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Stone, PH, Quirk WJ, Somervil.Rc.  1974.  Effect of Small-Scale Vertical Mixing of Horizontal Momentum in a General Circulation Model. Monthly Weather Review. 102:765-771.   10.1175/1520-0493(1974)102<0765:teossv>;2   AbstractWebsite

Several experiments are described in which the sub-grid-scale vertical eddy viscosity in the GISS global general circulation model was varied. The results show that large viscosities suppress large-scale eddies in middle and high latitudes, but enhance the circulation in the tropical Hadley cell and increase the extent of the tropical easterlies. Comparison with observations shows that the GISS model requires eddy viscosities 1 m2/s or less to give realistic results for middle and high latitudes, and eddy viscosities 100 m2/s to give realistic results for low latitudes. A plausible mechanism for the implied increase in small-scale mixing in low latitudes is cumulus convection.

Somerville, RCJ, Iacobellis SF.  1999.  Single-column models, ARM observations, and GCM cloud-radiation schemes. Physics and Chemistry of the Earth Part B-Hydrology Oceans and Atmosphere. 24:733-740.   10.1016/s1464-1909(99)00074-x   AbstractWebsite

Among the most serious sources of uncertainty in current general circulation models (GCMs) is the treatment of clouds and cloud-radiation interactions. We have used a single-column model (SCM) diagnostically to evaluate parameterizations against observations from the Atmospheric Radiation Measurement (ARM) Program. We find that schemes with explicit cloud water budgets and interactive radiative properties are potentially capable of matching observational data closely. In our SCM, using an interactive cloud droplet radius decreases the cloud optical thickness and cloud infrared emittance of high clouds, which acts to increase the downwelling surface shortwave flux and the outgoing longwave radiation. However, it is difficult to evaluate the realism of the vertical distribution of model-produced cloud extinction, cloud emittance, cloud liquid water content and effective cloud droplet radius until high-quality observations of these quantities become more widely available. We also find that in the SCM, cloud parameterizations often underestimate the observed cloud amount, and that ARM observations indicate the presence of clouds while the corresponding maximum relative humidity is less than 80%. This implies that the underlying concept of a critical gridpoint relative humidity of about 80% for cloud formation, as used in many GCM cloud parameterizations, may need to be reexamined. (C) 1999 Elsevier Science Ltd. All rights reserved.

Somerville, RCJ.  1977.  Pattern Recognition Techniques for Weather Forecast Verification. Contributions to Atmospheric Physics [Beitraege zur Physik der Atmosphaere.], Wiesbaden, Germany. 50:403-410. Abstract
Somerville, RCJ.  2014.  Is learning about climate change like having a colonoscopy? Earth's Future. 2:119-121.: Wiley Periodicals, Inc.   10.1002/2013EF000169   Abstract

Many people avoid having valuable medical tests from fear of the results
People resist learning about climate change, fearing unpleasant consequences
Research suggests addressing these concerns early, aids in communication

Somerville, RCJ.  2012.  Science, Politics, and Public Perceptions of Climate Change. Climate Change. ( Berger A, Mesinger F, Sijacki D, Eds.).:3-17.: Springer Vienna   10.1007/978-3-7091-0973-1_1   Abstract

Recent research has demonstrated that climate change continues to occur, and in several aspects, the magnitude and rapidity of observed changes frequently exceed the estimates of earlier projections, such as those published in 2007 by the Intergovernmental Panel on Climate Change in its Fourth Assessment Report. Measurements show that the Greenland and Antarctic ice sheets are losing mass and contributing to sea-level rise. Arctic sea ice has melted more rapidly than climate models had predicted. Global sea-level rise may exceed 1 m by 2100, with a rise of up to 2 m considered possible. Global carbon dioxide emissions from fossil fuels are increasing rather than decreasing. This chapter summarizes recent research findings and notes that many countries have agreed on the aspirational goal of limiting global warming to 2°C above nineteenth-century “preindustrial” temperatures, in order to have a reasonable chance for avoiding dangerous human-caused climate change. Setting such a goal is a political decision. However, science shows that achieving this goal requires that global greenhouse gas emissions must peak within the next decade and then decline rapidly. Although the expert scientific community is in wide agreement on the basic results of climate change science, much confusion persists among the general public and politicians in many countries. To date, little progress has been made toward reducing global emissions.

