CCN Measurements Using a Novel Instrument

Dr. Patrick Chuang, NCAR/ASP

A novel instrument for the measurement of cloud condensation nuclei (CCN), designed specifically for aircraft use, was constructed. Initially, the instrument design used a ramping supersaturation profile in a manner similar to that by Hudson (1990). Such a technique is attractive because it can yield CCN spectra in near real-time (less than 1 min), an important feature for aircraft measurement. However, subsequent analysis of our instrument shows that our implementation of this technique does not lead to accurately interpretable results. Implementing the device as a single-supersaturation instrument will be shown to result in accurate measurements.

The instrument was flown during the Second Aerosol Characterization Experiment (ACE-2) on board the CIRPAS Pelican. A CCN closure experiment, where measured CCN concentration is compared with that predicted from aerosol physical and chemical composition measurements, was performed. CCN and aerosol measurements below stratiform clouds are compared to nearly simultaneous in-cloud measurements of cloud droplet number and effective diameter measured by the Meteo-France Merlin-IV.

ction of buoyancy at small scales due to droplet evaporation near the cloud-clear air interface. Sedimentation of cloud droplets seems to play an important role in this process..

uilateral trangle that outlines the southern end of the watershed. We discuss the evolution of 2-m mixing ratio and temperature and its relationship to elevation and surface cover, and the evolution of PBL temperature and mixing ratio during the day, and then focus on the causes of temperature and mixing ratio evolution during the late morning (10-12 LST).

Major results are:

(a) a linear dependence of 2-m temperature with elevation, that is closely related to static stability during the night,

(b) a dependence of 2-m temperature on surface cover, once the elevation effect is removed,

(c) interesting inconsistencies involving the two aircraft and surface data, some of which may be related to surface cover,

(d) the influence of surface properties on PBL growth, and

(e) a strong suggestion of direct heating of the PBL by radiative flux divergence during the late morning, especially for the day with nonuniform soil moisture. Mesoscale (order 10 km) eddies may have also played a role in heating on this day.

and its inherent limitations on rainfall estimation, rain type classification and other PR-derived variables.

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