current corrugations can provide a source of free energy for the tearing mode and modify its stability [@Adler1980]. As a consequence, the zonal fields could be a possible triggering mechanism for Neoclassical Tearing Modes, as they could push the island above the seed limit. Implied in this reasoning is the assumption that the corrugations are sufficiently coherent for the tearing mode to have time to respond.

In this work we describe the effect of current corrugations of given shape and amplitude on the calculation of $\Delta'$. By using a simple slab model for the zonal fields we obtain an analytical scaling for the variation of the stability parameter, $\delta\Delta'$, with respect to the amplitude and the wave length of the “zonal” flows that generate the current corrugations. We then show numerically that the scaling applies also to more relevant cylindrical cases. We find that even relatively small current corrugations can induce large modifications of $\Delta'$ and therefore strongly affect the stability of the tearing mode.

A limitation of our work is the assumption, done for sake of simplicity, that the pressure is flat in the island region. Pressure gradients at the reconnecting surface, however, can play an important role in 