Magnetic Clouds:

A Possibility of Forecasting Geomagnetic Storms

I.ANTONIADOU(1), A.GERANIOS(1), Μ.VANDAS(2), O.MALANDRAKI(3)

(1) University of Athens, Greece(2) Astronomical Institute, Academy of Sciences, Bocni II 1401, 14131 Praha 4, Czech Republic(3) Research and Support Department, ESTEC, European Space Agency, Noordwijk, Netherlands.

Subjects of InterestSubjects of Interest

IntroductionIntroduction Magnetic CloudsMagnetic Clouds Geomagnetic storms andGeomagnetic storms and Dst indexDst index SimulationsSimulations ConclusionsConclusions

IntroductionIntroduction

Solar system is full ofSolar system is full of : :

Solar WindSolar Wind Magnetic FieldsMagnetic Fields Structures ejected from the Structures ejected from the

sunsun

There is a continual There is a continual dynamicdynamic interaction and interaction and correlation between thecorrelation between the Sun Sun and the planets of our Solar and the planets of our Solar System, through Solar Wind.System, through Solar Wind.

Direct measurements in Direct measurements in space space ::

► VELA , IMP-6VELA , IMP-6► Confirmation of theoretical Confirmation of theoretical

models about the models about the propagation of Solar Windpropagation of Solar Wind

► Showed new properties of Showed new properties of Solar WindSolar Wind

low plasma temperature low plasma temperature

PLASMA CLOUDSPLASMA CLOUDS

MAGNETIC CLOUDSMAGNETIC CLOUDS

Magnetic CloudsMagnetic Clouds

CharacteristicsCharacteristics::To identify an interplanery To identify an interplanery

structure structure asas a Magnetic Cloud the followinga Magnetic Cloud the followingcriteria must obeyedcriteria must obeyed::

Relatively strong magnetic Relatively strong magnetic fieldfield

Large and smooth rotation of Large and smooth rotation of the magnetic fieldthe magnetic field

Lower temperature than Lower temperature than averageaverage

Transient solar Transient solar mass ejectionsmass ejections

0

5

10

15

B (

nT

)

-100

-50

0

50

100

Θ (

ο)

0

50000

100000

150000

Τ (

οΚ

)

Magnetic cloudsMagnetic clouds

PropagationPropagation::

→ TOTAL PRESSURETOTAL PRESSURE:: Ρ = Β Ρ = Β22 / 8π + / 8π + nknk((TTee + + TTpp)) magneticmagnetic thermalthermal pressurepressure pressurepressureWhereWhere Β Β : : magnetic fieldmagnetic field n : n : density of electrons and protonsdensity of electrons and protons kk : : Boltzmann’s constantBoltzmann’s constant

ΤΤee ,Τ,Τpp : : electron and proton temperature respectivelyelectron and proton temperature respectively

Pressure inside the cloud is greater than surroundingsPressure inside the cloud is greater than surroundings the magnetic cloud is expandingthe magnetic cloud is expanding

Reduction of particles density during the expansionReduction of particles density during the expansion

Magnetic CloudsMagnetic Clouds

→ Cylindrical Model:Cylindrical Model:► Magnetic cloud forms a large Magnetic cloud forms a large

loop (flux-ropes), which can be loop (flux-ropes), which can be locally described as cylinderlocally described as cylinder

► Magnetic field lines are Magnetic field lines are attached to the sun surface attached to the sun surface

► Thermal connection with solar Thermal connection with solar coronacorona

Helical magnetic fieldHelical magnetic field

Structure of magnetic clouds

BB

22

Magnetic CloudsMagnetic Clouds

→ Spheroid model:Spheroid model:► Disconnection of the magnetic Disconnection of the magnetic

loop from the solar coronaloop from the solar corona► Closed areas of magnetic field Closed areas of magnetic field

into the solar windinto the solar wind► Thermal disconnection from the Thermal disconnection from the

solar coronasolar corona

Structure of magnetic clouds

poloidal magnetic field

toroidalmagnetic field

Simulations of Magnetic CloudsSimulations of Magnetic CloudsMeasurements from satellite Spheroid modelCylindrical model

Geomagnetic stormsGeomagnetic storms

Interaction between Magnetic clouds and Earth’s Interaction between Magnetic clouds and Earth’s MagnetosphereMagnetosphere

Geomagnetic stormsGeomagnetic storms ::

Disturbances in the Solar Wind and Earth’s MagnetosphereDisturbances in the Solar Wind and Earth’s Magnetosphere coupled system, caused by solar activitycoupled system, caused by solar activity

Energetic particles are transferred from the solar wind to the Energetic particles are transferred from the solar wind to the magnetospheremagnetosphere

CriterionCriterion::► Bz < 0 : Bz < 0 : Southward magnetic field magnetic reconnection Southward magnetic field magnetic reconnection

between the solar wind and the magnetospherebetween the solar wind and the magnetosphere

Dst IndexDst Index

Calculation of Dst Index-Burton’s ModelCalculation of Dst Index-Burton’s Model::

AssumptionAssumption::The strength of a geomagnetic storm can be study from The strength of a geomagnetic storm can be study from the the

changes of the ring currentchanges of the ring current

Dst indexDst index

BURTON’S MODELBURTON’S MODEL

*)(*)(

aDstEFdt

Dstd

2/1)(* dynPbDstDst

)(EF

0 mVEy /5,0

mVEy /5,0

b: Measures the changes of the Pdyn of the Solar Wind.c: Measures the magnetic field at the quiet time of the ring current.F(E): Is the ring current injection rate and depends only from the Ey (y-compoment of solar wind’s electric field) Ey = -(VxB)y

d: Measures the response of the injection rate 1/α: Measures the life-time of particles into the ring current.

α→3 ή 5 hours ,Εy > 4mV/m

α→7,7 hours ,Εy < 4mV/m b = 0,20 nT/(eV/cm3)1/2

c = 20 nT

2/1))(5.0( dyny PEd

d = 1,2x10-3 nT / (smV/m)

Simulations of Magnetic CloudsSimulations of Magnetic Clouds

0

200

400

600

800

V (

Km

/se

c)

-600

-400

-200

0

0 10 20 30 40 50 60 70

Dst

(nT)

0

10

20

30

40

50

60

B (

nT

)

-100

-50

0

50

100

Θ (

ο)

TIME (HOURS) FROM 19NOV.2003

0

5

10

15

20

B (

nT

)

-100

-50

0

50

100

Θ (

ο)

-120

-100

-80

-60

-40

-20

0

0 20 40 60 80 100

Dst

(n

T)

TIME (HOURS) FROM 6NOV.1997

0

200

400

600

V (

Km

/se

c)

ConclusionsConclusions

Continuous studies and observations have shown two Continuous studies and observations have shown two possible structures of magnetic clouds: cylindrical and possible structures of magnetic clouds: cylindrical and spheroid.spheroid.

When magnetic clouds interact with Earth’s magnetosphere When magnetic clouds interact with Earth’s magnetosphere it is possible to cause geomagnetic storms. it is possible to cause geomagnetic storms.

Study of these storms and forecasting of the space weather Study of these storms and forecasting of the space weather can be made using Dst index.can be made using Dst index.

AcknowledgementsThe project is co-funded by the European Social Fund and National Resources (EPEAEK II) Pythagoras.

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