Coronal Mass Ejections 2: Observational Properties

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Coronal Mass Ejections 2Observational Properties

• Morphology
• Properties of Substructures
• Magnetic structure
• Radio CMEs (meter microwaves)
• Basic Attributes Speed, CPA and Width
• CME Mass and temperature
• Solar Cycle variations
• Summary
• N. Gopalswamy
• NASA Goddard Space Flight Center, Greenbelt,
  Maryland
• International Symposium on the Physical
  Processes Associated with Solar Activity, Weihai,
  August 7, 2002

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CME Morphology

• Morphology Bubble-shaped in general (originally
  thought to be loop-shaped)
• Jets, amorphous structures and coreless CMEs are
  also often seen
• Need statistics

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Examples of CME Morphology

• CMEs with minimal structures

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Not all CMEs have a 3-part structure Flux rope
from a Transequatorial Eruption?
Void Speed 250 km/s Expansion rate 23 km/s
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Substructures of CME

• - CME is a magnetic framework that transports
  ionized mass into the heliosphere, consisting of
• Frontal structure
• Cavity
• Prominence Core
• Leaves behind Post-eruption Arcade
• May drive a shock if SuperAlfvenic
• Note Not all structures are present in all CMEs!

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Properties of CME Substructures

• Shock long wavelength radio (meter longer)
• Frontal structure (high n, coronal T, high B)
• - 108 cm-3 2 MK 1 G (white light,
  X-rays, meter waves)
• Cavity (low n, coronal T, higher B)
• - 107 cm-3 2 MK a few G ?
• (white light, X-rays, H-alpha)
• Prominence Core (highest n, lowest T, highest B)
• - 1011 cm-3 8000 K 10 G
• (microwave, X-rays, H-alpha, He10830, EUV,
  meterwave)
• Post-eruption Arcade (X-ray, EUV, He 10830,
  H-alpha)
• - 109 cm-3 10 MK a few G

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A Prominence Eruption Event 2001/12/20
SOHO/LASCO/C2 CME
17 GHz Prominence
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The Event Originated on the DiskNote the
Filament cavity
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Post Eruption arcade in EUV

• EUV movie from SOHO/EIT data
• Arcade formed at the pre-eruption location of the
  filament
• Note the dimming along the outer edges of the
  arcade

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The Eruption Region
BEFORE
AFTER
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Summary LASCO EIT
EIT RUNNING DIFFERENCE
FOOTPOINTS OF CME LOOPS?
PROMINENCE
LASCO/C2
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Radio Sun in Meterwaves

• Thermal emission optical depth could be large
  at low frequencies.
• Direct imaging using free free emission from
  the corona CMEs (Sheridan et al., 1978
  Gopalswamy and Kundu, 1992 Maia et al., 2000)

CLRO quiet Sun at 50 MHz Optical Sun blocked to
mimic eclipse
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Radio CMEs
Clark Lake CME Jan 16, 1986 Gopalswamy Kundu,
1992
Mass can be determined from observed brightness
temperature
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A Fast Eruption
17 GHz movie Full disk
And Just the Eruption region
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2001/04/18 Microwave CMESnapshots
Frontal Structure 2000 km/s
Core 1600 km/s
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Spatial Association
17 GHz, LASCO C2, C3 Expansion in 13 25 min
17 GHz 0217 0216 Expansion in one min
C2 230
C3 242
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EUV Dimming
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Microwave, SXT, EIT, LASCO
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Height-Time Plot

• CME speed 1925 km/s (microwaves)
• -- 2465 km/s White light
• Initial accel 440 ms-2
• later decel 10 ms-2
• Core 1625 km/s ? close to the LE speed in
  microwaves.

