 Bob Rauber University of Illinois
Research-Radar Polarization Studies |
| Radar Polarization will soon be introduced to the National Weather Service WSR-88D radar network. Detection of hazardous weather is one of the primary reasons that radar polarization is being adapted to the WSR-88Ds. Severe storm hazards are the primary focus, but can we use polarization technology to detect winter harzards as well? The dataset from the Mesoscale Alpine Project, conducted in the late 1990s in the Alpine region of Switzerland and Italy provided a unique opportunity to evaluate and understand whether supercooled water, the cause of aircraft icing in winter storms, could be detected using polarimetric radar. The availability of aircraft measurements of supercooled water droplets and ice particles in conjunction with collocated polarization radar measurements from NCAR' SPOL radar, presented a unique opportunity to evaluate particle classification and particularly focus on supercooled water identification. We have recently published a paper exploring the usefulness of the polariation technology to detect supercooled water using this unique dataset. |
| At the University of Illinois we have focused on improving radar based particle identification in two ways: first, we investigated the potential of improving supercooled water detection using particle classification with polarization radar. Second, we are developed a new technique for introducing probabilistic estimates of particle classification, providing a quantitative measure of the uncertainty of particle classification at each point in space. Data for this work came from the Mesoscale Alpine Program, specifically from the NCAR S-Pol radar and from instrumentation aboard the NCAR Electra research aircraft.
To do these evaluations, a “matched” data set (points at which aircraft observations could be compared directly to radar observations) was developed and divided into two categories, based on aircraft measurements of the presence or absence of supercooled water. Statistical analysis of the data revealed that our typing algorithm could identify supercooled water with some statistical confidence.Our results
show that t hree polarization radar parameters, the radar reflectivity factor at horizontal polarization (ZH), the differential reflectivity (ZDR), and the specific differential phase (KDP), are statistically distinguishable between conditions in mixed- and ice-phase clouds, even when an estimate of measurement uncertainty is included. We have developed robability distributions for discrimination of mixed-phase vs. ice-phase clouds from the matched radar and aircraft measurements thatcorrespond well to a basic physical understanding of ice particle growth by riming and vapor deposition, both of which may occur in mixed-phase conditions. These findings, particularly if they are more widely applicable to other types of stratiform clouds, should have an impact on the accuracy of detection of icing conditions in stratiform clouds once polarimetric radars come into common use in the WSR-88D network. |
Polarization Publications (UI authors in bold)
Plummer, D., S Göke, R. M. Rauber, and L. Di Girolamo,
2010: Discrimination of mixed- vs. ice-phase clouds using dual polarization radar with application to detection of aircraft icing regions. J. Appl. Meteor. Climatol., 49, 920-936. .
Master's Theses and Ph.D. Dissertations from our polarization research include:
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