HAARP data illustrates role of UH and IA waves in relation to electron gyro-harmonics.

HAARP data set to illustrate the role of UH and IA waves in relation to electron gyro-harmonics. Brenton J. Watkins, Geophysical Institute, University of Alaska Fairbanks, Fairbanks, AK, USA 99775. Email: [e-mail] or [e-mail] An ionospheric modification experiment was conducted at the HAARP facility in Alaska. High power ( ~ 1 GW ERP) HF waves were transmitted with four sequential frequencies 5.76, 5.78. 5.80, and 5.82 MHz. For each frequency the HF power was on for 60 seconds followed by 60 seconds power off. During daytime, experimental evidence indicates the 60 sec off-time is sufficient for the ionospheric plasma to revert to its natural state.The HF waves were transmitted in the magnetic zenith direction that is outside the ‘spitz’ angle and therefore involves reflection of the HF waves. A 446MHz diagnostic radar was used to scatter from Langmuir waves that result from the Parametric Decay Instability (L-PDI) that converts a portion of the HF wave energy to plasma waves, both ion-acoustic (IA) and Langmuir. The accompanied figure shows the total back-scattered power of Langmuir waves as function of range and time. The color scale represents relative power after processing. At initial times when the HF is turned on there are brief ( < 100ms) periods with strong signals. These are labelled ‘initial impulse signals’ on the figure and occur at or very close to the HF wave reflection height. The HF reflection heights occur above the electron gyro-harmonic heights marked with horizontal dotted lines. Following the brief initial signal the upper-hybrid parametric decay instability UH-PDI operates and effectively accelerates electrons via a Finite Larmor Radius process to create increased plasma densities. The height of the HF-plasma interaction therefore drops in response to increased plasma densities indicated by vertical dashed lines on the figure. When the HF interaction height reaches the electron gyro harmonic level the UH-PDI ceases to dominate and the L-PDI dominates shown by the red color signals on the figure. The field-aligned Langmuir waves are readily detected with backscatter radar. By contrast UH waves with irregularities perpendicular to field direction are not detected by radar. The resonant UH-PDI operates where the circular polarized HF wave (RHC with respect to the downward direction of the earth’s magnetic field) at a height below where the L-PDI operates.The presence of IA or Langmuir waves at and near a gyro harmonic is evidence for dominance of the non-resonant L-PDI. Very weak or no detectable radar signals indicate dominance of the resonant UH-PDI.