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 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 , , and 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 and hour UT.  Images of corona between 1.05 and 1.35 solar radii.  Fe XIII , , and nm.  Stokes I+Q, I-Q, I+U, I-U.  Spatial sampling: 4.5”/pixel.  Cadence: 29 seconds.  total images. λλλ Data Set 1 Data Set 2 Data Set 3

October 31, 2007 Data Acquisition λλλ 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: 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.