Satellite remote sensing enables the study of atmospheric aerosols at large spatial scales, with geostationary platforms making this possible at sub‐daily frequencies. High‐temporal‐resolution ...aerosol observations can be made from geostationary data by using robust numerical inversion methods such as the widely‐used optimal estimation (OE) theory. This is the case of the instantaneous Aerosol and surfacE Retrieval Using Satellites in GEOstationary orbit (iAERUS‐GEO) algorithm, which successfully retrieves aerosol optical depth (AOD) maps from the Meteosat Second Generation weather satellite based on a simple implementation of the OE approach combined with the Levenberg–Marquardt method. However, the exact gain in inversion performances that can be obtained from the multiple and more advanced possibilities offered by OE is not well documented in the current literature. Against this background, this article presents the quantitative assessment of OE for the future improvement of the iAERUS‐GEO algorithm. To this end, we use a series of comprehensive experiments based on AOD maps retrieved by iAERUS‐GEO using different OE implementations, and ground‐based observations used as reference data. First, we assess the varying importance in the inversion process of satellite observations and a priori information according to the content of satellite aerosol information. Second, we quantify the gain of AOD estimation in log space versus linear space in terms of accuracy, AOD distribution and number of successful retrievals. Finally, we evaluate the accuracy improvement of simultaneous AOD and surface reflectance retrieval as a function of the regions covered by the Meteosat Earth's disk.
The algorithm iAERUS‐GEO estimates maps of aerosol optical depth from the Meteosat Second Generation satellite, thanks to the use of optimal estimation and the Levenberg–Marquardt method (see example above for 20 July 2016 at 10:30 UTC). This article investigates the performances of this numerical inversion method for aerosol retrieval from geostationary weather satellites in the current implementation of iAERUS‐GEO as well as in more advanced configurations.
The Monitoring Nitrous Oxide Sources (MIN2OS) satellite project aims at monitoring global-scale nitrous oxide (N2O) sources by retrieving N2O surface fluxes from the inversion of space-borne N2O ...measurements that are sensitive to the lowermost atmospheric layers under favorable conditions. MIN2OS will provide emission estimates of N2O at a horizontal resolution of 1° × 1° on the global scale and 10 × 10 km2 on the regional scale on a weekly to monthly basis depending on the application (e.g., agriculture, national inventories, policy, scientific research). Our novel approach is based on the development of: 1) a space-borne instrument operating in the Thermal InfraRed domain providing, in clear sky conditions, N2O mixing ratio in the lowermost atmosphere (900 hPa) under favorable conditions (summer daytime) over land and under favorable and unfavorable (winter nighttime) conditions over the ocean and 2) an atmospheric inversion framework to estimate N2O surface fluxes from the atmospheric satellite observations. After studying three N2O spectral bands (B1 at 1240–1350 cm−1, B2 at 2150–2260 cm−1 and B3 at 2400–2600 cm−1), a new TIR instrument will be developed, centered at 1250–1330 cm−1, with a resolution of 0.125 cm−1, a Full Width at Half Maximum of 0.25 cm−1 and a swath of 300 km. To optimally constrain the retrieval of N2O vertical profiles, the instrument will be on-board a platform at ~830 km altitude in a sun-synchronous orbit crossing the Equator in descending node at 09:30 local time in synergy with two other platforms (Metop-SG and Sentinel-2 NG) expected to fly in 2031–32 aiming at detecting surface properties, agricultural information on the field scale and vertical profiles of atmospheric constituents and temperature. The lifetime of the MIN2OS project would be 4–5 years to study the interannual variability of N2O surface fluxes. The spectral noise can be decreased by at least a factor of 5 compared to the lowest noise accessible to date with the Infrared Atmospheric Sounding Interferometer-New Generation (IASI-NG) mission. The N2O total error is expected to be less than ~1% (~3 ppbv) along the vertical. The preliminary design of the MIN2OS project results in a small instrument (payload of 90 kg, volume of 1200 × 600 × 300 mm3) with, in addition to the spectrometer, a wide field and 1-km resolution imager for cloud detection. The instruments could be hosted on a small platform, the whole satellite being largely compatible with a dual launch on VEGA-C. The MIN2OS project has been submitted to the European Space Agency Earth Explorer 11 mission ideas.
•The MIN2OS satellite project aims at retrieving global-scale N2O sources.•MIN2OS is an IR spectrometer (1250–1330 cm-1) dedicated to N2O measurements.•MIN2OS will observe N2O in the lowermost troposphere at 10x10 km2 resolution.•A source inversion tool will estimate N2O surface fluxes from MIN2OS observations.•The MIN2OS project has been submitted to the ESA EE11 mission ideas.
