Biomass burning and urban emission impacts in the Andes Cordillera region based on in situ measurements from the Chacaltaya observatory, Bolivia (5240 m a.s.l.)

This study documents and analyses a 4-year continuous record of aerosol optical properties measured at the Global Atmosphere Watch (GAW) station of Chacaltaya (CHC; 5240 m a.s.l.), in Bolivia. Records of particle light scattering and particle light absorption coefficients are used to investigate how the high Andean Cordillera is affected by both long-range transport and by the fast-growing agglomeration of La Paz-El Alto, located approximately 20 km away and 1.5 km below the sampling site. The extended multiyear record allows us to study the properties of aerosol particles for different air mass types, during wet and dry seasons, also covering periods when the site was affected by biomass burning in the Bolivian lowlands and the Amazon Basin. The absorption, scattering, and extinction coefficients (median annual values of 0.74, 12.14, and 12.96 Mm(-1) respectively) show a clear seasonal variation with low values during the wet season (0.57, 7.94, and 8.68 Mm(-1) respectively) and higher values during the dry season (0.80, 11.23, and 14.51 Mm(-1) respectively). The record is driven by variability at both seasonal and diurnal scales. At a diurnal scale, all records of intensive and extensive aerosol properties show a pronounced variation (daytime maximum, night-time minimum), as a result of the dynamic and convective effects. The particle light absorption, scattering, and extinction coefficients are on average 1.94, 1.49, and 1.55 times higher respectively in the turbulent thermally driven conditions than the more stable conditions, due to more efficient transport from the boundary layer. Retrieved intensive optical properties are significantly different from one season to the other, reflecting the changing aerosol emission sources of aerosol at a larger scale. Using the wavelength dependence of aerosol particle optical properties, we discriminated between contributions from natural (mainly mineral dust) and anthropogenic (mainly biomass burning and urban transport or industries) emissions according to seasons and local circulation. The main sources influencing measurements at CHC are from the urban area of La Paz-El Alto in the Altiplano and from regional biomass burning in the Amazon Basin. Results show a 28 % to 80 % increase in the extinction coefficients during the biomass burning season with respect to the dry season, which is observed in both tropospheric dynamic conditions. From this analysis, long-term observations at CHC provide the first direct evidence of the impact of biomass burning emissions of the Amazon Basin and urban emissions from the La Paz area on atmospheric optical properties at a remote site all the way to the free troposphere.Peer reviewe

Biomass burning and urban emission impacts in the Andes Cordillera region based on in situ measurements from the Chacaltaya observatory, Bolivia (5240a.s.l.)

This study documents and analyses a 4-year continuous record of aerosol optical properties measured at the Global Atmosphere Watch (GAW) station of Chacaltaya (CHC; 5240a.s.l.), in Bolivia. Records of particle light scattering and particle light absorption coefficients are used to investigate how the high Andean Cordillera is affected by both long-range transport and by the fast-growing agglomeration of La Paz-El Alto, located approximately 20km away and 1.5km below the sampling site. The extended multi-year record allows us to study the properties of aerosol particles for different air mass types, during wet and dry seasons, also covering periods when the site was affected by biomass burning in the Bolivian lowlands and the Amazon Basin. The absorption, scattering, and extinction coefficients (median annual values of 0.74, 12.14, and 12.96Mm-1 respectively) show a clear seasonal variation with low values during the wet season (0.57, 7.94, and 8.68Mm-1 respectively) and higher values during the dry season (0.80, 11.23, and 14.51Mm-1 respectively). The record is driven by variability at both seasonal and diurnal scales. At a diurnal scale, all records of intensive and extensive aerosol properties show a pronounced variation (daytime maximum, night-time minimum), as a result of the dynamic and convective effects. The particle light absorption, scattering, and extinction coefficients are on average 1.94, 1.49, and 1.55 times higher respectively in the turbulent thermally driven conditions than the more stable conditions, due to more efficient transport from the boundary layer. Retrieved intensive optical properties are significantly different from one season to the other, reflecting the changing aerosol emission sources of aerosol at a larger scale. Using the wavelength dependence of aerosol particle optical properties, we discriminated between contributions from natural (mainly mineral dust) and anthropogenic (mainly biomass burning and urban transport or industries) emissions according to seasons and local circulation. The main sources influencing measurements at CHC are from the urban area of La Paz-El Alto in the Altiplano and from regional biomass burning in the Amazon Basin. Results show a 28% to 80% increase in the extinction coefficients during the biomass burning season with respect to the dry season, which is observed in both tropospheric dynamic conditions. From this analysis, long-term observations at CHC provide the first direct evidence of the impact of biomass burning emissions of the Amazon Basin and urban emissions from the La Paz area on atmospheric optical properties at a remote site all the way to the free troposphere. © Author(s) 2019

