A whirling mass of fluid or air. See Walker and Nickling (2002) PPG 26, 1 on helical vortices in dunes; Wiggs (2001) PPG on the roll-vortex theory of dune formation; Haines (1982) J. Applied Met. 21 on horizontal roll vortices and crown fires; and Davies and Thorne (2005) J. Geophys. Res. 110, C05017 on waves in the vortex ripple regime. Huang et al. (2000) Atmos. Env. 34 simulate a stable canyon vortex, and MacDonald (2000) Boundary-Layer Met. 97 has a numerical model to describe the spatially averaged wind speed profile within the urban canopy layer.

Power (2003) PPG 27 explains that the strong polar vortex in the Antarctic atmosphere isolates the polar air mass for much of the year. Over the Arctic region the polar vortex is weaker—resulting, in part, from the uneven distribution of land and water. Perlwitz and Graf (1995, J. Climate 8) show that the North Atlantic Oscillation tends to be positive during winters with an anomalously strong stratospheric polar vortex.