Division Technique de I'INSU

The Mw 7.7 2007 November 14 earthquake had an epicentre located close to the city of Tocopilla, at the southern end of a known seismic gap in North Chile. Through modelling of Global Positioning System (GPS) and radar interferometry (InSAR) data, we show that this event ruptured the deeper part of the seismogenic interface (30-50 km) and did not reach the surface. The earthquake initiated at the hypocentre and was arrested 150 km south, beneath the Mejillones Peninsula, an area already identified as an important structural barrier between two segments of the Peru-Chile subduction zone. Our preferred models for the Tocopilla main shock show slip concentrated in two main asperities, consistent with previous inversions of seismological data. Slip appears to have propagated towards relatively shallow depths at its southern extremity, under the Mejillones Peninsula. Our analysis of post-seismic deformation suggests that small but still significant post-seismic slip occurred within the first 10 d after the main shock, and that it was mostly concentrated at the southern end of the rupture. The post-seismic deformation occurring in this period represents 12-19 per cent of the coseismic deformation, of which 30-55 per cent has been released aseismically. Postseismic slip appears to concentrate within regions that exhibit low coseismic slip, suggesting that the afterslip distribution during the first month of the post-seismic interval complements the coseismic slip. The 2007 Tocopilla earthquake released only 2.5 per cent of the moment deficit accumulated on the interface during the past 130 yr and may be regarded as a possible precursor of a larger subduction earthquake rupturing partially or completely the 500-km-long North Chile seismic gap.

A fCO 2 sensor, based on a colorimetric method used for the CARIOCA buoys, has been installed on a Pilot Research Moored Array in the Tropical Atlantic (PIRATA) mooring at 6°S, 10°W, in the gulf of Guinea, in June 2006 during the EGEE 3 cruise. Hourly fCO 2 data recorded from June to December 2006 are presented. An alkalinity‐salinity relationship has been determined using data from different cruises, which allows the calculation of dissolved inorganic carbon. Although the tropical Atlantic is an important source of CO 2 , an unexpected area of low CO 2 concentrations is observed in the South Equatorial Counter Current with fCO 2 values close to equilibrium conditions or even slightly undersaturated with respect to the atmospheric fCO 2 value of 367.7 μ atm measured during the cruise. At the end of June, an increase of seawater fCO 2 to 400 μ atm is consistent with the beginning of the upwelling season occurring from July to September. Although the mooring is not located within the upwelling area, the spreading of the cold tongue explains the large CO 2 outgassing. The monthly CO 2 flux ranges from 1.19 mmol m −2 d −1 in June to a maximum of 8.37 mmol m −2 d −1 in October, when high fCO 2 values above 420 μ atm are maintained by the warming of surface water. Most of the fCO 2 distribution can be explained by physical processes and a strong relationship between fCO 2 and SST is determined for the upwelling season. From mid‐September, diurnal cycles can be detected. Using a dissolved inorganic carbon budget, periods where net community production or diurnal warming and cooling dominates are observed.

. The main features of the developed lidar instruments and first results are presented here.

Turbulent fluxes at the air‐sea interface were estimated in the framework of the African Monsoon Multidisciplinary Analysis (AMMA) international program. A specific flux measurement mast was designed so as to minimize aerodynamic flow distortion and vibrations. The mast was installed on the research vessel Atalante that cruised in the Gulf of Guinea during the onset of the African monsoon, in June–July 2006. Turbulent fluxes were calculated with an eddy covariance method and with a spectral method. Calculation of eddy correlation fluxes required a correction of flow distortion at turbulent scales, which was performed with a new statistical technique. Application of the spectral flux calculation method revealed that an imbalance term was required, in agreement with results from earlier experiments, and indicated that the value of the Kolmogorov constant (0.55) should not be modified. Bulk exchange coefficients calculated are in good agreement with earlier parameterizations in medium wind conditions.

Abstract This paper describes a fast method for estimation of dense 2D and 3D displacement fields from image correlation. It is based on a previously published local, or window‐based, optical flow algorithm which is ideally suited for parallel processors. We describe the algorithm, its extension to stereo image correlation and its implementation on Graphical Processing Unit (GPU). We present the properties of the estimated displacement fields on simulated images and evaluate their accuracy on real data from a rigid body movement experiment. The main features of the method are a dense output (i.e. a 2D or 3D displacement vector per pixel) and a highly parallel structure which allows very high computational performance. A pair of 4 megapixels stereoscopic images is processed in less than 0.2 s. on a Titan GPU. Finally, we present and comment several experimental results obtained with the proposed method during mechanical experiments conducted at ONERA.

