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Author: PHILIPPE.. LENA Publisher: ISBN: Category : Languages : fr Pages : 259
Book Description
L'ESTIMATION DU FLUX DE CHALEUR LATENTE A LA SURFACE DES OCEANS A PARTIR DE DONNEES SATELLITES A ETE PEU ETUDIEE A DES ECHELLES DE TEMPS INFERIEURES AU MOIS. NOUS PROPOSONS DANS CETTE THESE UNE METHODE SIMPLE DE CALCUL, APPLIQUEE A L'OCEAN INDIEN. CETTE METHODE UTILISE DIVERSES DONNEES SATELLITES, ET LES CHAMPS DU MODELE CEPMMT. LES DONNEES SATELLITES (SSM/I, AVHRR, AMI) PERMETTENT D'ESTIMER LES QUANTITES PHYSIQUES PRINCIPALES NECESSAIRES AU CALCUL DU FLUX DE CHALEUR LATENTE TANDIS QUE LE MODELE CEPMMT FOURNIT UNE VUE COMPLETE DE LA SITUATION METEOROLOGIQUE. LA PRECISION DES ALGORITHMES DE RESTITUTION DES PARAMETRES PHYSIQUES A PARTIR DE DONNEES SATELLITES EST TOUT D'ABORD EVALUEE SUR LA REGION DE L'OCEAN INDIEN. NOUS UTILISONS LES DONNEES AVHRR POUR ESTIMER LA TEMPERATURE DE SURFACE DE LA MER, LES DONNEES SSM/I POUR CONNAITRE LE CONTENU INTEGRE EN VAPEUR D'EAU ET UNE COMBINAISON DES DONNEES AMI, SSM/I POUR CALCULER L'INTENSITE DU VENT DE SURFACE. LES DONNEES DU CEPMMT SONT ENSUITE COMPAREES AUX QUANTITES MESUREES PAR CES CAPTEURS. NOUS ANALYSONS AINSI LES ECARTS OBSERVES ENTRE LES CHAMPS DU MODELE ET LES CHAMPS ISSUS DES DONNEES SATELLITES AFIN D'ETABLIR UNE COMBINAISON DE L'ENSEMBLE DE CES DONNEES. UNE CORRECTION DES PROFILS D'HUMIDITE DU MODELE EST ALORS PROPOSEE. CETTE CORRECTION UTILISE LE CONTENU INTEGRE EN VAPEUR D'EAU DEDUIT DES DONNEES SSM/I ET EST BASEE SUR LES OBSERVATIONS AVHRR ET SSM/I. L'ENSEMBLE DES DONNEES UTILISEES DEVIENT ALORS COHERENT. NOUS POUVONS ALORS CALCULER LE FLUX DE CHALEUR LATENTE PENTADAIRE MOYEN A LA SURFACE DE L'OCEAN INDIEN
Author: PHILIPPE.. LENA Publisher: ISBN: Category : Languages : fr Pages : 259
Book Description
L'ESTIMATION DU FLUX DE CHALEUR LATENTE A LA SURFACE DES OCEANS A PARTIR DE DONNEES SATELLITES A ETE PEU ETUDIEE A DES ECHELLES DE TEMPS INFERIEURES AU MOIS. NOUS PROPOSONS DANS CETTE THESE UNE METHODE SIMPLE DE CALCUL, APPLIQUEE A L'OCEAN INDIEN. CETTE METHODE UTILISE DIVERSES DONNEES SATELLITES, ET LES CHAMPS DU MODELE CEPMMT. LES DONNEES SATELLITES (SSM/I, AVHRR, AMI) PERMETTENT D'ESTIMER LES QUANTITES PHYSIQUES PRINCIPALES NECESSAIRES AU CALCUL DU FLUX DE CHALEUR LATENTE TANDIS QUE LE MODELE CEPMMT FOURNIT UNE VUE COMPLETE DE LA SITUATION METEOROLOGIQUE. LA PRECISION DES ALGORITHMES DE RESTITUTION DES PARAMETRES PHYSIQUES A PARTIR DE DONNEES SATELLITES EST TOUT D'ABORD EVALUEE SUR LA REGION DE L'OCEAN INDIEN. NOUS UTILISONS LES DONNEES AVHRR POUR ESTIMER LA TEMPERATURE DE SURFACE DE LA MER, LES DONNEES SSM/I POUR CONNAITRE LE CONTENU INTEGRE EN VAPEUR D'EAU ET