Transcript On the origin of spicules

Hinode III meeting, 2009 Dec 1-4, Tokyo
On the origin of spicules
Kazunari Shibata
Kwasan and Hida Observatories
Kyoto University
Thanks to Yuzon Zhang, T. Matsumoto, T. Anan
See their posters
Introduction
• Spicules were discovered in 19th century (Secci
1887), and named spicules by Roberts (1945).
But their origin has not yet been solved.
• Spicules are important not only for
chromospheric structure but also for
chromospheric and coronal heating.
Thus, spicules are one of the most important
subjects in solar physics using Hinode data.
De Pontieu et al. (2007) PASJ
• Using Are
Hinode
Ca really
II H data,
found
there
twothey
types
? that there
are two types of spicules
• Type I spicules are driven by shock waves that
Are
really
driven
by shock
waves
formspicules
as a result
of p-mode
leakage.
Similar
to AR
fibrilsp-mode
and QS mottles.
from
leakage ?
• Type II spicules exhibit upward motion, followed
by rapid fading from Hinode Ca II H passband,
Are
there
reallymoving
typephase.
II spicules
without
a downward
They are ?
shortlived (10-150s), fast (50-150 km/s), and
Are
they
longest
in CHreally
(~10Mm)driven
but shortby
in AR (~2Mm).
They appear to be driven
Reconnection
? by reconnection.
Historical review
Suematsu, Shibata, Nishikawa, Kitai
(1982) Solar Phys. 75, 99.
• They studied the consequence of a small
explosion (e.g., reconnection) in the
photosphere and low chromosphere using 1D
hydrodynamic numerical simulation, and
found that spicules are formed as a result of
shocks (magnetoacoustic slow mode shocks).
Spicule model by Suematsu et al. (1982)
density
velocity
Shock velocity amplitude
Increases with height
because density decreases
with height
shocks
Height (100 km)
Height (100km)
Spicule model by Suematsu et al. (1982)
shocks
Stein and Schwartz (1972)
ApJ 177, 807
Shock velocity amplitude
Increases with height
because density decreases
with height
Cf) Osterbrock (1961)
Shibata, Nishikawa, Kitai, Suematsu
(1982) Solar Phys. 77, 121
• They extended Suematsu et al. (1982)’ s model to
various jets whose origins are located at various
heights in the chromosphere. They found:
• If the explosion (reconnection) occurs below the
middle chromosphere, the jets are formed as a
result of shocks.
• If the explosion (reconnection) occurs above
middle chromosphere, the jets are directly driven
by explosion (reconnection).
Shibata
et al.
1982
Explosion
(reconnection)
driven
Shock driven
Shibata and Suematsu (1982)
Solar Phys. 78, 333
• They further extended the Suematsu et al.
model to spicules in coronal hole (CH) and
active region (AR).
• They explained why spicules are taller in CH,
and shorter in AR by using shock model.
Shibata
Suematsu
1982
Shibata-Suematsu (1982) paper
have not been cited well !
Suematsu (1990)
Proc of “Progress of Seismology of the Sun and Stars”
(see also Suematsu and Takeuchi (1991)
Lecture Notes in Physics 387, 259)
• He realized that p-mode oscillation can leak
into upper layer as propagating acoustic waves
(and shocks) if the flux tube is inclined, and
applied this idea to spicules.
• However, his results show that spicules with
this mechanism are too short to explain
observed spicules.
• He was really disappointed with this result, so
he did not write the refereed paper !
De Pontieu et al. (2004)
Nature 430, 536
• on inclined magnetic flux tubes, the p-modes leak
sufficient energy from the global resonant cavity
into the chromosphere to power shocks that
drive upward flows and form spicules.
• But this mechanism has already been rejected by
Suematsu (1990) !
• So we need to seek for other mechanism on the
origin of spicules.
• I myself preferred “explosion (reconnection)
model “ on the origin of spicules (Shibata et al.
1982, Shibata 1983).
Hollweg, Jackson, Galloway (1982)
Solar Phys.
• They performed the MHD simulation of
propagation of nonlinear Alfven waves in the
solar atmosphere along a flux tube, and found
that spicules are produced by such nonlinear
Alfven wave through mode coupling between
Alfven wave and slow/fast mode (Hollweg
1992).
• Hollweg (1982), and Sterling and Hollweg
(1988) proposed rebound shock model.
Kudoh and Shibata (1999)
• I was skeptical about the Alfven wave model
of spicules by Hollweg (1982, 1992),
so I began to examine the Alfven wave model
in detail with Dr. Kudoh in 1999.
• The results were against my expectation, and
the Alfven wave model was so successful :
• The Alfven wave model can explain not only
spicules but also coronal heating in the quiet
region.
Alfven wave model of spicules:
1.5D-MHD simulation (Kudoh-Shibata 1999)
Hinode observations
• De Pontieu et al. (2007, Science) discovered
ubiquitous Alfven waves on spicules.
