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1.
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   

2.
利用一个全球海气耦合模式(BCM),结合观测资料,讨论了热带太平洋强迫对北大西洋年际气候变率的影响。研究表明,BCM能够相对合理地模拟赤道太平洋的年际变率模态及相应的海温距平型和大气遥相关型,尽管其准3年的振荡周期过于规则。来自数值模式和观测上的证据都表明,北大西洋冬季海温的主导性变率模态,即自北而南出现的“- -”的海温距平型,受到来自热带太平洋强迫的显著影响,其正位相与赤道中东太平洋冷事件相对应。换言之,赤道太平洋暖事件的发生,在太平洋-北美沿岸激发出PNA遥相关型,进而通过在北大西洋产生类似NAO负位相的气压距平型,削弱本来与NAO正位相直接联系的三核型海温距平。北大西洋三核型海温距平对热带太平洋强迫的响应,要滞后2—3个月的时间。  相似文献   

3.
Remotely forced variability in the tropical Atlantic Ocean   总被引：1，自引：1，他引：1  
An ensemble of eight hindcasts has been conducted using an ocean-atmosphere general circulation model fully coupled only within the Atlantic basin, with prescribed observational sea surface temperature (SST) for 1950–1998 in the global ocean outside the Atlantic basin. The purpose of these experiments is to understand the influence of the external SST anomalies on the interannual variability in the tropical Atlantic Ocean. Statistical methods, including empirical orthogonal function analysis with maximized signal-to-noise ratio, have been used to extract the remotely forced Atlantic signals from the ensemble of simulations. It is found that the leading external source on the interannual time scales is the El Niño/Southern Oscillation (ENSO) in the Pacific Ocean. The ENSO signal in the tropical Atlantic shows a distinct progression from season to season. During the boreal winter of a maturing El Niño event, the model shows a major warm center in the southern subtropical Atlantic together with warm anomalies in the northern subtropical Atlantic. The southern subtropical SST anomalies is caused by a weakening of the southeast trade winds, which are partly associated with the influence of an atmospheric wave train generated in the western Pacific Ocean and propagating into the Atlantic basin in the Southern Hemisphere during boreal fall. In the boreal spring, the northern tropical Atlantic Ocean is warmed up by a weakening of the northeast trade winds, which is also associated with a wave train generated in the central tropical Pacific during the winter season of an El Niño event. Apart from the atmospheric planetary waves, these SST anomalies are also related to the sea level pressure (SLP) increase in the eastern tropical Atlantic due to the global adjustment to the maturing El Niño in the tropical Pacific. The tropical SLP anomalies are further enhanced in boreal spring, which induce anomalous easterlies on and to the south of the equator and lead to a dynamical oceanic response that causes cold SST anomalies in the eastern and equatorial Atlantic from boreal spring to summer. Most of these SST anomalies persist into the boreal fall season.
B. HuangEmail:
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4.
The oscillation characteristics of 1948 - 2003 South China Sea (SCS) summer monsoon intensity (SCSSMI) is analyzed by wavelet transform and the relationship between SCSSMI filtered by Lanczos filter at different time scale and oceanic thermal conditions is studied. The results show that SCSSMI exhibits dominant interannual (about 4 a), decadal (about 9 a) and interdecadal (about 38 a) oscillation periods. The interannual variation is the strongest and the interdecadal variation the weakest. The region of significant correlation between SCS summer monsoon intensity and oceanic thermodynamic variables at different time scale is greatly different. Significant correlation area of interannual variation of SCSSMI is concentrated in near equatorial region. Corresponding correlation displays quasi-biannual variability. If positive anomalies of SST and the depth of thermocline happen in eastern equatorial Indian Ocean and western equatorial Pacific, and negative anomalies of SST and the depth of thermocline happen in western equatorial Indian Ocean and eastern equatorial Pacific in previous autumn and winter, the interannual variation of SCSSMI will enhance. If the condition is contrary, interannual variation of SCSSMI will weaken. The interannual variation of SCSSMI will influence SST. The region surrounding SCS and east of Australia shows significantly negative correlation in autumn, and significantly positive correlation exhibits in west equatorial Indian Ocean, eastern equatorial Pacific and equatorial Atlantic in winter. The decadal variation of SCSSMI is modulated by PDO. Interdecadal variation of SCSSMI is relevant to the global warming and PDO.  相似文献   

