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Surface currents of the Indian Ocean

Surface currents of the Indian Ocean. Rick Lumpkin NOAA/AOML/PhOD Miami, Florida USA. Data Buoy Cooperation Panel (DBCP) 20 th Session – October 2004 Chennai, India. SVP surface drifting buoys (drifters). Spherical surface float SST, submergence Satellite transmitter Drogue:

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Surface currents of the Indian Ocean

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  1. Surface currents of the Indian Ocean Rick Lumpkin NOAA/AOML/PhOD Miami, Florida USA Data Buoy Cooperation Panel (DBCP) 20th Session – October 2004 Chennai, India

  2. SVP surface drifting buoys (drifters) • Spherical surface float • SST, submergence • Satellite transmitter • Drogue: • holey sock design • center depth: 15 m

  3. before 1998 1998-1999 2000-2001 after 2001 Data density Oct.1985-Apr.2004 405 drifter-years 701 drifters Drifter days per square degree

  4. Observations by year Blue: drogued Red: undrogued

  5. Pseudo-Eulerian averages (every other bin shown) 2° x 1° bins, Principal Component orientation. Blue: >20 drifter days. Yellow: 5-20 dd Red: <5 dd

  6. SST, U, V: X= <X> + Xa,1cos(2pt)+ Xa,2sin(2pt) + Xsa,1cos(4pt) + Xsa,2sin(4pt) + Xeddy MEAN ANNUAL SEMIANNUAL EDDY

  7. Mean currents Shaded: mean speed (cm/s)

  8. ECC SEC Mean zonal currents Solid: total currents Dashed: Ekman-removed currents

  9. Seasonal variability Shading: SST anomaly Arrows: surface currents NE Monsoon SW Monsoon

  10. North Equatorial Current/Southwest Monsoon Current Total currents Ekman- removed

  11. Monsoon-driven changes

  12. A= 1/2  Uann2 + Vann2 Amplitude of annual variations Equator: Ekman dynamics “break down”

  13. semiannual variations

  14. Where is “annual mean” meaningful? 4 3 2 1

  15. Quantifying modesof seasonal variation NE/SW Monsoon “EOFs”: Empirical Orthogonal Functions Ranked by variance explained. Currents: calculated for principal component. Semiannual response on equator, reflected in Arabian/Bengal sub-basins Equatorial convergence / divergence; East Indian Current

  16. Conclusions Data density: most observations in 1995-2003; good historical coverage for most of basin; poor coverage in western equatorial zone Mean currents: SW (summer) monsoon pattern dominates Seasonal changes: Resolution of seasonal amplitudes and phases throughout most of basin and in sub-basins. Primary mode: monsoon; higher modes associated with equatorial semiannual fluctuations and divergence/convergence, reflected in northern sub-basins.

  17. Rick Lumpkin (Rick.Lumpkin@noaa.gov) NOAA/AOML/PhOD Miami, Florida USA

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