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A meta-analysis reveals large potential of substituting synthetic nitrogen fertilizer with solid organic fertilizer for climate mitigation in China
No full textInternational audienceSubstituting synthetic fertilizers with solid organic fertilizers (e.g., solid manure and compost) contributes to mitigating climate change by increasing soil organic carbon stocks. However, net climate benefits of organic substitution (OS) remain unclear as organic inputs might increase emissions of nitrous oxide and methane, potent non-CO2 greenhouse gases (GHG) from croplands. Here we perform a meta-analysis of 1666 field paired observations with a machine learning model to explore the net climate benefits of OS and its climate mitigation potential for China. We show that OS achieves net mitigation of over 4 Mg carbon dioxide equivalent (CO2-eq) ha−1 yr−1 on dryland soils by increasing soil organic carbon without affecting non-CO2 GHG of both nitrous oxide and methane when compared to synthetic fertilizer on a total nitrogen basis. Conversely, OS has limit net climate benefits on paddy soils because of the increased methane emissions that almost offsets the annual soil carbon benefits. The net climate benefits were mostly determined by the duration of OS (∼25 % contributions), with limited long-term benefits but can be improved with optimal substitution ratio of organic N and type of organic fertilizers. We estimate that OS has technical potential to shift China's croplands from current a net carbon source of ∼300 Tg CO2-eq yr−1 to a small sink of 6 Tg CO2-eq yr−1, with the reduction potential equals to 2–3 % of total national emissions on a 20-year time span. Over 80 % of the mitigation potential lies in arable lands with neutral to alkaline pH, low soil organic carbon and temperate climate. These findings underscore the potential of OS for climate mitigation which requires alignment of targeted practices and cross-sectoral policies to guide China's OS implementation strategy
Sum rules via large deviations: polynomial potentials and multi-cut regime on the unit circle
No full textSum rules are elegant formulas that relate entropy functionals to coefficients associated with orthogonal polynomials [Sim11]. In a series of paper (see for example]), interesting connections have been established between the large theory of spectral measures built on random matrices and sum rules. In this work, we extend this approach by studying sum rules within random matrix models with polynomial potentials on the unit circle, with a particular focus on cases where the equilibrium measure lacks full support.</div
Investigating the Origin of Venus’ Clouds Using a Cloud Microphysics Model
No full textInternational audienceSulfuric acid clouds on Venus play a pivotal role in atmospheric radiation, chemistry, and material transport. Therefore, understanding the mechanisms underlying cloud formation on Venus is essential for gaining a better insight into the planet’s climate and atmospheric processes. Cloud formation on Venus begins with the nucleation process, which provides cloud condensation nuclei (CCN) necessary for subsequent condensational growth. Elemental sulfur is frequently assumed to be the primary CCN substance, as its vapor can be readily produced through photochemical reactions and solidifies upon condensation. Meteoric dust has been proposed as CCN as well and cloud droplets could also form by homogeneous nucleation.Cloud microphysics models are effective tools for exploring the mechanisms of cloud formation and have been widely applied in studies of Venus. Previous modeling studies that assumed elemental sulfur as CCN have successfully reproduced observed cloud structures [1,2,3,4]. However, these studies have typically simplified the CCN production process by directly injecting particles with predefined sizes ranging from 0.01 to 0.1 µm, rather than explicitly calculating the CCN production rate based on nucleation theory. In addition, the elemental sulfur CCN are also provided from the lower model boundary at ~40 km altitude in the previous studies, despite uncertainties about the stability of elemental sulfur as a solid phase at these altitudes. Consequently, the fundamental initial step of cloud formation on Venus remains poorly understood.In this study, we perform 1D cloud microphysics simulations incorporating elemental sulfur vapor and its nucleation process to investigate the origin of Venus’ clouds. A cloud microphysics model used here is the Simulator of Particle Evolution, Composition, and Kinetics (SPECK) [5]. SPECK accurately calculates condensation processes and is particularly suitable for aerosols with diverse compositions. Thus, it effectively simulates particle evolution from nucleation through condensation and coagulation, tracking interactions among particles with different composition. Our model includes