Alfvén Waves in the Solar Corona

S. Tomczyk, S. Mclntosh, S. Keil, P. Judge, T. Schad, D. Seeley, J. Edmondson

Science, Vol. 317, Sep., 2007

October 31, 2007

What’s new? BIG PUZZLE: Why does the temperature of the solar atmosphere

rise from 5000 to 2 million degrees Kelvin from the photosphere outward to the corona ?

October 31, 2007

MHD Waves Modes Fast and Slow Magnetoacoustic Mode:

Compressible Susceptible to damping Intensity oscillations observed with TRACE and SOHO

Alfvén Mode: Incompressible Transverse oscillation Propagate along field line Magnetic tension as the resorting force Observed in solar wind in situ Lack definitive observation in coronal plasma

October 31, 2007

Approach and Challenge Corona and scattering light; Not visible as intensity fluctuations; Velocity fluctuations:

Doppler shifts; Spectrograph: large FOV observation take too

long time compared to the wave periods.

Infrared coronal emission line: FeXIII 1074.7 nm; Narrow-band tunable filter: Doppler and

polarimetry.

October 31, 2007

Instrument

October 31, 2007

Instrument Hill-top facility at NSO/SP 20 cm One Shot Coronagraph Coronal Multi-channel Polarimeter

(CoMP) Corona emission lines: Fe XIII

1074.52, 1074.65, and 1074.78 nm

1024 x 1024 HgCdTe Detector CoMP polarimeter FOV: ± 1.4 solar radii Image scale: 4.5 arcsec/pixel Exposure time: 250 ms Bandwidth: 0.13 nm Stokes I, Q, U, V and Dopplergram

October 31, 2007

Data Acquisition Oct. 30, 2005 between 14.26 and 23.56 hour UT. Images of corona between 1.05 and 1.35 solar

radii. Fe XIII 1074.52, 1074.65, and 1074.78 nm. Stokes I+Q, I-Q, I+U, I-U. Spatial sampling: 4.5”/pixel. Cadence: 29 seconds. 70000 total images.

λ λ λ

Data

Set 1

Data

Set 2

Data

Set 3

October 31, 2007

Data Acquisition

λ λ λ

Data

Set 1

Data

Set 2

Data

Set 3

Dark and flat correction; Calibration processing; Central intensity of the line, the central

wavelength, and line width for each point in each image in the time series;

Line-of-sight (LOS) velocity; Degree of linear polarization: Azimuth angle:

Q

U1tan2

1

IUQp /)( 2/122

t

Observation

October 31, 2007

Result 2

October 31, 2007

Result 3

Phase travel-time analysis

Phase speed (1.31±0.24 Mm/s); Propagation trajectory (46.2±4.0°); Correlation length (~45 Mm); Correlation width (~9 Mm);

October 31, 2007

Result 4

October 31, 2007

Discussion Alfvén waves verification:

Phase speed (2 Mm/s) >> sound speed (0.2 Mm/s); Propagate along field lines; Intensity fluctuations are very small;

Presence of a 5-min signature: Tunnel through the complex chromosphere-transition region; Conversion mechanism is unknown;

Upward dominance: Energy estimation:

Energy flux not enough: Unresolved Alfvén waves ?

Coronal seismology: 1.5 ~ 5 Mm/s 8 ~ 26 gauss; Plasma density through ratio of FeXIII lines pair.

October 31, 2007

Summary An overwhelming flux of upward low-frequency wave

propagate throughout the solar corona; These waves are ubiquitous in space and time; These waves propagate at speeds typical of Alfvén

waves; Their direction of propagation mirrors the measured

magnetic field direction; The waves they resolved do not have enough energy to

heat the solar corona; They consider that these waves are indeed Alfvén waves; These waves offer the real possibility of probing the

plasma environment of the solar corona with a high degree of accuracy through coronal seismology.