The Bureau of Meteorology, Australia said a La Nina has developed in the tropical Pacific Ocean. After effective coupling between the ocean and the atmosphere, the tropical Pacific Ocean continues to cool. The configuration of clouds and winds in the atmosphere is consistent with the temperature of the ocean surface and subsoil. Further cooling of the Pacific is expected and conditions in La Nina are expected to prevail for an extended period, until early spring 2022.
The Bureau of Meteorology, Australia (BoM) and the Climate Prediction Center (CPC) of the National Oceanic and Atmospheric Administration (NOAA) maintain different scales and measurements to determine the El-Nino or La Nina establishment. While BoM follows a threshold of +/- 0.8 ° C, the National Center for Environmental Prediction (NCEP) of the NOOA sets the limits for sea surface temperature at +/- 0.5 ° C.
ENSO: Enso has a major influence on weather and climatic conditions such as heavy rains, floods and droughts. El Nino has a warming influence on global temperatures while La Nina has the opposite effect. In India, for example, El Nino is associated with a drought or weak monsoon, while La Nina is associated with a strong monsoon, above average rains and colder winters. El Niño and the Southern Oscillation, in short, are a periodic fluctuation of the sea surface temperature and atmospheric pressure of the overlying atmosphere across the equatorial Pacific Ocean.
El Nino and La Nina events tend to develop during the April-June period and they tend to peak in strength during October-February. Typically, these events persist for 9 to 12 months, although they sometimes last up to 2 years. La Nina influences the Indian subcontinent by carrying cold air from Siberia and southern China, which interacts with tropical heating to produce north-south low pressure systems. The cold air associated with these troughs extends much further into southern India. In general, La Nina’s cold air envelope occupies a larger part of India. Such a pattern means less impact of Western disturbances. The cold temperature may descend as far as Tamil Nadu, but may not affect northeast India as much.
IOD: The latest weekly Indian Ocean Dipole Index (IOD) value as of November 28 is -0.32 ° C. Although IOD is -ve, but still within neutral limits. The -ve event is likely to end soon. It could reach zero-zero by the end of December and lose importance thereafter. The displacement of the monsoon trough towards the southern hemisphere prevents the formation of an IOD event until April. Statistically, unlike El Nino and La Nina, IOD events have a normal distribution. They maintain a symmetrical bell-shaped curve with a neutral peak at 60% occasions and have an equal share of 20% each for the -ve and + ve events. Events generally start around April-May, peak between August and October, and then decline rapidly after the end of the northeast monsoon over southern India.
MJJ: Madden Julian Oscillation (MJO) is an intra-seasonal variability in wind and pressure patterns in different layers of the atmosphere. These changes can in turn impact surface and subsurface conditions across the ocean. The weakening or strengthening of the trade winds is an associated factor, modifying the degree of cooling associated with La Nina over the Pacific Ocean. MJO is now moving from the Maritime Continent to the Western Pacific in Phases 6 and 7. It is expanding but moving away from Indian waters. This could accelerate thunderstorm activity in the western Pacific. It is unlikely to trigger further disturbances in the Bay of Bengal and the Arabian Sea.
Sustained conditions in La Nina are expected to react and may result in severe winters for northern India. Frigid temperatures and freezing winds are most commonly seen from January to February. Sometimes its peak lasts from the 4th week of December to the 4th week of January.