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ongoing meta respect | 01.07.2005 15:04 | G8 2005 | Analysis | Social Struggles | Technology | London

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Climate Theory and Modeling

In the area of theory and modeling, branch research efforts are focused on two complementary streams: cloud-radiative processes and climate dynamics. Plane-parallel radiation codes are developed for use in calculating radiative effects of clouds, water vapor, and the liquid water drop-size distribution; for the estimation of surface energy balance; and for radiative-convective boundary layer equilibrium calculations. The radiation codes include effects of absorption, emission, and scattering of radiation due to water vapor, clouds, aerosols, CO2, O3, O2, and minor trace gases. Using multi-level energy-balance models derived from the radiation models, branch scientists have carried out a series of sensitivity experiments to study the effect of CO2, clouds, volcanic eruptions, and SO2 emission on global climate change. Work is underway to develop a versatile radiation modular code that separates spectral information from the radiative transfer computations so that it can be used readily in general circulation models to test out different climate feedback hypotheses. The full 3D radiative transfer problem through inhomogeneous clouds is being studied by both Monte Carlo and analytic methods, using a variety of cloud structure models with parameters determined by analysis of data from the DOE ARM and NASA FIRE field programs. Results of the 3D studies are parameterized in terms of "effective" cloud parameters for use in plane-parallel GCM codes, and also provide improved algorithms for the retreival of cloud parameters from remote sensing data.

For climate dynamics studies, a hierarchy of models ranging from one-dimensional radiative-convective models to coupled atmosphere-ocean-land models with full physics is used. A one-dimensional model (or single-column model, SCM) derived from the Goddard Laboratory for Atmospheres (GLA) Global Circulation Model (GCM) has been used to study the effect of radiation/dynamic feedback using the modified Arakawa-Schubert cumulus parameterization in leading to steady state or oscillatory behavior of tropical convection. In support of TOGA, intermediate two- and three-dimensional models are used to study the fundamental linkage between diabatic heating and dynamics of the tropical atmosphere, leading to theoretical interpretations of the observed multi-scale and multi-frequency nature of hydrological processes in the tropics from intraseasonal variations (such as the Madden-Julian oscillation, super cloud clusters, twin cyclones, and westerly wind bursts) to interannual time scales (as for example in El Niño).

In cooperation with Goddard's Global Modeling and Assimilation Office (GMAO) branch scientists are also involved in developing improved physical parameterizations (including cloud liquid water, cumulus heating, surface fluxes, boundary layer processes, and land-atmosphere interactions) in the GCMs. Using these GCMs (including the GEOS GCM and the fvGCM), climate simulation experiments are carried out to study global and regional climate, focusing on the mean and variability of the global water and energy cycles. Model results are compared with climatological observations as well as satellite and in situ observations obtained during special field experiments such as FIRE and TOGA/COARE. In support of TRMM, numerical experiments have also been carried out using the Goddard cumulus ensemble model to study the water budget and physics of tropical cumulus clusters and their changes as a function of surface temperature. Branch members participate in international model intercomparison projects to assess individual model performance against common references, to seek improvements in model physics, and to evaluate collective progress in climate modeling research.

Contact: David Mocko

Modeling Related Publications:

Yang, F., A. Kumar, and W. K.-M. Lau, 2005: Potential predictability of US summer climate with "perfect" soil moisture. J. Hydrometeorol.. (In press)

The potential predictability of surface-air temperature and precipitation over the United States was assessed for a GCM forced by observed sea surface temperatures and an estimate of observed soil moisture content. The latter was obtained by substituting the GCM simulated precipitation, which is used to drive the GCM’s land-surface component, with observed pentad-mean precipitation at each time step of the model’s integration. With this substitution, the simulated soil moisture correlates well with an independent estimate of observed soil moisture in all seasons over the entire US continent. Significant enhancements for the predictability of surface-air temperature and precipitation were found in boreal late spring and summer over the US continent. Anomalous pattern correlations of precipitation and surface-air temperature over the US continent in the June-July-August season averaged for the 1979-2000 period increased from 0.01 and 0.06 for the GCM simulations without precipitation substitution to 0.23 and 0.31, respectively, for the simulations with precipitation substitution. The results provide an estimate for the limits of potential predictability if soil moisture variability is to be perfectly predicted. However, this estimate may be model dependent, and needs to be substantiated by other modeling groups.
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Jin, M., and J. M. Shepherd, 2005: Inclusion of urban landscape in a climate model - How can satellite data help?. Bull. Am. Met. Soc.,
86, 681-896.

