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Holton: Dynamics of Large Scale Atmospheric Motions 1027 Hendon, H. H., and D. L. Hartmann, Stationary Tung, K. K., A theory of stationary long waves. Gent, P. R., and J. C. McWilliams, Intermediate waves on a sphere: sensitivity to thermal Part III: quasi-normal modes in a singular model solutions to the Lorenz euations: strange feedback, J. Atmos. Sci., 39, (Sept.) 1982. waveguide, Mon. Wea. Rev., 107, 751-774, 1979. attractors and other phenomena, J. Atmos. Sci. Horel, J. D., and J. M. Wallace, Planetary-scale Tung, K. K., and R. S. Lindzen, A theory of 39, 3-13, 1982. atmospheric phenomena associated with the stationary long waves. Part I: a simple theory Haidvogel, D. B., and I. M. Held, Homogeneous southern oscillation, Mon. Wea. Rev., 109, of blocking, Mon. Wea. Rev., 107, 714-734, quasi-geostrophic turbulence driven by a 813-829, 1981. 1979. uniform temperature gradient, J. Atmos. Sci., Hoskins, B. J., and D. J. Karoly, The steady Tung, K. K., and R. S. Lindzen, A theory of 37, 2644-2660, 1980. linear response of a spherical atmosphere to stationary long waves. Part II: resonant Rossby Held, I. M., and A. Y. Hou, Nonlinear axially thermal and orographic forcing, J. Atmos. waves in the presence of realistic vertical symmetric circulations in a nearly inviscid Sci., 38, 1179-1196, 1981. shears, Mon. Wea. Rev., 107, 735-756, 1979. atmosphere, J. Atmos. Sci., 37, 515-533, 1980. Kasahara, A., Effect of zonal flows on the Wallace, J. M., and D. S. Gutzler, Tele- Holopainen, E. 0., and A. H. Oort, On the role of free oscillations of a barotropic atmosphere, connections in the geopotential height field large-scale transient eddies in the mainte- J. Atmos. Sci., 37, 917-929, 1980. (Also see: during the Northern Hemisphere winter, Mon. nance of the vorticity and enstrophy of the time- Kasahara, Corrigendum, J. Atmos. Sci., 38, Wea. Rev., 109, 784-812, 1981. mean atmospheric flow, J. Atmos. Sci., 38, 2284-2285, 1981.) Webster, P. J., Mechanisms determining the 270-280, 1981. Lau, N.-C., A diagnostic study of recurrent atmospheric response to sea surface tempera- Kuettner, J.P., and T. H. R. O'Neill, ALPEX - meteorological anomalies appearing in a ture anomalies, J. Atmos. Sci., 38, 554-571, The GARP mountain subprogram. Bull. Am. 15-year simulation with a GFDL general circu- 1981. Meteorol. Soc., 62, 793-805, 1981. lation model, J. Atmos. Sci., 38, 2287-2311, Webster, P. J., Seasonality in the local and Lau, K.-M., Oscillations in a simple equatorial 1981. remote atmospheric response to sea surface climate system, J. Atmos. Sci., 38, 248-261, Lim, H., and C.-P. Chang, A theory for midlati- temperature anomalies, J. Atmos. Sci., 39, 1981. tude forcing of tropical motions during winter 41-52, 1982. Lau, K.-M., and Lim, H., Thermally driven motions monsoons, J. Atmos. Sci., 38, 2377-2392, 1981. Webster, P. J., and J. R. Holton, Cross- in an equatorial E-plane: Hadley and Walker Lin, B.-D., The behavior of winter stationary equatorial response to middle-latitude forcing circulations during the winter monsoon, Mon. planetary waves forced by topography and in a zonally varying basic state, J. Atmos. Wea. Rev., 110, 336-353, 1982. diabatic heating, J. Atmos. Sci., 39, 1206- Sci., 39, 722-733, 1982. Loesch, A. Z., and R. C. Deininger, Dynamics of 1226, 1982. Yao, M.-S., Maintenance of quasi-stationary closed systems of resonantly interacting Lindzen, R. S., T. Aso, and D. Jaquin, Linear- waves in a two-level quasi-geostrophic spectral equatorial waves, J. Atmos. Sci., 36, 1490- ized calculations of stationary waves in the model with topography, J. Atmos. Sci., 37, 1497, 1979. atmosphere, J. Meteor. Soc. Japan, 60, 66-77, 29-43, 1980. McGinley, J., A diagnosis of lee cycloganesis, 1982. Mon. Wea. Rev., 110, 1271-1287, 1982. Phillips, T. J., On the interaction of surface Other Topics Pfeffer, R. L., Wave-mean flow interactions in the heating anomalies with zonally symmetric and asymmetric atmospheric flows, J. Atmos. Sci., Crawford, S. L., and T. Sasamori, A study of the atmosphere, J. Atmos. Sci., 38, 1340-1359, 1981. 39, (in press), 1982. sensitivity of the winter mean meridional Shapiro, L. J., The effect of nonlinearities on Rooney, D. M., and G. S. Janowitz, Flow over the circulation to sources of heat and momentum, the evolution of barotropic easterly waves in Rocky and Andes Mountains: application of an Tellus, 33, 340-350, 1981. analytical model, J. Atmos. Sci., 36, 549- a nonuniform environment, J. Atmos. Sci., 37, Edmon, H. J., Jr., B. J. Hoskins, and M. E. 2631-2643, 1980. 