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1.
《大气科学进展》2013,(6)
An ocean general circulation model(OGCM)is used to demonstrate remote efects of tropical cyclone wind(TCW)forcing in the tropical Pacific.The signature of TCW forcing is explicitly extracted using a locally weighted quadratic least-squares regression(called as LOESS)method from six-hour satellite surface wind data;the extracted TCW component can then be additionally taken into account or not in ocean modeling,allowing isolation of its efects on the ocean in a clean and clear way.In this paper,seasonally varying TCW fields in year 2008 are extracted from satellite data which are prescribed as a repeated annual cycle over the western Pacific regions of the equator(poleward of 10 N/S);two long-term OGCM experiments are performed and compared,one with the TCW forcing part included additionally and the other not.Large,persistent thermal perturbations(cooling in the mixed layer(ML)and warming in the thermocline)are induced locally in the western tropical Pacific,which are seen to spread with the mean ocean circulation pathways around the tropical basin.In particular,a remote ocean response emerges in the eastern equatorial Pacific to the prescribed of-equatorial TCW forcing,characterized by a cooling in the mixed layer and a warming in the thermocline.Heat budget analyses indicate that the vertical mixing is a dominant process responsible for the SST cooling in the eastern equatorial Pacific.Further studies are clearly needed to demonstrate the significance of these results in a coupled ocean-atmosphere modeling context. 相似文献
2.
Rong-Hua Zhang 《Climate Dynamics》2014,42(1-2):467-485
Tropical instability waves (TIWs) arise from oceanic instability in the eastern tropical Pacific and Atlantic Oceans, having a clear atmospheric signature that results in coupled atmosphere–ocean interactions at TIW scales. In this study, the extent to which TIW-induced surface wind feedback influences the ocean is examined using an ocean general circulation model (OGCM). The TIW-induced wind stress (τTIW) part is diagnostically determined using an empirical τTIW model from sea surface temperature (SST) fields simulated in the OGCM. The interactively represented TIW wind tends to reduce TIW activity in the ocean and influence the mean state, with largest impacts during TIW active periods in fall and winter. In December, the interactive τTIW forcing induces a surface cooling (an order of ?0.1 to ?0.3 °C), an increased heat flux into the ocean, a shallower mixed layer and a weakening of the South Equatorial Current in the eastern equatorial Pacific. Additionally, the TIW wind effect yields a pronounced latitudinal asymmetry of sea level field across the equator, and a change to upper thermal structure, characterized by a surface cooling and a warming below in the thermocline, leading to a decreased temperature gradient between the mixed layer and the thermocline. Processes responsible for the τTIW–induced cooling effects are analyzed. Vertical mixing and meridional advection are the two terms in the SST budget that are dominantly affected by the TIW wind feedback: the cooling effect from the vertical mixing on SST is enhanced, with the maximum induced cooling in winter; the warming effect from the meridional advection is reduced in July–October, but enhanced in November–December. Additional experiments are performed to separate the relative roles the affected surface momentum and heat fluxes play in the cooling effect on SST. This ocean-only modeling work indicates that the effect of TIW-induced wind feedback is small but not negligible, and may need to be adequately taken into account in large-scale climate modeling. 相似文献
3.
1986—1987厄尔尼诺事件的数值模拟 总被引：1，自引：0，他引：1
用高分辨率自由表面热带太平洋环流模式，在观测到的风应力和热量、水汽通量驱动下，对１９８６—１９８７厄尔尼诺（Ｅ１Ｎｉｎｏ）事件进行了数值模拟。各种变量场的时空结构及其演变表明，模式成功地模拟出１９８６—１９８７厄尔尼诺现象。始于１９８６年年中，赤道西太平洋的西风异常所推动的向东表层洋流不断向中、东太平洋输送暖水，至１１月份，大量暖水在日界线附近堆积，造成海面上升（达３２ｃｍ）和斜温层（用２０℃等温线深度表示）加深。１９８６年年底的强西风异常激发出赤道Ｋｅｌｖｉｎ波，并向赤道东太平洋和南美沿岸传播，使那里的斜温层加深和海面上升，且具有双峰结构；Ｋｅｌｖｉｎ波所伴随的垂直冷平流的减弱造成赤道中、东太平洋海表温度上升；１９８７年春季在中、东太平洋和南美沿岸地区存在强的正海表温度异常，并伴随着整个赤道太平洋斜温层东西方向变平、赤道潜流弱而中心位置变浅。厄尔尼诺相伴随的热带太平洋环流异常首先于１９８７年年中从东太平洋开始消失，而中、西太平洋则一直维持到１９８８年初。 相似文献
4.
