Quantification of aerosol-cloud relationships through ground-based long-term dual-FOV Raman lidar measurements

The dual-FOV Raman lidar technique is capable to investigate aerosol-cloud interactions, which are of high relevance due to their currently poor understanding and their strong significance for Earth’s radiative budget. Dual-FOV Raman lidar cloud probings are performed in Leipzig, Germany, since 2010 on a regular basis. The obtained, extensive dataset is utilized to quantify aerosol-cloud relationships.

Figure 1 shows a dataset employed for a statistical approach of the magnitude of aerosol-cloud interactions. The cloud droplet number concentration (CDNC) in the lower part of the cloud is plotted in dependence of the aerosol extinction coefficient below the cloud. The scatter of the data is due to the multitude of effects, which have an impact on cloud microphysical properties. This multitude makes it very challenging to isolate and quantify the relevant effects. However, the data show a trend. Higher aerosol loads lead to an increased CDNC at cloud base. This finding is in accordance with the predictions of the Twomey effect. Aerosols from below the cloud are carried into the cloud with updrafts and get activated, forming new cloud droplet. The magnitude of this effect is obtained from the slope of the linear fit of the displayed data, denoted as ACI, which is common measure in climate science (cf. McComiskey et al., JGR, 114, 2009).