Indian Ocean Currents
Geography › Ocean Movements, Temperature and Salinity · Topic 11.3
The currents of the northern Indian Ocean reverse with the monsoon, flowing clockwise in summer under the southwest monsoon and anticlockwise in winter under the northeast monsoon, a pattern known as the monsoon drift. South of the equator, the currents form a permanent anticlockwise gyre made of the South Equatorial Current, the warm Agulhas Current, the West Wind Drift and the cold West Australian Current.
5 min read · UPSC Prelims · Geography · Ocean Movements, Temperature and Salinity
At a Glance
- North of the equator Reverses with the monsoon
- South of the equator Permanent anticlockwise gyre
- Fastest current Somali Current in summer
- Warm western boundary current Agulhas
- Unusual warm current Leeuwin, off western Australia
- Exam link UPSC Prelims, Geography: Ocean Movements, Temperature and Salinity
Where Does It Fit?
This is the third topic of the category on ocean movements, temperature and salinity. The previous topic listed the Pacific and Atlantic currents, and this one covers the Indian Ocean, where the northern currents reverse with the monsoon. The next topic describes the effects of currents. Previous topic: Pacific and Atlantic Ocean Currents. Next topic: Effects of Ocean Currents.
Why Do the Currents of the Northern Indian Ocean Reverse?
In short: the monsoon winds reverse twice a year, and the surface currents in the northern Indian Ocean follow them.
Unlike the Pacific and the Atlantic, the northern Indian Ocean is closed by the Asian landmass, and the winds there are the monsoon winds, as in The Indian Ocean. The seasonal reversal of the winds therefore reverses the surface circulation, which is called the monsoon drift.
| Season | Wind | Circulation in the north Indian Ocean |
|---|---|---|
| Summer (June to September) | Southwest monsoon | Clockwise: the southwesterly Monsoon Current flows east across the Arabian Sea and the Bay of Bengal; the Somali Current flows north along the African coast; the East Indian Coastal Current flows north along India’s east coast |
| Winter (December to February) | Northeast monsoon | Anticlockwise: the Northeast Monsoon Current flows west; the Somali Current flows south; the East Indian Coastal Current flows south along India’s east coast |
The Equatorial Countercurrent, which is a permanent feature of the other oceans, exists here only in winter, when it flows east between the equator and about 8 degrees south, because the southwest monsoon in summer replaces it. The seasonal pattern was well known to ancient mariners, who used the monsoon winds and currents for trade between Arabia, India and East Africa.
What Is Special About the Somali Current?
- Speed: in summer, the Somali Current is one of the fastest ocean currents in the world, with speeds of more than 2 m per second, and acts as a western boundary current in the northern Indian Ocean. It forms in a few weeks after the monsoon onset.
- Upwelling: the southwest wind blowing parallel to the coast of Somalia and Arabia pushes surface water offshore by Ekman transport, so cold, nutrient-rich water comes up. Sea surface temperatures fall by several degrees, and productivity is very high, with rich fisheries in the western Arabian Sea, as in Ocean Currents – Causes and Types.
- Monsoon link: the cool upwelled water reduces local evaporation, and the low-level Somali jet, the Findlater jet, carries moisture over the Arabian Sea to India, as in Jet Streams.
- Winter reversal: the current runs south, and the coast has weak upwelling.
What Are the Permanent Currents South of the Equator?
| Current | Nature | Description |
|---|---|---|
| South Equatorial Current | Warm | Flows west across the ocean at about 10 degrees south, driven by the southeast trades; divides near Madagascar |
| Mozambique and Madagascar currents | Warm | Branches that flow south along the African coast and the east coast of Madagascar |
| Agulhas Current | Warm | A strong, narrow western boundary current flowing south-west along the east coast of Africa, similar to the Gulf Stream; it meets the westerlies off South Africa and turns back eastward, shedding warm rings into the Atlantic |
| West Wind Drift | Cold | Part of the Antarctic Circumpolar Current flowing east in the south |
| West Australian Current | Cold | Flows north along the west coast of Australia, completing the gyre; contributes to the aridity of the coast |
| Leeuwin Current | Warm | Flows south along the west coast of Australia, against the usual pattern for west coasts; carried by the Indonesian Throughflow and supports unusual corals at high latitude |
The Indonesian Throughflow is the passage of Pacific water through the Indonesian seas into the Indian Ocean. It is the only low-latitude link between two oceans, and it transfers heat and fresh water, which affects the Indian Ocean Dipole and the monsoon, as in La Niña and El Niño Modoki. As an analytical point, the Indian Ocean current system is the best example of how ocean circulation is organised by the atmosphere, and the way it reverses is a test of the monsoon theory. The ocean is also warming fast, and marine heatwaves in the western Indian Ocean are reducing fish catches and bleaching corals.
