Fig. 10

Filament secondary circulation. The associated cross-front streamfunction \(\Phi\) at three different times in the filament life-cycle: (top-to-bottom) initial condition for frontogenesis (\(t = 0\)), during the peak time of frontal arrest (\(t = 6\) h), and during an extensive period of frontal decay (\(t = 2\) days). Notice the strong, narrow surface convergence that is the cause of the frontal sharpness. This is for the same simulation as in Fig. 9 (Sullivan and McWilliams 2018)