Seidel, D J., J K Angell, A Robock, B Hicks, K Labitzke, John R Lanzante, J Logan, Jerry D Mahlman, V Ramaswamy, W J Randel, E Rasmusson, R Ross, and S F Singer, 2005: Jim Angell's contributions to meteorology. Bulletin of the American Meteorological Society, 86(3), DOI:10.1175/BAMS-86-3-403.
Mahlman, Jerry D., and Ronald J Stouffer, 2002: Projection of future changes in climate In Encyclopedia of Global Environmental Change, Vol. I, Chichester, UK, John Wiley & Sons, 126-139.
Mahlman, Jerry D., 2001: Human-caused climate warming: Implications for practically everything In Solutions for an Environment in Peril, Baltimore, MD, The Johns Hopkins University Press, 141-155.
Eluszkiewicz, J, Richard S Hemler, Jerry D Mahlman, Lori Bruhwiler, and L L Takacs, 2000: Sensitivity of age-of-air calculations to the choice of advection scheme. Journal of the Atmospheric Sciences, 57(19), 3185-3201. Abstract PDF
The age of air has recently emerged as a diagnostic of atmospheric transport unaffected by chemical parameterizations, and the features in the age distributions computed in models have been interpreted in terms of the models' large-scale circulation field. This study shows, however, that in addition to the simulated large-scale circulation, three-dimensional age calculations can also be affected by the choice of advection scheme employed in solving the tracer continuity equation. Specifically, using the 3.0º latitude x 3.6º longitude and 40 vertical level version of the Geophysical Fluid Dynamics Laboratory SKYHI GCM and six online transport schemes ranging from Eulerian through semi-Lagrangian to fully Lagrangian, it will be demonstrated that the oldest ages are obtained using the nondiffusive centered-difference schemes while the youngest ages are computed with a semi-Lagrangian transport (SLT) scheme. The centered-difference schemes are capable of producing ages older than 10 years in the mesosphere, thus eliminating the "young bias" found in previous age-of-air calculations.
At this stage, only limited intuitive explanations can be advanced for this sensitivity of age-of-air calculations to the choice of advection scheme. In particular, age distributions computed online with the National Center for Atmospheric Research Community Climate Model (MACCM3) using different varieties of the SLT scheme are substantially older than the SKYHI SLT distribution. The different varieties, including a noninterpolating-in-the-vertical version (which is essentially centered-difference in the vertical), also produce a narrower range of age distributions than the suite of advection schemes employed in the SKYHI model. While additional MACCM3 experiments with a wider range of schemes would be necessary to provide more definitive insights, the older and less variable MACCM3 age distributions can plausibly be interpreted as being due to the semi-implicit semi-Lagrangian dynamics employed in the MACCM3. This type of dynamical core (employed with a 60-min time step) is likely to reduce SLT's interpolation errors that are compounded by the short-term variability characteristic of the explicit centered-difference dynamics employed in the SKYHI model (time step of 3 min). In the extreme case of a very slowly varying circulation, the choice of advection scheme has no effect on two-dimensional (latitude- height) age-of-air calculations, owing to the smooth nature of the transport circulation in 2D models.
These results suggest that nondiffusive schemes may be the preferred choice for multiyear simulations of tracers not overly sensitive to the requirement of monotonicity (this category includes many greenhouse gases). At the same time, age-of-air calculations offer a simple quantitative diagnostic of a scheme's long-term diffusive properties and may help in the evaluation of dynamical cores in multiyear integrations. On the other hand, the sensitivity of the computed ages to the model numerics calls for caution in using age of air as a diagnostic of a GCM's large-scale circulation field.
Pawson, S, K Kodera, Kevin P Hamilton, T G Shepherd, S R Beagley, B A Boville, J D Farrara, T D A Fairlie, A Kitoh, W A Lahoz, U Langematz, E Manzini, R John Wilson, and Jerry D Mahlman, et al., 2000: The GCM-reality intercomparison project for SPARC (GRIPS): scientific issues and initial results. Bulletin of the American Meteorological Society, 81(4), 781-796. Abstract
To investigate the effects of the middle atmosphere on climate, the World Climate Research Programme is supporting the project "Stratospheric Processes and their Role in Climate" (SPARC). A central theme of SPARC, to examine model simulations of the coupled troposphere-middle atmosphere system, is being performed through the initiative called GRIPS (GCM-Reality Intercomparison Project for SPARC). In this paper, an overview of the objectives of GRIPS is given. Initial activities include an assessment of the performance of middle atmosphere climate models, and preliminary results from this evaluation are presented here. It is shown that although all 13 models evaluated represent most major features of the mean atmospheric state, there are deficiencies in the magnitude and location of the features, which cannot easily be traced to the formulation (resolution or the parameterizations included) of the models. Most models show a cold bias in all locations, apart from the tropical tropopause region where they can be either too warm or too cold. The strengths and locations of the major jets are often misrepresented in the models. Looking at three-dimensional fields reveals, for some models, more severe deficiencies in the magnitude and positioning of the dominant structures (such as the Aleutian high in the stratosphere), although undersampling might explain some of these differences from observations. All the models have shortcomings in their simulations of the present-day climate, which might limit the accuracy of predictions of the climate response to ozone change and other anomalies forcing.
Changes in Heat Index (a combined measure of temperature and humidity) associated with global warming are evaluated based on the output from four extended integrations of the GFDL coupled ocean-atmosphere climate model. The four integrations are: a control with constant levels of atmospheric carbon dioxide (CO2), a second integration in which an estimate of the combined radiative forcing of greenhouse gases and sulfate aerosols over the period 1765-2065 is used to force the model, and a third (fourth) integration in which atmospheric CO2 increases at the rate of 1% per year to double (quadruple) its initial value, and is held constant thereafter. While the spatial patterns of the changes in Heat Index are largely determined by the changes in surface air temperature, increases in atmospheric moisture can substantially amplify the changes in Heat Index over regions which are warm and humid in the Control integration. The regions most prone to this effect include humid regions of the Tropics and summer hemisphere extra-tropics, including the southeastern United States, India, southeast Asia and northern Australia.
Koshyk, J N., Kevin P Hamilton, and Jerry D Mahlman, 1999: Simulation of the k-5/3 mesoscale spectral regime in the GFDL SKYHI general circulation model. Geophysical Research Letters, 26(7), 843-846. Abstract
Data from very high horizontal resolution simulations with the Geophysical Fluid Dynamics Laboratory SKYHI general circulation model are used to calculate the kinetic energy spectrum as a function of horizontal wavenumber, k, in the upper troposphere. The spectrum shows the familiar ~ -3 slope at scales longer than ~ 1000 km, in agreement with previous general circulation model and observational studies. At shorter scales, the spectrum becomes shallower with a slope ~ -5/3, also in agreement with available observations. The -5/3 slope spans about a decade of the resolved scales and this result represents the first successful simulation of such a broad range of the mesoscale regime by a global model. Partitioning of the flow between rotational and divergent components shows that the rotational part dominates at large scales and that there is approximate equipartition between rotational and divergent parts at mesoscales. Analysis of the parameterized kinetic energy dissipation shows that vertical diffusion dominates horizontal diffusion for a wide range of wavenumbers extending well into the k-5/3 regime.
