Quarterly Journal of the Royal Meteorological Society, 2011
† The contributions of P. R. A. Brown and R. Cotton were prepared in the course of their employme... more † The contributions of P. R. A. Brown and R. Cotton were prepared in the course of their employment at the Met Office, UK, and are published with the permission of the Controller of HMSO and the Queen's Printer for Scotland. A combination of modelling studies and ground-based and aircraft measurements is used to examine the development of ice particles in convective clouds observed over the Black Forest mountains during the Convective and Orographically-induced Precipitation Study (COPS). High concentrations of relatively small ice particles were observed in the weaker northern cell that developed on convergence lines over the mountains in the much-studied 15 July 2007 case. The conditions in the cloud were not conducive for the Hallett-Mossop process. Instead, the explanation for such high concentrations of ice is likely associated with the type of ice nuclei ingested into the cloud. Biological nuclei, oxidised organic aerosol particles in the polluted air vented from the Murg valley into the cloud base, and desert dust are all possible candidates. A model sensitivity test with biological nuclei produced similar concentrations of ice particles to the observations. In contrast, the high concentration of ice particles measured in clouds that advected over the Black Forest mountains on 11 July 2007 were likely due to the Hallett-Mossop process. The deep convective cell at the southern end of the COPS domain on 15 July 2007 developed in less polluted air than the shallower northern cloud. A model sensitivity test with lower aerosol loading produced a more vigorous cloud with a higher top, more precipitation, and greater reflectivity, more similar to the radar observations. The results suggest that aerosol particles vented out of the valleys could have a significant impact on orographically induced precipitation. Copyright
Summary. Mesoscale convective precipitation systems in the Alpine region are studied by analyzi... more Summary. Mesoscale convective precipitation systems in the Alpine region are studied by analyzing radar and rain gauge data. The data from weather radars in Austria, France, Germany, and Switzerland are combined into a composite. Availability of radar data restricts the study mainly to the northern part of the Alpine region. Mesoscale convective systems (MCS) occur often in this region and are
8) Institut géographique national (IGN) (9) Laboratoire de météorologie dynamique (LMD), CNRS et ... more 8) Institut géographique national (IGN) (9) Laboratoire de météorologie dynamique (LMD), CNRS et université Pierre-et-Marie-Curie (10) DIFA, Università degli Studi della Basilicata, Potenza, Italie (11) Deutsches Zentrum für Luft und Raumfahrt (DLR), Wessling, Allemagne (12) Direction interrégionale du Nord-Est (DIRNE), Météo-France (13) École et observatoire des sciences de la Terre (Eost), CNRS et université de Strasbourg Résumé L'étude des précipitations convectives induites par l'orographie (Cops selon l'acronyme anglais) est un projet international coordonné qui comprend une campagne d'observations de terrain et un programme scientifique et qui vise à améliorer la qualité des prévisions des précipitations orographiques convectives à la fois par l'observation quadridimensionnelle et la modélisation de leur cycle de vie. La campagne de terrain s'est déroulée en juin-juilletaoût 2007 sur l'est de la France et le sud-ouest de l'Allemagne. Son objectif majeur était de fournir un jeu d'observations météorologiques, in situ et à distance, aussi complet que possible et sur toute la profondeur de la colonne troposphérique. Après une brève revue d'ensemble du projet, l'article se concentre sur la contribution française à la campagne Cops, décrit le dispositif expérimental mis en oeuvre et met en valeur quelques observations clés.
