Anwendungen zur Abschätzung des Strahlungseinflusses von Aerosolen

The aim of this PhD research is to contribute to a better estimation of the radiation budget of the Earth and the atmosphere by delving into the further understanding of physical phenomena of the atmosphere. The studied phenomena are the atmospheric radiative transfer and aerosols. The radiative transfer code MOMO (Matrix Operator Model) has been extended from shortwave [0.2 – 4 μm] to the full spectral range [0.2 – 100 μm] in order to obtain a versatile radiative transfer code that can be used for different radiative transfer studies (e.g. inversion of remote sensing measurements, optimization and calibration of measurement instruments and methods, estimation of radiative transfer fluxes, estimation of radiative forcings and heating rates), with different exigencies of precision and rapidity and over the full spectral range. The extension of MOMO to the full range consisted of the integration of the emission of thermal infrared radiation by gases, aerosols and clouds into the matrix operator algorithm of the code. The extension of MOMO also required the development of a spectroscopy module for the modeling of the water vapor continuum of absorption in the thermal infrared. In MOMO, the gas transmission for spectral bands is modeled by means of a k-distribution method. This k-distribution algorithm has also been extended to the thermal infrared and now includes the gas emission of radiation. In a second step, MOMO has been applied in a study on the contribution of aerosols to the radiation budget. This application has been carried out in 3 steps: 1) The characterization of the aerosols by means of observations on a regional scale (measurement campaign or spaceborne measurements). 2) The development of a radiative transfer scheme with radiative transfer code MOMO in its full range version. 3) The estimation of the radiative fluxes and of instant aerosol radiative forcings and heating-rates. The results of this work demonstrate the importance of the instrumental synergy of in-situ measurements and lidar remote sensing for the characterization of aerosol microscopic properties (refractive index and size distribution). The latter method was applied to aerosols in the Mediterranean basin within the measurement campaign TRAQA. The results have revealed the differences between pollution aerosols and desert dust aerosols regarding their microscopic and radiative properties. Further case studies have shown that the presence of clouds below the aerosols has a decisive influence on the sign and on the order of magnitude of aerosol direct radiative forcing.Das Ziel dieser Doktorarbeit ist das Verständnis von physikalischen atmosphärischen Phänomenen zu vertiefen, um eine bessere Abschätzung der Strahlungsbilanz zu erhalten. Die Phänomene, die untersucht wurden sind der Strahlungstransport in der Atmosphäre und die Aerosole. Das Strahlungstransportprogramm MOMO (Matrix-Operator Method) wurde vom kurzwelligen Spektralbereich [0.2 – 4 μm] zum gesamten Spektralbereich [0.2 – 100 μm] erweitert. Dadurch erhielten wir ein Programm, das für Strahlungstransportsimulierungen unterschiedlicher Art und ohne spektrale Einschränkung verwendet werden kann. Die Erweiterung des Spektralbereiches MOMOs besteht in der Implementierung der Strahlungsemission von Gasen, Aerosolen und Wolken in den Matrix-Operator Algorithmus des Programms. Für die Erweiterung des Programms zum langwelligen Spektralbereich wurde auch ein spektroskopisches Modul entwickelt, um das Absorptionskontinuum von Wasserdampf im thermischen infraroten Spektralbereich zu modellieren. Innerhalb von MOMO wird die Transmission von Gasen für breite Spektralbände anhand einer sogenannten „k-Verteilung Methode“ modelliert. Des Weiteren wurde der k-Verteilungsalgorithmus MOMOs zum thermischen Infrarot erweitert, um die Strahlungsemission von Gasen zu berücksichtigen. In dieser Arbeit wurde MOMO verwendet, um den Beitrag der Aerosole zur Strahlungsbilanz abzuschätzen. Die Studie wurde in 3 Schritten durchgeführt: 1) Die Charakterisierung der Aerosole anhand von Beobachtungen auf der regionalen Skala (aus Messkampagnen oder Satellitendaten). 2) Die Entwicklung eines Schemas zur Strahlungssimulation mit der neuen Version MOMOs als Kern. 3) Die Abschätzung der Strahlungsflüsse und des Strahlungsantriebes und der Heizrate der Aerosole. Die Ergebnisse dieser Studie zeigen wie effizient die Synergie von in-situ Messungen und LIDAR-Messungen für die Charakterisierung der mikroskopischen Eigenschaften der Aerosole ist. Diese Methode wurde innerhalb der Messkampagne TRAQA (Aerosole in der Region des Mittelmeeres) zur Datenauswertung verwendet. Die Ergebnisse zeigen große Unterschiede zwischen Verschmutzungsaerosolen und Wüstenaerosolen bezüglich ihrer mikroskopischen Eigenschaften und Strahlungseigenschaften. Weitere Fallstudien in dieser Arbeit haben gezeigt, dass Wolken unter Aerosolschichten einen entscheidenden Einfluss auf sowohl das Vorzeichen als auch den Betrag des Strahlungsantriebes der Aerosole haben

