54 research outputs found
Supporting Data for "Climate Sensitivity and Relative Humidity Changes in Global Storm-Resolving Model Simulations of Climate Change"
No full text<p>Code and netcdf files of processed X-SHiELD and CMIP6 simulations to reproduce the figures of Timothy M. Merlis, Kai-Yuan Cheng, Ilai Guendelman, Lucas Harris, Christopher S. Bretherton, Maximilien Bolot, Linjiong Zhou, Alex Kaltenbaugh, Spencer K. Clark, Gabriel A. Vecchi, and Stephan Fueglistaler (2024): "Climate Sensitivity and Relative Humidity Changes in Global Storm-Resolving Model Simulations of Climate Change".</p>
The General Circulation of the Tropical Atmosphere and Climate Changes
Get PDFI examine the general circulation of the tropical atmosphere and climate changes. First, the response of the zonal surface temperature gradients and zonally asymmetric tropical overturning circulations (Walker circulations) to substantial changes in the longwave optical depth of the atmosphere in an idealized general circulation model (GCM) is compared with scaling theories. Second, the response of the hydrological cycle and monsoonal Hadley circulations to changes in top-of-atmosphere insolation associated with orbital precession is examined in an idealized GCM.
Zonal surface temperature gradients and Walker circulations are examined over a wide range of climates simulated by varying the optical thickness in an idealized atmospheric GCM with a climate-invariant zonally asymmetric ocean energy flux. The tropical zonal surface temperature gradient and Walker circulation generally decrease as the climate warms in the GCM simulations. A scaling relationship based on a two-term balance in the surface energy budget accounts for the changes in the zonally asymmetric component of the GCM-simulated surface temperature gradients. A scaling estimate for the Walker circulation based on differential changes (precipitation rates and saturation specific humidity) in the hydrological cycle accounts for the GCM simulations provided locally averaged quantities are used in the estimate.
The results of atmospheric GCM simulations with varied top-of-atmosphere insolation are analyzed to constrain orbitally-forced changes in the tropical atmospheric circulations and precipitation. When the perihelion is varied between solstices, there is more annual-mean precipitation in the hemisphere in which perihelion occurs during the summer solstice. In aquaplanet simulations, this is primarily associated with thermodynamic changes: there is a correlation between the seasonal cycle of the perturbed water vapor and the seasonal cycle of the Hadley circulation convergence. The monsoonal Hadley circulation does not respond to insolation gradients in a simple manner, as the atmosphere’s energy stratification changes. An idealized continent that has a simple treatment of land surface hydrology and inhomogeneous heat capacity allows an assessment of how land-sea contrasts can mediate the response to orbital precession. In these simulations, the response of precipitation to orbital precession depends on changes in the atmospheric circulation, which strengthens when perihelion occurs in the summer of the hemisphere with the land region. The changes in atmospheric circulation are related to changes in both the top-of-atmosphere energy balance and the thermodynamic properties of the surface.</p
Non‐Uniqueness in ITCZ Latitude Due To Radiation‐Circulation Coupling in an Idealized GCM
No full textAbstract An idealized aquaplanet moist global atmospheric model with realistic radiative transfer but no clouds and no convective parameterization is found to possess multiple climate equilibria. When forced symmetrically about the equator, in some cases the Inter Tropical Convergence Zone (ITCZ) migrates to an off‐equatorial equilibrium position. Mechanism denial experiments prescribing relative humidity imply that radiation‐circulation coupling is essential to this instability. The cross‐equatorial asymmetry occurs only when the underlying slab ocean is sufficiently deep and the atmosphere's spectral dynamical core is sufficiently coarse (∼T170 or less with our control parameters). At higher resolutions, initializing with an asymmetric state indicates metastability with very slow (thousands of days) return to hemispheric symmetry. There is some sensitivity to the model timestep, which affects the time required to transition to the asymmetric state, with little effect on the equilibrium climate. The instability is enhanced when the planetary boundary layer scheme favors deeper layers or by a prescribed meridional heat transport away from the equator within the slab. The instability is not present when the model is run with a convective parameterization scheme commonly utilized in idealized moist models. We argue that the instability occurs when the asymmetric heating associated with a spontaneous ITCZ shift drives a circulation that rises poleward of the perturbed ITCZ. These results serve as a warning of the potential for instability and non‐uniqueness of climate that may complicate studies with idealized models of the tropical response to perturbations in forcing
Simulations of Water Vapor and Clouds on Rapidly Rotating and Tidally Locked Planets: A 3D Model Intercomparison
No full textInternational audienceRobustly modeling the inner edge of the habitable zone is essential for determining the most promising potentially habitable exoplanets for atmospheric characterization. Global climate models (GCMs) have become the standard tool for calculating this boundary, but divergent results have emerged among the various GCMs. In this study, we perform an intercomparison of standard GCMs used in the field on a rapidly rotating planet receiving a G-star spectral energy distribution and on a tidally locked planet receiving an M-star spectral energy distribution. Experiments both with and without clouds are examined. We find relatively small difference (within 8 K) in global-mean surface temperature simulation among the models in the G-star case with clouds. In contrast, the global-mean surface temperature simulation in the M-star case is highly divergent (20–30 K). Moreover, even differences in the simulated surface temperature when clouds are turned off are significant. These differences are caused by differences in cloud simulation and/or radiative transfer, as well as complex interactions between atmospheric dynamics and these two processes. For example we find that an increase in atmospheric absorption of shortwave radiation can lead to higher relative humidity at high altitudes globally and, therefore, a significant decrease in planetary radiation emitted to space. This study emphasizes the importance of basing conclusions about planetary climate on simulations from a variety of GCMs and motivates the eventual comparison of GCM results with terrestrial exoplanet observations to improve their performance
Resolution dependence of tropical poleward energy transport in aquaplanet GCMs
No full text© 2025 The Author(s).
