Ankie Piters

ozone mini‐hole observed over Europe, influence of low stratospheric temperature on observations

A region of extreme low ozone values passed over North-western Europe during November 30, and December 1, 1999. The total ozone values were measured from the ground, with a Brewer Spectrophotometer, and from space with the GOME and TOMS satellite instruments. The ozone sonde measurement and the retrieved GOME ozone profile have shown that the main reduction in the ozone column occurred between the ozone maximum (22 km) and the tropopause. The low temperatures found in the stratosphere during this event have significant consequences for the ozone retrieval algorithm, both for satellite retrievals and for the Brewer measurements.

First Reprocessing of Southern Hemisphere Additional Ozonesondes (SHADOZ) Ozone Profiles (1998–2016): 2. Comparisons With Satellites and Ground‐Based Instruments

Abstract The Southern Hemisphere ADditional OZonesonde (SHADOZ) network was assembled to validate a new generation of ozone-monitoring satellites and to better characterize the vertical structure of tropical ozone in the troposphere and stratosphere. Beginning with nine stations in 1998, more than 7,000 ozone and P-T-U profiles are available from 14 SHADOZ sites that have operated continuously for at least a decade. We analyze ozone profiles from the recently reprocessed SHADOZ data set that is based on adjustments for inconsistencies caused by varying ozonesonde instruments and operating techniques. First, sonde-derived total ozone column amounts are compared to the overpasses from the Earth Probe/Total Ozone Mapping Spectrometer, Ozone Monitoring Instrument, and Ozone Mapping and Profiler Suite satellites that cover 1998-2016. Second, characteristics of the stratospheric and tropospheric columns are examined along with ozone structure in the tropical tropopause layer (TTL). We find that (1) relative to our earlier evaluations of SHADOZ data, in 2003, 2007, and 2012, sonde-satellite total ozone column offsets at 12 stations are 2% or less, a significant improvement; (2) as in prior studies, the 10 tropical SHADOZ stations, defined as within ±19° latitude, display statistically uniform stratospheric column ozone, 229 ± 3.9 DU (Dobson units), and a tropospheric zonal wave-one pattern with a 14 DU mean amplitude; (3) the TTL ozone column, which is also zonally uniform, masks complex vertical structure, and this argues against using satellites for lower stratospheric ozone trends; and (4) reprocessing has led to more uniform stratospheric column amounts across sites and reduced bias in stratospheric profiles. As a consequence, the uncertainty in total column ozone now averages 5%.

GODIVA, a European project for ozone and trace gas measurements from gome

GODIVA (GOME Data Interpretation, Validation and Application) is a European Commission project aimed at the improvement of GOME (Global Ozone Monitoring Experiment) data products. Existing data products include global ozone, NO2 columns and (ir)radiances. Advanced data products include O3 profiles, BrO, HCHO and OClO columns. These data are validated by ground-based and balloon borne instruments. Calibration issues are investigated by in-flight monitoring using several complementary calibration sources, as well as an on-ground replica of the GOME instrument. The results will lead to specification of operational processing of the EUMETSAT ozone Satellite Application Facility as well as implementation of the improved and new GOME data products in the NILU database for use in the European THESEO (Third European Stratospheric Experiment on Ozone) campaign of 1999.

Comparison of tropospheric NO 2 columns from MAX-DOAS retrievals and regional air quality model simulations

Multi-axis differential optical absorption spectroscopy (MAX-DOAS) tropospheric NO2 column retrievals from four European measurement stations are compared to simulations from five regional air quality models which contribute to the European regional ensemble forecasts and reanalyses of the operational Copernicus Atmosphere Monitoring Service (CAMS). Compared to other observational data usually applied for regional model evaluation, MAX-DOAS data are closer to the regional model data in terms of horizontal and vertical resolution, and multiple measurements are available during daylight, so that, for example, diurnal cycles of trace gases can be investigated. In general, there is good agreement between simulated and retrieved NO2 column values for individual MAX-DOAS measurements with correlations between 35 % and 70 % for individual models and 45 % to 75 % for the ensemble median for tropospheric NO2 vertical column densities (VCDs), indicating that emissions, transport and tropospheric chemistry of NOx are on average well simulated. However, large differences are found for individual pollution plumes observed by MAX-DOAS. Most of the models overestimate seasonal cycles for the majority of MAX-DOAS sites investigated. At the urban stations, weekly cycles are reproduced well, but the decrease towards the weekend is underestimated and diurnal cycles are overall not well represented. In particular, simulated morning rush hour peaks are not confirmed by MAX-DOAS retrievals, and models fail to reproduce observed changes in diurnal cycles for weekdays versus weekends. The results of this study show that future model development needs to concentrate on improving representation of diurnal cycles and associated temporal scalings. Published by Copernicus Publications on behalf of the European Geosciences Union. 2796 A.-M. Blechschmidt et al.: Comparison of NO2 columns from MAX-DOAS and regional air quality models

Data Quality and Validation of Satellite Measurements of Tropospheric Composition

Validation is the essential part of satellite remote sensing, since the retrieved data must be fit-for-purpose and their significance quantified, whether they are for scientific research or environmental monitoring. Data are validated by comparing satellite data sets with those obtained from ground-based, balloon and airborne instrumentation, or from instruments on other satellites, or with the output of models; all can be fraught with sampling difficulties and comparability. Chapter 7 discusses these problems in some detail and indicates the quality assurance that is used in the field. The possibilities of optimising retrieval algorithms are dealt with, as well the problem of instrument degradation over time. The differing needs for data on trace gases and cloud and aerosol data are mentioned, as are the use of correlative methods. The chapter concludes with requirements for future measurements and possible validation strategies.

Global stratospheric ozone profiles from GOME in near-real time

The Global Ozone Monitoring Experiment (GOME) on the European Space Agencys (ESA) platform European Remote Sensing Satellite (ERS)-2 provides ozone column densities derived from ultraviolet (UV) Earth-shine spectra in nadir. The UV part of the spectrum also contains information on the vertical ozone distribution. However, until now, ozone profiles were not derived on an operational basis. Numerical weather prediction could benefit from assimilation of stratospheric ozone profiles, if they are retrieved with sufficient coverage of the Earth and within 3–4 h after observation. This requires a fast retrieval algorithm and near-real time (NRT) availability of the spectra. In this Letter, the first operational retrieval of global stratospheric ozone profiles in NRT is described. NRT availability of the spectra is assured by including carefully selected parts of the raw data in the GOME instrument monitoring files, which are obtained directly from the ESA ground stations. An existing off-line profile retrieval algorithm has been adapted to produce reliable stratospheric profiles within strict time constraints. The consequences for the quality of the profiles have been discussed.

Co-ordination of the Validation Activities for SCIAMACHY

Validation of SCIAMACHY is essential to ensure the quality of the measurements. The activities are co-ordinated by the SCIAMACHY Validation and Interpretation Group (SCIAVALIG).

Validation and data assimilation for tropospheric satellite data products

The objectives of task group 4, Validation and Data Assimilation for Tropospheric Satellite Data Products, are to develop strategies for the geophysical validation of tropospheric satellite data products and apply them, and data assimilation models, on satellite data. Data assimilation is used for validation purposes and to augment the value of satellite measurements.