Auroral field-aligned currents by incoherent scatter plasma line observations in the E region

The aim of the Swedish-Japanese EISCAT campaign in February 1999 was to measure the ionospheric parameters inside and outside the auroral arcs. The ion line radar experiment was optimised to probe the E-region and lower F-region with as high a speed as possible. Two extra channels were used for the plasma line measurements covering the same altitudes, giving a total of 3 upshifted and 3 downshifted frequency bands of 25 kHz each. For most of the time the shifted channels were tuned to 3 (both), 4 (up), 5.5 (down) and 6.5 (both) MHz. Weak plasma line signals are seen whenever the radar is probing the diffuse aurora, corresponding to the relatively low plasma frequencies. At times when auroral arcs pass the radar beam, significant increases in return power are observed. Many cases with simultaneously up and down shifted plasma lines are recorded. In spite of the rather active environment, the highly optimised measurements enable investigation of the properties of the plasma lines. A modified theoretical incoherent scatter spectrum is used to explain the measure-ments. The general trend is an upgoing field-aligned suprathermal current in the diffuse aurora. There are also cases with strong suprathermal currents indicated by large differences in signal strength between up- and downshifted plasma lines. A full fit of the combined ion and plasma line spectra resulted in suprathermal electron distributions consistent with models

Ion temperature and velocity variations in the D- and E-region polar ionosphere during stratospheric sudden warming

The Tenth Symposium on Polar Science/Ordinary sessions: [OS] Space and upper atmospheric sciences, Wed. 4 Dec. /Entrance Hall (1st floor) at National Institute of Polar Research (NIPR

Optical and Ionospheric Phenomena at EISCAT under continuous X-mode HF pumping

We present experimental results from multiinstrument observations in the high-latitude ionospheric F2 layer at the EISCAT (European Incoherent Scatter Scientific Association) heating facility. The results come from a set of experiments, when an X-polarized HF pump wave at high heater frequencies (fH > 6.0 MHz) was injected into the F region of the ionosphere toward the magnetic zenith. Experiments were carried out under quiet magnetic conditions with an effective radiated power of 458–548 MW. HF pumping was produced at different heater frequencies, away from electron gyroharmonic frequencies, and different durations of heater pulses. We show the first experimental evidence of the excitation of artificial optical emissions at red (630 nm) and green (557.7 nm) lines in the high-latitude ionospheric F2 layer induced by an X-polarized HF pump wave. Intensities at red and green lines varied in the range 110–950 R and 50–350 R, respectively, with a ratio of green to red line of 0.35–0.5. The results of optical observations are compared with behaviors of the HF-enhanced ion and plasma lines from EISCAT UHF incoherent scatter radar data and small-scale field-aligned artificial irregularities from Cooperative UK Twin Located Auroral Sounding System observations. It was found that the X-mode radio-induced optical emissions coexisted with HF-enhanced ion and plasma lines and strong artificial field-aligned irregularities throughout the whole heater pulse. It is indicative that parametric decay or oscillating two-stream instabilities were not quenched by fully established small-scale field-aligned artificial irregularities excited by an X-mode HF pump wave

3-D extent of the main ionospheric trough - a case study

The EISCAT radar system has been used for the first time in a four-beam meridional mode. The FAST satellite and ALIS imaging system is used in conjunction to support the radar data, which was used to identify a main ionospheric trough. With this large latitude coverage the trough was passed in 21/2hours period. Its 3-dimensional structure is investigated and discussed. It is found that the shape is curved along the auroral oval, and that the trough is wider closer to the midnight sector. The position of the trough coincide rather well with various statistical models and this trough is found to be a typical one