Seasonality of the particle number concentration and size distribution : a global analysis retrieved from the network of Global Atmosphere Watch (GAW) near-surface observatories

Aerosol particles are a complex component of the atmospheric system which influence climate directly by interacting with solar radiation, and indirectly by contributing to cloud formation. The variety of their sources, as well as the multiple transformations they may undergo during their transport (including wet and dry deposition), result in significant spatial and temporal variability of their properties. Documenting this variability is essential to provide a proper representation of aerosols and cloud condensation nuclei (CCN) in climate models. Using measurements conducted in 2016 or 2017 at 62 ground-based stations around the world, this study provides the most up-to-date picture of the spatial distribution of particle number concentration (N-tot) and number size distribution (PNSD, from 39 sites). A sensitivity study was first performed to assess the impact of data availability on N-tot's annual and seasonal statistics, as well as on the analysis of its diel cycle. Thresholds of 50% and 60% were set at the seasonal and annual scale, respectively, for the study of the corresponding statistics, and a slightly higher coverage (75 %) was required to document the diel cycle. Although some observations are common to a majority of sites, the variety of environments characterizing these stations made it possible to highlight contrasting findings, which, among other factors, seem to be significantly related to the level of anthropogenic influence. The concentrations measured at polar sites are the lowest (similar to 10(2) cm(-3)) and show a clear seasonality, which is also visible in the shape of the PNSD, while diel cycles are in general less evident, due notably to the absence of a regular day-night cycle in some seasons. In contrast, the concentrations characteristic of urban environments are the highest (similar to 10(3)-10(4) cm(-3)) and do not show pronounced seasonal variations, whereas diel cycles tend to be very regular over the year at these stations. The remaining sites, including mountain and non-urban continental and coastal stations, do not exhibit as obvious common behaviour as polar and urban sites and display, on average, intermediate N-tot (similar to 10(2)-10(3) cm(-3)). Particle concentrations measured at mountain sites, however, are generally lower compared to nearby lowland sites, and tend to exhibit somewhat more pronounced seasonal variations as a likely result of the strong impact of the atmospheric boundary layer (ABL) influence in connection with the topography of the sites. ABL dynamics also likely contribute to the diel cycle of N-tot observed at these stations. Based on available PNSD measurements, CCN-sized particles (considered here as either >50 nm or >100 nm) can represent from a few percent to almost all of N-tot, corresponding to seasonal medians on the order of similar to 10 to 1000 cm(-3), with seasonal patterns and a hierarchy of the site types broadly similar to those observed for N-tot. Overall, this work illustrates the importance of in situ measurements, in particular for the study of aerosol physical properties, and thus strongly supports the development of a broad global network of near surface observatories to increase and homogenize the spatial coverage of the measurements, and guarantee as well data availability and quality. The results of this study also provide a valuable, freely available and easy to use support for model comparison and validation, with the ultimate goal of contributing to improvement of the representation of aerosol-cloud interactions in models, and, therefore, of the evaluation of the impact of aerosol particles on climate.Peer reviewe

How to obtain ocean turbulent dynamics at super resolution from optimal multiresolution analysis and multiplicative cascade?

International audienceA fundamental challenge in oceanography is the synoptic determination of ocean circulation using the data acquired from space, with a coherent depiction of its turbulent characteristics. This determination has the potential of revealing all aspects of the ocean dynamic variability on a wide range of spatio-temporal scales and will enhance our understanding of ocean–atmosphere exchanges at super resolution, as required in the present context of climate change. A method to obtain ocean dynamics products at different super resolutions is presented here, using an approximation of the energy cascade, expressed in a microcanonical formulation, and associated to turbulent signals provided by different products of Sea Surface Temperature (SST). The basics idea is to propagate across the scales motion information at lower resolution coming from GEKCO product [Sudre et al., 2013] in a multiresolution analysis computed on adimensional critical transition informations [Su-dre et al., 2015].REFERENCESSudre J., Maes C., and Garc ̧on V., 2013, On the global estimates of geostrophic and Ekman surface currents, Limnology and Oceanography: Fluids and Environments, vol. 3, pp. 1–20, DOI 10.1215/21573689-2071927.Sudre J., Yahia H., Pont O. and Garc ̧on V., 2015, Ocean turbulent dynamics at Superresolution from optimal multiresolution analysis and multiplicative cascade, IEEE transaction on geoscience and remote sensing, vol. 53, NO. 11, DOI 10.1109/TGRS.2015.2436431

