Fine Structure of Cloud Droplet Concentration as Seen from the Fast-FSSP Measurements. Part II: Results of In Situ Observations

M. Pinsky The Institute of Earth Sciences, The Hebrew University of Jerusalem, Jerusalem, Israel

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A. Khain The Institute of Earth Sciences, The Hebrew University of Jerusalem, Jerusalem, Israel

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Abstract

A new feature of cloud structure has been discovered while analyzing the measurements obtained in situ in 57 clouds by the Fast Forward-Scattering Spectrometer Probe (FSSP). By means of a novel technique of statistical analysis, it is shown that droplets form distinct “communities” of about 1-cm scale that differ in concentration, thus creating a highly inhomogeneous cloud microstructure (inch clouds). Those droplet clusters can be found all over the cloud volume and appear to be induced by droplet inertia within a turbulent flow. An increase in turbulence intensity and droplet inertia results in an increase of concentration fluctuations. The authors believe that this finding is the first direct evidence of turbulence–inertia impact on droplet motion in clouds that leads to formation of microstructure conductive to precipitation formation.

Corresponding author address: Alexander P. Khain, The Ring Family Dept. of Atmos. Sciences, The Institute of Earth Sciences, The Hebrew University of Jerusalem, Givat Ram, Jerusalem 91904, Israel. khain@vms.huji.ac.il

Abstract

A new feature of cloud structure has been discovered while analyzing the measurements obtained in situ in 57 clouds by the Fast Forward-Scattering Spectrometer Probe (FSSP). By means of a novel technique of statistical analysis, it is shown that droplets form distinct “communities” of about 1-cm scale that differ in concentration, thus creating a highly inhomogeneous cloud microstructure (inch clouds). Those droplet clusters can be found all over the cloud volume and appear to be induced by droplet inertia within a turbulent flow. An increase in turbulence intensity and droplet inertia results in an increase of concentration fluctuations. The authors believe that this finding is the first direct evidence of turbulence–inertia impact on droplet motion in clouds that leads to formation of microstructure conductive to precipitation formation.

Corresponding author address: Alexander P. Khain, The Ring Family Dept. of Atmos. Sciences, The Institute of Earth Sciences, The Hebrew University of Jerusalem, Givat Ram, Jerusalem 91904, Israel. khain@vms.huji.ac.il

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