(Anexo – 10) A MG EVA ILIANA MIRANDA RAMÓN

Ozone is the most important radiatively active trace gas in the stratosphere and essentially determines the vertical temperature profile in that region. The ozone layer protects the Earth's surface from harmful levels of UV radiation. In the troposphere, increases in ozone cause a positive radiative forcing, while in the stratosphere, ozone depletion leads to a negative radiative forcing. Due to its chemistry, which is influenced by the atmospheric temperature and dynamics, ozone is also an important constituent for understanding the interaction between climate and chemistry in the troposphere, stratosphere and mesosphere. In order to study the connection between the climate and chemistry, global measurements of ozone profiles are needed. Additional information of the interactions can be obtained when simultaneous measurements of other constituents participating in ozone chemistry (CH4, N2O, CFCs, H2O, NO2 and polar stratospheric clouds) are available. Atmospheric ozone amounts declined in the upper and lower stratosphere over the 1980s and 1990s and remain at levels below those present in the 1970s and earlier, largely due to anthropogenic sources of halogens.

Since the 1960s, stratospheric ozone has been monitored in situ by wet-chemical ozonesondes and

remotely by ground-based spectrometers. Since the late 1970s and 1980s, ozone has also been monitored by optical and microwave techniques from various satellites and ground-based stations. TOMS, (S)BUV, and OMI provide an established data record from the late 1970s onward, and high resolution ozone profile records from SAGE and SAGE II are available for 1979-2005 (with a gap of a few years in the early 1980s). Shorter-term data records are provided by instruments such as HALOE (1991-2005), MLS, GOME(-2), POAM II, POAM III, AIRS, IASI, MIPAS, SCIAMACHY, GOMOS, ACE-FTS, TES, and OSIRIS.

The total column measurements provide information on the overall ozone trends, while the ozone profile information is important for studies of atmospheric processes, as well as for calculations of the radiation balance. High resolution ozone profiles are especially important in the upper troposphere/lower stratosphere (UTLS) region: for example, in the case of an increasing mean meridional circulation, ozone- column reductions in the tropics are observed due to increased upward transport of low ozone amounts from troposphere to stratosphere.

Most ozone measurements use sunlight and are thus restricted to daytime. Thermal emission and stellar occultation measurements have a unique role in measuring ozone at high latitudes during the polar night.

The short-lived ozone and aerosol precursors – in particular NO2, SO2, HCHO and CO – have been added in the IP-10, in recognition of the emission-based view on climate forcing of ozone and secondary aerosols, relevant for climate mitigation and important for processes. The requirements for these precursor variables are given separately below.

Ozone analyses are obtained both from atmospheric reanalysis and as independent products directly from satellite observations as total column analyses and as profiles in the upper troposphere and lower stratosphere.

The following is required for this ECV:

Product A.9.1 Total column ozone Product A.9.2 Tropospheric ozone

Product A.9.3 Ozone profiles from upper troposphere to mesosphere Benefits

Support in the monitoring and assessment of:

• the impact of the Montreal Protocol and its amendments on the anthropogenically-induced removal of stratospheric ozone;

• the expected radiative influence of ozone on the climate system;

Target Requirements

Variable/ Parameter Horizontal Resolution

Vertical Resolution

Temporal

Resolution Accuracy Stability

Total ozone 20-50km N/A 4h max(2%; 5DU) <1%

Tropospheric ozone 20-50km 5km 4h 10-15% 1%

Ozone profile in upper troposphere and lower

stratosphere 100-200km 1-2km 4h 10% 1%

Ozone profile in upper

stratosphere and mesosphere 100-200km 3km daily 5-20% 1%

Rationale: Resolution requirements in part reflect the use of satellite datasets in reanalysis. For climate analysis, daily to weekly temporal resolution is adequate. Sub-diurnal temporal resolution is needed in the troposphere for air quality applications. The monthly means of total ozone, averaged over diurnal cycles, provides valuable information on long-term ozone trends. Changes in stratospheric ozone since 1850 are roughly 5 to 10 per cent of total column ozone (i.e., 14-29 DU). Tropospheric ozone radiative forcing is significant, with roughly 0.6 W/m2 (roughly equivalent to 10 DU (3 per cent of total column)). Targets correspond to radiative equivalence to 10 per cent of GHG forcing and should also capture 10 per cent of the expected decadal trend. The higher vertical resolution requirement in the UTLS is driven by the need to monitor the climate-chemistry interaction and especially the vertical transport of ozone.