The equatorial response to subtropical Pacific forcing was studied in a coupled climate model.The forcings in the western,central and eastern subtropical Pacific all caused a significant response in the equatorial thermocline,with comparable magnitudes.This work highlights the key role of air-sea coupling in the subtropical impact on the equatorial thermocline,instead of only the role of the ＂oceanic tunnel＂.The suggested mechanism is that the cyclonic （anticyclonic） circulation in the atmosphere caused by the subtropical surface warming （cooling） can generate an anomalous upwelling （downwelling） in the interior region.At the same time,an anomalous downwelling （upwelling） occurs at the equatorward flank of the forcing,which produces anomalous thermocline warming （cooling）,propagating equatorward and resulting in warming （cooling） in the equatorial thermocline.This is an indirect process that is much faster than the ＂oceanic tunnel＂ mechanism in the subtropical impact on the equator. 相似文献
5.
The Oregon State University coupled upper ocean-atmosphere GCM is evaluated in terms of the simulated winds, ocean currents and thermocline depth variations. Although the zonal wind velocities in the model are underestimated by a factor of about three and the zonal current velocities are underestimated by a factor of about five, the model is seen to qualitatively simulate the major features of the gyral scale currents, and the phases of the seasonal variation of the principal equatorial currents are in reasonable agreement with observations. The simulated tropical currents are dominated by Ekman transport and the eastern boundary currents do not penetrate far enough equatorward, while the western boundary currents do not penetrate far enough poleward. The subtropical trade wind belt and the mid-latitude westerlies are displaced equatorward of observations; hence, the mid-latitude eastward currents, principally the Kuroshio-North Pacific Drift and the Gulf Stream-North Atlantic Current are displaced equatorward. In spite of these shortcomings the surface current simulation of this two-layer upper ocean model is comparable with that of other ocean GCMs of coarse resolution. The coupled model successfully simulates the deepening of the thermocline westward across Pacific as a consequence of the prevailing Walker circulation. The region of most intense simulated surface forcing is located in the western Pacific due to a southwestward displacement of the northeast trade winds relative to observations; hence the equatorial Pacific is dominated by eastward propagation of thermocline depth variations. The excessively strong Ekman divergence and upwelling in the western Pacific cools the local warm pool, while incorrectly simulated westerlies in the eastern Pacific suppress upwelling and inhibit cooling from below. These features reduce the simulated trans-Pacific sea-surface temperature gradient, weakening the Walker circulation and the anomalies associated with the simulated Southern Oscillation.
Offprint requests to: KR Sperber 相似文献
6.
The complexity of the tropical climate system demands the development of a hierarchy of models to ensure our understanding of its response to anthropogenic forcing. The response of the tropical Pacific Ocean to radiative forcing has been studied previously with a box model. The model has provided insights into the tropical Pacific climate change that are otherwise not easily attainable. But that model only encompasses the tropical Pacific region. Recent studies have also shown that the Indian Ocean (IO) may be important in the response of the Pacific Walker circulation to radiative forcing, raising the need to expand the model to take into account the role of IO. This study presents the results concerning the tropical Pacific response to radiative forcing from an expanded-box model that includes the tropical IO, which influences the tropical Pacific through an inter-basin SST gradient.The three-box model predicts an enhanced zonal SST gradient in tropical Pacific in response to the increased radiative forcing, similar to the previous two-box model. It is further noted that in the three-box model, a warmer IO relative to the Pacific enhances Pacific easterlies and subsequently strengthens the equatorial ocean circulation. Because of this ocean dynamical cooling, the warming response in the Pacific is effectively reduced in the three-box model that includes the role of IO compared with that in the two-box model. The role of the IO warming trend in enhancing the Pacific trade winds is confirmed using an atmospheric general circulation model experiment. These results may help to fully explain the relatively small observed warming trend in the tropical Pacific compared to that in the tropical IO evident in 20th century SST reconstructions. 相似文献
7.
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.
相似文献8.
