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The Solar Corona B. C. Low High Altitude Observatory National Center for Atmospheric Research The National Center for Atmospheric Research is operated.

Dec 16, 2015

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Page 1: The Solar Corona B. C. Low High Altitude Observatory National Center for Atmospheric Research The National Center for Atmospheric Research is operated.

The Solar Corona

B. C. LowHigh Altitude Observatory

National Center for Atmospheric Research

The National Center for Atmospheric Research is operated by the University Corporation for Atmospheric Researchunder sponsorship of the National Science Foundation. An Equal Opportunity/Affirmative Action Employer.

Page 2: The Solar Corona B. C. Low High Altitude Observatory National Center for Atmospheric Research The National Center for Atmospheric Research is operated.

The White-Light Corona

Page 3: The Solar Corona B. C. Low High Altitude Observatory National Center for Atmospheric Research The National Center for Atmospheric Research is operated.

Mark IV CoronameterMauna Loa Solar Observatory

Page 4: The Solar Corona B. C. Low High Altitude Observatory National Center for Atmospheric Research The National Center for Atmospheric Research is operated.

The Magnetic Sun

Page 5: The Solar Corona B. C. Low High Altitude Observatory National Center for Atmospheric Research The National Center for Atmospheric Research is operated.

The Magnetic Corona

Activity Maximum 1980

Activity Minimum 1994

Page 6: The Solar Corona B. C. Low High Altitude Observatory National Center for Atmospheric Research The National Center for Atmospheric Research is operated.

A CME out to 32 R_Sun

Page 7: The Solar Corona B. C. Low High Altitude Observatory National Center for Atmospheric Research The National Center for Atmospheric Research is operated.

A Shower of MeV Protons

Page 8: The Solar Corona B. C. Low High Altitude Observatory National Center for Atmospheric Research The National Center for Atmospheric Research is operated.
Page 9: The Solar Corona B. C. Low High Altitude Observatory National Center for Atmospheric Research The National Center for Atmospheric Research is operated.

The 2-3 Million-Degree Corona

Page 10: The Solar Corona B. C. Low High Altitude Observatory National Center for Atmospheric Research The National Center for Atmospheric Research is operated.

Solar EUV Output

Page 11: The Solar Corona B. C. Low High Altitude Observatory National Center for Atmospheric Research The National Center for Atmospheric Research is operated.

Orbit Height of the SMM Satellite

Page 12: The Solar Corona B. C. Low High Altitude Observatory National Center for Atmospheric Research The National Center for Atmospheric Research is operated.

Coronal Drivers of Space Weather

• Variable heating of the Earth’s Upper Atmosphere

• Episodes of CME-Magnetospheric Interaction

• High-energy particles• Evolution of the corona-heliosphere

over the 11-year solar cycle

Page 13: The Solar Corona B. C. Low High Altitude Observatory National Center for Atmospheric Research The National Center for Atmospheric Research is operated.

The Solar Corona as a Hydromagnetic Atmosphere

• Maintained at million-degree temperatures – cooling time ~ 1 day – dissipative heating• A nearly perfect conductor of heat: – solar-wind expansion• A nearly perfect conductor of electricity: – low-beta plasma atmosphere dominated by a ~10G global magnetic field reversing in cycles of 11 years

2/5T ~

2/3T ~

Page 14: The Solar Corona B. C. Low High Altitude Observatory National Center for Atmospheric Research The National Center for Atmospheric Research is operated.

Time-Dependent Ideal MHD

..... 0)(pρdt

d

..... )Bv(t

B

0)v(ρt

ρ

..... r̂r

GMρpB)B(

1

dt

vdρ

γ

2Sun

Page 15: The Solar Corona B. C. Low High Altitude Observatory National Center for Atmospheric Research The National Center for Atmospheric Research is operated.

Magnetic Helicity

• The magnetic vector potential:

• Magnetic helicity:

• Helicity transport:

0

V

dV A.BA.B H ; h

B A. vv. . hht

;AB

Page 16: The Solar Corona B. C. Low High Altitude Observatory National Center for Atmospheric Research The National Center for Atmospheric Research is operated.

