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Results for “radiative-convective equilibrium”

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NASA NTRS1979

Atmospheric lapse rate regimes and their parameterization

Lapse rates, moist adiabatic lapse rates and the critical lapse rate for baroclinic adjustment are calculated and compared for the mean annual, January and July states in the Northern Hemisphere. The small seasonal changes in hemispheric mean lapse rates can be attributed to counteracting seasonal changes in the strength of moist convection and baroclinic eddies. A major conclusion is that the vertical temperature structure may be well approximated by a radiative-convective equilibrium model with two critical lapse rates, viz. the moist adiabatic lapse rate and the critical lapse rate for baroclinic adjustment.

Stone, P. H.↗

NASA NTRS1980

Greenhouse models of Venus' high surface temperature, as constrained by Pioneer Venus measurements

Recent measurements conducted from the Pioneer Venus probes and orbiter have provided a significantly improved definition of the solar net flux profile, the gaseous composition, temperature structure, and cloud properties of Venus' lower atmosphere. Using these data, we have carried out a series of one-dimensional radiative-convective equilibrium calculations to determine the viability of the greenhouse model of Venus' high surface temperature and to assess the chief contributors to the greenhouse effect. New sources of infrared opacity include the permitted transitions of SO2, CO, and HCl as well as opacity due to several pressure-induced transitions of CO2. We find that the observed surface temperature and lapse rate structure of the lower atmosphere can be reproduced quite closely with a greenhouse model that contains the water vapor abundance reported by the Venera spectrophotometer experiment. Thus the greenhouse effect can account for essentially all of Venus' high surface temperature. The prime sources of infrared opacity are, in order of importance, CO2, H2O, cloud particles, and SO2, with CO and HCl playing very minor roles.

Pollack, J. B.↗

NASA NTRS1985

Cloud optical thickness feedbacks in the CO2 climate problem

A radiative-convective equilibrium model is developed and applied to study cloud optical thickness feedbacks in the CO2 climate problem. The basic hypothesis is that in the warmer and moister CO2-rich atmosphere, cloud liquid water content will generally be larger than at present, so that cloud optical thickness will be larger too. For clouds other than thin cirrus, the result is to increase the albedo more than to increase the greenhouse effect. Thus the sign of the feedback is negative: cloud optical properties alter in such a way as to reduce the surface and tropospheric warming caused by the addition of CO2. This negative feedback can be substantial. When observational estimates of the temperature dependence of cloud liquid water content are employed in the model, the surface temperature change due to doubling CO2 is reduced by about one half.

Somerville, R. C. J.↗

NASA NTRS1990

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

Results from a one-dimensional radiative-convective equilibrium model (similar to that of Lacis et al., 1981) of surface-temperature changes induced by changes in the vertical distribution of O3 in the atmosphere are parameterized and applied to measurement data for the northern midlatitudes during the 1970s. The construction of the model is outlined, and the results are presented in tables and graphs and discussed in detail. It is found that decreases in O3 in the lower stratosphere in the 1970s caused atmospheric cooling greater than that due to CO2 (thus possibly obscuring the CO2 greenhouse effect) and surface cooling which outweighed the warming effect of increased O3 in the troposphere. The net surface cooling is shown to be equal to about half of the estimated CO2 warming effect for the period.

Lacis, Andrew A.↗

NASA NTRS1990

Global changes in the 0-70 km thermal structure of the Mars atmosphere derived from 1975 to 1989 microwave CO spectra

J = 1 - 2 (C-12)O (230 GHz) and (C-13)O (220 GHz) spectra of Mars obtained during the particularly favorable opposition of Mars in 1988 are analyzed. A CO mixing ratio is derived for November 1988 which agrees with a determination from 1967 observations. It is demonstrated that if the mixing ratio of CO was not drastically different in early 1980 and early 1982, the low- to midlatitude average thermal structure of the Mars atmosphere at these times was consistent with clear-air radiative-convective equilibrium conditions. Mars atmospheric temperature profiles derived from (C-12)O spectra are also presented.

