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Annales Geophysicae An interactive open-access journal of the European Geosciences Union
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Volume 15, issue 6
Ann. Geophys., 15, 734–739, 1997
https://doi.org/10.1007/s00585-997-0734-6
© European Geosciences Union 1997
Ann. Geophys., 15, 734–739, 1997
https://doi.org/10.1007/s00585-997-0734-6
© European Geosciences Union 1997

  30 Jun 1997

30 Jun 1997

Changes in cosmic ray cut-off rigidities due to secular variations of the geomagnetic field

A. Bhattacharyya1 and B. Mitra2 A. Bhattacharyya and B. Mitra
  • 1Indian Institute of Geomagnetism, Colaba, Bombay 400005, India
  • 2Department of Physics, Jadavpur University, Calcutta, India

Abstract. An analytical expression is derived for the cutoff rigidity of cosmic rays arriving at a point in an arbitrary direction, when the main geomagnetic field is approximated by that of an eccentric dipole. This expression is used to determine changes in geomagnetic cutoffs due to secular variation of the geomagnetic field since 1835. Effects of westward drift of the quadrupole field and decrease in the effective dipole moment are seen in the isorigidity contours. On account of the immense computer time required to determine the cutoff rigidities more accurately using the particle trajectory tracing technique, the present formulation may be useful in estimating the transmission factor of the geomagnetic field in cosmic ray studies, modulation of cosmogenic isotope production by geomagnetic secular variation, and the contribution of geomagnetic field variation to long term changes in climate through cosmic ray related modulation of the current flow in the global electric circuit.

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