Urban regions, which cover only approximately 0.2% of the earth’s land surface, contain about half of the human population (UNPD 2001). Modeling urban weather and climate is critical for human welfare, but has been hampered for at least two reasons: i) no urban landscape has been included in global and regional climate models (GCMs and RCMs, respectively), and ii) detailed information on urban characteristics is hard to obtain. With the ad¬vance of satellite observations, adding urban schemes into climate models in order to scale projections of global/regional climate to urban areas becomes es¬sential. Inclusion of urbanized landscape into climate models was discussed in depth at the fall American Geophysical Union (AGU) meeting of 2003 in the session entitled “Human-induced climate variations linked to urbanization: From observations to model¬ing,” which took place on 12 December 2003 in San Francisco, California. The following notes summa¬rize what is known and what needs to be advanced on this topic.
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Cahalan, R. F., L. Oreopoulos, A. Marshak, K. F. Evans, A. Davis, R. Pincus, K. Yetzer, B. Mayer, R. Davies, T. Ackerman,
H. Barker, E. Clothiaux, R. Ellingson, M. Garay, E. Kassianov, S. Kinne, A. Macke, W. OHirok, P. Partain, S. Prigarin, A. Rublev,
G. Stephens, F. Szczap, E. Takara, T. Varnai, G. Wen, and T. Zhuravleva, 2005: The International Intercomparison of 3D
Radiation Codes (I3RC): Bringing together the most advanced radiative transfer tools for cloudy atmospheres.
Bull. Amer. Meteor. Soc.. (In press)

The interaction of clouds with solar and terrestrial radiation is one of the most important topics of climate research. In recent years it has been recognized that only full three-dimensional (3D) treatment of this interaction can provide answers to many climate and remote sensing problems, leading to worldwide independent development of numerous 3D radiative transfer (RT) codes. The "International Intercomparison of 3-Dimensional Radiation Codes", or I3RC, described in this paper, sprung from the natural need to compare the performance of these 3D RT codes used in a variety of current scientific work in the atmospheric sciences. I3RC supports intercomparison and development of both exact and approximate 3D methods in its effort to: (1) understand and document the errors and limits of 3D algorithms and their sources; (2) provide “baseline” cases for future code development for 3D radiation; (3) promote sharing and production of 3D RT tools; (4) derive guidelines for 3D RT tool selection; and (5) improve atmospheric science education in 3D RT. Results from I3RC have been presented in two workshops, and are expected to guide improvements in both remote sensing and radiative energy budget computations in cloudy atmospheres.
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Marshak, A., Yu. Knyazikhin, M. L. Larsen, and W. J. Wiscombe, 2005:
Small-scale drop size variability: Empirical models for drop-size-dependent clustering in clouds. J. Atmos. Sci., 62, 551-558.


By analyzing aircraft measurements of individual drop sizes in clouds, it has been shown in a companion paper that the probability of finding a drop of radius r at a linear scale s decreases as s in power D(r), where D(r) is between 0 and 1. This paper shows striking examples of the spatial distribution of large cloud drops using models that simulate the observed power laws. In contrast to currently used models that assume homogeneity and a Poisson distribution of cloud drops, these models illustrate strong drop clustering, especially with larger drops. The degree of clustering is determined by the observed exponents D(r). The strong clustering of large drops arises naturally from the observed power-law statistics. This clustering has vital consequences for rain physics, including how fast rain can form. For radiative transfer theory, clustering of large drops enhances their impact on the cloud optical path. The clustering phenomenon also helps explain why remotely sensed cloud drop size is generally larger than that measured in situ.

