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Model calculations using estimated reaction rates of sulfur hexafluoride (SF6) with OH and 0('D) indicate that the atmospheric lifetime due to these processes may be very long (25,000 years). An upper limit for the UV cross section would suggest a photolysis lifetime much longer than 1000 years. The possibility of other removal mechanisms are discussed. The estimated lifetimes are consistent with other estimated values based on recent laboratory measurements. There appears to be no known natural source of SF6. An estimate of the current production rate of SF6 is about 5 kt/yr. Based on historical emission rates, we calculated a present-day atmospheric concentrations for SF6 of about 2.5 parts per trillion by volume (pptv) and compared the results with available atmospheric measurements. It is difficult to estimate the atmospheric lifetime of SF6 based on mass balance of the emission rate and observed abundance. There are large uncertainties concerning what portion of the SF6 is released to the atmosphere. Even if the emission rate were precisely known, it would be difficult to distinguish among lifetimes longer than 100 years since the current abundance of SF6 is due to emission in the past three decades. More information on the measured trends over the past decade and observed vertical and latitudinal distributions of SF6 in the lower stratosphere will help to narrow the uncertainty in the lifetime. Based on laboratory-measured IR absorption cross section for SF6, we showed that SF6 is about 3 times more effective as a greenhouse gas compared to CFC 11 on a per molecule basis. However, its effect on atmospheric warming will be minimal because of its very small concentration. We estimated the future concentration of SF6 at 2010 to be 8 and 10 pptv based on two projected emission scenarios. The corresponding equilibrium warming of 0.0035 C and 0.0043 C is to be compared with the estimated warming due to CO2 increase of about 0.8 C in the same period.

This paper documents the incorporation of the radiative effect of trace gases CH4, N2O, CF2Cl2, and CFCl3 into the National Center for Atmospheric Research community climate model (CCMl) longwave scheme, which presently includes the radiative effect of H2O, CO2, and O3. This development is intended for using the CCMl to study the combined greenhouse effect of increasing atmospheric CO2, CH4, CF2Cl2, CFCl3, and N2O. The radiative effect of the trace gases in a homogeneous layer is parameterized based on Wang and Shi's (1988) analytical expression for the total band absorptance. For an inhomogeneous path, a scaling approximation is used to calculate the effective total band model parameters. The same treatment of the overlapping gaseous absorption bands used in the present CCMl scheme is adopted for the new trace gases.

The potential complexity of the feedback between global mean cloud amount and global mean surface temperature when variations of the vertical cloud distribution are included is illustrated. This is done by studying the behavior of a one-dimensional radiative-convective model with two types of cloud variation: (1) variable cloud cover with constant optical thickness and (2) variable optical thickness with constant cloud cover. The variable parameter is calculated on the assumption that a correlation exists between cloud amount and precipitation or the vertical flux convergence of latent heat. Since the vertical latent heat flux is taken to be a fraction of the total heat flux, modeled by convective adjustment, the sensitivity of the results to two different critical lapse rates is examined. These are a constant 6.5 K/km lapse rate and a temperature-dependent, moist adiabatic lapse rate. The effects of the vertical structure of climate perturbations on the nature of the cloud feedback are also examined. The model results reveal that changes in the vertical cloud distribution and mean cloud optical thickness can be as important to climate variations as are changes in the total cloud cover.

It is shown quantitatively how radiative climatic forcing by aerosols depends on the physical properties of the aerosols. The special case of atmospheric aerosols produced by volcanic explosions is considered, and evidence is presented which indicates that even the simple climate models available today may be able to capture some of the basic effects of aerosols on global climate. Possible effects of anthropogenic aerosols are briefly examined. It is noted that additional evidence for the significant influence of aerosols on climate may be found in data obtained from recent spacecraft missions to Venus and Mars.

The United States Department of Energy and the People's Republic of China (PRC) Chinese Academy of Sciences signed an agreement on 19 August 1987 to carry out a joint research program on the study of CO2-induced climate changes. The joint program has four tasks—analysis of general circulation models (GCMs), preparation and analysis of proxy and instrumental data, the study of the relationship between large- and regional-scale climates, and CH4 measurements. The program structure, technical tasks, and the initial research progress are described.

