The growth of ice crystals in presence of supercooled liquid droplets represents the most important process for precipitation formation in the mid-latitudes. However, such mixed-phase interaction processes remain relatively unknown, as capturing the complexity in cloud dynamics and microphysical variabilities turns to be a real observational challenge. Ground-based radar systems equipped with fully polarimetric and Doppler capabilities in high temporal and spatial resolutions such as the S-band transportable atmospheric radar (TARA) are best suited to observe mixed-phase growth processes. In this paper, measurements are taken with the TARA radar during the ACCEPT campaign (analysis of the composition of clouds with extended polarization techniques). Besides the common radar observables, the 3-D wind field is also retrieved due to TARA unique three beam configuration. The novelty of this paper is to combine all these observations with a particle evolution detection algorithm based on a new fall streak retrieval technique in order to study ice particle growth within complex precipitating mixed-phased cloud systems. In the presented cases, three different growth processes of ice crystals, plate-like crystals, and needles are detected and related to the presence of supercooled liquid water. Moreover, TARA observed signatures are assessed with co-located measurements obtained from a cloud radar and radiosondes. This paper shows that it is possible to observe ice particle growth processes within complex systems taking advantage of adequate technology and state of the art retrieval algorithms. A significant improvement is made towards a conclusive interpretation of ice particle growth processes and their contribution to rain production using fall streak rearranged radar data.

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Clouds are a prominent part of the Earth hydrological cycle. In the mid latitudes, the ice phase of clouds is highly involved in the formation of precipitation. The ice particles in the clouds fall to earth either as snow flakes, in the winter month, or melting crystals that become rain drops. An efficient growth process is the interaction of ice crystals and supercooled liquid ater droplets in so called mixed-phase clouds. Mixed phase cloud systems contain both - ice crystals and super cooled cloud droplets - in the same volume of air. The interaction of ice and liquid phase leads to an enhanced growth of ice crystals and, therefore, enhances the amount of precipitation. However, such processes are still not fully understood. This work hows that such complex microphysical processes in mixed-phase clouds can be observed using state of the art ground based radar techniques. Analyzing spectral polarimetric radar data, different signatures of particle growth processes can be identified. The results presented are based on measurements obtained with the Transportable Atmospheric Radar (TARA) during the ACCEPT campaign (Analysis of the Composition of Clouds with Extended Polarization Techniques), in autumn 2014, Cabauw, the Netherlands. TARA is an S-band radar profiler that has full Doppler and spectral polarimetric measurement capabilities. TARAs unique three-beam configuration is also able to retrieve the full 3-D velocity vector. Because the high temporal and spatial resolutions and its configurations TARA can capture the complexity of cloud dynamics and microphysical variabilities involved in mixed-phase cloud systems. A new retrieval technique was applied to several case studies to qualitatively analyze ice particle growth processes within mixed phase cloud systems. These results demonstrate that using radar data re-arranged along fall streak, the interpretation of Doppler spectra and polarization parameters can improve. Based on synergetic measurements obtained during the ACCEPT campaign it was possible to detect possible to detect supercooled liquid water layers within the cloud system and relate them to TARA observations. Therefore, it was possible to even identify different growth processes, like particle riming, generation of the new particles, and particle diffusional growth within the TARA measurements. This demonstrates, that in order to observe ice particle growth processes within complex systems adequate radar technology and state of the art retrieval algorithms are required. Moreover, the ice particle growth processes within cloud systems can be linked directly to the increased rain intensities using along fall streak rearranged radar data. The last objective of the thesis is the extension of the spectral polarimetric measurement capabilities of TARA and the estimate of the differential phase and the specific differential phase in the spectral domain. These two parameters are frequently used to improve rain estimation, hydrometeor classifications and, currently, more and more to improve microphysical process understanding, e.g. the onset of the aggregation of ice particles. So far, the parameters are used only as integrated moments. Nevertheless, the work demonstrates that further work has to be done to completely understand the microphysical information of these spectral resolved parameters. Overall, this work demonstrates that spectral polarimetric radar data can be used to improve the microphysical process understanding. The presented work also shows that spectral polarimetric radar data can be used to estimate quantitative icrophysical properties related to ice particle growth.@en

