Observing Forbush decreases in cloud at Shetland

Meteorological measurements from Lerwick Observatory, Shetland (60 degrees 09'N, 1 degrees 08'W), are compared with short-term changes in Climax neutron counter cosmic ray measurements. For transient neutron count reductions of 10-12%, broken cloud becomes at least 10% more frequent on the neutron minimum day, above expectations from sampling. This suggests a rapid time scale (similar to 1 day) cloud response to cosmic ray changes. However, larger or smaller neutron count reductions do not coincide with cloud responses exceeding sampling effects. Larger events are too rare to provide a robust signal above the sampling noise. Smaller events are too weak to be observed above the natural variability. (C) 2010 Elsevier Ltd. All rights reserved.