Radio telescope probes the relationship between cosmic rays and lightning

Nature : The connection between cosmic rays and thunderstorms is one of many phenomena being investigated by researchers using the Low-Frequency Array (LOFAR), a network of radio antennas and particle detectors spread across five European countries. When cosmic rays hit Earth’s atmosphere, they collide with air molecules and create a shower of electrically charged particles that fall toward the ground. The particles emit radio waves, which can be detected by LOFAR. The researchers noticed that the radio waves fall in orderly patterns with their polarizations neatly aligned when the weather is fair, but they get scrambled when passing near thunderclouds, which consist of layers of positively and negatively charged particles. Although lightning strikes have long been known to provide a form of electrostatic discharge between electrically charged layers in a cloud or between clouds and the ground, what triggers a lightning strike has remained a mystery. Now the LOFAR researchers propose that it may be those cosmic rays raining in from distant space that push the clouds’ electric fields past the tipping point.