Tropospheric and stratospheric smoke over Europe as observed within EARLINET/ACTRIS in summer 2017

For several weeks in summer 2017, strong smoke layers were observed over Europe at numerous EARLINET stations. EARLINET is the European research lidar network and part of ACTRIS and comprises more than 30 ground-based lidars. The smoke layers were observed in the troposphere as well as in the stratosphere up to 25 km from Northern Scandinavia over whole western and central Europe to the Mediterranean regions. Backward trajectory analysis among other tools revealed that these smoke layers originated from strong wild fires in western Canada in combination with pyrocumulus convection. An extraordinary fire event in the mid of August caused intense smoke layers that were observed across Europe for several weeks starting on 18 August 2017. Maximum aerosol optical depths up to 1.0 at 532 nm were observed at Leipzig, Germany, on 22 August 2017 during the peak of this event. The stratospheric smoke layers reached extinction coefficient values of more than 600 Mm−1 at 532 nm, a factor of 10 higher than observed for volcanic ash after the Pinatubo eruption in the 1990s. First analyses of the intensive optical properties revealed low particle depolarization values at 532 nm for the tropospheric smoke (spherical particles) and rather high values (up to 20%) in the stratosphere. However, a strong wavelength dependence of the depolarization ratio was measured for the stratospheric smoke. This indicates irregularly shaped stratospheric smoke particles in the size range of the accumulation mode. This unique depolarization feature makes it possible to distinguish clearly smoke aerosol from cirrus clouds or other aerosol types by polarization lidar measurements. Particle extinction-to-backscatter ratios were rather low in the order of 40 to 50 sr at 355 nm, while values between 70-90 sr were measured at higher wavelengths. In the western and central Mediterranean, stratospheric smoke layers were most prominent in the end of August at heights between 16 and 20 km. In contrast, stratospheric smoke started to occur in the eastern Mediterranean (Cyprus and Israel) in the beginning of September between 18 and 23 km. Stratospheric smoke was still visible in the beginning of October at certain locations (e.g. Evora, Portugal), while tropospheric smoke was mainly observed until the end of August within Europe. An overview of the smoke layers measured at several EARLINET sites will be given. The temporal development of these layers as well as their geometrical and optical properties will be presented

Etude du transport isentrope de la vapeur d'eau dans la haute troposphère et la basse stratosphère

Water vapour is a primordial constituent of the atmosphere in view of its role on the earth surface temperature and its impact on the protective ozone layer. The ozone mixing ratios in stratosphere (~12 up to 50 km high) showed however high tendencies with great disagreements between the instruments. The first part of this thesis contributes to the evaluation of new instruments in the tropical higher troposphere and lower stratosphere. Bias between the instruments remain high and variabilities differ prevent from combining the data together to obtain long term tendencies. However some instruments could be used in scientific studies. The second part of this thesis study the mechanisms injecting water vapour in the lower stratosphere witch could explain a part of the tendencies observed. Among them, the quasi-horizontal meridian adiabatic exchanges between the subtropical troposphere (0-12 km) and the midlatitude stratosphere, not enough researched, is on the scope of this thesis. Thus an adiabatic model is adapted to transport water in its three phases with a simplified microphysical model. Many initialisations of the water vapour field are tested. Then the model is applied to a study case above Europe to quantify the transport of water vapour. The model is able to reproduce the observed cirrus and shows that this transport is as important as other transports as monsoon or deep convection.La vapeur d'eau est un constituant essentiel de l'atmosphère ayant un rôle sur la température à la surface de la terre et un impact sur la couche protectrice d'ozone. Les concentrations de vapeur d'eau en stratosphère (~12 à 50 km d'altitude) ont cependant montré de fortes tendances avec des désaccords importants entre les instruments. La première partie de cette thèse contribue à l'évaluation d'instruments récents dans la haute troposphère et basse stratosphère tropicale. Il s'avère que des biais importants entre les instruments et des variabilités différentes persistent empêchant de combiner les données pour fournir de longues tendances. Néanmoins, certains instruments peuvent être utilisés dans des études scientifiques. La seconde partie de cette thèse s'est focalisée sur les mécanismes introduisant de la vapeur d'eau en basse stratosphère pouvant expliquer une part des tendances observées. Parmi eux, les échanges méridiens quasi-horizontaux et adiabatiques entre la troposphère (0-12 km d'altitude) subtropicale et la stratosphère des moyennes latitudes encore peu documentés font l'objet de cette thèse. Ainsi un modèle adiabatique est adapté pour transporter l'eau sous ses trois phases avec un module de microphysique simplifié. Plusieurs initialisations du champ de vapeur d'eau sont testées. Puis le modèle est utilisé pour quantifier un cas d'étude au-dessus de l'Europe. Le modèle s'avère capable de reproduire les cirrus observés et montre que ce type d'apport de vapeur d'eau est aussi important que ceux liés à la mousson ou à la convection profonde

