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1.
NUMERICAL EXPERIMENT OF THE INFLUENCES OF HEAT AND WIND STRESS ON THE EQUATORIAL OCEAN CIRCULATION 总被引：1，自引：0，他引：1 
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下载免费PDF全文 A time-dependent linear model on the equatorial beta plane is developed in this paper.Its verticalstructure consists of two active layers with equal density and temperature above the thermocline and aquasi-stationary layer with constant density below the thermocline.The results of nurnericat experiments show that the direct influence of heat on the equatorial ocean ismuch smaller than that of wind stress.Nevertheless,through the tropical ocean-atmosphere interaction,the change of wind stress resulting from the thermal forcing may set a determinant effect on the equilibriumand anomalous development of the ocean-almosphere circulation. 相似文献
2.
3.
The mechanisms responsible for the mean state and the seasonal and interannual variations of the coupled tropical Pacific-global
atmosphere system are investigated by analyzing a thirty year simulation, where the LMD global atmospheric model and the LODYC
tropical Pacific model are coupled using the delocalized physics method. No flux correction is needed over the tropical region.
The coupled model reaches its regime state roughly after one year of integration in spite of the fact that the ocean is initialized
from rest. Departures from the mean state are characterized by oscillations with dominant periodicites at annual, biennial
and quadriennial time scales. In our model, equatorial sea surface temperature and wind stress fluctuations evolved in phase.
In the Central Pacific during boreal autumn, the sea surface temperature is cold, the wind stress is strong, and the Inter
Tropical Convergence Zone (ITCZ) is shifted northwards. The northward shift of the ITCZ enhances atmospheric and oceanic subsidence
between the equator and the latitude of organized convention. In turn, the stronger oceanic subsidence reinforces equatorward
convergence of water masses at the thermocline depth which, being not balanced by equatorial upwelling, deepens the equatorial
thermocline. An equivalent view is that the deepening of the thermocline proceeds from the weakening of the meridional draining
of near-surface equatorial waters. The inverse picture prevails during spring, when the equatorial sea surface temperatures
are warm. Thus temperature anomalies tend to appear at the thermocline level, in phase opposition to the surface conditions.
These subsurface temperature fluctuations propagate from the Central Pacific eastwards along the thermocline; when reaching
the surface in the Eastern Pacific, they trigger the reversal of sea surface temperature anomalies. The whole oscillation
is synchronized by the apparent meridional motion of the sun, through the seasonal oscillation of the ITCZ. This possible
mechanism is partly supported by the observed seasonal reversal of vorticity between the equator and the ITCZ, and by observational
evidence of eastward propagating subsurface temperature anomalies at the thermocline level.
Received: 7 April 1997 / Accepted: 15 July 1998 相似文献
4.
Observations show that the tropical E1 Nifio-Southern Oscillation （ENSO） variability, after removing both the long term trend and decadal change of the background climate, has been enhanced by as much as 60% during the past 50 years. This shift in ENSO amplitude can be related to mean state changes in global climate. Past global warming has caused a weakening of the Walker circulation over the equatorial Indo-Pacific oceans, as well as a weakening of the trade winds and a reduction in the equatorial upwelling. These changes in tropical climatology play as stabilizing factors of the tropical coupling system. However, the shallower and strengthening thermocline in the equatorial Pacific increases the SST sensitivity to thermocline and wind stress variabilities and tend to destabilize the tropical coupling system. Observations suggest that the destabilizing factors, such as the strengthening thermocline, may have overwhelmed the stabilizing effects of the atmosphere, and played a deterministic role in the enhanced ENSO variability, at least during the past half century. This is different from the recent assessment of IPCC-AR4 coupled models. 相似文献
5.
Roger L Hughes 《Dynamics of Atmospheres and Oceans》1981,5(3):147-157
The influence of a zonal slope in the thermocline on both wave- and wind-induced equatorial upwelling is studied. It is shown that the vertical displacement of the thermocline induced by a long Kelvin or planetary wave varies as the thermocline depth to the power , as the wave propagates into a region of changed thermocline depth The zonal and meridional velocities induced by a wave vary as the thermocline depth to the power . The wind-induced upwelling associated with a zonal slope of the thermocline is shown to be strongly confined to the equator. The importance of thermocline slope on the Ekman divergence is found to increase with time from the initial application of the wind stress perturbation. In the Pacific Ocean the meridional velocity may be altered by up to 60% by the thermocline slope before the influence of the boundaries becomes important. 相似文献
6.
