Non-linear resonant excitation of whistler mode waves in the earth's ionosphere using two high frequency transmitters

Abstract

We discuss the possibility of exciting whistler mode waves (WMWs) in the Earth's ionosphere, by using two high frequency beams of electromagnetic waves ( f 1∼ f 2) suitably orientated to the geomagnetic field H o, so that a non-linear resonant interaction can take place in the natural ionospheric plasma, approximately at the altitude of the F2 maximum electron density. Within the limitations imposed by ionospheric inhomogeneities in the interaction region, it should be possible to excite a WMW which propagates along a predetermined direction, e.g. parallel to H o. If we assume f 1 and f 2 to be approx 30 MHz (i.e. well above the ionospheric plasma frequency), this method would make it possible to select and vary the frequency range of the excited WMW up to a few hundreds kHz without substantial alterations to the high frequency transmitting system. Since the two beams should form an angle close to 90° to the direction of propagation of the WMW, this technique may prove particularly suitable for active wave experiments at low geomagnetic latitudes, where the geometry of the geomagnetic field limits the feasibility of direct wave injection experiments. Using the results of theoretical calculations of the three wave coupling coefficients, it will be shown that the transmitters required to produce WMWs with field strengths comparable to that of naturally occurring strong whistlers are substantial, but feasible.