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THE GEISA DATABANK 1997 EDITION

Introduction
Overview of the 1997 edition of the GEISA databank
References
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INTRODUCTION

Adequate tools are required to perform reliable radiative transfer calculations meeting the needs of communities involved in understanding the atmospheres of the Earth and other planets. In particular, accurate spectral analyses of Earth or planetary spectra observed by new generations of high spectral resolution vertical atmospheric sounders will result in an improved knowledge of their atmospheric and surface properties. The performance of instruments like AIRS (Atmospheric Infrared Sounder) in the USA, and IASI (Infrared Atmospheric Sounding Interferometer) in Europe, which have a better vertical resolution and accuracy compared to presently existing satellite infrared temperature sounders, is directly related to the quality of the spectroscopic parameters of the optically active atmospheric gases since these are essential input in the forward models used to simulate observed radiance spectra. The ARA (Atmospheric Radiation Analysis) group at LMD (Laboratoire de Météorologie Dynamique du CNRS, France) developed the GEISA (Gestion et Etude des Informations Spectroscopiques Atmosphériques: Management and Study of Atmospheric Spectroscopic Information) computer accessible database system (Chedin et al., 1982; Husson et al., 1992, 1994), in 1974. This early effort implemented the so-called line-by-line and layer-by-layer approach for forward radiative transfer modelling action. This activity is of interest to research groups involved in direct and inverse radiative transfer studies.

The role of molecular spectroscopy in modern atmospheric research has entered a new phase with the advent of highly sophisticated spectroscopic instruments and computers. Retrieval of the concentrations of radiatively active molecular species from observed spectra of planetary atmospheres using available spectroscopic databases and atmospheric models has become fairly routine. The molecular spectroscopist is constantly on demand to deliver data that are not only appropriate but essential for the analyses of the planetary atmospheric observations. GEISA is dedicated to meeting that goal.

Currently, GEISA participates in the ISSWG (IASI Sounding Working Group, with the purpose of assessing the IASI measurement capabilities, related with the CNES (Centre National d'Etudes Spatiales, France)/EUMETSAT (EUropean organization for METeorological SATellites) European Polar System (EPS), by simulating high-resolution adiances and/or using experimental data, as described in Jacquinet-Husson et al., 1998a.

OVERVIEW OF THE 1997 EDITION OF THE GEISA SPECTROSCOPIC DATABANK

The 1997 version of the GEISA databank(get the publication) (hereafter referred to as GEISA-97) contains line parameters for 42 molecules (96 isotopic species) with 1,346,266 entries between 0 and 22,656 cm^-1. It has molecules of interest for both terrestrial and other planetary atmospheres (for example, C₂H₄, GeH₄, C₃H₈, C₂N₂, C₄H₂, HC₃N, H₂S, HCOOH and C₃H₄, for the Giant Planets). GEISA-97 has been developed in close cooperation with the contributors of three spectroscopic databases, ATMOS-95 (Atmospheric Trace Molecule Spectroscopy) (Brown et al., 1996), HITRAN-96 (HIgh resolution TRANsmission) (Rothman et al., 1998) and TDS (Tomsk Dijon Spectroscopic project; Traitement des Données Spectroscopiques)/STDS (Spherical Top Data System) (Tyuterev et al., 1994; Wenger and Champion, 1998).

Since the release of the former edition in 1992 (Husson et al., 1992; 1994), GEISA-92 , two new species, HO₂ and ClONO₂, (formerly only present in the cross-sections file of GEISA-92), have been added for the first time, and seventeen existing molecules: O₃, N₂O, CH₄, NO, SO₂, NO₂, NH₃, HNO₃, OH, ClO, OCS, ¹³C¹²CH₆, CH₃D, C₂H₂, C₂H₄, H₂O₂, H₂S, have been updated for GEISA-97. These changes have added 10 new isotopes: three for the new molecules and seven for the already existing molecules (two in O₃, one in CO, two in OCS, one in C₂H₆, and one in C₂H₄) and the parameters of nineteen species have been updated or included.

The detailed summary of the line parameters in GEISA-97 is provided in Table 1. The items listed for each molecular species, given in column 1, are: the identification code (ID codes defined for the GEISA management software in Chedin et al., 1985, 1986), the number of lines, the intensity average, the mean halfwidth at half maximum, the identification codes of its various isotopes, and for each isotope: the number of lines, the transitions minimum and maximum wavenumbers (in cm^-1), and the lines intensities minimum and maximum values (in cm molecule^-1), in columns 2 to 11, respectively.

In addition to the individual lines spectroscopic data catalog, GEISA-97 also has a catalog of cross-sections at different temperatures and pressures for species (such as chlofluorocarbons) with complex spectra that are too dense for discrete parameterization.

The current version of the GEISA-97 cross-sections database contains 4,716,743 entries related to 23 molecules. The GEISA-97 cross-sections file content information are summarized in Table 2. In the first column are listed the molecules included with their name (for the CFC's) and corresponding chemical formula; colums 2 and 3 provide the cross-sections spectral intervals availability and temperature conditions; the related author references are in column 4. It should be noted that, for the majority of the molecules, the database comprises cross-sections for a set of temperatures and pressures corresponding to layers of the US standard atmosphere models, that allows simulations of the radiation propagation along slant paths in the atmosphere. Usually, the cross-sections are provided at uniform frequency steps for a given molecule, as in the case of the data listed in Table 2, except for the ones of Li and Varanasi, 1994; Varanasi and Nemtchinov, 1994; Varanasi et al., 1994, which are not given on uniform cm^-1 net steps. They were recorded for different conditions of pressure and temperature, at different resolutions, whith corresponding different step sizes.

REFERENCES

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