Assessment of MISR and MODIS cloud top heights through inter-comparison with a back-scattering lidar at SIRTA

One year of back-scattering lidar cloud boundaries and optical depth were analysed for coincident inter-comparison with the latest processed versions of the NASA-TERRA MISR stereo and MODIS CO2-slicing operational cloud top heights. Optically thin clouds were found to be accurately characterised by the MISR cloud top height product as long as no other cloud was present at lower altitude. MODIS cloud top heights were generally found within the cloud extent retrieved by lidar; agreement improved as cloud optical depth increased and when CO2-slicing was the only technique used for the retrieval. The difference between Lidar and MISR cloud top heights was found to lie between −0.1 and 0.4 km for low clouds and between 0.1 and 3.1 km for high clouds. The difference between Lidar and MODIS cloud top heights was found to lie between −1.2 and 1.5 km for low clouds and between −1.4 and 2.7 km for high clouds

Les différences de densité comme outils de rationalisation des propriétés d’absorption en UV-visible dans un laboratoire de chimie organique !

L\u27interaction entre un rayonnement UV-visible et la matière est au centre de plusieurs thématiques du laboratoire MOLTECH-Anjou : effet photovoltaïque, transferts de charge photoinduits, dichroïsme circulaire. Les méthodes de calculs basées sur la théorie TD-DFT permettent d’obtenir avec une certaine précision les propriétés des composés moléculaires synthétisés au laboratoire. Toutefois la TD-DFT n\u27est pas une « boîte noire » dont la réponse serait toujours facilement compréhensible surtout au moment de dialoguer avec les expérimentateurs. Alors que ces derniers restent attachés à l\u27idée d’une transition mono-électronique depuis une OM de départ vers une OM d\u27arrivée, les états excités simulés en TD-DFT sont souvent décrits comme des combinaisons de transitions. La rationalisation par l’analyse topologique entre les OM impliquées devient ainsi un travail extrêmement fastidieux pouvant rapidement débouché vers des erreurs d’interprétations. La conférence présentera les résultats récents obtenus avec un logiciel maison ABSiCC (Automating Boring Stuff in Computational Chemistry). En programmant certains outils récemment développés ou enrichis par les physico-chimistes de la communauté TD-DFT[1,2] il a été possible de rationaliser efficacement et pédagogiquement les propriétés de transferts de charge photoinduits de composés électroactifs basés sur le tetrathiafulvalene (TTF) de type push-pull et de proposer des pistes intéressantes concernant le dichroïsme circulaire.[3-5] [1] M Peach, DJ Tozer, Journal of Molecular Structure: THEOCHEM, 914, 110 (2009) [2] T Le Bahers, C Adamo, I Ciofini, Journal of Chemical Theory and Computation, 7, 2498 (2011) [3] F Pop, F Riobé, S Seifert, T Cauchy, J Ding, N Dupont, A Hauser, M Koch, N Avarvari, Inorg. Chem., 52, 5023 (2013) [4] F Pop, S Laroussi, T Cauchy, CJ Gomez-Garcia, JD Wallis, N Avarvari, Chirality, 2013. Vol. 25, p. 466-474. [5] Biet, T.; Fihey, A.; Cauchy, T.; Vanthuyne, N.; Roussel, C.; Crassous, J.; Avarvari, N. Chem. - Eur. J. 2013, 19, 13160–13167

Midlatitude Cirrus Clouds and Multiple Tropopauses from a 2002-2006 Climatology over the SIRTA Observatory

This study present a comparison of lidar observations of midlatitude cirrus clouds over the SIRTA observatory between 2002 and 2006 with multiple tropopauses (MT) retrieved from radiosounding temperature profiles. The temporal variability of MT properties (frequency, thickness) are discussed. Results show a marked annual cycle, with MT frequency reaching its lowest point in May (~18% occurrence of MT) and slowly rising to more than 40% in DJF. The average thickness of the MT also follows an annual cycle, going from less than 1 km in spring to 1.5 km in late autumn. Comparison with lidar observations show that cirrus clouds show a preference for being located close below the 1st tropopause. When the cloud top is above the 1st tropopause (7% of observations), in 20% of cases the cloud base is above it as well, resulting in a cirrus cloud "sandwiched" between the two tropopauses. Compared to the general distribution of cirrus, cross-tropopause cirrus show a higher frequency of large optical depths, while inter-tropopause cirrus show almost exclusively low optical depths (Tau < 0.03 in 90% of cases) typical of subvisible clouds. Results suggest the occurrence of inter-tropopause cirrus clouds is correlated with the frequency of multiple tropopauses

Simple turbulence measurements with azopolymer thin films

A simple method to measure the influence on the laser beam propagation by a turbid medium is proposed. This measurement is based on the inscription of a surface relief grating (SRG) on an azopolymer thin film. The grating obtained with a single laser beam after propagation into a turbulent medium is perturbed and directly analyzed by a CCD camera through its diffraction pattern. Later, by scanning the surface pattern with an atomic force microscope, the inscribed SRG is analyzed with the Radon transform. This method has the advantage of using a single beam to remotely inscribe a grating detecting perturbations during the beam path. A method to evaluate the refractive index constant structure is developed

A new method to measure atmospheric turbulence

Date du colloque&nbsp;: 09/2012</p

Redox-Driven Transformation of a Discrete Molecular Cage into an Infinite 3D Coordination Polymer

Two M12L6 redox‐active self‐assembled cages constructed from an electron‐rich ligand based on the extended tetrathiafulvalene framework (exTTF) and metal complexes with a linear geometry (PdII and AgI) are depicted. Remarkably, based on a combination of specific structural and electronic features, the polycationic self‐assembled AgI coordination cage undergoes a supramolecular transformation upon oxidation into a three‐dimensional coordination polymer, that is characterized by X‐ray crystallography. This redox‐controlled change of the molecular organization results from the drastic conformational modifications accompanying oxidation of the exTTF moiety

Image storage in coumarin-based copolymer thin films by photoinduced dimerization

We report a technique to encode grayscale digital images in thin films composed of copolymers containing coumarins. A nonlinear microscopy setup was implemented and two nonlinear optical processes were used to store and read information. A third-order process (two-photon absorption) was used to photoinduce a controlled dimer-to-monomer ratio within a defined tiny volume in the material, which corresponds to each recorded bit of data. Moreover, a second-order process (second-harmonic generation) was used to read the stored information, which has been found to be highly dependent upon the monomer-to-dimer ratio

Low-cost biospeckle imaging applied to the monitoring of seed germination

Low-cost biospeckle imaging applied to the monitoring of seed germination

Promoting Spontaneous Second Harmonic Generation through Organogelation

An organogelator based on the Disperse Red NLO-phore was synthesized according to a simple and efficient three-step procedure. The supramolecular gel organization leads to xerogels which display a spontaneous second harmonic generation (SHG) response without any need for pre-processing and this SHG activity appears stable over several months. These findings, based on an intrinsic structural approach are supported by favorable intermolecular supramolecular interactions, which promote a locally non-centrosymmetric NLO-active organization. This is in sharp contrast with most materials designed for SHG purposes, which generally require the use of expensive or heavy-to-handle external techniques for managing the dipoles alignment