www.igaco-o3.fi | Programme status | IGACO activities | Cluster A

19 Oct 2018

Activity Cluster A: Stratospheric Ozone

Activity A1: Measurement platform workshop

The global ozone measuring network consists of a suite of various platforms and instruments which perform similar measurements or, at least, measure the same quantities using different methods. Specialists in different measurement methods are not always aware of the differences between instruments (such as quantitative differences in precision and accuracy of the instruments in different atmospheric conditions and measurement geometries), especially when used in satellite validation campaigns. Interactions between satellite, aircraft, balloon and ground-based communities could and should also be improved. The goal is to provide an overview of the ongoing heterogeneous measurement activities.

Originally planned task:

  • Arrange a workshop of 2-3 days and report outcome
Coordinator: IGACO-O3/UV

Status: Closed. Ozone Theme Meetings arranged in 2008 and 2009. In addition, during the last year several systematic comparisons with various ozone instruments have been performed e.g. within ESA ozone CCI project.

Activity A2: Dobson/Brewer absolute calibration comparison

The objective is to improve our understanding of the absolute differences between Brewer and Dobson spectrophotometers. An absolute calibration is thus an important task, improving understanding and coherence of the global measurement network, which includes instruments of both types.

Originally planned task:

  • Perform an absolute calibration comparison at Izaņa using the European secondary standard Dobson spectrophotometer and the European standard Brewer spectrophotometer.
Coordinator: O3-SAG

Status: On-going. Measurements done in September 2008. Report on Dobson Langley plot campaign by Robert Evans. Collaboration between NOAA, Izaņa and German Meteorological Service on-going. Regular comparisons are done. Extended to SAOZ, Pandora and other DOAS instruments. Comparisons in Tenerife are planned in 2016. This activity is under the responsibility of SAG-O3.

Activity A3: Clarify differences in UV/VIS measurements of ozone

Comparisons between satellite, Brewer, and Dobson show distinct seasonal variations in their differences. Instrument designs as well as retrieval algorithms and reference absorption spectra are different. Currently it is not clear which of these factors plays the most important role in the observed variations.

It is important to understand the absolute calibration differences of Dobson and Brewer instruments (see Activity A2 above). This could be improved by, e.g., bringing reference instruments to the laboratory and making measurements in a highly controlled environment. This activity should also include UV/Vis DOAS instruments for completeness. The final goal is to propose methods that would lead to a consistent instrument-independent "ground truth" ozone data set, with a follow-on activity of developing improved retrieval algorithms using the results of these investigations. This would also include characterization and standardization of DOAS ozone retrievals and comparisons to Brewers, Dobsons, and satellites.

Originally planned tasks:

  • measure instrument slit functions and then determine ozone cross-sections in a laboratory using reference Brewer and Dobson instruments
  • process Brewer data with Dobson double pair algorithm and compare with Dobson results
  • apply DOAS-type retrievals (GOME, SCIAMACHY, OMI) to Brewers
  • identify and assess biases between satellite instruments
  • repeat with different operational and lab measured cross-section datasets
  • compare results and report
Coordinator: O3-SAG

Status: Closed in SAG 2015, report available. The work is included in ACSO activity (A9). Publication: Redondas et al., Evaluation of the use of five laboratory-determined ozone absorption cross sections in Brewer and Dobson retrieval algorithms, Atmos. Chem. Phys., 14, 1635-1648, 2014.

Activity A4: Improve ground-based and satellite measurements at high solar zenith angles and high latitudes

Validation of ground-based and satellite total ozone measurements are usually performed at mid latitudes where total ozone is near 300 DU. In general, the agreement between instruments is within 2 %, which provides confidence in the methods and algorithms under these conditions.

However, total column ozone retrievals show persistent differences of 5 - 10 % under conditions of low sun, high total column ozone and high column variability, especially at high latitudes where these conditions are very often met. Satellite and ground-based measurements must be compared under a greater variety of ozone column amounts and profile shapes if such differences are to be resolved.