Requirements for satellite instruments and satellite datasets

FCDR of appropriate UV/VIS and IR/microwave radiances, for example through:

• Nadir UV/VIS instruments for total column;

• Nadir IR sounding for profiles from lower troposphere to stratosphere;

• Nadir UV/VIS and IR sounding for profiles from lower troposphere to stratosphere;

• Limb sounding in IR/MW/UV/VIS from atmospheric emissions and scattered solar irradiance and occultation for profiles from upper troposphere to mesosphere;

Supplemented by:

• Simultaneous measurements of profiles of other trace gases participating in ozone chemistry in the upper troposphere and stratosphere.

Calibration, validation and data archiving needs

Comprehensive ground, ship-board, aircraft and balloon-borne measurements are required for calibration and validation, for example through:

• the Network for the Detection of Atmospheric Composition Change (NDACC) and the World Ozone and Ultraviolet Radiation Data Centre (WOUDC);

• the WMO GAW network of ground-based total-column ozone measurements;

• the WMO GAW and NASA/SHADOZ ozone networks of ozone-profile measurements;

• the MOZAIC/IAGOS commercial aircraft programme. Adequacy/inadequacy of current holdings

• Total column measurements provide a largely adequate data record of gross change and fluctuations;

• Vertical profile information from present instruments is most often of limited vertical resolution and/or low accuracy in the lower stratosphere and troposphere;

• Planned missions will ensure the continuity of the total ozone CDR, but the continuity of limb viewing and occultation missions is not guaranteed;

• Space agencies have on-going projects to create homogenous data records of total ozone, low- resolution ozone profiles and high-resolution ozone profiles, by combining several instruments;

• There is a need for more routine ozonesonde ascents to support calibration and validation. Immediate action, partnerships and international coordination

• Urgent continuation of the limb-viewing measurements of high-resolution ozone (presently only one limb-viewing instrument (NPP/JSS-J2) is planned to measure ozone profiles in the stratosphere, and it is expected that there will be serious gaps in the high-resolution ozone profile datasets in the future; for monitoring ozone at high latitudes it is also important to measure ozone in the dark (during the

polar night); no instruments are planned for continuing the ozone profile records in the mesosphere after the present instruments stop operating);

• Sustaining of current Envisat/Aura (SCIAMACHY/OMI) type missions and their data products to ensure continuity in the data record until the planned Sentinel 5P mission becomes operational;

• Sustaining of current limb missions (MLS, OSIRIS, ACE-FTS, GOMOS, MIPAS) and their data products to ensure continuity or minimize the gap in the data record prior to launch of a future limb mission;

• Reprocessing of identified datasets by improved calibration and retrieval and data merging algorithms, especially with regard to instrumental biases, including effects of drift in orbit;

• Pursuit of the opportunity for reprocessed products from particular instruments or series of instruments, along with the emerging opportunity for provision of integrated products through data assimilation (as provided by the ECMWF reanalyses, for example);

• Continuous research and related intermittent observations are necessary to fully understand ozone chemistry in the troposphere and stratosphere, including precursor trace gases of tropospheric ozone (see section 3.1.11);

• Coordination by WCRP SPARC, [IGBP] International Global Atmospheric Chemistry Program (IGAC), and Integrated Global Atmospheric Chemistry Observations (IGACO) Ozone/UV.

Link to GCOS Implementation Plan

• [IP-10 Action A26] Establish long-term limb-scanning satellite measurement of profiles of water

vapour, ozone and other important species from the UT/LS up to 50km;

• [IP-10 Action A32] Continue production of satellite ozone data records (column, tropospheric ozone and ozone profiles) suitable for studies of interannual variability and trend analysis; reconcile residual differences between ozone datasets produced by different satellite systems.

Other applications

• Climate-chemistry interaction studies;

• Air-quality forecasting;

• Monitoring and assessment of UV-B exposure at the surface, with its effects on human health and the biosphere;

• Monitoring and assessment of exposure to tropospheric ozone, with further effects on human health and agriculture;

• Enabling the atmospheric correction for several satellite instruments measuring temperature and water vapour profiles and surface and ocean properties.