Fan, Songmiao, M Gloor, Jerry D Mahlman, Stephen W Pacala, Jorge L Sarmiento, T Takahashi, and P P Tans, 1998: A large terrestrial carbon sink in North America implied by atmospheric and oceanic carbon dioxide data and models. Science, 282(5388), 442-446. Abstract PDF
Atmospheric carbon dioxide increased at a rate of 2.8 petagrams of carbon per year (Pg C year-1) during 1988 to 1992 (1 Pg = 1015 grams). Given estimates of fossil carbon dioxide emissions, and net oceanic uptake, this implies a global terrestrial uptake of 1.0 to 2.2 Pg C year-1. The spatial distribution of the terrestrial carbon dioxide uptake is estimated by means of the observed spatial patterns of the greatly increased atmospheric carbon dioxide data set available from 1988 onward, together with two atmospheric transport models, two estimates of the sea-air flux, and an estimate of the spatial distribution of fossil carbon dioxide emissions. North America is the best constrained continent, with a mean uptake of 1.7 ± 0.5 Pg C year-1, mostly south of 51 degrees north. Eurasia-North Africa is relatively weakly constrained, with a mean uptake of 0.1 ± 0.6 Pg C year-1. The rest of the world's land surface is poorly constrained, with a mean source of 0.2 ± 0.9 Pg C year-1.
Mahlman, Jerry D., 1998: Science and nonscience concerning human-caused climate warming. Annual Review of Energy and the Environment, 23, 83-105. Abstract PDF
The human-caused global warming problem is now the focus of intense international attention in many sectors of society. As we learn more about the science of the problem, the sense of controversy about the state of the science has actually increased, sharply so over the past decade. This essay highlights the fundamental aspects of the science underlying global warming. The vital roles of climate models and of climate data in sharpening scientific understanding are featured. Finally, the roles of controversy in the science and the sociology of this problem are addressed, and new insights are offered on the inevitability of future major conflicts and controversies as society begins to deal with the need to either reduce the use of fossil fuels considerably or adapt to substantial changes in Earth's climate.
Christensen, N, and Jerry D Mahlman, et al., 1997: Global Climate Change: Policy Making in the Context of Scientific and Economic Uncertainty, The Annapolis Center, Annapolis, MD: 15pp.
Mahlman, Jerry D., 1997: Dynamics of transport processes in the upper troposphere. Science, 276(5315), 1079-1083. Abstract PDF
A number of key problems in atmospheric chemistry are shaped by the strength and character of the various mechanisms acting to move and mix air in the upper troposphere. These transport processes are examined from a mechanistic perspective, with primary emphasis on the tropopause and middle-troposphere regions in the extratropics. The roles of vertical and horizontal transport "barriers" are explored, including the processes by which such barriers are created and are overcome. These transport considerations lead to a hypothesis concerning the processes that shape the tropopause itself. Some perspectives are offered on the still immature subject of transport in the upper troposphere of the tropics.
Mahlman, Jerry D., 1997: A scientist's perspective on integrated observing and long-term monitoring systems In 1st Symposium on Integrated Observing Systems, Boston, MA, American Meteorological Society, 76-78.
Mahlman, Jerry D., 1997: Uncertainties in projections of human-caused climate warming. Science, 278(5342), 1416-1417. PDF
Hamilton, Kevin P., R John Wilson, Jerry D Mahlman, and L Umscheid, 1995: Climatology of the SKYHI troposphere-stratosphere-mesosphere general circulation model. Journal of the Atmospheric Sciences, 52(1), 5-43. Abstract
The long-term mean climatology obtained from integrations conducted with different resolutions of the GFDL "SKYHI" finite-difference general circulation model is examined. A number of improvements that have been made recently in the model are also described. The versions considered have <3°C x <3.6°C, <2° x <2.4°C, and <1° x <1.2°C latitude-longitude resolution, and in each case the model is run with 40 levels from the ground to 0.0096 mb. The integrations all employ a fixed climatological cycle of sea surface temperature. Over 25 years of integration with the <3°C model and shorter integrations with the higher-resolution versions are analyzed. Attention is focused on the December-February and June-August periods.
The model does a reasonable job of representing the atmospheric flow in the troposphere and lower stratosphere. The simulated tropospheric climatology has an interesting sensitivity to horizontal resolution. In common with several spectral GCMs that have been examined earlier, the surface zonal-mean westerlies in the SKYHI extratropics become stronger with increasing horizontal resolution. However, this "zonalization" of the flow with resolution is not as prominent in the upper troposphere of SKYHI as it is in some spectral models. It is noteworthy that--without parameterized gravity wave drag--the SKYHI model at all three resolutions can simulate a realistic separation of the subtropical and polar night jet streams and a fairly realistic strength of the lower-stratospheric winter polar vortex.
The geographical distribution of the annual-mean and seasonal precipitation are reasonably well simulated. When compared against observations in an objective manner, the SKYHI global precipitation simulation is found to be as good or better than that obtained by other state-of-the-art general circulation models. However, some significant shortcomings remain, most notably in the summer extratropical land areas and in the tropical summer monsoon regions. The time-mean precipitation simulation is remarkably insensitive to the horizontal model resolution employed. The other tropospheric feature examined in detail is the tropopause temperature. The whole troposphere suffers from a cold bias of the order of a few degrees Celcius, but in the <3°C SKYHI model this grows to about <6°C at 100 mb. Interestingly, the upper-tropospheric bias is reduced with increasing horizontal resolution, despite that the cloud parameters in the radiation code are specified identically in each version.
The simulated polar vortex in the Northern Hemisphere winter in the upper stratosphere is unrealistically confined to high latitudes, although the maximum zonal-mean zonal wind is close to observed values. Near the strato- pause the June-August mean temperatures at the South Pole are colder than observations by ~<65°C, < 50°C, and <30°C in the < 3°C, <2°C, and < 1°C simulations, respectively. The corresponding zonal-mean zonal wind patterns display an unrealistically strong polar vortex. The extratropical stratospheric stationary wave field in the Northern Hemisphere winter is examined in some detail using the multi- year averages available from the <3°C SKYHI integration. Comparison with comparable long-term mean observations suggests that the model captures the amplitude and phase of the stationary waves rather well.
The SKYHI model simulates the reversed equator-pole temperature gradient near the summer mesopause. The simulated summer polar mesopause temperatures decrease with increasing horizontal resolution, although even at <1 degree C resolution the predicted temperatures are still warmer than observed. The increasing resolution is accompanied by increased westerly driving of the mean flow in the summer mesosphere by dissipating gravity waves. The present results suggest that the SKYHI model does explicitly resolve a significant component of the gravity waves required to produce the observed summer mesopause structure. The seminannual oscillation near the tropical stratopause is reasonably well simulated in the < 3°C version. The main deficiency is in the westerly phase, which is not as strong as observed. There is also a second peak in the amplitude of the semiannual wind oscillation at the top model level (0.0096 mb) corresponding to the observed mesopause semiannual oscillation. This simulated mesopause oscillation is weaker (by a factor of ~3) than that observed. The simulation in the tropical stratopause and mesosphere changes quite significantly with increasing resolution, however, in the tropical lower stratosphere of the <3°C model the zonal-mean zonal wind displays a very weak (~3 m s-1 peak to peak) interannual variation, which--while rather irregular--does display a roughly biennial period and the downward phase propagation that is characteristic of the observed quasibiennial oscillation.
Mahlman, Jerry D., 1995: Toward a scientific centered climate monitoring system. Climatic Change, 31, 223-230.
