This paper describes the 2020 release of the GEISA database (Gestion et Etude des Informations Spectroscopiques Atmosphériques: Management and Study of Atmospheric Spectroscopic Information), developed and maintained at LMD since 1974. GEISA is the reference database for several current or planned Thermal and Short-Wave InfraRed (TIR and SWIR) space missions IASI (Infrared Atmospheric Sounding Interferometer), IASI-NG (IASI New Generation), MicroCarb (Carbon Dioxide Monitoring Mission), Merlin (MEthane Remote sensing LIdar missioN). It is actually a compilation of three databases: the “line parameters database”, the “cross-section sub-database” and the “microphysical and optical properties of atmospheric aerosols sub-database”. The new edition concerns only the line parameters dataset, with significant updates and additions implemented using the best available spectroscopic data.The GEISA-2020 line parameters database involves 58 molecules (145 isotopic species) and contains 6,746,987 entries, in the spectral range from 10−6 to 35877 cm−1. In this version, 23 molecules have been updated (with 10 new isotopic species) and 6 new molecules have been added (HONO, COFCl, CH3F, CH3I, RuO4, H2C3H2 (isomer of C3H4)) corresponding to 15 isotopic species. The compilation can be accessed through the AERIS data and services center for the atmosphere website (https://geisa.aeris-data.fr/), with the development of a powerful graphical tool and convenient searching, filtering, and plotting of data using modern technologies (PostgreSQL database, REST API, VueJS, Plotly).Based on four examples (H2O, O3, O2 and SF6), this paper also shows how the LMD in house validation algorithm SPARTE (Spectroscopic Parameters And Radiative Transfer Evaluation) helps to evaluate, correct, reject or defer the input of new spectroscopic data into GEISA and this, thanks to iterations with researchers from different communities (spectroscopy, radiative transfer).

Observing the planet at global scale, twice a day, and measuring the whole infrared atmospheric spectrum (8,461 channels at 0.50 cm(-1) resolution), Infrared Atmospheric Sounder Interferometer (IASI)/METOP can concurrently detect clouds, determine the 3-D atmospheric structure (temperature, water vapor, ozone, etc.), surface properties (emissivity and temperature), as well as dust aerosol AOD and altitude. Observing morning (0930 hr) and nighttime (2130 hr), IASI is in relatively good phase with the most frequent times of occurrence of the main Saharan dust uplift mechanisms reported in the literature. Here we classify IASI dust observations according to both the dust loading (AOD) and the dust layer height, providing a more comprehensive picture of dust characteristics. This classification is analyzed at daily scale and its capability to detect dust uplift events is evaluated through comparisons with results from the particularly well documented June 2011 Fennec campaign. Then, a Dust Emission Index (DEI), specific to IASI, is constructed by selecting AOD-altitude bins with largest AODs and smallest altitudes likely indicative of freshly emitted dust. Applying this to the 12-year 2007-2018 period, we determine climatological DEI maps and comparisons are made with other equivalent existing results derived from ground-based or other satellite observations. Results of these comparisons demonstrate the capability of IASI to document the dust distribution over the whole Earth desert areas over a long period of time. The present approach is also suitable to the processing of the at least hourly observations of the coming Infrared Sounder instrument (IRS), planned on board Meteosat Third Generation (2021).

We give the first demonstration that humidity has indirect effects on atmospheric spectra near 4 μm, through the influence of collisions with H2O on both the collision‐induced band of N2 and the wings of the CO2 lines. This is shown by comparing computed and measured values of atmospheric transmissions and outgoing radiances. The usual assumption that collisions with H2O and dry air have equal effect on the N2 and CO2 absorptions leads to significantly underestimated absorptions for humid atmospheres. This bias is considerably reduced when the influences of H2O on the N2 and CO2 contributions to the spectra are taken into account using proper spectroscopic models. This opens perspectives of increased accuracy near 4 μm where the atmosphere is relatively transparent, for astronomical observations of outer objects from ground as well as for retrievals of the Earth land/sea surface temperatures from radiances recorded from space.