Etude du transport isentrope de la vapeur d'eau dans la haute troposphère et la basse stratosphère

La première partie de cette thèse contribue à l évaluation de différentes mesures de vapeur d eau dans la haute troposphère et basse stratosphère tropicale. Malgré que des biais importants soient observés entre les instruments, certains peuvent être utilisés dans des études scientifiques. La seconde partie de cette thèse s est focalisée sur les mécanismes introduisant de la vapeur d eau en basse stratosphère et plus particulièrement sur les échanges méridiens quasi-horizontaux et adiabatiques entre la troposphère subtropicale et la stratosphère des moyennes latitudes. Un modèle adiabatique est adapté pour transporter l eau sous ses trois phases avec un module de microphysique simplifié. Plusieurs initialisations de la vapeur d eau sont testées. Le modèle, utilisé pour quantifier un cas d étude au-dessus de l Europe, s avère capable de reproduire les cirrus observés et montre que ce type d apport de vapeur d eau est aussi important que ceux liés à la mousson ou à la convection profonde.PARIS-BIUSJ-Sci.Terre recherche (751052114) / SudocSudocFranceF

Atmospheric Rivers and Associated Precipitation over France and Western Europe: 1980–2020 Climatology and Case Study

International audienceAtmospheric rivers are important atmospheric features implicated in the global water vapor budget, the cloud distribution, and the associated precipitation. The ARiD (Atmospheric River Detector) code has been developed to automatically detect atmospheric rivers from water vapor flux and has been applied to the ECMWF ERA5 archive over the period 1980–2020 above the Atlantic Ocean and Europe. A case study of an atmospheric river formed in the East Atlantic on August 2014 that reached France has been detailed using ECMWF ERA5 reanalysis, ground based observation data, and satellite products such as DARDAR, AIRS, GPCP, and GOES. This atmospheric river event presents a strong interaction with an intense upper tropospheric jet stream, which induced stratosphere–troposphere exchanges by tropopause fold. A 1980–2020 climatology of atmospheric rivers over Europe has been presented. The west of France, Iberian Peninsula, and British Islands are the most impacted regions by atmospheric rivers with an occurrence of up to four days per month during the October–April period. Up to 40% of the precipitation observed on the west European coast can be linked to the presence of ARs. No significant trend in the occurrence of the phenomena was found over 1980–202

Mid-latitude cirrus analysis with lidars: clustering and match approach

A review of the recent and on going works about the characterization of mid-latitude cirrus through two advanced multi-channel lidar systems, located in the Mediterranean area, is presented. These systems, at the Observatory of Haute Provence (OHP, 43.9° N, 5.7° E) in France and at Rome Tor Vergata (RTV, 41.8° N, 12.6° E) in Italy, observe cirrus in operational or semi-operational mode. A statistical approach has been used to derive cirrus classification (and climatology) over the period 1996-2007 for OHP lidar measurements. Similarly, a preliminary cirrus classification has been performed on RTV lidar data for three years period and compared to the French one. Finally a study to assess the feasibility of a future observing strategy that couples lidar measurements to a Match approach has been conducted to characterize cirrus optical properties using both the French and the Italian site. A case of upper tropospheric thin cirrus advection has been identified and studied through this approach

Isentropic modeling of a cirrus cloud event observed in the midlatitude upper troposphere and lower stratosphere

