Search

This study investigates thermal circulations on Reunion Island (21°07'S 55°32'E), focusing on the complex terrain of the region. Observations from the BIO‐MAÏDO campaign, along with 2 days of high‐resolution simulation using the MesoNH model, were analyzed to understand the thermally‐driven mechanisms. This simulation was conducted with a horizontal resolution of 100 m and employed a vertically stretched grid, achieving a resolution of 1 m at the lowest levels. Two distinct wind regimes were identified, characterized by katabatic flows prevailing within a 30 m thick layer during nighttime, and an anabatic flow manifesting within a layer spanning from 150 to 200 m during the daytime. The simulation was confirmed through validation with surface measurements, and thus enabling a detailed study of thermal breeze circulations. Results reveal that the intensity of trade winds significantly influences the development of thermal circulations. Complex layered structures in the atmosphere were also identified. At an intensity of 7 m s−1, trade winds impede the development of thermal circulations atop the slope, and result in the emergence of a convergence zone between local and regional circulations. The analysis of the breeze establishment period indicates that the katabatic flow stabilizes in 35 min, quicker than the anabatic flow, which takes 110 min. Momentum and heat budget analysis provide insights into the primary drivers of thermal circulations: buoyancy acceleration, influenced by local surface heating during anabatic flow onset, and local surface cooling during katabatic flow onset. Plain Language Summary: This research explores thermal circulation in the northwestern region of Reunion Island, an area significantly influenced by the return flow of the trade winds, the trade winds themselves, and breezes. Data from the BIOMAÏDO campaign and simulation using the MesoNH model were employed to analyze the heat‐driven air movements in this specific region. The study identified two distinct wind patterns: a downward katabatic flow within a 30 m layer and a diurnal anabatic flow occurring between elevetions of 150–200 m. Validation through surface measurements corroborated the model simulation, facilitating a detailed analysis of thermal breeze circulations. The results indicate that strong directional winds significantly influence air movement patterns. At a speed of 7 m s−1, these winds inhibit upward air movement along the slopes, creating a convergence zone between local and larger‐scale wind patterns. Analysis of the breeze establishment periods indicated a faster stabilization of katabatic flow at 35 min compared to 110 min of anabatic flow. Momentum and heat budget analysis revealed the primary drivers: buoyancy acceleration, influenced by local surface heating during anabatic flow and by local surface cooling during katabatic flow. Key Points: Trade winds strongly impact thermal circulations on Reunion Island, creating complex atmospheric structuresKatabatic flow stabilizes faster (35 min) than anabatic flow (110 min), affecting the island's thermal breeze patternsBuoyancy acceleration, local surface heating, and cooling play significant roles in driving thermal circulations [ABSTRACT FROM AUTHOR]

For the first time, a plume-in-grid approach is implemented in a chemical transport model (CTM) to parameterize the effects of the non-linear reactions occurring within high concentrated NOx plumes from lightning NOx emissions (LNOx) in the upper troposphere. It is characterized by a set of parameters including the plume lifetime, the effective reaction rate constant related to NOx-O3 chemical interactions and the fractions of NOx conversion into HNO3 within the plume. Parameter estimates were made using the DSMACC chemical box model, simple plume dispersion simulations and the mesoscale 3-D Meso-NH model. In order to assess the impact of the LNOx plume approach on the NOx and O3 distributions at large scale, simulations for the year 2006 were performed using the GEOS-Chem global model with a horizontal resolution of 2° × 2.5°. The implementation of the LNOx parameterization implies NOx and O3 decrease at large scale over the region characterized by a strong lightning activity (up to 25 and 8%, respectively, over Central Africa in July) and a relative increase downwind of LNOx emissions (up to 18 and 2% for NOx and O3, respectively, in July) are derived. The calculated variability of NOx and O3 mixing ratios around the mean value according to the known uncertainties on the parameter estimates is maximum over continental tropical regions with ΔNOx [-33.1; +29.7] ppt and ΔO3 [-1.56; +2.16] ppb, in January, and ΔNOx [-14.3; +21] ppt and ΔO3 [-1.18; +1.93] ppb, in July, mainly depending on the determination of the diffusion properties of the atmosphere and the initial NO mixing ratio injected by lightning. This approach allows (i) to reproduce a more realistic lightning NOx chemistry leading to better NOx and O3 distributions at the large scale and (ii) focus on other improvements to reduce remaining uncertainties from processes related to NOx chemistry in CTM. [ABSTRACT FROM AUTHOR]