Reduction of the thermocline feedback associated with mean SST bias in ENSO simulation 总被引：1，自引：1，他引：0
Baoqiang Xiang Bin Wang Qinghua Ding Fei–Fei Jin Xiouhua Fu Hyung-Jin Kim 《Climate Dynamics》2012,39(6):1413-1430
Associated with the double Inter-tropical convergence zone problem, a dipole SST bias pattern (cold in the equatorial central Pacific and warm in the southeast tropical Pacific) remains a common problem inherent in many contemporary coupled models. Based on a newly-developed coupled model, we performed a control run and two sensitivity runs, one is a coupled run with annual mean SST correction and the other is an ocean forced run. By comparison of these three runs, we demonstrated that a serious consequence of this SST bias is to severely suppress the thermocline feedback in a realistic simulation of the El Ni?o/Southern Oscillation. Firstly, the excessive cold tongue extension pushes the anomalous convection far westward from the equatorial central Pacific, prominently diminishing the convection-low level wind feedback and thus the air-sea coupling strength. Secondly, the equatorial surface wind anomaly exhibits a relatively uniform meridional structure with weak gradient, contributing to a weakened wind-thermocline feedback. Thirdly, the equatorial cold SST bias induces a weakened upper-ocean stratification and thus yields the underestimation of the thermocline-subsurface temperature feedback. Finally, the dipole SST bias underestimates the mean upwelling through (a) undermining equatorial mean easterly wind stress, and (b) enhancing convective mixing and thus reducing the upper ocean stratification, which weakens vertical shear of meridional currents and near-surface Ekman-divergence. 相似文献
7.
To extend the linear stochastically forced paradigm of tropical sea surface temperature (SST) variability to the subsurface ocean, a linear inverse model (LIM) is constructed from the simultaneous and 3-month lag covariances of observed 3-month running mean anomalies of SST, thermocline depth, and zonal wind stress. This LIM is then used to identify the empirically-determined linear dynamics with physical processes to gauge their relative importance to ENSO evolution. Optimal growth of SST anomalies over several months is triggered by both an initial SST anomaly and a central equatorial Pacific thermocline anomaly that propagates slowly eastward while leading the amplifying SST anomaly. The initial SST and thermocline anomalies each produce roughly half the SST amplification. If interactions between the sea surface and the thermocline are removed in the linear dynamical operator, the SST anomaly undergoes less optimal growth but is also more persistent, and its location shifts from the eastern to central Pacific. Optimal growth is also found to be essentially the result of two stable eigenmodes with similar structure but differing 2- and 4-year periods evolving from initial destructive to constructive interference. Variations among ENSO events could then be a consequence not of changing stability characteristics but of random excitation of these two eigenmodes, which represent different balances between surface and subsurface coupled dynamics. As found in previous studies, the impact of the additional variables on LIM SST forecasts is relatively small for short time scales. Over time intervals greater than about 9?months, however, the additional variables both significantly enhance forecast skill and predict lag covariances and associated power spectra whose closer agreement with observations enhances the validation of the linear model. Moreover, a secondary type of optimal growth exists that is not present in a LIM constructed from SST alone, in which initial SST anomalies in the southwest tropical Pacific and Indian ocean play a larger role than on shorter time scales, apparently driving sustained off-equatorial wind stress anomalies in the eastern Pacific that result in a more persistent equatorial thermocline anomaly and a more protracted (and predictable) ENSO event. 相似文献
8.
夏季西太平洋副热带高压北跳及异常的研究 总被引：37，自引：4，他引：33
根据欧洲中心1980～1989年逐日200,500和850hPa风场、高度场及日本气象厅提供的GMS观测的黑体辐射温度（TBB）逐日资料,探讨了夏季西太平洋地区（125～145°E）副热带高压脊线季节性北跳、季内脊线位置的异常与低纬度的西风爆发和热带对流的关系。研究表明：初夏西太平洋地区低层赤道西风爆发后,西太平洋地区的赤道对流加强（赤道地区的TBB值减小）;赤道西风向北扩展,赤道强对流向北推移,热带对流加强（热带地区TBB值减小）。夏季西太平洋副热带高压脊线的二次北跳现象与低层赤道西风二次北跳及赤道对流向北推移密切相关。研究指出：夏季热带对流弱（强）,西太平洋副热带高压脊线位置相对偏南（北）,夏季西太平洋副热带高压脊线位置的异常与高、低层流场辐合、福散中心的位置及高层西风传播方向有关。 相似文献
9.
