07ATF 42
Vertical ozone
distributions and stratospheric columns of NO2, OClO, and BrO from GOME and
SCIAMACHY nadir satellite data: Data product optimisation and scientific
studies of the lower stratospheric chemistry and dynamics (GOMSTRAT)
Ozonvertikalverteilungen und stratosphärische Säulen von NO2, OClO und BrO aus GOME und SCIAMACHY Nadir
Satellitendaten: Optimierung der Datenprodukte und wissenschaftliche Studien
zur Chemie und Dynamik der unteren Stratosphäre
Mark Weber, Institut für Umweltphysik, Universität Bremen
The
main goal of this project is to derive high quality trace gas distributions,
ozone profiles and stratospheric NO2, BrO, O3, and OClO columns, from long-term
global UV/visible nadir spectra
measured by GOME and SCIAMACHY. They will be used to statistically analyse
certain aspects of chemical and dynamical processes, some of which are relevant
to possible climate change.
A prerequisite
for successful scientific studies using global satellite data is the
development of an improved and accelerated algorithm to retrieve ozone
profiles. In order to derive BrO and NO2 stratospheric columns a method to
separate the tropospheric and stratospheric contributions to the measured total
column has to be optimised and implemented.
The following tasks are planned:
Optimisation of non-standard GOME/SCIAMACHY nadir trace gas retrieval in order to otain high
quality global time series starting in 1995
Validation of non-standard GOME trace gas data by comparison with
independent measurements
Development of methods to separate tropospheric and stratospheric
contributions to total columns
Comparison of (stratospheric and tropospheric) GOME data with 3D CTMs
and primitive coupled climate-chemistry models with particular emphasis on
northern hemispheric mid- to high latitudes
Creating an updated and improved dynamical O3 climatology using combined
satellite and sonde measurements for the use as a-priori information in general
trace gas retrieval (airmass factor calculation, optimal estimation) and for improving initialisation of CTMs.
The new global data set of stratospheric key species are valuable for assessing long-term changes and provide constraints to halogen and nitrogen oxide budget in 3D chemical transport models. Long-term ozone time series of vertical profiles and total columns are complementing other satellite measurements in the assessment of global trends and possible recovery as a consequence of the Montreal protocol and its amendments.
Das Hauptziel dieses Projekts ist die verbesserte Bestimmung von
Säulendichten von O3, NO2, BrO, und OClO
aus den Nadirspektraldaten von GOME und SCIAMACHY. Die Langzeitmessungen
seit 1995 ermöglichen die Untersuchungen von chemischen und dynamischen
Prozessen in der Stratosphäre im Zusammenhang mit möglichen Klimaänderungen.
Eine wichtige Voraussetzung für erfolgreiche Anwendungen in wissenschaftlichen
Studien ist die Bereitstellung von hochqualitativen Datenprodukten durch
verbesserte Algorithmen und, im Fall der globalen Ozonprofilauswertung, durch
Einsatz beschleunigter Verfahren.
Die folgenden Arbeiten sind geplant:
Optimierung und Verbesserung der GOME Säulendichten
und die Bereitstellung der globalen Datensätze ab 1995
Adaption der Algorithmen auf die SCIAMACHY/ENVISAT
Spektraldaten (ab 2002)
Spezielle Untersuchungen zur Trennung von
stratosphärischen und troposphärischen Anteilen in der Säulendichte von NO2 und
BrO
Validierung der nicht standardisierten
Datenprodukte durch Vergleich mit unabhängigen Daten
Erstellen einer aktualisierten
Ozonprofilklimatologie für die Verwendung als A-priori Information im
Spurengasretrieval (Optimal Estimation,
Airmassfaktorbestimmung) und für die Initialisierung von Klima und
Chemie-Transportmodellen
Vergleich der GOME Säulendichten mit 3D
Chemie-Transportmodellen und gekoppelten Klimamodellen zur Untersuchung von
chemisch-dynamischen Prozeessen in hohen Breiten.
Globale Messungen von stratosphärischem BrO und NO2 können einen wichtigen
Beitrag zur Bestimmung des globalen Halogen- und NOx-Budgets liefern und dienen
möglicherweise als Constraint für CTMs und Klimamodelle. Die Langzeitreihen von
Ozonsäulendichten und –profile zusammen mit anderen historischen Datensätzen
spielen eine wichtige Rolle für weitere Untersuchungen im Zusammenhang zwischen
globalem Ozonabbau und dem Klimawandel, insbesondere unter dem Aspekt
internationaler Abkommen zum Schutz der Ozonschicht und Klimaerwärmung
(Montreal und Kyoto-Protokoll).
AWI Potsdam (DYCHO, 07ATC08)
DLR Insitut für Atmosphäre (KODYACS, 07ATF43)
During
the first year several steps were undertaken to improve and accelerate ozone
profile retrieval from nadir GOME spectral data. The extension of the retrieval
into the short wave length region (270-290 nm) permit a better characterisation
of the upper stratosphere (35-50 km altitude range. This spectral region was
difficult to use because of calibration uncertainties. By including dark current subtraction from solar
Fraunhofer line observations in the profile retrieval made this spectral region
usable. The new results have been validated with independent ozone sonde
measurements and they show particular improvements in the derivation of
tropical ozone profiles.
Initial
studies on the improved ozone column retrieval using the weighting function
DOAS (differential optical absorption spectroscopy) indicate that the quality
of the GOME total ozone can be significantly improved as was demonstrated by
comparison with ground-based data at selected Antarctic stations. By using
different fitting windows for NO2 in the UV and visible spectral range a better
separation of the stratospheric and tropospheric contributions to the NO2 total
column can be achieved. In the UV region the stratospheric contribution dominates
while in the visible spectral region a larger tropospheric contribution to the
observed total column is observed. This was verified by comparison with NO2
zenith-sky measurements from the ground, which show only little tropospheric
NO2 amounts.
