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On the Usage of Geomagnetic Indices for Data Selection in Internal Field Modelling
We present a review on geomagnetic indices describing global geomagnetic storm activity ( Kp , am , Dst and dDst/dt ) and on indices designed to characterize high latitude currents and substorms ( PC and AE -indices and their variants). The focus in our discussion is in main field modelling, where i...
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Published in: | Space science reviews 2017-03, Vol.206 (1-4), p.61-90 |
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Main Authors: | , , , , , , |
Format: | Article |
Language: | English |
Subjects: | |
Citations: | Items that this one cites Items that cite this one |
Online Access: | Get full text |
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Summary: | We present a review on geomagnetic indices describing global geomagnetic storm activity (
Kp
,
am
,
Dst
and
dDst/dt
) and on indices designed to characterize high latitude currents and substorms (
PC
and
AE
-indices and their variants). The focus in our discussion is in main field modelling, where indices are primarily used in data selection criteria for weak magnetic activity. The publicly available extensive data bases of index values are used to derive joint conditional Probability Distribution Functions (PDFs) for different pairs of indices in order to investigate their mutual consistency in describing quiet conditions. This exercise reveals that
Dst
and its time derivative yield a similar picture as
Kp
on quiet conditions as determined with the conditions typically used in internal field modelling. Magnetic quiescence at high latitudes is typically searched with the help of Merging Electric Field (
MEF
) as derived from solar wind observations. We use in our PDF analysis the
PC
-index as a proxy for
MEF
and estimate the magnetic activity level at auroral latitudes with the
AL
-index. With these boundary conditions we conclude that the quiet time conditions that are typically used in main field modelling (
PC
<
0.8
,
Kp
<
2
and
|
Dst
|
<
30
nT
) correspond to weak auroral electrojet activity quite well: Standard size substorms are unlikely to happen, but other types of activations (e.g. pseudo breakups
AL
>
−
300
nT
) can take place, when these criteria prevail. Although
AE
-indices have been designed to probe electrojet activity only in average conditions and thus their performance is not optimal during weak activity, we note that careful data selection with advanced
AE
-variants may appear to be the most practical way to lower the elevated RMS-values which still exist in the residuals between modeled and observed values at high latitudes. Recent initiatives to upgrade the
AE
-indices, either with a better coverage of observing stations and improved baseline corrections (the SuperMAG concept) or with higher accuracy in pinpointing substorm activity (the Midlatitude Positive Bay-index) will most likely be helpful in these efforts. |
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ISSN: | 0038-6308 1572-9672 1572-9672 |
DOI: | 10.1007/s11214-016-0301-0 |