Publications

The Weather Systems Processor (WSP) is an add-on system to the Airport Surveillance Radar-9 (ASR-9) that generates wind shear detection and storm tracking products for the terminal airspace. As the original system ages and pre-purchased replacement parts in the depot are used up, it becomes increasingly problematic to procure hardware components for repairs. Thus, a technical refresh is needed to sustain WSP operations into the future. This phase of the project targets the intermediate frequency digital receiver, the radar interface module, and the digital signal processor for replacement by updated hardware platforms. At the same time, the increase in computational capability allows for an upgrade in the signal processing algorithm, which will lead to data quality improvements.

MIT Lincoln Laboratory is tasked by the U.S. Federal Aviation Administration to investigate the use of the NEXRAD polarimetric radars for the remote sensing of icing conditions hazardous to aircraft. A critical aspect of the investigation concerns validation that has relied upon commercial airline icing pilot reports and a dedicated campaign of in situ flights in winter storms. During the month of February in 2012 and 2013, the Convair-580 aircraft operated by the National Research Council of Canada was used for in situ validation of snowstorm characteristics under simultaneous observation by NEXRAD radars in Cleveland, Ohio and Buffalo, New York. The most anisotropic and easily distinguished winter targets to dual pol radar are ice crystals. Accordingly, laboratory diffusion chamber measurements in a tightly-controlled parameter space of temperature and humidity provide the linkage between shape and the expectation for the presence/absence of water saturation conditions necessary for icing hazard in situ. In agreement with the laboratory measurements pertaining to dendritic and hexagonal flat plate crystals, the aircraft measurements have verified the presence of supercooled water in mainly low concentrations coincident with regions showing layered anomalies of positive differential reflectivity (ZDR) by ground-based radar, otherwise known as +ZDR 'bright bands'. Extreme values of ZDR (up to +8 dB) have also been found to be coincident with hexagonal flat plate crystals and intermittent supercooled water, also consistent with laboratory measurements. The icing conditions found with the anisotropic description are considered non-classical (condensation/collision-coalescence) and require the ascent of air and availability of ice nuclei. A modest ascent rate (

The Next Generation Weather Radar (NEXRAD) network completed a dual polarization upgrade in 2013. The radars now can be used to sense the type of scatterers that cause the radar returns. The scatterers can be hydrometeors, biologicals, or earth-sourced. The ability to reliably interpret the radar-sensed thermodynamic phase of the hydrometeors (solid, liquid, mix) in the context of cloud microphysics and precipitation physics makes it possible to assess the icing hazard potential to aviation. That assessment for Federal Aviation Administration (FAA) purposes would necessarily be performed by automated algorithms based in hydrometeor classification terms. The truth as to the icing hazard aloft (where the radar scans) is required to ascertain the value of such algorithms. The Buffalo Area Icing and Radar Study (BAIRS) of 2013 was a partnership between MIT Lincoln Laboratory (LL) and the National Research Council of Canada (NRC) to perform in situ icing missions within the surveillance range of the dual polarization NEXRAD in Buffalo, NY. The goal of these 2013 missions, and the subject of this report, was to target specific winter weather scenarios known to exhibit an aviation icing hazard for the purpose of quantifying the microphysical properties of the target zones and verifying the presence of supercooled liquid water (SLW) to support validation of hydrometeor classification algorithms. These are the first such missions to execute in situ measurements within a NEXRAD's surveillance range running with the fielded, operational NEXRAD hydrometeor classifier. NRC's Convair-580 instrumented research plane was used for three icing missions covering 14 hours. Three distinctly different winter weather scenarios were encountered. This document details the analysis of in situ data such as particle type and liquid water content (LWC) with NEXRAD dual polarization parameters for the three missions. The BAIRS analysis identified these key findings: -NEXRAD radar returns are prevalent in conditions of supercooled water, -NEXRAD classification shows positive results based on particle imagery, -NEXRAD "dry snow" class masks the presence of mixed phase potential icing hazard, -NEXRAD "unknown" class contains diverse regions of icing hazard potential, and there are methods to classify some of these regions, and -In situ aircraft observations are an important tool to both verify algorithm performance and guide further development.

This study is concerned with the use of cloud microphysical aircraft measurements (the Convair 580) to verify the origin of differential reflectivity (ZDR) measured with a ground-based radar (the WSR-88D KBUF radar in Buffalo, New York). The underlying goal is to make use of the radar measurements to infer the presence or absence of supercooled water, which may pose an icing hazard to aircraft. The context of these measurements is the investment by the Federal Aviation Administration in the use of NEXRAD polarimetric radar and is addressed in the companion paper by Smalley et al. (2013, this Conference). The highlight of the measurements on February 28, 2013 was the finding of sustained populations of hexagonal flat plate crystals over a large area northwest of the KBUF radar, in conditions of dilute and intermittent supercooled water concentration. Some background discussion is in order prior to the discussion of the aircraft/radar observations that form the main body of this study. The anisotropy of hydrometeors, the role of humidity and temperature in crystal shape, and the common presence of hexagonal flat plate crystals in the laboratory cold box experiment are all discussed in turn.