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Gottfried Hänel

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Gottfried Hänel and Kurt Bullrich

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Model calculations show that the aerosol particles within the lower troposphere usually contribute more than 80% to the total optical thickness of all particles within the atmosphere. For relative humidities higher than 99% within a thin layer of about 80 m thickness, the main contribution to the total optical thickness comes from this layer.

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Markus Degünther and Gottfried Hänel

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Through mathematical inversion of photometric data all optical properties of atmospheric particles necessary for radiative transfer calculations are derived simultaneously. These optical properties are the volume phase function, the volume extinction, and the volume absorption coefficient. Additionally, the apparent complex refractive index and the apparent volume fraction of soot within the particles are calculated from the absorption-to-extinction ratio. The phase function of the particles is approximated by a combination of two Henyey–Greenstein functions, one of them governing the forward and the other the backward scattering. This approximation contains only three constants, one for weighting of the two Henyey–Greenstein functions, and two asymmetry parameters. It describes very well the phase functions known from measurements on airborne particles in the entire range of scattering angles from 0° to 180°. Thus the new results can be used not only for climate modeling but also for remote sensing applications. First results from the new method are compiled and discussed.

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Gottfried Hänel and Karin Kastner

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The solar radiation budget is investigated with seven pyranometers. Three of these instruments have horizontally aligned sensors. The sensors of the remaining four instruments are vertically aligned in such a way that their normals point to the north, south, east, and west. With this system, the authors are able to detect all properties of interest for radiation budget considerations. These are the flux densities of direct solar, diffuse-sky, global, and reflected radiation; the vector of the solar net flux density; and the solar radiation supply (for atmospheric absorption and/or photochemical processes). Equations for the vector of the net flux density and the radiation supply in terms of the pyranometer readings are derived and discussed.

Whenever the solar radiation supply and the mean solar absorption coefficient of the atmosphere or of specific atmospheric species are known, the relevant solar volume absorption rate and the appertaining solar heating rate of the atmosphere can be calculated without any assumptions. This method is applicable during any weather situation throughout the entire atmosphere.

Simple parameterizations of the radiation supply and the total atmospheric heating during the daylight period due to absorption of solar radiation by particles are discussed.

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