The Geophysical Fluid Dynamics Laboratory (GFDL) has developed a coupled general circulation model (CM3) for atmosphere, oceans, land, and sea ice. The goal of CM3 is to address emerging issues in climate change, including aerosol-cloud interactions, chemistry-climate interactions, and coupling between the troposphere and stratosphere. The model is also designed to serve as the physical-system component of earth-system models and models for decadal prediction in the near-term future, for example, through improved simulations in tropical land precipitation relative to earlier-generation GFDL models. This paper describes the dynamical core, physical parameterizations, and basic simulation characteristics of the atmospheric component (AM3) of this model.
Relative to GFDL AM2, AM3 includes new treatments of deep and shallow cumulus convection, cloud-droplet activation by aerosols, sub-grid variability of stratiform vertical velocities for droplet activation, and atmospheric chemistry driven by emissions with advective, convective, and turbulent transport. AM3 employs a cubed-sphere implementation of a finite-volume dynamical core and is coupled to LM3, a new land model with eco-system dynamics and hydrology.
Most basic circulation features in AM3 are simulated as realistically, or more so, than in AM2. In particular, dry biases have been reduced over South America. In coupled mode, the simulation of Arctic sea ice concentration has improved. AM3 aerosol optical depths, scattering properties, and surface clear-sky downward shortwave radiation are more realistic than in AM2. The simulation of marine stratocumulus decks and the intensity distributions of precipitation remain problematic, as in AM2.
The last two decades of the 20th century warm in CM3 by .32°C relative to 1881-1920. The Climate Research Unit (CRU) and Goddard Institute for Space Studies analyses of observations show warming of .56°C and .52°C, respectively, over this period. CM3 includes anthropogenic cooling by aerosol cloud interactions, and its warming by late 20th century is somewhat less realistic than in CM2.1, which warmed .66°C but did not include aerosol cloud interactions. The improved simulation of the direct aerosol effect (apparent in surface clear-sky downward radiation) in CM3 evidently acts in concert with its simulation of cloud-aerosol interactions to limit greenhouse gas warming in a way that is consistent with observed global temperature changes.
Koster, Randal D., C Tony Gordon, and Sergey Malyshev, et al., October 2011: The second phase of the global land-atmosphere coupling experiment: Soil moisture contributions to subseasonal forecast skill. Journal of Hydrometeorology, 12(5), DOI:10.1175/2011JHM1365.1. Abstract
The second phase of the Global Land-Atmosphere Coupling Experiment (GLACE-2) is a multi-institutional numerical modeling experiment focused on quantifying, for boreal summer, the subseasonal (out to two months) forecast skill for precipitation and air temperature that can be derived from the realistic initialization of land surface states, notably soil moisture. An overview of the experiment and model behavior at the global scale is described here, along with a determination and characterization of multi-model “consensus” skill. The models show modest but significant skill in predicting air temperatures, especially where the rain gauge network is dense. Given that precipitation is the chief driver of soil moisture, and thereby assuming that rain gauge density is a reasonable proxy for the adequacy of the observational network contributing to soil moisture initialization, this result indeed highlights the potential contribution of enhanced observations to prediction. Land-derived precipitation forecast skill is much weaker than that for air temperature. The skill for predicting air temperature, and to some extent precipitation, increases with the magnitude of the initial soil moisture anomaly. GLACE-2 results are examined further to provide insight into the asymmetric impacts of wet and dry soil moisture initialization on skill.
Koster, Randal D., C Tony Gordon, and Sergey Malyshev, et al., January 2010: Contribution of land surface initialization to subseasonal forecast skill: First results from a multi-model experiment. Geophysical Research Letters, 37, L02402, DOI:10.1029/2009GL041677. Abstract
The second phase of the Global Land-Atmosphere Coupling Experiment (GLACE-2) is aimed at quantifying, with a suite of long-range forecast systems, the degree to which realistic land surface initialization contributes to the skill of subseasonal precipitation and air temperature forecasts. Results, which focus here on North America, show significant contributions to temperature prediction skill out to two months across large portions of the continent. For precipitation forecasts, contributions to skill are much weaker but are still significant out to 45 days in some locations. Skill levels increase markedly when calculations are conditioned on the magnitude of the initial soil moisture anomaly.
The formulation and simulation characteristics of two new global coupled climate models developed at NOAA's Geophysical Fluid Dynamics Laboratory (GFDL) are described. The models were designed to simulate atmospheric and oceanic climate and variability from the diurnal time scale through multicentury climate change, given our computational constraints. In particular, an important goal was to use the same model for both experimental seasonal to interannual forecasting and the study of multicentury global climate change, and this goal has been achieved.
