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Primary introduction to indian ocean dipole and it's impact
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INDIAN OCEAN DIPOLE
ByShubham Raghuwanshi
Overview
• Introduction to Indian Ocean• What is Indian ocean dipole ?• Evolution of Dipole• Impacts of IOD
Indian Ocean
• Third largest of the world's oceanic divisions• Covering 20% of water on earth surface• Located between 30E -120E and 30N -60S•The climate north of the equator is affected by a monsoon climate
Indian ocean general condition
• Wind blow from south west during (may-sep) and north-east during Nov-feb
• Warm water(SST) on eastern side and cooler on west• More fresh water input on eastern side than west• Upwelling system is located off the west• Deeper thermocline in the east than west• Convection is higher over eastern part and lesser over west• Wyrtki jets (over equatorial Indian ocean) transport warmer
upper layer water towards the east during April-may and oct-nov.
• Heat content is larger on eastern side than west• Lower salinity on east than west
Wind Pattern
Source: CSIR – National Institute of Oceanography
IOD• The departure of ocean–atmosphere system from this
mean state occurring during certain years, characterized by opposite sign of anomalies in the east and west is known as the Indian Ocean dipole
IOD• The Indian Ocean Dipole is defined by the difference
in sea surface temperature between two areas (or poles, hence a dipole) a western pole in the Arabian Sea (western Indian Ocean) and an eastern pole in the eastern Indian Ocean south of Indonesia.
• The IOD affects the climate of Australia and other countries that surround the Indian Ocean Basin, and is a significant contributor to rainfall variability in
this region.
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°
Source: http://www.enviroinfo.com.au/understanding-the-indian-ocean-dipole phenomenon/#.U3SfH4GSxVM
Source: Bureau of Meteorology Australia
Evolution of dipole• It’s a coupled ocean-atmosphere processes• Oceanic processes – Shoaling of thermocline– Variations in mixed layer depth
• Atmospheric process– Atmosphere-ocean heat fluxes– Large-scale atmospheric circulations
Dependence of IOD on El NINO
• During 1957-1999 about 50% of IOD events have occurred together with ENSO and the rest independently
• Some coupled model found relation between ENSO and IOD but others doesn’t
Impacts of IOD
• Affects the rainfall in tropical eastern Africa, Indonesia, Australia
• It’s found positive IOD event Intensify ISMR (Ashok et al 2001, guan et al 2003)
• Enhanced the impact of Enso on Australia
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.
References
• Noaa http://www.noaa.gov/• Bureau of Meteorology Australia
http://www.bom.gov.au/climate/IOD/about_IOD.shtml• Japan agency for marine earth science and technology
http://www.jamstec.go.jp/e/• Vinaychandran P N, Francis P A and Rao S A 2009 Indian ocean
Dipole: Processes and Impacts• Wang Xin & Wang Chunzai 2013 Different impacts of various El
Nino events on Indian ocean dipole
Thank You