ECOWAR/COBRA: A Research Contribution to Spectrally Resolved Observations of the Earth Emission Spectrum in the Water Vapour Rotation Band (17-50 micron) to Test Models of Atmospheric Radiative Transfer

There is a growing interest in the far infrared spectral region (17 to 50 micron) of the Earth emission spectrum, since this portion of the spectrum contains the characteristic, and fundamental, molecular rotational band for water vapour. Water vapour is, indeed, the main greenhouse gas in the atmosphere and it plays an important role in the mean and upper troposphere influencing the Earth radiative energy balance. Spectrally resolved observations and knowledge of radiative transfer for clear and cloudy skies in the water vapour rotational band are important to test climate models and ultimately resolve some of the contentious arguments about global change. The relevance to the Earth energy budget of the spectral region 17 to 50 micron has been put forward by many authors. Nevertheless, a) the spectral absorption properties of water vapour, in addition to its vertical distribution, have received very poor attention, and b) the far-infrared portion of the atmospheric emission spectrum has been largely unexplored and very few measurements have been made in the past. Nowadays, it is largely recognized that the lack of validation of far infrared model continuum and line parameters under atmospheric conditions is hampering a substantial progress in our ability to correctly parameterize water vapour optical properties in climate models. The ECOWAR (Earth COoling by WAter vapouR emission) or COBRA (an Italian acronym for analysis of the water vapour continuum absorption in the H2O rotational band) project is an experimental field campaign that contributes to bridge the knowledge gap about optical properties of water vapour in the far infrared through an observational programme. This work will review the status of ECOWAR/COBRA and its results at the end of the main steps of the programme (campaign in January 2007 and in March 2007). ECOWAR/COBRA is a co-ordinated project among four University research teams ( University of Bologna , Potenza and Roma), two institutes of the National Research Council (IFAC Florence and IMAA Tito Scalo) and INGV (National Institute of Geology and Vulcanology). The seven proposing teams blend expertise both in experimental and theoretical Atmospheric Sciences, therefore ECOWAR/COBRA has set up an end-to-end methodology which allows us not only to record the observations, but also to analyse them in order to validate atmospheric radiative transfer models and test the quality of water vapour continuum and line parameters. COBRA consists in a series of field campaigns aiming at sensing the water vapour rotational band. The observations will be then used a) to test models of atmospheric radiative transfer in clear and cloudy skies, within the water vapour rotational band, b) to test spectral absorption properties of water vapour in the rotational band from 200 to 600 (cm-1) c) to demonstrate the capability of the aforementioned band as a temperature and humidity sounding system, especially to improve the height discrimination of water vapour concentration. The project plans to integrate observations from the ground to those from satellite platforms, which should allow us to properly define the thermodynamic state of the atmosphere, and, hence, provide the ancillary information to reconstruct the down-welling and upwelling spectral radiance, along with the radiative diabatic effects in clear and cloudy sky.