What led to unusually low temperature at Ooty’s fingerpost?

Subject : Geography

Section: Climatology

Context:

The day before Pongal dawned on Udhagamandalam, a local temperature gauge measured a frigid ground temperature of –6.3 degree celsius in the Fingerpost locality.

What had caused the mercury to dip so low in Fingerpost?

The subzero temperature is caused due to the equatorial Pacific Ocean.
The La Niña winter plus a very strong Siberian High conspired to create a cooler-than-normal winter in South India.
- In La Niña years, the winds mostly tend to come from the north and bring down the pressure trough far into peninsular India.

La-Nina winter:

This is the La-Nina winter which means heady winds blow warm water on the sea surface away from the South American mainland, roughly off the coast of Ecuador.
This heat movement across the Pacific has global consequences. Over India, the La Niña can intensify summer monsoons, bring excess rainfall, and cause colder winters.
La Niña is the opposite of El Niño, in which equatorial waters off the South American coast become unusually warmer.
- One effect is that in winter, the subtropical westerly jet over North India is pushed southward, allowing the western disturbance to create cold winters in the north.
But in La Niña years, there is a ‘highway’ of chill wind coming southward from the Siberian High, “a cold, high-pressure block of air that is occupying the central Asian region and affecting winds coming into India.

Strong Siberian High:

The Siberian High is responsible for the bitter cold of the tundra and has been known to affect the weather from Italy to the Philippines.
But this time it is “anomalously strong”.
The temperature further dropped in Tamil Nadu’s interior areas, due to the withdrawal of the northeast monsoons, which allowed the cooler dry-land winds to strengthen.

Low-pressure trough:

Unlike the El Niño-driven cold air that sweeps India between the southeast and the northwest, in La Niña years, the winds mostly tend to come from the north and bring down the pressure trough far into peninsular India.
So they cover more area and affect more people.