UNE COMBINAISON DES DONNEES AMI, SSM/I POUR CALCULER L'INTENSITE DU VENT DE SURFACE. LES DONNEES DU CEPMMT SONT ENSUITE COMPAREES AUX QUANTITES MESUREES PAR CES CAPTEURS. NOUS ANALYSONS AINSI LES ECARTS OBSERVES ENTRE LES CHAMPS DU MODELE ET LES CHAMPS ISSUS DES DONNEES SATELLITES AFIN D'ETABLIR UNE COMBINAISON DE L'ENSEMBLE DE CES DONNEES. UNE CORRECTION DES PROFILS D'HUMIDITE DU MODELE EST ALORS PROPOSEE. CETTE CORRECTION UTILISE LE CONTENU INTEGRE EN VAPEUR D'EAU DEDUIT DES DONNEES SSM/I ET EST BASEE SUR LES OBSERVATIONS AVHRR ET SSM/I. L'ENSEMBLE DES DONNEES UTILISEES DEVIENT ALORS COHERENT. NOUS POUVONS ALORS CALCULER LE FLUX DE CHALEUR LATENTE PENTADAIRE MOYEN A LA SURFACE DE L'OCEAN INDIEN
Book Description
LE CALCUL DES FLUX TURBULENTS A L'INTERFACE OCEAN/ATMOSPHERE EST NECESSAIRE POUR ETABLIR DES BILANS D'ENERGIE PRECIS A LA SURFACE DE LA MER OU POUR FORCER DES MODELES DE CIRCULATION OCEANIQUE. AU COURS DE CE TRAVAIL, NOUS DECRIVONS EN DETAIL LA METHODE BULK QUI CONSTITUE UNE PARAMETRISATION DES ECHANGES TURBULENTS A L'INTERFACE AIR-MER. NOUS LEVONS UNE AMBIGUITE QUANT AU CALCUL DES VALEURS NEUTRES DES COEFFICIENTS D'ECHANGE, PUIS NOUS PROPOSONS UN ALGORITHME DE CALCUL DES FLUX. NOUS DEVELOPPONS UNE METHODE ORIGINALE D'ESTIMATION DE FLUX DE CHALEUR LATENTE PAR RADIOMETRIE HYPERFREQUENCE SPATIALE, INSPIREE DES TRAVAUX DE LIU 1990. LA METHODE CONSISTE EN UN RESEAU DE NEURONES ARTIFICIELS, DONT LES PARAMETRES D'ENTREE SONT LA TEMPERATURE DE SURFACE DE LA MER ET DES COMBINAISONS DE TEMPERATURES DE BRILLANCE SENSIBLES AUX DIFFERENTS PARAMETRES DU FLUX. NOUS APPLIQUONS CET ALGORITHME AUX DONNEES DES EXPERIENCES SEMAPHORE (EYMARD ET AL., 1993), CATCH/FASTEX (EYMARD ET AL., 1999) ET TOGA/COARE (WEBSTER AND LUKAS, 1992). NOS COMPARAISONS MONTRENT QUE LA METHODE DES RESEAUX DE NEURONES CONSTITUE UNE SOLUTION PRECISE DANS LA PLUPART DES CAS. NOUS TROUVONS QUE LES STRUCTURES HORIZONTALES DU FLUX ESTIMEES PAR LE RESEAU DE NEURONES SONT COHERENTES AVEC CELLES DES CHAMPS DE SURFACE ISSUS DES MODELES DE PREVISION METEOROLOGIQUE, POUR PLUSIEURS CAS DES EXPERIENCES SEMAPHORE ET CATCH. DANS CHAQUE SITUATION, NOUS SOULIGNONS QUE L'ECART ENTRE LES MESURES SPATIALES ET LES CHAMPS MODELE EST LIE AUX VARIATIONS SPATIALES DE LA STABILITE DANS LA COUCHE LIMITE DE SURFACE. POUR ESTIMER CE DERNIER PARAMETRE, NOUS PROPOSONS UN MODELE 2D STATIONNAIRE A Z=CTE, QUI DECRIT L'ADAPTATION DE LA TEMPERATURE DE L'AIR A CELLE DE LA SURFACE. NOUS PARAMETRISONS LES EFFETS DE LA VITESSE VERTICALE EN FONCTION DE LA DIVERGENCE DU VENT HORIZONTAL. CE MODELE TRES SIMPLE NOUS PERMET DE RESTITUER DES CHAMPS DE TA FIDELES A CEUX DES MODELES DE PREVISION, POUR TROIS SITUATIONS DE SEMAPHORE ET CATCH.
