Abstract
AbstractToday's geomagnetic field can prevent energetic particles, including solar energetic particles and galactic cosmic rays, from directly hitting the Earth's atmosphere. However, when the geomagnetic field strength is significantly decreased during geomagnetic field excursions or reversals, the geomagnetic field shielding effect becomes less prominent. Geomagnetic cutoff rigidity, as a quantitative estimation of the shielding effect, can be calculated using trajectory tracing or theoretical equations. We use a recent high‐resolution continuous geomagnetic field model (LSMOD.2) to study the geomagnetic cutoff rigidity during the Laschamps excursion. Global grids of the geomagnetic cutoff rigidities are presented, in particular for the excursion midpoint when the geomagnetic field is weak and not dipole‐dominated anymore at Earth's surface. We compare the cutoff rigidity calculation results between a trajectory tracing program and theoretical equations and we find that the influence of the non‐dipole component of the geomagnetic field cannot be ignored during the excursion. Our results indicate that the exposure of Earth's atmosphere to energetic particles of cosmic and solar origin is high and nearly independent of latitude in the middle of the Laschamps excursion. Our results will be useful for future studies associated with cosmic radiation dose rate and cosmogenic isotope production rate during the Laschamps excursion.
Highlights
The geomagnetic core field is generated in the Earth's outer core and it reaches out several Earth radii into space, protecting our planet from solar and cosmic energetic particles (e.g., Glassmeier & Vogt, 2010; Jackson & Finlay, 2015; Korte & Mandea, 2019)
Our results indicate that the exposure of Earth's atmosphere to energetic particles of cosmic and solar origin is high and nearly independent of latitude in the middle of the Laschamps excursion
It is clear that before and after the Laschamps excursion, the dipole power (DP) is significantly larger than non-dipole power (NDP) at Earth's surface, which indicates that the geomagnetic field is dipole-dominated
Summary
The geomagnetic core field is generated in the Earth's outer core and it reaches out several Earth radii into space, protecting our planet from solar and cosmic energetic particles (e.g., Glassmeier & Vogt, 2010; Jackson & Finlay, 2015; Korte & Mandea, 2019). A spherical harmonic (SH) paleomagnetic field model based on sediment and volcanic data and covering the Laschamps and Mono Lake excursions (in the past 50–30 thousand years) was presented by Brown et al (2018), with an updated version by Korte et al (2019) This model, called LSMOD., provides the possibility to study the geomagnetic field shielding against energetic particles during the Laschamps excursion based on a realistic global field structure. The geomagnetic cutoff rigidity strongly influences the cosmic radiation dose rate (e.g., Shea & Smart, 2000) and cosmogenic isotope (e.g., 10Be, 14C, 36Cl) production rate (Poluianov et al, 2016), which is the basis of the cosmogenic nuclides dating method (Gosse & Phillips, 2001) It plays a role for cloud condensation nuclei (e.g., Kirkby et al, 2011; Pierce & Adams, 2009) and possible biospheric effects (e.g., Glassmeier & Vogt, 2010; Wei et al, 2014) during the excursion.
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