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Richard H. Thuillier

Pacific Gas and Electric Company (PGandE) has sponsored development of a computer-based system for real-time analysis of local wind measurements in a complex-terrain setting. Mass-consistent modeling of tower- and Doppler-sounder data produces spatial wind-vector patterns on a color-graphic display. The system is currently deployed at the Diablo Canyon Nuclear Power Plant to assist meteorologists in supporting response to radiological emergencies.

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Richard H. Thuillier

Abstract

When designing field measurement networks, or when using the data from network archives, it is important to be aware of the influence that instrumentation, siting, data processing, and sensor exposure have upon the measurements. A unique opportunity arose to study this influence when in summer 1990, as part of the collaborative San Joaquin Valley Air Quality Study/Atmospheric Utility Signatures, Predictions and Experiments study (SJVAQS/AUSPEX), a vast meteorological measurement network was established for the central one-third of the state of California. Within the constraints of available resources, a variety of instruments, sites, site densities, sensor exposures, and data processing techniques were involved in the study. Based on the dataset from SJVAQS/AUSPEX, this paper was written to identify and quantify some common measurement influences for the benefit of users of the SJVAQS/AUSPEX data as well as the designers and users of other networks and datasets.

To characterize and quantify measurement influences, comparisons were made of data associated with different instrument types, sites, measurement heights, and temporal averaging methodologies. Comparative statistics were then developed and summarized. Little variability existed among the characteristics of surface instrumentation, but sounding instrumentation varied greatly in the degree to which atmospheric vertical structure was resolved. Vertical sampling resolutions ranged from 4.5 to 300 m, and winds were averaged over layer depths ranging from 15 to 600 m. The spatial location of measurements had a great influence on the measured direction of the wind. Hourly wind directions at neighboring surface sites differed by an average of 18° over the network with an rms variability of 55°. Upper-air values of these same statistics were 12° and 64°, respectively. A functional dependence of wind variability on site separation distance was apparent from the data. The influence of sensor exposure height on wind speed measurements, when comparing neighboring sites with different measurement heights, was less than expected. The average ratio in wind speed for such site pairs was only 1.18 (1.06 by day and 1.34 at night) for 10-m versus 2-m measurements. Temporal averaging methodology greatly influenced hourly wind values, especially for wind speeds less than 5 m s−1. Large differences were observed in hourly wind speed averages from scalar versus vector averaging, as well as in hourly wind direction averages from resultant versus unit vector averaging.

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Richard H. Thuillier and James S. Sandberg

As an extension of strong policy against open burning, the Bay Area Air Pollution Control District, in 1967, placed the previously unregulated burning of deciduous fruit and nut tree prunings under meteorological control pending the development of alternative methods of disposal. In applying the control program, temperature inversion criteria and all other factors involving vertical mixing, horizontal transport and contaminant buildup were weighed by District meteorologists in arriving at a daily burn, no-burn decision.

As an evaluation of program effectiveness, three years of forecasts for the December–April agricultural burning season have been verified in terms of various indices of air quality. BAAPCD's quantitative Combined Pollutant Index was found to be a reasonable basis for forecast verification. A critical CPI value of 30 appeared as the 80th percentile in the burn frequency distribution and as the 20th percentile in the no-burn distribution An objective technique was developed incorporating minimum temperature at San Jose, near the principal burning sites, with 3000-ft winds from the rawinsonde at Oakland. A test of this method on independent data during the 1970–1971 burning season established its usefulness as a burning forecast tool.

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