Detecting trends in climate variables has become of great importance in the context of the rapid evolution of the Earth's climate. Among the climate variables recognized as acting on climate variability, aerosols continue to contribute one of the largest uncertainties to the total radiative forcing estimate. The present study focuses on dust aerosols, a major contributor to total aerosol loading. Observation from space offers a good opportunity to follow aerosol evolution at global scale and over long time series. In this context, infrared observations, by allowing retrieving dust optical depth (AOD) day-time and night-time, over oceans and over continents, in particular over desert, is complementary to observations in the visible on which a majority of aerosol studies are so far based. The two spectral domains are not sensitive to the same range of particle size, coarse mode particles ( > 1 m) being preferentially observed in the infrared, when both coarse and fine mode particles (0.1-1 mu m) are observed in the visible making the distinction between the two modes difficult. Starting from METOP-A/IASI-derived dust AOD (July 2007 to June 2017), this study aims at detecting and estimating, day-time and night-time, dust AOD trends over Sahara, a region where dust aerosol emissions are frequent and often intense. Detecting trends in geophysical variable time series is a difficult task due to the frequent presence of serial correlation, to holes in the data, to "outliers", or to variables not normally distributed, etc. Here, trends are determined using the non-parametric Theil-Sen slope estimator followed by the Mann-Kendall statistical test for randomness against trend, the statistical hypothesis (H-0) being that the trend is equal to zero. Resulting trends are judged to be significantly different from zero if their so-called "confidence level" is above a given percentage, usually 95% (referred to as "real" trend in the following). Then, in a second step, supposing the statistical hypothesis is now that a non-zero trend of specified magnitude exists, we can calculate the probability that this hypothesis is true. The number of years of data required to detect a "real" trend of a specified magnitude with probability 0.9 ("probability-assigned real" trend) is finally determined following (Tiao et al., 1990). This approach is then applied to the 120 months of IASI-retrieved dust AOD. Main conclusions are that the present 10 year period of IASI observations is still too limited to provide enough reliable, probability-assigned, trends over Sahara and that a period of 14-15 years would largely increase their number and spatial coverage. This is fully compatible with the already planned length of the IASI series on board METOP-A to -C, taking into account the high demonstrated stability of this instrument.

Aerosols represent one of the dominant uncertainties in radiative forcing, partly because of their very high spatiotemporal variability, a still insufficient knowledge of their microphysical and optical properties, or of their vertical distribution. A better understanding and forecasting of their impact on climate therefore requires precise observations of dust emission and transport. Observations from space offer a good opportunity to follow, day by day and at high spatial resolution, dust evolution at global scale and over long time series. Infrared observations allow retrieving dust aerosol optical depth (AOD) as well as the mean dust layer altitude, daytime and nighttime, over oceans and over continents, in particular over desert. Moreover, coarse mode particles are preferentially observed in the infrared, when, in the visible, both larger and finer particles are observed making the distinction between the two modes difficult. Therefore, they appear complementary to observations in the visible. In this study, a decade of the Infrared Atmospheric Sounder Interferometer (IASI) on board European Satellite Metop-A observations, from July 2007 to December 2016, has been processed pixel by pixel, using a "Look-Up-Table"(LUT) physical approach. Important improvements have been brought to our former approach in order to extend it to: 1) daytime retrieval, 2) mid-latitude retrieval, 3) retrieval at the IASI pixel resolution, 4) near real time retrieval (day-1). Moreover, over continents, surface characteristics (pressure, temperature, as well as emissivity spectrum) are now better accounted for. Here, a particular attention is given to the validation of the IASI-retrieved AOD through comparisons with the Spectral Deconvolution Algorithm (SDA) 500 nm coarse mode AOD observed at 70 ground-based Aerosol RObotic NETwork (AERONET) sites during the 114 months processed. Even if such a comparison requires converting AOD from infrared to visible, inherently leading to significant uncertainties, the two AOD datasets compare well, with an overall correlation of 0.8. For a large majority of sites, correlation ranges from 0.7 to 0.9. Sites with highest correlation are well distributed within the "dust belt" (Sahara, Arabian Peninsula, Mediterranean basin, India and also the Caribbean). Correlations obtained for East-Asia are in general smaller, which might be due to a more complex dust structure (i.e., impact of pollution) and partly due to an increase of the AERONET coarse-mode AOD uncertainty. More generally, the good overall agreement between our restitutions and AERONET AOD demonstrates the ability of infrared sounders to infer dust properties, which opens interesting perspective for a synergy with visible observations.

