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FROM VOLUME 10, NUMBER 5, MAY 1997

PROFESSIONAL PUBLICATIONS...
GLOBAL MODELING

Item #d97may16

Two items in J. Geophys. Res., 102(D5), Mar. 20, 1997:

"Evaluation and Intercomparison of Global Atmospheric Transport Models Using 222Rn and Other Short-Lived Tracers," D.J. Jacob (Dept. Earth & Planetary Sci., Harvard Univ., 29 Oxford St., Cambridge MA 02138; e-mail: djj@io.harvard.edu), M.J. Prather et al., 5953-5970. Reports on an intercomparison, sponsored by the World Climate Research Program in 1993, to evaluate the capability of global models to capture the contributions of convective and synoptic processes to transport on a global scale.

"Results from the Intergovernmental Panel on Climate Change Photochemical Model Intercomparison (PhotoComp)," J. Olson (NASA-Langley Res. Ctr., Hampton VA 23681; e-mail: j.r.olson@larc.nasa.gov), M. Prather et al., 5979-5991. PhotoComp was a tightly controlled model experiment intended to determine the consistency among models used to predict changes in tropospheric ozone. Calculated tropospheric photodissociation rates displayed significant differences.

Item #d97may17

"Climate Forcing-Response Relationships for Greenhouse and Shortwave Radiative Perturbations," V. Ramaswamy (NOAA/GFDL, POB 308, Princeton NJ 08542; e-mail: vr@gfdl.gov), C.T. Chen, Geophys. Res. Lett., 24(6), 667-670, Mar. 15, 1997.

Experiments with a general circulation model are used to compare the nature of global radiative forcings (like CO₂) and localized forcings (like sulfate aerosols). The total climate feedback in the various experiments did not differ significantly, and the global-mean climate sensitivity was nearly the same for both global and spatially confined forcings. However, forcings confined to the Northern Hemisphere midlatitudes exhibited a steepening of the meridional gradient of temperature response.

Item #d97may18

"Linear Additivity of Climate Response for Combined Albedo and Greenhouse Perturbations," V. Ramaswamy (address above), C.T. Chen, ibid., 24(5), 567-570, Mar. 1, 1997.

Uses model experiments to explore the extent to which the radiative effects of globally distributed greenhouse gases and of regionally distributed sulfate aerosols are linearly additive. Concludes that certain aspects of climate responses are indeed additive, but there are several reservations.

Item #d97may19

"The Second Hadley Centre Coupled Ocean-Atmosphere GCM: Model Description, Spinup and Validation," T.C. Johns (Hadley Ctr., Meteor. Off., London Rd., Bracknell, Berkshire RG12 2SY, UK; e-mail: tcjohns@meto.govt.uk), R.E. Carnell et al., Clim. Dynamics, 13(2), 103-134, Feb. 1997.

Describes the new model and how its performance has improved over that of the previous version. Verification runs emphasize the importance of including forcing terms apart from greenhouse gases (such as sulfate aerosols) in climate simulations.

Item #d97may20

"On Modification of Global Warming by Sulfate Aerosols," J.F.B. Mitchell (Hadley Ctr., Meteor. Off., London Rd., Bracknell, Berkshire RG12 2SY, UK; e-mail: jfbmitchell@meteo.gov.uk), J. Clim., 10(2), 245-267, Feb. 1997.

Compares patterns of response in the surface climatology of a coupled ocean-atmosphere general circulation model forced by increased CO₂ alone, to patterns caused by forcing from both CO₂ and aerosols, from early industrial times to the end of the 21st century. Comparisons for 2030-2050, when the aerosol forcing is a maximum, showed that in summer, the cooling due to aerosols weakens the monsoon circulations and reverses some of the changes in the hydrologic cycle caused by greenhouse gases. Changes in aerosol concentrations of the magnitude projected in the scenarios would have a major effect on regional climate, especially over Europe and Southeast Asia.

Item #d97may21

"The Effect of Greenhouse SSTs on ENSO Simulations with an AGCM," I.N. Smith (Div. Atmos. Res., CSIRO, PMB 1, Mordialloc, Victoria 3195, Australia), M. Dix, R.J. Allan, ibid., 342-352.

Model experiments with 2 X CO₂ and prescribed sea surface temperatures suggest that increased static stability may dampen the effects of any nonlinear increase in evaporation and that any changes in the behavior of ENSO due to predicted temperature increases in the tropics may not be significant.

