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Storms and convection on Uranus and Neptune: impact of methane abundance revealed by a 3D cloud-resolving model
No full textInternational audienceContext. Uranus and Neptune have atmospheres dominated by molecular hydrogen and helium. In the upper troposphere (between 0.1 and 10 bars), methane is the third main molecule and condenses, yielding a vertical gradient in CH 4 . This condensable species being heavier than H 2 and He, the resulting change in mean molecular weight due to condensation comes as a factor countering convection, traditionally considered as ruled by temperature only. It makes both dry and moist convection more difficult to start. As observations also show latitudinal variations in methane abundance, one can expect different vertical gradients from one latitude to another. Aims. In this paper, we investigate the impact of this methane vertical gradient and the different shapes it can take, on the atmospheric regimes, especially on the formation and inhibition of moist convective storms in the troposphere of ice giants. Methods. We develop a 3D cloud-resolving model to simulate convective processes at the required scale. This model is nonhydrostatic and includes the effect of the mean molecular weight variations associated with condensation. Results. Using our simulations, we conclude that typical velocities of dry convection in the deep atmosphere are rather low (of the order of 1 m/s) but sufficient to sustain upward methane transport, and that moist convection at methane condensation level is strongly inhibited. Previous studies derived an analytical criterion on the methane vapor amount above which moist convection should be inhibited in saturated environments. In ice giants, this criterion yields a critical methane abundance of 1.2% at 80 K (this corresponds approximately to the 1 bar level). We first validate this analytical criterion numerically. We then show that this critical methane abundance governs the inhibition and formation of moist convective storms, and we conclude that the intensity and intermittency of these storms should depend on the methane abundance and saturation. -In the regions where CH 4 exceeds this critical abundance in the deep atmosphere (at the equator and the middle latitudes on Uranus, and all latitudes on Neptune), a stable layer almost entirely saturated with methane develops at the condensation level. In this layer, moist convection is inhibited, ensuring stability. Only weak moist convective events can occur above this layer, where methane abundance becomes lower than the critical value. The inhibition of moist convection prevents strong drying and maintains high relative humidity, which favors the frequency of these events. -In the regions where CH 4 remains below this critical abundance in the deep atmosphere (possibly at the poles on Uranus), there is no such layer. More powerful storms can form, but they are also a bit rarer. Conclusions. In ice giants, dry convection is weak, and moist convection is strongly inhibited. However, when enough methane is transported upwards, through dry convection and turbulent diffusion, sporadic moist convective storms can form. These storms should be more frequent on Neptune than on Uranus, because of Neptune's internal heat flow and larger methane abundance. Our results can explain the observed sporadicity of clouds in ice giants and can help us guide future observations to test the conclusions of this work
Winter climate preconditioning of summer vegetation extremes in the Northern Hemisphere
No full textInternational audienceThe impact of the spring climate on the Northern Hemisphere's summer vegetation activity and extremes has been extensively researched, but less attention has been devoted to whether and how the winter climate may additionally influence vegetation extremes in the summer. Here, we provide insights into the influence of winter temperature and precipitation on summer vegetation extremes in the Northern Hemisphere. To do this, we identify positive and negative extremes in the summer leaf area index (LAI, a proxy for vegetation activity) and assess winter effects on those extremes using logistic regression at the regional scale. Over a quarter of the regions in the Northern Hemisphere show strong winter climate preconditioning on summer LAI extremes, which is typically stronger for croplands than forests. In regions with strong winter preconditioning, the spring LAI mediates the link between winter climate and summer LAI extremes through the ecological memory in seasonal legacy effects. Our findings suggest that extremely low summer LAI in both croplands and forests is preconditioned by colder and drier winters, while extremely high summer LAI in forests is associated with warmer and wetter winters. For low summer LAI in croplands, warmer winters are associated with an increased likelihood of extremes in mid-latitude regions and a reduced likelihood in high-latitude regions. Consideration of winter preconditioning effects may improve our understanding of inter-annual variability of vegetation activity and support agricultural and land management practitioners in anticipating the detrimental effects of winter on crop yields and forest conditions
Évaluation de l’impact des activités urbaines sur le transfert de microplastiques dans l’atmosphère et leur infiltration dans les sols