Mahlman, Jerry D., J P Pinto, and L Umscheid, 1994: Transport, radiative, and dynamical effects of the antarctic ozone hole: A GFDL. Journal of the Atmospheric Sciences, 51(4), 489-508. Abstract PDF
The GFDL "SKYHI" general circulation model has been used to simulate the effect of the Antarctic "ozone hole" phenomenon on the radiative and dynamical environment of the lower atmosphere. Both the polar ozone destruction and photochemical restoration chemistries are calculated by parameterized simplifications of the still somewhat uncertain chemical processes. The modeled total column ozone depletions are near 25% in spring over Antarctica, with 1% depletion reaching equatorial latitudes by the end of the 4 1/2-year model experiment. In the lower stratosphere, ozone reductions of 5% reach to the equator. Large coolings of about 8 K are simulated in the lower stratosphere over Antarctica in late spring, while a general cooling of about 1-1.5 K is present throughout the Southern Hemisphere lower stratosphere. The model atmosphere experiences a long-term positive temperature-chemical feedback because significant ozone reductions carry over into the next winter. The overall temperature response to the reduced ozone is essentially radiative in character. However, substantial dynamical changes are induced by the ozone hole effect. The Antarctic middle stratosphere in late spring warms by about 6 K over Antarctica and the lower midlatitude stratosphere warms by approximately 1 K. These warming spots are produced mainly by an increased residual circulation intensity. Also, the Antarctic vortex becomes tighter and more confined as a result of the reduced ozone. These two dynamical effects combine to steepen the meridional slope of quasi-conservative trace constituent isolines. Thus, the entire transport, radiative, and dynamical climatology of the springtime stratosphere is affected to an important degree by the ozone hole phenomenon. Over the entire year, however, these dynamical effects are considerably smaller.
Strahan, S, and Jerry D Mahlman, 1994: Evaluation of the SKYHI general circulation model using aircraft N2O measurements 1. Polar winter stratospheric meteorology and tracer morphology. Journal of Geophysical Research, 99(D5), 10,305-10,318. Abstract PDF
Winter polar stratospheric nitrous oxide (N2O) measurements made during two NASA polar aircraft field campaigns are used to evaluate the dynamics of the Geophysical Fluid Dynamics Laboratory's `SKYHI' general circulation model. SKYHI has 1° latitude by 1.2° longitude grid spacing and 40 vertical levels (up to 80 km) and prescribed N2O dissociation coefficients. The model has been integrated a total of 20 months, producing one Antarctic and two Arctic winters. The climtologies of these winters are compared with the known northern and southern hemisphere climatologies and to the meteorological conditions during the time of the field campaigns. The two Arctic SKYHI winters show considerable interannual variability. In the lower stratosphere, SKYHI realistically simulates the magnitude and variability of winds and temperatures both inside and outside the polar vortex and can produce a credible sudden warming. In the Antarctic, the magnitude and variability of winds and temperatures around the polar vortex are quite realistic, but inside the vortex, temperatures are too low. Flight data from each mission have been averaged together to produce a contour map showing N2O morphology in and around the vortex. Because the N2O distribution in the lower stratosphere is under dynamical control, the mean N2O field can be used to interpret the dynamics of the polar stratosphere. At the Arctic vortex edge, AASE data show large gradients of N2O on isentropic surfaces, SKYHI vortex edge gradients are nearly as large, and model mixing ratios between 400 and 500 K (potential temperature) are similar to the observations. In the Antarctic, model mixing ratios are too high everywhere and the edge gradients are flatter than the observed gradients. The comparison of mean N2O fields suggests realistic wave activity in the SKYHI Antarctic winter.
Strahan, S, and Jerry D Mahlman, 1994: Evaluation of the SKYHI general circulation model using aircraft N2O measurements 2. Tracer variability and diabatic meridional circulation. Journal of Geophysical Research, 99(D5), 10,319-10,332. Abstract PDF
Winter polar stratospheric nitrous oxide (N2O) measurements made during two NASA polar aircraft field campaigns provide a unique opportunity to evaluate the performance of the 1 degree latitude resolution version of the Geophysical Fluid Dynamics Laboratory's `SKYHI' general circulation model. This high-resolution model has been integrated 20 months, producing one Antarctic and two Arctic winters. Power spectra of the dynamically controlled tracer N2O are used as a diagnostic of wave activity. Comparison of the spectra of SKYHI and the observations shows that the SKYHI Arctic winter lower stratosphere is dynamically active enough to generate realistic mesoscale tracer variability but that the SKYHI Antarctic has deficient variability at scales of 220-3000 km. Low-pass filtering is applied to a new type of analysis that attempts to discriminate between different sources of atmospheric variability, to the extent that different sources are characterized by different timescales. The goal is to diagnose mesoscale sources of tracer variability in the model and in the observations and then to assess whether SKYHI generates variability for the right physical reasons. This analysis shows that variability from `slow' processes such as planetary wave breaking dominates and is generated in realistic amounts in the SKYHI Arctic winters. The SKYHI Antarctic vortex shows insufficient `debris' from planetary wave breaking at scales below 700 km. The balance between diabatic descent inside the vortex and wave breaking in the `surf zone' generates N2O gradients at the vortex edge in the model and the real atmosphere. Because the diabatic circulation is driven by wave activity, the strength of model wave activity diagnosed by the spectral analysis and the mean N2O gradients can be used to evaluate SKYHI's diabatic circulation and net tracer transport. In the Arctic, SKYHI temperatures, spectral results, and realistic N2O gradients at the vortex edge suggest a reasonable diabatic meridional circulation and transport. Antarctic spectral results, low vortex temperatures, and flatter N2O gradients at the edge all support the conclusion that the diabatic circulation and wave activity in the model southern hemisphere is too weak.
Mahlman, Jerry D., 1992: Assessing global climate change: When will we have better evidence? In Climate Change and Energy Policy, New York, NY, American Institute of Physics, 17-31.
Mahlman, Jerry D., 1992: A looming Arctic ozone hole?Nature, 360(6401), 209-210. PDF
Mahlman, Jerry D., 1992: Understanding climate change In Climate Research Needs Workshop, November 19-22, 1991, Washington, D.C, Science and Policy Associates, Inc, 1-16.
Wallace, J M., D J Baker, M L Blackmon, Jerry D Mahlman, and J Shukla, 1991: Prospects for Extending the Range of Prediction of the Global Atmosphere, Washington, DC: National Academy Press, 33 pp.
To examine the effects of horizontal resolution on internal gravity waves simulated by the 40-level GFDL "SKYHI" general circulation model, a comparison is made between the 3 degree and 1 degree resolution models during late December. The stratospheric and mesospheric zonal flows in the winter and summer extratropical regions of the 1 degree model are much weaker and more realistic than the corresponding zonal flows of the 3 degree model. The weaker flows are consistent with the stronger Eliassen-Palm flux divergence (EPFD).
The increase in the magnitude of the EPFD in the winter and summer extratropical mesospheres is due mostly to the increase in the gravity wave VMFC. In the winter extratropical mesosphere, the increase of VMFC associated with large-scale eastward moving components also accounts for part of the increase in the gravity wave VMFC.
The gravity waves in the summer and winter mesosphere of the 1 degree model are associated with a broader frequency-spectra distribution, resulting in a more sporadic time-distribution of their VMFC. This broadening is due not only to the increase in resolvable horizontal wavenumbers but also occurs in the large-scale components owing to wave-wave interactions. It was found that the phase velocity and frequency of resolvable small-scale gravity waves are severely underestimated by finite difference approximations.
Mahlman, Jerry D., 1989: Mathematical modeling of greenhouse warming: How much do we know? In Global Change and Our Common Future, Papers From a Forum, Washington, DC, National Academy Press, 62-72.
Mahlman, Jerry D., 1989: Theoretical projections of stratospheric change due to increasing greenhouse gases and changing ozone concentrations In Ozone Depletion, Greenhouse Gases, and Climate Change, Washington, DC, National Academy Press, 66-78.
Mahlman, Jerry D., A F Tuck, and Ian E Galbally, 1989: The role of greenhouse gases in global chemical-dynamical processes In Report of the Tenth Session of the Joint Scientific Committee, Appendix B, Geneva, Switzerland, World Meteorological Organization, 1-11.