This paper highlights the advantages of an affordable multi-wavelength ground-based camera, called WaltRCam, for monitoring Aerosol Optical Depth (AOD) in a clear case over a peri-urban area. To ...simulate the performance of this low-cost camera, for which data are not yet available, we use data from an expensive hyperspectral camera (HSI) to mimic its characteristics. Our methodology is based on the construction of look-up tables using the DART (Discrete Anisotropic Radiative Transfer) 3D radiative transfer model. DART simulates the different spectra observed by the WaltRCam camera, which then provides the AODs for all image pixels in near-real-time. Moreover, DART is coupled to a 3D scale-model of the city of Toulouse (dating from 2014) to model complex urban geometries and to associate specific optical properties to the various objects that make up the environment. Moreover, we use a neural-network-based method to recognize the various objects in the image in order to take into account only pixels common between the observations. In this way, we take account of changes to the peri-urban area, such as vegetation growth, construction, demolition of buildings, etc. The results of this study show that the WaltRCam camera, by capturing eight wavelengths, can deliver convincing results compared with ground and satellite reference data, with a correlation coefficient of 0.9 and an average RMSE of less than 0.02.
Clouds affect the Earth climate with an impact that depends on the cloud nature (solid and/or liquid water). Although the Antarctic climate is changing rapidly, cloud observations are sparse over ...Antarctica due to few ground stations and satellite observations. The Concordia station is located on the eastern Antarctic Plateau (75∘ S, 123∘ E; 3233 m above mean sea level), one of the driest and coldest places on Earth. We used observations of clouds, temperature, liquid water, and surface irradiance performed at Concordia during four austral summers (December 2018–2021) to analyse the link between liquid water and temperature and its impact on surface irradiance in the presence of supercooled liquid water (liquid water for temperature less than 0 ∘C) clouds (SLWCs). Our analysis shows that, within SLWCs, temperature logarithmically increases from −36.0 to −16.0 ∘C when liquid water path increases from 1.0 to 14.0 g m−2. The SLWC radiative forcing is positive and logarithmically increases from 0.0 to 70.0 W m−2 when liquid water path increases from 1.2 to 3.5 g m−2. This is mainly due to the downward longwave component that logarithmically increases from 0 to 90 W m−2 when liquid water path increases from 1.0 to 3.5 g m−2. The attenuation of shortwave incoming irradiance (that can reach more than 100 W m−2) is almost compensated for by the upward shortwave irradiance because of high values of surface albedo. Based on our study, we can extrapolate that, over the Antarctic continent, SLWCs have a maximum radiative forcing that is rather weak over the eastern Antarctic Plateau (0 to 7 W m−2) but 3 to 5 times larger over West Antarctica (0 to 40 W m−2), maximizing in summer and over the Antarctic Peninsula.
A comprehensive analysis of the water budget over the Dome C (Concordia,
Antarctica) station has been performed during the austral summer 2018–2019
as part of the Year of Polar Prediction (YOPP) ...international campaign. Thin
(∼100 m deep) supercooled liquid water (SLW) clouds have been
detected and analysed using remotely sensed observations at the station
(tropospheric depolarization lidar, the H2O Antarctica Microwave Stratospheric and Tropospheric
Radiometer (HAMSTRAD), net
surface radiation from the Baseline Surface Radiation Network (BSRN)), radiosondes, and satellite observations (CALIOP, Cloud-Aerosol LIdar with Orthogonal Polarization/CALIPSO, Cloud Aerosol Lidar and Infrared
Pathfinder Satellite Observations) combined with a specific
configuration of the numerical weather prediction model: ARPEGE-SH (Action
de Recherche Petite Echelle Grande Echelle – Southern Hemisphere). The
analysis shows that SLW clouds were present from November to March, with the
greatest frequency occurring in December and January when ∼50 % of the days in summer time exhibited SLW clouds for at least 1 h. Two case studies are used to illustrate this phenomenon. On 24 December 2018, the atmospheric planetary boundary layer (PBL) evolved
following a typical diurnal variation, which is to say with a warm and dry
mixing layer at local noon thicker than the cold and dry stable layer at
local midnight. Our study showed that the SLW clouds were observed at Dome C
within the entrainment and the capping inversion zones at the top of the
PBL. ARPEGE-SH was not able to correctly estimate the ratio between liquid
and solid water inside the clouds with the liquid water path (LWP) strongly
underestimated by a factor of 1000 compared to observations. The lack of
simulated SLW in the model impacted the net surface radiation that was 20–30 W m−2 higher in the BSRN observations than in the ARPEGE-SH
calculations, mainly attributable to the BSRN longwave downward surface
radiation being 50 W m−2 greater than that of ARPEGE-SH. The second
case study took place on 20 December 2018, when a warm and wet episode
impacted the PBL with no clear diurnal cycle of the PBL top. SLW cloud
appearance within the entrainment and capping inversion zones coincided with
the warm and wet event. The amount of liquid water measured by HAMSTRAD was
∼20 times greater in this perturbed PBL than in the typical
PBL. Since ARPEGE-SH was not able to accurately reproduce these SLW clouds,
the discrepancy between the observed and calculated net surface radiation
was even greater than in the typical PBL case, reaching +50 W m−2,
mainly attributable to the downwelling longwave surface radiation from BSRN
being 100 W m−2 greater than that of ARPEGE-SH. The model was then run
with a new partition function favouring liquid water for temperatures below
−20 down to −40 ∘C. In this test mode, ARPEGE-SH has
been able to generate SLW clouds with modelled LWP and net surface radiation
consistent with observations during the typical case, whereas, during the
perturbed case, the modelled LWP was 10 times less than the observations and
the modelled net surface radiation remained lower than the observations by
∼50 W m−2. Accurately modelling the presence of SLW
clouds appears crucial to correctly simulate the surface energy budget over
the Antarctic Plateau.
