First observations of SPEAR-induced topside and bottomside sporadic E layer heating observed using the EISCAT Svalbard and SuperDARN radars

We present the first observations of heater‐induced simultaneous topside and bottomside sporadic E layer enhancements at very high latitudes (78.15°N) using the Space Plasma Exploration by Active Radar (SPEAR) heating facility and the European Incoherent Scatter (EISCAT) Svalbard Radar. During the experiment the SPEAR heating facility was transmitting with O‐mode polarization in a field‐aligned direction with a constant effective radiated power of ∼16 MW. Results show distinct heater‐induced enhancements in both the ion and plasma line spectra. The plasma line enhancements are observed at the SPEAR heater frequency of 4.45 MHz. The plasma line observations represent the highest spatial resolution data (100 m) obtained of such heater‐induced enhancements and indicate simultaneous enhancements at both the topside and bottomside of the layer, respectively (located at ∼107.5 and 109 km altitude, respectively). It is postulated that the results represent evidence of O‐ to Z‐mode conversion of the heater wave occurring at the bottom of the E layer, allowing propagation through the layer resulting in simultaneous topside enhancements. The Z‐mode enhancements are observed outside the Spitze angle, which is thought to be a result of field‐aligned irregularities causing an increase in angular extent of the observations. Additional data from the Super Dual Auroral Radar Network (SuperDARN) HF Finland radar are also shown, which indicate that upon a thinning of the sporadic E layer, the heater beam propagated into the F region, where it induced artificial field‐aligned irregularities. Key Points First observations of SPEAR‐induced O‐ and Z‐ mode heating Heater‐induced Z‐mode enhancements observed outside the Spitze angle Generation of ionopsheric field‐aligned irregularities