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Shell, KM, Somerville RCJ.  2007.  Direct radiative effect of mineral dust and volcanic aerosols in a simple aerosol climate model. Journal of Geophysical Research-Atmospheres. 112   10.1029/2006jd007197   AbstractWebsite

Airborne mineral dust can influence the climate by altering the radiative properties of the atmosphere, but the magnitude of the effect is uncertain. An idealized global model is developed to study the dust-climate system. The model determines the dust longwave and shortwave direct radiative forcing, as well as the resulting temperature changes, based on the specified dust distribution, height, and optical properties. Comparisons with observations and general circulation results indicate that the model produces realistic results for the present-day dust distribution as well as for volcanic aerosols. Although the model includes many simplifications, it can still provide insight into dust-climate system behavior. Recent observations suggest that dust may absorb less solar radiation than previously thought. Experiments with the model suggest that previous studies which used more absorbing dust may be underestimating the effect of dust. Increasing the solar single scattering albedo value from 0.85 to 0.97, corresponding to recent measurements, more than doubles the modeled global average top-of-the-atmosphere (TOA) shortwave direct forcing for the present-day dust distribution, while the surface shortwave forcing is halved. The corresponding temperature decreases are larger for the larger single scattering albedo, and the latent and sensible heat fluxes decreases are smaller. The dust forcing and climate response are approximately linear with respect to optical depth. However, the relationship depends on the relative magnitudes of shortwave versus longwave TOA forcing. Thus the net TOA forcing alone does not determine the steady state climate response.

Shell, KM, Somerville RCJ.  2005.  A generalized energy balance climate model with parameterized dynamics and diabatic heating. Journal of Climate. 18:1753-1772.   10.1175/jcli3373.1   AbstractWebsite

Energy balance models have proven useful in understanding mechanisms and feedbacks in the climate system. An original global energy balance model is presented here. The model is solved numerically for equilibrium climate states defined by zonal average temperature as a function of latitude for both a surface and an atmospheric layer. The effects of radiative, latent, and sensible heating are parameterized. The model includes a variable lapse rate and parameterizations of the major dynamical mechanisms responsible for meridional heat transport: the Hadley cell, midlatitude baroclinic eddies, and ocean circulation. The model reproduces both the mean variation of temperature with latitude and the global average heat budget within the uncertainty of observations. The utility of the model is demonstrated through examination of various climate feedbacks. One important feedback is the effect of the lapse rate on climate. When the planet warms as a result of an increase in the solar constant, the lapse rate acts as a negative feedback, effectively enhancing the longwave emission efficiency of the atmosphere. The lapse rate is also responsible for an increase in global average temperature when the meridional heat transport effectiveness is increased. The water vapor feedback enhances temperature changes, while the latent and sensible heating feedback reduces surface temperature changes.

Shell, KM, Somerville RCJ.  2007.  Sensitivity of climate forcing and response to dust optical properties in an idealized model. Journal of Geophysical Research-Atmospheres. 112   10.1029/2006jd007198   AbstractWebsite

An idealized global climate model is used to explore the response of the climate to a wide range of dust radiative properties and dust layer heights. The top-of-the-atmosphere (TOA) shortwave forcing becomes more negative as the broadband shortwave single scattering albedo increases and the broadband shortwave asymmetry parameter decreases, but the sensitivity is highly dependent on the location of the dust layer with respect to clouds. The longwave TOA forcing is most affected by the height of the dust layer. The net TOA forcing is most sensitive to the shortwave single scattering albedo and shortwave asymmetry parameter. The surface and atmospheric temperature responses are approximately linear with respect to the TOA forcing, as opposed to the surface or atmospheric forcings. Thus the TOA forcing can be used to estimate both the surface and atmospheric temperature responses to dust. The corresponding changes in latent and sensible heat fluxes are essential for the close relationship of the surface temperature response to the TOA forcing. Estimating the hydrological cycle response requires knowledge of the vertical distribution of dust with respect to clouds or other reflective particles. The sensitivity of the latent heat flux to variations in the shortwave single scattering albedo changes sign with dust height. The latent heat flux change becomes less negative as the shortwave single scattering albedo increases if the dust layer is below clouds. However, when the dust is above clouds, the latent heat response becomes more negative as the single scattering albedo increases.

