Friday, January 23, 2009

Cosmic Ray Decay Reveals Secrets of the Stratosphere

Not Brand Echh! © Marvel Comics
The number of high-energy cosmic-rays reaching a detector deep underground, closely matches temperature measurements in 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.

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 surprised the scientists was 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 oC 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. link

Ref.: Sudden stratospheric warmings seen in MINOS deep underground muon data. S.M. Osprey et al., Geophys. Res. Lett. in press.