2nd URSI AT-RASC, Gran Canaria, 28 May – 1 June 2018 Recent Advances in Active Ionospheric Modulation by High-Power HF Radio-waves and Sideband Detections Alireza Mahmoudian* (1) , Brett Isham (1) , Paul Bernhardt (2) , Eliana Nossa (3) , and Stan Briczinski (2) (1) Inter American University of Puerto Rico, Bayamon Campus, Puerto Rico, USA (2) Plasma Physics Division, Naval Research Laboratory, Washington D.C., USA (3) Arecibo Observatory, Arecibo, Puerto Rico, USA Abstract This paper presents our recent break through in the remote sensing of the near Earth space environment using high- power high-frequency (HF) radio waves transmitted from the ground and detection of the backscattered signal using HF receivers, GPS receiver, radars, and all-sky imagers. 1. Introduction Use of high-frequency (HF) heating experiments has been extended in recent years as a useful methodology for plasma physicists wishing to remotely study the properties and behavior of the ionosphere as well as nonlinear plasma processes [1]. The high-power transmitters used for these experiments are sometimes called HF facilities or HF heater, since the electric field in the transmitted radio-wave can reach over 1 V/m, more than strong enough to energize the ionospheric electrons within the beam of the transmitter, which then collide with the ions, randomizing and thermalizing their energy and increasing the electron and ion temperatures. High power electromagnetic waves transmitted from the ground interact with the local plasma in the ionosphere and can produce Stimulated Electromagnetic Emissions (SEEs) through the parametric decay instability (PDI). The classical SEE features known as wideband SEE (WSEE) with frequency offset of 1 kHz up to 100 kHz have been observed and studied in detail in the 1980s and 1990s [2]. Sideband emissions of unprecedented strength have been reported during recent campaigns at HAARP (High Frequency Active Auroral Research Program), reaching up to 10 dB relative to the reflected pump wave which are by far the strongest spectral features of secondary radiation that have been reported [3-7]. These emissions known as narrowband SEE (NSEE) are shifted by only up to a few tens of Hertz from radio-waves. 2. High-latitude observations Electron temperature assessment: The Magnetized Stimulated Brillouin Scatter (MSBS) is a strong NSEE mode involving a direct parametric decay of the pump wave into an ES and a secondary EM wave that sometimes could be stronger than the HF pump [3] The excited ES waves through MSBS process could be either Ion Acoustic (IA) or Electrostatic Ion Cyclotron (EIC). Our recent work has shown that IA line can be used for the assessment of electron temperature and artificial aurora due to electron acceleration during radio-wave heating of the ionosphere. Ion mass spectrometry: The primary ion constituent in the main F layer is O + . Previous observations have shown the association between sporadic ion and sporadic neutral sodium and other metal layers. Typically, the sporadic-E layer is believed to be composed of metallic ions (with dominant abundance by Na + , Mg + , and Fe + ). The first observation of MSBS EIC line produced by a minor ion species (Na + ) in the presence of sporadic E layer for pump frequency stepping near 3f ce is presented in Figure 1. The observations show the importance of tuning the pump frequency to distinguish one ion line from the other, demonstrating a potentially powerful remote sensing diagnostic utilizing MSBS lines as ion mass spectrometer to determine the minor species in the lower ionosphere. Figure 1. Time evolution of narrowband SEE spectra showing MSBS spectral lines with pump frequency stepping near 3f ce and associated with minor ionospheric constituents. Artificial GPS scintillation: We have reported the first modulation of GPS phase signal during radio-wave heating of the ionosphere at HAARP. The excited artificial GPS phase scintillation has been studied using a theoretical model of 4-wave decay instability involving the decay of the HF pump wave to plasma waves at the interaction altitude responsible for small scale plasma density fluctuations and Bragg scattering of the GPS signal. We have also investigated the possibility of decameter scale irregularities in Fresnel zone in the