Minimum-cost numerical prediction system for wind power in Uruguay, with an assessment of the diurnal and seasonal cycles of its quality

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.Este trabalho apresenta os resultados de um sistema de previsão numérica de custo mínimo para a energia elétrica gerada pelos parques eólicos operacionais no Uruguai. Ao manter em níveis mínimos, tanto os custos computacionais como a complexidade das correções empíricas dos resultados numéricos, obtemos uma referência para a habilidade de previsão de sistemas de previsão mais complexos, que é facilmente disponível durante os estágios de calibração e funcionamento operacional. O trabalho também visa explorar o ciclo diurno e sazonal da qualidade das previsões. Verifica-se que esse sistema de previsão simples produz resultados muito bons, embora as dependências da habilidade e erros de previsão em relação à estação do ano e à época de o dia é distinguível. Verifica-se também que é necessário levar em consideração os ciclos diurnos e sazonais durante a calibração das correções empíricas. Os bons resultados desta técnica simples poderiam ter sido possíveis devido à topografia relativamente suave do Uruguai

Seasonal Dependence of ENSO Teleconnections over South America and Relationships with Precipitation in Uruguay

The El Niño–Southern Oscillation (ENSO) has an established impact on precipitation in Uruguay during austral spring (October–December). This impact is absent in peak summer (January–February), and returns weakly in fall–winter (March–July). Interannual and intraseasonal variability of the atmospheric circulation over South America and the South Pacific is investigated using the NCEP–NCAR reanalysis data for these seasons. The leading empirical orthogonal function (EOF) of seasonally averaged 200-hPa winds over South America is found to be associated with ENSO through a pronounced Walker cell component in all seasons. However, during spring, this pattern acquires an extratropical teleconnection that links the circulation over southeastern South America (SESA) with ENSO. This extratropical teleconnection disappears in summer, when the circulation over SESA is dominated by variability in the South Atlantic convergence zone. In fall, extratropical South America again becomes affected by a wavelike pattern that extends over the South Pacific, but it is uncorrelated with ENSO. On intraseasonal timescales, a cluster analysis of daily geopotential height fields over the South Pacific sector reveals three wave train–like circulation regimes with similar structures in all seasons. During the transition seasons (but not summer), the frequencies of occurrence of two of these regimes are found to be significantly different from normal in years when the interannual wavelike EOFs are pronounced. Interannual anomaly patterns are constructed from the intraseasonal regimes according to these changes in their frequency of occurrence, and shown to resemble quite closely the interannual EOFs over the South Pacific sector. These results provide evidence that the interannual teleconnection patterns seen over the South Pacific in austral spring and fall–winter are due to changes in the frequency of occurrence and amplitude of intraseasonal circulation regimes. The Rossby wave source composited over ENSO years suggests that ENSO heating anomalies are able to trigger these changes in regime occurrence and amplitude during October–December through Rossby wave propagation, leading to the known ENSO teleconnection in austral spring. By contrast, the interannual teleconnection over the South Pacific during fall–winter appears to be due to essentially random changes in the frequency of occurrence of the intraseasonal circulation regimes, which are found to be much larger than during austral summer when no extratropical teleconnection pattern exists

The Influence of Recurrent Modes of Climate Variability on the Occurrence of Monthly Temperature Extremes over South America

