The unusually cold weather in the hill states of North India and parts of the plains, including the New Delhi, has been indirectly caused by the Polar Vortex that spins over the North Pole.Arctic winds are pushing various weather systems, including the western disturbance, downwards. It has indirectly resulted in severe and extended winters. The intensity and frequency of western disturbance have also increased.

                                           LEARNING WITH TIMES
The polar vortex is a large area of low pressure and cold air surrounding the Earth’s North and South poles. It ALWAYS exists near the poles, but weakens in summer and strengthens in winter.
The term vortex refers to the counter-clockwise flow of air that helps keep the colder air close to the poles. Often during winter in the Northern Hemisphere, the polar vortex will become less stable and expand, sending cold Arctic air southward.This is not confined to the United States. Portions of Europe and Asia also experience cold surges connected to the polar vortex.
These vortices exist because in the wintertime, the air that’s high over the poles gets really, really cold. That drastic contrast with the temperatures farther away from the pole, and the pressure contrast that results, cause really fast winds — with speeds of between 120 and 250 miles (193 and 402 kilometers) per hour — to swirl around the big pocket of cold air.results is a huge spinning cyclone with cold air inside it
The polar vortex doesn’t quite run that smoothly. For one thing, its shape typically is a bit irregular in its boundaries, with areas known as troughs where the cold air extends away from the pole, and other areas called ridges, where the warm air pokes toward it.

Additionally, the high-speed winds that form the polar vortex’s barrier can change in intensity from time to time. If the winds weaken too much, that can distort the vortex and make its boundaries even more irregular, so that a whole lot of cold air heads southward.