Doctor of Philosophy

dissertationThe Arctic region is warming particularly rapidly. Aerosol impacts on cloud microphysical parameters are still poorly understood. Aerosol-cloud interactions (ACI) play an important role for cloud radiative properties and climate change. A challenge in the study of ACI is the use of independent datasets for cloud microphysical parameters and aerosol content so they cannot influence one another. In this study, we combine measurements from satellite instruments POLDER-3 and MODIS to temporally and spatially colocate cloud microphysical properties with carbon monoxide concentrations from GEOS-Chem and FLEXPART, serving as a passive tracer of aerosol content. We also add ERA-I reanalysis of meteorological parameters to stratify me- teorological parameters such as specific humidity and lower tropospheric stability. Thus, observed differences in cloud microphysical parameters can be attributed to differences in aerosol content rather than meteorological variability. We define a net aerosol-cloud interaction parameter (ACInet) which can be interpreted as a measure of the sensitivity of a cloud at any given location to pollution plumes from distant sources. We use this parameter to study the impact of aerosols from anthropogenic and biomass burning sources from midlatitudes on liquid-cloud microphysical properties in Arctic, for a time period between 2005 and 2010, above ocean, and for controlled meteorological regimes. Our results suggest that the effect of biomass pollution plumes on clouds is smaller (ACInet close to 0) than that for anthropogenic pollution plumes (ACInet close to 0.30). Meteorological parameters can inhibit the aerosol-cloud interaction or favor the aerosol-cloud interaction. The impact of anthropogenic aerosol on thermodynamic phase transition are analyzed. The smaller the effective radius, the higher the supercooling temperature whereas the greater the aerosol concentration, the lower the supercooling temperature. Independently of changes in effective radius, decrease in energy barrier due to an increase in aerosol concentration can be up to 48

Exploring the Cloud Top Phase Partitioning in Different Cloud Types Using Active and Passive Satellite Sensors

One of the largest uncertainties in numerical weather prediction and climate models is the representation of mixed-phase clouds. With the aim of understanding how the supercooled liquid fraction (SLF) in clouds with temperature from -40$^\circ$C to 0$^\circ$C is related to temperature, geographical location, and cloud type, our analysis contains a comparison of four satellite-based datasets (one derived from active and three from passive satellite sensors), and focuses on SLF distribution near-globally, but also stratified by latitude and continental/maritime regions. Despite the warm bias in cloud top temperature of the passive sensor compared to the active sensor and the phase mismatch in collocated data, all datasets indicate, at the same height-level, an increase of SLF with cloud optical thickness, and generally larger SLF in the Southern Hemisphere than in the Northern Hemisphere (up to about 20\% difference), with the exception of continental low-level clouds, for which the opposite is true

Exploring the Cloud Top Phase Partitioning in Different Cloud Types Using Active and Passive Satellite Sensors

One of the largest uncertainties in numerical weather prediction and climate models is the representation of mixed-phase clouds. With the aim of understanding how the supercooled liquid fraction (SLF) in clouds with temperature from -40$^\circ$C to 0$^\circ$C is related to temperature, geographical location, and cloud type, our analysis contains a comparison of four satellite-based datasets (one derived from active and three from passive satellite sensors), and focuses on SLF distribution near-globally, but also stratified by latitude and continental/maritime regions. Despite the warm bias in cloud top temperature of the passive sensor compared to the active sensor and the phase mismatch in collocated data, all datasets indicate, at the same height-level, an increase of SLF with cloud optical thickness, and generally larger SLF in the Southern Hemisphere than in the Northern Hemisphere (up to about 20\% difference), with the exception of continental low-level clouds, for which the opposite is true

Sensitivity of cloud-phase distribution to cloud microphysics and thermodynamics in simulated deep convective clouds and SEVIRI retrievals

The formation of ice in clouds is an important process in mixed-phase clouds, and the radiative properties and dynamical developments of clouds strongly depend on their partitioning between the liquid and ice phases. In this study, we investigated the sensitivities of the cloud phase to the ice-nucleating particle (INP) concentration and thermodynamics. Moreover, passive satellite retrieval algorithms and cloud products were evaluated to identify whether they could detect cloud microphysical and thermodynamical perturbations. Experiments were conducted using the ICOsahedral Nonhydrostatic (ICON) model at the convection-permitting resolution of about 1.2 km on a domain covering significant parts of central Europe, and they were compared to two different retrieval products based on Spinning Enhanced Visible and InfraRed Imager (SEVIRI) measurements. We selected a day with multiple isolated deep convective clouds, reaching a homogeneous freezing temperature at the cloud top. The simulated cloud liquid pixel fractions were found to decrease with increasing INP concentration, both within clouds and at the cloud top. The decrease in the cloud liquid pixel fraction was not monotonic and was stronger in high-INP cases. Cloud-top glaciation temperatures shifted toward warmer temperatures with an increasing INP concentration by as much as 8$^◦$C