Brasseur, G P., and Jerry D Mahlman, et al., 1988: Group report: changes in antarctic ozone In The Changing Atmosphere, F. S. Rowland, and I. S. A. Isaksen, eds. New York, NY, John Wiley & Sons, 235-256.
Hamilton, Kevin P., and Jerry D Mahlman, 1988: General circulation model simulation of the semiannual oscillation of the tropical middle atmosphere. Journal of the Atmospheric Sciences, 45(21), 3212-3235. Abstract
A study has been made of the evolution of the zonal-mean zonal wind and temperature in a multiyear integration of the 40-level, 3° x 3.6° resolution "SKYHI" general circulation model (GCM) that has been developed at GFDL. In the tropical upper stratosphere the mean wind variation is dominated by a strong semiannual oscillation (SAO). The peak SAO amplitude in the model is almost 25 m s-1 and occurs near the 1 mb level. The phase of the SAO near the stratopause is such that maximum westerlies occur shortly after the equinoxes. These features are in good agreement with the available observations. In addition the meridional width of the stratopause SAO in the GCM compares well with observations.
A diagnostic analysis of the zonal-mean momentum balance near the tropical stratopause was performed using the detailed fields archived during the GCM integration. It appears that the easterly accelerations in the model SAO are provided by a combination of (i) divergence of the meridional component of the Eliassen-Palm flux associated with quasi-stationary planetary waves and (ii) mean angular momentum advection by the residual meridional circulation. The effects of the residual circulation dominate in the summer hemisphere, while the eddy contributions are more important in the winter hemisphere. The westerly accelerations in the model SAO result from the convergence of the vertical momentum transport associated with gravity waves that have a broad distribution of space and time scales. Thus, in contrast to some simple theoretical models, large-scale equatorial Kelvin waves appear to play only a very minor role in the dynamics of the SAO in the SKYHI GCM.
A second equatorial SAO amplitude maximum was found in the tropical upper mesosphere of the GCM. this apparently corresponds to the mesopause SAO that has been identified in earlier observational studies. While the observed phase of this oscillation is reproduced in the model, the simulated amplitude is unrealistically small.
The model integration included the computation of the concentration of N2O. The results show a fairly realistic simulation of the semiannual variation of tropical stratospheric N2O mixing ratio seen in satellite observations.
Mahlman, Jerry D., and L Umscheid, 1987: Comprehensive modeling of the middle atmosphere: the influence of horizontal resolution In Transport Processes in the Middle Atmosphere, Boston, MA, Reidel Publishing Co, 251-266. Abstract
Results are presented from the GFDL "SKYHI" general circulation model that illuminate the effects of increasing horizontal grid resolution. The model experiments reveal a very pronounced improvement of simulation skill at the highest resolution tested (1° latitude grid size). The zonal wind climatology is particularly affected with dramatic improvements in the stratospheric winter westerlies and the positions of the tropospheric subtropical jet streams. These improvements are apparently related to increases in tropospheric wave forcing, specifically the Eliassen-Palm flux. The 1 degree resolution model has successfully simulated a major mid-stratospheric sudden warming event. Some preliminary analysis and insights on the causes and character of the sudden warming event are presented.
Plumb, R A., and Jerry D Mahlman, 1987: The zonally averaged transport characteristics of the GFDL general circulation/transport model. Journal of the Atmospheric Sciences, 44(2), 298-327. Abstract PDF
The GFDL general circulation/tracer model has been used to generate the transport coefficients required in two-dimensional (zonally averaged) transport formulations. This was done by assuming a flux-gradient relationship and then, given gradient and flux statistics from two independent (and contrived) model tracer experiments, to derive the coefficients by inversion of this relation. Given the mean meridional circulation from the GCM, the antisymmetric and symmetric parts of the coefficients tensor determine the advective and diffusive contributions to the net meridional transport in the model. The effective transport circulation thus defined differs substantially from the Lagrangian mean and residual circulations and is in fact a simpler representation of the model circulation than either of these.
The diffusive component is coherently structured, comprising the following components:
Strong quasi-horizontal mixing in the midlatitude lower troposphere, apparently associated with fronts and the occlusion of synoptic systems.
A band of stronquasi-horizontal mixing stretching across the tropical upper troposphere and the subtropical winter stratosphere. This band follows the band of weak zonal mean winds and is a manifestation in the model of the "surf zone" recently identified by McIntyre and Palmer as a region of breaking planetary waves. Outside the "surf zone," in the stratosphere, consistent with other recent estimates.
Intense vertical mixing in the troposphere at and near the latitudes of the intertropical convergence zone.
Vertical mixing through much of the troposphere, a substantial component of which is associated with subgrid-scale mixing (model convective processes).
The validity of the flux-gradient relation as a parameterization of eddy transport processes was tested by implementing the parameterization in a two-dimensional model, using these derived coefficients. In comparison experiments it was found that the two-dimensional model could reproduce well the zonally-averaged evolution of tracers in the GCM; the quantitative errors that were found may in part result from the finite model resolution, rather than from errors in formulation. Therefore, although the flux-gradient relations is formally justified only in the small-amplitude limit, it appears to be a useful practical description of large-scale transport by finite amplitude eddies.
Ramanathan, V, and Jerry D Mahlman, et al., 1987: Climate-chemical interactions and effects of changing atmospheric trace gases. Reviews of Geophysics, 25(7), 1441-1482. Abstract PDF
The problem concerning the greenhouse effects of human activities has broadened in scope from the CO2-climate problem to the trace gas-climate problem. The climate effects of non-CO2 trace gases are strongly governed by interactions between chemistry, radiation, and dynamics. We discuss in detail the nature of the trace gas radiative heating and describe the importance of radiative-chemical interactions within the troposphere and the stratosphere. We make an assessment of the trace gas effects on troposphere-stratosphere temperature trends for the period covering the preindustrial era to the present and for the next several decades. Non-CO2 greenhouse gases in the atmosphere are now adding to the greenhouse effect by an amount comparable to the effect of CO2. The rate of decadal increase of the total greenhouse forcing is now 3-6 times greater than the mean rate for the period 1850-1960. Time-dependent calculations with a simplified one-dimensional diffusive ocean model suggest that a surface warming about 0.4 - 0.8 K should have occurred during 1850 to 1980. For the various trace gas scenarios considered in this study, the equilibrium surface warming for the period 1980 to 2030 ranges from 0.8 to 4.1 K. This wide range in the projected warming is due to the range in the assumed scenario as well as due to the threefold uncertainty in the sensitivity of climate models. For the 180-year period from 1850 to 2030, our analysis suggests a trace gas-induced cumulative equilibrium surface warming in the range of 1.5 to 6.1 K. The important non-CO2 greenhouse gases are CFCl3, CF2Cl2, CH4, N2O, O3, and stratospheric H2O. Chlorofluorocarbons (CFCs) (mainly CFCl3, and C2Cl2), through their indirect chemical effects on O3, have a potentially large stratospheric cooling effect, as large as that due to a CO2 increase. In addition to the direct radiative effect, many of the trace gases have indirect effects on climate. For example, addition of gases such as CH4, CO, and NOx can alter tropospheric O3, which is a radiatively active gas. Within the troposphere the indirect climate effects can be as large as the direct effects. On the other hand, within the stratosphere, temperature changes are largely determined by indirect effects of CFCs. Trace gases can also influence stratospheric H2O through their effect on tropical tropopause temperatures. Furthermore, increases in tropospheric H2O, through the temperature-H2O feedback, can perturb tropospheric chemistry and alter the concentration of CH4 and O3. The fundamental issue that needs to be addressed within the context of the trace gas-climate problem is the relative importance of transport, chemistry, and the indirect effects of trace gases in governing the long-term trends of tropospheric and stratospheric O3, CH4, and stratospheric H2O. Cloud feedback continues to be the major source of uncertainty in the surface temperature sensitivity of climate models. At present, the sign of this feedback is not known. The ocean sequesters the trace gas radiative heating into its interior and thus delays the equilibrium warming. The estimated e-folding time for the approach to equilibrium varies from a few decades to a century and depends nonlinearly on l-1 and linearly on k where l is the climate feedback parameter and k is the effective ocean thermal diffusivity. The magnitude of l, which also governs the equilibrium surface warming, is governed strongly by radiative and dynamical processes in the atmosphere, and hence the effect of oceans on transient climate change is determined by the interactions between atmospheric and oceanic dynamical as well as radiative processes. The next crucial issue concerns accurate determination of decadal trends in radiative forcings, trace gases, planetary albedo (to determine effects of aerosols and cloud feedback), and surface-troposphere-stratosphere temperatures. The observational challenges are formidable and must be overcome for a scientifically credible interpretation of the human impacts on climate.
