One-dimensional Radiative-convective Equilibrium Model Research Articles

The effects of consistent chemical kinetics calculations on the pressure-temperature profiles and emission spectra of hot Jupiters

In this work we investigate the impact of calculating non-equilibrium chemical abundances consistently with the temperature structure for the atmospheres of highly-irradiated, close-in gas giant exoplanets. Chemical kinetics models have been widely used in the literature to investigate the chemical compositions of hot Jupiter atmospheres which are expected to be driven away from chemical equilibrium via processes such as vertical mixing and photochemistry. All of these models have so far used pressure--temperature (P-T) profiles as fixed model input. This results in a decoupling of the chemistry from the radiative and thermal properties of the atmosphere, despite the fact that in nature they are intricately linked. We use a one-dimensional radiative-convective equilibrium model, ATMO, which includes a sophisticated chemistry scheme to calculate P-T profiles which are fully consistent with non-equilibrium chemical abundances, including vertical mixing and photochemistry. Our primary conclusion is that, in cases of strong chemical disequilibrium, consistent calculations can lead to differences in the P-T profile of up to 100 K compared to the P-T profile derived assuming chemical equilibrium. This temperature change can, in turn, have important consequences for the chemical abundances themselves as well as for the simulated emission spectra. In particular, we find that performing the chemical kinetics calculation consistently can reduce the overall impact of non-equilibrium chemistry on the observable emission spectrum of hot Jupiters. Simulated observations derived from non-consistent models could thus yield the wrong interpretation. We show that this behaviour is due to the non-consistent models violating the energy budget balance of the atmosphere.

Initiation of a Runaway Greenhouse in a Cloudy Column

Abstract A one-dimensional radiative–convective equilibrium model is used to investigate the influence of clouds on the onset of a runaway greenhouse under strong solar forcing. By comparing experiments with clear-sky conditions (clouds are transparent to radiation) to experiments with full-sky conditions (clouds are radiatively active), the authors find that the critical solar irradiance that is necessary to trigger a runaway greenhouse is increased from around 1.15–1.20 times the present-day total solar irradiance (TSI) on Earth S0 for clear-sky conditions to around 1.40–1.45S0 for full-sky conditions. Cloud thickness increases with TSI, leading to a substantially higher albedo, which in turn allows the climate to remain in equilibrium for markedly higher values of TSI. The results suggest that steady states with sea surface temperatures higher than 335 K exist for a large range of TSI. The thickening clouds in these states do not reduce the outgoing longwave radiation any more, implying that the thickening of clouds increases only their shortwave effect. This mechanism allows the column to remain in balance even at high sea surface temperatures. The authors find double equilibria for both clear-sky and full-sky conditions, but the range for which they occur extends to considerably higher values of TSIs for full-sky conditions. Moreover, when clouds are included in the radiative transfer calculations, climate instabilities are no longer caused by longwave effects but by the cloud albedo effect.

Robust increase in equilibrium climate sensitivity under global warming

[1] Equilibrium climate sensitivity (ECS) is a widely accepted measure of Earth's susceptibility to radiative forcing. While ECS is often assumed to be constant to a first order of approximation, recent studies suggested that ECS might depend on the climate state. Here it is shown that the latest generation of climate models consistently exhibits an increasing ECS in warmer climates due to a strengthening of the water-vapor feedback with increasing surface temperatures. The increasing ECS is replicated by a one-dimensional radiative-convective equilibrium model, which further shows that the enhanced water-vapor feedback follows from the rising of the tropopause in a warming climate. This mechanism is potentially important for understanding both warm climates of Earth's past and projections of future high-emission scenarios.

Radiative Constraints on the Hydrological Cycle in an Idealized Radiative–Convective Equilibrium Model

AbstractThe radiative constraints on the partitioning of the surface energy budget and, hence, on the strength of the hydrological cycle are analyzed in an idealized one-dimensional radiative–convective equilibrium model formulated in terms of the energy budgets at the top of the atmosphere, the subcloud layer, and the free atmosphere, which enables it to predict both surface relative humidity and the air–sea temperature difference. Using semigray radiative transfer, a semianalytical solution was obtained that explicitly shows how the surface latent heat flux (LHF) is related to the radiative properties of the atmosphere. This solution was also used in conjunction with a full radiative transfer code and was found to provide reasonably realistic quantitative estimates.In the model the LHF is fundamentally constrained by the net longwave flux divergence above the level of condensation by lifting (LCL) and by the atmospheric absorption of shortwave radiation, with only a weak indirect control by near-surface moisture. The latter implies that the Clausius–Clapeyron relation does not directly constrain the strength of the hydrological cycle. Under radiative perturbations, the changes in LHF are determined by the changes in the net longwave fluxes at the LCL, associated mainly with the changes in the longwave transmissivity, and by the changes in shortwave absorption by the atmosphere (e.g., by increased water vapor).Using a full radiative transfer model with interactive water vapor feedback with the semianalytical solution indicates a rate of change in LHF with greenhouse forcing of around 2 W m−2 K−1 of surface warming, which corresponds to the Planck feedback (∼3.2 W m−2 K−1) multiplied by a coefficient of order one that, to first approximation, depends only on the relative magnitudes of the net longwave radiation fluxes at the LCL and the top of the atmosphere (i.e., on the shape of the vertical profile of the net longwave flux).

