Convective-Area Contraction as an Amplifier of the SST Pattern Effect
Abstract
The top-of-atmosphere (TOA) radiative response to surface warming depends on the spatial pattern of sea-surface temperature (SST) change, not only its global mean. This dependence, known as the SST pattern effect, is dominated in the tropics by changes in marine low-cloud cover mediated by the estimated inversion strength (EIS). An additional and lessstudied control is the relative areas of convective, strong-greenhouse-effect regions and subsiding, dry regions. We develop a minimal two-column model of the tropical atmosphere in which the overturning mass flux and the convective area fraction both respond interactively to prescribed SST boundary conditions, combining a quasi-equilibrium-weak temperature gradient thermodynamic framework with a linearized dynamical closure. Increasing SST contrast between the columns drives an area-fraction feedback through two independent constraints: dynamically, the overturning mass flux strengthens with the boundary-layer temperature contrast; thermodynamically, the freetropospheric subsidence velocity is set by the ratio of radiative cooling to gross dry stability. The subsiding area expands with SST gradients to satisfy both constraints. This feedback amplifies the EIS-driven radiative response, accounting for 20-30% of the tropical TOA radiative imbalance anomaly in the two-column model and in prescribed-SST general-circulation-model experiments.
The models also exhibit a hydrological pattern effect: precipitation increases more when warming is concentrated in convective regions, an effect constrained energetically by free-tropospheric radiative cooling and consistent with the strengthening overturning. Since the convective zone contracts, rain rates within it increase by more than the tropical mean. The bimodal convectivesubsiding structure of the tropics, and the dynamical coupling between the two regimes, are essential to the tropical response to patterned SST changes.
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BibTeX
@misc{lecuyer2026convectivearea,
title = {{Convective-Area Contraction as an Amplifier of the SST Pattern Effect}},
author = {Jo Lecuyer and Gilles Bellon and Benoit Meyssignac},
howpublished = {HAL},
year = {2026},
month = jul,
url = {https://hal.science/hal-05762520v1},
note = {CC BY 4.0},
}
RIS
TY - UNPB
TI - Convective-Area Contraction as an Amplifier of the SST Pattern Effect
AU - Jo Lecuyer
AU - Gilles Bellon
AU - Benoit Meyssignac
PY - 2026
DA - 2026/07/25
PB - HAL
UR - https://hal.science/hal-05762520v1
AB - The top-of-atmosphere (TOA) radiative response to surface warming depends on the spatial pattern of sea-surface temperature (SST) change, not only its global mean. This dependence, known as the SST pattern effect, is dominated in the tropics by changes in marine low-cloud cover mediated by the estimated inversion strength (EIS). An additional and lessstudied control is the relative areas of convective, strong-greenhouse-effect regions and subsiding, dry regions. We develop a minimal two-column model of the tropical atmosphere in which the overturning mass flux and the convective area fraction both respond interactively to prescribed SST boundary conditions, combining a quasi-equilibrium-weak temperature gradient thermodynamic framework with a linearized dynamical closure. Increasing SST contrast between the columns drives an area-fraction feedback through two independent constraints: dynamically, the overturning mass flux strengthens with the boundary-layer temperature contrast; thermodynamically, the freetropospheric subsidence velocity is set by the ratio of radiative cooling to gross dry stability. The subsiding area expands with SST gradients to satisfy both constraints. This feedback amplifies the EIS-driven radiative response, accounting for 20-30% of the tropical TOA radiative imbalance anomaly in the two-column model and in prescribed-SST general-circulation-model experiments. The models also exhibit a hydrological pattern effect: precipitation increases more when warming is concentrated in convective regions, an effect constrained energetically by free-tropospheric radiative cooling and consistent with the strengthening overturning. Since the convective zone contracts, rain rates within it increase by more than the tropical mean. The bimodal convectivesubsiding structure of the tropics, and the dynamical coupling between the two regimes, are essential to the tropical response to patterned SST changes.
ER -