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| Titel |
A study of how aerosols affect low-level clouds over the Nordic Countries using MODIS, ground-based, ECMWF and weather radar data. |
| VerfasserIn |
M. K. Sporre, E. Swietlicki, P. Glantz, M. Kulmala  |
| Konferenz |
EGU General Assembly 2012
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 14 (2012) |
| Datensatznummer |
250065767
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| Zusammenfassung |
| Several types of data have been combined to investigate how aerosol particles and
meteorological parameters affect microphysical, radiative and precipitation properties of
low-level clouds over Sweden and Finland.
The cloud data was obtained from the MODIS (Moderate Resolution Imaging
Spectrometer) instrument on board the Terra and Aqua satellites. The satellite scenes were
screened manually for low-level clouds in limited areas around two background aerosol
measurement stations. One of the stations, Vavihill, is located in Southern Sweden (56.01Ë N
13.9Ë E) and 9 years of number size distribution data from a DMPS (Differential
Mobility Particle Sizer) instrument placed there was used in this study. Hyytiälä, the
other station, is situated in central Finland (61.51Ë N 24.17Ë E) and 10 years of
DMPS from this station data were analysed. Furthermore, modelled meteorological
parameters from the European Centre for Medium-Range Forecasts (ECMWF) as well as
ground-based precipitation measurements from the SMHI (Swedish Meteorological
and Hydrological Institute) and from FMI (Finish Meteorological Institute) have
been used in the study. Also, to be able to estimate precipitation rates in the clouds,
weather radar data obtained in the BALTEX (Baltic Sea Experiment) project were
utilized.
The study includes 229 cases from the Vavihill region and 313 cases from the Hyytiälä
area. The results from both regions show that aerosol concentrations measured at the
ground-based stations have significant negative correlations with the effective radius (re) of
the low-level clouds. The correlation is stronger when the re at 3.7μm is used rather than that
at 2.1μm and the highest correlations are obtained when aerosol number concentrations of
particles with sizes above 180 nm are used. The correlations between cloud optical thickness
(COT) and aerosol number concentrations are on the other hand are positive but lower than
for the re. Also, the COT correlate better with particles at larger size than the re and the
strongest correlation occur at aerosol number concentrations of particles above 500 nm.
However, the relative humidity at 1000 hPa is the variable that has the strongest
correlation with COT. Neither the ground-based precipitation data nor the weather
radar data show any significant correlations with the aerosol number concentrations
at both stations. Nevertheless, there is a significant but low positive correlation
between the re and the strength of the radar reflectivity factor. Hence, the first indirect
aerosol effect can be detected in this dataset but not the second indirect aerosol effect. |
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