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Analysis of an Ozone Episode during the San Diego Air Quality Study: The Significance of Transport Aloft. Bigler-Engler, Virginia; Brown, Hal W..
Journal of Applied Meteorology:
1995
Notes
San Diego is subject to transport of ozone and precursors from the Los Angeles area, 170 km to the northwest, as well as to high ozone concentrations from local emissions. The San Diego Air Quality Study was conducted during the summer of 1989. Air quality and meteorological data were obtained at the surface and aloft to provide a high quality database for photochemical modeling and control strategy development for both local and transport-influenced ozone episodes. Six high-ozone episodes were potentially suitable for photochemical modeling, including several from 21 to 29 September 1989; maximum 1-h ozone concentrations exceeded the federal ambient standard on six of the nine days and reached 0.17 ppm on two days. From review of preliminary surface and routine meteorological data and surface trajectory analysis, 25–26 September 1989 appeared to be a local episode with high ozone concentrations downwind from local (i.e., San Diego) emissions sources. This paper examines the candidate episode and finds that transport aloft from the Los Angeles area played a key role.
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An Analysis of Sierra Nevada Winter Orographic Storms: Ground-based Ice-Crystal Observations. Demoz, Belay B.; Zhang, Renyi; Pitter, Richard L..
Journal of Applied Meteorology:
1993
Notes
Systematic observations of the sizes, shapes, and degrees of riming of ice particles falling at a downwind station of a major mountain barrier are presented. The observational station was equipped to measure ice-particle masses from 1microg to a few milligrams and to measure ice-particle dimensions, habits, degrees of riming, and degrees of aggregation. The results are shown to be useful in learning where ice nucleation and growth take place in the cloud system. The present study analyzed dissipating and developing winter orographic storm systems, which are representative of more than 60% of the storms observed over the study region. It suggests that most of the needles and columns observed at the ground may be formed by secondary ice production. Heavy riming was associated with light precipitation, while high precipitation rates were correlated with a high number fraction of aggregate crystals. Aggregation was found to be important in the process of precipitation development and the aggregate mass was mostly contained in the dendritic crystal growth region.
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Effects of Soil Moisture on Temperatures, Winds, and Pollutant Concentrations in Los Angeles. Jacobson, Mark Z.
Journal of Applied Meteorology:
1999
Notes
This paper examines the effects of soil moisture initialization in a coupled air quality–meteorological model on temperature profiles, wind speeds, and pollutant concentrations. Three simulations, each with different initial soil moisture fields, were run. In the baseline simulation, predicted temperatures, wind speeds, and gas/aerosol pollutant concentrations accurately matched observations. In the other two simulations, soil moisture contents were initialized about 4% lower and higher, respectively, than in the baseline simulation. In the low-moisture case, predicted temperature profiles were hotter, near-surface wind speeds were faster, and near-surface pollutant concentrations were lower than observations and baseline predictions. In the high-moisture case, predicted temperatures were colder, wind speeds were slower, and pollutant concentrations were higher than observations and baseline predictions. Initial soil moisture contents affected vertical temperature profiles up to 600-mb altitude after two days. Elevated temperature changes were due in part to changes in sensible heat fluxes from the surface and in part to changes in elevated heat advection fluxes. Changes in temperature profiles affected wind speeds and boundary layer depths, which affected times and magnitudes, respectively, of peak concentrations. Slower wind speeds, associated with high soil moisture contents, delayed times of peak concentrations in the eastern Los Angeles basin. Faster wind speeds, associated with low soil moisture contents, advanced times of peak concentrations. High soil moisture contents resulted in thinner boundary layer depths, increasing average near-surface pollutant concentrations, including that of ozone. Low soil moisture contents resulted in thicker boundary layer depths, decreasing average concentrations, including that of ozone. At some locations, changes in the magnitude of peak ozone concentrations depended on how changes in soil moisture affected ozone precursors and destroyers.
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Modeling Utility Load and Temperature Relationships for Use with Long-Lead Forecasts. Robinson, Peter J..
Journal of Applied Meteorology:
1997
Notes
Models relating system-wide average temperature to total system load were developed for the Virginia Power and Duke Power service areas in the southeastern United States. Daily data for the 1985–91 period were used. The influence of temperature on load was at a minimum around 18°C and increased more rapidly with increasing temperatures than with decreasing ones. The response was sensitive to the day of the week, and models using separate weekdays as well as one using pooled data were created. None adequately accounted for civic holidays or for extreme temperatures. Estimates of average loads over a 3-month period, however, were accurate to within ±3%. The models were used to transform the probability distribution of 3-month average temperatures for each system, derived from the historical record, into load probabilities. These were used with the categorical temperature probabilities given by the National Weather Service long-lead forecasts to estimate the forecast load probabilities. In summer and winter the resultant change in distribution is sufficient to have an impact on the advance fuel purchase decisions of the utilities. Results in spring and fall are more ambiguous.
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Quantifying precipitation suppression due to air pollution. Givati, Amir; Rosenfeld, Daniel.
Journal of Applied Meteorology:
2004
Notes
Urban and industrial air pollution has been shown qualitatively to suppress rain and snow. Here we quantify the precipitation losses over topographical barriers downwind of major coastal urban areas in California and in the land of Israel, which amounts to 15 – 25% of the annual precipitation. The suppression occurs mainly in the relatively shallow orographic clouds within the cold air mass of cyclones. The suppression that occurs over the upslope side is coupled with similar percentage enhancement on the much drier downslope side of the hills. The evidence includes significant decreasing trends of the ratio of hill/coast precipitation during the 20th century inpolluted areas in line with the increasing emissions during the same period, whereas no trends are observed in similar nearby pristine areas. The evidence suggests that air pollution aerosols that are incorporated in orographic clouds slow down cloud-drop coalescence and riming on ice precipitation, hence delaying the conversion of cloud water into precipitation. This explains the pattern of greatest loss of precipitation at the mid-level of the upwind slopes, smaller losses at the crest, and enhancement at the downslope side of the hills.
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