3D Climate Modelling of TRAPPIST-1 c with a Venus-like atmosphere: Large-scale circulation and observational prospects D. Quirino1,2, G. Gilli1,3, T. Navarro4,5, M. Turbet6, T. Fauchez7,8, P. Machado1,21.InstituteofAstrophysicsandSpaceSciences(IA),Lisbon,Portugal(dfquirino@fc.ul.pt);2.FacultyofSciences,UniversityofLisbon,Lisbon,Portugal;3.InstituteofAstrophysicsofAndalusia(IAA–CSIC),Granada,Spain(gilli@iaa.es);4.TheMcGillSpaceInstitute,Montréal,QC,Canada;5.SpaceScienceInstitute,Boulder,CO,UnitedStates;6.LaboratoiredeMétéorologieDynamique/IPSL,CNRS,SorbonneUniversité,ÉcoleNormaleSupérieure,PSLResearchUniversity,ÉcolePolytechnique,75005Paris,France;7.NASAGoddardSpaceFlightCenter,Greenbelt,MD,UnitedStates;8.AmericanUniversity,Washington,DC,UnitedStates . IntroductionThe population of close-in Earth-sized exoplanets orbiting late-type M-dwarf stars has increased in the recent years (e.g., [1, 2]), creating an unique opportunity: best targets for terrestrial planets atmospheric studies. Methods Thermal Structure TRAPPIST-1 c atmosphere is warmer than Venus’s at and above the cloud deck region. The substellar and nightside equatorial profiles are similar from the ground to p ~ 0.01-bar. Between ~20-bar and ~ 0.01-bar, the nightside equatorial region [22.5º N/S] is warmer than the remaining nightside hemisphere, suggesting that a day-night heat redistribution mechanism is present in the equatorial region and throughout a significant atmospheric region. Thermal phase curves & transmission spectra Objectives Large-scale circulation Fig. 3. (Above) Time-averaged (10 orbits) temperature profiles for different regions of TRAPPIST-1 c, compared to the Venus International Reference Atmosphere (VIRA) profile. The red (blue) cross depict the approximate level of sulphuric acid condensation (freezing) point on Venus. Fig. 4. (Left). Zonal and time-averaged zonal wind field. The solid thick (thin) black lines represent isotachs with a 50 m/s (25 m/s) interval.Zonal circulation: eastward equatorial superrotationjet peaking 300 m/s in the uppermost levels of the atmosphere with a clear signature at the cloud top (p~37-mbar). Meridional circulation: two large cells, one per hemisphere (north and south), crossing the pole and redistributing heat f rom dayside to nightside. Fig. 5. (Above). Zonal and time-averaged mass streamfunctions: (a) dayside and (b) nightside. The integration exclude the terminators. Positive (negative) values, i.e., in red (blue), correspond to clockwise (anti-clockwise) motion. Fig. 6. (Left). Relation between thermal phase curves, outgoing long-wavelength radiation (OLR) and temperature fields. In the subplot a the red/blue arrows indicate the longitude corresponding to the orbital phase of peak emission, while the two-head arrow indicate each phase curve amplitude. Orbital phase 0 corresponds to the secondary eclipse, while πis the planetary transit. In subplots (b) and (c) the red/blue cross marks the longitude of the maximum peak emission over the equator. All data is time-averaged for ten orbits of TRAPPIST- 1 c.Fig. 7. (Above) Transit transmission spectra of TRAPPIST-1 c for JWST NIRSpecPrism (0.6 –5.3 μm) andMIRI (5 –20 μm) for: Venus-likeclouds(blue) andclear-sky(black), simulatedwiththePlanetarySpectrumGenerator . Different atmospheric levels can be surveyed with different thermal spectral bands: o CO2 absorption bands will sound mesospheric levels (p ~1-mbar) o Continuum bands will sound the cloud top (p ~ 37-mbar) CO2 absorption bands: larger amplitudes and later peak emission Smaller eastward hotspot offsetVenus-like clouds will screen almost all but the strongest CO2absorption bands in the transmission spectra. The 4.8-μm CO2might become detectable, which could indicate the presence of a high-pressure CO2 a tmosphere. We use the Generic-PCM initially developed by the Laboratoire de Météorologie Dynamique (Paris, France) for exoplanet and paleoclimate studies [13 - 15]. The Generic-PCM includes a dynamic