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1.
The vertical mesoscale flux in the nocturnal boundary layer is generally considered to be difficult to estimate because of the small mesoscale vertical velocities and the large random variation of the mesoscale fluxes. However, the mesoscale vertical flux of heat, computed from FLOSSII data, varies quasi-systematically with height, stability and time scale. Such systematic variation requires correction for sonic misalignment and averaging over a large quantity of data. The relation of the mesoscale heat flux to the vertical structure of the nocturnal boundary layer is examined. For the most common conditions, the vertical convergence of the mesoscale heat flux acts to reduce the nocturnal cooling rate. Important uncertainties are discussed as well as the need for improved observations. 相似文献
2.
Otávio L. G. Maioli Bastiaan A. Knoppers Débora A. Azevedo 《Journal of Atmospheric Chemistry》2009,64(2-3):159-178
Polycyclic aromatic hydrocarbons (PAHs) and aliphatic hydrocarbons (AHs), such as n-alkanes, hopanes and steranes, were studied in relation to total atmospheric suspended particulates (TSP). Two representative Brazilian cities affected by sugarcane monoculture practices, with their rural surroundings, were chosen for the study. The cities chosen were Maceió (state of Alagoas, NE-Brazil) and Campos dos Goytacazes (state of Rio de Janeiro, SE-Brazil). Samples were collected during the harvesting period, when sugarcane burning occurs, and during the non-harvesting period. The aliphatic hydrocarbon fingerprints suggest a marked contribution of biogenic inputs and a slight contamination by aliphatics in areas far from the urban regions. In the urban areas, some petroleum contributions were observed, marked by the presence of hopanes (m/z 191) and steranes (m/z 217) in the mass chromatographic profiles. A marked increase in PAH concentrations was detected during the sugarcane burning periods, mainly at Campos dos Goytacazes. In a similar approach, n-alkane concentrations and BaP/nC24 ratios were higher during the sugarcane burning periods. These increases were mainly associated with PAH production by the pyrogenic process in relation to aliphatic hydrocarbons with the same carbon numbers. The PAH isomeric ratios and the mixture of petrogenic and pyrogenic compounds of the TSP suggest atmospheric contamination for all regions as a whole, but the more elevated pyrogenic contribution during the sugarcane burning period implies that the impact of this activity is relevant. 相似文献
3.
Otávio C. Acevedo Osvaldo L. L. Moraes Gervásio A. Degrazia Luiz E. Medeiros 《Boundary-Layer Meteorology》2006,119(1):41-55
The determination of nocturnal surface fluxes in low wind conditions is a major problem for micrometeorological studies. The
eddy correlation technique, extensively used in field measurements, becomes inappropriate if not enough turbulent activity
exists. At the same time, the phenomenon of turbulence intermittency is responsible for the existence of localized events
of short duration within which a large fraction of the total nighttime scalar exchange occurs. The scalar flux within a certain
intermittent event varies considerably depending on the window used for the flux calculation. In many cases, events with very
different time durations occur in the same night, and therefore, the proper determination of the surface flux would require
averaging within data windows of different sizes for each event. In this work, the surface exchanges of temperature, moisture
and carbon dioxide are analysed at a micrometeorological tower at southern Brazil. Intermittent turbulence is a common occurrence
at the location. The analysis shows that the fluxes vary with turbulence intensity and the estimation technique. A variable-window
size method for flux estimation is suggested and shown to cause an increase in the magnitude of the nocturnal surface fluxes 相似文献
4.
Otávio C. Acevedo Osvaldo L. L. Moraes David R. Fitzjarrald Ricardo K. Sakai Larry Mahrt 《Boundary-Layer Meteorology》2007,125(1):49-61
Turbulent fluxes obtained using the conventional eddy covariance approach result in erratic results with large time fluctuations
in extremely stable conditions. This can limit efforts to estimate components of the nocturnal energy budget and respiratory
CO2 fluxes. Well-organized fluxes that show a clear dependence on turbulent intensity were obtained when multiresolution decomposition
was used to estimate turbulent exchanges. CO2, heat and water vapour fluxes were observed at a site in the eastern Amazon basin that had been cleared for agricultural
purposes. Temporal scales of the carbon transfer were determined and shown to be similar to those of latent heat, but as much
as three times larger than those of sensible heat. CO2 eddy diffusivities at the temporal scales on which most of the vertical CO2 exchange occurs are shown to be 50 times larger than the eddy diffusivity for heat. A process associated with the vertical
scale of the scalar accumulation layer is suggested to explain these different scales and turbulent diffusivities of carbon
and sensible heat transfer. For an appreciable range of turbulence intensities, the observed vertical turbulent carbon exchange
is insufficient to account for the locally respired CO2 estimated independently. Evidence that shallow drainage currents may account for this is given. 相似文献
5.
Pinheiro Maria Eduarda O. de Oliveira Pablo E. S. Acevedo Otávio C. 《Boundary-Layer Meteorology》2022,183(1):79-96
Boundary-Layer Meteorology - Vertical profiles of temperature, water vapour, and carbon dioxide ( $$\mathrm {CO}_{2}\,$$ ) densities are analyzed, together with the respective turbulent fluxes of... 相似文献
6.
