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1991
Iacobellis, SF, Somerville RCJ.  1991.  Diagnostic modeling of the Indian monsoon onset: Part 1: Model description and validation. Journal of the Atmospheric Sciences. 48:1948-1959.   10.1175/1520-0469(1991)048<1948:dmotim>2.0.co;2   AbstractWebsite

A new type of diagnostic model is developed and applied to the study of the onset of the Indian summer monsoon. The purpose of the model is to aid in the analysis of interactions between the physical processes that affect the monsoon onset. The model is one-dimensional and consists of a single atmospheric column coupled to an ocean mixed layer. The atmospheric component of the model includes representations of all the physical processes typically included in general circulation models, except that the fields of vertical motion and horizontal advection are specified at each time step from observational data rather than predicted. With these time-dependent observational inputs, the model is then integrated numerically to produce consistent profiles of atmospheric temperature and humidity, together with energy budget components and other diagnostic quantities. The atmospheric model is based on the thermodynamic energy equation and a conservation equation for water. Parameterizations of the effects of solar and terrestrial radiation, interactive cloudiness, convection, condensation, surface fluxes, and other processes are adapted from current practice in numerical weather prediction and general circulation modeling. The model includes 15 layers in the vertical and employs a time step of 1 hour. Results are presented from four-week integrations at different locations over the Arabian Sea during the 1979 monsoon onset period. Comparison of model results with independent observational data shows that the model demonstrates considerable skill in reproducing the large increase in precipitation associated with the monsoon onset, together with significant changes in surface fluxes, cloudiness, and other variables. This realism suggests that the model is a promising tool for achieving an increased understanding of the role of interacting physical processes and for developing improved prognostic models for simulating the monsoon onset.

Iacobellis, SF, Somerville RCJ.  1991.  Diagnostic modeling of the Indian monsoon onset: Part 2: Budget and sensitivity studies. Journal of the Atmospheric Sciences. 48:1960-1971.   10.1175/1520-0469(1991)048<1960:dmotim>2.0.co;2   AbstractWebsite

A one-dimensional diagnostic coupled air-sea model (described in the companion paper) is applied to the analysis of the heat and moisture budgets over the Arabian Sea during the 1979 monsoon onset period. The surface energy budget, which is dominated by a balance between net shortwave radiation and latent heat during the preonset period, is significantly altered just prior to the onset itself. At that time, cloud cover sharply increases and the net shortwave flux correspondingly decreases. Subsequently, increasing surface winds produce a large increase in the latent heat flux a few days after the onset. In the free atmosphere, the heat budget displays a similarly dramatic change. At 500 mb, radiative fluxes and horizontal and vertical advection dominate the heat budget before the onset. After the onset, however, the budget is primarily a balance between deep convective heating and vertical advective cooling. The 500-mb moisture budget displays a correspondingly strong effect. Before the onset, horizontal advection of moisture is the dominant term, while after the onset, the distribution by convection of the surface moisture flux, together with moisture removal by large-scale condensation, becomes important. Sensitivity studies with the model illuminate the role of interacting physical processes. Model results show that the moistening due to horizontal advection tends to alter the radiative fluxes so as to hinder the formation and maintenance of the inversion that characterizes preonset conditions, thus favoring the formation of deep convection. This result is consistent with a suggestion by Doherty and Newell. Additionally, the interaction between the atmosphere and the upper ocean is explored in a series of sensitivity experiments. The decrease in ocean mixed-layer temperature, which follows the monsoon onset, acts to reduce the latent heat flux significantly. This effect may influence the duration and intensity of the monsoon, as well as the total precipitation, and underscores the potential importance of an accurate specification of sea surface temperature for monsoon prediction.

