ORIGIN OF THE SLOW SOLAR WIND

 K. Fujiki ， T. Ohmi, M. Kojima, M. Tokumaru

Solar-Terrestrial Environment Laboratory, Nagoya University and

K. HakamadaDepartment of Engineering Physics, Chubu University

Slow solar wind from a small equatorial coronal hole

Slow solar wind from a polar coronal hole

19912000

Intermediate and slow streams originated not in smaller coronal holes at low latitudes and from open field regions just outside coronal hole boundaries. [Neugebauer et al., 1998]

The speed of the solar wind scales with the coronal hole area.[Nolte et al., 1976]

Relation between speed and coronal hole area

Wang & Sheely model

RADIAL DISTANCE

Magnetic field configuration

smaller expansion

larger expansion

high speed

low speed

Slow SW from an equatorial small CH

Solar Wind Structure at Solar Minimum

slower solar wind

Carrington Rotations 1899-1901

The slower wind originates from the vicinity of active regions

August 6 – October 17, 1995

Carrington Rotations 1895-1897

The slower wind also originates from the vicinity of active regions

April 19 – July 10, 1995

CR1897

HPS slow wind slow wind from seCHfast wind

106K

CR1897

HPS slow wind slow wind from seCHfast wind

CR1897

HPS slow wind slow wind from seCHfast wind

Parameter Slow (HPS) Slower (seCH) Fast (leCH)VP [km/s] 343±12 323±9 673±14

NP [cm-3] 11.7±3.3 10.2±0.6 3.2±0.5

TP [105 K] 0.39±0.14 0.55±0.11 2.20±0.39

TO [106 K] 1.85±0.24 1.99±0.19 1.42±0.13

Nα/ NP 0.009±0.003 0.031±0.008 0.039±0.004

Solar Wind in CR 1897 (June 12 – July 10, 1995)

Solar Wind in CR 1897 (June 12 – July 10, 1995)

Parameter Slow (HPS) Slow (seCH) Fast (leCH)VP [km/s] 343±12 323±9 673±14

NP [cm-3] 11.7±3.3 10.2±0.6 3.2±0.5

TP [105 K] 0.39±0.14 0.55±0.11 2.20±0.39

TO [106 K] 1.85±0.24 1.99±0.19 1.42±0.13

Nα/ NP 0.009±0.003 0.031±0.008 0.039±0.004

fast wind slow wind (HPS)

Source coronal hole helmet

N variance steady variable

Na/Np large small

slow wind (SCH)

coronal hole

steady

large

Slow SW from a polar CH

Polar Low-speed Solar Wind at Solar Activity Maximum of Cycle 22

Ohmi et al. [2001]

June 27, 1990

Polar Low-speed Solar Wind at Solar Activity Maximum of Cycle 23

Ohmi et al. [2002]

October 23, 1999

Small Polar Coronal Hole

ConclusionsIn addition to the slow solar wind from helmet streamer, the slow solar wind originates from small coronal holes.

slowerslower

fast

Wang and Sheely model of inverse correlation between velocity and expansion factor seems to explain these slower solar winds.

Magnetic Field in the Coronal Holes

high latitudeCH

12 G Fast wind

small polarCH

4 ～ 6 G Slow wind large flux expansion &

less magnetic energysmall

equatorialCH

18 G Slow wind large flux expansion &

large magnetic energy

Is it really possible to explain same acceleration mechanism?Photospheric Condition is significantly different.

Required

• More in situ observations of the slow stream from small coronal holes.

･･･ is difficult to observe the polar wind.

• Physical properties of density, acceleration profile, and temperature in corona of the slow streams.

　　　･･･ can be observed by SOLAR-B.(EIS/XRT)

~fin~