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Schlagwörter:
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Zusammenfassung:
Water vapour (H2O) is one of the operationally
retrieved key species of the Michelson Interferometer for
Passive Atmospheric Sounding (MIPAS) instrument aboard
the Environmental Satellite (ENVISAT) which was launched
into its sun-synchronous orbit on 1 March 2002 and operated
until April 2012. Within the MIPAS validation activities,
independent observations from balloons, aircraft, satellites,
and ground-based stations have been compared to European
Space Agency (ESA) version 4.61 operational H2O
data comprising the time period from July 2002 until March
2004 where MIPAS measured with full spectral resolution.
No significant bias in the MIPAS H2O data is seen in the
lower stratosphere (above the hygropause) between about
15 and 30 km. Differences of H2O quantities observed by
MIPAS and the validation instruments are mostly well within
the combined total errors in this altitude region. In the upper
stratosphere (above about 30 km), a tendency towards
a small positive bias (up to about 10 %) is present in the
MIPAS data when compared to its balloon-borne counterpart
MIPAS-B, to the satellite instruments HALOE (Halogen
Occultation Experiment) and ACE-FTS (Atmospheric
Chemistry Experiment, Fourier Transform Spectrometer),
and to the millimeter-wave airborne sensor AMSOS (Airborne
Microwave Stratospheric Observing System). In the
mesosphere the situation is unclear due to the occurrence
of different biases when comparing HALOE and ACE-FTS
data. Pronounced deviations between MIPAS and the correlative
instruments occur in the lowermost stratosphere and upper troposphere, a region where retrievals of H2O are most
challenging. Altogether it can be concluded that MIPAS H2O
profiles yield valuable information on the vertical distribution
of H2O in the stratosphere with an overall accuracy of
about 10 to 30% and a precision of typically 5 to 15% –
well within the predicted error budget, showing that these
global and continuous data are very valuable for scientific
studies. However, in the region around the tropopause retrieved
MIPAS H2O profiles are less reliable, suffering from
a number of obstacles such as retrieval boundary and cloud
effects, sharp vertical discontinuities, and frequent horizontal
gradients in both temperature and H2O volume mixing ratio
(VMR). Some profiles are characterized by retrieval instabilities.
