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Norman A. Phillips

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Norman A. Phillips

Abstract

A study is made of the hydrostatic and quasi-geostrophic motion of two superimposed layers of homogeneous and incompressible fluids of different densities, these fluids being contained between two rigid, horizontal plates. It is found that the local time derivatives of the pressure heights in the two layers and the height of their interface can be determined from partial differential equations similar to those developed by Charney for the equivalent-barotropic model.

The possibility of using this two-layer model to represent motions of a continuously stratified, baroclinic troposphere is explored by comparing the behavior of small perturbations superimposed on a zonal current in the two-layer model with the results of the continuous baroclinic perturbation theories of Eady and Fjørtoft. The remarkable similarity of behavior of the two-layer and the continuous perturbation models, which appears from this comparison, suggests that if the initial flow patterns of the two-layer model are determined from the initial flow patterns of the troposphere in a specified manner the later flow patterns in the troposphere can be inferred from the forecast flow patterns of the two-layer model.

This hypothesis is subjected to a preliminary test by computing the instantaneous sea-level pressure tendencies and vertical motions (in the middle troposphere) at the beginning of the severe storm of 24–25 November 1950 over eastern North America. The order of magnitude of the predicted quantities and their general distribution agree in many respects with the observed pressure changes and hydrometeors, but some disagreement exists. It is suggested that a part of this disagreement may be due to the effect of large normal accelerations on the validity of the quasi-geostrophic assumption.

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Norman A. Phillips

The many activities of Carl-Gustaf Rossby are described, beginning with his early adventures at sea, and presented in the context of the meteorological world of his time. His scientific ideas and papers are not discussed except for an important aspect of his typical approach to analysis of atmospheric and oceanic motion. His success in fostering interaction between different people and institutions is emphasized.

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NORMAN A. PHILLIPS

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A 48-hr. forecast for the entire Northern Hemisphere of a barotropic hydrostatic atmosphere is made with the “primitive equations.” Overlapping Mercator and stereographic grids are used, together with the finite-difference scheme proposed by Eliassen. Initial data corresponded to a Haurwitz-type pattern of wave number 4. The initial wind field was nondivergent and the initial geopotential field satisfied the balance equation. The computations seem to be stable and well behaved, except for two small temporary irregularities. The amplitude of the gravity-inertia waves present in the forecast geopotential field is about 1/30 that of the large-scale field. It can be shown that this is due to the neglect, in the initial data, of the quasi-geostrophically conditioned divergence field. The computational technique itself therefore does not give any unreal prominence to the “meteorological noise.” The computational characteristics and stability criterion of the Eliassen finite-difference system are investigated for a linearized version of the equations.

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Norman A. Phillips

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The flux of energy due to the pressure force acting across the boundary of a subsiding mass of cold air is investigated. It is shown that for mean values of the subsiding motion of the order of −1 cm sec−1 or larger, energy is transferred from the cold air to the surrounding atmosphere. A method is developed whereby this flux across a portion of a frontal surface can be calculated from a three-dimensional frontal analysis, and this technique is then applied to a specific example. The importance of the addition of this energy to the current flowing around the cold air is discussed, and it is suggested that at least a portion of the energy for the indirect circulations which are often observed downstream is supplied by the direct circulation involving the subsiding cold air mass.

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Norman A. Phillips and J. Shukla

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A simple model containing gravity waves of phase speed C and a basic current U is used to test the hypothesis that in a nested grid system of different mesh sizes a better computation on the fine grid results if the outer, coarse-grid forecast is not made independently of the limited-area, fine-grid forecast but interacts with the fine grid throughout the integration. This hypothesis, which is based on an appeal to the characteristics of the differential equation, is verified by the tests, especially when C is less than U. A two-step Lax-Wendroff scheme with the staggered arrangement of variables suggested by Eliassen is used in both grids.

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Yoshimitsu Ogura and Norman A. Phillips

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The approximate equations of motion derived by Batchelor in 1953 are derived by a formal scale analysis, with the assumption that the percentage range in potential temperature is small and that the time scale is set by the Brunt-Väisälä frequency. Acoustic waves are then absent. If the vertical scale is small compared to the depth of an adiabatic atmosphere, the system reduces to the (non-viscous) Boussinesq equations. The computation of the saturation vapor pressure for deep convection is complicated by the important effect of the dynamic pressure on the temperature. For shallow convection this effect is not important, and a simple set of reversible equations is derived.

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Norman A. Phillips and Simon W. Chang

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The principles of variational analysis are reviewed in a symbolic manner, with emphasis on the error introduced by a failure to use an exact constraint. A technique to approximate a nonlinear exact constraint is suggested, with the object of avoiding error magnification in regions of good data, in the process of analyzing slow mode amplitudes for nonlinear mode initialization. The technique amounts to subtractingall fast modes from the data fields that form the input to the variational analysis. The analysis procedure is then focused on only the analysis of slow mode fields. These general considerations are demonstrated by computations with the vortex model of Tribbia, and show how nonlinear mode techniques can improve initial analyses in a more significant way than the mere elimination of noise. A review of the relative merits and weaknesses of optimum interpolation and variational analysis suggests a logical way to use both techniques in an operational analysis system.