Otávio Cristiano Montanher Evlyn Márcia Leão de Morais Novo Edvard Elias de Souza Filho 《水文科学杂志》2013,58(13-14):1901-1912
ABSTRACTWe discuss the claim that the Amazon River has been subjected to a noticeable increase in suspended sediment transport (SST) in response to both climate and land-use changes. To study this, both satellite imagery and in situ data were compiled to produce a 32-year time series (1984–2016) of suspended sediment concentration. Both parametric and nonparametric statistics were applied to examine the SST time trend. The results indicate that there has been no statistically significant increase in SST in the last 32 years, independent of the statistical approach. The results indicate that, over the last 32 years at the Óbidos station, in Brazil, a recurring pattern of increase and decrease in SST has occurred, rather than a unidirectional systematic trend. This further explains the increasing trend reported in the literature and indicates that short time series are not recommended for time trend analyses due to the large inter-annual variability. 相似文献
7.
The Coupling State of an Idealized Stable Boundary Layer 总被引：1，自引：1，他引：0
Otávio C. Acevedo Felipe D. Costa Gervásio A. Degrazia 《Boundary-Layer Meteorology》2012,145(1):211-228
The coupling state between the surface and the top of the stable boundary layer (SBL) is investigated using four different schemes to represent the turbulent exchange. An idealized SBL is assumed, with fixed wind speed and temperature at its top. At the surface, two cases are considered, first a constant temperature, 20 K lower than the SBL top, and later a constant 2 K h−1 cooling rate is assumed for 10 h after a neutral initial condition. The idealized conditions have been chosen to isolate the influence of the turbulence formulations on the coupling state, and the intense stratification has the purpose of enhancing such a response. The formulations compared are those that solve a prognostic equation for turbulent kinetic energy (TKE) and those that directly prescribe turbulence intensity as a function of atmospheric stability. Two TKE formulations are considered, with and without a dependence of the exchange coefficients on stability, while short and long tail stability functions (SFs) are also compared. In each case, the dependence on the wind speed at the SBL top is considered and it is shown that, for all formulations, the SBL experiences a transition from a decoupled state to a coupled state at an intermediate value of mechanical forcing. The vertical profiles of potential temperature, wind speed and turbulence intensity are shown as a function of the wind speed at the SBL top, both for the decoupled and coupled states. The formulation influence on the coupling state is analyzed and it is concluded that, in general, the simple TKE formulation has a better response, although it also tends to overestimate turbulent mixing. The consequences are discussed. 相似文献
8.
Otávio de Oliveira Costa Filho Wagner Sessin 《Celestial Mechanics and Dynamical Astronomy》1999,74(1):1-17
This paper is concerned with the extended Delaunay method as well as the method of integration of the equations, applied to
first order resonance. The equations of the transformation of the extended Delaunay method are analyzed in the (p + 1)/p type resonance in order to build formal, analytical solutions for the resonant problem with more than one degree of freedom.
With this it is possible to gain a better insight into the method, opening the possibility for more generalized applications.
A first order resonance in the first approximation is carried out, giving a better comprehension of the method, including
showing how to eliminate the ‘Poincaré singularity’ in the higher orders.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
9.
Luís Gustavo N. Martins Scott D. Miller Otávio C. Acevedo 《Boundary-Layer Meteorology》2017,163(1):123-141
A methodology based on Empirical mode decomposition (EMD) was used to filter out non-turbulent motions from measurements of atmospheric turbulence over the sea, aimed at reducing their contribution to eddy-covariance (EC) estimates of turbulent fluxes. The proposed methodology has two main objectives: (1) to provide more robust estimates of the fluxes of momentum, heat and CO\(_2\); and (2) to reduce the number of flux intervals rejected due to non-stationarity criteria when using traditional EC data processing techniques. The method was applied to measurements from a 28-day cruise (HALOCAST 2010) in the Eastern Pacific region. Empirical mode decomposition was applied to 4-h long time series data and used to determine the cospectral gap time scale, \(T_\mathrm{{gap}}\). Intrinsic modes of oscillation with characteristic periods longer than the gap scale due to non-turbulent motions were assumed and filtered out. Turbulent fluxes were then calculated for sub-intervals of length \(T_\mathrm{{gap}}\) from the filtered 4-h time series. In the HALOCAST data, the gap scale was successfully identified in 89% of the 4-h periods and had a mean of 37 s. The EMD approach resulted in the rejection of 11% of the flux intervals, which was much less than the 68% rejected when using standard filtering methods based on data non-stationarity. For momentum and sensible heat fluxes, the averaged difference in flux magnitude between the traditional and EMD approaches was small (3 and 1%, respectively). For the CO\(_2\) flux, the magnitude of EMD flux estimates was on average 16% less than fluxes estimated from linear detrended 10-min time series. These results provide evidence that the EMD method can be used to reduce the effects of non-turbulent correlations from flux estimates. 相似文献
10.