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1.
The inter-basin teleconnection between the North Atlantic and the North Pacific ocean–atmosphere interaction is studied using
a coupled ocean–atmosphere general circulation model. In the model, an idealized oceanic temperature anomaly is initiated
over the Kuroshio and the Gulf Stream extension region to track the coupled evolution of ocean and atmosphere interaction,
respectively. The experiments explicitly demonstrate that both the North Pacific and the North Atlantic ocean–atmosphere interactions
are intimately coupled through an inter-basin atmospheric teleconnection. This fast inter-basin communication can transmit
oceanic variability between the North Atlantic and the North Pacific through local ocean-to-atmosphere feedbacks. The leading
mode of the extratropical atmospheric internal variability plays a dominant role in shaping the hemispheric-scale response
forced by oceanic variability over the North Atlantic and Pacific. Modeling results also suggest that a century (two centuries)
long observations are necessary for the detection of Pacific response to Atlantic forcings (Atlantic response to Pacific forcing). 相似文献
2.
The role of prescribing sea surface temperature in paleoclimate atmospheric simulations has been investigated by comparing
Last Glacial Maximum AGCMs experiments using different SSTs data sets as well as coupled atmosphere/oceanic mixed layer models.
Changes in the SSTs and sea-ice margin generate different patterns of zonal asymmetries in the atmospheric circulation that
are responsible for reorganisation of heat and moisture transport, leading to important variations of Northern Hemisphere
regional climates, particularly in winter. Additional sensitivity experiments have been carried out to isolate the individual
role of North Pacific and North Atlantic SSTs anomalies. We found that changes in North Pacific SSTs have a much stronger
impact over all the northern continental surfaces, including Europe and Siberia, than changes in the North Atlantic SSTs.
As these SSTs anomalies are of the order of the typical errors generated by coupled ocean-atmosphere models, this suggests
that these more complete models will likely still have problems in simulating the regional climate change at the LGM.
Received: 11 October 1999 / Accepted: 9 June 2000 相似文献
3.
We assess the effects of the North Atlantic Ocean Sea Surface Temperature (NASST) on North East Asian (NEA) surface temperature. We use a set of sensitivity experiments, performed with MetUM-GOML2, an atmospheric general circulation model coupled to a multi-level ocean mixed layer model, to mimic warming and cooling over the North Atlantic Ocean. Results show that a warming of the NASST is associated with a significant warming over NEA. Two mechanisms are pointed out to explain the NASST—North East Asia surface temperature relationship. First, the warming of the NASST is associated with a modulation of the northern hemisphere circulation, due to the propagation of a Rossby wave (i.e. the circumglobal teleconnection). The change in the atmosphere circulation is associated with advections of heat from the Pacific Ocean to NEA and with an increase in net surface shortwave radiation over NEA, both acting to increase NEA surface temperature. Second, the warming of the NASST is associated with a cooling (warming) over the eastern (western) Pacific Ocean, which modulates the circulation over the western Pacific Ocean and NEA. Additional simulations, in which Pacific Ocean sea surface temperatures are kept constant, show that the modulation of the circumglobal teleconnection is key to explaining impacts of the NASST on NEA surface temperature.
相似文献4.
《大气与海洋》2013,51(2):81-92
Abstract Evidence based on numerical simulations is presented for a strong correlation between the North Atlantic Oscillation (NAO) and the North Atlantic overturning circulation. Using an ensemble of numerical experiments with a coupled ocean‐atmosphere model including both natural and anthropogenic forcings, it is shown that the weakening of the thermohaline circulation (THC) could be delayed in response to a sustained upward trend in the NAO, which was observed over the last three decades of the twentieth century, 1970–99. Overall warming and enhanced horizontal transports of heat from the tropics to the subpolar North Atlantic overwhelm the NAO‐induced cooling of the upper ocean layers due to enhanced fluxes of latent and sensible heat, so that the net effect of warmed surface ocean temperatures acts to increase the vertical stability of the ocean column. However, the strong westerly winds cause increased evaporation from the ocean surface, which leads to a reduced fresh water flux over the western part of the North Atlantic. Horizontal poleward transport of salinity anomalies from the tropical Atlantic is the major contributor to the increasing salinities in the sinking regions of the North Atlantic. The effect of positive salinity anomalies on surface ocean density overrides the opposing effect of enhanced warming of the ocean surface, which causes an increase in surface density in the Labrador Sea and in the ocean area south of Greenland. The increased density of the upper ocean layer leads to deeper convection in the Labrador Sea and in the western North Atlantic. With a lag of four years, the meridional overturning circulation of the North Atlantic shows strengthening as it adjusts to positive density anomalies and enhanced vertical mixing. During the positive NAO trend, the salinity‐driven density instability in the upper ocean, due to both increased northward ocean transports of salinity and decreased atmospheric freshwater fluxes, results in a strengthening overturning circulation in the North Atlantic when the surface atmospheric temperature increases by 0.3°C and the ocean surface temperature warms by 0.5° to 1°C. 相似文献
5.
