Today, the upper troposphere is affected by increasing aircraft emissions.
The effect on climate is double tracked: emission and absorption of light by
soot and sulfur (direct effect) and the formation of contrails and eventually
cirrus clouds (indirect effect). The result of this is global warming.
The investigation of the processes in the upper troposphere is challenging
because of its great height. From 23rd April to 12th October 2003, during the
measurement campaign MARL@MOL, Lidar and Radiosondes were used to access this
region and analyse the influence of air traffic on the atmosphere. The
Meteorological Observatory Lindenberg (MOL) is a station of the German Weather
Service (DWD), situated in an air corridor for flights to the airports in
Berlin. It is a place of high contrail occurrence. The Mobile Aerosol Raman
Lidar (MARL) of the Alfred-Wegener-Institut (AWI) was set up at the station for
the duration of the campaign.
The MARL measures the backscatter coefficient, color ratio, depolarization,
lidar ratio of atmospheric aerosol and the water vapor mixing ratio of the air.
These quantities are very useful for estimating climate change. Two cameras
operating in the visible spectral range were used to identify contrails and were
able to distinguish them from natural and anthropogenic cirrus clouds. Initial
results indicate that the shape of contrail-particles differs from cirrus
cloud-particles and that the effective radius of contrail-particles increases
rapidly with time. Further investigations are necessary to calculate reliable
numerical values. However, the theory of small particles between 0.5 and 3 µm
(refer to: Gao et al, Science 2004) seems to be valid only for contrails with
lifetimes below 20 min.
The analysis of the relative humidity in cirrus clouds can reveal the
condensation process and indicate differences for cirrus clouds in polluted and
clean air (Immler and Schrems, GRL 2002a). In 90% of the observed cases the
relative humidity in cirrus clouds, measured with radiosondes in Lindenberg, was
found to be between 60 and 100% over ice. This value is way below the
theoretically expected values: more than a 100% is supposedly normal, and even
values up to 160% have been observed in clean air. Additionally, the relative
humidity measured by the Lindenberg Radiosonde RS-80A, method of standardized
frequencies (Leiterer, 2002), differs from the relative humidity measured by
MARL for distances above 5 km. The MARL results are more congruent with cloud
formation theory. This phenomenon poses a question on how reliable are the
results of the Sonde. On January 29th 2004, a measurement campaign in Sodankyla
started with the aim of comparing four different water vapor Radiosondes,
including the Lindenberg Radiosonde. If the Radiosonde turns out to be reliable
we would like to further discuss our findings.