By analyzing the climatologically averaged wind stress during 2000-2007,it is found that the easterly wind stress in the northern tropical Pacific Ocean from Quick Scatterometer(QSCAT) data was stronger than those from Tropical Atmosphere Ocean(TAO) data and from National Centers for Environmental Prediction/National Center for Atmospheric Research(NCEP/NCAR) reanalysis I.As a result,the Intertropical Convergence Zone(ITCZ) in the Pacific Ocean is more southward in the QSCAT data than in the NCEP/NCAR data.Relative to the NCEP wind,the southern shift of the ITCZ in the QSCAT data led to negative anomaly of wind stress curl north of a latitude of 6 N.The negative anomaly results in downward Ekman pumping in the central Pacific.The excessive local strong easterly wind also contributes to the downward Ekman pumping.This downward Ekman pumping suppresses the thermocline ridge,reduces the meridional thermocline slope and weakens the North Equatorial Countercurrent(NECC).These effects were confirmed by numerical experiments using two independent ocean general circulation models(OGCMs).Furthermore,the excessive equatorial easterly wind stress was also found to contribute to the weaker NECC in the OGCMs.A comparison between the simulations and observation data indicates that the stronger zonal wind stress and its southern shift of QSCAT data in the ITCZ region yield the maximum strength of the simulated NECC only 33% of the magnitude derived from observation data and even led to a "missing" NECC in the western Pacific. 相似文献
10.
An eigen analysis of the equatorial air-sea coupled model is carried out to understand the mechanism of the slowly varying mode for various zonal phase differences between SST and wind stress. The frequency and growth rate of the slow mode highly depend on the zonal phase difference between SST and wind stress anomalies and the wave scale. For ultra-long waves longer than 20,000 km, the system propagates westward regardless of the position of wind stress. However, for the long waves observed in the Pacific, the slow mode tends to propagate eastward when the SST and wind stress anomalies are close to each other (within a quadrature phase relationship). On the other hand, when the wind stress is located far away from SST, the slow mode tends to propagate westward. The coupled system produces the unstable modes when the westerly (easterly) wind stress is located in the west of warm (cold) SST. It is noted that for the Pacific basin scale,the eastward propagating unstable waves can be produced when the wind stress is located to the west of SST with a few thousand kilometer distance. Also examined in the present study is the relative role of the thermocline displacement and zonal advection effects in determining the propagation and instability of the coupled system. 相似文献
11.
1. IntroductionMany studies using a variety of coupled models have reproduced ENSO like features(e.g., Hirst, 1986, 1988; Zebiak and Cane, 1987; Battisti and Hirst, 1989; Jin and Neelin, 1993;Jin, 1997; Kirtman, 1997; Kang and An, 1998; Wakata and Sarachik, 1991). But, a variety ofsolutions have been reported depending on different parameterizations of atmospheric processes, particularly the relationship between wind stress and SST anomaly, indicating that therelationship has a large i… 相似文献
12.
—Upper ocean thermal data and surface marine observations are used to describe the three-dimensional, basinwide co-evolution
of interannual variability in the tropical Pacific climate system. The phase propagation behavior differs greatly from atmosphere
to ocean, and from equatorial to off-equatorial and from sea surface to subsurface depths in the ocean. Variations in surface
zonal winds and sea surface temperatures (SSTs) exhibit a standing pattern without obvious zonal phase propagation. A nonequilibrium
ocean response at subsurface depths is evident, characterized by coherent zonal and meridional propagating anomalies around
the tropical North Pacific: eastward on the equator but westward off the equator. Depending on geographic location, there
are clear phase relations among various anomaly fields. Surface zonal winds and SSTs in the equatorial region fluctuate approximately
in-phase in time, but have phase differences in space. Along the equator, zonal mean thermocline depth (or heat content) anomalies
are in nonequilibrium with the zonal wind stress forcing. Variations in SSTs are not in equilibrium either with subsurface
thermocline changes in the central and western equatorial Pacific, with the former lagging the latter and displaced to the
east. Due to its phase relations to SST and winds, the basinwide temperature anomaly evolution at thermocline depths on an
interannual time scale may determine the slow physics of ENSO, and play a central role in initiating and terminating coupled
air-sea interaction. This observed basinwide phase propagation of subsurface anomaly patterns can be understood partially
as water discharge processes from the western Pacific to the east and further to high latitudes, and partially by the modified
delayed oscillator physics.
Received: 17 January 1997 / Accepted: 10 March 1998 相似文献
13.
