Using the mean pressure gradient and NCEP/NCAR reanalysis to estimate the strength of the South Atlantic Anticyclone

•We proposed a new estimate (AWPG) of the South Atlantic Anticyclone (SAA) strength.•The AWPG is computed from NCEP/NCAR reanalysis data (sea level pressure, SLP).•A good correlation with significant wave height (SWH) and wind speed (WS) was observed.•Comparatively, the AWPG correlates better with SWH and WS than the maximum SLP does.•Limitations and advantages of this estimation are discussed.

A new methodology is proposed to estimate the strength of the South Atlantic Anticyclone (SAA), using the gridded sea level pressure (SLP) of the National Centers for Environmental Prediction/National Center for Atmospheric Research (NCEP/NCAR) Reanalysis data. The top quartile (1017.3 hPa) of the SLP data was found a reasonable criterion to delimit the SAA area. Consequently, we defined the SAA area as the quadrangle containing 80% of the observations with pressure >1017.3 hPa. In this quadrangle, an area weighted pressure gradient (AWPG) was computed for the whole area and for the north–south and west–east halves. When compared with maximum pressure, the AWPG showed a better correlation with the significant wave height (SWH) and wind speed (WS) derived from altimetry. The mean value of the AWPG was 8 × 10−4 Pa/m, with representative values of 9.1 × 10−4 Pa/m and 7.4 × 10−4 Pa/m for austral winter and summer, respectively. The phase difference between the monthly AWPG in the north and south sub-quadrangles accounts for the evolution of the spatial pattern of the anticyclone throughout a year. This quantitative approach proved to be a useful estimate of the strength of South Atlantic Anticyclone. Further improvements of this approach are discussed.