In News:

A recent study by the Indian Institute of Science (IISc) has challenged the conventional understanding of monsoon dynamics by highlighting the critical role of cloud band strength in determining the movement and intensity of rainfall during the Indian monsoon season.

Key Findings of the Study:

• Strength Determines Propagation: Only strong equatorial cloud bands are capable of northward movement, initiating wet spells over the Indian subcontinent. Weak cloud bands fail to propagate, contradicting earlier models that assumed uniform northward movement.
• Role of BSISO: The Boreal Summer Intraseasonal Oscillation (BSISO) governs alternating wet and dry spells by transporting cloud bands from the equator to India. The duration and intensity of wet spells are influenced by the size and strength of these cloud bands.
• Air-Sea Interaction: Interaction between the equatorial Indian Ocean’s sea surface and atmosphere significantly influences moisture buildup and wind strength. A stronger ocean-atmosphere coupling enhances moisture transport, intensifying the monsoon.
• Impact of Climate Change:
  • Warmer atmosphere → Increased background moisture.
  • Future wet spells may see 42%–63% more rainfall over India and adjoining seas.
• Improving Forecast Models: These insights will enhance the accuracy of seasonal and sub-seasonal monsoon prediction models, crucial for agriculture and disaster preparedness.

Understanding BSISO (Boreal Summer Intraseasonal Oscillation)

• A dominant monsoon variability pattern active from June to September.
• Modulates ‘active’ (rainy) and ‘break’ (dry) phases of the monsoon.
• Moves cloud activity and convection from the Indian Ocean towards the Western Pacific.
• ENSO link:
  • La Niña enhances BSISO propagation → stronger monsoon.
  • El Niño suppresses it → weaker monsoon.

Key Facts about the Indian Monsoon

Aspect                                     Details

Definition                                “Monsoon” comes from Arabic mausim meaning season.

Southwest Monsoon        June–September; moist winds from Indian Ocean bring ~80% of India’s

                                              annual rainfall.

Northeast Monsoon          October–December; brings rain to Tamil Nadu, coastal Andhra Pradesh.

Key Drivers                              ITCZ shift, Tibetan heating, Tropical Easterly Jet, Somali Jet.

Oceanic Influences           IOD (positive enhances, negative weakens monsoon), ENSO (El Niño

                                             weakens,La Niña strengthens monsoon).

Monsoon Importance     Critical for agriculture, water supply, economy; affects ~50% of India’s

                                             population directly.