The associations between extreme temperature months and four prominent modes of recurrent climate variability are examined over South America. Associations are computed as the percent of extreme temperature months concurrent with the upper and lower quartiles of the El Niño–Southern Oscillation (ENSO), the Atlantic Niño, the Pacific Decadal Oscillation (PDO), and the Southern Annular Mode (SAM) index distributions, stratified by season. The relationship is strongest for ENSO, with nearly every extreme temperature month concurrent with the upper or lower quartiles of its distribution in portions of northwestern South America during some seasons. The likelihood of extreme warm temperatures is enhanced over parts of northern South America when the Atlantic Niño index is in the upper quartile, while cold extremes are often association with the lowest quartile. Concurrent precipitation anomalies may contribute to these relations. The PDO shows weak associations during December, January, and February, while in June, July, and August its relationship with extreme warm temperatures closely matches that of ENSO. This may be due to the positive relationship between the PDO and ENSO, rather than the PDO acting as an independent physical mechanism. Over Patagonia, the SAM is highly influential during spring and fall, with warm and cold extremes being associated with positive and negative phases of the SAM, respectively. Composites of sea level pressure anomalies for extreme temperature months over Patagonia suggest an important role of local synoptic scale weather variability in addition to a favorable SAM for the occurrence of these extremes

Use of the WRF-DA 3D-Var Data Assimilation System to Obtain Wind Speed Estimates in Regular Grids from Measurements at Wind Farms in 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

Seasonal probability forecasts of december-january-february precipitation in northern Uruguay and Rio Grande do Sul obtained with the coupled forecast system v2 of NOAA and statistical downscaling 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

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.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

Descrição Estatística do Ciclo Diário do Vento nos Primeiros 100 Metros de Altura da C.L.P. na Localidade de Colônia Eulácio ( Uruguai)

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.Neste trabalho é apresentada a análise do ciclo diário do perfil do vento em altura para os primeiros 100 metros da camada limite planetária, considerando medições na torre Colonia Eulacio (Uruguai). A torre analisada conta com medições de alta resolução vertical, possuindo anemômetros instalados entre 10.1 m e 101.8 m, termômetros entre 3.4 m e 100.8 m, medidas de direção do vento e radiação solar. É apresentada a velocidade média a distintas alturas, o que permite caracterizar a natureza do fluxo como a intensidade de turbulência, e o desvio padrão da direção do vento. Os estados de estabilidade atmosférica se descrevem a partir do gradiente de temperaturas em altura (dT/dZ). Durante os momentos posteriores ao amanhecer (inestabilidade atmosférica) se observa uma dimuição da velocidade média nas maiores alturas de medições (81.8 m e 101.8 m) e um aumento da velocidade média nas menores alturas de medições (10.1 m e 25.7 m). A dispersão de dT/dZ é maior nos casos de estabilidade durante a noite, registrando-se valores superadiabáticos (-0.02 ◦ C/m) durante o dia. A intensidade de turbulência decresce com a altura para os diferentes estados de estabilidade associados ao ciclo diário, registrando-se aumento da mesma para condições de inestabilidade atmosférica

Predicción Climática Estacional de Precipitación Acumulada en Primavera y Verano en el Sur de Uruguay

Se desarrollan diferentes modelos pre-operativos de pronóstico dinámico-estadístico de precipitación estacional en el sur de Uruguay para primavera y verano. Para ello se utilizan regresiones lineales entre predicciones de variables dinámicas y observaciones de precipitación. Los pronósticos se inicializan en Agosto y Noviembre para los trimestres de Setiembre-Noviembre y Diciembre-Febrero, respectivamente. Las predicciones de las variables dinámicas son salidas de un ensamble del modelo de circulación general de la atmósfera ICTP MCGA forzado con condiciones de borde de temperatura de superficie del mar (TSM) pronosticadas por NCEP-CFSv2. Las observaciones de precipitación provienen de 10 estaciones meteorológicas ubicadas al sur del Río Negro. Los mejores índices predictores se encuentran mediante validación cruzada, utilizando ventanas de un año, con las variables dinámicas. Se concluye que el mejor índice predictor es el viento meridional en 200 hPa promediado en una región que incluye el Sudeste de Sudamérica y es tal que anomalías de componente norte están asociadas a lluvias por encima de lo normal en el sur del país. Se encuentra que para todo el sur del país los pronósticos tienen habilidad únicamente en primavera mientras que para la zona metropolitana de Montevideo los pronósticos muestran habilidad para ambas estaciones y principalmente para verano