since the beginning of the 1970s, are specifically linked to the warm phases of the two global modes and to cold/warm anomalies in the northern/southern tropical Atlantic. Idealized but realistic SSTA patterns, obtained from some basic linear combinations of the four main oceanic modes appear sufficient to generate quickly (from mid-July to the end of August) significant West African rainfall anomalies in model experiments, consistent with the statistical results. The recent negative impact on West African rainfall exerted by the global oceanic forcing is primarily due to the generation of subsidence anomalies in the mid-troposphere over West Africa. When an idealized north to south SSTA gradient is added in the tropical Atlantic, strong north to south height gradients in the middle levels appear. These limit the northward excursion of the rainbelt in West Africa: the Sahelian area experiences drier conditions due to the additive effect (subsidence anomalies+latitudinal blocking) while over the Guinea regions wet conditions do not significantly increase, since the subsidence anomalies and the blocking effect act here in opposite ways. Received: 26 June 1997 / Accepted: 3 October 1997  相似文献   

19.
海温异常对东亚夏季风影响机理的研究进展   总被引：16，自引：3，他引：13       下载免费PDF全文
从短期气候预测关注的外强迫信号角度出发,回顾了国内外在海温异常对东亚夏季风和我国汛期降水影响机理方面的主要研究进展,重点评述了热带太平洋ENSO循环、热带印度洋全区一致型海温模态、热带印度洋海温异常偶极子、南印度洋偶极子和北大西洋海温三极子模态的年际变化及其对东亚夏季风年际变率的影响。从研究成果在短期气候预测业务中应用的角度,重点关注海温异常和东亚夏季风年际变率以及我国汛期降水多雨带位置的关系,总结了海温异常作为外强迫信号对我国汛期降水预测的指示意义以及汛期降水预测的难度。最后指出气候预测业务对东亚夏季风影响的机理研究和动力气候模式发展方面的需求。  相似文献   

20.
利用NCEP/NCAR提供的大气月平均再分析资料、NOAA提供的ERSST.V4资料及ECMWF提供的ORAS4海洋再分析数据集,借助合成分析、相关分析和SVD分解等方法,对ENSO位相转换期北太平洋热带外大气对热带东太平洋海温的影响进行分析。结果表明:（1）6月关键区（155~130 °W,10~30 °N）存在海平面气压正异常与同期以及后期热带东太平洋出现海温负异常有关,E-L型事件（El Ni?o次年发生La Ni?a）在关键区出现海平面气压正异常的概率远大于E-N型事件（El Ni?o次年不发生La Ni?a）;（2）通过分析北太平洋3—6月海平面气压场和后期12月海温场SVD分解的结果,同样发现关键区海平面气压异常和后期12月热带东太平洋海温异常的负相关关系;（3）6月正位相OKJ波列的传播可能是导致同期关键区海平面气压正异常的原因之一;（4）6月关键区出现海平面气压正异常时,可能通过引起1~3个月后同区域出现更多向南海表层海流流速异常,有助于将中纬较冷的海水向赤道输送,引起12月热带东太平洋海温负异常,对于La Ni?a的形成起到一定促进作用。   相似文献   

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