Exploiting vertically pointing Doppler radar for advancing snow and ice cloud observations

• Main Author: Maahn, Maximilian
• Format: Doctoral or Postdoctoral Thesis
• Language: German; English
• Published: 2015
• Subjects: ddc:550; Svalbard; East Antarctica; Antarc*; Antarctica
• Online Access: https://kups.ub.uni-koeln.de/6002/; https://kups.ub.uni-koeln.de/6002/1/thesis_mmaahn_pub.pdf

Ice and snow particles play a key role in the atmosphere of the Earth and affect—among others—cloud physics and radiative properties, precipitation, and surface albedo. As a consequence, ice and snow have major impact on weather and climate. However, in situ observations of ice clouds and snowfall are difficult and sparse. This leads to a great potential of remote sensing, which can provide observations at high temporal and spatial resolutions. Among the various types of remote sensing instruments, ground-based vertically pointing Doppler radars are one of the most promising concepts: Doppler radars are the only instruments which can penetrate also optically thick clouds and, at the same time, are capable of measuring the fall velocity of hydrometeors. However, the observables of Doppler radars are only indirectly linked to cloud and precipitation properties. The required transfer functions are not uniquely defined resulting in substantial uncertainties of radar-based ice cloud and snowfall retrievals. In the context of studying ice and snow with radars, this study investigates two key issues: (I) the need for additional snowfall measurements with radar and (II) the potential of higher moments of the radar Doppler spectrum for observing ice cloud properties. To address Key Issue I, an improved spectral processing scheme for the MRR, a compact precipitation Doppler radar, is introduced. The scheme significantly enhances the radar sensitivity and allows observations of snowfall profiles (Publication I). One year of MRR observations from three polar sites in East Antarctica and Svalbard are investigated with respect to changes of snowfall within the vertical column (Publication II). The transformation found is used for assessing the snowfall measurement uncertainties of the radar onboard the CloudSat satellite which is the only source of global snowfall estimates. However, the lowest 1200 m above the surface are contaminated by ground clutter so that the measurements cannot be exploited (blind zone). The analysis ...