According to a new study published in the journal Nature Communications, the underlying physical process that creates ‘breaking wave’ cloud patterns in Earth’s atmosphere also frequently opens the gates to solar wind plasma that perturbs the planet’s magnetosphere.
Kelvin-Helmholtz instability clouds. Image credit: Astronautilus, rodjonesphotography.co.uk / CC BY 2.0.
The phenomenon involves ultra low-frequency Kelvin-Helmholtz waves (named for 19th century scientists Lord William Thomson Kelvin and Hermann von Helmholtz), which are ubiquitous throughout the Universe and create the distinctive patterns – from Earth’s clouds and ocean surfaces to atmospheres of Jupiter and Saturn to the Sun’s corona, but were not thought to be a common mechanism for changing the dynamics of Earth’s magnetic field.
“Our paper shows that these waves, which are created by what’s known as the Kelvin-Helmholtz instability, occur much more frequently than previously thought,” said co-author Dr Joachim Raeder of the University of New Hampshire.
“And this is significant because whenever the edge of Earth’s magnetosphere, the magnetopause, gets rattled it will create waves that propagate everywhere in the magnetosphere, which in turn can energize or de-energize the particles in the radiation belts.”
Dr Raeder and his Ph.D. student Shiva Kavosi surveyed seven years of in situ data from the NASA’s THEMIS mission and found that Kelvin-Helmholtz waves actually occur 19% of the time at the magnetopause and can change the energy levels of our planet’s radiation belts.
These changing energy levels can have impacts on how the radiation belts either protect or threaten spacecraft and Earth-based technologies.
“Previously, people thought Kelvin-Helmholtz waves at the magnetopause would be rare, but we found it happens all the time,” Dr Raeder said.
“In clouds, you see it because the lower atmosphere is more stagnant and you have a higher speed wind going over it, which creates that distinctive swirl pattern,” Kavosi said.
“The phenomenon is really ubiquitous in nature. Often, the waves are present in the atmosphere but not visible if there are no clouds. In that case, pilots cannot see them and aircraft may experience severe and unexpected turbulence.”
_____
Shiva Kavosi & Joachim Raeder. 2015. Ubiquity of Kelvin–Helmholtz waves at Earth’s magnetopause. Nature Communications 6, article number: 7019; doi: 10.1038/ncomms8019