The atmospheric circulation response to decadal fluctuations of the Atlantic meridional overturning circulation (MOC) in the IPSL climate model is investigated using the associated sea surface temperature signature. A SST anomaly is prescribed in sensitivity experiments with the atmospheric component of the IPSL model coupled to a slab ocean. The prescribed SST anomaly in the North Atlantic is the surface signature of the MOC influence on the atmosphere detected in the coupled simulation. It follows a maximum of the MOC by a few years and resembles the model Atlantic multidecadal oscillation. It is mainly characterized by a warming of the North Atlantic south of Iceland, and a cooling of the Nordic Seas. There are substantial seasonal variations in the geopotential height response to the prescribed SST anomaly, with an East Atlantic Pattern-like response in summer and a North Atlantic oscillation-like signal in winter. In summer, the response of the atmosphere is global in scale, resembling the climatic impact detected in the coupled simulation, albeit with a weaker amplitude. The zonally asymmetric or eddy part of the response is characterized by a trough over warm SST associated with changes in the stationary waves. A diagnostic analysis with daily data emphasizes the role of transient-eddy forcing in shaping and maintaining the equilibrium response. We show that in response to an intensified MOC, the North Atlantic storm tracks are enhanced and shifted northward during summer, consistent with a strengthening of the westerlies. However the anomalous response is weak, which suggests a statistically significant but rather modest influence of the extratropical SST on the atmosphere. The winter response to the MOC-induced North Atlantic warming is an intensification of the subtropical jet and a southward shift of the Atlantic storm track activity, resulting in an equatorward shift of the polar jet. Although the SST anomaly is only prescribed in the Atlantic ocean, significant impacts are found globally, indicating that the Atlantic ocean can drive a large scale atmospheric variability at decadal timescales. The atmospheric response is highly non-linear in both seasons and is consistent with the strong interaction between transient eddies and the mean flow. This study emphasizes that decadal fluctuations of the MOC can affect the storm tracks in both seasons and lead to weak but significant dynamical changes in the atmosphere. 相似文献
6.
Jennifer A. Graham David P. Stevens Karen J. Heywood Zhaomin Wang 《Climate Dynamics》2011,37(1-2):297-311
Recent observations suggest Antarctic Intermediate Water (AAIW) properties are changing. The impact of such variations is explored using idealised perturbation experiments with a coupled climate model, HadCM3. AAIW properties are altered between 10 and 20°S in the South Atlantic, maintaining constant potential density. The perturbed AAIW remains subsurface in the South Atlantic, but as it moves northwards, it surfaces and interacts with the atmosphere leading to density anomalies due to heat exchanges. For a cooler, fresher AAIW, there is a significant decrease in the mean North Atlantic sea surface temperature (SST), of up to 1°C, during years 51?C100. In the North Atlantic Current region there are persistent cold anomalies from 2,000?m depth to the surface, and in the overlying atmosphere. Atmospheric surface pressure increases over the mid-latitude Atlantic, and precipitation decreases over northwest Africa and southwest Europe. Surface heat flux anomalies show that these impacts are caused by changes in the ocean rather than atmospheric forcing. The SST response is associated with significant changes in the Atlantic meridional overturning circulation (MOC). After 50?years there is a decrease in the MOC that persists for the remainder of the simulation, resulting from changes in the column-averaged density difference between 30°S and 60°N. Rather than showing a linear response, a warmer, saltier AAIW also leads to a decreased MOC strength for years 51?C100 and resulting cooling in the North Atlantic. The non-linearity can be attributed to opposing density responses as the perturbed water masses interact with the atmosphere. 相似文献
7.
