Measurements of turbulent fluxes (momentum, sensible heat, latent heat and CO2) at two different heights were studied from data of a tower at Ostergarnsholm Island (Baltic Sea) during one week, while calculations using bulk formulations of fluxes were done with measurements in the tower and in two buoys moored at different locations. Different behaviors are found for the different fluxes. Measured latent heat flux shows higher correlation with calculations than measured sensible heat flux. For the CO2 flux, this relation was not found. Also all measured fluxes at the tower agree better with calculations when they are done under unstable conditions, meaning that the tower is better measuring the area where the measurements are taken in the buoys (near the tower). The studied period includes an upwelling and a high horizontal surface heterogeneity was found during most of the periods. It was seen using the comparison between calculated and measured fluxes and also using satellite images of the studied site. The footprint area is the area at some distance upwind from the tower where the surface conditions are influencing the measurements of the flux of some quantity at certain height in the tower, and this footprint area is continuously changing because its highly dependence with the stratification. Since during all the period the stratification was changing from slightly stable to slightly unstable conditions, the surface heterogeneity can also be seen in the variability of measured fluxes at different heights. One important conclusion in the study is that calculations of the fluxes using bulk formulations may not be useful when high variability of different parameters (as sea surface temperature and pCO2w ) is expected, as for example during upwelling situations and near coast, where the phytoplankton can significantly influence the concentration of CO2 at the surface. A wide study is done, including meteorological and oceanographic parameters, fluxes, comparisons, relations with parameters, transfer coefficients, dependences with the stratification and satellite images. / Mätningar av flöden (impuls, värme, vattenånga och CO2) vid två olika höjder studerades med data från en mast på ön Östergarnsholm (i Östersjön) under en vecka, beräkningar av flödena gjordes med mätningar av atmosfäriska parametrar från samma mast samt data från två bojar på två olika platser. Man fann olika beteenden för de beräknade och uppmätta flödena. Direkt (sensibelt) värme visade högre korrelation mellan beräkningar och uppmätta sensibla värmeflöden . För CO2- flödet fann man inte detta samband. För alla flödena överensstämmer mätningarna bättre med beräknade flöden när de är gjorda under instabila förhållanden, vilket betyder att under dessa förhållanden representerar mätningarna i masten bättre området där bojarna är placerade. Den studerade perioden inkluderar en period med upvällning (upwelling) och en hög horisontell variabilitet i ytparametrar under den största delen av denna period. Detta visades genom jämförelser mellan de beräknade och de uppmätta flödena och även genom satellitmätningar. Det område uppvind masten där ytan påverkar flöden uppmätta i masten på en viss nivå kallas ”footprint area”, och denna footprint area förändras kontinuerligt på grund av det stora beroendet av skiktningen i atmosfären. Eftersom skiktningen under hela perioden förändrades från något stabilt till något instabilt, kan ytvariabiliteten även ses i variationen av uppmätta flöden på olika höjder. En viktig slutsats i studien är att beräkningar av flödena som görs med standardformler inte bör användas vid förhållanden med hög horisontell och vertikal variation av olika parameter (som havsytetemperatur och pCO2w), som till exempel under uppvällningssituationer och nära kusten, där phytoplankton markant kan påverka koncentrationen av CO2 vid ytan. Studien inkluderar meteorologiska, oceanografiska parametrar, flöden, samband med parametrar, överförings koefficienter, beroende av stabilitet och satellitbilder. / Flujos turbulentos (momento, calor sensible, calor latente y CO2) en 2 alturas diferentes fueron estudiadas usando medidas de una torre en la Isla de Östergarnsholm (Mar Báltico) durante una semana. Los flujos también fueron calculados usando formulaciones con medidas de la torre y de dos boyas ancladas en diferentes localizaciones. Diferentes características para los distintos flujos fueron encontradas. El flujo de calor latente muestra una relación más alta con los cálculos que el flujo de calor sensible. No se encontró esta relación para el flujo de CO2. También, todos los flujos medidos en la torre coinciden mejor con los flujos calculados cuando estos son hechos bajo condiciones de estratificación inestable, significando que la torre mide mejor el área donde son cogidas las medidas en las boyas (cerca de la torre). El periodo estudiado incluye un afloramiento costero y se encontró una alta heterogeneidad horizontal en la superficie del mar durante la mayoría de los periodos. Esto fue estudiado usando las comparaciones entre flujos calculados y medidos y también usando imágenes de satélite. El footprint area puede ser definido como el área a una distancia desde la torre hacia donde sopla el viento donde las condiciones de la superficie influyen las medidas del flujo de alguna cantidad en la torre, y este footprint area está continuamente cambiando debido a su alta dependencia con la estratificación. Durante todo el periodo la estratificación estuvo cambiando desde ligeramente estable a ligeramente inestable, y por ello la heterogeneidad de la superficie puede ser vista en la variabilidad de los flujos medidos a diferentes alturas. Una conclusión importante en este estudio es que los cálculos de los flujos usando formulaciones podrían no ser útiles cuando se espera una alta variabilidad de los diferentes parámetros (temperatura superficial del mar y pCO2w), como por ejemplo durante situaciones de afloramiento y también cerca de costa, donde el fitoplancton puede influenciar significativamente la concentración de CO2 en la superficie. Se presenta un amplio estudio, incluyendo parámetros meteorológicos y oceanográficos, comparaciones de flujos, relaciones con parámetros, coeficientes de transferencia, dependencias con la estratificación e imágenes de satélite.

