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1.
In this paper, the influence of El Ni?o event on the Madden-Julian Oscillation(MJO) over the equatorial Pacific is studied by using reanalysis data and relevant numerical simulation results. It is clearly shown that El Ni?o can reduce the intensity of MJO. The kinetic energy of MJO over the equatorial Pacific is stronger before the occurrence of the El Ni?o event, but it is reduced rapidly after El Ni?o event outbreak, and the weakened MJO even can continue to the next summer. The convection over the central-western Pacific is weakened in El Ni?o winter. The positive anomalous OLR over the central-western Pacific has opposite variation in El Ni?o winter comparing to the non-ENSO cases. The vertical structure of MJO also affected by El Ni?o event, so the opposite direction features of the geopotential height and the zonal wind in upper and lower level troposphere for the MJO are not remarkable in the El Ni?o winter and tend to be barotropic features. El Ni?o event also has an influence on the eastward propa- gation of the MJO too. During El Ni?o winter, the eastward propagation of the MJO is not so regular and unanimous and there exists some eastward propagation, which is faster than that in non-ENSO case. Dynamic analyses suggest that positive SSTA(El Ni?o case) affects the atmospheric thickness over the equatorial Pacific and then the excited atmospheric wave-CISK mode is weakened, so that the intensity of MJO is reduced; the combining of the barotropic unstable mode in the atmosphere excited by external forcing(SSTA) and the original MJO may be an important reason for the MJO vertical structure tending to be barotropic during the El Ni?o.  相似文献   

2.
Based on the 18-year(1993–2010) National Centers for Environmental Prediction optimum interpolation sea surface temperature(SST) and simple ocean data assimilation datasets,this study investigated the patterns of the SST anomalies(SSTAs) that occurred in the South China Sea(SCS) during the mature phase of the El Ni?o/Southern Oscillation.The most dominant characteristic was that of the outof-phase variation between southwestern and northeastern parts of the SCS,which was influenced primarily by the net surface heat flux and by horizontal thermal advection.The negative SSTA in the northeastern SCS was caused mainly by the loss of heat to the atmosphere and because of the cold-water advection from the western Pacific through the Luzon Strait during El Ni?o episodes.Conversely,it was found that the anomalous large-scale atmospheric circulation and weakened western boundary current during El Ni?o episodes led to the development of the positive SSTA in the southwestern SCS.  相似文献   

3.
By analyzing the variability of global SST(sea surface temperature) anomalies,we propose a unified Ni o index using the surface thermal centroid anomaly of the region along the Pacific equator embraced by the 0.7°C contour line of the standard deviation of the SST anomalies and try to unify the traditional Ni o regions into a single entity.The unified Ni o region covers almost all of the traditional Ni o regions.The anomaly time series of the averaged SST over this region are closely correlated to historical Ni o indices.The anomaly time series of the zonal and meridional thermal centroid have close correlation with historical TNI(Trans-Ni o index) indices,showing differences among El Ni o(La Ni a) events.The meridional centroid anomaly suggests that areas of maximum temperature anomaly are moving meridionally(although slightly) with synchronous zonal movement.The zonal centroid anomalies of the unified Ni o region are found helpful in the classification of the Eastern Pacific(EP)/Central Pacific(CP) types of El Ni o events.More importantly,the zonal centroid anomaly shows that warm areas might move during a single warming/cooling phase.All the current Ni o indices can be well represented by a simple linear combination of unified Ni o indices,which suggests that the thermal anomaly(SSTA) and thermal centroid location anomaly of the unified Ni o region would yield a more complete image of each El Ni o/ La Ni a event.  相似文献   

