Thermal response of the F region ionosphere in artificial modification experiments by HF radio waves

Abstract

The thermal response of the nighttime F region ionosphere to local heating by HF radio waves has been observed with the incoherent scatter radar at Arecibo, Puerto Rico. The observations consist of high‐resolution space and time variation of the electron temperature as a high‐power HF transmitter is switched on and off with a period 240 s. As soon as the HF transmitter is turned on, the electron temperature begins to rise rapidly in a narrow altitude region near 300 km, below the F2 layer peak. The electron temperature perturbation subsequently spreads over a broader altitude region. The observations are compared with the anticipated thermal response of the ionosphere based on numerical solutions of the coupled time‐dependent heat conduction equations for the electron and composite ion gases and are found to be in good agreement over the entire altitude region covered by the observations. The calculations show that heat conduction is responsible for the spreading of the electron temperature enhancement outside the region where the radio wave energy is deposited. They also show that a smaller, but experimentally observable, ion temperature enhancement takes place while electron temperatures are enhanced by 40% or more of their equilibrium values. For the data presented they also show ionospheric absorption of roughly half the radiated HF energy, with anomalous absorption roughly equal to deviation absorption heating.

Rise and fall of electron temperatures: Ohmic heating of ionospheric electrons from underdense HF radio wave pumping

“…In such conditions much of the F-region energy deposition and electron heating occurs just below the reflection altitude [Robinson, 1989] and is due to nonohmic processes. From there heat is convected up and down along the magnetic field [Mantas et al, 1981;González et al, 2005]. The exact amount of energy deposited in the ionospheric electrons in this region is therefore difficult to calculate accurately from first principles.…”

Simulation study of the large-scale modification of the mid-latitude F-layer by HF radio waves with different powers

“…In particular, many experimental studies have been applied to the large-scale F-region modification by powerful HF radio waves and many interesting results were obtained (Utlaut and Violette, 1974;Gordon and Carlson, 1974;Mantas et al, 1981;Jones et al, 1986;Djuth et al, 1987;Duncan et al, 1988;Hansen et al, 1992;Mantas, 1994;Honary et al, 1995;Robinson et al, 1996;Frolov et al, 1997;Gustavsson et al, 2001;Rietveld et al, 2003;Ashrafi et al, 2007;Clausen et al, 2008;Pedersen et al, 2008). It turns out that significant variations in the electron temperatures and densities can be produced by powerful HF waves in the F-layer.…”

Simulation study of the high-latitude F-layer modification by powerful HF waves with different frequencies for autumn conditions

“…In particular, results of observations of the modification of F-region electron temperatures and densities during HF heating have been presented by several groups (Jones et al, 1986;Honary et al, 1995;Robinson et al, 1996;Tereshchenko et al, 2000;Gustavsson et al, 2001). In contrast to the limited work on the large-scale high-latitude F-region modification, many experimental studies have been applied to the large-scale mid-latitude F-region modification by powerful HF waves and many interesting results were obtained (Utlaut and Violette, 1974;Gordon and Carlson, 1974;Mantas et al, 1981;Djuth et al, 1987;Duncan et al, 1988;Hansen et al, 1992;Mantas, 1994;Frolov et al, 1997). It appears that the high-latitude F-region responds more seldom to high power radio waves actions than the mid-latitude Fregion.…”