Meter-scale Observations of Aircraft Wake Vortices in Precipitation using a High Resolution Solid-State W-band Radar

Meter-scale detection of aircraft wake vortices in light rain has been demonstrated using a low power (100 mW) solid-state W-band (94 GHz) radar system. The radar employs a 1.2 m diameter antenna on a scanning pedestal, providing a 1.5 meter 6-dB cross-track beam pattern at 500 meters range. Range resolution as fine as 1.0 m is achieved using stretch processing, which also provides processing gain on the order of 30 dB. Additional coherent gain is achieved through FFT processing at each range gate. Range sidelobe suppression of greater than 40 dB makes this system suitable for high spatial and temporal resolution meteorological research.

Aircraft wake vortex measurements in light rain were gathered in February and April of 2009 at Logan International Airport at a range of 500-600 meters. Spectral data in the absence of wake vortices exhibit very narrow spectral width (on the order of 20 cm-s-1) due to the lack of shear within the small resolution volume. Classic counter rotating vortices were observed when making RHI scans perpendicular to the aircraft flight vector. Reflectivity RHI plots showed clear evidence of enhanced droplet concentration between the vortices, with a dramatic reduction in droplet concentration in columns directly below and towards the outside of each vortex. These structures in reflectivity were observed to persist for approximately 60 seconds after passage of the aircraft, consistent with the typical lifetime of the vortex.