Tropical Monsoon Intra-seasonal Oscillation

• Tropical monsoon intra-seasonal oscillation (ISO), often called the Monsoon Intraseasonal Oscillation (MISO) or Boreal Summer Intraseasonal Oscillation (BSISO), drives active and break phases in Indian summer monsoon rainfall.
• This oscillation features eastward and northward propagation of convective bands over the Indian Ocean and monsoon regions, with periods of 10-20 days (quasi-biweekly) and 30-60 days.
• It causes wet active spells and dry breaks lasting 1-3 weeks, impacting agriculture in South Asia during May-October.
• Key drivers include Madden-Julian Oscillation (MJO) influences and local air-sea interactions.

Mid-latitude Oscillation

• Mid-latitude oscillations refer to patterns like the circumglobal teleconnection (CGT), which involve wave trains in upper-level winds influencing monsoon variability from extratropical regions.
• Mid-latitude ISOs arise from jet stream interactions with topography and exhibit low-frequency variability (10-60 days) in the Northern Hemisphere extratropics.
• The CGT pattern, a wavenumber-5 Rossby wave train along the subtropical jet, originates near the Caspian Sea and extends across Eurasia to the Pacific.
• It links North Atlantic variability, like NAO-related waves, to Asian circulation

Source: The Hindu