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The Solar Activity
CME vs. Flares
• CMEs usually happen with flares, which are much ho'er (up to 10 Million K, some>mes ho?er than sun’s core)
• Flares produce many more X-‐rays and radio waves • CMEs produce more energe5c par>cles (mostly protons -‐
SEPs) through shock waves
Coronal Mass Ejections :
Coronal Mass Ejections are among the most powerful active events on the Sun.
• CMEs jettison a huge volume of trapped plasma (about 10 billion tons, roughly 0.1 the coronal mass)
• During peak solar activity, 2-3 CMEs occur every day on average.
• A special type of CME is a called a ‘halo event’. These occur when the CME is directed right at the Earth….
Solar flares and the Magne>c Field Flares occur in regions of rapid magnetic field re-alignment.
1. Coronal loop 2. Field begins to inflate 3. Field twists as sunspots move at
different speeds due to differen>al rota>on
4. Field begins to pinch inwards (field lines of opposite sign a?ract)
5. Magne>c field breaks due to shear forces
6. Plasma blob is accelerated upward and addi>onal plasma is accelerated back towards the chromosphere
Sunspot Forma>on and Solar Flare Magne>c Reconnec>on and Solar Flares
The 11 Year Cycle
Corona X-‐ray Emissions Magne>c Field Map
Classification of Solar Flares:
GOES satellite at looks light intensity between 0.1 – 0.8 nm and 0.5 – 4 nm
Class Peak Intensity (W/m2) between 0.1 and 0.8 nm
Effect on Earth
B I < 10-‐6
C 10-‐6 ≤ I < 10-‐5 Minor events – few no>ceable consequences
M 10-‐5 ≤ I < 10-‐4 Medium events –brief radio blackouts near poles
X I ≥ 10-‐4 Major events – planet wide radio blackouts
Each category is subdivided 1-‐9 (ex: X1, X2…X9)
Solar Energetic Particles:
SEPs are constitute a significant radiation hazard to anything in space… and we can’t predict when they will happen.
A. Al-‐Sawad et al., ObservaCon of a solar energeCc parCcle event behind previous coronal mass ejecCon, A&A, 2009
Active Features: SDO Movie
• Active features produce structures that can detached from the Sun’s surface. The plasma carries away the magnetic field into space.
h?p://youtu.be/Yx6sON13ywg
Erup>ng Prominence
Activity: July 7, 2011
X-ray Flare: July 7, 2011
Coronal Mass Ejection: July 7, 2011
Coronal Mass Ejections (Revisited):
Coronal Mass Ejections are among the most powerful active events on the Sun.
• Related to flares – magnetic reconnection event
• Responsible for most (if not all) energetic protons reaching Earth.
It is a shock wave that can accelerate
particles via scattering.
• Large scale restructuring of the coronal magnetic field
Coronal Mass Ejections (Revisited):
Coronal Mass Ejections are among the most powerful active events on the Sun.
• Main distinction between flares and CMEs is where they occur
• CMEs are seen in the visible and associated with the release of plasma.
• Flares are observed in the X-rays and are associated with the acceleration and release of the plasma.
Solar flares vs CMEs
CME
Flare
Warning of Flares, Erup>ons and CMEs
• Cooler plasma takes about 3-‐4 days to reach Earth (travels at 100s of km/sec)
• X-‐rays, UV, Radio Waves, and Light take about 8 min (travels at c)
• X-‐ray and UV emissions dim with large removal of material
• Energe>c par>cles (protons) take a ~ hour (travel a li?le slower than c)
Faster moving photons and energe1c par1cles warn us that billions of tons of plasma might be on its way here.
The Sun in Interplanetary Space:
You may have noticed that many of these processes produce plasma streams that leave the Sun.
• In fact, much of the corona is escaping the Sun altogether!
• This stream of material is diffuse, but energetic. It defines interplanetary space and plays a role in the near-space environment of every object we can observe in the solar system.
• We call this flow of material the SOLAR WIND.
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Evidence of Solar Wind: Comets
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Evidence of Solar Wind: Comets
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Solar Wind
• Solar wind is the corona neutral plasma (equal number of electrons and protons) expanding into space at a high velocity.
• Sun’s magnetic field is embedded in this plasma.
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Where does the solar wind stop?
• Other stars have winds too, called stellar winds
• Hence, interstellar space is not really a vacuum.
• Tenuous magnetized plasma (and a little dust) known as the local interstellar medium (LISM) fills interstellar space.
• But “near” to our sun, the solar wind dominates over the LISM.
• This bubble where the solar wind dominates is known as the heliosphere
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Where is our solar system?
Speed ~ 220 km/s Transit >me ~ 225-‐250 million years
Light years
The boundary between the solar wind and interstellar medium
1. Bow shock: region
where the LISM begins to slow
2. Termination shock: region where the solar wind begins to slow
3. Heliopause: region where the solar wind and LISM are in balance
The two magnetized plasmas “bounce” off of each other in the outer solar system. At the boundary:
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Heliopause is well past orbit of Pluto
25 1 AU = 149,598,000 km
IBEX Observa>ons
Do we know exactly where the heliopause is located?
• Voyager I and II spacecraft • Launched in 1977 • Winter 2012 about 120 and
98 AU from earth (or 16/13 light hours)
• Voyager II passed the termination shock five times in 2007.
• The boundaries depend on solar activity (solar wind, CMEs…)
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Do we know exactly where the heliopause is located?
• June 2010: Voyager 1 finds solar wind speed goes to zero.
• Did the solar wind stop or turn?
• Es>mate 3-‐5 years to exit heliosheath
• Pu-‐238 power source will last through 2020 -‐ 2025
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