  We present a study on the coupling of haze and clouds in the atmosphere of
WASP-39b. We developed a cloud microphysics model simulating the formation of
Na2S and MgSiO3 condensates over photochemical hazes in gas giant atmospheres.
We apply this model to WASP-39b, recently observed with the JWST to study how
these heterogeneous components may affect the transit spectrum. We simulate
both morning and evening terminators independently and average their transit
spectra. While MgSiO3 formation has negligible impact on the spectrum, Na2S
condensates produce gray opacities in the water band, in agreement with HST and
JWST observations. Moreover, the formation of Na2S on the morning side depletes
the atmosphere of its sodium content, decreasing the strength of the Na line.
Combining morning and evening profiles results in a good fit of the Na
observations. These nominal results assume a small Na2S/haze contact angle
(5.7{\deg}). Using a larger value (61{\deg}) reduces the cloud density and
opacity, but the effect on the Na profile and spectral line remains identical.
In addition, the presence of haze in the upper atmosphere reproduces the
UV-visible slope observed in the HST and VLT data and contributes to the
opacity between the water bands at wavelengths below 2 microns. The averaged
spectra are rather insensitive to the variation of eddy diffusion and haze mass
flux tested in this study, though the UV-visible slope, probing the haze layer
above the clouds, is affected. Finally, our disequilibrium chemistry model,
including photochemistry, reproduces the SO2 and CO2 absorption features
observed.
