Ground-based remote sensing scheme for monitoring aerosol–cloud interactions

Abstract. A new method for continuous observation of aerosol–cloud interactions with ground-based remote sensing instruments is presented. The main goal of this method is to enable the monitoring of the change of the cloud droplet size due to the change in the aerosol concentration. We use high-resolution measurements from a lidar, a radar and a radiometer, which allow us to collect and compare data continuously. This method is based on a standardised data format from Cloudnet and can be implemented at any observatory where the Cloudnet data set is available. Two example case studies were chosen from the Atmospheric Radiation Measurement (ARM) Program deployment on Graciosa Island, Azores, Portugal, in 2009 to present the method. We use the cloud droplet effective radius (r_e) to represent cloud microphysical properties and an integrated value of the attenuated backscatter coefficient (ATB) below the cloud to represent the aerosol concentration. All data from each case study are divided into bins of the liquid water path (LWP), each 10 g m⁻² wide. For every LWP bin we present the correlation coefficient between ln r_e and ln ATB, as well as ACI_r (defined as ACI_r = −d ln r_e∕d ln ATB, change in cloud droplet effective radius with aerosol concentration). Obtained values of ACI_r are in the range 0.01–0.1. We show that ground-based remote sensing instruments used in synergy can efficiently and continuously monitor aerosol–cloud interactions.