Absorption of radio transmissions near the geomagnetic equator at medium frequencies: (Part 2) A propagation case study

Electromagnetic waves entering the ionosphere are usually split by the geomagnetic field into two "characteristic waves", the ordinary wave (O-wave), and the extra-ordinary wave (X- wave) which suffers heavy absorption across the medium frequency (MF) band. According to magnetionic theory, transmissions in the E-W direction from a vertical monopole near to the geomagnetic dip equator should couple almost entirely to the X-wave and suffer heavy absorption. However information recently obtained from Jicamarca observatory in Peru suggests that E-W transmissions from a medium wave transmitter under the dip equator could propagate by scattering from field aligned irregularities in the E layer, caused by plasma instabilities induced by the Equatorial Electrojet (EEJ). A case study is made based on a new station close to the dip equator using a frequency at the top of the MF band where absorption is a minimum. Magnetoionic absorption is investigated, and compared with measurements taken at three locations, during a quiet solar period, during the dry season to minimise skynoise, and also to reduce the risk of thunderstorm intensified sporadic E (Es).