The paper describes the 2-moment microphysical scheme LIMA (Liquid Ice Multiple Aerosols), which relies on the prognostic evolution of a three-dimensional (3-D) aerosol population, and the careful description of the nucleating properties that enable cloud droplets and pristine ice crystals to form. LIMA uses the aerosol nucleating properties to form cloud droplets and pristine ice crystals. Several modes of Cloud Condensation Nuclei (CCN) and Ice Freezing Nuclei (IFN) are considered individually. A special class of partially soluble IFN is also introduced. These "aged" IFN act first as CCN and then as IFN by immersion nucleation at low temperatures. All the CCN modes are in competition with each other, as expressed by the single equation of maximum supersaturation. The IFN are insoluble aerosols that nucleate ice in several ways (condensation, deposition and immersion freezing) assuming the singular hypothesis. The scheme also includes the homogeneous freezing of cloud droplets, the Hallett-Mossop ice multiplication process and the freezing of haze at very low temperature. LIMA assumes that water vapour is in thermodynamic equilibrium with the population of cloud droplets (adjustment to saturation in warm clouds). In ice clouds, the prediction of the number concentration of the pristine ice crystals is used to compute explicit deposition and sublimation rates (leading to free under/supersaturation over ice). The formation of hydrometeors is standard. The autoconversion, accretion and self-collection processes shape the raindrop spectra. The initiation of the large crystals and aggregates category is the result of the depositional growth of large crystals beyond a critical size. Aggregation and riming are computed explicitly. Heavily rimed crystals (graupel) can experience a dry or wet growth mode. An advanced version of the scheme includes a separate hail category of particles forming and growing exclusively in the wet growth mode. The sedimentation of all particle types is included. The LIMA scheme is inserted in the cloud-resolving mesoscale model Meso-NH. The flexibility of LIMA is illustrated by two 2-D experiments. The first one highlights the sensitivity of orographic ice clouds to IFN types and IFN concentrations. Then a squall line case discusses the microstructure of a mixed-phase cloud and the impacts of pure CCN and IFN polluting plumes. The experiments show that LIMA captures the complex nature of aerosol-cloud interactions leading to different pathways for cloud and precipitation formation. [ABSTRACT FROM AUTHOR]

Simulations with the chemistry-transport model WRF-Chem are compared to aerosol measurements performed at the puy de Dôme station with a compact Time-of-Flight Aerosol Mass Spectrometer (cToF-AMS) for two episodes in autumn 2008 and in summer 2010. The WRF-Chem model is used with the Volatility Basis Set (VBS) approach dedicated to the formation of secondary organic aerosol (SOA). The model systematically underestimates the observed concentrations of organic aerosol (OA), with significant differences observed for the summer case. For this event, where high OA concentrations were observed (12.5 µgm-3 in average), simulated OA mass concentration is 2.0µgm-3. For the autumn event, observed OA concentrations reached 2.6µgm-3. The simulated concentrations reached only 0.6µgm-3. During the summer event, several gas-phase volatile organic compounds (VOCs) were measured and were used to test the robustness of both emission/dry deposition and SOA formation processes. The concentrations of VOCs, and more specifically the anthropogenic ones, calculated by the model are estimated to be much lower than the observed ones. Hence, the emissions of all SOA precursors are multiplied by 2 in the model: this induces an increase of the mean OA mass concentration of 25% (+0.5µgm-3) and 18% (+0.4µgm-3), respectively for anthropogenic and bio-genic VOCs. The dry deposition of gas-phase organic condensable vapours (OCVs) is also critical to predict the SOA mass concentrations: dividing the deposition factor by 2 leads to an increase of OA mass by an additional 12% (+0.2µgm-3). However, these increases were not sufficient to explain the observed OA concentration, and the underestimation of the OA concentration levels seems to be principally related to a lack in the parameterization of SOA formation. Changing the oxidation rate of OCVs from 1.0x10-11 to 4.0x10-11 cm-3 molecule-1 s-1, doubling the SOA yields for anthropogenic VOCs and finally doubling the SOA yields for biogenic VOCs results in an increase of the mean OAmass concentration by 56% (+1.1 µgm-3), 61 % (+1.2µgm-3) and 40% (+0.8µgm-3), respectively. The consideration of both emission/dry deposition and SOA formation processes tests lead to a mean OA mass concentration of 10.7µgm-3 for 2010, a value that is close to the observations. For 2008, modifying solely the oxidation rate of OCVs and the SOA yields is sufficient to reproduce the observed level of mean OA mass (a mass of 2.4 µgm-3 is obtained by the model whereas a mass of 2.6 µgm-3 was observed). [ABSTRACT FROM AUTHOR]

