Fig. 3.

Curl of $\overrightarrow{\mathbf{W}}$. a The curl in London, the colors represent the module of ∇ × $\overrightarrow{\mathbf{W}}$ for each cell in km⁻¹. b The same for the null model, obtained by randomly reassigning directions to $\overrightarrow{\mathbf{W}}$ in each cell. In both cases, the x- and y-axis represent the Easting and Northing of the local Mercator projection in kilometers from Waterloo Bridge