Idealized Model Simulations Examining the Mesoscale Structure of Winter Lake-Effect Circulations

Abstract

An array of 35 idealized mesoscale model simulations was used to examine environmental and surface forcing factors controlling the meso-␤-scale circulation structure resulting from cold flow over an isolated axisymmetric body of water at the midlatitudes. Wind speed, lake-air temperature difference, ambient atmospheric stability, and fetch distance were varied across previously observed ranges. Simulated meso-␤-scale lake-effect circulations occurred within three basic regimes (e.g., vortices, shoreline bands, widespread coverage), similar to observed morphological regimes. The current study found that the morphological regimes of lake-effect circulations can be predicted using the ratio of wind speed to maximum fetch distance (U/L). Lake-effect environmental conditions producing low values of U/L (i.e., approximately Ͻ 0.02 m s Ϫ1 km Ϫ1 ) resulted in a mesoscale vortex circulation. Conditions leading to U/L values between about 0.02 and 0.09 m s Ϫ1 km Ϫ1 resulted in the development of a shoreline band, and U/L values greater than approximately 0.09 m s Ϫ1 km Ϫ1 produced a widespread coverage event. It was found that transitions from one morphological regime to another are continuous and within transitional zones the structure of a circulation may contain structural features characteristic of more than one regime. Results show that 1) the U/L criterion effectively classifies the morphology independently of the lake-air temperature difference for the parameter value combinations examined and 2) the Froude number, suggested as a potential lake-effect forecasting tool in previous studies, does not permit the unique classification of lakeeffect morphology.

Snow bands over the Gulf of Finland in wintertime

“…In both studied cases, the formation of snow bands agrees well with the results of Laird et al (2003a), who found that bands form when the ratio between the wind speed and fetch (V/L) is in the range of 0.02Á0.09 m s…”

“…Type V are associated with a mesoscale vortex. Laird et al (2003aLaird et al ( , 2003b identified three common snow band morphologies in numerical investigations, which were associated with vortices, widespread coverage and shoreline bands.…”

“…Norris et al (2012) found winds greater than 10 m s (1 in the investigation of the snow bands over the English Channel and Irish Sea. The ratio between the wind speed (V) and the fetch over the open water (L) was used to determine the lake-effect for idealised cases (Laird et al, 2003a). These authors found that when V/L is between 0.02 and 0.09 m s…”

Snowbands over the English Channel and Irish Sea during cold‐air outbreaks

“…Rather than wind speed, the ratio of ambient wind speed U to fetch length L determines lake-effect morphology for an idealized circular lake (Laird et al, 2003a). When U/L is less than 0.02 m s −1 km −1 , mesoscale vortices form.…”

Neural Network Based Seasonal Predictions of Lake-Effect Snowfall

“…Over the past 20 years, much progress has been made in simulating lake-effect circulations in the Great Lakes region with mesoscale models (Hjelmfelt, 1990;Laird et al, 2003aLaird et al, , 2003b. The processes generating lake-effect snow (Wiggin, 1950;Niziol, 1987;Niziol et al, 1995) have been studied in detail and short-term predictions have been significantly improved.…”