4.
El Nio events with an eastern Pacific pattern(EP) and central Pacific pattern(CP) were first separated using rotated empirical orthogonal functions(REOF).Lead/lag regression and rotated singular value decomposition(RSVD) analyses were then carried out to study the relation between the surface zonal wind(SZW) anomalies and sea surface temperature(SST) anomalies in the tropical Pacific.A possible physical process for the CP El Ni o was proposed.For the EP El Ni o,strong westerly anomalies that spread eastward continuously produce an anomalous ocean zonal convergence zone(ZCZ) centered on about 165°W.This SZW anomaly pattern favors poleward and eastward Sverdrup transport at the equator.For the CP El Nio,westerly anomalies and the ZCZ are mainly confined to the western Pacific,and easterly anomalies blow in the eastern Pacific.This SZW anomaly pattern restrains poleward and eastward Sverdrup transport at the equator;however,there is an eastward Sverdrup transport at about 5°N,which favors the warming of the north-eastern tropical Pacific.It is found that the slowness of eastward propagation of subsurface warm water(partly from the downwelling caused by Ekman convergence and the ZCZ) is due to the slowdown of the undercurrent in the central basin,and vertical advection in the central Pacific may be important in the formation and disappearance of the CP El Nio.  相似文献   

5.
Based on an analysis of 51-year(1965–2015) data, the influence of El Ni?o–Southern Oscillation(ENSO) events on tropical cyclone(TC) activity is examined over the western North Pacific(WNP). The total number of TCs formed in the entire WNP reduces by about 3.4 TCs per year in La Ni?a years, whereas TCs have an equivalent genesis number between El Ni?o years and climatology. During El Ni?o years, the frequency of TC formation increases remarkably in the southeast quadrant(140?E–180?, 0?–17?N) and decreases in the northwest quadrant(120?–140?E, 17?–30?N). During La Ni?a years, TCs tend to form in the northwest and southwest quadrants(120?–140?E, 0?–17?N) quadrants. TCs tend to become long-lived in the peak season(from July to September) of El Ni?o years and during strong El Ni?o events. TC genesis shows a southeastward positive shift in terms of lifetime and intensity during El Ni?o years, thus more super TCs(winds ≥ 58.64 m s-1) are formed in the southeast quadrant. Further analysis using the genesis potential index(GPI) indicates that the interannual variations in the TC genesis and track are significantly influenced by a combination of large-scale dynamic and thermodynamic conditions.  相似文献   

6.
The Sea Level Anomaly-Torque (SLAT, relative to a reference location in the Pacific Ocean), which means the total torque of the gravity forces of sea waters with depths equal to the Sea Level Anomaly (SLA) in the tropical Pacific Ocean, is defined in this study. The time series of the SLAT from merged altimeter data (1993-2003) had a great meridional variation during the 1997-1998 El Nio event. By using historical upper layer temperature data (1955-2003) for the tropical Pacific Ocean, the tempera- ture-based SLAT is also calculated and the meridional variation can be found in the historical El Nio events (1955-2003), which suggests that the meridional shifts of the sea level anomaly are also intrinsic oscillating modes of the El Nio cycles like the zonal shifts.  相似文献   

