H.W.J. Russchenberg

Cloudnet: Continuous Evaluation of Cloud Profiles in Seven Operational Models Using Ground-Based Observations

Cloud fraction, liquid and ice water contents derived from long-term radar, lidar and microwave radiometer data are systematically compared to models to quantify and improve their performance.

The Convective and Orographically Induced Precipitation Study:A Research and Development Project of the World Weather Research Program for Improving Quantitative Precipitation Forecasting in Low-mountain Regions

Abstract The international field campaign called the Convective and Orographically-induced Precipitation Study (COPS) took place from June to August 2007 in southwestern Germany/eastern France. The overarching goal of COPS is to advance the quality of forecasts of orographically-induced convective precipitation by four-dimensional observations and modeling of its life cycle. COPS was endorsed as one of the Research and Development Projects of the World Weather Research Program (WWRP), and combines the efforts of institutions and scientists from eight countries. A strong collaboration between instrument principal investigators and experts on mesoscale modeling has been established within COPS. In order to study the relative importance of large-scale and small-scale forcing leading to convection initiation in low mountains, COPS is coordinated with a one-year General Observations Period in central Europe, the WWRP Forecast Demonstration Project MAP D-PHASE, and the first summertime European THORPEX Regional...

Retrieval of information about turbulence in rain by using Doppler-polarimetric Radar

This paper considers new possibilities of turbulence intensity retrieval by using Doppler and Doppler-polarimetric radar sounding. Peculiarities of microwave scattering on moving droplets of different size and shape underlie new methods that are introduced, discussed, and checked by using radar data

Backscattering by and propagation through the melting layer of precipitation: a new polarimetric model

A simple physical model of the melting layer of precipitation is presented. It is able to simulate the polarization-dependence of radar reflections and radio signals propagating through the melting layer. The radar observables are calculated in the Rayleigh regime. The propagation observables are given in the range of 5-50 GHz, and are calculated with an extended Rayleigh approximation. The model requires the rain intensity and the mass density of the snowflakes as input parameters. Radar observations, made with the Delft Atmospheric Research Radar, are used to discuss physical processes in the melting layer. Finally, model simulations are compared with radar data obtained with the Chilbolton radar of the Rutherford Appleton Laboratories.

Advances in Continuously Profiling the Thermodynamic State of the Boundary Layer: Integration of Measurements and Methods

This paper describes advances in ground-based thermodynamic profiling of the lower troposphere through sensor synergy. The well-documented integrated profiling technique (IPT), which uses a microwave profiler, a cloud radar, and a ceilometer to simultaneously retrieve vertical profiles of temperature, humidity, and liquid water content (LWC) of nonprecipitating clouds, is further developed toward an enhanced performance in the boundary layer and lower troposphere. For a more accurate temperature profile, this is accomplished by including an elevation scanning measurement modus of the microwave profiler. Heightdependent RMS accuracies of temperature (humidity) ranging from 0.3 to 0.9 K (0.5–0.8 g m 3 )i n the boundary layer are derived from retrieval simulations and confirmed experimentally with measurements at distinct heights taken during the 2005 International Lindenberg Campaign for Assessment of Humidity and Cloud Profiling Systems and its Impact on High-Resolution Modeling (LAUNCH) of the German Weather Service. Temperature inversions, especially of the lower boundary layer, are captured in a very satisfactory way by using the elevation scanning mode. To improve the quality of liquid water content measurements in clouds the authors incorporate a sophisticated target classification scheme developed within the European cloud observing network CloudNet. It allows the detailed discrimination between different types of backscatterers detected by cloud radar and ceilometer. Finally, to allow IPT application also to drizzling cases, an LWC profiling method is integrated. This technique classifies the detected hydrometeors into three different size classes using certain thresholds determined by radar reflectivity and/or ceilometer extinction profiles. By inclusion into IPT, the retrieved profiles are made consistent with the measurements of the microwave profiler and an LWC a priori profile. Results of IPT application to 13 days of the LAUNCH campaign are analyzed, and the importance of integrated profiling for model evaluation is underlined.

The convective and orographically-induced precipitation study

Abstract The international field campaign called the Convective and Orographically-induced Precipitation Study (COPS) took place from June to August 2007 in southwestern Germany/eastern France. The overarching goal of COPS is to advance the quality of forecasts of orographically-induced convective precipitation by four-dimensional observations and modeling of its life cycle. COPS was endorsed as one of the Research and Development Projects of the World Weather Research Program (WWRP), and combines the efforts of institutions and scientists from eight countries. A strong collaboration between instrument principal investigators and experts on mesoscale modeling has been established within COPS. In order to study the relative importance of large-scale and small-scale forcing leading to convection initiation in low mountains, COPS is coordinated with a one-year General Observations Period in central Europe, the WWRP Forecast Demonstration Project MAP D-PHASE, and the first summertime European THORPEX Regional...