Somerville, RCJ.  1987.  The predictability of weather and climate. Climatic Change. 11:239-246.: Kluwer Academic Publishers   10.1007/bf00138802   AbstractWebsite

The last thirty years have seen the development of comprehensive numerical models of the large-scale circulation of the atmosphere, based on physical principles. Such models are quite skillful at describing the evolving weather up to a few days ahead, despite imperfect theory and inadequate observational data. Yet even a hypothetical perfect model, which exactly represented the dynamics of the real atmosphere, and which used data from the best conceivable observing system, could not produce an accurate forecast of indefinitely long range. Any forecast must eventually lose skill because of the intrinsic instability of the atmosphere itself.This limitation on the predictability of the detailed evolution of the atmosphere (“weather”) does not preclude the possibility of seasonal and longer-range forecasts of means and other statistical properties (“climate”). However, we are only beginning to learn what aspects of climate may be predictable, and what theoretical tools and observational data will be required to predict them.

Somerville, RCJ.  1967.  A Nonlinear Spectral Model of Convection in a Fluid Unevenly Heated from Below. Journal of the Atmospheric Sciences. 24:665-676.: American Meteorological Society   10.1175/1520-0469(1967)024<0665:ansmoc>;2   AbstractWebsite

A two-dimensional form of the Boussinesq equations is integrated numerically for the case of a rectangular channel with a temperature gradient maintained along the bottom. The side walls are insulating, the top wall has a constant temperature, and the velocity obeys free boundary conditions on all four walls. The fields of stream function and temperature departure are represented by truncated double Fourier series, and integration of the initial-value problem for the spectral amplitudes results in steady states which agree qualitatively with those of previous experimental and theoretical investigations.Calculations are presented at two levels of truncation (wave numbers 2 and 3) for a wide range of Prandtl numbers and a moderate range of horizontal Rayleigh numbers and top temperatures. For sufficiently large gravitational stability, a single asymmetric convection cell develops. Its intensity and asymmetry increase markedly with increasing horizontal Rayleigh number, decrease with increasing top temperature, and respond very slightly to changes in Prandtl number. As the top temperature is decreased below the temperature of the warm side of the bottom, however, the possibility is indicated that the single cell may be modified by a Bénard-like multi-cellular structure.

Somerville, R.  2011.  The co-evolution of climate models and the Intergovernmental Panel on Climate Change. The development of atmospheric general circulation models : complexity, synthesis, and computation. ( Donner L, Schubert WH, Somerville R, Eds.).:225-252., Cambridge ; New York: Cambridge University Press Abstract

"Presenting a comprehensive discussion of general circulation models of the atmosphere, this book covers their historical and contemporary development, their societal context, and current efforts to integrate these models into wider earth-system models. Leading researchers provide unique perspectives on the scientific breakthroughs, overarching themes, critical applications, and future prospects for atmospheric general circulation models. Key interdisciplinary links to other subject areas such as chemistry, oceanography and ecology are also highlighted. This book is a core reference for academic researchers and professionals involved in atmospheric physics, meteorology and climate science, and can be used as a resource for graduate-level courses in climate modeling and numerical weather prediction. Given the critical role that atmospheric general circulation models are playing in the intense public discourse on climate change, it is also a valuable resource for policy makers and all those concerned with the scientific basis for the ongoing public-policy debate"--"The aim of this volume is to describe the development of atmospheric general circulation models. We are motivated to do so by the central and essential role of these models in understanding, simulating, and predicting the atmosphere on a wide range of time scales. While atmospheric general circulation models are an important basis for many societal decisions, from responses to changing weather to deliberations on responding to anthropogenic climate change, the scientific basis for these models, and how they have come about and continue to develop, are not widely known. Our objective in editing this volume is to provide a perspective on these matters"--

Somerville, RCJ.  2000.  Using single-column models to improve cloud-radiation parameterizations. General circulation model development. ( Randall DA, Ed.).:641-657., San Diego: Academic Press Abstract

General Circulation Models (GCMs) are rapidly assuming widespread use as powerful tools for predicting global events on time scales of months to decades, such as the onset of EL Nino, monsoons, soil moisture saturation indices, global warming estimates, and even snowfall predictions. While GCMs have been praised for helping to foretell the current El Nino and its impact on droughts in Indonesia, its full power is only now being recognized by international scientists and governments who seek to link GCMs to help them estimate fish harvests, risk of floods, landslides, and even forest fires. Scientists in oceanography, hydrology, meteorology, and climatology and civil, ocean, and geological engineers perceive a need for a reference on GCM design. In this compilation of information by an internationally recognized group of experts, Professor Randall brings together the knowledge base of the forerunners in theoretical and applied frontiers of GCM development. General Circulation Model Development focuses on the past, present, and future design of numerical methods for general circulation modeling, as well as the physical parameterizations required for their proper implementation. Additional chapters on climate simulation and other applications provide illustrative examples of state-of-the-art GCM design. Key Features * Foreword by Norman Phillips * Authoritative overviews of current issues and ideas on global circulation modeling by leading experts * Retrospective and forward-looking chapters by Akio Arakawa of UCLA * Historical perspectives on the early years of general circulation modeling * Indispensable reference for researchers and graduate students.

