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A. H. Weber and R. J. Kurzeja

Abstract

This paper summarizes the results of meteorological and dispersion measurements during Savannah River Laboratory's Project STABLE (Stable Boundary Layer Experiment) field program. The field program took place at the Savannah River site on three nights during 12–17 April 1988. Meteorological data were collected from a 304-m tower, an array of eight 60-m towers, two sodars, a tethersonde, and a sonic anemometer.

Based on the classification scheme of Kurzeja et al. (1991) the first and third nights were classified as unsteady type IV nights because of the passage of microfronts on each night. The second night exhibited a continuous level of high turbulence with a weak surface-based inversion and was classified as a steady type III night.

The third night was especially interesting because of the considerable directional wind shear with height and the occurrence of two turbulent episodes. The directional shear may have been related to the passage of a high pressure center during the night.

The turbulent episodes lasted from 5 to 30 min and had a horizontal extent of at least 30 km. They were preceded by cooling near the surface and a shift to lower frequencies of the Brunt-Väisälä frequency NBV. It is suggested that a decrease with time of NBV or an increase in the standard deviation of the vertical component of velocity (σw) or σw/NBV might be used to forecast the onset of turbulent episodes reaching the surface.

Sulfur hexafluoride (SF6) tracer was released continuously during the experiments and measured 10–20 km downwind by a mobile continuous analyzer. The tracer transport was shown to be consistent with low-level winds on the 304-m tower, except on the third night. It was hypothesized that on the third night the spatial variability of the wind field was much more extreme than on the other nights and, hence, the winds from the 304-m tower did not reflect the true plume movement. A spatially averaged mean wind was more successful in explaining the observed horizontal plume movement. The wider-than-expected across-are concentration distribution on the third night was attributed to continuously varying shear; whereas the occasional secondary maxima in the tracer pattern were due to discontinuities in the vertical wind shear.

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J. J. Stephens, Peter S. Ray, and R. J. Kurzeja

Abstract

Approximations to the far-field, backscattering response for an electromagnetic impulse are shown for two water sphere sizes. For small electrical sizes, the scattering is described by an electric dipole; for large electrical sizes, a combination of reflection from the front interface, creeping waves, and surface currents excited as the impulse moves across the sphere is used.

It is shown that transient effects are confined effectively to an equivalent space period of less than six diameters and can be neglected in all operational applications of pulse radar to rain detection.

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R. J. Kurzeja, K. V. Haggard, and W. L. Grose

Abstract

Two experiments were performed with a nine-layer quasi-geostrophic spectral model to simulate the distribution of ozone below 60 km. Experiment I included thermal and orographic forcing of the planetary-scale waves while Experiment II did not include this forcing. Both experiments used a linear parameterization of ozone photochemistry.

The two experiments were qualitatively similar but a high latitude winter ozone buildup was seen only in Experiment I. This buildup resulted from a Brewer-Dodson circulation forced by large-amplitude planetary-wale waves in the winter lower stratosphere.

The model results also showed that photochemistry is important down to lower altitudes (20 km) in the summer stratosphere than was previously realized. An important photochemical discrepancy was noted between 22 and 30 km at low latitudes, where the model photochemical equilibrium mixing ratios were 25–40% larger than those inferred for the real stratosphere. This discrepancy may be due to insufficient NO2 in the model and can be resolved by more accurate daytime NO2 measurements.

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