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1. Introduction In the context of the two-layer quasigeostrophic (QG) model, it has been known for almost five decades that Ekman pumping, if present only at the lower boundary, can destabilize baroclinic waves. For example, Holopainen (1961) performed a linear stability analysis of the two-layer model and found that the lower boundary Ekman pumping broadens the marginally stable curve of the inviscid flow so as to destabilize both longer and shorter zonal waves. Essentially the same result
1. Introduction In the context of the two-layer quasigeostrophic (QG) model, it has been known for almost five decades that Ekman pumping, if present only at the lower boundary, can destabilize baroclinic waves. For example, Holopainen (1961) performed a linear stability analysis of the two-layer model and found that the lower boundary Ekman pumping broadens the marginally stable curve of the inviscid flow so as to destabilize both longer and shorter zonal waves. Essentially the same result
1. Introduction Surface currents associated with mesoscale ocean eddies impart a curl to the surface stress from the relative motion between surface air and water. This surface stress curl has a polarity opposite that of the vorticity of eddy surface currents and thus attenuates eddies by generating Ekman upwelling in the cores of anticyclonic eddies and downwelling in the cores of cyclonic eddies ( Dewar and Flierl 1987 ). An influence of eddy surface vorticity on Ekman pumping has also long
1. Introduction Surface currents associated with mesoscale ocean eddies impart a curl to the surface stress from the relative motion between surface air and water. This surface stress curl has a polarity opposite that of the vorticity of eddy surface currents and thus attenuates eddies by generating Ekman upwelling in the cores of anticyclonic eddies and downwelling in the cores of cyclonic eddies ( Dewar and Flierl 1987 ). An influence of eddy surface vorticity on Ekman pumping has also long
. 2020 ). The cool anomalies of the Cold Pool are often aligned with the eastern periphery of the SLD, as defined in sea surface height. In this paper, we examine if weakly nonlinear Ekman pumping ( Stern 1965 ), modified for low latitude, can explain changes in sea level height in SLD and larger Cold Pool region and spatial variation of SST anomalies in the Sri Lanka Dome and Southwest Monsoon Current System. a. The Southwest Monsoon Current and the Bay of Bengal Cold Pool The Southwest Monsoon
. 2020 ). The cool anomalies of the Cold Pool are often aligned with the eastern periphery of the SLD, as defined in sea surface height. In this paper, we examine if weakly nonlinear Ekman pumping ( Stern 1965 ), modified for low latitude, can explain changes in sea level height in SLD and larger Cold Pool region and spatial variation of SST anomalies in the Sri Lanka Dome and Southwest Monsoon Current System. a. The Southwest Monsoon Current and the Bay of Bengal Cold Pool The Southwest Monsoon
shear of the background zonal wind ( James and Gray 1986 ; James 1987 ). More recently, in the context of subcritical instability in a two-layer quasigeostrophic (QG) model ( Lee and Held 1991 ), Lee (2010b) found that in the model’s parameter space where total eddy energy increases with enhanced Ekman friction, Ekman pumping energizes eddies by directly enhancing eddy available potential energy. This process is also accompanied by a reduction of the barotropic decay of the eddies ( Lee 2010a
shear of the background zonal wind ( James and Gray 1986 ; James 1987 ). More recently, in the context of subcritical instability in a two-layer quasigeostrophic (QG) model ( Lee and Held 1991 ), Lee (2010b) found that in the model’s parameter space where total eddy energy increases with enhanced Ekman friction, Ekman pumping energizes eddies by directly enhancing eddy available potential energy. This process is also accompanied by a reduction of the barotropic decay of the eddies ( Lee 2010a
all three of these flow types interact, although our main focus will be on Ekman–NI and Ekman–geostrophic nonlinearities. Geostrophic modification of Ekman transport and pumping is the subject of nonlinear Ekman theory. Pioneering work by Stern (1965) considered a uniform wind stress τ blowing over a geostrophic vortex and found the pumping velocity to go like ∇ ⋅ [ ( τ × z ^ ) / ( f + ζ ) ] , where f is the Coriolis parameter and ζ is the relative vorticity associated with the vortex