The present paper selects the northern winter of December 1995–February 1996 for a case study on the impact of sea surface temperature (SST) anomalies on the atmospheric circulation over the North Atlantic and Western Europe. In the Atlantic, the selected winter was characterized by positive SST anomalies over the northern subtropics and east of Newfoundland, and negative anomalies along the US coast. A weak La Niña event developed in the Pacific. The North Atlantic Oscillation (NAO) index was low, precipitation over the Iberian Peninsula and northern Africa was anomalously high, and precipitation over northern Europe was anomalously low. The method of study consists of assessing the sensitivity of ensemble simulations by the UCLA atmospheric general circulation model (UCLA AGCM) to SST anomalies from the observation, which are prescribed either in the World Oceans, the Atlantic Ocean only, or the subtropical North Atlantic only. The results obtained are compared with a control run that uses global, time-varying climatological SST. The ensemble simulations with global and Atlantic-only SST anomalies both produce results that resemble the observations over the North Atlantic and Western Europe. It is suggested that the anomalous behavior of the atmosphere in the selected winter over those regions, therefore, was primarily determined by conditions within the Atlantic basin. The simulated fields in the tropical North Atlantic show anomalous upward motion and lower (upper) level convergence (divergence) in the atmosphere overlying the positive SST anomalies. Consistently, the subtropical jet intensifies and its core moves equatorward, and precipitation increases over northern Africa and southern Europe. The results also suggest that the SST anomalies in the tropical North Atlantic only do not suffice to produce the atmospheric anomalies observed in the basin during the selected winter. The extratropical SST anomalies would provide a key contribution through increased transient eddy activity, which causes an extension of the subtropical jet eastward from the coast of North America. 相似文献
8.
The Role of Warm North Atlantic SST in the Formation of Positive Height Anomalies over the Ural Mountains during January 2008 总被引：4，自引：0，他引：4
The most severe snowstorm and freezing-rain event in the past 50 years hit central and southern China in January 2008. One of the main reasons for the anomalous climate event was the occurrence of atmospheric circulation anomalies over middle and high latitudes, particularly the persistent blocking that occurred over the Ural Mountains. Along with atmospheric anomalies, a strong La Nia event in the Pacific and warm sea surface temperature anomalies (SSTAs) in the North Atlantic were the most significant in the lower boundary. Since a brief analysis suggests that La Nia exerts no significant impact on the Urals, the key point of focus in this study is on the role of the warmer SSTAs in the North Atlantic. Based on an observational composite, North Atlantic SSTAs pattern when the height anomaly over the Urals is strongly positive is found similar to that in January 2008, but no significant SSTAs occurred elsewhere, such as the Pacific. Using an atmospheric general circulation model, ECHAM5, the impact of North Atlantic SSTAs on the extratropical atmosphere circulation in the event was investigated. The results show that the warm SSTAs strengthened the blocking high over the Urals, through anomalous transient eddies. The consistency between the study model and the observational composite indicates that the warm SSTAs in the North Atlantic were indeed an important factor in the formation of the snowstorm disaster of January 2008. 相似文献
9.
Cold-season atmospheric response to the natural variability of the Atlantic meridional overturning circulation 总被引：3，自引：3，他引：0
The influence of the natural variability of the Atlantic meridional overturning circulation (AMOC) on the atmosphere is studied in multi-centennial simulations of six global climate models, using Maximum Covariance Analysis (MCA). In all models, a significant but weak influence of the AMOC changes is found during the Northern Hemisphere cold-season, when the ocean leads the atmosphere by a few years. Although the oceanic pattern slightly varies, an intensification of the AMOC is followed in all models by a weak sea level pressure response that resembles a negative phase of the North Atlantic Oscillation (NAO). The signal amplitude is typically 0.5?hPa and explains about 10% of the yearly variability of the NAO in all models. The atmospheric response seems to be due primarily due to an increase of the heat loss along the North Atlantic Current and the subpolar gyre, associated with an AMOC-driven warming. Sea-ice changes appear to be less important. The stronger heating is associated to a southward shift of the lower-tropospheric baroclinicity and a decrease of the eddy activity in the North Atlantic storm track, which is consistent with the equivalent barotropic perturbation resembling the negative phase of the NAO. This study thus provides some evidence of an atmospheric signature of the AMOC in the cold-season, which may have some implications for the decadal predictability of climate in the North Atlantic region. 相似文献
10.