A hypothesis is advanced that natural dynamical processes might explain much of the observed late winter ozone decreases over Antarctica. For this to be the case, sometime after 1979 there must have been a substantial reduction of the wintertime planetary-scale disturbance activity in the Southern Hemisphere troposphere. The expected stratospheric response to such a natural process is to reduce wintertime polar ozone, prolong the life of the polar vortex, reduce the transport of ozone out of the middle stratosphere, and to increase the possibility of polar rising motion shortly after the return of the sun to high latitudes. All of these effects are in qualitative agreement with the observed ozone changes.
The Geophysical Fluid Dynamics Laboratory (GFDL) three-dimensional general circulation/tracer model has been used to investigate the stratospheric behavior of N2O under a range of photodestruction hypotheses. A comparison of observations with these simulations shows that the atmospheric N2O lifetime lies between 100 and 130 years. For the three experiments conducted, it was found that the model-derived global one-dimensional eddy diffusion coefficients Kz for one experiment are appropriate for the other two experiments as well. In addition, the meridional slopes of N2O mixing ratio isolines are virtually identical in the lower stratosphere for all three experiments. The generality of these two results was explored with a simple "two-slab" model. In this model the equilibrium meridional slopes of trace gas isolines and Kz values are solved directly. The model predicts that long-lived gases with weak photodestruction rates should have similar meridional slopes, but the effect of faster destruction is to flatten the meridional slopes. The simple model also predicts that Kz depends upon chemical processes through a direct dependence upon the meridional slope for a given gas as well as upon the intensity with which upward propagating tropospheric disturbances force the stratospheric zonal winds. The three N2O experiments have been compared against detailed observational analyses. These analyses show that the model meridional N2O slopes are too flat by about 30%. The simple two-slab model indicates that this results from a somewhat weak forcing of the model stratospheric zonal winds. A comparison of the temporal variability of model N2O against the "Delta" statistics of Ehhalt et al. (1983) shows good agreement. Another simple theoretical model is proposed that shows why Delta statistics are so useful and predicts the circumstances under which different destruction chemistries should lead to different Delta statistics. These results have allowed a very general extrapolation of the three N2O numerical experiments to predicted structure for a wide class of long-lived trace gases. Specifically, the supporting theoretical developments allow predictions for the effect of chemistry on the global (one-dimensional) behavior, meridional-height (two-dimensional) structure and local temporal variability. Finally, some examples of transient behavior are presented through model time series at points corresponding to available measurements. These time series, with the support of horizontal N2O charts, show complex behavior, including pronounced seasonal cycles, transport-produced N2O "inversions", and detailed meridional transport events associated with transient stratospheric disturbances.
Miyahara, S, Yoshikazu Hayashi, and Jerry D Mahlman, 1986: Interactions between gravity waves and planetary-scale flow simulated by the GFDL "SKYHI" general circulation model. Journal of the Atmospheric Sciences, 43(17), 1844-1861. Abstract PDF
In order to study interactions between gravity waves and planetary scale flow in the middle atmosphere, a 3 degree latitude by 3.6 degree longitude version of the 40-level GFDL "SKYHI" general circulation model is analyzed using bihourly sampled output data.
It is shown by a space-time spectral analysis that gravity waves in the mean zonal westerlies (easterlies) mainly consist of westward-(eastward-) moving components, and carry easterly (westerly) momentum upward, and decelerate the mean zonal westerlies (easterlies) in the mesosphere.
Zonal momentum flux convergence due to gravity waves accounts for nearly all of the Eliassen-Palm (E-P) flux divergence in the summer mesosphere. This convergence accounts for 30%-50% of that in the winter upper mesosphere. However, this percentage is probably an underestimate, since the convergence is significantly enhanced in a high resolution (1 degree x 1.2 degree) model currently being integrated.
Vertical propagation of gravity waves is affected not only by the mean zonal wind but also by velocity perturbations associated with planetary waves. The drag force due to gravity waves acts to suppress stationary planetary waves in the winter mesosphere.
The Geophysical Fluid Dynamics Laboratory general circulation/transport model, with photochemistry in the top level (middle stratosphere) only, is used to simulate global tropospheric ozone distributions for upper and lower limits of surface removal rates. We compared these simulations with available observations and find that large-scale atmospheric transport plays a major role in the behavior of tropospheric ozone. Furthermore, we identify potential roles for tropospheric chemistry, discover defects in the model's mean cross-tropopause flux is in the range of previous estimates, and the shapes of the simulated vertical profiles of mixing ratio and percent standard deviation are in good agreement with observations. South of 40 degrees N, the simulated and observed latitude gradients are the same, the upper and lower limit calculations bracket measured values, and the seasonal cycles are well reproduced. While the transport model simulates a wide tange of tropospheric ozone climatology, there are a significant number of disagreements. The need for additional ozone destruction in the maritime boundary layer suggests a role for chemical destruction, while in the continental boundary layer, it appears that chemical production, a seasonal cycle in surface deposition, and improved boundary layer transport are all required. The two major defects in the simulated "free troposphere" are (1) excess ozone at high latitudes of the northern hemisphere (NH) and (2) spring rather than summer maxima and fall rather than winter minima at NH mid- and high latitudes. While defect 1 has a number of possible causes, deficiencies in model transport play a major role. Although similar transport defects have not been ruled out for defect 2, tropospheric chemistry appears to be needed. Separate calculations of the net chemical production and loss demonstrate that this is a complex problem. The most likely solution involves the transport control of NOx which controls the ozone chemistry.
Mahlman, Jerry D., 1985: Mechanistic interpretation of stratospheric tracer transport. Advances in Geophysics, 28A, 301-323.
A space-time spectral analysis is made of large-scale equatorial disturbances simulated by the 40-level, 5 degree latitude GFDL "SKYHI" general circulation model with annual mean conditions. Three kinds of eastward moving waves with wavenumbers 1-2 are found in the lower and upper stratosphere and mesosphere. These waves are characterized by small meridional winds and an eastward tilt with height and are identifiable with observed Kelvin waves. A time-height section reveals their vertical group propagation.
The lower stratospheric Kelvin wave is associated with periods of 10-30 days (eastward phase speed 15-46 m s-1) for wavenumber 1 and a vertical wavelength of ~10 km, corresponding to that observed in 1968 by Wallace and Kousky. The upper stratospheric Kelvin wave is associated with periods of 5-7 days (66-92 m s-1) for wavenumber 1 and a vertical wavelength of ~20 km, corresponding to that observed by Hirota. The mesospheric Kelvin wave is associated with periods of 3-4 days (115-154 m s-1) for wavenumber 1 and a vertical wavelength of ~40 km, corresponding to that recently discovered by Salby and others. All these Kelvin waves transport energy and eastward momentum upward and contribute to the maintenance of the eastward flow.