Clancy, R. Todd↗

NASA NTRS1991

Uranus atmospheric dynamics and circulation

The observations, models, and theories relevant to the atmospheric dynamics and meteorology of Uranus are discussed. The available models for the large-scale heat transport and atmospheric dynamics as well as diagnostic interpretations of the Voyager data are reviewed. Some pertinent ideas and questions regarding the global circulation balance are considered, partly in comparison with other planetary atmospheres. The available data indicate atmospheric rotation at midlatitudes nearly 200 m/s faster than that of the planetary magnetic field. Analysis of the dynamical deformation of the shape and size of isobaric surfaces measured by the Voyager radio-occultation experiment suggests a subrotating equator at comparable altitudes. Infrared temperature retrievals above the cloud deck indicate a smaller equator-to-pole contrast than expected for purely radiative-convective equilibrium, but show local variations implying a latitudinally correlated decrease with altitude in the cloud-tracked wind.

Allison, Michael↗

NASA NTRS1992

Integration of satellite and surface data using a radiative-convective oceanic boundary-layer model

A mixing-line boundary-layer model is used to retrieve cloud-top height from satellite-derived cloud-top temperatures, using 700-hPa National Meteorological Center (NMC) analyses and the Comprehensive Ocean and Atmosphere Data Set (COADS) surface data as supporting datasets. Results are compared with the fixed-lapse-rate method of retrieving boundary-layer depth from sea surface temperatures (SST) and cloud-top temperatures. A radiative-convective equilibrium boundary-layer model is used to retrieve boundary-layer structure given SST and surface wind, satellite cloud-top temperatures and cloud fraction, and the 700-hPa NMC thermodynamic analyses. Good agreement is found between the COADS data and the model solutions for low-level temperature and moisture. This suggests that equilibrium boundary-layer models may be of use over remote oceans in the retrieval of boundary-layer structure.

Betts, Alan K.↗

NASA NTRS1994

Radiative-convective model with an explicit hydrologic cycle. 2: Sensitivity to large changes in solar forcing

The one-dimensional radiative-convective equilibrium model with an explicit hydrologic cycle introduced in part 1 is used to study the sensitivity of the model's atmosphere to large changes in the solar forcing, when various cumulus convection parameterizations are used. When the concentration of the absorbing as in the atmosphere is temperature dependent, equilibrium is impossible for values of the solar forcing larger than a critical value. This result is referred to as a runaway greenhouse. The cumulus convection parameterization schemes currently in use in global climate models (GCMs) employ different assumptions about moistening. This causes the critical solar forcing above which a runaway greenhouse occurs to be very sensitive to the cumulus convection scheme employed. Furthermore, we show that the sensitivity of the equilibrium temperature to changes in the solar forcing depends crucially on the microphysics of cumulus convection. For fixed cloud conditions, the critical forcing for a runaway greenhouse to occur is between approximately 1.22 and 1.49 times the global mean value for the Earth, and for clear sky conditions, it is a few percent lower. The runaway greenhouse in the experiments with the mass flux schemes generally occurs more rapidly than in the experiments with the adjustment schemes. In addition, the inability of the hard convective adjustment scheme to produce an efficient vertical transport of moisture, together with the saturation requirement for convection to occur, leads to the breakdown of the radiative-convective equilibria when other processes are not available to provide the necessary vertical transport of water vapor.

Renno, Nilton O.↗

NASA NTRS1998

Multiple Equilibria Associated with Response of the ITCZ to Seasonal SST Forcing

Supported by numerical experiment results, the abrupt change of the location of the intertropical convergence zone (ITCZ), from the equatorial trough flow regime to the monsoon trough flow regime is interpreted as a subcritical instability. The existence of these multiple quasi-equilibria is due to the balance of two "forces" on the ITCZ: one toward the equator, due to the earth's rotation, has a nonlinear latitudinal dependence; and the other toward the latitude of the sea surface (or ground) temperature peak has a relatively linear latitudinal dependence. This work pivots on the finding that the ITCZ and Hadley circulation can still exist without the pole-to-equator gradient of radiative-convective equilibrium temperature.