Author: Jason Brent Roberts Publisher: ISBN: Category : Meteorology Languages : en Pages :
Book Description
ABSTRACT: A major theme of recent research is the investigation of the nature of climate variability and the current capability to measure, model, and predict it. This is a formidable task that involves understanding complex interactions and exchanges of energy between the major elements of the Earth system. With their ability to store and release vast quantities of heat, the oceans are an integral element of climate variability. Accurately modeling coupled atmosphere-ocean variability relies upon a proper characterization of the exchanges of heat and momentum across the air-sea interface. The exchange of heat takes place through net shortwave and terrestrial radiative fluxes and turbulent exchanges of heat and moisture. Estimating these interactions with sufficient accuracy is a difficult challenge. These processes contain inherent errors due to insufficient knowledge of physics, observational uncertainty, and parameterization deficiencies. Uncertainties arising from the estimation of the surface turbulent and radiative processes generate limitations to the understanding of the primary mechanisms governing oceanic variability. This work elucidates the impact of uncertainties in the estimation of turbulent and radiative heat fluxes on the analysis of the mixed layer temperature balance, an effect that has not been properly quantified although recognized in most previous analyses. In particular, this work focuses on variability at seasonal and intraseasonal time scales. The analyses of this work include- i) an updated characterization of uncertainties in current state-of-the-art estimates of the turbulent and radiative heat fluxes, ii) an examination of the closure of the mixed layer temperature balance on seasonal and intraseasonal time scales, iii) an evaluation of the sensitivity of the mixed layer temperature balance to differences between surface heat flux estimates, iv) the development of a flexible approach by which to determine required accuracies of the net surface heat flux, and v) an exploration of the role of mixed layer depth variability on the mixed layer temperature balance. Taken together, the results of these analyses provide a framework to understand the impact of surface heat flux uncertainties within the context of upper ocean mixed layer variability. The analyses performed in this study have exploited a set of eight turbulent and six radiative heat flux estimates. An intercomparison of these products has revealed that the typical spread between products has been reduced relative to previous generations of estimates. Differences between radiative and turbulent heat flux estimates are typically within 15-20% of one another on regional and seasonal scales although larger uncertainties remain in traditionally problematic regions (e.g., cloud-topped boundary layers, western boundary currents). On both intraseasonal and seasonal time scales, the ocean mixed layer is controlled most strongly by the net shortwave and turbulent latent heat fluxes over the world oceans with the exception of the deep tropics wherein oceanic processes are also important. The current ensemble mean estimates of the net surface heat fluxes and oceanic process are capable of resolving the upper ocean mixed layer temperature seasonal cycle quite well in many locations; areas of strong net heat flux warming are somewhat problematic. On intraseasonal time scales, small signal to noise ratios and large residual imbalances leave little room to make definitive conclusions on the role of individual elements of mixed layer forcing. However, general features of the relative importance of surface heat flux variability versus oceanic variability are supported from previous studies. The mixed layer temperature balance is found to be most sensitive to uncertainties in the latent and net shortwave heat fluxes. The timing of the shoaling of the mixed layer depth is also important to the sensitivity of the mixed layer temperature balance. Taking into account mixed layer depth variability is found to be important to understanding the role of the net surface heat fluxes in generating mixed layer temperature warming and cooling. Current estimates of the net heat flux uncertainty are outside of the traditional 10 W m &minus 2 goal on seasonal time scales and spatial scales on the order of 1000 km. The approach designed within this investigation suggests that a 10 W m &minus 2 limit is somewhat too restricting if the aim is to resolve the seasonal mixed layer temperature evolution. In short, the use of the ocean mixed layer temperature balance has provided a unique framework for translating uncertainties in the surface heat flux estimates into a practical context. It is hoped that a better appreciation of these uncertainties will lead to an improved ability to model and understand the mechanisms by which the oceans contribute to variability of Earth's climate.
