  In this article we present results of the study on the association between
the muon flux variation at ground level, registered by the
\textit{\textit{New-Tupi}} muon telescopes ($22^0 53'00''S,\; 43^0 06'13'W$; 3
m above sea level) and a geomagnetic storm of 25\,--\,29 August 2015 that has
raged for several days as a result of a coronal mass ejection (CME) impact on
Earth's magnetosphere. A sequence of events started with an M3.5 X-ray class
flare on 22 August 2015 at 21:19 UTC. The \textit{\textit{New-Tupi}} muon
telescopes observed a Forbush decrease (FD) triggered by this geomagnetic
storm, with onset on 26 August 2015. After the Earth crossed a heliospheric
current sheet (HCS), an increase in the particle flux was observed on 28 August
2015 by spacecrafts and ground level detectors. The observed peak was in
temporal coincidence with the impact of a high speed stream (HSS). We study
this increase, that has been observed with a significance above 1.5\% by ground
level detectors in different rigidity regimes. We also estimate the lower limit
of the energy fluence injected on Earth. In addition, we consider the origin of
this increase, such as acceleration of particles by shock waves on the front of
the HSS and the focusing effect of the HCS crossing. Our results show possible
evidence of a prolonged energetic (up to GeV energies) particle injection
within the Earth atmosphere system, driven by the HSS. In most cases these
injected particles are directed to polar regions. However, the particles from
the high energy tail of the spectrum can reach middle latitudes, and that could
have consequences for the atmospheric chemistry, for instance, the creation of
NOx species may be enhanced and can lead to increased ozone depletion. This
topic requires further study.