By using the wavelet transform method,the ENSO (2-7 a) signal and the decadal variability (8-20 a) are filtered out from the long-term SST data sets in order to investigate characteristics of the decadal variability and its impact on the ENSO.It is found that there are two different kinds of decadal SSTA modes-horseshoe and horse saddle patterns in the tropical Pacific.The horseshoe pattern represents that the decadal SSTA variability in the central Pacific is in phase with that in the eastern Pacific.The horse saddle pattern is named that they are out of phase.The former constituted the decadal variability before 1990s and the latter mainly prevailed during 1990s.As the response of atmosphere to the ocean,two decadal wind patterns appear in association with the SST decadal modes.One is characterized by anomalous development of the zonal wind,the other by anomalous development of the meridional wind.These two kinds of modes can also be regarded as different phases of the decadal oscillation.Further studies have shown that the influences of the two kinds of modes on the ENSO are different.The horse saddle mode has a stronger impact on the ENSO than the horseshoe mode.A possible mechanism for the influence of the decadal variability on the ENSO signal is presented.The central part of the thermocline along the equatorial Pacific moves up or down simultaneously with its eastern part while the decadal variability bears the horseshoe pattern.But the two segments of the thermocline in the central and eastern Pacific act oppositely while the decadal variability shows the horse saddle pattern.In this case it has an-influence on the individual ENSO'events by the superposition of the decadal variability. 相似文献
14.
Ariane Koch-Larrouy Matthieu Lengaigne Pascal Terray Gurvan Madec Sebastien Masson 《Climate Dynamics》2010,34(6):891-904
The sensitivity of the tropical climate to tidal mixing in the Indonesian Archipelago (IA) is investigated using a coupled
general circulation model. It is shown that the introduction of tidal mixing considerably improves water masses properties
in the IA, generating fresh and cold anomalies in the thermocline and salty and cold anomalies at the surface. The subsurface
fresh anomalies are advected in the Indian Ocean thermocline and ultimately surface to freshen the western part of the basin
whereas surface salty anomalies are advected in the Leuwin current to salt waters along the Australian coast. The ~0.5°C surface
cooling in the IA reduces by 20% the overlying deep convection. This improves both the amount and structure of the rainfall
and weakens the wind convergence over the IA, relaxes the equatorial Pacific trade winds and strengthens the winds along Java
coast. These wind changes causes the thermocline to be deeper in the eastern equatorial Pacific and shallower in the eastern
Indian Ocean. The El Nino Southern Oscillation (ENSO) amplitude is therefore slightly reduced while the Indian Ocean Dipole/Zonal
Mode (IODZM) variability increases. IODZM precursors, related to ENSO events the preceding winter in this model, are also
shown to be more efficient in promoting an IODZM thanks to an enhanced wind/thermocline coupling. Changes in the coupled system
in response tidal mixing are as large as those found when closing the Indonesian Throughflow, emphasizing the key role of
IA on the Indo-Pacific climate. 相似文献
15.
S.-I. An 《Theoretical and Applied Climatology》2005,81(1-2):121-132
Summary In this study, it is demonstrated that the amplitude of the equatorial upper-ocean zonal current anomaly induced by the fast-varying wind forcing (shorter than a year) is much greater than that induced by the slowly varying wind forcing (longer than 2 year), and the center of maximum zonal current anomaly shifts from the central Pacific to the western Pacific with an increase in the timescale of wind forcing. As a result, the zonal advective feedback (the zonal advection of mean sea surface temperature by anomalous current) in a slowly varying climate system becomes weaker and barely induces a low-frequency mode such as El Niño-Southern Oscillation. On the other hand, both amplitude and zonal location of the maximum thermocline anomaly are little changed by the change in the timescale of wind forcing – confined at the strong equatorial upwelling region of the eastern Pacific. Accordingly, the thermocline feedback (the vertical advection of anomalous subsurface temperature by the mean upwelling) is more favorable to generate a low-frequency mode.The relative roles of these two feedbacks are further explored under the coupled-system context. The eigen analysis of the stripped-down version of an intermediate ocean-atmosphere coupled model shows that by altering the regime space from the weakly coupled to the strongly coupled, the dominant process that leads the leading eigen mode changes from the zonal advective feedback to the thermocline feedback, and at the same time the frequency of the leading mode also changes from the high-frequency to the low-frequency. It implies that each feedback tends to favor the different timescale coupled mode. 相似文献
16.
Spatial and temporal structures of interannual-to-decadal variability in the tropical Pacific Ocean are investigated using results from a global atmosphere–ocean coupled general circulation model. The model produces quite realistic mean state characteristics, despite a sea surface temperature cold bias and a thermocline that is shallower than observations in the western Pacific. The periodicity and spatial patterns of the modelled El Niño Southern Oscillations (ENSO) compare well with those observed over the last 100 years, although the quasi-biennial timescale is dominant. Lag-regression analysis between the mean zonal wind stress and the 20°C isotherm depth suggests that the recently proposed recharge-oscillator paradigm is operating in the model. Decadal thermocline variability is characterized by enhanced variance over the western tropical South Pacific (~7°S). The associated subsurface temperature variability is primarily due to adiabatic displacements of the thermocline as a whole, arising from Ekman pumping anomalies located in the central Pacific, south of the equator. Related wind anomalies appear to be caused by SST anomalies in the eastern equatorial Pacific. This quasi-decadal variability has a timescale between 8 years and 20 years. The relationship between this decadal tropical mode and the low-frequency modulation of ENSO variance is also discussed. Results question the commonly accepted hypothesis that the low-frequency modulation of ENSO is due to decadal changes of the mean state characteristics. 相似文献
17.
