What can we learn about coronal mass ejections through spectroscopic observations

Hui Tian High Altitude Observatory,

National Center for Atmospheric Research

ASP research review

2011/10/5

Observation of the coronaHabbal et al. 2010, ApJ

Fe X 174 Å, imager Fe X 6374 Å, solar eclipse

Lower corona, coronagraph Extended corona, coronagraph

SOHO LASCO-2 White lightGround &

spaceEclipseCoronagraph

UV & X-raySpace ImagerCoronagraphSpectrograph/

spectrometer

Coronal mass ejections (CMEs)

Credit: STEREO Science Center

Occurring frequencySolar maximum: 3-5 per daySolar minimum: 1 every 3-5

days Mass: 2 × 1014-16 g Speed: 200-2000 km/s Sometimes dimmings in EUV & X-ray

Credit: STEREO Science Center

Space weather

Credit: SwRICredit: SOHO Daily MPEG

Earth-directed CMEs are potentially dangerous to our high-tech systems

Satellite anomalies, orbit changes, health of astronauts

Disruption of GPS & other spacecraft signals, radio signals

Damage of electric power grids & pipelines

Imaging observations at the Earth orbit can not observe the evolution of Earth-directed CMEs

EUV spectroscopy

Curdt et al. 2001, A&A

Combine imaging & spectroscopic observations

Line profiles in the ejecta

Two well-separated components A nearly stationary background A high-speed components (~200 km/s) representing the

emission of the ejecta Calculate the real speed: v=Sqrt(vpos

2+vlos2)

Spectroscopic observations of coronal dimmings

Attrill et al. 2010, Sol. Phys. McIntosh, ApJ, 2009

~20 km/s Blue shift: outflows refilling the corona Enhanced line width: growth of wave amplitude

Blueward asymmetry of line profiles in dimming regions

Two emission components in dimming regions

Two emission components A nearly stationary background A weak high-speed (~100 km/s)

components representing outflows

Blue shift of ~ 20 km/s and enhanced line width are caused by the superposition of the two components

Only a small portion of the materials in the dimming region are flowing outward The outflow speed is around 100 km/s

ConclusionSpectroscopic observations can provide

valuable information on the kinematics of CMEs

3-D CME evolutions can be obtained by simultaneous imaging and spectroscopic observations

The outflow speed in the dimming region is of the order of 100 km/s, not ~20 km/s