The main source of the ionization of the Earth’s atmosphere is the cosmic radiation that depends on solar activity as well as geomagnetic activity. Galactic cosmic rays constitute a permanent radiation background and contribute significantly to the radiation exposure inside the atmosphere. In this work, the cosmic-ray-induced ionization of the Earth’s atmosphere, due to both solar and galactic cosmic radiation during the recent solar cycles 23 (1996–2008) and 24 (2008–2019), was studied globally. Estimations of the ionization were based on the CRAC:CRII model by the University of Oulu. The use of this model allowed for extensive calculations from the Earth’s surface (atmospheric depth 1033 g/cm²) to the upper limit of the atmosphere (atmospheric depth 0 g/cm²). Monte Carlo simulations were performed for the estimation quantities of radiobiological interest with the validated software DYASTIMA/DYASTIMA-R. This study was focused on specific altitudes of interest, such as the common flight levels used by commercial aviation.

Cosmic radiation is a major factor of ionization of the Earth's atmosphere. Both solar and galactic cosmic rays, which depend on solar activity and geomagnetic field, affect the radiation exposure in the atmosphere. Several models have been created for the estimation of the ionization and radiation dosimetry. In this work, as regards the ionization rate computations the CRAC:CRII model by the University of Oulu (https://cosmicrays.oulu.fi/CRII/CRII.html) was used, while for the estimation of the ambient equivalent dose rate (dH*(10)/dt) we used the validated software DYASTIMA / DYASTIMA-R by the University of Athens (http://cosray.phys.uoa.gr/index.php/applications/dyastima). Both tools are of great importance as they allow us to calculate the respective quantities all over the globe, at the entire atmosphere and for different time periods and solar cycle phases. The study concerns the last two solar cycles 23 and 24 (1996–2019) and specific flight levels of commercial aviation (FL310, FL350 and FL390). The dependance of CRII and dH*(10)/dt on geomagnetic cut-off rigidity, solar activity, cosmic ray intensity, as well as the altitude inside the atmosphere, affect the radiation exposure of the air crew members and frequent flyers, which make the results very interesting for the aviation industry.

In recent decades, the exposure of aviation crews and passengers to cosmic radiation has been progressively increasing due to the growing need of flights. Therefore, there is a need for radiation assessment software tools to act as a complement to other radiation protection techniques and countermeasures. In this work, the exposure to cosmic radiation is estimated for flights from Athens International Airport to various international destinations, by performing Monte Carlo simulations with the validated tool DYASTIMA/DYASTIMA-R. The results of the estimated total ambient dose equivalent, as well as the ambient dose equivalent rate for different flights, applying a typical flying level and constant atmospheric conditions, are presented for the first time. This study is carried out for different phases of solar activity for the time period from 1996 to 2019, which includes the two recent Solar Cycles 23 and 24.