The
new algorithms that have been developed
are planned to be used in
the reprocessing of GOME data starting
in 1995 and later to be adapted to
SCIAMACHY which was launched aboard ENVISAT in March 2002.
During
the second year the development of the weighting function DOAS retrieval for
GOME total ozone has been continued. Particular attention has been paid into
the creation of look-up-tables (reference intensities and weighting functions
derived from radiative transfer model calculation) in order to enable
processing of global data sets. Comparison with ground-based Dobson and Brewer
data from selected mid-latitude stations have shown that the seasonal signature
seen in the differences between the official
total ozone version (distributed by the European Space Agency, Version
3) and ground-based data has vanished in the comparison of the new algorithm.
It is apparent that the new algorithm represents a significant improvement over
previous data versions.
From
global sonde data (WOUDC data base) and SAGE II and POAM III satellite data
covering the nineties an updated ozone profile climatology has been derived.
This climatology has been created for
five latitude bands (high latitude, mid-latitude, and tropics in steps of 30°)
and mean profiles shapes have been determined for different total column
amounts (in steps of 30 DU). In addition a division into seasons (winter/spring and summer/fall) to
account for the differences between low ozone profile shapes related to ozone
hole depletion and summer photochemistry has been introduced. This new data set
is very valuable for the use as initial guess and a-priori information in ozone
retrieval (column and profile retrieval) and can be also used for
initialisation of chemical transport models.
Using
the eight year total ozone (Version 3) and
OClO column density data record
from GOME, inter-annual variability of both trace gases in mid- to high
latitude during winter/spring seasons
have been investigated. During winter planetary waves regulate ozone
transport into high latitudes through the Brewer-Dobson circulation mechanism.
Since planetary waves show large inter-annual variability, particularly in the
northern hemispheres, the amount of ozone build-up also varies strongly from
year to year. Stratospheric temperatures in polar winter are also strongly
influenced by planetary wave forcing. Little planetary wave activity in
mid-latitudes leads to polar stratospheric temperatures that are lower and
closer to the radiative equilibrium temperature and, therefore, high ozone destruction related to heterogeneous chemistry on polar
stratospheric clouds are observed. Both, reduced transport and enhanced
chemistry contribute then to the low total ozone observed in polar spring. In
winters with high dynamical activity, stratospheric temperatures are higher, as frequently observed in the
northern hemisphere, and the increased transport in combination with reduced
heterogeneous chemical processing results in higher ozone levels. A very
compact relationship between eddy heat flux at 100hPa (a proxy for the wave energy deposited into the stratosphere)
and total ozone ratio (March over September mean in NH and September
over March mean in SH) as well to the winter integrated max OClO column density inside the polar
vortex (a measure of the chlorine activation succeeding heterogeneous chemistry
upon polar stratospheric clouds) were found that underlines the dynamical
control of ozone transport and chemistry during winter/spring at high
latitudes. The so-called Antarctic anomaly in 2002, where for the first time a
major stratospheric warming and a split of the ozone hole was observed in the
southern hemisphere, confirmed this close coupling of dynamics and
chemistry, This important link may be crucial for a better
understanding of the connection between
climate change and stratospheric
ozone recovery in the future.
K. Bramstedt, J. Gleason, D. Loyola, W. Thomas, A.
Bracher, M. Weber, and J. P. Burrows, Comparison of total ozone from the satellite
instruments GOME and TOMS with measurements from the Dobson network 1996-2000,
2002, Atmos. Chem. Phys. Discuss., 2, 1131-1157.
M. Coldewey-Egbers, M. Weber,
M. Buchwitz, and J.P. Burrows, Application of a modified DOAS method for total
ozone retrieval from GOME data at high polar latitudes, 2003, Adv. Space
Res., accepted for publication.
B.-M. Sinnhuber, M. Weber, A.
Amankwah, and J.P. Burrows, Total ozone during the unusual Antarctic winter of
2002, Geophys. Res. Lett. 30, 1850,
doi:10.1029/2002GL016798, 2003.
A. Richter and J.P. Burrows,
Retrieval of tropospheric NO2 from GOME Measurements, Adv. Space Res. 29,
1673-1683, 2002.
S. Tellmann, V.V. Rozanov, M.
Weber, and J.P. Burrows, Improvements in the tropical ozone profile retrieval
from GOME UV/vis nadir spectra, 2003, Adv. Space Res., accepted for
publication.
M.
Weber, S. Dhomse, F. Wittrock, A. Richter, B.-M. Sinnhuber, and J.P. Burrows,
Dynamical Control of NH and SH Winter/Spring Total Ozone from GOME Observations
in 1995-2002, Geophys. Res. Lett., 30, 1853, doi:10.1029/2002GL016799, 2003.
M. Weber, S. Dhomse, F. Wittrock, A. Richter, B.-M. Sinnhuber, and J.P.
Burrows, Der Einfluss der Dynamik auf den Ozontransport und die Ozonchemie in
hohen Breiten, Ozonbulletin des Deutschen Wetterdienstes, Nr. 93, 25. Juni
2003.
Data Availability:
GOME NO2, BrO, OClO column densities
GOME total ozone and ozone profiles
Ozone profile climatology 1990-2000
classified by total ozone and climate region (30° latitude bands) and divided
into two seasons (winter/spring and summer/fall)
see http://www.iup.physik.uni-bremen.de/gome,
http://www.doas-bremen.de/