Abstract
We test the existing theories regarding the thresholds for the parametric decay instability (PDI), the oscillating two‐steam instability (OTSI), and the thermal parametric instability (TPI) using the European Incoherent Scatter (EISCAT) facility's ionospheric heater. In these processes, the pump wave can couple to various electrostatic waves in the F layer ionosphere, which can be observed using the EISCAT UHF radar (PDI and OTSI) or by HF radar (TPI). On 19 October 2012, the heater power was stepped from ∼0.5 MW to ∼100 MW effective radiated power in seven steps using a 1 min on, 1 min off cycle. We use an electric field model, taking into account D region absorption, to compare theory with our observations. In all three cases, we find good agreement. In addition, the growth of striations formed during the TPI causes anomalous absorption of the heater wave, which we observe as decreased UHF ion line and plasma line backscatter power. We show evidence that heating for a prolonged period of time reduces the UHF ion line intensity throughout the experiment.
Highlights
AltitudeElectron Temperature (K)[20] The electric field in free space is given by: Â E0 = Ã0.25 r r N4 p effective radiated powers (ERPs) RF (11)where 0 is the permeability of free space, effective radiated power (ERP) is the pump power on the ground, and RF is the distance to the bottom of the F region.[21] We have a solution of the electric field of the pump wave which accounts for the swelling of the electric field as it approaches reflection which can be compared to the electric field thresholds of the instabilities.2.2
Bryers et al [2012] showed that for O-mode pumping, the energy from the pump wave is absorbed by the electrons close to the upper hybrid resonance (UHR) height, and heat conducts up and down the magnetic field
[46] We have demonstrated that the theoretical thresholds of three plasma wave instabilities are consistent with modeling of an ionospheric plasma pumping experiment
Summary
[20] The electric field in free space is given by: Â E0 = Ã0.25 r r N4 p ERP RF (11). [21] We have a solution of the electric field of the pump wave which accounts for the swelling of the electric field as it approaches reflection which can be compared to the electric field thresholds of the instabilities. D Region Absorption [22] In order to account for the D region absorption of the pump wave, we use the model of Senior et al [2010]. We require the use of this model in order to reduce the free space electric field which is used in calculating equation (9). The goal of the experiment was to compare the theoretical electric field thresholds of the PDI, OTSI, and TPI given by equations (5), (6), and (8), respectively, to the modeled electric field of the pump wave to test their agreement.
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