Modification of arctic clouds by long-range aerosol transport

Les interactions des aérosols avec les nuages en Arctique peuvent avoir de fortes conséquences sur le forçage radiatif. Néanmoins cette interaction reste encore mal comprise. Dans cette étude nous utilisons les instruments satellitaires POLDER-3 & MODIS pour obtenir des informations sur les propriétés microphysiques des nuages que nous co-localisons temporellement et spatialement avec la concentration en monoxyde de carbone, traceur passif du contenu en aérosols, issue des modèles numériques GEOS-Chem et FLEXPART. Nous co-localisons également les données avec les réanalyses de ERA-Interim pour pouvoir contrôler les paramètres météorologiques tel que l’humidité spécifique et la stabilité de la basse troposphère. Afin d’étudier l'impact des panaches de pollution sur la microphysique des nuages, nous définissons le paramètre ACInet qui décrit l'interaction aérosol nuage. Nos résultats suggèrent que les parcelles d'air venant de feux de biomasses ont un effet limité sur la microphysique des nuages. Au contraire, l'effet des aérosols venant de sources anthropiques ont un effet proche d'un maximum théorique. Nous étudions alors l'impact de différents paramètres météorologiques sur l'ACInet. Nous avons également analysé l'impact des aérosols d'origine anthropiques sur la transition de phase liquide-glace des nuages. Nos résultats indiquent que le contenu en aérosols a un effet net de diminution de la température de transition de phase, ce qui est susceptible d'avoir de fortes conséquences sur la durée de vie des nuages.The Arctic region is warming particularly rapidly. The aerosol-cloud interaction (ACI) plays an important role on cloud radiative properties and climate change but aerosol impact on cloud microphysical parameters is still poorly understood.In this study we combine measurements from the satellite instruments POLDER-3 and MODIS to temporally and spatially co-localize cloud microphysical properties with carbon monoxide concentrations, passive tracer of aerosol content, from GEOS-Chem and FLEXPART. We also add ERA-I reanalysis of meteorological parameters to stratify meteorological parameters, such as specific humidity and lower tropospheric stability. Thus, observed differences in cloud-microphysical-parameters can be attributed to differences in aerosol content and not in meteorological parameters. We define a net ACI (ACInet) which can be interpreted as a measure of the sensitivity of a cloud at any given location to pollution plumes from distant sources. We study the impact of aerosols from anthropogenic and biomass-burning sources on liquid-cloud microphysical properties in Arctic, between 2005 and 2010, above ocean, and for different meteorological regimes. Our results suggest that the effect of biomass pollution plumes is smaller than the effect of anthropogenic pollution plumes. Meteorological parameters can significantly influence the ACI. We analyze the impact of anthropogenic aerosol on thermodynamic phase transition. The smaller the effective radius, the greater the supercooled temperature, whereas the greater the aerosol concentration, the smaller the supercooled temperature

Exploring the Cloud Top Phase Partitioning in Different Cloud Types Using Active and Passive Satellite Sensors

One of the largest uncertainties in numerical weather prediction and climate models is the representation of mixed‐phase clouds. With the aim of understanding how the supercooled liquid fraction (SLF) in clouds with temperature from −40°C to 0°C is related to temperature, geographical location, and cloud type, our analysis contains a comparison of four satellite‐based datasets (one derived from active and three from passive satellite sensors), and focuses on SLF distribution near‐globally, but also stratified by latitude and continental/maritime regions. Despite the warm bias in cloud top temperature of the passive sensor compared to the active sensor and the phase mismatch in collocated data, all datasets indicate, at the same height‐level, an increase of SLF with cloud optical thickness, and generally larger SLF in the Southern Hemisphere than in the Northern Hemisphere (up to about 20% difference), with the exception of continental low‐level clouds, for which the opposite is true

Sensitivity of cloud-phase distribution to cloud microphysics and thermodynamics in simulated deep convective clouds and SEVIRI retrievals

