Evaluation of long‐term surface‐retrieved cloud droplet number concentration with in situ aircraft observations. Issue 5 (6th March 2016)

• Record Type: Journal Article
• Authors: Lim, Kyo‐Sun Sunny; Riihimaki, Laura; Comstock, Jennifer M.; Schmid, Beat; Sivaraman, Chitra; Shi, Yan; McFarquhar, Greg M.
• Is Part Of: Journal of geophysical research. Volume 121:Issue 5(2016)
• Page Start: 2318
• Page End: 2331
• Publication Date: 2016-03-06
• Subjects: cloud droplet number concentration -- multifilter rotating shadow band radiometer -- microwave radiometer -- cloud droplet effective radius -- RACORO field campaign -- ARM SGP; Atmospheric physics -- Periodicals; Geophysics -- Periodicals; 551.5
• DOI: 10.1002/2015JD024082
• Languages: English
• ISSNs: 2169-897X

Abstract

Abstract: 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. Key Points: New ARM droplet number concentration data product evaluated with aircraft data Adiabaticity parameter improves retrieval but still gives high values in low LWP Using diagnosed liquid water path from coordinated MFRSR and MWR retrieval improves solution