An ionospheric modification experiment using very high power, high frequency transmission

Abstract

An experiment resulting in ionospheric modification of the F region through heating by an HF transmitting facility located near Boulder, Colorado, has begun. This facility has a transmitter capable of producing nearly 2 Mw of average power, which, when used in conjunction with a 10-element ring array antenna, results in a power-aperture product of the order of 104 Mw m². Salient effects observed with radio-wave measurements after the heating transmitter had been turned on are: a prompt ionospheric response appearing within 30 sec as a deformation in the traces on ionosonde records; a development and growth of spread F starting within tens of seconds, frequently followed by multiple splitting of the O and X traces; appearance of a new time-varying broad-band echo which, at times, occurs after 10 min or more of heating and which changes in range with time; and a decrease, within 10 sec, of about 10 db in the amplitude of the O component alone, measured on an oblique path when heating with the O wave. Photometric measurements of 6300-A airglow from the heated region indicate about a 30% rise in electron temperature. Infrared radiation at 1.27 µ is enhanced in a region located down the magnetic field lines traversing the higher region initially heated by the radio wave.