5.
The interannual variability associated with the El Ni?o/Southern Oscillation (ENSO) cycle is investigated using a relatively high-resolution (T42) coupled general circulation model (CGCM) of the atmosphere and ocean. Although the flux correction is restricted to annual means of heat and freshwater, the annual as well as the seasonal climate of the CGCM is in good agreement with that of the atmospheric model component forced with observed sea surface temperatures (SSTs). During a 100-year simulation of the present-day climate, the model is able to capture many features of the observed interannual SST variability in the tropical Pacific. This includes amplitude, lifetime and frequency of occurrence of El Ni?o events and also the phase locking of the SST anomalies to the annual cycle. Although the SST warming during the evolution of El Ni?os is too confined spatially, and the warming along the Peruvian coast is much too weak, the patterns and magnitudes of key atmospheric anomalies such as westerly wind stress and precipitation, and also their eastward migration from the western to the central equatorial Pacific is in accord with observations. There is also a qualitative agreement with the results obtained from the atmospheric model forced with observed SSTs from 1979 through 1994. The large-scale dynamic response during the mature phase of ENSO (December through February) is characterized by an eastward displacement and weakening of the Walker cell in the Pacific while the Hadley cell intensifies and moves equatorward. Similar to the observations, there is a positive correlation between tropical Pacific SST and the winter circulation in the North Pacific. The deepening of the Aleutian low during the ENSO winters is well captured by the model as well as the cooling in the central North Pacific and the warming over Canada and Alaska. However, there are indications that the anomalies of both SST and atmospheric circulation are overemphasized in the North Pacific. Finally, there is evidence of a coherent downstream effect over the North Atlantic as indicated by negative correlations between the PNA index and the NAO index, for example. The weakening of the westerlies across the North Atlantic in ENSO winters which is related to a weakening and southwestward displacement of the Icelandic low, is in broad agreement with the observations, as well as the weak tendency for colder than normal winters in Europe. Received: 31 October 1995 / Accepted: 29 May 1996  相似文献   

6.
 This study examines time evolution and statistical relationships involving the two leading ocean-atmosphere coupled modes of variability in the tropical Atlantic and some climate anomalies over the tropical 120 °W–60 °W region using selected historical files (75-y near global SSTs and precipitation over land), more recent observed data (30-y SST and pseudo wind stress in the tropical Atlantic) and reanalyses from the US National Centers for Environmental Prediction (NCEP/NCAR) reanalysis System on the period 1968–1997: surface air temperature, sea level pressure, moist static energy content at 850 hPa, precipitable water and precipitation. The first coupled mode detected through singular value decomposition of the SST and pseudo wind-stress data over the tropical Atlantic (30 °N–20 °S) expresses a modulation in the thermal transequatorial gradient of SST anomalies conducted by one month leading wind-stress anomalies mainly in the tropical north Atlantic during northern winter and fall. It features a slight dipole structure in the meridional plane. Its time variability is dominated by a quasi-decadal signal well observed in the last 20–30 ys and, when projected over longer-term SST data, in the 1920s and 1930s but with shorter periods. The second coupled mode is more confined to the south-equatorial tropical Atlantic in the northern summer and explains considerably less wind-stress/SST cross-covariance. Its time series features an interannual variability dominated by shorter frequencies with increased variance in the 1960s and 1970s before 1977. Correlations between these modes and the ENSO-like Nino3 index lead to decreasing amplitude of thermal anomalies in the tropical Atlantic during warm episodes in the Pacific. This could explain the nonstationarity of meridional anomaly gradients on seasonal and interannual time scales. Overall the relationships between the oceanic component of the coupled modes and the climate anomaly patterns denote thermodynamical processes at the ocean/atmosphere interface that create anomaly gradients in the meridional plane in a way which tends to alter the north–south movement of the seasonal cycle. This appears to be consistent with the intrinsic non-dipole character of the tropical Atlantic surface variability at the interannual time step and over the recent period, but produces abnormal amplitude and/or delayed excursions of the intertropical convergence zone (ITCZ). Connections with continental rainfall are approached through three (NCEP/NCAR and observed) rainfall indexes over the Nordeste region in Brazil, and the Guinea and Sahel zones in West Africa. These indices appear to be significantly linked to the SST component of the coupled modes only when the two Atlantic modes+the ENSO-like Nino3 index are taken into account in the regressions. This suggests that thermal forcing of continental rainfall is particularly sensitive to the linear combinations of some basic SST patterns, in particular to those that create meridional thermal gradients. The first mode in the Atlantic is associated with transequatorial pressure, moist static energy and precipitable water anomaly patterns which can explain abnormal location of the ITCZ particularly in northern winter, and hence rainfall variations in Nordeste. The second mode is more associated with in-phase variations of the same variables near the southern edge of the ITCZ, particularly in the Gulf of Guinea during the northern spring and winter. It is primarily linked to the amplitude and annual phase of the ITCZ excursions and thus to rainfall variations in Guinea. Connections with Sahel rainfall are less clear due to the difficulty for the model to correctly capture interannual variability over that region but the second Atlantic mode and the ENSO-like Pacific variability are clearly involved in the Sahel climate interannual fluctuations: anomalous dry (wet) situations tend to occur when warmer (cooler) waters are present in the eastern Pacific and the gulf of Guinea in northern summer which contribute to create a northward (southward) transequatorial anomaly gradient in sea level pressure over West Africa. Received: 14 April 1998 / Accepted: 24 December 1998  相似文献   