AGS 2246700
NTU-114V1063-1
NA23OAR4320198The tropical atmosphere plays an important role in transporting energy poleward and driving the global circulation. However, understanding and simulating this fundamental aspect of our climate remains difficult due to its sensitivity to convective parameterizations and horizontal resolution. This study focuses on benchmarking the resolution dependence of tropical poleward energy transport in two aquaplanet atmospheric general circulation models with disabled convective parameterizations: a nonhydrostatic high-resolution (100–6 km) finite-volume cubed-sphere model with a full physics package and a lower-resolution (300–100 km) hydrostatic spectral model with idealized moist physics. Despite differences in their physics and numerics, both models demonstrate that column-integrated poleward moist static energy transport by the mean meridional circulation increases with resolution in the deep tropics, while transport by transient eddies decreases. These changes are associated with enhanced gross moist stability that switches from negative to positive due to an increasingly top-heavy mean circulation and reduced eddy activity diffusing water vapor along an unchanging mean moisture gradient. Further analysis rules out extratropical baroclinic eddies and radiation as the main drivers of these changes. Instead, the resolution dependence of both the mean meridional circulation and transient eddies appears to reflect the resolution dependence of tropical explicit (unparameterized) deep convection. We speculate the multiscale interactions of convection allow for a coupling between gross moist stability and eddy moisture flux, leading to their concurrent changes with resolution. We discuss the implications of this resolution dependence for developing theories and models of the tropical atmosphere.National Science Foundation (US)Ministry of Education (Taiwan)European CommissionMinisterio de Ciencia e Investigación (España)Agencia Estatal de Investigación (España)Cooperative Institute for Modeling the Earth System (US)Depto. de Física de la Tierra y AstrofísicaFac. de Ciencias FísicasInstituto de Geociencias (IGEO)TRUEpu
Changes in zonal surface temperature gradients and Walker circulations in a wide range of climates
Get PDFVariations in zonal surface temperature gradients and zonally asymmetric tropical overturning circulations (Walker circulations) are examined over a wide range of climates simulated with an idealized atmospheric general circulation model (GCM). The asymmetry in the tropical climate is generated by an imposed ocean energy flux, which does not vary with climate. The range of climates is simulated by modifying the optical thickness of an idealized longwave absorber (representing greenhouse gases).The zonal surface temperature gradient in low latitudes generally decreases as the climate warms in the idealized GCM simulations. A scaling relationship based on a two-term balance in the surface energy budget accounts for the changes in the zonally asymmetric component of the GCM-simulated surface temperature.The Walker circulation weakens as the climate warms in the idealized simulations, as it does in comprehensive simulations of climate change. The wide range of climates allows a systematic test of energetic arguments that have been proposed to account for these changes in the tropical circulation. The analysis shows that a scaling estimate based on changes in the hydrological cycle (precipitation rate and saturation specific humidity) accounts for the simulated changes in the Walker circulation. However, it must be evaluated locally, with local precipitation rates. If global-mean quantities are used [...
Interacting components of the top-of-atmosphere energy balance affect changes in regional surface temperature
No full textThe role of interactions between components of the top-of-atmosphere (TOA) energy balance in determining regional surface temperature changes, such as polar amplification, is examined in diffusive energy balance model (EBM) simulations. These interactions have implications for the interpretation of local feedback analyses when they are applied to regional surface temperature changes. Local feedback analysis succeeds at accounting for the EBM-simulated temperature change given the changes in the radiative forcing, atmospheric energy transport, and radiative feedbacks. However, the inferences about the effect of individual components of the TOA energy balance on regional temperature changes do not account for EBM simulations in which individual components are prescribed or “locked.” As changes in one component of the TOA energy balance affect others, unambiguous attribution statements relating changes in regional temperature or its intermodel spread to individual terms in the TOA energy balance cannot be made
Interacting components of the top‐of‐atmosphere energy balance affect changes in regional surface temperature
No full textA model intercomparison of the tropical precipitation response to a CO2 doubling in aquaplanet simulations
Get PDFIn the present-day climate, the mean Intertropical Convergence Zone (ITCZ) is north of the equator. We investigate changes in the ITCZ latitude under global warming, using multiple atmospheric models coupled to an aquaplanet slab ocean. The reference climate, with a warmer north from prescribed ocean heating, is perturbed by doubling CO2. Most models exhibit a northward ITCZ shift, but the shift cannot be accounted for by the response of energy flux equator where the atmospheric energy transport (F-A) vanishes. The energetics of the simulated circulation shifts are subtle: changes in the efficiency with which the Hadley circulation transports energy, the total gross moist stability (m), dominate over mass flux changes in determining F-A. Even when F-A approximate to 0, the ITCZ can shift significantly due to changes in m, which have often been neglected previously. The dependence of ITCZ responses on m calls for improved understanding of the physics determining the tropical Delta m.clos
- …
