Status on Equatorial Indian Ocean – OceanSITES Long-term measurements of currents in the equatorial Indian Ocean using deep-sea moorings – Project funded by INCOIS/ MoES by Dr. VSN Murty National Institute of Oceanography Regional Centre 176 Lawsons Bay Colony, Visakhapatnam OceanSITES meeting in SIO 30 Nov – 2 Dec. 2011

Equatorial Indian Ocean Observational Array since 2000 The current meter moorings project is being executed since February Servicing of the moorings is being done regularly onboard ORV Sagar Kanya. EQCM1 EQCM2 EQCM3

Mooring Location Duration of the moorings at each location D: Deployment R: Recovery EQCM 1 [Equator, 93°E] D 13 Feb 00 To R 21 Dec 02 D 23 Dec 00 to R 30 Mar 02 D 01 Apr 2002 To R 23 Sep 2003 D 25 Sep 2003 to R 05 Nov 2004 D 07 Nov2004 To R 13 Sep 2006 D 15 Sep 2006 To R 04 Jan 2009 D 05 Jan 2009 To R 03 Oct 2009 EQCM 2 [Equator, 83°E] D 14 Dec 00 To R 24 Mar 02 D 26 Dec 2002 To R 17 Sep 2003 D 19 Sep 2003 To R 24 Oct 2004 D 26 Oct 2004 To R 19 Sep 2006 D 21 Sep 2006 To R 30 May 2008 D 01 Jun 2008 To R 08 Oct 2009 EQCM 3 [Equator, 77°E] D 10 Sep 2003 To R 17 Oct 2004 D 18 Oct 2004 To R 25 Sep 2006 D 27 Sep 2006 To R 25 May 2008 D 27 May 2008 To R 22 Oct 2009 Update status of 4 deep-sea current meter moorings in equatorial Indian Ocean Each mooring has one uplooking 75 kHz ADCPs at 400 m and RCMs at 3 levels of nominal depths of 1000 m, 2000 m and 4000 m. OOS program would continue till Planning to extend the program for another 5 years [ ]

Mooring Location Duration of the moorings at each location D: Deployment R: Recovery – EQCM1 – [1N, 93E] EQCM 1 – [Eq., 93E] EQCM1 – 1S, 93E] D 01 Oct 2009 R 11 Oct 2010 D 05 Oct 2010 R 9Oct 2010 D 02 Oct 2009 R 6 Oct 2010 D 11 Oct 2010 R 2011 D 10 Oct 2010 R 2011 D 08 Oct 2010 R 2011 NOT DONE due to non-availability of the vessels EQCM 2 [Equator, 83°E] D 10 Oct 2009 R 01 Oct 2010D 03 Oct 2010 R 2011 NOT DONE due to non-availability of the vessels EQCM3 – [1N, 77E] EQCM 3 – [Eq., 77E] EQCM3 – 1S, 77E] D 21 Oct 2009 R 23 Sep 2010 D 24 Oct 2009 R 25 Sep 2010 D 20 Oct 2009 R 28 Sep 2010 D 24 Sep 2010 R 2011 D 27 Sep2010 R 2011 D 29 Sep 2010 R 2011 NOT DONE due to non-availability of the vessels Update status of 7 deep-sea current meter moorings in equatorial Indian Ocean Each mooring has one uplooking 75 kHz ADCPs at 400 m and RCMs at 3 levels of nominal depths of 1000 m, 2000 m and 4000 m.

OOS – Deep Sea Current meter moorings that are to be Included in the OceanSITES list from the Indian Ocean 1)1N, 93E 2)Eq., 93E 3)1S, 93E 4)Eq., 83E 5)1N, 77E 6)Eq., 77E 7)1S, 77E

To generate long-term currents data from the equatorial Indian Ocean from 7 deep-sea mooring locations spread across and along the equator from 77E to 93E. To describe the intraseasonal, interannual and long-term variability of currents in the equatorial Indian Ocean. To decipher the ocean processes and dynamics those impact the surface and subsurface variability by employing various model simulations to understand climate variability of the region. To study the deep-sea circulation from observations and model simulations in the equatorial Indian Ocean. Objectives

