Deep Underground Reveal Secrets Of Upper Atmosphere
Cosmic-rays detected half a mile underground in a disused U.S. iron-mine can be used to detect major weather events occurring 20 miles up in the Earth’s upper atmosphere, a new study has revealed.
Published in the journal Geophysical Research Letters and led by scientists from the UK’s National Centre for Atmospheric Science (NCAS) and the Science and Technology Facilities Council (STFC), this remarkable study shows how the number of high-energy cosmic-rays reaching a detector deep underground, closely matches temperature measurements in the upper atmosphere (known as the stratosphere). For the first time, scientists have shown how this relationship can be used to identify weather events that occur very suddenly in the stratosphere during the Northern Hemisphere winter. These events can have a significant effect on the severity of winters we experience, and also on the amount of ozone over the poles – being able to identify them and understand their frequency is crucial for informing our current climate and weather-forecasting models to improve predictions.
Working in collaboration with a major U.S.-led particle physics experiment called MINOS (managed by the U.S. Department of Energy’s Fermi National Accelerator Laboratory), the scientists analysed a four-year record of cosmic-ray data detected in a disused iron-mine in the U.S. state of Minnesota. What they observed was a strikingly close relationship between the cosmic-rays and stratospheric temperature – this they could understand: the cosmic-rays, known as muons are produced following the decay of other cosmic rays, known as mesons. Increasing the temperature of the atmosphere expands the atmosphere so that fewer mesons are destroyed on impact with air, leaving more to decay naturally to muons. Consequently, if temperature increases so does the number of muons detected.
What did surprise the scientists, however, were the intermittent and sudden increases observed in the levels of muons during the winter months. These jumps in the data occurred over just a few days. On investigation, they found these changes coincided with very sudden increases in the temperature of the stratosphere (by up to 40 deg C in places!). Looking more closely at supporting meteorological data, they realised they were observing a major weather event, known as a Sudden Stratospheric Warming. On average, these occur every other year and are notoriously unpredictable. This study has shown, for the first time, that cosmic-ray data can be used effectively to identify these events.