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

Abstract

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

Reconstruction and Prediction of Variations in the Open Solar Magnetic Flux and Interplanetary Conditions

“…Some of these cosmogenic isotopes are stored in terrestrial reservoirs (notably 10 Be in ice sheets and 14 C in tree trunks), into which dateable cores can be drilled. Because the flux of cosmic rays is modulated by the heliospheric field (Parker, 1965;Potgieter, 1998Potgieter, , 2013, the abundances of these isotopes gives unique information on the long-term variability of the Sun (O'Brien, 1979;Stuiver and Quay, 1980;O'Brien et al, 1991;Beer, 2000;Muscheler et al, 2007;McCracken and Beer, 2007;McCracken, 2007;Solanki et al, 2004) once the effects of the secular variation in the geomagnetic field (which also shields Earth's atmosphere from cosmic rays) have been accounted for (Bhattacharyya and Mitra, 1997;Masarik and Beer, 1999). Comprehensive reviews of the methods and the underpinning science are present in Usoskin (2013) and Beer et al (2012).…”

Cosmic rays and space weather: effects on global climate change

“…Expected changes of cutoff rigidities were found in many papers (e.g. Bhattacharyya and Mitra, 1997;Shea and Smart, 2003;Kudela and Bobik, 2004;see review in Dorman, 2009). Results of trajectory calculations of R C changes are shown in Table 2 (from Shea and Smart, 2003).…”