More than half the winter is gone and most of India has hardly even noticed the cold. Temperatures are 4-5 degrees Celsius above the normal for this time of the year.
This could turn out to be the warmest winter in India in several years. Scientists are blaming both global and regional/local factors. Globally, it is the persisting El Niño phenomenon, one of the strongest ever, that is believed to be having a warming effect over the Indian subcontinent. The warmer winter in India is part of a global weather pattern dictated by an unusual warming of ocean waters thousands of miles away.
At the more local level, the lack of winter rain, caused by a combination of atmospheric processes — some of them unexpected and unusual at this time of the year — has kept the chill away.
El Niño refers to a condition in the equatorial Pacific Ocean, off the coast of Peru and Ecuador, in which sea surface temperatures become unusually warm. This warming of the sea influences weather events across the globe, resulting in enhanced rainfall in the US (California) and Europe (Britain), and dry spells in India, Indonesia and Australia. Some of the worst wildfires in Indonesia have occurred this year, are being attributed to the El Niño.
The current El Niño, however, is one of the longest and strongest ever. By the time neutral conditions are expected to be established in the Pacific Ocean later this year, the El Niño would have persisted for 15 months, spanning two seasons. Some scientists had called it a “double El Niño” last year.
The Absent Westerlies
The last week of December and first week of January see rain in most of Northern and Eastern India. It pulls down temperatures, and introduces a chill in the air. This rain is brought by the Westerlies, a wind system that moves in the mid-latitudes, 30 to 60 degrees, in the northern hemisphere from west to east. These winds shift slightly southward during this time, and flow through most of northern and central India.
This year, the Westerlies have been kept north of the Indian landmass by two different wind systems.
- An anticyclonic wind system (High pressure system) that is usually located south of the Indian peninsula has been pushed northward, and is located where the Westerlies are usually found at this time of the year. This anti-cyclonic system is warmer and drier.
- Around the same latitude, but much higher in the atmosphere, are located another wind system called the Jetstreams. The Jetstreams, also moving west to east, are found in the upper troposphere, between 5 km and 12 km above the earth’s surface. These generally operate in the mid-latitudes, north of the Indian landmass. But this year, they are positioned much to the south, aligned to the foot of the Himalayas and the Gangetic plains.
- These two systems together have prevented the penetration of the Westerlies into northern and central India, thereby denying these areas their winter rain.