While short, seasonal, and long-term weather phenomena over the Pacific to the poles influence the monsoon, its onset over Kerala appears to be delayed due to a superstorm.
As the monsoon advances, scientists attribute the delay in its onset over Kerala to Typhoon Mawar, which is weakening over the Pacific.
Mawar is temporarily stalling a weather phenomenon called Madden-Julian Oscillation (MJO) from advancing to the Indian Ocean, said Abhilash Sukumarapillai, director of Advanced Centre for Atmospheric Radar Research (ACARR), Cochin University of Science and Technology.
“That is the primary cause of monsoon onset delay,” Sukumarapillai told South First.
Variations of MJO influence monsoon
MJO is a system involving clouds, rainfall, winds, and pressure that traverses the tropics and returns to its starting point in 30 to 60 days. Its variations influence the monsoon onset over Kerala around 1 June.
An ACARR study showed that out of eight MJO phases, the first and the third are the most conducive to the formation of storm systems over the Arabian Sea.
“By the end of this week, when the MJO moves toward the Indian Ocean, the arrival of the monsoon will be smoother,” Sukumarapillai said.
A more static and slower phenomenon is the El Niño, involving surface warming of the central and eastern tropical Pacific Ocean.
Alternating with a cool phase called La Niña, and together with the Southern Oscillation denoting the large-scale fluctuations in air pressure between the western and eastern tropical Pacific, they cause El Niño/La Niña Southern Oscillation (ENSO), which influences global weather.
El Niño is associated with droughts in India.
IMD expects minimal impacts
While awaiting the monsoon’s onset, India Meteorological Department (IMD) expects minimal El Niño impacts later in the season. The World Meteorological Organization (WMO) has noted that after eight warmest years on record, an El Niño could spike global heating.
Even more remotely, polar climate variability is affecting the monsoon, scientists said. Climate variability involves deviations of climatic statistics over a month, season or year when compared to long-term statistics for that period. ENSO and MJO are examples.
Meanwhile, climate change refers to a statistically significant variation in either the mean state of the climate or its variability, persisting for extended decades or even longer.
“Polar climate variability has a significant relationship with the Indian monsoon,” said Madhavan Nair Rajeevan, Ministry of Earth Sciences distinguished scientist at the National Centre for Earth Science Studies (NCESS), Thiruvananthapuram.
“Especially the Arctic warming and Arctic sea ice could be impacting the Indian monsoon,” he said.
Indian summer monsoon rain varies on different time scales.
Variability influenced by conditions like ENSO
“This variability is influenced by tropical ocean conditions, especially ENSO and other slowly varying conditions like sea ice, snow cover and soil moisture,” Rajeevan noted in a recent talk.
“The Arctic and the Antarctic regions are the cooling chambers of our planet. Having a very limited supply of solar radiation, they attract warm air and ocean currents from the tropics, cool them down and send them back towards the equator. This way, the polar regions regulate the distribution of heat on the Earth,” Rajeevan said.
This mechanism depends on the interactions between sea ice, glaciers, the ocean, and the atmosphere.
There are several routes for this polar influence. They include mid-latitude air circulation that moves massive amounts of heat towards the poles, Atlantic Meridional Overturning Circulation (AMOC) that involves a large system of ocean currents that carry warm water from the tropics northwards into the North Atlantic, and ENSO.
Several studies suggest that the loss of Arctic sea ice and associated changes could weaken the Indian summer monsoon, reduce rain during the season, and increase the frequency of heavy precipitation events.
It will, however, be premature to comment anything on Kerala based on this relationship, Rajeevan said.
Impact of Arctic climate on Indian subcontinent
The polar connection has been at work for over a 1,000 years. National Centre for Polar and Ocean Research’s Vikash Kumar and colleagues probed a half-metre sediment sample from the seafloor near an ice-covered Norwegian Arctic archipelago to understand sea conditions between AD 1106 and AD 1967.
They found warm and cold Arctic climatic spells were connected to respective intense and weak rainfall over the Indian subcontinent.
The question is what happens in a changing climate?
The Arctic region is undergoing some of the most noticeable signs of climate change as the sea ice changes, snow cover shrinks, ice sheets melt, glaciers retreat and permafrost thaws. Arctic surface air temperature has increased four times faster than the global average as the effect of climate change.
“More rapid warming of the Arctic can have a direct impact on the monsoon,” Kumar told South First.
As Rajeevan puts it, “More exploratory data analysis and coupled climate model studies are required for better understanding.”