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| A. Kylling, A. R. Webb, R. Kift, G. P. Gobbi, L. Ammannato, F. Barnaba, A. Bais, S. Kazadzis, M. Wendisch, E. Jakel, S. Schmidt, A. Kniffka, S. Thiel, W. Junkermann, M. Blumthaler, R. Silbernagl, B. Schallart, B. Kjeldstad, T. M. Thorseth, R. Scheirer, and B. Mayer | [abstract]
In September 2002 an extensive campaign to study the influence of clouds on the spectral actinic flux in the lower troposphere was carried out in East Anglia, England. Measurements of the actinic flux, the irradiance and aerosol and cloud properties were made from four ground stations and by aircraft. For cloudless conditions the measurements of the actinic flux were reproduced by a 1-D radiative transfer model within the measurement and model uncertainties of about ±5%. For overcast days 1-D radiative transfer calculations reproduce the overall behaviour of the actinic flux measured by the aircraft. Furthermore the actinic flux is increased by between 60–100% above the cloud when compared to a cloudless sky with the largest increase for the optically thickest cloud. Similarily the below cloud actinic flux is decreased by about 55–65%. Just below the cloud top the downwelling actinic flux has a maximum which is seen in both the measurements and the model results. For broken clouds the traditional cloud fraction approximation is not able to simultaneously reproduce the measured above cloud enhancement and below cloud reduction in the actinic flux. | [keywords]
actinic flux, lower troposphere, cloudless, broken cloud, overcast | | Atmospheric Chemistry and Physics, 5 (7), pp. 1975-1997, 2005 | | http://www.scopus.com/scopus/inward/record.url?eid=2-s2.0-24644465068&partnerID=40 |  back to publications list |
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