PINAKI MAJUMDAR
Jamshedpur, May 7: Jharkhand or for that matter most states of eastern India including neighbouring Bihar and Bengal have had fewer of their trademark pre-monsoon thunderstorms called Nor’westers over the past few years.
This year not a single Nor’wester (or Kalbaishakhi in local parlance) hit Jharkhand resulting in extreme temperatures and relentless heat waves which continued for the last one fortnight
Weather scientists say they are unsure whether this decline or the vanishing act of Nor’westers just reflects natural fluctuations or indicates a long-term trend.
The Nor’westers – set off by a combination of eastern Indian topography, ground heating and moisture incursion into the atmosphere – normally hit Jharkhand and its neighbouring states between March and May every year. But, unfavourable atmospheric conditions appear to have reduced their frequency.
The weather dynamics of Nor’westers in Jharkhand
Jharkhand normally experiences nine to 10 high-intensity storms with thundershowers driven by the moisture incursion from the Bay of Bengal during the Nor’wester season, but the state’s storm count has fluctuated from 15 in 2012 to six in 2013, seven in 2014, six in 2015. In the subsequent years, it shows a declining trend.
“Humidity plays an important role, but westerly winds dominating during April and May has prevented moisture incursion and hence, it prevented the storm,” explained, Abhishek Anand, the director of Ranchi Meteorological Centre. Not a single storm took place in April And May so far because of such unfavourable conditions, he added.
Under prevailing conditions, cloud shells formed at relatively low heights and were unable to retain moisture – this is said to be unfavourable for rain and storms. Such clouds should form at a height of at least 12 km for them to trigger storms and rain, pointed out a senior weather official at Patna Met Centre, which too monitors weather conditions of Jharkhand.
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“Dry westerly winds are unfavourable for Nor’westers,” explained another weather official who is also the agrometeorology adviser at Birsa Agricultural University in Kanke, on the outskirts of Ranchi.
Jharkhand’s plateau topography is a key factor that influences the birth of Nor’westers.
“Topography doesn’t change, other factors do,” said a senior scientist at India Meteorological Department, New Delhi, who has been studying Nor’westers and their mechanisms for over a decade now.
When the day’s temperature rises six degrees above normal, excess ground heating of land results in convective currents that help in the formation of low cumulonimbus clouds bringing rain and gusty winds, brewing a typical Nor’wester, he explained.
The heat and humidity over the Chotanagpur Plateau help thunderclouds to form and travel east, said a duty officer at IMD, Ranchi.
“This year some districts close to Bengal experienced easterly winds, but the flow was too weak for adequate moisture incursion – unless the winds are strong, they cannot trcigger a storm,” pointed out the duty officer.
Climate change’s effect on Nor’westers uncertain but thundershowers expected in Jharkhand
Scientists say the impact of global warming-induced climate change on Nor’westers is still unclear.
“Intense heating means more convection, which should actually translate into more storms,” said a Met official.
He went on to say, “But, nature has its own checks. Cloud formation reduces the amount of solar radiation falling on a surface, which could lower ground heating. We really don’t know what impact, if any, global warming has or will have on Nor’westers.”
Whatever be the reason but weathermen in Jharkhand are apprehensive of thundershowers activity in isolated areas in the next few days.
“Situations are becoming conducive for Nor’wester activity over Jharkhand. We are expecting moderate to heavy rain accompanied by lightning at some places and hail storm activity in the next one or two days, ” said an official at Ranchi Met Centre.