Nous étudions les flux turbulents de chaleur sensible et de chaleur latente, qui sont mal compris et mal mesurés sur les glaciers, à l'aide de campagnes de terrain déployées dans la zone d'ablation du glacier tropical du Zongo (16°S, Bolivie, 4900-6000 m) durant la saison sèche de l'hiver austral et sur le glacier alpin de Saint-Sorlin (Alpes Françaises, 45°N, 2600-3400 m) durant l'été boréal. Un mât de 6 m permettait la mesure des profils verticaux de vitesse de vent et de température de l'air et des mâts de 2 m comportaient des systèmes de covariances turbulentes (CT). Nous étudions l'évolution temporelle des flux turbulents et l'applicabilité de la méthode aérodynamique des profils en terrain complexe de montagne. Les hypothèses sont discutées via la caractérisation des régimes de vent et de la turbulence. Nous calculons ensuite les flux et les erreurs associées. Sur le Zongo, sous forçage synoptique faible, un écoulement catabatique s'installe de la fin d'après-midi jusqu'au matin, avec un maximum de vitesse de vent à environ 2 m de hauteur. Les forçages synoptiques forts s'alignent approximativement avec le glacier, provoquant un intense écoulement descendant, et dans ce cas nous n'observons pas de maximum de vitesse de vent. Souvent, autour de midi, des vents ascendants sont observés. Sur le glacier de Saint-Sorlin les forçages associés à des épisodes de Foehn ou à des dépressions se déplaçant depuis l'ouest, s'alignent approximativement avec le glacier, générant des vents forts descendants. Quand le forçage synoptique est modéré, un maximum de vitesse de vent est observé nuit et jour 50% du temps. Des vents ascendants sont observés 15% du temps, quand le forçage synoptique est faible. La couche de surface est perturbée par des tourbillons de couches externes sous vent fort, ou de lentes oscillations en écoulement catabatique. Ces perturbations influencent les flux turbulents. Les erreurs aléatoires sur la méthode des profils sont dues principalement à des incertitudes sur la température. L'erreur reste faible sur les flux moyens. La couche de surface est rarement plus épaisse que 2 m et la méthode des profils appliquée à l'aide des mesures plus obtenus plus haut sous-estime les flux de surface de 20% à 70% . Quand un maximum de vitesse de vent est observé, les flux sont sous-estimés même à 2 m. L'influence des perturbations de la couche de surface n'est pas capturée par la méthode des profils, et les flux sont environ 40% inférieurs à ceux mesurés par CT. Ces derniers sont affectés par d'importantes erreurs aléatoires, en raison d'un échantillonnage statistique insuffisant des grands tourbillons. La méthode sous-estime probablement les flux à cause d'une sous-estimation de la vitesse verticale (~15%) et de la divergence verticale des flux. Sur le glacier du Zongo, l'air de haute altitude est très sec et la sublimation (quelques mm d'eau par jour) est un important puits d'énergie à la surface. Le flux de chaleur sensible est un important gain d'énergie la nuit sous l'influence de vents forts (de 30 à 50 W m-2), car l'inversion de température est marquée. Quand un maximum de vitesse de vent est observé, les flux sont faibles (de 5 à 20 W m-2) car la vitesse du vent est faible. La somme des flux turbulents est faible dans ces deux cas car ils sont opposés et les biais se compensent. En vent ascendant, le flux de chaleur sensible est faible (<5 W m-2) car la stratification est neutre, mais le flux de chaleur latente reste important (de -25 à -35 W m-2), le flux net est donc important et les biais ne se compensent plus. Sur le glacier de Saint-Sorlin, le flux de chaleur latente est faible car l'air est humide, et le flux de chaleur sensible peut être intense (~25 W m-2) quand la vitesse du vent est élevée. Le flux net est fort par vent fort et les biais sur les flux calculés par la méthode des profils peuvent être élevés. / We study turbulent fluxes of sensible and latent heat, that are a poorly-known and difficult term to measure over glaciers, with the help of two field campaigns deployed over the ablation zone of Zongo glacier (16°S, Bolivia, 4900-6000 m.a.s.l.) during the austral winter dry season and over the Saint-Sorlin glacier (French Alps, 45°N, 2600-3400 m.a.s.l.) during the boreal summer. A 6-m mast allowing for wind speed and air temperature vertical profile measurements was installed, along with 2-m masts holding eddy-covariance systems. The focus is on the temporal evolution of turbulent fluxes and the applicability of the aerodynamic profile method in the complex terrain of high mountains. The assumptions of the method are discussed by characterizing the wind regimes and the turbulence. We then compute fluxes and associated errors. Above Zongo glacier, under weak synoptic forcing, katabatic flows are observed from late afternoon to early morning, with a wind-speed maximum at around 2 m. Strong synoptic forcing roughly aligns with the glacier, leading to strong downslope flows for which no wind-speed maximum is observed. Most of the days around noon, upslope flows are observed. On Saint-Sorlin glacier in summer, flows associated with low-pressure systems coming from the west or Foehn events roughly align with the glacier, leading to strong downslope winds. Wind-speed maxima are observed night and day, ~50% of the time, when synoptic forcing is moderate. Upslope flows are observed 15% of the time, when