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1.
Assessing the Influence of the ENSO on Tropical Cyclone Prevailing Tracks in the Western North Pacific 总被引:3,自引:0,他引:3
Using a statistical model for simulating tropical cyclone (TC) formation and a trajectory model for simulating TC tracks, the influence of the El Nino-Southern Oscillation (ENSO) on the peak-season (July-September) TC prevailing tracks in the western North Pacific basin is assessed based on 14 selected El Nino and 14 selected La Nina years during the period 1950-2007. It is found that the combination of statistical formation model and a trajectory model can simulate well the primary features of TC prevai... 相似文献
2.
Five sets of model sensitivity experiments are conducted to investigate the influence of tropical cyclone (TC) genesis location and atmospheric circulation on interannual variability of TC intensity in the western North Pacific (WNP). In each experiment, bogus TCs are placed at different initial locations, and simulations are conducted with identical initial and boundary conditions. In the first three experiments, the specified atmospheric and SST conditions represent the mean conditions of El Nio, La Nia, and neutral years. The other two experiments are conducted with the specified atmospheric conditions of El Nio and La Nia years but with SSTs exchanged. The model results suggest that TCs generated in the southeastern WNP incurred more favorable environmental conditions for development than TCs generated elsewhere. The different TC intensities between El Nio and La Nia years are caused by difference in TC genesis location and low-level vorticity (VOR). VOR plays a significant role in the intensities of TCs with the same genesis locations between El Nio and La Nia years. 相似文献
3.
Relationships between the East Asian-western north pacific monsoon and ENSO simulated by FGOALS-s2 总被引:4,自引:1,他引:3
The relationships between ENSO and the East Asian-western North Pacific monsoon simulated by the Flexible Global Ocean-Atmosphere-Land System model, Spectral Version 2 (FGOALS-s2), a state-of-the-art coupled general circulation model (CGCM), are evaluated. For El Nio developing summers, FGOALS-s2 reproduces the anomalous cyclone over the western North Pacific (WNP) and associated negative precipitation anomalies in situ. In the observation, the anomalous cyclone is transformed to an anomalous anticyclone over the WNP (WNPAC) during El Nio mature winters. The model reproduces the WNPAC and associated positive precipitation anomalies over southeastern China during winter. However, the model fails to simulate the asymmetry of the wintertime circulation anomalies over the WNP between El Nio and La Nia. The simulated anomalous cyclone over the WNP (WNPC) associated with La Nia is generally symmetric about the WNPAC associated with El Nio, rather than shifted westward as that in the observation. The discrepancy can partially explain why simulated La Nin a events decay much faster than observed. In the observation, the WNPAC maintains throughout the El Nio decaying summer under the combined effects of local forcing of the WNP cold sea surface temperature anomaly (SSTA) and remote forcing from basinwide warming in the tropical Indian Ocean. FGOALS-s2 captures the two mechanisms and reproduces the WNPAC throughout the summer. However, owing to biases in the mean state, the precipitation anomalies over East Asia, especially those of the Meiyu rain belt, are much weaker than that in the observation. 相似文献
4.
Severe flooding occurred in southern and northern China during the summer of 2016 when the 2015 super El Nio decayed to a normal condition. However, the mean precipitation during summer(June–July-August) 2016 does not show significant anomalies, suggesting that — over East Asia(EA) — seasonal mean anomalies have limited value in representing hydrological hazards. Scrutinizing season-evolving precipitation anomalies associated with 16 El Nio episodes during 1957–2016 reveals that, over EA, the spatiotemporal patterns among the four categories of El Nio events are quite variable, due to a large range of variability in the intensity and evolution of El Nio events and remarkable subseasonal migration of the rainfall anomalies. The only robust seasonal signal is the dry anomalies over central North China during the El Nio developing summer. Distinguishing strong and weak El Nio impacts is important. Only strong El Nio events can persistently enhance EA subtropical frontal precipitation from the peak season of El Nio to the ensuing summer, by stimulating intense interaction between the anomalous western Pacific anticyclone(WPAC) and underlying dipolar sea surface temperature anomalies in the Indo-Pacific warm pool, thereby maintaining the WPAC and leading to a prolonged El Nio impact on EA. A weak El Nio may also enhance the post-El Nio summer rainfall over EA, but through a different physical process: the WPAC re-emerges as a forced response to the rapid cooling in the eastern Pacific. The results suggest that the skillful prediction of rainfall over continental EA requires the accurate prediction of not only the strength and evolution of El Nio, but also the subseasonal migration of EA rainfall anomalies. 相似文献
5.
