Measurements of radar reflectivity in dBZ (panel a) and differential reflectivity in dB (b). Panel (c) shows hydrometeor classifications made with the NCAR HCA (7: rain/hail mixture; 8: graupel/hail; 9: graupel/rain; 10: dry snow; 11: wet snow; 12: ice crystals, 13: irregular ice crystals). Color coding in panels (a) – (c) is for reflectivity (aqua: ≥ 10 dBZ and < 30 dBZ; green ≥ 30 dBZ and < 40 dBZ; red: ≥ 40 dBZ). Panel (d) shows icing–potential designations [1: no icing (green region); 2: possible icing (yellow); 3: icing likely (red)]. The aircraft track (as in Fig. 3) is under laid. Red portions indicate periods during which super–cooled water was detected. The radar cross–section is roughly at a height of 5.7 km. The small cluster of reflectivity measurements near x = –7.6, y = –31 km show the aircraft location.
Weather radar is the fundamental remote sensing weather instrument for the National Airspace System. While the FAA is heavily invested in NEXRAD hardware, few existing advances in weather radar science have been incorporated into products.
Photograph of the Aerocommander wind shield after exiting the cloud turret in Fig. 2. The image is from 055015 UTC. The ambient temperature was –7.1°
Around the 2011 time–frame, the NEXRAD network will be upgraded to use dual polarization, which allows the radar to determine the shapes of hydrometeors and to discriminate between liquid (rain and drizzle) and frozen (snow, ice pellets, and hail) precipitation. The hydrometeor discrimination algorithm (HCA) has been developed and tested on limited data sets (e.g. from the Cimarron Radar in Norman, OK and SPol in Colorado and Oregon, and CP–2 in Queensland, Australia). Preliminary results are promising, and applications to inflight icing identification are being considered in collaboration with the AWRP InFlight Icing Product Development Team. Additionally, data quality will be greatly enhanced because precipitation, clutter, birds, chaff and bugs have unique signatures that are extracted by the algorithm. Dual–polarization radar also appears to be useful for estimating equivalent liquid water content from snow, which is necessary for evaluating deicing holdover times.