Published: 11 March 2013

Cloud droplet number concentration is an important factor in understanding aerosol-cloud interactions. As aerosol concentration increases, it is expected that droplet number concentration, N_d, will increase and droplet size decrease for a given liquid water path, which will greatly affect cloud albedo as smaller droplets reflect more shortwave radiation. However, the magnitude and variability of these processes under different environmental conditions is still uncertain. McComiskey et al. (2009) have implemented a method, based on Boers and Mitchell (1994), for calculating N_d from ground-based remote sensing measurements of optical depth and liquid water path. This method has been implemented as the Droplet Number Concentration (NDROP) value-added product (VAP).

The NDROP VAP provides an estimate of the cloud droplet number concentration of overcast water clouds retrieved from a cloud optical depth from the multifilter rotating shadowband radiometer (MFRSR) and liquid water path retrieved from the microwave radiometer (MWR). When cloud layer information is available from vertically pointing lidar and radars in the Active Remote Sensing of Clouds (ARSCL) VAP, NDROP also provides estimates of the adiabatic liquid water path and an adiabatic parameter (beta) that indicates how divergent the liquid water path is from the adiabatic case. Quality check flags (qc_drop_number_conc), an uncertainty estimate (drop_number_conc_toterr), and a cloud layer type flag (cloud_base_type) are useful indicators of the quality and accuracy of any given value of the retrieval.

NDROP is currently in evaluation mode, and any comments on the data set are welcome. The evaluation data are available for five years from the Southern Great Plains (SGP). This VAP will run autonomously when the evaluation is completed. More information is available at the VAP web page and in the README file that accompanies the data files in the Data Archive’s evaluation area.

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