Item #d97may22

"Simulated ENSO in a Global Coupled Ocean-Atmosphere Model: Multidecadal Amplitude Modulation and CO₂ Sensitivity," T.R. Knutson (NOAA/GFDL, POB 308, Princeton NJ 08542; e-mail: tk@gfdl.gov), S. Manabe, D. Gu, ibid., 10(1), 138-161, Jan. 1997.

Results suggest that the impact of increased CO₂ on ENSO is unlikely to be clearly distinguishable from climatic variability in the near future-unless ENSO is substantially more sensitive to increased CO₂ than indicated in the present study.

Item #d97may23

"Modeling the Exchanges of Energy, Water, and Carbon Between Continents and the Atmosphere," P.J. Sellers (Johnson Space Flight Ctr., NASA, Mail Code CB, Houston TX 77058), R.E. Dickinson et al., Science, 275(5299), 502-509, Jan. 24, 1997.

Reviews the past 20 years' development of land surface parameterization resulting from advances in plant research, satellite data interpretation, and large-scale field experiments. Schemes will soon be able to model the biological and physical responses of the Earth system to future global change.

Item #d97may24

"An Integrated Biosphere Model of Land Surface Processes, Terrestrial Carbon Balance, and Vegetation Dynamics," J.A. Foley (Inst. Environ. Studies, Univ. Wisconsin, 1225 S. Dayton, Madison WI 53706; e-mail: jfoley@facstaff.wisc.edu), I.C. Prentice et al., Global Biogeochem. Cycles, 10(4), 603-628, Dec. 1996.

Presents a new terrestrial biosphere model which incorporates land surface biophysics, terrestrial carbon fluxes and global vegetation dynamics in a single, physically consistent modeling framework. It provides a means of simulating both rapid biophysical processes and long-term ecosystem dynamics in atmospheric models.

Item #d97may25

"Climate Change from Increased CO₂ and Direct and Indirect Effects of Sulfate Aerosols," G.A. Meehl (Clim. & Global Dynamics Div., NCAR, POB 3000, Boulder CO 80307; e-mail: meehl@ncar.ucar.edu), W.M. Washington et al., Geophys. Res. Lett., 23(25), 3755-3758, Dec. 15, 1996.

Gives preliminary results from the first climate sensitivity experiments that included the indirect forcing effect of sulfate aerosols (through clouds), in addition to the direct aerosol effect on albedo and the effect of transient greenhouse gas forcing. Simulations corresponding to roughly 35 years into the future indicate tropospheric warming almost everywhere, as the CO₂ forcing overwhelms the negative radiative forcing from the sulfate aerosols. There is also a general indication of weakening of the south Asian monsoon.

Item #d97may26

"Comparisons of Time Series from Two Global Models with Tide Gauge Data," R. Tokmakian (Dept. Oceanog., Naval Postgrad. Sch., 833 Dyer Rd., Rm. 328, Monterey CA 93943; e-mail: robint@ucar.edu), Geophys. Res. Lett., 23(25), 3759-3762, Dec. 15, 1996.

Demonstrates that two global ocean models, being used to understand ocean dynamics by a large number of investigators, adequately represent local instantaneous sea level. Discusses implications for global climate modeling.

Item #d97may27

"A University Perspective on Global Climate Modeling," D.A. Randall (Dept. Atmos. Sci., Colorado State Univ., Fort Collins CO 80523), Bull. Amer. Meteor. Soc., 77(11), 2685-2690, Nov. 1996.

Analyzes the roughly two dozen global modeling groups in the U.S., dividing them into four categories: laboratories and universities, and development and applications. Most groups are focusing on applications rather than development, contrary to the early days of modeling, especially in universities. A key role of university groups is to train new model developers. Outlines a simple but functional conceptual organization of U.S. modeling groups to promote model development and meet the needs of policy makers.

Item #d97may28

"Intercomparison of Heating Rates Generated by Global Climate Model Longwave Radiation Codes," F. Baer (Dept. Meteor., Univ. Maryland, College Pk. MD 20742; e-mail: baer@atmos.umd.edu), N. Arsky et al., J. Geophys. Res., 101(D21), 26,589-26,603, Nov. 27, 1996.

