Measurements of HF backscatter cross section for striations created by ionospheric heating at different power levels

Ionospheric field‐aligned irregularities induced by the Tromsø heating facility have been studied by means of an HF backscatter radar. A power law relation between the received echo power and the stepwise changed heater power is found with an exponent varying between 1.5 and 1.9. The radar cross section at 14 MHz is found to be in the order of 35–55 dBsm, and a maximum volume cross section 3.6×10−7 m−1. Examples of three typical recording sequences for three different environmental ionospheric conditions are discussed. During favourable conditions backscatter echoes are observed at the lowest heater ERP of 14 MW. The cross section then saturates at 98 MW ERP and exhibits a pronounced decrease at higher heater ERP. During less favourable conditions the saturation level is not reached even at full power of 280 MW ERP. A correlation seems to exist between variations in the derived Hall current and the variation in cross section of the heater‐induced field‐aligned irregularities.