Publications

Export 5 results:
Sort by: [ Author  (Desc)] Title Type Year
A B C D E F [G] H I J K L M N O P Q R S T U V W X Y Z   [Show ALL]
G
Ghan, S, Randall D, Xu KM, Cederwall R, Cripe D, Hack J, Iacobellis S, Klein S, Krueger S, Lohmann U, Pedretti J, Robock A, Rotstayn L, Somerville R, Stenchikov G, Sud Y, Walker G, Xie SC, Yio J, Zhang MH.  2000.  A comparison of single column model simulations of summertime midlatitude continental convection. Journal of Geophysical Research-Atmospheres. 105:2091-2124.   Doi 10.1029/1999jd900971   AbstractWebsite

Eleven different single-column models (SCMs) and one cloud ensemble model (CEM) are driven by boundary conditions observed at the Atmospheric Radiation Measurement (ARM) program southern Great Plains site for a 17 day period during the summer of 1995. Comparison of the model simulations reveals common signatures identifiable as products of errors in the boundary conditions. Intermodel differences in the simulated temperature, humidity, cloud, precipitation, and radiative fluxes reflect differences in model resolution or physical parameterizations, although sensitive dependence on initial conditions can also contribute to intermodel differences. All models perform well at times but poorly at others. Although none of the SCM simulations stands out as superior to the others, the simulation by the CEM is in several respects in better agreement with the observations than the simulations by the SCMs. Nudging of the simulated temperature and humidity toward observations generally improves the simulated cloud and radiation fields as well as the simulated temperature and humidity but degrades the precipitation simulation for models with large temperature and humidity biases without nudging. Although some of the intermodel differences have not been explained, others have been identified as model problems that can be or have been corrected as a result of the comparison.

Gall, R, Blakeslee R, Somerville RCJ.  1979.  Baroclinic Instability and the Selection of the Zonal Scale of the Transient Eddies of Middle Latitudes. Journal of the Atmospheric Sciences. 36:767-784.   10.1175/1520-0469(1979)036<0767:biatso>2.0.co;2   AbstractWebsite

Because the linear growth rates of baroclinic waves on realistic zonal flows are largest at relatively high zonal wavenumbers (e.g., 15), the observed peaks in the transient kinetic energy spectrum cannot be explained simply by peaks in the linear growth-rate spectrum. When the growth-rate spectrum is fairly flat, as suggested by recent studies, then as the waves evolve, the decrease of the instability of the zonal flow and the increase of dissipation in the developing waves become important in determining which wavelength will dominate after the waves are fully developed. In particular, the stabilization of the zonal flow because of northward and upward eddy transport (which is primarily confined to the lower troposphere in all baroclinic waves) causes the instability of the short baroclinic waves (wavenumber > 10) to decrease more rapidly than that of the intermediate-scale waves (wavenumber <10). In addition, as it is usually modeled, dissipation increases with time more rapidly in the short waves. Therefore, the growth of the short waves is terminated by these two processes before the growth of the intermediate-scale waves, which can thus achieve greater equilibrium amplitudes.We have obtained these results in a numerical experiment with a simplified general circulation model, in which waves of all wavelengths are allowed to develop simultaneously from small random perturbations on a flow that is initially zonally symmetric. The kinetic energy spectrum in this experiment does not display a −3 power law in the wavenumber band 10–20, even after the spectrum in this spectral region has been equilibrated for a simulated week or more. This result apparently supports the recent hypothesis of Andrews and Hoskins that atmospheric fronts rather than quasi-geostrophic turbulence are responsible for the observed −3 spectrum at wavenumbers > 10.

Gall, R, Blakeslee R, Somerville RCJ.  1979.  Cyclone-Scale Forcing of Ultralong Waves. Journal of the Atmospheric Sciences. 36:1692-1698.   10.1175/1520-0469(1979)036<1692:csfouw>2.0.co;2   AbstractWebsite

A numerical experiment is carried out with a simplified general circulation model. In this experiment, instabilities of all wavelengths are allowed to develop simultaneously from small perturbations on a zonally symmetric flow. The initial development of the ultralong waves in this experiment is apparently forced by the interaction between the cyclone-scale waves and the basic flow in which they are embedded. Because the spectrum of the developing baroclinic waves is not monochromatic, the interaction between the cyclones and the basic flow varies with longitude, and waves longer than the cyclone scale are forced. The structure of the ultralong waves in the numerical experiment is consistent with this forcing mechanism. One implication for numerical weather prediction is that errors in forecasts of ultralong waves may be due in part to errors in the cyclone scale.

Galchen, T, Somerville RCJ.  1975.  Numerical-Solution of Navier-Stokes Equations with Topography. Journal of Computational Physics. 17:276-310.   10.1016/0021-9991(75)90054-6   AbstractWebsite

A finite difference scheme for solving the equations of fluid motion in a generalized coordinate system has been constructed. The scheme conserves mass and all the first integral moments of the motion. The scheme also advectively “almost conserves” second moments, in that the magnitude of implicit numerical smoothing is typically about an order smaller than explicit viscosity and diffusion. Calculations with the model support the theoretical conjecture that the difference scheme is stable whenever the analogous Cartesian scheme is stable. The scheme has been used to calculate dry atmospheric convection due to differential heating between top and bottom of mountainous terrain. The general small-scale characteristics of mountain up-slope winds have been simulated. In addition, the results have demonstrated the crucial role played by the eddy diffusivities and the environmental stability, in determining both the quantitative and the qualitative features of the circulation.

Galchen, T, Somerville RCJ.  1975.  On the Use of a Coordinate Transformation for Solution of Navier-Stokes Equations. Journal of Computational Physics. 17:209-228.   10.1016/0021-9991(75)90037-6   AbstractWebsite

The equations of fluid motion have been formulated in a generalized noncartesian, non-orthogonal coordinate system. A particular coordinate transformation, which transforms a domain with an irregular lower boundary into a cube, has been constructed. The transformed system, unlike the original one, has flat boundaries and homogeneous boundary conditions. Where the topography is flat, the original and transformed systems are identical, and extra terms do not appear. A finite difference scheme for solving the transformed equations has been constructed and will be described in a subsequent issue of this journal.