International audienceThe formation of ice in clouds is an important process in mixed-phase clouds, and the radiative properties and dynamical developments of clouds strongly depend on their partitioning between the liquid and ice phases. In this study, we investigated the sensitivities of the cloud phase to the ice-nucleating particle (INP) concentration and thermodynamics. Moreover, passive satellite retrieval algorithms and cloud products were evaluated to identify whether they could detect cloud microphysical and thermodynamical perturbations. Experiments were conducted using the ICOsahedral Nonhydrostatic (ICON) model at the convection-permitting resolution of about 1.2 km on a domain covering significant parts of central Europe, and they were compared to two different retrieval products based on Spinning Enhanced Visible and InfraRed Imager (SEVIRI) measurements. We selected a day with multiple isolated deep convective clouds, reaching a homogeneous freezing temperature at the cloud top. The simulated cloud liquid pixel fractions were found to decrease with increasing INP concentration, both within clouds and at the cloud top. The decrease in the cloud liquid pixel fraction was not monotonic and was stronger in high-INP cases. Cloud-top glaciation temperatures shifted toward warmer temperatures with an increasing INP concentration by as much as 8˚C. Moreover, the impact of the INP concentration on cloud-phase partitioning was more pronounced at the cloud top than within the cloud. Furthermore, initial and lateral boundary temperature fields were perturbed with increasing and decreasing temperature increments from 0 to ±3 and ±5 K between 3 and 12 km, respectively. Perturbing the initial thermodynamic state was also found to systematically affect the cloud-phase distribution. However, the simulated cloud-top liquid pixel fraction, diagnosed using radiative transfer simulations as input to a satellite forward operator and two different satellite remote-sensing retrieval algorithms, deviated from one of the satellite products regardless of perturbations in the INP concentration or the initial thermodynamic state for warmer subzero temperatures while agreeing with the other retrieval scheme much better, in particular for the high-INP and high-CAPE (convective available potential energy) scenarios. Perturbing the initial thermodynamic state, which artificially increases the instability of the mid- and upper-troposphere, brought the simulated cloud-top liquid pixel fraction closer to the satellite observations, especially in the warmer mixed-phase temperature range

Temporal Evolution of Wildfire Plumes Along Long-Range Transport Provides Information on Cloud Processes

International audienceThe number and intensity of wildfires are increasing due to climate change, as evidenced by the devastating wildfires in North America, Europe and Siberia last summer. As a result, more aerosols from biomass burning are released into the atmosphere, with local and remote effects on e.g., air quality. Here we present how space-based observations, models, and simulated air parcel trajectories can help to better represent and parameterize the long-range transport and evolution of biomass burning plumes, focusing on a case study of wildfires in the western United States in 2020.Several geostationary satellites are needed to represent long-range aerosol transports. We use the aerosol optical depth (AOD) from the Aerosol and surface albEdo Retrieval Using a directional Splitting method-application to GEOstationary data (AERUS-GEO) algorithm, which incorporates measurements from the American, European, and Japanese geostationary satellites. We collocate AOD with a passive tracer of combustion plumes, carbon monoxide (CO), from the Infrared Atmospheric Sounding Interferometer (IASI) suite of polar-orbiting satellites. We also examine the retrievals of CO and AOD from the analysis of the Copernicus Atmosphere Monitoring Service (CAMS). Finally, Hybrid Single-Particle Lagrangian Integrated Trajectory (HYSPLIT) backward and forward trajectories are used to analyze the transport of the air parcels.Some plumes from the western USA were transported across the Atlantic and detected by a ground-based station in northern France. Our results show that CO and AOD from the satellite instruments and CAMS are in good agreement, with a higher correlation over the USA than over Europe. From backward and forward trajectories of air parcels during these wildfire events, we show that the temporal evolution of the ratio of AOD and CO can be a sign of aerosol removal processes such as precipitation. Therefore, the analysis of atmospheric components retrieved from geostationary satellite measurements or models could potentially be used to infer information about cloud processes acting on aerosols and could be used to improve the representation in models

Temporal Evolution of Wildfire Plumes Along Long-Range Transport Provides Information on Cloud Processes

International audienceThe number and intensity of wildfires are increasing due to climate change, as evidenced by the devastating wildfires in North America, Europe and Siberia last summer. As a result, more aerosols from biomass burning are released into the atmosphere, with local and remote effects on e.g., air quality. Here we present how space-based observations, models, and simulated air parcel trajectories can help to better represent and parameterize the long-range transport and evolution of biomass burning plumes, focusing on a case study of wildfires in the western United States in 2020.Several geostationary satellites are needed to represent long-range aerosol transports. We use the aerosol optical depth (AOD) from the Aerosol and surface albEdo Retrieval Using a directional Splitting method-application to GEOstationary data (AERUS-GEO) algorithm, which incorporates measurements from the American, European, and Japanese geostationary satellites. We collocate AOD with a passive tracer of combustion plumes, carbon monoxide (CO), from the Infrared Atmospheric Sounding Interferometer (IASI) suite of polar-orbiting satellites. We also examine the retrievals of CO and AOD from the analysis of the Copernicus Atmosphere Monitoring Service (CAMS). Finally, Hybrid Single-Particle Lagrangian Integrated Trajectory (HYSPLIT) backward and forward trajectories are used to analyze the transport of the air parcels.Some plumes from the western USA were transported across the Atlantic and detected by a ground-based station in northern France. Our results show that CO and AOD from the satellite instruments and CAMS are in good agreement, with a higher correlation over the USA than over Europe. From backward and forward trajectories of air parcels during these wildfire events, we show that the temporal evolution of the ratio of AOD and CO can be a sign of aerosol removal processes such as precipitation. Therefore, the analysis of atmospheric components retrieved from geostationary satellite measurements or models could potentially be used to infer information about cloud processes acting on aerosols and could be used to improve the representation in models