No full textPlastics have permeated society and are used in all sectors of industry, from packaging to construction to the automotive industry. One consequence of this extensive, unregulated use is the now ubiquitous presence of plastic debris of all sizes in ecosystems. Plastic pollution, and in particular the presence and effects of microplastics in the environment, has been studied since 1972 and has been the focus of increasing scientific interest over the last two decades. Microplastics have been identified in virtually all environments, from marine sediments to mountaintops, While it is considered to be a dominant source of microplastics, the impact of local urban activities on the fate of microplastics in the environment remains poorly understood. This work aims to provide new insights into the relationships between anthropic activities, specifically road traffic, atmospheric deposition of microplastics, and infiltration of microplastics into roadside soils.Firstly, the methodological choices of this PhD are presented with an insight into the current challenges of microplastic quantification in continental environments in the literature. After collection, samples undergo a treatment consisting of density-based separations with NaI and oxidative treatments. The microplastic content of each sample is characterized and quantified using a micro-FTIR imaging analysis, followed by a post-treatment using the open software SiMPle.The impact of urban activities on microplastics in the atmospheric compartment was then addressed. Microplastic bulk atmospheric deposition was measured over 5 campaigns in 4 different sites of interest, with variable levels of urban pressure, including rural and urban sites. Key results were observed, including significantly lower deposition rates in an urban site during a Covid-related national lockdown (median 5.3 MP m-2 d-1) than in a period of normal activity (median 29.2 MP m-2 d-1). When comparing different sites in similar campaigns, higher deposition rates were observed in urban areas than in rural, agricultural sites, suggesting an effect of local activity on depositions. The characteristics of the deposited microplastics also varied with the level and type of activity. Different dominant polymers, and differences in size distribution, were observed.Thirdly, the infiltration of microplastics and tyre and road wear particles into the soil of a biofiltration swale located on the side of a high-traffic highway was quantified. After manually coring soil samples from the biofiltration swale, both microplastics and tyre and road wear particles were quantified using two specialized analytical methodologies. Significantly higher concentrations were measured on the surface than in the deeper samples, with a clear decrease in number of particles and concentration. This suggests the majority of particles were filtered by the soil and remained close to the surface. Despite consisting in different particles with different sources, similar vertical profiles were for tyre wear particles and microplastics, albeit tyre wear particles had significantly higher concentrations than other microplastics (median 2.32 mg g-1 for SBR, against a median of 0.05 mg g-1 for other microplastics in the surface samples).This PhD contributed to the overall understanding of microplastic transfer mechanics and the role of less-studies microplastic transport vectors and reservoirs in urban environments. In particular, it helped highlighting an immediate impact of traffic on microplastic contamination and accumulation.Les matières plastiques sont utilisées dans tous les domaines industriels de l'emballage à la construction, en passant par l'industrie automobile ou l’agriculture. Une conséquence de cette utilisation extensive et non réglementée est la présence ubiquitaire de déchets plastiques de toutes tailles dans les écosystèmes. La pollution plastique, en particulier la présence et les effets des microplastiques dans l'environnement, est étudiée depuis 1972 et suscite un intérêt scientifique croissant depuis les deux dernières décennies. Des microplastiques ont été décris dans pratiquement tous les environnements, des sédiments marins aux sommets de montagnes. Si l’activité urbaine est suspectée d’affecter la production et le devenir des microplastiques dans l'environnement, ses effets exacts restent mal établis. Cette thèse vise à apporter de nouvelles informations sur les relations entre les activités anthropiques, en particulier le trafic routier, et la déposition atmosphérique de microplastiques, ainsi que leur infiltration dans les sols en bordure de route. Tout d'abord, les choix méthodologiques de cette thèse sont présentés au regard de leur ancrage dans la littérature, avec un aperçu des défis actuels pour la quantification des microplastiques dans les environnements continentaux. Après une étape de collecte, les échantillons sont traités par séparation densimétrique à l’aide de NaI, et par digestion oxydative. Les microplastiques de chaque échantillon sont ensuite caractérisés et quantifiés à l’aide d’une analyse par imagerie cartographique micro-IRTF suivie d’un post-traitement par le logiciel logiciel SiMPle. L'impact des activités urbaines sur le transfert de microplastiques dans le compartiment atmosphérique est ensuite abordé. 