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Abstract
The Directional Radiance Distribution Measurement (DIRAM) device was designed and built to determine the angular distribution of shortwave radiance as a function of height in cloudy and clear-sky conditions at various surface albedos. The construction contains 42 sensors, consisting of a collimation system and a detector, which are mounted in two domes (21 in each). The collimators are made of solid PERSPEX cylinders, 8 mm in diameter and ∼24 mm long, which are fully transparent in the visible range. Three diaphragms are carved in each cylinder to reduce the field of view to ∼7° and to reduce the stray light. The detector is a commerially available silicon photodiode for the visible spectral range. The domes can be placed at ground level, or on top and below a research aircraft. The collimators collect broadband visible radiation in 42 regularly distributed viewing angles. The aperture of each sensor is about 7°. The 42 signals are continuously stored by a datalogger with variable frequency up to 10 Hz. The angular dependence of solar radiation scattered from clouds (or the earth's surface) can be determined. The purpose is to collect data on the scattering of solar radiation by clouds (and surface) in order to gain more insight in the shortwave atmospheric radiation budget. Optical properties such as angular discrimination of the collimators and sensitivity of the device were investigated and summarized. During a test flight the operational aspects were investigated. It appeared that the device was able to collect data without interruption in severe conditions (vibrations, strong temperature, and humidity changes).
Abstract
The Directional Radiance Distribution Measurement (DIRAM) device was designed and built to determine the angular distribution of shortwave radiance as a function of height in cloudy and clear-sky conditions at various surface albedos. The construction contains 42 sensors, consisting of a collimation system and a detector, which are mounted in two domes (21 in each). The collimators are made of solid PERSPEX cylinders, 8 mm in diameter and ∼24 mm long, which are fully transparent in the visible range. Three diaphragms are carved in each cylinder to reduce the field of view to ∼7° and to reduce the stray light. The detector is a commerially available silicon photodiode for the visible spectral range. The domes can be placed at ground level, or on top and below a research aircraft. The collimators collect broadband visible radiation in 42 regularly distributed viewing angles. The aperture of each sensor is about 7°. The 42 signals are continuously stored by a datalogger with variable frequency up to 10 Hz. The angular dependence of solar radiation scattered from clouds (or the earth's surface) can be determined. The purpose is to collect data on the scattering of solar radiation by clouds (and surface) in order to gain more insight in the shortwave atmospheric radiation budget. Optical properties such as angular discrimination of the collimators and sensitivity of the device were investigated and summarized. During a test flight the operational aspects were investigated. It appeared that the device was able to collect data without interruption in severe conditions (vibrations, strong temperature, and humidity changes).
Abstract
A climatological study has been carried out of the occurrence and properties of a large number of dry and sunny spells in recent summers (1976–83). The frequency of the spells, which are very favorable for atmospheric photochemical activity, were found to be significantly higher in the investigated period than in previous years. A detailed examination of 25 episodes has been carried out. During the episodes, 72 h back trajectories have been computed, and information provided on temperature, humidity, cloud cover and inversion height. The trajectories, determined at different altitudes for five receptor locations [Soltau, Freiburg (FRG), De Bilt (Netherlands), Soissons, Nancy (France)] in Europe, show a predominance for advection from eastern to western Europe. For the two more northerly European locations [Soltau (FRG) and de Bilt (the NL)], the air trajectories also pass over less densely populated or maritime regions. Ozone concentrations recorded at a station in the Netherlands, are examined in relation to the direction of the arriving air mass.
Abstract
A climatological study has been carried out of the occurrence and properties of a large number of dry and sunny spells in recent summers (1976–83). The frequency of the spells, which are very favorable for atmospheric photochemical activity, were found to be significantly higher in the investigated period than in previous years. A detailed examination of 25 episodes has been carried out. During the episodes, 72 h back trajectories have been computed, and information provided on temperature, humidity, cloud cover and inversion height. The trajectories, determined at different altitudes for five receptor locations [Soltau, Freiburg (FRG), De Bilt (Netherlands), Soissons, Nancy (France)] in Europe, show a predominance for advection from eastern to western Europe. For the two more northerly European locations [Soltau (FRG) and de Bilt (the NL)], the air trajectories also pass over less densely populated or maritime regions. Ozone concentrations recorded at a station in the Netherlands, are examined in relation to the direction of the arriving air mass.
Abstract
A model is developed to describe the dispersion of pollutants in a coastal area when stable air masses are transported inland. It is assumed that a convective mixed layer develops over land, the height of which increases with distance from the shoreline. The vertical distribution of pollutants is assumed to be homogeneous within the mixed layer and the distribution in the stable layer aloft is assumed to be Gaussian. Pollutant concentrations in the mixed layer are obtained by analytical integration of the mass conservation equation. It is shown that the earlier and much higher estimates of continuous shoreline fumigation by Lyons and Cole (1973) and Meroney et al. (1975) can be derived from our expressions by simplifying substitutions.
Abstract
A model is developed to describe the dispersion of pollutants in a coastal area when stable air masses are transported inland. It is assumed that a convective mixed layer develops over land, the height of which increases with distance from the shoreline. The vertical distribution of pollutants is assumed to be homogeneous within the mixed layer and the distribution in the stable layer aloft is assumed to be Gaussian. Pollutant concentrations in the mixed layer are obtained by analytical integration of the mass conservation equation. It is shown that the earlier and much higher estimates of continuous shoreline fumigation by Lyons and Cole (1973) and Meroney et al. (1975) can be derived from our expressions by simplifying substitutions.
Abstract
An instrument to measure ultraviolet actinic flux in and outside clouds was constructed and calibrated. Characteristics of the instrument axe: 1) it is equipped with gallium phosphide photodiodes, 2) its isotropic directional response is almost perfect due to the special design of the optical diffusers, and 3) it is a lightweight construction (150 g) allowing the use of a balloon or a kit as an observation platform.
Ground-level observations and vertical profiles, measured with this UV photometer in clear air and in stratocumulus during the Atlantic Stratocumulus Transition Experiment in the Azores, confirm that the Madronich radiation transfer model is valid for clouds.
Abstract
An instrument to measure ultraviolet actinic flux in and outside clouds was constructed and calibrated. Characteristics of the instrument axe: 1) it is equipped with gallium phosphide photodiodes, 2) its isotropic directional response is almost perfect due to the special design of the optical diffusers, and 3) it is a lightweight construction (150 g) allowing the use of a balloon or a kit as an observation platform.
Ground-level observations and vertical profiles, measured with this UV photometer in clear air and in stratocumulus during the Atlantic Stratocumulus Transition Experiment in the Azores, confirm that the Madronich radiation transfer model is valid for clouds.
