Somali jet

Geography glossary

Also called: Findlater jet · Topic: Atmospheric Pressure, Winds and General Circulation · NCERT: Beyond NCERT

Meaning

The Somali jet, also called the Findlater jet, is a fast, narrow band of wind close to the ground, about 1–1.5 km up. It blows from the southern Indian Ocean, crosses the equator along the East African coast, and then flows as a south-westerly wind over the Arabian Sea to the west coast of India during the summer monsoon.

It matters because it carries much of the monsoon's moisture to India. It is also a common exam trap, because it is a low-level jet, not an upper-air jet like the other main jets.

Explanation

What kind of jet it is

  • Jet stream: a narrow band of very fast wind. Most jets blow high in the upper troposphere, about 9–16 km up, just below the tropopause (the boundary between the troposphere and the stratosphere above it).
  • Low-level jet: a fast wind band near the ground. The Somali jet is one. It blows at only about 1–1.5 km.
  • Cross-equatorial: it starts in the Southern Hemisphere and crosses the equator into the Northern Hemisphere.
  • Season: it blows only during the summer (south-west) monsoon.
  • Discovery: J. Findlater first described it in 1969. That is why it is also called the Findlater jet.

How it forms and moves (cause → process → result)

  • Start: south-east trades in the southern Indian Ocean
  • Trade winds (steady winds that blow towards the equator) move north-west over the southern Indian Ocean.

  • In summer, these winds are pulled north towards the hot Indian landmass and its low pressure.

  • Crossing the equator near East Africa

  • The wind crosses the equator near the coast of Kenya and Somalia.

  • The East African highlands act like a wall on the western side. They squeeze the wind into a narrow, fast band along the coast.

  • Turning into a south-westerly

  • The Coriolis force (the turning effect of the Earth's spin) bends winds to the right in the Northern Hemisphere.

  • Once the wind crosses the equator, it is turned to the right. The south-east wind becomes a south-westerly.

  • Result: moisture reaches India

  • The south-westerly blows over the warm Arabian Sea and picks up a lot of water vapour.
  • It reaches the west coast of India and carries much of the monsoon's moisture.

Its place among the main jets

Jet Height Direction Season
Somali (Findlater) jet 1–1.5 km (low level) South-westerly, crosses the equator Summer monsoon
Polar front jet 9–12 km Westerly All year; strongest in winter
Subtropical westerly jet (STJ) 12–14 km Westerly Over India mainly in winter
Tropical easterly jet (TEJ) 13–16 km Easterly Summer only
  • The monsoon team: three things work together to set up and supply the south-west monsoon:
  • the STJ's jump north of the Tibetan Plateau in early summer;
  • the TEJ high above;
  • the Somali jet near the ground, which brings in the moisture.

Where it occurs

  • Southern Indian Ocean: this is where it starts, as the south-east trades.
  • East African coast (Kenya and Somalia): this is where it crosses the equator.
  • East African highlands: these channel the wind into a narrow jet along the coast.
  • Arabian Sea: it blows across this sea as a south-westerly and picks up moisture.
  • West coast of India: this is where it delivers the monsoon's moisture.
  • Time: only in the summer monsoon season.

Don't confuse with

  • Tropical easterly jet (TEJ): an upper-air jet at 13–16 km near 15°N that blows from the east. It is driven by the heating of Tibet (Koteswaram, 1958). The Somali jet is a low-level south-westerly at 1–1.5 km.
  • Subtropical westerly jet (STJ): a westerly jet at 12–14 km that sits over India mainly in winter and steers western disturbances. The Somali jet is a summer jet and has nothing to do with western disturbances.
  • Polar front jet stream: a westerly jet at 9–12 km over ~40–60° latitude that guides temperate cyclones. The Somali jet is tropical, low-level and cross-equatorial.
  • Upper-air jets in general: these are strongest in winter and blow just below the tropopause. The Somali jet blows near the ground and only in summer.

Prelims Hooks

  • Lowest to highest jet: Somali jet (1–1.5 km) → polar front jet (9–12 km) → subtropical westerly jet (12–14 km) → tropical easterly jet (13–16 km).
  • Classic trap: the Somali jet is a low-level jet, not an upper-tropospheric jet.
  • Feature–place match: the Somali jet crosses the equator along the East African coast (Kenya and Somalia).
  • Direction: it starts as south-east trades and becomes a south-westerly after crossing the equator, because of the Coriolis force.
  • Person–jet pairs: Somali jet → J. Findlater (1969); tropical easterly jet → P. Koteswaram (1958).
  • Role: it carries much of the moisture of India's south-west monsoon across the Arabian Sea.

Mains Points

  • Moisture supply for the monsoon (GS-I):
  • The Somali jet carries much of the monsoon's moisture from the Arabian Sea to India's west coast.

  • It works together with the STJ's early-summer jump north and the TEJ to set up and supply the south-west monsoon.

  • Timing and strength risks (GS-I/GS-III):

  • A shift in the timing of the Somali jet, the TEJ or the STJ can delay or weaken the monsoon.

  • A weak monsoon affects rain-fed farming, water storage and food security. This is why watching these winds matters for seasonal forecasting.

  • Role of landforms in wind systems (GS-I):

  • The East African highlands channel the cross-equatorial flow into a narrow jet.
  • This is a good example of how relief (the shape of the land) and the Coriolis force together shape a regional wind system that affects a country thousands of kilometres away.

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