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Explained: How a warm Pacific has stolen your winter

Among the biggest El Niños in history — the same phenomenon that hit the 2015 monsoon — is now producing unusually warm temperatures across India.

Written by Amitabh Sinha
January 8, 2016 12:51:20 am
el-nino In India, the warming impact of El Niño on winter is extra pronounced this year. It has overshadowed the effects of local weather patterns that are usually more prominent at this time of the year.

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. In parts in western Rajasthan on Wednesday, the average temperature was 8 degrees Celsius above normal.

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, the ‘Godzilla’

In India, the impact of El Niño is felt as suppressed monsoon rainfall. 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 and Europe, and dry spells in India, Indonesia and Australia. There is a strong correlation between an El Niño event and a poor monsoon in India.

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What has been noticed somewhat less is that winters that follow an El Niño event are slightly warmer than usual. Scientists say the Pacific warming spreads to the Indian Ocean with a lag of about 2-3 months, leading to a warming over the subcontinent. Past data provides some evidence for this, though the warming is not very noticeable every time, mainly because local factors override the impact of 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, and the latest advisory from the National Oceanic and Atmospheric Administration (NOAA) of the US says the current El Niño “will rank among the three strongest episodes” since 1950.

Many are calling this the “Godzilla” El Niño. It has already resulted in record rainfall events in California, and the warmest ever December — 8 degrees Celsius warmer than normal, according to a BBC report a few days ago — in the UK. Some of the worst wildfires in Indonesia have occurred this year, are being attributed to the El Niño.

In India, the warming impact of El Niño on winter is extra pronounced this year. It has overshadowed the effects of local weather patterns that are usually more prominent at this time of the year. The El Niño could lead to 1-2 degrees Celsius abnormal rise in temperatures this season, according to J Srinivasan of the Divecha Centre of Climate Change at the Indian Institute of Science, Bangalore.

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 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.

Scientists say that these two systems together have prevented the penetration of the Westerlies into northern and central India, thereby denying these areas their winter rain. Rainfall in the country as a whole was 86 per cent below normal in the last week of December, and 68 per cent below normal in the first week of 2016.

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