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  • Author or Editor: John J. Carroll x
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John J. Carroll
and
Ming Liu

Abstract

The authors have developed a relatively simple, first-order closure, Eulerian diffusion model, in which turbulent coherent structures of the convective boundary layer are explicitly included as periodic velocities imposed on a stationary and horizontally homogeneous wind field. The dimensions of the convective updrafts and downdrafts are assumed to be inversely proportional to the ratio of their respective vertical speeds and are constant with height, and the updraft and downdraft areas are constant in the horizontal. Sinusoidal vertical velocity variations are specified with amplitudes proportional to the mean vertical velocity profiles for skewed distributions described by Weil. The horizontal velocity components of the coherent structures are calculated using the continuity equation. Model simulations for conditions on the afternoon of Wangara day 33 reproduce the major features of the complicated plume dispersion behavior observed in the water tank experiments and the CONDORS experiments. The model produces results comparable to those obtained by complex large-eddy simulation models and random walk Lagrangian models, but is computationally much less demanding. Sensitivity tests are presented that show that the model is insensitive to physically realistic ranges of the modeling parameters.

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John J. Carroll
and
Ronald L. Baskett

Abstract

The results of a field study utilizing ground-based and aircraft measurements of meteorological parameters and several air pollutants are described for two summer periods in the vicinity of Yosemite National Park, California. These results are related to observed air quality and atmospheric circulation patterns in neighboring parts of the state and to transport by the local mountain-valley wind system. The conclusion is reached that maximum air quality degradation in the study area does not occur during persistent periods of large-scale stagnation, but occurs as the result of transport from area sources up to 200 km away by the typical extended sea breeze circulation which develops following such a period.

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Laura L. Zaremba
and
John J. Carroll

Abstract

This study utilized conditional sampling to identify three frequent wind regimes in the lower Sacramento Valley. The major flow features of the mean diurnal wind patterns in the southern Sacramento Valley and surrounding areas were analyzed for each wind regime. Afternoon wind directions at a pivotal observing site (Davis, CA) in the south-central part of the valley were used to classify the regimes as south wind (marine air intrusion), north wind (no marine air intrusion), and transitional wind days. In the summer of 1991, these occurred 72%, 14%, and 14% of the days, respectively. Daily data from 21 surface observing stations were segregated by wind regime, then averaged for quarters of the day to produce wind roses grouped by regime and time of day. These data were then plotted on a base map. The most frequent direction in each of these wind roses was used to construct streamlines for the area by quarter of the day for each regime. These analyses provide a climatology of the diurnal variation of the average wind flow for each of these frequent flow regimes, providing a wind climatology with greater spatial and temporal resolution than those in extant publications. These analyses are especially useful for evaluating transport patterns of air pollutants or contaminants.

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