(with James Friend) Through the breaking of the axial symmetry of the surface acoustic wave SAW irradiation into a sessile drop, we show that it is possible to induce an azimuthal streaming flow within the drop.1 Due to the boundary conditions imposed by the substrate and the drop free surface, a helical microcentrifugatory flow is produced, which we exploit for rapid micromixing and bioparticle concentration/separation. In the latter, rich and peculiar complex pattern formation dynamics are also observed; at low input powers, the colloidal particles assemble into linear concentric rings that resemble fingerprint-like patterns (Regime A) through a particle drift mechanism that arises as a consequence of the capillary force acting on the particles in concert with the interfacial acceleration of the low amplitude 20 MHz standing wave vibrations induced at the free surface of the drop by the 20 MHz surface acoustic wave travelling beneath it. Upon increasing the input power, the colloidal particles in the linear ring-like assemblies then cluster to form point-wise colloidal islands (Regime B). These islands appear to form at the intersection between the nodal lines of the 20 MHz standing wave vibration at the interface with the circular nodal ring of a 1 kHz order vibration associated with the capillary-viscous resonance of the drop. The number and position of the colloidal island assemblies is seen to be dependent on the drop size. If the input power is kept constant and the drop is allowed to evaporate, the number of islands can be observed to decrease successively. Further increases in the input power leads to the onset of significant fluid streaming within the drop (Regime C). When streaming commences, the particles disperse and the colloidal island assemblies are destroyed. After a short transient, however, the streaming ceases and the colloidal islands are observed to reform until the streaming recommences and erases them again. This cyclic phenomenon occurs aperiodically and the streaming direction (clockwise/anticlockwise) appears to be random, suggesting that this is a transient metastable state triggered by a peculiar instability arising from the highly nonlinear coupling between the acoustic, hydrodynamic and capillary forces. As the input power is increased (Regime D), however, the streaming becomes stronger and more consistent, leading to permanent dispersion of the particles such that the interfacial colloidal patterns are no longer evident.