大西洋多年代际振荡（AMO）是指发生在北大西洋的海表温度（SST）冷暖异常多年代际（50～80年）振荡的现象。通常AMO被认为是受大西洋经向翻转环流（AMOC）及其对应的海洋动力过程（经向热量输运）的影响。近年来有观点认为,AMO是大气随机热力强迫的产物,大气主导了海气间的热量交换进而影响AMO。弄清AMO和北大西洋海表热通量的因果关系是辨析AMO动力和热力驱动机制的关键。本文利用基于信息流理论的因果分析方法,研究了1880年以来观测的AMO与北大西洋海表热通量间的因果关系。结果表明,在多年代际尺度上,从AMO到海表热通量的信息流要远大于二者相反方向的信息流,这说明AMO是北大西洋海表热通量异常的因,海洋主导了海气间的热量交换。大气随机热力强迫机制无法解释AMO与热通量两者因果分析的结果。对泛大西洋地区的陆地气温和AMO指数进行分析,进一步表明由于海洋主导了海气热量交换,AMO的海温异常加热/冷却控制了绝大多数地区气温的多年代际变化。利用海温驱动的大气环流模式的模拟结果验证了AMO的海温异常对周边陆地气温强迫作用。本文的结果为辨析AMO的动力和热力驱动机制提供了新线索,进一步表明AMO并非是大气随机热力强迫的产物,海洋环流可能是AMO的主要驱动因子。 相似文献
11.
S. Rahmstorf 《Climate Dynamics》1996,12(12):799-811
The 'conveyor belt' circulation of the Atlantic Ocean transports large amounts of heat northward, acting as a heating system
for the northern North Atlantic region. It is widely thought that this circulation is driven by atmospheric freshwater export
from the Atlantic catchment region, and that it transports freshwater northward to balance the loss to the atmosphere. Using
results from a simple conceptual model and a global circulation model, it is argued here that the freshwater loss to the atmosphere
arises mainly in the subtropical South Atlantic and is balanced by northward freshwater transport in the wind-driven subtropical
gyre, while the thermohaline circulation transports freshwater southward. It is further argued that the direction of freshwater transport is closely linked to the dynamical regime and stability
of the 'conveyor belt': if its freshwater transport is indeed southward, then its flow is purely thermally driven and inhibited
by the freshwater forcing. In this case the circulation is not far from Stommel's saddle-node bifurcation, and a circulation
state without NADW formation would also be stable.
Received: 10 February 1996 / Accepted: 30 May 1996 相似文献
12.
Lin-Lin Pan 《Climate Dynamics》2007,29(6):647-659
This paper explores the role of synoptic eddy feedback in the air-sea interaction in the North Atlantic region, particularly
the interaction between the North Atlantic Oscillation (NAO) and the North Atlantic sea surface temperature anomalies (SSTA)
tripole. A linearized five-layer primitive equation atmospheric model with synoptic eddy and low-frequency flow (SELF) interaction
is coupled with a linearized oceanic mixed-layer model to investigate this issue. In this model, the “climatological” storm
track/activity (or synoptic eddy activity) is characterized in terms of spatial structures, variances, decay time scales and
propagation speeds through the complex empirical orthogonal function (CEOF) analysis on the observed data, which provides
a unique tool to investigate the role of synoptic eddy feedback in the North Atlantic air–sea coupling. Model experiments
show that the NAO-like atmospheric circulation anomalies can produce tripole-like SSTA in the North Atlantic Ocean, and the
tripole-like SSTA can excite a NAO-like dipole with an equivalent barotropic structure in the atmospheric circulation, which
suggests a positive feedback between the NAO and the SSTA tripole. This positive feedback makes the NAO/SSTA tripole-like
mode be the leading mode of the coupled dynamical system. The synoptic eddy feedback plays an essential role in the origin
of the NAO/SSTA tripole-like leading mode and the equivalent barotropic structure in the atmosphere. Without synoptic eddy
feedback, the atmosphere has a baroclinic structure in the response field to the tripole-like SSTA forcing, and the leading
mode of the dynamic system does not resemble NAO/SSTA tripole pattern. 相似文献
13.
