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

• Published in: Geophysical research letters Vol. 38; no. 17
• Main Authors: Kanitz, T., Seifert, P., Ansmann, A., Engelmann, R., Althausen, D., Casiccia, C., Rohwer, E. G.
• Format: Journal Article
• Language: English
• Published: Washington, DC Blackwell Publishing Ltd 01-09-2011; American Geophysical Union; John Wiley & Sons, Inc
• Subjects: aerosol impact; Aerosols; Anthropogenic factors; Arenas; Atmospheric aerosols; Atmospheric sciences; Biological materials; Chemistry; Clouds; Earth sciences; Earth, ocean, space; Exact sciences and technology; Forest fires; Freezing; heterogeneous freezing; Ice formation; ice nucleation; Lidar; Physics; Radiation; Southern Hemisphere; South America; Southern Africa; Europe; Africa; South Africa; Chile; Central Europe; Germany; Germany, Sachsen, Leipzig; South Africa, Western Cape, Cape Town; capes; Mid latitude; Southern Hemisphere; research vessels; aerosols; ice; clouds; urban areas; pollution; troposphere; Radar remote sensing; freezing; materials; Radar observation; Lidar; Forest fire; dust; Anthropogenic factor
• ISSN: 0094-8276; 1944-8007
• DOI: 10.1029/2011GL048532

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.
Key Points
Heterogeneous freezing in the Northern and Southern Hemisphere
Discussion of sources of natural and anthropogenic ice nuclei
Determination of cloud phase state by depolarization lidar