This paper presents the basic features of a newly developed planetary boundary layer (PBL) parameterization, and the performance assessment of a version of the University of California, Los Angeles (UCLA), Atmospheric General Circulation Model (AGCM) to which the parameterization is incorporated. The UCLA AGCM traditionally uses a framework in which a sigma-type vertical coordinate for the PBL shares a coordinate surface with the free atmosphere at the PBL top. This framework facilitates an explicit representation of processes concentrated near the PBL top, which is crucially important especially for predicting PBL clouds. In the new framework, multiple layers are introduced between the PBL top and earth's surface, allowing for predictions of the vertical profiles of potential temperature, total water mixing ratio, and horizontal winds within the PBL. The vertically integrated ''bulk'' turbulent kinetic energy (TKE) is also predicted for the PBL. The PBL-top mass entrainment is determined through an equation including the effects of TKE and the radiative and evaporative cooling processes concentrated near the PBL top. The surface fluxes are determined from an aerodynamic formula in which the velocity scale depends both on the square root of TKE and the grid-scale PBL velocity at the lowermost model layer. The turbulent fluxes within the PBL are determined through an approach that includes the effects of both large convective and small diffusive eddies. AGCM simulations with the new formulation of PBL are analyzed with a focus on the seasonal and diurnal variations. The simulated seasonal cycle of stratocumulus over the eastern oceans is realistic, as are the diurnal cycles of the PBL depth and precipitation over land. The simulated fluxes of latent heat, momentum, and shortwave radiation at the ocean surface and baroclinic activity in the middle latitudes show significant improvements over the previous versions of the AGCM based on the single-layer PBL.
In this work is presented a statistical description of wind profile in the first 100 m of height of the Planetary Boundary Layer, taking account the measurements in the tower Colonia Eulacio Uruguay. This tower has high vertical resolution of wind velocity measurements, form 10.1 m to 101.8 m. Thermometer are installed in 3.4 m and 100.8 m, also the tower is equipped with wind vane and pyranometer. We present the diurnal cycle of mean wind, intensity of turbulence in dependence of height, also standard deviation of direction is described as a measure of turbulence in wind. Stability state is computed with vertical gradient of temperature. Before sunrise (unstable condition) is seen a decrease in mean velocity of top levels (81.8 m and 101.8 m) and increase in lower levels (10.1 m and 25.7 m). Higher dispersion in dT/dz can be seen during night time (stable condition), superadiabatic values -0.02 ◦C/m can be seen during daytime with slow dispersion. Intensity of turbulence decrease with height, for all stability conditions, is seen a increase in intensity of turbulence for unstable condition.
This work presents the results of a numerical forecast system of minimum cost for the electric power generated by wind farms in Uruguay. By keeping at minimum levels both the computational costs and the complexity of the empirical corrections of the numerical results, we obtain a benchmark for the forecast skill of more complex forecast systems, that is easily available during their calibration stages and operative functioning. The work also aims to explore the diurnal and seasonal cycle of the forecasts quality. It is found that this simple forecast system produces very good results, albeit the dependencies of the forecast skill and errors respect to the season of the year and the time of the day are distinguishable. It is also found that it is necessary to take into account the diurnal and the seasonal cycles during the calibration of the empirical corrections. The good results of this simple technique might had been possible due to the relative smooth topography of Uruguay.
This work assessed the quality of wind speed estimates in Uruguay. These estimates were obtained using the Weather Research and Forecast Model Data Assimilation System (WRF-DA) to assimilate wind speed measurements from 100 m above the ground at two wind farms. The quality of the estimates was assessed with an anemometric station placed between the wind farms. The wind speed estimates showed low systematic errors at heights of 87 and 36 m above the ground. At both levels, the standard deviation of the total errors was approximately 25% of the mean observed speed. These results suggested that the estimates obtained could be of sufficient quality to be useful in various applications. The assimilation process proved to be effective, spreading the observational gain obtained at the wind farms to lower elevations than those at which the assimilated measurements were taken. The smooth topography of Uruguay might have contributed to the relatively good quality of the obtained wind estimates, although the data of only two stations were assimilated, and the resolution of the regional atmospheric simulations employed was relatively low.
