Anticyclonic precession of a plume in a rotating environment

Abstract

Abstract Motivated by potential effects of the Earth's rotation on the Deepwater Horizon oil plume, we conducted laboratory experiments on saltwater point plumes in a homogeneous rotating environment across a wide range of Rossby numbers 0.02≤ R o ≤1.3. We report a striking physical instability in the plume dynamics near the source: after approximately one rotation period, the plume tilts laterally and starts to precess anticyclonically. The mean precession frequency scales linearly with the rotation rate Ω as . We find no evidence of a critical Rossby number above which precession ceases. We infer that a conventionally defined Rossby number is not an appropriate parameter when the plume is maintained over a long time: provided Ω ≠ 0, rotation is always important to the dynamics. This indicates that precession may occur in persistent oceanic or atmospheric plumes even at low latitudes. Key Points We report a new phenomenon in the dynamics of plumes in a rotating environment: The anticyclonic precession of the plume axis The precession is independent of the source size, the buoyancy flux, and the water depth and scales linearly with the rotation rate We infer that the plume in a rotating environment will always start to precess if it is maintained over a sufficiently long time