Generated a decade long time series current data at 93E location, 9 years long time series data at 83E and 7 years long time series at 77E in the eastern equatorial Indian. Additionally 4 moorings were deployed in at 1°N, 77°E; 1°S, 77°E, and 1°N, 93°E; 1°S, 93°E. Up-to-date data till 2010 were submitted to INCOIS and NIO, Goa. Identified and documented the intraseasonal variability in meridional currents at biweekly (14 day) period in the upper 1000 m from both observations and OGCM model simulations [Sengupta, Retish, VSN Murty and V Fernando, JGR, 2004]. Identified and documented the intraseasonal variability in meridional currents at day period in the deep-ocean waters (2000 m and 4000m) and its linkage to the surface wind forcing, from observations and OFES model simulations [Ogato, Masumoto, VSN Murty and MSS Sarma, JGR, 2008]. Achievements

Identified and documented the intraseasonal variability in observed equatorial currents in relation to the Indian Ocean Dipole mode events [David, D.T., S. Prasanna Kumar, P. Byju, M.SS. Sarma, A. Suryanarayana and VSN Murty (JGR (Oceans), 2011].

360 nm Plan of Cruises from 2012 onwards during XII plan – i) Two separate cruises to complete servicing of 7 moorings ii) To orient optimum technical staff in the deep-sea mooring operations

Thank You

David, D.T., S. Prasanna Kumar, P. Byju, M.S.S. Sarma, A. Suryanarayana and V.S.N. Murty (2011) Observational evidence of lower frequency Yanai wave in the central equatorial Indian Ocean. J. Geophys. Res., 116(6); 2011; doi: /2010JC006603, 17 pp. Ogata, T.; Sasaki, H.; Murty, V.S.N.; Sarma, M.S.S.; Masumoto, Y. (2008) Intraseasonal meridional current variability in the eastern equatorial Indian Ocean. J. Geophys. Res. (C: Oceans): 113(7); doi: /2007JC004331, 15 pp. Cadden; D.D.H.; Subrahmanyam; B.; Chambers; D.P.; Murty; V.S.N. (2008) Surface and subsurface geostrophic current variability in the Indian Ocean from altimetry. Mar. Geod.: 32; Sengupta, D., Senan, Retish. Murty, V.S.N., Fernando, Vijayan. (2004). A biweekly mode in the equatorial Indian Ocean. J. Geophys. Res., 109, C10003, doi: , 2004JC Publications

Conclusions The presentation highlights the recent studies in the EIO using the OOS currents data. Current variability across-the equator at 93E location is presented for the period from Sept October Spring EUC occurred consistently in March-April at 93E. Monsoon season intraseasonal jets are noticed in July-August. Observational evidence to the meandering of the EUC and Jet. Meandering is more visible in Spring season.

Conclusions The presentation highlights the recent studies in the EIO using the OOS currents data. Current variability across-the equator at 93E location is presented for the period from Sept October Spring EUC occurred consistently in March-April at 93E. Monsoon season intraseasonal jets are noticed in July-August. Observational evidence to the meandering of the EUC and Jet. Meandering is more visible in Spring season.

Conclusions The presentation highlights the recent studies in the EIO using the OOS currents data. Current variability across-the equator at 93E location is presented for the period from Sept October Spring EUC occurred consistently in March-April at 93E. Monsoon season intraseasonal jets are noticed in July-August. Observational evidence to the meandering of the EUC and Jet. Meandering is more visible in Spring season.

Last servicing of 7 mooring was done during October – November 2010 Servicing of these Moorings could not be done in 2011 due to non-availability of the vessels.

Current variability at 93E location during

Zonal current structure ( m) at 0,93E during Sep 2006 – Dec S 6-D 25-F 17-M 6-A 26-O 15-J 5-Ap 25-J 14-Sep 4-D 2008 Dominant eastward flows in the entire sub-surface layer

Zonal current structure ( m) at Eq., 93E during Jan Oct J 2-F 1-M 28-M 24-A 21-M 17-J 14-Jy 10-Au 6-Sep 3-O 2009 Winter & Spring EUC in Monsoon season EUC in 2009

Zonal current structure ( m) at Eq., 93E during Oct Oct O 11-N 18-D 24-Jan 2-M 8-Apr 15-M 21-Ju 28-Jy 2-Sep 9-O 2010 Fall Jet in Nov 2009, Spring EUC & Jet 10. Intraseasonal monsoon jets.