Abstract: The dopaminergic mesocorticolimbic system plays an important role in the reinforcing effects of ethanol. Opioid peptides modulate the activity of this system and have been suggested to mediate, at least in part, the reinforcing properties of ethanol. Thus, beta-endorphin (β-END) could participate in the development of ethanol reinforcement and addiction. The aim of this work was to investigate the acute and chronic ethanol effects on β-END content in regions of the mesolimbic system and to examine if chronic ethanol treatment alters ligand binding to mu opioid receptor (μOR). Male Wistar rats received a single acute ethanol dose of 2.5g/kg or water by intra-gastric administration. For chronic ethanol treatment experiments, one group of rats was given ethanol (10% v/v solution) to drink, two groups were given equivalent volumes of sucrose (14.14% isocaloric solution) or water, respectively, and a fourth group had ad libitum access to food and water. Treatment was followed for 4weeks. Beta-endorphin content in brain regions was quantified by radioimmunoassay and ligand binding studies to μOR were performed by quantitative autoradiography using 8nM [3H]-DAMGO as radioligand. Acute ethanol decreased β-END content in the hypothalamus (26%) 1h after administration. No ethanol effects were observed in the midbrain, ventral tegmental area, substantia nigra, nucleus accumbens, nucleus accumbens-septum and prefrontal cortex. Chronic ethanol treatment neither changed β-END levels nor [3H]-DAMGO binding to mu opioid receptors in any of the regions studied. However, β-END levels in the sucrose group were significantly increased in the nucleus accumbens and substantia nigra, in comparison to all other groups. These findings suggest that different neural mechanisms and specific brain regions may be involved in the reinforcing effects of ethanol and sucrose. [Copyright &y& Elsevier]

This paper reports the first record of extreme ozone measurement in Africa. As part of the AMMA program, the ozone vertical profile recorded on 20 December over Cotonou presents exceptionally high ozone concentrations with up to 295 ppbv at 1 km altitude. Retroplumes from the Flexpart model show that the air masses sampled at 1 km over Cotonou on this day come from the burning area situated north-east of Cotonou and pass over Lagos, Nigeria, which is highly impacted by urban pollution. We used the Master Mechanism box model to simulate the chemical composition of the plume during its transit. We find that neither the biomass burning emissions of ozone precursors nor additional urban emissions from Lagos are high enough to simulate more than 120-150 ppbv of ozone. The only way to reach almost 300 ppb of ozone within a few hours is to feed the air mass with large amounts of reactive VOCs as those recorded in the vicinity of petrochemical area. Sensitivity tests show that 250-600 ppbv of VOCs combined with 35-80 ppb of NOx allow the ozone concentrations to be higher than 250 ppb. Nigeria is the first African country with gas extraction and petrochemical industries, and petrochemical explosions frequently happen in the vicinity of Lagos. The hypothesis of a petrochemical explosion in this area is the most likely scenario which explains the 295 ppbv ozone maximum measured over Cotonou, downwind of Lagos. [ABSTRACT FROM AUTHOR]

This paper assesses the impact of aerosol properties on the formation and the development of radiation fog. Simulations were performed using the Meso-NH meteorological model including the ORILAM aerosol scheme coupled with a two-moment microphysical cloud scheme (number concentration of cloud droplets and cloud water content). The activation scheme used was taken from the work of Abdul-Razzak and Ghan (2004). "Off-line" sensitivity analysis of CCN (Cloud Condensation Nuclei) activation was performed on number, median diameter and chemical compounds of aerosols. During this "off-line" study, the interactions with the other physical processes (e.g. radiative) were not taken into account since the cooling rate was imposed. Different regimes of CCN activation and a critical value of aerosol number concentration were found. This critical aerosol number corresponds to the maximum of activated cloud droplets for a given cooling rate and given aerosol chemical properties. As long as the aerosol number concentration is below this critical value, the cloud droplet number increases when the aerosol number increases. But when the aerosol number concentration exceeds this critical value, the cloud droplet number decreases when aerosol number increases. A sensitivity study on aerosol chemical composition showed that the CCN activation was limited in the case of hydrophilic aerosol composed of material with a solubility in the 10% range. An event observed during the ParisFOG field experiment was simulated. This case took place in the polluted sub-urban area of Paris (France) characterized by particle concentrations of 17 000 aerosols per cm³. 1D simulations successfully reproduced the observed temporal evolution of the fog layer. Beyond the initial fog formation at the surface, cloud droplet formation occurred at the top of the fog layer where the cooling rate was maximum, reaching more than -10 Kh-1. These simulations confirm that the aerosol particle number concentration is a key parameter for the accurate prediction of the microphysical properties of a fog layer and also influences the vertical development of fog. The important of the interaction between microphysical and radiative processes is illustrated, showing how the life cycle of a fog layer is determined by the CCN number concentration and chemical properties. [ABSTRACT FROM AUTHOR]