Shell, KM, Frouin R, Nakamoto S, Somerville RCJ.  2003.  Atmospheric response to solar radiation absorbed by phytoplankton. Journal of Geophysical Research-Atmospheres. 108   10.1029/2003jd003440   AbstractWebsite

[1] Phytoplankton alter the absorption of solar radiation, affecting upper ocean temperature and circulation. These changes, in turn, influence the atmosphere through modification of the sea surface temperature (SST). To investigate the effects of the present-day phytoplankton concentration on the atmosphere, an atmospheric general circulation model was forced by SST changes due to phytoplankton. The modified SST was obtained from ocean general circulation model runs with space- and time-varying phytoplankton abundances from Coastal Zone Color Scanner data. The atmospheric simulations indicate that phytoplankton amplify the seasonal cycle of the lowest atmospheric layer temperature. This amplification has an average magnitude of 0.3 degreesK but may reach over 1 degreesK locally. The surface warming in the summer is marginally larger than the cooling in the winter, so that on average annually and globally, phytoplankton warm the lowest layer by about 0.05 degreesK. Over the ocean the surface air temperature changes closely follow the SST changes. Significant, often amplified, temperature changes also occur over land. The climatic effect of phytoplankton extends throughout the troposphere, especially in middle latitudes where increased subsidence during summer traps heat. The amplification of the seasonal cycle of air temperature strengthens tropical convection in the summer hemisphere. In the eastern tropical Pacific Ocean a decreased SST strengthens the Walker circulation and weakens the Hadley circulation. These significant atmospheric changes indicate that the radiative effects of phytoplankton should not be overlooked in studies of climate change.

Shen, SSP, Velado M, Somerville RCJ, Kooperman GJ.  2013.  Probabilistic assessment of cloud fraction using Bayesian blending of independent datasets: Feasibility study of a new method. Journal of Geophysical Research: Atmospheres.   10.1002/jgrd.50408   AbstractWebsite

We describe and evaluate a novel method to blend two observed cloud fraction (CF) datasets through Bayesian posterior estimation. The research reported here is a feasibility study designed to explore the method. In this proof-of-concept study, we illustrate the approach using specific observational datasets from the U. S. Department of Energy Atmospheric Radiation Measurement Program's Southern Great Plains site in the central United States, but the method is quite general and is readily applicable to other datasets. The total sky image (TSI) camera observations are used to determine the prior distribution. A regression model and the active remote sensing of clouds (ARSCL) radar/lidar observations are used to determine the likelihood function. The posterior estimate is a probability density function (pdf) of the CF whose mean is taken to be the optimal blend of the two observations. The data at hourly, daily, 5-day, monthly, and annual time scales are considered. Some physical and probabilistic properties of the CFs are explored from radar/lidar, camera, and satellite observations and from simulations using the Community Atmosphere Model (CAM5). Our results imply that (a) the Beta distribution is a reasonable model for CF for both short- and long-time means, the 5-day data are skewed right, and the annual data are almost normally distributed, and (b) the Bayesian method developed successfully yields a pdf of CF, rather than a deterministic CF value, and it is feasible to blend the TSI and ARSCL data with a capability for bias correction.

Solomon, S, Qin D, Manning M, Alley RB, Berntsen TK, Bindoff N, Chen Z, Chidthaisong A, Gregory JM, Hegeri GC, Heimann M, Hewitson B, Hoskins BJ, Joos F, Jouzel J, Kattsov V, Lohmann U, Matsuno T, Molina M, Nicholls N, Overpeck JT, Raga G, Ramaswamy V, Ren J, Rusticucci M, Somerville RCJ, Stocker TF, Whetton P, Wood RA, Wratt D.  2007.  Technical Summary. Climate change 2007 : the physical science basis : contribution of Working Group I to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change. ( Solomon S, Qin D, Manning M, Chen Z, Marquis M, Averyt K, Tignor M, Miller H, Eds.)., Cambridge; New York: Cambridge University Press Abstract
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Soloviev, GI, Shapiro VD, Somerville RCJ, Shkoller B.  1996.  The tilting instability with buoyant forcing in a two-dimensional viscous fluid. Journal of the Atmospheric Sciences. 53:2671-2684.   10.1175/1520-0469(1996)053<2671:ttiwbf>2.0.co;2   AbstractWebsite