A parameterization for the absorption of solar radiation as a function of the amount of water vapor in the earth's atmosphere is obtained. Absorption computations are based on the Goody band model and the near-infrared absorption band data of Ludwig et al. A two-parameter Curtis-Godson approximation is used to treat the inhomogeneous atmosphere. Heating rates based on a frequently used one-parameter pressure-scaling approximation are also discussed and compared with the present parameterization.

The Mount Agung volcanic eruption in 1963 provides the best-documented global radiative perturbation to the earth's atmosphere currently available. Data on stratospheric aerosols produced by this eruption have been used as input to a model for the atmospheric thermal structure. The computed magnitude, sign, and phase lag of the temperature changes in both the stratosphere and the troposphere are in good agreement with observations, providing evidence that the climatic response to a global radiative perturbation is significant, as well as support for the use of theoretical models to predict climatic effects.

Nitrous oxide, methane, ammonia, and a number of other trace constituents in the earth's atmosphere have infrared absorption bands in the spectral region 7 to 14 µm and contribute to the atmospheric greenhouse effect. The concentrations of these trace gases may undergo substantial changes because of man's activities. Extensive use of chemical fertilizers and combustion of fossil fuels may perturb the nitrogen cycle, leading to increases in atmospheric N_2O, and the same perturbing processes may increase the amounts of atmospheric CH_4 and NH_3. We use a one-dimensional radiative-convective model for the atmospheric thermal structure to compute the change in the surface temperature of the earth for large assumed increases in the trace gas concentrations; doubling the N_2O, CH_4, and NH_3 concentrations is found to cause additive increases in the surface temperature of 0.7°, 0.3°, and 0.1°K, respectively. These systematic effects on the earth's radiation budget would have substantial climatic significance. It is therefore important that the abundances of these trace gases be accurately monitored to determine the actual trends of their concentrations.

An interactive two-dimensional model of the stratosphere, consisting of a primitive equation dynamics module, a simplified HO(x) ozone model, and a full radiative transfer scheme, is used to study the effect of eddy diffusion in the model. Consideration is given to the effects of nonlocal forcing from dissipation in the model troposphere and frictional drag at mesospheric levels, mechanical damping in the stratosphere itself, and potential vorticity flux due to large scale waves. It is found that the ozone distributions generated with the model are very sensitive to the choice of values for the friction and the eddy diffusion coefficients. It is shown that reasonable latitudinal gradients of ozone may be obtained by using small values for the mechanical damping for the mid- and high-latitude stratopsphere.

A modified two-flux approximation is employed to compute the transfer of radiation in a finite, inhomogeneous, turbid atmosphere. A perturbation technique is developed to allow the treatment of nongray gaseous absorption with multiple scattering. The perturbation method, which employs a backscatter factor as a parameter, can be used with anisotropic particle scattering as well as Rayleigh scattering. This method is used to study the effect of aerosols on radiative solar heating and infrared cooling as well as the radiative-convective temperature distribution in the earth's atmosphere. It is found that the effect of aerosols in the infrared cannot be neglected; while in the visible, the effect can be of the same order as that due to absorption by water vapor. For a high surface albedo (greater than 0.30) heating of the earth-atmosphere system results due to the presence of aerosols. The aerosols also reduce the amount of convection needed to maintain a stable atmosphere. For the case of a dense haze a temperature inversion is found to exist close to the ground.

Analytical expressions for the total band absorptance and absorption-coefficient distribution function for radiatively-important, atmospheric gases are derived from the Malkmus narrow-band model and the wide-band approximation of Edwards and Menard. For individual absorption bands, the expressions are functions of the band width, the mean line-half-width to spacing ratio and two parameters describing the spectral variation of the mean line intensity. Procedures to calculate these absorption band parameters directly from the AFGL absorption line data are presented. The accuracy of the formulation is demonstrated by good agreement in the 15-μm CO 2 band, the H 2 O rotational band and the 9.6-μm O 3 band for the absorptances calculated from analytical expressions, line-by-line calculations and available measurements. This formulation thus provides a useful approach to calculate the coupled radiative processes of absorption and multiple scattering due to atmospheric gases and particles.