Oceanic vertical mixing is known to influence the state of the equatorial ocean which affects the climate system, including the amplitude of El Niño/Southern Oscillation (ENSO). Recent measurements of ocean currents at high vertical resolution capture numerous small vertical scale structures (SVSs) within and above the equatorial thermocline that contribute significantly to vertical mixing but which are not sufficiently resolved by coarse resolution ocean models. We investigate the impact of the vertical mixing induced by the SVSs on the mean state and interannual variability in the tropical Pacific by using a coupled general circulation model. The vertical mixing induced by the SVSs is represented as an elevated vertical diffusivity from the surface down to the 20 °C isotherm depth, a proxy for the depth of the thermocline. We investigate different forms for the elevated mixing. It is found that the SVS-induced mixing strongly affect the mean state of the ocean leading to a warming of sea surface temperature (SST) and associated deepening and sharpening of the thermocline in the eastern equatorial Pacific. We find that the SST warming induced by the elevated mixing is further strengthened through the Bjerknes feedback and SST-shortwave flux feedback. We also find a reduction in the number of large amplitude ENSO events and in certain cases an increase in the skewness of ENSO. 相似文献
9.
Using an intermediate ocean–atmosphere coupled model (ICM) for the tropical Pacific, we investigated the role of the ocean dynamical thermostat (ODT) in regulating the tropical eastern Pacific sea surface temperature (SST) under global warming conditions. The external, uniformly distributed surface heating results in the cooling of the tropical eastern Pacific “cold tongue,” and the amplitude of the cooling increases as more heat is added but not simply linearly. Furthermore, an upper bound for the influence of the equatorially symmetric surface heating on the cold tongue cooling exists. The additional heating beyond the upper bound does not cool the cold tongue in a systematic manner. The heat budget analysis suggests that the zonal advection is the primary factor that contributes to such nonlinear SST response. The radiative heating due to the greenhouse effect (hereafter, RHG) that is obtained from the multi-model ensemble of the Climate Model Intercomparison Project Phase III (CMIP3) was externally given to ICM. The RHG obtained from the twentieth century simulation intensified the cold tongue cooling and the subtropical warming, which were further intensified by the RHG from the doubled CO2 concentration simulation. However, the cold tongue cooling was significantly reduced and the negative SST response region was shrunken toward the equator by the RHG from the quadrupled CO2 concentration simulation, while the subtropical warming increased further. A systematic RHG forced experiment having the same spatial pattern of RHG from doubled CO2 concentration simulation with different amplitude of forcing revealed that the ocean dynamical response to global warming tended to enhance the cooling in the tropical eastern Pacific by virtue of meridional advection and upwelling; however, these cooling effects could not fully compensate a given RHG warming as the external forcing becomes larger. Moreover, the feedback by the zonal thermal advection actually exerted the warming over the equatorial region. Therefore, as the global warming is intensified, the cooling over the eastern tropical Pacific by ODT and the negative SST response area are reduced. 相似文献
10.
F. Codron 《Climate Dynamics》2001,17(2-3):187-203
The changes of the variability of the tropical Pacific ocean forced by a shift of six months in the date of the perihelion
are studied using a coupled tropical Pacific ocean/global atmosphere GCM. The sensitivity experiments are conducted with two
versions of the atmospheric model, varied by two parametrization changes. The first one concerns the interpolation scheme
between the atmosphere and ocean models grids near the coasts, the second one the advection of water vapor in the presence
of downstream negative temperature gradients, as encountered in the vicinity of mountains. In the tropical Pacific region,
the parametrization differences only have a significant direct effect near the coasts; but coupled feedbacks lead to a 1 °C
warming of the equatorial cold tongue in the modified (version 2) model, and a widening of the western Pacific large-scale
convergence area. The sensitivity of the seasonal cycle of equatorial SST is very different between the two experiments. In
both cases, the response to the solar flux forcing is strongly modified by coupled interactions between the SST, wind stress
response and ocean dynamics. In the first version, the main feedback is due to anomalous upwelling and leads to westward propagation
of SST anomalies; whereas the version 2 model is dominated by an eastward-propagating thermocline mode. The main reason diagnosed
for these different behaviors is the atmospheric response to SST anomalies. In the warmer climate simulated by the second
version, the wind stress response in the western Pacific is enhanced, and the off-equatorial curl is reduced, both effects
favoring eastward propagation through thermocline depth anomalies. The modifications of the simulated seasonal cycle in version
2 lead to a change in ENSO behavior. In the control climate, the interannual variability in the eastern Pacific is dominated
by warm events, whereas cold events tend to be the more extreme ones with a shifted perihelion.
Received: 14 December 1999 / Accepted: 24 May 2000 相似文献
11.
