EAC bifurcation

EAC bifurcation work

This work is continued from Hobart. Click here to bring up the work done in Hobart.

  1. A linear Rossby model
    The model consists of interior wind-forced 1st baroclinic mode Rossby waves only. c=2.5 m/s. The forcing is FSU winds (c_D=1.2x10^-3) from 1975 through Sep 1992, then ACOM3 winds from Oct 1992 through Jul 2000. Model solutions are interface height h, this is converted to depth integrated steric height by P = hc^2/g.
    "Interannual variability" here refers to a quantity demeaned by its climatological annual cycle, then smoothed with a 7-month running mean.
    1. RW travel time across the S Pacific (c=2.5 m/s)
    2. RMS of RW DISH: 30-month damping   No damping   Ratio of RMS   
    3. (a) RW model (x,t) sections: 27.5°S   25°S   20°S   15°S   10°S   5°S   
      (b) With corresponding ACOM3 DISH:  27.5°S   25°S   20°S   15°S   10°S   5°S   
    4. Check the trend in ACOM3 DISH: 
      Mean over 5°S-27.5°S   Basinwide mean (and linear trend)   
    5. RW model (x,t) sections, with ACOM3 DISH minus 4 m^2/yr trend: 
      27.5°S   25°S   20°S   15°S   10°S   5°S   
    6. ACOM3 DISH along the eastern boundary (BC for RW model?)   
      Mean over Eq-20°S, overlay SOI

      In view of the obvious importance of signals coming off the eastern boundary (plots 1.5 above), a different strategy was taken. Lacking an obvious way to simulate the signals along the eastern boundary from the winds, these runs use the ACOM3 eastern boundary fluctuations as a boundary condition. However, there is no way to extend this boundary condition back in time before the beginning of the model run. Therefore the next set of plots shows the Rossby model with both the eastern boundary condition and an initial condition (Oct 1992) from the ACOM results. No FSU winds were needed, as the RW model run began in Oct 1992. The plots show, separately and combined, the three contributions to the resulting Rossby model: from the interior winds, from the eastern boundary radiated westward at the Rossby speed c_r, and from Oct 1992 radiated forward at c_r. Various choices of c and damping timescale are shown. The best agreement (quantitative check to come soon) appears to be with 48-month damping and c=3.0 m/s).
      A 4 m2/yr trend was removed from the boundary and initial conditions and from the ACOM3 fields shown as comparison (see plots 1.4 above). All quantities are interannual anomalies as defined above.
      (x,t) sections. Note, these plots are very wide (5 panels side-by-side).

    7. c=2.5 m/s, 30-month damping: 25°S   20°S   15°S   10°S   5°S   
    8. c=3.0 m/s, 30-month damping: 25°S   20°S   15°S   10°S   5°S   
    9. c=3.0 m/s, 48-month damping: 25°S   20°S   15°S   10°S   5°S   
    10. c=3.5 m/s, 48-month damping: 25°S   20°S   15°S   10°S   5°S   
    11. c=3.0 m/s, no damping: 25°S   20°S   15°S   10°S   5°S   

    12. (y,t) sections at 160°E-170°E (compare ACOM3):  c=2.5 and 3.0 m/s   c=3.5  m/s

    13. Correlations between the RW model and ACOM3 DISH (combined)
      Individual correlation plots show detail:  30-month damping, c=2.5 m/s    30-month damping, c=3 m/s    48-month damping, c=3 m/s   48-month damping, c=3.5 m/s    No damping, c=3 m/s   

Related pages
Kessler home page
Figures page
Island Rule calculations
Work done in Hobart