Time Structure of the Average Rotation Measure for Accretion Disk in Shearing Box Approximation

Temporal structure of the average rotation measure and the evolution of energetic characteristics of accretion disk in a shearing box approximation are considered. The temporal structure of rotation measure consists of both low- and high-frequency alternating sign oscillations. The mechanisms responsible for these oscillations and their connection with the disk dynamo are discussed. The 2D distributions and the vertical structure of rotation measure and magnetic energy are analysed for times corresponding to extrema and close to zero values of rotation measure. It is shown that the extrema of rotation measure are formed on account of several individual turbulent structures with large amplitudes that are related to magnetorotational and Parker instabilities. It is found that the spatial locations of these structures correspond to areas with high local magnetic energy. The possibility of estimating the period of disk dynamo using measurements of rotation measure is discussed. Cases of Sgr A* and M87* are considered.