7.
ENSO cycle and climate anomaly in China   总被引：2，自引：0，他引：2  
The inter-annual variability of the tropical Pacific Subsurface Ocean Temperature Anomaly (SOTA) and the associated anomalous atmospheric circulation over the Asian North Pacific during the El Ni o-Southern Oscillation (ENSO) were investigated using National Centers for Environmental Prediction/ National Center for Atmospheric Research (NCEP/NCAR) atmospheric reanalysis data and simple ocean data simulation (SODA). The relationship between the ENSO and the climate of China was revealed. The main results indicated the following: 1) there are two ENSO modes acting on the subsurface tropical Pacific. The first mode is related to the mature phase of ENSO, which mainly appears during winter. The second mode is associated with a transition stage of the ENSO developing or decaying, which mainly occurs during summer; 2) during the mature phase of El Ni o, the meridionality of the atmosphere in the mid-high latitude increases, the Aleutian low and high pressure ridge over Lake Baikal strengthens, northerly winds prevail in northern China, and precipitation in northern China decreases significantly. The ridge of the Ural High strengthens during the decaying phase of El Ni o, as atmospheric circulation is sustained during winter, and the northerly wind anomaly appears in northern China during summer. Due to the ascending branch of the Walker circulation over the western Pacific, the western Pacific Subtropical High becomes weaker, and south-southeasterly winds prevail over southern China. As a result, less rainfall occurs over northern China and more rainfall over the Changjiang River basin and the southwestern and eastern region of Inner Mongolia. The flood disaster that occurred south of Changjiang River can be attributed to this. The La Ni a event causes an opposite, but weaker effect; 3) the ENSO cycle can influence climate anomalies within China via zonal and meridional heat transport. This is known as the "atmospheric-bridge", where the energy anomaly within the tropical Pacific transfers to the mid-high latitude in the northern Pacific through Hadley cells and Rossby waves, and to the western Pacific-eastern Indian Ocean through Walker circulation. This research also discusses the special air-sea boundary processes during the ENSO events in the tropical Pacific, and indicates that the influence of the subsurface water of the tropical Pacific on the atmospheric circulation may be realized through the sea surface temperature anomalies of the mixed water, which contact the atmosphere and transfer the anomalous heat and moisture to the atmosphere directly. Moreover, the reason for the heavy flood within the Changjiang River during the summer of 1998 is reviewed in this paper.  相似文献   

8.
This paper analyzes the characteristics of super typhoons(STYs)over the western North Pacific(WNP)from 1965 to2005 and describes the seasonal variability of STY activity.The relation between STY activity and the El Nio-Southern Oscillation(ENSO)as well as the possible reason for the influence of the ENSO on STY activity are also investigated.The results showed thatabout one fifth of the tropical cyclones(TCs)over the WNP could reach the rank of STY.Most STYs appeared from July to Novem-ber while there was a highest ratio between number of STYs and total number of TCs in November.Most STYs appeared east of thePhilippine Sea.In El Nio years,affected by sea surface temperature(SST),monsoon trough and weak vertical wind shear,TC for-mation locations shifted eastward and there were more STYs than in La Nia years when the affecting factors changed.  相似文献   

9.
The relationship of the interannual variability of the transport and bifurcation latitude of the North Equatorial Current (NEC) to the El Ni o-Southern Oscillation (ENSO) is investigated. This is done through composite analysis of sea surface height (SSH) observed by satellite altimeter during October 1992-July 2009, and correspondingly derived sea surface geostrophic currents. During El Nio/La Ni a years, the SSH in the tropical North Pacific Ocean falls/rises, with maximum changes in the region 0-15°N, 130°E-160°E. The decrease/increase in SSH induces a cyclonic/anticyclonic anomaly in the western tropical gyre. The cyclonic/anticyclonic anomaly in the gyre results in an increase/decrease of NEC transport, and a northward/southward shift of the NEC bifurcation latitude near the Philippine coast. The variations are mainly in response to anomalous wind forcing in the west-central tropical North Pacific Ocean, related to ENSO events.  相似文献   

10.
An analysis was performed in this study to investigate synchronous fluctuations in abundance and distribution of Ommastrephes bartramii in the Northwest Pacific Ocean and Dosidicus gigas in the Southeast Pacific Ocean. The impacts of two Ni?o indices and regional water surface temperature on the two squids during 2006–2015 were evaluated, which possibly can explain the observed synchronicity. Catch per unit effort(CPUE) and the latitudinal gravity centers(LATG) of fishing effort were used to indicate squid abundance and distribution, respectively. The results indicated that both the CPUE and LATG showed highly interannual variations and synchronous fluctuation with significant negative associations between the two squid species from September to November. Strong positive cross-correlations with 2-month lag was found between sea surface temperature(SST) anomaly in the Ni?o 3.4 and Ni?o 1+2 regions, which have significant linkage with the SST on the fishing ground of O. bartramii and D. gigas, respectively. Moreover, the proportion of favorable-SST area(PFSST) and the latitudinal location of the optimal SST for O. bartramii and D. gigas were positively correlated with the CPUE and LATG, respectively. Increased O. bartramii PFSST clearly corresponded to decreased D. gigas PFSST in phase as well as the latitudinal location of the optimal SST from September to November over 2006– 2015. Our findings suggest that synchronous changes in abundance and distribution of the two squids were due to simultaneous variations in the PFSST and the latitudinal location of the optimal SST front which were affected by the SSTA changes in the Ni?o 3.4 and Ni?o 1+2 regions.  相似文献   

