Showing papers in "Journal of the Atmospheric Sciences in 1980"
TL;DR: In this article, the spectral albedo of snow is calculated at any wavelength in the solar spectrum and which accounts for diffusely or directly incident radiation at any zenith angle.
Abstract: We present a method for calculating the spectral albedo of snow which can be used at any wavelength in the solar spectrum and which accounts for diffusely or directly incident radiation at any zenith angle. For deep snow, the model contains only one adjustable parameter, an effective grain size, which is close to observed grain sizes. A second parameter, the liquid-equivalent depth, is required only for relatively thin snow. In order for the model to make realistic predictions, it must account for the extreme anisotropy of scattering by snow particles. This is done by using the “delta-Eddington” approximation for multiple scattering, together with Mie theory for single scattering. The spectral albedo from 0.3 to 5 μm wavelength is examined as a function of the effective grain size, the solar zenith angle, the snowpack thickness, and the ratio of diffuse to direct solar incidence. The decrease in albedo due to snow aging can be mimicked by reasonable increases in grain size (50–100 μm for new snow...
1,487 citations
TL;DR: In this paper, it was shown that small highly absorbing particles, present in concentrations of only 1 part per million by weight (ppmw) or less, can lower snow albedo in the visible by 5-15% from the high values (96-99%) predicted for pure snow in Part I.
Abstract: Small highly absorbing particles, present in concentrations of only 1 part per million by weight (ppmw) or less, can lower snow albedo in the visible by 5–15% from the high values (96–99%) predicted for pure snow in Part I. These particles have, however, no effect on snow albedo beyond 0.9 μm wavelength where ice itself becomes a strong absorber. Thus we have an attractive explanation for the discrepancy between theory and observation described in Part I, a discrepancy which seemingly cannot be resolved on the basis of near-field scattering and nonsphericity effects. Desert dust and carbon soot are the most likely contaminants. But careful measurements of spectral snow albedo in the Arctic and Antarctic paint to a “grey” absorber, one whose imaginary refractive index is nearly constant across the visible spectrum. Thus carbon soot, rather than the red iron oxide normally present in desert dust, is strongly indicated at these sites. Soot particles of radius 0.1 μm, in concentrations of only 0.3 pp...
1,286 citations
TL;DR: In this paper, a 16-year period (1962-77) with respect to the phase of the equatorial quasi-biennial oscillation (QBO) was used to find that the observed zonal mean geopotential height at high latitudes is significantly lower during the westerly phase of QBO than during the easterly phase in all months composited.
Abstract: Monthly mean Northern Hemisphere 50 mb geopotential heights for a 16-year period (1962-77) are composited with respect to the phase of the equatorial quasi-biennial oscillation (QBO). The observed zonal mean geopotential height at high latitudes is significantly lower during the westerly phase of the equatorial QBO than during the easterly phase in all months composited. For this 16-year sample we find that in early winter (November-December) the amplitude of planetary wavenumber 1 is nearly 40% stronger during the easterly phase of the equatorial QBO. In late winter (January-March) the amplitude of planetary wavenumber 2, on the other hand, is nearly 60% stronger during the westerly phase of the equatorial QBO. Data from an additional 6-year sample show a similar wavenumber 1 signal during the November-December period. However, an additional 4-year sample does not support our conclusions concerning wavenumber 2 during the January-March period. Composites based on zonal wind data from a longitudi...
931 citations
TL;DR: In this paper, the Eliassen-Palm (EP) cross sections are used to measure the magnitude of transient and irreversible eddy processes at each height and latitude, and is proportional to the northward flux of quasi-geostrophic (not Ertel's) potential vorticity.