The COAST-HF-MAREL-Iroise buoy is a scientific plateform to monitor at high frequency (subhourly) and for long term (since 2000) the coastal ecosystem of the Bay of Brest, which is impacted by both continental and Iroise Sea inputs.This buoy is a part of the national observation network COAST-HF - COAstal ocean observing system-HighFrequency (http://www.coast-hf.fr) from the ILICO research infrastructure (https://www.ir-ilico.fr) and is property of IUEM (Institut Universitaire Européen de la Mer) and Ifremer. The buoy is moored at 200 m of the coast at the outlet of the Bay of Brest where manual sampling is also performed for the weekly observation network SOMLIT-Portzic (https://www.somlit.fr/). Both data base are complementary so that manual data are used to qualify and/or correct buoy’s data (e. g. for temperature, salinity and dissolved oxyge). Corrected data are subsequently called « adjusted-parameter » in the Iroise data base. Manual SOMLIT-Portzic data are also systematically used to convert fluorescence sensor data collected in raw fluorescence unit(FFU) into « eq-µg/L of chlorophyll » : all fluorescence data are then available as « adjusted-fluorecence » in the data base. Precision estimated of the complete data collection process is : temperature (±0.1°C), conductivity (±0.3mS/cm), dissolved oxygen (±10%), in vivo fluorescence (±10%), and turbidity (±10%). By the mean of two additional sensors, these core parameters are completed by aerial Photosynthetic Activated Radiation (PAR) and FugacityCO2 (±3µatm). The data can be viewed on the website: https://data.coriolis-cotier.org/platform/6200450.

Abstract In order to better understand the water vapor (WV) intrusion into the tropical stratosphere, a mesoscale simulation of the tropical tropopause layer using the BRAMS (Brazilian version of Regional Atmospheric Modeling System (RAMS)) model is evaluated for a wet season. This simulation with a horizontal grid point resolution of 20 km × 20 km cannot resolve the stratospheric overshooting convection (SOC). Its ability to reproduce other key parameters playing a role in the stratospheric WV abundance is investigated using the balloon‐borne TRO‐Pico campaign measurements, the upper‐air soundings over Brazil, and the satellite observations by Aura Microwave Limb Sounder, Microwave Humidity Sounder, and Geostationary Operational Environmental Satellite 12. The BRAMS exhibits a good ability in simulating temperature, cold‐point, WV variability around the tropopause. However, the simulation is typically observed to be warmer by ∼2.0°C and wetter by ∼0.4 ppmv at the hygropause, which can be partly affiliated with the grid boundary nudging of the model by European Centre for Medium‐Range Weather Forecasts operational analyses. The modeled cloud tops show a good correlation (maximum cross‐correlation of ∼0.7) with Geostationary Operational Environmental Satellite 12. Furthermore, the overshooting cells detected by Microwave Humidity Sounder are observed at the locations, where 75% of the modeled cloud tops are higher than 11 km. Finally, the modeled inertia‐gravity wave periodicity and wavelength are comparable with those deduced from the radio sounding measurements during TRO‐Pico campaign. The good behavior of BRAMS confirms the SOC contribution in the WV abundance, and variability is of lesser importance than the large‐scale processes. This simulation can be used as a reference run for upscaling the impact of SOC at a continental scale for future studies.

