 |
| Titel |
Estimating the Influence of Biological Ice Nuclei on Clouds with Regional Scale Simulations |
| VerfasserIn |
Matthias Hummel, Corinna Hoose, Caroline Schaupp, Ottmar Möhler |
| Konferenz |
EGU General Assembly 2014
|
| Medientyp |
Artikel
|
| Sprache |
Englisch
|
| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 16 (2014) |
| Datensatznummer |
250091248
|
| Publikation (Nr.) |
 EGU/EGU2014-5527.pdf |
|
|
|
|
|
| Zusammenfassung |
| Cloud properties are largely influenced by the atmospheric formation of ice particles. Some
primary biological aerosol particles (PBAP), e.g. certain bacteria, fungal spores or pollen,
have been identified as effective ice nuclei (IN). The work presented here quantifies the IN
concentrations originating from PBAP in order to estimate their influences on clouds with the
regional scale atmospheric model COSMO-ART in a six day case study for Western Europe.
The atmospheric particle distribution is calculated for three different PBAP (bacteria, fungal
spores and birch pollen). The parameterizations for heterogeneous ice nucleation
of PBAP are derived from AIDA cloud chamber experiments with Pseudomonas
syringae bacteria and birch pollen (Schaupp, 2013) and from published data on
Cladosporium spores (Iannone et al., 2011). A constant fraction of ice-active bacteria
and fungal spores relative to the total bacteria and spore concentration had to be
assumed.
At cloud altitude, average simulated PBAP number concentrations are ~17L-1 for
bacteria and fungal spores and ~0.03L-1 for birch pollen, including large temporal
and spatial variations of more than one order of magnitude. Thus, the average,
“diagnostic” in-cloud PBAP IN concentrations, which only depend on the PBAP
concentrations and temperature, without applying dynamics and cloud microphysics, lie at
the lower end of the range of typically observed atmospheric IN concentrations .
Average PBAP IN concentrations are between 10-6L-1 and 10-4L-1. Locally but
not very frequently, PBAP IN concentrations can be as high as 0.2L-1 at -10Ë
C.
Two simulations are compared to estimate the cloud impact of PBAP IN, both including
mineral dust as an additional background IN with a constant concentration of 100L-1. One
of the simulations includes additional PBAP IN which can alter the cloud properties
compared to the reference simulation without PBAP IN. The difference in ice particle and
cloud droplet concentration between both simulations is a result of the heterogeneous ice
nucleation of PBAP. In the chosen case setup, two effects can be identified which are
occurring at different altitudes. Additional PBAP IN directly enhance the ice crystal
concentration at lower parts of a mixed-phase cloud. This increase comes with a decrease in
liquid droplet concentration in this part of a cloud. Therefore, a second effect takes
place, where less ice crystals are formed by dust-driven heterogeneous as well as
homogeneous ice nucleation in upper parts of a cloud, probably due to a lack of liquid water
reaching these altitudes. Overall, diagnostic PBAP IN concentrations are very low
compared to typical IN concentration, but reach maxima at temperatures where
typical IN are not very ice-active. PBAP IN can therefore influence clouds to some
extent.
Iannone, R., Chernoff, D. I., Pringle, A., Martin, S. T., and Bertram, A. K.: The
ice nucleation ability of one of the most abundant types of fungal spores found in
the atmosphere, Atmos. Chem. Phys., 11, 1191-1201, 10.5194/acp-11-1191-2011,
2011.
Schaupp, C.: Untersuchungen zur Rolle von Bakterien und Pollen als Wolkenkondensations-
und Eiskeime in troposphärischen Wolken, Ph.D. thesis, Institute of Environmental Physics,
Heidelberg University, Heidelberg, Germany, 2013. |
|
|
|
|
|
|