In this paper, the impact of ENSO on the precipitation over China in the winter half-year is investigated diagnostically. The results show that positive precipitation anomalies with statistical significance appear over southern China in El Nio episodes, which are caused by the enhanced warm and humid southwesterlies along the East Asian coast in the lower troposphere. The enhanced southwesterlies transport more water vapor to southern China, and the convergence of water vapor over southern China increases the precipitable water and specific humidity. In La Nia episodes,although atmospheric elements change reversely, they are not statistically significant as those in El Nio periods. The possible physical mechanism of the different impact of ENSO cycle on the precipitation over southern China is investigated by analyzing the intraseasonal oscillations(ISOs) in El Nio and La Nia winter half-years, respectively. By comparing the characteristics of ISOs in El Nio and La Nia, a physical mechanism is proposed to explain the different responses of the precipitation over China to ENSO in the winter half-year. In El Nio episodes, over western North Pacific(WNP) and South China Sea(SCS) the ISOs are inactive and exert little effect on water vapor transport and convergence, inducing positive precipitation anomalies with statistical significance over southern China in El Nio episodes. In La Nia episodes, however, the ISOs are active, which weaken the interannual variation signals of ENSO over WNP and southern China and lead to the insignificance of the interannual signals related to ENSO. Therefore, the different responses of precipitation over China to ENSO in the winter half-year are possibly caused by the difference of intraseasonal oscillations over WNP and SCS between El Nio and La Nia. 相似文献
6.
A season-reliant empirical orthogonal function(S-EOF) analysis was applied to the seasonal mean SST anomalies(SSTAs) based on the HadISST1 dataset with linear trend removed at every grid point in the South Pacific(60.5-19.5 S,139.5 E-60.5 W) during the period 1979-2009.The spatiotemporal characteristics of the dominant modes and their relationships with ENSO were analyzed.The results show that there are two seasonally evolving dominant modes of SSTAs in the South Pacific with interannual and interdecadal variations;they account for nearly 40% of the total variance.Although the seasonal evolution of spatial patterns of the first S-EOF mode(S-EOF1) did not show remarkable propagation,it decays with season remarkably.The second S-EOF mode(S-EOF2) showed significant seasonal evolution and intensified with season,with distinct characteristics of eastward propagation of the negative SSTAs in southern New Zealand and positive SSTAs southeast of Australia.Both of these two modes have significant relationships with ENSO.These two modes correspond to the post-ENSO and ENSO turnabout years,respectively.The SEOF1 mode associated with the decay of the eastern Pacific(EP) and the central Pacific(CP) types of ENSO exhibited a more significant relationship with the EP/CP type of El Nin o than that with the EP/CP type of La Nin a.The S-EOF2 mode contacted with the EP type of El Nin o changing into the EP/CP type of La Nin a showed a more significant connection with the EP/CP type of La Nin a. 相似文献
7.
A comparison of sensitivity in extratropical circulation in the Northern Hemisphere(NH)and Southern Hemisphere(SH)is conducted through observational analyses and diagnostic linear model experiments for two types of El Nio events,the traditional El Nio with the strongest warmth in the eastern tropical Pacific(EP El Nio)and the El Nio Modoki with the strongest warmth in the central tropical Pacific(CP El Nio).It is shown that CP El Nio favors the occurrence of a negative-phase Northern Annular Mode(NAM),while EP El Nio favors that of the Pacific-North American(PNA)pattern.In SH,both EP and CP El Nio induce a negative phase Southern Annular Mode(SAM).However,the former has a greater amplitude,which is consistent with the stronger sea surface temperature(SST)warmth.The difference in the two types of El Nio events in NH may originate from the dependence of heating-induced extratropical response on the location of initial heating,which may be associated with activity of the stationary wave.In SH,the lack of sensitivity to the location of heating can be associated with weaker activity of the stationary wave therein. 相似文献
8.
