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Tropical Northern Atlantic Index (TNA)
The TNA SST anomaly index is an indicator of the surface temperatures in the eastern tropical North Atlantic Ocean. It is calculated with SSTs in the box 55°W - 15°W, 5°N - 25°N.
In the full series case, monthly averages are shown by the plus signs, three month running mean filtered index values are shown by the shaded regions. In the "last two years" case, weekly averages are shown by the plus signs and the monthly average values are shown by the shaded regions.The weekly standard deviation of the index over the period 1991-2020 is indicated on the plot.
The TNA and TSA indices were defined in a paper by Enfield et al. (JGR, 1999), where dipolar patterns across the tropical Atlantic were found with a periodicity of 8-12 years for the boreal winter-spring, and 2.3 years for the boreal summer-fall.
The index is calculated using the Reynolds OIv2 SST analysis, made available through by NOAA/ESRL, and is updated weekly (last update 11-FEB-2024). get series (netcdf 24kB) » get error (netcdf 24kB) »
The anomaly is calculated relative to a monthly climatological seasonal cycle based on the years 1991-2020. The monthly climatology is linearly interpolated to determine weekly anomalies.Spatial averaging of the gridded analysis was weighted by surface area.
The uncertainty of the index is estimated to be 0.0465 degrees C over the period 1982-present, and is based on the uncertainty estimate obtained from the objective interpolation analysis.
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