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京都大学 / 新制・課程博士 / 博士(理学) / 甲第23712号 / 理博第4802号 / 新制||理||1687(附属図書館) / 京都大学大学院理学研究科地球惑星科学専攻 / (主査)教授 竹見 哲也, 准教授 重 尚一, 教授 榎本 剛 / 学位規則第4条第1項該当 / Doctor of Science / Kyoto University / DGAM

A Météo France, le modèle opérationnel AROME a une résolution horizontale de 2,5 km. L'augmentation des moyens de calcul permettra au prochain modèle opérationnel de tourner à des résolutions de l'ordre ou inférieures au kilomètre. Il entrera donc dans une gamme de résolution appelée zone grise de la turbulence. A ces échelles, les plus grandes structures turbulentes, qui étaient jusqu'alors entièrement sous-maille, devraient être en partie résolues. Cette thèse a permis de définir ce que les modèles devaient obtenir aux échelles kilométriques et sub-kilométriques, c'est-à-dire les parts sous-maille et résolue de référence de la turbulence dans la zone grise. Ces références ont été établies dans le cas de couches limites convectives en convection libre ou forcée, nuageuse ou non. Elles permettent de prouver qu'à hauteur de couche limite égale, les thermiques sont plus larges dans les couches surmontées de nuages. Elles indiquent surtout que, quelle que soit la configuration, les paramétrisations actuelles ne sont pas capables de reproduire la zone grise. Ces échelles demandent donc de développer une nouvelle paramétrisation de la turbulence. La représentation de la turbulence non locale est la part qu'il faut faire évoluer. Nous avons donc pris le parti de modifier le schéma de thermique en flux de masse. Pour étudier les structures cohérentes sous-maille de couche limite, nous avons créé une analyse conditionnelle permettant de circonscrire la part de thermique qui influence le schéma sous-maille en fonction de la résolution. Cet outil nous a permis de définir les caractéristiques des thermiques sous-maille dans la zone grise, mais également de vérifier à micro-échelle les hypothèses de méso-échelle des schémas en flux de masse. Nous avons démontré que toutes les hypothèses ne sont pas valables. Finalement nous avons établi le système d'équations d'un schéma en flux de masse qui fonctionne aux échelles kilométriques. / The turbulence is well-represented on grid coarser than 2 km. Indeed, in meso-scale models, the turbulence is entirely sub-grid. The turbulence is also well-represented at very high resolution (10 to 100 m) by LES models for which turbulence is mainly resolved. However we do not know which part of the turbulence should be resolved and which part of it should be parameterized when a model runs at kilometric scales, the so-called “Terra Incognita“ from Wyngaard (2004). Thanks to increasing computational resources, in a near future, limited area NWP models will reach grid spacings on the order of 1 km or even 500 m. The aim of this study is to develop a parameterization which will provide adequate turbulence to these new-generation, high-resolution models. At first, this study describes a new diagnostic based on LES, which clarifies which part of turbulence should be parameterized at kilometric scales. This reference called “partial similarity function“ is a precious tool to quantify the error made by atmospheric models when running at kilometric scales. These errors are quantified for a state-of-the-art meso-scale model (Méso-NH) with several turbulence mixing options : different mixing lengths, different dimensionalities, a K-gradient scheme or an EDMF approach (K-gradient with a mass-flux scheme). K-gradient turbulence schemes are unable to reproduce the counter-gradient zone. In the grey-zone, this characteristic has a disastrous effect. As the instability is too large, the boundary layer is mixed by the dynamic of the model and the resolved mixing is too strong. The counter-gradient zone can be reproduced by adding a mass-flux scheme to the K-gradient turbulence scheme (Pergaud et al. (2009)). However the mass-flux scheme in its original form only produces wholly subgrid thermals at a grid size for which boundary-layer thermals should be partly resolved. In this case, the subgrid mixing is too strong. So the question arises as what is a subgrid thermal in the “grey zone“, when the mesh contains one thermal at the most and a part of the thermal has to be resolved by the advection scheme of the model. A conditional sampling is defined in order to detect the subgrid part of the thermals. It allows to determine the characteristics of the subgrid thermals in the “grey zone“ and to find out which assumptions of the mass-flux schemes are not verified. In the light of this study, the mass-flux scheme equations are established by taking the thermal fraction and the resolved vertical velocity into account. Finally, the system of equations is closed. The new parameterization is valid in the grey zone.

