Density of Atmosphere and Cosmic Rays
I attended a presentation by a high school student who is
a member of QuarkNet. He performed a cosmic ray flux experiment
looking for changes in flux looking vertically with coincident
counters. A thunderstorm occurred during his overnight collection,
calibration, etc. seemed to be appropriate.
The student claimed that the decrease in flux was due to a
higher density in the atmosphere (liquid and solid water in the
clouds is denser than atmospheric gases). I thought that since the
barometric pressure was low, the density would be less (p = rho * g *
delta y). Please help us understand what happens to the density of
the atmosphere during a thunderstorm.
Also, if there are any suggestions about improving the controls in
this experiment, it would be greatly appreciated.
The density of the air is less in low pressure areas, so
I do not think that that is the physical consideration.
A better explanation of the reduced flux may be that
hydrometeors (water droplets, ice crystals, and even
hail) in the thunderstorm and surrounding clouds
absorbed cosmic radiation as it came through the
atmosphere, thereby preventing it from reaching the
vertical column of air that he was measuring.
David R. Cook
Climate Research Section
Environmental Science Division
Argonne National Laboratory
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Update: June 2012