Magnetic Helicity & Linkage Numbers

N H

Page 17: The Solar Corona B. C. Low High Altitude Observatory National Center for Atmospheric Research The National Center for Atmospheric Research is operated.

The Hydromagnetic Induction Equation

“The magnetic field is frozen into the embedding plasma with perfect electrical conductivity. The perfect conductor is a singular limit of the weakly resistive conductor; being nearly perfect is not the same as just being perfect. ”

BBvB 2

t

1Lv

4

R 002M

c

Page 18: The Solar Corona B. C. Low High Altitude Observatory National Center for Atmospheric Research The National Center for Atmospheric Research is operated.

The Surprisingly Dissipative Corona

• Quiescent heating & flares – heating by a turbulent dissipation of spontaneous current sheets (Parker 1994)

1Lv

R 00M

Page 19: The Solar Corona B. C. Low High Altitude Observatory National Center for Atmospheric Research The National Center for Atmospheric Research is operated.

Petschek Reconnection

Page 20: The Solar Corona B. C. Low High Altitude Observatory National Center for Atmospheric Research The National Center for Atmospheric Research is operated.

A Good Question

• If magnetic reconnection under conditions of high electrical conductivity makes a plasma readily dissipative, what are we to say about its canonical properties of being an excellent electrical conductor? Can magnetic reconnection short away all the electric currents in a magnetized plasma under conditions of ?

1Lv

R 00M

Page 21: The Solar Corona B. C. Low High Altitude Observatory National Center for Atmospheric Research The National Center for Atmospheric Research is operated.

Limits on Magnetic Reconnection under

• Longevity of astronomical-scale magnetic flux, e.g., potential fields as minimum-energy ground states: “very hard to get rid of magnetic flux”.

• Conservation of (relative) magnetic helicity within “sufficiently large” magnetic structures (Taylor 1974, Berger 1984): “very hard to get rid of magnetic twist”.

1Lv

R 00M

Page 22: The Solar Corona B. C. Low High Altitude Observatory National Center for Atmospheric Research The National Center for Atmospheric Research is operated.

Petschek Reconnection

Page 23: The Solar Corona B. C. Low High Altitude Observatory National Center for Atmospheric Research The National Center for Atmospheric Research is operated.

Coalescence of Two Ropes of Twisted Fields

N H

Page 24: The Solar Corona B. C. Low High Altitude Observatory National Center for Atmospheric Research The National Center for Atmospheric Research is operated.

The Ideal and Dissipative Nature of High-Temperature Plasmas

• Magnetic reconnection under does not destroy but transfer magnetic flux and helicity among subsystems of flux.

• Despite its dissipative nature, there is a limit to how much magnetic energy magnetic reconnection can liberate. The approximate conservation of magnetic helicity stores magnetic energy against flaring – origin of long-lived coronal structures.

1Lv

R 00M

Page 25: The Solar Corona B. C. Low High Altitude Observatory National Center for Atmospheric Research The National Center for Atmospheric Research is operated.

Emergence of a Twisted Magnetic Field(The Magnetic End-Product of a Confined Flare)

Manchester et al. 2004

Page 26: The Solar Corona B. C. Low High Altitude Observatory National Center for Atmospheric Research The National Center for Atmospheric Research is operated.

Magnetic Flux Ropes in the Solar Atmosphere

Potential State withZero Helicity

Minimum-Energy Statewith a conserved Net Helicity

Page 27: The Solar Corona B. C. Low High Altitude Observatory National Center for Atmospheric Research The National Center for Atmospheric Research is operated.

Sigmoidal Plasma Structures and Magnetic Flux Ropes

The sigmoid separatrix flux surface (Parker 1994,Titov & Demoulin 1999, Low

& Berger 2003)

Fan & Gibson (2003)

Page 28: The Solar Corona B. C. Low High Altitude Observatory National Center for Atmospheric Research The National Center for Atmospheric Research is operated.

Preferred Sigmoidal X-ray Plasma Structures in the two Hemispheres

• Left- and right-handed twisted flux ropes are preferred in the northern and southern hemispheres respectively (Canfield, Petstov, Rust, …..).

