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Edward Ryznar

Abstract

Solar irradiances, atmospheric turbidity and meteorological variables measured at the University of Michigan are analyzed to determine effects of the 30 m wind direction on irradiance and turbidity changes caused by the El Chichón volcanic cloud. Results for the period with the largest volcanic effects, from 26 October 1982 through mid-June 1983, are compared with results for the same eight-month period in 1979–80, 1980–81, 1981–82 and 1983–84.

Effects of boundary-layer turbidity for winds from southerly directions occasionally masked effects of the stratospheric volcanic cloud on solar irradiances and sunphotometer estimates of Angström turbidity parameters. As a result, volcanic effects could be quantified most reliably for winds only from northerly directions. The largest changes occurred with 30 m winds from the north-northwest octant, for which the volcanic cloud caused the average 500 nm aerosol optical depth to increase from 0.15 to 0.28, the turbidity coefficient to increase from 0.08 to 0.17, and the wavelength exponent to decrease from near unity to 0.6. The ratio of diffuse-to-direct solar irradiance increased from 0.10 to 0.21.

For winds from southerly directions, average turbidity was larger and more variable, and irradiance and turbidity changes due to the volcanic cloud were smaller. The smallest changes occurred with 30 in winds from the east-southeast octant, for which the cloud caused the optical depth to increase from 0.29 to 0.31, the turbidity coefficient to increase from 0.09 to 0.16, and the wavelength exponent to decrease from 1.3 to 0.9. The ratio of diffuse-to-direct irradiance increased from 0.15 to 0.22.

Daily totals of solar irradiances for 22 cloudless days from 26 October 1982 to 8 June 1983 showed the following average percentage changes from average conditions caused by the cloud: direct normal, −24; diffuse, +87; global, −5; global spectral (630–2800 nm), −1; and south-facing 42.3°-inclined, −5.

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Edward Ryznar

Abstract

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Edward Ryznar

Abstract

The effects of turbulent fluctuations of atmospheric density are seen as rapid changes in the brightness of a distant light source (scintillation) and in the position and size of distant objects (shimmer). The results of an investigation of the effects in a horizontal optical path 543 m long and 1.5 m high over a uniform snow surface are described.

It was found that deterioration in visual resolution caused by shimmer was most pronounced when the atmosphere was clear, a time when the detection and recognition of distant objects were otherwise unimpeded. Visual resolution deteriorated and scintillation intensity increased systematically with increasing inversion magnitude in turbulent flow. Resolution was best in windy and cloudy conditions and poorest on clear nights with light wind speeds.

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Edward Ryznar and Michael R. Weber

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Edward Ryznar, Dennis G. Baker, and Harry Moses

Twenty-five meteorological stations are in operation inland from two nuclear power plants located on the Lake Michigan shoreline in southwestern lower Michigan. Their purpose is to provide data to enable meteorological effects of mechanical-draft cooling towers at the Palisades Nuclear Plant and a once-through cooling system at the Donald C. Cook Nuclear Plant to be evaluated. Temperature, relative humidity, and precipitation are measured at all stations, total solar radiation and wind velocity at four, and visibility at three. The stations, equipment, and calibration methods are described, and examples of types of meteorological analyses are presented.

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C. Bruce Baker, William R. Kuhn, and Edward Ryznar

Abstract

Direct normal and diffuse solar irradiances and 500 nm aerosol optical depths measured at the University of Michigan departed far from normal on 26 October 1982, when it is concluded that the main stratospheric cloud from the El Chichon volcanic eruption arrived at the 42°N latitude of the radiation measurement facility. For clear-sky data analyzed through 19 January 1983, direct solar is about 25% less than normal and diffuse solar is about 85% greater. For the same aerosol optical depths and solar zenith angles, the ratio of diffuse to direct is about 30% greater for about 0.3 cm of precipitable water but nearly the same for 0.9 cm. Aerosol optical depths are nearly three times greater for wind directions that naturally advect the cleanest air. The effect of circumsolar irradiance on the methods used to measure direct normal and diffuse irradiances cause the former to be overestimated and the latter to be underestimated.

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Edward Ryznar, Michael R. Weber, and Thomas S. Hallaron

Abstract

Measurements of turbidity were made at the University of Michigan irradiance and meteorological measurement facility just prior to, during and after the passage of the volcanic cloud from the 18 May 1980 eruption of Mount St. Helens. They were made with a Volz sunphotometer at wavelengths of 500 and 880 nm.

The volcanic cloud gradually moved over the measurement facility on the afternoon of 20 May and remained over it until 2300 GMT 21 May. Its effects on the turbidity coefficient and wavelength exponent in Ångström's turbidity equation are evaluated by comparing results for 20 and 22 May, both of which were cloudless days, with those on 21 May. The volcanic cloud increased the turbidity coefficient by a factor of about 8 and decreased the wavelength exponent by a factor of about 3 compared to average values for 20 and 22 May. Some uncertainty in the results is caused by cirriform clouds in addition to the volcanic cloud on 21 May. These results and effects of the volcanic cloud on recordings of global, direct normal and diffuse solar irradiances are described.

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