Search Results

You are looking at 1 - 6 of 6 items for

  • Author or Editor: P. F. Meischner x
  • All content x
Clear All Modify Search
P. F. Meischner, V. N. Bringi, D. Heimann, and H. Höller

Abstract

A multiscale analysis of a squall line system is reported in this paper. It is shown that the squall line was initiated as part of a synoptic-scale frontal zone. The main emphasis then is on the polarimetric and Doppler radar measurements which give insight into the meso- and microscale structure of the kinematics and the precipitation microphysics especially within the new cells growing ahead of the squall line, and within the main precipitation system. The principal polarimetric measurements considered are the differential reflectivity (ZDR) and a related new derived parameter termed the difference reflectivity or ZDP which is useful in detection of rain-ice mixed phase precipitation. A limited amount of time series data have been analyzed to derive the specific differential phase (KDP) and the backscatter differential phase (δ) between horizontal and vertical polarizations. A brief overview of the microphysical interpretation of these parameters is provided. The newly grown clouds are identified as positive ZDR columns, i.e., regions of low reflectivity and unusually large ZDR. Within the high reflectivity part of the squall line, intense precipitation in the form of raindrops mixed with small, melting hail may be inferred. The radar observations were shown to be in good agreement with a hail melting model. A conceptual model of the squall line is provided based on the Doppler and polarimetric data. It demonstrates the internal circulation structure as well as the contribution of melting ice particles to the cold pool dynamics.

Full access
V. Chandrasekar, J. Hubbert, V. N. Bringi, and P. F. Meischner

Abstract

Equations are derived for transforming radar data obtained with ±45° linear polarization states to conventional radar parameters measured at horizontal and vertical polarization states. The derivation is based on the covariance matrix and assumes a diagonal propagation matrix and a reciprocal scattering matrix with nonzero cross-polar terms. Time series data gathered during the summers of 1990 and 1992 with the German Aerospace Research Establishment (DLR) C-band polarimetric radar, POLDIRAD, located in Oberpfaffenhofen, Germany, are used to validate the polarization transformation method. Data collected in two convective precipitation shafts are analyzed and the resulting signatures are microphysically interpreted. The analysis and the presented data validate the polarization transformation method derived here under the assumption of a diagonal propagation matrix.

Full access
V. Chandrasekar, J. Hubbert, V. N. Bringi, and P. F. Meischner

Abstract

A fully polarimetric radar system consists of an orthogonal dual-polarized transmission mode and a dual-channel receive mode that are typically set to be copolar and cross polar to the transmit state of polarization. The transmit polarization state is switched every pulse repetition time (PRT) between any two orthogonal stales. This paper presents an interpolation technique to construct time series of instantaneous scattering matrices (ISM) from fully polarimetric time series measurements obtained at every PRT from distributed scatterers. It is also shown theoretically that propagation effects need not be removed before transformation. The constructed series of ISMs are then transformed to other polarization bases. The resulting new ISMs are then used to calculate the radar parameters in the new basis. The suggested procedure is studied using data (collected at linear ±45° as well as horizontal and vertical polarization bases) from POLDIRAD, the dual-channel, polarimetric C-band radar operated by the German Aerospace Research Establishment.

Full access
H. Höller, M. Hagen, P. F. Meischner, V. N. Bringi, and J. Hubbert

Abstract

Hailstorm processes are studied using multiparameter radar observations of thunderstorm evolution. The storm turned out to be of hybrid type, having both multicellular (oscillatory nature of hail production) and supercellular (quasi-steady state of basic dynamics) characteristics. Its reflectivity field showed a V-like pattern not yet described in the literature as a typical severe storm pattern. The flow was characterized by an updraft zone surrounding an embedded downdraft collocated with the main precipitation shaft.

The precipitation mainly originated from graupel particles growing at the fringes of the main updraft zone, whereas an accumulation zone of big drops was not present. In the weaker parts of the updraft the falling graupel melted and reached the ground as rain, whereas in the main updraft region those raindrops could be recirculated and subsequently freeze or be captured by hailstones already present aloft. In this region of high liquid water content large hail could be grown; it fell out in the main downdraft region immediately beside the main updraft zone. Comparison of the radar-derived hailswath and ground observations of hail damage gave encouraging verification of the LDR-ZDR hail signature defined in this paper.

Full access
Eugenio Gorgucci, Gianfranco Scarchilli, V. Chandrasekar, P. F. Meischner, and M. Hagen

Abstract

Quantitative application of radar measurements at C band requires correction for attenuation. Algorithms to correct for attenuation and differential attenuation are evaluated based on theoretical analysis as well as radar data. The error structure of three different attenuation correction algorithms based on (a) reflectivity, (b) reflectivity and differential reflectivity, and (c) specific differential propagation phase is analyzed. The error structure of two algorithms to correct the differential attenuation based on (a) reflectivity and differential reflectivity, and (b) specific differential propagation phase is presented. Data from the polarimetric C-band Doppler radar POLDIRAD operated by DLR (Germany) are utilized to intercompare the attenuation and differential attenuation correction algorithms. Radar data and theoretical analysis show that the attenuation correction algorithm using reflectivity and differential reflectivity agrees well with the attenuation correction algorithm based on specific differential phase. Similarly, radar data and theoretical analysis indicate that the algorithms to correct for differential attenuation compare well with each other. In addition the fractional standard error of comparison between the algorithms to correct for attenuation and differential attenuation is in good agreement with theoretical results, providing an indirect verification of the accuracies of the algorithms.

Full access
P. F. Meischner, M. Hagen, T. Hauf, D. Heimann, H. Höller, U. Schumann, W. Jaeschke, W. Mauser, and H. R. Pruppacher

CLEOPATRA (Cloud Experiment Oberpfaffenhofen and Transports) is described. This field program was performed in southern Germany 50 km north of the Alpine foothills, an area of known enhanced thunderstorm activity. The general goal is to quantify elements of the hydrological cycle on a regional scale in dependence upon precipitation events and the vegetation state. Embedded goals are to describe the mechanisms that force organizations of deep convective systems, to compare theories and observations of atmospheric depositions, and to test and compare observational methods from ground, aircraft, and space. The observational setup, including 10 research aircraft, four radar systems, and different ground-based networks, was operational from 11 May until 31 July 1992 to cover an essential period of the growing season.

Full access