Showing papers by "Kevin J. Noone published in 1998"

Small ice crystals in cirrus clouds : A model study and comparison with in situ observations

Abstract: An air parcel model including homogeneous freezing nucleation of ice crystals has been used to study the formation and development of cirrus clouds. In situ measurements taken during March 1994 over southern Germany were used for comparison with model predictions. Typical experimental data were chosen for a base-case model run. Using measured aerosol properties as input values, the model predicts the measured ice crystal size distribution. In particular, both measurements and model results show the presence of numerous small ice crystals (diameter between 1 and 20 μm). Both measurements and model results also show that small aerosol particles (below 0.1 μm diameter) are active in forming cirrus cloud particles. The modeled microphysical properties including ice crystal size distribution, number concentration, and the residual particle size distribution are in good agreement with the experimental data. Based on the measured parameter values, a model sensitivity study considering air parcel updraft...

Aerosol particles and clouds: which particles form cloud droplets?

Abstract: Measurements of cloud droplet residuals, which represent the cloud droplet nuclei (CDN) that formed cloud droplets, were made in ambient clouds with a 1-min time resolution. Only a weak relationship was found between the CDN number and volume concentrations, because the particles dominating the two concentrations resided in different size ranges. A comparison between the total particle size distribution and the size distribution of the CDN showed that only a small fraction of the total number of particles at a given size (smaller than 0.2 μmm diameter) formed cloud droplets. Among the CDN, however, 75% of the number of particles were smaller than 0.2 μmm diameter. Concurrent measurements showed that hygroscopic particles of the same size and larger remained in the interstitial air. The same feature was observed over longer time periods on a 1-min basis. Suggested hypotheses to explain why only a few of the smaller hygroscopic particles formed cloud droplets while larger particles remained in the interstitial air are that the growth of the droplet could have been influenced by the composition of individual particles and/or that entrainment introduced hygroscopic particles in the interstitial air. DOI: 10.1034/j.1600-0889.1998.00005.x

Dynamical Influences on Cirrus Cloud Formation Process

Abstract: An air parcel model has been used to study dynamic influences on cirrus cloud microphysical processes. Representative data selected from a measurement campaign carried out over southern Germany during March 1994 were used for a base-case model run where a modeled air parcel moved in a wave trajectory with a period similar to the measured Brunt–Vaisala frequency and an amplitude of about 30 m. Six case studies were performed for this paper. In each case, ice crystal nucleation processes were examined as an air parcel moved with trajectories having different wave forms. A random walk trajectory simulating turbulence with turbulent structure was also considered. The relationships between the parameters in the air parcel trajectories and crystal microphysical properties are discussed. Simulation results show that after two wave cycles, the model-produced crystal spectra are usually narrower than typical measurement data;however, broader spectra can be produced for certain types of trajectories. The b...