A063-0009
Impact of aerosol conditions on hemispheric differences in ice formation in stratiform clouds

Wednesday, 9 December 2020
Poster
Martin Radenz1, Patric Seifert2, Johannes Bühl1, Damao Zhang3, Holger Baars1, Ronny Engelmann1, Boris Barja Gonzalez4, Rodanthi-Elisavet Mamouri5, Felix Zamorano4, Heike Kalesse6 and Albert Ansmann1, (1)Leibniz Institute for Tropospheric Research, Leipzig, Germany, (2)Leibniz Institute for Tropospheric Research - TROPOS, Leipzig, Germany, (3)Pacific Northwest National Laboratory, Richland, WA, United States, (4)Universidad de Magallanes, Laboratorio de Investigaciones Atmosféricas, Punta Arenas, Chile, (5)ERATOSTHENES Center of Excellence, Limassol, Cyprus, (6)University of Leipzig, Leipzig, Germany
Abstract:
We present a ground-based remote sensing study of the efficiency of heterogeneous ice formation in stratiform clouds, taking into account temperature, surface-coupling, and aerosol load. Stratiform clouds are highly relevant in terms of their impact on the Earth’s radiation budget and they serve as a well-defined natural laboratory for observing primary heterogeneous ice formation.

This study uses ground-based remote sensing observations obtained by the mobile Leipzig Aerosol and Cloud Remote Observation System (LACROS). The instrumentation of LACROS comprises a 35-GHz scanning cloud radar, a Raman and depolarization lidar, a 14-channel microwave radiometer, a Doppler lidar, a vertically pointing 24-GHz micro rain radar and a disdrometer.

Data from LACROS field campaigns in Leipzig (51.4°N 12.4°E, Germany), Limassol (34.7°N 33.0°E, Cyprus) and Punta Arenas (53.1°S 70.9°W, Chile) are used to get insights into ice formation in stratiform mixed-phase clouds in regions with different aerosol loadings. Each of these datasets covers more than 12 months, observations at Punta Arenas are still ongoing.

Statistics on the abundance of ice-formation in stratiform clouds are compiled. In Leipzig and Limassol all clouds with cloud top temperatures below -15 °C formed ice, while in Punta Arenas only 60-80 % of the clouds do. At cloud top temperatures above, -10°C a correlation between the surface-coupling of a cloud and the likelihood of ice formation was found in Leipzig and Punta Arenas.

The new radar-lidar dataset is compared to existing lidar-only statistics of ice formation in stratiform clouds by applying a lidar ice detection threshold of extinction values lower than 15 Mm-1. With that filtering method, we were able to reproduce prior lidar-only statistics.

Finally, the ground-based datasets were compared to similar statistics derived from combined CALIPSO and CloudSat observations. In agreement to prior studies, ice produced in stratiform clouds over Punta Arenas shows 6 dB lower radar reflectivity factors than their northern-hemispheric counterparts. When linking this difference to the heterogeneous ice formation at cloud top, the findings can be attributed to – on the average – lower INP concentrations in the southern mid-latitudes.

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