scholarly journals Seasonal variation of eddy kinetic energy of the North Pacific Subtropical Countercurrent simulated by an eddy-resolving OGCM

2007 ◽  
Vol 34 (7) ◽  
Author(s):  
Yign Noh ◽  
Bo Young Yim ◽  
Sung Hyup You ◽  
Jong Hwan Yoon ◽  
Bo Qiu
Keyword(s):  
Seasonal Variation ◽  
Kinetic Energy ◽  
North Pacific ◽  
Eddy Kinetic Energy ◽  
The North ◽  
Subtropical Countercurrent ◽  
The North Pacific ◽  
North Pacific Subtropical Countercurrent

scholarly journals Eddy Lifetime, Number, and Diffusivity and the Suppression of Eddy Kinetic Energy in Midwinter

2018 ◽  
Vol 31 (14) ◽  
pp. 5649-5665 ◽  
Author(s):  
Sebastian Schemm ◽  
Tapio Schneider
Keyword(s):  
Kinetic Energy ◽  
North Pacific ◽  
Storm Track ◽  
Heat Fluxes ◽  
Eddy Kinetic Energy ◽  
Eddy Diffusivities ◽  
The North ◽  
Conversion Rates ◽  
Velocity Variance ◽  
The North Pacific

Abstract The wintertime evolution of the North Pacific storm track appears to challenge classical theories of baroclinic instability, which predict deeper extratropical cyclones when baroclinicity is highest. Although the surface baroclinicity peaks during midwinter, and the jet is strongest, eddy kinetic energy (EKE) and baroclinic conversion rates have a midwinter minimum over the North Pacific. This study investigates how the reduction in EKE translates into a reduction in eddy potential vorticity (PV) and heat fluxes via changes in eddy diffusivity. Additionally, it augments previous observations of the midwinter storm-track evolution in both hemispheres using climatologies of tracked surface cyclones. In the North Pacific, the number of surface cyclones is highest during midwinter, while the mean EKE per cyclone and the eddy lifetime are reduced. The midwinter reduction in upper-level eddy activity hence is not associated with a reduction in surface cyclone numbers. North Pacific eddy diffusivities exhibit a midwinter reduction at upper levels, where the Lagrangian decorrelation time is shortest (consistent with reduced eddy lifetimes) and the meridional parcel velocity variance is reduced (consistent with reduced EKE). The resulting midwinter reduction in North Pacific eddy diffusivities translates into an eddy PV flux suppression. In contrast, in the North Atlantic, a milder reduction in the decorrelation time is offset by a maximum in velocity variance, preventing a midwinter diffusivity minimum. The results suggest that a focus on causes of the wintertime evolution of Lagrangian decorrelation times and parcel velocity variance will be fruitful for understanding causes of seasonal storm-track variations.

scholarly journals Instability of the North Pacific Subtropical Countercurrent

2014 ◽  
Vol 44 (3) ◽  
pp. 818-833 ◽  
Author(s):  
Y.-L. Chang ◽  
L.-Y. Oey
Keyword(s):  
Normal Mode ◽  
North Pacific ◽  
Baroclinic Instability ◽  
Growth Time ◽  
Initial Value ◽  
The North ◽  
Subtropical Countercurrent ◽  
Instability Growth ◽  
The North Pacific ◽  
North Pacific Subtropical Countercurrent

Abstract The North Pacific Subtropical Countercurrent (STCC) has a weak eastward velocity near the surface, but the region is populated with eddies. Studies have shown that the STCC is baroclinically unstable with a peak growth rate of 0.015 day−1 in March, and the ~60-day growth time has been used to explain the peak eddy kinetic energy (EKE) in May observed from satellites. It is argued here that this growth time from previously published normal-mode instability analyses is too slow. Growth rates calculated from an initial-value problem without the normal-mode assumption are found to be 1.5 to 2 times faster and at shorter wavelengths, due to the existence of (i) nonmodal solutions and (ii) sea surface temperature front in the mixed layer in winter. At interannual time scales it is shown that because of rapid surface adjustments, the STCC geostrophic shear, hence also the instability growth, is approximately in phase with surface forcing, leading to EKE modulation that peaks approximately 10 months later. However, the EKE can only be partially explained by this mechanism of modulation by baroclinic instability. It is suggested that the unexplained variance may be caused additionally by modulation of the EKE by dissipation.

scholarly journals SSH Wavenumber Spectra in the North Pacific from a High-Resolution Realistic Simulation

2012 ◽  
Vol 42 (7) ◽  
pp. 1233-1241 ◽  
Author(s):  
Hideharu Sasaki ◽  
Patrice Klein
Keyword(s):  
High Resolution ◽  
Kinetic Energy ◽  
North Pacific ◽  
North Pacific Ocean ◽  
Spectral Characteristics ◽  
Turbulence Theory ◽  
Realistic Simulation ◽  
The North ◽  
Altimetric Data ◽  
The North Pacific

Abstract Following recent studies based on altimetric data, this paper analyses the spectral characteristics of the sea surface height (SSH) using a new realistic simulation of the North Pacific Ocean with high resolution ( in the horizontal and 100 vertical levels). This simulation resolves smaller scales (down to ≈10 km) than altimetric data (limited to 70 km because of the noise level). In high eddy kinetic energy (EKE) regions (as in the western part), SSH spectral slope almost follows a k−4 (with k the wavenumber) or slightly steeper law in agreement with altimeter studies. The new result is that, unlike altimeter studies, such a k−4 slope is also observed in low EKE regions (as in the eastern part). In these regions, this slope mostly concerns scales not well resolved by altimetric data. Such k−4 SSH spectral slopes are weaker from what is expected from quasigeostrophic turbulence theory but closer to surface quasigeostrophic (SQG) turbulence theory. The consequence is that the small scales concerned by these spectral slopes, in particular in low EKE regions, may significantly affect the larger ones because of the inverse kinetic energy cascade. These results need to be confirmed using a longer numerical integration. They also need to be corroborated by high-resolution observations.

Sign in / Sign up

Export Citation Format

Share Document