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arXiv · 1905.12401

Atmospheric bistability and abrupt transitions to superrotation: wave-jet resonance and Hadley cell feedbacks

Corentin Herbert·Rodrigo Caballero·Freddy Bouchet
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Abstract

Strong eastward jets at the equator have been observed in many planetary atmospheres and simulated in numerical models of varying complexity. However, the nature of the transition from a conventional state of the general circulation, with easterlies or weak westerlies in the tropics, to such a superrotating state remains unclear. Is it abrupt or continuous? This question may have far-reaching consequences, as it may provide a mechanism for abrupt climate change in a planetary atmosphere, both through the loss of stability of the conventional circulation and through potential noise-induced transitions in the bistability range. We study two feedbacks which may lead to bistability between a conventional and a superrotating state: the Hadley cell feedback and a wave-jet resonance feedback. We delineate the regime of applicability of these two mechanisms in a simple model of zonal acceleration budget at the equator. Then, we show using numerical simulations of the axisymmetric primitive equations that the wave-jet resonance feedback indeed leads to robust bistability, while the bistability governed by the Hadley cell feedback, although observed in our numerical simulations, is much more fragile in a multilevel model.

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Corentin Herbert, Rodrigo Caballero, Freddy Bouchet. 2019-05-29. Atmospheric bistability and abrupt transitions to superrotation: wave-jet resonance and Hadley cell feedbacks. https://doi.org/10.1175/jas-d-19-0089.1

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