Journal Article

Diurnal Variability Modulates Episodic Convection in Hothouse Climates Over Ocean and Swamp‐Like Surface Conditions

Steiger, Nathan, Habib, Namrah, Dagan, Guy

2026

Overview

Hot and moist “hothouse” climates occurred in Earth's past and are expected in Earth's far future climate, driven by increasing solar luminosity. In hothouse climate regimes, precipitation transitions from a quasi‐steady state, as in present‐day tropical convection, to an “episodic deluge” or relaxation‐oscillator (RO) regime where precipitation occurs in intense bursts separated by multi‐day dry spells. Recent studies suggest that the transition to RO convection regimes is radiatively driven. However, the transition from steady state to RO convection has only been studied with radiative convective equilibrium (RCE) simulations with constant insolation, excluding the diurnal cycle. Precipitation and convection are strongly linked to the diurnal cycle in Earth's present climate over both land and ocean. We explore the impact of the diurnal cycle on the transition from steady state to RO convection using two sets of small‐domain RCE simulations with ocean and swamp‐like surface boundary conditions. Our RCE simulations with ocean boundary conditions show convection transitions to an episodic deluge regime at 322 K and the diurnal cycle modulates precipitation to occur during late‐night or near dawn, when convective inhibition is the weakest. Our RCE simulations with swamp‐like boundary conditions, which allow for mean surface temperature variations, show that as RO states emerge, the diurnal cycle modulates precipitation to primarily occur during the late‐afternoon to about dusk; but as the mean SST increases, precipitation occurs during the late‐night to dawn. These results show that the diurnal cycle strongly influences the timing of convection and precipitation patterns in extreme climates. In hot and wet “hothouse” climate conditions, rainfall transitions from a pattern that fluctuates from about a mean of 3 mm to more intense outbursts that are separated by multi‐day dry spells. Previous studies on hothouse climates did not consider the role of the diurnal cycle even though it strongly controls precipitation in Earth's current climate. This study uses radiative‐convective equilibrium simulations to investigate the impact of rising temperatures on the transition to hothouse conditions, incorporating the diurnal cycle with both swamp‐like and open ocean surface conditions. We find that episodic precipitation occurs at surface temperatures above 322 K even when accounting for the diurnal cycle. However, the diurnal cycle significantly influences the timing of convection and rainfall at high temperatures with precipitation primarily starting late at night or in the early morning. We study hothouse climates using radiative convective equilibrium simulations with a diurnal cycle over ocean and swamp‐like conditions A transition from steady state to episodic precipitation occurs when accounting for diurnal variability at high surface temperatures The diurnal cycle modulates the episodic precipitation events with precipitation occurring primarily during the dawn or dusk hours

• Publisher: John Wiley & Sons, Inc,American Geophysical Union (AGU)
• Subject: Atmosphere / Boundary conditions / Climate / Climatic extremes / convection / Cooling / diurnal / Diurnal cycle / Dry spells / Earth / Equilibrium / Extreme weather / Future climates / Heat engines / hothouse / Hypotheses / Oceanic convection / Oceans / Precipitation / Precipitation patterns / Radiation / RCE / Simulation / Steady state / Surface temperature / Swamps / Temperature / Temperature variations / Tropical convection