synoptic forcing is weak. The surface layer is disturbed by outer-layer eddies in strong flows and by slow oscillations if katabatic flow prevails. These disturbances influence turbulent fluxes. Random errors on the fluxes derived from the profile method are mainly due to temperature uncertainties. Errors remain small on the mean fluxes. The surface layer is rarely deeper than 2 m on both glaciers and the profile method with measurements made above that height underestimates the surface fluxes by 20% to 70%. When a wind-speed maximum is observed, fluxes are underestimated even at 2 m. The influence on the fluxes of the surface-layer disturbances is not captured by the profile method, and fluxes are about 40% smaller than the eddy-covariance fluxes. The latter are affected by large random errors due to inadequate statistical sampling of large-scale eddies and are probably underestimated, mainly due to vertical wind speed underestimation (~15%) and to vertical flux divergence. Above Zongo glacier, due to the dry high-elevation air, sublimation (a few millimeters w. e. per day) is a large energy loss for the surface. Sensible heat flux is a large energy gain in strong nocturnal downslope flows (from 30 to 50 W m-2) and strong winds, due to a marked temperature inversion. When a wind-speed maximum is observed, low wind speeds cause small turbulent fluxes (from 5 to 20 W m-2). The sum of turbulent fluxes is small in those two cases because the fluxes are opposed in sign and the biases mostly compensate. In upslope flows, the sensible heat flux is small (<5 W m-2) due to near-neutral stratification, but latent heat losses remain large (around -25 to -35 W m-2), so that the net turbulent flux is large and the biases do not compensate. Above Saint-Sorlin glacier, the latent heat flux remains small because the air is generally humid, whereas the sensible heat flux can be large (~25 W m-2) when wind speed is high. The net flux is large when wind speed is high, and the biases on net turbulent fluxes derived from the profiles can be significant.

Turbulent exchange of scalars is analyzed for a year of turbulence data, above and within an Araucaria Forest in southern Brazil. Sensible and latent heat fluxes, as well as CO2 fluxes are calculated by the eddy covariance method and analyzed in terms of the seasonal variation of their daily cycles. Diurnal and nocturnal vertical velocity spectra, sensible and latent heat flux cospectra andCO2 flux cospectra are also calculated using the multiresolution decomposition in both levels. Seasonal variations in spectra and cospectra are analyzed, as well as nocturnal and diurnal differences and the differences between the levels. Emphasis is given to the mechanisms controlling the connection between the two levels and its implications on scalar flux quantification. All scalars show a clear seasonality along the year. CO2 fluxes are negative during the day and positive at night above the canopy. In the lower level, CO2 fluxes are mostly positive along the day, with the same magnitude observed in the upper level during the night, indicating that nocturnal emission is dominated by lower levels of the forest, originated predominantly close to the floor. This fact is attributed to periods with low turbulence intensity when CO2 respired accumulates near the surface and gets transported horizontally, being captured by the lower system but missed by the upper one. Sensible heat fluxes show opposite signal in both levels, being more intense above the canopy, with a small contribution from the lower level to the total flux due the low penetration of radiation within the canopy. Latent heat fluxes are mostly positive in both levels, with the larger values above the canopy, indicating that the canopy is responsible for most of the forest evapotranspiration. Analysis of multiresolution spectra and cospectra shows that, above the canopy, the nocturnal time scale of turbulent exchange is smaller than during the day. Between the two levels, the opposite occurs, and the time scale within the canopy shifts towards the larger scales. There is a connection between the two levels, and not only in the highly turbulent nights, but also intermittently in more stable conditions. During these events of connection, the turbulence time scales above and within the canopy become very similar, and the differences in scalar concentration vanish. When calm periods precede highly turbulent ones, a good portion of scalars that accumulated at the canopy during the earlier calm period gets transferred by intermittent events. We show that this process is systematic enough to affect the overall fluxes when the turbulence history is taken into account, and the effect of this process is more intense for CO2 fluxes than for energy fluxes. / As trocas turbulentas de escalares são analisadas, para um ano de dados, acima e no interior de uma Floresta de Araucária localizada no centro-sul do estado do Paraná. Fluxos de calor sensível, calor latente e CO2 são calculados pelo método da covariância de vórtices e analisados de acordo com as variações sazonais dos seus ciclos diários. São calculados também espectros da velocidade vertical e coespectros dos fluxos de calor sensível, calor latente e CO2, para os períodos diurno e noturno, separadamente, através da decomposição em multirresolução, analisando as suas variações sazonais e