Observations of Misovortices within a Long-lake-axis-parallel Lake-effect Snow Band during the OWLeS Project

Recent lake-effect snow field projects in the eastern Great Lakes region have revealed the presence of misovortices with diameters between 40 and 4000 m along cyclonic horizontal shear zones within long lake-axis-parallel bands. One particular band in which an abundance of misovortices developed occurred on 7 January 2014.

The leading hypothesis for lake-effect misovortexgenesis is the release of horizontal shearing instability (HSI). An analysis of three-dimensional dual-Doppler wind syntheses reveal that two criteria for HSI are satisfied along the horizontal shear zone, strongly suggesting that HSI was the likely cause of the misovortices in this case. Furthermore, the general lack of anticyclonic-cyclonic vortex couplets throughout the event reveal that tilting of horizontal vorticity into the vertical is of less importance compared to the release of HSI and subsequent strengthening via vortex stretching.

A WRF simulation depicts misovortices along the horizontal shear zone within the simulated band. The simulated vortices display remarkable similarities to the observed vortices in terms of intensity, depth, spacing, and size. The simulated vortices persist over the eastern end of the lake; however, once the vortices move inland, they quickly dissipate. HSI criteria are also calculated from the WRF simulation and are satisfied along the shear zone. Competing hypotheses of misovortexgenesis are presented, with results indicating that the release of HSI is the likely mechanism of vortex formation.