Atmosphere Overview

In February 2016, the Canadian-led Atmospheric Chemistry Experiment (ACE) satellite mission will complete its twelfth year of measurements.  The long lifetime of ACE has provided a valuable time series of composition measurements that contribute to our understanding of ozone recovery, climate change and pollutant transport.  These profiles of atmospheric trace gases and aerosols provide altitude-resolved data that are necessary for understanding processes that occur at specific altitudes or over limited vertical length scales.

The SCISAT/ACE mission uses infrared and UV-visible spectroscopy to make its solar occultation measurements.  There are two instruments on board SCISAT.  The ACE Fourier Transform Spectrometer (ACE-FTS) is an infrared FTS operating between 750 and 4400 cm^-1 and the ACE-MAESTRO (Measurements of Aerosol Extinction in the Stratosphere and Troposphere Retrieved by Occultation) is a dual UV-visible-NIR spectrophotometer which was designed to extend the ACE wavelength coverage to the 280-1030 nm spectral region.  From these measurements, altitude profiles of atmospheric trace gas species, temperature and pressure are retrieved.  In addition to the mission and instrument status, a review of current science and validation results from the ACE mission will be presented in this paper.

The industrial revolution, which began in the UK in the late 18^th century, has been fuelled by the use of cheap energy from fossil fuel combustion. It has facilitated a dramatic rise in both the human population, now above 7 Billion with 50% now living in urban agglomerations, and its standard of living. It is anticipated that by 2050 there will be of the order of 8.3 to 10 billion people, 75% living in cities. Anthropogenic activity has resulted in pollution from the local to the global scale changes in land use, the destruction of stratospheric ozone, the modification of biogeochemical cycling, acid deposition, impacted on ecosystems and ecosystem services, destruction of biodiversity and climate change. The impact of man has moved the earth from the Holocene to the new geological epoch of the Anthropocene.To improve our understanding of the earth atmosphere system and the accuracy of the prediction of its future changes, knowledge of the amounts and distributions of trace atmospheric constituents are essential -“One cannot manage what is not measured”.

To assess accurately the impact of man on the earth system, an integrated observing system, comprising ground and space based segments is required to improve our science and to provide an evidence base needed for environmental policymakers. In particular observations  of stratospheric ozone, short lived climate pollutants (ozone, and its precursors and  aerosols) in the troposphere and estimates of the surface fluxes of long lived greenhouse gases are needed from the local to the global scale. These observations need to be coupled with measurements of the changing conditions (surface clouds, land, ocean and the cryosphere) to assess the feedback.

It is now 21 years since the launch of the first European space based passive remote sensing instrument the Global Ozone Monitoring Experiment aboard ERS-2. The subject has come of age.  GOME was a smaller scale version of SCIAMACHY, which then followed on Envisat. This presentation describes results from the SCIAMACHY (SCanning Imaging Absorption spectroMeter for Atmospheric CHartographY on ESA Envsiat 2002 to 2012) and its spin offs GOME (ESA ERS-2 1995 to 2011) and GOME-2 (ESA/EUMETSAT Metop series). The challenges of the successors of SCIAMACHY such as  Sentinel4/GeoScia Sentinel 5 on Metop Second generation, which will fly in ~4 years time, and the initiatives proposed CarbonSat/CarbonSat Constellation  and SCIA-ISS will also be introduced.

MIPAS on ENVISAT performed almost continuous measurements of atmospheric composition for approximately 10 years, from June 2002 to April 2012. During this period the first effects of the reduction in the emissions of CFCs following the ratification of the Montreal protocol in 1987 can be observed.
Even if ten years is a short period to derive statistically robust trends, it has been shown that useful information on long-term variation of atmospheric constituents can be derived from the analysis of MIPAS measurements. Previous versions of MIPAS dataset were affected by an instrumental drift caused by the ageing of the detectors that introduced a non negligible systematic error in the trend estimation. The latest full mission reprocessed dataset V7 uses the L1 spectra that have been corrected for the drift of the non-linearity response of the detectors. Furthermore, the L2 processor has been upgraded with new functionalities that improve the quality of the retrieved products.
We present here the results of the trend studies from the analysis of the new MIPAS V7 products with particular emphasis on ozone-depleting species: CFC-11, CFC-12, CCl4 and HCFC-22.

The OMPS limb profiling (LP) sensor was launched on NOAA’s Suomi NPP satellite on Oct 28, 2011. It measures the solar radiation in UV/VIS/NIR scattered by the earth’s limb from which one can derive vertical profiles of stratospheric ozone and aerosols with better than 2 km vertical resolution. One can also measure the height of cirrus clouds, and study the evolution of polar stratospheric and mesospheric clouds. OMPS LP continues the long-term record of ozone and aerosols at high vertical resolution produced by variety of sensors on US, Canadian and European satellites flown since 1985. Most of these sensors have ceased to operate or are well beyond their designed lifetime. Another OMPS LP sensor is planned to be launched in 2021 on JPSS-2 satellite. We will discuss key results derived from this combined record. We will also discuss the synergy between OMPS LP and nadir-viewing UV/VIS/NIR sensors. Several such sensors are currently operating and many more are planned in the next decade for both LEO and GEO platforms. We will show how OMPS LP data can be used to assess and improve the performance of these sensors so that one can make accurate estimates of tropospheric ozone by combining limb and nadir data. OMPS LP data are particularly useful for correcting the radiances measured by UV nadir profiling sensors, which tend to be susceptible to straylight errors and instrument degradation. Finally, we will discuss how we are using aerosol vertical profiles measured by OMPS LP and SO2 column amounts measured by the nadir sensors to evaluate and improve stratospheric aerosol models. Such studies are necessary to understand the climatic impact of major volcanic eruptions and to evaluate the geoengineering impact of injecting SO2 in the stratosphere to reduce greenhouse warming effects.  

European Space Agency’s GOMOS (Global Ozone Monitoring by Occultation of Stars) instrument on-board Envisat satellite operated during 2002 – 2012. During the ten years of the mission, GOMOS instrument successfully measured vertical profiles of O3, NO2, NO3 and aerosols, including polar mesospheric clouds and polar stratospheric clouds, using UV-VIS channel and O2 and H2O using two near-IR channels.  The best quality of data was obtained during the night time, but recently also the data processing of the day time observations have been improved.  

The two photometers of GOMOS have been used to retrieve high vertical resolution temperature profiles as well as for studying turbulence and gravity waves. Constituents with weak spectral signatures, such as OClO and Na, can be detected using temporal averaging.  

GOMOS measurements provide global coverage with about 200-400 daily profile measurements. Vertically the measurements extend from 5 km to 100 km with varying valid altitude range depending on constituent. Stellar occultation technique ensures high vertical resolution of 2-4 km, very accurate altitude registration and relatively simple data retrieval. The self-calibrating feature of the occultation technique is particularly suitable for long term trend analysis and therefore useful for studying climate-chemistry interactions. In particular, the high quality night time observations of ozone, NO2 and NO3 have been used in several time series analysis and studies related to middle atmosphere chemistry and dynamics including effects of the energetic particles.  The joint SAGE II and GOMOS ozone profile time series have shown upper stratospheric ozone recovery at most latitudes outside the polar regions.

In this presentation we discuss the highlights of GOMOS measurements and introduce the recent improvements on the data quality, including, in particular, day time measurements and ozone profiles in the very interesting upper troposphere – lower stratosphere region.