Author: June Raven Marion Publisher: ISBN: Category : Eddies Languages : en Pages : 148
Book Description
In this thesis, data collected during the Dynamics of the Madden Julian Oscillation (DYNAMO) field campaign, conducted in the Indian Ocean in Fall of 2011, is used to compute heat fluxes at the air-sea interface by evaluating eddy covariances and bulk aerodynamic formulae. Errors in daily average gridded fluxes computed with the COARE version 3.5 bulk aerodynamic formula are assessed with respect to five independent in situ time series from DYNAMO and the Tropical Ocean-Global Atmosphere Coupled Ocean-Atmosphere Response Experiment (TOGA-COARE) in the Western Pacific (Nov. 1992 - Feb. 1993). Oregon State University (OSU), the NOAA Physical Science Division (PSD), and University of Connecticut (UConn) deployed three nearly collocated covariance flux measurement systems on the R/V Revelle during DYNAMO. Covariance and bulk fluxes are compared among these systems, and the experimental setup and calculation methods used for the OSU system are described. OAFlux and TropFlux are two gridded flux products, both of which use global atmospheric reanalyses and in situ observations to produce estimates of surface heat and momentum flux. An array of 106 buoys deployed in the Pacific, Atlantic, and Indian Oceans provide valuable in situ observations of surface meteorological variables including air and ocean temperatures, wind speed and relative humidity. The buoy data is assimilated into the reanalyses and incorporated into the bias correction strategy employed by TropFlux, and the optimal interpolation weights of OAFlux. Locations not constrained by observations have higher root mean square difference between these two products than those near buoys. In fact, OAFlux and TropFlux can sometimes disagree by 100% of the mean flux when buoy data sources are not nearby. Estimating net air-sea surface heat flux to an accuracy of 10 W/m2 requires resolution of diurnal solar warming of the ocean surface, known as the diurnal warm layer (Price, et al., 1986), and diffusive cooling of the viscous sub-layer known as the cool skin (Saunders, 1967). Warm layer and cool skin corrections to the bulk ocean temperature are modeled in the COARE bulk flux algorithm (Fairall et al., 1996). Rigorously calibrated and quality controlled DYNAMO data is used to assess the sensitivity of bulk flux calculations to warm layer and cool skin phenomena. Ignoring both corrections results in positive biases of 1.9 W/m2 and 8.7 W/m2 for sensible and latent heat respectively, mostly because of systematic overestimates of the SST due to the prominence of the cool skin. Two new techniques for including the effects of the warm layer and cool skin on daily fluxes are presented and tested using DYNAMO observations. Both techniques make use of a simple solar radiation model that distributes the daily average solar radiation in a half cosine over 12 hours of the day at hourly resolution. In the first technique the COARE algorithm computes warm layer and cool skin corrections hourly with the solar radiation model. This reduces the root mean square errors of sensible and latent heat fluxes to 0.7 and 2.9 W/m2. This improvement requires more than 10 bulk aerodynamic computations per day, a considerable computational expense when evaluating fluxes for decades of global gridded data. In the second technique, the daily average flux is evaluated beforehand in COARE using the solar radiation model with a range of daily average radiation and wind speed values. The results are sorted by solar radiation and wind speed in a lookup table that specifies an adjustment to the fluxes due to the warm layer and cool skin corrections. The adjustment corrects the daily fluxes computed without the warm layer and cool skin corrections. Using the lookup table corrections reduces the root mean square errors to 0.96 and 3.5 W/m2, nearly as well as the more computationally intensive diurnal solar model. The cool skin correction makes the biggest difference to the fluxes. Ignoring it can cause 10% overestimation of sensible and latent heat flux. Though they ignore the cool skin, both OAFlux and TropFlux estimate the R/V Revelle sensible and latent fluxes to within 0.1% of the mean flux. It is possible that fortuitous errors in the gridded products compensate the neglected effect of the cool skin. Diurnal warm layers intermittently warm the surface temperature during the convectively suppressed phase of the MJO. The warmest net (warm layer minus cool skin) daily mean difference between the bulk and interface temperature reaches 1° C, which is significant compared to the sea-air temperature difference on the order of 2° C. Observations of stronger diurnal warm layers in the convectively suppressed phase suggest that systematic intraseasonal modulation of the warm layer affects air-sea interaction in the MJO.
Author: PHILIPPE.. LENA
Author: PHILIPPE.. LENA
Author: Denis Bourras
Author: Jason Brent Roberts
Author: Edward Joseph Metzger
Author: S. K. Esbensen
Author: 
Author: Elena Martín Domínguez
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Author: June Raven Marion
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