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N. A. Phillips

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J. G. Charney and N. A. Phillips

Abstract

An n-level generalization of the 2½-dimensional model is derived by specialization of the complete three-dimensional quasi-geostrophic equations. In the case n = 1, it reduces to the two-dimensional single-layer barometric model. In the case N = 2, it reduces to the double-layer barotropic model, or — what is shown to be mathematically equivalent —the 2½-dimensional model. Methods of numerical integration of the 2- and 2½-dimensional equations, and the machine requirements for such integrations, are discussed.

The results of a series of six two-dimensional and six 2½-dimensional forecasts for 12 and 24 hours are presented. Although the 2½-dimensional forecasts are noticeably superior to the two-dimensional forecasts, it is apparent that considerable improvement will be possible with models in which there are fewer artificial constraints. A method of integration is therefore proposed for the n-level generalization of the 2½-dimensional model, and computation schemes are outlined for the general three-dimensional quasi-geostrophic equations. The semi-Lagrangian coordinate system with potential temperature as vertical coordinate is shown to exhibit favorable properties for machine integration.

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A. P. Khain, V. Phillips, N. Benmoshe, and A. Pokrovsky

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Some observational evidence—such as bimodal drop size distributions, comparatively high concentrations of supercooled drops at upper levels, high concentrations of small ice crystals in cloud anvils leading to high optical depth, and lightning in the eyewalls of hurricanes—indicates that the traditional view of the microphysics of deep tropical maritime clouds requires, possibly, some revisions. In the present study it is shown that the observed phenomena listed above can be attributed to the presence of small cloud condensation nuclei (CCN) with diameters less than about 0.05 μm. An increase in vertical velocity above cloud base can lead to an increase in supersaturation and to activation of the smallest CCN, resulting in production of new droplets several kilometers above the cloud base. A significant increase in supersaturation can be also caused by a decrease in droplet concentration during intense warm rain formation accompanied by an intense vertical velocity. This increase in supersaturation also can trigger in-cloud nucleation and formation of small droplets. Another reason for an increase in supersaturation and in-cloud nucleation can be riming, resulting in a decrease in droplet concentration. It has been shown that successive growth of new nucleated droplets increases supercooled water content and leads to significant ice crystal concentrations aloft. The analysis of the synergetic effect of the smallest CCN and giant CCN on production of supercooled water and ice crystals in cloud anvils allows reconsideration of the role of giant CCN. Significant effects of small aerosols on precipitation and cloud updrafts have been found. The possible role of these small aerosols as well as small aerosols with combination of giant CCN in creating conditions favorable for lightning in deep maritime clouds is discussed.

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D. Cunnold, F. Alyea, N. Phillips, and R. Prinn

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A three-year integration of a global three-dimensional model including dynamics and simple photo- chemistry is used to predict ozone. Distributions of NO3 and odd hydrogen deduced by McConnell and McElroy are used to incorporate in a simple way the chemical effect of these species. Good agreement with observation is obtained for stratospheric motion patterns, meridional circulations, ozone density as a function of height and latitude, eddy transports of ozone, surface destruction of ozone, and correlations of ozone with other variables. The annual cycle of columnar ozone in high latitudes is present, but at a smaller amplitude than observed. Vertical transport of ozone downward from the main generation level at 30 km is accomplished primarily by small-scale eddy diffusion between 20 and 30 km and again near the ground; large-scale vertical transport dominates inbetween. The model predicts a secondary maximum in ozone mixingg ratio at 45 km somewhat equatorward of the winter-polar-night zone. This feature, recently observed from satellite measurements, is thought to he caused by the temperature-dependence of reaction rates in the Chapman scheme.

The principal deficiency of the model is an underprediction of the spring ozone concentration in high latitudes in the lower stratosphere.

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