Abstract: “Eliassen-Palm (EP) cross sections” are meridional cross sections showing the Eliassen-Palm flux F by arrows and its divergence by contours For large-scale, quasi-geostrophic motion F is defined to have φ and ρ components r0 cosφ[−u′v′, fv′θ′/θp] where φ is latitude, ρ pressure, θ potential temperature, r0 the radius of the earth, bars and primes denote zonal means and deviations and (u,v) is horizontal velocity The theoretical reasons for using EP cross sections diagnostically are reviewed The divergence of F reflects the magnitude of transient and irreversible eddy processes at each height and latitude, and is proportional to the northward flux of quasi-geostrophic (not Ertel's) potential vorticity It is a direct measure of the total forcing of the zonal-mean state by the eddies The direction of F indicates the relative importance of the principal eddy fluxes of heat and momentum If the eddy dynamics is Rossby wavelike, then F is also a measure of net wave propagation from one height and
922 citations
TL;DR: In this article, a simple approximate theory is developed for the case in which the fluid is sufficiently inviscid that the poleward flow in the Hadley cell is nearly angular momentum conserving.
Abstract: The structure of certain axially symmetric circulations in a stably stratified, differentially heated, rotating Boussinesq fluid on a sphere is analyzed. A simple approximate theory [similar to that introduced by Schneider (1977)] is developed for the case in which the fluid is sufficiently inviscid that the poleward flow in the Hadley cell is nearly angular momentum conserving. The theory predicts the width of the Hadley cell, the total poleward heat flux, the latitude of the upper level jet in the zonal wind, and the distribution of surface easterlies and westerlies. Fundamental differences between such nearly inviscid circulations and the more commonly studied viscous axisymmetric flows are emphasized. The theory is checked against numerical solutions to the model equations.
867 citations
TL;DR: In this article, a parameterization formulation for incorporating the effects of midlatitude deep convection into mesoscale-numerical models is presented, based on the hypothesis that the buoyant energy available to a parcel, in combination with a prescribed period of time for the convection to remove that energy, can be used to regulate the amount of convection in a mesh grid element.
Abstract: A parameterization formulation for incorporating the effects of midlatitude deep convection into mesoscale-numerical models is presented. The formulation is based on the hypothesis that the buoyant energy available to a parcel, in combination with a prescribed period of time for the convection to remove that energy, can be used to regulate the amount of convection in a mesoscale numerical model grid element. Individual clouds are represented as entraining moist updraft and downdraft plumes. The fraction of updraft condensate evaporated in moist downdrafts is determined from an empirical relationship between the vertical shear of the horizontal wind and precipitation efficiency. Vertical transports of horizontal momentum and warming by compensating subsidence are included in the parameterization. Since updraft and downdraft areas are sometimes a substantial fraction of mesoscale model grid-element areas, grid-point temperatures (adjusted for convection) are an area-weighted mean of updraft, downdr...
693 citations
TL;DR: In this paper, a height profile of ablated mass from meteors is calculated, assuming an incoming mass of 10 to the -16th g/sq cm/s (44 metric tons per day) and the velocity distribution of Southworth and Sekanina, which has a mean of 14.5 km/s.
Abstract: A height profile of ablated mass from meteors is calculated, assuming an incoming mass of 10 to the -16th g/sq cm/s (44 metric tons per day) and the velocity distribution of Southworth and Sekanina, which has a mean of 14.5 km/s. The profile peaks at 84 km. The fluxes of micrometeorites and residual meteoroids are also calculated. The coagulation of the evaporated silicates into 'smoke' particles is then followed by means of a model adapted from a previous study of the stratospheric sulfate layer. Numerous sensitivity tests are made. Features of the results are a sharp cutoff of the particle distribution above 90 km, and a surface area close to 10 to the -9th sq cm/cu cm all the way from 30 to 85 km. Some confirmation is obtained from balloon studies of condensation nuclei, although the various measurements differ greatly. The optical scattering and extinction are shown to be undetectable. Several potential applications are suggested: nucleation of sulfate particles and noctilucent clouds, scavenging of metallic ions and atoms, and perhaps other aeronomical effects. The latter are limited to processes that can be influenced by a collision time of the order of a day.
