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Auroral Precipitation Boundary

Note: This plot is updated every two hours.


This plot shows the diurnal variation of the location of the equatorward edge of auroral electron precipitation at local geomagnetic midnight as derived from calculations of the total precipitation power measured by the NOAA TIROS satellites (currently, NOAA-15, -17, -19 and METOP-02). Data from the northern hemisphere are plotted as green circles, data from the southern hemisphere as red circles, and the heavy line is a centered, 6-hour weighted average of data from both hemispheres. The dashed line indicates the boundary latitude for a power value of zero.

The power data are provided by the NOAA/SWPC, and the boundary plotted here is calculated using a simple relationship between the power and the boundary location derived from a two-piece linear regression between power observed on the NOAA POES satellite and boundary locations observed on the USAF DMSP satellites. The NOAA/SWPC WWW site has more information about the NOAA POES auroral analyses and other NOAA POES particle analyses. Similar auroral boundary information from the USAF DMSP/SSJ4 instrument is provided here.

NOTE: Although we are receiving data from post-NOAA-15 POES satellites, we will continue to use the relationship between the power index and the auroral boundary location derived from NOAA-15 data until we have time to investigate this relationship using data from more recent NOAA POES satellites.


Auroral Boundary Index Plot

Note: This plot is updated every three hours.


The parameter shown in this plot is an auroral boundary index derived from the boundary shown in the previous plot. This index is calculated from an NWRA-developed algorithm relating the location of the auroral precipitation boundary to the geomagnetic Kp index. This algorithm was derived from an analysis of DMSP data conducted by the USAF Research Laboratory (AFRL) described in the following paper:

Gussenhoven, M.S., D.A. Hardy, and N. Heinemann, Systematics of the equatorward diffuse auroral boundary, J. Geophys. Res., 88, 5692-5708, 1983.

NOTE: This index is referred to in the cited paper, and by the USAF organizations that used the index operationally, as an effective Kp index, or Kpe. The index can be used as a surrogate for Kp in models that set the location of the auroral electron precipitation using the model of this boundary described in the cited paper. While the index can also be used as a Kp surrogate in other models that require a Kp input, great care should be taken in doing this. This site provides near real-time "quicklook" values and definitive Kp values updated twice a month (once during the days 16-20 with the first 15 days of the current month and once during the days 1-5 with the second half of the previous month).

The NOAA-15 analyses used in these plots were obtained from the NOAA SWPC. A good description of the relationship between Kp and the aurora can be found on the NOAA WWW site.

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