Eduardo Marone

On non-linear analysis of tidal observations

Abstract Synthetic series, denoting a simple tidal record, and 1 year of real sea level record of Ingeniero White, Argentina (38° 47′S, 62° 16′W) are analyzed by classical methods of time series analysis, with adequate linear spectral estimators and by methods of bispectral analysis. The tidal synthetic series is used to verify, in a simple way, the accuracy of the methodology to assess the non-linear spectral energy. It is shown that classical spectral estimators fail to differentiate linear from non-linear energy. The proposed methodology estimates the linear and non-linear constituents separately. This is done by using Capon or Pisarenkos spectral predictors and subtracting them (the linear spectra) from the total spectra obtained via Fast Fourier Transform (FFT). The use of bispectral estimators, on the other hand, allows the identification of the non-linear interactions. The application of the bispectral analysis in the identification of non-linear constituents is made by studying the bispectra of the seasonal sea level data. Results show that maximum non-linear energy due to second order interactions occurs in the terdiurnal bands among all seasons. Three main groups of non-linear tidal interactions can be identified: the low frequency group, including the mean sea level and the diurnal bands, the mean frequency group that include the semidiurnal and the terdiurnal bands, and the high frequency group that embraces the fourth diurnal and the higher order bands. The most common non-linear tidal constituent interactions occur among themselves, producing non-linear tidal constituents with frequency double of the original periodicities. The mean sea level shows significant non-linear tidal energy, also a link with different tidal bands.

“Radiational tides” as nonlinear effects: bispectral interpretation

Abstract In this work it is shown that “radiational tides” could be interpreted as nonlinear effects by using the results of nonlinear tidal analysis. A one-year record (1979) of hourly sea level data from Ingeniero White, Argentina (38°47′S, 62°16′W) was analysed using spectral and bispectral methodologies (Marone and Mesquita, I994), in order to separate linear from nonlinear effects. The results show the same pattern observed when 1980s hourly data were analysed in the cited work. The concept of “radiational tides” was introduced to explain the extra terms used to fit the astronomical tidal potential onto real tidal records (Munk and Cartwright, 1966). Originally, it had a mathematical reasoning based on a physical hypothesis. Later it was proposed that “radiational tides” are a nonlinear effect due to the linkage of linear tidal constituents (Godin, 1986). The original physical interpretation based upon local solar radiational inputs was unsuitable, because one can find “radiational tides” being more important in high latitudes than in tropical or subtropical regions. The current hypothesis in this way relates the “radiational tide” with some global or meso-scale radiational effects of the sun. Anyway, this explanation seems to be incomplete, because the different values of the S 2 constituents for narrow ports show that local effects are important. Godin (1986) suggested that nonlinear second order interactions are the most reasonable explanation for the unexpected large values of some tidal constituents, especially in the semidiurnal band. Using the bispectral analysis of sea-level records it was possible to show that a remarkable nonlinear interaction exists besides the diurnal band and that energy is transferred to the semidiurnal band. This fact justifies the interpretation of “radiational tides” as mainly a quadratic frictional linkage between the diurnal constituents. The results suggest that the term “radiational tides” must be used carefully because, using nonlinear time series analyses, results suggest that the hypothesis of nonlinear linkage is the correct one.

Chapter 23 – Extreme Sea Level Events, Coastal Risks, and Climate Changes: Informing the Players

Floods are probably the most devastating natural hazards that the local society faces nowadays, being a problem that concerns both the local population and the management authorities. With the expected sea level rise during the next years and tropical storms that would become stronger and more frequent, the scenarios of local impacts of sea level rise and storm surges in coastal areas need to be addressed. In this chapter, we present some results of our studies related to coastal floods in Southern Brazil and the subsequent setups according to the main scenarios for 2099 of the Intergovernmental Panel on Climate Change. The objective of this work is also to show different language approaches to communicate these results to all the players involved in these problems: the decision makers and the general public, not only academics. The results are shown using the traditional scientific format accompanied by “translations,” located in boxes, in a more simple language. The translation we mentioned is not just the need of putting in plain words our scientific results when communicating outside the academic world, nor just a need of not being “cryptic.” This reaches beyond from the obvious, because we, scientists, had not been formally trained to explain things other than in a scientific language. We hope this chapter will also serve as an alert for training young scientists in the use of appropriate language and the need of being socially sympathetic in doing so. One of our ethical responsibilities as geoscientists is to ensure that our discoveries are properly disseminated, particularly when they could affect the livelihood of other human beings and/or the environment. By doing so, we construct bridges between academics and stakeholders, because the potential solutions for the problems that could affect the region in the near future are in the hands of this social component.

A Road Map for a Deontological Code for Geoscientists Dealing with Natural Hazards

Many professions have codes of conduct or deontological rules, but geoscientists dealing with natural hazards have been working on their own in the last decades not yet completing the task. A series of recent natural hazards that have hit the society in several parts of the world have made the call. Deontology is one of the main ethical decision-making approaches for driving actions leading to what is moral/ethically correct. To contribute with the construction of such a code, we present a road map to formulate this code based in the question-driven approach. Some considerations may be presented as guidelines: (a) it cannot be designed to the self-protection of the geoscientists but to safeguard society and the environment (even if it will contribute to); (b) it has to be constructed collectively; (c) it requires deep changes in educational systems, better preparing the citizens to deal with some scientific concepts. Without (c), (a) and (b) would not be enough. In addition, in constructing a geoethics code, we have to consider the three periods in the time-line of an extreme event: before, during, and after. Each period has particularities that will indicate different actions and conducts. Finally, the code, constructed collectively among practitioners, cannot be just a collection of “steps to be followed” but a real bridge between the moral consequences of being the privileged small part of the society who hold the scientific knowledge and the full society and the environment, for which we use to say we work for.

Communicating natural hazards: marine extreme events and the importance of variability and forecast errors

Abstract Scientific knowledge has to meet some necessary conditions. Among these, it has to be properly communicated. Usually, scientists (mis)understand this requirement and believe that publishing their results in peer-reviewed journals is enough. Society demands the availability of information in other formats. This is particularly relevant when dealing with natural hazards, which affect the life and fate of human beings. Natural hazards and extreme events are becoming more frequent and energetic, and future scenarios sustain that this tendency will remain or even increase. Furthermore, in trying to explain scientific results to untrained members of society, scientists usually focus more on forecasts than on the prediction errors. Talking about our forecast limitations outside of academia seems shameful, rather than being a logical limitation of sciences and regardless of the fact that discussing limitations is not something of which to be ashamed. Using numerical modelling combined with field observations to predict extreme marine events we hope to show here that it is possible to be less cryptic. Also, the general public needs to know enough to properly deal with variability and uncertainties. Scientists have the ethical responsibility of communicating the uncertainties of our results to society because these limitations are neither obvious nor irrelevant.