Chertock, B, Frouin R, Somerville RCJ.  1991.  Global Monitoring of Net Solar Irradiance at the Ocean Surface - Climatological Variability and the 1982-1983 Elnino. Journal of Climate. 4:639-650.   10.1175/1520-0442(1991)004<0639:gmonsi>2.0.co;2   AbstractWebsite

A new method has been used to generate the first satellite-based long-term climatology of surface solar irradiance over the world oceans. These monthly mean data cover the period November 1978 through October 1985 on a global, 9-degrees latitude-longitude spatial grid. The large-scale variability of surface solar irradiance is assessed over the world oceans for the entire (84-month) record. The results demonstrate the ability of the method to reveal large-scale seasonal and interannual phenomena. The reduction in surface solar irradiance due to clouds is evaluated globally both on monthly and long-term climatological scales. Monthly cloud forcing anomalies are found to display eastward propagation over the course of the 1982-1983 El Nino event. The mean January climatology is found to be consistent with the climatology obtained from a general circulation model run in perpetual January mode. This study marks the first large-scale observation-based examination of cloud solar forcing at the ocean surface. In addition, empirical orthogonal function (EOF) analysis is employed to investigate modes of seasonal and nonseasonal variability. Nonseasonal EOF modes of surface solar irradiance are related to nonseasonal EOF modes of outgoing longwave radiation (OLR). The dominant modes during the 1982-1983 El Nino are associated with eastward propagation in both the shortwave and longwave fields. These dominant nonseasonal EOF modes of surface solar irradiance are found to display features and amplitude variations that are identical to those of the corresponding nonseasonal EOF modes of OLR. The association of these modes with EL Nino is quantified using the correlation of the mode amplitudes with the Southern Oscillation index (SOI). In each case modes 1 and 2 are positively correlated with the SOI, and mode 1 has a strong correlation of 0.75 for the shortwave and 0.76 for the longwave field. Finally, a study of the regionally averaged behavior of surface solar irradiance and sea surface temperature (SST) in a section of the tropical Pacific (9-degrees-N-9-degrees-S, 117-degrees-144-degrees-W) during this same period indicates that fluctuations of surface solar irradiance in the tropical Pacific are sometimes a regional response to underlying changes in SST (and associated changes in cloudiness), rather than a driving mechanism responsible for variations in SST.

1989
Isakari, SM, Somerville RCJ.  1989.  Accurate numerical solutions for Daisyworld. Tellus Series B-Chemical and Physical Meteorology. 41:478-482.   10.1111/j.1600-0889.1989.tb00324.x   AbstractWebsite

The numerical solutions of the Daisyworld model of Watson and Lovelock contain significant quantitative errors. We give accurate numerical solutions for the same cases. We also show how the errors may have been caused by failure to enforce computational constraints such as strict tests of steadiness. The errors which we find do not qualitatively alter the main conclusions of Watson and Lovelock, but they illustrate a peril. The Daisyworld model is an example of a mathematical system which is too idealized to be compared with observations but too complex to be solved analytically. Such systems can be probed only by numerical simulations, so it is crucial that the computations be trustworthy.

1987
Chertock, B, Iacobellis S, Somerville C.  1987.  Remote sensing studies of oceanic cloud-radiation feedbacks. Atmospheric radiation progress and prospects (Proceedings of the Beijing International Radiation Symposium, August 26-30, 1986). ( Liou K, Chou H, Eds.).:508-514., Beijing, China: Science Press and American Meteorological Society Abstract
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Somerville, RCJ.  1987.  The predictability of weather and climate. Climatic Change. 11:239-246.: Kluwer Academic Publishers   10.1007/bf00138802   AbstractWebsite

The last thirty years have seen the development of comprehensive numerical models of the large-scale circulation of the atmosphere, based on physical principles. Such models are quite skillful at describing the evolving weather up to a few days ahead, despite imperfect theory and inadequate observational data. Yet even a hypothetical perfect model, which exactly represented the dynamics of the real atmosphere, and which used data from the best conceivable observing system, could not produce an accurate forecast of indefinitely long range. Any forecast must eventually lose skill because of the intrinsic instability of the atmosphere itself.This limitation on the predictability of the detailed evolution of the atmosphere (“weather”) does not preclude the possibility of seasonal and longer-range forecasts of means and other statistical properties (“climate”). However, we are only beginning to learn what aspects of climate may be predictable, and what theoretical tools and observational data will be required to predict them.

