Monday, January 23, 2012

No respite from biting cold till March; February maybe winter at its harshest; above normal monsoons, floods highly likely this year


The colder than normal, if not harsh winter in South Asia can be attributed to the combined effect of La Niña and the Indian Ocean Dipole (IOD), oceanic processes in the Central Pacific and Indian Ocean, respectively. Both factors tend to draw the cold air of higher latitudes to the tropical and sub-tropical Asia.

The La Niña appeared to have peaked this month with NIÑO3.4 values at 0.8 deg C and Southern Oscillation Index (SOI) value at +12.8. The La Niña has started to markedly weaken with most models suggesting an end of the event during the coming autumn season. But as the late John Daly, a great among climatologists, observed, the Southern Oscillation is the primary driver of year-to-year global temperature, with a 6 to 9 month lag time.

Accordingly, while the La Niña has peaked and weakening, its impact on global temperature is just starting to kick in. We are now seeing the La Niña effect beginning to be the prime driver of winter in the Northern Hemisphere. Winter had been mild within the mid-latitudes till mid January because Arctic Oscillation (AO) and its cousin North Atlantic Oscillation (NAO) had been in their positive phases. But a pattern change has taken place with winter intensifying despite the AO and NAO remaining largely positive as the La Niña is beginning to swamp their effect.

Joe D'Aleo reports: "The Northern Hemisphere came hard out of the box early with well above normal snow. Then a strng [polar vortex] took over and preventing the snow from expanding very far into the lower 48 and west into Europe. A breakdown of that vortex is underway and snow has started to fall in the northern US and in Europe. Here is the current snowpack."




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