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Estimated Midnight Equatorward Boundary of the Aurora

DMSP dmspssj4 mid small.gif


Contact Persons

Web Site


The DMSP particle detectors were designed by Dave Hardy of the Air Force Research Laboratory, and the Auroral Boundary Indices are provided with permission from the Space Vehicle Directorate, Air Force Research Laboratory, Kirtland AFB, NM 87117, via the Cedar Database at the National Center for Atmospheric Research which is supported by the National Science Foundation. [NOTE: The 'via' part could change depending on where the data are accessed.] (Please send a courtesy copy or reference to any publications using the boundary index to Dr. Gordon.)


  • 01/28/03: All 1983-present data were replaced and replotted. A complete re-analysis was done by AFRL in 12/02. The average changes were: 17% fewer points in 1983-1991, 12% more points in 1992-1997, and 8% fewer points in 1998-2001. The maximum changes were 28% fewer points in 1989 and 26% more points in 1992. The values changed by only a few tenths of a degree.
  • 10/16/13: All 1982-present data were replaced, and more variables were added. See (the first link above) for the most recent descriptions and data files. The description, plots, and data links below were not revised from older and much fewer estimates last updated here on 01 February 2006.

OLD Data Description

The Defense Meteorological Satellite Program (DMSP) has launched DMSP satellites since the mid 1970s. All the satellites have had precipitating particle spectrometer sensors (SSJ2-J4) on board. The SSJ4 sensor was first flown on DMSP-F6 in late 1982, so 1983 is the start of the automatically computed equivalent boundary data set. The official name of the index is "The Air Force Research Laboratory Auroral Boundary Index" and should be acknowledged as being provided by the USAF Research Laboratory, Hanscom AFB, MA. A courtesy copy of any publications using the index should also be sent to Dr. M. Susan Gussenhoven-Shea or her replacement, Dr. Katharine Kadinsky-Cade, at Air Force Research Laboratory, VSBXS, 29 Randolph Road, Hanscom Air Force Base, MA 01731-3010.

For most of the DMSP orbits on a given day, the auroral oval is crossed twice in each hemisphere, once on the ascending leg, and once on the descending leg. The auroral oval expands during increased auroral or magnetic activity and the equtorward boundary is strongly related to Kp (Gussenhoven et al., 1981). The poleward boundary is more difficult to detect than the equatorward boundary, so only the equatorward boundary is found automatically. Hand selection of the equatorward boundary is described in Gussenhoven et al. [1981, 1983]. The magnetic latitude of the equatorward boundary of the aurora is found for a particular orbit at a particular MLT. Then the magnetic latitude of the equivalent equatorward boundary at midnight magnetic local time (0 MLT) can be estimated by statistically determining the position of the auroral oval for every local time sector as a function of some magnetic activity index, such as Kp.

A computer algorithm was written to select the boundaries imitating the rules for hand selection with a quality flag of: 'best', 'good', 'not good'. Only those flagged as 'best' are released. Determination of the quality depends on a variety of factors. Generally,the clearest boundaries occur premidnight, that is, on the evening side, but not prior to 17 MLT. The next best are on the dawn side. Here, however, the flux levels are decreasing and the boundaries are not sharp. The worst boundaries are on the dayside, and near midnight when the oval is cut obliquely. Therefore, the preponderance of boundaries with the 'best' flag are on the evening side. Only 1/3 of the total are 'best' boundaries.

The equivalent equatorward boundary determined for 0 MLT is always defined positive, regardless of the hemisphere of the satellite. These data are also available as yearly files from the contact persons. The ftp and web sites at AFRL have been disconnected. Publically available plots from 1983 are available below.


Gussenhoven, M. S., D. A. Hardy and W. J. Burke, DMSP/F2 electron observations of equatorward auroral boundaries and their relationship to magnetospheric electric fields, J. Geophys. Res., 86, 768-778, 1981.
Gussenhoven, M. S., D. A. Hardy and N. Heinemann, Systematics of the equatorward diffuse auroral boundary, J. Geophys. Res., 88, 5692-5708, 1983.
Hardy, D. A., E. G. Holeman, W. J. Burke, L. C. Gentile and K. H. Bounar (2008), Probability distributions of electron precipitation at high magnetic latitudes, Journal of Geophysical Research, Volume 113, Issue A6, doi10.1029/2007JA012746.

Start and Stop Dates: (From Ernie Holeman, revised in consultation with Barbara Emery)

  • SSJ4 F06 1982 362 1987 203
  • SSJ4 F07 1983 328 1988 117
  • SSJ4 F08 1987 176 1994 213
  • SSJ4 F09 1988 39 1992 94
  • SSJ4 F10 1990 341 1997 318
  • SSJ4 F11 1991 337 1999 161
  • SSJ4 F12 1994 246 2002 215
  • SSJ4 F13 1995 88 2009 322
  • SSJ4 F14 1997 118 2005 272
  • SSJ4 F15 1999 351 2007 334
  • SSJ5 F16 2003 247
  • SSJ5 F17 2006 315
  • SSJ5 F18 2009 296

OLD Summary Plots for Estimated Midnight Equatorward Boundary of the Aurora

-Revised 01 Feb 2006 by Barbara Emery with most recent revision of top-most information on 16 Oct 2013