The purpose of this paper is to show how already existing Doppler radar information, provided, fo... more The purpose of this paper is to show how already existing Doppler radar information, provided, for example, by the German Weather Service's (DWD) radar network, can be combined to wind vector fields using multiple-Doppler techniques. At the same time, an alternative to monostatic multiple-Doppler measurements, called a bistatic Doppler radar network, is introduced to measure wind velocity within areas which
Precipitating convection in a mountain region of moderate topography is investigated, with partic... more Precipitating convection in a mountain region of moderate topography is investigated, with particular emphasis on its initiation in response to boundary-layer and mid-and upper-tropospheric forcing mechanisms. The data used in the study are from COPS (Convective and Orographically-induced Precipitation Study) that took place in southwestern Germany and eastern France in the summer of 2007. It is found that the initiation of precipitating convection can be roughly classified as being due to either: (i) surface heating and low-level flow convergence; (ii) surface heating and moisture supply overcoming convective inhibition during latent and/or potential instability; or (iii) mid-tropospheric dynamical processes due to mesoscale convergence lines and forced mean vertical motion. These phenomena have to be adequately represented in models in order to improve quantitative precipitation forecast. Selected COPS cases are analysed and classified into these initiation categories. Although only a subset of COPS data (mainly radiosondes, surface weather stations, radar and satellite data) are used here, it is shown that convective systems are captured in considerable detail by sensor synergy. Convergence lines were observed by Doppler radar in the location where deep convection is triggered several hours later. The results suggest that in many situations, observations of the location and timing of convergence lines will facilitate the nowcasting of convection. Further on, forecasting of the initiation of convection is significantly complicated if advection of potentially convective air masses over changing terrain features plays a major role. The passage of a frontal structure over the Vosges -Rhine valley -Black Forest orography was accompanied by an intermediate suppression of convection over the wide Rhine valley. Further downstream, an intensification of convection was observed over the Black Forest due to differential surface heating, a convergence line, and the flow generated by a gust front.
Abstract A novel object-based quality measure, which contains three distinct components that cons... more Abstract A novel object-based quality measure, which contains three distinct components that consider aspects of the structure (S), amplitude (A), and location (L) of the precipitation field in a prespecified domain (eg, a river catchment) is introduced for the verification of ...
Journal of Atmospheric and Oceanic Technology, 2004
By installing and linking additional receivers to a monostatic Doppler radar, several wind compon... more By installing and linking additional receivers to a monostatic Doppler radar, several wind components can be measured and combined into a wind vector field. Such a bistatic Doppler radar network was developed in 1993 by the National Center for Atmospheric Research and has been in operation at different research departments. Since then, the accuracy of wind vectors has been investigated mainly based on theoretical examinations. Observational analysis of the accuracy has been limited to comparisons of dual-Doppler-derived wind vectors always including the monostatic Doppler radar. Intercomparisons to independent wind measurements have not yet been accomplished. In order to become an alternative to monostatic multiple-Doppler applications, the reliability of wind vector fields has to be also proven by observational analysis. In this paper wind vectors measured by a bistatic Doppler radar network are evaluated by 1) internally comparing results of bistatic receivers; 2) comparing with independent wind measurements observed by a second Doppler radar; and 3) comparing with in situ flight measurements achieved with a research aircraft during stratiform precipitation events. Investigations show how reliable bistatically measured wind fields are and how they can contribute highly to research studies, weather surveillance, and forecasting. As a result of the intercomparison, the instrumentation error of the bistatic receivers can be assumed to be within 1 m s Ϫ1 . Differences between bistatic Doppler radar and independent measurements range mainly between 2 and 3 m s Ϫ1 .
Journal of Atmospheric and Oceanic Technology, 2006
Over the last few years the use of weather radar data has become a fundamental part of various ap... more Over the last few years the use of weather radar data has become a fundamental part of various applications like rain-rate estimation, nowcasting of severe weather events, and assimilation into numerical weather prediction models. The increasing demand for radar data necessitates an automated, flexible, and modular quality control. In this paper a quality control procedure is developed for radar reflectivity factors, polarimetric parameters, and Doppler velocity. It consists of several modules that can be extended, modified, and omitted depending on the user requirement, weather situation, and radar characteristics. Data quality is quantified on a pixel-by-pixel basis and encoded into a quality-index field that can be easily interpreted by a nontrained end user or an automated scheme that generates radar products. The qualityindex algorithms detect and quantify the influence of beam broadening, the height of the first radar echo, ground clutter contamination, return from non-weather-related objects, and attenuation of electromagnetic energy by hydrometeors on the quality of the radar measurement. The quality-index field is transferred together with the radar data to the end user who chooses the amount of data and the level of quality used for further processing. The calculation of quality-index fields is based on data measured by the polarimetric C-band Doppler radar (POLDIRAD) located in the Alpine foreland in southern Germany. * Current affiliation: MeteoSwiss, Locarno, Switzerland.
Horizontal wind vector fields can be measured in real time by a bistatic Doppler radar network an... more Horizontal wind vector fields can be measured in real time by a bistatic Doppler radar network and can be applied directly for hazard warnings and weather surveillance. Most applications, however, especially for meteorological research and operational ...
