Objectives:
- To understand the dynamics and the long-term variability of ocean currents in the equatorial Indian Ocean
- To study the upper ocean variability in the thermohaline structures, currents (VM-ADCP), nutrients, chlorophyll and Primary Production in the equatorial Indian Ocean
- To study the deep-sea circulation in the equatorial Indian Ocean
- To study the dynamics and thermodynamics of the equatorial Indian Ocean by enhancing the time-series current measurements through additional moorings towards predicting the intra-seasonal and interannual variability.
- To study the biogeochemistry of the equatorial Indian Ocean by enhancing the multi-disciplinary observations through repeat hydrographic sections and additional sensors (physical and biochemical) and sediment traps on the moorings towards understanding the regional CO2 flux.
- To address the impact of convection over the equatorial Indian Ocean on the monsoon activity over the Indian sub-continent.
- To study the role of basin scale oceanic processes on the moisture transport into the Indian sub-continent to understand the hydrological cycle over Indian subcontinent.
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Team Members:
Murty,
V.S.N.
Sarma, M.S.S.
Suryanarayana, A.
Charyulu, R.J..K
Sardar, A.
Gracias, D.
Fernando, V.
Almeida, A.M.
Agaevadekar, Y..
Khalap, S.
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General description
Among the world Oceans, the tropical ocean basins,
encompassing the equatorial regions, have special
place in modulating the regional as well as global
climate. The research on the equatorial regions
has been recognized since the last 3 decades and
the Equatorial Pacific and Atlantic were largely
studied with respect to equatorial dynamics and
air-sea interaction through observations and models.
One best example is the El Nino and El Nino-Southern
Oscillation (ENSO) in the equatorial Pacific and
its linkage to the global climate and its possible
influence on the Indian Monsoon Rainfall. Amongst
the three equatorial regions, the research on
the equatorial Indian Ocean has gained momentum
with the set up of the Indian Ocean Panel (IOP)
as a part of the CLIVAR and GOOS programs. The
Indian Ocean as such is typical for its northern
extent being limited to the tropical belt and
experiences semi-annual wind forcing. The unique
features of the equatorial Indian Ocean are the
occurrence of equatorial Jets at semi-annual intervals
during the monsoon transitions (April-May and
October – November) and the absence of equatorial
upwelling on the annual scale, unlike the equatorial
Pacific. Most of the equatorial Indian Ocean comes
under the influence of the Indo-Pacific warm pool.
Cross-equatorial flow both in the atmosphere and
in the upper ocean in the western equatorial Indian
Ocean is the most dominant feature during the
southwest monsoon. The eastern equatorial Indian
Ocean, being influenced by the Indo-Pacific warm
pool, acts as the source region for atmospheric
convection that triggers westerly wind bursts
over the western equatorial Pacific thereby affecting
the upper oceanic conditions there leading to
the generation of El Nino over the equatorial
Pacific. The equatorial dynamics holds on the
linear wave theory and explains that the dynamics
are dominated by the propagation of low frequency
waves – both Kelvin and Rossby waves. At
interannual time scales, an interesting feature
highlighting the variability in the Sea Surface
Temperature (SST) with cold temperature anomalies
off Sumatra coast in the eastern equatorial Indian
Ocean and warm temperature anomalies in the western
equatorial Indian Ocean is reported recently.
This feature is recognized as the internal mode
of the Indian Ocean and is widely known as the
Indian Ocean Dipole/Zonal Mode (IODZM). The influence
of the IODZM on the upper ocean variability and
the subcontinent monsoon rainfall are yet to be
understood.
While many theoretical and numerical modeling
studies are in progress, long-term ocean observations
including that of currents are lacking in the
equatorial Indian Ocean. During late 1970s, there
were time series measurements for a shorter period
in the western and central equatorial Indian Ocean.
During the World Ocean Circulation Experiment
(WOCE), the German group deployed current meter
moorings in the region between the Equator and
south of Sri Lanka coast along 80E.
In order to enhance the time series observations
and to study the intraseasonal and interannual
variability of currents in the eastern equatorial
Indian Ocean, a long-term time-series current
measurements program has been established at the
National Institute of Oceanography (NIO) with
the funding support from the former Department
of Ocean Development (DOD) and presently the Ministry
of Earth Sciences (MoES) through the Indian National
Center for Ocean Information System (INCOIS),
Hyderabad.
