Weather forecasting · GS-I
IMD Update: Possible Bay of Bengal Cyclone by Monday; AP, Odisha on Alert ↗
Consider the following statements regarding tropical cyclogenesis over the Bay of Bengal and associated meteorological phenomena:
- The intensification sequence for a tropical disturbance over the Indian Ocean, as classified by the IMD, follows the order: low-pressure area → depression → deep depression → cyclonic storm, before further strengthening into a severe cyclonic storm.
- The Madden-Julian Oscillation (MJO) is a seasonal phenomenon that recurs annually and primarily influences sea-surface temperatures in the Bay of Bengal, thereby controlling cyclone intensity but not genesis.
- Under IMD's cyclone naming protocol for the North Indian Ocean, names are contributed by member countries of the World Meteorological Organization's Regional Specialised Meteorological Centre (RSMC) roster, and a disturbance is assigned a name only after it attains the status of a cyclonic storm.
Which of the statements given above is/are correct?
Explanation
Statement 1 is correct. The IMD classifies tropical disturbances in ascending order of intensity: low-pressure area → depression → deep depression → cyclonic storm → severe cyclonic storm → very severe cyclonic storm → extremely severe cyclonic storm → super cyclonic storm. This is the standard intensification ladder used in operational forecasting. Statement 2 is incorrect for two substantive reasons. First, the Madden-Julian Oscillation (MJO) is not a seasonal annual cycle — it is an intra-seasonal oscillation with a period of roughly 30–60 days, meaning it can occur multiple times a year and is distinct from the annual monsoon cycle. Second, the MJO's primary influence on cyclogenesis is through enhancing atmospheric convective activity and low-level wind convergence, thereby favouring both the genesis and intensification of cyclones — not merely through sea-surface temperature modulation. The MJO's 'active phase' over the Indian Ocean creates an environment conducive to cyclone formation, which is why IMD tracks its phase when issuing extended-range outlooks. Statement 3 is correct. Under the North Indian Ocean naming protocol coordinated through IMD (the RSMC for the region), member countries — including Bangladesh, India, Iran, Maldives, Myanmar, Oman, Pakistan, Qatar, Saudi Arabia, Sri Lanka, Thailand, UAE, and Yemen — contribute names in rotation. Critically, a disturbance is given a name only when it intensifies to the threshold of a cyclonic storm (≥ 3-minute sustained winds of 63 km/h); before that it carries only a tracking identifier (such as the model tag '98B') and a numbered designation as a depression.