Misovortex Characteristics and Development along Lake-effect Bands during the OWLeS Project

During the winter of 2013-14, scientists from eleven institutions gathered in upstate New York to conduct a first-of-its-kind field campaign on Lake Ontario-generated lake-effect snowstorms called the Ontario Winter Lake-effect Systems (OWLeS) Project. The University of Wyoming King Air aircraft, heavily instrumented for in-situ and remote sensing of the atmosphere, three Doppler on Wheels (DOW) radars, five (four mobile) rawinsonde systems, and the University of Alabama – Huntsville Mobile Integrated Profiling System (MIPS) were some of the key facilities used to study lake-effect storms. The key objectives were focused in three areas: structure and dynamics of long lake-axis-parallel (LLAP) storms, upwind and downwind causes and effects of lake-effect systems, and orographic influences on these storms. A large amplitude, blocking upper-level ridge over western North America, with a downstream trough over eastern North America, dominated the synoptic pattern for most of the field project. This trough led to frequent intrusions of arctic air over and near Lake Ontario, sometimes originating from cross-polar flow. There was a total of 24 IOPs during the OWLeS field campaign, more than double what climatology suggested would occur!

Dual-Doppler analyses from DOW data will be shown of the many vortices (sub-km to multi-km diameters) observed within LLAP storms. The evolution of the width, depth, and spacing between vortices from the 7 Jan 2014 event will be compared to previous lake-effect studies in this region and over the Sea of Japan. Other characteristics that will be discussed include relative vorticity values, vertical motions within and nearby the vortices, and proximity thermodynamic measurements in order to test hypotheses to explain their development. Many of the vortices formed on boundaries, boundaries that may form due to cold pools originating from sublimating ice particles near the ground near the northern edge of the band (which had a very sharp reflectivity gradient). Strong horizontal shear was near the boundary (faster westerly momentum within the north side of the band and much weaker momentum just to the north of the band edge), but the cause of this shear is still under investigation. Therefore horizontal shear instability can explain miso-vortex development, but tilting and stretching of vorticity will also be tested as an explanation for the larger vortices (e.g., similar to mesocyclone development in supercell thunderstorms?). WRF model simulations replicated the line of vortices seen in this case and will be compared to the DOW observations.

Lastly, lightning occurred during the same period and within 5-10 km when the misocyclones were frequent during the 7 Jan event. Surface reports by student research assistants in the field reported an increase in the frequency of strong wind gusts nearby the line of misovortices and lightning.