as diferenças entre o período diurno e noturno e entre os níveis de análise. É dada ênfase aos mecanismos que controlam a conexão entre os níveis e as implicações nas quantificações dos fluxos de escalares. Todos os escalares mostram uma clara variação sazonal dos fluxos ao longo do ano. Fluxos de CO2 são negativos durante o dia e positivos durante a noite no nível superior. No interior do dossel, os fluxos são predominantemente positivos durante todo o dia, tendo, à noite, magnitude semelhante ao nível superior, indicando que a respiração noturna é dominada pelos níveis mais baixos da floresta, sendo predominantemente originados próximo ao solo. Este fato é normalmente atribuído aos períodos de pouca turbulência onde o CO2 respirado acumula próximo à superfície e é transportado horizontalmente, sendo registrado no nível inferior mas não acima do dossel. Fluxos de calor sensível possuem, em geral, sinal contrário em ambos os níveis, sendo mais intenso no nível superior, com uma contribuição muito pequena do interior do dossel para o fluxo total devido à pouca penetração de radiação no interior da floresta. Fluxos de calor latente foram predominantemente positivos em ambos os níveis, tendo maior intensidade no nível superior, mostrando que a copa é responsável pela maior parte da evapotranspiração da floresta. A análise dos espectros e coespectros da decomposição em multirresolução mostra que, acima do dossel, as trocas turbulentas tendem a ocorrer em escalas temporais menores à noite do que durante o dia. Entre os dois níveis ocorre o contrário, e, no interior do dossel, as escalas temporais das trocas turbulentas movem-se em direção às maiores escalas temporais em relação ao nível superior. Há um acoplamento dinâmico entre os dois níveis da floresta, e não somente durante as noites altamente turbulentas, ocorrendo também intermitentemente em condições mais estáveis. Durante os eventos de acoplamento, as escalas de tempo da turbulência entre o interior da floresta e o topo mostram-se similares, assim como as diferenças na concentração de escalares entre os dois níveis deixam de existir. Quando períodos calmos precedem períodos intensamente turbulentos, uma grande porção dos escalares acumulados no nível do dossel durante os períodos de pouca atividade turbulenta pode ser transferida por estes eventos intermitentes. Foi mostrado que este processo é sistemático o suficiente para afetar os fluxos médios quando a história da turbulência é considerada, e o efeito deste processo é mais intenso para os fluxos de CO2 do que para os fluxos de energia.

Carbon dioxide and Radon nocturnal vertical accumulations over a pasture site at the Amazon region are investigated. The site is characterized by a strong thermal stability along the night, which is responsible for suppressing a good portion of the local turbulent mixing. Therefore, it is problematic to use techniques such as the eddy covariance for estimating nocturnal turbulent fluxes. The analysis considers the seasonal variation of the averaged nocturnal profiles between the wet season, from January to June and the dry season, from July to December. Radon profiles are analyzed with the purpose of helping to understand the physical processes affecting CO2 profiles, by comparing them to an independent and inert scalar. The analysis also considers the prevailing nocturnal wind direction. Results indicate that there is a large difference between CO2 fluxes and vertical gradients from one season to the other. Nocturnal CO2 vertical gradients between the two uppermost levels at the micrometeorological tower are often positive, indicating that the concentration increases with height. Such inversions are rarely observed on the Radon profiles, which follow the canonical form of a monotonical decrease with height. At the dry season, gradient inversions are more frequent and are, in general, associated to a direction inversion of the turbulent vertical CO2 flux, indicating that there is a downward vertical transport of this scalar at the measurement level. It causes flux convergence and an intense accumulation just above the surface. A cospectral analysis shows that such downward transport happens on the largest temporal scales of the motion, suggesting that it is associated to exchange between the surrounding forest and the pasture, in the form of mesoscale fluxes. Seasonally averaged behavior is well defined and uniform along the night, but case studies show that the processes are dominated by specific intense events. Radon fluxes measured during experimental field campaigns are used to estimate CO2 fluxes from the relationship between the vertical gradients of both scalars on six nights, three on each season. The comparison to the eddy covariance fluxes is satisfactory during the wet season, but poor during the dry season and the motives for that are discussed. / As acumulações verticais noturnas de dióxido de Carbono e de Radônio são investigadas em um sítio de pastagem na região Amazônica. Este sítio é caracterizado por forte estabilidade térmica durante a noite, que suprime uma boa porção da mistura turbulenta local, de forma que técnicas como a covariância dos vórtices apresentam dificuldades para a estimativa de fluxos turbulentos noturnos. A análise considera a variação sazonal dos perfis médios noturnos entre a estação úmida, de janeiro a junho e a seca, de julho a