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>2.0.co;2 AbstractSome 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 1â€“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.

Berque, J, Lubin D, Somerville RCJ.
2011.

Transect method for Antarctic cloud property retrieval using AVHRR data. International Journal of Remote Sensing. 32:2887-2903.

10.1080/01431161003745624 AbstractFor studies of Antarctic climate change, the Advanced Very High Resolution Radiometer (AVHRR) offers a time series spanning more than two decades, with numerous overpasses per day from converging polar orbits, and with radiometrically calibrated thermal infrared channels. However, over the Antarctic Plateau, standard multispectral application of AVHRR data for cloud optical property retrieval with individual pixels is problematic due to poor scene contrasts and measurement uncertainties. We present a method that takes advantage of rapid changes in radiances at well-defined cloud boundaries. We examine a transect of AVHRR-measured radiances in the three thermal infrared channels across a boundary between cloudy and cloud-free parts of the image. Using scatter diagrams, made from the data along this transect, of the brightness temperature differences between channels 3 and 4, and channels 4 and 5, it is possible to fit families of radiative transfer solutions to the data to estimate cloud effective temperature, thermodynamic phase, and effective particle radius. The major approximation with this method is that along such a transect, cloud water path has considerable spatial variability, while effective radius, phase, and cloud temperature have much less variability. To illustrate this method, two AVHRR images centred about the South Pole are analysed. The two images are chosen based on their differing contrasts in brightness temperature between clear and cloud-filled pixels, to demonstrate that our method can work with varying cloud top heights. In one image the data are consistent with radiative transfer simulations using ice cloud. In the other, the data are inconsistent with ice cloud and are well simulated with supercooled liquid water cloud at 241.5 K. This method therefore has potential for climatological investigation of the radiatively important phase transition in the extremely cold and pristine Antarctic environment.

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 AbstractThe 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.

Hathaway, DH, Somerville RCJ.
1983.

Three-Dimensional Simulations of Convection in Layers with Tilted Rotation Vectors. Journal of Fluid Mechanics. 126:75-&.

10.1017/s0022112083000051 AbstractThree-dimensional and time-dependent numerical simulations of thermal convection are carried out for rotating layers in which the rotation vector is tilted from the vertical to represent various latitudes. The vertical component of the rotation vector produces narrow convection cells and a reduced heat flux. As this vertical component of the rotation vector diminishes in the lower latitudes, the vertical heat flux increases. The horizontal component of the rotation vector produces striking changes in the convective motions. It elongates the convection cells in a northâ€“south direction. It also tends to turn upward motions to the west and downward motions to the east in a manner that produces a large-scale circulation. This circulation is directed to the west and towards the poles in the upper half of the layer and to the east and towards the equator in the bottom half. Since the layer is warmer on the bottom this circulation also carries an equatorward flux of heat. When the rotation vector is tilted from the vertical, angular momentum is always transported downwards and toward the equator. For rapidly rotating layers, the pressure field changes in a manner that tends to balance the Coriolis force on vertical motions. This results in an increase in the vertical heat flux as the rotation rate increases through a limited range of rotation rates.

Hathaway, DH, Somerville RCJ.
1987.

Thermal Convection in a Rotating Shear Flow. Geophysical and Astrophysical Fluid Dynamics. 38:43-&.

10.1080/03091928708210105 AbstractA three-dimensional and time-dependent numerical model is used to simulate thermal convection imbedded in a shear flow in a rotating atmosphere. The fluid is confined to a plane parallel layer with periodic side boundaries, and the rotation vector is tilted from the vertical to represent a low-latitude region. An eastward mean flow is imposed which is constant with depth but has a jet-like profile in latitude. The convection is driven by a prescribed vertical temperature difference. Interactions between the shear flow and the convection extract energy from the mean flow and decrease the mean shear in the nonrotating case. In the presence of rotation, however, the convection can feed energy into the jet and enhance the mean shear. Mean meridional circulations are also produced by the effects of rotation. The Coriolis force on the vertical flows in these circulations contributes to the changes in the mean zonal wind. Three rotating cases are examined which show this behavior in varying degrees. A simple mechanism is described which explains how the convection can produce this countergradient flux of momentum in a rotating layer. Although the system studied is highly idealized, it exhibits momentum fluxes and wave-like patterns which, for certain parameter values, are similar to those observed on Jupiter.

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

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