Investigations of clouds by radar

Analysis of the state and the dynamics of single clouds and cloud systems based on data from the IMK C-Band Doppler radar and the IMK cloud radar.

The high resolution in space and time of radar data also allows the observation and analysis of the temporal and spatial dynamics of atmospheric systems. A feature of a Doppler radar is the ability to obtain also the (radial) windfield by Doppler shift of the radar signal. Moreover, under certain conditions the three dimensional horizontal windfield can be calculated (volume velocity processing, VVP). The mentioned atmospheric systems are normally related to clouds and precipitation. Single phenomena (gust fronts, tornadoes), however, show specific reflectivity and flow signatures without cloud formation.
The Institute operates two radars: since 1994 a C-Band Doppler radar (wave length: 5.3 cm)
with which clouds containing precipitation particles can be detected, and since June 2005 a scanning 35 GHz cloud radar (wave length: 8.4 mm) with which clouds without precipitation
elements are observed.  The C-Band radar is operated with a continuous scanning schedule, the cloud radar is operated occasionally only.  The complete volume data of the C-Band radar are archived since start of operation.

MIRA36S cloud radar (Metek Comp., Elmshorn, Germany)

A topic of the investigations is the analysis of tracks of convective cells, mostly thunderstorms. To this end, the tracking algorithm TRACE3D has been developed. It identifies convective cells by specific reflectivity signatures from data of the C-Band radar and follows them in space and time using successive radar images. TRACE3D is built such that also the variation in the vertical can be obtained – at least in proximity of the radar location.TRACE3D has been used in the past to discover orographic conditions influencing cloud tracks.

The Figure shows all tracks on convective cells from the year 2000 for wind directions
ranging from 250 to 252° determined by the tracking algorithm TRACE3D. The wind
directions have been derived by the VVP method (volume velocity processing) at heights
between 2 and 4 km. Specific events as cell splitting are omitted here.

The cloud radar MIRA36S (manufacturer: METEK, Elmshorn, Germany) has a special feature: It is of scanning type which is seldomly realized. It covers the whole azimuth range and elevations to plus/minus 45 degree measured from the zenith. Thus, also voume scancs can be taken. In receiving mode the cloud radar analyses polarization of the signal such that
the shape of the scattering particles can be inferred. In this way spherical drops can be discriminated from aspherical ones the ice particles.


The now available combination of a Doppler wind Lidar, a cloud and a C-Band radar makes it possible to follow the development of precipitation from the earliest onset, in particular in cases of strong convection.

To detect precipitation existing beyond the visibility of radars two additional measuring systems are operated: A K-Band FMCW radar (24 GHz) allowing to derive profiles of drop size distributions from the Doppler shift of falling hydrometeors. The range of that radar is restricted to the lowermost 2 km of the atmosphere. These instruments are complemented
by  two distrometers (Joss-Waldvogel and Parsivel) measuring the size distributions at ground with high temporal resolution. The Parsivel instrument discriminates between different types of hydrometeors. This instrument has been developed at the Institute and can now be ordered from the Ott company (Kempten, Germany).

In summary, precipitation falling in the near environment of all instruments can be analysed without gap.