Shear Flow‐Interchange Instability in Nightside Magnetotail Observed as "Auroral Beads” at Substorm Onset

Low‐frequency shear flow‐interchange waves transmit sheared zonal flows along magnetic flux tubes toward the ionosphere from the near‐Earth nightside plasma sheet create the "auroral beads” observed in Canada and Alaska observed as the geomagnetic substorm onset. A set of nonlinear pde’s is derived and solved to model the growth and saturation of the auroral beads. The relation with the Kalmoni model (2015, https://doi.org/10.1002/2015JA021470) for shear flow‐ballooning instability is explained. The shear flow‐interchange instability appears to be responsible for substorm onset. The growth starts in the midnight region of the nightside magnetotail producing in the nonlinear stage the auroral beads characteristic of geomagnetic substorm onset.