Seven frequently used algorithms were compared to assess their variability to input data. Differences in algorithm output were pronounced when clouds were present, particularly if clouds were thicker than one model level. For some cloud configurations, the resulting heating rate profiles appear to have no correspondence whatsoever to one another. The importance of these differences to ultimate GCM climate predictions is currently under study.

Item #d97may29

"The Project for Intercomparison of Land-Surface Parameterization Schemes (PILPS): 1992 to 1995," A. Henderson-Sellers, K. McGuffie, A.J. Pitman (Sch. Earth Sci., Macquarie Univ., North Ryde, Sydney, 2109 NSW, Australia; e-mail: apitman@penman.es.mq.edu.au), Clim. Dynamics, 12(12), 849-859, Nov. 1996.

Describes the planned five phases of the PILPS of the World Climate Research Program, and the status of each. The earlier phases show that individual land-surface schemes capture specific components of land-surface interactions with reasonable accuracy, but no one scheme captures the whole system satisfactorily and accurately. The final phase will couple selected land-surface schemes to the NCAR climate system model and to the Australian Bureau of Meteorology limited area model.

Item #d97may30

"Detecting Greenhouse-Gas-Induced Climate Change with an Optimal Fingerprint Method," G.C. Hegerl, (Max Planck Inst. Meteor., Bundestr. 55, D-21046 Hamburg, Ger.), J. Clim., 9(10), 2281-2306, Oct. 1996.

This study attempts to detect anthropogenic climate change in the observational record of near-surface temperatures by trying to identify as a "fingerprint" the spatial and temporal changes in temperature that are expected to characterize anthropogenic change, should it be present. A coupled ocean-atmosphere general circulation model is used, both to estimate the fingerprint and to estimate natural climatic variability. The estimate of natural variability is then used to statistically modify (optimize) the fingerprint to reduce the confounding influence of random fluctuations.

The null hypothesis, that the latest observed 20-year and 30-year trend of near-surface temperature (ending in 1994) is part of natural climate variability, is rejected with a risk of less than 2.5%-5%. However, to attribute the observed warming uniquely to anthropogenic greenhouse gas forcing, more information is needed on the climate's response to other forcing mechanisms (e.g., changes in solar radiation, or volcanic or anthropogenic sulfate aerosols) and their interactions. Furthermore, the estimate of internal (natural) climate variability is still uncertain. With these caveats, the conclusion remains that a statistically significant, externally induced warming has been observed.

Item #d97may31

"An Accurate Parameterization of the Solar Radiative Properties of Cirrus Clouds for Climate Models," Q. Fu (Dept. Oceanog., Dalhousie Univ., Halifax NS B3H 4J1, Can.; e-mail: qfu@atm.dal.ca), J. Clim., 9(9), 2058-2082, Sep. 1996.

The parameterization is based on improved light scattering calculations using ice crystal size distortions measured by aircraft. Evaluation of the parameterization demonstrates its reliability for climate model applications.

Item #d97may32

"An Ocean Dynamical Thermostat," A.C. Clement (Lamont-Doherty Earth Observ., Rte. 9W, Palisades NY 10964; e-mail: clement@lamont.ldeo.columbia.edu), R. Seager et al., ibid., 2190-2196.

Investigates the role of ocean dynamics in the regulation of tropical sea surface temperature using a coupled ocean-atmosphere model. Results suggest that ocean dynamics can be a complicating but essential element in climate change studies.

Item #d97may33

"Future Ocean Uptake of CO₂: Interaction Between Ocean Circulation and Biology," E. Maier-Reimer (M. Planck Inst. Meteor., Bundesstr. 55, D-20146 Hamburg, Ger.), U. Mikolajewicz, A. Winguth, Clim. Dynamics, 12(10), 711-721, Sep. 1996.

Experiments using an ocean GCM subjected to global warming coupled with a model of ocean biogeochemical cycling. Results justify the practice of running climate models and carbon cycle models independently, as feedbacks are slight.

Item #d97may34

"Climate: The Elements," J.A.T. Bye (Flinders Inst. for Atmos. & Marine Sci., Flinders Univ., GPO Box 2100, Adelaide 5001, Australia), R.A.D. Byron-Scott, A.H. Gordon, J. Clim., 9(7), 1546-1560, July 1996.

Presents an analytical climate model and examines the statistics of simulated climates generated by atmospheric random forcing.