Somerville, RCJ, Iacobellis SF.  1987.  Cloud-radiation interactions: Effects of cirrus optical thickness feedbacks. Short- and Medium-Range Numerical Weather Prediction. ( Matsuno T, Ed.).:177-185., [Tokyo]: Meteorological Society of Japan Abstract
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Hathaway, DH, Somerville RCJ.  1987.  Thermal Convection in a Rotating Shear Flow. Geophysical and Astrophysical Fluid Dynamics. 38:43-&.   10.1080/03091928708210105   AbstractWebsite

A three-dimensional and time-dependent numerical model is used to simulate thermal convection imbedded in a shear flow in a rotating atmosphere. The fluid is confined to a plane parallel layer with periodic side boundaries, and the rotation vector is tilted from the vertical to represent a low-latitude region. An eastward mean flow is imposed which is constant with depth but has a jet-like profile in latitude. The convection is driven by a prescribed vertical temperature difference. Interactions between the shear flow and the convection extract energy from the mean flow and decrease the mean shear in the nonrotating case. In the presence of rotation, however, the convection can feed energy into the jet and enhance the mean shear. Mean meridional circulations are also produced by the effects of rotation. The Coriolis force on the vertical flows in these circulations contributes to the changes in the mean zonal wind. Three rotating cases are examined which show this behavior in varying degrees. A simple mechanism is described which explains how the convection can produce this countergradient flux of momentum in a rotating layer. Although the system studied is highly idealized, it exhibits momentum fluxes and wave-like patterns which, for certain parameter values, are similar to those observed on Jupiter.

1986
Hathaway, DH, Somerville RCJ.  1986.  Nonlinear Interactions between Convection, Rotation and Flows with Vertical Shear. Journal of Fluid Mechanics. 164:91-&.   10.1017/s0022112086002483   AbstractWebsite

A three-dimensional and time-dependent numerical model is used to study the nonlinear interactions between thermal convective motions, rotation, and imposed flows with vertical shear. All cases have Rayleigh numbers of 104 and Prandtl numbers of 1.0. Rotating cases have Taylor numbers of 104.For the non-rotating cases, the effects of the shear on the convection produce longitudinal rolls aligned with the shear flow and a downgradient flux of momentum. The interaction between the convection and the shear flow decreases the shear in the interior of the fluid layer while adding kinetic energy to the convective motions. For unit Prandtl number the dimensionless flux of momentum is equal to the dimensionless flux of heat.For rotating cases with vertical rotation vectors, the shear flow favours rolls aligned with the shear and produces a downgradient flux of momentum. However, the Coriolis force turns the flow induced by the convection to produce a more complicated shear that changes direction with height. As in the non-rotating cases, the convective motions become more energetic by extracting energy from the mean flow. For Richardson numbers larger than about − 1.0, the dominant source of eddy kinetic energy is the shear flow rather than buoyancy.For rotating cases with tilted rotation vectors the results depend upon the direction of the shear. For weak shear, convective rolls aligned with the rotation vector are favoured. When the shear flow is directed to the east along the top, the rolls become broader and the convection weaker. For large shear in this direction, the convective motions are quenched by the competition between the shear flow and the tilted rotation vector. When the shear flow is directed to the west along the top, strong shear produces rolls aligned with the shear. The heat and momentum fluxes become large and can exceed those found in the absence of a tilted rotation vector. Countergradient fluxes of momentum can also be produced.

1985
Engquist, BE, Osher S, Somerville RCJ.  1985.  Large-Scale Computations in Fluid Mechanics. Lectures in Applied Mathematics. :779.: American Mathematical Society AbstractWebsite
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Hathaway, DH, Somerville RCJ.  1985.  Numerical simulation in three space dimensions of time-dependent thermal convection in a rotating fluid. Lectures in Applied Mathematics. 22:309-319. Abstract

Three-dimensional time-dependent convection in a plane layer of fluid, uniformly heated from below and subject to vertical shear and to rotation about an axis tilted from the vertical, was simulated by the numerical solution of the Boussinesq equations, including all Coriolis terms. Rotation about a vertical axis produces smaller convection cells with diminished heat fluxes and considerable vorticity. When the rotation axis is tilted from the vertical to represent tropical latitudes, the convection cells become elongated in a N-S direction. Imposed flows with constant vertical shear produce convective rolls aligned with the mean flow. When the rotation vector is tilted from the vertical, the competing effects due to rotation and shear can stabilize the convective motions.

