Consistency of low-frequency rotation of surface winds over Canada

Episodes of wind anemometer rotation indicate the passage of atmospheric vortices. Net wind rotation is subsequently comprised of all vortices reflected by the meteorological station record. Spatial consistency of periods of point wind rotation, as well as stability of spatial pattern of rotations over many decades would add new determinism to atmospheric dynamics. In order to clarify the structure of this spatial pattern, more than 30 years of observations of hourly surface winds from Canadian Weather Energy and Engineering Dataset (CWEEDS, 149 meteostations) were analyzed with respect to long-term wind direction drift or rotation. It appears that most of the Canadian landmass, including the High Arctic, exhibits a remarkably steady rotation of wind direction. The period of anticyclonic rotation recorded in 97% of stations (at 144 locations) directly correlated with latitude and ranged from 7 days at Medicine Hat (50o N, 110o W) and 9 days at Windsor (42o N, 83o W) to 25 days at Cambridge Bay (70o N, 96o W) and Resolute (75o N, 95o W). Only five locations in the vicinity of the Rocky Mountains and Pacific coast were found to have a “reverse”, i.e. cyclonic rotation and subsequently fell off the noted 7-25 days range. The vertical structure of wind rotation up to 150m a.g.l. was assessed by analyzing wind profiles of Chalk River Laboratories sodar and found being relatively uniform with height. The observed beyond-synoptic periodicity of surface winds, which represents a net anticyclonic imbalance of cyclonic and anticyclonic synoptic events, otherwise known as asymmetry, appears a deterministic, virtually ubiquitous and highly persistent feature of continental surface wind in mid- and high latitudes. Apparent consequences (periodic reoccurrence of pollutants in the atmosphere) and more speculative associations (i.e. with Rossby waves) are discussed.