The tropical Pacific has begun to experience a new type of El Nio, which has occurred particularly frequently during the last decade, referred to as the central Pacific(CP) El Nio. Various coupled models with different degrees of complexity have been used to make real-time El Nio predictions, but high uncertainty still exists in their forecasts. It remains unknown as to how much of this uncertainty is specifically related to the new CP-type El Nio and how much is common to both this type and the conventional Eastern Pacific(EP)-type El Nio. In this study, the deterministic performance of an El Nio–Southern Oscillation(ENSO) ensemble prediction system is examined for the two types of El Nio. Ensemble hindcasts are run for the nine EP El Nio events and twelve CP El Nio events that have occurred since 1950. The results show that(1) the skill scores for the EP events are significantly better than those for the CP events, at all lead times;(2) the systematic forecast biases come mostly from the prediction of the CP events; and(3) the systematic error is characterized by an overly warm eastern Pacific during the spring season, indicating a stronger spring prediction barrier for the CP El Nio. Further improvements to coupled atmosphere–ocean models in terms of CP El Nio prediction should be recognized as a key and high-priority task for the climate prediction community. 相似文献
9.
《大气和海洋科学快报》2012,(5)
正In recent decades, the typical El Nio events with the warmest SSTs in the tropical eastern Pacific have become less common, and a different of El Nio with the warmest SSTs in the central Pacific, which is flanked on the east and west by cooler SSTs, has become more fre-quent. The more recent type of El Nio was referred to as central Pacific El Nio, warm pool El Nio, or dateline El Nio, or the El Nio Modoki. Central Pacific El Nio links to a different tropical-to-extratropical teleconnection and exerts different impacts on climate, and several classification approaches have been proposed. In this study, a new classification approach is proposed, which is based on the linear combination (sum or difference) of the two leading Empirical Orthogonal Functions (EOFs) of tropical Pacific Ocean sea surface temperature anomaly (SSTA), and the typical El Ni o index (TENI) and the central El Nio index (CENI) are able to be derived by projecting the observed SSTA onto these combinations. This classification not only reflects the characteristics of non-orthogonality between the two types of events but also yields one period peaking at approximate two to seven years. In particular, this classification can distin-guish the different impacts of the two types of events on rainfall in the following summer in East China. The typical El Nio events tend to induce intensified rainfall in the Yangtze River valley, whereas the central Pacific El Nio tends to induce intensified rainfall in the Huaihe River valley. Thus, the present approach may be appropriate for studying the impact of different types of El Nio on the East Asian climate. 相似文献
10.
《大气和海洋科学快报》2012,(5)
The authors demonstrate that the El Ni o events in the pre-and post-1976 periods show two ampli-tude-duration relations. One is that the stronger El Ni o events have longer durations, which is robust for the moderate El Ni o events; the other is that the stronger El Ni o events have shorter durations but for strong El Nio events. By estimating the sign and amplitude of the nonlinear dynamical heating (NDH) anomalies, the authors illustrate that the NDH anomalies are negligible for moderate El Nio events but large for strong El Nio events. In particular, the large NDH anomalies for strong El Nio events are positive during the growth and mature phases, which favor warmer El Nio events. During the decay phase, however, the negative NDH anomalies start to arise and become increasingly significant with the evolution of the El Nio events, in which the negative NDH anomalies dampen the sea surface temperature anomalies (SSTA) and cause the El Nio events to reach the SST normal state earlier. This pattern suggests that the nonlinearity tends to increase the intensities of strong El Nio events and shorten their duration, which, together with the previous results showing a positive correlation between the strength of El Nio events and the significance of the effect of nonlinear advection on the events (especially the suppression of nonlinearity on the SSTA during the decay phase), shows that the strong El Nio events tend to have the amplitude-duration relation of the stronger El Nio events with shorter durations. This result also lends support to the assertion that moderate El Nio events possess the amplitude-duration relation of stronger El Nio events with longer durations. 相似文献
11.
