NONLINEAR SHOCK STRUCTURE IN A WEAKLY IONIZED MAGNETOPLASMA

The formation of a neutral induced weak nonlinear shock structure in a weakly ionised magnetoplasma has been analytically investigated. Usin g the reductive perturbation method, basic dynamical equations of a th ree-component (electron, ion and neutral) plasma have been reduced to a well-known Burger equation which can support a weak shock solution. Its stationary and initial value solutions have been derived to descri be the characteristics of the weak shock profile. Asymptotic behavior of the Burger solution results in a saw-tooth structure which has a pr actical implication to predict the nonlinear steepened structure of th e nighttime irregularity in the lower portion of the Earth's ionospher e. Accordingly, it is suggested that the observation of saw-tooth shap e of nighttime irregularity at 92 km could be attributed to the nonlin ear saturation of the NILF mode instability as proposed by Dwivedi and Das in 1992. However, exact experimental verification of this suggest ion requires more data on nighttime irregularity in the mesophere and lower thermosphere (80-95 km) for a wide range of scale sizes extendin g up to about 1 km and above.