Transcript THE NEW SOLAR CORONA

THE NEW SOLAR
CORONA
Ashwanden, Markus J., Arthur I. Poland, and Douglas M. Rabin
Annual Review of Astronomy and Astrophysics 2001. 39:175-210
Presented by
Joseph M. Vann
PHYSICS 681
SOLAR PHYSICS AND INSTRUMENTATION
December 6, 2005
“The Sun is New each day.”
“Everything Flows.”
Heraclitus (ca. 530-575 BC)
“Alles Vergängliche
Ist nur ein Gleichnis.”
(“All that is transitory is but a symbol.”)
J. W. von Goethe (1749-1832)
Faust, II, 12104-12105
PHYSICAL MODELING BEGAN
WITH GRAVITATIONALLY
STRATIFIED LAYERS
QUESTIONS ARE POSED
WITHIN THIS SYSTEM:
How hot is the corona?
What are its radiative, conductive and advective losses?
What heats the gas?
How strong is the magnetic field?
WHILE STILL BASIC, WE NOW KNOW NO SIMPLE
ANSWERS TO SUCH QUESTIONS ARE POSSIBLE.
THE SOLAR CORONA IS MORE DYNAMIC AND
COMPLEX IN STRUCTURE THAN ONCE REALIZED.
THE RISE AND FALL OF
CORONIUM
• DURING THE 1869 TOTAL ECLIPSE OF THE SUN YOUNG AND
HARKNESS FOUND A BRIGHT EMISSION LINE AT 530.3 nm –
THE “GREEN LINE” – UNKNOWN IN LABORATORY SPECTRA.
MANY OTHER LINES, INCLUDING A RED LINE WOULD BE
OBSERVED. THE NEW LINES WERE THOUGHT TO BE THOSE
OF A NEW ELEMENT, YET UNDISCOVERED ON EARTH.
• LIKE HELIUM, A NEW ELEMENT HAD BEEN DISCOVERED ON
THE SUN AND IT WAS NAMED CORONIUM, BUT IT, LIKE
NEBULIUM, BASED ON SIMILILARY UNIDENTIFIED LINES
FOUND IN GASIOUS NEBULAS, WOULD NEVER MAKE IT TO
THE PERIODIC TABLE.
CORONLIUM AND NEBULIUM –
THE SAGA CONTINUES
IN THE 1930s AND 1940s LINES FOR CORONIUM AND
NEBULUM WERE REPRODUCED USING EXTREMELY
HOT SPARKS (~ 106 K).
GROTRIAN (1939) DETERMINED THAT THE RED LINE
WAS ACTUALLY 14-TIMES IONIZED IRON – FE XV
AND EDLÉN (1942) DETERMINED THAT THE “GREEN
LINE” WAS 13-TIMES IONIZED IRON – FE XIV.
EDLÉN ALSO IDENTIFIED 19 OTHER LINES AS BEING
MULTIPLY- IONIZED ATOMS OF ELEMENTS SUCH AS
IRON AND NICKEL.
DUE TO THE HIGH IONIZATION POTENTIALS
INVOLVED, IT WAS NOW KNOWN THAT
TEMPERATURES IN THE CORONA WERE OF THE
ORDER OF 106 K.
THE CORONA IS HOTTER THAN
THE CHROMOSPHERE
A NEW QUESTION ARISES:
HOW IS THE CORONA HOTTER THAN REGIONS
CLOSER TO THE CORE?
CORONA TEMPERATURES ARE TYPICALLY 106 TO
2X106 K – EVEN HIGHER IN LOCAL REGIONS.
CHROMOSPHERE TEMPERATURES ARE TYPICALLY
4400 TO 20,000 K.
THE ANSWER IS STILL NOT COMPLETE BUT COMPLEX
MAGNETIC FIELD GEOMETRIES AND CLOSED
LOOPS ARE CLEARLY INVOLVED.
THE MULTITEMPERATURE STRUCTURE OF THE SOLAR CORONA
STRUCTURAL ELEMENTS OF
THE CORONA
• K CORONA (CONTINUOUS, GERMAN:
KONTINUIERLICH) – PRODUCES WHITE LIGHT
EMISSION FROM SCATTERING OF PHOTOSPHERIC
LIGHT FROM FREE ELECTRONS. NO FRAUNHOFER
LINES ARE OBSERVED. THE REGION IS LOCATED
MOSTLY BETWEEN 1-2 SOLAR RADII.
• F CORONA (FRAUNHOFER) – PRODUCED BY
SCATTERING OF PHOTOSPHERIC LIGHT FROM
DUST GRAINS BEYOND 2-3 SOLAR RADII.
FRAUNHOFER LINES ARE VISIBLE. F CORONA
MERGES INTO THE ZODIACAL LIGHT.