Bulletin of the American Meteorological Society, 2008
Quantitative precipitation forecasting (QPF) in low-mountain regions is a great challenge for the... more Quantitative precipitation forecasting (QPF) in low-mountain regions is a great challenge for the atmospheric sciences community. On the one hand, orographic enhancement of precipitation in these regions can result in severe flash-flood events. On the other hand, the relative importance of forcing mechanisms leading to convection initiation (CI) is neither well understood nor adequately reproduced by weather forecast models. This results in poor QPF skill, both in terms of the spatial distribution of precipitation and its temporal evolution.
QUARTERLY JOURNAL OF THE ROYAL METEOROLOGICAL SOCIETY, 2011
Quantitative precipitation forecasting (QPF) in low-mountain regions is a great challenge for the... more Quantitative precipitation forecasting (QPF) in low-mountain regions is a great challenge for the atmospheric sciences community. On the one hand, orographic enhancement of precipitation in these regions can result in severe flash-flood events. On the other hand, the relative importance of forcing mechanisms leading to convection initiation (CI) is neither well understood nor adequately reproduced by weather forecast models. This results in poor QPF skill, both in terms of the spatial distribution of precipitation and its temporal evolution.
Quarterly Journal of the Royal Meteorological Society, 2003
Raindrop size distribution data obtained from two Joss-Waldvogel disdrometers located at Locarno-... more Raindrop size distribution data obtained from two Joss-Waldvogel disdrometers located at Locarno-Monti, Switzerland during the Mesoscale Alpine Programme (MAP) Special Observation Period are analysed to obtain appropriate relationships of radar re ectivity, Z, with both water content, W , and surface rainfall, R, for use in MAP applications. The disdrometer data are accumulated into 10-minute samples to reduce sampling error associated with the »1 m 3 sample volume of the instruments. Based on previous studies, relations of the form W D qZ .4=7/ and Z D aR 1:5 are assumed and the coef cients q and a are estimated from the data. The combined dataset of 10-minute samples from the two disdrometers and the 10-minute data divided into two independent subsets yielded similar mean values of the coef cients. The recommended relationships are W D 3:4Z .4=7/ and Z D 216R 1:5 . The uncertainties in these mean relationships as expressed in terms of §1 standard deviation are approximately equivalent to a §4.4 dBZ error for the Z-W relationship, and to a §2.4 dBZ error for the Z-R relationship.
Quarterly Journal of the Royal Meteorological Society, 2011
† The contributions of P. R. A. Brown and R. Cotton were prepared in the course of their employme... more † The contributions of P. R. A. Brown and R. Cotton were prepared in the course of their employment at the Met Office, UK, and are published with the permission of the Controller of HMSO and the Queen's Printer for Scotland. A combination of modelling studies and ground-based and aircraft measurements is used to examine the development of ice particles in convective clouds observed over the Black Forest mountains during the Convective and Orographically-induced Precipitation Study (COPS). High concentrations of relatively small ice particles were observed in the weaker northern cell that developed on convergence lines over the mountains in the much-studied 15 July 2007 case. The conditions in the cloud were not conducive for the Hallett-Mossop process. Instead, the explanation for such high concentrations of ice is likely associated with the type of ice nuclei ingested into the cloud. Biological nuclei, oxidised organic aerosol particles in the polluted air vented from the Murg valley into the cloud base, and desert dust are all possible candidates. A model sensitivity test with biological nuclei produced similar concentrations of ice particles to the observations. In contrast, the high concentration of ice particles measured in clouds that advected over the Black Forest mountains on 11 July 2007 were likely due to the Hallett-Mossop process. The deep convective cell at the southern end of the COPS domain on 15 July 2007 developed in less polluted air than the shallower northern cloud. A model sensitivity test with lower aerosol loading produced a more vigorous cloud with a higher top, more precipitation, and greater reflectivity, more similar to the radar observations. The results suggest that aerosol particles vented out of the valleys could have a significant impact on orographically induced precipitation. Copyright
Summary. Mesoscale convective precipitation systems in the Alpine region are studied by analyzi... more Summary. Mesoscale convective precipitation systems in the Alpine region are studied by analyzing radar and rain gauge data. The data from weather radars in Austria, France, Germany, and Switzerland are combined into a composite. Availability of radar data restricts the study mainly to the northern part of the Alpine region. Mesoscale convective systems (MCS) occur often in this region and are
8) Institut géographique national (IGN) (9) Laboratoire de météorologie dynamique (LMD), CNRS et ... more 8) Institut géographique national (IGN) (9) Laboratoire de météorologie dynamique (LMD), CNRS et université Pierre-et-Marie-Curie (10) DIFA, Università degli Studi della Basilicata, Potenza, Italie (11) Deutsches Zentrum für Luft und Raumfahrt (DLR), Wessling, Allemagne (12) Direction interrégionale du Nord-Est (DIRNE), Météo-France (13) École et observatoire des sciences de la Terre (Eost), CNRS et université de Strasbourg Résumé L'étude des précipitations convectives induites par l'orographie (Cops selon l'acronyme anglais) est un projet international coordonné qui comprend une campagne d'observations de terrain et un programme scientifique et qui vise à améliorer la qualité des prévisions des précipitations orographiques convectives à la fois par l'observation quadridimensionnelle et la modélisation de leur cycle de vie. La campagne de terrain s'est déroulée en juin-juilletaoût 2007 sur l'est de la France et le sud-ouest de l'Allemagne. Son objectif majeur était de fournir un jeu d'observations météorologiques, in situ et à distance, aussi complet que possible et sur toute la profondeur de la colonne troposphérique. Après une brève revue d'ensemble du projet, l'article se concentre sur la contribution française à la campagne Cops, décrit le dispositif expérimental mis en oeuvre et met en valeur quelques observations clés.
