Abstract:
We have compared in situ measurements
near the leading-edges of wave-clouds observed during
the SUCCESS experiment with numerical simulations.
Observations of high supersaturations with respect to ice (> 50%) near the leading edge of a very cold wave cloud (T < -60°C) are approximately consistent
with recent theoretical and laboratory studies suggesting
that large supersaturations are required to homogeneously freeze sulfate aerosols. Also, the peak ice crystal
number densities observed in this cloud (about 4 cm¯³)
are consistent with the number densities calculated in
our model. In the warmer wave-cloud (T ~ -37°C) relatively
large ice number densities were observed (20-40
cm¯³). Our model calculations suggest that these large
number densities are probably caused by activation of
sulfate aerosols into liquid droplets followed by subsequent
homogeneous freezing. If moderate numbers of
effective heterogeneous freezing nuclei (0.5-1cm¯³) had
been present in either of these clouds, then the number
densities of ice crystals and the peak relative humidities
should have been lower than the observed values.