1984
Somerville, RCJ, Remer LA.  1984.  Cloud Optical-Thickness Feedbacks in the Co2 Climate Problem. Journal of Geophysical Research-Atmospheres. 89:9668-9672.   10.1029/JD089iD06p09668   AbstractWebsite

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 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 act as a thermostat and 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 caused by doubling CO2 is reduced by about one half. This result is obtained for global and annual average conditions, no change in cloud amount or altitude, and constant relative humidity. These idealizations, together with other simplifications typical of one-dimensional radiative-convective climate models, render the result tentative. Further study of cloud optical property feedbacks is warranted, however, because the climate is apparently so sensitive to them.

Roads, JO, Somerville RCJ.  1984.  Linear Predictability: Effects of Stationary Forcing. Aip Conference Proceedings. :557-570. AbstractWebsite
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1983
Barnett, TP, Somerville RCJ.  1983.  Advances in Short-Term Climate Prediction. Reviews of Geophysics. 21:1096-1102.   10.1029/RG021i005p01096   AbstractWebsite

Dynamical and several empirical and statistical approaches to short term climate prediction are surveyed. General circulation models have displayed considerable potential for this application. Physical/synoptic and purely statistical methods have been intensively developed and tested in recent years. Important problems have been recognized in areas such as predictability, forecast verification and evaluation, and combining complementary approaches to prediction.

Hathaway, DH, Somerville RCJ.  1983.  Three-Dimensional Simulations of Convection in Layers with Tilted Rotation Vectors. Journal of Fluid Mechanics. 126:75-&.   10.1017/s0022112083000051   AbstractWebsite

Three-dimensional and time-dependent numerical simulations of thermal convection are carried out for rotating layers in which the rotation vector is tilted from the vertical to represent various latitudes. The vertical component of the rotation vector produces narrow convection cells and a reduced heat flux. As this vertical component of the rotation vector diminishes in the lower latitudes, the vertical heat flux increases. The horizontal component of the rotation vector produces striking changes in the convective motions. It elongates the convection cells in a north–south direction. It also tends to turn upward motions to the west and downward motions to the east in a manner that produces a large-scale circulation. This circulation is directed to the west and towards the poles in the upper half of the layer and to the east and towards the equator in the bottom half. Since the layer is warmer on the bottom this circulation also carries an equatorward flux of heat. When the rotation vector is tilted from the vertical, angular momentum is always transported downwards and toward the equator. For rapidly rotating layers, the pressure field changes in a manner that tends to balance the Coriolis force on vertical motions. This results in an increase in the vertical heat flux as the rotation rate increases through a limited range of rotation rates.

1982
Roads, JO, Somerville RCJ.  1982.  Predictability of Ultralong Waves in Global and Hemispheric Quasi-Geostrophic Barotropic Models. Journal of the Atmospheric Sciences. 39:745-755.   10.1175/1520-0469(1982)039<0745:pouwig>2.0.co;2   AbstractWebsite

A global quasi-geostrophic barotropic model, including orography, zonal forcing and frictional dissipation, is compared to two hemispheric models, one with antisymmetric equatorial boundary conditions and one with symmetric boundary conditions. The stationary solutions in the global model and the hemispheric models are found to be different, because the hemispheric models lack either the symmetric or antisymmetric waves, and because the nonlinear feedbacks are much larger in the hemispheric models. Time-dependent calculations show that the hemispheric models can excite anomalous Rossby waves and can produce erroneous short-range forecasts in middle latitudes. We conclude that global models are preferred for making both short-range and long-range forecasts for middle latitudes.

1980
Somerville, RCJ.  1980.  Tropical Influences on the Predictability of Ultralong Waves. Journal of the Atmospheric Sciences. 37:1141-1156.   10.1175/1520-0469(1980)037<1141:tiotpo>2.0.co;2   AbstractWebsite

Some implications of predictability theory for ultralong waves are examined in an ensemble of real-data forecasts carried out with a primitive-equation numerical model in both global and hemispheric configurations. Although the model is adiabatic and almost inviscid, its skill at forecasting the 5-day evolution of ultralong waves in middle latitudes of the Northern Hemisphere is approximately equivalent to that of a physically comprehensive general circulation model. The ultralong wave forecasts produced by a hemispheric version of the model are markedly less skillful than those made by the global version, especially in the latter part of the 5-day period. When the initial state of the hemispheric version is modified by using a smooth field in the tropics in place of analyzed observed data, the skill of the prediction is degraded further, and the effect is apparent early in the 5-day period.These adverse tropical influences on middle-latitude forecast skill are essentially confined to the ultralong waves (zonal wavenumbers 1–3). They appear to be typical of hemispheric integrations with conventional numerical weather prediction models and conventional analysis and initialization techniques. The resulting forecast errors may be associated with the spurious excitation of large-amplitude external modes. These effects of tropical deficiencies in the prediction model and in the initial data provide a partial explanation for the poor skill of typical actual forecasts of ultralong waves, relative to the skill expected on the basis of predictability theory. The results also suggest that improvements in hemispheric analysis and initialization procedures are urgently required. Until such improvements are implemented, the use of global rather than hemispheric models, even for forecasts of only a few days, might be beneficial in operational practice.