11.
Sea surface height (SSH) variability in the Mindanao Dome (MD) region is found to be one of the strong variations in the northern Pacific. It is only weaker than that in the Kuroshio Extension area, and is comparable to that in the North Pacific Subtropical Countercurrent region. Based on a 1.5-layer reduced gravity model, we analyzed SSH variations in this region and their responses to northern tropical Pacific winds. The average SSH anomaly in the region varies mainly on a seasonal scale, with significant periods of 0.5 and 1 year, ENSO time scale2-7years, and time scale in excess of 8 years. Annual and long-term variabilities are comparably stronger. These variations are essentially a response to the northern tropical Pacific winds. On seasonal and ENSO time scales, they are mainly caused by wind anomalies east of the region, which generate westward-propagating, long Rossby waves. On time scales longer than 8 years, they are mostly induced by local Ekman pumping. Long-term SSH variations in the MD region and their responses to local winds are examined and discussed for the first time .  相似文献   

12.
Based on daily precipitation data from 109 stations in the Yangtze River Basin(YRB) over the past 36 years(1980 – 2015),the Empirical Orthogonal Function(EOF) is employed to analyze changes in autumn precipitation. We used the monthly mean reanalysis datasets of atmospheric circulation and sea surface temperature(SST) to investigate the possible causes of the two leading modes, based on which the predictive equations were constructed and tested. The results of the EOF analysis show that the variance contribution of the first mode is 31.07%, and the spatial distribution shows a uniform variation over the whole region. The variance contribution of the second mode is 15.02%, and the spatial distribution displays a north-south dipole pattern in the YRB. The leading mode shows a dominant interannual variation, which is mainly due to the West Pacific subtropical high and anticyclones over the Philippine islands. The SST field corresponds to the positive phase of the eastern Pacific El Ni?o and the tropical Indian Ocean dipole. The second mode may be related to the Indian Ocean-East Asian teleconnection and early withdrawal of the summer monsoon.The SST field corresponds to a weaker central Pacific El Ni?o. Through a stepwise regression analysis, SST anomalies in some areas during summer show a good predictive effect on the autumn precipitation mode in the YRB region.  相似文献   

13.
Although the mid-late Holocene cold and dry event about 4000 years ago(the 4 ka event) has been observed almost globally, it was most prominent in terrestrial climate proxies from the lower latitudes. Here we evaluate the oceanic response to this event in terms of a Holocene sea surface temperature(SST) record reconstructed using the K'37U index for Core B3 on the continental shelf of the East China Sea. The record reveals a large temperature drop of about 5℃ from the mid-Holocene(24.7℃ at 5.6 ka) to the 4 ka event(19.2℃ at 3.8 ka). This mid-late Holocene cooling period in Core B3 correlated with(i) decreases in the East Asia summer monsoon intensity and(ii) the transition period with increased El Nino/Southern Oscillation activities in the Equatorial Pacific. Our SST record provides oceanic evidence for a more global nature of the mid-late Holocene climate change, which was most likely caused by a southward migration of the Intertropical Converge Zone in response to the decreasing summer solar insolation in the Northern Hemisphere. However, the large SST drop around Core B3 indicates that the mid-late Holocene cooling was regionally amplified by the initiation/strengthening of eddy circulation/cold front which caused upwelling and resulted in additional SST decrease. Upwelling during the mid-late Holocene also enhanced with surface productivity in the East China Sea as reflected by higher alkenone content around Core B3.  相似文献   