Genesis of a florencite-bearing kaolin deposit on ordovician schists at Saint-Aubin-des-Châteaux, Armorican Massif, France

International audienceSeveral kaolinite occurrences of economic interest have been reported in Europe and are usually interpreted as resulting from weathering during the Paleogene tropical climate. However, a hydrothermal contribution is also recognized in some kaolinite occurrences. Such occurrences are common throughout the Hercynian Armorican Massif, where they are developed mostly on granitoids. The kaolin deposit of the Tertre Rouge pit, South Brittany (France), has been mined for the past 70 years. It is the only deposit developed from carbon-rich (~1% C) Ordovician schists affected by a low-grade metamorphic event during the late Hercynian orogeny. Herein, we report the results of a detailed field and petrological study combining optical microscopy with SEM investigation, XRD analyses, and ICP-OES and ICPMS geochemical data. A typical weathering profile was identified in the pit. It is marked from the bottom to the top by an increasing kaolinite volume (~45%) at the expense of muscovite/illite, a decreasing volume of chlorite and graphite, and numerous occurrences of Fe oxides/oxyhydroxides that replaced former pyrites or sulfates in veins. Despite this intense weathering, the analyzed Tertre Rouge schists preserved a black shale bulk chemical composition characterized by lithophile trace elements contents at 2× to 5× the Upper Continental Crust composition. This was made possible by accessory minerals inherited from the parent rock, especially Al phosphates, namely florencite (Ce), which were systematically identified as the main concentrators of LREE and Sr. Their occurrence in the Tertre Rouge kaolinized schist confirms the regional Sr and P geochemical anomalies previously reported in the Paleozoic sedimentary formations in this area of the Armorican Massif. High temperature clay minerals, pyrophyllite (>270 °C) and nacrite/dickite (generally considered to be high-T kaolinite polymorphs), were also identified inside the weathered zone, filling millimeter-thick veinlets cutting across or lying parallel to the cleavage plane S of the schist. We ascribe this high-temperature clay mineral assemblage to a hydrothermal event related to the numerous documented evidences of Late Hercynian fluid circulations in Central/South Armorican tectonometamorphic domains. Hence, we strongly favor a two-stage formation for the Tertre Rouge kaolin deposit, including a minor hydrothermal contribution to weathering-related kaolinite

Inferring fluid motion at submesoscale from high resolution remotely sensed data

OSTST meeting 2011 http://depts.washington.edu/uwconf/ostst2011/OSTST_Program_2011.pdfInternational audienc

Optimal decomposition for the evaluation of ocean dynamics

International audienceThe dynamics of the ocean flow are governed by the cascade process where the energy is injected in the system at the largest scale and dissipated at viscous scale. In between, the energy crosses all the intermediary scales and is responsible for the creation of oceanographic structures at different scales. To obtain the motion field of ocean dynamics [1] at the high resolution of Sea Surface Temperature (SST) Modis data (spatial resolution : 4 km) using one single image, we associate the Microcanonical Multiscale Formalism (MMF) [2] and the Microcanonical Cascade (MC) which represent these processes where the energy is transferred from scale to scale [3]. To link two different scales (or, in a remote sensing context, the same image at two different resolutions), the MC requires the exact determination of an optimal wavelet which separates completely the Multiscale Operator and the wavelet transform at the highest resolution. This exact determination of the optimal wavelet for a given dataset is difficult and there is no systematic algorithm to find it. Our goal is to best approximate the optimal wavelet for SST data by using Q-test [4]. References [1] H. Yahia, J. Sudre, C. Pottier and V. Garçon, 2010, Motion analysis in oceanographic satellite images using multiscale methods and the energy cascade, Pattern Recognition, DOI: 10.1016/J.patcog.2010.04.011 [2] A. Turiel, H. Yahia and C. Perez-Vicente, 2008 Microcanonical Multifractal Formalism: a geometrical approach to multifractal systems. Part I: Singularity Analysis, Journal of Physics A 41:015501. [3] C. Pottier, A. Turiel, V. Garçon, 2008, Inferring missing data in satellite chlorophyll maps using turbulent cascading, Remote Sensing of Environment, 112,4242-4260, 10.1016/j.rse.2008.07.010 [4] O. Pont, A Microcanonical cascade formalism for multifractal systems ans its application to data inference and forecasting. PhD thesis, Dept. of Fundamental Physics, University of Barcelona, 200