The 510-year, 120-stalion proxy precipitation records published by the State Meteorological Administration of the People's Republic of China were used to study the large-scale climate patterns, including the climate regions and interregional relationships. In this paper, we present a study of the sensitivity of the climate patterns of recent years (1950–1979) to choice of stations and statistical techniques. First, the original highly inhomogeneous 120-station network is reduced to a quasi-uniform network comprising 93 stations. Next, based on the reduced network, two new networks arc derived-a47-station network with the same spatial domain and a 29-station network with half the domain. The climate patterns for these station networks are compared by use of two different statistical procedures, principal component analysis/cluster analysis and factor analysis with orthogonal and oblique rotations. It is found that the climate patterns remain similar when the density and domain of the 120-station network are systematically reduced. It is also found that similar climate patterns are obtained using either of the chosen statistical techniques, although factor analysis appears to be more sensitive to changes in the network than principal component/cluster analysis. Examination of measurement data also reveals large-scale climate patterns similar to those derived from the proxy data. Finally, the climate patterns are shown to be consistent with geophysical factors.

The 1982 balloon measurements of temperature, ozone, humidity, and ground-based measurements of turbidity at Syowa station (69°S, 39°E) in Antarctica are used to study the solar and thermal radiative effects due to gases and aerosols. Our calculations indicated that, with the observed temperature, the thermal radiative cooling due to CO2 and O3 emissions yielded a net radiative cooling in the lower stratosphere throughout the year if the effects of aerosols were excluded. However, the results are very sensitive to the reported ambient temperature. Contribution by aerosols to solar heating was found to be smaller than that due to O3 absorption. The aerosols played a more important role in the long-wave radiation by providing a thermal heating from March to September. During the winter months the thermal heating almost compensated for the cooling due to CO2 and O3 emissions resulting in a near radiative equilibrium state. This sets the stage for a net radiative warming in spring from absorption of solar energy, which may provide energy for an upwelling motion responsible for the ozone hole. Both the temperature distribution and aerosol properties should be studied in more detail in connection with the dynamical thesis for the O3 hole and its interannual variations.

In the face of the faint young sun-climate paradox, the plausible effects of dynamical heat-flux feedbacks on global stability were examined using a coupled high- and low-latitude radiative-dynamical model. The global stability is found to depend very strongly on the vertical heat transport, which is also closely coupled to the meridional heat transport. This coupling and the associated dynamical heat-flux feedbacks, treated within the framework of the radiative-dynamical model, was found to produce a fairly strong negative feedback. Our results indicate that the dynamical heat-flux feedbacks inherent in the climate system may potentially enhance the global stability.

The effect of overlapping of atmospheric HThe effect of overlapping of atmospheric H2O, CO2 and O3 absorption bands on the radiation budget perturbation caused by CO2 doubling is investigated. Sinc...

An analyis of a time series consisting of an annual index of dryness/wetness for the years 1470 to 1974 in Beijing, China is presented. Its power spectrum shows that dominant cycles occur with long periods of the order of 80 years. Cycles with periods of 11 and 22 years are weak or non-existent, but a significant signal at 18.7 years (which is also the period of a component of the lunar tide generating force) is detected. The long term variations in Beijing precipitation appear to lag long term (Gleissberg) variations in solar activity by nearly 75 years. A pattern which spans nearly 150 years in the Beijing record is found to be repeated with notable similarity.

The feedback between 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. It is found that the fixed cloud temperature parameterization breaks ...

It is shown that an exact closed form expression for the total band absorptance of infrared-radiating gases can be obtained by employing the Malkmus narrow band model and the Edwards and Menard wide band approximation. Comparisons with other approximate analytical expressions are presented.