585 citations
TL;DR: In this paper, a two-stream approximation to radiative transfer theory for particulate media is shown to be represented by identical forms of coupled differential equations if the intensity is replaced by integrals of the intensity over hemispheres.
Abstract: Existing two-stream approximations to radiative transfer theory for particulate media are shown to be represented by identical forms of coupled differential equations if the intensity is replaced by integrals of the intensity over hemispheres. One set of solutions thus suffices for all methods and provides convenient analytical comparisons. The equations also suggest modifications of the standard techniques so as to duplicate exact solutions for thin atmospheres and thus permit accurate determinations of the effects of typical aerosol layers. Numerical results for the plane albedos of plane-parallel atmospheres are given for conventional and modified Eddington approximations, conventional and modified two-point quadrature schemes, the hemispheric-constant method and the delta-function method, all for comparison with accurate discrete-ordinate solutions. A new two-stream approximation is introduced that reduces to the modified Eddington approximation in the limit of isotropic phase functions and to the exact solution in the limit of extreme anisotropic scattering. Comparisons of plane albedos and transmittances show the new method to be generally superior over a wide range of atmospheric conditions (including cloud and aerosol layers), especially in the case of nonconservative scattering.
528 citations
TL;DR: The authors used a simple general circulation model with a limited computational domain, highly idealized geography, no seasonal variation of insolation, and a simplified interaction between cloud and radiative transfer.
Abstract: A study of the climatic effect of doubling or quadrupling of CO2 in the atmosphere has been continued by the use of a simple general circulation model with a limited computational domain, highly idealized geography, no seasonal variation of insolation, and a simplified interaction between cloud and radiative transfer. The results from the numerical experiments reveal that the response of the model climate to an increase of CO2 content in air is far from uniform geographically. For example, one can identify the high-latitude region of the continent where the runoff rate increases markedly, a zonal belt of decreasing soil moisture around 42° latitude, and a zone of enhanced wetness along the east coast of the subtropical portion of the model continent. The general warming and the increase of moisture content of air, which results from a CO2 increase, contributes to the large reduction of the meridional temperature gradient in the lower model troposphere because of 1) poleward retreat of highly refl...
488 citations
TL;DR: In this paper, the role of the jet stream frontal zone clear air turbulence (CAT) as a mechanism for the exchange of air and chemical trace constituents between the stratosphere and the troposphere is discussed.
Abstract: Evidence is presented which illustrates the role of jet stream-frontal zone clear air turbulence (CAT) as a mechanism for the exchange of air and chemical trace constituents between the stratosphere and the troposphere. Three-dimensional air motion sensing instrumentation and fast-response ozone and condensation nuclei analysers on board research aircraft permit the quantitative evaluation of the turbulent flux of chemical constituents across the tropopause. The observations reveal that tropopause folds are mixing regions whose chemical characteristics lie somewhere in between those of the troposphere and the stratosphere. The temporal changes of ozone and condensation nuclei brought about through the vertical flux divergence of these quantities suggest that turbulent mixing processes are of first-order importance as a mechanism for stratospheric-tropospheric exchange in the vicinity of jet stream-frontal zone-associated topopause folds.
455 citations
TL;DR: In this article, the authors evaluated the second-moment budgets of turbulence kinetic energy, temperature and humidity variances, and temperature fluxes for a baroclinic, convective boundary layer using data obtained from the NCAR Electra aircraft during the AMTEX.
Abstract: Terms in the budgets of turbulence kinetic energy, temperature and humidity variances, and temperature and humidity fluxes have been evaluated for a baroclinic, convective boundary layer using data obtained from the NCAR Electra aircraft during the Air Mass Transformation Experiment (AMTEX). Although the mean temperature and momentum budgets, which were also evaluated, are strongly influenced by the horizontal temperature gradient, the second-moment budgets are little affected. The mean momentum budget is not well balanced, probably due to a combination of neglect of horizontal advection (aircraft advection measurements are shown to be statistically unreliable) and error in the surface geostrophic wind. For the most part, the measured terms in the second-moment budgets agree with previous estimates. Turbulence dissipation, however, was systematically less than that found in previous tower-based experiments. We find that over most of the mixed layer the temperature variance is maintained by turbul...
