Events of increased particle number concentrations around trade wind cumuli near Barbados
B. Wehner1, F. Ditas1, A. Wiedensohler1 and H. Siebert1
1Leibniz Institute for Tropospheric Research (TROPOS), 04318 Leipzig, Germany
Keywords: new particle formation, clouds, ultrafine particles.
Presenting author email: [email protected]
Beside numerous measurements at ground-based stations, new particle formation has been occasionally observed in higher altitudes of the troposphere. However, such measurements are rare and thus the relevant processes and meteorological conditions under which particle formation and growth occur are still not completely understood.
In November 2010 and April 2011 the CARRIBA
(Cloud, Aerosol, Radiation, and TuRbulence in the trade wInd regime over BArbados) campaign (Siebert et al., 2012) has been performed to observe the role of aerosol particles within the life cycle of trade wind cumuli. During these campaigns more than 30 research flights using the helicopter-borne platform ACTOS (Airborne Cloud and Turbulence Observation System) have been
done. For measuring aerosol particles a new FastCPC
Figure 1. Time series of specific humidity r, total particle
(Wehner et al., 2011) has been implemented on ACTOS
number concentration N, liquid water content LWC, and
to measure the total particle number concentration N
with a time resolution of 10 Hz. The aerosol particle number size distribution from 6 nm to 2.5 m was measured using an SMPS (designed by TROPOS) and an OPC (Model 1.129, Grimm Aerosol Technik, Ainring, Germany). Furthermore, ACTOS contains various instruments
thermodynamic parameters, such as temperature, humidity and wind vector. Results & Discussion
The flight pattern of the individual flights started
Figure 2. Length of events of increased N.
usually with a vertical profile over the sea east of the
island of Barbados. After that ACTOS was usually
After a quality check, 95 events of increased
carried to a field of shallow cumuli with typical cloud
particle number concentrations have been detected. Most
of them occur close to cloud edges (~95%) others
During individual flights, N was nearly constant
without any cloud nearby. More than 50% of them lasted
around clouds about a few hundred cm-3. During
between 1 and 5 s corresponding to a horizontal
approximately 70 % of all flights one or more events
extension between 20 and 100 m. The detection of such
with significantly increased (more than a factor of 5)
small regions was possible due to the combination of the
values of N have been observed. These events were often
low true airspeed of 20 m/s and the fast measuring
connected to clouds, i.e. the number concentration
instrumentation. The implication of such particle bursts
increased close to cloud edges. However, in a few cases
for further cloud development is not yet fully understood.
In conclusion, the cloud system does not only act as a
Figure 1 shows an example for increased particle
particle sink for CCN but also as a particle source. The
number concentrations near cumulus clouds. The liquid
relevance of new particle formation for the particle
water content (LWC) is used as cloud indicator. Here,
balance in general will be part of an on-going discussion.
the background value of N is around 300 cm-3, while
some peaks reach values above 4000 cm-3 near a cloud.
Anthropogenic pollution as particle source can be
Forschungsgemeinschaft (SI 1534/3-1 and WE 1900/18-1).
Siebert, H., et al. (2012), The fine-scale structure of the trade wind
regime over Barbados - An introduction to the CARRIBA project -,
Figure 1 shows no obvious correlation between
Atmos. Chem. Phys. Discuss., 12, 28609 - 28660.
specific humidity r or vertical wind speed w and
Wehner, B., et al.: Characterization of a new fast mixing type CPC and
observed increased particle number concentration. This
its application for atmospheric particle measurements, Atmos. Meas.
is similar to most other cases and a more detailed
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