all three of these flow types interact, although our main focus will be on Ekman–NI and Ekman–geostrophic nonlinearities. Geostrophic modification of Ekman transport and pumping is the subject of nonlinear Ekman theory. Pioneering work by Stern (1965) considered a uniform wind stress τ blowing over a geostrophic vortex and found the pumping velocity to go like ∇ ⋅ [ ( τ × z ^ ) / ( f + ζ ) ] , where f is the Coriolis parameter and ζ is the relative vorticity associated with the vortex
1370 $OURNAL OF PHYSICAL OCEANOGRAPHY Vo~.~v~26On Nonlinear Ekman Surface-Layer Pumping JOHN E. HARTDepartment of Astrophysical, Planetary and Atmospheric Sciences, University of Colorado, Boulder, Colorado27 February 1995 and 9 November 1995 Simple expressions are presented for the corrections to the classic Ekman pumping law W, = t-curl(~0/f)due to nonlinear advection effects in the
1370 $OURNAL OF PHYSICAL OCEANOGRAPHY Vo~.~v~26On Nonlinear Ekman Surface-Layer Pumping JOHN E. HARTDepartment of Astrophysical, Planetary and Atmospheric Sciences, University of Colorado, Boulder, Colorado27 February 1995 and 9 November 1995 Simple expressions are presented for the corrections to the classic Ekman pumping law W, = t-curl(~0/f)due to nonlinear advection effects in the
DECEMBER 1993 L 1U 2523Thermocline Forced by Varying Ekman Pumping.Part II: Annual and Decadal Ekman Pumping ZHENGYU LIUUCAR Visiting Scientist Program, Department of Atmospheric and Oceanic Sciences, Princeton University, Princeton, New Jersey(Manuscript received 16 January 1992, in final form 14 August 1992) ABSTRACT Thermocline variability
DECEMBER 1993 L 1U 2523Thermocline Forced by Varying Ekman Pumping.Part II: Annual and Decadal Ekman Pumping ZHENGYU LIUUCAR Visiting Scientist Program, Department of Atmospheric and Oceanic Sciences, Princeton University, Princeton, New Jersey(Manuscript received 16 January 1992, in final form 14 August 1992) ABSTRACT Thermocline variability
current aloft. Thus, although that current may be in geostrophic balance and almost nondivergent, the transverse flow in the Ekman layer is divergent or convergent. Continuity of fluid demands a compensating vertical velocity, which extends through the water column. This is called Ekman pumping. Ekman pumping is important for several reasons. First, it plays a significant dynamical role by stretching or squeezing the ocean’s interior flow; this, in turn, affects the vorticity of the ocean circulation
current aloft. Thus, although that current may be in geostrophic balance and almost nondivergent, the transverse flow in the Ekman layer is divergent or convergent. Continuity of fluid demands a compensating vertical velocity, which extends through the water column. This is called Ekman pumping. Ekman pumping is important for several reasons. First, it plays a significant dynamical role by stretching or squeezing the ocean’s interior flow; this, in turn, affects the vorticity of the ocean circulation
VOLUME23 JOURNAL OF PHYSICAL OCEANOGRAPHY DECEMBER 1993Thermocline Forced by Varying Ekman Pumping. Part I: Spinup and Spindown ZHENGYU LIUUCAR Visiting Scientisl Program, Department of Atmospheric and Oceanic Sciences, Princeton University, Princeton, New Jersey(Manuscript received 16 January 1992, in final form 14 August 1992)ABSTRACT A two-layer planetary geostrophic model is used to
VOLUME23 JOURNAL OF PHYSICAL OCEANOGRAPHY DECEMBER 1993Thermocline Forced by Varying Ekman Pumping. Part I: Spinup and Spindown ZHENGYU LIUUCAR Visiting Scientisl Program, Department of Atmospheric and Oceanic Sciences, Princeton University, Princeton, New Jersey(Manuscript received 16 January 1992, in final form 14 August 1992)ABSTRACT A two-layer planetary geostrophic model is used to
1. Introduction Ekman pumping is the vertical flow at the interface between the boundary layer and the interior flow that is created by cross-isobaric convergence or divergence within the boundary layer. Pedlosky (1987) studied the effect of a moving free surface or a sloping rigid surface on the pumping. (The two cases are depicted schematically in Fig. 1 ). In this article, we show that Pedlosky’s assumptions that the density is constant and that the geostrophic velocity and eddy viscosity
1. Introduction Ekman pumping is the vertical flow at the interface between the boundary layer and the interior flow that is created by cross-isobaric convergence or divergence within the boundary layer. Pedlosky (1987) studied the effect of a moving free surface or a sloping rigid surface on the pumping. (The two cases are depicted schematically in Fig. 1 ). In this article, we show that Pedlosky’s assumptions that the density is constant and that the geostrophic velocity and eddy viscosity