New progress
• Suzuki and Inutsuka (2005, 2006) extended
Kudoh-Shibata (1999) model to solar wind, and
successfully explained acceleration of fast solar
wind by low frequency Alfven waves.
• Matsumoto and Shibata (2009) further extended
Suzuki-Inutsuka model to include observed
photospheric velocity fields as the source of
Alfven waves, which was amazingly successful to
reproduce spicules, corona, and solar wind
See poster by Matsumoto
Real spicules and simulated spicules
(Matsumoto and Shibata 2009)
Do we need other sources of
Alfven waves ?
• In addition to simple photospheric granular
buffeting (e.g., Matsumoto and Shibata 2009),
there is also a possibility that Alfven waves are
generated by reconnection (Yokoyama 1998,
Takeuchi and Shibata 2001, Isobe et al. 2008).
• In fact, Hinode discovered ubiquitous horizontal
field in the photosphere (Lites et al. 2007,
Ishikawa and Tsuneta 2008), which might trigger
reconnection in the photosphere and low
chromosphere
Suematsu (2008)
Proc. Hinode I
Why Suematsu-san did not write
chromosphere
a refereed paper on spicules ?
photosphere
This is an interesting idea, but
there are no convincing theory
Speculative magnetic reconnection model to explain the double
and
threadsimulations.
structure of spicule and following evolution (expansion thread
Unipole
Shear or twisting motion in
the photosphere
separation, lateral motion and spinning as a whole body).
Hinode Dublin, 21 Aug. 2007
23
New observational analyses in Kyoto
• Anan et al. (2010) studied spicules in plage
regions using Hinode SOT/CaII data, and found
that they were shorter in length than the
quiet region limb spicules, and followed
ballistic motion under constant deceleration.
• The majority (80%) of the plage spicules
showed the cycle of rise and retreat, while
10% of them faded out without a complete
retreat phase.
See poster by Anan
New Observational ayalyses
• Yuzon Zhang et al. (Benjing, China)
reanalyzed spicules studied by de Pontieu et al.
(2007, PASJ), and found that there appears
basically no two types of spicules from
statistical point of view.
Yuzon Zhang (2009)’s analysis
Yuzon Zhang’s analysis of velocities of
type I and II spicules
Type II
type I QS
Type II CH
De Pontieu et al.
(2007, PASJ)
Summary
• It is difficult to classify spicules into two types from statistical
point of view (Yuzon Zhang et al. 2009, Anan et al. 2010).
There are faster spicules, but this does not mean that their
phsyical mechanism is different from that of other slower
spicules.
• The stratification effect and resulting shocks (Shibata et al.
1982) should be understood correctly. If reconnection
occurs below middle chromosphere, the model becomes the
shock and/or Alfven wave model.
• The Alfven wave model is amazingly successful at the present
stage (Matsumoto and Shibata 2009). Even in this model,
shocks are important in the upper chromosphere (Saito et al.
2001). Extension to 2D and 3D are necessary.
• The reconnection model (like Suematsu, Katsukawa, Isobe)
should be examined more with 3D simulations.
An Example of Tracing Spicule
• The example is “Type II” spicule, No. 17 (from 11:40:43 to 11:45:21 UT on
2007-03-19, with the serial frame No. 140 to 198. )
Spicule No.17 (No. 150 Frame)
11:41:31 UT
The line perpendicular
to the limb
Time-slice image
along the yellow line.
Frame 140,
11:40:43 UT
Frame 198,
11:45:21 UT
The processing of Spicule No. 17. The upper and down panel are the same, just with different
image quality. The following four pages show a whole lifetime of this spicule.
Shock propagation speed and
velocity amplitude (Shibata et al. 1982)
Atmospheric model in
coronal hole (CH), quiet sun (QS),
active region (AR)
AR
QS
CH
AR
QS
CH
Shibata & Suematsu 1982
Historical review
• Spicules ascend with an average apparent
velocity of about 25 km/s to an average
maximum height of 9000 km, and then either
fade away or fall back with a velocity similar to
the ascent velocity (Beckers 1972, Suematsu et al.
1982).
• There were some controvesies whether spicules
show ballistic motion or not (Athay 1976). But,
Nishikawa (1988) showed that ballistic model
cannot be rejected if we use high spatial
resolution data taken at Hida Observatory.
1.5D MHD simulation of coronal and
solar wind acceleration (Matsumoto 2009)
Observed value
Troidal Velocity [km/s]
Vr km/s
• zzz
Cf) Suzuki & Inutsuka 2005.
Discovery of Ubiquitous Horizontal
Magnetic Fields
Lites et al. (2007), Ishikawa and Tsuneta (2008)
Vertical
Horizontal
magnetic
magnetic
fluxflux
3D magnetoconvection simulaiton
(Isobe et al., 2008, ApJ Lett)
Discovery of ubiquitous
horizontal fields by
Hinode (Lites et al. 2007,
Ishikawa and Tsuneta
2008) suggest ubiquitous
reconnection in the
photosphere and
resulting generation
of ubiquitous Alfven waves
Reconnection in photosphere/chromosphere => Alfven waves