D. A. Lorentzen

GPS scintillation and irregularities at the front of an ionization tongue in the nightside polar ionosphere

In this paper we study a tongue of ionization (TOI) on 31 October 2011 which stretched across the polar cap from the Canadian dayside sector to Svalbard in the nightside ionosphere. The TOI front arrived over Svalbard around 1930 UT. We have investigated GPS scintillation and irregularities in relation to this TOI front. This is the first study presenting such detailed multi-instrument data of scintillation and irregularities in relation to a TOI front. Combining data from an all-sky imager, the European Incoherent Scatter Svalbard Radar, the Super Dual Auroral Radar Network Hankasalmi radar, and three GPS scintillation and total electron content (TEC) monitors in Longyearbyen and Ny-Alesund, we observe bursts of phase scintillation and no amplitude scintillation in relation to the leading gradient of the TOI. Spectrograms of 50Hz phase measurements show highly localized and variable structuring of the TOI leading gradient, with no structuring or scintillation within the TOI or ahead of the TOI.

The absolute sensitivity of digital colour cameras

A new and improved method to obtain the average spectral pixel responsivity and the quantum efficiency of Digital Single Lens Reflex (DSLR) cameras is outlined. Two semi-professional cameras, the Nikon D300 and the Canon 40D, are evaluated. The cameras red, green and blue pixel responsivities and quantum efficiency are retrieved by illuminating an integrating sphere with a wavelength tunable monochromator. 31 intensity calibrated monochromatic spectral lines from 4000 to 7000 A, with a bandpass of approximately 12 A, were used as a library to solve the main equations of observation for the cameras. Both cameras have peak sensitivity in the blue and minimum sensitivity in the red. The Canon 40D has blue and green channel sensitivity close to the Nikon D300. The Canon red channel has half the sensitivity of the Nikon camera.

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.

Sensitivity calibration of digital colour cameras for auroral imaging

A method to sensitivity calibrate Digital Single Lens Reflective (DSLR) cameras is outlined. A low intensity calibrated light source tunable in wavelength is described. 31 monochromatic lines from 4000 to 7000 A with a bandpass of approximately 12 A were used to find the spectral responses for the D70 and the D200 cameras manufactured by Nikon. The source radiance ranged from about 300 to 1.6k R/A. The cameras were operated in manual mode with 4 seconds exposure time at ISO 1600, which are typical settings required for night time photography of the aurora. For the Nikon D200 camera, the blue, green and red spectral responsivities peak at 4600, 5300 and 5900 A, respectively. The response was high for the blue colour channel with a clear cut-off at 4100 A for the UV part of the spectrum. The red channel response indicates low sensitivity above 6600 A. The D70 shows similar spectral responsivity, except that it peaks in the green colour channel and it is more sensitive to both UV and NIR radiation. Both cameras are capable of detecting night- and dayside auroral at 4 second exposure time. For optimal auroral imaging capability, the green and red spectral responsivities need to be shifted up by about 300 and 400 A in wavelength.

Hyperspectral all-sky imaging of auroras

A prototype auroral hyperspectral all-sky camera has been constructed and tested. It uses electro-optical tunable filters to image the night sky as a function of wavelength throughout the visible spectrum with no moving mechanical parts. The core optical system includes a new high power all-sky lens with F-number equal to f/1.1. The camera has been tested at the Kjell Henriksen Observatory (KHO) during the auroral season of 2011/2012. It detects all sub classes of aurora above ~½ of the sub visual 1kR green intensity threshold at an exposure time of only one second. Supervised classification of the hyperspectral data shows promise as a new method to process and identify auroral forms.

Absolute calibration of optical devices with a small field of view

In connection with the upcoming International Polar Year (2007-8) a network of high-sensitivity optical devices will be operating in the Arctic to record and monitor weak luminescence in the upper atmosphere, mainly the auroras and night-sky luminescence. The need to compare the data of the optical measurements at different points requires high accuracy of their intercalibration in terms of international standards. This article gives a review of mathematical methods for processing the data of photometers with a small field of view and describes the experimental apparatus (located at Svalbard University on Spitsbergen) for their absolute calibration. The universitys specialized optical laboratory is described, and the results of the certification and monitoring of the brightness of secondary standards of the calibration lamps used to calibrate the optical devices are presented.

Swarm and ESR observations of the ionospheric response to a field‐aligned current system in the high‐latitude midnight sector

We present a conjunction between the Swarm fleet and the European Incoherent Scatter Svalbard Radar (ESR) on 9 January 2014. The Swarm orbit in the early phase of the mission gives us the unique opportunity of sequencing the temporal evolution of the observed field-aligned current system in the nightside, near magnetic local midnight. These field-aligned currents are seen to move poleward through the radar field of view and to affect the observed ionosphere. The upward field-aligned current (FAC) is responsible, at least in part, for the heating of the ionospheric electrons. It is less clear whether the downward FAC cools the ionosphere. We use the TRANSCAR model of the ionosphere to quantify the thermoelectric effect that comes into play. Finally, we compare the plasma parameters measured by the Langmuir probe on board Swarm and the ESR and conclude on an agreement within the errors.

Shock aurora: Field‐aligned discrete structures moving along the dawnside oval

Generatedby interplanetary shocks or solarwindpressurepulses, shock aurorahas transient, global, and dynamic significances and provides a direct manifestation of the solar wind-magnetosphere-ionosphere interaction. As a part of a series of studies of the shock aurora, this paper focuses on the interaction at the morning magnetopause and its auroral manifestation at ~06 magnetic local time, where the velocity and magnetic field shears dominate the interaction. Flow shears can generate wave-like structures inside a viscous boundary layer or even larger-scale vortices. These structures couple to the ionosphere via quasi-static field-aligned currents or via kinetic Alfvén waves. Potential drops along field-aligned filaments may be generated accelerating electrons to form auroral manifestations of the structures. A shock aurora event at dawnside is used to test this scenario. The findings include moving auroral streaks/rays that have a vertical profile from red (at ~250 km altitude) to purple (at ~100 km). The streaks moved antisunward along the poleward boundary of the oval at an ionospheric speed of ~3 km s . It was mapped to the magnetopause flank at ~133 km s , which was consistent with the observed speed of the magnetopause surface waves generated by the Kelvin-Helmholtz instability. The calculated field-aligned potential drop using Haerendel’s analytic model was ~5 kV that reasonably explained the observations. The results support the above scenario and reveal that magnetic and velocity shears at the flanks of the magnetospause may be the main cause of the fast moving shock aurora streaks.

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.

Ion velocity filter effect observed in dayside hydrogen aurora

[1] Observations of dayside auroral hydrogen emissions of H α (A656.3 nm) were carried out using spectrometers on Svalbard at Ny-Alesund (NYA: 76.3°N, 111.0°E CGM) and Longyearbyen (LYR: 75.3°N, 111.9°E CGM). Using a Monte Carlo model, simulated Doppler profiles were fitted to the spectra to estimate precipitating proton energy. A difference in energy was found between the sites for approximately 45 minutes. When combined with measurements of antisunward convection, the energies are consistent with the inverse variation of ion energy with latitude observed by satellites in the cusp region, known as the ion velocity filter. This is the first measurement of the ion velocity filter effect in the dayside aurora using ground-based optical instrumentation. The increasing difference in energy observed is interpreted as a measure of the decreasing merging rate at the magnetopause.