This paper compares data from linearized and nonlinear Zebiak–Cane model, as constrained by observed sea surface temperature anomaly(SSTA), in simulating central Pacific(CP) and eastern Pacific(EP) El Nio. The difference between the temperature advections(determined by subtracting those of the linearized model from those of the nonlinear model),referred to here as the nonlinearly induced temperature advection change(NTA), is analyzed. The results demonstrate that the NTA records warming in the central equatorial Pacific during CP El Nio and makes fewer contributions to the structural distinctions of the CP El Nio, whereas it records warming in the eastern equatorial Pacific during EP El Nio, and thus significantly promotes EP El Nio during El Nio–type selection. The NTA for CP and EP El Nio varies in its amplitude,and is smaller in CP El Nio than it is in EP El Nio. These results demonstrate that CP El Nio are weakly modulated by small intensities of NTA, and may be controlled by weak nonlinearity; whereas, EP El Nio are significantly enhanced by large amplitudes of NTA, and are therefore likely to be modulated by relatively strong nonlinearity. These data could explain why CP El Nio are weaker than EP El Nio. Because the NTA for CP and EP El Nio differs in spatial structures and intensities, as well as their roles within different El Nio modes, the diversity of El Nio may be closely related to changes in the nonlinear characteristics of the tropical Pacific. 相似文献
12.
With the Zebiak–Cane model, the present study investigates the role of model errors represented by the nonlinear forcing singular vector(NFSV) in the "spring predictability barrier"(SPB) phenomenon in ENSO prediction. The NFSV-related model errors are found to have the largest negative effect on the uncertainties of El Nio prediction and they can be classified into two types: the first is featured with a zonal dipolar pattern of SST anomalies(SSTA), with the western poles centered in the equatorial central–western Pacific exhibiting positive anomalies and the eastern poles in the equatorial eastern Pacific exhibiting negative anomalies; and the second is characterized by a pattern almost opposite to the first type. The first type of error tends to have the worst effects on El Nin?o growth-phase predictions, whereas the latter often yields the largest negative effects on decaying-phase predictions. The evolution of prediction errors caused by NFSVrelated errors exhibits prominent seasonality, with the fastest error growth in spring and/or summer; hence,these errors result in a significant SPB related to El Nin?o events. The linear counterpart of NFSVs, the(linear) forcing singular vector(FSV), induces a less significant SPB because it contains smaller prediction errors. Random errors cannot generate an SPB for El Nio events. These results show that the occurrence of an SPB is related to the spatial patterns of tendency errors. The NFSV tendency errors cause the most significant SPB for El Nio events. In addition, NFSVs often concentrate these large value errors in a few areas within the equatorial eastern and central–western Pacific, which likely represent those areas sensitive to El Nio predictions associated with model errors. Meanwhile, these areas are also exactly consistent with the sensitive areas related to initial errors determined by previous studies. This implies that additional observations in the sensitive areas would not only improve the accuracy of the initial field but also promote the reduction of model errors to greatly improve ENSO forecasts. 相似文献
13.
In recent decades, the typical El Nio events with the warmest SSTs in the tropical eastern Pacific have become less common, and a different of El Nio with the warmest SSTs in the central Pacific, which is flanked on the east and west by cooler SSTs, has become more fre-quent. The more recent type of El Nio was referred to as central Pacific El Nio, warm pool El Nio, or dateline El Nio, or the El Nio Modoki. Central Pacific El Nio links to a different tropical-to-extratropical teleconnection and exerts different impacts on climate, and several classification approaches have been proposed. In this study, a new classification approach is proposed, which is based on the linear combination (sum or difference) of the two leading Empirical Orthogonal Functions (EOFs) of tropical Pacific Ocean sea surface temperature anomaly (SSTA), and the typical El Ni o index (TENI) and the central El Nio index (CENI) are able to be derived by projecting the observed SSTA onto these combinations. This classification not only reflects the characteristics of non-orthogonality between the two types of events but also yields one period peaking at approximate two to seven years. In particular, this classification can distin-guish the different impacts of the two types of events on rainfall in the following summer in East China. The typical El Nio events tend to induce intensified rainfall in the Yangtze River valley, whereas the central Pacific El Nio tends to induce intensified rainfall in the Huaihe River valley. Thus, the present approach may be appropriate for studying the impact of different types of El Nio on the East Asian climate. 相似文献
14.
