A study of low-frequency response of the atmosphere to the sea surface temperature variations (original) (raw)
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Atmospheric Response to Sea Surface Temperature Anomalies Over the Equatorial Pacific Ocean
한국기상학회 학술대회 논문집, 1995
Atmospheric response to mid-latitude sea surface temperature (SST) anomalies is a long-standing and perplexing problem. There have been extensive studies on the issue of atmospheric response to mid-latitude SST anomalies from observational, theoretical, and modelling perspectives. This paper serves as a brief review focusing on large-scale SST anomalies. Here, convincing new observational evidence and modelling results are presented, and the process of noticing the importance of storm track and oceanic fronts is introduced. It has now been established that the atmospheric response to mid-latitude SST anomalies is largely controlled by the response of the storm track and that among the components of a mid-latitude SST anomaly, the disturbance to oceanic fronts plays a crucial role in simulating a significant storm track response. RÉSUMÉ [Traduit par la rédaction] La réaction de l'atmosphère aux anomalies de la température de surface de la mer (SST) des latitudes moyennes est depuis longtemps un problème préoccupant. Il existe des études approfondies portant sur la réaction de l'atmosphère aux anomalies de SST des latitudes moyennes. Elles se fondent sur des observations, la théorie et la modélisation. Nous présentons dans cet article une brève revue portant sur les anomalies de SST à grande échelle. Nous mentionnons de nouveaux résultats convaincants issus d'observations et de modélisation, et attirons aussi l'attention sur le processus qui consiste à remarquer l'importance de la trajectoire des systèmes et des fronts sur l'océan. Il est maintenant établi que la réaction de l'atmosphère aux anomalies de SST des latitudes moyennes est largement régie par la réaction de la trajectoire de la tempête et que, parmi les composantes d'une anomalie de SST des latitudes moyennes, la perturbation des fronts sur l'océan joue un rôle crucial dans la simulation d'une réaction évidente de la trajectoire du système.
Journal of Geophysical Research, 1995
We describe a heat anomaly transport in the upper ocean mixed layer in the Kuroshio extension region and the subtropical gyre of the northwest Pacific. Emphasis is on behavior in the cool season (December-March) during the Asian Winter Monsoon. The heat anomaly transport is estimated by applying an inversion technique to the stochastic partial differential equation for the heat anomaly balance of advection, diffusion, stabilizing feedback, and atmospheric forcing. The inversion consists of (1) derivation of statistical parametric model from the heat anomaly balance equation; (2) fitting the derived statistical model to the sea surface temperature (SST) anomaly covariances; and (3) calculation of the heat anomaly net advection velocity, horizontal diffusion coefficient, feedback factor and atmospheric forcing correlation from the parameters of the evaluated statistical model. The inversion was applied to the Comprehensive Ocean-Atmosphere Data Set Compressed Marine Reports SST dam, averaged at 1 ø latitude x 2' longitude boxes on a 10-day mean basis from 1965 to 1990. The estimates of the net advection velocity are consistent in magnitude and direction with the general circulation in the surface layer of the Northwest Pacific in winter. SST anomalies are transported to the west at -0.15 m s -• in the northern part of the North Equatorial Current. Between 21 ø and 29øN in the recirculating region, SST anomalies propagate westward with the mean velocity less than 0.1 m s '•. South and east of Honshu the observed pattern of the SST anomaly transport agrees broadly with the circulations of the Kuroshio current and its extension and the Oyashio current. South of Honshu, the eastward transport is about 200-300 km wide; its absolute velocity is up to 0.2 m s -•. One branch of the transport separates from the coast near the large meander path of the Kuroshio current and follows the east-southeast direction. The second separation from the coast occurs south of Hokkaido. Over the analysis domain the estimates of the diffusion coefficient are in the range of 3x 103 to 6x 103 m 2 s -•. The higher values of the diffusion coefficient confirm the enhancement of the mesoscale eddy processes near the subtropical convergence zone. The analysis supports Hasselmann's (1976) theory in which generation of midlatitude SST anomalies lasting the dominant timescale of atmospheric processes is primarily attributed to the short period stochastic weather forcing. However, the analysis indicates that the inertia of SST anomalies to their "memory" of earlier winds can not be neglected in the vicinity of the western boundary and in the tropics. 