Quantifying Ionospheric Effects on Global 21-cm Observations
  We modelled the two major layer of Earth's ionosphere, the F-layer and the
D-layer, by a simplified spatial model with temporal variance to study the
chromatic ionospheric effects on global 21-cm observations. From the analyses,
we found that the magnitude of the ionospheric disruptions due to ionospheric
refraction and absorption can be greater than the expected global 21-cm signal,
and the variation of its magnitude can differ, depending on the ionospheric
conditions. Within the parameter space adopted in the model, the shape of the
global 21-cm signal is distorted after propagating through the ionosphere,
while its amplitude is weakened. It is observed that the ionospheric effects do
not cancel out over time, and thus should be accounted for in the foreground
calibration at each timestep to account for the chromaticity introduced by the
ionosphere.
