Universität zu Köln

Kasradze, Ketevan (2016). An extended variational atmospheric chemistry data assimilation system for combined space and air borne trace gas retrievals. PhD thesis, Universität zu Köln.

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Abstract

A four-dimensional variational data assimilation system for stratospheric trace gas observations has been extended and evaluated to draw full advantage from stratospheric remote sounding data and upper troposphere lower stratosphere (UTLS) in-situ aircraft measurements. The UTLS is the transition layer between the tratosphere and the troposphere and is marked by strong spatial and temporal variability of dynamic structures and distribution of trace gases. Aircraft measurements, highly resolving the UTLS filamental structures, are of most interest for local studies. Although, the satellite instruments are delivering an unprecedented wealth of observations of a number of stratospheric trace gases with global coverage, they are scattered and have a limited resolution in space or time. Combining these measurements and applying advanced data assimilation techniques to compare benefits from satellite and air borne data, and to analyse the chemical composition of the tropopause and lower stratosphere, was the issue of this work. For this purpose, a model grid refinement and full revision of the chemical mechanism were performed. The resolution of the horizontal grid points was increased from about 240 km to 150 km, resulting in 23 042 grid points per model level. The vertical resolution was increased with twelve additional layers, especially in the UTLS region. Hence, the vertical separation between grid levels is now less than 1 km below 22 km altitude. The chemistry module was extended and revised to better represent chemical processes in the UTLS region. All reaction rates were updated according to the recommendations of the NASA's Jet Propulsion Laboratory. In total, a number of 197 photolysis, gas phase, and heterogeneous reactions of 51 stratospheric trace gases is considered by the chemistry module now. The meteorological fields are computed online by the global forecast model GME of German Weather Service. A comprehensive set of case studies has been conducted in order to test and evaluate the extended system. Retrievals of various stratospheric trace gases derived from measurements of the Earth Observing System Microwave Limb Sounder, as well as retrievals of aircraft measurements have been assimilated. The analyses show a perfect performance with respect to the assimilated ozone observations. For assimilation of water observations in UTLS additional preconditioning issue is desirable. Comparison with independent observations from satellite instruments and radiosondes demonstrates a very good performance of the extended assimilation system.

Item Type:	Thesis (PhD thesis)
Creators:	Creators Email ORCID ORCID Put Code Kasradze, Ketevan k.kasradze@gmail.com UNSPECIFIED UNSPECIFIED
URN:	urn:nbn:de:hbz:38-69335
Date:	2 September 2016
Language:	English
Faculty:	Faculty of Mathematics and Natural Sciences
Divisions:	Faculty of Mathematics and Natural Sciences > Department of Geosciences > Institute for Geophysics and Meteorology
Subjects:	Generalities, Science Natural sciences and mathematics
Uncontrolled Keywords:	Keywords Language data assimilation, stratosphere, observations English
Date of oral exam:	28 June 2016
Referee:	Name Academic Title Elbern, Hendrik PD Dr. Wahner, Andreas Prof. Dr.
Refereed:	Yes
URI:	http://kups.ub.uni-koeln.de/id/eprint/6933