Some planetary atmospheres exhibit prograde winds at the equator, which is known as superrotation. Because tropical-extratropical interactions are fundamentally altered in this setting, it has been argued that the transition to strong superrotation may occur abruptly. One of the mechanisms thought to drive superrotation in small planets and/or slow rotators is the resonant interaction between extratrotropical Rossby waves and equatorial Kelvin waves.

Using simulations with an idealized GCM, we will show that this instability can also spinup superrotation with terrestrial parameters when extratropical baroclinic eddies are weak. The transition to superrotation occurs abruptly in this model, and two different stable climates are possible over the transition region. Our results may have implications for the superrotation of past terrestrial climates.

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