1. Introduction Since the late 1950s, sea surface temperature (SST) anomalies have been regarded as one of the key elements of climate variations [Bjerknes, 1959; Namias, 1959]. During the past three decades many publications have described the generation and evolution of SST anomalies (c.f. review of Frankignoul [1985]). They considered a heat budget of the top layer of the ocean, atmospheric forcing of the sea, feedbacks, and multiple timescale interactions in the coupled oceanatmosphere system. The concept of the uniform mixed layer [Kraus and Turner, 1967, Niiler and Kraus, 1977] played a major role in the formulation of a model for the upper sea heat anomaly balance. Statistical studies of the global SST Copyright 1995 by the American Geophysical Union. Paper number 94JC03041. 0148-0227/95/94JC-03041 $05.00 anomaly variability in terms of empirical orthogonal functions were originated by Davis [1976]. Numerical simulations of SST anomalies with ocean general circulation models were initiated by Haney et al. [1978]. At the beginning of the 1980s it was generally accepted that the SST anomaly behavior differs between the tropics and midlatitudes. The tropical SST anomalies were suggested to be generated by the large-scale ocean-atmosphere feedback processes [see Philander, 1990]. White et al. [1985] and Pazan et al. [1986] examined heat content redistribution in the tropical western Pacific during E1 Nifio-Southern Oscillation events. The heat content redistribution was shown to be associated with wind-driven baroclinic Rossby and Kelvin wave activity. Recent numerical experiments indicate that there are at least two classes of ocean-atmosphere modes in tropics. In the first class of modes, SST and surface wind variations can be in phase, but other oceanic parameters, for example, thermocline depth variations, have a phase lag that represents the inertia of the ocean and its "memory" of earlier 4845 4846 OSTROVSKII AND PITERBARG: HEAT ANOMALY TRANSPORT IN NW PACIFIC winds [Philander et al., 1992]. In numerical models that capture this class of modes the ocean response to the wind is of the "delayed oscillator" type, and the simulated Southern Oscillation can be made irregular by introducing highfrequency modes such as atmospheric "weather" forcing. The second class of ocean-atmosphere modes in the tropics is characterized by phase differences between SST and surface wind fluctuations [Lau et al., 1992].
Climate Dynamics, 1999
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.
Dynamics of Interannual Variability in Summer Precipitation over East Asia *
Journal of Climate, 2011
The summertime mei-yu–baiu rainband over East Asia displays considerable interannual variability. A singular value decomposition (SVD) analysis for interannual variability reveals that precipitation anomalies over the mei-yu–baiu region are accompanied by in situ anomalies of midtropospheric horizontal temperature advection. Anomalous warm (cool) advection causes increased (decreased) mei-yu–baiu precipitation locally by inducing adiabatic ascent (descent). The anomalous precipitation acts to reinforce the vertical motion, forming a feedback system. By this mechanism, the remotely forced anomalous atmospheric circulation can induce changes in mei-yu–baiu precipitation. The quasi-stationary precipitation anomalies induced by this mechanism are partially offset by transient eddies. The SVD analysis also reveals the association of mei-yu–baiu precipitation anomalies with several teleconnection patterns, suggesting remote induction mechanisms. The Pacific–Japan (PJ) teleconnection patte...
Climate anomalies north of 55 °N associated with tropical climate extremes
International Journal of Climatology, 1994
The relationship between extremes in tropical climate phenomena, e.g. ENSO and Indian summer monsoon, and the lower tropospheric temperature north of 55 O N is examined. For this purpose we carry out a dynamic statistical analysis applied to the data set of monthly mean 500-1000 hPa thickness from January 1949 to December 1991 (German Weather Service (DWD) analyses). To test the null hypothesis of identical horizontal mean distributions of the polar temperature field in irrespective of the sign of extreme tropical episodes a multivariate significance test is performed and the level of recurrence is estimated. In order to improve the signal-to-noise ratio, the data are projected onto the eigenmodes of an advection-diffusion model. Comparing composites of warm versus cold ENSO events, the model indicates a significant difference in the winter lower tropospheric temperature pattern in northern latitudes. This pattern contains a warmer lower troposphere over the northern North American continent in winter, corresponding to other studies. The multivariate analysis further shows that the Indian summer monsoons with deficient rainfall are preceded by a strong cold anomaly in the lower troposphere over the northern Asian continent early in the year, corresponding to the known hypothesis of Asian-snow-monsoon coupling. KEY WORDS ENSO Monsoon Arctic 'troposphere' temperature anomalies Multivariate statistics