Concerns have been raised in recent years about the possibilities that the atmospheric O3 concentration might be perturbed as a result of anthropogenic activities, such as the uses of CFCs, application of nitrogen fertilizers, fossil fuel consumptions, aircraft emissions, etc. The O3 perturbation could have serious consequences for mankind. Reducing the O3 amount, for example, could increase the amount of solar UV radiation reaching the earth surface with possible damaging effect to the biological system. Further, change in the amount of O3 could change the distribution of solar heating and thermal cooling in the atmosphere and result in a change of temperature and thus, the climate.

The observational data of temperature, humidity, clouds, and solar radiation reaching the surface have been analyzed for two stations, Minqin and Tongliao, inside the desert regions located in northern China. The results suggest that the humidity and cloudiness were greater during the wet year (1964) than during the dry year (1972), while there were no large differences in monthly mean temperature between these two years. We also found that there was an excellent correlation between the solar flux reaching the ground and the amount of low clouds. The difference between the calculated and observed solar flux, which might reflect the contributions of clouds and aerosols, was also examined.

Expressions describing radiative heat transfer in a coupled Mie and Rayleigh scattering atmosphere have been obtained by employing the modified two-stream approximation. The effect of tropospheric aerosols on the albedo as well as on heating rates in the wavelength region from 0.3 to 2.0 microns is studied. The present study indicates that the distinction between cooling or warming of the earth-atmosphere system for a realistic aerosol model proposed by McClatchey will depend on the surface reflectivity being smaller or larger than approximately 0.37. The effect of aerosols on the heating rate close to the surface has the same order of magnitude as atmospheric water vapor.

The greenhouse effect due to nitrous oxide in the present atmosphere is about 0.8°K. Increase in atmospheric N_2O due to perturbation of the nitrogen cycle by man may lead to an increase in surface temperature as large as 0.5°K by 2025, or 1.0°K by 2100. Other climatic effects of N_2O are briefly discussed.

Study of climatic effects of increase in concentration of atmospheric trace gases has so far focused on the direct greenhouse warming. The indirect effect on climate of the seasonal and latitudinal O3 changes associated with trace gases has not been explored. Here, we use simple 1- and 2-D models to demonstrate that changes in the O3 vertical distribution, in particular in the middle and upper troposphere, could trigger a response in meridional heat flux with subsequent feedback effect on climate. Discussion on the effects of trace gases and their induced O3 changes on future climate on the decadal time scale is also presented.

The radiative forcing due to changes in ozone in the troposphere and stratosphere is calculated using a number of different radiative transfer codes and the results are compared. The calculations use a tightly specified set of input parameters. The 14 µm band of ozone is shown to make a significant contribution to the forcing for changes in stratospheric ozone, although, because of line overlap, it is of less importance for tropospheric ozone changes. The main cause of the spread in results is differenees in the solar forcings; these differences are believed to reflect simplifications used in parameterizations rather than the actual uncertainty in modelling solar irradiances.

We compare seasonal changes in cloud-radiative forcing (CRF) at the top of the atmosphere from 18 atmospheric general circulation models, and observations from the Earth Radiation Budget Experiment (ERBE). To enhance the CRF signal and suppress interannual variability, we consider only zonal mean quantities for which the extreme months (January and July), as well as the northern and southern hemispheres, have been differenced. Since seasonal variations of the shortwave component of CRF are caused by seasonal changes in both cloudiness and solar irradiance, the latter was removed. In the ERBE data, seasonal changes in CRF are driven primarily by changes in cloud amount. The same conclusion applies to the models. The shortwave component of seasonal CRF is a measure of changes in cloud amount at all altitudes, while the longwave component is more a measure of upper level clouds. Thus important insights into seasonal cloud amount variations of the models have been obtained by comparing both components, as generated by the models, with the satellite data. For example, in 10 of the 18 models the seasonal oscillations of zonal cloud patterns extend too far poleward by one latitudinal grid.