This paper presents a first demonstration of range-resolved differential absorption LIDAR (DIAL) measurements of the water vapor main isotopologue H 2 16 O and the less abundant semi-heavy water isotopologue HD 16 O with the aim of determining the isotopic ratio. The presented Water Vapor and Isotope Lidar (WaVIL) instrument is based on a parametric laser source emitting nanosecond pulses at 1.98 µm and a direct-detection receiver utilizing a commercial InGaAs PIN photodiode. Vertical profiles of H 2 16 O and HD 16 O were acquired in the planetary boundary layer in the suburban Paris region up to a range of 1.5 km. For time averaging over 25 min, the achieved precision in the retrieved water vapor mixing ratio is 0.1 g kg −1 (2.5% relative error) at 0.4 km above ground level (a.g.l.) and 0.6 g kg −1 (20%) at 1 km a.g.l. for 150 m range bins along the LIDAR line of sight. For HD 16 O, weaker absorption has to be balanced with coarser vertical resolution (600 m range bins) in order to achieve similar relative precision. From the DIAL measurements of H 2 16 O and HD 16 O, the isotopic abundance δ D was estimated as −51‰ at 0.4 km above the ground and −119‰ in the upper part of the boundary layer at 1.3 km a.g.l. Random and systematic errors are discussed in the form of an error budget, which shows that further instrumental improvements are required on the challenging path towards DIAL-profiling of the isotopic abundance with range resolution and precision suitable for water cycle studies.

The Gamma-ray Cherenkov Telescope (GCT) is one of the telescopes proposed for the Small Sized Telescope (SST) section of CTA. Based on a dual-mirror Schwarzschild-Couder design, which allows for more compact telescopes and cameras than the usual single-mirror designs, it will be equipped with a Compact High-Energy Camera (CHEC) based on silicon photomultipliers (SiPM). In 2015, the GCT prototype was the first dual-mirror telescope constructed in the prospect of CTA to record Cherenkov light on the night sky. Further tests and observations have been performed since then. This report describes the current status of the GCT, the results of tests performed to demonstrate its compliance with CTA requirements, and the optimisation of the design for mass production. The GCT collaboration, including teams from Australia, France, Germany, Japan, the Netherlands and the United Kingdom, plans to install the first telescopes on site in Chile for 2019-2020 as part of the CTA pre-production phase.

A small-size meteorological mast, BEAR (Budget of Energy for Arctic regions) has been developed as a part of a new autonomous buoy for monitoring the sea ice mass balance. BEAR complements observations of the thickness and thermodynamic properties of the ice/snow pack determined by the so-called Ice-T (Ice-Thickness) buoy, giving access to bulk fluxes and energy budget at the surface, using meteorological measurements. The BEAR mast has been tested with success during ten days in April-May 2010 at Ny Alesund, in the Svalbard archipelago (Norway) showing that meteorological data were close to measurements at the same level of the Italian Climate Change Tower (CCT) from the ISAC-CNR. A discussion is undertaken on bulk fluxes determination and uncertainties. Particularly, the strategy to systematically use different relevant fluxes parameterizations is pointed out to explore flux range uncertainty before to analyze energy budget. Net radiation, bulk fluxes and energy budget are estimated using as average 10 minutes, 24 hours and the ten days of the experiment. The observation period was very short, but we observe a spring transition when the net radiation begins to warm the surface while the very small turbulent heat flux cools the surface.

MICADO is the ELT first light instrument, an imager working at the diffraction limit of the telescope thanks to two adaptive optics (AO) modes: a single conjugate one (SCAO), available at the instrument first light and developed by the MICADO consortium, and a multi conjugate one (MCAO), developed by the MORFEO consortium. Although the project final design review process is about to be completed, the review board and ESO acknowledged that "the review of the final design can be considered complete for the majority of the MICADO sub-systems" and agreed that MICADO can start manufacturing. For the MICADO SCAO module, we have started the manufacturing of several parts: the majority of the SCAO optics and of the SCAO mechanics, the real-time computer software and the instrument control software. This manufacturing is ordered in several steps to allow the progressive integration of a first full AO close loop with the final SCAO parts. In this contribution, we will focus on the first two steps: on our AO Sésame bench and the so-called "β flat configuration". We will present the status of this manufacturing and the first results obtained.

We present the design of a differential absorption LIDAR targeting HDO/H 2 16 O isotopic ratio measurement with high vertical resolution. This approach is enabled by infrared water vapor spectroscopy and recent high power multi-species parametric emitter developments.

