1 / 15

Large-scale decadal changes of sea level in the Indo-Pacific region

Large-scale decadal changes of sea level in the Indo-Pacific region. Tony Lee, Ichiro Fukumori, Cecile Cabanes, and Lee-Lueng Fu NASA Jet Propulsion Laboratory, California Institute of Technology. Relative phasing Forcing Vertical structure Implications to meridional circulation

azizi
Download Presentation

Large-scale decadal changes of sea level in the Indo-Pacific region

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. Large-scale decadal changes of sea level in the Indo-Pacific region Tony Lee, Ichiro Fukumori, Cecile Cabanes, and Lee-Lueng Fu NASA Jet Propulsion Laboratory, California Institute of Technology • Relative phasing • Forcing • Vertical structure • Implications to meridional circulation • Implications to horizontal circulation Analyze altimeter & scatterometer data, model sensitivity, assimilation.

  2. Qiu (2002): intensified North Pacific Current & changing shape of Western Subarctic Gyre in the 90s. • Lee & Fukumori (2003): variation of tropical-subtropical exchange; compensation of boundary & interior pycnocline transports. • Lee (2004): 90’s weakening of shallow overturning cell in the South Indian Ocean. • McPhaden & Zhang (2004): Rebound of tropical-subtropical interior pycnocline transport from multi-decadal weakening. • Fu (2005): Subsiding SSH trend in recent years. • Roemmich et al. (2006): Spin-up of the S. Pacific subtropical gyre. SAM forcing. • Qiu & Chen (2006): Decadal variability of SSH in the South Pacific. T/P + JASON-1 T/P + JASON-1 1 2 5 4 3 6 7 Linear trend of SSH estimated from T/P & JASON-1 data

  3. 3-year smoothed SSH trend 1993-2000 SSH time series show change of trend around 1999-2001.

  4. Model-data comparison of SSH time series Model simulation has some skill. Assimilation closer to observations. Longer period perspective: SSH data capture part of decadal fluctuations

  5. Sensitivity experiments suggest dominant role of wind Some effect of buoyancy forcing

  6. Forced by near-local wind in the east. Locally forced Tilted lines reflect Rossby wave effect Forced by Pacific wind Stronger trade wind contribute to rising SSH in the west; enhanced by “local” curl. Weaker trade wind Trends of observed SSH & wind stress curl for 1993-2000 T/P & JASON-1 ERS-1 & -2

  7. SSH near New Zealand: • Rossby-wave propagation vs. local Ekman pumping. • GCM vs. 1st-mode Rossby-wave model. • Local Ekman pumping cannot account for change; Rossby-wave propagation important; forcing not too far east. • 1st-mode Rossby-wave model under-estimates change.

  8. Vertical structure: time-depth distribution of dynamic height (cm) Primarily baroclinic Baroclinic + barotropic Some barotropic contribution Problem for 1st-mode R. wave model

  9. Implications to meridional circulation: Strengthening shallow overturning cells in the Pacific 1993-2000. Weakening shallow overturning cell in the South Indian Ocean. Both reverse in recent years. More Ekman divergence Less southward warm Ekman flow Trend of zonal wind stress 1993-2000 (ERS) Stronger trade wind Weaker trade wind Trend of SSH 1993-2000 (T/P & JASON-1) More thermocline divergence Less northward flow of cold water

  10. Decadal variation of Indo-Pacific trade winds (“biases” adjusted among products) Averaged zonal wind at 10S in the Indian Ocean “Phase change” around 1999-2000 Averaged zonal wind in the equatorial Pacific 2.5S-2.5N

  11. Have discussed forcing, vertical structure, & meridional circulation. Next: change of horizontal circulation, but first…

  12. Comparison of SSH trend (1993-2000): data, simulation, & assimilation Much improvement by assimilation; used for analysis of gyre changes.

  13. Barotropic stream function anomalies from ECCO KF assimilation + red is clockwise. 96-98 93-95 99-01 02-03

  14. Difference of barotropic stream function: (1999-2001) – (1993-1995) Weakening Western Subarctic Gyre Strengthening North Central Pacific Gyre Strengthening Kuroshio recirculation gyre Strengthening South Pacific Subtropical Gyre Anomalous cyclonic gyre

  15. Summary • SSH data show decadal fluctuations in many parts of the Indo-Pacific Ocean with a tendency change around 1999-2001; PDO & AO forcing. • Changes at mid- to high-latitude Pacific & western tropical Pacific primarily caused by “near-local” (to-the-east) wind stress curl; Rossby-wave propagation important. • Much decadal changes in the Indian Ocean are forced by Indian-Ocean wind; but that near western Australia is forced by Pacific wind. • Tropical SSH changes: primarily 1st baroclinic mode. • Mid- to high-latitude changes: both baroclinic & barotropic. • 1st-mode Rossby-wave model under-estimates SSH change near New Zealand (missing contribution by other modes, e.g., barotropic). • Implications to circulation: speedup & slowdown of shallow overturning cells in the tropics & horizontal gyres at mid- to high-latitude Pacific.

More Related