M. G. Johnsen

Multifrequency tympanometry. Preliminary experiences with a commercially available middle-ear analyzer.

Normal ears and ears affected by various pathologies were studied with a clinical middle-ear analyzer according to the multifrequency tympanometric concept, by which the resonance frequency of the tympanic membrane/middle-ear system can be determined. This frequency varies considerably in normal ears with a mean value close to 1 kHz. Ears with pathologies in the tympanic membrane and otosclerotic ears have resonance frequencies differing significantly from those of normal ears. The effects may be explained by considering mass and stiffness components.

Circumpolar ground‐based optical measurements of proton and electron shock aurora

Meridian scanning photometer (MSP) data are combined with global ultraviolet images from the Polar Ultraviolet Imager instrument to estimate the timing and propagation speed of shock auroras previously studied using solely space-based ultraviolet auroral imagery. The multispectral nature of the MSPs, including the presence of a Balmer beta channel, enables the discrimination between proton and electron aurora. Following a near-magnetic noon onset, the occurrence of auroral emissions created by shocked precipitating protons and electrons is observed to propagate tailward, along the auroral oval with speeds of several km/s, consistent with the shock propagation speed in the solar wind. In two cases, shock aurora propagation speeds along the auroral oval determined from satellite imagery are confirmed, to within calculated uncertainties, with ground-based timing. The majority of instruments detect low-energy discrete auroral arcs poleward of diffuse, higher-energy aurora. Evidence of a previously reported two-pulse proton aurora shock onset is detected at some, but not all, locations.

How Often Do Thermally Excited 630.0 nm Emissions Occur in the Polar Ionosphere

This paper studies thermally excited emissions in the polar ionosphere derived from European Incoherent Scatter Svalbard radar measurements from the years 2000–2015. The peak occurrence is found around magnetic noon, where the radar observations show cusp-like characteristics. The ionospheric, interplanetary magnetic field and solar wind conditions favor dayside magnetic reconnection as the dominant driving process. The thermal emissions occur 10 times more frequently on the dayside than on the nightside, with an average intensity of 1–5 kR. For typical electron densities in the polar ionosphere (2× 1011 m−3), we find the peak occurrence rate to occur for extreme electron temperatures (>3000 K), which is consistent with assumptions in literature. However, for extreme electron densities (> 5 × 1011 m−3), we can now report on a completely new population of thermal emissions that may occur at much lower electron temperatures (∼2300 K). The empirical atmospheric model (NRLMSISE-00) suggests that the latter population is associated with enhanced neutral atomic oxygen densities.

EISCAT Observation of Wave‐Like Fluctuations in Vertical Velocity of Polar Mesospheric Summer Echoes Associated With a Geomagnetic Disturbance

By analyzing a data set from the European Incoherent SCATter (EISCAT) Very High Frequency (VHF) radar at Tromsø, we find that both radar reflectivity and upward ion velocity in a polar mesospheric summer echo (PMSE) layer simultaneously increased at the commencement of a local geomagnetic disturbance, which occurred at midnight on 9 July 2013. The onset of the upward velocity was followed by periodic repetition of ~5 min during the initial 30-min stage, and then at later stage the vertical velocity oscillated with ~7and ~20-min periodicities at 85to 90-km altitudes. The ~5-min periodicity is close to the buoyancy period, and the ~7and ~20min periodicities are consistent with gravity waves, thus suggesting that gravity waves can be generated by the effects of the geomagnetic disturbance. On the other hand, the variation of PMSE intensity (85–90 km) was in phase with fluctuations of electron densities (90–110 km) with ~12and ~13-min periodicities at the initial and later stages, respectively. The initial creation of PMSE can be attributed to both the sudden onset of particle precipitation and ice particles produced by adiabatic cooling during the rapid updraft, as detected by large upward velocity. Our periodogram analysis suggests that variations of PMSE intensity seem to follow the same periods with E region electron density, which is moduled by energetic electron precipitation, while vertical velocity oscillates at atmospheric gravity wave periods.

The thermospheric auroral red line Angle of Linear Polarization

The auroral red line at 630 nm is linearly polarized. Up to now, only its Degree of Linear Polarization had been studied. In this article, we examine for the first time the Angle of Linear Polarization (AoLP) and we compare the measurements to the apparent angle of the magnetic field at the location of the red line emission. We show that the AoLP is a tracer of the magnetic field configuration. This opens new perspectives, both in the frame of space weather and in the field of planetology.