Made available in DSpace on 2014-06-11T19:24:45Z (GMT). No. of bitstreams: 0 Previous issue date: 2006-08-07Bitstream added on 2014-06-13T18:06:45Z : No. of bitstreams: 1 borin_i_me_sjrp.pdf: 342800 bytes, checksum: 1147f680ab77277198c9eb4e1a22188d (MD5) / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / A cinética de secagem osmo-convectiva de fatias de abóbora (Cucurbita moschata) tratadas em soluções concentradas de sacarose e sacarose/NaCl foi estudada. As condições de tratamento osmótico mais eficientes (50% sacarose; 47% sacarose - 3% NaCl, 40% sacarose e 37% sacarose - 3% NaCl; p/p) foram selecionadas com base na relação perda de água/ganho de solutos e no conteúdo de sal no produto final. Após a desidratação osmótica (DO), as fatias de abóboras foram submetidas à secagem a 60 e 70oC. A influência dos pré-tratamentos e da temperatura sobre a cinética de secagem foi estudada através dos coeficientes efetivos de difusão de umidade determinados segundo a Lei de Fick. Os maiores coeficientes foram obtidos a 70oC. O sal contribuiu para aumentar a perda de água durante a DO. No entanto, a difusividade da água, durante a secagem, não foi afetada significativamente por esse soluto, uma vez que, para a mesma temperatura, as diferenças entre os coeficientes determinados nas diversas amostras pré-tratadas foram pequenas. Coeficientes efetivos de difusão determinados nas amostras pré-tratadas e não tratadas também foram similares. Avaliando-se as características sensoriais das fatias submetidas à secagem a 70oC, pôde-se constatar que os prétratamentos melhoraram a cor e a aparência geral das mesmas, quando comparadas com as amostras sem tratamento. / Osmo-convective drying kinetics of sliced pumpkin (Cucurbita moschata) treated in sucrose and sucrose-NaCl solutions was studied. Efficient conditions for osmotic dehydration (50% sucrose, 47% sucrose - 3% NaCl, 40% sucrose and 37% sucrose - 3% NaCl, w/w) were selected based on the ratio water loss/ solute gain and on final salt content. After pre treatment, slices were dried at 60 and 70oC. The influence of the pre-treatments and the temperatures on airdrying kinetics of the pumpkins was studied. The effective water diffusion coefficients were determined according to Fick's second law applied to infinite slab. As expected higher coefficients were obtained at 70oC. The salt contributed to increase the water loss during osmotic dehydration. However, the water diffusivity during air-drying was not significantly affected by this solute, since the effective coefficients determined for the different pre-treated samples dried at the same temperature were very close. The effective diffusion coefficients determined in pre-treated and non-treated samples were also similar. Sensory evaluation of the samples dried at 70oC was carried out. The color and the general appearance of the dried pumpkin slices were improved by the previous osmotic dehydration treatments in comparison with non-treated samples.

