Análise espectral da precipitação do Verão na África Austral e sua relação com o fenómeno El Niño Oscilação Austral

Abstract

The present thesis puts an end to a series of works, initiated by Dr. Lobo when in his degree thesis he sought to find the influences of ENSO in the climatic variety of Mozambique. In the second part of this series, prepared by Dr. Mavie, the relationship between the interannual climatic variability of Mozambique and the phenomenon ENSO (El Nino Oscilação Austral) is investigated, following the detailed study of the influences of ENSO, characterized by SOL, for different advances . At the end of this series of studies, we analyzed the long time series of precipitation in southern Africa to try to detect and evaluate the anomalies of precipitation that are not purely random in climatic variability. Or in simple words, this thesis seeks to find and evaluate the characteristics of precipitation that are significantly different from those that should be expected due to the occurrence of precipitation originating from purely normal or random phenomena in the interannual variability of precipitation, and to relate to the ENSO phenomenon. Tests are carried out in relation to the null hypothesis of red noise for the spectral densities of precipitation and SOI anomalies (ENSO indicator). The spectral analysis seeks to identify and associate the precipitation cycles and the SOI considering the periods of advance of the SOI of 3.6 and 9 months and advances of 1 year. Crossover spectra of precipitation and SOI are also analyzed, with the aforementioned advances in order to investigate the degree of relationship between the two series (coherence) and the time lag of the series of the two phenomena (SOI and precipitation anomalies). Strong associations are noted between precipitation variability and SOI, for cycles with different periods, such that precipitation delays are in many cases coincident with the winter season, which presupposes, for such cycles, a weak contribution to precipitation variability. total; However, the influences of ENSO on summer precipitation are evident mainly in cycles corresponding to periods of 3 and 2 years, which may be associated with advances in the SOI of 1 year and advances of 3 months. The variability of precipitation is more intense, when the maximum response of ENSO occurs in the summer season.