The Stormy Sun-Earth Connection

lightning
A powerful lightning storm strikes from clouds to the sea near the city of Hong Kong. Solar activity may play a role in strikes like these. d3sign/Getty Images

When you got outdoors for play or work, it probably never occurs to you that the lovely yellow Sun that heats and warms our planet is also responsible for a whole raft of other actions that affect us and our planet. It's true — and without the Sun we wouldn't have the beauty of the northern and southern lights, or — as it turns out — some of the lightning strikes that come during thunderstorms. Lightning strikes?

 Really? Let's take a look at how that might be a solar effect.

The Sun-Earth Connection

The Sun is a somewhat active star. It regularly sends out giant outbursts called solar flares and coronal mass ejections. The material from these events rides out from the Sun on the solar wind, which is a constant stream of energetic particles called electrons and protons. When those charged particles get to Earth, some interesting things can happen. 

First, they encounter Earth's magnetic field, which protects the surface and lower atmosphere from the solar wind by deflecting the energetic particles around the planet. Those particles DO interact with the topmost layers of the atmosphere, often creating northern and southern lights. If the solar "storm" is strong enough, our technology can be affected — telecommunications, GPS satellites, and electrical grids — can be disrupted or even shut down. 

What About the Lightning?

When these charged particles  have enough energy to penetrate down into the cloud-forming regions of the Earth's atmosphere, they can affect our weather.

 Scientists found evidence that some lightning strikes on Earth may well be triggered by energetic particles from the Sun that reach our planet via the solar wind. They measured significant increases in lightning rates across Europe (for example) that occurred for up to 40 days after the arrival of particles carried by high-speed solar winds.

 

Nobody's quite sure how this works, but scientists are working to understand the interactions. Their data show that electrical properties of the air are somehow changed as the incoming charged particles collide with the atmosphere.

Can Solar Activity Help Weather Prediction?

If you could predict an increase in lightning strikes by using solar wind streams, that would be a real boon to weather forecasters. Since the solar wind can be tracked by spacecraft, having advance knowledge of solar wind storms would give weather forecasters a significant chance to warn people about upcoming thunder and lightning storms and their severity.

It turns out that astronomers have long known that cosmic rays, which are tiny high-speed particles from across the universe have been thought to play a part in severe weather on Earth. The ongoing studies of charged particles and lightning shows that lower-energy particles created by our own Sun also affect lightning.

This is related to a phenomenon called "space weather" which is defined as geomagnetic disturbances caused by solar activity.  It can affect us here on Earth and in near-Earth space. This new edition of the "Sun-Earth" connection, lets astronomers and weather forecasters learn more about both space weather and Earth weather.

How Did Scientists Figure This Out?

The record lightning strikes over Europe was compared with data from NASA's Advanced Composition Explorer (ACE) spacecraft, which lies between the Sun and the Earth and measures the characteristics of solar winds. It is one of NASA's workhorse space weather and solar activity observatories.

After the arrival of the solar wind at the Earth, the researchers showed there was an average of 422 lightning strikes across the UK in the following 40 days, compared to an average of 321 lightning strikes in the 40 days before the solar wind's arrival. They noted that the rate of lightning strikes peaked between 12 and 18 days after the arrival of the solar wind. Long-term studies of the connection between the Sun's activity and Earthly thunderstorms should give scientists useful tools not just for understanding the Sun, but also to help predict storms here at home.