Elevated convection and stratiform flows in continental winter cyclones: high-resolution measurements from the Wyoming Cloud Radar

During the Profiling of Winter Storms (PLOWS) campaign, the NCAR C-130 with the Wyoming Cloud Radar (WCR) onboard flew across precipitation bands within the wrap-around and warm-frontal regions of continental extratropical cyclones. The three-beam configuration allowed the radar to measure reflectivity and Doppler velocity at high resolution (~15m horizontal, ~30m vertical) in a vertical plane extending above and below the flight track. The WCR observations are critical to bridging the gap between ground-based radar observations, which provide volume measurements over large areas but at relatively poor resolution, and the inherently 1-dimensional observations from in situ probes on the C130.

Given the small range of terminal velocities for ice-phase hydrometeors, Doppler velocities from the up- and down-pointing beams can be readily converted to vertical air velocity by applying corrections for particle fallspeed and for contributions from the horizontal wind into the (nearly-vertical) beams. Doppler velocities from the down-slant beam (in the same plane as the downward looking beam, but displaced 33° aft of nadir) can be combined with velocities from the down beam to separate vertical and along-track velocity components for the vertical plane below the aircraft.

Vertical stratification of the horizontal velocities, prevalent outside regions of active turbulence, is readily apparent in both the along-track velocity component and the radial velocity measurements from the down-slant beam. This stratification not only provides a direct and compelling means for distinguishing stratiform and convective regions within the bands but also insight into the underlying convective mechanisms themselves. We show that banded features observed with the WSR-88D do not necessarily capture the nature or distribution of convection within the storms, but rather appear where the low level beam intersects fall streaks originating in elevated convection either above the warm front or at cloud top.