Subseasonal‐to‐seasonal forecast skill in the California Current System and its connection to coastal Kelvin waves

Author(s):  
Dillon J. Amaya ◽  
Michael G. Jacox ◽  
Juliana Dias ◽  
Michael A. Alexander ◽  
Kristopher B. Karnauskas ◽  
...  
Fluids ◽  
2021 ◽  
Vol 6 (3) ◽  
pp. 111
Author(s):  
Leonid M. Ivanov ◽  
Collins A. Collins ◽  
Tetyana Margolina

Using discrete wavelets, a novel technique is developed to estimate turbulent diffusion coefficients and power exponents from single Lagrangian particle trajectories. The technique differs from the classical approach (Davis (1991)’s technique) because averaging over a statistical ensemble of the mean square displacement (<X2>) is replaced by averaging along a single Lagrangian trajectory X(t) = {X(t), Y(t)}. Metzler et al. (2014) have demonstrated that for an ergodic (for example, normal diffusion) flow, the mean square displacement is <X2> = limT→∞τX2(T,s), where τX2 (T, s) = 1/(T − s) ∫0T−s(X(t+Δt) − X(t))2 dt, T and s are observational and lag times but for weak non-ergodic (such as super-diffusion and sub-diffusion) flows <X2> = limT→∞≪τX2(T,s)≫, where ≪…≫ is some additional averaging. Numerical calculations for surface drifters in the Black Sea and isobaric RAFOS floats deployed at mid depths in the California Current system demonstrated that the reconstructed diffusion coefficients were smaller than those calculated by Davis (1991)’s technique. This difference is caused by the choice of the Lagrangian mean. The technique proposed here is applied to the analysis of Lagrangian motions in the Black Sea (horizontal diffusion coefficients varied from 105 to 106 cm2/s) and for the sub-diffusion of two RAFOS floats in the California Current system where power exponents varied from 0.65 to 0.72. RAFOS float motions were found to be strongly non-ergodic and non-Gaussian.


2017 ◽  
Vol 7 (1) ◽  
Author(s):  
F. Chan ◽  
J. A. Barth ◽  
C. A. Blanchette ◽  
R. H. Byrne ◽  
F. Chavez ◽  
...  

2019 ◽  
Vol 148 (1) ◽  
pp. 259-287
Author(s):  
R. M. Samelson ◽  
L. W. O’Neill ◽  
D. B. Chelton ◽  
E. D. Skyllingstad ◽  
P. L. Barbour ◽  
...  

Abstract The influence of mesoscale sea surface temperature (SST) variations on wind stress and boundary layer winds is examined from coupled ocean–atmosphere numerical simulations and satellite observations of the northern California Current System. Model coupling coefficients relating the divergence and curl of wind stress and wind to downwind and crosswind SST gradients are generally smaller than observed values and vary by a factor of 2 depending on planetary boundary layer (PBL) scheme, with values larger for smoothed fields on the 0.25° observational grid than for unsmoothed fields on the 12-km model grid. Divergence coefficients are larger than curl coefficients on the 0.25° grid but not on the model grid, consistent with stronger scale dependence for the divergence response than for curl in a spatial cross-spectral analysis. Coupling coefficients for 10-m equivalent neutral stability winds are 30%–50% larger than those for 10-m wind, implying a correlated effect of surface-layer stability variations. Crosswind surface air temperature and SST gradients are more strongly coupled than downwind gradients, while the opposite is true for downwind and crosswind heat flux and SST gradients. Midlevel boundary layer wind coupling coefficients show a reversed response relative to the surface that is predicted by an analytical model; a predicted second reversal with height is not seen in the simulations. The relative values of coupling coefficients are consistent with previous results for the same PBL schemes in the Agulhas Return Current region, but their magnitudes are smaller, likely because of the effect of mean wind on perturbation heat fluxes.


2016 ◽  
Vol 121 (10) ◽  
pp. 7244-7262 ◽  
Author(s):  
Zelalem Engida ◽  
Adam Monahan ◽  
Debby Ianson ◽  
Richard E. Thomson

2018 ◽  
Vol 68 (7) ◽  
pp. 761-777 ◽  
Author(s):  
Fanny Chenillat ◽  
Peter J. S. Franks ◽  
Xavier Capet ◽  
Pascal Rivière ◽  
Nicolas Grima ◽  
...  

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