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CME, Streamer WaveCME classified as partial
halo, but true width only 70 deg
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Basic Attributes of a CMESpeed, Width CPA
N
Base Difference Fn Fo Running Difference Fn
Fn-1 Fn, Fn-1, Fo are images at times tn , tn-1
and to CPA Angle made by CME apex with solar
North Width PA2 PA1 Speed dh/dt
PA1
Position Angle From North
(h,t)
CPA
W
PA2
Width
S
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Height-Time Plot

• Track a particular feature in successive images
  to obtain the height-time plot.
• The slope gives the speed of the CME
• Quadratic fit gives the
• acceleration

(tn ,hn)
(t0 ,h0 )
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An Accelerating CME
Linear fit is no good
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A Decelerating CME
Linear fit is probably OK, but Quadratic fit is
better
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Height-time Plots of many CMEs
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Generic h-t profiles

• Accelerating CME Propelling force is dominant
  (6/21/98)
• Constant Speed CME Balanced ? (2/17/00)
• Decelerating CME Retarding (Drag Gravity)
  force dominant (5/11/98)

_at_ 2.5 Rs
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SPEED Distribution
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WIDTH Distribution
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ACCELERATION Distribution
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Mass Estimates
Typical mass 2 x 1015 g
White light Calculate the number of electrons
within the bright region from the measured
brightness and Thomson-scattering formula.
Estimate the line of sight depth Recall that
each electron is associated with a mass of 2 x
10-24 g (fully ionized 10 He) (Poland et al.,
1981) Meter wave radio X-rays
Estimates are crude!!
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CME Rate

• Partly determines mass, energy, angular momentum,
  and magnetic flux from the Sun
• Maybe of fundamental importance to understand the
  initiation process
• Depends on the sensitivity of the individual
  coronagraphs

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LASCO CME Rate
Count the number of CMEs in each Carrington
rotation period, and divide by the number of
days in that period Error bars based on
downtimes and max and min rates lt 1 per day
during min. 5 per day during max Different
from 1973 (0.74) 1980 (0.90)
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Rate Total Number (1996-2001)
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Special Populations

• Fast
• Fast and Wide (SEP)
• Halo (geomagnetic storms)

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Halo CMEs

• Halo CMEs may be Earth-directed or
  anti-Earth-directed
• May affect geospace if Earth-directed
• Relation to CMEs at 1 AU is now possible
• Helped understand the three-dimensional structure
  of CMEs

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Fast-wide CMEs Potentially Geoeffective
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Halo CMEs

• Frontside halo CMEs are potentially geoeffective
  they cause geomagnetic storms if any of the
  substructures contains southward B component.

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Solar Cycle Variation of CME speed
Pre-SOHO era CME speed was thought to be
constant
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CME Temperature

• CME is a multithermal plasma (core 8000 K
  frontal cavity at 2 MK), but the primary
  structure forms out of coronal material
• EUV and X-ray dimming imply the depletion of
  coronal material
• Green line transients 1.8 MK

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How Energetic is a CME?

• Mass M 2x1013 kg (20 billion tons)
• Velocity V 1000 km/s 106 m/s
• Kinetic Energy ½ MV2 1025 J
• Compare this with a car M 2000 kg V 36 km/h
  10 m/s, so KE 105 J
• KE_cme/KE_car 1020
• ? CME is 0.1 million trillion times more
  energetic than a car!!

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CME Properties

• Typical mass 1015 g ( 1 billion ton)
• Speed lt 20 to gt 2500 km/s
• Typical Kinetic Energy 1024 J
• Average Width 70 degrees
• Accelerate and then decelerate
• Temperature 8000 K (core) to 2 MK (front)
• Solar Minimum One in two days Solar Max a few
  per day.
• CME speed is higher during solar maxima

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Xie Xie !
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What is Space Weather?

• Is the physical conditions in the space between
  Sun and Earth
• Humans venture into near-Earth space Environment
• Spacecraft in lots of places in space
• Earth is also coupled to the space around it

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What is a Geomagnetic Storm?

• Earths magnetic field is disturbed.
• Measurements of horizontal component of Earths
  magnetic field show disturbance lasting for a few
  days
• This is a result of currents induced in Earths
  magnetosphere when CMEs impinge on Earth

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CMEs Can Cause Bad Weather in Space

• CMEs carry plasma and magnetic field can
  severely disturb the magnetosphere
• CMEs send out solar cosmic rays ? radiation
  hazard to astronauts and danger to spacecraft
  electronics
• Spacecraft may be destroyed due to change in
  orbit ? cell phones, pagers may be affected
• CMEs induce surges in power lines, rail roads and
  pipelines affecting society
• Study of CMEs will help us develop an umbrella
  to overcome bad weather

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Concluding Remarks

• Coronal Mass Ejections is a fascinating physical
  phenomenon involving interaction between magnetic
  field and plasma
• CMEs have direct implications to life on Earth
  and human endeavor in space.