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.
Aerosol and cloud microphysics covariability in the northeast Pacific boundary layer estimated with ship‐based and satellite remote sensing observations
