1 / 28

Low-frequency variability of western boundary current extensions: a bifurcation analysis

Low-frequency variability of western boundary current extensions: a bifurcation analysis. François Primeau and David Newman Department of Earth System Science University of California, Irvine. Elongation-contraction of Kuroshio Extension, [Qiu JPO 2000].

teagan-gaines
Download Presentation

Low-frequency variability of western boundary current extensions: a bifurcation analysis

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Low-frequency variability of western boundary current extensions: a bifurcation analysis • François Primeau and David Newman • Department of Earth System Science • University of California, Irvine

  2. Elongation-contraction of Kuroshio Extension, [Qiu JPO 2000]

  3. Stable and Unstable States of the Kuroshio Extension System [Qiu and Chen, JPO 2005]

  4. Numerical Bifurcation Analysis North Atlantic North Pacific Schmeits and Dijkstra JPO 2001

  5. None of the steady-state solution have a jet extension that extends past 145oE, but the observations show that the Pacific jet extends beyond 160oE.

  6. Bifurcation plot for the 1.5 layer QG model: •Steady states with elongated and contracted jet extensions •Solution branches connected via pitchfork bifurcations [Primeau JPO 2002]

  7. Ground state gyre mode 2.0 yr period [Simonnet 2005]

  8. 1-bump jet gyre mode 6.4 year period [Simonnet 2005]

  9. 2-bump jet gyre mode 13.7 yr period [Simonnet 2005]

  10. Goal of the study • To see if the multiple equilibria persist in more realistic models and delineate where in parameter space different solution branches exist and cease to exists • Devise a strategy for finding solutions on disconnected branches • The ultimate goal is to track the elongated and contracted solution branches through a hierarchy of models of increasing realism and try to strengthen the connection to the observations

  11. Without QG symmetry, ( ) pitchfork bifurcation points become cusp points Fold in solution surface cusp point and loci of turning points

  12. Use continuation method in a two-parameter setting

  13. Two parameter continuation strategy: 1. Biharmonic friction (Eh), controls model nonlinearity 2. Wind-stress profile shape parameter (As), controls the asymmetry of the forcing

  14. Parameter Chart

  15. Bifurcation plot

  16. Time average h C.I. 20 m Standard deviation h C.I. 5 m

  17. 6.6 months Frequency (cycles / year)

  18. 1.5 years 6.6 months Frequency (cycles / year)

  19. 1.5 years 6.6 months Frequency (cycles / year)

  20. 1.5 years 10 years 6.6 months Frequency (cycles / year)

  21. 1.5 years 10 years 6.6 months Frequency (cycles / year)

  22. 1.5 years 10 years 6.6 months Frequency (cycles / year)

  23. Conclusions • Two parameter continuation technique is effective for finding “isolated” branches in more realistic models without the QG symmetry. • A gyre mode with a ~10 year period is at the origin of the decadal variability in a wind-driven shallow water model. • Solutions that bifurcate further down the bifurcation tree have a more elongated jet and can be more stable that solutions with a weaker contracted jet in accord with observations of Qiu and Chen (2005).

More Related