1979
Gall, R, Blakeslee R, Somerville RCJ.  1979.  Baroclinic Instability and the Selection of the Zonal Scale of the Transient Eddies of Middle Latitudes. Journal of the Atmospheric Sciences. 36:767-784.   10.1175/1520-0469(1979)036<0767:biatso>2.0.co;2   AbstractWebsite

Because the linear growth rates of baroclinic waves on realistic zonal flows are largest at relatively high zonal wavenumbers (e.g., 15), the observed peaks in the transient kinetic energy spectrum cannot be explained simply by peaks in the linear growth-rate spectrum. When the growth-rate spectrum is fairly flat, as suggested by recent studies, then as the waves evolve, the decrease of the instability of the zonal flow and the increase of dissipation in the developing waves become important in determining which wavelength will dominate after the waves are fully developed. In particular, the stabilization of the zonal flow because of northward and upward eddy transport (which is primarily confined to the lower troposphere in all baroclinic waves) causes the instability of the short baroclinic waves (wavenumber > 10) to decrease more rapidly than that of the intermediate-scale waves (wavenumber <10). In addition, as it is usually modeled, dissipation increases with time more rapidly in the short waves. Therefore, the growth of the short waves is terminated by these two processes before the growth of the intermediate-scale waves, which can thus achieve greater equilibrium amplitudes.We have obtained these results in a numerical experiment with a simplified general circulation model, in which waves of all wavelengths are allowed to develop simultaneously from small random perturbations on a flow that is initially zonally symmetric. The kinetic energy spectrum in this experiment does not display a −3 power law in the wavenumber band 10–20, even after the spectrum in this spectral region has been equilibrated for a simulated week or more. This result apparently supports the recent hypothesis of Andrews and Hoskins that atmospheric fronts rather than quasi-geostrophic turbulence are responsible for the observed −3 spectrum at wavenumbers > 10.

Gall, R, Blakeslee R, Somerville RCJ.  1979.  Cyclone-Scale Forcing of Ultralong Waves. Journal of the Atmospheric Sciences. 36:1692-1698.   10.1175/1520-0469(1979)036<1692:csfouw>2.0.co;2   AbstractWebsite

A numerical experiment is carried out with a simplified general circulation model. In this experiment, instabilities of all wavelengths are allowed to develop simultaneously from small perturbations on a zonally symmetric flow. The initial development of the ultralong waves in this experiment is apparently forced by the interaction between the cyclone-scale waves and the basic flow in which they are embedded. Because the spectrum of the developing baroclinic waves is not monochromatic, the interaction between the cyclones and the basic flow varies with longitude, and waves longer than the cyclone scale are forced. The structure of the ultralong waves in the numerical experiment is consistent with this forcing mechanism. One implication for numerical weather prediction is that errors in forecasts of ultralong waves may be due in part to errors in the cyclone scale.

Somerville, RCJ, Galchen T.  1979.  A Numerical Simulation of Convection with Mean Vertical Motion. Journal of the Atmospheric Sciences. 36:805-815.   10.1175/1520-0469(1979)036<0805:nsocwm>2.0.co;2   AbstractWebsite

The flow in a convectively unstable layer of fluid may be strongly influenced by large-scale ascent or descent. We consider cellular convection between horizontal surfaces on which vertical velocity is maintained at a constant value. Using an efficient numerical model to simulate the evolution of the convection in three space dimensions and time, we investigate the effect of the imposed vertical velocity on the flow.For moderately supercritical values of the Rayleigh number and for Prandtl numbers near unity, convection is known to occur in the form of steady rolls if the specified mean vertical motion is zero, i.e., in the case of the conventional Bénard problem for a Boussinesq fluid. Our model also produces rolls under these circumstances. For sufficiently large values of the imposed vertical velocity, however, the numerically simulated rolls are replaced by polygonal cells in which the direction of flow depends on whether ascent or descent is prescribed at the boundaries, in accordance with recent theoretical and laboratory results of R. Krishnamurti. We have also investigated the dependence of the convection on the Rayleigh and Prandtl numbers within limited ranges of these parameters, and we discuss several aspects of agreement and disagreement among analytical theory, laboratory experiment and numerical simulation.

