Eddy activity in the central Bay of Bengal (BoB) is revealed using satellite observations and hydrographic data. Altimetric data show that eddies are generated near the eastern boundary, propagate southwestward, and have periods predominantly in the 30-to 120-day band. Temperature profiles from the Research Moored Array for African-Asian-Australian Monsoon Analysis and Prediction (RAMA) buoy at 90°E, 15°N, have their highest amplitude in the depth range of the thermocline, indicating that the eddies are associated with a vertical motion of the thermocline (a first-baroclinic-mode response). To investigate the cause of the eddies, we obtained a suite of solutions to nonlinear and linear versions of a 1½-layer (reduced-gravity) model. They demonstrate that equatorial wind forcing, Myanmar bump and Andaman Island, and nonlinearity are all essential for eddy formation. Among the nonlinear terms, the advection terms are the primary cause.Plain Language Summary This study combines observations and model to understand eddy generation in the central Bay of Bengal. When equatorial wind-driven downwelling (upwelling) Kelvin waves propagate to the tip of the Irrawaddy Delta off Myanmar, anticyclonic (cyclonic) eddies are generated there that subsequently propagate southwestward. The eddies are mainly driven by equatorial zonal winds, with both nonlinearity and coastline geometry essential for eddy generation.

Intraseasonal‐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.