7.
Many coupled general circulation models (CGCMs) suffer from serious model bias in the zonal gradient of sea surface temperature (SST) in the equatorial Atlantic. The bias of the equatorial Atlantic SST (EASST) may affect the interannual variability of the equatorial Atlantic, which in turn may influence the state of the tropical Pacific. In this paper we investigate the impact of the bias and the interannual variability of the EASST on the tropical Pacific in a CGCM. To determine the impact of the interannual variability of the EASST on the tropical Pacific, we compare a run in a fully coupled mode (CTL run) and a run in which the EASST is nudged toward the climatological monthly mean of the SST in the CTL run, but full air-sea coupling is allowed elsewhere (AT_m run). We find that, when the interannual variability of the EASST is excluded, the thermocline depth in the eastern equatorial Pacific is deepened, and the amplitude of the El Niño/Southern Oscillation is reduced by 30 % compared to the CTL run. The impact of the bias of the EASST on the tropical Pacific is investigated by comparing the AT_m run and a run in which the EASST is nudged toward the observed climatological monthly mean SST (AT_o run). It is found that, when the bias of the EASST is removed (i.e. AT_o run), the Gill–Matsuno type response to the warm SST anomalies in the western equatorial Atlantic induces low-level cyclonic anomalies in the eastern South Pacific, which leads to a deeper thermocline and colder SST in the South Pacific as compared to AT_m. The colder SST in the South Pacific reduces the precipitation along the South Pacific convergence zone. Our results of the model experiments demonstrate the importance of the EASST to the tropical Pacific climate.  相似文献   

8.
Tian  Feng  Zhang  Rong-Hua  Wang  Xiujun 《Climate Dynamics》2021,56(11):3775-3795

Phytoplankton pigments (e.g., chlorophyll-a) absorb solar radiation in the upper ocean and induce a pronounced radiant heating effect (chlorophyll effect) on the climate. However, the ocean chlorophyll-induced heating effect on the mean climate state in the tropical Pacific has not been understood well. Here, a hybrid coupled model (HCM) of the atmosphere, ocean physics and biogeochemistry is used to investigate the chlorophyll effect on sea surface temperature (SST) in the eastern equatorial Pacific; a tunable coefficient, α, is introduced to represent the coupling intensity between the atmosphere and ocean in the HCM. The modeling results show that the chlorophyll effect on the mean-state SST is sensitively dependent on α (the coupling intensity). At weakly represented coupling intensity (0 ≤ α < 1.01), the chlorophyll effect tends to induce an SST cooling in the eastern equatorial Pacific, whereas an SST warming emerges at the strongly represented coupling intensity (α ≥ 1.01). Thus, a threshold exists for the coupling intensity (about α = 1.01) at which the sign of SST responses can change. Mechanisms and processes are illustrated to understand the different SST responses. In the weak coupling cases, indirect dynamical cooling processes (the adjustment of ocean circulation, enhanced vertical mixing, and upwelling) tend to dominate the SST cooling. In the strong coupling cases, the persistent warming induced by chlorophyll in the southern subtropical Pacific tends to induce cross-equatorial northerly winds, which shifts to anomalous westerly winds in the eastern equatorial Pacific, consequently reducing the evaporative cooling and weakening indirect dynamical cooling; eventually, SST warming maintains in the eastern equatorial Pacific. These results provide new insights into the biogeochemical feedback on the climate and bio-physical interactions in the tropical Pacific.

