Journal of Conference Abstracts

Plume Instability in Rotating Compositional Convection

Sabine Claszen (sac@willi.uni-geophys.gwdg.de)¹, Moritz Heimpel (heimpel@artemis.ess.ucla.edu)² & Ulrich Christensen (urc@willi.uni-geophys.gwdg.de)¹

¹Institut fuer Geophysik, Herzberger Landstr. 180, Goettingen, 37075, Germany

²Depatment of Earth and Space Science, UCLA, 595 Circle Drive East, Los Angeles, CA, 90095-1567, U.S.A.

The onset and structure of compositional convection in a rotating system are investigated experimentally. A vertically oriented cylindrical annulus filled with NH₄Cl ­ H₂O solution is cooled from the bottom and can be rotated about its axis at rates ranging up to 10.5 rad s^-1, corresponding to Ekman numbers down to 7.4 x 10^-6. The Coriolis force has a strong effect on the structure of plumes above the mush-liquid interface. Helical motion of the conduit, which is weakly developed in the non-rotating case, is amplified by Coriolis forces that twist the plume conduits to lie nearly horizontally. This results in secondary plumes (or blobs) that rise from the sub-horizontal primary plume conduits. This new instability could be an efficient mechanism for producing small-scale flow in the form of buoyant blobs that ascend through the polar regions of the outer core.