Please use this identifier to cite or link to this item: http://hdl.handle.net/2445/119114
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dc.contributor.advisorRodó López, Xavier-
dc.contributor.authorPetrova, Desislava Bozhidarova-
dc.contributor.otherUniversitat de Barcelona. Facultat de Física-
dc.date.accessioned2018-01-18T12:00:29Z-
dc.date.available2018-03-13T23:01:29Z-
dc.date.issued2017-09-13-
dc.identifier.urihttp://hdl.handle.net/2445/119114-
dc.description.abstract[eng] El Niño Southern Oscillation arises in the tropical Pacific due to coupled atmosphere-ocean interactions. The nature of the dynamical system of the atmosphere is chaotic and its predictability is sensitive to initial conditions, which constraints our ability to foresee the evolution of ENSO for very long time in advance. This dissertation is dedicated to extending the state-of-the-art prediction of the phenomenon. It focuses on the identification of precursory signals in the ocean and atmosphere that improve the understanding and long-lead forecasts of ENSO. A new statistical modelling technique based on dynamic components and state-space methods is developed. Very early premonitory signals that are a result of an in-depth analysis of the processes accompanying the origin and evolution of El Niño, especially in the subsurface ocean, which is less impacted by initial conditions, are established. These tracers are defined in the far western and central tropical Pacific and are shown to anticipate El Niño two and a half years before its peak. Initial intensification of the easterly winds at this time is associated with convergence of mass, downwelling and warming of the subsurface ocean layers in the far west. Thus the South Equatorial Current and the Equatorial Undercurrent are strengthened, which leads to the propagation of warm subsurface anomalies eastward. These anomalous patterns later lead to changes in the circulation and warming of the surface of the ocean in the central tropical Pacific, which leads to the suppression of the easterly winds. The area of tropical convection shifts to the east, which weakens the Walker circulation and triggers the Bjerknes feedback. This allows the further propagation of the subsurface warm anomalies, which reach the eastern Pacific and are upwelled to the surface, which marks the onset of an El Niño . Warm anomalies in the subsurface equatorial ocean have been previously used as precursors in statistical ENSO models via the integration of the upper ocean heat content or the incorporation of anomalies of the 20°C isotherm. In this way the propagation feature of the anomalies is not considered, and no direct connection is made between the first anomalous patterns and the occurrence of a warm event. Hence, the predictive potential of the incipient warming in the western Pacific is not harnessed. Thus, the work presented in the dissertation provides implications for the possibility to improve the long-lead capabilities of other models. The definition of ENSO predictors at specific depths and regions in the ocean and atmosphere requires the reliable surface and subsurface measurements of various climate variables. Regular measurements have only begun with the satellite era in the 1980s, and with the placement of an observation system after the Tropical Ocean Global Atmosphere Program (1985-1994). Forecasts with the model developed here substantially improve after 1994, and the change is distinct for the long-lead forecasts that rely on good-quality subsurface information about the ocean thermal structure. Therefore, the higher temporal and spatial resolution data sets of key variables are now long enough for statistical forecasting models to make better use of. The practical utility of multi-year forecasts is also explored. A well established link exists between ENSO and local climate in the coastal areas of Ecuador. Following El Niño is a warmer surface temperature and enhanced precipitation. These two variables control the dynamics of mosquito population, and in this way affect the incidence of dengue. An experiment is performed where long-lead forecasts of El Niño are used within a dengue model and the prospects for developing an early warning system is investigated.-
dc.description.abstract[spa] El Niño Oscilación Sur (ENSO) es un fenómeno climático interanual que surge en el Pacífico tropical como resultado de las interacciones acopladas entre la atmósfera y el océano. Es el modulador más prominente de la variabilidad climática en esta escala del tiempo. La naturaleza del sistema dinámico de la atmósfera es caótica y su predictibilidad es sensible a las condiciones iniciales, lo que limita nuestra capacidad de prever la evolución del ENSO por un período de tiempo ilimitado de antemano. Esta tesis se dedica a explorar la posibilidad de extender y mejorar la predicción de última generación. En particular, se centra en la identificación de señales precursoras en el océano y en la atmósfera que mejoran la comprensión y los pronósticos a largos plazos de los eventos. Además, se desarrolla una nueva técnica de modelación estadística basada en componentes dinámicos y métodos de modelos de espacio de estado, y las covariables precursoras seleccionadas se incorporan en su diseño. Esta metodología extremadamente flexible ha sido probada y verificada en otras áreas de la ciencia como la ingeniería y la econometría, pero está comenzando a entrar en el campo de la ciencia del clima. En esta tesis se demuestra que en cierta medida esta estrategia metodológica puede unir los conceptos puramente dinámicos y puramente estadísticos de un ejercicio de pronóstico. También se explora la utilidad práctica de los pronósticos multi-anuales de El Niño. Un vínculo bien establecido es el existente entre ENSO y el climá local en las zonas costeras de Ecuador. Después de un evento de El Niño hay una temperatura superficial más cálida y una precipitación intensificada. Estas dos variables controlan la dinámica de la población de mosquitos y de esta manera afectan la incidencia de dengue. Se realiza un experimento en el que las predicciones de largo plazo de El Niño se utilizan en un modelo de predicción del dengue en el sur de la costa de Ecuador. El análisis sirve como una demostración del potencial para un servicio climático operacional en apoyo de la comunidad de salud pública en Ecuador.-
dc.format.extent240 p.-
dc.format.mimetypeapplication/pdf-
dc.language.isoeng-
dc.publisherUniversitat de Barcelona-
dc.rightscc-by-nd, (c) Petrova,, 2017-
dc.rights.urihttp://creativecommons.org/licenses/by-nd/3.0/-
dc.subject.classificationClimatologia-
dc.subject.classificationPrevisió del temps-
dc.subject.classificationCorrent del Niño-
dc.subject.otherClimatology-
dc.subject.otherWeather forecasting-
dc.subject.otherEl Niño Current-
dc.titleA new approach to El Niño Southern Oscillation origin and forecasting: implications for predictability = Un nuevo enfoque para el origen y la predicción de El Niño Oscilación Sur: implicaciones para la predictibilidad-
dc.typeinfo:eu-repo/semantics/doctoralThesis-
dc.typeinfo:eu-repo/semantics/publishedVersion-
dc.date.updated2018-01-18T12:00:29Z-
dc.rights.accessRightsinfo:eu-repo/semantics/openAccess-
dc.identifier.tdxhttp://hdl.handle.net/10803/459303-
Appears in Collections:Tesis Doctorals - Facultat - Física

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