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9.
１．ＩｎｔｒｏｄｕｃｔｉｏｎＳｏｕｔｈＡｓｉａａｎｄＥａｓｔＡｓｉａａｒｅａｈｕｇｅｍｏｎｓｏｏｎｓｙｓｔｅｍ,ｉｎｗｈｉｃｈｔｈｅＥａｓｔＡｓｉａｎｍｏｎｓｏｏｎｉｓｉｔｓｓｕｂｍｏｎｓｏｏｎｓｙｓｔｅｍ．ＢｅｃａｕｓｅｔｈｅＥａｓｔＡｓｉａｎｓｕ...  相似文献   

10.
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11.
The surface ocean explains a considerable part of the inter-annual Tropical Atlantic variability. The present work makes use of observational datasets to investigate the effect of freshwater flow on sea surface salinity (SSS) and temperature (SST) in the Gulf of Guinea. In particular, the Congo River discharges a huge amount of freshwater into the ocean, affecting SSS in the Eastern Equatorial Atlantic (EEA) and stratifying the surface layers. The hypothesis is that an excess of river runoff emphasize stratification, influencing the ocean temperature. In fact, our findings show that SSTs in the Gulf of Guinea are warmer in summers following an anomalously high Congo spring discharge. Vice versa, when the river discharges low freshwater, a cold anomaly appears in the Gulf. The response of SST is not linear: temperature anomalies are considerable and long-lasting in the event of large freshwater flow, while in dry years they are less remarkable, although still significant. An excess of freshwater seems able to form a barrier layer, which inhibits vertical mixing and the entrainment of the cold thermocline water into the surface. Other processes may contribute to SST variability, among which the net input of atmospheric freshwater falling over EEA. Likewise the case of continental runoff from Congo River, warm anomalies occur after anomalously rainy seasons and low temperatures follow dry seasons, confirming the effect of freshwater on SST. However, the two sources of freshwater anomaly are not in phase, so that it is possible to split between atypical SST following continental freshwater anomalies and rainfall anomalies. Also, variations in air-sea fluxes can produce heating and cooling of the Gulf of Guinea. Nevertheless, atypical SSTs cannot be ascribed to fluxes, since the temperature variation induced by them is not sufficient to explain the SST anomalies appearing in the Gulf after anomalous peak discharges. The interaction processes between river runoff, sea surface salinity and temperature play an effective role in the interannual variability in the EEA region. Our results add a new source of variability in the area, which was often neglected by previous studies.  相似文献   

12.
Abstract

Seasonal and interannual variations of the SST 16–19°C zone in the western North Pacific are described. Temperatures ranging from 16 to 19°C correspond with those of the Subtropical Mode Water (SMW) first reported and named by Masuzawa (1969). In the cooling season, this zone gradually moves southward and about December crosses latitudes 35–37°N where the Kuroshio axis lies. From January to April, the zone stagnates and spreads from the Kuroshio axis to about 28°N, i.e. to a width of about 700 km at 145°E in midwinter. This stagnation and widening are a manifestation of the existence of a thick mixed layer of SMW, i.e. the formation of a large amount of SMW, which is confirmed by several examples of the subsurface temperature distribution. In the heating season, the zone migrates northward with a narrow width as a result of the warming of the surface layer through the air‐sea interface. SST maps in March, and other related data, show the large interannual variations of the zone, especially in the sea west of the Izu Ridge.  相似文献   

13.
Freshwater flux (FWF) directly affects sea surface salinity (SSS) and hence modulates sea surface temperature (SST) in the tropical Pacific. This paper quantifies a positive correlation between FWF and SST using observations and simulations of the fifth phase of the Coupled Model Intercomparison Project (CMIP5) to analyze the interannual variability in the tropical Pacific. Comparisons among the displacements of FWF, SSS and SST interannual variabilities illustrate that a large FWF variability is located in the west-central equatorial Pacific, covarying with a large SSS variability, whereas a large SST variability is located in the eastern equatorial Pacific. Most CMIP5 models can reproduce the fact that FWF leads to positive feedback to SST through an SSS anomaly as observed. However, the difference in each model's performance results from different simulation capabilities of the CMIP5 models in the magnitudes and positions of the interannual variabilities, including the mixed layer depth and the buoyancy flux in the equatorial Pacific. SSS anomalies simulated from the CMIP5 multi-model are sensitive to FWF interannual anomalies, which can lead to differences in feedback to interannual SST variabilities. The relationships among the FWF, SSS and SST interannual variabilities can be derived using linear quantitative measures from observations and the CMIP5 multi-model simulations. A 1 mm d-1 FWF anomaly corresponds to an SSS anomaly of nearly 0.12 psu in the western tropical Pacific and a 0.11°C SST anomaly in the eastern tropical Pacific.  相似文献   

