Why does lightning appear less when people are locked down because of Covid-19?

Massachusetts Institute of Technology (USA) researchers have found another effect of the blockade during the Covid-19 epidemic, which is a reduction in lightning flashes in the atmosphere.

This decrease in the number of lightning strikes coincides with a decrease in the amount of people emitting aerosols (small particles suspended in the air in the lower layers, including dust particles, smoke, water, heavy metal particles. ).

The reduction in the number of lightning bolts in the atmosphere has been recorded by scientists during the blockade because of the Covid-19 epidemic

According to scientists, aerosols in the atmosphere contribute to lightning, and human activities such as burning fossil fuels produce aerosols. When people reduce their activities, they release less aerosols, which reduces the concentration of aerosols in the atmosphere.

Physical meteorologist at Massachusetts Institute of Technology, Earle Williams, said the team used three different methods to measure lightning. "All the results show the same trend - that is, reduced lightning activity is associated with reduced aerosol concentrations," he said.

Some aerosols in the atmosphere can combine with water vapor to form clouds. Mr. Williams said when the cloud has a lot of aerosol particles will form more droplets and less likely to agglomerate into large raindrops.

The droplets stay in the cloud, contributing to the formation of small hailstones called graupels and even smaller ice crystals.

The collision between the graupel and the crystal produces negatively charged graupels in the lower part of the cloud and positively charged crystals at the top of the cloud. Scientists think the large difference in electrical charge between the two parts of the cloud is what causes lightning.

"If the air were less polluted, the clouds would create larger and warmer raindrops. That would reduce lightning activity," Mr. Williams said.

As countries close and blockade during the pandemic, people release less aerosols into the atmosphere. Thermal power plants also reduce capacity. People drive less. Similarly, pollution from aviation activities is also significantly reduced.

This reduction in pollution is likely the main reason why Mr. Williams and his colleagues observed a decrease in the number of lightning strikes. These include lightning strikes to the ground, lightning in the clouds, lightning between clouds and the air.

During the peak period of lockdown in countries, researchers measured lightning strikes that were 19% less frequent than the annual average.

In addition, the study also found that the places where the amount of aerosols in the atmosphere decreased more sharply were the places where the lightning decreased the most.

Southeast Asia, Europe, and much of Africa saw the steepest reductions in both aerosols and atmospheric lightning, while the Americas experienced negligible changes.