In addition, gravity waves of zonal wavenumbers 1-30 and periods of 0.7-2 days have been found, particularly in the model's equatorial stratosphere and mesosphere. Their eastward and westward moving components transport eastward and westward momentum upward and contribute to the momentum balance as much as, or even more than, Kelvin waves with periods longer than two days.
Mahlman, Jerry D., D G Andrews, T Hartmann, T Matsuno, and R J Murgatroyd, 1984: Transport of trace constituents in the stratosphere In Dynamics of the Middle Atmosphere, Terra Scientific Publishing Co, Tokyo, Japan, 387-416. Abstract
r understanding of stratospheric trace constituent transport is reviewed, beginning with the evolution of viewpoints on the subject over the past half century. We then discuss the available observed characteristics of trace constituents and the challenges posed by them.
To provide a framework for further developments, we present a simplified conceptual view of processes leading to irreversible transport. Next, methods of approach to such problems are outlined, including discussions of possibilities for physically based parameterized transport models. Finally, we pose a set of unanswered questions as possible guides to future research on the subject.
Mahlman, Jerry D., and L Umscheid, 1984: Dynamics of the middle atmosphere: Successes and problems of the GFDL "SKYHI" general circulation model In Dynamics of the Middle Atmosphere, Terra Scientific Publishing Co, Tokyo, Japan, 501-525. Abstract
The seasonal variation of the circulation of the middle atmosphere is investigated using a medium resolution (5 degrees latitude by 6 degrees longitude) version of the GFDL "SKYHI" general circulation model. The model includes rather complete tropospheric physical and dynamical processes as well as a state-of-the-art radiative transfer algorithm.
Simulation successes in the model middle atmosphere include: the cold equatorial tropopause; the midlatitude warm belt in the winter lower stratosphere; clear separation of the subtropical and polar night jet streams; stratospheric summer easterlies of the proper speed and extent; a strong sudden warming type event just above the stratopause; closing off of the polar night jet stream in the mesosphere; and a pronounced equatorial semi-annual oscillation.
Model results which must be regarded as failures include: excessively cold polar night vortices with associated overly intense zonal winds; an underestimate of the amount of wave activity escaping the troposphere; a mesospheric summertime easterly jet which does not close off; and no evidence of a quasi-biennial oscillation in the equatorial lower stratosphere.
Andrews, D G., Jerry D Mahlman, and R W Sinclair, 1983: Eliassen-Palm diagnostics of wave-mean flow interaction in the GFDL "SKYHI" general circulation model. Journal of the Atmospheric Sciences, 40(12), 2768-2784. Abstract PDF
e Eliassen-Palm flux is important in analytical studies of small-amplitude waves where it provides a powerful and elegant tool for the description of wave propagation in mean zonal shear flows, as well as for analysis of the effective mean zonal force induced by the waves. Furthermore, it has recently been used as a diagnostic in a number of studies of atmospheric data and numerical models of specific dynamic phenomena. In this paper, it is applied to the GFDL SKYHI global general circulation model of the troposphere- stratosphere-mesosphere, and computations of the primitive equations, isobaric coordinate form of the Eliassen-Palm flux, and its divergence under conditions of annual-mean insolation are described. The Eliassen-Palm flux diagnostics show a clear picture of planetary wave propagation from the midlatitude troposphere into the stratosphere and mesosphere. In the Tropics, the presence of Kelvin waves confuses the picture somewhat (because their phase speeds are eastward with regard to the mean flow) and necessitates additional analysis, which is given elsewhere. The Eliassen-Palm diagnostics lead to new insights on the forcing of mean flows by the eddies. The implications of the fact that the model waves are not close to nonacceleration conditions and the importance of mean diabatic effects in the 30-day average statistics are considered in an appendix. An important finding is that zonal westerly flows are strongly decelerated by eddies in the midlatitude upper troposphere and the mesosphere, in sharp contrast to the apparent implication of traditional zonal mean balances. Conversely, the forcing of mean accelerations by waves in the Tropics is essentially in agreement with that found in earlier studies. These inferences from the Eliassen-Palm diagnostics concerning the effect of eddies on zonal flows were tested in a companion model experiment in which eddies propagating out of the troposphere are strongly damped. This experiment shows the resultant zonal flow accelerations to be fully consistent with the inferences from the Eliassen-Palm diagnostics.
Tropospheric N2O climatologies are simulated with the GFDL general circulation/tracer model for three idealized source specifications: (1) a constant surface flux of 1.44 x 109 molecules cm-2 s-1 distributed uniformly over the earth's surface, with a global source strength of 17 tg N2O yr-1 and an atmospheric lifetime of 131 yr; (2) a 13 month integration of the stable N2O field from experiment 1 with its N2O source removed; (3) a constant surface flux of 2.24 x 1010 molecules cm-1 s-1 over only those land areas with precipitation in excess of an arbitrary limit of 127 cm yr-1, but with the same global strength (17 tg N2O yr-1) and atmospheric lifetime (131 yr) as in experiment 1. In the boundary layer, the model produces an interhemispheric gradient with a minimum in the northern hemisphere (NH). This is due to the greater downward transport in the NH which results in more dilution of NH boundary layer N2O mixing ratios by the N2O-poor air from the lower stratosphere. The boundary layer distribution of N2O is also influenced by the distribution of the surface source. The lack of an N2O maximum in the model's NH boundary layer suggests that, unlike the model's idealized source, the true source has a large excess in the Northern Hemisphere. Above the boundary layer, the N-S gradient is controlled by the large-scale vertical transport that produces a NH minimum in N2O mixing ratio. The impact of the surface source distribution is small. Current measurements at 500 mb have too low a precision to confirm or disprove the model prediction of an interhemispheric gradient with a NH minimum in the middle troposphere. The sources of temporal variability in the model's N2O fields are transient motions of all scales acting on mixing ratio gradients, both vertcal and horizontal. The model finds that a small surface source of 17 tg N2O yr-1, sufficient to balance stratospheric destruction, is more than able to maintain the observed variability in the boundary layer.
Andrews, D G., Jerry D Mahlman, and R W Sinclair, 1981: The use of the Eliassen-Palm flux as a diagnostic of wave, mean-flow interaction in a general circulation model. Handbook for MAP, 2, 99-100.
Liu, S C., D Kley, M McFarland, Jerry D Mahlman, and Hiram Levy II, 1981: Reply. Journal of Geophysical Research, 86(C12), 12,165-12,166.
Mahlman, Jerry D., D G Andrews, H U Dutsch, D L Hartmann, T Matsuno, R J Murgatroyd, and J F Noxon, 1981: Transport of trace constituents in the stratosphere. Handbook for MAP, 3, 14-43. Abstract
Our understanding of stratospheric trace constituent transport is reviewed, beginning with the evolution of viewpoints on the subject over the past half century. We then discuss the available observed characteristics of trace constituents and the challenges posed by them.
To provide a framework for further developments, we present a simplified conceptual view of processes leading to irreversible transport. Next, methods of approach to such problems are outlined, including discussions of possibilities for physically based parameterized transport models. Finally, we pose a set of unanswered questions as possible guides to future research on the subject.
Fels, S, Jerry D Mahlman, M Daniel Schwarzkopf, and R W Sinclair, 1980: Stratospheric sensitivity to perturbations in ozone and carbon dioxide: Radiative and dynamical response. Journal of the Atmospheric Sciences, 37(10), 2265-2297. Abstract PDF
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 insolation version of the recently developed GFDL 40-level general circulation model (GCM). Supporting the 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. The temperature change in the CO2 experiment is remarkably uniform in latitude.
