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Extreme Ice Crystal Events Linked to Biomass and Fossil Fuel Combustion

D. Baumgardner1, G. Binimelis2 and M. Gallagher3

1Droplet Measurement Technologies, Boulder, CO 80301; 919-457-2996, E-mail: darrel@dropletmeasurement.com
2Universidad Nacional Autonoma de Mexico, Mexico City, Mexico
3University of Manchester, Manchester, United Kingdom

Eight years of upper tropospheric (UT) ice crystal measurements with the Backscatter Cloud Probe (BCP), as part of the In-Service Aircraft for a Global Observing System (IAGOS), have been analyzed to assess the frequency and characteristics of extreme ice crystal events (EIE), defined in this study as encounters with clouds that have number concentrations exceeding 5000 L-1. A total of 6490 events, in clouds of horizontal extent > 2.5 km, were identified during the period from December 2011 to March 2020 in the global band between 30°S and 30°N. Evaluation of in situ measurements of carbon monoxide (CO) in these UT clouds, combined with back-trajectories and CO emission inventories, allow the identification of regional anthropogenic sources. An evaluation of low- and upper-level kinematic variables from the Modern-Era Retrospective analysis for Research and Applications, Version 2 (MERRA-2), combined with spatial distribution of aerosol optical depth and regions of biomass burning, reveal the physical mechanism by which the particles are lofted to flight levels in regions of deep convection. The maps of lightning frequency derived from the World Wide Lightning Location Network (WWLLN) contribute additional evidence of the role of deep convection lofting ice forming aerosols to the UT. The MERRA-2 analysis shows clear spatial correlations that link dust, black carbon, organic carbon and sulfate particles with regions of EIE. The results from this study have important ramifications related to climate change, satellite measurement validation, weather forecasting and aircraft operations.

Figure 1

Figure 1. Worldwide distribution of extreme ice events (EIE) when ice clouds concentrations exceed 5000 L-1 (2011-2020). The color scale indicates the concentration ice crystal concentration (L-1). The black stars indicate the location of megacities.

Figure 2

Figure 2. Carbon monoxide (CO) concentration anomalies (color scale) co-located with all upper tropospheric ice clouds.