Logo do repositório

Percorrer por autor "Bertucci, Bruna"

A mostrar 1 - 2 de 2
  • Evidence for a Time Lag in Solar Modulation of Galactic Cosmic Rays
    Publication . Tomassetti, Nicola; Orcinha, Miguel; Barão, Fernando; Bertucci, Bruna
    The solar modulation effect of cosmic rays in the heliosphere is an energy-, time-, and particle-dependent phenomenon that arises from a combination of basic particle transport processes such as diffusion, convection, adiabatic cooling, and drift motion. Making use of a large collection of time-resolved cosmic-ray data from recent space missions, we construct a simple predictive model of solar modulation that depends on direct solar-physics inputs: the number of solar sunspots and the tilt angle of the heliospheric current sheet. Under this framework, we present calculations of cosmic-ray proton spectra, positron/electron and antiproton/proton ratios, and their time dependence in connection with the evolving solar activity. We report evidence for a time lag ${\rm{\Delta }}T=8.1\pm \,1.2$ months, between solar-activity data and cosmic-ray flux measurements in space, which reflects the dynamics of the formation of the modulation region. This result enables us to forecast the cosmic-ray flux near Earth well in advance by monitoring solar activity.
    2017-11-08Artigo científico Acesso aberto Ver mais
  • Testing diffusion of cosmic rays in the heliosphere with proton and helium data from AMS
    Publication . Tomassetti, Nicola; Barão, Fernando; Bertucci, Bruna; Fiandrini, Emanuele; Figueiredo, José; Barreira, João; Orcinha, Miguel
    After six years of continuous observations in space, the Alpha Magnetic Spectrometer experiment has released new data on the temporal evolution of the proton and helium fluxes in cosmic rays. These data revealed that the ratio between proton and helium fluxes at the same value of rigidity $R=p/Z$ (momentum/charge ratio) is not constant at $R\lesssim$ 3 GV. In particular, the ratio is found to decrease steadily during the descending phase of Solar Cycle 24 toward the next minimum. We show that such a behavior is a remarkable signature of the $\beta\times\lambda(R)$ dependence in the diffusion of cosmic rays in heliosphere, where $\beta$ is their adimensional speed and $\lambda(R)$ is their mean free path, a universal function of rigidity for all nuclei. This dependence is responsible for distinctive charge/mass dependent effects in the time-dependent modulation of low-rigidity particles.
    2018-12-19Artigo científico Acesso aberto Ver mais