Interactive comment on “ Statistics of vertical velocities in supercooled cloud layers over Leipzig and Praia measured with Doppler lidar ” by Johannes
We appreciate the unconcealed review provided for our manuscript. The main point of the critics points to the fact that we emphasize a potential relationship between vertical motion and ice formation. In fact, the manuscript is supposed to ’just’ provide a study that compares regional differences in vertical air motions in mid-level stratiform clouds (which is barely available to date). We did not aim on providing full conclusions on the effect of the air motion on the microphysical properties of the cloud layer which might, however, be part of future studies. Similar studies have been presented, e.g. by Hill et
The effect of dynamics on mixed-phase clouds: Theoretical considerations
Abstract A theoretical framework has been developed describing nonequilibrium formation and maintenance of mixed-phase clouds. The necessary and sufficient conditions required to activate liquid water within a preexisting ice cloud, and thus convert it to mixed phase, are considered for three scenarios: (i) uniform ascent, (ii) harmonic vertical oscillations, and (iii) turbulent fluctuations. The general conditions are the following: First necessary condition: The vertical velocity of an ice cloud parcel must exceed a threshold velocity to activate liquid water. Second necessary condition: The activation of liquid water within an ice cloud parcel, below water saturation, requires a vertical ascent above some threshold altitude to bring the vapor pressure of the parcel to water saturation. Only when the first and second conditions are true do these conditions become sufficient for the activation of liquid water in ice clouds. These required conditions for the generation of mixed-phase cloud are supported b...
Simultaneous radar and aircraft observations of mixed‐phase cloud at the 100 m scale
Three UK C‐130 aircraft flights performed in conjunction with the Chilbolton Advanced Meteorological Radar were carried out in mixed‐phase clouds. The aircraft instrumentation included the Small Ice Detector (SID) and Nevzorov probe that are both capable of discriminating between liquid and ice phase. It was found that particle sphericity measured by the SID could be successfully used as a proxy for particle phase. Using a combination of the SID and other probes it is possible to determine whether a 100 m cloud segment is ice, liquid or mixed‐phase. Regions as short as 100 m exhibited mixed‐phase characteristics. There was generally good agreement between water phase indicated by the SID and Nevzorov probes, with any differences arising from the fact that the SID provides a number‐weighted estimate of dominant phase, while the Nevzorov probe provides a mass‐weighted estimate. The radar and aircraft observations show that when high values of differential reflectivity are observed the nearby presence of liquid water is indicated. When large ice crystals are present in deeper cloud they can suppress the differential reflectivity signal. Therefore the absence of a high differential reflectivity signal does not necessarily mean that liquid water is absent. © Royal Meteorological Society, 2004. P. R. Field's and P. R. A. Brown's contributions are Crown copyright.