Tuesday, 4 August 2015: 5:15 PM
Republic Ballroom AB (Sheraton Boston )
A number of strong, persistent long-lake-axis-parallel (LLAP) lake-effect snow bands were observed during the Ontario Winter Lake-effect Systems (OWLeS) field project. Such single lake-scale band suppresses convective cells aligned in street by a helical roll circulation, as typically observed in cold-air outbreaks over open water. The key question addressed in this study is what drives the development of a single band. As part of OWLeS, the University of Wyoming King Air flew several transects at three flight levels across a deep LLAP band on 11 December 2013 over the east end of Lake Ontario. Vertical-plane dual-Doppler analysis from the Wyoming Cloud Radar, with antennas in nadir and slant forward directions, reveal a strong, lake-scale secondary circulation across the LLAP band, with a ~5 m s-1 updraft in the band's core which extended to a depth of about three kilometers, convergence near the surface and divergence aloft. Flight-level observations and near-shore radiosondes on opposite sides of the LLAP band suggest that the band is solenoidal, i.e. has a warm core. The collapse of the convergence and updraft to small scales is due in part to frontogenic forcing, due to colder air north of Lake Ontario. The LLAP band contains convective cells, some with updrafts peaking at over 10 m s-1. Subsidence on the margins of the LLAP band appears to suppress the depth and intensity of convection there.
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