Dobosy, RJ, Somerville RCJ.  1979.  Test of Simple Momentum Boundary-Layer Parameterizations in a Numerical Weather Prediction Model. Contributions to Atmospheric Physics [Beitraege zur Physik der Atmosphaere.], Wiesbaden, Germany. 52:190-203. Abstract
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1978
Baker, WE, Kung EC, Somerville RCJ.  1978.  An Energetics Analysis of Forecast Experiments with NCAR General Circulation Model. Monthly Weather Review. 106:311-323.   10.1175/1520-0493(1978)106<0311:aeaofe>2.0.co;2   AbstractWebsite

The energetics in numerical weather forecast experiments with the NCAR general circulation model have been analyzed. The 6-layer, 5-degree, second-generation global model was used to make two 10-day forecasts with the same initial conditions. The two experiments differed primarily in the methods of convective parameterization.Hemispheric integrals of the model energies and energy transformations are presented in the context of their approach to a quasi-equilibrium climatology. Spectral and spatial analyses of the eddy energies and transformations provide further insight into the model response to the initial conditions. After the initial adjustment, the eddy kinetic energy appears to lag the conversion from eddy available potential energy to eddy kinetic energy by at least 48 h in the long waves (wavenumbers 1–4) and by approximately 24 h in the baroclinic waves (wavenumbers 5–7), whereas little or no time lag is apparent in the short waves (wavenumbers 8–12).The sensitivity of the forecast energetics to two different convective parameterizations is also examined. There is little appreciable difference between the two experiments in the eddy kinetic energy integrals during the first 36 h of the forecast, but temporal patterns of the eddy transformations are distinctly different after 12 h.

1977
Baker, WE, Kung EC, Somerville RCJ.  1977.  Energetics Diagnosis of the NCAR General Circulation Model. Monthly Weather Review. 105:1384-1401.   10.1175/1520-0493(1977)105<1384:edotng>2.0.co;2   AbstractWebsite

A comprehensive energetics analysis has been performed on the NCAR general circulation model. The analysis involves January and July simulation experiments with the 6-layer, 5-degree, second-generation model with two different convective schemes. Spectral analysis of the energy transformations in the wave-number domain was performed separately on a global and hemispheric basis as well as for the tropics and mid-latitudes. Latitudinal distributions of energy variables were also examined.A qualitative agreement with observational estimates is generally recognized in the transformations of eddy energies. Quantitatively, however, the eddy energies, conversions and energy transfer between wavenumbers are weaker than observational estimates. It is noteworthy that substantial differences exist in the energetics of the two versions of the model with different convective schemes.

Somerville, RCJ.  1977.  Pattern Recognition Techniques for Weather Forecast Verification. Contributions to Atmospheric Physics [Beitraege zur Physik der Atmosphaere.], Wiesbaden, Germany. 50:403-410. Abstract
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1976
Somerville, RCJ, Quirk WJ, Hansen JE, Lacis AA, Stone PH.  1976.  Search for Short-Term Meteorological Effects of Solar Variability in an Atmospheric Circulation Model. Journal of Geophysical Research-Oceans and Atmospheres. 81:1572-1576.   10.1029/JC081i009p01572   AbstractWebsite

A set of numerical experiments is carried out to test the short-range sensitivity of the Giss (Goddard Institute for Space Studies) global atmospheric general circulation model to changes in solar constant and ozone amount. These experiments consist of forecasts initialized with actual atmospheric data. One set of forecasts is made with a standard version of the model, and another set uses the model modified by very different values of the solar constant (two thirds and three halves of the standard value) and of the ozone amount (zero and twice the standard amount). Twelve-day integrations with these very large variations show such small effects that the effects of realistic variations would almost certainly be insignificant meteorologically on this time scale.