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- Author or Editor: Benjamín Rosenblüth x
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Abstract
The most common procedures to prewhite a climatological time series are considered and compared with those based on Fourier analysis. In particular, advantages and shortcomings of the anomaly method and the seasonal differences are noted. Some modifications for the Fourier prewhitened synthesis are introduced to preserve the smoothness of the spectra. A simple recursion filter with prewhitening ability is presented and compared with the other filter using synthetic and a real time cries. Special attention is given to the case of short time series. The anomaly method and the recursion filter appear as suitable procedures to replace a Fourier technique giving both similar outputs but differing in the details. The seasonal differences, although very simple to apply, introduce substantial modifications in the output and should be avoided. When the data series contains a few times the cycle to be eliminated the recursion filter seems to be safer than the anomaly method.
Abstract
The most common procedures to prewhite a climatological time series are considered and compared with those based on Fourier analysis. In particular, advantages and shortcomings of the anomaly method and the seasonal differences are noted. Some modifications for the Fourier prewhitened synthesis are introduced to preserve the smoothness of the spectra. A simple recursion filter with prewhitening ability is presented and compared with the other filter using synthetic and a real time cries. Special attention is given to the case of short time series. The anomaly method and the recursion filter appear as suitable procedures to replace a Fourier technique giving both similar outputs but differing in the details. The seasonal differences, although very simple to apply, introduce substantial modifications in the output and should be avoided. When the data series contains a few times the cycle to be eliminated the recursion filter seems to be safer than the anomaly method.
Abstract
Biological productivity in the ocean along the Chilean coast is tied to upwelling that is primarily forced by equatorward wind stress and wind stress curl on the ocean surface. Southerly alongshore flow is driven by the southeast Pacific (SEP) anticyclone, and its intensity and position vary on a range of time scales. Variability of the SEP anticyclone has been linked to large-scale circulations such as El Niño–Southern Oscillation and the Madden–Julian oscillation. The actual timing, duration, and nature of the seasonal meridional drift of the SEP anticyclone are associated with the onset, demise, and strength of the local upwelling season. Seasonal variation is especially marked at the Punta Lavapié (37°S) upwelling focus, where there is a clear upwelling season associated with a change of the cumulative upwelling index (CUI) slope between positive and negative. The Punta Lengua de Vaca (30°S) focus typically exhibits upwelling year-round and has less distinct transitions, making it more difficult to identify an enhanced upwelling season. A two-phase linear regression model, which is typically used to detect subtle climate changes, is applied here to detect seasonal changes in CUI at Punta Lengua de Vaca. This method objectively finds distinct transitions for most years. The spring-to-summer transition is more readily detected and the slackening of the upwelling-favorable winds, warmer waters, and longer wind strengthening–relaxation cycles change the coastal upwelling ecosystem. While the spring-to-summer transition at Punta Lengua de Vaca could be influenced by large-scale circulations, the actual dates of transition are highly variable and do not show a clear relationship.
Abstract
Biological productivity in the ocean along the Chilean coast is tied to upwelling that is primarily forced by equatorward wind stress and wind stress curl on the ocean surface. Southerly alongshore flow is driven by the southeast Pacific (SEP) anticyclone, and its intensity and position vary on a range of time scales. Variability of the SEP anticyclone has been linked to large-scale circulations such as El Niño–Southern Oscillation and the Madden–Julian oscillation. The actual timing, duration, and nature of the seasonal meridional drift of the SEP anticyclone are associated with the onset, demise, and strength of the local upwelling season. Seasonal variation is especially marked at the Punta Lavapié (37°S) upwelling focus, where there is a clear upwelling season associated with a change of the cumulative upwelling index (CUI) slope between positive and negative. The Punta Lengua de Vaca (30°S) focus typically exhibits upwelling year-round and has less distinct transitions, making it more difficult to identify an enhanced upwelling season. A two-phase linear regression model, which is typically used to detect subtle climate changes, is applied here to detect seasonal changes in CUI at Punta Lengua de Vaca. This method objectively finds distinct transitions for most years. The spring-to-summer transition is more readily detected and the slackening of the upwelling-favorable winds, warmer waters, and longer wind strengthening–relaxation cycles change the coastal upwelling ecosystem. While the spring-to-summer transition at Punta Lengua de Vaca could be influenced by large-scale circulations, the actual dates of transition are highly variable and do not show a clear relationship.
