Condensation cloud

Abstract: A new cloud simulation chamber was built at the Meteorological Research Institute (MRI) to investigate the details of the fundamental processes of cloud formation. The MRI cloud chamber was designed as an adiabatic-expansiontype cloud chamber covering temperatures from 30 to−100°C, pressures from 1030 to 30 hPa, and an evacuation rates corresponding to ascent rates from 0 to 30 m s −1 . Improvements to the cooling system and cloud characterization instrumentation distinguish the new facility from past devices of this type that are no longer functional (e.g., the Colorado State University dynamic cloud chamber), and the capabilities exceed those of any other active facility (e.g., the Aerosol Interactions and Dynamics in the Atmosphere (AIDA) chamber) for covering a range of atmospheric conditions while reproducing approximately adiabatic parcel conditions. Results from the preliminary experiments demonstrate the accuracy of coordinated pressure and temperature controls to reproduce cloud formation processes (both dry and wet adiabatic expansion processes) and the ability of the chamberʼs instrumentation to measure aerosol, cloud droplet, and ice crystal characteristics. Performance tests demonstrate the chamberʼs usefulness as a facility to investigate cloud droplet and ice crystal formation processes through the activation of various types of aerosol particles.

Abstract: . Cumulus clouds have long been recognized as being the results of ascending moist air from below the cloud base. Cloud droplet nucleation is understood to take place near the cloud base and inside accelerating rising cloudy air. Here we describe circumstances under which cloud droplet nucleation takes place at the interface of ascending cloudy air and clear air. Evaporation is normally expected to occur at this interface. However, continuity of moving air requires cloud-free air above the boundary of rising cloudy air to move upwards in response to the gradient force of perturbation pressure. We used a one and half dimensional non-hydrostatic cloud model and the Weather Research and Forecast model to investigate the impacts of this force on the evolution of cloud spectra. Our study shows that expansion and cooling of ascending moist air above the cloud top causes it to become supersaturated with condensation rather than evaporation occurring at the interface. We also confirm that Eulerian models can describe the cloud droplet activation and prohibit spurious activation at this interface. The continuous feeding of newly activated cloud droplets at the cloud summit may accelerate warm rain formation.

Abstract: [1] A long-term numerical simulation is performed to investigate idealized characteristics of the cloud layer of Jupiter's atmosphere using a two-dimensional cloud convection model that treats thermodynamics and microphysics of the three cloud components, H2O, NH3, and NH4SH. A prominent result obtained is intermittent emergence of vigorous cumulonimbus clouds rising from the H2O condensation level to the tropopause. Due to the active transport associated with these clouds, the mean vertical distributions of cloud particles and condensible gases are distinctly different from the hitherto accepted three-layered structure; considerable amounts of H2O and NH4SH cloud particles exist above the NH3 condensation level, while the mixing ratios of all condensible gases decrease with height from the H2O condensation level. The mean vertical profile of NH3 vapor is consistent with the results of radio observations in that the abundance of NH3 is subsolar below the NH3 cloud base.