Context: The rainfall over the Southern peninsular of India - region receiving the majority of its rainfall as a result of Northeast monsoon has been deficient so far. 

More on the news: The reason is a prevalent La Niña condition, along with a low pressure belt that is currently lying to the north of its normal position.

About the Northeast monsoon:

 Source: JV IAS

  • Two seasons of rainfall in India: 
    • Southwest monsoon (about 75 percent of the country’s annual rainfall) between June and September and 
    • Northeast monsoon during October to December.
  • Affected region: Also called the winter monsoon, it is a comparatively small-scale monsoon, which is confined to the Southern peninsula - Tamil Nadu, Puducherry, Karaikal, Yanam, coastal Andhra Pradesh, Kerala, north interior Karnataka, Mahe and Lakshadweep.
    • Tamil Nadu records about 48 percent of its annual rainfall during these months.
  • Mechanism: 
    • Withdrawal of the Southwest monsoon: After this, by mid-October the wind pattern rapidly changes from the south-westerly to the north-easterly direction. 
    • Peak time for cyclonic activity: From October to December is the peak time for cyclonic activity in the North Indian Ocean region - covering the Arabian Sea and the Bay of Bengal.
    • Low pressure system: The winds associated with the formation of low pressure systems, depressions, or cyclones influence this monsoon, and cause rainfall. 

La Niña and El Nino: 

Source: Public Citizen

  • El Niño (Spanish for ‘little boy’): 
    • It is the abnormal surface warming observed along the eastern and central regions of the Pacific Ocean - region between Peru and Papua New Guinea. 
    • The expression is heard more commonly in India.  
  • La Niña (Spanish for ‘little girl’): It is an abnormal cooling of these surface waters.
  • ENSO: Together El Niño and La Niña phenomena are termed as El Niño Southern Oscillation (ENSO). 
    • These are large-scale ocean phenomena which influence the global weather - winds, temperature and rainfall. 
    • They have the ability to trigger extreme weather events like droughts, floods, hot and cold conditions, globally.
  • Connection between La Niña and the Northeast monsoon:
    • Negative impact on the Northeast monsoon: 
      • While La Niña conditions enhance the rainfall associated with the Southwest monsoon, it has a negative impact on rainfall associated with the Northeast monsoon.
      • Reason: During La Niña years, the low pressure or cyclones formed in the Bay of Bengal remain significantly to the north of their normal position. 
    • Position of the Inter Tropical Convective Zone (ITCZ): Its current position has also contributed to the poor rainfall during the ongoing monsoon season. 
      • The ITCZ is a low-pressure belt, whose northward and southward movements along the equator determine the precipitation in the tropics. 
      • Currently, the ITCZ is located to the north of its normal position.

Image Source: The Financial Express