The purpose of this paper is to show how already existing Doppler radar information, provided, fo... more The purpose of this paper is to show how already existing Doppler radar information, provided, for example, by the German Weather Service's (DWD) radar network, can be combined to wind vector fields using multiple-Doppler techniques. At the same time, an alternative to monostatic multiple-Doppler measurements, called a bistatic Doppler radar network, is introduced to measure wind velocity within areas which
Precipitating convection in a mountain region of moderate topography is investigated, with partic... more Precipitating convection in a mountain region of moderate topography is investigated, with particular emphasis on its initiation in response to boundary-layer and mid-and upper-tropospheric forcing mechanisms. The data used in the study are from COPS (Convective and Orographically-induced Precipitation Study) that took place in southwestern Germany and eastern France in the summer of 2007. It is found that the initiation of precipitating convection can be roughly classified as being due to either: (i) surface heating and low-level flow convergence; (ii) surface heating and moisture supply overcoming convective inhibition during latent and/or potential instability; or (iii) mid-tropospheric dynamical processes due to mesoscale convergence lines and forced mean vertical motion. These phenomena have to be adequately represented in models in order to improve quantitative precipitation forecast. Selected COPS cases are analysed and classified into these initiation categories. Although only a subset of COPS data (mainly radiosondes, surface weather stations, radar and satellite data) are used here, it is shown that convective systems are captured in considerable detail by sensor synergy. Convergence lines were observed by Doppler radar in the location where deep convection is triggered several hours later. The results suggest that in many situations, observations of the location and timing of convergence lines will facilitate the nowcasting of convection. Further on, forecasting of the initiation of convection is significantly complicated if advection of potentially convective air masses over changing terrain features plays a major role. The passage of a frontal structure over the Vosges -Rhine valley -Black Forest orography was accompanied by an intermediate suppression of convection over the wide Rhine valley. Further downstream, an intensification of convection was observed over the Black Forest due to differential surface heating, a convergence line, and the flow generated by a gust front.
Abstract A novel object-based quality measure, which contains three distinct components that cons... more Abstract A novel object-based quality measure, which contains three distinct components that consider aspects of the structure (S), amplitude (A), and location (L) of the precipitation field in a prespecified domain (eg, a river catchment) is introduced for the verification of ...
Journal of Atmospheric and Oceanic Technology, 2004
By installing and linking additional receivers to a monostatic Doppler radar, several wind compon... more By installing and linking additional receivers to a monostatic Doppler radar, several wind components can be measured and combined into a wind vector field. Such a bistatic Doppler radar network was developed in 1993 by the National Center for Atmospheric Research and has been in operation at different research departments. Since then, the accuracy of wind vectors has been investigated mainly based on theoretical examinations. Observational analysis of the accuracy has been limited to comparisons of dual-Doppler-derived wind vectors always including the monostatic Doppler radar. Intercomparisons to independent wind measurements have not yet been accomplished. In order to become an alternative to monostatic multiple-Doppler applications, the reliability of wind vector fields has to be also proven by observational analysis. In this paper wind vectors measured by a bistatic Doppler radar network are evaluated by 1) internally comparing results of bistatic receivers; 2) comparing with independent wind measurements observed by a second Doppler radar; and 3) comparing with in situ flight measurements achieved with a research aircraft during stratiform precipitation events. Investigations show how reliable bistatically measured wind fields are and how they can contribute highly to research studies, weather surveillance, and forecasting. As a result of the intercomparison, the instrumentation error of the bistatic receivers can be assumed to be within 1 m s Ϫ1 . Differences between bistatic Doppler radar and independent measurements range mainly between 2 and 3 m s Ϫ1 .
