  We quantify the effects of refraction in transit transmission spectroscopy on
spectral absorption features and on temporal variations that could be used to
obtain altitude-dependent spectra for planets orbiting stars of different
stellar types. We validate our model against altitude-dependent transmission
spectra of the Earth from ATMOS and against lunar eclipse spectra from Palle et
al. (2009). We perform detectability studies to show the potential effects of
refraction on hypothetical observations of Earth analogs with the James Webb
Space Telescope (JWST) Near-Infrared Spectrograph (NIRSPEC). Due to refraction,
there will be a maximum tangent pressure level that can be probed during
transit for each given planet-star system. We show that because of refraction,
for an Earth-analog planet orbiting in the habitable zone of a Sun-like star
only the top 0.3 bars of the atmosphere can be probed, leading to a decrease in
the signal to noise ratio (SNR) of absorption features by 60%, while for an
Earth-analog planet orbiting in the habitable zone of an M5V star it is
possible to probe almost the entire atmosphere with minimal decreases in SNR.
We also show that refraction can result in temporal variations in the transit
transmission spectrum which may provide a way to obtain altitude-dependent
spectra of exoplanet atmospheres. Additionally, the variations prior to ingress
and subsequent to egress provide a way to probe pressures greater than the
maximum tangent pressure that can be probed during transit. Therefore, probing
the maximum range of atmospheric altitudes, and in particular the near-surface
environment of an Earth-analog exoplanet, will require looking at
out-of-transit refracted light in addition to the in-transit spectrum.
