Episodic Deluges In Simulated Hothouse Climates

Schematic view of the phases of the relaxation oscillator convective regime. (Bottom) Snapshots of outgoing solar radiation (OSR) during the (a) recharge, (b) triggering, and (c) discharge phases, obtained 1.95 days, 4 hours, and 0 hours before the next hour of peak precipitation (tpeak), respectively. These snapshots are from the high-resolution fixed-SST simulation at a surface temperature of 330 K. High values of OSR indicate cloud cover. Neither the graphical width of the phases nor the vertical thickness of the atmospheric layers in this schematic are proportional to the amount of time or space they occupy.

Earth's distant past and potentially its future include extremely warm "hothouse" climate states, but little is known about how the atmosphere behaves in such states.

One distinguishing characteristic of hothouse climates is that they feature lower-tropospheric radiative heating, rather than cooling, due to the closing of the water vapor infrared window regions. Previous work has suggested that this could lead to temperature inversions and significant changes in cloud cover, but no previous modeling of the hothouse regime has resolved convective-scale turbulent air motions and cloud cover directly, thus leaving many questions about hothouse radiative heating unanswered.

Here, we conduct simulations that explicitly resolve convection and find that lower-tropospheric radiative heating in hothouse climates causes the hydrologic cycle to shift from a quasi-steady regime to a "relaxation oscillator" regime, in which precipitation occurs in short and intense outbursts separated by multi-day dry spells.
The transition to the oscillatory regime is accompanied by strongly enhanced local precipitation fluxes, a significant increase in cloud cover, and a transiently positive (unstable) climate feedback parameter. Our results indicate that hothouse climates may feature a novel form of "temporal" convective self-organization, with implications for both cloud coverage and erosion processes.

Jacob Seeley, Robin Wordsworth

Subjects: Earth and Planetary Astrophysics (astro-ph.EP); Adaptation and Self-Organizing Systems (nlin.AO); Atmospheric and Oceanic Physics (physics.ao-ph)
Journal reference: Nature 599, 74-79 (2021)
DOI: 10.1038/s41586-021-03919-z
Cite as: arXiv:2111.03109 [astro-ph.EP] (or arXiv:2111.03109v1 [astro-ph.EP] for this version)
Submission history
From: Jacob Seeley
[v1] Thu, 4 Nov 2021 19:11:07 UTC (18,827 KB)

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