Magnetic energy, E_B, is significantly amplified over long times due to repeated shear bursts in (above) simulation g1 and (below) simulation g11 (parameters described in Table 1). The signature of the shear burst, identified here with arrows, is clearly visible in the simultaneous peaks of the magnitude of the magnetic shear tensor ∇_iB_j, and magnetic stretching tensor B_i∇_iu_j, which have been normalized to their initial-time values for easy comparison. The magnitude of the velocity shear tensor ∇_iv_j closely follows the magnetic shear. The magnitude of these tensors is calculated as a sum of the squares of the elements. Shear, and therefore magnetic stretching, drive the intermittent growth of magnetic energy.