Observation of the aurora borealis from Glen Ullin, North Dakota, 1981-2011.
This paper examines the frequency with which the aurora borealis was observed from Glen Ullin, North Dakota by Jay Brausch in comparison to sunspot and geomagnetic activity. Jay Brausch is a dedicated amateur observer of the aurora borealis and noctilucent clouds residing at Glen Ullin, North Dakota, USA, 46[degrees]48'N, 101[degrees]46'W. Geomagnetically he is closer to the auroral zone than the United Kingdom and is much better placed to ob serve this phenomenon. He was awarded the Merlin Medal and Gift of the BAA in 1996 for the quality of his work and of his auroral photography.
An auroral apparition may appear as a green glow with or without one or more arcs in the northern sky. Active nights will include passive or moving and pulsating rays. In a major event the aurora will rise to, and sometimes beyond, the zenith. Jay has photographed many of these events and copies are held by the BAA.
In Figure 1, the frequency with which Jay has detected auroral activity has been plotted for the years 1982 to 2011. The mean annual value of the sunspot index, R, is shown in Figure 2 and has been calculated from the BAA Solar Section circulars and records.
Dr Hans Joachim Lindte and the Adolf-Schmidt Observatorium fur Geomagnetismus at Niemegk, Germany send monthly details of the planetary magnetic indices to author RL. In Figure 3 are plotted the annual frequencies with which the planetary geomagnetic index Kp attained a value of 5 or more in any three-hour period in the 24-hour day. In addition is plotted the annual frequency with which the impact of activity in the solar wind caused a magnetic storm sudden commencement.
The peak of North Dakotan auroral activity appears to take place after sunspot maximum and when the spots are declining. This appears also to be the case with geomagnetic disturbances indicated by Kp. The frequency of geomagnetic storm sudden commencements, however, does not seem to follow the sunspot cycle. The decline in auroral activity between the years 2006 and 2011 is evident and is similar to the experience of Scottish observers, which relates to the extended sunspot minimum. The geomagnetic index, Kp, shows a comparable decline.
The distribution of the auroral apparitions with respect to months of the year is given in Table 1. The maximum frequencies of auroral sightings occur around the equinoxes and the minimum frequencies occur in midwinter. According to United States Air Force cloud records worldwide, Glen Ullin is one of the most cloud-free sites from which Aurora Section members observe. The lack of aurorae observed in winter does not appear to be an effect of cloudier conditions at this time of year.
Address: Block 1, Flat 2, East Parkside, Edinburgh EHI6 5XJ.
Received 2012 April 22; accepted 2012 June 27
Table 1. Auroral apparitions at Glen Ullin by month, 1981-2011 Jan Feb Mar Apr May Jun No. of aurorae 121 157 177 208 174 185 Jul Aug Sep Oct Nov Dec No. of aurorae 193 265 279 253 170 122
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|Author:||Livesey, Ron; Brausch, Jay|
|Publication:||Journal of the British Astronomical Association|
|Date:||Oct 1, 2013|
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