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Jerome Spar

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Jerome Spar

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Jerome Spar

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Jerome Spar

Abstract

Local numerical forecasts generated by interpolation from the National Meteorological Center primitive equation model are evaluated for the 1969–70 winter season in the eastern United States. A marked under-prediction of precipitation frequency appears to he due, at least in part, to the interpolation system.

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JEROME SPAR

Abstract

The global response of the atmosphere, as simulated by the Mintz-Arakawa, two-level, general circulation model, to a persistent anomalous pool of warm sea-surface temperatures (SST) in the extratropical Pacific Ocean is examined in this descriptive study in terms of the meridional pole-to-pole profile of the zonally averaged 600-mb surface for periods up to 90 days. Following an initial hydrostatic inflation of the isobaric surface in the latitude of the warm pool, effects spread poleward within the hemisphere, then begin to appear after about 2–3 weeks in high latitudes of the opposite hemisphere, but with little or no response in the Tropics. The same sea temperature anomaly field generates a stronger response in winter than in summer and a very different reaction when located in the Southern Hemisphere than when in the Northern Hemisphere. After a month of thermal forcing, the response to an SST anomaly is at least as large in the opposite hemisphere as in the hemisphere of the anomaly. A winter hemisphere responds more rapidly to an SST anomaly in the opposite hemisphere than does a summer hemisphere. Vacillation between low and high meridional wave number patterns is observed in the computed reaction to the warm pool.

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JEROME SPAR

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A fast-moving, rapidly-deepening cyclone is analyzed mainly by means of hourly airways sequence reports in the Atlantic coastal plain of the United States.

Six-hourly rainfall maps are presented showing the concentration of heavy rain along the cyclone path, and the strongly convective character of the cyclonic precipitation.

Gusty surface winds are found mainly in the warm sector during the early stages of the cyclone. The momentum of the surface gusts is derived from that of higher layers and comes down to the surface in bursts through the unstable warm air. Because the stability of the frontal zone prevents the downward transport of gust momentum, the surface winds in the cold air are much lighter than in the warm air. However, in places the front is penetrated by the gusts, and the resulting vertical mixing brings warm air to the surface causing an acceleration of the surface warm front. As the cyclone deepens, the gust velocities increase in the cold air in proportion to the increase of pressure gradient. The momentum of the low-level jet at the top of the friction layer penetrates to the surface most readily when the surface pressure gradient force does not oppose the direction of the jet.

An analysis of hourly pressure changes shows the existence of large-amplitude, high-speed pressure pulses moving across the cyclone. The pulses result in deformation of the pressure field, the generation of secondary centers, and erratic motion of the cyclone.

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Jerome Spar

Abstract

Hourly forecasts for five cities in the eastern United States have been generated by interpolation as by-products of the primitive equation (PE) numerical prediction program at the National Meteorological Center since November 1967. Some results derived from the 1967-68 and 1968-69 winter seasons are examined in terms of the snow prediction problem. The two winter forecast samples are shown to be in-compatible presumably as a consequence of PE program changes. The effects of inhomogeneity on the development of local synthetic (statistical-dynamical) forecast equations are discussed.

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Jerome Spar
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JEROME SPAR

Abstract

The theory and computation of integrated water vapor transport vectors are described and it is shown how the synoptic analysis of these vectors may be used for quantitative precipitation forecasting. An example of the vector field and the precipitation forecast is given. Although the prognostic formula does not give correct point values of the precipitation, reasonably good agreement is found between the distributions of forecast and observed precipitation. The technique is probably too laborious for daily forecasting routine but may be useful in the evaluation of rainmaking experiments.

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Jerome Spar

Abstract

A quantitative theory is derived showing the relation between temperature and surface pressure oscillations. By extension of methods used by Jeffreys and Bartels, a solution is obtained for the linearized hydro-dynamic equations in terms of spherical surface harmonic functions. The solution gives the surface pressure variation as a function of an integral containing the temperature variation throughout the atmosphere. The theory is applied to the problem of evaluating the amplitude of the annual surface pressure oscillation over the whole sphere. The temperature integral is computed from mean data for January and July and subjected to spherical harmonic analysis. The mean semi-annual surface pressure change is then evaluated from the coefficients of the harmonic series for the temperature integral and compared with observations.

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