When solar wind hits the magnetosphere, it creates breaking waves known to scientists as Kelvin-Helmholtz waves. This wave activity is seasonal, researchers found; it increases around the spring and fall seasons (equinoxes) and decreases around summer and winter (solstices).
Newswise — New knowledge on "space waves" could potentially lead to improved space-weather forecasts and safer satellite navigation in radiation belts, as stated by researchers at Embry-Riddle Aeronautical University.
As per the recent publication in the journal Nature Communications on May 4, 2023, by the researchers at Embry-Riddle Aeronautical University, their latest study reveals that alterations in the Earth's magnetic inclination towards or away from the Sun, occurring on a seasonal or daily basis, can prompt modifications in space waves with long wavelengths.
The Kelvin-Helmholtz waves, which manifest at the interface of the Earth's magnetic field and the solar wind, are susceptible to occurrence during the transitional periods of spring and fall, as per the findings of the researchers. Conversely, these waves tend to be less frequent during the summer and winter seasons.
The Sun emits plasma or solar wind, which moves at velocities of up to 1 million miles per hour, and transfers energy, mass, and momentum to the Earth's magnetic shield. In the process, it creates space waves.
Due to the resistance provided by the Earth's magnetic shield, high-speed solar wind cannot penetrate it directly. As a result, the solar wind rumbles along the magnetosphere, causing Kelvin-Helmholtz waves with peaks as high as 15,000 kilometers and lengths up to 40,000 kilometers.
Astronaut Safety and Satellite Communication
Dr. Shiva Kavosi, a research associate at Embry-Riddle and the primary author of the "Nature Communications" paper, explained that these Kelvin-Helmholtz waves allow the solar wind plasma particles to move into the magnetosphere, which can cause changes in the fluxes of energetic particles in the radiation belt. These high-radiation areas are hazardous for astronaut safety and satellite communications. On the Earth's surface, these occurrences can affect Global Positioning Systems and power grids.
According to Kavosi, comprehending the characteristics of space waves and the factors that enhance their intensity is critical to comprehend and predict space weather. She further explained that space weather incidents are becoming a growing concern, yet in numerous instances, the mechanisms regulating it are still unknown. Thus, any advancements made in understanding the causes behind space weather disruptions would aid in the provision of more precise forecasts and warnings.
In an attempt to comprehend the origins of the seasonal and daily variations in geomagnetic activity, researchers have proposed various hypotheses. One of these is the Russell-McPherron effect, which was first explained in 1973. This theory describes why auroras are brighter and more frequent in the spring and fall, based on the interplay between the Earth's dipole tilt and a weak magnetic field near the Sun's equator.
Dr. Katariina Nykyri, who is a professor of physics and an associate director for the Center of Space and Atmospheric Research at Embry-Riddle, stated that they do not have all the answers as yet. However, their study indicates that the Russell-McPherron effect is not the sole reason for the seasonal variation of geomagnetic activities. Equinox-driven events that are influenced by the Earth's dipole tilt, as well as the R-M effects, could potentially function simultaneously.
Nykyri also stated that in the future, constellations of spacecraft in the solar wind and magnetosphere could provide a more thorough understanding of the complex, multi-scale physics of space weather phenomena. She added that such a system would enable operators of rocket launches and electrical power grids to receive advanced warnings of space weather.
The "Nature Communications" paper concludes that "KH waves activity display seasonal and daily variations, indicating the crucial role of dipole tilt in regulating Kelvin-Helmholtz instability across the magnetopause with respect to time."
The research article, “Seasonal and Diurnal Variations of Kelvin-Helmholtz Instability at Terrestrial Magnetopause,” was authored by Embry-Riddle researchers Nykyri and Kavosi; C.J. Farrugia and Jimmy Raedar of the University of New Hampshire, Institute for the Study of Earth, Oceans and Space; and J.R. Johnson of Andrews University. The DOI is 10.1038/s41467-023-37485-x. The public link is https://www.nature.com/articles/s41467-023-37485-x.
The work was supported by NASA grants (numbers 80NSSC18K0661, SA405826326 80NSSC18K1381, 80NSSC22K0304 and 80NSSC22K0515) as well as support from the Magnetospheric Multiscale mission (MMS) at the University of New Hampshire.
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