three condensable vapor species: sulfuric acid, water, and elemental sulfur (S8). The homogeneous nucleation of sulfuric acid occurs via binary nucleation with water [6], while the nucleation of S8 is computed using a classical homogeneous nucleation theory. The size bins of the model range from 1 nm to 30 µm, and homogeneously nucleated particles are introduced into the smallest bin size of 1 nm. The model also considers the heterogeneous nucleation of sulfuric acid and water on the formed elemental sulfur particles. The vertical model domain spans altitudes from 40 km to 100 km, encompassing the entire cloud structure from the lower clouds to the upper haze. In addition to homogeneously nucleated particles, our model incorporates meteoric smoke particles (MSPs) as CCN with a radius of 1 nm. MSPs, assumed to consist of olivine, are introduced at the top of the model domain since the production of MSP is expected to occur around 115 km [7]. A parameter study is conducted with respect to the meteoric dust ablation flux ranging from 1 t d-1 to 1000 t d-1.Figure 1. (a) Homogeneous nucleation rate of sulfuric acid and water (blue solid line) and S8 (red-dashed line). (b) Heterogeneous nucleation rate of sulfuric acid onto S8 particles. Our results indicate that different nucleation processes dominate at different altitudes. Specifically, homogeneous nucleation of elemental sulfur prevails below 70 km altitude, whereas homogeneous nucleation of sulfuric acid dominates above 80 km (Figure 1a). The S8 particles are eventually activated through heterogeneous nucleation and become coated by sulfuric acid solution (Figure 1b). This suggests that cloud particles below 70 km and haze particles above 70 km have distinct origins. Parameter studies varying the MSP injection flux by three orders of magnitude resulted in negligible differences in the upper haze structure, consistent with previous findings [2]. Additionally, we confirmed that elemental sulfur particles evaporate below the cloud base due to higher temperatures. This result raises questions about the previous assumption that elemental sulfur serves as CCN around the cloud base, highlighting the possibility that alternative CCN substances such as minerals [8] or salts [9] may be more suitable.
The third BepiColombo flyby to Mercury: ground based observation of the exosphere and in-situ measurements
No full textInternational audienceOn 19 June 2023 the ESA-JAXA double spacecraft BepiColombo performed its third flyby around Mercury with a closest approach on the nightside at an altitude of 200 km above the surface and an almost equatorial trajectory that crossed the tail magnetosphere (Figure 1, left).During the days around the flybys many instruments onboard the spacecraft were operative to get new in-situ measurements of the planetary environment, providing data of magnetic field, of the solar wind and plasma, ions, electrons and neutral particles, radiation, dust particles.Also from the Earth, an observing campaign of Mercury was performed from the solar telescope THEMIS in the Canary Island of Tenerife, to detect the exospheric morphology and variability for the 5 days around the flyby. Thanks to the favourable orbital configuration (Figure 1, right), the good performances of the high resolution spectrograph MTR and of the specific characteristics of the solar telescope THEMIS and its adaptive optics, it is possible to observe Mercury during all the daytime, i.e. many hours/day.The high resolution spectrograph can image separately the two D emission lines at 5890-96 A of sodium, and a scanning system provide a full image of the planet in about 30 minutes. Sodium is a well-known exospheric component of Mercury, and it is well detectable also from the ground, thanks to the fact that its emission lies in a region free from telluric lines, and it is then able to provide a time series of sodium exospheric images to study its morphology and variability.The exosphere, that is neutral gaseous environment of the planet, is the result of many different interactions occurring between the outer space (solar wind particles and radiation, dust…) with the planetary surface, causing release of particles. The interplanetary magnetic field, interacting with the intrinsic planetary magnetic field, seems to be a primary driver of the two peculiar peaks of emission occurring at high latitude, often observed during ground based observations (Figure 2).To study to exosphere thus means to enhance our understanding of Mercury’s overall environment and the physical processes that generate and sustain it.In our work we provide the results coming from the analysis of the days around the third flyby at Mercury by completing ground-based data with in-situ measurements of the magnetic field and the ion and electron populations
Influence of chemical and morphological properties on the mid-infrared refractive indices of Titan aerosol analogs
