Validation of MIPAS-ENVISAT Hsub2/subO operational data collected between July 2002 and March 2004

摘要

Water vapour (H₂O) is one of the operationally retrieved key species ofthe Michelson Interferometer for Passive Atmospheric Sounding (MIPAS)instrument aboard the Environmental Satellite (ENVISAT) which was launchedinto its sun-synchronous orbit on 1 March 2002 and operated until April2012. Within the MIPAS validation activities, independent observations fromballoons, aircraft, satellites, and ground-based stations have been comparedto European Space Agency (ESA) version 4.61 operational H₂O datacomprising the time period from July 2002 until March 2004 where MIPASmeasured with full spectral resolution. No significant bias in the MIPASH₂O data is seen in the lower stratosphere (above the hygropause)between about 15 and 30 km. Differences of H₂O quantities observed byMIPAS and the validation instruments are mostly well within the combinedtotal errors in this altitude region. In the upper stratosphere (above about30 km), a tendency towards a small positive bias (up to about 10%) ispresent in the MIPAS data when compared to its balloon-borne counterpartMIPAS-B, to the satellite instruments HALOE (Halogen Occultation Experiment)and ACE-FTS (Atmospheric Chemistry Experiment, Fourier TransformSpectrometer), and to the millimeter-wave airborne sensor AMSOS (Airborne MicrowaveStratospheric Observing System). In the mesosphere the situation is uncleardue to the occurrence of different biases when comparing HALOE and ACE-FTSdata. Pronounced deviations between MIPAS and the correlative instrumentsoccur in the lowermost stratosphere and upper troposphere, a region whereretrievals of H₂O are most challenging. Altogether it can be concludedthat MIPAS H₂O profiles yield valuable information on the verticaldistribution of H₂O in the stratosphere with an overall accuracy ofabout 10 to 30% and a precision of typically 5 to 15% – well withinthe predicted error budget, showing that these global and continuous dataare very valuable for scientific studies. However, in the region around thetropopause retrieved MIPAS H₂O profiles are less reliable, sufferingfrom a number of obstacles such as retrieval boundary and cloud effects,sharp vertical discontinuities, and frequent horizontal gradients in bothtemperature and H₂O volume mixing ratio (VMR). Some profiles arecharacterized by retrieval instabilities.