scholarly journals Interannual variability of the North Pacific Subtropical Countercurrent: role of local ocean–atmosphere interaction

2011 ◽  
Vol 68 (1) ◽  
pp. 113-126 ◽  
Author(s):  
Fumiaki Kobashi ◽  
Shang-Ping Xie
Keyword(s):  
Interannual Variability ◽  
North Pacific ◽  
The North ◽  
Subtropical Countercurrent ◽  
Ocean Atmosphere ◽  
Ocean Atmosphere Interaction ◽  
Atmosphere Interaction ◽  
The North Pacific ◽  
North Pacific Subtropical Countercurrent

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.

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