  TRAPPIST-1e is a potentially habitable terrestrial exoplanet orbiting an
ultra-cool M Dwarf star and is a key target for observations with the James
Webb Space Telescope (JWST). One-dimensional photochemical modelling of
terrestrial planetary atmospheres has shown the importance of the incoming
stellar UV flux in modulating the concentration of chemical species, such as
O$_3$ and H$_2$O. In addition, three-dimensional (3D) modelling has
demonstrated anisotropy in chemical abundances due to transport in tidally
locked exoplanet simulations. We use the Whole Atmosphere Community Climate
Model Version 6 (WACCM6), a 3D Earth System Model, to investigate how
uncertainties in the incident UV flux, combined with transport, affect
observational predictions for TRAPPIST-1e (assuming an initial Earth-like
atmospheric composition). We use two semi-empirical stellar spectra for
TRAPPIST-1 from the literature. The UV flux ratio between them can be as large
as a factor of 5000 in some wavelength bins. Consequently, the
photochemically-produced total O$_3$ columns differ by a factor of 26. Spectral
features of O$_3$ in both transmission and emission spectra vary between these
simulations (e.g. differences of 19 km in transmission spectra effective
altitude for O$_3$ at 0.6 $\mu$m). This leads to potential ambiguities when
interpreting observations, including overlap with scenarios that assume
alternative O$_2$ concentrations. Hence, to achieve robust interpretations of
terrestrial exoplanetary spectra, characterisation of the UV spectra of their
host stars is critical. In the absence of such stellar measurements,
atmospheric context can still be gained from other spectral features (e.g.
H$_2$O), or by comparing direct imaging and transmission spectra in
conjunction.