• E CORONA (EMISSION) - SOURCE OF EMISSION
LINES FROM HIGHLY IONIZED IONS IN CORONA.
OVERLAPS K AND F REGIONS.
SPACE EXPLORATION OF THE
CORONA
THE TEMPERATURE OF THE CORONA IS SO HIGH THAT MUCH
OF THE RADIATION IS IN THE FORM OF UV AND X-RAYS
WHICH CANNOT BE OBSERVED ON EARTH.
X-RAY EMISSIONS WERE FIRST DETECTED BY BURNIGHT IN
1949 USING A PINHOLE CAMERA ABOARD A ROCKET.
MANY OBSERVATIONS WERE MADE IN THE 1960s AND 1970s BY
US AND SOVIET ROCKETS, ESPECIALLY USEFUL DATA CAME
FROM THE 1973-74 NASA SKYLAB MISSION. THE IMAGES
REVEALED A COMPLEX OF LOOPS WHICH EVOLVED GREATLY
OVER THEIR SEVERAL DAY LIFETIMES.
THERE WERE LARGE-SCALE LOOPS WHICH REACHED OVER
THE POLES, ALMOST TO THE EQUATOR, ENDING IN AREAS OF
DEPLETED EMISSIONS, CORONAL HOLES.
CORONAL HOLES ARE DARK REGONS OF THE CORONA WITH
STRONGLY-REDUCED EMISSIONS OF UV AND X-RAYS. THEY
ARE ASSOCIATED WITH THE SOLAR WIND.
LATER SPACECRAFT ADDED TO
KNOWLEDGE OF THE CORONA
NASA SOLAR MAXIMUM MISSION (19801989)
YOHKO (“SUNBEAM”) – LAUNCHED 1991
SOHO (SOLAR AND HELIOSPHERIC
OBSERVATORY) – LAUNCHED 1995
TRACE (TRANSITION REGION AND
CORONAL EXPLORER) – LAUNCHED
1998
MAGNETIC ORGANIZATION
IT IS DIFFICULT TO MEASURE MAGNETIC FIELDS IN THE CORONA.
METHODS INCLUDE :
IMAGING SPECTROSCOPY AT RADIO WAVELENGTHS ABOVE ACTIVE REGIONS.
ZEEMAN SPECTROPOLARIMETRY IS USEFUL FOR BOTH COHERENT AND INCOHERENT
LIGHT BUT IS HANDICAPPED IN THE CORONA BY LOWER FIELD STRENGTHS AND
HIGHER TEMPERATURES (THUS THERMAL LINE WIDTHS) BUT IS USED FOR CORONAL
INVESTIGATIONS OF IR.
HANLE EFFECT (MAGNETICALLY-INDUCED RADIATIVE SCATTERING OF COHERENT LIGHT
RESULTING IN DEPOLARIZATION AND ROTATION OF THE PLANE OF POLARIZATION) IS
USED FOR STUDYING PROMINANCES.
THE HANLE EFFECT IS SENSITIVE TO MUCH WEAKER FIELDS THAN THE ORDINARY ZEEMAN
EFFECT. HOWEVER, THE HANLE EFFECT IS INSENSITIVE TO VERTICAL MAGNETIC
FIELDS AND IS USELESS IN MEASURING FLUX TUBE FIELDS. THE HANLE EFFECT CAN
ONLY DETERMINE TWO COMPONENTS OF THE STOKES VECTOR, WHILE THE ZEEMAN
EFFECT, IN PRINCIPLE, GIVES THE ENTIRE VECTOR. THE HANLE EFFECT IS USEFUL IN
MEASURING TANGLED MAGNETIC FIELDS WHERE THE POLARARITIES ARE MIXED WHILE
THE ZEEMAN EFFECT IS USELESS FOR SUCH FIELDS.
PROPAGATING WAVES IN THE
CORONA
PASSING OF WAVE FRONT DISTURBS LOCAL DENSITY BUT WITHOUT
BULK FLOW
THREE TYPES OF PROPAGATING WAVES IN THE CORONA:
ALVENIC – PERIODIC MOTION PERPENDICULAR TO MAGNETIC LINES
OF FORCE
MAGNETOSONIC WAVES
FAST
SLOW
SHOCK WAVES
P-MODE OSCILLATIONS OF THE SOLAR INTERIOR ARE THE STRONGEST
DRIVERS OF WAVE MOTION. THEY CAN EXCITE UPWARD
PROPAGATING WAVES IN GRAVITATIONALLY STRATIFIED FLUX
TUBES PASSING THROUGH THE PHOTOSPHERE AND
CHROMOSPHERE.
