Mainz, Universiẗat, Diss., 2001.

A linha de instabilidade (LI) pré-frontal que atingiu a Região Metropolitana de São Paulo em 26 de abril de 2007 foi monitorada e analisada por meio de medições de superfície, altitude, radar e satélite. As análises indicam que havia ambiente sinótico favorável para a formação e manutenção da LI. Na região de formação da LI havia ar relativamente quente e úmido em baixos níveis e ar relativamente frio e seco em níveis médios com convergência de massa em baixos níveis e divergência em altos níveis, além de gradiente de temperatura produzido pela aproximação do sistema frontal. A LI foi monitorada pelo radar meteorológico MXPOL e permitiu a avaliação dinâmica e microfísica do sistema. Esta última realizada por meio da classificação de hidrometeororos com as variáveis polarimétricas medidas com o MXPOL. Preliminarmente, os dados de refletividade diferencial (ZDR) e refletividade efetiva (Z) foram consistidos por meio do método da autoconsistência (Vivekanadan et al., 2003), entre essas duas variáveis e a fase diferencial específica (KDP). Removido os viéses de ZDR (-0,36 dB) e da refletividade efetiva (-0,46 dBZ), a classificação de hidrometeoros, em dezessete categorias (gotículas a granizo, insetos, ecos de terreno e de segunda viagem), foi realizada pelo método de lógica fuzzy (Vivekanadan et al., 2003). A classificação de hidrometeoros foi realizada em planos de elevação constante (PPI). Os tipos e estratificação de hidrometeoros são compatíveis com estudos anteriores. Por exemplo, a banda brilhante foi classificada com uma região de mistura de gelo e gotas líquidas com predominância de gotas abaixo e cristais de gelo acima desta. A dinâmica interna da LI foi avaliada por meio da velocidade radial e evidenciou um jato de baixos níveis, convergência ciclônica na dianteira do sistema, e divergência em altos níveis, entre outras características. O rápido deslocamento da LI resultou em precipitação de 7 mm e rajadas de vento de 18 m s-1. Assim, o impacto mais significativo desse sistema na RMSP foi produzido pelo vento. / A prefrontal squal line (LI) that reached tne metropolitan area of São Paulo on April 26 2007 was monitored and analyzed by means of of surface and upper air measurements, weather radar and satellite data. Analyses indicate a favorable synoptic environment to form and sustain the LI. In its genesis region there was relatively warm and moiture air near the surface and relatively cold and dry air aloft with mass convergence below and divergence aloft, as well as temperature gradient along its path induced by the associated cold front. This LI was measured with the MXPOL weather radar and allowed a mesoscale dynamic analysis as well as a microphysics of this weather system. The later was performed by means of a hydrometeor classification with the polarimetric data sets of MXPOL. Initially, the differential reflectivity (ZDR) and the efective reflectivity (Z) were corrected by the selfconsistency method (Vivekanandan et al., 2003) together with the specific diferrential phase (KDP). Ounce removed the ZDR (-0,36 dB) and Z (-0,46 dBZ) biases, the hydrometeoro classification (small drops to hail, insects, ground clutter and second trip echoes) was carrie out by the fuzzy logic method (Vivekanadan et al., 2003). The hydrometeor classification was made at constant elevation angles (PPI) across the LI. The hydrometeoro types are compatible to similar studies. For instance, the bright band was classified as a region mixed phase with drops below and ice crystals aboce it. The LI internal dynamics was analyzed with the help of the radial velocity and indicated a low level jet, cyclonic convergence at the leading edge and divergence aloft at the convective band, among other features. This fast moving LI produced 7 mm of rainfall and wind gust of 18 m s-1. Its most significant impact over RMSP was caused by the wind intensity.