Two versions of the coupled model are described, called CM2.0 and CM2.1. The versions differ primarily in the dynamical core used in the atmospheric component, along with the cloud tuning and some details of the land and ocean components. For both coupled models, the resolution of the land and atmospheric components is 2° latitude × 2.5° longitude; the atmospheric model has 24 vertical levels. The ocean resolution is 1° in latitude and longitude, with meridional resolution equatorward of 30° becoming progressively finer, such that the meridional resolution is 1/3° at the equator. There are 50 vertical levels in the ocean, with 22 evenly spaced levels within the top 220 m. The ocean component has poles over North America and Eurasia to avoid polar filtering. Neither coupled model employs flux adjustments.
The control simulations have stable, realistic climates when integrated over multiple centuries. Both models have simulations of ENSO that are substantially improved relative to previous GFDL coupled models. The CM2.0 model has been further evaluated as an ENSO forecast model and has good skill (CM2.1 has not been evaluated as an ENSO forecast model). Generally reduced temperature and salinity biases exist in CM2.1 relative to CM2.0. These reductions are associated with 1) improved simulations of surface wind stress in CM2.1 and associated changes in oceanic gyre circulations; 2) changes in cloud tuning and the land model, both of which act to increase the net surface shortwave radiation in CM2.1, thereby reducing an overall cold bias present in CM2.0; and 3) a reduction of ocean lateral viscosity in the extratropics in CM2.1, which reduces sea ice biases in the North Atlantic.
Both models have been used to conduct a suite of climate change simulations for the 2007 Intergovernmental Panel on Climate Change (IPCC) assessment report and are able to simulate the main features of the observed warming of the twentieth century. The climate sensitivities of the CM2.0 and CM2.1 models are 2.9 and 3.4 K, respectively. These sensitivities are defined by coupling the atmospheric components of CM2.0 and CM2.1 to a slab ocean model and allowing the model to come into equilibrium with a doubling of atmospheric CO2. The output from a suite of integrations conducted with these models is freely available online (see http://nomads.gfdl.noaa.gov/).
Manuscript received 8 December 2004, in final form 18 March 2005
Guo, Zhichang, Paul A Dirmeyer, Randal D Koster, Gordon Bonan, Edmond Chan, Peter Cox, C Tony Gordon, Shinjiro Kanae, Eva Kowalczyk, David Lawrence, P Liu, Cheng-Hsuan Lu, Sergey Malyshev, B McAveney, J L McGregor, K Mitchell, D Mocko, T Oki, K W Oleson, A J Pitman, Y C Sud, C M Taylor, D Verseghy, R Vasic, Y Xue, and T Yamada, 2006: GLACE: The Global Land–Atmosphere Coupling Experiment. Part II: Analysis. Journal of Hydrometeorology, 7(4), DOI:10.1175/JHM511.1. Abstract
The 12 weather and climate models participating in the Global Land–Atmosphere Coupling Experiment
(GLACE) show both a wide variation in the strength of land–atmosphere coupling and some intriguing
commonalities. In this paper, the causes of variations in coupling strength—both the geographic variations
within a given model and the model-to-model differences—are addressed. The ability of soil moisture to
affect precipitation is examined in two stages, namely, the ability of the soil moisture to affect evaporation,
and the ability of evaporation to affect precipitation. Most of the differences between the models and within
a given model are found to be associated with the first stage—an evaporation rate that varies strongly and
consistently with soil moisture tends to lead to a higher coupling strength. The first-stage differences reflect
identifiable differences in model parameterization and model climate. Intermodel differences in the evaporation–
precipitation connection, however, also play a key role.
Koster, Randal D., Zhichang Guo, Paul A Dirmeyer, Gordon Bonan, Edmond Chan, Peter Cox, H Davies, C Tony Gordon, and Sergey Malyshev, et al., 2006: GLACE: The Global Land–Atmosphere Coupling Experiment. Part I: Overview. Journal of Hydrometeorology, 7(4), DOI:10.1175/JHM510.1. Abstract
The Global Land–Atmosphere Coupling Experiment (GLACE) is a model intercomparison study focusing on a typically neglected yet critical element of numerical weather and climate modeling: land–atmosphere coupling strength, or the degree to which anomalies in land surface state (e.g., soil moisture) can affect rainfall generation and other atmospheric processes. The 12 AGCM groups participating in GLACE performed a series of simple numerical experiments that allow the objective quantification of this element for boreal summer. The derived coupling strengths vary widely. Some similarity, however, is found in the spatial patterns generated by the models, with enough similarity to pinpoint multimodel “hot spots” of land–atmosphere coupling. For boreal summer, such hot spots for precipitation and temperature are found over large regions of Africa, central North America, and India; a hot spot for temperature is also found over eastern China. The design of the GLACE simulations are described in full detail so that any interested modeling group can repeat them easily and thereby place their model’s coupling strength within the broad range of those documented here.