TL;DR: In this article, a global, three-dimensional, time-dependent numerical model of the thermosphere has been created to simulate the dynamical behavior of the earth's thermospheres under a wide variety of geophysical conditions.
Abstract: A global, three-dimensional, time-dependent numerical model of the thermosphere has been created to simulate the dynamical behavior of the earth's thermosphere under a wide variety of geophysical conditions. Comparison of the model's predictions with the available data from ground-based, rocket and satellite techniques has shown that thermospheric dynamics can be realistically simulated by considering only three processes which deposit energy, or energy and momentum, in the thermosphere. Comparisons between the simulations and available data allow assessment of the magnitudes of the various processes as functions, particularly, of solar and geomagnetic activity. The model is fully self-consistent in solving the neutral gas equations of momentum, energy and continuity, including all the Coriolis, inertial, viscosity and nonlinear terms, but assumes that the thermosphere contains a single species whose mean molecular weight varies only with the pressure. At times when the mean meridional wind is la...
TL;DR: The role of bromine compounds in the photochemistry of the natural and perturbed stratosphere has been reexamined using an expanded reaction scheme and the results of recent laboratory studies of several key reactions as discussed by the authors.
Abstract: The role of bromine compounds in the photochemistry of the natural and perturbed stratosphere has been reexamined using an expanded reaction scheme and the results of recent laboratory studies of several key reactions. The most important finding is that through the reaction BrO + CIO → Br + Cl + O2, there is a synergistic effect between bromine and chlorine which results in an efficient catalytic destruction of ozone in the lower stratosphere. One-dimensional photochemical model results indicate that BrO is the major bromine species throughout the stratosphere, followed by BrONO2, HBr, HOBr and Br. We show from the foregoing that bromine is more efficient than chlorine as a catalyst for destroying ozone, and discuss the implications for stratospheric ozone of possible future growth in the industrial and agricultural use of bromine. Bromine concentrations of 20 pptv (2 × 10^−11), as suggested by recent observations, can decrease the present-day integrated ozone column density by 2.4%, and can enhance ozone depletion from steady-state chlorofluoromethane release at 1973 rates by a factor of 1.1–1.2.
TL;DR: In this paper, a combined longwave and shortwave radiative transfer model was used to determine effects of Saharan dust on the radiative fluxes and heating/cooling rates in the atmosphere.
Abstract: A combined longwave and shortwave radiative transfer model was used to determine effects of Saharan dust on the radiative fluxes and heating/cooling rates in the atmosphere. Cases are treated for cloud-free and overcast conditions over the ocean and for cloud-free sky over desert. A benchmark comparison, made for the cloud-free ocean case between our calculations and those from Wiscombe’s detailed model, yielded results which were in close agreement. For moderately heavy dust amounts commonly measured over the Sahara and the eastern tropical Atlantic Ocean, typical calculated aerosol heating rates for the combined longwave and shortwave spectrum were in excess of 1 K day−1 for all three cases for most of the atmosphere beneath the top of the dust layer (500 mb). For the ocean case, maximum heating rates are found near the level of maximum concentration (700 mb), and also near the surface beneath the Saharan air layer (below 900 mb). Net fluxes determined at the top of the atmosphere for the ocean...
TL;DR: In this article, it was shown that the growth rate of the most rapidly growing instability is linearly proportional to the surface meridional temperature gradient, and the coefficient of proportionality is also easily determined.
