Nonlinear interactions between the Amazon River basin and the Tropical North Atlantic at interannual timescales
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We study the physical processes involved in the potential influence of Amazon (AM) hydroclimatology over the Tropical North Atlantic (TNA) Sea Surface Temperatures (SST) at interannual timescales, by analyzing time series of the precipitation index (P-E) over AM, as well as the surface atmospheric pressure gradient between both regions, and TNA SSTs. We use a recurrence joint probability based analysis that accounts for the lagged nonlinear dependency between time series, which also allows quantifying the statistical significance, based on a twin surrogates technique of the recurrence analysis. By means of such nonlinear dependence analysis we find that at interannual timescales AM hydrology influences future states of the TNA SSTs from 0 to 2 months later with a 90–95% statistical confidence. It also unveils the existence of two-way feedback mechanisms between the variables involved in the processes: (1) precipitation over AM leads the atmospheric pressure gradient between TNA and AM from 0 to 2 month lags, (2) the pressure gradient leads the trade zonal winds over the TNA from 0 to 3 months and from 7 to 12 months, (3) the zonal winds lead the SSTs from 0 to 3 months, and (4) the SSTs lead precipitation over AM by 1 month lag. The analyses were made for time series spanning from 1979 to 2008, and for extreme precipitation events in the AM during the years 1999, 2005, 2009 and 2010. We also evaluated the monthly mean conditions of the relevant variables during the extreme AM droughts of 1963, 1980, 1983, 1997, 1998, 2005, and 2010, and also during the floods of 1989, 1999, and 2009. Our results confirm that the Amazon River basin acts as a land surface–atmosphere bridge that links the Tropical Pacific and TNA SSTs at interannual timescales. The identified mutual interactions between TNA and AM are of paramount importance for a deeper understanding of AM hydroclimatology but also of a suite of oceanic and atmospheric phenomena over the TNA, including recently observed trends in SSTs, as well as future occurrences and impacts on tropical storms and hurricanes throughout the TNA region, but also on fires, droughts, deforestation and dieback of the tropical rain forest of the Amazon River basin.
KeywordsNonlinear processes Amazonia Tropical North Atlantic Hydroclimatology SST Interannual variability
Alejandro Builes-Jaramillo was partially supported by the program “Research Grants—Short-Term Grants, 2015 (57130097)” of the Deutscher Akademischer Austauschdienst (DAAD) and by the Humboldt University of Berlin. The contribution of Norbert Marwan was supported by the Project DFG RTG 2043/1 Natural hazards and risks in a changing world. The work of G. Poveda was supported by Universidad Nacional de Colombia at Medellín, as a contribution to the AMAZALERT research programme, funded by the European Commission. Recurrence analysis was carried out with the CRP Toolbox for MATLAB developed by Norbert Marwan and available at http://tocsy.pik-potsdam.de/CRPtoolbox.
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