Search Results

You are looking at 1 - 10 of 49 items for :

  • Author or Editor: Richard J. Reed x
  • Refine by Access: All Content x
Clear All Modify Search
Richard J. Reed

Abstract

The relative importance of horizontal advection and vertical motion in producing the day-to-day changes in total ozone amount is calculated, and the manner in which these two factors combine to produce the well-known ozone-weather relationships is explained. The calculations show that at most one third of the range of daily values is attributable to vertical motions, the remainder presumably being the result of horizontal advection.

Full access
Richard J. Reed

Abstract

The potential vorticity on isentropic surfaces is used to study a characteristic type of upper-level frontogenesis — the development of a sloping stable layer marked by strong vertical wind shear and rapid upward decrease in humidity. In the case studied it was found that the intense portion of the frontal zone consisted of a thin wedge of stratospheric air which had descended to very low levels (700 to 800 millibars), the frontal boundaries being a folded portion of the original tropopause.

The circulation within the frontal zone was indirect solenoidal, and surface cyclogenesis accompanied or slightly preceded the strengthening of the upper-level front. Although the frontal zone formed entirely within a polar air-mass, the strong adiabatic heating at and near the warm boundary could give the false impression that tropical air was present there at the end stage.

Full access
Richard J. Reed

Abstract

A two-level graphical prediction model is extended so as to include the effects of heating of cold air by relatively warm water. Orographic effects are also included in the model.

The model is applied to a case of a major storm development in the Gulf of Alaska attended by a strong outbreak of Arctic air from the Alaskan mainland. In this case the effects of nonadiabatic heating and orography appeared to be significant and in a direction which tended to improve the forecast.

Full access
Richard J. Reed

Abstract

A method is presented for preparing 1000-millibar (surface) prognostic charts. The method makes use of the graphical technique developed by Fjörtoft and is based on a baroclinic model which resembles closely that employed by Estoque in the prediction of cyclone development.

Three cases tested to date have yielded correlations of 0.93, 0.89 and 0.88 between predicted and observed 1000-mb height changes.

Full access
Richard J. Reed

Measurements of elevation and azimuth angles, taken every six seconds by an AN/GMD-1 rawin set, are used to compute the detailed wind structure in an intense frontal zone. It is found that the vertical wind shear is discontinuous at the frontal boundaries as anticipated from the thermal wind equation.

Full access
Richard J. Reed

Daily synoptic analyses for five winter and summer seasons are used to obtain mean frontal positions for the Northern Hemisphere. These positions are found to differ in several important respects from earlier estimates based on mean-pressure and -temperature charts.

In winter, three axes of high frontal frequency, or principal frontal zones, appear which are termed the Pacific polar front, the Atlantic polar front, and the Eurasian polar front. There is also some evidence of a weak Atlantic arctic front. A fourth belt of high frontal frequency parallels the Rocky Mountains.

In summer, four principal frontal zones are delineated: a Pacific polar front, an Atlantic polar front, an Eurasian polar front, and a Siberian-Canadian arctic front.

The locations and intensities of the oceanic fronts are shown to be closely related to the sea-surface temperature distributions. The formation of a Siberian-Canadian arctic front in summer is attributed to the strong thermal contrast that develops along the borders of the arctic seas. The position of the Eurasian polar front in winter also appears to be affected by the thermal characteristics of the underlying surface, being most distinct where open seas adjoin relatively cold land.

Full access
Richard J. Reed

Abstract

This paper examines the meteorological conditions and physical processes associated with the development of strong downslope winds that caused extensive property damage in two areas of western Washington on 28 November 1979. These areas wore located downwind of the two largest and lowest passageways through the Cascade Range: the Columbia River Gorge and the Stampede Pass region. Findings are as follows:

1) The destructive winds, marked by gusts of 25–30 m s−1, appeared in conjunction with the formation of a deep cyclone offshore and the simultaneous development of an unusually powerful anticyclone inland.