Abstract: The Charney problem for baroclinic instability involves the quasi-geostrophic instability of a zonal flow on a β plane where the zonal flow is characterized by a constant vertical shear. The atmosphere is non-Boussinesq and continuous. The solution of this problem involves confluent hypergeometric functions, and the mathematical difficulty of the problem, for the most part, has precluded extracting simple results of some generality. In this note, it is shown that there does exist a very simple, powerful approximate result for the growth rate of the most rapidly growing instability, viz., that this growth rate is linearly proportional to the surface meridional temperature gradient. The coefficient of proportionality is also easily determined. Moreover, the result extends to substantially more general profiles than those in the Charney problem.
TL;DR: In this article, a two-dimensional anelastic cloud model which incorporates detailed treatments of the water and ice phase is presented, where liquid phase processes considered include condensation, quasi-stochastic coalescence, fallout and breakup, while the ice phase processes include diffusional and accretional growth of ice particles.
Abstract: A two-dimensional anelastic cloud model which incorporates detailed treatments of the water and ice phase is presented. The liquid phase processes considered include condensation, quasi-stochastic coalescence, fallout and breakup, while the ice phase processes include diffusional and accretional growth of ice particles. Results of two cloud simulations are presented. The first case assumes an atmosphere with maritime cloud condensation nuclei (CCN) activation characteristics and considers the warm rain processes only. It was found that with the appearance of precipitation, the model-predicted supersaturations within updraft regions often reach values larger than 5% with respect to water. The second case assumes an atmosphere with continental CCN characteristics and includes the ice phase processes leading to the formation of graupel. The results of the second case illustrate the importance of cloud vertical motions in transporting ice particles from preferential nucleation regions in the upper po...
TL;DR: In this paper, the authors employed an annual mean insulation version of the recently developed GFDL 40-level general circulation model (GCM) to assess the stratospheric effects of two different perturbations: a uniform 50% reduction in ozone; and a uniform doubling of carbon dioxide.
Abstract: We have attempted to assess the stratospheric effects of two different perturbations: 1) a uniform 50% reduction in ozone; and 2) a uniform doubling of carbon dioxide. The primary studies employ an annual mean insulation version of the recently developed GFDL 40-level general circulation model (GCM). Supporting auxiliary calculations using purely radiative models are also presented. One of these, in which the thermal sensitivity is computed using the assumption that heating by dynamical processes is unaffected by changed composition, gives results which generally are in excellent agreement with those from the GCM. Exceptions to this occur in the ozone reduction experiment at the tropical tropopause and the tropical mesosphere. The predicted response to the ozone reduction is largest at 50 km in the tropics, where the temperature decreases by 25 K; at the tropical tropopause, the decrease is 5 K. The carbon dioxide increase results in a 10 K decrease at 50 km, decreasing to zero at the tropopause....
TL;DR: In this article, it was shown that entrainment leads to the generation of turbulence kinetic energy in a stratocumulus layer when the virtual temperature jump at the cloud top is weaker than a critical value.
Abstract: It is shown that entrainment leads to the generation of turbulence kinetic energy in a stratocumulus layer when the virtual temperature jump at the cloud top is weaker than a critical value. The critical value increases as the relative humidity of the air above the cloud top decreases. This result is interpreted as a criterion for the instability of the layer cloud to penetrative downdrafts. The role of the instability in determining the subtropical and tropical distributions of boundary-layer cloudiness is assessed.
TL;DR: In this article, the authors determined the instability of dry air mixing into a cloud top and derived the buoyancy-flux instability criterion based on a three-dimensional boundary-layer turbulence model with stratocumulus.
