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Abstract

Convection in a container, heated from below, cooled from above and rapidly rotated
around a vertical axis, starts from its sidewall. When the imposed vertical temperature
gradient is not sufficiently large for bulk modes to set in, thermal convection can
start in the form of wall modes, which are observed near the sidewall as pairs of
hot ascending and cold descending plumes that drift along the wall. With increasing
temperature gradient, different wall and bulk modes occur and interact, leading finally
to turbulence. A recent numerical study by Favier & Knobloch (J. Fluid Mech., 895,
2020, R1) reveals an extreme robustness of the wall states. They persist above the
onset of bulk modes and turbulence, thereby relating them to the recently discovered
boundary zonal flows in highly turbulent rotating thermal convection. More exciting
is that the wall modes can be thought of as topologically protected states, as they
are robust with respect to the sidewall shape. They stubbornly drift along the wall,
following its contour, independent of geometric obstacles.