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  • Last Update : 08:39 pm

Under the weather

  • Published at 06:16 pm April 30th, 2018
  • Last updated at 01:23 pm May 3rd, 2018
Under the weather

It is not unlikely that Kalboishakhi or Nor’westers with hails and lightning will occur during the pre-monsoon season (March-May) in Bangladesh.

However, this week we have observed Kalboishaki almost every day, with storm winds of around 80km per hour peppered with lightning storms. Many scientists have linked such unusual extreme weather events with climate change triggered by global warming.

Global warming and climate change

However, extreme event attribution is the subject of considerable debates and confusion in the media. To overcome this challenge, event attribution research should be conducted in order to investigate the contribution of anthropogenic climate change to the probability of occurrence of specific events. Multi-model ensemble simulations of the climate model can help detect climate change signals for such extreme events.

With the help of high resolution Global Circulation Models (GCM), it is possible to adequately reproduce the dynamics associated with extreme weather events with or without climate change.

However, it is also true that extreme event attribution will not be able to provide evidence of any anthropogenic traces for every extreme event.

Due to the lack of recorded data or greater computational powers, it is not always possible to conduct such studies which are essential for claiming loss and damage attributed from climate change.

A lightning bolt carries around 30 kilo-amps of electrical current when it makes contact with the ground. Considering the rate of mortality from lightning strikes, it is the second most lethal form of natural disaster in the country

El Niño–Southern Oscillation (ENSO)

At this moment, we can observe two active large scale atmospheric processes: After closely monitoring the Sea Surface Temperature (SST) of the Niño regions in the Pacific Ocean, La Niña, the cooling phase of the El Niño–Southern Oscillation (ENSO) has been confirmed.

It has met the criteria of all the four seasons of three months each during which the SST is below about 0.5 degrees Celsius than the long-term (30 years) average.

However, it is expected that a gradual return from the La Niña conditions to neutral conditions will be observed from April to May.

Under the La Niña conditions, winters tend to feature cooler-than-average conditions. In the first week of January, North America’s East Coast is shivering in a record-breaking cold wave termed the “bomb cyclone” that dumped snow as far south as Florida.

In many parts of the US and Canada, temperatures were fall below -29C, bringing with it record-low temperatures. In Oymyakon, Russia, the temperature was recorded as low as -67C -- the second lowest recorded temperature in their history.

This winter, Bangladesh experienced its lowest recorded temperature in 50 years on January 9, as the mercury dropped to 2.6C in Tetulia upazila, Panchagarh.

La Niña also caused heavy rains over Malaysia, the Philippines, and Indonesia. The teleconnections between La Niña and the heavy precipitation over the Indian sub-continent is yet to be established. However, we have observed severe floods in the Ganges-Brahmaputra-Meghna basins during the La Niña years, which include 1974, 1984, 1988, 1998, and 2017.

Madden–Julian oscillation (MJO)

Another large-scale coupling between atmospheric circulation known as Madden–Julian oscillation (MJO) affect global weather patterns as well as the Indian summer monsoon.

This is a travelling pattern that propagates eastward at approximately 4 to 8 m/s through the atmosphere above the warm parts of the Indian and Pacific oceans. It is a pulse of cloud and rains, and has a cycle of about 45 to 60 days.

According to Skymet weather report, in the last four days, the MJO has been in the Indian Ocean. Due to its present position, rainfall activity has increased over Indonesia, Sri Lanka, the Maldives, and has even extended up to South India. It will again likely revisit during June of this year when enhanced monsoon rain is expected.

Thunderstorms and lightning

The influence of global warming, La Niña conditions, and the entrance of MJO in the Bay of Bengal regions for the last couple days should have influence on recent occurrences of strong thunderstorms and lightning.

Every year, more than 200 people die in Bangladesh in lightning strikes as per reports from various newspapers. In 2016, the government declared lightning as a disaster after the death of about 65 people within two days, from lightning strikes.

Lightning strikes the Earth more than 100 times each second, totalling 8 million times every day. A lightning bolt carries around 30 kilo-amps of electrical current when it makes contact with the ground.

Considering the rate of mortality from lightning strikes, it is the second-most lethal form of natural disaster in the country.

However, spreading lightning safety awareness can help save a lot of lives. The most important thing to do is take shelter from lightning storms if you are outdoors. When you first hear thunder, you should immediately seek shelter.

AKM Saiful Islam is a Professor of the Institute of Water and Flood Management at BUET.

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