14.
Pascal Terray 《Climate Dynamics》2011,36(11-12):2171-2199
The main goal of this paper is to shed additional light on the reciprocal dynamical linkages between mid-latitude Southern Hemisphere climate and the El Ni?o-Southern Oscillation (ENSO) signal. While our analysis confirms that ENSO is a dominant source of interannual variability in the Southern Hemisphere, it is also suggested here that subtropical dipole variability in both the Southern Indian and Atlantic Oceans triggered by Southern Hemisphere mid-latitude variability may also provide a controlling influence on ENSO in the equatorial Pacific. This subtropical forcing operates through various coupled air?Csea feedbacks involving the propagation of subtropical sea surface temperature (SST) anomalies into the deep tropics of the Atlantic and Indian Oceans from boreal winter to boreal spring and a subsequent dynamical atmospheric response to these SST anomalies linking the three tropical basins at the beginning of the boreal spring. This atmospheric response is characterized by a significant weakening of the equatorial Atlantic and Indian Inter-Tropical Convergence Zone (ITCZ). This weakened ITCZ forces an equatorial ??cold Kelvin wave?? response in the middle to upper troposphere that extends eastward from the heat sink regions into the western Pacific. By modulating the vertical temperature gradient and the stability of the atmosphere over the equatorial western Pacific Ocean, this Kelvin wave response promotes persistent zonal wind and convective anomalies over the western equatorial Pacific, which may trigger El Ni?o onset at the end of the boreal winter. These different processes explain why South Atlantic and Indian subtropical dipole time series indices are highly significant precursors of the Ni?o34 SST index several months in advance before the El Ni?o onset in the equatorial Pacific. This study illustrates that the atmospheric internal variability in the mid-latitudes of the Southern Hemisphere may significantly influence ENSO variability. However, this surprising relationship is observed only during recent decades, after the so-called 1976/1977 climate regime shift, suggesting a possible linkage with global warming or decadal fluctuations of the climate system.  相似文献   

15.
Richter  Ingo  Tokinaga  Hiroki 《Climate Dynamics》2020,55(9-10):2579-2601

General circulation models of the Coupled Model Intercomparison Project Phase 6 (CMIP6) are examined with respect to their ability to simulate the mean state and variability of the tropical Atlantic and its linkage to the tropical Pacific. While, on average, mean state biases have improved little, relative to the previous intercomparison (CMIP5), there are now a few models with very small biases. In particular the equatorial Atlantic warm SST and westerly wind biases are mostly eliminated in these models. Furthermore, interannual variability in the equatorial and subtropical Atlantic is quite realistic in a number of CMIP6 models, which suggests that they should be useful tools for understanding and predicting variability patterns. The evolution of equatorial Atlantic biases follows the same pattern as in previous model generations, with westerly wind biases during boreal spring preceding warm sea-surface temperature (SST) biases in the east during boreal summer. A substantial portion of the westerly wind bias exists already in atmosphere-only simulations forced with observed SST, suggesting an atmospheric origin. While variability is relatively realistic in many models, SSTs seem less responsive to wind forcing than observed, both on the equator and in the subtropics, possibly due to an excessively deep mixed layer originating in the oceanic component. Thus models with realistic SST amplitude tend to have excessive wind amplitude. The models with the smallest mean state biases all have relatively high resolution but there are also a few low-resolution models that perform similarly well, indicating that resolution is not the only way toward reducing tropical Atlantic biases. The results also show a relatively weak link between mean state biases and the quality of the simulated variability. The linkage to the tropical Pacific shows a wide range of behaviors across models, indicating the need for further model improvement.

  相似文献   

16.
Abstract

Monthly mean sea‐level pressure (SLP) data from the Northern Hemisphere for the period January 1952‐December 1987 are analysed. Fluctuations in this field over the Arctic on interannual time‐scales and their statistical association with fluctuations farther south are determined. The standard deviation of the interannual variability is largest compared with that of the annual cycle along the seaboards of the major land masses. The SLP anomalies are generally in phase over the entire Arctic Basin and extend south over the northern Russia and Canada, but tend to be out of phase with fluctuations at mid‐latitudes. The anomalies are most closely associated with fluctuations over the North Atlantic and Europe except near the Chukchi Sea to the north of Bering Strait. The associations with the North Pacific fluctuations become increasingly more prominent at most Arctic sites (e.g. the Canadian Arctic Archipelago) as the time‐scale increases.