14.
Thirteen-year satellite-derived data are used to investigate the temporal variability of net primary production (NPP) in the Oman upwelling zone and its potential forcing mechanisms. The NPP in the Oman upwelling zone is characterized by an abnormal decrease during El Ni o events. Such an NPP decrease may be related to El Ni o-driven anomalous summertime weak wind. During the summer following El Ni o, the anomalous northeasterly wind forced by southwest Indian Ocean warming weakens the southwest monsoon and warms the Arabian Sea. The abnormal wind weakens the coastal Ekman transport, offshore Ekman pumping and horizontal advection, resulting in reduced upward nutrient supply to the euphotic zone. A slightly declining trend in NPP after 2000 associated with a gradual decrease in surface monsoon winds is discussed.  相似文献   

15.
The standard deviation of the central Pacific sea surface temperature anomaly (SSTA) during the period from October to February shows that the central Pacific SSTA variation is primarily due to the occurrence of the Central Pacific El Nio (CP-El Nio) and has a connection with the subtropical air-sea interaction in the northeastern Pacific. After removing the influence of the Eastern Pacific El Nio, an S-EOF analysis is conducted and the leading mode shows a clear seasonal SSTA evolving from the subtropical northeastern Pacific to the tropical central Pacific with a quasi-biennial period. The initial subtropical SSTA is generated by the wind speed decrease and surface heat flux increase due to a north Pacific anomalous cyclone. Such subtropical SSTA can further influence the establishment of the SSTA in the tropical central Pacific via the wind-evaporation-SST (WES) feedback. After established, the central equatorial Pacific SSTA can be strengthened by the zonal advective feedback and thermocline feedback, and develop into CP-El Nio. However, as the thermocline feedback increases the SSTA cooling after the mature phase, the heat flux loss and the re-versed zonal advective feedback can cause the phase transition of CP-El Nio. Along with the wind stress variability, the recharge (discharge) process occurs in the central (eastern) equatorial Pacific and such a process causes the phase consistency between the thermocline depth and SST anomalies, which presents a contrast to the original recharge/discharge theory.  相似文献   

16.
This paper investigates the response of the thermocline depth(TD) in the South China Sea(SCS) to the El Ni?o-Southern Oscillation(ENSO) events using 51-year(from 1960 to 2010) monthly seawater temperature and surface wind stress data acquired from the Simple Ocean Data Assimilation(SODA), together with heat flux data from the National Centers for Environmental Prediction(NCEP), precipitation data from the National Oceanic and Atmospheric Administration(NOAA) and evaporation data from the Woods Hole Oceanographic Institution(WHOI). It is indicated that the response of the SCS TD to the El Ni?o or La Ni?a events is in opposite phase. On one hand, the spatial-averaged TDs in the SCS(deeper than 200 m) appear as negative and positive anomalies during the mature phase of the El Ni?o and La Ni?a events, respectively. On the other hand, from June of the El Ni?o year to the subsequent April, the spatial patterns of TD in the north and south of 12°N appear as negative and positive anomalies, respectively, but present positive and negative anomalies for the La Ni?a case. However, positive and negative TD anomalies occur almost in the entire SCS in May of the subsequent year of the El Ni?o and La Ni?a events, respectively. It is suggested that the response of the TD in the SCS to the ENSO events is mainly caused by the sea surface buoyancy flux and the wind stress curl.  相似文献   

