A common microphysical structure for midlevel mixed-phase cloud in the mid-latitudes: Results from the cloud layer experiment (CLEX-9) Conference Paper uri icon

abstract

  • Comprehensive measurements of midlevel mixed-phase clouds in the mid-latitude region were conducted during the CLEX-9 campaign in North Platte (41.13N, 100.68W) Nebraska from October to November 2001. The experiment was accomplished by employing the University of Wyoming King Air (UWKA) aircraft equipped with typical in-situ cloud microphysical instruments. The campaign flew ten flight missions in eight different days, accumulated more than 16 hours of in-cloud observational data. Approximately 2/3 of the thirty (30) total measured effective cloud profiles show a common feature that super-cooled liquid droplets were topped or near the top of the clouds with ice particles falling as virga beneath. We refer to this common structure as liquid topped mixed-phase cloud. This discovery confirms an earlier speculation that the midlevel mixed-phase clouds in the mid-latitude region possesses a microphysical structure similar to that recently reported for mixed-phase Arctic stratus. Another interesting phenomena is that the remaining 1/3 of the total measured effective cloud profiles are ice dominated cloud with little liquid water content. To understand the radiative transfer properties of this liquid topped mixed-phase altocumulus cloud and its contribution to the satellite remote sensing, a cloud profile with a nearly simultaneous TERRA/MODIS satellite overpass has been thoroughly sampled and is being parameterized for the purpose of the radiative transfer study. The cloud has been sliced into thin layers of 100 meter thickness. The droplet and ice crystal size distributions at each layer have been derived. The cloud habits have been simply divided into three categories of liquid droplet, sector plate, and aggregate/dendrite. The three habit fractions as a function of height have been determined. A very large fraction of water appeared at the cloud top and sharply decreased to a very small value. The small sector plate crystals were distributed in all cloud layers, but peaked immediately beneath the thin water layer. The large aggregates/dendrites were also distributed everywhere in the cloud, but had maximum habit fractions at the cloud bottom. The following summarizes additional ongoing and future research associated with the radiative transfer study of midlevel, mixed-phase clouds: The optical properties of individual particle have been computed. A new mixture scheme for modeling the mixed-phase cloud is being developed. The bulk cloud particle optical properties at each sliced layer will be computed and tabulated into a library. Combining this pre-computed cloud library, in-situ atmospheric profiles, and surface parameters, the upwelling radiance to the satellite sensor will be accurately estimated. Finally, a study on the sensitivity of satellite sensor channels to variability in the specific cloud profile presented herein and TERRA/MODIS validation will be documented in future papers.

published proceedings

  • 12th Conference on Cloud Physics, and 12th Conference on Atmospheric Radiation

author list (cited authors)

  • Niu, J., Carey, L. D., Yang, P., Kankiewicz, J. A., & Vonder Haar, T. H.

complete list of authors

  • Niu, J||Carey, LD||Yang, P||Kankiewicz, JA||Vonder Haar, TH

publication date

  • December 2006