1. Indian Ocean Basin Brief
CDR Carl Allen Hager, USN
(w)
CDR Carl Allen Hager

2. The Indian Ocean

3. “Take Aways” Indian Ocean Describe the concept of an atmospheric cell
In association with the NE/SW Monsoons, describe:
Meteorological conditions
Directionality of the Somalia current
Western basin productivity
Equatorial current design by comparison to the Pacific Ocean
Relative position of the ITCZ

4. Outline Basin Characteristics Monsoons Surface Currents References
Indian Ocean
Outline
Basin Characteristics
Hydrology
Geology
Monsoons
Northeast
Southeast-
Surface Currents
References
Summary

5. Basin Characteristics
Indian Ocean
Location: body of water between Africa, Antarctica, Asia, and Australia
Includes Andaman Sea, Arabian Sea, Bay of Bengal, Great Australian Bight, Gulf of Aden, Gulf of Oman, Mozambique Channel, Persian Gulf, Red Sea, Strait of Malacca, and other tributary water bodies
Nearly 10,000 km wide at the tips of Africa and Australia and 10,000 km from Antarctica to inner Bay of Bengal; its area is 73.6 million sq km (20% of earth’s water surface); slightly less than 8x the size of the US
Major sea routes connect the Middle East, Africa, and East Asia with Europe and the Americas; strategic importance far outweighs the economic value of its minerals or marine life

7. Basin Characteristics
Indian Ocean
Surface currents controlled by the monsoon.
Deepwater circulation controlled by inflows from the Atlantic Ocean, the Red Sea, and Antarctic currents.
North of 20o S, minimum sfc temp is 22oC (72oF), exceeding 28oC (82oF) to the east; southward of 40o S, temps drop quickly.
Surface salinities range from 32-37, with the highest concentration in Arabian Sea.
Pack ice and icebergs are found throughout the year south of 65o S (ave. north limit~45o).

8. Basin Characteristics
Indian Ocean
The African, Australian, Indian, and Antarctic crustal plates converge; juncture marked by inverted Y
Ridge systems: Central Indian Ridge, SW Indian Ridge, SE Indian Ridge and 90oE Ridge
Deepest point: Java Trench (7,450 m)
86% of main basin is pelagic sediments; remaining 14% is terrigenous sediments; glacial outwash dominates extreme southern latitudes

9. Basin Characteristics
Indian Ocean
Continental Drift

10. Basin Characteristics
Indian Ocean
Age of Ocean Crust

11. Basin Characteristics
Indian Ocean
Plate Motion

12. Image source: Woods Hole Institute

13. Climate / Monsoons Indian Ocean Climate is controlled by:
Northeast Monsoon (December to April)
Winter / Dry
Southwest Monsoon (June to October)
Summer / Wet
Tropical cyclones occur during May/June and Oct/Nov in northern Indian Ocean and Jan/Feb in southern Indian Ocean

14. Climate / Monsoons Indian Ocean
‘Monsoon’ derived from an Arab word meaning ‘winds that change seasonally’
….or the Latin word “Monswine” – which means “its gonna rain till pigs float on the roof”
Due to differential heating of land and water; water has a higher capacity for storing heat than does land (diurnal variability of differential heating results in ‘sea/land breezes’)

15. Climate / Monsoons
Indian Ocean
Sea Breeze Land Breeze

16. Climate / Monsoons Indian Ocean North-East Monsoon (northern winter)
Air over southern Asia is cooler and denser than air over the ocean; continental air sinks.
Sinking air over Asia results in greater atmospheric pressure over land than ocean.
Resulting pressure gradient leads to a northerly (north-easterly) flow of air from Asia to south of the Equator; Prevailing winds drive a southward flowing Somali current.
Characterized by dry, cool air over India and surrounding areas.

17. January global atmosphere circulation
Lutgens & Tarbuck, The Atmosphere p. 203

18. January Rainfall and Wind Vectors
ITCZ

19. Climate / Monsoons (Jan / NE)
Indian Ocean
Somalia
ITCZ
ITCZ Migration and Wind Direction off Somalia

20. Climate / Monsoons Indian Ocean South-West Monsoon (northern summer)
Air over southern Asia is warmer and less dense; continental air rises.
Rising air over Asia results in an atmospheric low pressure system over land. This is the “Wet” Season!!
Resulting pressure gradient leads to a southerly (south-westerly) flow of air from the ocean to the continent.
Prevailing winds drive a northward flowing Somali current.

21. July global atmosphere circulation
Lutgens & Tarbuck, The Atmosphere p. 203

22. ITCZ Migration and Wind Direction off Somalia
Climate / Monsoons
Indian Ocean
ITCZ
Somalia
ITCZ Migration and Wind Direction off Somalia

23. July Rainfall and Wind Vectors
ITCZ

24. Surface Currents
Indian Ocean

25. Eastern Pacific Equatorial Surface Currents
Indian Ocean
N E C
E C C
S E C
Eastern Pacific Equatorial Surface Currents

26. Winter (January) Indian Ocean circulation
E U C
Open University, Ocean Circulation p. 136

28. Summer (July) Indian Ocean circulation
Open University, Ocean Circulation p. 136

30. Miscellaneous Indian Ocean
East African rift valley and the Red Sea represent the youngest stages of development of ocean basins (embryonic and young, respectively). The Himalaya Mountains exemplify the final stage of ocean evolution (relict scar).
Agulhas Current (warm, southward flowing current) is the second swiftest current in all the world’s oceans and is the deadliest. Rogue waves abound.
The Indian Ocean has its own El Nino-like phenomenon with a warm pool of water that moves eastward in a cycle of 3-7 years.

31. References Indian Ocean
Clark, C. O., J. E. Cole, and P. J. Webster, 2000: Indian Ocean SST and Indian summer rainfall: predictive relationships and their decadal variability. Journal of Climate, 13(24),
Holton, J. R., 1992: An Introduction to Dynamic Meteorology. Academic Press San Diego, 511 pp.
Lau, K. –M. and S. Yang, 1997: Climatology and inter annual variability of the Southeast Asian summer monsoon. Advances in Atmospheric Sciences, 14, 141—162.
Open University Course Team, 1989: Ocean Circulation. Butterworth Heinemann, Milton Keynes, England, 238 pp.
Open University Course Team, 1997: The Ocean Basins: Their Structure and Evolution. Butterworth Heinemann, Milton Keynes, England, 185 pp.
Sempere, J. –C. and E. M. Klein, 1995: New insights in crustal accretion from Indian Ocean spreading centers. EOS Transactions, 76(11), 113, 116.
Tomczak, M. and J. S. Godfrey, 1994: Regional Oceanography: An Introduction. Pergamon, Oxford, 422 pp.

32. “Take Aways” Indian Ocean Describe the concept of an atmospheric cell
In association with the NE/SW Monsoons, describe:
Meteorological conditions
Directionality of the Somalia current
Western basin productivity
Surface equatorial current design and its comparison to the Pacific Ocean
Relative position of the ITCZ

33. Summary Basin Characteristics Monsoons Surface Currents References
Indian Ocean
Summary
Basin Characteristics
Hydrology
Geology
Monsoons
Northeast
Southeast-
Surface Currents
References