Аннотация:The time evolution of the magnetic field aligned fine-scale irregularities in the electron concentration, existing in the near-earth rarefied plasma, is studied with the help of the model simulation. A two-dimensional mathematical model, developed earlier in the Polar Geophysical Institute, is utilized to investigate the temporal history of the sheetlike irregularity, created initially in the F-region ionosphere, during the period sufficient for the irregularity to decay completely. The utilized model is based on a numerical solution of the Vlasov-Poisson system of equations, with the Vlasov equations describing the distribution functions of charged particles and the Poisson equation governing the self-consistent electric field. The system of equations is numerically solved applying a macroparticle method.