Atmosphere-Ocean, 1992
The climatologies of upper-air persistent circulation anomalies found in observations of the Northern Hemisphere and in a General Circulation Model (GCM) integration are compared with each other and with those found in previous studies. The model simulation is that of the Canadian Climate Centre GCM run at resolution 720. The objective criteria that define the persistent events d~ffer from those of some earlier investigations in that the anomalies are not required to be as nearly stationary. It is found that the GCM generates persistent circulation anomalies downstream of the synoptic-scale storm tracks, in very nearly the correct geographical locations, but that the frequency of occurrence is too low in the model. A kinetic energy and streamfunction variance analysis is presented for both datasets to clarIfy the d~fferences between the observed and simulated distributions of circulation anomalies. It is evident that, apart from the mean annual cycle, the middle-latitude transient eddies of the model are too weak. RESUMÉ Nous présentons la climatologie des anomalies persistantes des vents à 50 kPa sur l'hémisphère Nord telles que retrouvées dans des données d'observations et dans une intégration du modèle de circulation générale du Centre climatologique canadien, dans sa version à résolution 720. Ces climatologies sont comparées entre elles et avec celles provenant d'études antérieures. Les critères définissant les anomalies persistantes diffèrent de ceux utilisés précédemment en ce que nous permettons aux patrons d'anomalie de se déplacer un peu plus. Nous trouvons que le modèle génère des anomalies persistantes en aval des régions d'activité synoptique maximale, en accord avec les observations, mais avec une fréquence inférieure à celle observée. Pour clarifier cette d~fférence entre le modèle et les observations nous présentons une analyse de l'énergie cinétique transitoire et de la variance de la fonction de courant pour les deux ensembles de données. Il est clair qu 'aux latitudes moyennes les ondes transitoires du modèle, à l'exception du cycle saisonnier, ont trop peu d'amplitude.
Journal of Climate, 2003
Various earlier studies have demonstrated that rainfall in the Maritime Continent-Indonesia region is strongly related to the El Niño-Southern Oscillation (ENSO) during the dry half of the year but has a very weak association with ENSO during the summer-wet season months. This relationship is investigated over a wider domain through the use of outgoing longwave radiation (OLR) data as a proxy for rainfall.
Climate Dynamics, 1999
The thirty year simulation of the coupled global atmosphere-tropical Pacific Ocean general circulation model of the Laboratoire de Métérologie Dynamique and the Laboratoire d’Océanographie Dynamique et de Climatologie presented in Part I is further investigated in order to understand the mechanisms of interannual variability. The model does simulate interannual events with ENSO characteristics; the dominant periodicity is quasi-biennial, though strong events are separated by four year intervals. The mechanism that is responsible for seasonal oscillations, identified in Part I, is also active in interannual variability with the difference that now the Western Pacific is dynamically involved. A warm interannual phase is associated with an equatorward shift of the ITCZ in the Western and Central Pacific. The coupling between the ITCZ and the ocean circulation is then responsible for the cooling of the equatorial subsurface by the draining mechanism. Cold subsurface temperature anomalies then propagate eastward along the mean equatorial thermocline. Upon reaching the Eastern Pacific where the mean thermocline is shallow, cold subsurface anomalies affect surface temperatures and reverse the phase of the oscillation. The preferred season for efficient eastward propagation of thermocline depth temperature anomalies is boreal autumn, when draining of equatorial waters towards higher latitudes is weaker than in spring by a factor of six. In that way, the annual cycle acts as a dam that synchronizes lower frequency oscillations.