EIT IMAGES OF MORETON-LIKE WAVES
MORETON WAVES ARE WAVES EXCITED BY ERUPTIONS IN THE
CHROMOSPHERE AND CORONA WHICH PROPAGATE BOTH ALONG
THE SOLAR SURFACE AND UPWARD THROUGH THE CORONA INTO
INTERPLANETARY SPACE.
EVOLUTION OF THE CORONA CARTOON
INCREASED
KNOWLEDGE, MUCH
OF IT GAINED BY
SPACECRAFT, HAS
REVOLUTIONIZED
OUR KNOWLEDGE
OF THE STRUCTURE
AND DYNAMICS OF
THE SOLAR
CORONA.
PLASMA β IS THE RATIO
OF GAS PRESSURE TO
MAGNETIC PRESSURE:
β = 2µP
B2
MAGNETIC PRESSURE
EXCEEDS STATIC GAS
PRESSURE UP TO
100Mm IN THE CORONA.
TRACE OBSERVATIONS OF ACTIVE-REGION LOOPS 6NOV1999
MOST OF THE LOOPS
ARE FILLED WITH
PLASMA UP TO THE
LOOP TOPS (~150Mm)
SO LOOPS NOT IN
HYDROSTATIC
EQUILIBRIUM – THEY
REQUIRE DYNAMIC
MODELS.
MAGNETIC STRUCTURES REVEALED BY YOHKO
COLLIDING AND
RECONECTING FLUX
TUBES PRODUCE A
CASCADE OF SHOCK
WAVES THAT PROPAGATE
RAPIDLY UPWARD AND
DUMP KINETIC ENERGY
INTO THE CORONA VIA
ACOUSTIC WAVES.
MHD SIMULATIONS
DEMONSTRATE THAT
SHOCK WAVES OF
COLLIDING
CHROMOSPHERIC FLUX
TUBES EXCITE SURFACE
AND BODY ALFVEN WAVES
SUITABLE FOR CORONAL
HEATING.
CORONAL MASS EJECTION OF 6 NOV1997 AS OBSERVED BY SOHO
CORONAL MASS EJECTIONS
(CMEs), FLARES, AND ERUPTIVE
FILAMENTS ARE EXAMPLES OF
PHENOMENA ASSOCIATED WITH
RAPID, LARGE-SCALE MAGNETIC
FIELD DESTABILIZATIONS.
THEY OCCUR EITHER
SEPARATELY OR TOGETHER, IN
ANY COMBINATION. IT IS
USELESS TO ARGUE DOES ONE
CAUSE ANOTHER – RATHER
THEY ARE ALL THE RESULT OF
MAGNETIC REORGANIZATION.
TRACE IMAGE OF FILAMENT ACTIVATION 29SEPT2000
FILAMENTS (CALLED
PROMINANCES WHEN
OBSERVED ON THE
SOLAR LIMB) ARE
CLOUDS OF RELATIVELY
COOL MATERIAL
SUSPENDED ABOVE THE
SOLAR PHOTOSPHERE.
EMERGENCE OF NEW
FLUX IN THE REGION OF
A FILAMENT SEEMS TO
BE IMPORTANT FOR THE
FORMATION OF AN
INSTABILITY – IT MAY
LEAD TO THE FILAMENTS
DISAPPEARANCE, TO
EJECTION, OR TO
HEATING AND EJECTION
OF A CME.
TRACE OBSERVATIONS OF THE 14JULY1998 1255UT FLARE
SOLAR FLARES ARE
THE MOST ENERGETIC
(1029 – 1032 ERGS) AND
RAPID (MILLISEC)
PHEONOMENA
OBSERVED ON THE
SOLAR CORONA.
RADIO BURSTS ARE
EMITTED IN THE SHOCK
WAVE PRODUCED BY
FLARES AND ERUPTIVE
PROMINANCES.
SECOND BASTILLE DAY FLARE OBSERVED BY YOHKO 14JULY2000
SOLAR FLARES ARE
ASSOCIATED WITH CME’S
BUT ARE NOT THEIR
“CAUSE.” THE QUESTION
IS MORE COMPLICATED –
FLARES, ERUPTIVE
FILAMENTS, AND CME’S
ARE ALL THE RESULT OF
MAGNETIC
REORGANIZATION.
WE STILL DON’T KNOW
HOW MAGNETIC ENERGY
IS DISSIPATED SO
QUICKLY INTO HEATING
AND PARTICLE
ACCELERATION.
THE DOMINANT
MECHANISM APPEARS TO
BE GYRO-RESONANT
WAVE- PARTICLE
INTERACTION.
OUTLOOK
1. We still do not have a reliable diagnostic of
physical processes that heat the corona.
2. We do not know what accelerates the solar
wind.
3. We have fewer reasons than ever to believe
that these questions have a single answer.
4. A new fleet of spacecraft has been developed
to add to our knowledge.