Chao, Winston C.↗

NASA NTRS2017

Sonora: A New Generation Model Atmosphere Grid for Brown Dwarfs and Young Extrasolar Giant Planets

Brown dwarf and giant planet atmospheric structure and composition has been studied both by forward models and, increasingly so, by retrieval methods. While indisputably informative, retrieval methods are of greatest value when judged in the context of grid model predictions. Meanwhile retrieval models can test the assumptions inherent in the forward modeling procedure. In order to provide a new, systematic survey of brown dwarf atmospheric structure, emergent spectra, and evolution, we have constructed a new grid of brown dwarf model atmospheres. We ultimately aim for our grid to span substantial ranges of atmospheric metallilcity, C/O ratios, cloud properties, atmospheric mixing, and other parameters. Spectra predicted by our modeling grid can be compared to both observations and retrieval results to aid in the interpretation and planning of future telescopic observations. We thus present Sonora, a new generation of substellar atmosphere models, appropriate for application to studies of L, T, and Y-type brown dwarfs and young extrasolar giant planets. The models describe the expected temperature-pressure profile and emergent spectra of an atmosphere in radiative-convective equilibrium for ranges of effective temperatures and gravities encompassing 200 less than or equal to T(sub eff) less than or equal to 2400 K and 2.5 less than or equal to log g less than or equal to 5.5. In our poster we briefly describe our modeling methodology, enumerate various updates since our group's previous models, and present our initial tranche of models for cloudless, solar metallicity, and solar carbon-to-oxygen ratio, chemical equilibrium atmospheres. These models will be available online and will be updated as opacities and cloud modeling methods continue to improve.

emergent spectra↗

NASA NTRS2016

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.

planets and satellites↗

DOE OSTI2022

A Vertically Resolved MSE Framework Highlights the Role of the Boundary Layer in Convective Self-Aggregation

Abstract Convective self-aggregation refers to a phenomenon in which random convection can self-organize into large-scale clusters over an ocean surface with uniform temperature in cloud-resolving models. Previous literature studies convective aggregation primarily by analyzing vertically integrated (VI) moist static energy (MSE) variance. That is the global MSE variance, including both the local MSE variance at a given altitude and the covariance of MSE anomalies between different altitudes. Here we present a vertically resolved (VR) MSE framework that focuses on the local MSE variance to study convective self-aggregation. Using a cloud-resolving simulation, we show that the development of self-aggregation is associated with an increase of local MSE variance, and that the diabatic and adiabatic generation of the MSE variance is mainly dominated by the boundary layer (BL; the lowest 2 km). The results agree with recent numerical simulation results and the available potential energy analyses showing that the BL plays a key role in the development of self-aggregation. Additionally, we find that the lower free troposphere (2–4 km) also generates significant MSE variance in the first 15 days. We further present a detailed comparison between the global and local MSE variance frameworks in their mathematical formulation and diagnostic results, highlighting their differences.

54 ENVIRONMENTAL SCIENCES↗

NASA NTRS2007

Cloud Resolving Modeling

One of the most promising methods to test the representation of cloud processes used in climate models is to use observations together with cloud-resolving models (CRMs). CRMs use more sophisticated and realistic representations of cloud microphysical processes, and they can reasonably well resolve the time evolution, structure, and life cycles of clouds and cloud systems (with sizes ranging from about 2-200 km). CRMs also allow for explicit interaction between clouds, outgoing longwave (cooling) and incoming solar (heating) radiation, and ocean and land surface processes. Observations are required to initialize CRMs and to validate their results. This paper provides a brief discussion and review of the main characteristics of CRMs as well as some of their major applications. These include the use of CRMs to improve our understanding of: (1) convective organization, (2) cloud temperature and water vapor budgets, and convective momentum transport, (3) diurnal variation of precipitation processes, (4) radiative-convective quasi-equilibrium states, (5) cloud-chemistry interaction, (6) aerosol-precipitation interaction, and (7) improving moist processes in large-scale models. In addition, current and future developments and applications of CRMs will be presented.

Tao, Wei-Kuo↗

NASA NTRS1992

Tropical boundary layer equilibrium in the last ice age

A radiative-convective boundary layer model is used to assess the effect of changing sea surface temperature, pressure, wind speed, and the energy export from the tropics on the boundary layer equilibrium equivalent potential temperature. It remains difficult to reconcile the observations that during the last glacial maximum (18,000 yr BP) the snowline on the tropical mountains fell 950 m, while the tropical sea surface temperatures fell only 1-2 K.

Betts, Alan K.↗

NASA NTRS1980

Effect of ice-albedo feedback on global sensitivity in a one-dimensional radiative-convective climate model

The feedback between the ice albedo and temperature is included in a one-dimensional radiative-convective climate model. The effect of this feedback on global sensitivity to changes in solar constant is studied for the current climate conditions. This ice-albedo feedback amplifies global sensitivity by 26 and 39%, respectively, for assumptions of fixed cloud altitude and fixed cloud temperature. The global sensitivity is not affected significantly if the latitudinal variations of mean solar zenith angle and cloud cover are included in the global model. The differences in global sensitivity between one-dimensional radiative-convective models and energy balance models are examined. It is shown that the models are in close agreement when the same feedback mechanisms are included. The one-dimensional radiative-convective model with ice-albedo feedback included is used to compute the equilibrium ice line as a function of solar constant.

