WRF Sensitivity Analysis in Wind and Temperature Fields Simulation for the Northern Sahara and the Mediterranean Basin

Different configurations for the Weather Research and Forecasting (WRF) model were evaluated to improve wind and temperature fields predictions in the Northern Sahara and the Mediterranean basin. Eight setups, associated with different combinations of the surface layer physical parameters, the land surface model, and the grid nudging parameters, were considered. Numerical simulations covered the entire month of November 2017. Model results were compared with surface data from meteorological stations. The introduction of the grid nudging parameters leads to a general improvement of the modeled 10 m wind speed and 2 m temperature. In particular, nudging of wind speed parameter inside the planetary boundary layer (PBL) provides the most remarkable differences. In contrast, the nudging of temperature and relative humidity parameters inside the PBL may be switched off to reduce computational time and data storage. Furthermore, it was shown that the prediction of the 10 m wind speed and 2 m temperature is quite sensitive to the choice of the surface layer scheme and the land surface model. This paper provides useful suggestions to improve the setup of the WRF model in the Northern Sahara and the Mediterranean basin. These results are also relevant for topics related with the emission of mineral dust and sea spray within the Mediterranean region

Bed dynamics in a microtidal swash zone under small wave conditions

National audienceThe knowledge of the swash zone is of primary importance to understand the morphological evolution of sedimentary beaches. The swash zone is highly dynamic, with instantaneous sediment fluxes often being several orders of magnitude greater than their surf zone counterparts. Despite of the increased research efforts dedicated to the swash hydro- and morphodynamics during the last decades, several key processes remain to be understood before the swash morphodynamics can be predicted and modeled. A large part of existing studies have focused on meso to macrotidal swash zones exposed to moderate to storm wave conditions. The present communication reports on a field study of small-scale swash bed processes in microtidal and small wave conditions. It is shown that even such calm conditions can result in significantly dynamic swash zone. The selected field site is the Pont de Rousty sandy beach, Camargue, France. A high-resolution survey of the swash zone sand bed has been performed over a cross-shore transect on both hydro and morphodynamic aspects. The instrumentation included a set of both buried and non-buried pressure sensors, a network of ultrasonic altimeters, a 3D high resolution acoustic velocimeter and other pressure and velocity sensors deployed outside the swash zone to measure the incoming forcing. Results show that the swash bed and slope permanently evolve under the action of waves. Each swash event can individually induce bed level variations ranging from 1 to 5mm but larger evolution (up to 4cm) are observed at longer time scales. Ongoing work is focused, on one hand, to the role played by the swash physical parameters (velocity, duration, height, etc) on the event-related transport and, on the other hand, to the identification of a " bottom-up " relationship between the succession of individual actions of swash events and the long term evolution of swash morphology

Physicochemical characteristics of aerosols measured in the spring time in the Mediterranean coastal zone

Aerosol particles in coastal areas result from a complex mixing between sea-spray aerosols locally generated at the sea surface by breaking waves and a continental component arising from natural and/or anthropogenic sources. This paper presents physicochemical characterisation of aerosols observed during meteorological conditions characteristics of coastal areas. In particular, we study the influence of sea-breezes and land-breezes as well as the fetch variation, which superpose on larger synoptic conditions, on aerosol properties. This was achieved using a physical, chemical and optical analysis of the aerosol data acquired in May 2007 on the French Mediterranean coast. The aerosol distributions were measured using a TSI SMPS 3081 model and the chemical characterization was made using an Ion Chromatography analysis (IC) and a thermo-optical technique. In addition, aerosol optical characteristics were provided by aethalometer (absorption) and nephelometer (scattering) measurements. For low wind speeds, we detect high aerosol number concentrations as well as high NO3- and carbonaceous compounds contributions, which are observed even when the aerosol is sampled in pure maritime air masses. These results indicate that air masses are strongly impacted by pollution transported over the Mediterranean. In addition, the combination of low wind speeds and land/sea breezes lead to the production of new ultrafine particle formation events that seem to take place over the sea before being transported back to the coast. Under higher wind speed conditions, aerosol number and mass concentrations of smaller sizes are significantly lowered due to the dispersion of anthropogenic pollutants. Optical measurements reveal that mean scattering and absorbing coefficients are about 15.2 Mm-1 and 3.6 Mm-1, respectively. Associated mean aerosol single scattering albedo is found to be about 0.87 and 0.94 (at 520 nm) for continental and maritime influences

