Geomagnetic indices for the period
from June 2014 to March 2015

M. Nosé and T. Iyemori
World Data Center for Geomagnetism, Kyoto
Kyoto University, Japan

2015/03/04

3rd AOSWA Workshop/Space Weather Event Report1Data Holdings of WDC for Geomagnetism, Kyoto
1. Collection of geomagnetic field data
 1848 to Present (Primarily 1957 and after)
 ~400 geomagnetic observatories
 Microfilm (~9300 volumes), Microfiche (~10000 sheets),
Data book (~3400 volumes), Digital data (~20 TB)

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Data Service of WDC for Geomagnetism, Kyoto
2. Distribution of geomagnetic field data
http://wdc.kugi.kyoto-u.ac.jp
 Online data plot
 Digital data download Realtime plot
 Digital images of magnetograms
 Earth’s magnetic field tutorial Magnetic field model … and much more!

3. Calculation of geomagnetic indices(AE, Dst, and ASY/SYM indices)3

(1) AE Index

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AE (Auroral Electrojet) Index
General Features
 Proposed by Davis and Sugiura [1966]
 Intends to measure the intensity of auroral electrojet flowing in the ionosphere5AE Index

Derived from geomagnetic field variations in the H component
Uses data from 12 stations at auroral/sub-auroral latitude (61°-70° GMLAT)
1-min resolution

80°70°60°

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AE Index
Derivation scheme
1. Variations in the H component
are calculated for each station by∆H = Hobserved − Hquiet
where Hquiet is a quiet-time value(i.e., average over theinternational 5 quietest days).

Hobserved of 12 stations
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AE Index
2. ∆H from the 12 stations aresuperimposed.
3. AU is the upper envelope of thesuperimposed data.
AL is the lower envelope.
4. AE can be calculated as follows.
AE = AU − AL

Superimposed ∆H8Collection of Real-time Data for AE Index

Realtime derivation started in 1996



BRW, CMO

YKC, FCC, PBQ(SNK)








University of Icelandsftp with ~1 hour delay

ABK




Technical University of DenmarkE-mail with ~5 min delay

LRV



Geological Survey of Canada
E-mail with ~15 min delay

NAQ




US Geological Survey
http with ~5 min delay

80°
70°
60°

Geological Survey of Sweden
E-mail with ~1 hour delay

DIK, CCS, TIK, PBK

Arctic and Antarctic Research InstituteE-mail with ~5 min delay

9AE Index of Yesterday

No data only from CCS10

AE Index in Archive

Real-time value: 2014/12-present Derived from data of 10-11 stations
 Possibly includes artificial noises or baseline shift
Provisional/Final value: 1978/01-2014/11
 Derived from data with noise removal by visual inspection
 Updated when additional data are supplied from stations
 For some periods, data from 12 stations are available.

Real-time value

http://wdc.kugi.kyoto-u.ac.jp/aedir/index.html

Provisional value11(2) Dst Index

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Dst Index
General Features
 Proposed by Sugiura [1964].
 Intends to measure the magnitude of the current which produces the axiallysymmetric disturbance field(not only the ring current but also other currents)

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Dst Index

Derived from geomagnetic field variations in the H component
Uses data from 4 stations at low latitude (|GMLAT|<35°).
1-hour resolution

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Dst Index
Deviation scheme
1. Variations in the H component arecalculated for each station by∆H = Hobserved − Hsecular − HSq
where Hsecular is secular variationsand HSq is Sq variations.

Observed variations Secular variations

Example of quiet period
Sq variations15

Dst Index
2. ∆H from 4 stations are corrected
for latitude and averaged
longitudinally with the followingequation.

16Collection of Real-time Data for Dst Index

Realtime derivation started in 1996



KAK


HON, SJGKakioka Magnetic Observatory
sftp with ~5 min delay
US Geological Survey
http with ~5 min delay

HER



Hermanus Magnetic Observatory
sftp with ~60 min delay

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Dst Index in Recent Days

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Dst Index in ArchiveReal-time value: 2014/01-present Derived from real-time data of 4 stations
 Possibly includes artificial noises or baseline shift
Provisional value: 2012/01-2013/12
 Derived from data with noise removal by visual inspection
 Updated when final data is supplied from stations
Final value: 1957/01-2011/12
 Derived after calculation of secular variations and Sq variations

Real-timevalue
Provisionalvalue

http://wdc.kugi.kyoto-u.ac.jp/dstdir/index.html

Finalvalue19(3) AE and Dst indicesfor the period
from June 2014 to March 201520

Dst index for 2014/06-2014/10

Event B

Event C

Event A21

Dst index for 2014/11-2015/03

Event D

WorkshopDstmin=-99 nT

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Periodicity of substorms∆t=1-2 hr∆t~3 hr∆t=2-3 hr∆t~1 hr23

Fluctuations in AE index during storm recovery(2014/09/13, Selected event B)

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Magnetic field variations at
AE stations (2014/09/13)


Pc5 pulsations?
May contribute to generationof radiation belt electrons via
drift-bounce resonance.

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Fluctuations in AE index during storm recovery(2014/11/05, Selected event D)

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Magnetic field variations at
AE stations (2014/11/05)


Pc5 pulsations?
May contribute to generationof radiation belt electrons via
drift-bounce resonance.

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SummaryAE index
 Real-time data are transferred continuously.
 Real-time value: 2014/12-present Derived from 9-11 stations. Possibly includes noises or baseline shift.
 Updated every 20 min.
 Provisional/Final value: 1978/01-2014/11
 Derived from 9-12 stations. Derivation is about 2-3 months behind.
Dst index
 Real-time data are transferred continuously.
 Real-time value: 2014/01-present Possibly includes noises or baseline shift.
 Updated every 30 min.
 Provisional value: 2013/01-2014/12
 Final value: January 1957/01-2012/12 Updated when final data is supplied from stations.
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Summary
AE and Dst indices for the period from June 2014 to March 2015
 The largest magnetic storm occurred on January 7, 2015 with Dstmin=-99 nT.
 Periodicity of substorms were found in the AE index.
 During the recovery phase of magnetic storms, magnetic field at auroral
latitude sometimes shows strong variations in Pc5 frequency range.

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