In this paper, we address the issues of the representation of boreal fires in a global chemistry and transport model (GEOS‐Chem) as well as their contribution to the Arctic aerosol optical thickness ...and black carbon (BC) deposition, with a focus on the 2003 Russian fires. We use satellite observations from the MOPITT, POLDER and MODIS sensors to evaluate the model performances in simulating the fire pollution export over the North Pacific. Our results show that aerosol and carbon monoxide (CO) outflow is best reproduced in our model when fire emissions are (1) increased to 72 Tg for CO, 0.5 Tg C for BC, and 5.3 Tg C for organic carbon over the entire fire season; (2) prescribed on a daily basis; and (3) injected up to 4.5 km in July and August. The use of daily, rather than monthly, biomass burning emission inventories improves significantly the representation of the aerosol outflow, but has little impact on CO. The injection of fire emissions above the boundary layer influences both the CO and aerosol columns but only during the late fire season. The model improvements with respect to the standard configuration induce an increase of a factor up to 2 on the aerosol optical thickness and the mass of BC deposited in the Northern Hemisphere. According to our improved simulation, the 2003 Russian fires contributed to 16–33% of the aerosol optical thickness and to 40–56% of the mass of BC deposited, north of 75°N in spring and summer. They contribute to the aerosol optical thickness by more than 30% during the days of Arctic haze events in spring and summer.
In the framework of the
Chemistry-Aerosol Mediterranean Experiment (ChArMEx;
http://charmex.lsce.ipsl.fr, last access: 22 June 2018) project, we study the evolution of surface ozone over the ...Mediterranean Basin
(MB) with a focus on summertime over the time period 2000–2100, using the
Atmospheric Chemistry and Climate Model Intercomparison Project (ACCMIP)
outputs from 13 models. We consider three different periods (2000, 2030 and
2100) and the four Representative Concentration Pathways (RCP2.6, RCP4.5,
RCP6.0 and RCP8.5) to study the changes in the future ozone and its budget.
We use a statistical approach to compare and discuss the results of the
models. We discuss the behavior of the models that simulate the surface ozone
over the MB. The shape of the annual cycle of surface ozone simulated by
ACCMIP models is similar to the annual cycle of the ozone observations, but
the model values are biased high. For the summer, we found that most of the
models overestimate surface ozone compared to observations over the most
recent period (1990–2010). Compared to the reference period (2000), we found
a net decrease in the ensemble mean surface ozone over the MB in 2030 (2100)
for three RCPs: −14 % (−38 %) for RCP2.6, −9 % (−24 %) for RCP4.5
and −10 % (−29 %) for RCP6.0. The surface ozone decrease over the MB
for these scenarios is much more pronounced than the relative changes of the
global tropospheric ozone burden. This is mainly due to the reduction in
ozone precursors and to the nitrogen oxide (NOx = NO +
NO2)-limited regime over the MB. For RCP8.5, the ensemble mean
surface ozone is almost constant over the MB from 2000 to 2100. We show how
the future climate change and in particular the increase in methane
concentrations can offset the benefits from the reduction in emissions of
ozone precursors over the MB.
