Abstract
Abstract. Vertical profiles of stratospheric water vapour measured by the Michelson Interferometer for Passive Atmospheric Sounding (MIPAS) with the full resolution mode between September 2002 and March 2004 and retrieved with the IMK/IAA scientific retrieval processor were compared to a number of independent measurements in order to estimate the bias and to validate the existing precision estimates of the MIPAS data. The estimated precision for MIPAS is 5 to 10% in the stratosphere, depending on altitude, latitude, and season. The independent instruments were: the Halogen Occultation Experiment (HALOE), the Atmospheric Chemistry Experiment Fourier Transform Spectrometer (ACE-FTS), the Improved Limb Atmospheric Spectrometer-II (ILAS-II), the Polar Ozone and Aerosol Measurement (POAM III) instrument, the Middle Atmospheric Water Vapour Radiometer (MIAWARA), the Michelson Interferometer for Passive Atmospheric Sounding, balloon-borne version (MIPAS-B), the Airborne Microwave Stratospheric Observing System (AMSOS), the Fluorescent Stratospheric Hygrometer for Balloon (FLASH-B), the NOAA frostpoint hygrometer, and the Fast In Situ Hygrometer (FISH). For the in-situ measurements and the ground based, air- and balloon borne remote sensing instruments, the measurements are restricted to central and northern Europe. The comparisons to satellite-borne instruments are predominantly at mid- to high latitudes on both hemispheres. In the stratosphere there is no clear indication of a bias in MIPAS data, because the independent measurements in some cases are drier and in some cases are moister than the MIPAS measurements. Compared to the infrared measurements of MIPAS, measurements in the ultraviolet and visible have a tendency to be high, whereas microwave measurements have a tendency to be low. The results of χ2-based precision validation are somewhat controversial among the comparison estimates. However, for comparison instruments whose error budget also includes errors due to uncertainties in spectrally interfering species and where good coincidences were found, the χ2 values found are in the expected range or even below. This suggests that there is no evidence of systematically underestimated MIPAS random errors.
Highlights
Water vapour in the upper troposphere and stratosphere is of great importance for several reasons
Halogen Occultation Experiment (HALOE) was operating in solar occultation geometry and measured water vapour profiles during sunrise and sunset events relative to the satellite (Russell III et al, 1993)
There is no clear indication of a bias of Michelson Interferometer for Passive Atmospheric Sounding (MIPAS) H2O profiles in the stratosphere
Summary
Water vapour in the upper troposphere and stratosphere is of great importance for several reasons. It is a greenhouse gas and plays a dominant role in the radiative budget of the Earth. Satellite-borne instruments offer the opportunity to measure stratospheric water vapour with global coverage. One such instrument is the Michelson Interferometer for Passive Atmospheric Sounding (MIPAS) on board the research satellite Envisat, operated by the European Space Agency (ESA). One of these processors is the scientific MIPAS processor – developed by the “Institut fur Meteorologie und Klimaforschung”, Karlsruhe, Germany (IMK) and the “Instituto de Astrofısica de Andalucıa”, Granada, Spain (IAA) – of which the H2O data product is validated in this paper
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