Self-Organized Criticality in Magnetic Substorms

Understanding The Mechanics of Space Weather

Solar Weather Terms

Coronal Mass Ejections (CMEs) Solar Wind Magnetosphere Magnetic Reconnection Van Allen Radiation Belts Ring Current Disturbance Storm Time (DST)

Necessity for Understanding DST Ring Current field capable of

inducing large currents in power lines, satellites, computer chip factories etc.

Source (left): http://optics.org/objects/ole_feat/Source (right): www.physics.co.il/News.asp

Coronal Mass Ejections Solar blob of electrified gas Occurrence:

Solar Minimum: ~ 1 CME per week Solar Maximum: 2-3 per day

Source: http://www.spacescience.org/ExploringSpace/VirtualExhibit/SpaceIsNotEmpty/

Magnetosphere

Source (bottom): http://istp.gsfc.nasa.gov/istp/news/img.htmlSource (top): www.spaceweather.com/aurora/ images/31mar01/haug1.jpg

Dipole Magnetic Field Protects earth, deflecting solar

activity Causes particles to spiral into atmosphere at poles (aurora)

Solar Wind & Magnetosphere

Source (above): http://istp.gsfc.nasa.gov/istp/news/img.htmlSource (left):http://www-istp.gsfc.nasa.gov/Education/wsolwind.html

Magnetic Reconnection

Occurs during loading phase of cycle (typically 40 minutes)

Magnetosphere tail becomes severely stretched

Magnetic field lines become aligned anti-parallel

Field cancels, energy conserved in several ways including injection of energetic particles

Plasmoid drifts off with solar wind

Magnetic Reconnection

Source: http://istp.gsfc.nasa.gov/istp/news/img.html

Magnetic Reconnection

Source: http://istp.gsfc.nasa.gov/istp/news/img.html

Van Allen Belt & Ring Current Drift of energetic particles Production of “Ring Current” in belt,

radius 2RE (Earth Radius) Current produces own field interacting with magnetosphere

Source: http://www.tiscali.co.uk/reference/encyclopaedia/hutchinson/m0010420.html

DST - Description

Disturbance Storm Time index Measures strength of ring current

field based on interaction with earth’s magnetosphere

Measured in units of nanoTesla (nT)

DST – Scatterplot (2001)D

ST

Inde

x va

lue

(nT

)

Time (Hours)

DST – Probability Distribution

Pro

babi

lity

DST Index value (nT)

DST – PeriodicitiesP

ower

Spe

ctra

l Den

sity

PeaksCorrespondsto27.12 days

Self Organized Criticality (SOC) Statistical analysis, independent of

time Event based, critical climax and

relaxing Classic example: Avalanches in a

sand pile

Source: http://www.londontoday.net/photo/industry/v001/images/full/

Power Laws in SOC

Event Size vs Number of Events; straight line in log-log space

lnN(s) = - * ln(s)

N(s) = s-

Events of a bigger size should occur less frequently than events of a smaller size

DST – A SOC System

ln(size of event)

ln(n

umbe

r of

occ

urre

nces

) T=0.6923

Use for SOC Model

Precursors for magnetic reconnection discovered, severity of substorm can be determined

Ability to predict length of an event based on initial size of storm?

Source: http://www.spacescience.org/ExploringSpace/VirtualExhibit/SpaceIsNotEmpty/