Caractérisation physico-chimique des aérosols dans la zone côtière : preuve de la persistance de la suie de carbone dans la couche limite atmosphérique marine de fond (MABL)

International audienceAerosol particles in coastal areas result from a complex mixing between sea-spray aerosols locally generated at the sea surface by breaking waves and a continental component issued from natural and/or anthropogenic sources. The aim of this paper is to study how the aerosols mix in the coastal marine atmosphere to evaluate the impact of the background pollution on the atmospheric aerosols. To this end, we have carried out a qualitative analysis of particulate matter sampled at two French coastal areas using a non-destructive methodology combining scanning electron microscopy (SEM)/X-ray fluorescence, transmission electron microscopy (TEM), X-ray diffraction, and Raman spectroscopy. Our analysis shows a dominant contribution of anthropogenic aerosols through strong levels of submicronic carbon soot and sulfate particles, even observed when the aerosol is sampled during pure maritime-air mass episodes. Our results also evidence the non-mixing between sea-spray, mainly composed of coarse aerosol particles, and this anthropogenic particulate matter of smaller sizes.Les particules d'aérosols dans les zones côtières résultent d'un mélange complexe entre les aérosols d'embruns générés localement à la surface de la mer par le déferlement des vagues et une composante continentale issue de sources naturelles et/ou anthropiques. L'objectif de cet article est d'étudier comment les aérosols se mélangent dans l'atmosphère marine côtière pour évaluer l'impact de la pollution de fond sur les aérosols atmosphériques. Pour cela, nous avons réalisé une analyse qualitative des particules prélevées sur deux zones côtières françaises en utilisant une méthodologie non-destructive combinant la microscopie électronique à balayage (MEB)/fluorescence X, la microscopie électronique à transmission (MET), la diffraction des rayons X et la spectroscopie Raman. Notre analyse montre une contribution dominante des aérosols anthropiques à travers de forts niveaux de particules submicroniques de suie de carbone et de sulfate, même observés lorsque l'aérosol est échantillonné lors d'épisodes de masse d'air maritime pure. Nos résultats mettent également en évidence la non-mixité entre les embruns marins, principalement composés de grosses particules d'aérosols, et cette matière particulaire anthropique de plus petite taille

On the use of long-term observation of water level and temperature along the shore for a better understanding of the dynamics: example of Toulon area, France

International audienceA dense network of instruments has been deployed within harbours along the Mediterranean coast, in the Toulon Metropole area, between the Hyères islands and the Sanary Bay in the framework of the observation network HTM-NET. Each station is equipped with two piezometric sensors, the first immersed and the second emerged, which allows the calculation of the water level. Both piezometric sensors are also equipped with a temperature sensor. Water level and temperature data are analyzed and discussed, also considering meteorological data provided by Météo-France stations. The tide gauges provide information about tide harmonic components, extreme water level and seiching. Moreover, significant differences are observed between sheltered zones in enclosed bays and offshore zones, such as between the back of the Bay of Toulon and at the Port-Cros Island. Differences in water level up to 0.10m are indeed observed under windy conditions, of same order as the tidal range (order of 0.20m) or the annual level variability due to the volumetric expansion (order of 0.10m). Water level variations, up to about 1m, are found to be mainly due to atmospheric effects, with a more or less isostatic behavior according to the weather events. In addition, seiching with an amplitude of few centimeters is observed within the Little Bay of Toulon, for east wind conditions. The near-surface water temperature is measured at the submerged piezometer location (depth of immersion range 0.10m-1.80m according to the station and to the water level). The analysis of the temperature associated with the weather conditions allows to detail a strong variability of the upwelling intensity under Mistral wind conditions in summer, leading to more or less pronounced temperature drops according to the shore configuration. The Bay of Toulon is more prone to the generation of upwellings than the neighboring bays. During winter, water exchanges between the Little Bay of Toulon and offshore are also clearly observed during windy conditions. The HTM-NET long-term observation network thus provides useful insights to increase our knowledge of the hydrodynamics and mass fluxes, and therefore enhances our modeling capacity and risk assessment at the scale of a bay