A GFDL 3-D global generalized tracer field is adapted to provide a preliminary simulation of the reactive nitrogen (NOY) climatology in an unpolluted troposphere which has, as its sole source, downward transport of stratospheric NOY. The tracer field is scaled so that its downward cross-tropopause flux is balanced by the stratospheric production of NOY. While the model results show stratospheric NOY to be a significant source for the remote troposphere, they do not rule out additional contributions from either the long-range transport of combustion NOY or the insitu production by lightning. The model NOY climatology in the unpolluted troposphere shows a strong interhemispheric asymmetry due to greater downward NOY flux in the northern hemisphere and a steep drop off to a minimum in the tropics resulting from a combination of model features (tropical rainbelt, ITCZ, and Indidan monsoon) which have been well documented in the real atmosphere.
Liu, S C., D Kley, M McFarland, Jerry D Mahlman, and Hiram Levy II, 1980: On the origin of tropospheric ozone. Journal of Geophysical Research, 85(C12), 7546-7552. Abstract PDF
The effects of NOx (NO + NO2) intrusion from the stratosphere on photochemical ozone production in the upper troposphere are investigated. Using the currently accepted reaction rate coefficients, we find that this upper tropospheric ozone source may be significantly larger than the direct injection of ozone from the stratosphere. Many features of the observed tropospheric temporal and spatial ozone distributions appear to be better explained by this upper tropospheric ozone source hypothesis than by either the classical 'dynamical control' or 'photochemical control' hypotheses. In addition, we find that NOx emissions from high flying subsonic aircraft in the northern hemisphere may cause an ozone increase in the troposphere. The calculated tropospheric ozone increase due to these NOx emissions is not inconsistent with the increases observed by the northern hemispheric ozonesonde stations.
Mahlman, Jerry D., Hiram Levy II, and Walter Moxim, 1980: Three-dimensional tracer structure and behavior as simulated in two ozone precursor experiments. Journal of the Atmospheric Sciences, 37(3), 655-685. Abstract PDF
The GFDL, II-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 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 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 analysis of the processes affecting the 10-mb, zonal-mean mixing ratio is presented. The results show that the midstratospheric ozone production and losses are strongly sensitive to circulation features, changing overhead sun angle, and temperature. These various effects lead to some substantial interhemispheric and seasonal asymmetries in ozone production. An analysis of the transport processes is performed, leading to the pronounced poleward-downward slope of tracer isopleths. The results demonstrate that adiabatic and diabatic effects in the eddies, as well as diabatic effects in the zonal mean, all contribute importantly to the creation of these sloping surfaces. As an aid to tracer transport analysis, a Lagrangian nontransport theorem is derived for an integration following a fluid particle. Some Lagrangian drift-type calculations are performed in the model January mean flow. The results show a slow, but substantial, particle convergence just to the cyclonic shear side of the time-mean jet stream axis. This is a region in which the traditional zonal-mean budget analysis shows a large cancellation between eddy and meridional circulation flux convergence. Also, the analysis demonstrates indirectly the important contributions of transient disturbances to the movement of heat and tracers irreversibly into the stratospheric polar vortex.
Moxim, Walter, and Jerry D Mahlman, 1980: Evaluation of various total ozone sampling networks using the GFDL 3-D tracer model. Journal of Geophysical Research, 85(C8), 4527-4539. Abstract
Data sets generated by the Geophysical Fluid Dynamics Laboratory (GFDL) 3-D general circulation--tracer model for an ozone experiment are used to compare the accuracy of various total ozone networks in calculating global and hemispheric means of total ozone and annual trends of monthly mean total ozone. The advantage of this approach is that exact model integrals and trends are known, thus providing an ability to examine the errors expected in present and hypothesized sampling networks. The effects of both spatial and temporal sampling errors are presented.
Because the 3-D tracer model uses the same time-dependent wind fields from year to year, the influence of interannual meteorological variability and the sampling error resulting from long-term ozone trends cannot be evaluated. By using varying numbers of observations per month, total ozone networks of 9, 53, and 181 stations are compared. In addition, a case of 53, plus 15 new, judiciously placed stations is examined. Model network evaluations of global mean ozone show underestimnates of 1-3% occurring because of a compensation of Northern and Southern Hemispheric errors as large as -6 and +3%, respectively. The error of global mean ozone from random sampling networks for various months is examined, showing rapid improvement from 9 to 1% for an increase in the number of random stations from 5 to 100. Markedly slower improvement is seen with further increases in the number of stations. One-year trend analyses of total ozone are compared for various networks and individual stations. Sampling errors of nearly 1%/yr. are seen for the 53 station case, when using four perfect, equally spaced observations per month. The errors grow substantially larger with fewer observations. The effect on global and hemispheric means from stations that did not take measurements during cloudy periods is also investigated. Results indicate that the weak annual mean cloud bias error (0.285%) is overwhelmed by the larger error produced by the decrease in effective network density.
Levy II, Hiram, Jerry D Mahlman, and Walter Moxim, 1979: Preliminary report on the numerical simulation of the three-dimensional structure and variability of atmospheric N2O. Geophysical Research Letters, 6(3), 155-158. Abstract PDF
A numerical simulation of atmospheric N2O using the GFDL 3-D tracer model with a small uniform surface source (15 Mton yr-1) and stratospheric destruction (150-yr lifetime) was run to a state near transport and chemical statistical equilibrium. The resulting N2O tropospheric distribution is relatively uniform with a slight excess in the Southern Hemisphere. In the model stratosphere, there is a sharp poleward decrease in N2O mixing ratio away from high values in the Tropics, with pronounced winter minima at 50 degrees S and 60 degrees N. Even with the small uniform surface source, relative standard deviations of N2O in the surface layer range from 0.1 to 0.8%, are well within the range of recent measurements. Additional experiments suggest that motions acting upon N2O accumulation in the source region boundary layer and upon the mixing ratio gradient between the troposphere and lower stratosphere are the major sources of tropospheric N2O variability.
Mahlman, Jerry D., 1979: Structure and interpretation of blocking anticyclones as simulated in a GFDL general circulation model In Proceedings of the (Thirteenth) Stanstead Seminar held at Bishop's University, Lennoxville, Québec, Canada, Montréal, Canada, McGill University, 70-76.
Mahlman, Jerry D., and Walter Moxim, 1978: Tracer simulation using a global general circulation model: results from a midlatitude instantaneous source experiment. Journal of the Atmospheric Sciences, 35(8), 1340-1374. Abstract PDF
An 11-level general circulation model with seasonal variation is used to perform an experiment on the dispersion of passive tracers. Specially constructed time-dependent winds from this model are used as input to a separate tracer model. The methodologies employed to construct the tracer model are described.
The experiment presented is the evolution of a hypothetical instantaneous source of tracer on 1 January with maximum initial concentration at 65 mb, 36 degrees N, 180 degrees E. The tracer is assumed to have no sources or sinks in the stratosphere, but is subject to removal processes in the lower troposphere.
The experimental results reveal a number of similarities to observed tracer behavior, including the average poleward-downward slope of mixing ratio isopleths, strong tracer gradients across the tropopause, intrusion of tracer into the Southern Hemisphere lower stratosphere, and the long-term interhemispheric exchange rate. The model residence times show behavior intermediate to those exhibited for particulate radioactive debris and gaseous C14O2. This suggests that caution should be employed when either radioactive debris or C14O2 data are used to develop empirical models for prediction of gaseous tracers which are efficiently removed in the troposphere.
In this experiment, the tracer mixing ratio and potential vorticity evolve to very high correlations. Mechanisms for this correlation are discussed. The zonal mean tracer balances exhibit complex behavior among the various transport terms. At early stages, the tracer evolution is dominated by eddy effects. Later, a very large degree of self-cancellation between mean cell and eddy effects is observed. During seasonal transitions, however, this self-cancellation diminishes markedly, leading to significant changes in the zonal mean tracer distribution. A possible theoretical explanation is presented.
