The account of the geomagnetic field on the acoustic-gravity waves propagation in the ionosphere

Abstract:

Questions of acoustic-gravity waves (AGW) generation and its propagation in the ionosphere are the subject of recent analytical and experimental studies. These studies are performed for AGW of different spatial scales in the approximation of the neutral atmosphere excluding the existence of its ionized component. The increased ionospheric conductivity however creates conditions for magneto-hydrodynamic (MHD) waves propagation that can be detected as a geomagnetic field disturbances. The types of AGW and MHD waves commonly referred to different wave classes of ionospheric disturbances so they are usually considered independently. The ionosphere however is a space which density and ionization stratified, so at different disturbance propagation stages in its motion may be involved ionized and neutral component. Joint influence of gravity and magnetic fields leads to the possibility of propagation in the ionosphere wave disturbances like a magneto-gravity waves (MGW). MGW can be separated in the single class of low-frequency waves due to differences between their transfer mechanism from the AGW and MHD disturbances.

We carried out the analysis of the MGW propagation possibility in the ionospheric F2 layer for subauroral and middle latitudes. This takes into account the combined influence of the magnetic field and gravity in the hydrodynamic equations. The executed MGW dispersion equations allowed determining their characteristic frequencies, wavelengths and propagation velocities. On the base of synchronous experimental data of ionospheric F2 layer concentration variations and geomagnetic disturbances, facts of MGW existence are confirmed. In considered cases MGW were generated by intense eastward electrojet in the sub-auroral area and by two strong earthquakes (M > 6) in the mid-latitudes. Therefore the responsibility of MGW for a part of traveling ionospheric disturbances is demonstrated and the possibility of their use for environmental monitoring is confirmed.