On the Shedding of Jupiter's Red Flakes

During 2019, the Great Red Spot (GRS) of Jupiter repeatedly shed large (100,000 km²) chunks of itself as red "flakes" on its southern side. Rather than assuming that the GRS is disintegrating (why would it?), we propose a more benign hypothesis that we test with 3D numerical simulations. There are 2 distinct outer boundaries associated with a GRS or any other Jovian vortex (n.b., neither of which is likely to be coincident with the boundary of its cloud cover): (1) the boundary of its potential vorticity (PV) anomaly, and (2) its last "closed streamline". An isolated vortex has nested closed streamlines, both interior to it and exterior it. The latter all circumscribe the vortex. However, an anti-cyclone embedded in an anti-cyclonic zonal shear only has exterior closed streamlines that are near the PV boundary. Farther from its PV boundary, it has "open streamlines" that circumscribe the planet as part of the zonal flow, but not the vortex. Generically, the last close streamline contains at least one stagnation point. We show that when there is large area between the last closed streamline and the PV boundary, small vortices that are "fed" to the GRS will merge with it. However, when that area is small, small vortices that try to merge with the GRS (say by impacting its northeast side) will be expelled at or near a stagnation point (say, on its southern side). The height in the atmosphere at which the small vortex is initially located need not be the height at which its PV is expelled. Thus, our plausible explanation of the of recent Red Flakes is that area between the PV boundary of the GRS and its last closed streamline has shrunk. Numerical results and observations are compared with this hypothesis.