THE savage cold in India, China and Japan is part of the same weather system — the Northeast Monsoon.

Monsoon is thought of as a summer phenomenon, but it simply means a seasonal change in wind — it comes from the Arab word for season, mausim.

It is driven by a huge difference in temperature between land and sea. In the summer the intense heat over Asia sends up a plume of warm air that sucks in cooler, moist air from the sea, and when that wet, southerly wind hits land it sets off the rains of the Southwest Monsoon.

As winter sets in, freezing air chills the heart of Asia, forming a colossal high- pressure system over Mongolia and Russia, but because the seas off Asia are still warm the winds are drawn down towards the warm China Seas.

The unusually intense freeze in past weeks has been set off by outbreaks of exceptionally bitter cold, dry air from the north — Oymyakon in Siberia’s so-called “Pole of Cold” hit minus 54C (-66F) last Friday. This cold air swept around Asia, flooding China and passing into India. When that cold, dry air hit the relatively warm, moist air off the Chinese coast, it also erupted into huge storms that have dropped snowfalls over Japan and parts of China.

As the Northeast Monsoon winds pick up more warmth and moisture over tropical seas, they bring heavy rains to places such as Indonesia, where rainfalls last week caused landslides in Java that killed more than 100 people.

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