The statistical prediction of local sea surface winds at a number of locations over the global ocean (Northeast Pacific, Northwest Atlantic and Pacific, tropical Pacific and Atlantic) is investigated using a surface wind statistical downscaling model based on multiple linear regression. The predictands (mean and standard deviation of both vector wind components and wind speed) calculated from ocean buoy observations on daily, weekly and monthly temporal scales are regressed on upper level predictor fields (derived from zonal wind, meridional wind, wind speed, and air temperature) from reanalysis products. The predictor fields are subject to a combined Empirical Orthogonal Function (EOF) analysis before entering the regression model. It is found that in general the mean vector wind components are more predictable than mean wind speed in the North Pacific and Atlantic, while in the tropical Pacific and Atlantic the difference in predictive skill between mean vector wind components and wind speed is not substantial. The predictability of wind speed relative to vector wind components is interpreted by an idealized Gaussian model of wind speed probability density function, which indicates that the wind speed is more sensitive to the standard deviations (which generally are not well predicted) than to the means of vector wind component in the midlatitude region and vice versa in the tropical region. This sensitivity of wind speed statistics to those of vector wind components can be characterized by a simple scalar quantity theta=arctan(mu/sigma) (in which mu is the magnitude of average vector wind and sigma is the isotropic standard deviation of the vector winds). The quantity theta is found to be dependent on season, geographic location and averaging timescale of wind statistics. While the idealized probability model does a good job of characterizing month-to-month variations in the mean wind speed based on those of the vector wind statistics, month-to-month variations in the standard deviation of speed are not well modelled. A series of Monte Carlo experiments demonstrates that the inconsistency in the characterization of wind speed standard deviation is the result of differences of sampling variability between the vector wind and wind speed statistics. / Graduate

A statistical downscaling approach based on multiple linear-regression is used to investigate the predictability of land surface winds over the Canadian prairies and Ontario. This study's model downscales mid-tropospheric predictors (wind components and speed, temperature, and geopotential height) from reanalysis products to predict historical wind observations at thirty-one airport-based weather surface stations in Canada. The model's performance is assessed as a function of: season; geographic location; averaging timescale of the wind statistics; and wind regime, as defined by how variable the vector wind is relative to its mean amplitude. Despite large differences in predictability characteristics between sites, several systematic results are observed. Consistent with recent studies, a strong anisotropy of predictability for vector quantities is observed, while some components are generally well predicted, others have no predictability. The predictability of mean quantities is greater on shorter averaging timescales. In general, the predictability of the surface wind speeds over the Canadian prairies and Ontario is poor; as is the predictability of sub-averaging timescale variability. These results and the relative predictability of vector and scalar wind quantities are interpreted with theoretically- and empirically-derived wind speed sensitivities to the resolved and unresolved variability in the vector winds. At most sites, and on longer averaging timescales, the scalar wind quantities are found to be highly sensitive to unresolved variability in the vector winds. These results demonstrate limitations to the statistical downscaling of wind speed and suggest that deterministic models which resolve the short-timescale variability may be necessary for successful predictions. / Graduate

Surface wind speeds are an important and revealing component of the structure of tropical cyclones (TCs). To understand the asymmetric structure of surface winds in TCs associated with differences in formation region, environmental wind shear, storm forward motion, and TC strength and intensification, a twelve year database of satellite scatterometer data are utilized to produce composite total wind speed and Fourier-derived, low wavenumber analyses. A quantified asymmetry is determined as a function of TC intensity and reveals the tropical storms are influenced by wind shear at all TC-centric radii but only for areas away from the radius of maximum wind in hurricanes. Additionally, an increase of absolute angular momentum flux has a preference for the downshear-right quadrant, and the low wavenumber maximum develops downwind of this momentum transport. Further evaluation of the asymmetric structure with respect to wind shear’s relation to motion and impacts during TC intensity change are also considered. A composite rapid intensification event is produced and compared to overlapping satellite rain estimates. Results indicate that the TC becomes more symmetric during intensification and the phase of the maximum asymmetry rotates from a downshear-left direction to upshear-left direction after the intensification slows. The rain or convective maximum is generally located upwind of the surface wind maximum at the early stages of intensification and is coincident with the region of large angular momentum transport, which supports the idea that the surface wind asymmetry is likely a consequence of convective or other processes. Using data from a regional TC model, it is also determined that the scatterometer data are useful for model verification of tropical storms and non-major hurricanes and performs similar to or better than the standard tool at forecast lead times up to 60 hours. Preliminary comparisons of model-derived surface wind asymmetry relative to rain generally confirm the observational results.

