JET STREAMS

1. What are Jet Streams?
Jet streams are high-speed, narrow bands of strong winds that blow in the upper troposphere from west to east.
They are found near the tropopause. Width: 160–480 km; Thickness: 2–3 km; Length: thousands of km; Speed: 300–500 km/hr.
They are geostrophic winds flowing parallel to isobars.

2. Definition
Jet Streams are circumpolar, narrow, concentrated bands of high-velocity, upper tropospheric, geostrophic winds, bounded by low-speed winds.

3. Geostrophic Wind
Geostrophic wind results from balance between Pressure Gradient Force and Coriolis Force.
In upper atmosphere friction is negligible, air flows parallel to isobars at very high speed.

4. Why winds don’t flow directly from Equator to Poles?
Due to strong Coriolis force in upper troposphere, circulation breaks into Hadley, Ferrel and Polar cells.

5. Genesis of Jet Streams
Formed due to:
- Thermal gradient between equator and poles
- Pressure gradient between equator and poles
- Vertical pressure gradient over poles
Greater the temperature contrast, stronger the jet.

6. Characteristics
- Very high velocity (300–500 km/hr)
- Meandering (Rossby waves)
- Three-dimensional flow
- Seasonal shifting
- West to east movement
Dimensions: width 100–400 km; depth 2–3 km; length 3000+ km; altitude near tropopause.

7. Types of Jet Streams
a) Polar Front Jet Stream – 40°–60° latitude, irregular, important for cyclones
b) Subtropical Westerly Jet – around 30°–35°, south of Himalayas in winter
c) Tropical Easterly Jet – develops in summer over India due to Tibetan heating
d) Polar Night Jet – winter stratospheric jet around poles
e) Local Jet Streams – due to local conditions

8. Rossby Waves & Index Cycle
Stage 1: Stationary front forms
Stage 2: Wave formation due to push of winds
Stage 3: Mature meandering stage
Stage 4: Breakdown and heat exchange

9. Significance
- Control mid-latitude cyclones
- Influence monsoon
- Shape global weather
- Important for aviation
- Enable heat exchange

10. Factors Affecting Flow
- Landmasses
- Coriolis force
- Ocean temperatures (ENSO)
- Polar stratospheric temperature
- Seasonal solar shift

11. Jet Streams and Weather
They separate cold and warm air masses, move weather systems, and influence extreme events.

12. Jet Streams and Air Travel
Eastward flights faster, westward slower. Wind shear in jets is dangerous for aircraft.

13. Jet Streams and Indian Monsoon
Winter: STJ south of Himalayas blocks monsoon.
Summer: STJ shifts north, TEJ forms, monsoon begins.
Withdrawal: Tibetan cooling brings STJ south again, dry winter sets in.

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Subject: Geography

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