The Global E-Region Dynamo

The E-region dynamo functions because at heights of about 100-150 kin the ions and electrons move differently when acted upon by a neutral-air wind. In consequence the winds drive electric currents which set up polarization fields. The E-region wind system comprises a variety of modes (solar diurnal, semidiurnal, terdiurnal, lunar semidiurnal, etc.), which differ in the efficiency with which they can generate electric current. Strong winds also exist in the F region where the conductivity (though small) suffices to allow appreciable currents to flow. The E and F regions are coupled both dynamically and electrically in a complex way. In addition the dynamo regions in opposite hemispheres are coupled via geomagnetic field lines. Detailed calculations have shown that the tidal theory can account quite well for many features of the Sq and L magnetic variations, and this provides strong evidence for its basic correctness. However, some difficulties remain to be cleared up