Method to retrieve cloud condensation nuclei number concentrations using lidar measurements
Abstract. Determination of cloud condensation nuclei (CCN) number
concentrations at cloud base is important to constrain aerosol–cloud
interactions. A new method to retrieve CCN number concentrations using
backscatter and extinction profiles from multiwavelength Raman lidars is
proposed. The method implements hygroscopic enhancements of backscatter and
extinction with relative humidity to derive dry backscatter and extinction
and humidogram parameters. Humidogram parameters, Angstrom
exponents, and lidar extinction-to-backscatter ratios are then linked to the
ratio of CCN number concentration to dry backscatter and extinction
coefficient ( ARξ ). This linkage is established based on
the datasets simulated by Mie theory and κ -Kohler theory with in-situ-measured particle size distributions and chemical compositions. CCN
number concentration can thus be calculated with ARξ and
dry backscatter and extinction. An independent theoretical simulated dataset
is used to validate this new method and results show that the retrieved CCN
number concentrations at supersaturations of 0.07 %, 0.10 %, and
0.20 % are in good agreement with theoretical calculated values.
Sensitivity tests indicate that retrieval error in CCN arises mostly from
uncertainties in extinction coefficients and RH profiles. The proposed
method improves CCN retrieval from lidar measurements and has great
potential in deriving scarce long-term CCN data at cloud base, which benefits
aerosol–cloud interaction studies.