A linha de instabilidade (LI) pré-frontal que atingiu a Região Metropolitana de São Paulo em 26 de abril de 2007 foi monitorada e analisada por meio de medições de superfície, altitude, radar e satélite. As análises indicam que havia ambiente sinótico favorável para a formação e manutenção da LI. Na região de formação da LI havia ar relativamente quente e úmido em baixos níveis e ar relativamente frio e seco em níveis médios com convergência de massa em baixos níveis e divergência em altos níveis, além de gradiente de temperatura produzido pela aproximação do sistema frontal. A LI foi monitorada pelo radar meteorológico MXPOL e permitiu a avaliação dinâmica e microfísica do sistema. Esta última realizada por meio da classificação de hidrometeororos com as variáveis polarimétricas medidas com o MXPOL. Preliminarmente, os dados de refletividade diferencial (ZDR) e refletividade efetiva (Z) foram consistidos por meio do método da autoconsistência (Vivekanadan et al., 2003), entre essas duas variáveis e a fase diferencial específica (KDP). Removido os viéses de ZDR (-0,36 dB) e da refletividade efetiva (-0,46 dBZ), a classificação de hidrometeoros, em dezessete categorias (gotículas a granizo, insetos, ecos de terreno e de segunda viagem), foi realizada pelo método de lógica fuzzy (Vivekanadan et al., 2003). A classificação de hidrometeoros foi realizada em planos de elevação constante (PPI). Os tipos e estratificação de hidrometeoros são compatíveis com estudos anteriores. Por exemplo, a banda brilhante foi classificada com uma região de mistura de gelo e gotas líquidas com predominância de gotas abaixo e cristais de gelo acima desta. A dinâmica interna da LI foi avaliada por meio da velocidade radial e evidenciou um jato de baixos níveis, convergência ciclônica na dianteira do sistema, e divergência em altos níveis, entre outras características. O rápido deslocamento da LI resultou em precipitação de 7 mm e rajadas de vento de 18 m s-1. Assim, o impacto mais significativo desse sistema na RMSP foi produzido pelo vento. / A prefrontal squal line (LI) that reached tne metropolitan area of São Paulo on April 26 2007 was monitored and analyzed by means of of surface and upper air measurements, weather radar and satellite data. Analyses indicate a favorable synoptic environment to form and sustain the LI. In its genesis region there was relatively warm and moiture air near the surface and relatively cold and dry air aloft with mass convergence below and divergence aloft, as well as temperature gradient along its path induced by the associated cold front. This LI was measured with the MXPOL weather radar and allowed a mesoscale dynamic analysis as well as a microphysics of this weather system. The later was performed by means of a hydrometeor classification with the polarimetric data sets of MXPOL. Initially, the differential reflectivity (ZDR) and the efective reflectivity (Z) were corrected by the selfconsistency method (Vivekanandan et al., 2003) together with the specific diferrential phase (KDP). Ounce removed the ZDR (-0,36 dB) and Z (-0,46 dBZ) biases, the hydrometeoro classification (small drops to hail, insects, ground clutter and second trip echoes) was carrie out by the fuzzy logic method (Vivekanadan et al., 2003). The hydrometeor classification was made at constant elevation angles (PPI) across the LI. The hydrometeoro types are compatible to similar studies. For instance, the bright band was classified as a region mixed phase with drops below and ice crystals aboce it. The LI internal dynamics was analyzed with the help of the radial velocity and indicated a low level jet, cyclonic convergence at the leading edge and divergence aloft at the convective band, among other features. This fast moving LI produced 7 mm of rainfall and wind gust of 18 m s-1. Its most significant impact over RMSP was caused by the wind intensity.

Im Rahmen dieser Studie wurden Beobachtungen eines bodengebundenen, scannenden, polarimetrischen Wolken-Doppler-Radars genutzt, um Vertikalprofile der Form und Ausrichtung von bis zu 5 Hydrometeor-Typen in Mischphasenwolken abzuleiten. Voraussetzung für die neue Methodik war ein bestehender Ansatz, der Elevationsscans (Range-Height-Indikator, RHI) der differentiellen Reflektivität ZDR und des Korrelationskoeffizienten RHV nutzt, die von einem 35-GHz (Ka-Band) Wolken-Doppler-Radar beobachtet wurden. ZDR und RHV am Ort des maximalen Signals in den beobachteten Dopplerspektren werden anschließend mit entsprechenden simulierten Elevationsabhängigkeiten von ZDR und RHV verglichen. Das Ergebnis des Retrievals, das mittels eines Fits der simulierten und beobachteten ZDR und RHV