Aerosol indirect effects on continental low-level clouds over Sweden and Finland
Aerosol effects on low-level clouds over the Nordic Countries are investigated by combining in situ ground-based aerosol measurements with remote sensing data of clouds and precipitation. Ten years of number size distribution data from two aerosol measurement stations (Vavihill, Sweden and Hyytiälä,...
| Main Authors: | , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2014-11-01
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| Series: | Atmospheric Chemistry and Physics |
| Online Access: | http://www.atmos-chem-phys.net/14/12167/2014/acp-14-12167-2014.pdf |
| Summary: | Aerosol effects on low-level clouds over the Nordic Countries are
investigated by combining in situ ground-based aerosol measurements with
remote sensing data of clouds and precipitation. Ten years of number size
distribution data from two aerosol measurement stations (Vavihill, Sweden
and Hyytiälä, Finland) provide aerosol number concentrations in the
atmospheric boundary layer. This is combined with cloud satellite data from
the Moderate Resolution Imaging Spectroradiometer and weather radar data
from the Baltic Sea Experiment. Also, how the meteorological conditions
affect the clouds is investigated using reanalysis data from the European Centre for Medium-Range Weather Forecasts.
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The cloud droplet effective radius is found to decrease when the aerosol
number concentration increases, while the cloud optical thickness does not
vary with boundary layer aerosol number concentrations. Furthermore, the
aerosol–cloud interaction parameter (ACI), a measure of how the effective
radius is influenced by the number concentration of cloud active particles,
is found to be somewhere between 0.10 and 0.18 and the magnitude of the ACI
is greatest when the number concentration of particles with a diameter
larger than 130 nm is used. Lower precipitation intensity in the weather
radar images is associated with higher aerosol number concentrations. In
addition, at Hyytiälä the particle number concentrations is
generally higher for non-precipitating cases than for precipitating cases.
The apparent absence of the first indirect effect of aerosols on low-level
clouds over land raises questions regarding the magnitude of the indirect
aerosol radiative forcing. |
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| ISSN: | 1680-7316 1680-7324 |