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| Titel |
Observations of ice nuclei and heterogeneous freezing in a Western Pacific extratropical storm |
| VerfasserIn |
J. L. Stith, C. H. Twohy, P. J. DeMott, D. Baumgardner, T. Campos, R. Gao, J. Anderson |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1680-7316
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| Digitales Dokument |
URL |
| Erschienen |
In: Atmospheric Chemistry and Physics ; 11, no. 13 ; Nr. 11, no. 13 (2011-07-01), S.6229-6243 |
| Datensatznummer |
250009882
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| Publikation (Nr.) |
 copernicus.org/acp-11-6229-2011.pdf |
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| Zusammenfassung |
| In situ airborne sampling of refractory black carbon (rBC) particles and Ice
Nuclei (IN) was conducted in and near an extratropical cyclonic storm in the
western Pacific Ocean during the Pacific Dust Experiment, PACDEX, in the
spring of 2007. Airmass origins were from Eastern Asia. Clouds associated
primarily with the warm sector of the storm were sampled at various
locations and altitudes. Cloud hydrometeors were evaporated by a counterflow
virtual impactor (CVI) and the residuals were sampled by a single particle
soot photometer (SP2) instrument, a continuous flow diffusion chamber ice
nucleus detector (CFDC) and collected for electron microscope analysis. In
clouds containing large ice particles, multiple residual particles were
observed downstream of the CVI for each ice particle sampled on average. The
fraction of rBC compared to total particles in the residual particles
increased with decreasing condensed water content, while the fraction of IN
compared to total particles did not, suggesting that the scavenging process
for rBC is different than for IN. In the warm sector storm midlevels at
temperatures where heterogeneous freezing is expected to be significant
(here −24 to −29 °C), IN concentrations from ice particle residuals
generally agreed with simultaneous measurements of total ice concentrations
or were higher in regions where aggregates of crystals were found,
suggesting heterogeneous freezing as the dominant ice formation process in
the mid levels of these warm sector clouds. Lower in the storm, at warmer
temperatures, ice concentrations were affected by aggregation and were
somewhat less than measured IN concentrations at colder temperatures. The
results are consistent with ice particles forming at storm mid-levels by
heterogeneous freezing on IN, followed by aggregation and sedimentation to
lower altitudes. Compositional analysis of the aerosol and back trajectories
of the air in the warm sector suggested a possible biomass burning source
for much of the aerosol. Comparison of the particles from the CFDC with the
other aerosol in the residuals of ice particles suggested that the largest
portion of IN had similar inferred origins (from biomass burning with minor
amounts of rBC) as the other aerosol, but contained slightly elevated
amounts of calcium and less influence from sea salt. |
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