First European Space Weather Week 2004 1

Magnetic environment:

science of GIC

Ari Viljanen and Risto Pirjola

Finnish Meteorological Institute

Antti Pulkkinen

NASA/GSFC

This presentation is a contribution to

First European Space Weather Week 2004 2

Contents

1) General scientific background

2) Operative calculation & some science

3) On-going and future science

First European Space Weather Week 2004 3

Before the modern ”space weather”, there was GIC

B(r,t)

)j (r,tn (r,t)

E(r,t)

air dragS/C anomalies

signal degradation

cosmic rays

GIC

particle radiation

auroras

First European Space Weather Week 2004 4

GIC deals with the inductive coupling

between the ionosphere and the earth

Activity of the Sun

Propagation of the solar wind

Magnetospheric processes

Ionospheric processes

Geoelectric fieldat the Earth's surface

Earth's structure(induction)

GIC in ground–basedtechnological systems

GIC problems

Possible countermeasures,alarm systems, etc.

Network configuration

Figure 1: Schematic GIC chain. ”Science blocks” marked by blue.

First European Space Weather Week 2004 5

1. Modelling of the geoelectric field

• Ionospheric currents or ground magnetic data

• Earth’s conductivity

These results also applicable in magnetotelluric studies.

2. Modelling of GIC

• Discretely grounded systems

• Continuously grounded systems

3. Analysis of GIC effects

First European Space Weather Week 2004 6

GIC and dB/dt are closely related

06:30 06:40 06:50 07:00 07:10 07:20 07:30

-50

0

50

GIC

[A]

Mäntsälä 29.10. 2003 (10 s values)

natural gas pipeline

06:30 06:40 06:50 07:00 07:10 07:20 07:30

-20

-10

0

10

20

-dX

/dt [

nT/s

]

Nurmijärvi observatory

Figure 2: Largest GIC measured in the Finnish natural gas pipeline.

First European Space Weather Week 2004 7

GIC is a manifestation of Faraday’s law

hor. ground electric field E dH/dt

geomagnetically induced current (GIC)

Roughly speaking:

~ 90 deg

any angle

hor. magnetic field H

spat

ial i

nteg

ratio

n

Figure 3: Measured: ground magnetic field variation.

To be determined: E and GIC.

First European Space Weather Week 2004 8

Space currents cause the varying magnetic field

equivalent current J

horizontal field H

Figure 4: Potential theory states that the ground magnetic variation

field can be explained by an equivalent current distribution at the iono-

spheric plane. Approximately, rotate H 90 degrees clockwise.

First European Space Weather Week 2004 9

Ionospheric currents flow all the time

max(|H|) = 3843 nT

20031030 20:07:00

0 o

20oE

40o E

60 oN

65 oN

70 oN

Figure 5: Interpolated and rotated ground H at 20:07:00 UT on October

30, 2003, at the time of the GIC blackout in southern Sweden.

First European Space Weather Week 2004 10

Diversity of dB/dt is eye-catching

Two nearby timesteps, nearly identical patterns of ground H,

but very different dH/dt:

max(|dH/dt|) = 28.4 nT/s

20031030 20:06:30

0 o

20oE

40o E

60 oN

65 oN

70 oN

max(|dH/dt|) = 34.1 nT/s

20031030 20:08:40

0 o

20oE

40o E

60 oN

65 oN

70 oN

First European Space Weather Week 2004 11

Small scales are important

t1

t1t -2

First European Space Weather Week 2004 12

Arising questions:

• Which ionospheric events cause large GIC?

How do these events couple to magnetospheric and solar

wind dynamics?

• What are the characteristic spatial and temporal scales related to

these events?

Are there any characteristic scales?

• Can we forecast such events?

What features of these events can we forecast?

First European Space Weather Week 2004 13

Earth has a remarkable effect on the geoelectric field

Ionospheric currents → primary field Ep

Telluric currents → secondary field Ehor,s ≈ −Ehor,p

Earth conductivity models are obtained from magnetotelluric studies.

