Intraseasonal and seasonal variations in in the eastern equatorial Indian Ocean. Y. Masumoto, H. Hase, Y. Kuroda, and H. Sasaki

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1 Intraseasonal and seasonal variations in in the eastern equatorial Indian Ocean -A -A high-resolution OGCM and and ADCP Observation- Y. Masumoto, H. Hase, Y. Kuroda, and H. Sasaki FRCGC/IORGC/ESC JAMSTEC

2 Background! The equatorial Indian Ocean is covered by warm water pool! Understanding of variability in the Equatorial Indian Ocean is a key for the climate studies! The equatorial region is subjected to the variations with a variety of time- and space-scales " Intraseasonal " Semiannual (Wyrtki jets) " Annual (Monsoon) " Interannual (IOD) " Decadal But, we do not know yet the details of the variability!

3 IORGC/JAMSTEC Indian Ocean Observations TRITONs (Kuroda et al.) ADCP ADCP Mooring (Eq., 90E) Nov months 9 months 12 months Oct Jul Jul. 2003

4 High-resolution OGCM (OFES) Hindcast Run Computational domain : 75 S-75 N Horizontal grid spacing : 0.1 Number of vertical levels : 54 (20 levels in 200m depth) Bathymetry : 1/30 OCCAM data set Initial Condition : Annual mean temperature and salinity fields (WOA98) without motion Forcing : Daily mean NCEP/NCAR re-analysis from 1950 to 2003 : Restoring to monthly SSS(WOA98) Boundary condition : Restoring to monthly temperature and salinity fields(woa98) at all levels near the north and south boundaries Parameterization : Bi-harmonic (Horizontal) KPP (Vertical) (Masumoto et al., 2004)

5 Zonal Current Variability

6 ADCP zonal currents at 0 N, 90 E Period 1 Period 2 Period

7 ADCP - OFES Comparison (40m)

8 Zonal Current and Zonal Wind Stress on the Equator OFES U (Eq., 40m) NCEP Tau-x (Eq.)

9 Zonal Currents at 80 E and 90 E U (total; > 80 days) U ( < 80 days)

10 Meridional Current Variability

11 ADCP Meridional currents at 0 N, 90 E Period 1 Period 2 Period

12 ADCP - OFES Comparison

13 Relation between V and Wind Stress V (Eq., 40m) 2.5 m/s

14 Relation between SST and U, V at 90 E

15 Summary " Intraseasonal variability of the upper-layer velocity in the eastern equatorial Indian Ocean is investigated by use of the ADCP data and the OFES results. Intraseasonal variability is significant in both zonal and meridional currents. The dominant period is days and days, respectively. Interannual modulation of the intraseasonal variability is also observed. The amplitude of the intraseasonal variability in the zonal currents is almost the same at 80 E and 90 E, although the magnitude of the semiannual signal is rather weak at 90 E. Westward phase propagation for the 15-day variability in the meridional velocity is reproduced by OFES. Some of the events are associated with the propagation of the wind stress curl, but some are not. OFES indicates the intraseasonal variability in the SST of +/- 0.6 C, which shows a negative correlation with the zonal velocity field.

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17 Recommendations! The equatorial region is subjected to the variations with a variety of time- and space-scales " Intraseasonal " Semiannual (Wyrtki jets) " Annual (Monsoon) " Interannual (IOD) " Decadal An observing system similar to the one in the Pacific to detect and understand the variability in more detail!

18 CLIVAR/IOGOOS Tropical Mooring Array On going buoys Plan for FY2005-FY2010 Need evaluation of observing system design in terms of the predictability of the climate variability SINTEX-F1 or SINTEX-F2???

19 Future perspective for mooring array (CLIVAR, IO-GOOS) OASIS OOS Deep Sea & Shallow Water Buoys I-MAP A multi-national project to observe ocean conditions in the tropical western Indian Ocean. TAO-type buoys. On-going moorings OASIS (Japan) OOS (India) Deep Sea buoys (India) Shallow Water buoys (India) Planed moorings I-MAP (multi-national, leaded by South Africa) LODYC (France) INSTANT (multi-national) LODYC Upward looking ADCP mooring at 76E on the equator. Two additional ADCPs on the top of OOS buoys, or independent locations. INSTANT An international project to measure the flow from the Pacific to the Indian Oceans. Current meters, ADCP, etc. PMEL TAO-type array on the equator at first, and expand to off-equatorial area.

20 ADCP - OfES Comparison (40m)

21 Wavelet Spectra (ADCP; 40m depth) Zonal Current Meridional Current

22 Wavelet Spectra for Zonal Currents at 80 E and 90 E

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24 Power spectrum density of currents at 0N, 90E! Broad time-scale with strong days variability, shallower than 120 m depth! days variability above 100 m depth

25 Time series of zonal currents at 0N, 90E Typical Wyrtki jet structure

26 Horizontal Structure of 15-day Variability QuickTimeý Dz ÉtÉHÉg - JPEG êlí ÉvÉçÉOÉâÉÄ Ç Ç±ÇÃÉsÉNÉ`ÉÉǾå ÇÈÇžÇ½Ç ÇÕïKóvÇ-ÇÅB