Abstract: The criterion for instability of dry air mixing into a cloud top is determined both graphically and mathematically. It is found to be identical to the buoyancy-flux instability criterion of Randall (1976) based on stratocumulus mixed-layer jump-model equations which yield a cloud top jump in θe, for marginal stability of order Δθe=−1 to −3 K (θe), is equivalent potential temperature). Numerical calculations from a three-dimensional boundary-layer turbulence model with stratocumulus are examined from the viewpoint of cloud top entrainment instability. The entrainment rate is found to increase decisively when Δθe, drops below the critical value. The resulting rapid entrainment is found to dry out the cloud from the bottom up, leaving the cloud-base height intact; in conjunction with the negative Δθe value, this causes ∂θe/∂z in the cloud layer to become negative. This in turn sets the stage for the final phase of stratocumulus breakup, whereby conditional instability of the first kind begins to ope...
TL;DR: In this paper, a semi-empirical theory is developed for evaluating the interaction of randomly oriented, nonspherical particles with the total intensity component of electromagnetic radiation, which is used when the particle size parameter x (ratio of particle circumference to wavelength) is less than some upper bound x sub zero (about 5).
Abstract: A semiempirical theory is developed which is based on simple physical principles and comparisons with laboratory measurements. The ultimate utility of this approach rests on its ability to successfully reproduce the observed single-scattering phase function for a wide variety of particle shapes, sizes and refractive indices. This approximate theory is developed for evaluating the interaction of randomly oriented, nonspherical particles with the total intensity component of electromagnetic radiation. Mie theory is used when the particle size parameter x (ratio of particle circumference to wavelength) is less than some upper bound x sub zero (about 5). For x greater than x sub zero, the interaction is divided into three components: diffraction, external reflection and transmission. The application of the theory is illustrated by considering the influence of the shape of tropospheric aerosols on their contribution to the earth's global albedo.
TL;DR: In this paper, the authors defined the nature of vertical air motion in and around GATE cumulonimbus clouds and analyzed time series of vertical velocity at a frequency of 1 Hz.
Abstract: This is the first part of a two-part paper defining the nature of the vertical air motion in and around GATE cumulonimbus clouds. The statistics are from a total of 104 km of flight legs, flown on six days in GATE, at altitudes from near the surface to 8100 m. The basic data sets analyzed are time series of vertical velocity at a frequency of 1 Hz. For the purpose of study, convective events are divided into two categories: drafts, requiring only that vertical velocity be continuously positive (negative) for 500 m and exceed an absolute value of 0.5 m s−1 for 1 s; and cores, the stronger portions of the stronger drafts, requiring that upward (downward) vertical velocity be continuously greater than an absolute value of 1 m s−1 for 500 m. The distributions of average vertical velocity, maximum vertical velocity, diameter and mass flux are given for drafts and cores at five altitude intervals between 150 m and 8 km. In all cases, the distributions are approximately log-normal. Above cloud base, upd...
TL;DR: In this article, the authors extended the two-dimensional slab-symmetric numerical cloud model used by Soong and Ogura (1973) for studying the evolution of an isolated cumulus cloud to investigate the statistical properties of cumulus clouds which would be generated under a given large-scale forcing composed of the horizontal advection of temperature and water vapor mixing ratio, vertical velocity, sea surface temperature and radiative cooling.
Abstract: The two-dimensional slab-symmetric numerical cloud model used by Soong and Ogura (1973) for studying the evolution of an isolated cumulus cloud is extended to investigate the statistical properties of cumulus clouds which would be generated under a given large-scale forcing composed of the horizontal advection of temperature and water vapor mixing ratio, vertical velocity, sea surface temperature and radiative cooling. Random disturbances of small amplitude are introduced into the model at low levels to provide random motion for cloud formation. The model is applied to a case of suppressed weather conditions during BOMEX for the period 22–23 June 1969 when a nearly steady state prevailed. The composited temperature and mixing ratio profiles of these two days are used as initial conditions and the time-independent large-scale forcing terms estimated from the observations are applied to the model. The result of numerical integration shows that a number of small clouds start developing after 1 h. So...
TL;DR: In this paper, the properties of convective drafts and cores are compared to results of previous work, and the implications of the results in Part I are discussed, as well as the results of Part II are discussed.
