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Isaac M. Held and Tapio Schneider

in the interior essentially determines the mass flux, this part of the midlatitude circulation problem effectively reduces to developing a theory for the vertical structure of the eddy PV flux in the interior, given the vertical integral of this flux. This part of the theory must predict the structure of the extratropical tropopause and the troposheric static stability. In theories for the wind-driven oceanic thermocline, Ekman pumping near the surface similarly drives the interior flow. However

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B. Wang, A. Barcilon, and Z. Fang

intrinsic ENSO oscillation and acquires the oscillation period of the external annual forcing. The deterministic chaos found in these intermediate coupled models is characteristic of low-order dynamic systems ( Tziperman et al. 1995 ; Chang et al. 1995 ). However, the irregular interannual oscillation simulated by coupled general circulation models (CGCMs) ( Philander et al. 1992 ) does not appear to be of the low-order chaos. The nonlinear time series analysis performed by Chang et al. (1996

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Jian Ma and Jin-Yi Yu

between the equatorial thermocline and the Walker circulation. The stronger the Walker circulation is, the more EP El Niño events occur. These recent studies relate the EP El Niño to the Walker circulation and the CP El Niño to the Hadley circulation ( Yu et al. 2010 ; Yu et al. 2012 ). Here, we present evidence that a similar relationship exists between the relative Walker and/or Hadley circulation strength and anthropogenic surface warming patterns in the equatorial Pacific. This similarity

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Eli Galanti and Eli Tziperman

cycle is the seasonal movement of the Pacific intertropical convergence zone and its effect on the atmospheric heating and hence on the coupled ocean–atmosphere instability. Other seasonal climatological factors that might enhance the coupled ocean–atmosphere instability possibly leading to ENSO events are large zonal gradients of mean SST, shallow thermocline, strong zonal winds, high SST ( Hirst 1986 ), and strong upwelling ( Battisti 1988 ). Battisti and Hirst (1989) found that setting the

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Lawrence N. Lahiff

Methods of Ordinary Dfferential Equations, Springer-Verlag, 107-127.Jordan, C. L., 1958: Mean soundings for the West Indies area. J. Meteor., I~, 91-97.Kraus, E. B., 1972: Atmosphere-Ocean Interaction. Oxford Uni versity Press, 254 pp. , 1973: Comparison between ice age and present general circulations. Nature, 245, 129-133.---, and J. S. Turner, 1967: A one-dimensional model of the seasonal thermocline: II. The general theory and its conse quences. Tellus, 19, 98-106.Krishnamurti, T. N

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Axel Timmermann, Fei-Fei Jin, and Jan Abshagen

amplitude modulation is the result of stationary autoregressive statistics or whether it is a manifestation of deterministic processes shaping long-term ENSO dynamics. Further support for the deterministic hypotheses comes from coupled general circulation model simulations (CGCM; see Timmermann et al. 2001 ). Timmermann et al. (2001) show that the ENSO dynamics simulated by the CGCM ECHAM4/OPYC can be reduced to a nonlinear four-dimensional ordinary differential equation system, that exhibits similar

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Kirk Brain and Michael D. Cox

various terms in the heat balance are very muchsmaller below the thermocline than .at the surface. Inorder to show the detail at mid-depths a logarithmicspacing is used. The three major terms 0~ (stable),-VV~ and --wO~ are shown at the top of Fig. 3. Thevertical diffusion is positive over most of the section,transfering heat from the surface down into the ocean.This transfer is essential in setting up the densitygradients that drive the thermohaline circulation. Anexception to the general rule occurs

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Fei-Fei Jin and J. David Neelin

. J. David Neelin, Dept. of Atmospheric Sciences, UCLA, 405 Hilgard Ave., Los Angeles, CA90024-1565.perature (SST) in the Pacific cause the trade winds tostrengthen or slacken, and that this in turn drives theocean circulation changes that produce anomalousSST. Beginning at about the same time, the foundationsfor modeling the tropical coupled system were laidthrough the study of the individual components: thedynamics of the equatorial ocean response to windstress in shallow-water models (e

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Carlos R. Mechoso, J. David Neelin, and Jin-Yi Yu

–ocean general circulation models (CGCMs) have demonstrated ability to capture an interannual variability that strongly resembles ENSO without appealing to artificial devices such as flux correction at the atmosphere–ocean interface. This success strongly suggests that CGCMs fields can be used for analyses of the mechanisms at work for ENSO's origin and evolution. The University of California, Los Angeles (UCLA) CGCM is one of the models able to produce ENSO-like climate variability with reasonable frequency

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Mark A. Cane

; Schopfand Suarez 1988, 1990; Cane et al. 1990).Neelin also states that a hallmark of the fast-wave limitis Sverdrup balance; on the equator this is Eq. (50) ofN: gO~h'e = Ae ( 1 ) where hl is the thermocline displacement, Ae is the zonal wind stress divided by layer depth, and g is the acceleration of gravity. Now, in all the ocean-dynamics explanations this same relation holds to leading order in to, the frequency of the oscillation

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