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It is well known that intense auroral disturbances occur in association with substorms and are characterized by a well-defined evolution of global auroral morphology.

With a special section in the October 15 issue of GRL, ISTP auroral science teams have been investigating a less known class of intense auroral-zone disturbances – non-substorm generated aurora.

ISTP scientists featured in GRL special sectionon non-substorm auroral disturbances

POLAR PIXIE X-ray auroral images on GRL cover

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SSISTP scientists featured in GRL special section

on non-substorm auroral disturbances

MEASUREMENTS:

The GRL studies use the ISTP observatories as a true constellation. Linking the auroral disturbances to geosynchronous and outer magnetosphere influences required observations from POLAR, WIND, GEOTAIL, LANL geosynchronous satellites, and the CANOPUS and other ground magnetic observatories and photometers.

In addition, the PIXIE auroral imager on POLAR is uniquely suited to distinguish between substorm and non-substorm aurora:

- PIXIE responds to X-rays produced by the high energy “tail” of the auroral electron distribution.

- the strength of this high energy tail is related to the strength of the magnetosphere cross-tail electric field which is reduced during substorms but remains enhanced during other activity.

- thus, the X-ray emissions can distinguish between substorm and non-substorm related auroral activity

POLAR

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Anderson, P. C., D. L. McKenzie, L. R. Lyons, and M. Hairston, Global x-ray observations of magnetospheric convection-driven auroral disturbances, Geophys. Res. Lett., 27, 3233-3236, 2000

OBSERVATIONS I:

A) POLAR PIXIE X-ray aurora taken during the expansion phase of a substorm showing a classic aurora across the nightside oval.

B) POLAR PIXIE X-ray aurora, confined to the morning sector, associated with enhanced magnetospheric convection during steady, but strongly southward IMF – “convection bays”.

C) Geosynchronous energetic electron fluxes which are associated with substorm activity are enhanced during the event shown in A) but are absent during the event shown in B).

A B

C

ISTP scientists featured in GRL special sectionon non-substorm auroral disturbances

from the special issue:

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SSISTP scientists featured in GRL special section

on non-substorm auroral disturbances

OBSERVATIONS II:

- Another type of non-substorm aurora, poleward boundary intensifications (PBI), is associated with transient Earthward flowing bursts (bursty bulk flows) in the magnetotail.

- The flow bursts occur in all regions of the plasma sheet during quiet times as well as during substorms.

- The PBI are the most common type of auroral-zone disturbance, occurring during all levels of geomagnetic activity.

- Thus, the auroral poleward boundary intensifications can be considered perpetual activity of the magnetosphere – not substorm related phenomena.

Lyons, L. R., E. Zesta, J. C. Samson, G. D. Reeves, Auroral disturbances during the January 10, 1997 magnetic storm, Geophys. Res. Lett., 27, 3237-3240, 2000.

Zesta, E. and L. R. Lyons, The auroral signature of Earthward flow bursts observed in the magnetotail, Geophys. Res. Lett., 27, 3233-3236, 2000.

from the special issue:

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SSIMPLICATIONS:

• These and other ISTP analyses show there are several other types of auroral disturbances than substorms that are associated with different types of magnetospheric processes.

• The precipitation of energetic particles creating intense aurora contribute to the process producing the Geomagnetic Induced Currents (GIC) of concern to space weather interests.

• Predictions of the geographic longitude, and relative timing, of GIC onsets will differ significantly depending on whether substorm or other processes apply.

ISTP scientists featured in GRL special sectionon non-substorm auroral disturbances

substorm aurora non-substorm aurora

geographic area of influence can vary widely