Transit spectra computed from a 3D simulation of GJ 1214 b atmosphere by Charnay et al. (2015) with Pythmosph3R (black) and a mean profile approximation (see text). Spectra are shown with (right panels) and without (left panels) the radiative effects from the KCl and ZnS clouds. In both cases the atmosphere is extrapolated vertically beyond the top of the simulation. Cloud particle radius is fixed to 0.5 μm. The plots on the lower part show the difference between the two methods. The purple line indicates the photon noise with a JWST aperture, an exposure time of twice the transit duration and a (low) resolution of R = 100.