Zonal current structure ( m) at 93E, 1N during O 8-N 15-D 22-Jan 28-F 7-Apr 14-M 21-Ju 28-Jy 4-Sep 11-O 2010 EUC in March 2010 & Semi-annual variation is evident.

Zonal current structure ( m) at Eq., 93E during O 11-N 18-D 24-Jan 2-M 8-Apr 15-M 21-Ju 28-Jy 2-Sep 9-O 2010 Fall Jet in Nov 2009, Spring EUC & Jet 10. Intraseasonal monsoon jets.

3-O 8-N 15-D 21-Jan 27-F 5-Apr 12-M 18-Ju 25-Jy 30-Au 6-O 2010 Zonal current structure ( m) at 93E, 1S during Oct Fall Jet 09 Spring EUC & Jet 10. Intraseasonal Monsoon Jets

Zonal current structures in upper 400 m at 1N, Eq., 1S at 93E show similar structures at Eq. and 1S, suggesting the extent of Jets and EUC across the Equator up to 1S. 1S, 93E 6 Oct Apr Oct N, 93E Eq, 93E

Meridional current structure across the Equator at 93E during O 8-N 15-D 21-Jan 27-F 5-Apr 12-M 18-Ju 25-Jy 30-Aug 6-O2010 1N, 93E Eq, 93E 1S, 93E

Thank You

Period in days EIO experienced IOD event in 2002 Intraseasonal variability at d penetrates up to 4000 m depth and the ISV period increases with depth: 75 d at m and 85 d at 2 km.

Period in days Intraseasonal variability at d penetrates up to 4000 m depth and the ISV period increases with depth: 85 d at m and 110 d at 2-4 km. EIO experienced IOD events in 2005 and in 2006

Impact of equatorial zonal currents on the alongshore currents off east coast of India 1.Zonal current variability at Eq., 93E during May – Oct Alongshore current variability off Visakhapatnam at the same period 3. Comparison of the zonal currents and alongshore currents at 48 m depth 4. Spectra in the alongshore currents at different depths.

Zonal current structure (48 – 96 m) at Eq., 93E from May-Oct Alongshore current structure (48 – 96 m) at Visakhapatnam

With a lag of 21 days, the alongshore currents do relate to the Zonal current at the Equator and the linkage is through Kelvin Waves

Spectra of alongshore currents off Visakhapatnam at 24, 56 & 92 m The spectral peaks at 21 d and 24 d at 24 m, 56 m depth reveal the Equatorial connection in the shelf currents at 100 m water depth

360 nm Plan of Cruises from 2012 onwards during XII plan – i) Two separate cruises to complete servicing of 7 moorings ii) To orient optimum technical staff in the deep-sea mooring operations

Conclusions The presentation highlights the recent studies in the EIO using the OOS currents data. Current variability across-the equator at 93E location is presented for the period from Sept October Spring EUC occurred consistently in March-April at 93E. Monsoon season intraseasonal jets are noticed in July-August. Observational evidence to the meandering of the EUC and Jet. Meandering is more visible in Spring season.

Meridional currents show the observational evidence of the opposing currents at 1N and 1S at biweekly intervals – more clear in winter months. During the IOD events the intraseasonal variability at day period penetrates up to 4 km. The zonal currents at Eq, 93E during May-October 2010 are compared with the alongshore currents off Visakhapatnam during the same period. A lag of 21 days in the alongshore currents relates the alongshore currents with the equatorial zonal currents through the propagation of downwelling and upwelling Kelvin waves. Conclusions contd…

Zonal current structures in the upper 400 m at 1N/1S, 77E & Eq., 83E do suggest large scale extent of Equatorial Undercurrent (EUC) across Equator. Fall jet – 3 d Spring jet – 15 d 1N, 77E Eq, 83E 1S, 77E 6 Oct Apr Oct. 2010

Period in days Intraseasonal variability at day period is dominant.

OFES simulations showing large scale meander of spring and fall jets in EIO October 11, 2003April 14, 2004

Comparison of OFES and ADCP currents Semi-annual period of 180 day in U and bi-weekly wave of 15 day period in V are evident. ADCP data analysis at 77E At 38 mAt 94 m