High concentrations of ice crystals in upper-tropospheric tropical clouds: is there a link to biomass and fossil fuel combustion?
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Published:2022-02-18
Issue:4
Volume:22
Page:2269-2292
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ISSN:1680-7324
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Container-title:Atmospheric Chemistry and Physics
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language:en
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Short-container-title:Atmos. Chem. Phys.
Author:
Raga Graciela B.ORCID, Baumgardner DarrelORCID, Rios Blanca, Díaz-Esteban YanetORCID, Jaramillo AlejandroORCID, Gallagher MartinORCID, Sauvage BastienORCID, Wolff Pawel, Lloyd Gary
Abstract
Abstract. Eight years of upper-tropospheric (UT) ice crystal measurements
with the backscatter cloud probe (BCP), installed on commercial aircraft
operated 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 (EIEs), defined in this study as encounters with
clouds that have number concentrations exceeding 5000 L−1. A total of
3196 events, in clouds of horizontal extent ≥ 2.5 km, were identified during the period from December 2011 to March 2020 in
the latitude band between 30∘ S and 30∘ N. Regions of
anthropogenic sources of carbon monoxide, with particles that can alter
cloud microphysics, were attributed to these EIEs in UT clouds using the
SOFT-IO model. The evaluation of low- and upper-level kinematic variables
from the European Centre for Medium-Range Weather Forecasts (ERA5)
reanalysis, combined with spatial distributions of aerosol optical depth and
regions of biomass burning, highlights the physical mechanisms 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), provide additional evidence of the role of deep convection
in transporting aerosol particles, cloud hydrometeors and carbon monoxide to
aircraft cruising altitudes. The evaluation of aerosol particle mass
concentrations and composition from the Modern-Era Retrospective analysis
for Research and Applications, Version 2 (MERRA-2) contributes additional
evidence for a link between regions of EIEs and surface emissions of dust,
black carbon (BC), organic carbon (OC) and sulfate particles. Given the
composition of the source aerosols and the role of deep convection in their
transport to the UT, the sampled ice clouds likely originate from the
homogeneous or heterogeneous freezing of droplets formed on these particles,
as has been reported in previous studies. The results from this study,
which have been obtained from a large sample of measurements, have
ramifications related to satellite measurement validation, weather
forecasting and climate change. In addition, over 2000 of the randomly
sampled clouds had derived ice water contents larger than 1 g m−3, a
concentration that is considered potentially hazardous to commercial
aircraft operations.
Publisher
Copernicus GmbH
Subject
Atmospheric Science
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