for climate research developed at the Geophysical Fluid Dynamics Laboratory (GFDL) are presented. The atmosphere model, known as AM2, includes a new gridpoint dynamical core, a prognostic cloud scheme, and a multispecies aerosol climatology, as well as components from previous models used at GFDL. The land model, known as LM2, includes soil sensible and latent heat storage, groundwater storage, and stomatal resistance. The performance of the coupled model AM2–LM2 is evaluated with a series of prescribed sea surface temperature (SST) simulations. Particular focus is given to the model's climatology and the characteristics of interannual variability related to E1 Niño– Southern Oscillation (ENSO).
One AM2–LM2 integration was performed according to the prescriptions of the second Atmospheric Model Intercomparison Project (AMIP II) and data were submitted to the Program for Climate Model Diagnosis and Intercomparison (PCMDI). Particular strengths of AM2–LM2, as judged by comparison to other models participating in AMIP II, include its circulation and distributions of precipitation. Prominent problems of AM2– LM2 include a cold bias to surface and tropospheric temperatures, weak tropical cyclone activity, and weak tropical intraseasonal activity associated with the Madden–Julian oscillation.
An ensemble of 10 AM2–LM2 integrations with observed SSTs for the second half of the twentieth century permits a statistically reliable assessment of the model's response to ENSO. In general, AM2–LM2 produces a realistic simulation of the anomalies in tropical precipitation and extratropical circulation that are associated with ENSO.
Koster, Randal D., Paul A Dirmeyer, Zhichang Guo, Gordon Bonan, Edmond Chan, Peter Cox, C Tony Gordon, Shinjiro Kanae, Eva Kowalczyk, David Lawrence, Ping Liu, Cheng-Hsuan Lu, and Sergey Malyshev, et al., August 2004: Regions of Strong Coupling Between Soil Moisture and Precipitation. Science, 305(5687), DOI:10.1126/science.11002171138-1140. Abstract
Previous estimates of land-atmosphere interaction (the impact of soil moisture on precipitation) have been limited by a lack of observational data and by the model dependence of computational estimates. To counter the second limitation, a dozen climate-modeling groups have recently performed the same highly controlled numerical experiment as part of a coordinated comparison project. This allows a multimodel estimation of the regions on Earth where precipitation is affected by soil moisture anomalies during Northern Hemisphere summer. Potential benefits of this estimation may include improved seasonal rainfall forecasts.
Davey, M K., M Huddleston, Kenneth R Sperber, P Braconnot, F O Bryan, D Chen, R Colman, C Cooper, U Cubasch, P Delecluse, D G DeWitt, L Fairhead, G M Flato, C Tony Gordon, T Hogan, M Ji, , A Kitoh, Thomas R Knutson, M Latif, H Le Treut, Tim Li, Syukuro Manabe, C R Mechoso, Gerald A Meehl, Scott B Power, E Roeckner, L Terray, A Vintzileos, R Voss, Bin Wang, W M Washington, I Yoshikawa, J-Y Yu, S Yukimoto, and S E Zebiak, 2002: STOIC: A study of coupled model climatology and variability in tropical ocean regions. Climate Dynamics, 18(5), 403-420. Abstract PDF
We describe the behavior of 23 dynamical ocean-atmosphere models, in the context of comparison with observations in a common framework. Fields of tropical sea surface temperature (SST), surface wind stress and upper ocean vertically averaged temperature (VAT) are assessed with regard to annual mean, seasonal cycle, and interannual variability characteristics. Of the participating models, 21 are coupled GCMs, of which 13 use no form of flux adjustment in the tropics. The models vary widely in design, components and purpose; nevertheless several common features are apparent. In most models without flux adjustment, the annual mean equatorial SST in the central Pacific is too cool and the Atlantic zonal SST gradient has the wrong sign. Annual mean wind stress is often too weak in the central Pacific and in the Atlantic, but too strong in the west Pacific. Few models have an upper ocean VAT seasonal cycle like that observed in the equatorial Pacific. Interannual variability is commonly too weak in the models: in particular, wind stress variability is low in the equatorial Pacific. Most models have difficulty in reproducing the observed Pacific 'horseshoe' pattern of negative SST correlations with interannual Niño 3 SST anomalies, or the observed Indian-Pacific lag correlations. The results for the fields examined indicate that several substantial model improvements are needed, particularly with regard to surface wind stress.
