🔆 Indian Monsoon Mechanism – Jet Stream Theory
📍 About Jet Stream Theory
✅ Most accepted modern theory for monsoon origin.
✅ Focus on Sub-Tropical Jet Stream (STJ) in the upper troposphere.
✅ Burst & withdrawal of monsoon = linked to north-south migration of STJ.
📍 How Jet Streams Affect Weather
✅ Ridges (high pressure) → anticyclonic, clear weather.
✅ Troughs (low pressure) → cyclonic, rainfall/depressions.
✅ Jet streaks create divergence/convergence in upper air → triggers surface lows & highs.
✅ Coriolis effect → converts these surface lows/highs into cyclonic/anticyclonic systems.
🔆 Indian Monsoon Mechanism – Role of STJ
📍 Winter STJ (Hindrance Phase)
✅ STJ flows south of Himalayas → creates ridge (high pressure) over N-W India.
✅ Steers Western Disturbances into India → winter rainfall in Punjab, Haryana, snowfall in Himalayas.
✅ No South-West monsoon because:
1. ITCZ shifts south.
2. Strong divergence due to ridge over N-W India.
3. Tibet = high pressure zone.
📍 Summer STJ (Onset Phase)
✅ From March → STJ weakens & shifts northwards.
✅ By June → STJ moves north of Himalayas → removes ridge over N-W India.
✅ Low pressure over N-W India + cross-equatorial winds → sudden burst of monsoon.
✅ Easterly Jet emerges over Peninsular India → strengthens South-West monsoon.
🔆 Why No South-West Monsoon Before June?
📍 March–May Summer Period
✅ Strong heating creates low pressure in N-W India.
✅ But STJ ridge still south of Himalayas → upper divergence blocks surface convergence.
✅ Descending dry air = hot winds (loo), dry & rainless despite high temps.
📍 Key Dynamics
✅ Onset → STJ shifts north of Tibet → monsoon enters.
✅ Withdrawal → STJ shifts back south of Himalayas → monsoon retreats.
Essence:
The Sub-Tropical Jet Stream is the switch that controls India’s monsoon → its northward migration triggers onset, while southward shift causes withdrawal.
✨ #IndianMonsoon #JetStreamTheory #geography
📍 About Jet Stream Theory
✅ Most accepted modern theory for monsoon origin.
✅ Focus on Sub-Tropical Jet Stream (STJ) in the upper troposphere.
✅ Burst & withdrawal of monsoon = linked to north-south migration of STJ.
📍 How Jet Streams Affect Weather
✅ Ridges (high pressure) → anticyclonic, clear weather.
✅ Troughs (low pressure) → cyclonic, rainfall/depressions.
✅ Jet streaks create divergence/convergence in upper air → triggers surface lows & highs.
✅ Coriolis effect → converts these surface lows/highs into cyclonic/anticyclonic systems.
🔆 Indian Monsoon Mechanism – Role of STJ
📍 Winter STJ (Hindrance Phase)
✅ STJ flows south of Himalayas → creates ridge (high pressure) over N-W India.
✅ Steers Western Disturbances into India → winter rainfall in Punjab, Haryana, snowfall in Himalayas.
✅ No South-West monsoon because:
1. ITCZ shifts south.
2. Strong divergence due to ridge over N-W India.
3. Tibet = high pressure zone.
📍 Summer STJ (Onset Phase)
✅ From March → STJ weakens & shifts northwards.
✅ By June → STJ moves north of Himalayas → removes ridge over N-W India.
✅ Low pressure over N-W India + cross-equatorial winds → sudden burst of monsoon.
✅ Easterly Jet emerges over Peninsular India → strengthens South-West monsoon.
🔆 Why No South-West Monsoon Before June?
📍 March–May Summer Period
✅ Strong heating creates low pressure in N-W India.
✅ But STJ ridge still south of Himalayas → upper divergence blocks surface convergence.
✅ Descending dry air = hot winds (loo), dry & rainless despite high temps.
📍 Key Dynamics
✅ Onset → STJ shifts north of Tibet → monsoon enters.
✅ Withdrawal → STJ shifts back south of Himalayas → monsoon retreats.
Essence:
The Sub-Tropical Jet Stream is the switch that controls India’s monsoon → its northward migration triggers onset, while southward shift causes withdrawal.
✨ #IndianMonsoon #JetStreamTheory #geography
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