The atmospheric radiation response to solar-particle-events

Area of Science:

• Space Physics
• Atmospheric Science
• Radiation Dosimetry

Background:

• High-energy solar particles (from solar flares and coronal mass ejections) impact Earth's atmosphere, increasing radiation levels.
• Static geomagnetic field models inadequately describe particle access during geomagnetic disturbances.
• Satellite measurements of solar particle fluxes are often too distant and spatially averaged for local Earth surface predictions.

Purpose of the Study:

• To develop a method for calculating solar-particle effective dose rates at Earth's surface.
• To utilize ground-level neutron monitor data as adjoint sources for atmospheric flux.
• To analyze the magnitude and distribution of solar-particle dose rates during a specific event.

Main Methods:

• Using ground-level neutron monitor counting rates as adjoint sources.
• Calculating atmospheric flux immediately above monitors.
• Determining solar-particle effective dose rates as a function of Earth's surface position.
• Applying the method to the September 29-30, 1989 ground-level event (GLE 42).

Main Results:

• The method successfully obtained the magnitude and distribution of solar-particle effective dose rates for GLE 42.
• Softer particle spectra in solar particle events lead to greater sensitivity to the geomagnetic field compared to galactic cosmic rays.
• Solar particle events exhibit a near-absence of the "knee" in dose rate near 60 degrees geomagnetic latitude, unlike cosmic rays.

Conclusions:

• The developed method provides a more accurate way to assess solar-particle radiation doses at Earth's surface.
• Understanding the geomagnetic field's influence on softer solar particle spectra is crucial.
• The distinct latitudinal distribution of solar particle events differs significantly from galactic cosmic rays.