Elevated electron temperatures in the auroral E layer measured with the Chatanika Radar

Abstract

An extensive series of spectral measurements has been made in the auroral E region with the Chatanika incoherent scatter radar. Becasue of the small scale length for variations of electron density, temperatures, and ion-neutral collisions we used the operating mode with the best possible range resolution-9 km. About 5% of the time the data exhibited an unusual spectral shape that was most pronounced at 105 and 110 kin. Instead of being almost Gaussian with only a small hint of two peaks, the spectra are much wider, with two well-developed peaks. After carefully considering the validity of the measurements and their interpretation, we conclude that the unusual spectra are due to greatly enhanced electron temperatures. At 110 km, the electron temperature may increase from 250 K to 800 K, while the ion temperature remains near 250 K. This enhancement of the electron temperature extends from 99 km to at least 116 km. We show that the temperature increase is too large to be accounted for by auroral particle precipitation, though it coincides in time with ion temperature enhancements at altitudes above 125 km. Because these latter enhancements are believed to be due to joule heating, we deduce that electric fields of 24-40 mV/m are present and that the electrons are moving through the ions and neutrals at speeds of 500-800 m/s. Despite these velocities, we find that joule heating of the electrons also cannot account for the elevated electron temperatures. Several consequences of the elevated electron temperatures are discussed. One is that the rate constants for molecular recombination are reduced. Another is that during periods of significant joule heating, the deduced electron density profile, when fully corrected for temperatures, has a significantly lower peak altitude and greater density than that deduced under the usual assumption of equal electron and ion temperatures. Since conductivities, currents, ionization rates, and differential energy spectra are dependent upon the density profile, care must be taken to account properly for the temperature effects when deriving these quantities.

On the usefulness of <i>E</i> region electron temperatures and lower <i>F</i> region ion temperatures for the extraction of thermospheric parameters: a case study

“…Schlegel and St.-Maurice (1981) and Wickwar et al (1981) discovered that, if the electric ®eld strength exceeds about 40 mV/m at high latitudes, the electron temperature around 105±115 km is correlated with the electric ®eld strength (while being generally anti-correlated with electron precipitation at those heights). These basic results were con®rmed by many subsequent studies (see review by for papers prior to 1990; also see Jones et al, 1991;Williams et al, 1992;Haldoupis et al, 1993) and are now accepted as a fact of life in high latitude ionospheric phenomenology.…”

Velocity of E-region HF echoes under strongly-driven electrojet conditions

“…During electron heating events, or in the lower parts of the E-region, these corrections can be substantial (e.g., Sudan, 1995, 1997;Kagan and St.-Maurice, 2004;St.-Maurice and Kissack, 2000;Kissack et al, 1995Kissack et al, , 2008 and we should note that their effects have clearly been observed in the equatorial electrojet (St.-Maurice et al, 2003). An additional problem is that while C S is fairly stable in the equatorial ionosphere, it can vary significantly in the high-latitude region in the presence of electric fields that become so strong that the FB waves themselves will heat the electrons to temperatures well above the ambient atmospheric temperature (e.g., Schlegel and St.-Maurice, 1981;St.-Maurice et al, 1981Wickwar et al, 1981;Jones et al, 1991;Dimant and Milikh, 2003;Milikh and Dimant, 2003;Bahcivan, 2007). Despite extensive data studies on the electron temperature variation with the E × B drift that have been published in the past, the evaluation of C S as a function of the E ×B drift magnitude has rarely been computed as concurrent ion temperatures were usually not reported.…”

Auroral E-region electron density height profile modificationby electric field driven vertical plasma transport:some evidence in EISCAT CP-1 data statistics

“…Therefore it is independent of |E| and levels off at the most probable peak altitude. Interpretation C: levelling-off of h peak at ∼112 km is to be seen in the context of anomalous heating due to FarleyBuneman instability in association with Hall currents which flow preferentially at this altitude (Schlegel and St.-Maurice, 1981;Wickwar et al, 1981). The fact that this feature appears in our statistics shows the high occurrence of this instability (cf.…”