Dual ion-line structures observed at the HAARP ionospheric modification facility.
Abstract
We present results for experiments using high-power O-mode HF waves generated by the HAARP ionospheric modification facility. The data pertain to ion-line data resulting from the parametric decay instability (PDI). The HF interaction with the F-region ionosphere occurs near, but below, the HF reflection height. For the upgoing HF electromagnetic wave the PDI results in a forward scattered Langmuir wave and a backscattered ion-acoustic wave. After the subsequent reflection the down-going HF wave again participates in the PDI resulting in a down-going Langmuir wave and upgoing ion-acoustic wave. A UHF diagnostic radar was used to detect the HF-enhanced ion-acoustic waves. Since the diagnostic radar has only one receiver it was not possible to additionally detect Langmuir waves.In most cases the up and down-going plasma waves occur at approximately the same altitude.However we show that in many cases the up and down-going ion-acoustic waves occur at two separate heights separated by as much as 5-7 km. We suggest this height difference results from wave propagation effects near the reflection height. Doppler spectral analysis of the scattered radar signals indicate that the plasma wave intensity is greater for the height layer with downward ion-acoustic waves, corresponding to the upgoing HF electromagnetic wave. This altitude layer with stronger wave scattering may occur above or below another layer with weaker wave activity that corresponds to the downward HF electromagnetic wave after reflection. These observations are consistent with many past ion-line observations at HAARP and other facilities that show the downward travelling HF-enhancedion-acoustic waves generally show greater scattered power than upward waves. The new aspect of these observations is the frequently observed separation in altitude of the two layers, and we have found that this behavior depends on the particular HF frequency used. For example we show from an experiment that stepped in 10kHz increments of the HF frequency 4.10, 4.20,4.30,4.40,4.50 MHz that the ion-lines separated into two distinct height layers only for the 4.20 and 4.50 MHz cases. In some examples the height layer with upgoing ion-acoustic waves is extremely weak or non-existent. We suggest that the weaker or non-existent PDI wave structures that correspond to the downward electromagnetic wave after reflection likely results when the power of the HF wave falls below the threshold for the PDI.
- Publication:
-
42nd COSPAR Scientific Assembly
- Pub Date:
- July 2018
- Bibcode:
- 2018cosp...42E3631W