Study of the greenhouse effects of increasing atmospheric trace gases has so far relied mainly on the use of one-dimensional models, especially the radiative-convective models (cf. World Meteorological Organization, 1982; National Research Council, 1983). Here we use the two-dimensional (altitude-latitude) radiative-dynamical model of Wang et al. (1984) to investigate the effects on vertical and meridional temperatures of increases of atmospheric methane, nitrous oxide, and chlorofluorocarbons. The model, consisting of a high-latitude zone and a low-latitude zone, couples the meridional and vertical temperature structure through energy balance between radiative flux and vertical and meridional heat transports. First, we show that the thermal radiation flux perturbations, i.e., the driving force for the subsequent climate change, caused by increases of these trace gases and carbon dioxide, are different in nature. Next, a comparison of model-calculated present climate and climate change between the one-dimensional and two-dimensional models is performed. The results indicate that the two-dimensional model simulates much more realistic temperature and humidity distributions. For a doubling of the atmospheric CO2 concentration of 330 parts per million by volume, the two-dimensional model computes a global surface warming of 3.7 K with larger high-latitude amplification, which is in good agreement with results obtained from general circulation models. For the study of the surface warming due to increases of trace gases, it is found that the one-dimensional model using a 6.5 K km−1 critical lapse rate for convective adjustment appears to calculate a much larger surface warming than the two-dimensional model. On the other hand, the one-dimensional model using the moist adiabatic critical lapse rate, although it can not simulate adequately the present tropospheric temperature structure, calculates surface warming effects in close agreement with those of two-dimensional model results. We have used the two-dimensional model to estimate on the time scale of decades the potential greenhouse effects due to increases of these gases. Although the calculations depend largely on the adopted scenarios for future increases, the results nevertheless reveal that the trace gases could potentially augment the surface warming due to carbon dioxide increase by more than 60%.

This paper describes the implementation of an efficient and accurate multiple scattering parameterization within the LOWTRAN and FASCODE transmittance/radiance models. The parameterization is based on a stream approximation in which the local radiance field needed to evaluate the multiple scattering source function is estimated from the local radiation fluxes. The latter are calculated based on a parameterized two-flux for individual layers and an adding method for combining layers. Because of the line-by-line nature of FASCODE, it is straightforward to implement the multiple scattering treatment. For LOWTRAN, an interface scheme was developed using the k-distribution method to match the multiple scattering approach to the band model calculation of gas absorption. The interface scheme represents the LOWTRAN band model by a sum of pseudomonochromatic calculations. The approach is valid for any band model for which k-distribution parameters can be evaluated. The accuracy of the multiple scattering parameterization has been demonstrated by comparing it with more detailed calculations for a variety of atmospheric conditions. RMS errors in radiance considering all possible viewing angles are

A coupled high and low latitude radiative-dynamical model of the annual mean northern hemisphere has been constructed in order to study the interactions of the vertical and meridional heat fluxes and their feedback effect on model climate sensitivity. The model's climate sensitivity to solar constant changes and CO2 increases is investigated, and the effect of feedback in the dynamical fluxes on model climate sensitivity is examined. Nonlinear interactions between heat fluxes and other feedbacks such as radiation-temperature, ice albedo, and humidity are also discussed.

The effect of overlapping of atmospheric HThe effect of overlapping of atmospheric H 2 O, CO 2 and 0 3 absorption bands on the radiation budget perturbation caused by CO 2 doubling is investigated. Since the effect depends on the amount of gases in the atmosphere as well as on the strength of the absorption bands, we examine the effect associated with the variation of gas abundance using a narrow band representation for the absorption bands. This band representation allows for the absorption band structure and thus accounts for the correlation of the spectral feature of the absorbing gases. It is found that the presence of H 2 O and 0 3 has a relatively small influence on the C0 2 -induced perturbation of both solar and thermal radiation in the stratosphere. However, in troposphere and surface, the overlapping effect appears to be quite significant and changes the vertical distribution of the C0 2 -induced radiation energy perturbation. For example, in the infrared, the effect is to reduce the effectiveness for CO 2 to emit and in the mean time increases the tropospheric absorption of downward thermal flux from the stratosphere due to CO 2 increase; the net effect of the overlapping of gases is to increase the tropospheric warming and decrease the surface warming caused by CO 2 increase. It is also found that the overlapping effect exhibits strong seasonal and latitudinal variations due primarily to variations in atmospheric H 2 O. DOI: 10.1111/j.1600-0889.1983.tb00012.x