1st Observations of SPEAR (Space Plasma Exploration by Active Radar) induced plasma line spectral enhancements in a naturally occurring sporadic E-region

This paper will present the 1^st observations of sporadic E-layer heating at high latitudes (78°N) using the SPEAR heating facility and the EISCAT Svalbard Radar (ESR). During the experiment the SPEAR heating facility was transmitting with O-mode polarization in a field aligned direction with a constant ERP of ~16MW. Results show distinct heating enhancements in the plasma line spectra, corresponding to the SPEAR heater frequency of 4.45MHz. High spatial resolution (100m) plasma line data indicate simultaneous enhancements at both the top and bottom side of the layer respectively (located at ~107.5 and 109km 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 structure, both temporally and spatially, of these enhancements will be discussed in detail.