Impact of satellite-derived effective cloud fraction on calculated actinic flux, photodissociation rates, and OH production
TNO Milieu, Energie en Procesinnovatie
de Winter-Sorkina, R.
Clouds are a large error source in the retrieval of tropospheric column densities and concentration profiles of trace gas species from satellites and in the calculation of their photodissociation rates. The Global Ozone Monitoring Experiment instrument on the ERS-2 satellite is capable of detecting clouds, and a number of methods have been developed to retrieve their properties. In our previous study it was shown that these cloud retrieval methods calculate an effective cloud fraction that is related to a cloud with a high optical thickness. Furthermore, the retrieved solutions are nonunique, as different combinations of optical thickness, cloud fraction, and cloud top height can give the same albedo at the top of the atmosphere. The impact of the scaling of various cloud solutions to an effective cloud fraction on the vertical photodissociation profiles of ozone (O3) and nitrogen dioxide (NO2) and on the tropospheric column production of the hydroxyl radical (OH) is studied in this paper, using the tropospheric ultraviolet-visible radiative transfer model. Results show that for selected cloud solutions, local differences in the vertical OH primary production profile can be from +7% for small solar zenith angles to -14% for large angles with a cloud between 2 and 3 km. Column-integrated OH primary production differences can be between +9% and -7% depending on the solar zenith angle when a cloud is located between 2 and 3 km but can increase to +23% and -81% for a cloud at higher altitudes. NO2 photodissociation was shown to be locally more influenced by the scaling of clouds to an effective cloud fraction, but for the tropospheric column difference this influence is less prominent.
To reference this document use:
Journal of Geophysical Research D: Atmospheres, 107 (107), AAC 1-1-AAC 1-12