Abstract. During the Water Vapor Lidar Network Assimilation (WaLiNeAs) campaign, eight lidars specifically designed to measure water vapor mixing ratio (WVMR) profiles were deployed on the western Mediterranean coast. The main objectives were to investigate the water vapor content during case studies of heavy-precipitation events in the coastal western Mediterranean and assess the impact of high spatiotemporal WVMR data on numerical weather prediction forecasts by means of state-of-the-art assimilation techniques. Given the increasing occurrence of extreme events due to climate change, WaLiNeAs is the first program in Europe to provide network-like, simultaneous and continuous water vapor profile measurements over a period of 3–4 months. This paper focuses on the WVMR profiling datasets obtained from three of the lidars run by the French part of the WaLiNeAs team. These three lidars were deployed in the cities of Coursan, Le Grau-du-Roi and Cannes. This measurement setup enabled monitoring of the water vapor content of the lower troposphere over periods of 3 months in fall and winter 2022, with some interruptions, and 4 months in summer 2023. The lidars measured the WVMR profiles from the surface up to approximately 6–10 km at nighttime and 1–2 km during daytime. They had a vertical resolution of 100 m and a time resolution between 15 and 30 min, and they were selected to meet the needs of weather forecasting with an uncertainty lower than 0.4 g kg−1. The paper presents details about the instruments, the experimental strategy and the datasets provided. The final dataset (https://doi.org/10.25326/537; Chazette et al., 2023) is divided into two sub-datasets: the first with a time resolution of 15 min, which contains a total of 26 423 WVMR vertical profiles, and the second with a time resolution of 30 min to improve the signal-to-noise ratio and signal altitude range.

The Cherenkov Telescope Array (CTA) project, led by an international collaboration of institutes, aims to create the world's largest next generation observatory for Very High Energy (VHE) gamma-ray astronomy. It will be devoted to observations in a wide band of energy, from a few tens of GeV to a few hundreds of TeV with Large, Medium and Small-sized telescopes. The Small-Size Telescopes (SSTs) are dedicated to the highest energy range above a few TeV and up to 300 TeV. GCT is an imaging atmospheric Cherenkov telescope (IACT) proposed for the subarray of about 70 SSTs to be installed on the Southern site of CTA in Chile. The Observatory of Paris and the National Institute for Earth Sciences and Astronomy (INSU/CNRS) have developed the mechanical structure, mirrors (aspherical lightweight aluminium segments) and control system of the GCT. The GCT is based on a Schwarzschild- Couder (S-C) dual-mirror optical design which has the advantages, compared to the current IACTs, to offer a wide field of view (~ 9°) while decreasing the cost and volume (~ 9 m x 4 m x 6 m for ~ 11 tons) of the telescope structure, as well as the camera. The prototype (pGCT) has been installed at the Meudon's site of the Observatory of Paris and was the first S-C telescope and the first CTA prototype to record VHE events on-sky in November 2015. After three years of intensive testing, pGCT has now been commissioned. This paper is a status report on the complete GCT telescope optical system and the performance it can provide for CTA.

As part of the EUREC4A-OA project (H. Bellenger, S. Speich, LMD), which is the French oceanographic component of the larger EUREC4A field experiments, the “flux mast” national instrument was installed on the Reseach Vessel R/V Atalante from Genavir. The flux mast holds instruments that measure atmospheric turbulence and meteorological variables. The collected data are used to estimate the turbulent fluxes of momentum and heat at the air-sea interface. Specifically, the flux mast instruments measure air pressure, air temperature, humidity, air refraction index, H2O, the three components of the wind vector, and the upward and downward solar and infrared radiation fluxes. The fluxes calculated are the latent and sensible heat fluxes, and the friction velocity.

Abstract. The physical and biogeochemical processes governing the air–sea CO2 flux in the Southern Ocean are still widely debated. The Southern Ocean Carbon and Heat Impact on Climate cruise in summer 2022 aimed at studying these processes in the Weddell Sea and in its vicinity. A CARbon Interface OCean Atmosphere (CARIOCA) drifting buoy was deployed in January 2022 in the subpolar Southern Ocean, providing hourly surface ocean observations of fCO2 (fugacity of CO2), dissolved oxygen, salinity, temperature, and chlorophyll a fluorescence for 17 months. An underwater glider was piloted with the buoy for the first 6 weeks of the deployment to provide vertical ocean profiles of hydrography and biogeochemistry. These datasets reveal an anomalously strong ocean carbon sink for over 2 months, occurring in the region of Bouvet Island and associated with large plumes of chlorophyll a (Chl a). Based on Lagrangian backward trajectories reconstructed using various surface currents fields, we identified that the water mass reaching the Bouvet Island region originated from the southwest, from the vicinity of the sea ice edge in spring 2021. A strong phytoplankton bloom developed there in November 2021. We propose that it was promoted by early sea ice retreat in 2021 in the Weddell Sea. These waters, depleted in carbon, then traveled to the position of the CARIOCA buoy. The very low values of ocean fCO2, measured by the buoy (down to 310 µatm), are consistent with net community production previously observed during blooms occurring near the sea ice edge, partly compensated by air–sea CO2 flux along the water mass trajectory. Early sea ice retreat might therefore have caused a large CO2 sink farther north than usual in summer 2022, in the Atlantic sector of the subpolar Southern Ocean. Such events might become more frequent in the future as a result of climate change.