10˚

10˚

15˚

15˚

20˚

20˚

25˚

25˚

30˚

30˚

35˚

35˚

40˚

40˚

55˚ 55˚

60˚ 60˚

65˚ 65˚

70˚ 70˚

75˚ 75˚

80˚ 80˚

0 500km

B50LOV

B16JOK

B23ULL

B34MIS

B42SAL

B47LEH

B48TOP

B49UPO

B26NUR

B31PEL

B32HAN

B33OUL

B35SOD

B30YLIB22

BODB15ARV

B11HEM

B14LYC

B10NOR

B05ARE

B09BRA

B08SOD

B13HAR

B21SKE

B37VIR

B38PUU

B45NII

B46ILO

B39JUU

B40LOT

B41KUO

B29VIH

B20VOL B28

KIV

B27KOR

B19HON

B18AUR

B17HII

B25RAK

B24SIN

B36PEI

B44PERB02

LUD

B01ASK

B12MAR

B07UPS

A01KIRi

A02MUOi

A03ABKi

A04KILi

A05ANDi

A06MASi

A07TROi

A08KEVi

A09SORi

A10BJNi

A11HOPi

A12HORi

A13LYRi

A14NALi

A15IVA

A16LOVi

A18KVIs

A19NORs A20

OULs

A23LAU

B E A RBaltic Electromagnetic Array Research

Norwegian Sea

BothnianBay

Gulf ofBothnia

LakeLadoga

Gulf of Finland

Baltic Sea

Barents Sea

WhiteSea

Vanern

LakeOnega

MTS: Bx,By,Bz,Ex,EyOulu

& NurmijarviUppsala

& EdinburghGoettingen

& Potsdam

St. Petersburg

Lviv, Ukraina

Observatories

GDS: Bx,By,BzIMAGE/SAMNET

TK ’99

First European Space Weather Week 2004 14

Operative method - ground B

max = 382 nT

20010411 21:30:00

Figure 6: Measured ground horizontal field rotated 90 deg clockwise to

mimic ionospheric equivalent currents.

First European Space Weather Week 2004 15

Operative method - interpolated B

20010411 21:30:00

0 o 20oE

40o E

60 oN

65 oN

70 oN

75 oN max(H)

414 nT

Figure 7: Use of equivalent currents is a robust interpolation method.

First European Space Weather Week 2004 16

Operative method - earth’s conductivity

3 km

6 km

5 km

7 km

23 km

106 km

5000 ohmm5000 ohmm

500 ohmm

100 ohmm

10 ohmm

20 ohmm

1000 ohmm

1 ohmm

Figure 8: Rough model of southern Finland. The local magnetotelluric

relationship E(ω) ∼ Z(ω) · B(ω) is the first approximation.

First European Space Weather Week 2004 17

Operative method - geoelectric field

max = 63 mV/km

21:29:00

max = 57 mV/km

21:30:00

max = 158 mV/km

21:31:00

max = 432 mV/km

21:32:00

max = 470 mV/km

21:33:00

max = 334 mV/km

21:34:00

max = 226 mV/km

21:35:00

max = 152 mV/km

21:36:00

Figure 9: Snapshots of the calculated electric field.

GIC is basically a measure for the electric field integrated along the

conductors. The conductor system defines the relevant scales.

First European Space Weather Week 2004 18

Operative method - power grid

220 kV

400 kV

Rauma

First European Space Weather Week 2004 19

Operative method - GIC

15 16 17 18 19 20 21 22 23 24-12

-10

-8

-6

-4

-2

0

2

4

6

UT [h]

GIC

[A]

Rauma, 20010411

modelledmeasured

Figure 10: Measured and modelled transformer neutral GIC.

First European Space Weather Week 2004 20

Operative method - ESA SDA Gasum Now!

First European Space Weather Week 2004 21

Science is progressing

Classify quantitatively ionospheric currents causing large GIC. Apply

pattern recognition methods originally used for auroral all-sky images.

20031030 20:07:00

0 o

20oE

40o E

60 oN

65 oN

70 oN

Figure 11: Scalar representation of equivalent currents.

First European Space Weather Week 2004 22

Forecasting GIC is demanding

-1500

-1000

-500

0

X [n

T]

NUR, 29.10. 2003

black: measured, blue: "forecasted"

6 6.5 7 7.5 8-20

0

20

UT [h]

dX/d

t [nT

/s]

Figure 12: Artificial example: not enough to forecast B fairly accurately.

First European Space Weather Week 2004 23

Summarising

• Recordings of the geomagnetic field reveal ionospheric (equivalent)

currents

• Solid earth studies reveal the Earth’s conductivity structure

• Ionospheric phenomena affecting GIC have highly varying spatial

scales, which are determined by dB/dt

• Operative nowcasting of GIC is well established

• Quantitative classification of GIC events is advancing

• Producing reliable GIC forecasts may require completely new ideas

• Producing GIC forecasts as accurately as forecasts for terrestrial

weather may be impossible forever

First European Space Weather Week 2004 24

There are many scientific challenges of a general interest

• Investigate the basic nature of spatio-temporal variability of our

geomagnetic environment

• Understand how our geomagnetic environment couples to the large

scale dynamics of the magnetosphere

• Understand implications of the coupling and apply new knowledge

to science of GIC