When the solar wind hits the Earth’s magnetosphere, a surprising stillness ensues

The energy of the solar wind interacting with the magnetospheric “bubble” around the Earth creates waves of energy that seem to stop.

This new discovery, resulting from research by Imperial scientists, improves our understanding of the conditions around Earth that contribute to “space weather,” which can impact our technology, from orbiting communications satellites to power lines in the world. ground.

The Sun releases a flow of charged particles called the solar wind. On the surface of the Earth, we are protected from this dam by the magnetosphere, a bubble created by the Earth’s magnetic field.

When the solar wind hits the magnetosphere, waves of energy are transferred along the boundary between the two. Scientists thought the waves should ripple in the direction of the solar wind, but the new study, published today in Nature Communication, reveals that some waves do the exact opposite.

Standing waves

Previously, principal investigator Dr. Martin Archer of the Department of Physics at Imperial Oil and his colleagues had established that the boundary of the magnetosphere vibrated like a drum. When a pestle-like impulse of the solar wind hits the very front of our magnetospheric bubble, the waves rush to the Earth’s magnetic poles and are reflected.

The latest work examines the waves that form across the surface of the magnetosphere, using a combination of models and observations from NASA’s THEMIS (Time History of Events and Macroscale Interactions during Substorms) satellites.

The researchers found that when the pulses of the solar wind hit the magnetosphere, the waves that form not only come and go along the field lines of the Earth, but also travel against the solar wind.

The team used models to illustrate how the energy of the wind coming from the Sun and that of the waves going against it could cancel each other out, creating “standing waves” that involve a lot of energy but appear to be going nowhere. .

Dr Archer said: “It is similar to what happens if you try to climb an escalator down. You will feel like you are not moving at all, even if you put in a lot of effort.”

These standing waves can persist longer than those that move with the solar wind. This means they take longer to accelerate particles in near-Earth space, leading to potential impacts in areas like Earth’s radiation belts, auroras, or the ionosphere.

The researchers also say that standing waves can occur elsewhere in the universe, from magnetospheres of other planets to the outskirts of black holes.

Sound waves

The researchers also translated the electromagnetic signals from THEMIS satellites into audio, which allows us to listen to the sounds of waves crossing the magnetospheric boundary.

Dr Archer added, “While in a simulation we can see what’s going on everywhere, satellites can only measure these waves when they only give us time series and wavy lines. This type of data is actually best suited to our sense of hearing. than sight, so listening to data can often give us a more intuitive idea of ​​what’s going on.

“You can hear the deep breathing sound of the permanent surface waves lingering throughout, increasing in volume with each pulse. The higher pitched sounds, associated with other types of waves, don’t last as long.”