Cette thèse a permis d'explorer l'apport des variables polarimétriques radar (aux longueurs d'onde centimétriques), sensibles aux propriétés microphysiques des hydrométéores, pour les modèles de prévision numérique à échelle convective. Dans la première partie de la thèse, un opérateur d'observation radar polarimétrique, cohérent avec les paramétrisations microphysiques à 1 moment couramment utilisées par les modèles opérationnels à échelle convective a été développé. Des comparaisons entre données simulées et observées pour tous les types de radar (S, C et X) ont été réalisées pour deux cas d'étude convectifs, et ont permis de valider l'opérateur d'observation. La deuxième partie de cette thèse a été consacrée à la conception et au test d'une méthode d'assimilation des variables polarimétriques, s'appuyant sur la méthode opérationnelle 1D+3D-Var, d'assimilation des réflectivités radar dans le modèle AROME. La méthode de restitution bayésienne 1D des profils d'humidité a été adaptée, afin d'inclure la phase différentielle spécifique et la réflectivité différentielle, en plus de la réflectivité, dans le vecteur d'observation. Plusieurs options de la méthode de restitution ont été testées et évaluées par des comparaisons aux observations radar et GPS. Des expériences d'assimilation menées sur deux cas convectifs ont ensuite été réalisées et ont permis d'évaluer l'impact des observations polarimétriques sur les champs analysés d'humidité ainsi que sur les prévisions de réflectivité et de cumuls de précipitation. / This PhD has explored the benefits of polarimetric variables (for centimeter wavelength radars), which are sensitive to the microphysical properties of hydrometeors, for convective scale numerical prediction models. In the first part of the PhD, a radar forward operator, consistent with the bulk 1 moment microphysical schemes typically used by the operational convective scale models, has been designed. Comparisons between observed and simulated variables for all radar types (S, C, X) have been performed for two convective cases, and helped validate the forward operator. Following these comparisons, quality controls have been specified so as to limitate the errors on the polarimetric variables before using them for assimilation. In the second part of the PhD, an assimilation method for polarimetric variables, based on the operational 1D+3D-Var assimilation method used for radar reflectivities in AROME model has been designed. The Bayesian retrieval of 1D humidity profiles has been adapted in order to include differential reflectivity and specific differential phase within the observation vector. Different options of the methodology have been tested and evaluated by comparisons with radar and GPS observations. Assimilation experiments conducted for two convective cases demonstrated an impact on analysed humidity fields. The effect of the assimilation of polarimetric variables on forecasted reflectivities and precipitation accumulations was also evaluated.

L'influence de la variation de masse volumique pour le développement des instabilités primaires d'un jet plan est étudiée par simulation numérique directe des équations deNavier-Stokes incompressibles. Chaque méthode numérique retenue ainsi que la construction du programme sont détaillées pas à pas en insistant particulièrement sur le choix desconditions aux limites. La méthode est validée par une étude linéaire qui présente des résultats pour une large gamme de valeurs du rapport de densité. À partir de ce code nonlinéaire, on étudie la transition convective/absolue subie par le mode variqueux lorsque lerapport de densité diminue pour di_érents profils dont le Bickley et le presque top-hat. Une remise en cause du critère de stabilité marginale est proposée. En outre, l'observation inattendue de modes globaux amortis pour les rapports de densité voisins de 1 dans le cas d'un profil presque top-hat nous conduit à proposer une hypothèse en étudiant l'équationanalytique implicite qui définit la relation de dispersion du mode variqueux pour un profiltop-hat. Une courte étude expérimentale dans laquelle on présente les différentes techniques employées, ainsi que les premières mesures de vitesse et de densité, complète ce travail, endonnant des informations sur les fréquences caractéristiques.

