A study of vertical cutoff rigidities using sixth degree simulations of the geomagnetic field

Abstract

Using sixth degree simulations of the quiescent geomagnetic field, we have studied the vertical cutoff rigidities of more than three hundred positions on the earth's surface. Twenty‐six of these positions are near the South African magnetic anomaly, and six other points are in a region of the North Atlantic where Pomerantz and Agarwal have reported anomalous results. The cutoff rigidities have been obtained by detailed computation of the trajectories of cosmic rays at 0.01‐bv rigidity intervals to allow for the effects of the penumbra. Differences greater than 15% from the Quenby and Wenk threshold values have been found in the vicinity of South Africa, the South Atlantic, and the Canary Islands. Various latitude surveys are shown to exhibit consistency when plotted against the cutoff rigidities determined by this computational method. It is concluded that, though there is essentially no difference between the cutoff rigidities obtained using two currently accepted field models, these simulations of the geomagnetic field are not completely adequate over some parts of the earth to describe the cosmic‐ray effects in their entirety. Cutoff rigidities for a number of neutron monitors are listed.

On Magnetospheric Transmissivity of Cosmic Rays

“…Using the magnetopause model on the day side gives the information whether the traced CR particle accesses the magnetosphere from the day side or not. The night side boundary is taken as a sphere of 25 R E radius similarly to earlier calculations by other authors (e.g., [2,16] used 25 R E boundaries for all sectors of local time). In such an approach there is, however, a discontinuity at X = 0.…”

Numerical model for computation of effective and ambient dose equivalent at flight altitudes

“…Several models, tools, algorithms to calculate geomagnetic cut-off rigidity, particle trajectories and the asymptotic viewing cones were proposed during the years (McCracken et al 1962(McCracken et al , 1968Shea et al 1965;Smart et al 2000). As the internal field we consider the IGRF geomagnetic model, which is a Gauss spherical harmonic model of the geomagnetic field, based on magnetic field measurements from geomagnetic stations, magnetometers and satellites (Langel 1987).…”

Anomalous behavior of cutoff rigidity variation in the region of the Mexico station during a magnetic superstorm on 20 November 2003

“…The standard technique of cutoff rigidity calculations was described by Smart et al (1965Smart et al ( , 1975. In this work the trajectory calculations were performed with the use of the technique described by Pchelkin and Vashenyuk (2001), which includes the contribution of the penumbra more accurately as compared to the standard technique.…”