A team of British and American scientists has discovered a new method to detect major weather events occurring 32 km up in the Earth's stratosphere. Cosmic rays, detected 0.8 km beneath the planet's surface in an obsolete iron mine, have the potential to identify weather events that happen during the Northern Hemisphere winter. Scientists from the UK's National Centre for Atmospheric Science (NCAS) and the Science and Technology Facilities Council (STFC) teamed up with colleagues from the US project MINOS to evaluate cosmic-ray data detected in a disused iron mine in the midwest state of Minnesota. The aim of the MINOS project is to investigate the properties of neutrinos (particles with zero charge and zero mass) and measure muons originating high up in the atmosphere as background noise in the detector. The four-year data showed that a number of high-energy cosmic rays (the energy charged particles from outer space that strike the Earth from every direction) reach a detector deep underground and match temperature measurements in the stratosphere (also known as the upper atmosphere), the researchers said. 'It's fun sitting half a mile underground doing particle physics,' remarked the University of Oxford's Dr Giles Barr, co-author of the study. 'It's even better to know that from down there, we can also monitor a part of the atmosphere that is otherwise quite tricky to measure.' According to the scientists, their findings provide insight into how cosmic rays can be used to identify weather events that may have a significant effect on the severity of winters that people experience. It should also be noted that the weather events may also influence the amount of ozone over the poles. Existing climate and weather-forecasting models used to improve weather forecasts would benefit considerably from new techniques to identify weather events and understand their frequency. 'Up until now we have relied on weather balloons and satellite data to provide information about these major weather events,' explained Dr Scott Osprey, lead scientist for the NCAS. 'Now we can potentially use records of cosmic ray data dating back to 50 years to give us a pretty accurate idea of what was happening to the temperature in the stratosphere over this time. Looking forward, data being collected by other large underground detectors around the world can also be used to study this phenomenon.' The scientists said the cosmic rays (also known as muons) are generated following the decay of other cosmic rays (known as mesons). Researchers recognise that when the atmosphere's temperature rises, it expands, leading to the destruction of fewer mesons on air impact. This leaves more mesons to decay naturally to muons, and so the number of muons detected increases. But what struck the scientists in this study was that they observed sporadic and sudden increases in the levels of muons during the winter months. The increases were generated in just a few days, they noted. Their assessment of the data showed that these changes coincided with sudden rises in the stratosphere's temperature. They even observed a 40°C temperature increase in some places. What they discovered was a major weather event, known as a Sudden Stratospheric Warming. These events typically occur every other year and at random, they said. Consequently, the cosmic-ray data revealed in this latest study can be used to effectively identify these events. 'This study is a great example of what can be done through international partnerships and cross-disciplinary research,' Dr Osprey underlined. 'One can only guess what other secrets are waiting to be revealed.' The results of the findings were published in the Geophysical Research Letters journal.