Correction of snow effects on Oulu data using local snow depth data
Pauli Väisänen, UniOulu, Ilya Usoskin, University of Oulu/SGO
The University of Oulu neutron monitor (NM) started its operation in 1964 on the Kontinkangas campus, where it operated until 1974 and was located in a building with a roof where snow can be accumulated during winters. The amount of snow is known to affect count rates by reducing the NM count rate. Comparing the measured NM count rates to theoretical count rates determined by using a numerical model and the modulation potential, inferred independently from other NMs, deviations of up to 5 % can be observed on snowy winters. Although there are no recordings of snow depth on the building roof itself, digitized daily-snow-depth data from the Linnanmaa weather station, some 6 km north-northwest of the Kontinkangas location, are available. This has allowed us to determine corrections to the data. For individual snow periods, we found a good linear relation between the snow depth and deviation in the measured Oulu NM count rates from those theoretically expected. This relation can be used to correct the Oulu NM data for wintertimes before 1974. Since the move of the Oulu NM location to a new pyramid-shaped building in 1974, snow has never affected the NM count rate again.