2) The pressure gradient was greatly enhanced in the vicinity of the mountain range attaining values as large as 12 mb (100 km)−1.

3) Hydrostatically, the large pressure differences can be attributed to the effect of the barrier in separating cold air on the cast side from warmer air on the West.

4) Trajectory tracing revealed that the temperature difference formed rapidly as a result of the presence of strong subsidence on the Ice side and the absence of low-level subsidence in the confined, inland basin on the windward side.

5) The undisturbed flow normal to the barrier ranged from light easterly at lower levels (5–10 m s−1 at most), to zero in the layer between 600 and 700 mb, to light westerly above.

Calculations are carried out to demonstrate that the wind speeds were consistent with the observed pressure differences. The large-scale pressure gradient was well predicted 36 h in advance by the limited-area fine-mesh model (LFM) of the National Meteorological Center.

Full access
Richard J. Reed

Abstract

Two case studies of cyclogenesis that occurred in polar air streams behind or poleward of major frontal bands are presented. Based on the results of the studies, and on other evidence, characteristics of the type of disturbance in question are described. The cyclones in polar air masses are generally of small dimension, being spaced at intervals of 1000–1500 km when they occur in multiple form. They form most often over the oceans in winter, originating in regions of low-level heating and enhanced convection and acquiring a comma-shaped cloud pattern as they mature. They are associated with well-developed baroclinity throughout the troposphere and are located on the poleward side of the jet stream in a region marked by strong cyclonic wind shear and by conditional instability through a substantial depth of the troposphere.

Instability mechanisms for their formation are discussed. It is concluded that they are primarily a baroclinic phenomenon that owe their below average size to the effect that small static stabilities at low levels have in reducing the wavelength of maximum instability and to the fact that they develop on already perturbed large-scale states rather than on uniform zonal flows. Conditional instability of the second kind and barotropic instability cannot be ruled out as possible important additional influences in their formation.

Full access
RICHARD J. REED

Abstract

All available meteorological rocket soundings through the summer of 1966 are harmonically analyzed to obtain the amplitude and phase of the semidiurnal variation of the meridional wind component in summer for stations located near 30° and 37°N and of the zonal wind component in summer for the stations near 30°N. The results support the earlier finding that a phase reversal occurs at a height of 45–50 km rather than at the theoretically predicted height of 25–30 km. It is suggested that the difference between observation and theory may be attributed to the neglect of the basic wind structure in the theoretical calculation.

Full access
Richard J. Reed

Abstract

Useful forecasts may be obtained by graphical integrations of the dynamical prediction equations for a barotropic and a two-level baroclinic atmosphere. Such forecasts may be prepared without the aid of special equipment and are therefore particularly valuable as a means of training forecasters in physical prognosis.

The present paper reviews the physical principles, modeling assumptions, and methods of solution used in graphical prediction and introduces a method of obtaining surface forecasts which is considerably faster and simpler than previous methods. The predicted surface pressure is shown to be the sum of two components: (1) the pressure advected to the spot by one-half the 500-mb. wind and (2) a pressure change reflected down from aloft (actually one-half the 500-mb. height change expressed in equivalent pressure units at 1000 mb.). The movement of surface pressure systems is thus seen to be largely dependent on upper-level steering, while the deepening is found to be related to the vorticity advection at high levels, since this mainly determines the 500-mb. height changes.

Twenty sample surface forecasts prepared by the graphical method during July 1959 are presented and compared with the forecasts for the same dates issued by the National Weather Analysis Center. Little difference in accuracy is apparent.

Typical shortcomings and failures of the graphical prognoses are discussed. It is believed that the most serious errors are due to the use of only the initial 500-mb. charts in advecting the pressure systems. If the 500-mb. forecasts had been available earlier, it appears that a significant increase in accuracy could have been achieved by using both initial and forecast 500-mb. contours in performing the advections.

Full access