A Numerical Study on Appearance of the Runaway Greenhouse State of a Three-Dimensional Gray Atmosphere

Abstract A numerical study on the runaway greenhouse state is performed by using a general circulation model (GCM) with simplified hydrologic and radiative processes. Except for the inclusion of three-dimensional atmospheric motion, the system utilized is basically equivalent to the one-dimensional radiative–convective equilibrium model of Nakajima et al. in which the runaway greenhouse state is defined. The results of integrations with various values of solar constant show that there exists an upper limit of the solar constant with which the atmosphere can reach a statistical equilibrium state. When the value of solar constant exceeds the limit, 1600 W m−2, the atmosphere sets in a “thermally runaway” state. It is characterized by continuous increase of the amount of water vapor, continuous decrease of the outgoing longwave radiation, and continuous warming of the atmosphere and the ground surface. The upper-limit value of the solar constant obtained by the GCM experiments corresponds to the upper limit ...

水の物理過程が大気大循環に及ぽす影響について

In Part 1 (Miyoshi and Morita, 1993), we investigated how the general circulation of the atmosphere was affected by all the physical processes of H 2 O. In this study, we divide all the physical processes of H 2 O into the radiative process of H 2 O and the hydrological cycle, and investigate the effect of both of the processes separately by a series of GCM experiments. Results are as follows. The north-to-south temperature gradient and the zonal wind distribution below 5 km height is strongly affected by the radiative process of H 2 O. The strength of the meridional circulation, the magnitude of the poleward energy transport, the magnitude of the sensible and latent heat fluxes and the magnitude of the diabatic heating rate in the atmosphere also depend on the radiative process of H 2 O. Thus, the differences of the general circulation between with and without all the physical processes of H 2 O is mostly caused by the radiative process of H 2 O. The zonal wind distributions above 5 km height, on the other hand, are affected by not only the radiative process of H 2 O but also by the hydrological cycle. Numerical experiments using a vertically one-dimensional radiative-convective equilibrium model are performed. By comparing the radiative-convective equilibrium temperature with the temperature in the GCM, the relation between the poleward heat transport by the dynamics and the physical processes of H 2 O is also examined. In the experiments without the radiative process of H 2 O, the temperature near the surface in the GCM is almost the same as the radiative-convective temperature. At low latitudes, the temperature difference between the GCM and the radiative-convective model is larger in the experiments with the radiative process of H 2 O than in the experiments without the radiative process of H 2 O.

A Study on the “Runaway Greenhouse Effect” with a One-Dimensional Radiative–Convective Equilibrium Model

Abstract A simple one-dimensional radiative–convective equilibrium model is used to investigate the relationship between the surface temperature and the outgoing infrared radiation at the top of the atmosphere. The model atmosphere has a gray infrared absorption coefficient and is composed of a radiative equilibrium stratosphere and a moist adiabat troposphere. An upper limit of the outgoing infrared radiation is found to exist. The existence of the upper limit is characterized by the radiation limits that appear when the optical depth of the entire atmosphere becomes sufficiently deep and the temperature structure around the levels where the optical depth is about unity approaches a fixed profile. This appearance of an upper limit differs from that found by Komabayashi and Ingersoll, which is obtained from the constraint of the stratospheric radiation balance. As one of those radiation limits, the outgoing infrared radiation has an asymptotic limit as the surface temperature increases. This is caused by ...

Radiative forcing of climate by changes in the vertical distribution of ozone

We describe a simple method for evaluating the radiative forcing of surface temperature caused by changes in the vertical distribution of ozone. The method employs a parameterization based on one‐dimensional radiative‐convective equilibrium calculations; these calculations predict that the surface temperature should warm in response to both decreases in ozone above 30 km and increases in ozone below 30 km. The parameterization is used to investigate the response of surface temperature to observed changes in the vertical distribution of ozone at northern mid‐latitudes. We show that the observed ozone trends, taken at face value, suggest a cooling of the surface temperature at northern mid‐latitudes during the 1970s equal in magnitude to about half the warming predicted for CO2 for the same time period. However, the measurement uncertainty of the observed trends is large, with the best estimates for mid‐latitude cooling being −0.05±0.05°C. The surface cooling is caused by ozone decreases in the lower stratosphere, which outweigh the warming effects of ozone increases in the troposphere. The results obtained differ from predictions based on one‐dimensional photochemical model simulations of ozone trends for the 1970s, which suggest a warming of the surface temperature equal to ∼20% of the warming contributed by CO2. Also, the ozone decreases observed in the lower stratosphere during the 1970s produce atmospheric cooling by several tenths of a degree in the 12‐ to 20‐km altitude region over the northern mid‐latitudes. This temperature decrease is larger than the cooling due to CO2 and thus may obscure the expected stratospheric CO2 greenhouse signature.

Cloud Decoupling of the Surface and Planetary Radiative Budgets

Abstract We employ a one-dimensional radiative-convective equilibrium model with multiple cloud layers to demonstrate that the surface equilibrium temperature is highly sensitive to the vertical distribution of effective cloud base heights. It is also demonstrated that the reflected solar flux from an ensemble of cloud layers is independent of the vertical distribution of these cloud layers and is a function only of the total water path integrated in the vertical, a property which also determines the solar radiation reaching the surface. The downward longwave radiation, on the other hand, depends strongly on the effective cloud base height as well as the background water vapor distribution. It is argued that the longwave radiative transfer processes of cloud tend to decouple the radiative budgets at the top of the atmosphere and the surface. Thus, for a given total atmospheric optical thickness, it is possible to obtain different values of surface temperature under conditions of radiative equilibrium at t...