For this tracer dispersion problem, probably the most significant model shortcoming is the inability of the general circulation model to produce the midwinter stratospheric sudden warming phenomenon.
Mahlman, Jerry D., and Walter Moxim, 1976: A method for calculating more accurate budget analyses of "sigma" coordinate model results. Monthly Weather Review, 104(9), 1102-1106. Abstract PDF
The so-called "sigma" coordinate system has seen increasing use in numerical models developed for general circulation and climate simulation, as well as for weather forecasting. Concurrently, there is an increasing demand for accurate analysis of the interactive physical processes included in these model integrations. However, because of the necessity to transform the model information from sigma levels back to more conventional coordinate surfaces (such as pressure), significant inaccuracies usually result. To reduce these inaccuracies, an alternative analysis procedure is introduced which avoids the usual ambiguous evaluation of vertical velocity in the transformed coordinate. Tests of this alternative method show that substantial increases in model analysis accuracy can be obtained.
Manabe, Syukuro, and Jerry D Mahlman, 1976: Simulation of seasonal and interhemispheric variations in the stratospheric circulation. Journal of the Atmospheric Sciences, 33(11), 2185-2217. Abstract PDF
This paper describes the stratosphere as simulated by the time integration of a global model of the atmosphere as developed at the Geophysical Fluid Dynamics Laboratory of NOAA.
It is shown that the model is capable of simulating a number of the features of the seasonal variation in the stratosphere. For example, it qualitatively reproduces the seasonal reversals of zonal wind direction in the mid-stratosphere between westerlies in winter and the zonal easterlies prevailing during the summer season. In the mid-latitude region of the lower model stratosphere, zonal mean temperature is highest in the winter when solar radiation is weak. At the cold equatorial tropopause of the model, the seasonal variation of temperature is also quite different from that which would be expected from the seasonal variation of solar radiation. These results are in qualitative agreement with the observed variation.
Attempts are made to identify the factors which are responsible for the various aspects of the seasonal variation of the model stratosphere, based upon detailed budget analyses of angular momentum, heat and eddy kinetic energy. It is found that, with the exception of the high latitude regions, the seasonal variation of temperature in the lower model stratosphere is essentially controlled by dynamical effects rather than by the seasonal variation of local heating due to solar radiation.
The stratosphere as simulated by the global model has large interhemispheric asymmetries in the shape of the polar westerly vortex, the magnitudes and the distributions of eddy kinetic energy, and the meridional circulation in the winter hemisphere. Interhemispheric asymmetries in orography are apparently responsible for the interhemispheric differences in the quasi-stationary component of energy flux from the troposphere to the stratosphere of the model, and thus account for many of the asymmetries in the stratospheric circulation. In particular, the simulated stratospheric Aleutian anticyclone is shown to be related to the presence of the strong quasi-stationary tropospheric jet stream off the east coast of Asia.
Some of the important shortcomings of the model in simulating the stratosphere include an exaggeration of the magnitudes of the various components of the eddy kinetic energy budget at the top computational level (10 mb) of the model and an overestimation of the intensity of the polar westerly vortex. Also, the model fails to reproduce the mid-winter "sudden stratospheric warming" phenomenon and the quasi-biennial wind reversal in the equatorial stratosphere. It is suggested that the performance of the model at the top level suffers from the coarseness in the vertical finite-difference resolution and the lid boundary condition imposed at the top of the model atmosphere.
Mahlman, Jerry D., 1975: Some fundamental limitations of simplified transport models as implied by results from a three-dimensional general-circulation/tracer model In Fourth Conference on CIAP, U.S. Department of Transportation, 132-146.
Miller, Arthur J., R J List, and Jerry D Mahlman, 1974: Surface deposition in the United States In Health and Safety Laboratory, U.S. Atomic Energy Commission Fallout Program Quarterly Summary Report, I49-I63. Abstract
Comparison is made of the surface deposition patterns over the United States as depicted by observations of Strontium 90 in soil, tritium rainout and Strontium 90 in pot and ion-exchange collectors versus the results generated by the general circulation tracer model from the Geophysical Fluid Dynamics Laboratory. It is found that the three observed data sets exhibit certain common characteristics:
A general maximum in the Great Plains states.
A general minimum in the Southwest.
A relatively high value, if not an absolute maximum, in the Salt Lake City area.
The results of the general circulation tracer model calculations present a reasonable "first depiction" of the details of surface deposition and are very encouraging as an indicator of the transport of such conservative trace substances.
Mahlman, Jerry D., 1973: On the maintenance of the polar front jet stream. Journal of the Atmospheric Sciences, 30(4), 544-557. Abstract PDF
A calculation of the mean transverse circulation about the polar front jet stream is performed by using a diagnostic balance, w-equation method. The results show a thermally-direct mean transverse circulation about the jet stream system for this case study.
An examination of the kinetic energy balance of this jet stream reveals that the direct transverse circulation is probably strong enough to maintain the jet against frictional dissipation but not enough to provide large lateral export of energy. However, significant amounts of energy are transferred upward across the tropopause.
Further considerations are employed to argue that the mean transverse circulation obtained here is compatible with the observed distributions of temperature and potential vorticity about the jet core.
Mahlman, Jerry D., 1973: Preliminary results from a three-dimensional, general-circulation/tracer model In Proceedings of the Second Conference on the Climatic Impact Assessment Program, No. DOT-TSC-OST-73-4, Washington, DC, Department of Transportation, 321-337. Abstract
Some initial results from a three-dimensional tracer model are presented. The tracer model uses time-evolving, three-dimensional output from the general-circulation model described by Mahlman and Manabe. In the tracer integrations, three-dimensional advection and horizontal sub-grid-scale diffusion are calculated. Arbitrary parameterizations of sources and sinks can be included. The advective terms and time differencing are formulated so as to suppress artificial numerical damping.
Currently, two major experiments are being conducted. The first is a diffuse point-source injection into the Northern Hemisphere, mid-latitude winter stratosphere. The other is a vertically stratified tracer with a crudely simulated photochemical equilibrium at the upper level and a precipitation-dependent sink at the lowest levels.
The results of both experiments show many similarities to the behavior of analagous stratospheric trace substances. The first experiment shows features close to those of radioactive debris from recent Chinese bomb tests. The second experiment exhibits many features in common with those of observed ozone.
Mahlman, Jerry D., and Syukuro Manabe, 1972: Numerical simulation of the stratosphere: implications for related climate change problems In Climatic Impact Assessment Program, Proceedings of the Survey Conference, Washington, DC, Department of Transportation, 186-193. Abstract
Current results are presented from an atmospheric simulation model which extends to a height of about 30 km. The model is global and contains 11 vertical levels with a horizontal resolution of about 265 km. Realistic topography, an annual march of radiation, sea surface temperature, and water vapor effects are included.
Zonal-mean cross-sections of temperature and zonal wind are shown and compared with reality. The results indicate close agreement with observations except for a few important exceptions; e.g., the simulated stratospheric polar night vortex is about a factor of two stronger than the observed. Synoptic charts for the 38-millibar pressure level are shown for different seasons of the year. These reveal a satisfactory simulation of the stratospheric winter Aleutian anticyclone and polar vortex, as well as the summertime easterlies.
Special attention is directed toward the problems of using atmospheric simulation models to study mechanisms acting to redistribute trace substances. Numerical and physical problems of modeling tracer advection, sub-grid-scale transfer, sources, and sinks are discussed in relation to the climate change problem. On the basis of current experience, some speculations are offered on efforts toward solving problems in which the distribution of tracers affects, and is affected by, the dynamics of the stratosphere.
