Validation of MIPAS-ENVISAT H&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt;O operational data collected between July 2002 and March 2004

G Wetzel,M Milz,G Zhang,H Oelhaf,H Fischer,J Ovarlez,M Iarlori,C Schiller,A Lengel,C Piccolo,V Rizi,Lucia Mona ,Gwenaël Berthet ,Andreas Fix ,Ilaria Rosati ,Piera Raspollini ,Astrid Bracher ,G P Stiller ,Anne Kleinert ,Mark Weber ,J B Renard ,Susanne Rohs ,Gelsomina Pappalardo ,Stefan Müller ,Dietrich G Feist

doi:10.5194/acp-13-5791-2013

Abstract

Abstract. 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.

Highlights

Water vapour (H2O) is a highly variable atmospheric constituent
The mean deviation for all direct collocations found between Michelson Interferometer for Passive Atmospheric Sounding (MIPAS) and Airborne Microwave Stratospheric Observing System (AMSOS) measured H2O is positive at all 3.3.1 Halogen Occultation Experiment (HALOE) comparison altitudes with values reaching 10 to 20 % above 30 km
HPa or 28–30 km), a tendency towards a positive bias that is increasing with altitude in the MIPAS satellite and MIPAS-B comparisons can be recognized, which is significant with respect to the standard error of the mean though being mostly within the combined total errors

Summary

Introduction

Water vapour (H2O) is a highly variable atmospheric constituent. It plays a dominant role in the transfer of energy in the atmosphere. Level 1b and level 2 processing of data version 4.61 (high spectral resolution mode) including all steps from raw data to calibrated spectra and profiles of atmospheric parameters has been performed by ESA using the operational processors described by Kleinert et al (2007) for level 1b and Raspollini et al (2006) for level 2. Other error sources are treated as systematic This approach was applied to all validation studies of MIPAS operational trace gas products as a matter of consistency (Cortesi et al, 2007; Payan et al, 2009; Wang et al, 2007; Wetzel et al, 2007). The comparison between the standard deviation of the mean difference and the combined random error helps to validate the precision of MIPAS since both terms should be of comparable magnitude. The comparison between the VMR difference of MIPAS versus the correlative instruments and the combined systematic error in the case of statistical comparisons or total error in the case of single comparisons is appropriate to identify unexplained biases in the MIPAS H2O observations when they exceed these combined error limits

Intercomparison of balloon-borne observations

Intercomparison of aircraft observations

Findings

H O-DIAL