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Solar Modulation Corrections for Cosmic-ray Soil and Snow Sensors Using the Global Neutron Monitor Network
  • David Lewis McJannet,
  • Darin Desilets
David Lewis McJannet
Commonwealth Scientific and Industrial Research Organisation (CSIRO)

Corresponding Author:david.mcjannet@csiro.au

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Darin Desilets
Hydroinnova LLC
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Cosmic-ray neutron sensors (CRNS) have been used in many studies for measuring soil moisture and snow pack over intermediate scales. Corrections for geomagnetic latitude, barometric pressure and atmospheric humidity are well established, however, corrections for the effect of solar activity on neutron count rates have been overly simplistic, typically relying on one neutron monitor station and accounting for latitude and elevation crudely or not at all. Recognizing the lack of a generalised and scientifically robust approach to neutron intensity correction, we developed a new approach for correcting CRNS count rates based on analysis of data from 110 quality-controlled neutron monitor stations from around the world spanning more than seven decades. Count rates from each monitor were plotted against the count rates from Climax, CO, USA or Jungfraujoch, Switzerland depending on the time period covered. Relationships between relative counting rates at the site of interest versus the reference neutron monitors were found to be strongly linear. The dimensionless slope of this linear relation, referred to as τ, was shown to increase with increasing geomagnetic latitude and elevation. This dependence of τ on geomagnetic latitude and elevation was represented using an empirical relationship based on a single reference neutron monitor. This generalised approach enables τ to be derived for any location on Earth and also lends itself to roving CRNS studies. The correction procedure also includes a location-dependent normalisation factor which enables easy substitution of an alternative reference neutron monitor into the correction procedure.