In a laboratory experiment modeling conditions in the auroral ionosphere, magnetic and density fluctuations are observed to grow spontaneously within a field aligned density depletion. The plasma has both cross-field pressure gradients and magnetically field-aligned currents. The magnetic fluctuations, identified as shear Alfv¿n waves, are coupled with the density fluctuations depending upon the plasma beta, &bgr;. The fluctuations exhibit a coherent eigenmode structure at higher &bgr; and evolve towards broadband Alfv¿n turbulence as &bgr; is lowered. We identify the cross field pressure gradient as the dominant driving source for the fluctuations. ¿ American Geophysical Union 1996