Ground‐based observations of F region aurora associated with the magnetospheric cusp

Abstract

A multinational program of optical observations of the dayside aurora was carried out at Longyearbyen and Ny Alesund, Svalbard, during the winter of 1978-1979. Observations were made of the temporal and spatial variations of the particle precipitation region characterized by a predominance of [O I] 6300-A emission previously mapped by satellites and associated with the magnetospheric cusp. This region expands and moves equatorward at a rate proportional to the negative excursion of the H component of the disturbance geomagnetic field measured at a station in the nightside at the latitude of maximum disturbance (approximately 10 ø farther south than the latitude of the cusp). The intensity ratios of 5577-A [O I], 6300-A [O I], and 4278-A N2 +, normally used to determine the energy of the incoming particles, are often not quantitatively useful for this purpose, owing to the predominating enhancement of N2 + emissions by resonantly scattered sunlight; however, comparisons of relative values show that there is a considerable variation in the energy of the incoming electrons during magnetic activity. The derivation of realistic values of energy of auroral primaries must rely on a combination of spectrometer and meridian-scanning photometer observations. A few examples of such a derivation yield characteristic energies of auroral primaries which vary between 2 key and <100 eV in the cusp aurora. The higher values are associated with occasional rayed bands, and the lower with the large, structureless emitting region associated with the cusp. Because of the high altitude of this region, resonance scattering is the most important source of N: + emission, and the process O+(:D) + N: -• N2+(A:•) + O is an important source of N2 + ions. Thus the observed N: + 4278-/• emission is greater than would be expected for impact excitation alone, and the 'midday gap' in 5577-/• emission is simply a result of the low characteristic energy of the incoming particle spectrum. The rayed bands occurring occasionally throughout the cusp region are spectroscopically very similar to polar cap arcs and appear simultaneously with increasing nightside activity, an indication that they could not have drifted from the nightside. Spectrometry of auroral and atmospheric emissions reveals enhanced atomic emissions as well as redistri•aution of vibrational and rotational emissions which should be expected for sunlit aurora produced in the F region by relatively low energy (100 eV) particles precipitating in the cusp region. F region neutral winds display a strong, steady cross-polar flow in the direction of the magnetic noon-midnight meridian with vortices near 6 and 18 hours MLT. The wind strength is relatively greater on the dawnside and on the nightside, increasing with magnetic activity.the inaccessibility of ground observatories located both at a high enough geographic latitude to avoid scattered sunlight and at an appropriate geomagnetic latitude to be under the cusp during slightly disturbed conditions. The only accessible station in the northe...

Synoptic distribution of dayside aurora: Multiple-wavelength all-sky observation at Yellow River Station in Ny-Ålesund, Svalbard

“…5a). In order to make statistical studies, we firstly make the dayside auroral keogram for every day in 84-day observations, then obtain the average auroral intensity keogram of each emission line in zenith angle-UT coordinates, and finally transform the averaged keogram into MLT-MLAT (magnetic latitude) coordinates using the method developed by Yang et al (1997a), and by assuming the maximum heights of auroral emissions are 120 km (427.8 nm), 150 km (557.7 nm) and 220 km (630.0 nm), respectively (Deehr et al, 1980;Sigernes et al, 1996;Sandholt et al, 2002a). At the same time, averaged emissions are corrected in order to take account the Van Rhijn effect (Yang et al, 1997b), which produces an attenuation of recorded emissions.…”

Correlated optical and ULF magnetic observations of the winter cusp – Boundary layer system

“…This magnetic latitude makes Longyearbyen a cusp station, and local magnetic noon occurs approximately at 0830 UT. The Longyearbyen station collects optical data from December through January of each season, and collects digital magnetic data year round, Deehr et al [1980]. The optical data used here were acquired with an MSP which has five photometers with differing wavelength filters; a tilting filter mechanism is used to perform background subtraction, Eather and Reasoner [1989] in that they are only red, with no green, and that these arcs happen during a cusp passage that has a distinct midday Olson and Sampson [1979] for details).…”

Influence of the ionosphere on the altitude of discrete auroral arcs

“…The problem of background contamination was solved with the introduction of the tilting filters, and the interest in altitude/luminosity profiles was replaced by studies of the relative morphologies of individual emissions, especially for the separation of hydrogen emission from electron-induced aurora (Deehr and Lummerzheim, 2001). Photon counting, combined with computer control was introduced by 1976 (Romick, 1976), so only one season of simultaneous msp measurements were made between FYU and PKR before the Fort Yukon msp was moved to Longyearbyen, Svalbard in the summer of 1978 (Deehr et al, 1980) Extensive observing efforts during the IGY culminated in a series of height measurements of discrete auroral arcs for six days near the end of March 1960. These arcs were chosen from strip chart data and the triangulation and plotting procedures were carried out by hand.…”