München 2004 – wissenschaftliches Programm

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UP: Umweltphysik

UP 12: Poster: Satelliten und Anwendungen

UP 12.10: Poster

Dienstag, 23. März 2004, 14:00–16:00, Schellingstr. 3

Cloud effects in SCIAMACHY tropospheric NO₂ — •Andreas Richter, Hendrik Nüß, Bernd Sierk, and John P. Burrows — Institut für Umweltphysik, Universität Bremen, Otto-Hahn-Allee, D-28359 Bremen

The SCIAMACHY instrument on ENVISAT provides amongst other quantities accurate nadir measurements of the UV/visible radiances scattered back from the atmosphere. From these measurements, tropospheric columns of NO₂ can be retrieved using the well known DOAS method and some assumptions on the stratospheric NO₂ fields.

Most of the tropospheric NO₂ is located close to the surface as - with the exception of lightning - the sources are at the ground and the lifetime of NO₂ is short. Thus, one would expect to see a clear reduction in tropospheric NO₂ signal in the presence of clouds, and in fact this is observed in many cases. However, there are also numerous situations where large signals are observed over cloud covered pixels, often linked to weather fronts and transport events.

In this study, the effects of clouds on tropospheric NO₂ columns derived from SCIAMACHY measurements are evaluated and possible explanations discussed. In addition, measurements form the GOME instrument on ERS-2 are used to check if the findings are consistent with those from the long GOME time series available, and in howfar they depend on the size of the ground-pixels of the measurements.