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James E. Hoke, Norman A. Phillips, Geoffrey J. Dimego, James J. Tuccillo, and Joseph G. Sela

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The three components of the Regional Analysis and Forecast System (RAFS) of the National Meteorological Center (NMC) are described. This system was implemented in March 1985 to supplement guidance from NMC's limited-area fine-mesh model (LFM), especially for precipitation forecasting. The three components of the RAFS are the regional optimum interpolation analysis, the Baer–Tribbia nonlinear normal mode initialization, and the nested grid model—a grid point, primitive-equation model in sigma coordinates. Postprocessing of model forecasts and plans for system improvement are also discussed.

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M. Ades, R. Adler, Rob Allan, R. P. Allan, J. Anderson, Anthony Argüez, C. Arosio, J. A. Augustine, C. Azorin-Molina, J. Barichivich, J. Barnes, H. E. Beck, Andreas Becker, Nicolas Bellouin, Angela Benedetti, David I. Berry, Stephen Blenkinsop, Olivier. Bock, Michael G. Bosilovich, Olivier. Boucher, S. A. Buehler, Laura. Carrea, Hanne H. Christiansen, F. Chouza, John R. Christy, E.-S. Chung, Melanie Coldewey-Egbers, Gil P. Compo, Owen R. Cooper, Curt Covey, A. Crotwell, Sean M. Davis, Elvira de Eyto, Richard A. M de Jeu, B.V. VanderSat, Curtis L. DeGasperi, Doug Degenstein, Larry Di Girolamo, Martin T. Dokulil, Markus G. Donat, Wouter A. Dorigo, Imke Durre, Geoff S. Dutton, G. Duveiller, James W. Elkins, Vitali E. Fioletov, Johannes Flemming, Michael J. Foster, Richard A. Frey, Stacey M. Frith, Lucien Froidevaux, J. Garforth, S. K. Gupta, Leopold Haimberger, Brad D. Hall, Ian Harris, Andrew K Heidinger, D. L. Hemming, Shu-peng (Ben) Ho, Daan Hubert, Dale F. Hurst, I. Hüser, Antje Inness, K. Isaksen, Viju John, Philip D. Jones, J. W. Kaiser, S. Kelly, S. Khaykin, R. Kidd, Hyungiun Kim, Z. Kipling, B. M. Kraemer, D. P. Kratz, R. S. La Fuente, Xin Lan, Kathleen O. Lantz, T. Leblanc, Bailing Li, Norman G Loeb, Craig S. Long, Diego Loyola, Wlodzimierz Marszelewski, B. Martens, Linda May, Michael Mayer, M. F. McCabe, Tim R. McVicar, Carl A. Mears, W. Paul Menzel, Christopher J. Merchant, Ben R. Miller, Diego G. Miralles, Stephen A. Montzka, Colin Morice, Jens Mühle, R. Myneni, Julien P. Nicolas, Jeannette Noetzli, Tim J. Osborn, T. Park, A. Pasik, Andrew M. Paterson, Mauri S. Pelto, S. Perkins-Kirkpatrick, G. Pétron, C. Phillips, Bernard Pinty, S. Po-Chedley, L. Polvani, W. Preimesberger, M. Pulkkanen, W. J. Randel, Samuel Rémy, L. Ricciardulli, A. D. Richardson, L. Rieger, David A. Robinson, Matthew Rodell, Karen H. Rosenlof, Chris Roth, A. Rozanov, James A. Rusak, O. Rusanovskaya, T. Rutishäuser, Ahira Sánchez-Lugo, P. Sawaengphokhai, T. Scanlon, Verena Schenzinger, S. Geoffey Schladow, R. W Schlegel, Eawag Schmid, Martin, H. B. Selkirk, S. Sharma, Lei Shi, S. V. Shimaraeva, E. A. Silow, Adrian J. Simmons, C. A. Smith, Sharon L Smith, B. J. Soden, Viktoria Sofieva, T. H. Sparks, Paul W. Stackhouse Jr., Wolfgang Steinbrecht, Dimitri A. Streletskiy, G. Taha, Hagen Telg, S. J. Thackeray, M. A. Timofeyev, Kleareti Tourpali, Mari R. Tye, Ronald J. van der A, Robin, VanderSat B.V. van der Schalie, Gerard van der SchrierW. Paul, Guido R. van der Werf, Piet Verburg, Jean-Paul Vernier, Holger Vömel, Russell S. Vose, Ray Wang, Shohei G. Watanabe, Mark Weber, Gesa A. Weyhenmeyer, David Wiese, Anne C. Wilber, Jeanette D. Wild, Takmeng Wong, R. Iestyn Woolway, Xungang Yin, Lin Zhao, Guanguo Zhao, Xinjia Zhou, Jerry R. Ziemke, and Markus Ziese
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