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Global cloud top height retrieval using SCIAMACHY limb spectra: model studies and first results

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journal contribution
posted on 09.11.2016, 11:15 by K-U. Eichmann, L. Lelli, C. von Savigny, Harjinder Sembhi, J. P. Burrows
Cloud top heights (CTHs) are retrieved for the period 1 January 2003 to 7 April 2012 using height-resolved limb spectra measured with the SCanning Imaging Absorption SpectroMeter for Atmospheric CHartographY (SCIAMACHY) on board ENVISAT (ENVIronmental SATellite). In this study, we present the retrieval code SCODA (SCIAMACHY cloud detection algorithm) based on a colour index method and test the accuracy of the retrieved CTHs in comparison to other methods. Sensitivity studies using the radiative transfer model SCIATRAN show that the method is capable of detecting cloud tops down to about 5 km and very thin cirrus clouds up to the tropopause. Volcanic particles can be detected that occasionally reach the lower stratosphere. Upper tropospheric ice clouds are observable for a nadir cloud optical thickness (COT)  ≥  0.01, which is in the subvisual range. This detection sensitivity decreases towards the lowermost troposphere. The COT detection limit for a water cloud top height of 5 km is roughly 0.1. This value is much lower than thresholds reported for passive cloud detection methods in nadir-viewing direction. Low clouds at 2 to 3 km can only be retrieved under very clean atmospheric conditions, as light scattering of aerosol particles interferes with the cloud particle scattering. We compare co-located SCIAMACHY limb and nadir cloud parameters that are retrieved with the Semi-Analytical CloUd Retrieval Algorithm (SACURA). Only opaque clouds (τN,c > 5) are detected with the nadir passive retrieval technique in the UV–visible and infrared wavelength ranges. Thus, due to the frequent occurrence of thin clouds and subvisual cirrus clouds in the tropics, larger CTH deviations are detected between both viewing geometries. Zonal mean CTH differences can be as high as 4 km in the tropics. The agreement in global cloud fields is sufficiently good. However, the land–sea contrast, as seen in nadir cloud occurrence frequency distributions, is not observed in limb geometry. Co-located cloud top height measurements of the limb-viewing Michelson Interferometer for Passive Atmospheric Sounding (MIPAS) on ENVISAT are compared for the period from January 2008 to March 2012. The global CTH agreement of about 1 km is observed, which is smaller than the vertical field of view of both instruments. Lower stratospheric aerosols from volcanic eruptions occasionally interfere with the cloud retrieval and inhibit the detection of tropospheric clouds. The aerosol impact on cloud retrievals was studied for the volcanoes Kasatochi (August 2008), Sarychev Peak (June 2009), and Nabro (June 2011). Long-lasting aerosol scattering is detected after these events in the Northern Hemisphere for heights above 12.5 km in tropical and polar latitudes. Aerosol top heights up to about 22 km are found in 2009 and the enhanced lower stratospheric aerosol layer persisted for about 7 months. In August 2009 about 82 % of the lower stratosphere between 30 and 70° N was filled with scattering particles and nearly 50 % in October 2008.

Funding

This work was funded in part by ESA within the SCIAMACHY Quality Working Group (SQWG) project and the Sentinel5-Precursor L2 development project (DLR grant 50EE1247). The work was supported by the European Space Agency (ESA), the German Ministry of Education and Research (BMBF), the German aerospace centre (DLR), the University of Bremen and the Ernst Moritz Arndt University of Greifswald, Germany. SCIAMACHY was jointly funded by Germany, the Netherlands, and Belgium. The article processing charges for this open-access publication were covered by the University of Bremen

History

Citation

Atmospheric Measurement Techniques, 9, 793-815, 2016

Author affiliation

/Organisation/COLLEGE OF SCIENCE AND ENGINEERING/Department of Physics and Astronomy

Version

VoR (Version of Record)

Published in

Atmospheric Measurement Techniques

Publisher

European Geosciences Union (EGU), Copernicus Publications

issn

1867-1381

eissn

1867-8548

Acceptance date

08/02/2016

Copyright date

2016

Available date

09/11/2016

Publisher version

http://www.atmos-meas-tech.net/9/793/2016/

Notes

The Supplement related to this article is available online at doi:10.5194/amt-9-793-2016-supplement.

Language

en

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