The GEISA database (Gestion et Etude des Informations Spectroscopiques Atmosphériques: Management and Study of Atmospheric Spectroscopic Information) has been developed and maintained by the ARA/ABC(t) group at LMD since 1974. GEISA is constantly evolving, taking into account the best available spectroscopic data. This paper presents the 2015 release of GEISA (GEISA-2015), which updates the last edition of 2011 and celebrates the 40th anniversary of the database. Significant updates and additions have been implemented in the three following independent databases of GEISA.The “line parameters database” contains 52 molecular species (118 isotopologues) and transitions in the spectral range from 10−6 to 35,877.031cm−1, representing 5,067,351 entries, against 3,794,297 in GEISA-2011. Among the previously existing molecules, 20 molecular species have been updated. A new molecule (SO3) has been added. HDO, isotopologue of H2O, is now identified as an independent molecular species. Seven new isotopologues have been added to the GEISA-2015 database.The “cross section sub-database” has been enriched by the addition of 43 new molecular species in its infrared part, 4 molecules (ethane, propane, acetone, acetonitrile) are also updated; they represent 3% of the update. A new section is added, in the near-infrared spectral region, involving 7 molecular species: CH3CN, CH3I, CH3O2, H2CO, HO2, HONO, NH3.The “microphysical and optical properties of atmospheric aerosols sub-database” has been updated for the first time since 2003. It contains more than 40 species originating from NCAR and 20 from the ARIA archive of Oxford University.As for the previous versions, this new release of GEISA and associated management software facilities are implemented and freely accessible on the AERIS/ESPRI atmospheric chemistry data center website.

Five years (July 2007 to June 2012) of CO tropospheric columns derived from the hyperspectral Infrared Atmospheric Sounding Interferometer (IASI) on-board Metop-A are used to study the impact of fires on the concentrations of CO in the troposphere. Following Chédin et al. (2005, 2008), who found a quantitative relation between the daily tropospheric excess of CO2 and fire emissions, we show that tropospheric CO also displays a diurnal signal with a seasonality that agrees well with the seasonal evolution of fires given by Global Fire Emission Database version 3 (GFED3.1) and Global Fire Assimilation System version 1 (GFAS1.0) emissions and Moderate Resolution Imaging Spectroradiometer (MODIS) Collection 5 burned area product. Unlike day- or night-time CO fields, which mix local emissions with nearby emissions transported to the region of study, the day–night difference of CO allows to highlight the CO signal due to local fire emissions. A linear relationship between CO fire emissions from the GFED3.1 and GFAS1.0 inventories and the diurnal difference of IASI CO was found over various regions in the tropics, with a better agreement with GFAS1.0 (correlation coefficient of R2 ∼ 0.7) than GFED3.1 (R2 ∼ 0.6). Based on the specificity of the two main phases of the combustion (flaming vs. smoldering) and on the vertical sensitivity of the sounder to CO, the following mechanism is proposed to explain such a CO diurnal signal: at night, after the passing of IASI at 21:30 local time (LT), a large amount of CO emissions from the smoldering phase is trapped in the boundary layer before being uplifted the next morning by natural and pyroconvection up to the free troposphere, where it is seen by IASI at 09:30 LT. The results presented here highlight the need to take into account the specificity of both the flaming and smoldering phases of fire emissions in order to fully take advantage of CO observations.

