As the EISCAT UHF radar system in Northern Scandinavia started its operations in the early 1980s, the collected data covers several solar cycles. The long time-series of collected data provides us the opportunity to study long-term variations and trends of ionospheric parameters in the auroral zone.

In the present study we have used the EISCAT Tromsø UHF data to investigate variations of the Hall conductivity and ion temperatures in the E-region around noon. Both the ion temperature and the peak altitude of the Hall conductivity are confirmed to depend strongly on solar zenith angle. However, the dependence on solar activity seems to be weak.

In order to search for trends in these parameters, the ion temperature and peak altitude of the Hall conductivity data were adjusted for their seasonal and solar cycle dependence. A very weak descent (~0.2 km/ decade) was seen in the peak altitude of the Hall conductivity. The ion temperature shows a significant cooling trend (~10 K/ decade). This trend seems to be affected by a trend in the MSIS neutral temperature.

In this paper, we discuss what causes the characteristics of the variations in the electric conductivities and ion temperatures.