Synergy between ground-based remote sensing systems in microphysical analysis of cirrus clouds

A broad suite of ground-based remote sensing instruments of the Meteorological Observatory Lindenberg, Germany, is combined for the first time to synergistically analyze cirrus cloud microphysics, including a Raman lidar, a Ka band cloud radar and a 5 degrees tilted ceilometer. 84 days of cirrus cloud measurements have been selected to study the correlation between, and the dependences of, the different measured variables. The presented study investigates the effect of the spatial orientation and the shape of solid cloud particles on particle optical properties and their relation to wind and turbulence parameters. A sensitive indicator of particle spatial orientation is the particle depolarization ratio (PDR). When ice crystals are horizontally aligned, mirror reflections can occur, which is evidenced by low PDR if observed with a vertically pointing Raman lidar. Observations are grouped according to the prevailing weather condition. It is found that on some days PDR is constant for long time periods. Interestingly, during warm fronts the PDR is generally small (< 0.2), while during cold fronts it is high (> 0.4). Moreover, the mean lidar ratio of cirrus with high PDR is about 20 sr, two times larger than of cirrus with low PDR. Similar dependences on PDR have been found for the particle extinction coefficient, and for the backscatter coefficient from the tilted ceilometer, but for the Raman lidar backscatter coefficient in perpendicular polarization the opposite behavior is observed.