Convective plumes in rotating systems

Abstract

Convective plumes emanating from fixed buoyant sources such as volcanoes, hot springs and oil spills are common in the atmosphere and the ocean. Most of what we know about their dynamics comes from scaling laws, laboratory experiments and numerical simulations. A plume grows laterally during its ascent mainly due to the process of turbulent entrainment of fluid from the environment into the plume. In an unstratified system, nothing hampers the vertical motion of the plume. By contrast, in a stratified system, as the plume rises, it reaches and overshoots the neutral buoyancy height -due to the non-zero momentum at that height. This rising fluid is then dense relative to the environment and slows down, ceases to rise and falls back to the height of the intrusion. For buoyant plumes occurring in the ocean or atmosphere, the rotation of the Earth adds an additional constraint via the conservation of angular momentum. In fact, the effect of rotation is still not well understood, and we addressed this issue in the study reported here. We looked for the steady states of an axisymmetric model in both the rotating and non-rotating cases. At the non-rotating limit, we isolated two regimes of convection depending on the buoyancy flux/momentum flux ratio at the base of the plume, in agreement with scaling laws. However, the inclusion of rotation in the model strongly affects these classical convection patterns: the lateral extension of the plume is confined at the intrusion level by the establishment of a geostrophic balance, and non-trivial swirl speed develops in and around the plume.

Subglacial discharge‐driven renewal of tidewater glacier fjords

“…Our simulations also suggest that the outflowing plume may be susceptible to instability as it flows down‐fjord, resulting in larger volume transports and dilution than predicted by the buoyant plume theory [ Cowton et al ., ; Slater et al ., ] used in our vertical plume parameterization. In the near‐glacier field, the outflowing plume develops into a anticyclonic vortex, with cyclonic rotation in the deep return flow (Figures and ), similar to previous theoretical [ Speer , ; Speer and Marshall , ], laboratory [ Fernando et al ., ], and numerical modeling studies [ Deremble , ] of convective point source plumes in rotating systems. For the shallow grounding line case, the surface‐confined plume exhibits instability in both the near‐glacier region and along the north wall of the fjord (Figures b–d).…”

The Role of Curvature in Modifying Frontal Instabilities. Part II: Application of the Criterion to Curved Density Fronts at Low Richardson Numbers

“…This model is thought to accurately reflect less intense vortices or older vortices that may have traveled far from their point of origin (Paillet et al 2002). Gula et al 2016;Brannigan et al 2017;Perfect et al 2018), and (iii) buoyancy-induced forcing of fluid parcels (Helfrich and Battisti 1991;D'Asaro et al 1994;Legg and McWilliams 2001;Hogan and Hurlburt 2006;Deremble 2016;Gordon et al 2017;Garabato et al 2017;Meunier et al 2018). Note that these boundary layers including ocean surface, bottom, and ice-ocean boundary layers.…”

Formation–breakdown cycle of turbulent jets in a rotating fluid

“…We conclude with a brief comment regarding two very recent computational studies by Deremble (2016) and by Tomàs et al (2016) and one experimental study by Frank et al (2017). These three studies investigated buoyant plumes in rotating systems.…”