The present work analyses the inter-seasonal predictability of precipitation during the austral summer in a subregion of Southeastern South America that includes Rio Grande do Sul and Northern Uruguay (RGS-NU), and proposes a methodology to produce probabilistic precipitation forecasts for this region, based on the use of NOAA CFS v2. It is found that the correlation between ENSO and the precipitation over RGS-NU during December-January-February is statistically significant after the late 70's, but not before. Considering that this relationship changes in different multidecadal periods, it is useful to explore a forecast system based on numerical models. We studied the hindcasts from NOAA CFS v2 initialized during October of the years 1983 to 2009, and found that the hindcasts of meridional wind at 850 hPa averaged over certain region of South America have statistically significant skill, in terms of correlation, to predict the observed precipitation over RGS-NU. The proposed forecasts are based on this relationship. The CFS v2 hindcasts also show realistic anomalous circulation patterns associated with the anomalous precipitation in the region and the season considered. This suggests that the forecasts may be further improved by using regional models combined with the CFS v2 outputs. Keywords: Seasonal forecast, Statistical downscaling, Southeastern South America, Hindcasts RESUMO: PREVISÃO PROBABILISTICA SAZONAL DA PRECIPITAÇÃO DE DEZEMBRO-JANEIRO-FEVEREIRO NO NORTE DO URUGUAI E RIO GRANDE DO SUL OBTIDA COM O MODELO ACOPLADO DE PREVISÃO DA NOAA E DOWNSCALING ESTATÍSTICA: O presente trabalho analisa a previsibilidade inter-sazonal da precipitação durante o verão austral em uma sub-região do Sudeste da América do Sul, que inclui Rio Grande do Sul e o Norte do Uruguai (RGS-NU), e propõe uma metodologia para produzir previsões probabilísticas da precipitação baseada no uso do CFS v2 da NOAA. Verifica-se que a correlação entre o ENOS e a precipitação sobre RGS-NU em dezembro-janeiro-fevereiro é estatisticamente significativa nos últimos 30 anos, mas não nos 30 anos anteriores a estes. Em vista desta mudança na relação em diferentes períodos multi-decenais, consideramos útil explorar um sistema de prognósticos baseados em modelo numérico, o CFS v2 da NOAA. Estudamos as previsões retrospectivas do CFS v2 iniciadas em outubro dos anos 1983 a 2009, e achamos que o valor médio das previsões retrospectivas de vento meridional em 850 hPa sobre determinada região da América do Sul, têm habilidade estatisticamente significativa, em termos de coeficiente de correlação, de prever a precipitação observada em RGS-NU. Esta relação é a base da metodologia para produzir previsões da precipitação. As previsões retrospectivas do CFS v2 também mostram padrões de circulação anômala realistas, associados com as precipitações na região e na época considerada. Isto é encorajador, no sentido de que há potencial para melhorar ainda mais as previsões através do uso de modelos regionais combinados com as saídas do CFS v2.
O presente trabalho analisa o comportamento do perfil vertical do vento nos primeiros 100 metros da camada limite planetária, através da análise de dados observados em uma torre de medição meteorológica no Uruguai, assim como dados simulados pelo modelo numérico WRF-ARW, os quais compreendem o período de 1 ano. Da torre de medição analisada (Colonia Eulacio), foram utilizadas informações referentes a velocidade média do vento em intervalos horários para as alturas de 10.1 metros e 101.8 metros. O modelo WRF-ARW foi executado para o mesmo período dos dados analisados, e configurado com distintas combinações de parametrizações físicas de camada limite planetária e camada limite superficial, buscando assim identificar dentre as diferentes simulações realizadas, qual o comportamento das mesmas em estimar a velocidade média do vento nos períodos anual, estacional durante o ciclo diário para as duas distintas alturas de interesse. Todas as parametrizações analisadas apresentaram um bom ajuste ao ciclo diário quando se comparou o nível eta correspondente a altura de 101.8 metros. Quando se analisou o ciclo diário do nível eta correspondente a 10.1 metros, somente a parametrização física de camada limite planetária Mellor-Yamada-Janjic conseguiu representar os aumentos de velocidade média do vento durante períodos diurnos em todas as estações do ano (inverno, primavera, verão e outono), resultando em uma maior correlação linear e menor erro média absoluto da mesma em relação as outras parametrizações físicas utilizadas no modelo.Palavras chave: Perfil vertical do vento, camada limite planetária, ciclo diário, modelo WRF-ARW.The aim of this article is to analyze the behaviour of the wind speed vertical profile for the first 100 meters of the planetary boundary layer. This is done by analyzing 1 year of ARW-WRF (Weather Research and Forecasting) model outputs as well as anemometric measurements from a tower installed in Uruguay. Colonia Eulacio tower, the tower used, measures wind speed at heights of 10.1 meters and 101.8 meters. In this article, mean hourly wind speeds at each height are used. Different parametrizations of surface layer and planetary boundary layers were set to ARW-WRF modelations, in order to compare their capability to model hourly mean wind speeds from tower measurements considering 101.8m as well as 10.1m height data. Such comparison was done for the whole year as well as for each season. A day-cicle comparison was also performed. All the parametrizations considered showed a good modelation of the Day-cicle for 101.8 meters height data. Regarding 10.1 meters height data, only Mellor-Yamada-Janjic (MYJ) showed a proper modelation of the day-cicle, being the only parametrization capable of representing correctly the mean speed rise during the day for all seasons. As a consequence, MYJ showed the biggest linear correlation factor as well as the lower mean absolute error.
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