Contrasting the impact of aerosols at northern and southern midlatitudes on heterogeneous ice formation

Abstract

Three cloud data sets, each covering four months of observations, were recently recorded with a lidar at Punta Arenas (53°S), Chile, at Stellenbosch (34°S, near Cape Town), South Africa, and aboard the research vessel Polarstern during three north‐south cruises. By comparing these observations with an 11–year cloud data set measured with a lidar at Leipzig (51°N), Germany, the occurrence of heterogeneous ice formation (as a function of cloud top temperature) for very different aerosol conditions in the northern and southern hemisphere is investigated. Large differences in the heterogeneous freezing behavior in the mostly layered clouds are found. For example, <20%, 30%–40% and around 70% of the cloud layers with cloud top temperatures from −15°C to −20°C, showed ice formation over Punta Arenas, Stellenbosch, and Leipzig, respectively. The observed strong contrast reflects the differences in the free tropospheric aerosol conditions at northern midlatitudes, that are controlled by anthropogenic pollution, mineral dust, forest fire smoke, terrestrial biological material and high southern midlatitudes with clean marine conditions.

Strong aerosol–cloud interaction in altocumulus during updraft periods: lidar observations over central Europe

“…Lidars are used since the 1970s to monitor clouds and their evolution, although primarily cirrus and mixed-phase clouds (Platt, 1973(Platt, , 1977Sassen, 1991). Our group also contributed to these observations over the last 25 years (Ansmann et al, 1993(Ansmann et al, , 2005Ansmann et al, 2009;Seifert et al, 2007Seifert et al, , 2010Seifert et al, , 2015Kanitz et al, 2011). Observations are rare in the case of liquid-water clouds because lidars are not appropriate for clouds with typical optical depths of 10 and more.…”

Immersion freezing of ice nucleation active protein complexes

“…Atmospheric observations indicate that heterogeneous ice nucleation in mixed-phase clouds can already occur at temperatures higher than −20 • C (Ansmann et al, 2009;Seifert et al, 2010;Kanitz et al, 2011). In contrast, laboratory studies showed that the majority of non-biological substances found in atmospheric ice crystal residues, i.e., natural mineral dust (e.g., Twohy and Poellot, 2005;Pratt et al, 2009;Kamphus et al, 2010), are only ice active at lower temperatures (e.g., Hoose and Möhler, 2012;Murray et al, 2012).…”

An overview of the first decade of Polly&lt;sup&gt;NET&lt;/sup&gt;: an emerging network of automated Raman-polarization lidars for continuous aerosol profiling

“…Based on these measurements and the Polarstern cruise data, Kanitz et al (2011) contrasted the temperature dependence of heterogeneous ice formation efficiency between the Southern Hemisphere and the Northern Hemisphere. At comparable temperatures, a much higher fraction of icecontaining clouds was found in the Northern Hemisphere, suggesting that the increased aerosol load in the northernhemispheric free troposphere is responsible for this contrast.…”