dezembro. Perfis de Radônio são analisados com o objetivo de se entender os processos que afetam os perfis de CO2 ao se comparar com um escalar independente e inerte. A análise também considera a direção do vento predominante durante a noite. Os resultados indicam que há uma grande diferença entre os fluxos e gradientes noturnos de CO2 entre as duas estações. Os gradientes verticais noturnos de CO2 entre os dois níveis mais altos da torre micrometeorológica freqüentemente são positivos, indicando aumento da concentração com a altura. Tais inversões são observadas com muito menos freqüência nos perfis de Radônio, que seguem a forma canônica de diminuição monotônica com a altura. Na estação seca as inversões de gradiente são mais freqüentes e estão, em geral, associadas à inversão da direção do fluxo vertical turbulento de CO2, indicando que no nível de medida há um transporte vertical para baixo deste escalar, o que proporciona convergência de fluxos e intensa acumulação junto à superfície. Uma análise coespectral mostra que este transporte para baixo ocorre nas maiores escalas temporais do movimento, sugerindo que esteja associado com transferências entre a floresta vizinha e a pastagem, na forma de fluxos de mesoescala. Os comportamentos médios sazonais são bem definidos, e uniformes ao longo da noite, mas estudos de caso mostram que estes processos são dominados por eventos específicos. Os fluxos de Radônio medidos em campanhas experimentais são utilizados para estimar os fluxos de CO2 através da relação entre os gradientes entre os dois escalares em seis noites, três em cada estação. A comparação com os fluxos determinados pela covariância dos vórtices é satisfatória na estação úmida, mas ruim na estação seca e os motivos são discutidos.

This work is about to verify the performance of the boundary layer budgeting method as alternative for measuring the surface turbulent fluxes in conditions that allow the validation of the measurements with data taken from a tower equipped with sensors, which were processed through the eddy correlation method. A research is made on the knowledge generated to the present, which reveals the limitations of the eddy correlation method and the promises of the boundary layer budgeting in relation to measuring the surface turbulent fluxes. This work describes its theoretical underpinnings, regarding the energy budget in the atmosphere and the role of turbulence in the transport phenomena and in energy exchanges. These concepts are interpreted physically and described in the form of ruling equations and hypotheses used for the analysis of the behavior of such phenomena. The eddy correlation is described as a method that directly measures the sensible heat and latent heat fluxes in function of the data picked up by the sensors. The boundary layer budgeting method, by its turn, is described from the general formulation of scalar accumulation, on which are taken the hypotheses of elimination of the horizontal advection and of any sources or drains in the atmosphere. The context of the measuring work is described in the following, from the presentation of the project, its places, and its campaigns and to the day and times in which the measurements took place. The instruments used for data acquisition are also described, as well as the processing systematics of the raw data. The obtained results reveal significant differences in the sensible heat flux estimates, which increase with the progress of the night and smaller differences in the latent heat flux, which remain constant in the time. / Este trabalho trata de verificar o desempenho do método de balanço da camada limite como alternativa para a medição dos fluxos turbulentos superficiais em condições que permitem a validação das medidas com dados tomados a partir de uma torre equipada com sensores, os quais foram processados com o método de correlação de vórtices. É feita uma pesquisa do conhecimento gerado até o presente, que revela as limitações da sistemática de medição por correlação de vórtices e as promessas do método de balanço em relação à medição dos fluxos turbulentos. É descrita neste trabalho a fundamentação teórica necessária, a respeito do balanço energético na atmosfera e do papel da turbulência nos fenômenos de transporte e de troca de energia. Tais conceitos são interpretados fisicamente e descritos na forma de equações governantes e hipóteses utilizadas para a análise do comportamento de tais fenômenos. A correlação de vórtices é descrita como um método que mede diretamente os fluxos de calor sensível e de calor latente em função dos dados recolhidos pelos sensores. O método de balanço da camada limite, por sua vez é descrito a partir da formulação geral de acumulação de escalares, sobre a qual são tomadas as hipóteses de eliminação da advecção horizontal e de quaisquer fontes ou sumidouros na atmosfera. O contexto das medições é descrito a seguir, a partir da apresentação do projeto, dos locais, das campanhas e do dia e dos horários em que as medições foram realizadas. A instrumentação utilizada para a aquisição dos dados é também descrita, assim como a sistemática de processamento dos dados brutos. Os resultados obtidos revelam diferenças significativas na estimativa do fluxo de calor sensível, que aumentam com o avanço da noite e diferenças menores no fluxo de calor latente, que permanecem praticamente constantes no tempo.