Nitrous oxide (N2O) is a greenhouse gas difficult to estimate by satellite because of its weak spectral signature in the infra-red band and its low variability in the troposphere. Nevertheless, this ...study presents the evaluation of new tropospheric N2O observations from the Infrared Atmospheric Sounder Interferometer (IASI) on Metop-A using the Toulouse N2O Retrieval Version 2.0 tool. This tool is based on the Radiative Transfer for Tiros Operational Vertical sounder (RTTOV) model version 12.3 coupled to the Levenberg-Marquardt optimal estimation method enabling the simultaneous retrieval of methane, water vapour, temperature profiles together with surface temperature and emissivity within the 1240–1350 cm−1 window. In this study, we focused on the upper troposphere (300 hPa) where the sensitivity of IASI is significant. The IASI N2O data has been evaluated using aircraft N2O observations from the High-performance Instrumented Airborne Platform for Environmental Research Pole-to-Pole Observations (HIPPO) campaigns in 2009, 2010, and 2011 and from the National Oceanic and Atmospheric Administration’s (NOAA) Global Greenhouse Gas Reference Network (GGGRN) in 2011. In addition, we evaluated the IASI N2O using ground-based N2O measurements from 9 stations belonging to the Network for the Detection of Atmospheric Composition Change (NDACC). We found a total random error of ∼2 ppbv (0.6%) for one single retrieval at 300 hPa. Under favorable conditions, this error is also found in the vertical level pressure range 300–500 hPa. It decreases rapidly to ∼0.4 ppbv (0.1%) when we average on a 1° × 1° box. In addition, independent observations allows the estimation of bias with the IASI TN2OR v2.0 N2O. The bias between IASI and aircraft N2O data at 300 hPa is ∼1.0 ppbv (∼0.3%). We found an estimated random error of ∼2.3 ppbv (∼0.75%). This study also shows relatively high correlations between IASI data and aircraft in situ profiles but more varying correlations over the year 2011 depending on the location between IASI and NDACC remote sensing data. Finally, we present daily, monthly, and seasonal IASI N2O horizontal distributions in the upper troposphere as well as cross sections for different seasons that exhibit maxima in the Tropical band especially over Africa and South America.
This paper presents the first results about the assimilation of CALIOP (Cloud-Aerosol Lidar with Orthogonal Polarization) extinction coefficient measurements onboard the CALIPSO (Cloud-Aerosol Lidar ...and Infrared Pathfinder Satellite Observations) satellite in the MOCAGE (MOdèle de Chimie Atmosphérique à Grande Echelle) chemistry transport model of Météo-France. This assimilation module is an extension of the aerosol optical depth (AOD) assimilation system already presented by Sic et al. (2016). We focus on the period of the TRAQA (TRAnsport à longue distance et Qualité de l'Air dans le bassin méditerranéen) field campaign that took place during summer 2012. This period offers the opportunity to have access to a large set of aerosol observations from instrumented aircraft, balloons, satellite and ground-based stations. We evaluate the added value of CALIOP assimilation with respect to the model free run by comparing both fields to independent observations issued from the TRAQA field campaign.
We present an Observing System Simulation Experiment (OSSE) dedicated to the evaluation of the added value of the Sentinel-4 and Sentinel-5P missions for tropospheric nitrogen dioxide (NO2). ...Sentinel-4 is a geostationary (GEO) mission covering the European continent, providing observations with high temporal resolution (hourly). Sentinel-5P is a low Earth orbit (LEO) mission providing daily observations with a global coverage. The OSSE experiment has been carefully designed, with separate models for the simulation of observations and for the assimilation experiments and with conservative estimates of the total observation uncertainties. In the experiment we simulate Sentinel-4 and Sentinel-5P tropospheric NO2 columns and surface ozone concentrations at 7 by 7 km resolution over Europe for two 3-month summer and winter periods. The synthetic observations are based on a nature run (NR) from a chemistry transport model (MOCAGE) and error estimates using instrument characteristics. We assimilate the simulated observations into a chemistry transport model (LOTOS-EUROS) independent of the NR to evaluate their impact on modelled NO2 tropospheric columns and surface concentrations. The results are compared to an operational system where only ground-based ozone observations are ingested. Both instruments have an added value to analysed NO2 columns and surface values, reflected in decreased biases and improved correlations. The Sentinel-4 NO2 observations with hourly temporal resolution benefit modelled NO2 analyses throughout the entire day where the daily Sentinel-5P NO2 observations have a slightly lower impact that lasts up to 3–6 h after overpass. The evaluated benefits may be even higher in reality as the applied error estimates were shown to be higher than actual errors in the now operational Sentinel-5P NO2 products. We show that an accurate representation of the NO2 profile is crucial for the benefit of the column observations on surface values. The results support the need for having a combination of GEO and LEO missions for NO2 analyses in view of the complementary benefits of hourly temporal resolution (GEO, Sentinel-4) and global coverage (LEO, Sentinel-5P).
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