Comparison of two remote sensing methods for the evaluation of ocean dynamics

International audienceThe dynamics of the ocean flow are governed by the cascade process where the energy is injected in the system at the largest scale and dissipated at viscous scale. In between, the energy crosses all the intermediary scales and is responsible for the creation of oceanographic structures at different scales. To obtain the motion field of ocean dynamics [1] at the high resolution of Sea Surface Temperature (SST) Modis data (spatial resolution : 4 km) using one single image, we associate the Microcanonical Multiscale Formalism (MMF) [2] and the Microcanonical Cascade (MC) which represent these processes where the energy is transferred from scale to scale [3]. To link two different scales (or, in a remote sensing context, the same image at two different resolutions), the MC requires the exact determination of an optimal wavelet which separates completely the Multiscale Operator and the wavelet transform at the highest resolution. This exact determination of the optimal wavelet for a given dataset is difficult and there is no systematic algorithm to find it. Our goal is to best approximate the optimal wavelet for SST data by using Q-test [4]. References [1] H. Yahia, J. Sudre, C. Pottier and V. Garçon, 2010, Motion analysis in oceanographic satellite images using multiscale methods and the energy cascade, Pattern Recognition, DOI: 10.1016/J.patcog.2010.04.011 [2] A. Turiel, H. Yahia and C. Perez-Vicente, 2008 Microcanonical Multifractal Formalism: a geometrical approach to multifractal systems. Part I: Singularity Analysis, Journal of Physics A 41:015501. [3] C. Pottier, A. Turiel, V. Garçon, 2008, Inferring missing data in satellite chlorophyll maps using turbulent cascading, Remote Sensing of Environment, 112,4242-4260, 10.1016/j.rse.2008.07.010 [4] O. Pont, A Microcanonical cascade formalism for multifractal systems ans its application to data inference and forecasting. PhD thesis, Dept. of Fundamental Physics, University of Barcelona, 200

Comparison of two remote sensing methods for the evaluation of ocean dynamics

International audienceThe dynamics of the ocean flow are governed by the cascade process where the energy is injected in the system at the largest scale and dissipated at viscous scale. In between, the energy crosses all the intermediary scales and is responsible for the creation of oceanographic structures at different scales. To obtain the motion field of ocean dynamics [1] at the high resolution of Sea Surface Temperature (SST) Modis data (spatial resolution : 4 km) using one single image, we associate the Microcanonical Multiscale Formalism (MMF) [2] and the Microcanonical Cascade (MC) which represent these processes where the energy is transferred from scale to scale [3]. To link two different scales (or, in a remote sensing context, the same image at two different resolutions), the MC requires the exact determination of an optimal wavelet which separates completely the Multiscale Operator and the wavelet transform at the highest resolution. This exact determination of the optimal wavelet for a given dataset is difficult and there is no systematic algorithm to find it. Our goal is to best approximate the optimal wavelet for SST data by using Q-test [4]. References [1] H. Yahia, J. Sudre, C. Pottier and V. Garçon, 2010, Motion analysis in oceanographic satellite images using multiscale methods and the energy cascade, Pattern Recognition, DOI: 10.1016/J.patcog.2010.04.011 [2] A. Turiel, H. Yahia and C. Perez-Vicente, 2008 Microcanonical Multifractal Formalism: a geometrical approach to multifractal systems. Part I: Singularity Analysis, Journal of Physics A 41:015501. [3] C. Pottier, A. Turiel, V. Garçon, 2008, Inferring missing data in satellite chlorophyll maps using turbulent cascading, Remote Sensing of Environment, 112,4242-4260, 10.1016/j.rse.2008.07.010 [4] O. Pont, A Microcanonical cascade formalism for multifractal systems ans its application to data inference and forecasting. PhD thesis, Dept. of Fundamental Physics, University of Barcelona, 200