Abstract: The properties of convective drafts and cores are presented in Part I. By our definition a convective updraft must have a positive vertical velocity for 0.5 km, and exceed 0.5 m s−1 for 1 s; a convective updraft core must exceed 1 m s−1 for 0.5 km. Downdrafts and downdraft cores are defined analogously. Here the properties of the drafts and cores are compared to results of previous work. In addition, the implications of the results in Part I are discussed. GATE cores and drafts are comparable in size and intensity to those measured in hurricanes but weaker than those measured in continental thunderstorms. The lesser intensity seems related to the nearly moist adiabatic GATE sounding. The mass flux by GATE cores is consistent with large-scale requirements. It is fairly evenly distributed over a range of core size and intensity. Updraft core vertical velocity and diameter are positively correlated, primarily the result of a few large strong events. The vast majority of GATE convective cores are suf...
TL;DR: In this article, the first iteration of the recently developed nonlinear normal mode initialization procedure for primitive equation models leads to quasi-rotational dynamical and diagnostic equations agreeing with those of quasi-geostrephic theory in a simple Boussinesq f plane model.
Abstract: The first iteration of the recently developed nonlinear normal mode initialization procedure for primitive equation models leads to quasi-rotational dynamical and diagnostic equations agreeing with those of quasi-geostrephic theory in a simple Boussinesq f plane model. The proper initialization of a quasi-rotational model, however. requires a nonlinear modification of the geostrophic state traditionally used. Various generalizations are discussed briefly.
TL;DR: In this article, daily observations of albedo and outgoing terrestrial radiation derived from NOAA Scanning Radiometer measurements are used to relate cloudiness variations to regional features of the general circulation and to estimate the relative importance of the albedos and infrared effects of clouds on the net radiation balance of the earth on a regional basis.
Abstract: Daily observations of albedo and outgoing terrestrial radiation derived from NOAA Scanning Radiometer measurements are used to relate cloudiness variations to regional features of the general circulation and to estimate the relative importance of the albedo and infrared effects of clouds on the net radiation balance of the earth on a regional basis. The results indicate that there are clear relationships between the variability in outgoing IR and features of the atmospheric circulation, which appear to be linked to changes in cloudiness. A method requiring only measurements of planetary albedo and total outgoing IR is devised to evaluate the relative importance of the albedo and IR effects of the current distribution of cloud for the net radiation balance of the earth. The results obtained from this method suggest that globally the effect on the radiation balance of the high albedo of clouds is two or more times greater than the effect of clouds in reducing outgoing IR, so that an increase in the...
TL;DR: The two-dimensional cloud ensemble model developed by Soong and Ogura (1980) is used to simulate the response of deep clouds to mesoscale lifting using data obtained in the Global Atmospheric Research Program (GARP) Atlantic Tropical Experiment (GATE) as discussed by the authors.
Abstract: The two-dimensional cloud ensemble model developed by Soong and Ogura (1980) is used to simulate the response of deep clouds to mesoscale lifting using data obtained in the Global Atmospheric Research Program (GARP) Atlantic Tropical Experiment (GATE). The input to the model includes the mesoscale vertical velocity, horizontal advections of temperature and mixing ratio of water vapor, radiative cooling and sea surface temperature. The cloud ensemble feedback effects due to the condensation and evaporation of cloud liquid drops and vertical fluxes of heat and moisture are determined by the model. The simulated upward mass flux inside the model clouds is about three times the mass flux due to mesoscale lifting. The downward mass flux inside clouds is also large, leaving a small downward mass flux in the cloud-free area. The major portion of the heat flux is produced by the updraft inside clouds. On the other hand, the moisture fluxes due to both updraft and downdraft are important. In the cloud-fre...
TL;DR: In this article, a low-order primitive-equation (PE) model consisting of nine ordinary differential equations with bottom topography was derived from the shallow-water equations, and a loworder quasi-geostrophic (QG) model with three equations was derived by dropping the time derivatives in the divergence equations.
