Cosmic ray modulation and radiation dose of aircrews during the solar cycle 24/25

Abstract

Weak solar activity and high cosmic ray flux during the coming solar cycle are qualitatively anticipated by the recent observations that show the decline in the solar activity levels. We predict the cosmic ray modulation and resultant radiation exposure at flight altitude by using the time‐dependent and three‐dimensional model of the cosmic ray modulation. Our galactic cosmic ray (GCR) model is based on the variations of the solar wind speed, the strength of the heliospheric magnetic field, and the tilt angle of the heliospheric current sheet. We reproduce the 22 year variation of the cosmic ray modulation from 1980 to 2015 taking into account the gradient‐curvature drift motion of GCRs. The energy spectra of GCR protons obtained by our model show good agreement with the observations by the Balloon‐borne Experiment with a Superconducting magnetic rigidity Spectrometer (BESS) and the Payload for Antimatter Matter Exploration and Light‐nuclei Astrophysics (PAMELA) except for a discrepancy at the solar maximum. Five‐year annual radiation dose around the solar minimum at the solar cycle 24/25 will be approximately 19% higher than that in the last cycle. This is caused by the charge sign dependence of the cosmic ray modulation, such as the flattop profiles in a positive polarity.

Radiation Dose Nowcast for the Ground Level Enhancement on 10–11 September 2017

“…First, we prepared simulated data sets of time profiles of proton spectra for arbitrary pitch angles as obtained by solving 1‐D focused transport equations, varying the time profiles of the initial proton spectrum as controlled by fast, medium, and slow “IPs” and the power‐law spectral index, among other parameters (Kubo et al, ). Second, these data sets were combined with an antiproton trace model in the magnetosphere to derive the proton flux at the top of atmosphere anywhere in the world (Miyake et al, ). Finally, the fluxes of protons and their secondary particles as well as the associated radiation doses in the atmosphere were calculated from the top‐of‐atmosphere proton flux using an air shower simulation database developed with the Particle and Heavy Ion Transport code System (Sato, Iwamoto, et al, ).…”

“…Predicting intense solar energetic particle (SEP) events such as GLE events is challenging and one of the most important aspects of space weather research (Kataoka et al, ). We have recently developed a physics‐based framework called WASAVIES (WArning System for AVIation Exposure to Solar energetic particles) to nowcast and forecast the development of a GLE and the corresponding radiation dose, as described in a series of papers (Kataoka et al, ; Kubo et al, ; Miyake et al, ; Sato et al, ). The detailed calculation algorithm of the latest version of the automated WASAVIES system and its verification are reported in a companion paper (Sato, Kataoka, et al, , S18 hereafter).…”

Nowcast and forecast of galactic cosmic ray (GCR) and solar energetic particle (SEP) fluxes in magnetosphere and ionosphere – Extension of WASAVIES to Earth orbit

“…The U 1AU,IP,c (t, E 0 , u) database was developed by solving one-dimensional focused transport equations by using the method developed by Kubo et al (2015), while P G;O;Kp;h t (E 0 , u) was prepared by tracing the trajectories of anti-protons emitted from the top of the atmosphere by using the proton trace model (Miyake et al, 2017) based on the empirical geomagnetic field model T89 (Tsyganenko, 1989). The other databases were constructed by performing Monte Carlo simulations by using the PHITS version 2.88 (Sato et al, 2018a).…”

Real Time and Automatic Analysis Program for WASAVIES: Warning System for Aviation Exposure to Solar Energetic Particles

“…In this calculation, we employed the empirical geomagnetic field model T89 (Tsyganenko, ), which simply characterizes the geomagnetic activity based on the Kp index, which ranges from 0 to 8. The details of the antiproton trace algorithm were described in Miyake et al (). The pitch angle was calculated against the ambient magnetic field directions, which were assumed to be tilted by θ t from the ecliptic plane.…”