558, 1979. Mcintyre, Eliassen-Palm cross sections for the Salby, M. L., On the solution of the homogeneous Smith, R. B., Synoptic observations and theory troposphere, J. Atmos. Sci., 37, 2600-2616, of orographically disturbed wind and pressure, vertical structure problem for long-period 1980. J. Atmos. Sci., 39, 60-70, 1982. oscillations, J. Atmos. Sci., 36, 2350-2359, Errico, R. M., The strong effects of non- 1979. Webster, P. J., and L. C. Chou, Seasonal struc- quasigeostrophic dynamic processes on ture of a simple monsoon system, J. Atmos. Salby, M. L., The influence of realistic dissi- atmospheric energy spectra, J. Atmos. Sci., Sci., 37, 354-367, 1980. pation on planetary normal structures, __ J. 39, 961-968, 1982. Webster, P. J., and L. C. Chou, Low-frequency Atmos. Sci., 37, 2186-2199, 1980. Gallimore, R. G., and D. R. Johnson, The forcing transitions of a simple monsoon system, J. Salby, M. L., Rossby normal modes in nonuniform of the meridional circulation of the isentropic Atmos. Sci., 37, 368-382, 1980. background configurations. Part I: simple zonally averaged circumpolar vortex, J. Atmos. Williams, G. P., Planetary circulations: 3. The fields, J. Atmos. Sci., 38, 1803-1826, 1981. Sci., 38, 583-599, 1981. terrestrial quasi-geostrophic regime, J. Atmos. Salby, M. L., Rossby normal modes in nonuniform Gallimore, R. G., and D. R. Johnson, A numerical Sci., 36, 1409-1435, 1979. background configurations. Part II: equinox and diagnostic model of the zonally averaged solstice conditions, J. Atmos. Sci., 38, 1827- circulation in isentropic coordinates, J. Atmos. 1840, 1981. Sci., 38, 1870-1890, 1981. Smith, R. B., Some aspects of the quasi- Geisler, J. E., A linear model of the Walker geostrophic flow over mountains, J. Atmos. circulation, J. Atmos. Sci., 38, 1390-1400, (Received October 12, 1982; Sci., 36, 2385-2393, 1979. 1981. accepted January 27, 1983.) REVIEWS OF GEOPHYSICS AND SPACE PHYSICS, VOL. 21, NO. 5, PAGES 1027-1042, JUNE 1983 U.S. NATIONAL REPORT TO INTERNATIONAL UNION OF GEODESY AND GEOPHYSICS 1979-1982 MESOSCALE METEOROLOGY Kerry Emanuel and Frederick Sanders Department of Meteorology and Physical Oceanography Massachusetts Institute of Technology Cambridge, Massachusetts 02139 Introduction by analysis of special data and of routine surface observations. Nonlinear dynamics, The last four years have seen a considerable often combined with nontrivial cloud micro- expansion in research on mesoscale atmospheric physics, poses formidable theoretical problems. phenomena. The motivation is three-fold: the Hence, the research and operational communities prospect of greater forecast accuracy, an have recently formulated initial plans for emerging ability to observe the mesoscale, a national project on mesoscale meteorology and the challenge of understanding extremely (UCAR, 1982). complex physical mechanisms. The current level The definition of mesoscale phenomena is of accuracy of storm warnings and other local not universally accepted; the simplest one is forecasts can be substantially advanced only morphological: "mesoscale" refers to those by an improved ability to deal with structures systems which are too large to be observed smaller than the traditional synoptic scale. completely from a single point (lacking a These structures are beginning to be described capability for remote sensing) and too small to be observed unambiguously by the routine Copyright 1983 by the American Geophysical Union. upper-level sounding network over the conti- nental areas, with station spacing of a few Paper number 3R0576. hundred kilometers (Ligda, 1951). A physical 0034-6853/83/003R-0576515.00 definition, on the other hand, seems better 1028 Emanuel and Sanders: Mesoscale Meteorology as a guide to research. It has been suggested Experiment (GATE), and a number of others. Much that mesoscale circulations are dynamically other work was based on the close study of data characterized by the importance of the Coriolis available routinely in the United States, typi- force, but not by the dominance that assures cally for cases of spectacular phenomenology. quasi-geostrophic flow. This definition From these observations, a picture has emerged appears to exclude higher-frequency gravity which seems to be valid throughout a large range waves and all equatorial disturbances except of latitudes, confirming suggestions and infer- those of low frequency. It would include ences from earlier studies by Newton (1950) and intense extratropical cyclones, which have Fujita and Brown (1958) for middle latitudes, been regarded as synoptic scale events. Some and by Zipser (1969) for the tropics. Initially, other physical characteristic, such as the there is sporadic convection (e.g. Leary and relative importance of cloud microphysics, Houze, 1979b; Maddox, 1980a); then the convection might also be used as a definition, but many consolidates and a thick layer of stratiform mesoscale phenomena do not involve condensation. cloud appears in the middle and upper troposphere, Although an entirely adequate physical definition producing long-lasting and significant amounts may not be necessary, a dynamically self- of rain and having in some respects a life of consistent definition of "mesoscale" seems its own. This layer represents the accumulation desirable. For the present, however, we shall of debris from the convection, which remains err on the side of insufficient, rather than active at its upshear edge, and may be aided by additional condensation in an internal mesoscale excessive, exclusivity.
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