A fast H 2 O total column density product from GOME ? Validation with in-situ aircraft measurements

• Main Authors: Wagner, T., Heland, J., Zöger, M., Platt, U.
• Other Authors: Institut für Umweltphysik Heidelberg, Universität Heidelberg Heidelberg = Heidelberg University, Deutsches Zentrum für Luft- und Raumfahrt (DLR)
• Format: Article in Journal/Newspaper
• Language: English
• Published: HAL CCSD 2003
• Subjects: [SDU.OCEAN]Sciences of the Universe [physics]/Ocean; Atmosphere; Arctic; Antarctic; The Antarctic; albedo; Antarc*
• Online Access: https://hal.science/hal-00295268; https://hal.science/hal-00295268/document; https://hal.science/hal-00295268/file/acp-3-651-2003.pdf

International audience Atmospheric water vapour is the most important greenhouse gas which is responsible for about 2/3 of the natural greenhouse effect, therefore changes in atmospheric water vapour in a changing climate (the water vapour feedback) is subject to intense debate. H 2 O is also involved in many important reaction cycles of atmospheric chemistry, e.g. in the production of the OH radical. Thus, long time series of global H 2 O data are highly required. Since 1995 the Global Ozone Monitoring Experiment (GOME) continuously observes atmospheric trace gases. In particular it has been demonstrated that GOME as a nadir looking UV/vis-instrument is sensitive to many tropospheric trace gases. Here we present a new, fast H 2 O algorithm for the retrieval of vertical column densities from GOME measurements. In contrast to existing H 2 O retrieval algorithms it does not depend on additional information like e.g. the climatic zone, aerosol content or ground albedo. It includes an internal cloud-, aerosol-, and albedo correction which is based on simultaneous observations of the oxygen dimer O 4 . From sensitivity studies using atmospheric radiative modelling we conclude that our H 2 O retrieval overestimates the true atmospheric H 2 O vertical column density (VCD) by about 4% for clear sky observations in the tropics and sub-tropics, while it can lead to an underestimation of up to -18% in polar regions. For measurements over (partly) cloud covered ground pixels, however, the true atmospheric H 2 O VCD might be in general systematically underestimated. We compared the GOME H 2 O VCDs to ECMWF model data over one whole GOME orbit (extending from the Arctic to the Antarctic) including also totally cloud covered measurements. The correlation of the GOME observations and the model data yield the following results: a slope of 0.96 (r 2 = 0.86) and an average bias of 5%. Even for measurements with large cloud fractions between 50% and 100% an average underestimation of only -18% was found. This high accuracy of our ...