Modelling of cosmic ray modulation in the heliosphere by stochastic processes

PhD (Space Physics), North-West University, Potchefstroom Campus, 2013The transport of cosmic rays in the heliosphere is studied by making use of a newly developed modulation model. This model employes stochastic differential equations to numerically solve the relevant transport equation, making use of this approach’s numerical advantages as well as the opportunity to extract additional information regarding cosmic ray transport and the processes responsible for it. The propagation times and energy losses of galactic electrons and protons are calculated for different drift cycles. It is confirmed that protons and electrons lose the same amount of rigidity when they experience the same transport processes. These particles spend more time in the heliosphere, and also lose more energy, in the drift cycle where they drift towards Earth mainly along the heliospheric current sheet. The propagation times of galactic protons from the heliopause to Earth are calculated for increasing heliospheric tilt angles and it is found that current sheet drift becomes less effective with increasing solar activity. Comparing calculated propagation times of Jovian electrons with observations, the transport parameters are constrained to find that 50% of 6 MeV electrons measured at Earth are of Jovian origin. Charge-sign dependent modulation is modelled by simulating the proton to anti-proton ratio at Earth and comparing the results to recent PAMELA observations. A hybrid cosmic ray modulation model is constructed by coupling the numerical modulation model to the heliospheric environment as simulated by a magneto-hydrodynamic model. Using this model, it is shown that cosmic ray modulation persists beyond the heliopause. The level of modulation in this region is found to exhibit solar cycle related changes and, more importantly, is independent of the magnitude of the individual diffusion coefficients, but is rather determined by the ratio of parallel to perpendicular diffusion.Doctora

The radiation environment over the African continent at aviation altitudes: first results of the RPiRENA-based dosimeter

The radiation environment over the African continent, at aviation altitudes, remains mostly uncharacterized and unregulated. In this paper, we present initial measurements made by a newly developed active dosimeter onboard long-haul flights between South Africa and Germany. Based on these initial tests, we believe that this low-cost and open-source dosimeter is suitable for continued operation over the African continent and can provide valuable long-term measurements to test dosimetric models and inform aviation policy

A Multi‐Purpose Heliophysics L4 Mission

The Earth-Sun Lagrangian point 4 is a meta-stable location at 1 AU from the Sun, 60° ahead of Earth's orbit. It has an uninterrupted view of the solar photosphere centered on W60, the Earth's nominal magnetic field connection to the Sun. Such a mission on its own would serve as a solar remote sensing observatory that would oversee the entire solar radiation hemisphere with significant relevance for protecting Moon and Mars explorers from radiation exposure. In combination with appropriately planned observatories at L1 and L5, the three spacecraft would provide 300° longitude coverage of photospheric magnetic field structure, and allow continuous viewing of both solar poles, with >3.6° elevation. Ideally, the L4 and L5 missions would orbit the Sun with a 7.2° inclination out of the heliographic equator, 14.5° out of the ecliptic plane. We discuss the impact of extending solar magnetic field observations in both longitude and latitude to improve global solar wind modeling and, with the development of local helioseismology, the potential for long-term solar activity forecasting. Such a mission would provide a unique opportunity for interplanetary and interstellar dust science. It would significantly add to reliability of operational observations on fast coronal mass ejections directed at Earth and for human Mars explorers on their round-trip journey. The L4 mission concept is technically feasible, and is scientifically compelling.ISSN:1542-739

ORCA (Antarctic Cosmic Ray Observatory): 2018 Latitudinal Survey

A set of detectors devoted to investigate secondary cosmic rays has performed a latitudinal observation from Vigo (Spain) to Juan Carlos I Spanish Antarctic Station (Livingston Island, Antarctic Peninsula) aboard the Sarmiento de Gamboa oceanographic vessel from November $14^{th}$ to January $2^{nd}$. The experiment is split into two modules, one composed by a stack of 3NM64, three BF3 bare counters (NEMO) and a muon telescope (MITO) with a mini neutron monitor in a $20^{\prime}$ maritime container on the Sarmiento de Gamboa$^{\prime}$s deck and a second module (TRISTAN) consisting of a set of 3 RPC planes with a lead layer in between the second and the third plane placed in a separate temperature controlled room below the ship$^{\prime}$s deck. The complete set of instruments is the Antarctic Cosmic Ray Observatory (ORCA) that has been be installed in the Juan Carlos I Spanish Antarctic Base in Livingston Island (Antarctica). The latitudinal survey took ORCA throughout the South Atlantic magnetic anomaly along the Brazilian coast. ORCA is able to measure fluxes of neutrons of different energies, charged particles (mostly muons) and muon incident directions on the detector surface. In this work, we present the preliminary results of the latitudinal survey