Το αντικείμενο της διατριβής είναι η παρατηρησιακή και αριθμητική μελέτη των δυναμικών και φυσικών διεργασιών που συνδέονται με τη θερινή καταιγιδοφόρο δραστηριότητα στον Ελλαδικό χώρο. Αναλυτικότερα τα εξεταζόμενα αντικείμενα είναι τα εξής: 1. Η μελέτη των ηλεκτρικών εκκενώσεων στον Ελλαδικό χώρο κατά τη θερινή περίοδο για 4 τουλάχιστον έτη. Για την πραγματοποίηση των στόχων του παραπάνω αντικειμένου έχει ήδη γίνει η συλλογή και η επεξεργασία των ηλεκτρικών εκκενώσεων στη περιοχή του ευρύτερου Ελλαδικού χώρου για τις θερινές περιόδους των ετών 2003 έως και 2006. Τα δεδομένα που έχουν χρησιμοποιηθεί προέρχονται από το σύστημα καταγραφής των ηλεκτρικών εκκενώσεων της Βρετανικής Μετεωρολογικής Υπηρεσίας ATD (Arrival Time Difference). Τα γεγονότα τα οποία κατεγράφησαν στον Ελλαδικό χώρο για την περίοδο μελέτης, μετά τον απαραίτητο έλεγχο ποιότητας, κατανεμήθηκαν σε πλέγμα διαστάσεων 0,1° x 0,1° και υπολογίστηκε η πυκνότητα των ηλεκτρικών εκκενώσεων ανά τετραγωνικό χιλιόμετρο ανά θερινή περίοδο. Στις περιοχές με τις υψηλότερες τιμές πυκνότητας ηλεκτρικών εκκενώσεων συγκαταλέγονται η Μακεδονία, η Ήπειρος, ο ορεινός κεντρικός ηπειρωτικός κορμός καθώς και οι ορεινές περιοχές της Πελοποννήσου, γεγονός που αποτελεί μία πρώτη ένδειξη της σύνδεσης που υπάρχει μεταξύ της θέρμανσης του εδάφους, λόγω της ηλιακής ακτινοβολίας, και της ανάπτυξης θερινών καταιγίδων. Η άποψη αυτή ενισχύεται και από το γεγονός ότι το μέγιστο της δραστηριότητας παρατηρείται τις μεσημεριανές και πρώτες απογευματινές ώρες. 2. Η μελέτη των παραμετροποιήσεων ανοδικών κινήσεων (convection) και μικροφυσικής των αριθμητικών μοντέλων πρόγνωσης καιρού με στόχο την ορθότερη πρόβλεψη της θερινής καταιγιδοφόρου δραστηριότητας που συνοδεύεται από έντονη ηλεκτρική δραστηριότητα. Στο αντικείμενο αυτό κύριος στόχος είναι η σύγκριση τριών διαφορετικών σχημάτων παραμετροποίησης που χρησιμοποιούνται στο αριθμητικό μοντέλο πρόγνωσης καιρού MM5. Τα σχήματα αυτά είναι τα κάτωθι: Kain – Fritch, Betts – Miller – Janjic και Grell και χρησιμοποιούνται στην παραμετροποίηση του μοντέλου για τον υπολογισμό της βροχόπτωσης που προέρχεται από τις κατακόρυφες κινήσεις μεταφοράς. Κατά τη σύγκριση των τριών σχημάτων παραμετροποίησης τα καλύτερα στατιστικά σκορ εμφανίζει το σχήμα Kain – Fritch ενώ τα αποτελέσματα που δίνει το σχήμα του Grell είναι αρκετά κοντά με αυτά του προαναφερθέντος σχήματος. 3. Η τροποποίηση του σχήματος παραμετροποίησης κατακόρυφων κινήσεων στην ατμόσφαιρα των Kain – Fritsch με στόχο τη βελτιστοποίηση των αποτελεσμάτων της προβλεπόμενης βροχόπτωσης στην περιοχή του Ελλαδικού χώρου, κατά τη θερμή περίοδο του έτους Στο αντικείμενο αυτό έχει μελετηθεί στατιστικά η ικανότητα πρόβλεψης του πεδίου της βροχόπτωσης, εφαρμόζοντας ποικίλες τροποποιήσεις του σχήματος παραμετροποίησης Kain – Fritsch. Πιο συγκεκριμένα πέρα από την βασική έκδοση του σχήματος που χρησιμοποιείται στην επιχειρησιακή αλυσίδα του προγνωστικού μοντέλου ΜΜ5, αναπτύχθηκαν οκτώ συνολικά τροποποιήσεις. Εφαρμόζοντας τις παραπάνω τροποποιήσεις, πραγματοποιήθηκαν συνολικά 180 πειράματα για συνολικά 20 διαφορετικές ημέρες με έντονη βροχόπτωση κατά την θερμή περίοδο των ετών 2005 – 2007. Η σύγκριση των αποτελεσμάτων παρείχε ενθαρρυντικά στοιχεία, καθώς ωθώντας το σχήμα να παράξει περισσότερο υετό παρατηρήθηκε βελτίωση στην ικανότητα του μοντέλου να προβλέπει τον υετό. / The present Ph.D. Thesis is divided into three main parts. In the first part the lightning activity over Greece during the warm season (May-September) of the years 2003 through 2006 is investigated, in relation with the synoptic meteorological conditions that prevailed in the region. The study is based on the use of cloud-to-ground lightning activity data and of upper-air analyses. The analysis of the spatial variability of lightning shows that the highest “relative” flash densities are observed in Northern and Western Greece and in Central and Western Peloponnissos. The study of the synoptic patterns related to lightning is based on the analysis of 60 active and 60 inactive days in terms of lightning activity over Greece. The days with high lightning activity are characterised by a short wave trough at the 500 hPa level over the Ionian Sea. On the