Model errors offset by constant and time-variant optimal forcing vector approaches(termed COF and OFV, respectively)are analyzed within the framework of El Nio simulations. Applying the COF and OFV approaches to the well-known Zebiak–Cane model, we re-simulate the 1997 and 2004 El Nio events, both of which were poorly degraded by a certain amount of model error when the initial anomalies were generated by coupling the observed wind forcing to an ocean component. It is found that the Zebiak–Cane model with the COF approach roughly reproduced the 1997 El Nio, but the 2004 El Nio simulated by this approach defied an ENSO classification, i.e., it was hardly distinguishable as CP-El Nio or EP-El Nio. In both El Nio simulations, substituting the COF with the OFV improved the fit between the simulations and observations because the OFV better manages the time-variant errors in the model. Furthermore, the OFV approach effectively corrected the modeled El Nio events even when the observational data(and hence the computational time) were reduced.Such a cost-effective offset of model errors suggests a role for the OFV approach in complicated CGCMs. 相似文献
15.
In recent years, El Nio Modoki (a type of pseudo-El Nio) has been distinguished as a unique large-scale ocean warming phenomenon happening in the central tropical Pacific that is quite different from the traditional El Nio. In this study, EOF analysis was used to successfully separate El Nio and El Nio Modoki. The abilities of the NINO3 index, NINO3.4 index, NINO1+2 index and NINO4 index in characterizing El Nio were explored in detail. The resulting suggestion was that, comparatively, NINO3 is the op... 相似文献
16.
Distinguished Effects of Interannual Salinity Variability on the Development of the Central-Pacific El Ni o Events 下载免费PDF全文
《大气和海洋科学快报》2012,(2)
El Nio events in the central equatorial Pacific (CP) are gaining increased attention,due to their increasing intensity within the global warming context.Various physical processes have been identified in the climate system that can be responsible for the modulation of El Nio,especially the effects of interannual salinity variability.In this work,a comprehensive data analysis is performed to illustrate the effects of interannual salinity variability using surface and subsurface salinity fields from the Met Office ENSEMBLES (EN3) quality controlled ocean dataset.It is demonstrated that during the developing phase of an El Nio event,a negative sea surface salinity (SSS) anomaly in the western-central basin acts to freshen the mixed layer (ML),decrease oceanic density in the upper ocean,and stabilize the upper layers.These related oceanic processes tend to reduce the vertical mixing and entrainment of subsurface water at the base of the ML,which further enhances the warm sea surface temperature (SST) anomalies associated with the El Nio event.However,the effects of interannually variable salinity are much more significant during the CP-El Nio than during the eastern Pacific (EP) El Nio,indicating that the salinity effect might be an important contributor to the development of CP-El Nio events. 相似文献
17.