Why Is This Topic Important?
- Unique feature Reversal with monsoon
- Fisheries Somali upwelling
- Monsoon link Moisture transport
What Came Next?
The next topic describes the effects of ocean currents on climate, fisheries and navigation. Next topic: Effects of Ocean Currents.
Key People and Terms
- Monsoon drift Seasonally reversing surface circulation
- Somali Current Fast current off East Africa
- Agulhas Current Warm current off southeast Africa
- Leeuwin Current Warm current off western Australia
- Indonesian Throughflow Pacific water flowing into the Indian Ocean
- Ekman transport Net surface water movement driven by wind
Exam Corner
Points to Remember
- Northern currents reverse with the monsoon.
- Summer circulation is clockwise.
- The Somali Current causes upwelling in summer.
- Agulhas is warm; West Australian is cold.
- The countercurrent exists only in winter.
Do Not Confuse With
- Agulhas and Benguela currents Indian Ocean warm versus Atlantic cold
- West Australian and Leeuwin currents Cold northward versus warm southward
- Summer and winter monsoon drift Clockwise versus anticlockwise
Memory Hook
North turns with the monsoon; south keeps its gyre: Agulhas warm, Western Australia cold.
Mains Angle
Questions ask why the Indian Ocean is different. These points add depth.
- Cause Closed north and monsoon winds
- Effect Upwelling and fish
- Link Throughflow and Dipole
A Question You May Face
An original practice question, not a past paper question.
“Why do the surface currents of the northern Indian Ocean change direction seasonally, unlike those of the Pacific and the Atlantic?”
How to Answer
- Basin Closed in the north.
- Winds Monsoon reversal.
- Currents Summer and winter patterns.
- Impact Upwelling and moisture.
GS Relevance
Frequently Asked Questions
Why do the currents of the northern Indian Ocean reverse?
The northern Indian Ocean is closed by the Asian landmass and is dominated by the monsoon winds, which reverse direction between summer and winter. The surface currents follow the winds, flowing clockwise in the summer southwest monsoon and anticlockwise in the winter northeast monsoon, a pattern called the monsoon drift.
What is the Somali Current?
The Somali Current flows along the coast of East Africa. In the summer it flows northward as a fast current of more than 2 metres per second, with strong upwelling of cold, nutrient-rich water, and in winter it reverses and flows southward. It is the only western boundary current that reverses seasonally.
What is the Agulhas Current?
The Agulhas Current is a warm, fast and narrow current that flows southwestward along the east coast of southern Africa. It is the western boundary current of the Indian Ocean gyre, comparable to the Gulf Stream, and it turns back east near South Africa, releasing warm eddies into the Atlantic.
What is the Leeuwin Current?
The Leeuwin Current is a warm current that flows south along the west coast of Australia. It is unusual because western coasts in these latitudes normally have cold currents. It carries warm water from the Indonesian Throughflow, and allows tropical corals to grow farther south than usual.
What is the Indonesian Throughflow?
The Indonesian Throughflow is a flow of warm Pacific water through the Indonesian seas into the Indian Ocean. It is the only low-latitude passage between two oceans, and it carries heat and fresh water that influence the Indian Ocean temperature, the Leeuwin Current, and the monsoon.
PYQ Practice — Statement Analysis
1 The Somali Current flows northward in summer.
The southwest monsoon drives it.
2 The West Australian Current is warm.
It is a cold current.
3 The Equatorial Countercurrent in the Indian Ocean exists in winter.
It is replaced by the monsoon flow in summer.
4 The Agulhas Current flows along the east coast of Africa.
It is a warm current.
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