The tilting instability is an instability of a two-dimensional fluid that transforms convective motion into shear flow. As a generalization of previous analytical work on the tilting instability in an ideal fluid, the authors investigate the instability with thermal buoyancy included as a source supporting convection against viscous dissipation; The results show two distinct instabilities: for large Rayleigh numbers, the instability is similar to the tilting instability in an inviscid fluid; for small Rayleigh numbers, it resembles a dissipative (i.e., viscous) instability driven by thermal buoyancy. This paper presents a linear stability analysis together with numerical solutions describing the nonlinear evolution of the flow for both types of instabilities. It is shown that the tilting instability develops for values of the aspect ratio (the ratio of the horizontal spatial scale to the vertical scale) that are less than unity. In the case of an ideal fluid, the instability completely transforms the convection into a shear flow, while the final stage of the dissipative instability is one of coexisting states of convection and horizontal shear flow. This study is confined to two dimensions, and the role of the tilling instability in three dimensions remains a subject for future research. In two dimensions, however, the tilting instability can readily generate shear flows from convective motions, and this mechanism may well be important in the interpretation of the results of two-dimensional numerical simulations.

Somervil.Rc, Stone PH, Halem M, Hansen JE, Hogan JS, Druyan LM, Russell G, Lacis AA, Quirk WJ, Tenenbau.J.  1974.  GISS Model of Global Atmosphere. Journal of the Atmospheric Sciences. 31:84-117.   10.1175/1520-0469(1974)031<0084:tgmotg>2.0.co;2   AbstractWebsite

A model description and numerical results are presented for a global atmospheric circulation model developed at the Goddard Institute for Space Studies (GISS). The model version described is a 9-level primitive-equation model in sigma coordinates. It includes a realistic distribution of continents, oceans and topography. Detailed calculations of energy transfer by solar and terrestrial radiation make use of cloud and water vapor fields calculated by the model. The model hydrologic cycle includes two precipitation mechanisms: large-scale supersaturation and a parameterization of subgrid-scale cumulus convection.Results are presented both from a comparison of the 13th to the 43rd days (January) of one integration with climatological statistics, and from five short-range forecasting experiments. In the extended integration, the near-equilibrium January-mean model atmosphere exhibits an energy cycle in good agreement with observational estimates, together with generally realistic zonal mean fields of winds, temperature, humidity, transports, diabatic heating, evaporation, precipitation, and cloud cover. In the five forecasting experiments, after 48 hr, the average rms error in temperature is 3.9K, and the average rms error in 500-mb height is 62 m. The model is successful in simulating the 2-day evolution of the major features of the observed sea level pressure and 500-mb height fields in a region surrounding North America.

Somerville, R, Lauder P, Rogo R.  1993.  Change on Planet Earth. : UCSD Extension, University of California, San Diego AbstractWebsite
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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>2.0.co;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.

Somerville, RCJ, Hassol SJ.  2011.  Communicating the science of climate change. Physics Today. 64:48-53.   10.1063/PT.3.1296   AbstractWebsite

It is urgent that climate scientists improve the ways they convey their findings to a poorly informed and often indifferent public.

Somerville, RCJ, Remer LA.  1984.  Cloud Optical-Thickness Feedbacks in the Co2 Climate Problem. Journal of Geophysical Research-Atmospheres. 89:9668-9672.   10.1029/JD089iD06p09668   AbstractWebsite

A radiative-convective equilibrium model is developed and applied to study cloud optical thickness feedbacks in the CO2 climate problem. The basic hypothesis is that in the warmer and moister CO2-rich atmosphere, cloud liquid water content will generally be larger too. For clouds other than thin cirrus the result is to increase the albedo more than to increase the greenhouse effect. Thus the sign of the feedback is negative: cloud optical properties act as a thermostat and alter in such a way as to reduce the surface and tropospheric warming caused by the addition of CO2. This negative feedback can be substantial. When observational estimates of the temperature dependence of cloud liquid water content are employed in the model, the surface temperature change caused by doubling CO2 is reduced by about one half. This result is obtained for global and annual average conditions, no change in cloud amount or altitude, and constant relative humidity. These idealizations, together with other simplifications typical of one-dimensional radiative-convective climate models, render the result tentative. Further study of cloud optical property feedbacks is warranted, however, because the climate is apparently so sensitive to them.

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
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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>2.0.co;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>2.0.co;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
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Somerville, R.  1996.  The Forgiving Air : Understanding Environmental Change. :xiv,195p.., Berkeley, Calif.: University of California Press Abstract
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