Coherent Scattering of Microwaves by Particles: Evidence from Clouds and Smoke

Many radar measurements of the atmosphere can be explained in terms of two scattering mechanisms: incoherent scattering from particles, and coherent scattering from variations in the refractive index of the air, commonly called clear-air or Bragg scattering. Spatial variations in the liquid water content of clouds may also give a coherent contribution to the radar return, but it is commonly believed that this coherent scattering from the droplets is insignificant because variations in humidity have a much larger influence on the refractive index than equal variations in liquid water content. It is argued that the fluctuations in water vapor mixing ratio in clouds can be much smaller than those in liquid water mixing ratio. In this article an expression for the strength of the coherent scattering from particles will be derived for fluctuations caused by turbulent mixing with clean (i.e., particle-free) air, where it will be assumed that the particles follow the flow, that is, their inertia is neglected. It will be shown that the coherent contribution adds to the incoherent contribution, the latter always being present. The coherent particle scattering can be stronger than the incoherent scattering, especially at longer wavelengths and high particle concentrations. Recently published dual-frequency measurements of developing cumulus clouds and smoke show a correlation for which no explanation has been found in terms of incoherent particle scattering and coherent air scattering. Scatterplots of the reflectivity factors at both frequencies show a clustering of points in between the values that correspond to pure clear-air and pure incoherent scattering. Those differences in the radar reflectivity factors could be due to a mixture of Bragg scattering and incoherent particle scattering, but then no correlation is expected, because the origin of the scattering mechanism that dominates at each wavelength is different. However, coherent scattering from the particles can cause the radar reflectivities of dual-wavelength radar measurements to become correlated with each other. It may explain the slopes and the differences seen in the scatterplots of the radar reflectivities of cloud and smoke measurements, with reasonable values of the parameters involved. However, the correlation between the radar reflectivities is very tight near the cloud top and seems to be present in adiabatic cores as well. This is an indication that, apart from mixing with environmental air, the inertia of the droplets could also be important for the creation of small-scale fluctuations in droplet concentration.

Estimation of Specific Differential Phase and Differential Backscatter Phase From Polarimetric Weather Radar Measurements of Rain

The estimation of the specific differential phase particularly in the presence of the differential backscatter phase and nonuniform propagation paths is a long-standing goal in weather radar polarimetry. Furthermore, a reliable estimator of the differential backscatter phase for precipitation measurements has not been proposed yet, although it contains valuable information about the presence of non-Rayleigh scattering and the microphysics of precipitation. In this letter, we introduce a novel method to estimate the specific differential phase and the differential backscatter phase from polarimetric weather radar measurements of rain. This estimation does pay off particularly at the X-band where the scattering regime is non-Rayleigh already in moderate rain. In this case, the differential backscatter phase is useful as an additional weather radar observable with manifold applications such as rain rate estimation, microphysical retrieval, and operational radar calibration. The novel method also provides an improved range resolution of the specific differential phase compared to conventional estimators. We illustrate the estimation of the differential phases with data from the Delft University of Technologys polarimetric X-band International Research Centre for Telecommunications and Radar drizzle radar.

Ground-Based Atmospheric Remote Sensing in the Netherlands: European Outlook

This paper describes the contours of a Dutch monitoring and research site for climate change and related atmospheric processes. The station has large benefits for atmospheric science, both in The Netherlands and internationally. It provides a platform for collaboration in this important field, and will provide the routine observations needed to assess the impact of the different atmospheric parameters on the local climate. The station fits in directly in the selected group of global monitoring networks that are currently operational or being set up to address the problems of climate. In addition, the station can play a major role in supporting world-wide satellite measurements of climate related parameters. The only way to get a global picture of the essential climate change parameters can be found in the combination of satellite measurements and ground-based stations equipped with advanced remote sensing and in situ instrumentation. Furthermore, the combined expertise of European universities and research institutes, encompassing the whole field of atmospheric research, offers a unique chance for the training of young scientists. The research site is an attractive center for international young scientists to develop and deepen their skills. Copyright

Combined Observational and Model Investigations of the Z–LWC Relationship in Stratocumulus Clouds

In situ measurements indicate the complexity and nonunique character of radar reflectivity–liquid water content (Z–LWC) relationships in stratocumulus and cumulus clouds. Parameters of empirical (statistical) Z–LWC dependences vary within a wide range. Respectively, the accuracy of retrieval algorithms remains low. This situation is partially related to the fact that empirical algorithms and parameters are often derived without a corresponding understanding of physical mechanisms responsible for the formation of the Z–LWC diagrams. In this study, the authors investigate the processes of formation of the Z–LWC relationships using a new trajectory ensemble model of the cloud-topped boundary layer (BL). In the model, the entire volume of the BL is covered by Lagrangian parcels advected by a turbulent-like velocity field. The time-dependent velocity field is generated by a turbulent model and obeys the correlation turbulent laws. Each Lagrangian parcel represents the “cloud parcel model” with an accurate description of processes of diffusion growth–evaporation of aerosols and droplets and droplet collisions. The fact that parcels are adjacent to each other allows one to calculate sedimentation of droplets and precipitation (drizzle) formation. The characteristic parcel size is 50 m; the number of parcels is 1840. The model calculates droplet size distributions (DSDs), as well as their moments (e.g., aerosol and drop concentration, mass content, radar reflectivity) in each parcel. In the course of the model integration, Z–LWC relationships are calculated for each parcel, as well as the scattering diagram including all parcels. The model reproduces in situ observed types of the Z–LWC relationships. It is shown that different regimes represent different stages of cloud evolution: diffusion growth, beginning of drizzle formation, and stage of heavy drizzle, respectively. The large scattering of the Z–LWC relationships is found to be an inherent property of any drizzling cloud. Different zones on the Z–LWC diagram are related to cloud volumes located at different levels within a cloud and having different DSD. This finding allows for improvement of retrieval algorithms.