Uma versão do POM - Princeton Ocean Model foi implementada no litoral norte do Estado de São Paulo, região compreendida entre as longitudes 46o e 44o30\'W e latitudes 24o30\' e 23o18\'S, abrangendo as cidades de Bertioga, São Sebastião, Caraguatatuba e Ubatuba, da linha da costa até aproximadamente a isóbata de 100 m, para estudos da resposta do mar ao vento. Para tanto foram realizados diferentes experimentos numéricos, combinando diferentes períodos e forçantes (de maré, vento e campos médios mensais de temperatura e salinidade). As respostas das simulações foram comparadas entre si, com estudos anteriores e a dados reais de diferentes fontes (marégrafo, correntômetro e altímetro). As simulações reproduziram razoavelmente os dados medidos, demostrando uma boa calibração do modelo. Foi observado o padrão de correntes predominantes para sudoeste, infuenciado pela Alta Subtropical do Atlântico Sul e seus ventos de nordeste, bem como eventuais efeitos de frentes frias com ventos de sudoeste e correntes para nordeste.Também se observou que as frentes frias mais intensas não ocorreram nos meses de inverno para os processamentos do ano de 2005, que apresentou várias situações anômalas, como por exemplo: um mês de Fevereiro com excepcional persistência de ventos do quadrante sul; ventos muito fracos em Março; Junho também com ventos fracos e praticamente ausência de frentes frias; e Setembro e Outubro com incursões muito freqüentes de frentes. Apesar das anomalias dos ventos e correspondentes campos de correntes, variações dos valores médios mensais de elevação da superfície do mar foram mais regulares, reproduzindo inclusive os valores medidos por altimetria, com um ciclo sazonal bem definido, o que provavelmente se deve ao fato das elevações da superfície do mar serem mais dependentes da circulação geral no Atlântico Sul e menos dependentes de ventos locais. Também foram analisados através da modelagem, os campos hidrodinâmicos causados por diversas combinações de condições de maré (típicas e extremas) e de efeitos meteorológicos (predominantes e extremos). O processamento final do modelo indicou que a circulação de maré é uma boa aproximação da circulação total, com exceção de períodos em que ocorrem eventos meteorológicos extremos. / A version of POM - Princeton Ocean Model was used in the northern coastal area of São Paulo State, longitudes 46o ? 44o30\'W and latitudes 24o30\' ? 23o18\'S, with the cities of Bertioga, São Sebastião, Caraguatatuba e Ubatuba in the domain, from the coast to the 100m isobath, to study the sea response to the wind forcing. For this purpose, several numerical experiment were performed, involving different periods and forcings (including tides, winds and monthly means fields of temperature and salinity). The simulations results were compared to other studies, with real observations from several sources methods (tide gauge, current meter and altimeter). The simulations reproduced reasonably the real datas, showing a good model calibration. Standard currents to the southeast, were observed, due to the South Atlantic Subtropical High influence and its northeast winds, as well as eventual northeast currents generated by cold fronts with southeast winds. It was also observed that the strongest cold fronts did not occur in winter\'s months in the model runs of the year of 2005, which presented several anomalies, as for example: February exceptional southern winds persistence; very weak winds in March; June practically without colds fronts and weak winds too; and September and October with frequent cold fronts incursions. Despite the wind anomalies and correspondent currents fields, the monthly means elevations of sea surface has regular pattern, reproducing the altimeter data, with clear seasonal cycle, probably because the sea surface elevations depend more on the general circulation in the South Atlantic and not on the local winds. Through the modeling hydrodynamical fields generated by differents tidal conditions (typical and extremes) and by several meteorological effect (standard and extremes) were analyzed. The last model processement indicate that tidal circulation is a god approximation of the total circulation, except when extreme meteorological events occur.

