New axisymmetric helical magnetorotational instability in dissipative rotating flows with positive shear

We present a new type of axisymmetric magnetorotational instability which is capable of destabilizing viscous and resistive magnetized flows with radially increasing angular velocity. Using short-wavelength WKB approach, supported by 1D linear stability calculations in Taylor-Couette flow, we show that this instability works only when a combination of axial and azimuthal magnetic fields is applied and when the magnetic Prandtl number is different from one. It might have grave consequences for the stability of the equator-near parts of the solar tachocline, and for the dynamo action in this region