Abstract
Abstract. Multi-year ground-based remote-sensing datasets were acquired with the Leipzig Aerosol and Cloud Remote Observations System (LACROS) at three sites. A highly polluted central European site (Leipzig, Germany), a polluted and strongly dust-influenced eastern Mediterranean site (Limassol, Cyprus), and a clean marine site in the southern midlatitudes (Punta Arenas, Chile) are used to contrast ice formation in shallow stratiform liquid clouds. These unique, long-term datasets in key regions of aerosol–cloud interaction provide a deeper insight into cloud microphysics. The influence of temperature, aerosol load, boundary layer coupling, and gravity wave motion on ice formation is investigated. With respect to previous studies of regional contrasts in the properties of mixed-phase clouds, our study contributes the following new aspects: (1) sampling aerosol optical parameters as a function of temperature, the average backscatter coefficient at supercooled conditions is within a factor of 3 at all three sites. (2) Ice formation was found to be more frequent for cloud layers with cloud top temperatures above -15∘C than indicated by prior lidar-only studies at all sites. A virtual lidar detection threshold of ice water content (IWC) needs to be considered in order to bring radar–lidar-based studies in agreement with lidar-only studies. (3) At similar temperatures, cloud layers which are coupled to the aerosol-laden boundary layer show more intense ice formation than decoupled clouds. (4) Liquid layers formed by gravity waves were found to bias the phase occurrence statistics below -15∘C. By applying a novel gravity wave detection approach using vertical velocity observations within the liquid-dominated cloud top, wave clouds can be classified and excluded from the statistics. After considering boundary layer and gravity wave influences, Punta Arenas shows lower fractions of ice-containing clouds by 0.1 to 0.4 absolute difference at temperatures between −24 and -8∘C. These differences are potentially caused by the contrast in the ice-nucleating particle (INP) reservoir between the different sites.
Highlights
Clouds and aerosol are inseparably linked via complex pathways of interaction whose outcome manifests in the macroscopic properties of precipitation and radiation fields
This study investigated contrasts in aerosol–cloud interactions in shallow supercooled stratiform clouds observed with the ground-based remote-sensing supersite Leipzig Aerosol and Cloud Remote Observations System (LACROS) at Leipzig, Limassol, and Punta Arenas
Sampling the profiles of optical properties with temperature as a vertical coordinate revealed aerosol load at temperatures between −15 and 0 ◦C being within a factor of 2 at Punta Arenas and Limassol
Summary
Clouds and aerosol are inseparably linked via complex pathways of interaction whose outcome manifests in the macroscopic properties of precipitation and radiation fields. Aerosol particles are required as cloud condensation nuclei (CCN) on which cloud droplets can form. The ways in which aerosol and cloud particles interact are controlled by the dynamics and thermodynamics of the atmospheric environment, with temperature being the most important driver. Thermodynamic processes are considered to dominate the cloud microphysical properties over aerosol-related processes because the thermodynamics con-. M. Radenz et al.: Hemispheric contrasts in stratiform mixed-phase clouds trol the amount of water vapor that is available for being transferred to either the liquid or the ice phase. Radenz et al.: Hemispheric contrasts in stratiform mixed-phase clouds trol the amount of water vapor that is available for being transferred to either the liquid or the ice phase This dominance makes it difficult to isolate aerosol-related effects in observations of cloud properties
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
