Sumner Barr

Effects of synoptic patterns on atmospheric chemistry and aerosols during the Arctic Ocean Expedition 1996

Effects of synoptic patterns on atmospheric chemistry and aerosols during the Arctic Ocean Expedition 1996

The random force theory applied to regional scale tropospheric diffusion

Abstract Twelve examples of long-duration (1- to 50-h) diffusing clouds and plumes, culled from archived data on early nuclear rocket and Plowshare experiments and satellite-observed volcano plumes, are compared individually with a ‘random-force’ theory (Gifford, 1982a, Atmospheric Environment16, 505–512) of long-range atmospheric diffusion. The resulting fitted curves yield sets of 12 estimates of each of the dynamical parameters of the theory, the Lagrangian integral time-scale of atmospheric turbulence, tL, and the large-scale atmospheric eddy-diffusivity, K, and of other quantities that can be formed from these, such as the lateral turbulent velocity, \ gu 2 1 2 the turbulence intensity, i, and the average atmospheric eddy-energy dissipation rate, e.The Lagrangian time-scale values are all within a factor of about two of the value 104 s, confirming the suggestion (Gifford, 1984, Boundary-Layer Met. 30, 159–175) that tL equals the reciprocal of the geostrophic frequency. Stratospheric values of K and e are an order of magnitude greater than those observed within the troposphere. Values of other quantities are more scattered but yield, in each instance, reasonable averages.

Tropospheric relative diffusion to hemispheric scales

Abstract A three-range model of the atmospheric energy spectrum, suggested by the recent GASP spectra and consisting of an enstrophy-cascade range (I), an energy-cascade range (II), and a dissipation range (III), is applied to the problem of long-range atmospheric diffusion. Clouds and plumes are observed to diffuse rapidly and coherently in range-II. This spreading extends to hundreds of kilometers, at rates satisfactorily described by existing diffusion theories, including similarity theories. The Lagrangian time-scale of the range-II diffusion is shown to be defined by tII = 1/f, where /tf is the Coriolis parameter. Diffusion at greater distances is much less regular because it is due to the quasi-two-dimensional, range-I eddies. Clouds and plumes are quickly distorted into streaks and patches by the 2D motions of range-I; but individual pieces of cloud continue to be diffused at the asymptotic (parabolic) rate of the range-II 3-D eddy turbulence. The effect of these processes is a lumpy, streaky cloud, clearly depicted by the results of a numerical modeling study. Concentrations of a unique tracer (heavy methane), released in the troposphere near Antarctica and followed by surface and aircraft observations for several weeks, support this characterization of the longrange diffusion process.

A long-range atmospheric tracer field test

Abstract A long-range application of a heavy methane atmospheric tracer system has been carried out using both 12 CD 4 and 13 CD 4 . The experiment had several objectives including testing a newly developed cyrogenic air sampler, testing a new sample handling apparatus and demonstrating the use of heavy methanes over transport distances up to 2500 km and travel times of more than 100 h. A simple diffusion estimation method applied in conjunction with trajectories produced by NOAA from upper air meteorological data yields good agreement with the tracer data on dosage and arrival time. The duration of observed tracer at the long-range stations was longer than estimated with simple concepts.

Plume dispersion in a nocturnal drainage wind

Abstract A series of tracer experiments were conducted under nocturnal drainage wind conditions in a complex terrain setting in the Piceance Basin of western Colorado. Concurrent meteorological information including profiles of wind and temperature as well as gross turbulence fluctuations from fixed 2-m stations provided the basis to test plume growth and dilution prescriptions for this moderately complex site. Plume parameters exhibited slightly greater diffusion than would be indicated by simple stability-based prediction methods or the gross turbulence indicators. Two terrain-related mechanisms appear to contribute to the development of the plume. A meandering component immediately downwind of the confluence of two valleys gives the appearance of an abnormally wide time-integrated plume. Further downstream the mean wind direction stabilizes and the plume dimension reflects diffusive spread due to small-scale turbulence.

Meteorological Analysis of the Eruption of Soufriere in April 1979

Meteorological upper-air data, in conjunction with satellite imagery, lidar light detection and ranging returns, and aircraft sampling, aid in the determination of plume altitude and transport. The estimated trajectories indicate that the ash was transported eastward across the Atlantic to Africa in 3 to 5 days and that there was modest meridional transport as far as 15� poleward during the first week of travel.

Fluorescent particle lidar

A lidar system designed to detect the return from small fluroescent particles has been built. (AIP)

Free tropospheric ozone production after deep convection of dispersing tropical urban plumes

Abstract Ozone generation is computed in a one-dimensional photochemistry code following convective redistribution of tropical urban effluent into the free troposphere. Simulations are run at several stages of pollutant dilution by surrounding surface air. A threshold boundary layer NO x concentration of 300 pptv is established for significant production enhancements at upper levels. Areas defined by the 300 pptv level are examined in the Gaussian dispersion framework based on a wet season plume event observed in Amazonia. Pollution travels slowly in the sluggish winds of the equatorial trough. Daily storms are likely to interrupt the effluent while coverages are still on the order of few thousand square kilometers and NO x concentrations are above the threshold. Dry season plume sizes are difficult to assess because local concentration data are scarce, but it is conceivable that the faster trade winds lead to a several fold extension.

HORIZONTAL VARIABILITY AND BOUNDARY-LAYER MODELING

Micrometeorologists have traditionally set aside consideration of horizontal variability and have studied boundary-layer structure with horizontal homogeneity. The numerical forecasting of boundary-layer structures, over normally varying terrain and including normal disturbances such as fronts, requires selection of an ‘appropriate’ horizontal scale.A simple analysis of steady-state balance between horizontal advection and vertical diffusion provides estimates of the vertical scale (or depth) of surface-induced features. The scale height is a function of the horizontal scale of the variations. Models neglecting important terrain scales of length below ~ 1000 km can predict down to levels of ~ 0.5 to 1 km while those that neglect important terrain scales below ~ 100 km can predict down to ~ 0.2 to 0.6 km. Below these levels, any predicted features will be dominated by the vertical diffusion so that they are solutions of a one-dimensional boundary-value problem.The boundary-induced advection effects dominate free atmosphere advection effects in the lowest few hundred meters as well. This means that if mesoscale advections are resolved and terrain influences are strong, the predictions in the layer ~ 0.2 to 0.8 km can provide mesoscale detail without mesoscale initial conditions above the surface, because the surface forcing will dominate the solution.

ROMPEX—The Rocky Mountain Peaks Experiment of 1985: Preliminary Assessment

Abstract During the late summer of 1985 a field experiment was conducted to investigate mountaintop winds over a broad area of the Rocky Mountains extending from south central Wyoming through northern New Mexico. The principal motivation for this experiment was to further investigate an unexpectedly strong and potentially important wind cycle observed at mountaintop in north central Colorado during August 1984. These winds frequently exhibited nocturnal maxima of 20 to 30 m·s−1 from southeasterly directions and often persisted for eight to ten hours. It appears that these winds originate as outflow from intense mesoscale convective systems that form daily over highland areas along the Continental Divide. However, details of the spatial extent and variability of these winds could not be determined from “routine” regional weather data that are mostly collected in valleys. Although synoptic conditions during much of the 1985 experiment period did not favor diurnally recurring convection over the study area, ...