Somerville, RCJ, Galchen T.  1979.  A Numerical Simulation of Convection with Mean Vertical Motion. Journal of the Atmospheric Sciences. 36:805-815.   10.1175/1520-0469(1979)036<0805:nsocwm>;2   AbstractWebsite

The flow in a convectively unstable layer of fluid may be strongly influenced by large-scale ascent or descent. We consider cellular convection between horizontal surfaces on which vertical velocity is maintained at a constant value. Using an efficient numerical model to simulate the evolution of the convection in three space dimensions and time, we investigate the effect of the imposed vertical velocity on the flow.For moderately supercritical values of the Rayleigh number and for Prandtl numbers near unity, convection is known to occur in the form of steady rolls if the specified mean vertical motion is zero, i.e., in the case of the conventional Bénard problem for a Boussinesq fluid. Our model also produces rolls under these circumstances. For sufficiently large values of the imposed vertical velocity, however, the numerically simulated rolls are replaced by polygonal cells in which the direction of flow depends on whether ascent or descent is prescribed at the boundaries, in accordance with recent theoretical and laboratory results of R. Krishnamurti. We have also investigated the dependence of the convection on the Rayleigh and Prandtl numbers within limited ranges of these parameters, and we discuss several aspects of agreement and disagreement among analytical theory, laboratory experiment and numerical simulation.

Somerville, RCJ, Jouzel J.  2007.  Le groupe intergouvernemental d'experts sur l'evolution du climat: le consensus a l'échelle planétaire. Comprendre le changement climatique. ( André JC, Fellous JL, Gautier C, Eds.).:27-44., Paris: O. Jacob Abstract
Somerville, R.  1996.  The Forgiving Air : Understanding Environmental Change. :xiv,195p.., Berkeley, Calif.: University of California Press Abstract
Somerville, RCJ, Iacobellis SF.  1987.  Cloud-radiation interactions: Effects of cirrus optical thickness feedbacks. Short- and Medium-Range Numerical Weather Prediction. ( Matsuno T, Ed.).:177-185., [Tokyo]: Meteorological Society of Japan Abstract
Somerville, RCJ.  1971.  Bénard convection in a rotating fluid. Geophysical Fluid Dynamics. 2:247-262.: Taylor & Francis   10.1080/03091927108236061   AbstractWebsite

Abstract The steady nonlinear regime of Bénard convection in a uniformly rotating fluid is treated using a two-dimensional primitive-equation numerical model with rigid boundaries. Quantitative comparisons with laboratory heat transport data for water are made in the parameter ranges for which the experimental flows are approximately two-dimensional and steady. When an experimentally realistic spatial periodicity is imposed upon the numerical solution, the model simulates the experimental determinations of Nusselt number fairly accurately. In particular, it predicts the observed non-monotonic dependence on Taylor number. When spatial periodicities corresponding to those of the linear stability problem are specified, however, the accuracy of the simulation is less and the Taylor number dependence is monotonic.The steady nonlinear regime of Bénard convection in a uniformly rotating fluid is treated using a two-dimensional primitive-equation numerical model with rigid boundaries. Quantitative comparisons with laboratory heat transport data for water are made in the parameter ranges for which the experimental flows are approximately two-dimensional and steady. When an experimentally realistic spatial periodicity is imposed upon the numerical solution, the model simulates the experimental determinations of Nusselt number fairly accurately. In particular, it predicts the observed non-monotonic dependence on Taylor number. When spatial periodicities corresponding to those of the linear stability problem are specified, however, the accuracy of the simulation is less and the Taylor number dependence is monotonic.

Somerville, RCJ.  2011.  How much should the public know about climate science? Climatic Change. 104:509-514.   10.1007/s10584-010-9938-y   AbstractWebsite
Somerville, RCJ.  1980.  Tropical Influences on the Predictability of Ultralong Waves. Journal of the Atmospheric Sciences. 37:1141-1156.   10.1175/1520-0469(1980)037<1141:tiotpo>;2   AbstractWebsite