Appropriate calculation of surface turbulent fluxes between the atmosphere and the underlying surface is one of the major challenges in geosciences. In practice, the surface turbulent fluxes are estimated from the mean surface meteorological variables based on the bulk transfer model combined with Monnin-Obukhov Similarity (MOS) theory. Few studies have been done to examine the extent that to which this flux parameterization framework can be applied to different weather and surface conditions. A novel validation method is developed in this thesis research, which is applied to evaluate the surface flux parameterization using in-situ observations. The main findings are: (a) the theoretical prediction that uses MOS theory does not match well with those directly computed from the observations collected in the coastal region. (b) Large spread in exchange coefficients mainly occurs in the calm wind regime with strong stability. (c) Large turbulent eddies, which depend largely on the mean flow and surface conditions, tend to break the constant flux assumption in the surface layer.

Les échanges de chaleur et de quantité de mouvement à l'interface-océan atmosphère jouent un rôle majeur dans la formation et la dynamique des masses d'air et d'eau. Malgré des décennies de recherche, nous avons encore besoin d'améliorer nos connaissances sur ces échanges, et plus spécifiquement nos connaissances sur les flux turbulents, qui sont des variables clés dans les modèles météorologiques et de climat. Dans ces modèles, les processus turbulents sont des processus sous-maille, non-résolus explicitement, ainsi les flux turbulents doivent être modélisés, au travers de paramétrisations, qui sont pour la plupart réalisées à partir de la théorie des similitudes de Monin-Obukhov [1954]. Cependant, d'une part, l'utilisation d'un modèle implique que les coefficients doivent être ajustés. D'autre part, le modèle lui-même peut demander des améliorations. Malheureusement, l'obtention d'estimations de flux avec une bonne précision est un gros défi, à cause des effets intrusifs de la plate-forme sur la mesure, de la précision limité des instruments et des capacités d'échantillonnages propres de chaque instrument.Notre étude porte sur l'estimation des flux turbulents en mer à partir de mesures réalisées avec la nouvelle plate-forme OCARINA (trimaran autonome) lors des campagnes STRASSE 2012 et AMOP 2014. Nous analysons les caractéristiques de la turbulence dans la couche limite de surface, nous estimons les flux turbulents par différentes méthodes, et nous comparons les valeurs des flux en fonction des conditions environnementales, en prenant en compte l'état de mer. / Exchanges of heat and momentum at the air-sea interface play a major role in the formation and the dynamics of water and air masses. In spite of decades of research, we still need to improve our knowledge of these exchanges, and more specifically our knowledge of turbulent fluxes, which are key variables in meteorological and climate models. In these models, sub-grid turbulent processes, thus turbulent fluxes also have to be modeled, which is mostly done with the Monin-Obukhov (1954, MOS hereafter) similarity theory. However, on the one hand, the use of a model implies that coefficients have to be adjusted. On the other hand, the model itself may require improvements. Unfortunately, obtaining flux estimates that have a good accuracy is a challenging effort, because of the intrusive effect of the platform, the limited accuracy the instruments, and because the instruments have their own sampling volume.Our study focuses on the estimation of turbulent fluxes at sea from measurements made with the new OCARINA platform (autonomous trimaran) during two campaigns : STRASSE 2012 and AMOP 2014. We analyze the characteristics of turbulence in the surface boundary layer, we estimate the turbulent fluxes by different methods, and compare the values of fluxes depending on environmental conditions, taking into account the sea state.

<p>Knowledge of the turbulent fluxes at the sea surface is important for understanding the interaction between atmosphere and ocean. With better knowledge, improvements in the estimation of the heat exchange coefficients can be made and hence models are able to predict the weather and future climate with higher accuracy.</p><p>The exchange coefficients of latent and sensible heat during stable stratification vary in the literature. Therefore it is necessary to investigate the processes influencing the air-sea exchange of water vapour and heat in order to estimate these values. With measurements from a tower and a directional waverider buoy at the site Östergarnsholm in the Baltic Sea, data used in this study have been sampled from the years 2005-2007. This site represents open-ocean conditions during most situations when the wind comes from the south-east sector. The neutral exchange coefficients, CEN and CHN, have been calculated along with the non-dimensional profile functions for temperature and wind to study the dependence of stability and other parameters of relevance.</p><p>It was found that CEN increased slightly with wind speed and reached a mean value of approximately 1.45×10-3. The highest values of CEN were observed during near neutral conditions and low wave ages. CHN attained a mean value of approximately 0.77×10-3 and did not show any relation to wind speed or to wave age. No significant dependence with wind or wave direction could be shown for either CEN or CHN in the sector 80-220°. The stability correction, performed to reduce the dependence on stratification for CEN and CHN, was well performed for stabilities higher than 0.15. The stability is represented by a relationship between the height and the Obukhov-length (z/L).</p><p>Validity of the non-dimensional profile functions for temperature and wind showed that, for smaller stabilities, these functions gave higher values than the corresponding functions recommended by Högström (1996). The profile funtions for temperature was shown to have a larger scatter while the profile functions for wind was less scattered and deviated more from the functions given by Högström</p> / <p>Kunskap om turbulenta flöden i det marina gränsskiktet är viktigt för att förstå växelverkan mellan atmosfär och hav. Med bättre kunskap kan förbättringar i bestämningen av utbyteskoefficienterna för latent och sensibelt värme erhållas. Det medför att modeller kan prognostisera väder och framtida klimat med högre noggrannhet.