Wielicki, B A., T Wong, Richard P Allan, A Slingo, J T Kiehl, Brian J Soden, C Tony Gordon, Arthur J Miller, S-K Yang, David A Randall, F Robertson, J Susskind, and H Jacobowitz, 2002: Evidence for large decadal variability in the tropical mean radiative energy budget. Science, 295(5556), 841-844. Abstract PDF
It is widely assumed that variations in Earth's radiative energy budget at large time and space scales are small. We present new evidence from a compilation of over two decades of accurate satellite data that the top-of-atmosphere (TOA) tropical radiative energy budget is much more dynamic and variable than previously thought. Results indicate that the radiation budget changes are caused by changes in tropical mean cloudiness. The results of several current climate model simulations fail to predict this large observed variation in tropical energy budget. The missing variability in the models highlights the critical need to improve cloud modeling in the tropics so that prediction of tropical climate on interannual and decadal time scales can be improved.
Gudgel, Richard G., Anthony Rosati, and C Tony Gordon, 2001: The sensitivity of a coupled atmospheric-oceanic GCM in prescribed low-level clouds over the ocean and tropical landmasses. Monthly Weather Review, 129(8), 2103-2115. Abstract PDF
The sensitivity of a coupled general circulation model (CGCM) to tropical marine stratocumulus (MSc) clouds and low-level clouds over the tropical land is examined. The hypothesis that low-level clouds play an important role in determining the strength and position of the Walker circulation and also on the strength and phase of the El Niño–Southern Oscillation (ENSO) is studied using a Geophysical Fluid Dynamics Laboratory (GFDL) experimental prediction CGCM. In the Tropics, a GFDL experimental prediction CGCM exhibits a strong bias in the western Pacific where an eastward shift in the ascending branch of the Walker circulation diminishes the strength and expanse of the sea surface temperature (SST) warm pool, thereby reducing the east–west SST gradient, and effectively weakening the trade winds. These model features are evidence of a poorly simulated Walker circulation, one that mirrors a “perpetual El Niño” state. One possible factor contributing to this bias is a poor simulation of MSc clouds in the eastern equatorial Pacific (which are essential to a proper SST annual cycle). Another possible contributing factor might be radiative heating biases over the land in the Tropics, which could, in turn, have a significant impact on the preferred locations of maximum convection in the Tropics. As a means of studying the sensitivity of a CGCM to both MSc clouds and to varied radiative forcing over the land in the Tropics, low-level clouds obtained from the International Satellite Cloud Climatology Project (ISCCP) are prescribed. The experiment sets consist of one where clouds are fully predicted, another where ISCCP low-level clouds are prescribed over the oceans alone, and a third where ISCCP low-level clouds are prescribed both over the global oceans and over the tropical landmasses. A set of ten 12-month hindcasts is performed for each experiment.
The results show that the combined prescription of interannually varying global ocean and climatological tropical land low-level clouds into the CGCM results in a much improved simulation of the Walker circulation over the Pacific Ocean. The improvement to the tropical circulation was also notable over the Indian and Atlantic basins as well. These improvements in circulation led to a considerable increase in ENSO hindcast skill in the first year by the CGCM. These enhancements were a function of both the presence of MSc clouds over the tropical oceans and were also due to the more realistic positioning of the regions of maximum convection in the Tropics. This latter model feature was essentially a response to the change in radiative forcing over tropical landmasses associated with a reduction in low cloud fraction and optical depth when ISCCP low-level clouds were prescribed there. These results not only underscore the importance of a reasonable representation of MSc clouds but also point out the considerable impact that radiative forcing over the tropical landmasses has on the simulated position of the Walker circulation and also on ENSO forecasting.
The seasonal cycle of SST observed in the eastern equatorial Pacific is poorly simulated by many ocean-atmosphere coupled GCMs. This deficiency may be partly due to an incorrect prediction of tropical marine stratocumulus (MSc). To explore this hypothesis, two basic multiyear simulations have been performed using a coupled GCM with seasonally varying solar radiation. The model's cloud prediction scheme, which under-predicts tropical marine stratocumulus, is used for all clouds in the control run. In contrast, in the "ISCCP" run, the climatological monthly mean low cloud fraction is specified over the open ocean, utilizing C2 data from the International Satellite Cloud Climatology Project (ISCCP). In this manner, the treatment of MSc clouds, including the annual cycle, is more realistic than in previous sensitivity studies.
Robust surface and subsurface thermodynamical and dynamical responses to the specified MSc are found in the Tropics, especially near the equator. In the annual mean, the equatorial cold tongue extends farther west and intensifies, while the east-west SST gradient is enhanced. A double SST maximum flanking the cold tongue becomes asymmetric about the equator. The SST annual cycle in the eastern equatorial Pacific strengthens, and the equatorial SST seasonal anomalies migrate farther westward. MSc-induced local shortwave radiative cooling enhances dynamical cooling associated with the southeast trades. The surface meridional wind stress in the extreme eastern equatorial Pacific remains southerly all year, while the surface zonal wind stress and equatorial upwelling intensify, as does the seasonal cycle of evaporation, in better agreement with observation. Within the ocean, the thermocline steepens and the Equatorial Undercurrent intensifies. When the low clouds are entirely removed, the SST warms by about 5.5 K in the western and central tropical Pacific, relative to "ISCCP," and the model's SST bias there reverses sign.
