Rain, wind bring pollution down

NEW DELHI: North India , which is in the midst of a wet spell that’s likely to last till Saturday, can expect more rain just after Holi next week, with temperatures generally remaining below normal for the next 14 days, the met department forecasts.This is a continuing pattern of very frequent weather disturbances, which set in after the record-breaking chill across the region in December. Meteorologists say this pattern of rapid succession of western disturbances (WDs) hitting north India may be linked to unusual weather unfolding far, far away — a record freeze in the Arctic region.Arctic sea ice cover — for long a stark reminder of global warming because of its rapid decline — is actually at a 10-year high this winter, according to Weather.com.What’s causing the freeze is a wind circulation called the polar vortex, which has been the strongest on record this season.The polar vortex is an anti-clockwise moving current that circles the Arctic region. A strong vortex keeps the Arctic cold trapped within the polar region.“A record strong polar vortex supported by other global forcings has led to 20 WDs hitting north India since January 1, which is likely to be a record of sorts,” said R K Jenamani , senior scientist at the IMD ’s National Weather Forecasting Centre here.A western disturbance is a pulse of low pressure that travels east from southern Europe, and usually brings wet weather to north India. The normal number of such WDs impacting north India in January-February is around 12. This year, however, there has been one every three-four days.Not all WDs bring rain/snow in north India. But the disturbance does lead to a change in wind direction, a rise in temperature during the approach and a fall thereafter. The high frequency of WDs has prevented temperature extremes during this winter, after the record cold spell in December,” Jenamani said.There were as many as 10 WDs this January. Six of these were “active”, which mean these caused rain and snow. This resulted in countrywide rainfall being 73% higher than normal. While nine WDs were recorded in February, only two were active ones. Which is why February recorded subdued rainfall.However, the WD that hit India on March 3 is an active one, and is likely to cause rainfall and snow in the higher hills till Saturday. Till 8.30am on Thursday, Delhi’s Safdarjung observatory recorded 4.2mm rainfall, while Palam recorded 5.6mm.Friday is forecast to be cloudy with moderate rain or thundershowers, and hailstorms in a few areas. The maximum and minimum temperatures in the city will be around 23 and 14 degrees Celsius, respectively.The frequent WDs, and the resulting rain, change in wind direction and/or strong winds, have also helped keep air pollution levels down. Thursday’s rain was no exception. “An improvement to the lower end of satisfactory to the good category is expected on Friday. The air quality is likely to stay in the good to the satisfactory category on Saturday, while the satisfactory category is predicted for Sunday,” a SAFAR report said.Another active WD is likely to impact north India on March 11 to 13, which is likely to bring wet weather across the region, the met department said.These two wet spells are also likely to keep temperatures below normal in the region for the next two weeks, according to IMD’s extended range forecast. Maximum temperatures are likely to stay below normal on average across the country during this period, according to the forecast.It is difficult to predict for how long this pattern of frequent WDs will continue, Jenamani said.