One component of the Supra Institutional Project
(SIP1306) looks into the long-term measurements
of currents in the equatorial Indian Ocean through
current meter moorings along the equator under
the MoES funded Ocean Observing System (OOS) program,
so far, a 4 year time-series record was obtained
at 93°E, 3 year time series record at 83°E
and 2 year time series record at 76°/77°E.
A second component of the Supra Institutional
Project (SIP1306) looks into the physical forcing
and the biogeochemical response of the equatorial
Indian Ocean through repeated water-column measurements
along two cross-equatorial sections (77oE &
83oE) under the funding by Ministry of Earth Sciences
(MoES) through the Indian National Center for
Ocean Information System (INCOIS), Hyderabad.
Externally funded projects linked under
SIP1306
| Sr. No. |
Project Leader |
Project No. |
Duration |
Total Amount in Lakhs |
| 1 |
Ramesh Babu V. |
MoES |
2007-09 |
500.00 |
| 2 |
Murty V.S.N. |
GAP
2017 |
2007-12 |
986.93 |
| 3 |
Prasanna Kumar S. |
GAP
1970
GAP
2030 |
2007-12
2007-12 |
94.00
80.17 |
| 4 |
Muraleedharan P.M. |
GAP 1933
GAP 1917 |
2007-10
2007-10 |
85.64
18.00 |
Mooring
Cruise
Track for
biogeochemical measurements |
Cruise under
taken so far |
 |
| Cruise |
Period |
No CTD station |
No. of PP stations |
| SK
121 |
10 May 2005
8 June 2005 |
43 |
10 |
| SK
127 |
1 - 27 August 2006 |
34 |
10 |
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Collaborations
- International collaborations
- Pacific Marine Environmental Laboratory
(PMEL)/National Oceanic Atmospheric Administration
(NOAA): With the initial steps taken by
NIO in collaborating with PMEL and successful
participation of PMEL technicians for deployment
of Atlas type moorings in the equatorial
Indian Ocean, a series of Atlas moorings
were deployed along 80.5E. The Atlas moorings
measure surface meteorological parameters
(winds, pressure, air temperature, sea surface
temperature, atmospheric humidity, solar
radiation) and upper ocean parameters (Temperature
and salinity) up to 500 m depth. [Contact
persons and co-ordinators: VSN Murty and
McPhaden Michael J.]
- Japan Agency for Marine-Earth Science
and Technology Center (JAMSTEC): Am MoU
was established between NIO and JAMSTEC
in 2000 and was extended for another 5 years
till 2012 to continue the bilateral collaboration
in ocean and atmospheric sciences. So far
6 exchange visits took place from both sides
since 2002. Joint-data analysis and joint-authorship
publications were resulted from the MoU.
[Contact persons and co-ordinators: VSN
Murty and K. Mizuno and Yukio Masumoto]
- National collaborations
- Center for Atmospheric Sciences (CAOS),
Indian Institute of Sciences (IISc)
- Indian Institute of Tropical Meteorology
(IITM, Pune)
- Space Applications Center (SAC), Ahemdabad.
Scientific components and achievements:
The long-term measurements of currents at the
equator, 93°E mooring location in the eastern
equatorial Indian Ocean revealed the presence
of high frequency intraseasonal variability of
period 10-20 day period (biweekly) in the meridional
currents [Murty et al., 2002 and Figure 2 (lower
panel)].

The zonal velocity is dominantly the low frequency
semi-annual variation with superimposed intraseasonal
variability (~40-60 day period) (Figure 2 top
panel). The observed currents are compared with
the simulations from an Ocean General Circulation
Model (OGCM) [Center for Oceanic and Atmospheric
Sciences, Indian Institute of Science, Bangalore).
A good comparison is revealed at 10-20 day biweekly
period both from observations and model simulations
[Sengupta et al., 2004) (Figure 3).

The international collaboration for the Indian
Ocean observations for basin scale studies is
shown in Figure 4, while Figure 5 highlights the
proposed mooring array [RAMA] as part of IndOOS.
The realization of RAMA moored array with the
efforts from India, US, Japan and China is shown
in Figure 6.
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