Solar wind acceleration

Shinsuke Imada
National Astronomical Observatory Japan

Remote-sensing Observation
before Hinode
Magnetic field

X-Ray

SOHO/MDI
Solar wind velocity

Yohoko/SXT
Solar wind structure dramaticallychanges with solar activity.
At the solar minimum phase, thefast wind is concentrate on thepolar region. On the other hand,at the maximum phase it is not
so much simple.

IPS

Polar Coronal hole
(fast solar wind)
Soho/SUMER observation
Tu et al., 2005

In-situ measurement
Radial distance: solar wind velocity
Red: Outward IMF
Blue: Inward IMF

Fast solar wind show the steadyflow ~700km/sec, magnetic
fields direction is also one
polarityOn the other hand, slow windshow the fluctuate structure.
Not only the velocity but alsomagnetic field direction.
Ulysses observation
McComas et al., 2000

Hinode Observation (Slow Wind)
Harra et al, 2008

Sakao et al, 2007

Transient Coronal Hole (Dimming)

Imada et al, 2007

What is the difference between
Slow and Fast?
Magnetic field configuration
smaller expansion
high speed

larger expansion
low speed
RADIAL DISTANCE

Wang and Sheeley 1990

Larger expansion  Heating near the Sun
Temperature gradient is large
Large density (not mass flux) into
interplanetary
This is one of the reason why we canobserve slow wind region by HinodeWhat is for Solar-C?
• The origin of steady fast solar wind.
(injection to solar wind)This is very difficult because the density isvery low. Need high-throughput EUV
spectrograph (This will be discussed
today).

Parker’s solar wind modelWhy fast solar wind is so steady?
• Slow solar wind origin is not steady This will be understand in more detailwith Hinode Observation.
• Is fast solar wind origin steady?
 maybe not
Magnetic field in the Polar region(Tsuneta-san’s Talk)
X-ray jets & Plume(Cirtain-san’s Talk)
Chromosphere (Tomorrow Talk)

What is for Solar-C?
• Can we observe critical point (velocity ~sound speed)?
 in-situ measurement helpful
It is up to payload..
Actully, Ulysses reveals many of them (notstatistically).
Combination of photospheric magnetic filed
and in-situ measurement.

Combination remote-sensing andin-situZhang et al, 2003
Magnetic field extrapolation
Origin of fast solar winddensity, temperature,
velocity, waves
charge state ratioSummary• Origin of fast solar wind. “steady or
unsteady?”
We need high throughput EUV
spectrometer to observe darker region• Combination with in-situ measurement is
helpful for understanding the critical point.
It is up to payload.
This analysis need precise modeling.

Inward and Outward Alfenwave

Parker’s Solar wind modelFrom Photosphere to Corona
Photosphere/
ChromosphereHigh βCoronaSolar wind

Low βHigh βCoronal Funnel

Transient Coronal Hole (Dimming)

Height

60Mm

Extrapolation for Z-direction
FeXV
FeXIV
FeXIII

40Mm

FeXII

20Mm

FeX

0Mm

FeXI

FeVIII
OV
HeII
√Ａ	

logT

Velocity

Log(n)

From Photosphere to Corona
Photosphere/
ChromosphereHigh βCoronaSolar wind

Low βHigh βHinode will reveal
the relation

How about thisrelation?

Steady or Unsteady injection?

For observing injection region• High sensitivity
to observe very darker region• Magnetic field measurement inchromosphere/transition region
to observe expansion factor• High cadence observation
to observe dynamic features
Observe from Polar region is better..