5 campagnes de suivies des retombées atmosphériques globales ont été réalisées sur 4 sites d'intérêt comprenant des zones urbaines et rurales. Des résultats majeurs ont pu être notés. Tout particulièrement, des taux de déposition significativement plus faibles ont été mesurées dans un site urbain pendant un confinement lié à la covid-19 (médiane de 5,3 MP m-2 j-1) par rapport à une période d'activités normales sur le même site (médiane de 29,2 MP m-2 j-1). Lors de la comparaison de différents sites au cours de campagnes similaires, des taux de déposition plus élevés ont été observés dans les zones urbaines que dans les zones rurales dominées par l'agriculture. Les caractéristiques des microplastiques déposés ont également changé en fonction du niveau et du type d'activité, avec notamment des différences dans les polymères dominants et la distribution des tailles de microplastiques. Troisièmement, l'infiltration de microplastiques et de particules de pneus dans le sol d'une noue filtrante située le long d'une route à fort trafic a été quantifiée. Des échantillons de sol de la noue filtrante ont été manuellement prélevé par carottage, puis leur teneur en microplastiques et en particules de pneus ont été quantifiés à l'aide de deux méthodologies spécialisées. Des concentrations significativement plus élevées ont été mesurées en surface par rapport aux échantillons plus profonds, avec une diminution nette de la concentration suggérant que la majorité des particules ont été filtrées par le sol et sont restées près de la surface. Malgré des particules différentes avec des sources différentes, des profils verticaux similaires ont été observés pour les particules d'usure des pneus et les microplastiques, bien que les particules d'usure des pneus aient des concentrations significativement plus élevées que les autres microplastiques (médiane de 2,32 mg g -1 pour le SBR en surface, contre une médiane de 0,05 mg g -1 pour les autres microplastiques).Ces travaux contribuent à une meilleure compréhension des mécanismes de transfert des microplastiques et du rôle des vecteurs de transport et des réservoirs moins étudiés dans la contamination et l'accumulation des microplastiques dans les environnements urbains
Planetary-Scale Wave Activity in Venus Cloud Layer Simulated by the Venus PCM
No full textInternational audienceThe Venus atmosphere Superrotation (SR) is successfully simulated with the high-resolution (1.25° × 1.25° in longitude and latitude) runs of the Venus Planetary Climate Model (PCM). The results show a clear spectrum and structure of atmospheric waves, primarily with periods of 5.65 and 8.5 days. The simulation reproduces long-term quasi-periodic oscillation of the zonal wind and primary planetary-scale wave seen in observations. These oscillations occur with a period of 163-222 days, although their existence is still debated in observations. The Rossby waves show similarity in wave characteristics and angular momentum (AM) transport due to Rossby-Kelvin instability by comparing the 5.65-day wave in Venus PCM with the 5.8-day wave simulated by AFES-Venus, another Venus General Circulation Model. Similarities are also evident between the 8.5-day wave in Venus PCM and the 7-day wave obtained in AFES-Venus. The long-term variations in the AM budget indicate that the 5.65-day wave is the dominant factor of the oscillation on the SR, and the 8.5-day wave plays a secondary role. When the 5.65-day wave grows, its AM and heat transport are enhanced and accelerate (decelerate) the lower-cloud equatorial jet (cloud-top mid-latitude jets). Meanwhile, the 8.5-day wave weakens, reducing its deceleration effect on the lower-cloud equator. This further suppresses the meridional gradient of the background wind and weakens instability, leading to the decay of the 5.65-day wave. And vice versa when the 5.65-day wave decays
New Routine Nlte15Μmcool-E V1.0 For Calculating The Non-Local Thermodynamic Equilibrium (Non-Lte) Co2 15 Μm Cooling In General Circulation Models (Gcms) Of Earth'S Atmosphere
No full textInternational audienceWe present a new routine for calculating the non-local thermodynamic equilibrium (non-LTE) 15 µm CO2 cooling-heating of mesosphere and lower thermosphere in general circulation models. It uses the optimized models of the non-LTE in CO2 for day and night conditions and delivers cooling-heating with an error not exceeding 1 K d-1 even for strong temperature disturbances. The routine uses the accelerated lambda iteration and opacity distribution function techniques for the exact solution of the non-LTE problem and is about 1000 times faster than the standard matrix and line-by-line solution. It has an interface for feedbacks from the model and is ready for implementation. It may use any quenching rate coefficient of the CO2(ν2)+O(3P) reaction, handles large variations in O(3P), and allows the user to vary the number of vibrational levels and bands to find a balance between the calculation speed and accuracy. The suggested routine can handle the broad variation in CO2 both below and above the current volume mixing ratio, up to 4000 ppmv. This allows the use of this routine for modeling Earth's ancient atmospheres and the climate changes caused by increasing CO2
Polar Low Circulation Enhances Greenland's West Coast Cloud Surface Warming
No full textInternational audienceMass loss of the Greenland Ice Sheet (GrIS) plays a major role in the global sea level rise. The west coast of the GrIS has contributed 1,000 Gt of the 4,488 Gt GrIS mass loss between 2002 and 2021, making it a hotspot for GrIS mass loss. Surface melting is driven by changes in the radiative budget at the surface, which are modulated by clouds. Previous works have shown the impact of North Atlantic transport for influencing cloudiness over the GrIS. Here we used space-based lidar cloud profile observations to show that a polar low circulation promotes the presence of low clouds over the GrIS west coast that warm radiatively the GrIS surface during the melt season. Polar low circulation transports moisture and low clouds from the sea to the west of Greenland up over the GrIS west coast through the melt season. The concomitance of the increasing presence of low cloud in fall over the Baffin Sea due to seasonal sea-ice retreat and a maximum occurrence of Polar low circulation in September results in a maximum of low cloud fraction (∼14% at 2.5 km above sea level) over the GrIS west coast in September. These low clouds warm radiatively the GrIS west coast surface up to 80 W/m2 locally. This warming contributes to an average increase of 10 W/m2 of cloud surface warming in September compared to July on the GrIS west coast. Overall, this study suggests that regional atmospheric processes independent from North Atlantic transport may also influence the GrIS melt