The stability of the Atlantic thermohaline circulation against meltwater input is investigated in a coupled ocean-atmosphere
general circulation model. The meltwater input to the Labrador Sea is increased linearly for 250 years to a maximum input
of 0.625 Sv and then reduced again to 0 (both instantaneously and linearly decreasing over 250 years). The resulting freshening
forces a shutdown of the formation of North Atlantic deepwater and a subsequent reversal of the thermohaline circulation of
the Atlantic, filling the deep Atlantic with Antarctic bottom water. The change in the overturning pattern causes a drastic
reduction of the Atlantic northward heat transport, resulting in a strong cooling with maximum amplitude over the northern
North Atlantic and a southward shift of the sea-ice margin in the Atlantic. Due to the increased meridional temperature gradient,
the intertropical convergence zone over the Atlantic is displaced southward and the westerlies in the Northern Hemisphere
gain strength. We identify four main feedbacks affecting the stability of the thermohaline circulation: the change in the
overturning circulation of the Atlantic leads to longer residence times of the surface water in high-northern latitudes, which
allows them to accumulate more precipitation and runoff from the continents. As a consequence the stratification in the North
Atlantic becomes more stable. This effect is further amplified by an enhanced northward atmospheric water vapour transport,
which increases the freshwater input into the North Atlantic. The reduced northward oceanic heat transport leads to colder
sea-surface temperatures and an intensification of the atmospheric cyclonic circulation over the Norwegian Sea. The associated
Ekman transports cause increased upwelling and increased freshwater export with the East Greenland Current. Both the cooling
and the wind-driven circulation changes largely compensate for the effects of the first two feedbacks. The wind-stress feedback
destabilizes modes without deep water formation in the North Atlantic, but has been neglected in almost all studies so far.
After the meltwater input stops, the North Atlantic deepwater formation resumed in all experiments and the meridional overturning
returned within 200 years to a conveyor belt pattern. This happened although the formation of North Atlantic deep water was
suppressed in one experiment for more than 300 years and the Atlantic overturning had settled into a circulation pattern with
Antarctic bottom water as the only source of deep water. It is a clear indication that cooling and wind-stress feedback are
more effective, at least in our model, than advection feedback and increased atmospheric water vapour transport. We conclude
that the conveyor belt-type thermohaline circulation seems to be much more stable than hitherto assumed from experiments with
simpler models.
Received 31 January 1996/Accepted 22 August 1996 相似文献
14.
Latitudinal heat transport in the ocean and atmosphere represents a fundamental process of the Earth's climate system. The ocean component of heat transport is effected by the thermohaline circulation. Changes in this circulation, and hence latitudinal heat transport, would have a significant effect on global climate. Paleoclimate evidence from the Greenland ice cores and deep sea sediment cores suggests that during much of glacial time the climate system oscillated between two different states. Bimodal equilibrium states of the thermohaline circulation have been demonstrated in climate models. We address the question of the role of the atmospheric hydrological cycle on the global thermohaline circulation and the feedback to the climate system through changes in the ocean's latitudinal heat transport, with a simple coupled ocean-atmosphere energy-salt balance model. Two components of the atmospheric hydrological cycle, i.e., latitudinal water vapor transport and the net flux of water vapor from the Atlantic to the Pacific Ocean appear to play separate roles. If the inter-basin transport is sufficiently large, small changes in water vapor transport over the North Atlantic can effect bifurcation or a rapid transition between two different equilibria in the global thermohaline circulation; maximum difference between the modes occurs in the North Atlantic. If the inter-basin transport is from the Pacific to the Atlantic and sufficiently large, latitudinal vapor transport in the North Pacific controls the bifurcations, with maximum changes occurring in the North Pacific. For intermediate values of inter-basin transport, no rapid transitions occur in either basin. In the regime with vapor flux from the Atlantic to the Pacific, the on mode has strong production of deep water in the North Atlantic and a large flux of heat to the atmosphere from the high latitude North Atlantic. The off mode has strong deep water production in the Southern Ocean and weak production in the North Pacific. Heat transport into the high latitude North Atlantic by the ocean is reduced to about 20% of the on mode value. For estimated values of water vapor transport for the present climate the model asserts that while water vapor transport from the Atlantic to the Pacific Ocean is sufficiently large to make the North Atlantic the dominant region for deep water production, latitudinal water vapor transport is sufficiently low that the thermohaline circulation appears stable, i.e., far from a bifurcation point. This conclusion is supported to some extent by the fact that the high latitude temperature of the atmosphere as recorded in the Greenland ice cores has changed little over the last 9000 years. 相似文献
15.
