Sea-Surface Temperature Anomaly Generation in Relation to Atmospheric Storms (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, 2003
Temporal and spatial structures of turbulent latent and sensible heat flux anomalies are examined in relation to dominant patterns of sea surface temperature anomalies (SSTA) observed over the North Pacific. Relative importance among observed anomalies in SST, surface air temperature and wind speed in determining the anomalous turbulent heat fluxes is assessed through linearizing the observed flux anomalies. Over the central basin of the North Pacific, changes in the atmospheric variables, including air temperature and wind speed, are primarily responsible for the generation of local SST variations by changing turbulent heat flux, which supports a conventional view of extratropical air-sea interaction. In the region where ocean dynamics is very important in forming SSTAs, in contrast, SSTAs that have been formed in early winter play the primary role in determining mid-and late-winter turbulent heat flux anomalies, indicative of the SST forcing upon the overlying atmosphere. Specifically, both decadal scale SSTAs in the western Pacific subarctic frontal zone and El Niño related SSTAs south of Japan are found to be engaged actively in such forcing on the atmosphere. The atmospheric response to this forcing appears to include the anomalous storm track activity. The observed atmospheric anomalies, which may be, in part, forced by the preexisting SSTAs in those two regions, act to force SSTAs in other portions of the basin, leading to the time evolution of SSTAs as observed in the course of the winter season.
Journal of Climate, 2005
The surface heat flux response to underlying sea surface temperature (SST) anomalies (the surface heat flux feedback) is estimated using 42 yr of ship-derived monthly turbulent heat fluxes and 17 yr (1984)(1985)(1986)(1987)(1988)(1989)(1990)(1991)(1992)(1993)(1994)(1995)(1996)(1997)(1998)(1999)(2000) of satellite-derived monthly radiative fluxes over the global oceans for individual seasons. Net surface heat flux feedback is generally negative (i.e., a damping of the underlying SST anomalies) over the global oceans, although there is considerable geographical and seasonal variation. Over the North Pacific Ocean, net surface heat flux feedback is dominated by the turbulent flux component, with maximum values (28 W m Ϫ2 K Ϫ1 ) in December-February and minimum values (5 W m Ϫ2 K Ϫ1 ) in May-July. These seasonal variations are due to changes in the strength of the climatological mean surface wind speed and the degree to which the near-surface air temperature and humidity adjust to the underlying SST anomalies. Similar features are observed over the extratropical North Atlantic Ocean with maximum (minimum) feedback values of approximately 33 W m Ϫ2 K Ϫ1 (9 W m Ϫ2 K Ϫ1 ) in December-February (June-August). Although the net surface heat flux feedback may be negative, individual components of the feedback can be positive depending on season and location. For example, over the midlatitude North Pacific Ocean during late spring to midsummer, the radiative flux feedback associated with marine boundary layer clouds and fog is positive, and results in a significant enhancement of the month-to-month persistence of SST anomalies, nearly doubling the SST anomaly decay time from 2.8 to 5.3 months in May-July.
Re-emergence of North Atlantic subsurface ocean temperature anomalies in a seasonal forecast system
Climate Dynamics, 2019
A high-resolution coupled ocean atmosphere model is used to study the effects of seasonal re-emergence of North Atlantic subsurface ocean temperature anomalies on northern hemisphere winter climate. A 50-member control ensemble is integrated from 1 September 2007 to 28 February 2008 and compared with a parallel ensemble with perturbed ocean initial conditions. The perturbation consists of a density-compensated subsurface Atlantic temperature anomaly corresponding to the observed subsurface temperature anomaly for September 2010. The experiment is repeated for two atmosphere horizontal resolutions (~ 60 km and ~ 25 km) in order to determine whether the sensitivity of the atmosphere to re-emerging temperature anomalies is dependent on resolution. A wide range of re-emergence behavior is found within the perturbed ensembles. While the observations seem to indicate that most of the re-emergence is occurring in November, most members of the ensemble show re-emergence occurring later in the winter. However, when re-emergence does occur it is preceded by an atmospheric pressure pattern that induces a strong flow of cold, dry air over the mid-latitude Atlantic, and enhances oceanic latent heat loss. In response to re-emergence (negative SST anomalies), there is reduced latent heat loss, less atmospheric convection, a reduction in eddy kinetic energy and positive low-level pressure anomalies downstream. Within the framework of a seasonal forecast system the results highlight the atmospheric conditions required for re-emergence to take place and the physical processes that may lead to a significant effect on the winter atmospheric circulation.
Understanding the Persistence of Sea Surface Temperature Anomalies in Midlatitudes
Journal of Climate, 2003
An extension of the simple stochastic climate model of Frankignoul and Hasselman that includes the effects of seasonal variations in upper-ocean mixed layer depth upon the persistence of winter sea surface temperature (SST) anomalies is proposed. Seasonal variations in mixed layer depth allow for the ''reemergence mechanism,'' whereby thermal anomalies stored in the deep winter mixed layer persist at depth through summer and become partially reentrained into the mixed layer during the following winter. In this way, SST anomalies can recur from winter to winter without persisting through the intervening summer. Reformulating the simple stochastic climate model in terms of an effective ocean thermal capacity given by the depth of the winter mixed layer, thereby implicitly taking into account reemergence, is shown to provide a favorable fit to the observed winterto-winter SST autocorrelations in the North Atlantic and Pacific, and represents a considerable improvement over the original model. The extended model also compares favorably with results from an entraining bulk ocean mixed layer model coupled to an atmospheric general circulation model. The authors propose that the extended model be adopted as the new ''null hypothesis'' for interannual SST variability in middle and high latitudes.
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].
Sea surface temperature variability: patterns and mechanisms
Annual review of marine science, 2010
Patterns of sea surface temperature (SST) variability on interannual and longer timescales result from a combination of atmospheric and oceanic processes. These SST anomaly patterns may be due to intrinsic modes of atmospheric circulation variability that imprint themselves upon the SST field mainly via surface energy fluxes. Examples include SST fluctuations in the Southern Ocean associated with the Southern Annular Mode, a tripolar pattern of SST anomalies in the North Atlantic associated with the North Atlantic Oscillation, and a pan-Pacific mode known as the Pacific Decadal Oscillation (with additional contributions from oceanic processes). They may also result from coupled ocean-atmosphere interactions, such as the El Niño-Southern Oscillation phenomenon in the tropical Indo-Pacific, the tropical Atlantic Niño, and the cross-equatorial meridional modes in the tropical Pacific and Atlantic. Finally, patterns of SST variability may arise from intrinsic oceanic modes, notably the ...
J 7 . 2 Persistent Locally Coupled Anomalies in the Ocean-Atmosphere
2001
The coupling of atmospheric flow with slowevolving anomalous surface boundary conditions, particularly the Sea Surface Temperature (SST), has the potential to improve the skill of short-term climate prediction (e.g. Shukla et al 2000). Because of the ocean's larger thermal inertia, the ocean can either strengthen or weaken atmospheric anomalies depending on the phase relationship between ocean and atmosphere anomalies. This in turn depends on whether the coupling is two-way or one-way, and on whether the atmosphere is predominantly forcing the ocean or vice versa. In the one-way ocean-atmosphere interaction (usually referred to "AMIP runs" for the Atmospheric Model Intercomparison Project, Gates et al, 1999), SST anomalies are always assumed to amplify/damp the atmospheric anomalies. This approach is commonly applied in the operational dynamical extended range forecasting. The skill obtained with this approach in the seasonal and interannual predictions is primarily du...