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Validation of 'cloud-free' tropical UTLS MIPAS ozone and water vapour.

Harjinder Sembhi(1) and John. J. Remedios(1)

(1) University of Leicester, University Road, LE1 7RH, United Kingdom

Abstract

Understanding the dynamical, chemical and radiative processes that control the variation and distribution of trace gases in the tropical upper troposphere and lower stratosphere (UTLS), 12 to 21 km, is vital to characterise how this sparsely monitored region influences and connects to the global atmosphere. Satellite instruments overcome the temporal and spatial coverage restrictions of ground- and air-based instruments, potentially allowing continuous global atmospheric information to be obtained. This can enable investigation of large-scale transport, in addition to UTLS processes such deep convection, stratospheric dehydration and tropospheric ozone production.

The Michelson Interferometer for Passive Atmospheric Sounding (MIPAS) is a high resolution Infrared Fourier Transform Spectrometer that observes the Earth’s limb from 68 km to the lower atmosphere at 6 km. Measuring tropical UTLS trace gas concentrations with remote sensing instruments like MIPAS is problematic as scattering due to cloud and aerosol particles at these altitudes can lead to distortion of the retrieved trace gas concentrations. A cloud detection algorithm incorporated into the operational MIPAS processor is used to remove cloud contaminated data from Level 2 vertical profiles. However, analysis of water vapour and ozone profiles display ‘false’ data values that may still be affected by contaminant cloud and aerosol particles. This suggests the operational cloud detector is not removing corrupt level 2 data effectively.

This paper will describe how a Leicester cloud detection methodology produces potentially cloud-free profiles and how this method can be used observe cloud distribution and occurrence in the tropical UTLS. To validate and assess the accuracy and precision of these cloud-free MIPAS water vapour and ozone data comparisons are made to 1) the solar occultation infrared instrument, HALOE and 2) in situ measurements obtained by the SHADOZ network. With emphasis on the UTLS and TTL layers, the seasonality of cloud "decontaminated" MIPAS ozone and water vapour in this region will be presented.

 

Full paper

Keywords: ESA European Space Agency - Agence spatiale europeenne, observation de la terre, earth observation, satellite remote sensing, teledetection, geophysique, altimetrie, radar, chimique atmospherique, geophysics, altimetry, radar, atmospheric chemistry