International audienceThis publication provides a detailed study of one cirrus cloud observed by lidar at the Observatory of Haute-Provence (∼44°N) in January 2006 in the vicinity of the tropopause (12–14 km/∼136–190 hPa/328–355 K). The higher part of the air mass observed comes from the wet subtropics while the lower part comes from the midlatitudes. Both are advected by the Azores anticyclone, encounter cold temperatures (∼205 K) above the North Atlantic Ocean, and flow eastward along the anticyclonic flank of the polar jet stream. A simulation of this cloud by an isentropic model is tested to see if synoptic-scale atmospheric structures could explain by itself the presence of such clouds. The developments made in the Modélisation Isentrope du transport Méso-échelle de l'Ozone Stratosphérique par Advection (MIMOSA) model to take into account the three phases of water and their interactions allow reproduction of the occurrence of the cirrus and its temporal evolution. MIMOSA-H2O reproduces the atmospheric water vapor structures observed with Atmospheric Infrared Sounder (AIRS) with, however, an apparent wet bias of around 50%. Reliable water vapor fields appear to be the main condition to correctly simulate such cirrus clouds. The model reproduces the cirrus cloud altitude for fall speeds around 1 cm/s and gives ice water content around 3–4 mg/m3. Fall speed is also a critical parameter, and a better parameterization with altitude or other atmospheric conditions in the modeling of such cirrus clouds is required. This study also shows that supersaturation threshold impacts strongly the vertical and horizontal extension of the cirrus cloud but more slightly the ice water path

Subgrid-scale cirrus observed by lidar at mid-latitude : variability of the cloud optical depth

International audienceThe temporal variability of the 532-nm optical depth of cirrus clouds observed with a lidar at Observatory of Haute-Provence (43.9°N, 5.7°E, and 683-m altitude), has been analyzed. While advection dominates at the first order, variability of the optical depth on timescales of minutes can be related to spatial fluctuations of cloud properties on typical scales of a few kilometers. Log-normal distributions of the optical depth have been used to model the variability of the cirrus optical depth as observed by lidars. These investigations have been performed for three independent classes of cirrus. The log-normal distribution of the optical depth is applicable to the classes of thin clouds; however, for thick clouds, likely due to successive freezing/defreezing effects, the distribution is rather bimodal. This work compares the effects of visible solar light scattered by inhomogeneous cirrus to effects generated by homogeneous clouds having a constant geometrical thickness using the short-scale lidar observations of optical depth distribution and an analytical approach. In the case of thin cirrus, the scattering of solar light reaching the ground is stronger for inhomogeneous than homogeneous cirrus. In case of thick cirrus, multiple-scattering processes need to be considered. The conclusion is that log-normal distribution of the cirrus optical depth should be considered in any radiative calculation in case of model grids larger than a few kilometers whatever the cirrus type is

Microphysical modelling of a midlatitude "polar stratospheric cloud" event: Comparisons against multiwavelength ground-based and spaceborne lidar data

International audienceA high-resolution transport model containing a fully explicit size-resolving microphysical scheme is used to study a large-scale polar stratospheric cloud (PSC) case detected by lidar at midlatitudes between 17 and 23 February 2008. The model simulations, initialized using European Centre for Medium-Range Weather Forecasts (ECMWF) fields and Microwave Limb Sounder (MLS) Aura data, are validated locally against ground-based (Institute for Tropospheric Research Multiwavelength Atmospheric Raman lidar for Temperature, Humidity, and Aerosol profiling (IfT MARTHA)) lidar measurements at Leipzig and globally against spaceborne (Cloud-Aerosol LIdar with Orthogonal Polarization/Cloud-Aerosol-Lidar and Infrared Pathfinder Satellite Observations (CALIOP/CALIPSO)) lidar backscatter measurements. By assuming a 1 K cold bias on the ECMWF temperatures and under the assumption of equilibrated spherical PSC particles, our model produces fields of optical and microphysical parameters like the total surface area density (A) and volume (V). A, and V, as well as the median radius of the PSC size distribution, compare favorably to the corresponding values derived from multiwavelength lidar backscatter measurements. Around 21 km, A and V are found to be around 10 μm2 cm−3 and 1 μm3 cm−3, respectively. The median radius of the Supercooled Ternary Solution particle size distribution is estimated to be around 0.3 μm using both the model calculations and the lidar-derived size distribution parameters. Overall, despite the simplifications on the microphysical scheme, the model is able to reproduce the salient features of the local and global lidar observations. The results clearly demonstrate the value of CALIOP products for large-scale studies, exploiting chemistry-transport models