</p><p>Utbyteskoefficienterna för latent och sensibelt värme har för stabil skiktning olika värden i litteraturen. Detta gör det nödvändigt att undersöka de processer som påverkar utbytet av vattenånga och värme mellan luft och hav för att kunna bestämma dessa värden. Data som har använts i den här studien insamlades mellan år 2005 och 2007 från en boj och ett torn vid mätplatsen Östergarnsholm i Baltiska havet. För det flesta situationer, när vinden blåser från syd-ost, representerar mätplatsen ett förhållande likvärdigt det över öppet hav. De neutrala utbyteskoefficienterna, CEN och CHN, och de dimensionslösa profilfunktionera för temperatur och vind, och , har beräknats för att studera beroendet av stabilitet samt andra relevanta parametrar.</p><p>Beräkningarna visade att CEN ökade något med vindhastighet och hamnade på ett medelvärde av ungefär 1.45×10-3. De högsta värdena på CEN observerades vid nära neutrala förhållanden och låga vågåldrar. CHN uppmättes till att ha ett medelvärde på ungefär 0.77×10-3 och uppvisade inget beroende med vindhastighet eller vågålder. Inget märkbart beroende med vind- eller vågriktning kunde visas för CEN eller CHN i sektorn 80-220°. Stabilitetskorrektionen, utförd för att reducera beroendet av atmosfärens skiktning för CEN och CHN, var bra för stabiliteter högre än 0.15. Stabiliteten representeras av förhållandet mellan höjden och Obukhov-längden (z/L).</p><p>Utvärdering av de dimensionslösa funktionerna för temperatur och vind visade att dessa funktioner, för små stabiliteter, gav högre värden än motsvarande funktioner som rekommenderas av Högström (1996). Värdena på profilfunktionerna för temperatur hade större spridning än värdena på profilfunktionerna för vind och avvek mer från funktionerna givna av Högström.</p>

Em dosséis com arquitetura foliar complexa, a radiação solar difusa pode potencializar a capacidade fotossintética, porque os penetra de modo mais eficiente. Apesar dos diversos estudos realizados nesse sentido em diferentes regiões do globo, os mecanismos e impactos do efeito da fertilização difusa sobre a América do Sul ainda continuam sendo pouco conhecidos. O Arco do Desflorestamento da Amazônia é um cenário ideal para sua maior investigação, tanto pela presença de complexos ecossistemas, quanto pela grande carga de aerossóis lançada para a atmosfera, em decorrência da queima de biomassa. Um estudo baseado em três diferentes localidades do Arco do Desflorestamento da Amazônia foi conduzido, a fim de relacionar a profundidade óptica dos aerossóis com alguns fluxos de superfície. Os resultados mostraram efeitos significativos da presença dos aerossóis tanto na troca de gás carbônico entre a vegetação e a atmosfera, quanto na troca de energia. Ainda, os fluxos mostraram ser sensíveis também às mudanças na temperatura, umidade e vento, além da influência do próprio ciclo diurno. Em cenários hipotéticos, foi possível isolar apenas o efeito do aerossol. O comportamento do fluxo de gás carbônico à presença dos aerossóis não foi o mesmo para as três localidades, o que indica uma grande dependência do fenômeno com as características da vegetação local. Na Reserva Biológica do Jaru e Ilha do Bananal, as trocas de gás carbônico entre a atmosfera e a superfície são favorecidas na presença de aerossóis, podendo atingir valores até 55% maiores em Jaru. Entretanto, Sinop apresentou uma redução de aproximadamente 12% no valor médio do fluxo de gás carbônico, para o período avaliado. Os fluxos de energia mostraram ser afetados negativamente pela presença dos aerossóis. Na Ilha do Bananal, a média do fluxo de calor sensível em cenários sem aerossóis foi em torno de 60% maior, e de até 13% maior para o fluxo de calor latente em Sinop. Devido aos processos de absorção e espalhamento da radiação solar pelos aerossóis, menos energia atinge a superfície e, portanto, há menos disponibilidade para a realização de tais trocas, como esperado. / In complex architecture canopies, the diffuse solar radiation can enhance photosynthetic capacity, as it penetrates more efficiently on them. Although several studies have been conducted on this topic over the world, the mechanisms and impacts of the \"diffuse fertilization effect\" over South America still remains poorly understood. The Amazon Deforestation Arch provides an ideal scenario for its further investigation, by the presence of complex ecosystems and by the large amounts of aerosols released into the atmosphere due to biomass burning. A study based on three different sites in the Amazon Deforestation Arch was conducted in order to relate the aerosol optical depth with some surface fluxes. The results showed significant effects of the aerosol presence in both, the exchange of carbon dioxide between the vegetation and the atmosphere, and the energy exchange. Still, the fluxes also showed to be sensitive to changes in temperature, humidity and wind velocities, as well as the influence of the diurnal cycle itself. In hypothetical scenarios, it was possible to isolate only the aerosol effect. The carbon dioxide flux behavior due to the aerosol presence was not the same for all the three locations, showing that it depends on the local vegetation characteristics. At the Jaru Biological Reserve and Bananal Island, the carbonic gas exchanges between the atmosphere and the surface increased under the aerosol presence, achieving values up to 55% higher in Jaru. However, Sinop showed a decrease by approximately 12% in the average value of the carbon dioxide flux for the evaluated period. Energy fluxes showed to be negatively affected by the presence of aerosols. In the Bananal Island the average of sensitive heat flux in scenarios without aerosols was around 60% higher, and up to 13% higher for the latent heat flux in Sinop. Due to absorption and scattering of solar radiation by the aerosols, less energy reaches the surface, and therefore there is less availability to perform such exchanges, as expected.