The interaction of ice crystals with supercooled liquid droplets in mixed-phase clouds leads to an enhanced growth of ice particles. However, such processes are still not clearly understood although they are important processes for precipitation formation in midlatitudes. To better understand how ice particles grow within such clouds, changes in the microphysical parameters of a particle population falling through the cloud have to be analyzed. The Transportable Atmospheric Radar (TARA) can retrieve the full 3D Doppler velocity vector based on a unique three-beam configuration. Using the derived wind information, a new fall streak retrieval technique is proposed so that microphysical changes along those streaks can be studied. The method is based on Doppler measurements only. The shown examples measured during the Analysis of the Composition of Clouds with Extended Polarization Techniques (ACCEPT) campaign demonstrate that the retrieval is able to capture the fall streaks within different cloud systems. These fall streaks can be used to study changes in a single particle population from its generation (at cloud top) until its disintegration. In this study fall streaks are analyzed using radar moments or Doppler spectra. Synergetic measurements with other instruments during ACCEPT allow the detection of liquid layers within the clouds. The estimated microphysical information is used here to get a better understanding of the influence of supercooled liquid layers on ice crystal growth. This technique offers a new perspective for cloud microphysical studies.@en

Mixed phase clouds contain both ice particles and super-cooled cloud water droplets in the same volume of air. Currently, one of the main challenges is to observe and understand how ice particles grow by interacting with liquid water within the mixed-phase clouds. In the mid latitudes this process is one of the most efficient processes for precipitation formation. The case study presented here is based on observations obtained with the Transportable Atmospheric RAdar (TARA), S-band precipitation radar profiler, from Delft University of Technology during the Analysis of the Composition of mixed-phase Clouds with Extended Polarization Techniques campaign (ACCEPT) at Cabauw The Netherlands, autumn 2014. The high temporal (3 seconds) and spatial resolutions (21 m) as well as the Doppler and polarimetric capabilities of TARA are used to estimate size and shape information of the measured hydrometeors. In addition, the unique 3 beam configuration of TARA provides 3-D dynamical information within the cloud system. Based on the dynamical information it is possible to retrieve the fall steak signatures of falling ice particles within radar measurements. Those signatures allow to follow particle population from their generation (at cloud top) to their disintegration. So this technique offers a new perspective for cloud microphysical evolution studies. Using retrieved profiles of radar moments and spectral information along the fall streaks, microphysical information are estimated leading to a better understanding of the influence of super-cooled liquid layer on ice crystals growth under ambient conditions. A synergetic setup of instruments during the ACCEPT campaign was used to liquid layers within the cloud system. So several type of ice crystal growth processes could be detected and will be presented and discussed. @en

Within mixed-phase clouds the interaction of ice crystals with super-cooled liquid water leads to an enhanced growth of the ice particles. The growth of ice particles from mixed-phase interactions is an important process for precipitation formation in the mid-latitudes. However, such a process is still not clearly understood, nowerdays. To understand the ice particle growth within these clouds the microphysical changes of a single particle population falling through the cloud have to be analysed. Using the 3 beam configuration of the Transportable Atmospheric Radar (TARA) we retrieve the full 3-D Doppler velocity vector. This retrieved dynamical information is used to retrieve the path of a single particle population through the measured cloud system – the so called fall streak – so that microphysical changes along those path can be studied. A way to study changes in ice particle microphysics is to analyse radar Doppler spectra. Microphysical changes along the path of a population of ice particles through a mixed-phase cloud can be correlated to changes in the retrieved radar spectrograms. The instrumental synergy setup during the ACCEPT campaign (Analysis of the Composition of Clouds with Extended Polarization Techniques campaign), fall 2014, Cabauw the Netherlands, allows to detect liquid water layers within mixed-phase clouds. Therefore, identified changes within the retrieved spectrograms can be linked to the presence of super-cooled liquid layers. In this work we will explain the backtracking methodology and its use for the interpretation of velocity spectra. The application of this new methodology for ice particle growth process studies within mixed-phase clouds will be discussed. @en