Evidencing of multiplicative cascading and intermittency in real/synthetic oceanographic signals: application to the evaluation of ocean dynamics

International audienceMost existing methods in analyzing motion in Computer Vision do not take into account key features of ocean dynamics: turbulence and intermittency, which contribute importantly to the shape and motion of observed and acquired coherent structures. Besides, the specificities of these remotely sensed acquisitions (Sea Surface Temperature, chlorophyll a concentration) lead to question the pertinence of existing Computer Vision approaches to analyze motion in these types of image sequences. To compute the motion field at high resolution associating the Microcanonical Multiscale Formalism (MMF) [1] and the Microcanonical Cascade (MC) [2], one needs to give prominence to the intermittency and cascade properties observed in SST Modis data and/or synthetic signals from an ocean model. We propose here to evaluate the ocean dynamics with respect to intermittency/cascading properties evaluation for data acquired by satellites or synthetic data coming from a simulation model. We then apply the combination of MMF and MC to obtain high resolution (4km) motion fields [3]. References [1] A. Turiel, H. Yahia and C. Perez-Vicente, 2008 Microcanonical Multifractal Formalism: a geometrical approach to multifractal systems. Part I: Singularity Analysis Journal of Physics A 41:015501. [2] C. Pottier, A. Turiel, V. Garçon, 2008, Inferring missing data in satellite chlorophyll maps using turbulent cascading, Remote Sensing of Environnement, 112,4242-4260, 10.1016/j.rse.2008.07.010 [3] H. Yahia, J. Sudre, C. Pottier and V. Garçon, 2010, Motion analysis in oceanographic satellite images using multiscale methods and the energy cascade, Pattern Recognition, DOI: 10.1016/J.patcog.2010.04.01

Validation of high and super resolution ocean dynamics products

International audienceIn this work we present the validation of two products showing ocean dynamics at high resolution. The first one is calculated from a combination of geostrophic currents derived from satellite absolute dynamic topography, and blended wind driven currents following the methodology proposed by Sudre et al. (2013) [1]. The second ocean dynamics product at super resolution (1/24°) is established on an approximation of the energy cascade, expressed in a microcanonical formulation, and associated to turbulent signal provided by SST MODIS-Aqua product at 1/24° [2]. The basic idea is to use optimal cascading to decrease the spatial resolution of SST MODIS-Aqua product at 1/24°, then use the motion information available at lower resolution coming from the first product just described , transmit that information along the scales back to higher spatial resolution using the cascade to obtain a 1/24° resolution motion field [3]. These two products are validated with drifters drogued at 15-m depth from the Global Drifter Program at AOML and other in-situ currents products. [1]J. Sudre, C. Maes, and V. Garçon, 2013, On the global estimates of geostrophic and Ekman surface currents, Limnology and Oceanography: Fluids and Environments, vol. 3, pp. 1-20, DOI 10.1215/21573689-2071927. [2]H. Yahia, J. Sudre, C. Pottier and V. Garçon, 2010, Motion analysis in oceanographic satellite images using multiscale methods and the energy cascade, Pattern Recognition, DOI: 10.1016/J.patcog.2010.04.011. [3]J. Sudre, H. Yahia, V. Garçon, O. Pont, and C. Pottier, Ocean turbulent dynamics at super resolution: A true picture, in prep