  We study experimentally and numerically the onset of tip streaming in an
electrified droplet. The experiments show that, for a sufficiently small
dimensionless conductivity, the droplet apex oscillates before ejecting a
liquid jet. This effect is caused by the limited charge transfer from the bulk
to the interface. This reduces the electrostatic pressure at the droplet's
stretching tip, preventing liquid ejection. This reduction of electrostatic
pressure is compensated for by the electric shear stress arising during the
apex oscillations, which eventually leads to the jet formation. The stability
limit calculated from the global stability analysis perfectly agrees with the
experimental results. However, this analysis predicts non-oscillatory,
non-localized instability in all the cases, suggesting that both the
oscillatory behavior and the small local scale characterizing tip streaming
arise during the nonlinear droplet deformation.