No full textInternational audienceIn the atmosphere of Saturn's largest satellite, Titan, the solid particles in suspension (photochemistry organic aerosols) play an important role notably to the attenuation of the solar spectrum by absorption and scattering. To constrain these interactions, the optical properties of Titan’s atmospheric aerosols, refractive index n and extinction coefficient k were recovered from observations [1, 2, 3, 4]. The refractive indices database has been expanded using solid analogs of Titan's aerosols produced and analyzed in laboratory [5, 6, 7]. The experimental data are generally consistent with the optical properties derived from Titan’s aerosols, including the contribution to the extinction and albedo of Saturn's moon [5, 7, 8]. However, comparisons of vibrational modes in the mid-infrared (MIR) suggest a difference in composition between laboratory analogs and Titan’s aerosols [9, 10]. These discrepancies in the refractive indices of solids can originate from their morphological and chemical properties. Indeed, numerous experimental studies have revealed the variability in the morphology and chemical composition of solid analogs formed in simulations of Titan's atmospheric chemistry
The importance of oceanic emissions for modelling Arctic aerosols and clouds
No full textInternational audienceEmissions of primary aerosols and aerosol precursors from the ocean are key for the Arctic climate. Among those, secondary aerosols from oceanic dimethylsulfide (DMS) are a key species for aerosol-radiation and aerosol-cloud interactions. However, the representation of DMS in atmospheric models is challenging, which generates large uncertainties in the Arctic aerosol budget. In this work we evaluate the sensitivity of simulated Arctic aerosols and clouds in the WRF-Chem atmospheric chemistry model, over a complete annual cycle, to (1) the representation of DMS chemistry in the atmosphere and (2) the oceanic DMS concentration product used as boundary condition. For (2), we compare the results obtained using the Lana et al. (2011) global climatology versus dedicated simulations of the Arctic Ocean biogeochemistry with NEMO-CSIB. We find that aerosol number concentrations can change by up to more than 100%, including over sea ice, depending on the model configuration, with a greater sensitivity to the chemistry mechanism than to the oceanic DMS product. This change is negative in the summer, which leads to decreased cloud droplet number and increased (decreased, respectively) shortwave (longwave, respectively) radiation at the surface over sea ice. The opposite effect is found in late spring and autumn. Overall, we find that using a more complex chemistry and better description of Arctic Ocean DMS has an impact on the surface energy budget of +4 W/m2 on average for the year 2018, both over sea ice and the open ocean. This configuration also performs best compared to observations. Additional experiments evaluating the changes of aerosol number under future oceanic DMS concentrations, potential emissions of DMS through sea ice, and the role of methanesulfonic acid (MSA) nucleation in summertime aerosol number concentration are presented. This work demonstrates the importance of accurately modeling DMS for simulations of the Arctic aerosol budget and climate, and the value-added of forcing atmospheric models with ocean biogeochemistry simulations
The response of the Martian ionosphere to short and long term solar energetic particles, a scientifc goal of the ESA M7 candidate M-MATISSE
No full textInternational audienceThe response of the Martian environment to Space Weather activity is not yet very well characterised as many factors from both the planet and from outside play large roles in the observed dynamics, particularly in the ionosphere. One of the most intense factor is when showers of Solar Energetic Particles (SEP) hit the planet as they are able to penetrate down to the surface and produce significant levels of aurora emissions. Moreover, both SEP protons and electrons are able to create ionospheric layers in the mesosphere, which in turn produce significant radio attenuation. In this study, we analyse data from all the active missions at Mars covering the track of the SEP particles up to the surface in order to provide the most complete characterization of the response of the Martian plasma system to Space Weather with respect to the solar cycle. We also evaluate short term responses, such as during the February 2022 and May 2024 events, when despite very large SEPs hitting Mars, the ionosphere did not absorb as many particles as it was expected. The main objective of this work is to provide the best possible characterisation of the Martian radiation environment in order to support to support the ESA M7 Mars, Magnetosphere, ATmosphere, Ionosphere, Space Weather SciencE (M-MATISSE) candidate