other hand, during the days with no lightning a northwest flow prevails over Greece. It was also found that high lightning activity is related with high values of absolute vorticity, equivalent potential temperature and convective available potential energy. In the second part the sensitivity of numerical model quantitative precipitation forecasts to the choice of the convective parameterization scheme (CPS) is examined for twenty selected cases characterized by intense convective activity over Greece, during the warm period of 2005 – 2007. Namely, the study is conducted using MM5 model and the following three different CPSs: Kain – Fritsch, Grell and Betts – Miller – Janjic. Sixty numerical simulations were carried out. The simulated precipitation was verified against raingauge measurements and lightning data. Verification results showed that for all three schemes the model presented a tendency to overestimate light to moderate rain while in general it underestimated the high precipitation amounts. The validation against both sources of data showed that among the three CPSs, the more consistent behaviour in quantitative precipitation forecasting was obtained by the Kain – Fritsch scheme that provided the best statistical scores. However, the differences of the results of statistical analysis between the Kain – Fritsch and Grell schemes were not large. In the third part the sensitivity of quantitative precipitation forecasts to various modifications of the Kain – Fritsch (KF) convective parameterization scheme (CPS) is examined for twenty selected cases characterized by intense convective activity and widespread precipitation over Greece, during the warm period of 2005-2007. The modifications include: (i) the maximization of the convective scheme precipitation efficiency, (ii) the change of the convective time step, (iii) the forcing of the convective scheme to produce more/less cloud material, (iv) changes to the trigger function and (v) the alteration of the vertical profile of updraft mass flux detrainment. In general, forcing the model to produce less cloud material improves the precipitation forecast for the moderate and high precipitation amounts.

Les écoulements diphasiques sont couramment utilisés dans de nombreux domaines dont, en particulier, le domaine spatial. La performance de ces systèmes est entièrement régie par les couplages se produisant entre les écoulements et les transferts de chaleur. Cette particularité a conduit, depuis les dernières décennies, au développement de nombreuses études sur les écoulements diphasiques en microgravité. Afin d'accroître la connaissance sur le comportement thermo-hydraulique de ces systèmes thermiques, la présente étude se focalise sur l'étude de la condensation dans un mini-tube en présence ou non de la force gravitationnelle. Pour étudier l'effet de la gravité sur cette configuration, un premier modèle instationnaire d'écoulement diphasique a été développé. Parallèlement, une analyse des effets de la gravité sur l'hydrodynamique et les transferts thermique a été menée dans deux sections d'essai possédant un diamètre interne commun de 3,4 mm et des vitesses massiques faibles à modérées. La première étude a été réalisée au cours de la 62e campagne de vols paraboliques de l'ESA. Elle a été dédiée à la détermination des coefficients de transfert de chaleur quasi-locaux se produisant à l'intérieur d'un tube de cuivre. Afin de visualiser également les régimes d'écoulement présents, un tube en verre a été inséré au sein de cet échangeur. L'effet de la gravité sur les écoulements et les transferts a ainsi été déterminé. La seconde expérience, menée au sol, a porté sur l'étude d'un écoulement de vapeur descendant au sein d'un tube en saphir placé verticalement. Un protocole de mesure permettant d'obtenir simultanément l'épaisseur du film de liquide ruisselant et le coefficient d'échange local associé a été développé. / Liquid-vapor two-phase flows have common applications in many fields including space thermal management systems. The performances of such systems are entirely associated to the coupling between thermal and hydrodynamic phenomena. Therefore, two-phase flows in microgravity