Knowledge Gaps in Quantifying the Climate Change Response of Biological Storage of Carbon in the Ocean
No full textInternational audienceThe ocean is responsible for taking up approximately 25% of anthropogenic CO2 emissions and stores >50 times more carbon than the atmosphere. Biological processes in the ocean play a key role, maintaining atmospheric CO2 levels approximately 200 ppm lower than they would otherwise be. The ocean's ability to take up and store CO2 is sensitive to climate change, however the key biological processes that contribute to ocean carbon storage are uncertain, as are how those processes will respond to, and feedback on, climate change. As a result, biogeochemical models vary widely in their representation of relevant processes, driving large uncertainties in the projections of future ocean carbon storage. This review identifies key biological processes that affect how ocean carbon storage may change in the future in three thematic areas: biological contributions to alkalinity, net primary production, and interior respiration. We undertook a review of the existing literature to identify processes with high importance in influencing the future biologically-mediated storage of carbon in the ocean, and prioritized processes on the basis of both an expert assessment and a community survey. Highly ranked processes in both the expert assessment and survey were: for alkalinity—high level understanding of calcium carbonate production; for primary production—resource limitation of growth, zooplankton processes and phytoplankton loss processes; for respiration—microbial solubilization, particle characteristics and particle type. The analysis presented here is designed to support future field or laboratory experiments targeting new process understanding, and modeling efforts aimed at undertaking biogeochemical model development
Surface Cloud Warming Increases as Late Fall Arctic Sea Ice Cover Decreases
No full textInternational audienceDuring the Arctic night, clouds regulate surface energy budgets through longwave warming alone. During fall, any increase in low-level clouds will increase surface cloud warming and could potentially delay sea ice formation. While an increase in clouds due to fall sea ice loss has been observed, quantifying the surface warming is observationally challenging. Here, we use a new observational data set of surface cloud warming at instantaneous 330 m × 90 m spatial resolution. By instantaneously co-locating surface cloud warming and sea ice observations in regions where sea ice varies, we find October large surface cloud warming values (>80 W m−2) are much more frequent (∼+50%) over open water than over sea ice. Notably, in November large surface cloud warming values (>80 W m−2) occur more frequently (∼+200%) over open water than over sea ice. These results suggest more surface warming caused by low-level opaque clouds in the future as open water persists later into the fall
The Amazon plume in 2020-2023: its shelf carbon budget and water origin revisited
No full textInternational audienceThe Amazon shelf of South America is known to be highly contrasted in its surface carbon dioxide concentrations, from very high concentrations near the estuary, and very low concentrations downstream in the saltier Amazon plume, which results in a great contrast in carbon dioxide exchange with the atmosphere. During three cruises in 2020-2023 (Eurec4A-OA, Tara-Microbiomes legs 5, 6 and 7, Amaryllis), dissolved inorganic carbon (DIC) concentration, its isotopic composition (δ13C-DIC), the water isotopic composition (d18O-H2O and d2H-H2O), as well as inorganic nutrients and surface CO2 partial pressure (pCO2) were measured on the Amazon shelf of South America during three cruises in different seasons. These data are used to better understand mixing in the continuum between river water and open-ocean waters, and the biogeochemical processes taking place on the shelf close to the Amazon and Para river estuaries. The water isotopes are furthermore used to identify different freshwater origins.The accuracy of the data is discussed as well as its representativeness. The data are then combined to first identify large variations of the river freshwater sources, compatible with 2021 being a year of very large discharge, and 2023 a year of exceptional low discharge. In addition, the data mostly from August and September 2021 identify a smaller influence of sources and sinks of dissolved inorganic carbon in the mixing shelf region than what had been earlier observed during the Amasseds cruise data in November-December 1991, a much lower river discharge period. This indicates that there might be a larger seasonal and/or interannual variability of these processes than what was earlier assessed. Measured pCO2 data on the Amazon shelf in 2021 are then discussed in this context
Comment les retraités façonnent la structure sociale des villes françaises?
No full textInternational audienceLes recherches sur la structure sociale des villes françaises tiennent rarement compte de la population retraitée, dont le poids démographique est pourtant croissant. En l’intégrant à l’analyse, cette enquête offre une image renouvelée de la ségrégation des aires urbaines hexagonales