Capillary origami: spontaneous wrapping of a droplet with an elastic sheet

The interaction between elasticity and capillarity is used to produce three dimensional structures, through the wrapping of a liquid droplet by a planar sheet. The final encapsulated 3D shape is controlled by tayloring the initial geometry of the flat membrane. A 2D model shows the evolution of open sheets to closed structures and predicts a critical length scale below which encapsulation cannot occur, which is verified experimentally. This {\it elastocapillary length} is found to depend on the thickness as $h^{3/2}$, a scaling favorable to miniaturization which suggests a new way of mass production of 3D micro- or nano-scale objects.Comment: 5 pages, 5 figure

Origami Capillaire

Le pelage d'un chien qui sort de l'eau s'agrège en touffes : ceci est un exemple commun de l'effet des forces capillaires sur des structures élastiques. D'un point de vue pratique, la déformation de structures flexibles par les forces de tension de surface peut conduire à de graves dommages sur des microsystèmes mécaniques (à petite échelle, les forces capillaires deviennent prépondérantes). Cependant ce collage permet également l'auto-association de microstructures selon des motifs bien définis. Au delà de la flexion de tiges, que se passe-t-il si on pose une goutte d'eau sur une feuille très flexible ? La feuille peut-elle enrober spontanément la goutte ? Nous déterminerons quel est le critère d'enrobage et décrirons les differentes formes obtenues. En particulier, nous montrerons comment un tel mécanisme d'origami capillaire peut s'avérer pertinent pour l'élaboration de micro-structures tridimensionnelles à partir de patrons bidimensionnels

1D radiative transfer simulation of complex aerosol-cloud structure. Sensitivity study and implication to regional forcing estimates

The spatial distribution of aerosol and clouds in the atmosphere leads, in a significant number of cases, to the occurrence of a complex vertical stratification and large horizontal variability. This is especially the case when low and mid- level clouds are embedded over the ocean in absorbing aerosol layers near polluted areas or biomass burning regions. This implies at the same time difficulties to determine representative optical and microphysical properties in any vertical column from remote sensing observations, and problems to perform accurate radiation budget analysis at the regional scale. A set of representative cases for such complex aerosol and clouds structures has been looked at. The last version of the radiative transfer (RT) code MOMO (Matrix Operator MOdel) of Free University of Berlin has been used to simulate 1-D radiative transfer in shortwave (SW) and in longwave (LW) and perform sensitivity tests for a few representative cases. The parameters identified to characterize the impact of errors in RT simulations are: 1) the heights and thicknesses of aerosol and clouds layers, and 2) clouds and aerosol optical properties (cloud effective radius, cloud liquid water content, cloud phase, aerosol single scattering albedo, extinction coefficient, asymmetry factor). Simulations of radiative fluxes, spectral radiances and irradiances, net fluxes for different altitudes and radiative heating-rates in SW and LW have been performed using the above described parameters and background vertical profiles for temperature and moisture as inputs of the RT model. First application is the improvement of satellite retrievals of clouds properties. Indeed, for instrument channels used to retrieve the clouds properties, complex structures with embedded aerosol and clouds layers may lead to similar top of atmosphere spectral radiances as compared to single layer structures having other properties (e.g. an absorbing aerosol layer over warm clouds as in the Gulf of Guinea would impact the retrieval of cloud properties). Examples are given and discussed. Another application is the error analysis in the computation of radiative forcing in a given region, using similar typical aerosol and cloud structure as identified from observations. The sensitivity analysis is used to identify criticality of input parameters. Outputs are the top of atmosphere and surface radiative forcings for mixed aerosol and cloud layers. Uncertainties resulting from spatial or temporal variability are then discussed