Investigating the discrepancy between observed and modelled ozone on Mars using ACS and NOMAD data
No full textInternational audienceThe photochemistry of ozone in the Martian atmosphere is generally considered to be well understood. Ozone forms through a three-body reaction involving O and O₂, both products of CO₂ photolysis, and it is destroyed by odd-hydrogen species (HOₓ) generated from water vapour photolysis, which helps to explain the observed anticorrelation between ozone and water vapour [1,2]. However, current photochemical models cannot reproduce ozone observations from various missions (e.g., Trace Gas Orbiter (TGO), Mars Express), with models generally suffering from a negative bias [2,3]. This discrepancy highlights gaps in our knowledge of the photochemical links between odd-oxygen (Oₓ), odd-hydrogen, and water vapour in the Martian atmosphere. A recent study investigated different factors that could influence the ozone content and concluded that the underestimation of ozone in the MPCM might be due to heterogeneous uptake of HOₓ species on water ice clouds or an overestimation of HOₓ photochemistry efficiency in the model [2].We build on that explorative study and use the latest configuration of the Mars Planetary Climate Model (MPCM) with initial conditions from the Mars Climate Database (MCD) v6.1 [4] to investigate how different parameters could influence the ozone vertical profiles. We study data collected in MYs 34 and 35, including Ox, HOx, CO, and water vapour retrievals from the ACS (Atmospheric Chemistry Suite) and NOMAD (Nadir and Occultation for MArs Discovery) instruments aboard TGO. This approach allows us to examine any altitude-dependent changes in chemistry. We will present the results from a systematic investigation into the impact of various assumed model parameters, e.g., absorption cross sections, reaction rates, and heterogeneous chemistry, on these species. We will also consider the impact of introducing new chemistry into the model, e.g., chlorine photochemistry that was recently implemented in the MPCM by Benne et al. (2025) (in review). We will conclude our presentation by highlighting the parameters with the greatest impact on model ozone, the interactions and variations of ozone and its precursors across the two MYs, and prioritising the future research required to bridge the gap between model and observed Martian ozone
Homogeneous nucleation on Mars. An unexpected process that deciphers mysterious elongated clouds
No full textInternational audienceHomogeneous nucleation has not been considered a possibility in cloud formation processes in the atmosphere of Mars (e.g. Clancy et al., 2017), since Määttänen et al. (2005) made a careful analysis that indicated that extreme supersaturations in the order of 10⁵ were required. Such extreme supersaturations were considered unlikely, especially because the abundant dust in the atmosphere of Mars was expected to deplete water in excess of saturation very quickly by heterogeneous nucleation.The Arsia Mons Elongated Cloud (AMEC) is an eye-catching and mysterious cloud occurring recurrently every morning during the perihelion season over the Arsia Mons volcano on Mars (Hernández-Bernal et al., 2021). It shows a peculiar elongated shape that in only 3 hours expands up to 1800 km from its origin point. Hernández-Bernal et al. (2022) investigated this cloud based on the LMD Mars Mesoscale model (Spiga and Forget, 2009). The tail of the cloud was not reproduced in the model, but a cold pocket with temperatures down to 30K below the environment and supersaturation up to 105 appeared next to Arsia Mons, in a position, altitude, and local time and season coincident with the origin point of the AMEC in observations. In this work we show that these are conditions conducive to homogeneous nucleation, and when we introduce this process as a new cloud formation process in the LMD Mars Mesoscale model, we obtain a good representation of the AMEC, and its long tail.This provides an excellent explanation for this mysterious cloud and shows that homogeneous nucleation is possible and can have significant effects in the atmosphere of Mars, contrary to the widespread assumptions during the last twenty years of Mars exploration. The finding of supersaturations up to 108 in the surveys performed by Fedorova et al. (2020; 2023) observationally supports that these extreme supersaturations can indeed happen in the atmosphere of Mars and homogeneous nucleation could be happening in other clouds. As a first example, we find that the Perihelion Cloud Trails (Clancy et al., 2009; 2021) could be the result of homogeneous nucleation, as our mesoscale model also predicts cold pockets spatially coincident with locations where Clancy et al. observed cloud trails. We intend to explore these and other clouds on Mars possibly involving homogeneous nucleation
Mars water cycle: an 11 Mars year climatology of water vapor by SPICAM on Mars Express