IASI (Infrared Atmospheric Sounder Interferometer)-derived monthly mean infrared (10 μm) dust aerosol optical depth (AOD) and altitude are evaluated against ground-based Aerosol RObotic NETwork of sun photometers (AERONET) measurements of the 500 nm coarse-mode AOD and CALIOP (Cloud-Aerosol Lidar with Orthogonal Polarization) measurements of altitude at 38 AERONET sites (sea and land) within the tropical belt (30° N–30° S). The period covered extends from July 2007 to June 2013. The evaluation goes through the analysis of Taylor diagrams and box-and-whiskers plots, separating situations over oceanic regions and over land. For the AOD, such an evaluation raises the problem of the difference between the two spectral domains used: infrared for IASI and visible for AERONET. Consequently, the two measurements do not share the same metrics. For that reason, AERONET coarse-mode AOD is first "translated" into IASI-equivalent infrared AOD. This is done by the determination, site by site, of an infrared to visible AOD ratio. Because translating visible coarse-mode AOD into infrared AOD requires accurate knowledge of variables, such as the infrared refractive index or the particle size distribution, quantifying the bias between these two sources of AOD is not straightforward. This problem is detailed in this paper, in particular in Appendix A. For the sites over oceanic regions, the overall AOD temporal correlation comes to 0.86 for 786 items (IASI and AERONET monthly mean bins). The overall normalized standard deviation (i.e. ratio of the standard deviation of the test data (IASI) to that of the reference data (AERONET)) is 0.93, close to the desired value of 1. Over land, essentially desert, correlation is 0.74 for 619 items and the normalized standard deviation is 0.86. This slight but significant degradation over land most probably results from the greater complexity of the surface (heterogeneity, elevation) and, to a lesser extent, to the episodic presence of dust within the boundary layer (particularly for sites close to active sources) to which IASI, as any thermal infrared sounder, is poorly sensitive, unlike AERONET. Site by site, disparities appear that are principally due to either the insufficient number of AERONET observations throughout the period considered, to the complexity of the location leading to the mixing of several aerosol types (in the case of the Persian Gulf, for example), to surface heterogeneities (elevation, emissivity, etc.), or to the use of a single aerosol model (called "MITR"). Results using another aerosol model, with a different refractive index, are presented and discussed. Concerning altitude over oceanic regions, correlation is 0.70 for 853 items and the normalized standard deviation is 0.92. A systematic bias of −0.4 km (IASI–CALIOP) is observed, with a standard deviation of 0.48 km. This result is satisfactory, considering the important differences between the two instruments (space–time coverage, definition of the altitude). Altitude results over land, essentially over deserts, are not satisfactory for a majority of sites. The smaller sensitivity of IASI to altitude compared to its sensitivity to AOD, added to the difficulties met for the determination of the AOD over land (surface heterogeneities), explain this result. Work is in progress to solve this difficulty. We conclude that the present results demonstrate the usefulness of IASI data, which are planned to cover a long period of time, as an additional constraint to a better knowledge of the impact of aerosols on the climate system.

