Researchers have solved one of the biggest mysteries behind sunspot cycles

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The Solar Cycle XRay
A solar cycle: a montage of ten years' worth of Yohkoh SXT images, demonstrating the variation in solar activity during a sunspot cycle, from after August 30, 1991, to September 6, 2001. (Credits - Wikimedia Commons)

Waxing and waning of sunspots is a part of the natural cycle of Sun. However, astronauts do not yet understand this phenomenon fully. Now, new research has brought the conclusion that particular “terminator” events are responsible for ending the sunspot cycles which means that they can be predicted in a better way. Predicting sunspot cycles would mean that advanced warning of the various types of solar storms that could change infrastructure and electronics on Earth. The study has been published in the Solar Physics and Scientific Reports

These findings are based on 140 years of solar observations. They include recordings of coronal bright points which occur during relatively calm periods on the Sun. Researchers say that movement and final disappearance of these points mark a terminator event. Scott McIntosh, an astrophysicist from National Center for Atmospheric Research, US said that this evidence was hidden in the observations for more than a century however we were not aware of what we were finding. Combination of such a wide scale of observations gives new insights to how the interior of the Sun drives solar cycle. 

A sunspot cycle lasts nearly 11 years. After a solar minimum, sunspots slowly increase in number, forming at a latitude of 35 degrees in both hemispheres before reaching the equator and then dying. This takes nearly a decade to complete, with the midpoint being called the solar maximum when the sunspot activity is highest. Recent solar maximum was in April 2014.

The coronal bright points also travel towards the equator from higher latitudes. They overlap with sunspots at some points and scientists think them to be the markers for toroidal magnetic field movement. These wrap around the Sun also moving towards equator. When magnetic fields rise to Sun’s surface, scientists propose that sunspots emerge for joining the coronal bright points. Plasma is built as the spots move and is released when one wave of toroidal magnetic field hits the another in the opposite direction on the equator. 

This release is often quite dramatic. Research tells that solar tsunami of plasma is unleashed, which travels further away from the equator at 300 metres per second. This again meets another toroidal magnetic field in the opposite direction, leading to the formation of sunspots and the cycle continues. 

Although this is a hypothesis presently with the accumulated data and educated guesswork and scientists will be testing their models when the current solar cycle ends and start again the next year. This research shows that observations and multiple data streams can unlock the discoveries which would be more difficult otherwise. Bob Leamon from University of Maryland says that the terminators were identified by observing different types of solar activity, magnetic fields, spectral irradiance, radio flux along with bright points. This shows that along with spacecrafts, we need to use all the data available to understand how things work. 

Journal Reference: Scientific Reports

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