As part of the EUREC4A-OA project (H. Bellenger, S. Speich, LMD), which is the French oceanographic component of the larger EUREC4A field experiments, the OCARINA wave-following platform was deployed from the host Reseach Vessel R/V Atalante from Genavir. OCARINA holds instruments that measure atmospheric turbulence and other environmental variables. The collected data are used to estimate the turbulent fluxes of momentum and heat at the air-sea interface. Specifically, the instruments on OCARINA measure air pressure, air temperature, humidity, the three components of the wind vector, the upward and downward solar and infrared radiation fluxes, and basic sea wave characteristics, such as the most significant wave height. Three methods are used to calculate the turbulent fluxes, namely the Eddy-Covariance (EC) method, the Inertial-Dissipation (ID) method, and the bulk method.

The Gamma-ray Cherenkov Telescope (GCT) is a candidate for the Small Size Telescopes (SSTs) of the Cherenkov Telescope Array (CTA). Its purpose is to extend the sensitivity of CTA to gamma-ray energies reaching 300 TeV. Its dual-mirror optical design and curved focal plane enables the use of a compact camera of 0.4 m diameter, while achieving a field of view of above 8 degrees. Through the use of the digitising TARGET ASICs, the Cherenkov flash is sampled once per nanosecond contin-uously and then digitised when triggering conditions are met within the analogue outputs of the photosensors. Entire waveforms (typically covering 96 ns) for all 2048 pixels are then stored for analysis, allowing for a broad spectrum of investigations to be performed on the data. Two prototypes of the GCT camera are under development, with differing photosensors: Multi-Anode Photomultipliers (MAPMs) and Silicon Photomultipliers (SiPMs). During November 2015, the GCT MAPM (GCT-M) prototype camera was integrated onto the GCT structure at the Observatoire de Paris-Meudon, where it observed the first Cherenkov light detected by a prototype instrument for CTA.

Abstract. During the Water Vapor Lidar Network Assimilation (WaLiNeAs) campaign, 8 lidars specifically designed to measure water vapor mixing ratio (WVMR) profiles were deployed on the western Mediterranean coast. The main objectives were to investigate the water vapor content during case studies of heavy precipitation events in the coastal Western Mediterranean and assess the impact of high spatio-temporal WVMR data on numerical weather prediction forecasts by means of state–of–the–art assimilation techniques. Given the increasing occurrence of extreme events due to climate change, WaLiNeAs is the first program in Europe to provide network–like, simultaneous and continuous water vapor profile measurements. This paper focuses on the WVMR profiling datasets obtained from three of the lidars managed by the French component of the WaLiNeAs team. These lidars were deployed in the towns of Coursan, Grau du Roi and Cannes. This measurement setup enabled monitoring of the water vapor content within the low troposphere along a period of three months over autumn – winter 2022 and four months in summer 2023. The lidars measured the WVMR profiles from the surface up to approximately 6–10 km at night, and 1–2 km during daytime; with a vertical resolution of 100 m and a time sampling between 15 – 30 min, selected to meet the needs of weather forecasting with an uncertainty lower than 0.4 g kg-1. The paper presents details about the instruments, the experimental strategy, as well as the datasets given in NETcdf format. The final dataset is divided in two datasets, the first with a time resolution of 15 min, which contains a total of 26 423 WVMR vertical profiles and the second with a time resolution of 30 min to improve the signal to noise ratio and signal altitude range.