Premium
Evaluation of long‐term surface‐retrieved cloud droplet number concentration with in situ aircraft observations
Author(s) -
Lim KyoSun Sunny,
Riihimaki Laura,
Comstock Jennifer M.,
Schmid Beat,
Sivaraman Chitra,
Shi Yan,
McFarquhar Greg M.
Publication year - 2016
Publication title -
journal of geophysical research: atmospheres
Language(s) - English
Resource type - Journals
eISSN - 2169-8996
pISSN - 2169-897X
DOI - 10.1002/2015jd024082
Subject(s) - liquid water path , effective radius , cloud base , environmental science , overcast , liquid water content , radiometer , microwave radiometer , remote sensing , cloud top , radiative transfer , meteorology , cloud computing , cloud physics , cloud height , atmospheric sciences , cloud cover , physics , aerosol , optics , geology , computer science , sky , quantum mechanics , galaxy , operating system
A new operational retrieval of cloud droplet number concentration ( N D ) at cloud base has been produced from surface remote sensors at the Atmospheric Radiation Measurement (ARM) Southern Great Plains site for 13 years from January 1998 to January 2011. The retrieval is based on surface radiometer measurements of cloud optical depth from the multifilter rotating shadow band radiometer and liquid water path from the microwave radiometer (MWR). It is only applicable for single‐layered overcast warm (stratus or stratocumulus) clouds. Evaluation with in situ aircraft measurements during the extended‐term aircraft field campaign, Routine ARM Aerial Facility (AAF) Clouds with Low Optical Water Depths (CLOWD) Optical Radiative Observations (RACORO), shows that the retrieved N D robustly reproduces the primary mode of the in situ measured probability density function (PDF) but produces too wide a distribution, primarily caused by frequent high cloud droplet number concentration. Our analysis shows that the error in the MWR retrievals at low liquid water paths is one possible reason for this deficiency. Modification through the diagnosed liquid water path from the coordinate solution improves not only the PDF of the retrieved N D but also the relationship between the cloud droplet number concentration and cloud droplet effective radius. Consideration of entrainment effects rather than assuming an adiabatic cloud improves the values of the N D retrieval by reducing the magnitude of cloud droplet number concentration. Aircraft measurements and retrieval comparisons suggest that retrieving the vertical distribution of cloud droplet number concentration and effective radius is feasible with an improvement of the parameter representing the mixing effects between environment and clouds and with a better understanding of the effect of mixing degree on cloud properties.