ENSO-like interannual variability with a characteristic timescale of 3-5 yr is found in all simulations, though its amplitude varies. The "ISCCP" equatorial cold tongue inhibits the eastward progression of ENSO-like warm events east of the date line. When the specified low cloud fraction in "ISCCP' is reduced by 20%, the interannual variability amplifies somewhat and the coupled model responds more like a delayed oscillator. The apparent sensitivity in the equatorial Pacific to a 20% relative change in low cloud fraction may have some cautionary implications for seasonal prediction by coupled GCMs.
Gordon, C T., Anthony Rosati, and Richard G Gudgel, 1999: Tropical interannual variability response of a coupled model to specified low clouds In Proceedings of the Twenty-Fourth Annual Climate Diagnostics and Prediction Workshop, Springfield, VA, NTIS, 331-334.
Gudgel, Richard G., Anthony Rosati, and C Tony Gordon, 1999: The impact of prescribed tropical land and ocean clouds on the Walker circulation in the GFDL coupled ocean-atmosphere GCM In Proceedings of the Twenty-Fourth Annual Climate Diagnostics and Prediction Workshop, Springfield, VA, NTIS, 307-310. Abstract
The role that tropical land and ocean clouds play in the GFDL coupled ocean-atmosphere GCM is studied through a series of 10 one-year model runs. In the tropics, a strong bias in the GFDL coupled GCM is evident in the western Pacific where excessive convection erodes the SST warm pool, reducing the SST pacific gradient, and effectively weakening the trade winds. This bias is exacerbated by the poor simulation of eastern equatorial Pacific marine stratus clouds which are essential to a proper seasonal cycle (annual as opposed to biannual) of the trade winds and the SST's. As a means to better understand the importance of ocean-only versus ocean and land tropical cloud prediction, low-level ISCCP clouds are used to study the effects on the GFDL atmosphere-only and coupled model simulation. The prescription of tropical low-level ocean and land clouds into the GCM resulted in a better simulation of the Walker circulation in both coupled and uncoupled modes. This climatological improvement to the Walker circulation corresponded with an improvement in the ability of the coupled GCM to simulate ENSO (El Niño/Southern Oscillation). The more reasonably represented land surface heating in the tropics led to more well-defined and positioned regions of convergence and divergence both at the surface and aloft. The GCM appears to be quite sensitive to the pronounced horizontal and vertical topographical structure in the Indonesian Archipelago and in tropical South America. This is most notable in the sensitivity of the model to small cloud fraction changes over these regions. This emphasizes the importance of reasonably representing the land surface heating in these regions. Whereas this sensitivity is evident in both the coupled and uncoupled simulations not only in terms of the model's climate but also in term of the model's ability to simulate ENSO, it underscores the importance of producing reasonable heating profiles over the land regions in the tropics.
Gordon, C T., Anthony Rosati, and Richard G Gudgel, 1998: Tropical sensitivity to specified ISCCP low clouds in a coupled model In Proceedings of the Twenty-Second Annual Climate Diagnostics and Prediction Workshop, Springfield, VA, NTIS, 232-235.
Gordon, C T., Anthony Rosati, and Richard G Gudgel, 1996: The impact of specified ISCCP low clouds in coupled model integrations In 11th Conference on Numerical Weather Prediction, Boston, MA, American Meteorological Society, 8-10.
Gordon, C T., Anthony Rosati, and Richard G Gudgel, 1996: The impact of specified ISCCP low clouds in coupled model integrations In Research Activities in Atmospheric and Oceanic Modelling, CAS/JSC Working Group on Numerical Experimentation, Report No. 23 WMO/TD No. 734, World Meteorological Organization, 9.12-9.13.
Stern, William F., and C Tony Gordon, 1996: Specifying and modeling snow cover in multi-year GCM integrations In Research Activities in Atmospheric and Oceanic Modelling, CAS/JSC Working Group on Numerical Experimentation, Report No. 23 WMO/TD No. 734, World Meteorological Organization, 4.43-4.44.
Gordon, C T., 1995: Results pertaining to clouds, radiation and equatorial temporal variability from a 40 year GCM integration In Proceedings of the First International AMIP Scientific Conference, WCRP-92, WMO/TD No. 273, Geneva, Switzerland, World Meteorological Organization, 407-412.
