Cloud phase and relative humidity distributions over the Southern Ocean in austral summer based on in situ observations and CAM5 simulations

AbstractCloud phase and relative humidity (RH) distributions at -67°–0°C over the Southern Ocean during austral summer are compared between in situ airborne observations and global climate simulations. A scale-aware comparison is conducted using horizontally averaged observations from 0.1–50 km. Cloud phase frequencies, RH distributions and liquid mass fraction are found less affected by horizontal resolutions than liquid and ice water content (LWC, IWC), liquid and ice number concentrations (Ncliq, Ncice), and ice supersaturation (ISS) frequency. At -10°–0°C, observations show 27%–34% and 17%–37% of liquid and mixed phases, while simulations show 60%–70% and 3%–4%, respectively. Simulations overestimate (underestimate) LWC and Ncliq in liquid (mixed) phase, overestimate Ncice in mixed phase, underestimate IWC in ice and mixed phases, and underestimate (overestimate) liquid mass fraction below (above) -5°C, indicating that observational constraints are needed for different cloud phases. RH frequently occu...