Detection of Variabilities and Trends in the Tropical and South Atlantic Ocean Using Hydrodynamic Numerical Modeling

Abstract

This project aims to detect variabilities and trends in outputs of a three dimensional hydrodynamical numerical model based on a version of the Princeton Ocean Model (POM), covering the region between 85°S-30°N and 70°W-25°E, with 0.5° x 0.5° resolution. Surface data of temperature and salinity, from Climate Forecast System Reanalysis (CFSR), together with meteorological data of winds and surface fluxes, generated by reanalyzes of NCEP/NCAR global model, were used as model forcings. The temperature-salinity data, meteorological data and model results cover the period from 1980 to 2009 (30 years). The model was validated through comparisons with outputs of oceanic buoy data from the PIRATA project (for the period 1997-2009) and satellite measurements by MODIS sensor (for the period [2003][2004][2005][2006][2007][2008][2009]. Model results and sea surface temperature data from PIRATA display strong correlations, both in the annual and higher frequencies signals. Even filtering the annual and semi-annual signals in the surface temperature series, model results and buoy data have mean value of linear correlation 0.59 ± 0.07 and mean value of Wilmott parameter 0.57 ± 0.15. The model results showed a mean difference of temperature to PIRATA series of 0.44 ± 0.26°C, denoting a slight underestimation of the temperatures computed by the model. The comparison of temperature profiles from the model to the PIRATA buoys shows that the model can be considered valid to surface data, but need some improvement in depth. Harmonic and statistical analyzes of selected points, applied to meteorological parameters, sea surface elevation, temperature, salinity and currents provide information on the variabilities and trends in the Tropical and South Atlantic Ocean. As an example, an extremely high trend of surface temperature was found in the Equatorial region and in the latitude belt of 40°S, for the period 2003-2009, reaching above +0.2°C/year. In this period, a trend of -0.01 m/s/year was computed for the equatorial surface currents, surrounded by trends of +0.01 m/s/year off the African coast, at about 3°N and 3°S. However, an analysis in a longer period of time would be needed for more conclusive statements. Analyses of the distributions of the standard deviations show that seasonality is not always the main factor responsible for most of the standard deviation, such as for the intensity of the currents in the equatorial region.