全球海洋大气耦合环流模式中的ENSO特征对气候背景态改变的敏感性 总被引：3，自引：0，他引：3
文中利用一个高分辨率全球海-气耦合环流模式设计两组长期积分试验,揭示了在不同气候背景态下热带太平洋年际变化特征及模式ENSO循环控制机理的差异。通过分析海表温度、上层海洋热容量和低层风场异常的年际变化特征及其和赤道中东太平洋海表温度异常的关系,揭示了基于不同气候背景场的ENSO循环的不同演变过程。结果表明:ENSO年际变率特征(包括振幅、频率等)对气候背景态相当敏感,在不同的背景场下ENSO循环的控制模态可以明显不同。试验表明,当热带太平洋东冷西暖的背景热力梯度接近多年气候平均时,模式ENSO循环表现为所谓的“时滞振子”模态控制,而随着东西向背景热力梯度显著减小,ENSO循环则可以表现为驻波模态控制。研究结果为认识年代际背景变化影响年际ENSO循环的机理提供了一种启示。 相似文献
18.
Xianghui FANG Fei ZHENG Kexin LI Zeng-Zhen HU Hongli REN Jie WU Xingrong CHEN Weiren LAN Yuan YUAN Licheng FENG Qifa CAI Jiang ZHU 《大气科学进展》2023,40(1):6-13
Based on the updates of the Climate Prediction Center and International Research Institute for Climate and Society(CPC/IRI) and the China Multi-Model Ensemble(CMME) El Ni?o-Southern Oscillation(ENSO) Outlook issued in April 2022, La Ni?a is favored to continue through the boreal summer and fall, indicating a high possibility of a three-year La Ni?a(2020–23). It would be the first three-year La Ni?a since the 1998–2001 event, which is the only observed three-year La Ni?a event since 1980. By exam... 相似文献
19.
潘怡航 《Acta Meteorologica Sinica》1982,40(1):24-34
根据1949—1979年逐月资料,指出赤道东太平洋海表温度与西太平洋台风发生频率之间存在明显的时滞遥相关。通过个例对比与长期资料验证,揭露了当赤道东太平洋海表温度较正常为冷(暖)时,西太平洋低纬地区低空东西风辐合区两边的两个反方向的纬圈环流加强(减弱),辐合区两边的东西风加强(减弱),在菲律宾以东台风发生源地上的赤道辐合带(ITCZ)出现频繁(不活跃),因而台风生成偏多(偏少)。 相似文献
20.
Tropical Atlantic biases and their relation to surface wind stress and terrestrial precipitation 总被引：4，自引：3，他引：1
Ingo Richter Shang-Ping Xie Andrew T. Wittenberg Yukio Masumoto 《Climate Dynamics》2012,38(5-6):985-1001
Most coupled general circulation models (GCMs) perform poorly in the tropical Atlantic in terms of climatological seasonal cycle and interannual variability. The reasons for this poor performance are investigated in a suite of sensitivity experiments with the Geophysical Fluid Dynamics Laboratory (GFDL) coupled GCM. The experiments show that a significant portion of the equatorial SST biases in the model is due to weaker than observed equatorial easterlies during boreal spring. Due to these weak easterlies, the tilt of the equatorial thermocline is reduced, with shoaling in the west and deepening in the east. The erroneously deep thermocline in the east prevents cold tongue formation in the following season despite vigorous upwelling, thus inhibiting the Bjerknes feedback. It is further shown that the surface wind errors are due, in part, to deficient precipitation over equatorial South America and excessive precipitation over equatorial Africa, which already exist in the uncoupled atmospheric GCM. Additional tests indicate that the precipitation biases are highly sensitive to land surface conditions such as albedo and soil moisture. This suggests that improving the representation of land surface processes in GCMs offers a way of improving their performance in the tropical Atlantic. The weaker than observed equatorial easterlies also contribute remotely, via equatorial and coastal Kelvin waves, to the severe warm SST biases along the southwest African coast. However, the strength of the subtropical anticyclone and along-shore winds also play an important role. 相似文献