MATERI KULIAH : AMGPERTEMUAN KE : , TGL :

OLEH : Drs. SOETAMTO, MSi

&

The Unique Indian Ocean The Unique Indian Ocean

What is IOD? First described by Dr. Saji et al. in 1999 Second mode of EOF, explains about 12% of the total

variation of anomalous Indian Ocean sea-surface temperatures

Dipole Mode Index (DMI)

Evolution of a Dipole Mode EventAn IOD event usually starts around May or Jun, intensifies in the following months and peaks between Aug and Oct and then rapidly decays.

Positive & Negative Phases of IOD

Positive: cooler in the tropical eastern Indian Ocean and warmer in the tropical western Indian OceanNegative: warmer in the tropical eastern Indian Ocean and cooler in the tropical western Indian Ocean

Positive IOD Phase Negative IOD Phase

Measure of IOD : Dipole Mode Index

DMI=SSTA West -SSTA East

West = 50°E-70°E;10°S-10°N

East = 90°E-110°E;10° S-0°

Vinayachandran et al., 2009

Positive IOD

Negative Dipole

IOD Influence on Surrounding Climate

• A positive phase of the IOD tends to cause droughts in East Asia and Australia, and flooding in parts of the Indian subcontinent and East Africa. 

Australian droughts• A 2009 study by Ummenhofer et al. at the University of New

South Wales Climate Change Research Centre, has demonstrated a significant correlation between the IOD and drought in the southern half of Australia, in particular the south-east.

Seasonal Evolution: Ocean

Seasonal Evolution: Atmosphere

October 2006 Anomalies October 2006 Anomalies SST (shaded)SST (shaded)

winds (vectors)winds (vectors) and OLR (contour)and OLR (contour)

Indian Ocean Dipole EventsIndian Ocean Dipole Events

QSCAT Wind Anomalies for 2006

APRAPR MAYMAY

JUNJUN SEPSEP

OCTOCT DECDEC

Mixed Layer Heat Balance (East) : 1993-98

Heat flux

Entrainment

Advection

Mixed Layer Heat Balance (West) : 1993-98

Heat flux

Entrainment

Advection

Murtugudde et al., 2000, JGR

75-85E, 5S-5N

95-105E,10S-Eq.

Mixed Layer Heat Balance (anomalies) : 1997-98

Upper Ocean (50m) Heat Budget: 2006Upper Ocean (50m) Heat Budget: 2006

EASTEAST

WESTWEST

Equatorial JetsWinds and SST May October

Vinayachandran et al., GRL, 1999

Anomalies: winds and SST

Equatorial Zonal Winds

Francis et al., Tellus, 2007

Equatorial Jets during IOD events

Impact of Equatorial Jets

Hastenrath et al., 1993, JGR

Subsurface anomalies

Thermocline Anomalies & Wave Propagations

Thermocline Anomalies & Wave Propagations

Observational Evidence

Upwelling off SumatraUpwelling off Sumatra

Murtugudde et al., 2000, JGR; Vinayachandran and Mathew, 2003, GRLMurtugudde et al., 2000, JGR; Vinayachandran and Mathew, 2003, GRL

Impact of IOD on Ocean BiologyImpact of IOD on Ocean Biology

Extremes of the Indian Summer Monsoon Rainfall, IOD & ENSO (period:1979-2003)

Gadgil et al., 2003

Fluxes

Advection

Entrainment

September November

ProcessesProcesses

SSS Anomaly non-IOD CompositeSSS Anomaly non-IOD Composite

Summary

• Indian Ocean Dipole :Dominant signal in the inter-annual variability.

• Coupled ocean – atmospheric phenomenon in the Indian Ocean. SST, thermocline, winds convection all take part in an IOD event.

• OGCMs reproduce IOD events well and illustrate the role of ocean dynamics in the evolution of SST anomalies.

• Unresolved issues: Triggering, dependence on ENSO, intraseasonal oscillations, impact on monsoons.