Originally planned tasks:

  • measurement campaign
  • analysis and report
Coordinator: NASA/ESA

Status: On-going. Sauna campaigns in 2006 and 2007. ESA CAL-VAL activities as part of CEOS ICAL work (2011-2013). Nordic Brewer campaign 2011 reported in "CEOS
Intercalibration of Ground-Based Spectrometers and Lidars". Stray light issues
discussed in publication by Karppinen et al. (2013).

Activity A5: Systematic comparison of total ozone measurements from ground and space

Ground-based measurements are needed and used to validate the quality of spacecraft total ozone observations. The ensemble of all ground-based measurements with composite series of satellite instruments confirm the good long-term stability of currently used satellite records.

Status: This is considered to be a part of automatic quality assurance and seen as a long-term activity.

Activity A6: Brewer and Dobson network updates

More than 20 Brewer spectrophotometers have been decommissioned by the U.S. Environment Protection Agency (EPA). The equipment has been transferred to NOAA/ESRL/GMD. The goal of this activity is to upgrade the EPA decommissioned Brewers to enhance ozone measurement capability and to deploy the instruments to new sites across the NOAA network.

In order to improve the global coverage (filling gaps) of the Dobson network, some of existing instruments could also be relocated to either existing or new stations. This would also require capacity building activities (e.g. training for spectrophotometer operators etc.).

Originally planned tasks:

  • develop a plan of how to best use the existing equipment in order to have a homogeneous global coverage for Dobson/Brewer measurements
  • upgrade decommissioned Brewers and deploy to new sites
  • initiate necessary capacity building activities to ensure continuous operation of instruments
Coordinator: O3-SAG

Status: Long-term activity.

Activity A7: Acquire Brewer Umkehr data

Over the Brewer network, more than 20 years of data have been collected, but not as yet processed with the Umkehr algorithm. Should this be done, a new ozone profile data set would be available for the scientific community.

Originally planned tasks:

  • acquire the Brewer raw Umkehr measurement data
  • process and make the retrieved ozone profiles available in a consistent manner
  • compare to correlative data sets (collocated Umkehr Brewer-Dobson measurements, satellites, sondes etc.)
Coordinator: O3-SAG

Status: On-going.

Activity A8: Long-term ozone profile records and data harmonisation

Ozone profile measurements have been made using different methods for decades.
However, different measurements have different characteristics, similarly to total ozone measurements (see, e.g., activities A3 and A5 above). The aim of this activity is to improve the knowledge of the properties of these data and thus improve the usability of the world-wide data set.

Originally planned tasks:

  • comparison of ozone profile measurements from ground (sondes, LIDAR, Umkehr, microwave) and space
  • comparison and harmonisation of data taking into account for vertical resolution differences for trend assessment
  • assessment of other trace gas profile observations (e.g. H2O, NO2) relevant for stratospheric chemistry
Coordinator: IGACO-O3/UV

Status: On-going.
SI2N: Three work shops arranged.
Special issue: ACP/AMT/ESSD (so far 30/51 submitted articles). To be finalized in 2015.
Activity supported by finalized projects: GOZCARDS, SBUV homogenization
Activity supported also by on-going projects: ESA-CCI ozone, ozone sonde homogenization.
More information: http://igaco-o3.fmi.fi/VDO/

Activity A9: Absorption cross sections of ozone (ACSO)

Concerns the possible introduction of new ozone absorption cross sections used for retrieval of atmospheric ozone values in the Huggins band (instead of the presently used Bass and Paur spectral data).

Originally planned task:

  • review the impact of a change in ozone absorption cross sections and to formulate recommendations
Coordinator: ACSO Expert Team

Status: To be closed. Four workshops have been arranged and several reports are done. Summary report to be published in 2015. More information: http://igaco-o3.fmi.fi/ACSO/