Miyakoda, Kikuro, Joseph J Sirutis, Anthony Rosati, C Tony Gordon, Richard G Gudgel, William F Stern, Jeffrey L Anderson, and A Navarra, 1995: Atmospheric parameterizations in coupled air-sea models used for forecasts of ENSO In Proceedings of the International Scientific Conference on the Tropical Ocean Global Atmosphere (TOGA) Programme, WCRP-91, WMO/TD No. 717, Geneva, Switzerland, World Meteorological Organization, 802-806. Abstract
In order to investigate the feasibility of seasonal forecasts, a prediction system is developed. Here the main theme is the study of atmospheric physics parameterization for coupled air-sea modeling. The oceanic GCM uses 1 degree global grid with a finer resolution in the equatorial belt. The atmospheric GCM has the spectral T30 representation, which includes all of the usual physics parameterizations. Using a first version of the model (Coupled Model I) and a set of appropriate initial conditions, the capability of El Niño and La Niña forecasting with a 13 month lead time was tested, resulting in successful forecasts of the 1982/83 and 1988/89 events (Rosati et al., 1995b). However, longer runs of this system have revealed a sizable systematic error in simulations with a tendency to cool most of the world ocean, particularly the western tropical Pacific, and also without an adequate annual cycle of the SST in the eastern tropical Pacific.
In order to improve some of these features, particularly the ENSO phenomena, various versions of the atmospheric parameterizations and mountain representation are incorporated into the atmospheric GCM, and the model simulations are examined. The experiments are divided into two steps: one is with the uncoupled atmospheric model, and the other is with the coupled model. In the first step, five year simulations are carried out with the observed SST prescribed, and the results are compared with observations, which enables one to make the critical validation of the model. The second step is to couple the atmospheric and oceanic models, and integrate them from a January 1982 initial condition for 7 years, and also for another initial condition, i.e., January, 1988 for 13 months.
Compared with the boundary forced simulation, the coupling process introduces more degree of freedom, with increase of the sensitivity as well as the complexity considerably. In particular, the El Niño simulation is sensitive to any change of physics. For this reason, the objective of the simulation is focused only on the equatorial Pacific process and secondly the Indian monsoon, as opposed to the overall improvement of the general circulation. In other words, the approach is close to that of mechanistic modeling with specific targets rather than that of a GCM with broader objectives. The research is proceeding in two directions. One is: investigating the model's sensitivity for El Niño and La Niña processes to variation in a coupling parameter. The second is: after a number of trial-and-error experiments on various combinations of the parameterizations, the second atmospheric model, i.e., Model II, is selected. It is shown that Coupled Model II performs substantially better in some aspects but worse in other aspects than Coupled Model I. The improvement is found in the SST: warming occurs not only over the equatorial Pacific but also over the whole globe. The SST increase is achieved by the strong effect of the cumulus convection. On the other hand, some deficiencies remain the same in both models, i.e., the large positive errors of the SST in the eastern oceans, the lack of an annual cycle of the SST in the eastern equatorial Pacific, and the failure in forecast of the second El Niño. In summary, the prediction of the Southern Oscillation has been achieved by the two models for a full first cycle but not for the second cycle .
Gordon, C T., 1992: Comparison of 30-day integrations with and without cloud-radiation interaction. Monthly Weather Review, 120(7), 1244-1277. Abstract PDF
A parameterization package for cloud-radiation interaction is incorporated into a spectral general circulation model (GCM). Fractional cloud amount is predicted quasi-empirically; cloud optical depth is specified for warm clouds and anvil cirrus, but depends on temperature for other subfreezing clouds; the long-and shortwave thermal, and dynamical response to cloud-radiation interaction are investigated for the extended forecast range, primarily by performing two sets of 30-day integrations from real initial conditions for three Northern Hemisphere (NH) winter and three NH summer cases: (i) CLDRADI, with cloud-radiation interaction; and (ii) LONDON, with this GCM's traditional specification of climatological zonal-mean cloud amount and global-mean cloud optical properties.
The 30-day mean CLDRADI fields of total and high cloud amount and corresponding outgoing longwave radiation (OLR) fields are plausible in many respects, especially in the tropics, where the latter exhibit South Pacific convergence zone (SPCZ)-like and some intertropical convergence zone (ITCZ)-like features, in qualitative agreement with Nimbus-7 and Earth Radiation Budget Experiment (ERBE) observations. Also, the predicted monthly mean OLR anomalies (relative to model climatology) respond to interannual variations in sea surface temperature. Cloud amount and cloud optical depth are apparently underestimated, however, over the higher-latitude oceans, especially over the Southern Hemisphere (SH) circumpolar low pressure belt and Antarctica. The zonal mean bias in shortwave and net radiation remains large at high latitudes in the summer hemisphere, despite the improved longitudinal structure in the tropics.