• Helicity Rule holds for all solar cycles.

North

South

Page 29: The Solar Corona B. C. Low High Altitude Observatory National Center for Atmospheric Research The National Center for Atmospheric Research is operated.
Page 30: The Solar Corona B. C. Low High Altitude Observatory National Center for Atmospheric Research The National Center for Atmospheric Research is operated.
Page 31: The Solar Corona B. C. Low High Altitude Observatory National Center for Atmospheric Research The National Center for Atmospheric Research is operated.
Page 32: The Solar Corona B. C. Low High Altitude Observatory National Center for Atmospheric Research The National Center for Atmospheric Research is operated.
Page 33: The Solar Corona B. C. Low High Altitude Observatory National Center for Atmospheric Research The National Center for Atmospheric Research is operated.

A Role of CMEs in Coronal Evolution

• Large-scale expulsion of coronal mass clear out into interplanetary space:

• Is there a collective effect of the CMEs on the solar corona over an 11-year solar cycle? Is energy release the only consequence of the CMEs for the corona?

g1510

SolarWindCMEs dt

dM

dt

dM

05.0

Page 34: The Solar Corona B. C. Low High Altitude Observatory National Center for Atmospheric Research The National Center for Atmospheric Research is operated.

Magnetic-flux Emergence and the Complementary Roles of Flares and CMEs

• Magnetic reconnection as flares serves to shed excess energy and simplify field topologies but cannot destroy the large-scale magnetic flux threading across the solar photosphere.

• Under its approximate conservation law, the magnetic-helicity emerging into the corona can be removed either by the mutual cancellation of opposite helicities or by an outward transport into interplanetary space, in order to avoid an unbounded accumulation in the corona – the global helicity rule identifies the latter mechanism with the CMEs.

Page 35: The Solar Corona B. C. Low High Altitude Observatory National Center for Atmospheric Research The National Center for Atmospheric Research is operated.

Creation & Removal of Magnetic Flux Across a Geometric Surface

Page 36: The Solar Corona B. C. Low High Altitude Observatory National Center for Atmospheric Research The National Center for Atmospheric Research is operated.

CMEs and Coronal Magnetic-Field Reversals

• CMEs are episodes of hydromagnetic expulsions of the magnetic flux and helicity of the old cycle out into the interplanetary solar wind, to make room for the new-cycle flux of the opposite polarity (Low & Zhang 2004).

• SMM & LASCO observations suggest a direct association between the progress of a field reversal at a solar pole and the rates of CMEs taking off near that (Gopalswamy et al. 2003).

Page 37: The Solar Corona B. C. Low High Altitude Observatory National Center for Atmospheric Research The National Center for Atmospheric Research is operated.

Gopalswamy et al. 2003

Page 38: The Solar Corona B. C. Low High Altitude Observatory National Center for Atmospheric Research The National Center for Atmospheric Research is operated.

The Solar-Heliospheric Outflow of Magnetic Flux and Helicity

• There is a global transport of magnetic flux system from the solar interior out into the solar wind, obeying the Helicity Rule. Complementary roles for flares & prominence and CME eruptions.

• Sub-photospheric origin of atmospheric magnetic helicity–are we seeing clear through into the interior dynamo?

• The hydromagnetic interplay between dissipative (flares) and ideal (CMEs) processes is the basic drama of solar activity that is the origin of space weather (Zhang & Low 2005, Ann. Rev. Astron Astrophys.).

Page 39: The Solar Corona B. C. Low High Altitude Observatory National Center for Atmospheric Research The National Center for Atmospheric Research is operated.

References

• Hundhausen, A. J. 1997, in Cosmic Winds and the Heliosphere, ed. J. R.Jokipii, C. P. Sonnett, \& M. S. Giampapa, U. of Arizona Press, p. 259

• Low, B. C. 2001, JGR 106, 25141 & references therein

• Zhang, M., \& B. C. Low 2005, ARAA vol. 43, in press, download: /toshi/ftp/pub/zhm/ZhangLow.pdf & references therein.