A comparison between resonant and nonresonant heating at EISCAT

Abstract

[1] We compare the height-integrated electron heating rates from O-and X-mode HF pump waves to extract the components due to resonant and nonresonant heating mechanisms in the ionosphere. We present results from a November 2011 campaign in Norway, using the European Incoherent Scatter (EISCAT) heater facility and UHF radar. We show that the theoretical nonresonant, ohmic heating due to the electromagnetic pump wave electric field agrees with observations for X-mode pumping. For O-mode pumping, the observed height-integrated heating rate exceeds the theoretical ohmic electron heating rate by a factor of 2-5, the excess being attributed to resonant heating mechanisms. In addition, a persistent UHF ion-line enhancement is observed for O-mode and, more unusually, X-mode pumping. We attribute the latter to O-mode leakage in the X-mode pulse. For O-mode, we see a descent in altitude of the ion-line enhancement and show that this is most likely due to ionization from pump-induced fluxes of suprathermal electrons. We estimate the ionization rate and determine an enhanced electron flux showing that approximately 10-20% of the pump power is transferred to high energy suprathermal electrons.

First observation of the anomalous electric field in the topside ionosphere by ionospheric modification over EISCAT

“…The green and yellow colors within the images indicate natural aurora and clouds reflecting sodium street lighting, respectively. The pump‐induced optical emissions are a clear indication of suprathermal electrons from wave‐plasma resonance near the HF reflection altitude [ Bryers et al ., ].…”

“…These values are certainly among the most intense ever observed at EISCAT [cf. Kosch et al ., ] and a clear indication of a significant flux of pump‐induced suprathermal electrons exceeding 11 eV [ Bryers et al ., ].…”

Electron heating by HF pumping of high-latitude ionospheric F-region plasma near magnetic zenith

“…However, electron heating effects from pumping with LHCP dominate over those with RHCP. Bryers et al (2013) estimated the height-integrated heating source for Omode pumping to be approximately a factor of 3 larger than for X-mode pumping, for a pump duty cycle of 50 % and the O-mode pump frequency not near an electron gyroharmonic, with the X-mode frequency near a gyroharmonic (their Fig. 5), however.…”

“…Small-scale filamentary magnetic field-aligned plasma density irregularities were found to be strongest in magnetic zenith, both when the Sura beam was vertical and at an angle in between the vertical and magnetic zenith (Tereshchenko et al, 2004). Further, initial experiments with the Sura HF beam directed either 12 • south of vertical or 16 • both showed the strongest optical emissions at 630.0 nm near magnetic zenith at 18-19 • south (Grach et al, 2007).…”

Survey of conditions for artificial aurora experiments by the second electron gyro-harmonic at EISCAT Tromsø using dynasonde data

“…The weather condition is another important factor affecting the optical observations, but we do not treat the weather condition in the present study for simplicity. Due to such restrictions, some of heating experiments were successful (e.g., Gustavsson et al 2005;Bryers et al 2013;Kosch et al 2005Kosch et al , 2007bKosch et al , 2009Kosch et al , 2014aBlagoveshchenskaya et al 2015), but the others were unsuccessful. Thus, it is vitally important to understand when such successful conditions are likely satisfied for planning heating experiments in campaigns.…”