The influence of the spring AO on ENSO has been demonstrated in several recent studies. This analysis further explores the physical process of the influence of AO on ENSO using the NCEP/NCAR reanalysis data over the period 1958–2010. We focus on the formation of the westerly wind burst in the tropical western Pacific, and examine the evolution and formation of the atmospheric circulation, atmospheric heating, and SST anomalies in association with the spring AO variability. The spring AO variability is found to be independent from the East Asian winter monsoon activity. The spring AO associated circulation anomalies are supported by the interaction between synoptic-scale eddies and the mean-flow and its associated vorticity transportation. Surface wind changes may affect surface heat fluxes and the oceanic heat transport, resulting in the SST change. The AO associated warming in the equatorial SSTs results primarily from the ocean heat transport in the face of net surface heat flux damping. The tropical SST warming is accompanied by anomalous atmospheric heating in the subtropical north and south Pacific, which sustains the anomalous westerly wind in the equatorial western Pacific through a Gill-like atmospheric response from spring to summer. The anomalous westerly excites an eastward propagating and downwelling equatorial Kelvin wave, leading to SST warming in the tropical central-eastern Pacific in summer-fall. The tropical SST, atmospheric heating, and atmospheric circulation anomalies sustain and develop through the Bjerknes feedback mechanism, which eventually result in an El Niño-like warming in the tropical eastern Pacific in winter. 相似文献
12.
We propose a dynamical interpretation of the inverse relationship between the tropical eastern Pacific annual-cycle (AC) amplitude and the El Niño-Southern Oscillation (ENSO) amplitude, based on a pre-industrial simulation of Geophysical Fluid Dynamics Laboratory Couple climate model 2.0 with a fixed concentration of greenhouse gases spanning approximately 500 years. The slowly varying background conditions over more than a decade alternately provided favorable conditions for two opposite regimes, namely the ‘strong AC—weak ENSO regime’ and the ‘weak AC—strong ENSO regime’. For the weak AC—strong ENSO regime, the tropical eastern Pacific shows meridional-asymmetric surface warming with an emphasis on the southern part, leading to weakening of both the zonal trade wind and the cross equatorial southerly wind, as well as deepening of both the thermocline and mixed layer. The deeper mixed layer, weaker southerly wind, and reduced zonal gradient of the mean sea surface temperature due to tropical eastern Pacific warming all acts to reduce the AC. Conversely, the ENSO was intensified by the deeper mixed layer and deeper thermocline depth (thermocline feedback), but suppressed by the deeper thermocline depth (Ekman feedback) and the reduced zonal temperature gradient. We also computed the coupling strengths of the ENSO and AC, defined as the linear regression coefficients of the zonal and meridional wind stresses against the eastern Pacific SST, respectively. The coupling strengths of both the AC and ENSO are larger when they are intensified, and vice versa. All processes for the weak AC—strong ENSO regime operate in the opposite manner for the strong AC—weak ENSO regime. 相似文献
13.
ABSTRACT The role of ocean dynamics in maintaining the Pacific Decadal Variability （PDV） was investigated based on simulation results from the Parallel Ocean Program （POP） ocean general circulation model developed at the Los Alamos National Laboratory （LANL）. A long-term control simulation of the LANL-POP model forced by a reconstructed coupled wind stress field over the period 1949-2001 showed that the ocean model not only simulates a reasonable climatology, but also produces a climate variability pattem very similar to observed PDV. In the Equatorial Pacific （EP） region, the decadal warming is confined in the thin surface layer. Beneath the surface, a strong compensating cooling, accompanied by a basin-wide-scale overturning circulation in opposition to the mean flow, occurs in the thermocline layer. In the North Pacific （NP） region, the decadal variability nonetheless exhibits a relatively monotonous pattern, characterized by the dominance of anomalous cooling and eastward flows. A term balance analysis of the perturbation heat budget equation was conducted to highlight the ocean＇s role in main- taining the PDV-like variability over the EP and NP regions. The analyses showed that strong oceanic adjustment must occur in the equatorial thermocline in association with the anomalous overturning circulation in order to maintain the PDV-like variability, including a flattening of the equatorial thermocline slpoe and an enhancement of the upper ocean＇s stratification （stability）, as the climate shifts from a colder regime toward a warmer one. On the other hand, the oceanic response in the extratropical region seems to be confined to the surface layer, without much participation from the subsurface oceanic dynamics. 相似文献
14.