Sud, Y. C., D. M. Mocko, and S.-J. Lin, 2005: Performance of McRAS vis-a-vis CCM3 clouds and radiation
parameterizations in the fvGCM for the anomalously wet May and June 2003 over the continental United States and Amazonia.
J. Geophys. Res., submitted. (Submitted)


An objective assessment of the impact of any new cloud-scheme in a model entails an examination of both short-term weather and monthly-/seasonal-averaged climate predictions. This assessment is achieved in this investigation with a set of ensemble forecasts that enable evaluation over both weather and climate time-scales. We evaluated our cloud parameterization scheme, named McRAS, along with an improved radiation scheme, in the finite-volume GCM against the NCAR-CCM3 cloud/radiation schemes that are operational in the fvGCM to assess their relative performance. We chose the boreal summer months of May and June 2003 that were characterized by an anomalously wet eastern half of the continental United States and northern regions of Amazonia. Our evaluation used an ensemble of daily 10-day forecasts for the period. Each forecast was started from the analyzed initial state of the atmosphere and continuously spun-up soil-moisture from the previous 1-day forecasts. Monthly statistics of these forecasts with up to 10-day lead-time provided a robust estimate of the behavior of the simulated monthly rainfall anomalies. Patterns of simulated versus observed rainfall, 500-hPa heights, and top-of-the-atmosphere net radiation were recast into regional anomaly correlations. These correlations were compared among the simulations with the separate schemes. The results show that fvGCM with McRAS and improved radiation performed discernibly better than the original fvGCM. The McRAS cloud scheme also showed a reasonable positive response to the observed SST on mean monthly rainfall fields at different time-leads. This analysis represents a systematic evaluation prior to selection of new scheme in a global model.

View ALL Climate Related Modeling Pulications
________________________________ 2004 Technical Highlights Contents
Appendix A3. Highlighted Articles

Climate and Radiation Branch
Chiu, J.-Y.C., A. Marshak, and W.J. Wiscombe, 2004: The effect of surface heterogeneity on cloud absorption estimates,
Geophys. Res. Lett.,31, L15105, doi:10.1029/2004GL020104.

Ichoku, C., Y.J. Kaufman, L.A. Remer, and R. Levy, 2004: Global aerosol remote sensing from MODIS, Adv. Space Res., 34, 820–827.

Jin, M., 2004: Analysis of skin temperature variations using long-duration AVHRR observations, Bull. Am. Meteor. Soc., 85(4), 587-600, doi:10.1175/BAMS-85-4-587.

King, M.D., S. Platnick, P. Yang, G.T. Arnold, M.A. Gray, J. Riedi, S.A. Ackerman, and K.N. Liou, 2004: Remote sensing of liquid water and ice cloud optical thickness and
effective radius in the Arctic: Application of airborne multispectral MAS data, J. Atmos. Oceanic Technol.,21, 857–875.

Koren, I., Y.J. Kaufman, L.A. Remer, and J.V. Martins, 2004: Measurement of the effect of Amazon smoke on inhibition of cloud formation, Science, 303, 1342–1345.

Levy, R.C., L.A. Remer, and Y.J. Kaufman, 2004: Effects of neglecting polarization on the MODIS aerosol retrieval over land, IEEE Trans. Geosci. Remote Sen., 42(11), 2576–2583.

Marshak, A., Y. Knyazikhin, K. Evans, and W. Wiscombe, 2004: The “RED versus NIR” plane to retrieve broken-cloud optical depth from ground-based measurements,
J. Atmos. Sci., 61, 1911–1925.

Oreopoulos, L., M.-D. Chou, M. Khairoutdinov, H.W. Barker, and R.F. Cahalan, 2004: Performance of Goddard Earth Observing System GCM column radiation models under
heterogeneous cloud conditions, Atmos. Res., 72, 365–382.


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