Werte erhalten wird, ist ein Paar des polarizability ratio (dichtegewichtetes Achsenverhältnis) und dem degree of orientation, einem Maß für die bevorzugte Ausrichtung der Teilchen. Diese Arbeit widmet sich der Erweiterung der ursprünglichen Ansatzes der Form- und Ausrichtungsbestimmung. Die Methode nutzt die vollständigen beobachteten Dopplerspektren von ZDR und RHV für alle Elevationswinkel der vom 35-GHz Wolkenradar durchgeführten RHI-Scans. Die Aufteilung der Doppler-Spektren in 5 Teile ermöglicht die Ermittlung von Vertikalprofilen der Hydrometeor-Verteilung. In dieser Arbeit wird zunächst der ursprüngliche Ansatz zur Bestimmung der Form und Ausrichtung von Hydrometeors rekapituliert. Anschließend werden das Splitting-Verfahren und die Schritte der Datenanalysekette vorgestellt. Insbesondere auf die Korrektur von Horizontalwindeffekten auf die Doppler-Spektren wird eingegangen. Die Anwendbarkeit des neuen, erweiterten Ansatzes wird anhand von vier Fallstudien demonstriert. Ein Fall diskutiert die Identifizierung von Variationen der Form- und Ausrichtung innerhalb einer Hydrometeor-Population, die vollständig der gleichen primären Form-klasse angehört. Zwei Fallstudien zeigen die Anwendung des Algorithmus in Umgebungen mit mehreren Hydrometeortypen, einschließlich der Identifizierung von sekundärer Eisbildung. In der vierten Fallstudie wurde der Einfluss der Kristallmorphologie und -orientierung auf die Lichtstreuung in einer Mischphasenwolke charakterisiert. Die spektral aufgelöste Form- und Orientierungsbestimmung zeigt, dass vertikal ausgedehnte Mischphasenwolken praktisch immer eine Mischung verschiedener Hydrometeorarten oder eine beträchtliche Variation einer einzigen Hydrometeorart enthalten. Diese Information ist insofern von Bedeutung, als dass viele bestehende Fernerkundungsdaten auf der Annahme beruhen, dass nur eine einzige Hydrometeor-Population vorhanden ist.:1 Introduction 2 Introduction to mixed-phase clouds and ice crystals 2.1 Introduction to mixed–phase clouds 2.2 Ice formation 2.3 Morphology of ice crystals 2.4 Ice crystal growth and secondary ice formation processes 2.4.1 Riming: interaction between supercooled liquid droplets and ice crystals 2.4.2 Aggregation: interaction between ice crystals 2.4.3 Secondary ice production 2.5 Relation between fall speed and shape of ice particles 3 Simulating backscattering by hydrometeors in the microwave regime 3.1 Overview of scattering approaches 3.2 Spheroidal scattering approach 4 Radar observations of atmospheric hydrometeors 4.1 Polarimetric cloud radars 4.1.1 Radar reflectivity 4.1.2 Differential reflectivity 4.1.3 Correlation coefficient 4.1.4 Linear depolarization ratio 4.1.5 Doppler capability 4.2 Retrieving hydrometeor shape and orientation 4.2.1 Modeling part 4.2.2 Observational part 4.2.3 Comparing modeling and observational parts 5 Instrumentation and Dataset 5.1 Hybrid-mode cloud radar Mira-35 5.2 ACCEPT campaign 5.3 Retrieval of shape and orientation of the main hydrometeor population from STSR cloud radar observations 5.3.1 Toward extension of the main-peak approach 6 Doppler-spectra separation method for retrieving shape and orientation of multiple hydrometeor populations 6.1 Spectrally resolved approach 6.2 The influence of air motion on the Doppler spectra observed by a scanning cloud radar 6.2.1 Retrieval of horizontal wind from PPI scans 6.2.2 Aliasing problem and Doppler shift correction 6.2.3 An illustrative example showcasing the correction of horizontal wind effects 6.3 Application of spectrally resolved approach on the case study from 07 Nov 2014, 09:15 – 09:30UTC 7 Results: Application of the spectrally resolved approach on Analysis of the Composition of Cloud with Extended Polarization Techniques (ACCEPT) data 7.1 Case study 10 Nov 2014, 01:15 – 01:30: Shape variability within a deep mixed-phase cloud 7.2 Case study 03 Nov 2014, 20:30 – 20:45: Secondary ice formation 7.3 Case study 18 Nov 2014, 01:15 – 01:30: Impact of crystal morphology on light scattering in a mixed-phase cloud 7.3.1 Relationship between lidar depolarization ratio and ice crystal morphology 7.3.2 Investigation of particle shape and orientation of a low-depolarization cloud layer 8 Summary & Conclusion List of Abbreviations and Acronyms List of Symbols Bibliography / In the framework of this study ground-based scanning polarimetric cloud Doppler radar observations were utilized to derive vertical profiles of the shape and orientation of up to 5 different hydrometeor types in mixed-phase clouds. Prerequisite for the new methodology was an existing approach that uses elevation (range-height indicator, RHI) scans of differential reflectivity