S P A R C Stratospheric Processes And their Role in Climate A project of the World Climate Research Programme Home Initiatives Organisation Publications Meetings Acronyms and Abbreviations Useful Links

Summary of the COSPAR 2004 - Session A1.1

Paris, France, 20-25 July 2004

John P. Burrows, University of Bremen, Germany (burrows@iup.physik.uni-bremen.de)

The system comprising the sun, the atmosphere and the earth is complex, having many non-linear feedbacks. During the past three decades the role of anthropogenic activity has become increasingly recognised as being one of the most important sources of changing emissions to the atmosphere.  Understanding the behaviour of the Sun-Atmosphere-Earth system requires a detailed understanding of the physical, biological and chemical processes, which determine its nature and behaviour. Both natural phenomena and anthropogenic activity result in changing atmospheric composition, which impacts on the Earth’s radiation balance and its chemistry. Knowledge of the distribution of atmospheric constituents and parameters is required to test and improve our understanding of the Sun-Atmosphere-Earth system, whose conditions are essential to the maintenance of life on earth.

Session A1.1, "Atmospheric Remote Sensing: Earth’s Surface, Troposphere, Stratosphere and Mesosphere”, of COSPAR 35 Scientific Assembly addressed our current ability and future potential to objectively measure atmospheric parameters of relevance to atmospheric chemistry, global climate change and numerical weather prediction. The focus of the session was remote sensing from space but in addition ground based, aircraft and balloon borne measurements also featured prominently.  This is a relatively young research area and is being driven by the need to understand the changing composition of the Earth’s atmosphere and its consequences for global climate change.

As part of the evolution of the needs of COSPAR, following the Houston COSPAR 34 Assembly in 2002, Committee A overhauled the structure of its sessions.  In this context Session A1.1 was designed to be one continuous session running throughout COSPAR 35 on topics of relevance to the remote sensing of the atmosphere and the Earth’s surface.  This approach amalgamated sessions, which at previous COSPAR Scientific Assemblies had been independent from one another, and focused on different subregions of the earth-atmosphere system. The new structure enabled attendees researching the different regions of the atmosphere to obtain a holistic view of current research throughout this multi-disciplinary area.  In particular, the reporting of research in the overlap areas between different regions of the atmosphere, such as the planetary boundary layer, the tropopause, the stratopause and the mesopause, which in the past have often fallen between different sessions, benefited from this new approach.

Session A1.1 was comprised of sub-sessions that were dedicated to the following topics: a) Troposphere: Surface and Aerosol - Parts I and II; b) Troposphere: Cloud and Weather; c) Troposphere: Trace Gases, d) Stratosphere, e) Mesosphere, and f) Instruments and Missions.

During the first four and half days, contributions were primarily about current space missions and the exploitation of the existing data, and the development of new techniques. The final day was focused on the development of and the planning for new missions by the agencies. In addition to the A1.1 Session itself, one of the A1.1 community (P. J. Crutzen) gave an invited interdisciplinary lecture on "ENVISAT: first results" and the A1.1 community participated in the relevant panel events.

Session A1.1 was comprised of approximately 220 contributions with roughly 50 %, being given as oral presentations and about 50 % in the complimentary poster session.  The posters were hung for the entire week and individual posters were highlighted in the relevant sub-session. The attendees welcomed this approach to the A1.1 Poster Sessions.  The attendance at each of the sessions was typically about 60 to 70 people, with over 200 COSPAR associates taking part over the week.

The session was opened with introductory remarks by J. P. Burrows and P. Schluessel. The members of the programme committee for Session A1.1, the COSPAR 35 Local Organising Committee and the Overall Programme Committee were explicitly thanked for their support. The duration and wide ranging nature of the A1.1 Session resulted in additional work for these committees, compared with that required at previous COSPAR Scientific Assemblies.

TOP

The session started with the remote sensing of the troposphere. The first sub-session was devoted to aerosol and surface. Both active and passive remote sensing techniques were described.  Results from successful ground based, airborne and space based LIDAR experiments were presented and discussed e.g. LITE, GLAS and the forthcoming Calypso and CloudSat missions.  Retrieval of aerosol parameters from the measurements of AVHRR datasets from various platforms provides a long data set of information. Aerosol retrieval from passive remote sensing over the ocean is less difficult than over land.  However, significant progress has been made, with the derivation of aerosol parameters over land surface now becoming feasible from algorithms applied to the data measured by the sensors POLDER, ATSR-1, -2, AATSR, MODIS, MISR, MERIS, SeaWifs, and TOMS. The surface spectral reflectance and its applications were also discussed in this part of the meeting.

