Climatological mean and interannual variance of United States surface wind speed, direction and velocity

Abstract

Means and variances of monthly mean wind speed, direction and velocity (the mean resultant vector) are derived for the period 1961-1990 at 216 stations in the coterminous United States. Direction and velocity means and variances are calculated using a complex-arithmetic extension of the equations for scalar mean and variance. Variance is derived from the 30-year time series of monthly means. While analyses of monthly mean wind fields are common, accompanying analyses of speed, direction, and velocity variance do not generally accompany them. Mean monthly wind direction and velocity fields show a typical seasonal progression from westerly and northwesterly winds in winter, to southerly winds in summer. Scalar and vector wind speeds are highest in winter and spring, and lowest in the summer. Seasonal variation in the mean fields is related to seasonal changes in mean sea level pressure, particularly east of the Rocky Mountains. In the western United States, mean winds often reflect channeling by local topography. The interannual variance of mean monthly wind speed, direction and velocity are related to seasonal variability in synoptic-scale features, such as the frequency of cyclones and anticyclones. Low variance occurs at a number of stations in the west, where topography restricts the range of wind variability. High velocity variance appears when both speed and direction variability are high, but it can occur also when speed variance is high and direction variance is low (or 6ice 6ersa). Low velocity variance can result from low speed and direction variance, or from low mean wind velocities. The mean and variance characteristics of surface winds provide additional information on the surface climatology of the coterminous United States, and serve as a useful adjunct to other extant land-surface climatologies.

Changes in terrestrial near-surface wind speed and their possible causes: an overview

“…Tuller (2004) found a correlation between long-term decreases in SWS and PGF at most stations in western Canada's inshore regions. A close correlation between the monthly average SWS and PGF in the United States has also been documented (Klink 1999a). Based on calculations, approximately 22-47% of the changes in the monthly mean SWS have been induced by changes in the longitudinal PGF in Minnesota (Klink 2007), and 40% of the changes in the average SWS have been induced by changes in the PGF in Colorado (Clifton and Lundquist 2012).…”

“…Some studies have represented the potential causes of decreases in the terrestrial SWS in terms of global and regional perspectives (McVicar et al 2012a;Klink et al 1999aKlink et al , b, 2002Klink et al , 2007. However, it is difficult to separate and quantify the respective effects of various mechanisms on SWS changes.…”

“…Some researchers have noted correlations between rising temperatures and decreases in SWS and have tended to explain decreases in SWS as a reduction in the driving force in the atmosphere associated with the changes in air temperature (Gadgil 2007;Trenberth et al 2007). Klink (1999a) concluded that the downward trends in SWS over the United States could be explained by an increase in the mean air temperature at higher latitudes relative to the tropics. Pirazzoli and Tomasin (2003) found that the changes in SWS in the Mediterranean and Adriatic areas were similar to the changes observed in air temperatures.…”

Trends in mean monthly maximum and minimum surface wind speeds in the coterminous United States, 1961 to 1990

“…Other locations in the west show lower maximum speeds because of the more varied topography. Low maximum wind speeds in the southeastern United States reflect the dominance of high pressure in this area during most months of the year (Klink 1999). For most locations, maximum winds are faster in winter and spring and slower during the summer and autumn.…”

“…The link between local surface winds and continental-scale pressure patterns appears to be stronger in some parts of the country than in others (Klink 1999). Surface cyclone and anticyclone frequencies and intensities themselves may be related to large-scale surface temperature trends (Agee 1991), though these relationships can be different in different parts of the country (Angel & Isard 1998).…”