|H2O from GOME and SCIAMACHY|
|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. H2O 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 H2O data are highly required.|
New UV/vis satellite sensors like GOME, SCIAMACHY or OMI are capable of measuring the total atmospheric H2O column (including also the surface near concentrations). Thus these sensors allow to investigate the global long term evolution of H2O and possibly also to identify a trend due to climate change. Such studies can in particular focus on different regions and seasons. H2O column data from GOME and SCIAMACHY might be also of great value for meteorological weather forecast.
|Total atmospheric vertical column densities|
|Figure 1. In the upper panel a raw spectrum measured by GOME for the
wavelength range of the H2O analysis is shown. Below the results of the spectral
evaluation for H2O, O2, and O4 for this GOME spectrum are presented. The thick
lines show the trace gas absorption spectra scaled to the respective absorptions
detected in the measured GOME spectrum (thin lines). |
|The determination of the absolute atmospheric H2O VCD is complicated
by two major problems. First DOAS H2O analysis is subject to saturation.
Second, the surface-near H2O concentration is often shielded by clouds. Both
problems can be corrected for by our H2O DOAS analysis using also the absorption
of the oxygen dimer O4. For details see Wagner et al. . |
The DOAS analysis of H2O and O4 is shown in Fig 1. A comparison with model data is presented in Fig. 2. Further GOME H2O algorithms were also developed by collegues from other institutions [NoŽl et al., 1999; Maurellis et al., 2000; Casadio et al., 2000; NoŽl et al., 2000; 2002, Lang et al., 2002].
|Figure 2. Comparison of the GOME H2O analysis with modelled H2O VCDs
(ECMWF). The same orbit was also analysed by Maurellis et al. (2000) (from
which whom the model data are taken) and Lang et al. (2002). |
|TREND ANALYSIS |
|An interesting application of satellite H2O measurements is the
investigation of possible trends of the atmospheric water vapor concentration,
in particular as a consequence of climate change. For this purpose the H2O
analysis was be kept as simple as possible: we investigated the H2O in a smaller
wavelength range and without saturation and cloud correction. An example for
the GOME H2O SCDs over the Sahara for a period of 7 years is presented in
Fig. 3. In this case no significant trend was found. |
|Figure 3. 7 years of GOME H2O SCDs over the Sahara. A seasonal cycle
is clearly visible. No significant H2O trend was determined for the time series.|
|Casadio, S., Zehner, C., Pisacane, G., and Putz, E., Empirical retrieval
of the atmospheric air mass factor (ERA) for the measurement of water vapour
vertical content using GOME data, Geophys. Res. Lett., 27, 1483-1486, 2000. |
Lang, R., Williams, J.E., van der Zande, W.J., and Maurellis, A.N., Application of the Spectral Structure Parameterization technique: retrieval of total water vapour coloumns from GOME, Atmos. Chem. Phys. Discuss., 2, 1097-1130, 2002.
Maurellis, A.N., Lang, R., van der Zande, W.J., Aben, I., Ubachs, W., Precipitable Water Column Retrieval from GOME data, Geophys. Res. Lett., 27, 903-906, 2000.
NoŽl, S., Buchwitz, M., Bovensmann, H., Hoogen, R., Burrows, J.P., Atmospheric Water Vapor Amounts Retrievd from GOME Satellite data, Geophys. Res. Lett., 26, 1841-1844, 1999.
NoŽl, S., Bovensmann, H., Burrows, J. P., Water vapour retrieval from GOME data including cloudy scenes, Proc. ENVISAT/ERS Symposium, Gothenburg, 2000.
NoŽl, S., Buchwitz, M., Bovensmann, H., and Burrows, J. P., Retrieval of Total Water Vapour Column Amounts from GOME/ERS-2 Data , Adv. Space Res., 29, 1697-1702, 2002.
Wagner, T., J. Heland, M. ZŲger, and U. Platt, A fast H2O total column density product from GOME - validation with in-situ aircraft measurements, Atmos. Chem. Phys. Discuss., 3, 323-353, 2003.