In this study we investigate the role of heat, freshwater and momentum fluxes in changing the oceanic climate and thermohaline
circulation as a consequence of increasing atmospheric CO2 concentration. Two baseline integrations with a fully coupled ocean atmosphere general circulation model with either fixed
or increasing atmospheric CO2 concentrations have been performed. In a set of sensitivity experiments either freshwater (precipitation, evaporation and
runoff from the continents) and/or momentum fluxes were no longer simulated, but prescribed according to one of the fully
coupled baseline experiments. This approach gives a direct estimate of the contribution from the individual flux components.
The direct effect of surface warming and the associated feedbacks in ocean circulation are the dominant processes in weakening
the Atlantic thermohaline circulation in our model. The relative contribution of momentum and freshwater fluxes to the total
response turned out to be less than 25%, each. Changes in atmospheric water vapour transport lead to enhanced freshwater input
into middle and high latitudes, which weakens the overturning. A stronger export of freshwater from the Atlantic drainage
basin to the Indian and Pacific ocean, on the other hand, intensifies the Atlantic overturning circulation. In total the modified
freshwater fluxes slightly weaken the Atlantic thermohaline circulation. The contribution of the modified momentum fluxes
has a similar magnitude, but enhances the formation of North Atlantic deep water. Salinity anomalies in the Atlantic as a
consequence of greenhouse warming stem in almost equal parts from changes in net freshwater fluxes and from changes in ocean
circulation caused by the surface warming due to atmospheric heat fluxes. Important effects of the momentum fluxes are a poleward
shift of the front between Northern Hemisphere subtropical and subpolar gyres and a southward shift in the position of the
Antarctic circumpolar current, with a clear signal in sea level.
Received: 3 May 1999 / Accepted: 11 December 1999 相似文献
16.
AbstractThe potential influence of a developing La Niña on Arctic sea-ice annual variability is investigated using both observational data and an atmospheric general circulation model. It is found that during the developing phase of an eastern Pacific (EP) La Niña event in June, July, and August (JJA) and September, October, and November (SON), the sea-ice concentration (SIC) over the Barents–Kara Seas declines more than 15%. The local atmospheric circulation pattern associated with the EP La Niña is characterized as a weak decrease in geopotential height over the Barents–Kara Seas, combined with an anticyclone in the North Atlantic. The corresponding southerly winds push warm waters northward into the key sea-ice reduction region and directly accelerate sea-ice melt. Meanwhile, the abundant moisture contained in the lower troposphere is transported into the Arctic region by winds resulting from the local barotropic structure. The humid atmosphere contributes to both net shortwave and longwave radiation and thus indirectly accelerates the decline in sea ice. Simulations by the European Centre Hamburg Model, version 5.4, are forced by observed sea surface temperature anomalies associated with EP La Niña events. The results of the simulations capture the North Atlantic anticyclone and reproduce the moisture transport, which supports the premise that an EP La Niña plays a crucial role in sea-ice reduction over the Barents–Kara sector from the perspective of atmospheric circulation and net surface heat flux. 相似文献
17.
利用全球海洋—大气快速耦合模式（Fast Ocean-Atmosphere Model,FOAM）,采用模式中的初值方法,研究了湾流区海温再现过程及其对北半球大气环流和气候的影响。FOAM模式很好地模拟了北大西洋湾流区的海温＂再现＂过程,模式中海面热通量异常与SST异常表现出不同步的响应特征。海面热通量异常在初冬季节达到最大值,而SST异常滞后,在冬季晚期达到最大值,从而在初冬和晚冬对北半球大气环流造成不同的影响。初冬季节北半球大气环流主要受海洋热通量异常的强迫,在北大西洋和北太平洋上空呈现相当正压的异常低压槽响应,北极地区为异常高压脊,类似北极涛动的负位相,可能造成欧洲南部和北非大陆气温偏高,亚洲大陆气温偏低。而晚冬季节北半球大气环流主要受SST异常的驱动,在北大西洋和北太平洋上空表现为相当正压的异常高压脊响应,北极地区为异常低压槽,类似北极涛动的正位相,可能造成欧洲南部和北非大陆气温偏低,亚洲大陆气温偏高,中国东部降水异常偏多30%左右。北太平洋大气环流的异常由北大西洋湾流区海洋热通量和SST异常强迫下游大气环流所激发,进一步通过Rossby驻波的能量频散东传至北太平洋而造成的。 相似文献
18.