Inversion for the heat anomaly transport from the SST time series in the Northwestern Pacific
Journal of Geophysical Research Atmospheres
We describe a heat anomaly transport in the upper ocean mixed layer in the Kuroshio extension region and the subtropical gyre of the northwest Pacific. Emphasis is on behavior in the cool season (December-March) during the Asian Winter Monsoon. The heat anomaly transport is estimated by applying an inversion technique to the stochastic partial differential equation for the heat anomaly balance of advection, diffusion, stabilizing feedback, and atmospheric forcing. The inversion consists of (1) derivation of statistical parametric model from the heat anomaly balance equation; (2) fitting the derived statistical model to the sea surface temperature (SST) anomaly covariances; and (3) calculation of the heat anomaly net advection velocity, horizontal diffusion coefficient, feedback factor and atmospheric forcing correlation from the parameters of the evaluated statistical model. The inversion was applied to the Comprehensive Ocean-Atmosphere Data Set Compressed Marine Reports SST dam, averaged at 1 ø latitude x 2' longitude boxes on a 10-day mean basis from 1965 to 1990. The estimates of the net advection velocity are consistent in magnitude and direction with the general circulation in the surface layer of the Northwest Pacific in winter. SST anomalies are transported to the west at -0.15 m s -• in the northern part of the North Equatorial Current. Between 21 ø and 29øN in the recirculating region, SST anomalies propagate westward with the mean velocity less than 0.1 m s '•. South and east of Honshu the observed pattern of the SST anomaly transport agrees broadly with the circulations of the Kuroshio current and its extension and the Oyashio current. South of Honshu, the eastward transport is about 200-300 km wide; its absolute velocity is up to 0.2 m s -•. One branch of the transport separates from the coast near the large meander path of the Kuroshio current and follows the east-southeast direction. The second separation from the coast occurs south of Hokkaido. Over the analysis domain the estimates of the diffusion coefficient are in the range of 3x 103 to 6x 103 m 2 s -•. The higher values of the diffusion coefficient confirm the enhancement of the mesoscale eddy processes near the subtropical convergence zone. The analysis supports Hasselmann's (1976) theory in which generation of midlatitude SST anomalies lasting the dominant timescale of atmospheric processes is primarily attributed to the short period stochastic weather forcing. However, the analysis indicates that the inertia of SST anomalies to their "memory" of earlier winds can not be neglected in the vicinity of the western boundary and in the tropics. 1. Introduction Since the late 1950s, sea surface temperature (SST) anomalies have been regarded as one of the key elements of climate variations [Bjerknes, 1959; Namias, 1959]. During the past three decades many publications have described the generation and evolution of SST anomalies (c.f. review of Frankignoul [1985]). They considered a heat budget of the top layer of the ocean, atmospheric forcing of the sea, feedbacks, and multiple timescale interactions in the coupled oceanatmosphere system. The concept of the uniform mixed layer [Kraus and Turner, 1967, Niiler and Kraus, 1977] played a major role in the formulation of a model for the upper sea heat anomaly balance. Statistical studies of the global SST Copyright 1995 by the American Geophysical Union. Paper number 94JC03041. 0148-0227/95/94JC-03041 $05.00 anomaly variability in terms of empirical orthogonal functions were originated by Davis [1976]. Numerical simulations of SST anomalies with ocean general circulation models were initiated by Haney et al. [1978]. At the beginning of the 1980s it was generally accepted that the SST anomaly behavior differs between the tropics and midlatitudes. The tropical SST anomalies were suggested to be generated by the large-scale ocean-atmosphere feedback processes [see Philander, 1990]. White et al. [1985] and Pazan et al. [1986] examined heat content redistribution in the tropical western Pacific during E1 Nifio-Southern Oscillation events. The heat content redistribution was shown to be associated with wind-driven baroclinic Rossby and Kelvin wave activity. Recent numerical experiments indicate that there are at least two classes of ocean-atmosphere modes in tropics. In the first class of modes, SST and surface wind variations can be in phase, but other oceanic parameters, for example, thermocline depth variations, have a phase lag that represents the inertia of the ocean and its "memory" of earlier 4845 4846 OSTROVSKII AND PITERBARG: HEAT ANOMALY TRANSPORT IN NW PACIFIC winds [Philander et al., 1992]. In numerical models that capture this class of modes the ocean response to the wind is of the "delayed oscillator" type, and the simulated Southern Oscillation can be made irregular by introducing highfrequency modes such as atmospheric "weather" forcing. The second class of ocean-atmosphere modes in the tropics is characterized by phase differences between SST and surface wind fluctuations [Lau et al., 1992].
Atmospheric response to observed intraseasonal tropical sea surface temperature anomalies
Geophysical Research Letters, 2004
1] The major tropical convective and circulation features of the intraseasonal or Madden -Julian oscillation (MJO) are simulated as a passive response to observed MJO sea surface temperature (SST) anomalies in an atmospheric general circulation model (AGCM), strengthening the case for ocean -atmosphere interactions being central to MJO dynamics. However, the magnitude of the surface fluxes diagnosed from the MJO cycle in the AGCM, that would feed back onto the ocean in a coupled system, are much weaker than in observations. The phasing of the convectivedynamical model response to the MJO SST anomalies and the associated surface flux anomalies is too fast compared to observations of the (potentially) coupled system, and would act to damp the SST anomalies.