Wang, W.-C.↗

NASA NTRS1994

Venus climate stability and volcanic resurfacing rates

The climate of Venus is to a large degree controlled by the radiative properties of its massive atmosphere. In addition, outgassing due to volcanic activity, exospheric escape processes, and surface/atmosphere interactions may all be important in moderating the abundances of atmospheric CO2 and other volatiles. We have developed an evolutionary climate model for Venus using a systems approach that emphasizes feedbacks between elements in the climate system. Modules for atmospheric radiative transfer, surface/atmosphere interactions, tropospheric chemistry, and exospheric escape processes have so far been developed. Climate feedback loops result from interconnections between modules, in the form of the environmental parameters pressure, temperature, and atmospheric mixing ratios. The radiative transfer module has been implemented by using Rosseland mean opacities in a one dimensional grey radiative-convective model. The model has been solved for the static (time independent) case to determine climate equilibrium points. The dynamics of the model have also been explored by employing reaction/diffusion kinetics for possible surface atmosphere heterogeneous reactions over geologic timescales. It was found that under current conditions, the model predicts that the climate of Venus is at or near an unstable equilibrium point. The effects of constant rate volcanism and corresponding exsolution of volatiles on the stability of the climate model were also explored.

Bullock, M. A.↗

NASA NTRS1989

Climatic equilibrium of the atmospheric convective boundary layer over a tropical ocean

A radiative-convective boundary layer model was developed by coupling a thermodynamic model of a partially mixed convective boundary layer (CBL) with a radiation model, and energy balance constraints were used to study coupled boundary layer (CBL) equilibrium over three timescales (about 1 day, about 10 days, and more than 100 days). It is shown that the variation in cloud top decreases with greater coupling to the atmosphere and the ocean. The slope of the latent heat flux with increasing SST decreases with more tropospheric coupling, and reverses sign with a coupled ocean.

Ridgway, W.↗

NASA NTRS2000

Significant Features Found in Simulated Tropical Climates Using a Cloud Resolving Model

Cloud resolving model (CRM) has widely been used in recent years for simulations involving studies of radiative-convective systems and their role in determining the tropical regional climate. The growing popularity of CRMs usage can be credited for their inclusion of crucial and realistic features such like explicit cloud-scale dynamics, sophisticated microphysical processes, and explicit radiative-convective interaction. For example, by using a two-dimensional cloud model with radiative-convective interaction process, found a QBO-like (quasibiennial oscillation) oscillation of mean zonal wind that affected the convective system. Accordingly, the model-generated rain band corresponding to convective activity propagated in the direction of the low-level zonal mean winds; however, the precipitation became "localized" (limited within a small portion of the domain) as zonal mean winds were removed. Two other CRM simulations by S94 and Grabowski et al. (1996, hereafter G96), respectively that produced distinctive quasi-equilibrium ("climate") states on both tropical water and energy, i.e., a cold/dry state in S94 and a warm/wet state in G96, have later been investigated by T99. They found that the pattern of the imposed large-scale horizontal wind and the magnitude of the imposed surface fluxes were the two crucial mechanisms in determining the tropical climate states. The warm/wet climate was found associated with prescribed strong surface winds, or with maintained strong vertical wind shears that well-organized convective systems prevailed. On the other hand, the cold/dry climate was produced due to imposed weak surface winds and weak wind shears throughout a vertically mixing process by convection. In this study, considered as a sequel of T99, the model simulations to be presented are generally similar to those of T99 (where a detailed model setup can be found), except for a more detailed discussion along with few more simulated experiments. There are twelve major experiments chosen for presentations that are introduced in section two. Several significant feature analyses regarding the rainfall properties, CAPE (Convective Available Potential Energy), cloud-scale eddies, the stability issue, the convective system propagation, relative humidity, and the effect on the quasi-equilibrium state by the imposed constant. radiation or constant surface fluxes, and etc. will be presented in the meeting. However, only three of the subjects are discussed in section three. A brief summary is concluded in the end section.

Shie, C.-L.↗