Characterization of carbonaceous aerosols over the Northern Adriatic Sea in the JERICO-NEXT project framework

The coastal aerosol represents a complex mixing between sea spray aerosols locally generated at the sea surface and a component generated by natural and/or anthropogenic sources on the nearby land. The aim of this paper is to study the atmospheric concentrations of carbonaceous compounds as measured in the coastal zone of the Northern Adriatic Sea between April 2017 and April 2018. The results show a quite large contribution of carbonaceous compounds, even when the sampled air mass is predominantly maritime. Although it is generally assumed that 70% and 90% of bulk organic carbon (OC) and elemental carbon (EC) concentrations, respectively, are found in the fine mode, we observed higher OC and EC concentrations in the coarse fraction (up to about 37% and 25%, respectively). This confirms the occurrence of mixing between anthropogenic matter and sea spray, mainly composed of coarse aerosol particles, during the atmospheric transport over the Mediterranean basin

Caractérisation physico-chimique des aérosols dans la zone côtière : preuve de la persistance de la suie de carbone dans la couche limite atmosphérique marine de fond (MABL)

International audienceAerosol particles in coastal areas result from a complex mixing between sea-spray aerosols locally generated at the sea surface by breaking waves and a continental component issued from natural and/or anthropogenic sources. The aim of this paper is to study how the aerosols mix in the coastal marine atmosphere to evaluate the impact of the background pollution on the atmospheric aerosols. To this end, we have carried out a qualitative analysis of particulate matter sampled at two French coastal areas using a non-destructive methodology combining scanning electron microscopy (SEM)/X-ray fluorescence, transmission electron microscopy (TEM), X-ray diffraction, and Raman spectroscopy. Our analysis shows a dominant contribution of anthropogenic aerosols through strong levels of submicronic carbon soot and sulfate particles, even observed when the aerosol is sampled during pure maritime-air mass episodes. Our results also evidence the non-mixing between sea-spray, mainly composed of coarse aerosol particles, and this anthropogenic particulate matter of smaller sizes.Les particules d'aérosols dans les zones côtières résultent d'un mélange complexe entre les aérosols d'embruns générés localement à la surface de la mer par le déferlement des vagues et une composante continentale issue de sources naturelles et/ou anthropiques. L'objectif de cet article est d'étudier comment les aérosols se mélangent dans l'atmosphère marine côtière pour évaluer l'impact de la pollution de fond sur les aérosols atmosphériques. Pour cela, nous avons réalisé une analyse qualitative des particules prélevées sur deux zones côtières françaises en utilisant une méthodologie non-destructive combinant la microscopie électronique à balayage (MEB)/fluorescence X, la microscopie électronique à transmission (MET), la diffraction des rayons X et la spectroscopie Raman. Notre analyse montre une contribution dominante des aérosols anthropiques à travers de forts niveaux de particules submicroniques de suie de carbone et de sulfate, même observés lorsque l'aérosol est échantillonné lors d'épisodes de masse d'air maritime pure. Nos résultats mettent également en évidence la non-mixité entre les embruns marins, principalement composés de grosses particules d'aérosols, et cette matière particulaire anthropique de plus petite taille

A world-wide comparison of aerosol data

A comparison of aerosol data acquired at five different sites around the globe is presented. All data has been acquired with the same instrumentation and representative size distributions for marine air masses at 10 m/s wind speed have been selected for comparison. Differences in the concentrations of larger and smaller aerosols at the various sites are explained in terms of fetch, trade winds, shielding, pollution, seawater temperature and phytoplankton bloom. The differences in size distribution induce significant differences in the extinction coefficients from the VIS to the LWIR at the various sites. Consequently, the transmission over a specific range also varies significantly. This suggests that a detailed analysis of the conditions at each site is necessary in order to understand the exact aerosol behavior and to correctly predict electro-optical propagation effects due to aerosols