Some implications of predictability theory for ultralong waves are examined in an ensemble of real-data forecasts carried out with a primitive-equation numerical model in both global and hemispheric configurations. Although the model is adiabatic and almost inviscid, its skill at forecasting the 5-day evolution of ultralong waves in middle latitudes of the Northern Hemisphere is approximately equivalent to that of a physically comprehensive general circulation model. The ultralong wave forecasts produced by a hemispheric version of the model are markedly less skillful than those made by the global version, especially in the latter part of the 5-day period. When the initial state of the hemispheric version is modified by using a smooth field in the tropics in place of analyzed observed data, the skill of the prediction is degraded further, and the effect is apparent early in the 5-day period.These adverse tropical influences on middle-latitude forecast skill are essentially confined to the ultralong waves (zonal wavenumbers 1–3). They appear to be typical of hemispheric integrations with conventional numerical weather prediction models and conventional analysis and initialization techniques. The resulting forecast errors may be associated with the spurious excitation of large-amplitude external modes. These effects of tropical deficiencies in the prediction model and in the initial data provide a partial explanation for the poor skill of typical actual forecasts of ultralong waves, relative to the skill expected on the basis of predictability theory. The results also suggest that improvements in hemispheric analysis and initialization procedures are urgently required. Until such improvements are implemented, the use of global rather than hemispheric models, even for forecasts of only a few days, might be beneficial in operational practice.

Somerville, RCJ.  2019.  Chapter 8: Communicating Climate Change Science. Bending the Curve: Climate Change Solutions. ( Ramanathan V, Ed.).: Regents of the University of California.
Somerville, R.  2008.  The Forgiving Air : Understanding Environmental Change, Second Edition. :202p.., Boston, Mass.: American Meteorological Society Abstract
Somerville, RCJ, Iacobellis S, Lee WH.  1996.  Effects of cloud-radiation schemes on climate model results. World Resource Review. 8:321-333. Abstract

A current dilemma of climate modeling is that model results are strongly sensitive to the treatment of certain poorly-understood physical processes, especially cloud-radiation interactions. Thus, different models with alternative plausible parameterizations often give widely varying results. Yet, we typically have had little basis for estimating which parameterization is more realistic. Of the many physical processes involved in climate simulations, feedbacks due to cloud-radiation interactions are thought to be the largest single source of uncertainty. In fact, most of the global differences in results between leading climate models, as measured by their sensitivity to greenhouse gases, can be traced to different model treatments of cloud-radiation interactions.Using a modern atmospheric general circulation model (the National Center for Atmospheric Research Community Climate Model: CCM2), we have investigated the effects on climate sensitivity of several different cloud-radiation parameterizations. At the same time, we have validated these parameterizations directly with observations from field experiments. In addition to the original cloud-radiation scheme of CCM2, we tested four parameterizations incorporating prognostic cloud water: one version with prescribed cloud radiative properties and three other versions with interactive cloud radiative properties. Comparisons with measurements suggest that schemes with explicit cloud water budgets and interactive radiative properties are potentially capable of matching observational data closely.

Somerville, RCJ, Quirk WJ, Hansen JE, Lacis AA, Stone PH.  1976.  Search for Short-Term Meteorological Effects of Solar Variability in an Atmospheric Circulation Model. Journal of Geophysical Research-Oceans and Atmospheres. 81:1572-1576.   10.1029/JC081i009p01572   AbstractWebsite

A set of numerical experiments is carried out to test the short-range sensitivity of the Giss (Goddard Institute for Space Studies) global atmospheric general circulation model to changes in solar constant and ozone amount. These experiments consist of forecasts initialized with actual atmospheric data. One set of forecasts is made with a standard version of the model, and another set uses the model modified by very different values of the solar constant (two thirds and three halves of the standard value) and of the ozone amount (zero and twice the standard amount). Twelve-day integrations with these very large variations show such small effects that the effects of realistic variations would almost certainly be insignificant meteorologically on this time scale.

Somerville, RCJ.  2008.  If I were president: A climate change speech. Bulletin of the American Meteorological Society. 89:1180-1182. Abstract
Somerville, R, Lauder P, Rogo R.  1993.  Change on Planet Earth. : UCSD Extension, University of California, San Diego AbstractWebsite
Somerville, RCJ, Lipps FB.  1973.  A Numerical Study in Three Space Dimensions of Bénard Convection in a Rotating Fluid. Journal of the Atmospheric Sciences. 30:590-596.: American Meteorological Society   10.1175/1520-0469(1973)030<0590:ansits>;2   AbstractWebsite

The primitive, nonlinear, Boussinesq equations of motion, continuity and thermodynamic energy are integrated numerically in three space dimensions and time to study convection driven by unstable vertical density gradients and subject to Coriolis forces. Parameter values are chosen to permit quantitative comparison with data from laboratory experiments for rotating Bénard convection in water. The model realistically simulates the structure of the convection cells, their horizontal scale, and the mean vertical heat transport. The experimentally observed phenomenon of a non-monotone dependence of heat transport on rotation rate is reproduced and shown to be a consequence of the rotational constraint on the wavelength of the cells.