Infrared Atmospheric Sounder Interferometer (IASI) observations covering the period from July 2007 to December 2011 are interpreted in terms of monthly mean, 1°×1°, 10 μm dust Aerosol Optical Depth (AOD), mean altitude and coarse mode effective radius. The geographical study area includes the northern tropical Atlantic and the northwest Arabian Sea, both characterised by strong, regular dust events. The method developed relies on the construction of Look-Up-Tables computed for a large selection of atmospheric situations and observing conditions. At a regional scale, a good agreement is found between IASI-retrieved 10 μm AOD and total visible optical depth at 550 nm from either the Moderate resolution Imaging Spectroradiometer (MODIS/Aqua or Terra), or the Multi-angle Imaging SpectroRadiometer (MISR), or the Polarization and Anisotropy of Reflectances for Atmospheric Science coupled with Observations from a Lidar (PARASOL). Taking into account the ratio existing between infrared and visible AODs, the diversity between the different 550 nm AODs is similar to the difference between these and the IASI AODs. The infrared AOD to visible AOD ratio, partly reflecting the varying distribution of the dust layer between the dust coarse mode particles seen by IASI, and the fine mode seen by the other instruments, is found to vary with the region observed with values close to already published values. Comparisons between the climatologies of the 10 μm IASI AOD and of the PARASOL non-spherical coarse mode AOD at 865 nm, both expected to be representative of the dust coarse mode, lead to conclusions differing according to the region considered. These differences are discussed in the light of the MODIS Angström exponent (865–550 nm). At local scale, around six Aerosol Robotic Network (AERONET) sites, close or far from the dust sources, a similar satisfactory agreement is found between IASI and the visible AODs and the differences between these products are shown and analysed. IASI-retrieved dust layer mean altitudes also compare well with the Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP/CALIPSO) aerosol mean layer altitude, both in terms of climatology and of zonal evolution throughout the Atlantic. Comparisons between the IASI-retrieved dust coarse mode effective radius and retrievals from AERONET at the six sites brings into evidence an almost systematic bias of about +0.35 μm (IASI-AERONET). Removing this bias leads to a satisfactory agreement between the climatologies of these two products. Overall, these results illustrate the dust westward transport characterised by a fast decrease of the dust optical depth, a somewhat slower decrease of the altitude, and an effective radius remaining almost constant during summer throughout the northern tropical Atlantic. They also demonstrate the capability of high resolution infrared sounders to contribute improving our understanding of processes related to the aerosols (transport, sources, cycles, effect of aerosols on the terrestrial radiation, etc.).

Since July 2007, monthly averages of mid-tropospheric methane have been retrieved in the tropics over land and sea, by day and night, from IASI onboard MetOp-A, yielding a complete view of the geographical distribution, seasonality and long-term tendency of methane in the mid-troposphere. Retrieved methane displays a clear seasonal cycle of ~25 ppbv in the northern tropics, with a maximum in November and a minimum in April–May, a more complex cycle of ~15 ppbv in the southern tropics, and a south-to-north latitudinal variation of ~30 ppbv – in good agreement with regular aircraft measurements of the CONTRAIL program. Comparisons with CARIBIC aircraft measurements made at ~11 km yield an averaged difference between collocated IASI estimates and CARIBIC measurements of 7.2 ppbv with a standard deviation of 13.1 ppbv. Comparisons with aircraft measurements made above 6 km during five HIPPO campaigns give an averaged difference between collocated IASI estimates and HIPPO measurements of 5.1 ppbv with a standard deviation of 16.3 ppbv. These comparisons show that IASI captures well the evolution of mid-tropospheric methane. In particular, in 2007 and 2008, IASI shows an increase of mid-tropospheric methane in the tropical region of 9.5 ± 2.8 and 6.3 ± 1.7 ppbv yr−1, respectively – in excellent agreement with the rate of increase measured at the surface after almost a decade of near-zero growth. IASI also indicates a slowing down of this increase in the following years to ~2 ppbv yr−1, with the highest increase in 2010. Assuming that the recent evolution of methane is mostly due to an increase in surface emissions, IASI might indicate a decrease in tropical wetland emissions for the period 2009–2011 compared to 2007–2008, in agreement with decreasing tropical precipitation over this period, together with an increase in biomass burning emissions in 2010 in the southern tropics.

