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The measuring height of the spectra is just above the melting level.
Two spectral bands are obvious:
A narrow one on the right and a broader one on the
left. We assign the narrow band to cloud droplets and the broad band
to larger ice crystals with a mean fall velocity of 2 m/s
relative to the cloud droplets. Both spectral bands show the same
undulation, which we interpret as the effect of turbulence advecting
the whole ensemble of particles.
The measuring height of the spectra is just below the melting level.
Here are 3 - sometimes even 4 - spectral bands. The additional high-speed
mode is probably caused by the presence of a third family of particles
below the melting layer - namely drizzle-droplets.
The typical fall velocity (relative to the thin
"cloud band") is 4 m/s, which corresponds to droplets with 0.8mm diameter.
No Precipitation reached the ground.
The red lines show "newest" profiles of radar reflectivity. The
time resolution is 0.1sec and the height resolution is 30m.
Weather situation: Stratiform clouds with approx. 1000 to 1400m
cloud base height.
The reflectivity-maximum in about 2600m is at the 0°C level, where
falling ice crystals begin to melt (bright band). The green line indicates
the minimum detectable reflectivity.
Time history of "instantaneous" Doppler Spectra. The color indicates the spectral power. The time runs from bottom to top spanning a total interval of 10sec. The velocity axis spans-3m/s (downward) to +3 m/s (upward) in the upper figure and -5.6 m/s to +2.8 m/s in the lower figure.
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Last modified: Aug 13th, 2001