ZDR and correlation coefficient RHV observed by a 35-GHz (Ka-band) cloud Doppler radar as well as simulations of the latter. ZDR and RHV from the location of the maximum signal in the observed Doppler spectra are compared with corresponding simulated elevation dependencies of ZDR and RHV. The retrieval output, which is obtained by a fit of simulated and observed ZDR and RHV, is then a pair of the polarizability ratio (density-weighted axis ratio) and the degree of orientation, a measure of the preferable orientation of the particles. This thesis is dedicated to an extension of the original shape and orientation retrieval. The method utilizes the entire observed Doppler spectra of ZDR and RHV from all elevation angles of the RHI scans performed by the 35-GHz cloud radar. The split- up of the Doppler spectra into 5 parts enables the retrieval of vertical profiles of the hydrometeor distribution. Within the thesis, the original shape retrieval approach is recapitulated. Subsequently, the splitting procedure and required preparatory steps in the data analysis chain are introduced. Specifically, a correction of horizontal wind effects on the Doppler spectra had to be implemented. The remainder of the thesis is dedicated to demonstrate the applicability of the new spectrally shape and orientation retrieval approach by means of four case studies. One case demonstrates the detection of variabilities in shape and orientation within a hydrometeor population belonging entirely to the same primary shape class. Two case studies were selected to evaluate the application of the spectrally resolved approach in an environment of multiple hydrometeor types, including its utilization for identification of secondary ice production. In the fourth case study the characterization of the impact of crystal morphology and orientation on light scattering in a mixed-phase cloud was performed. The spectrally resolved shape and orientation retrieval demonstrates that vertically extensive mixed-phase clouds contain virtually always a mix of different hydrometeor types or a considerable variation of a single hydrometeor type. This information holds relevant as many existing remote sensing retrievals rely on the assumption of the presence of a single hydrometeor population, only.:1 Introduction 2 Introduction to mixed-phase clouds and ice crystals 2.1 Introduction to mixed–phase clouds 2.2 Ice formation 2.3 Morphology of ice crystals 2.4 Ice crystal growth and secondary ice formation processes 2.4.1 Riming: interaction between supercooled liquid droplets and ice crystals 2.4.2 Aggregation: interaction between ice crystals 2.4.3 Secondary ice production 2.5 Relation between fall speed and shape of ice particles 3 Simulating backscattering by hydrometeors in the microwave regime 3.1 Overview of scattering approaches 3.2 Spheroidal scattering approach 4 Radar observations of atmospheric hydrometeors 4.1 Polarimetric cloud radars 4.1.1 Radar reflectivity 4.1.2 Differential reflectivity 4.1.3 Correlation coefficient 4.1.4 Linear depolarization ratio 4.1.5 Doppler capability 4.2 Retrieving hydrometeor shape and orientation 4.2.1 Modeling part 4.2.2 Observational part 4.2.3 Comparing modeling and observational parts 5 Instrumentation and Dataset 5.1 Hybrid-mode cloud radar Mira-35 5.2 ACCEPT campaign 5.3 Retrieval of shape and orientation of the main hydrometeor population from STSR cloud radar observations 5.3.1 Toward extension of the main-peak approach 6 Doppler-spectra separation method for retrieving shape and orientation of multiple hydrometeor populations 6.1 Spectrally resolved approach 6.2 The influence of air motion on the Doppler spectra observed by a scanning cloud radar 6.2.1 Retrieval of horizontal wind from PPI scans 6.2.2 Aliasing problem and Doppler shift correction 6.2.3 An illustrative example showcasing the correction of horizontal wind effects 6.3 Application of spectrally resolved approach on the case study from 07 Nov 2014, 09:15 – 09:30UTC 7 Results: Application of the spectrally resolved approach on Analysis of the Composition of Cloud with Extended Polarization Techniques (ACCEPT) data 7.1 Case study 10 Nov 2014, 01:15 – 01:30: Shape variability within a deep mixed-phase cloud 7.2 Case study 03 Nov 2014, 20:30 – 20:45: Secondary ice formation 7.3 Case study 18 Nov 2014, 01:15 – 01:30: Impact of crystal morphology on light scattering in a mixed-phase cloud 7.3.1 Relationship between lidar depolarization ratio and ice crystal morphology 7.3.2 Investigation of particle shape and orientation of a low-depolarization cloud layer 8 Summary & Conclusion List of Abbreviations and Acronyms List of Symbols Bibliography