Shortwave radiative heating rate profiles in hazy and clear atmosphere: a sensitivity study

International audienceAerosols have an impact on shortwave heating rate profiles (additional heating or cooling). In this survey, we quantify the impact of several key-parameters on the heating rate profiles of the atmosphere with and without aerosols. These key-parameters are: (1) the atmospheric model (tropical, midlatitude summer or winter, US Standard), (2) the integrated water vapor amount (IWV ), (3) the ground surface (flat and rough ocean, isotropic surface albedo for land), (4) the aerosol composition (dusts, soots or maritimes mixtures with respect to the OPAC-database classification), (5) the aerosol optical depth and (6) vertical postion, and (7) the single-scattering albedo (?o) of the aerosol mixture. This study enables us to evaluate which parameters are most important to take into account in a radiative energy budget of the atmosphere and will be useful for a future study: the retrieval of heating rates profiles from satellite data (CALIPSO, MODIS, MERIS) over the Mediterranean Sea. All the heating rates are computed by using the vector irradiances computed at each pressure level in the spectral interval 0.2 - 3.6μm (shortwave) by the 1D radiative transfer model for atmosphere and ocean: MOMO (Matrix-Operator MOdel) of the Institute for Space Science, FU Berlin

Extension of radiative transfer code MOMO, matrix-operator model to the thermal infrared. Clear air validation by comparison to RTTOV and application to CALIPSO-IIR

International audience1-D radiative transfer code MOMO (Matrix-Operator Model), has been extended from View the MathML source band to the whole View the MathML source spectrum. MOMO can now be used for computation of full range radiation budgets (shortwave and longwave). This extension to the longwave part of the electromagnetic radiation required to consider radiative transfer processes that are features of the thermal infrared: the spectroscopy of the water vapor self- and foreign- continua of absorption at View the MathML source and the emission of radiation by gases, aerosol, clouds and surface. MOMO's spectroscopy module, CGASA (Coefficient of Gas Absorption), has been developed for computation of gas extinction coefficients, considering continua and spectral line absorption. The spectral dependences of gas emission/absorption coefficients and of Planck's function are treated using a k-distribution. The emission of radiation is implemented in the adding-doubling process of the matrix operator method using Schwarzschild's approach in the radiative transfer equation (a pure absorbing/emitting medium, namely without scattering). Within the layer, the Planck-function is assumed having an exponential dependence on the optical-depth. In this paper, validation tests are presented for clear air case studies: Comparisons to the analytical solution of a monochromatic Schwarzschild's case without scattering show an error of less than 0.07% for a realistic atmosphere with an optical depth and a blackbody temperature that decrease linearly with altitude. Comparisons to radiative transfer code RTTOV are presented for simulations of top of atmosphere brightness temperature for channels of the space-borne instrument MODIS. Results show an agreement varying from 0.1 K to less than 1 K depending on the channel. Finally MOMO results are compared to CALIPSO Infrared Imager Radiometer (IIR) measurements for clear air cases. A good agreement was found between computed and observed radiance: biases are smaller than 0.5 K and RMSE (Root Mean Square Error) varies between 0.4 K and 0.6 K depending on the channel. The extension of the code allows the utilization of MOMO as forward model for remote sensing algorithms in the full range spectrum. Another application is full range radiation budget computations (heating rates or forcings)

Origamis Capillaires

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