“…(; ) for more details). D TW focuses on air flows since this distance involves gradients of absolute values of geopotential heights (Woodcock, ; Obled et al, ; Bontron, ; Wetterhall et al, ; Brigode et al, ). The formula for estimating D TW between two synoptic situations (Z1) and (Z2) characterized by geopotential height fields on a gridded domain oriented south–north (index i ) and west–east (index j ) is where e G is the difference, around a given grid point, between the Z1 and Z2 geopotential gradients, while G L is the maximum of these two gradients in the direction considered ( i or j ), …”