Intraseasonal‐to‐semiannual variability of sea‐surface height in the astern, equatorial Indian Ocean and southern Bay of Bengal

Abstract

AbstractIntraseasonal‐to‐semiannual variability of sea‐surface height (SSH) in the eastern, equatorial Indian Ocean (EEIO) and southern Bay of Bengal (BoB) is investigated using altimetric data, and solutions to 1½ layer (first baroclinic mode) and linear, continuously stratified (LCS; multibaroclinic‐mode) models. The amplitude and dominant periods of SSH variability differ regionally. Large‐amplitude variability is found along the west coast of Sumatra, in a zonal band across the BoB centered along 5°N, east of Sri Lanka, and in the northwestern BoB, respectively. Along the Sumatran west coast, SSH variability peaks at 30–60, 90, and 180 days. Along 5°N and east of Sri Lanka, the 30–60 day variability is dominant. Sensitivity experiments using a nonlinear version of the 1½ layer model forced by realistic winds reproduce the observed patterns of intraseasonal variability in the southern BoB. At 30–60 days, the solutions show that eddies (nonlinear Rossby waves) propagating from the east, rather than local wind forcing, account for most of the variance east of Sri Lanka; furthermore, they demonstrate that the variance is significantly enhanced by the nonlinear transfer of 90–120 day energy into the intraseasonal band of 30–60 days. The LCS solutions show that the first two baroclinic modes explain most of the SSH variance at 90–180 days. The second baroclinic mode dominates the SSH variance at 180 days, a consequence of basin resonance and strong wind forcing.