If you are down South, you already must be feeling the nip in the air and if you are up North, then it's sweater season! Well, all of this is courtsey, La Nina. This is the second time in a row that oceanic and atmospheric phenomenon has occurred and is impacting weather patterns around the globe. La Nina means 'Little Girl' in Spanish. Now that we have got the literal meaning out of the way, here is what it means for the climate.

What is La Nina?
A natural ocean-atmospheric phenomenon, it is marked by the cooler-than-average sea surface temperatures across the central and eastern Pacific Ocean near the equator. Also known as El Viejo or anti-El Nino (warmer-than-average sea surface temperatures across the same region).

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How does this phenomenon actually begin?
A cooler patch of water over the Pacific Ocean needs to react with the atmosphere for this phenomenon to occur. When a build-up of these cooler-than-usual waters occurs, La Nina happens between the Tropic of Cancer and the Tropic of Capricorn. The very strong trade winds on their way east plus the ocean currents cause colder water to rise to the surface, causing an upswelling. It is this upswelling that brings about a frigid drop in sea-surface temperatures.

But how is it possible that it affects the climatic condition of the entire world?
La Nina affects three parameters — atmospheric pressure, atmospheric circulation and the rainfall patterns. The large-scale movement of air, known as atmospheric circulation, when combines with the ocean current, distributes thermal energy and thus, these changes create variability in climate across the globe.

So, what effect will it have on India?
La Nina is usually related to harsher winters in India, especially in the northern part of the country. Temperatures are expected to drop down to three degrees, especially in January and February and severe winter shivers will be setting in and unexpected rains will lower the temperature further.

How does it affect the other parts of the world?
While the phenomenon causes below-normal temperatures across Northern Hemisphere, draughts are the norm in Southern US and flooding in Pacific Northwest and Canada.