Meteorological and Cosmic Ray Measurements in North Wales


Natural radioactivity can make each of the Geiger counters fire (shown as        on the diagram) separately, causing one event to be counted.

However, cosmic rays travel so fast that they can make the two Geiger counters fire almost simultaneously. An electronic circuit can be used to identify these coincidences. A cosmic ray detector like this is called a cosmic ray telescope.


We have been measuring atmospheric solar radiation and cosmic rays at and near Snowdon Summit in North Wales since 2005. This website presents near real-time data from Snowdon Summit; archive data is also provided to view and download.

The equipment includes a cosmic ray detector. Cosmic rays are high-energy particles from outer space, beyond the solar system. They continually enter Earth's atmosphere, where they hit molecules of air and create air showers, cascades of more high-energy particles. This apparatus counts the number of cosmic ray particles (muons) produced by the air showers.

Since cosmic rays interact with the air, it is possible that they could indirectly affect the weather or radiation (light and heat) in Earth's atmosphere. To test this idea, the experiment includes two different types of radiometer, instruments that measure light and heat. Comparing the radiometer measurements to the cosmic ray counts helps scientists to understand processes in the air above us.

Because cosmic rays come from space, the cosmic ray counts increase with height. This is why the results from a mountain site are interesting.

Cosmic Ray Station

The cosmic ray data are

freely available online.

Snowdon Mountain
Snowdon cosmic ray

The top section of the plot (right, click to enlarge) shows solar radiation (i.e. sunshine) as black points, and sunshine reflected from the ground as green points (in summer, little sunshine is reflected; in winter most sunshine can be reflected due to snow). The middle portion of the plot shows a Geiger counter, measuring natural radioactivity which is recorded here in counts per minute (cpm). The white lines in the middle of the Geiger plots trace a 6 hour average. The lower portion of the plot indicates daily cosmic ray events. Older data (Nov 2016 - March 2017) are available here.

The plot is updated regularly (up to every 15 minutes) but the nature of this remote site means there are inevitably delays sometimes in providing fresh data. The most recent data is shown on the plot.

Real time radioactivity and cosmic ray data

Cosmic Ray Station

Cosmic Ray Station

Cosmic Ray Station

Cosmic Ray Detector

Geiger counters are used to detect high-energy particles in the air, mostly from natural radioactivity emitted by the soil, but sometimes also from cosmic rays. Two Geiger counters are used here.

Further Information

Contact: Karen Aplin (PI)

This outreach project is currently funded by the Royal Astronomical Society's RAS200 project.
It has previously been funded by
STFC, NERC, and the Royal Meteorological Society.

              counter firing annotation
Cosmic ray triggers detectors together
Radioactivity triggers detectors separately

Further Information