The initial errors constitute one of the main limiting factors in the ability to predict the El Nio–Southern Oscillation(ENSO) in ocean–atmosphere coupled models. The conditional nonlinear optimal perturbation(CNOP) approach was employed to study the largest initial error growth in the El Nio predictions of an intermediate coupled model(ICM). The optimal initial errors(as represented by CNOPs) in sea surface temperature anomalies(SSTAs) and sea level anomalies(SLAs) were obtained with seasonal variation. The CNOP-induced perturbations, which tend to evolve into the La Nia mode, were found to have the same dynamics as ENSO itself. This indicates that, if CNOP-type errors are present in the initial conditions used to make a prediction of El Nio, the El Nio event tends to be under-predicted. In particular, compared with other seasonal CNOPs, the CNOPs in winter can induce the largest error growth, which gives rise to an ENSO amplitude that is hardly ever predicted accurately. Additionally, it was found that the CNOP-induced perturbations exhibit a strong spring predictability barrier(SPB) phenomenon for ENSO prediction. These results offer a way to enhance ICM prediction skill and, particularly,weaken the SPB phenomenon by filtering the CNOP-type errors in the initial state. The characteristic distributions of the CNOPs derived from the ICM also provide useful information for targeted observations through data assimilation. Given the fact that the derived CNOPs are season-dependent, it is suggested that seasonally varying targeted observations should be implemented to accurately predict ENSO events. 相似文献
18.
The NCEP–NCAR reanalysis dataset and the Had ISST dataset(1959–2014) are used to analyze the impact of two types of El Nio events, i.e., eastern Pacific El Nio(EP-El Nio) and central Pacific El Nio(CP-El Nio) events, on the duration of major and minor sudden stratospheric warmings(SSWs) in Northern Hemisphere winter(November to February). Although the frequency of major and minor SSWs during different types of El Nio shows no distinct differences, the duration of both major and minor SSWs during CP-El Nio is shorter than that during EP-El Nio. The spatial distribution of geopotential height anomalies preceding major SSWs resembles the western Pacific(WP) teleconnection pattern, while the spatial distribution of geopotential height anomalies preceding minor SSWs bears similarity to the Pacific–North America(PNA)teleconnection pattern. An enhancement of the strength of both wavenumber 1 and wavenumber 2 is found before major SSWs. Before minor SSWs, wavenumber 1 is also strengthened, but wavenumber 2 is weakened. The analysis also reveals that EP-El Nio tends to induce positive phases of PNA and WP teleconnections, while CP-El Nio induces negative-phase WP teleconnection. As the positive phases of the PNA and WP teleconnections are related to the strengthening of wavenumber 1, EP-El Nio causes an enhancement of wavenumber 1 in the high-latitude upper troposphere and an enhancement of the upward wave flux in the high-latitude stratosphere, accompanied by a negative anomaly in Eliassen–Palm flux divergence in the subpolar stratosphere, which accounts for the longer SSW duration during EP-El Nio than during CP-El Nio. 相似文献
19.
The influence of El Nio-Southern Oscillation (ENSO) on the convectively coupled Kelvin waves over the tropical Pacific is investigated by comparing the Kelvin wave activity in the eastern Pacific (EP) El Nio, central Pacific (CP) El Nio, and La Nia years, respectively, to 30-yr (1982-2011) mean statistics. The convectively coupled Kelvin waves in this study are represented by the two leading modes of empirical orthogonal function (EOF) of 2-25-day band-pass filtered daily outgoing longwave radiation (OLR), with the estimated zonal wavenumber of 3 or 4, period of 8 days, and eastward propagating speed of 17 ms-1 . The most significant impact of ENSO on the Kelvin wave activity is the intensification of the Kelvin waves during the EP El Nios. The impact of La Nia on the reduction of the Kelvin wave intensity is relatively weaker, reflecting the nonlinearity of tropical deep convection and the associated Kelvin waves in response to ENSO sea surface temperature (SST) anomalies. The impact of the CP El Nio on the Kelvin waves is less significant due to relatively weaker SST anomalies and smaller spatial coverage. ENSO may also alter the frequency, wavelength, and phase speed of the Kelvin waves. This study demonstrates that low-frequency ENSO SST anomalies modulate high-frequency tropical disturbances, an example of weather-climate linkage. 相似文献
20.
It has long been acknowledged that there are two types of El Nio events, i.e., the eastern Pacific El Nio (EE) and the central Pacific El Nio (CE), according to the initial position of the anomalous warm water and its propagation direction. In this paper, the oceanic and atmospheric evolutions and the possible mechanisms of the two types of El Nio events were examined. It is found that all the El Nio events, CE or EE, could be attributed to the joint impacts of the eastward advection of warm water from... 相似文献