Uma versão do POM - Princeton Ocean Model foi implementada no litoral norte do Estado de São Paulo, região compreendida entre as longitudes 46o e 44o30\'W e latitudes 24o30\' e 23o18\'S, abrangendo as cidades de Bertioga, São Sebastião, Caraguatatuba e Ubatuba, da linha da costa até aproximadamente a isóbata de 100 m, para estudos da resposta do mar ao vento. Para tanto foram realizados diferentes experimentos numéricos, combinando diferentes períodos e forçantes (de maré, vento e campos médios mensais de temperatura e salinidade). As respostas das simulações foram comparadas entre si, com estudos anteriores e a dados reais de diferentes fontes (marégrafo, correntômetro e altímetro). As simulações reproduziram razoavelmente os dados medidos, demostrando uma boa calibração do modelo. Foi observado o padrão de correntes predominantes para sudoeste, infuenciado pela Alta Subtropical do Atlântico Sul e seus ventos de nordeste, bem como eventuais efeitos de frentes frias com ventos de sudoeste e correntes para nordeste.Também se observou que as frentes frias mais intensas não ocorreram nos meses de inverno para os processamentos do ano de 2005, que apresentou várias situações anômalas, como por exemplo: um mês de Fevereiro com excepcional persistência de ventos do quadrante sul; ventos muito fracos em Março; Junho também com ventos fracos e praticamente ausência de frentes frias; e Setembro e Outubro com incursões muito freqüentes de frentes. Apesar das anomalias dos ventos e correspondentes campos de correntes, variações dos valores médios mensais de elevação da superfície do mar foram mais regulares, reproduzindo inclusive os valores medidos por altimetria, com um ciclo sazonal bem definido, o que provavelmente se deve ao fato das elevações da superfície do mar serem mais dependentes da circulação geral no Atlântico Sul e menos dependentes de ventos locais. Também foram analisados através da modelagem, os campos hidrodinâmicos causados por diversas combinações de condições de maré (típicas e extremas) e de efeitos meteorológicos (predominantes e extremos). O processamento final do modelo indicou que a circulação de maré é uma boa aproximação da circulação total, com exceção de períodos em que ocorrem eventos meteorológicos extremos. / A version of POM - Princeton Ocean Model was used in the northern coastal area of São Paulo State, longitudes 46o ? 44o30\'W and latitudes 24o30\' ? 23o18\'S, with the cities of Bertioga, São Sebastião, Caraguatatuba e Ubatuba in the domain, from the coast to the 100m isobath, to study the sea response to the wind forcing. For this purpose, several numerical experiment were performed, involving different periods and forcings (including tides, winds and monthly means fields of temperature and salinity). The simulations results were compared to other studies, with real observations from several sources methods (tide gauge, current meter and altimeter). The simulations reproduced reasonably the real datas, showing a good model calibration. Standard currents to the southeast, were observed, due to the South Atlantic Subtropical High influence and its northeast winds, as well as eventual northeast currents generated by cold fronts with southeast winds. It was also observed that the strongest cold fronts did not occur in winter\'s months in the model runs of the year of 2005, which presented several anomalies, as for example: February exceptional southern winds persistence; very weak winds in March; June practically without colds fronts and weak winds too; and September and October with frequent cold fronts incursions. Despite the wind anomalies and correspondent currents fields, the monthly means elevations of sea surface has regular pattern, reproducing the altimeter data, with clear seasonal cycle, probably because the sea surface elevations depend more on the general circulation in the South Atlantic and not on the local winds. Through the modeling hydrodynamical fields generated by differents tidal conditions (typical and extremes) and by several meteorological effect (standard and extremes) were analyzed. The last model processement indicate that tidal circulation is a god approximation of the total circulation, except when extreme meteorological events occur.

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