The interannual variability of the European winter air temperature is partially caused by anomalous atmospheric circulation
and the associated advection of air masses, mainly linked to the North Atlantic Oscillation (NAO). However, a considerable
part of the temperature variability is not linearly described by atmospheric circulation anomalies. Here, a long control simulation
with a coupled atmosphere-ocean climate model is analyzed, with the goal of decomposing the European temperature (ET) anomalies
in a part linked to the anomalous atmospheric circulation and a residual. The amount of interannual variability of each contribution
is roughly 50%, although at subdecadal (overdecadal) time scales the variability of the residuals is dominant. These residuals
are found to be linked to temperature anomalies of the same sign in the whole North Atlantic and Greenland, in contrast to
the well-known temperature zonal seesaw associated with the NAO. The association between the residuals and other processes
in the North Atlantic has been also analyzed. The thermohaline circulation, closely connected in the model to the intensity
of the Gulf Stream, lags the evolution of the temperature residuals by several years and thus is not able to control their
evolution. The variability of the oceanic convection in the Northern North Atlantic, on the other hand, correlates with the
temperature residual at lags close to zero. It is hypothesized that oceanic convection produces a sea-surface temperature
fingerprint that leads to the ET residuals. The implications of these results for multi-year predictability and for empirical
climate reconstructions are discussed. 相似文献
19.
A. V. Murav’ev I. A. Kulikova Yu. D. Resnyanskii 《Russian Meteorology and Hydrology》2010,35(2):79-93
The spatial and temporal relationships between sea surface temperature anomalies (SSTA) in the North Atlantic and the large-scale
mid-troposphere circulation features in the Northern Hemisphere during the summer and the winter seasons are investigated.
Results are based on atmospheric circulation indices (CI), introduced by Wallace and Gutzler for physical reasoning the low
frequency atmospheric oscillations. Extreme levels and extreme situations in the mid-troposphere were defined and the SSTA
composite charts were constructed with backward lags from 0 to 3 months. Analysis shows that several CI extreme phases of
different signs are associated with synchronous and asynchronous SSTA composites of statistically separable types, or even
antipodes, which may be interpreted as the intraseasonal influence of the ocean on the large-scale mid-troposphere anomaly
features. Noteworthy is the role of the North Atlantic tropical zone in formation of ridges and blocking situations both in
synchronous and asynchronous aspects. The North Atlantic SSTA relations to the West Atlantic Oscillation are shown to be significantly
weaker that the same to the East Atlantic Oscillation. 相似文献
20.
Christophe Cassou Marie Minvielle Laurent Terray Claire P��rigaud 《Climate Dynamics》2011,36(1-2):19-39
The links between the observed variability of the surface ocean variables estimated from reanalysis and the overlying atmosphere decomposed in classes of large-scale atmospheric circulation via clustering are investigated over the Atlantic from 1958 to 2002. Daily 500?hPa geopotential height and 1,000?hPa wind anomaly maps are classified following a weather-typing approach to describe the North Atlantic and tropical Atlantic atmospheric dynamics, respectively. The algorithm yields patterns that correspond in the extratropics to the well-known North Atlantic-Europe weather regimes (NAE-WR) accounting for the barotropic dynamics, and in the tropics to wind classes (T-WC) representing the alteration of the trades. 10-m wind and 2-m temperature (T2) anomaly composites derived from regime/wind class occurrence are indicative of strong relationships between daily large-scale atmospheric circulation and ocean surface over the entire Atlantic basin. High temporal correlation values are obtained basin-wide at low frequency between the observed fields and their reconstruction by multiple linear regressions with the frequencies of occurrence of both NAE-WR and T-WC used as sole predictors. Additional multiple linear regressions also emphasize the importance of accounting for the strength of the daily anomalous atmospheric circulation estimated by the combined distances to all regimes centroids in order to reproduce the daily to interannual variability of the Atlantic ocean. We show that for most of the North Atlantic basin the occurrence of NAE-WR generally sets the sign of the ocean surface anomaly for a given day, and that the inter-regime distances are valuable predictors for the magnitude of that anomaly. Finally, we provide evidence that a large fraction of the low-frequency trends in the Atlantic observed at the surface over the last 50?years can be traced back, except for T2, to changes in occurrence of tropical and extratropical weather classes. All together, our findings are encouraging for the prospects of basin-scale ocean dynamical downscaling using a weather-typing approach to reconstruct forcing fields for high resolution ocean models (Part II) from coarse resolution climate models. 相似文献