Four years of tropospheric integrated content of CO were retrieved from infrared hyperspectral observations of AIRS onboard Aqua and IASI onboard MetOp-A, for the period July 2007–June 2011. The retrieval method is based on a double differential approach that relies on the difference between brightness temperatures observed by the sounder and BT simulated by the Automatised Atmospheric Absorption Atlas (4A) radiative transfer model on colocated ECMWF reanalyses, for several couples of channels located in the 4.67 μm CO band. AIRS and IASI give access to similar integrated contents of CO with a maximum sensitivity near 450 hPa and a half-height width of the weighting function between 200 and 750 hPa depending on the thermal contrast (i.e., the difference between the surface temperature and the temperature of the first pressure level). However, differences in their spectral and radiometric characteristics yield differences in the retrieval characteristics with AIRS selected couples of channels being more sensitive to surface characteristics. Moreover, IASI covers the whole CO absorption band, with a 3 times better spectral resolution, giving access to channels presenting a 3 times higher signal to noise ratio. This results in a better precision and lower standard deviation of the IASI retrievals. Conservatively, comparisons with CARIBIC aircraft measurements yield an averaged relative difference of 3.4% for IASI and 4.9% for AIRS. On average, AIRS and IASI retrievals are in very good agreement, showing the same seasonality, seasonal amplitudes, interannual variability and spatial distribution. The analysis of the monthly evolution of CO particularly highlights the expected strong influence of biomass burning on the evolution of CO in several tropical regions. In particular, a sharp increase in CO in 2010 in the southern tropics, especially over South America and South Africa, is observed, and is shown to be related to El Niño and to the Atlantic Multidecadal Oscillation.

Fires emit annually more than 2 GtC in the atmosphere, an amount which represents about one third of anthropic emissions, and which plays a key role in the interannual variations of three major gases: CO2 (90% of the emissions), CO (9%) and CH4 (<1%). To study fire emissions, we look at the concentrations of emitted gases and study the links between CO2, CO and CH4 in the troposphere. Spatial observations give access to a global coverage, which is especially needed in the tropics where 80% of the emissions are located and where ground measurements are sparse.

The updated 2009 edition of the spectroscopic database GEISA (Gestion et Etude des Informations Spectroscopiques Atmospheriques; Management and Study of Atmospheric Spectroscopic Information) is described in this paper. GEISA is a computer-accessible system comprising three independent sub-databases devoted, respectively, to: line parameters, infrared and ultraviolet/visible absorption cross-sections, microphysical and optical properties of atmospheric aerosols. In this edition, 50 molecules are involved in the line parameters sub-database, including 111 isotopologues, for a total of 3,807,997 entries, in the spectral range from 10(-6) to 35,877.031 cm(-1).The successful performances of the new generation of hyperspectral sounders depend ultimately on the accuracy to which the spectroscopic parameters of the optically active atmospheric gases are known, since they constitute an essential input to the forward radiative transfer models that are used to interpret their observations. Currently, GEISA is involved in activities related to the assessment of the capabilities of IASI (Infrared Atmospheric Sounding Interferometer; http://smsc.cnes.fr/lASI/index.htm) on board the METOP European satellite through the GEISA/IASI database derived from GEISA. Since the Metop-A (http://www.eumetsat.int) launch (19 October 2006), GEISA is the reference spectroscopic database for the validation of the level-1 IASI data. Also, GEISA is involved in planetary research, i.e., modeling of Titan's atmosphere, in the comparison with observations performed by Voyager, or by ground-based telescopes, and by the instruments on board the Cassini-Huygens mission.GEISA, continuously developed and maintained at LMD (Laboratoire de Meteorologie Dynamique, France) since 1976, is implemented on the IPSL/CNRS (France) "Ether" Products and Services Centre WEB site (http://ether.ipsl.jussieu.fr), where all archived spectroscopic data can be handled through general and user friendly associated management software facilities. More than 350 researchers are registered for on line use of GEISA. (C) 2011 Elsevier Ltd. All rights reserved.

Satellite observations provide a continuous survey of the state of the atmosphere over the whole globe, and their record length exceeds now more than 25 years. The International Satellite Cloud Climatology Project (ISCCP), using data from a combination of geostationary and polar orbiting imagers, contributed to the understanding of numerous cloud physical processes. Due to their relatively high spectral resolution, IR vertical sounders provide reliable properties of cirrus clouds (day and night). Especially in the tropics, where the cirrus amount is abundant, ISCCP misidentifies about one third of these clouds as midlevel clouds. Therefore, IR sounders provide complementary information to ISCCP.