Knowledge of the turbulent fluxes at the sea surface is important for understanding the interaction between atmosphere and ocean. With better knowledge, improvements in the estimation of the heat exchange coefficients can be made and hence models are able to predict the weather and future climate with higher accuracy. The exchange coefficients of latent and sensible heat during stable stratification vary in the literature. Therefore it is necessary to investigate the processes influencing the air-sea exchange of water vapour and heat in order to estimate these values. With measurements from a tower and a directional waverider buoy at the site Östergarnsholm in the Baltic Sea, data used in this study have been sampled from the years 2005-2007. This site represents open-ocean conditions during most situations when the wind comes from the south-east sector. The neutral exchange coefficients, CEN and CHN, have been calculated along with the non-dimensional profile functions for temperature and wind to study the dependence of stability and other parameters of relevance. It was found that CEN increased slightly with wind speed and reached a mean value of approximately 1.45×10-3. The highest values of CEN were observed during near neutral conditions and low wave ages. CHN attained a mean value of approximately 0.77×10-3 and did not show any relation to wind speed or to wave age. No significant dependence with wind or wave direction could be shown for either CEN or CHN in the sector 80-220°. The stability correction, performed to reduce the dependence on stratification for CEN and CHN, was well performed for stabilities higher than 0.15. The stability is represented by a relationship between the height and the Obukhov-length (z/L). Validity of the non-dimensional profile functions for temperature and wind showed that, for smaller stabilities, these functions gave higher values than the corresponding functions recommended by Högström (1996). The profile funtions for temperature was shown to have a larger scatter while the profile functions for wind was less scattered and deviated more from the functions given by Högström / Kunskap om turbulenta flöden i det marina gränsskiktet är viktigt för att förstå växelverkan mellan atmosfär och hav. Med bättre kunskap kan förbättringar i bestämningen av utbyteskoefficienterna för latent och sensibelt värme erhållas. Det medför att modeller kan prognostisera väder och framtida klimat med högre noggrannhet. Utbyteskoefficienterna för latent och sensibelt värme har för stabil skiktning olika värden i litteraturen. Detta gör det nödvändigt att undersöka de processer som påverkar utbytet av vattenånga och värme mellan luft och hav för att kunna bestämma dessa värden. Data som har använts i den här studien insamlades mellan år 2005 och 2007 från en boj och ett torn vid mätplatsen Östergarnsholm i Baltiska havet. För det flesta situationer, när vinden blåser från syd-ost, representerar mätplatsen ett förhållande likvärdigt det över öppet hav. De neutrala utbyteskoefficienterna, CEN och CHN, och de dimensionslösa profilfunktionera för temperatur och vind, och , har beräknats för att studera beroendet av stabilitet samt andra relevanta parametrar. Beräkningarna visade att CEN ökade något med vindhastighet och hamnade på ett medelvärde av ungefär 1.45×10-3. De högsta värdena på CEN observerades vid nära neutrala förhållanden och låga vågåldrar. CHN uppmättes till att ha ett medelvärde på ungefär 0.77×10-3 och uppvisade inget beroende med vindhastighet eller vågålder. Inget märkbart beroende med vind- eller vågriktning kunde visas för CEN eller CHN i sektorn 80-220°. Stabilitetskorrektionen, utförd för att reducera beroendet av atmosfärens skiktning för CEN och CHN, var bra för stabiliteter högre än 0.15. Stabiliteten representeras av förhållandet mellan höjden och Obukhov-längden (z/L). Utvärdering av de dimensionslösa funktionerna för temperatur och vind visade att dessa funktioner, för små stabiliteter, gav högre värden än motsvarande funktioner som rekommenderas av Högström (1996). Värdena på profilfunktionerna för temperatur hade större spridning än värdena på profilfunktionerna för vind och avvek mer från funktionerna givna av Högström.