Cloud-radiation interaction elicits a cirrus warming response, which reduces the tropical upper-tropospheric cold bias by ~1-2 K. Over Antarctica, the warm bias in SH summer and cold bias in SH winter are both considerably reduced. During NH winter, the tropical upper troposphere experiences a significant westerly acceleration, including a sign reversal of the zonal-mean zonal wind. By being more conducive to meridional propagation, CLDRADI's tropical westerlies may contribute to the amplification of the quasi-stationary planetary waves in the SH summer extratropics. Otherwise, the impact of cloud-radiation interaction on extratropical geopotential height is generally minimal at extended range.
Gordon, C T., William F Stern, and R D Hovanec, 1985: A simple scheme for generating two layers of radiatively constrained effective clouds in GCMs. Journal of Geophysical Research, 90(D6), 10,563-10,585. Abstract PDF
GCM-dependent, radiatively constrained cloud amount fields could be preferable to currently available observed fields for calculating radiative fluxes in GCM's used in long-range weather forecast studies. Motivated by this premise, we formulate an economical effective cloud algorithm for GCM's called "SATCLD," which utilizes compact, readily accessible analyses of observed satellite-derived radiative flux data. We then examine the plausibility of preliminary effective cloud fields. Analysis of SATCLD and other cloud fields and associated radiative fluxes (diagnosed by our GCM's cloud radiation model from observed atmospheric temperature and water vapor data) also provides some insight into biases in our GCM's cloud radiation model and surface albedo field. "SATCLD" generates effective low and high cloud amounts at each GCM grid point by minimizing the sum of the squares of the local residual (i.e., model-diagnosed minus observed) shortwave and longwave radiative fluxes. The preliminary SATCLD effective cloud amount fields seem plausible in many respects, based upon comparison with the satellite-derived 3DNEPH and surface-based SFCOBS analyses. In the tropics, the SATCLD effective high cloud amount is rather well correlated with 3DNEPH, while systematic differences in low cloud amount are evident in July. Off the west coasts of Central and South America and southern Africa, the SATCLD effective low cloud resembles SFCOBS in July. At mid-latitudes, the strongest similarities are between SATCLD versus 3DNEPH high cloud amount in July and SATCLD versus SFCOBS low cloud amount over the oceans. The SATCLD analysis is ill conditioned in the polar night region. Limitations of the present scheme as well as deficiencies in our GCM's cloud-radiation model and surface albedo fields and in the archived satellite data are discussed. Suggestions are made for reducing discrepancies between effective versus real clouds without sacrificing consistency between GCM-diagnosed versus observed radiative fluxes.
Gordon, C T., R D Hovanec, and William F Stern, 1984: Analyses of monthly mean cloudiness and their influence upon model-diagnosed radiative fluxes. Journal of Geophysical Research, 89(D3), 4713-4738. Abstract PDF
Two different monthly mean analyses of low, middle, and high cloud amounts for January 1977 and July 1979 are compared: 3DNEPH is a condensed version (northern hemisphere only) of the Air Force 3D-Neph analysis, which incorporates satellite data plus surface observations of clouds and auxiliary meteorological data. SFCOBS is objectively analyzed from surface observations of clouds. The SFCOBS and 3DNEPH analyses of low cloud amounts agree qualitatively in the winter extratropics. The 3DNEPH ITCZ is much more sharply defined than the SFCOBS. The sensitivity of radiative fluxes to 3DNEPH, SFCOBS, and zonal mean 3DNEPH clouds is then evaluated. The fluxes are diagnosed by a cloud-radiation model utilizing "observed" monthly mean temperature and water vapor fields and are verified against satellite data. The outgoing longwave radiative flux clearly verifies best for 3DNEPH clouds and worst for zonal mean 3DNEPH clouds in the tropics. It is predominately controlled by surface temperature in the winter extratropics. Generally speaking, the shortwave fluxes do not verify as well as the longwave fluxes. Also, outside of the winter extratropics, the net radiative fluxes correlate poorly with observation. Biases in the zonal mean long and shortwave fluxes can be reduced by adjusting other cloud-related parameters. Based upon the above results, it may be worthwhile to construct a monthly mean cloud climatology from a condensed version of the 3D-Neph. However, alternative strategies should also be explored, such as the development of cloud analysis schemes that constrain the model-diagnosed net radiative flux to be consistent with observation.