关于ENSO本质的进一步研究 总被引：28，自引：5，他引：23
基于ENSO是热带太平洋海气相互作用产物的科学观点,一系列的分析研究表明:赤道太平洋次表层海温异常(SOTA)有明显的年际变化(循环),并且与ENSO发生密切相关;ENSO的真正源区在赤道西太平洋暖池,赤道西太平洋暖池正(负)SOTA沿赤道温跃层东传到东太平洋,导致El Nino(La Nina)的爆发;在暖池正(负)SOTA沿赤道温跃层东传的同时,将有负(正)SOTA沿10°N和10°S两个纬度带向西传播,从而构成SOTA的循环;热带太平洋SOTA年际循环的驱动者主要是由异常东亚季风所引起的赤道西太平洋纬向风的异常.进而,可以提出关于ENSO本质的一种新理论,即ENSO实质上主要是由异常东亚季风引起的赤道西太平洋异常纬向风所驱动的热带太平洋次表层海温距平的年际循环.
相似文献
15.
—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
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.
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
18.
Local and remote impacts of a tropical Atlantic salinity anomaly 总被引：1，自引：1，他引：0
The climatic impacts of an enhanced evaporation prescribed during 50 years in the tropical Atlantic are investigated in a coupled ocean–atmosphere general circulation model. Locally, the salinity increase leads to a rapid deepening and cooling of the surface mixed layer. This induces a deepening of the equatorial undercurrent and an intensification of the south equatorial current. A remote atmospheric response to the tropical Atlantic perturbation is detected in the North Atlantic sector after ten years. It has the form of a robust wave-like tropospheric perturbation seemingly excited by the weakening of atmospheric deep convection over the Amazonian basin. Meanwhile, the salt anomaly is carried northward by the mean oceanic circulation. It is traced up to the convection sites and then on its return path at depth towards lower latitudes. Consistent with the density increase, deep convection is enhanced after the arrival of the salt anomaly and the Atlantic meridional overturning circulation (AMOC) intensifies about 20 years after the beginning of the perturbation. The adjustment of the tropical Atlantic to the AMOC intensification then modifies its initial response to the freshwater forcing, leading to a weaker cooling in the northern tropical Atlantic than in the southern tropical Atlantic, a slight northward shift of the tropical Atlantic precipitation pattern and an intensification of the North Brazil current. On the other hand, no significant anomalous precipitations are found in the Pacific. The initial remote atmospheric response is also modulated, by an NAO-like response to the AMOC intensification. 相似文献
19.
The tropical Indian Ocean climate variability is investigated using an artificial neural network analysis called self-organizing map (SOM) for both observational data and coupled model outputs. The SOM successfully captures the dipole sea surface temperature anomaly (SSTA) pattern associated with the Indian Ocean Dipole (IOD) and basin-wide warming/cooling associated with ENSO. The dipole SSTA pattern appears only in boreal summer and fall, whereas the basin-wide warming/cooling appears mostly in boreal winter and spring owing to the phase-locking nature of these phenomena. Their occurrence also undergoes significant decadal variation. Composite diagrams constructed for nodes in the SOM array based on the simulated SSTA reveal interesting features. For the nodes with the basin-wide warming, a strong positive SSTA in the eastern equatorial Pacific, a negative Southern Oscillation, and a negative precipitation anomaly in East Africa are found. The nodes with the positive IOD are associated with a weak positive SSTA in the central equatorial Pacific or positive SSTA in the eastern equatorial Pacific, a positive (negative) sea level pressure anomaly in the eastern (western) tropical Indian Ocean, and a positive precipitation anomaly over East Africa. The warming in the central equatorial Pacific appears to correspond to El Niño Modoki discussed recently. These results suggest usefulness of SOM in studying large-scale ocean–atmosphere coupled phenomena. 相似文献
20.
Tropical cyclone heat potential (TCHP) in the ocean can affect tropical cyclone intensity and intensification. In this paper, TCHP change under global warming is presented based on 35 models from CMIP5 (Coupled Model Intercomparison Project, Phase 5). As the upper ocean warms up, the TCHP of the global ocean is projected to increase by 140.6% in the 21st century under the RCP4.5 (+4.5 W m-2 Representative Concentration Pathway) scenario. The increase is particularly significant in the western Pacific, northwestern Indian and western tropical Atlantic oceans. The increase of TCHP results from the ocean temperature warming above the depth of the 26°C isotherm (D26), the deepening of D26, and the horizontal area expansion of SST above 26°C. Their contributions are 69.4%, 22.5% and 8.1%, respectively. Further, a suite of numerical experiments with an Ocean General Circulation Model (OGCM) is conducted to investigate the relative importance of wind stress and buoyancy forcing to the TCHP change under global warming. Results show that sea surface warming is the dominant forcing for the TCHP change, while wind stress and sea surface salinity change are secondary. 相似文献