Search Results

You are looking at 21 - 30 of 70 items for

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

Abstract

No abstract available.

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
RICHARD J. REED

Abstract

The annual temperature regime in the tropical stratosphere between 100 mb. and 10 mb. is examined on the basis of five years of data from six stations, ranging in latitude from 9° N. to 34° N. The principal result of interest is the finding of a pronounced semiannual component in the temperature variation above the 30-mb. level (24 km.), especially at stations near the equator. It is suggested that this may be caused by the direct absorption of solar ultraviolet radiation by ozone in a region where the heating cycle is predominantly semiannual.

Full access
Richard J. Reed
and
Richard H. Johnson

Abstract

Composite fields of the large-scale variables determined from three months of observations at a triangular array of stations are used to determine the vorticity budget of easterly wave disturbances in the tropical western Pacific. The measurements reveal substantial imbalances which are largest in the disturbed or convectively active region of the waves. In this region there exists an apparent vorticity sink for the large-scale motions in the lower half of the troposphere and an apparent source in a relatively thin layer of the upper troposphere.

Cumulus modelling assumptions are employed to estimate vertical cloud mass flux and vertical profiles of cloud vorticity. It is concluded that the low-level sink and upper-level source can be attributed to the removal of vorticity-rich air from the lower layers and its deposition aloft by deep convection.

Full access
Richard J. Reed
and
Adrian J. Simmons

Abstract

The effect of surface sensible and latent heat fluxes on explosive cyclogenesis has been found to be quite variable. Sensitivity tests reveal little or no influence in some cases and dramatic effects in others. However, in nearly all cases where little impact was found, the predicted deepening rate was significantly less than the observed rate, opening the possibility that the unexplained deepening might be a consequence of a shortcoming of the flux formulation.

We present here the results of a test of the impact of the fluxes in a case of extreme deepening that was accurately predicted by the ECMWF T106 operational model. In the test the fluxes were switched off during the 24-h period of most rapid deepening. The result was to change the predicted deepening rate of 48 mb by only 1 mb. This confirms that in certain circumstances the concurrent fluxes can have negligible effect on the deepening despite their great importance in other situations.

It is shown that downward heat and moisture fluxes (cooling and drying) occurred in the warm sector close to the low center, whereas upward heat and moisture fluxes (warming and moistening) occurred in the cold air well to the rear of the low. It is known from theory that this pattern is not conducive to cyclonic development. The cause of the vast difference in the effect of the fluxes on cyclone development is discussed in terms of the stage of development, the geographical location, and the degree of atmospheric preconditioning.

Full access
Jordan G. Powers
and
Richard J. Reed

Abstract

An observational study, employing spectral methods, is first made to establish a background for a modeling effort of the mesoscale gravity-wave event of 15 December 1987. The waves are found to have wavelengths of 100–160 km, phase speeds of approximately 30 m s−1, and lifetimes of over 6 h. Conditions for their maintenance are evaluated, indicating the presence of a wave duct and a supportive role for wave-CISK. Convection, shearing instability, and geostrophic adjustment are all implicated as possible source mechanisms for the observed waves.

The case is then simulated with the Pennsylvania State University–National Center for Atmospheric Research MM4 mesoscale forecast model, with the following primary objectives: (i) to test the model's ability to simulate a mesoscale gravity-wave event, (ii) to examine in detail the environments of mesoscale gravity-wave development, and (iii) to investigate the mechanisms of mesoscale gravity-wave generation and maintenance. The full-physics control experiment employed a 30-km grid, the Hsie et al. scheme for explicit moist processes, and a modified Arakawa–Schubert cumulus parameterization. From this experiment it is found that the model can successfully simulate mesoscale gravity waves and can capture many aspects of an observed wave event. For this case the model mesoscale gravity waves arose, matured, and decayed in the same regions as those observed and had similar timing and amplitudes. Model wave speeds, however, were 1–1.8 times those observed. The model output showed that although a good wave duct covered the wave activity area, the model waves were maintained and amplified by wave-CISK processes. These waves appeared to be generated by convection of mesoscale extent above a stable duct. This convection moved with the waves and was associated with steering levels.

Model sensitivity experiments showed that (i) the model mesoscale gravity waves do not stern from initial data imbalances, (ii) model mesoscale gravity-wave development does not occur when latent heating is removed, (iii) model mesoscale gravity-wave production is not necessarily limited to the early hours of a simulation, and (iv) model mesoscale gravity waves can be produced using grid sizes up to 45 km. As applied to the actual case, it is concluded from the simulations that both ducting and wave-CISK contributed to the maintenance of the observed waves. Convection is indicated as the primary wave source, although evidence of shearing instability is also found. The model results, however, do not support the idea of generation by geostrophic adjustment.

Full access
Richard J. Reed
and
Mark D. Albright

Abstract

Low-level (300 m) aircraft observations, taken within an intense extratropical storm during Intensive Observation Period 2 of the Experiment on Rapidly Intensifying Cyclones over the Atlantic, are used to document the near-surface frontal structure in the interior of the storm at 1800 UTC 14 December 1988, when the storm was at its maximum depth (959 mb). The flight data revealed that a well-defined occluded front spiraled into the low, making one-and-one-half turns about the center. The front followed the inner boundary of a spiral cloud and moisture band seen in satellite visible, infrared, and water vapor imagery. The results provide support for the idea that sharp occluded, or occluded-like, fronts can wrap around the core of deep ocean storms and that satellite imagery can be helpful in locating such fronts.

Full access