condition have emerged as an active research area in the last decades. In order to complete the state of the art and to contribute to the increase in the knowledge of hydrothermal behavior of two-phase thermal management systems, the present study was conducted on convective condensation inside a mini tube, both in normal and micro gravity conditions. To analyze the effect of gravity on such flows, a preliminary transient modeling of the two-phase flow has been established. Simultaneously, an experimental investigation was carried out on the hydrodynamic and thermal behaviors of condensation flows in two test sections of 3.4 mm inner diameter at low and intermediate mass velocities. The first experiment was conducted during the 62nd ESA parabolic flights campaign. The test section was made with copper and allowed measurements of the quasi-local heat transfer coefficient. A glass tube was also inserted in the middle of the test section for the visualization of the two-phase flow regime. From this study, the changes in heat transfer coefficient and flow regime according to gravity variations were determined. The second experiment was carried out on ground in a sapphire tube installed vertically considering downward flow. The set-up was designed in order to measure simultaneously the local heat transfer coefficient and the thickness of the liquid film falling down along the tube wall.

Orientador: Maria Aparecida Mauro / Banca: Fábio Yamashita / Banca: Róger Darros Barbosa / Resumo: A cinética de secagem osmo-convectiva de fatias de abóbora (Cucurbita moschata) tratadas em soluções concentradas de sacarose e sacarose/NaCl foi estudada. As condições de tratamento osmótico mais eficientes (50% sacarose; 47% sacarose - 3% NaCl, 40% sacarose e 37% sacarose - 3% NaCl; p/p) foram selecionadas com base na relação perda de água/ganho de solutos e no conteúdo de sal no produto final. Após a desidratação osmótica (DO), as fatias de abóboras foram submetidas à secagem a 60 e 70oC. A influência dos pré-tratamentos e da temperatura sobre a cinética de secagem foi estudada através dos coeficientes efetivos de difusão de umidade determinados segundo a Lei de Fick. Os maiores coeficientes foram obtidos a 70oC. O sal contribuiu para aumentar a perda de água durante a DO. No entanto, a difusividade da água, durante a secagem, não foi afetada significativamente por esse soluto, uma vez que, para a mesma temperatura, as diferenças entre os coeficientes determinados nas diversas amostras pré-tratadas foram pequenas. Coeficientes efetivos de difusão determinados nas amostras pré-tratadas e não tratadas também foram similares. Avaliando-se as características sensoriais das fatias submetidas à secagem a 70oC, pôde-se constatar que os prétratamentos melhoraram a cor e a aparência geral das mesmas, quando comparadas com as amostras sem tratamento. / Abstract: Osmo-convective drying kinetics of sliced pumpkin (Cucurbita moschata) treated in sucrose and sucrose-NaCl solutions was studied. Efficient conditions for osmotic dehydration (50% sucrose, 47% sucrose - 3% NaCl, 40% sucrose and 37% sucrose - 3% NaCl, w/w) were selected based on the ratio water loss/ solute gain and on final salt content. After pre treatment, slices were dried at 60 and 70oC. The influence of the pre-treatments and the temperatures on airdrying kinetics of the pumpkins was studied. The effective water diffusion coefficients were determined according to Fick's second law applied to infinite slab. As expected higher coefficients were obtained at 70oC. The salt contributed to increase the water loss during osmotic dehydration. However, the water diffusivity during air-drying was not significantly affected by this solute, since the effective coefficients determined for the different pre-treated samples dried at the same temperature were very close. The effective diffusion coefficients determined in pre-treated and non-treated samples were also similar. Sensory evaluation of the samples dried at 70oC was carried out. The color and the general appearance of the dried pumpkin slices were improved by the previous osmotic dehydration treatments in comparison with non-treated samples. / Mestre