Abstract: The attractor set of a forced dissipative dynamical system is for practical purposes the set of points in phase-space which continue to be encountered by an arbitrary orbit after an arbitrary long time. For a reasonably realistic atmospheric model the attractor should be a bounded set, and most of its points should represent states of approximate geostrophic equilibrium. A low-order primitive-equation (PE) model consisting of nine ordinary differential equations is derived from the shallow-water equations with bottom topography. A low-order quasi-geostrophic (QG) model with three equations is derived from the PE model by dropping the time derivatives in the divergence equations. For the chosen parameter values, gravity waves which are initially present in the PE model nearly disappear after a few weeks, while the quasi-geostrophic oscillations continue undiminished. The states which are free of gravity waves form a three-dimensional stable invariant manifold within the nine-dimensional phase spac...
TL;DR: In this paper, a two-layer baroclinic model is used to study the planetary-scale motions of a thermally driven atmosphere in the presence of topography, and in doing so to extend previous results obtained with a barotropic model.
Abstract: A two-layer baroclinic model is used to study the planetary-scale motions of a thermally driven atmosphere in the presence of topography, and in doing so to extend previous results obtained with a barotropic model. Highly truncated spectral equations are used to obtain multiple wavelike stationary equilibrium states, to examine the instabilities that produce them, and to study the instabilities that feed on them and give rise to traveling planetary waves. Although the equilibria cannot exist without orography, their energy comes from the potential energy of the mean flow, not from kinetic energy transfer via the mountain torque. Low-index (blocking) equilibria as well as high-index equilibria require a large thermal driving and are associated with both orographic and baroclinic instability of the Hadley circulation. It is suggested that blocking in nature is a quasi-stable circulation arising from orographic instability with strong thermal driving; and that observed low-frequency, propagating planetary waves are due to instabilities of the quasi-stationary, topographically forced equilibria.
TL;DR: The GFDL 11-level general circulation/tracer model was used for two experiments designed to prepare the way for a self-consistent model of atmospheric ozone as mentioned in this paper, which showed remarkably similar behavior in the lower stratosphere.
Abstract: The GFDL 11-level general circulation/tracer model is used for two experiments designed to prepare the way for a self-consistent model of atmospheric ozone. The first experiment invokes a very simple condition at the top model level, an instantaneous relaxation to a specified 10 mb average observed ozone value. The tracer is inert below the top level until it is removed in the lower troposphere. The second experiment introduces a simplified, but reasonably realistic ozone chemistry at the top level including Chapman, nitrogen and hydrogen loss processes. Below the top level, ozone is inert, and is removed in the lower troposphere by the same mechanism as in the first experiment. These two experiments, in spite of their very different middle stratospheres, show remarkably similar behavior in the lower stratosphere. A comparison of model values and fluxes with available observations shows general qualitative agreement as well as some notable discrepancies. In the second experiment, a detailed analy...
TL;DR: In this paper, a mean-field closure approach was used to develop scaling expressions for the structure parameters generated by the entrainment process at the top of a convective boundary layer.
Abstract: The refractive index structure parameter CN2 has contributions from the temperature and humidity structure parameters Cr2 and CQ2 and from the joint structure parameter CTQ. We briefly review the behavior of these structure parameters in the surface layer. We show that the surface-layer similarity expressions for Cr2, CTQ and CQ2 yield, in the unstable limit, mixed-layer scaling laws which are in good agreement with data at small z/zi, where zi is the mixed-layer depth. However, we show that entrainment effects cause large departures from these laws in mid and upper regions of the convective boundary layer. Using Deardorff's idealization of the structure of the interfacial region at the top of a convective boundary layer, we use a “mean-field closure” approach to develop scaling expressions for the structure parameters generated by the entrainment process there. The available data on CT2, CTQ and CQ2 near the convective boundary-layer top, from both steady and evolving cases, are shown to be cons...