Gordon, C T., and William F Stern, 1984: Medium range prediction by a GFDL global spectral model: results for three winter cases and sensitivity to dissipation. Monthly Weather Review, 112(2), 217-245. Abstract PDF
A preliminary evaluation is made of the medium range predictive capability of a GFDL global spectral model of the atmosphere, based upon three winter blocking cases. Analogous forecasts by a GFDL global grid point model provide a background standard of comparison. The spectral model is rhomboidally truncated at wavenumber 30, has 9 sigma levels, incorporates sub-grid scale physical processes commonly associated with general circulation models and employs semi-implicit time differencing. The grid point model has somewhat finer horizontal resolution and fairly similar sub-grid scale physical processes, and employs explicit time differencing. The spectral model is up to 6 times more economical. The level of forecast skill for the 5 to 15 day range is generally less than practically useful and is more case-dependent than spectral versus grid point model-dependent. In the most successful case, i.e., 16 January 1979, an observed Atlantic blocking ridge is simulated quite well, especially by the spectral model. The predicted Atlantic ridges tend to retard approaching upstream transient disturbances. A zonal bias of the midlatitude circulation, which develops in all three spectral and grid point model predictions is most pronounced in the spectral model forecast from 1 January 1977. Results of a diffusion sensitivity experiment and other evidence suggest that insufficient frictional dissipation may have enhanced the zonal bias of the above forecast. The bias diminishes, consistent with a redistribution of spectral kinetic energy among zonal wavenumbers 0, 1 and 2, if a static stability-dependent parameterization of vertical mixing or stronger Δ4 horizontal diffusion are used. Also, the predicted-enstrophy spectrum at midlatitudes steepens, given the stronger Δ4 horizontal diffusion.
January 1977 was a month noted for its extraordinary weather over North America. The winter was dominated by two persistent large amplitude ridges positioned over the west coast of North America and the Icelandic region of the Atlantic Ocean. A very intense trough reached deep into the eastern United States and caused one of the coldest Januaries on record. One-month integrations of various GCMs were conducted in order to test their ability to simulate this blocking event. Reasonably high resolution finite difference and spectral models available at GFDL were used. Each GCM was integrated from three different analyses of the initial conditions. For some models, a fairly accurate forecast was obtained and considerable skill was recognized in the simulation of the 30-day evolution in terms of the 5-day or 10-day mean flow fields, including the period of record breaking coldness over the eastern United States. The main conclusion is that proper treatment of the subgrid-scale processes as well as sufficient spatial resolution are essential for the simulations of this phenomenon as an initial value problem. Weak zonal wind poleward of about 40 degrees N and upstream of the blocking ridge appears to be crucial for the successful simulation of the sustained blocking ridge.
A multi-level, global, spectral transform model of the atmosphere, based upon spherical harmonics, has been developed at GFDL. The basic model has nine sigma levels in the vertical and rhomboidal spectral truncation at wavenumber 30. However, finer spectral or vertical resolution versions are available as well. The model's efficient semi-implicit time differencing scheme does not appear to adversely affect medium range predictions. The model has physical processes commonly associated with grid point GCM's. Two unique features are a linearized virtual temperature correction and an optional, spectrally-computed non-linear horizontal diffusion scheme. A parameterization of vertical mixing based upon the turbulent closure method is also optional.
The GFDL spectral model has been widely utilized at GFDL for extended range weather prediction experiments. In addition, it has been adapted and applied to climate studies, four-dimensional data assimilation experiments and even to the atmosphere of Venus. These applications are briefly reviewed.
Gordon, C T., and William F Stern, 1982: Sensitivity of GCM-diagnosed radiative fluxes to "observed" monthly mean distributions of cloudiness In Proceedings of the Sixth Annual Climate Diagnostics Workshop, Washington, DC, NOAA, 268-278.
Gordon, C T., L Umscheid, and Kikuro Miyakoda, 1972: Simulation experiments for determining wind data requirements in the tropics. Journal of the Atmospheric Sciences, 29(6), 1064-1075. Abstract PDF
Numerical simulation experiments are performed with a 9-level global general circulation model to help determine how much wind data in the tropics are needed for the reconstruction of meteorological fields. Prediction runs are updated every 12 hr with hypothetical data generated from the same model.
It is found that the asymptotic root mean square (rms) wind errors in the tropics, particularly in the 11S-11N "equatorial" latitude belt, fail to meet the GARP data requirements for the FGGE if surface pressure and temperature data alone are used for updating. The addition of tropical wind data at just two vertical levels leads to a significant, but insufficient, reduction of rms wind errors within the "tropics" (26S-26N); the largest errors remain near the equator. However, these errors become acceptably small if wind data are inserted at all 9 levels within the equatorial region. Another result is that insertion of tropical wind data at just two levels has a sizable influence upon wind errors even in the extratropics.
A critique of some implicit assumptions made in simulation experiments of the type we have performed is included.