No full textInternational audienceWater vapor has long been a key target in Martian exploration, as its detection confirmed the existence of an active water cycle driven by dynamic exchanges between surface ice reservoirs and the atmosphere. Since its first spectroscopic identification in 1963, ongoing observations—most notably from orbiting spacecraft—have significantly advanced our understanding of the spatial and temporal behavior of water on Mars.In this study, we present a comprehensive climatology of water vapor column abundances spanning 11 Martian years (MY), derived from observations by the Spectroscopy for the Investigation of the Characteristics of the Atmosphere of Mars (SPICAM) instrument aboard the European Space Agency’s Mars Express mission [1]. Operating in nadir, SPICAM measures the near-infrared sunlight reflected from the Martian surface and atmosphere, providing daytime water vapor data with broad seasonal and latitudinal coverage. However, due to its reliance on solar illumination, SPICAM is unable to probe the polar night, where water vapor is predicted to be extremely scarce and mostly below the instrument’s detection threshold.Despite the limitations imposed by the orbital configuration of Mars Express—which results in uneven spatial and temporal coverage—SPICAM has successfully monitored the Martian atmosphere across nearly all seasons and latitudes during local daytime conditions. This long-term dataset offers a unique opportunity to study interannual variability in the water cycle, including responses to major atmospheric perturbations.Our climatology includes two Martian years that experienced Global Dust Events (GDEs), allowing us to conduct a preliminary assessment of how such planet-encircling storms impact water vapor distribution. We also perform cross-comparisons with water vapor datasets from other past and ongoing missions, addressing a long-standing challenge in reconciling inter-mission measurements.To enhance the completeness of the climatology, we apply the kriging method—a well-established geostatistical interpolation method based on Gaussian process regression—to estimate water vapor values in regions and seasons with sparse coverage. This gap-filling enables a more continuous picture of the Martian water cycle and facilitates the analysis of year-to-year variability.Finally, by averaging over the full 11-MY dataset, we construct a reference annual cycle of water vapor on Mars, which serves as a baseline for future comparisons, model validation, and the identification of anomalous behavior.To further improve the accuracy and vertical sensitivity of water vapor retrievals, we also incorporate results from a synergistic retrieval approach developed by [2] and [3] This method combines simultaneous nadir-pointing observations from SPICAM (in the near-infrared) and the Planetary Fourier Spectrometer (PFS, in the thermal infrared), both aboard Mars Express. Individually, each instrument is sensitive to different portions of the atmospheric column—SPICAM to the lower atmosphere under illuminated conditions, and PFS to higher altitudes through thermal emission. When used together in a joint retrieval framework, they offer a more complete and vertically constrained view of water vapor distribution than either instrument alone.The synergy method thus yields more accurate water vapor column abundances and enables the first nadir-based estimates of vertical partitioning of water vapor—an aspect traditionally inaccessible to single-instrument nadir retrievals. The resulting composite dataset, which spans almost the entire SPICAM survey, has proven to be highly robust and serves as an important reference for climatological studies. Notably, the synergy also reveals significant discrepancies with predictions from the Mars Climate Database, especially in the northern hemisphere during summer, highlighting potential limitations in current models of water vapor transport and vertical confinement.Finally, in addition to nadir observations, SPICAM also conducted measurements in solar occultation mode [4], which allowed the retrieval of vertical profiles of water vapor at high vertical resolution (~1–2 km), primarily during the twilight terminator. These observations complement the nadir dataset by providing a window into the vertical structure of water vapor in the lower and middle atmosphere (typically from 10 to 70 km), including its diurnal variations and seasonal evolution. Solar occultation data are especially valuable in characterizing the hygropause altitude, tracking the seasonal ascent and descent of water vapor, and capturing sharp vertical gradients during northern summer, when water transport to high altitudes is most active.This work not only contributes to a more detailed understanding of Mars’ water cycle dynamics but also provides critical observational constraints for atmospheric models and climate evolution studies