Journal of Atmospheric and Oceanic Technology, 2006
Over the last few years the use of weather radar data has become a fundamental part of various ap... more Over the last few years the use of weather radar data has become a fundamental part of various applications like rain-rate estimation, nowcasting of severe weather events, and assimilation into numerical weather prediction models. The increasing demand for radar data necessitates an automated, flexible, and modular quality control. In this paper a quality control procedure is developed for radar reflectivity factors, polarimetric parameters, and Doppler velocity. It consists of several modules that can be extended, modified, and omitted depending on the user requirement, weather situation, and radar characteristics. Data quality is quantified on a pixel-by-pixel basis and encoded into a quality-index field that can be easily interpreted by a nontrained end user or an automated scheme that generates radar products. The qualityindex algorithms detect and quantify the influence of beam broadening, the height of the first radar echo, ground clutter contamination, return from non-weather-related objects, and attenuation of electromagnetic energy by hydrometeors on the quality of the radar measurement. The quality-index field is transferred together with the radar data to the end user who chooses the amount of data and the level of quality used for further processing. The calculation of quality-index fields is based on data measured by the polarimetric C-band Doppler radar (POLDIRAD) located in the Alpine foreland in southern Germany. * Current affiliation: MeteoSwiss, Locarno, Switzerland.
Horizontal wind vector fields can be measured in real time by a bistatic Doppler radar network an... more Horizontal wind vector fields can be measured in real time by a bistatic Doppler radar network and can be applied directly for hazard warnings and weather surveillance. Most applications, however, especially for meteorological research and operational ...
Bulletin of the American Meteorological Society, 2008
Quantitative precipitation forecasting (QPF) in low-mountain regions is a great challenge for the... more Quantitative precipitation forecasting (QPF) in low-mountain regions is a great challenge for the atmospheric sciences community. On the one hand, orographic enhancement of precipitation in these regions can result in severe flash-flood events. On the other hand, the relative importance of forcing mechanisms leading to convection initiation (CI) is neither well understood nor adequately reproduced by weather forecast models. This results in poor QPF skill, both in terms of the spatial distribution of precipitation and its temporal evolution.
QUARTERLY JOURNAL OF THE ROYAL METEOROLOGICAL SOCIETY, 2011
Quantitative precipitation forecasting (QPF) in low-mountain regions is a great challenge for the... more Quantitative precipitation forecasting (QPF) in low-mountain regions is a great challenge for the atmospheric sciences community. On the one hand, orographic enhancement of precipitation in these regions can result in severe flash-flood events. On the other hand, the relative importance of forcing mechanisms leading to convection initiation (CI) is neither well understood nor adequately reproduced by weather forecast models. This results in poor QPF skill, both in terms of the spatial distribution of precipitation and its temporal evolution.
Quarterly Journal of the Royal Meteorological Society, 2003
Raindrop size distribution data obtained from two Joss-Waldvogel disdrometers located at Locarno-... more Raindrop size distribution data obtained from two Joss-Waldvogel disdrometers located at Locarno-Monti, Switzerland during the Mesoscale Alpine Programme (MAP) Special Observation Period are analysed to obtain appropriate relationships of radar re ectivity, Z, with both water content, W , and surface rainfall, R, for use in MAP applications. The disdrometer data are accumulated into 10-minute samples to reduce sampling error associated with the »1 m 3 sample volume of the instruments. Based on previous studies, relations of the form W D qZ .4=7/ and Z D aR 1:5 are assumed and the coef cients q and a are estimated from the data. The combined dataset of 10-minute samples from the two disdrometers and the 10-minute data divided into two independent subsets yielded similar mean values of the coef cients. The recommended relationships are W D 3:4Z .4=7/ and Z D 216R 1:5 . The uncertainties in these mean relationships as expressed in terms of §1 standard deviation are approximately equivalent to a §4.4 dBZ error for the Z-W relationship, and to a §2.4 dBZ error for the Z-R relationship.
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Papers by Martin Hagen