Associations between the SLP fluctuations and atmospheric indices that represent processes affecting sea‐ice drift (wind stress and wind stress curl) are determined. In every case local associations dominate, but some remote ones are also evident. For example, changes in the magnitude of the wind stress curl over the Beaufort Sea are increased if the atmospheric circulation over the North Pacific is intensified; wind stress over the region where sea ice is exchanged between the Beaufort Gyre and the Transpolar Drift Stream is modulated by both the Southern and North Atlantic Oscillations.

Severe sea‐ice conditions in the Greenland Sea (as measured by the Koch Ice Index) coincide with a weakened atmospheric circulation over the North Atlantic.  相似文献   

17.
针对近赤道海温对西太平洋副高影响的复杂性和不确定性问题,引入自适应模糊推理系统方法,系统地分析了西太平洋副高强度对赤道东太平洋、赤道西太平洋和赤道印度洋等海区海温状况和冷暖变化的响应态势和响应程度。研究表明:副高对赤道东太平洋海温的变冷(增暖)过程将出现正距平的增强(减弱)响应,响应幅度随时间减弱(增强);副高对赤道印度洋海温增暖(变冷)的响应态势与对赤道东太平洋海温的响应态势相反,响应幅度远小于赤道东太平洋海温变化的响应幅度;副高对赤道西太平洋海温的增暖急缓表现出不同的响应态势,迅速增暖利于副高衰减,缓慢增暖则利于副高增强,而对于海温的变冷过程则有滞后的增强响应趋势。此外,上述海区的海温冷暖变化幅度和速度是导致副高变异的主要因素,较之海温基本热力状况对副高强度的影响更为显著。  相似文献   

18.
Tropical zonally symmetric atmospheric warming occurs during ENSO’s warm phase, and lags the equa- torial east Pacific sea surface temperatures (SSTs) by 3–4 months. The role of the Indian and Atlantic oceans on the atmospheric delayed response has been pointed out by earlier studies. For 1951–2004, a regression analysis based on the observed SST data shows the western Pacific has a similarly important role as the Indian and Atlantic. Nevertheless, there is time mismatch of around 1–2 months between the zon...  相似文献   

19.
Abstract

A new ENSO SST index is documented that is strongly correlated to the core ENSO phenomenon. The SST anomaly in much of the east‐central and eastern tropical Pacific is closely related to ENSO. However, the anomaly from approximately the centre of the eastern half of the equatorial Pacific westward to near the date line is suggested to be most strongly ENSO‐related when data spanning the most recent several decades are used. This is the case both with respect to (1) strength of association with other oceanic/atmospheric ENSO‐related anomalies (both simultaneously and as a time‐delayed predictand), and (2) impact on remote worldwide climate anomalies. This observational insight was lacking in the early 1980s when the four “Niño” regions were developed. While a firmer dynamical foundation for this regional preference still needs to be established, the region straddling Niño 3 and Niño 4 may be regarded as an appropriate general SST index of the ENSO state by researchers, diagnosticians and forecasters. A dataset of this index, called “Niño 3.4” (5°N‐5°S, 120–170°W), is maintained on the Internet, shown in the Climate Diagnostics Bulletin, and provided in the Appendix of this note.  相似文献   

20.
ABSTRACT In this paper, interannual variations in the barrier layer thickness （BLT） are analyzed using Argo three-dimensional temperature and salinity data, with a locus on the effects of interannually varying salinity on the evolution of the El Nifio Southern Oscillation （ENSO）. The interannually varying BLT exhibits a zonal seesaw pattern across the equatorial Pacific during ENSO cycles. This phenomenon has been attributed to two different physical processes. During E1 Nifio （La Nifia）, the barrier layer （BL） is anomalously thin （thick） west of about 160°E, and thick （thin） to the east. In the western equatorial Pacific （the western part： 130°-160°E）, interannual variations of the BLT indicate a lead of one year relative to those of the ENSO onset. The interannual variations of the BLT can be largely attributed to the interannual temperature variability, through its dominant effect on the isothermal layer depth （ILD）. However, in the central equatorial Pacific （the eastern part： 160~E- 170~W）, interannual variations of the BL almost synchronously vary with ENSO, with a lead of about two months relative to those of the local SST. In this region, the interannual variations of the BL are significantly affected by the interannually varying salinity, mainly through its modulation effect on the mixed layer depth （MLD）. As evaluated by a onedimensional boundary layer ocean model, the BL around the dateline induced by interannual salinity anomalies can significantly affect the temperature fields in the upper ocean, indicating a positive feedback that acts to enhance ENSO.  相似文献   

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