17.
Principal component analysis (PCA) as used by meteorologists and oceanographers is a powerful tool for analysis of the spatial and temporal variability of physical fields.This study was aimed at applying "quasi-local PCA for singular factor" to make the cumulative percentage for the first principal component as great as possible, so that a multi-dimensional problem can be reduced to a single-dimensional one, and then stepwise regression analysis can be used to parameterize the relationship between El Nino events and the hydrographic factor anomalies along 137 癊 in winter.The results show that the salinity anomalies on 30 m level, the sigmat on 250 m level, and the temperature on 300 m level at 8 癗 are most closely related with El Nino events because of thermocline movement caused by enhanced upwelling in this area during El Nino years.  相似文献   

18.
Lag correlations between sea surface temperature anomalies(SSTA) in the southeastern tropical Indian Ocean(STIO) in fall and Nio 3.4 SSTA in the eastern equatorial Pacific in the following fall are subjected to decadal variation,with positive correlations during some decades and negative correlations during others. Negative correlations are smaller and of shorter duration than positive correlations. Variations in lag correlations suggest that the use of the Indian Ocean Dipole(IOD) as a predictor of the El Nio Southern Oscillation(ENSO) at a lead time of one year is not effective during some decades. In this study,lag correlations between IOD and ENSO anomalies were analyzed to investigate why the IOD-ENSO teleconnection disappears during decades with negative correlations. Anomalies induced by the IOD in the equatorial Pacific Ocean during decades with negative correlations are still present,but at a greater depth than in decades with positive correlations,resulting in a lack of response to oceanic channel dynamics in the cold tongue SSTA. Lag correlations between oceanic anomalies in the west Pacific warm pool in fall and the equatorial Pacific cold tongue with a one-year time lag are significantly positive during decades with negative correlations. These results suggest that oceanic channel dynamics are overwhelmed by oceanatmosphere coupling over the equatorial Pacific Ocean during decades with negative correlations. Therefore,the Indonesian throughflow is not effective as a link between IOD signals and the equatorial Pacific ENSO.  相似文献   

19.
Principal component analysis (PCA) used by meteorologists and oceanographers is a powerful tool for the analysis of the spatial and temporal variability of physical fields .This study is aimed at applying " quasi-local PCA for singular factor " to make the cumulative percentage for the first principal component as great as possible , so that the many-dimension problem can be reduced to a single-dimension one , and at combining PCA with stepwise regression analysis to parameterize the relationship between El Nino events and the anomalies in hydrographic factors along 137°E in summer.The results show that the hydrography on 30-50 m levels at 7-9° N along 137° E in summer is very closely correlated with El Nino events because of the thermocline movement caused by enhanced upwelling in this area during El Nino years .  相似文献   

20.
The thermal condition anomaly of the western Pacific warm pool and its zonal displacement have very important influences on climate change in East Asia and even the whole world. However, the impact of the zonal wind anomaly over the Pacific Ocean on zonal displacement of the warm pool has not yet been analyzed based on long-term record. Therefore, it is important to study the zonal displacement of the warm pool and its response to the zonal wind anomaly over the equatorial Pacific Ocean. Based on the NCDC monthly averaged SST (sea surface temperature) data in 2°×2° grid in the Pacific Ocean from 1950 to 2000, and the NCEP/NCAR global monthly averaged 850 hPa zonal wind data from 1949 to 2000, the relationships between zonal displacements of the western Pacific warm pool and zonal wind anomalies over the tropical Pacific Ocean are analyzed in this paper. The results show that the zonal displacements are closely related to the zonal wind anomalies over the western, central and eastern equatorial Pacific Ocean. Composite analysis indicates that during ENSO events, the warm pool displacement was trigged by the zonal wind anomalies over the western equatorial Pacific Ocean in early stage and the process proceeded under the zonal wind anomalies over the central and eastern equatorial Pacific Ocean unless the wind direction changes. Therefore, in addition to the zonal wind anomaly over the western Pacific, the zonal wind anomalies over the central and eastern Pacific Ocean should be considered also in investigation the dynamical mechanisms of the zonal displacement of the warm pool.  相似文献   

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