The sub-session Troposphere: Cloud and Weather addressed remote sensing of relevance to the hydrological cycle and weather prediction. A wide range of presentations described passive and active remote sensing by means of microwave, infrared and visible/ultraviolet spectroscopy; both absorption and scattering being the source of information about cloud parameters and water vapour distributions. Algorithms, exploiting the O2 absorption bands in back-scattered solar radiation, and infrared emission, for the retrieval of cloud parameters were described. These offer many potential advantages for improving our understanding of clouds and improving the predictive capability of models. Measurements of water vapour in the tropopause region, which are of great significance for understanding stratosphere-troposphere exchange, were reported from aircraft measurements. There were also several contributions about the observation of cirrus and subvisible clouds.

The detection of trace gases in the troposphere has been an area of growth in the last 10 years.  The sub-session  Troposphere: Trace Gases focused on this topic. The results of retrieval studies using data from the nadir looking sensors MOPITT on NASA TERRA, GOME-1 on ERS-2 and SCIAMACHY on ENVISAT were prominent. In addition, presentations on the retrieval of limb sounding instrumentation to probe the upper troposphere presented interesting new results. Considerable progress has been made on the retrieval of trace gases of relevance to air quality such as CO2, CO, NO2, and formaldehyde, HCHO. The advantages of the different approaches to retrieve water vapour were also discussed. Inversion of back-scattered solar radiation has been shown to yield tropospheric water vapour columns over land.

The retrieval of tropospheric constituents remains an area of growth for the research community. The retrieval possibilities for tropospheric constituents by means of UV and visible spectroscopy with the current generation of instruments have made considerable progress, and these data have been exploited in a variety of interesting ways. Observations of solar near infrared (NIR) and short wave infrared (SWIR) spectral regions are being exploited for the first time. In this context, SCIAMACHY data is yielding the distributions of the atmo-spheric columns of greenhouse gases (GHGs), CO2  and CH4 , from space. This is a first step of limited accuracy in the assessment of the sources of GHGs, which the NASA OCO instrument intends to improve upon for CO2.

The capabilities of the sensors aboard the NASA Aura satellite, which was successfully launched the week before COSPAR, were also presented in both the tropospheric and stratospheric sub-sessions. In the stratospheric session, there was an overview of the first 25 years of the NASA TOMS measurements. This instrument along with the BUV instruments have not only provided a unique view of global ozone, and the development of the ozone hole, but also provided measurements of sulphur dioxide, SO2 from volcanoes, and the ultraviolet absorbing aerosol. Similarly, an overview of sounding the atmosphere from balloons was a highlight of this session. Both TOMS and the balloon measurements have been two of the most productive sources of information about the stratosphere in the last 25 years.

The discussion of the results from the ENVISAT sensors MIPAS, GOMOS and SCIAMACHY and the ODIN sensors OSIRIS and the microwave limb sounder (MLS) dominated a large part of the stratospheric sub-session. The first results were shown from the Canadian SCISAT mission, which has two solar occultation instruments on it, an ACE and MAESTRO. Exciting results from the long duration mission SAGE-II and the new SAGE-III were discussed. Calibration and validation of the sensors was discussed and results presented. The measurements of stratospheric constituents during the anomalous warming of the stratospheric vortex above the Antarctic in spring of 2002 were also discussed. The ENVISAT data have provided some unique insight into this surprising stratospheric event. Interesting new results have been obtained about the development of polar stratospheric clouds, and their role in the catalytic decomposition of stratospheric ozone.

The session about the mesosphere was dominated by results from ENVISAT, ODIN, and SABER. The observations of mesospheric OH and polar mesospheric or noctilucent clouds and the determination of mesospheric temperature were highlights. The measurements of the instruments during the Solar Proton Events of October and November 2003 have provided some unique insight into the interaction between the eruptions from the sun and their impact on the mesosphere and stratosphere. The current missions observing the mesosphere and above are providing a wealth of new information about these regions within the Sun-Atmosphere-Earth System.

The final day of the meeting was dedicated to the plans of the agencies for future missions of relevance to this community. Unfortunately, the future after ENVISAT and Aura for atmospheric chemistry research from instrumentation on space-based platforms is unclear. However, the operational satellites from EUMETSAT and the NPOESS system will provide some valuable data. The further developments of the NASA OCO, which aims to extend and enhance the measurement of CO2  from space by using the NIR and SWIR absorption bands of CO2 was discussed. Of interest were the studies of instrumentation and the potential benefits for tropospheric research and applications of passive observations from geostationary orbit. Teams in Europe, America and Japan presented their concepts. New concepts for instrumentation from LEO were also presented. Whether from GEO or LEO, researchers have recognised the need for synergistic use of different spectral regions to probe tropospheric composition.

The session closed with thanks to all the participants, who had made this a memorable meeting. The future of the research of the Sun-Atmosphere-Earth System depends on the continued efforts of this community, which would not be possible without support from the space agencies and their governments.

TOP