Here are some of my favorite measurements, made during my PhD in the CLARA-project.
Clara was a national Dutch project which aimed at getting a better understanding
of the interaction between clouds and radiation by improving the measurement of
In the upper part of the melting layer the reflections by the falling ice crystals increase as the refractive index of water is higher then that of ice. In the lower part of the melting layer the reflections decrease again as the particles become smaller. These smaller particles reflect less power, but also fall faster and thus decreases the number density and total reflection.
Below 2 km the measurement shows some vertical stripes. An FM-CW radar uses a Fourier transform to convert frequency into range information. The cross talk from this transform makes stripes from these point targets. The origin of these reflections is not known. For more on this phenomenon see the section on Angels below.
Normally they are seen as small dots (or stripes), see e.g. the reflections below the altostratus cloud. The picture below was made from a raw data file, which has a time resolution of 5 ms. The background is the radar reflection as function of height and time in seconds. The line is the average reflection, averaged over the heights shown. This high temporal resolution provides new insight on these angels. An interference pattern is seen in the power. The phase of this angel has a sinus pattern. The measured thickness of the object may be due to signal processing.
More information is found in this article. I would like contact with people who have an idea on what can cause this phenomenon.
The second picture shows the dynamics of this cumulus cloud. The grey background is again the radar reflection; the contours give the velocity as measured by the radar. Negative velocity means the scatterers move upward, positive downward. There are two thermal plumes visible in this cloud, which move up with high speed, up to 5 m/s.
The background of the first picture is the lidar reflection of this cloud. In the middle of the cloud, at 4300 m, the lidar receives almost no reflections. The radar does receive reflections from this layer. The explanation is probably that the crystals in this dark layer are not horizontally aligned. The blue line gives the wind direction measured by a radiosonde. The wind direction changes drastically in this layer. This can cause the crystals to be no longer horizontally aligned.
The two small pictures give the lidar reflection and the width of the Doppler velocity spectrum. In this layer the lidar reflections are low; at the same height the width of the Doppler spectrum is much higher, indicating the presence of turbulence in this layer.
This melting layer for the lidar is sometimes seen to give low reflections. The lidar measurement presented here has the deepest dark band we found up to now. In ten percent of the lidar backscatter profiles the dark band is more than 20 dB deep compared to the rain. More information on the lidar dark band is in these articles from 1998, and 2000.
This set-up is not carefully calibrated yet. The beam width of both antenna systems is about the same and the range and time resolution of both radar's is the same.