  We show that atmospheric electric fields may affect the cosmic ray
observations in several ways and may lead to an overestimation of the cosmic
ray energies. The electric field in thunderclouds can be as high as a few
kV/cm. This field can accelerate the shower electrons and can feed some
additional energy into the shower. Therefore, ground array observations in
certain weather conditions may overestimate the energy of ultrahigh-energy
cosmic rays if they don't take this effect into account. In addition, the
electric field can bend the muon trajectories and affect the direction and
energy reconstruction of inclined showers. Finally, there is a possibility of
an avalanche multiplication of the shower electrons due to a runaway breakdown,
which may lead to a significant miscalculation of the cosmic ray energy.
