We examine solar polar region spicules using high-cadence Ca II data from the Solar Optical Telescope (SOT) on the Hinode spacecraft. We sharpened the images by convolving them with the inverse-point-spread function of the SOT Ca II filter, and we are able to see some of the spicules originating on the disk just inside the limb. Bright points are frequently at the root of the disk spicules. These "Ca II brightenings" scuttle around at approx.few x 10 km/s, live for approx.100 sec, and may be what are variously known as "H_{2V} grains," "K_{2V} grains," or "K_{2V} bright points." When viewed extending over the limb, some of the spicules appear to expand horizontally or split into two or more components, with the horizontal expansion or splitting velocities reaching approx.50 km/s. This work was funded by NASA's Science Mission Directorate through the Living With a Star Targeted Research and Technology Program, the Supporting Research and Program, the Heliospheric Guest Investigator Program, and the Hinode project

DeForest, Craig E.

Moore, Ronald L.

Sterling, Alphonse C.

NASA Technical Reports Server

Title: Solar Polar Spicules Observed with Hinode
Author: Alphonse C. Sterling, Ronald L. Moore, Craig E. DeForest
Abstract:
We examine solar polar region spicules using high-cadence Ca II data from 
the Solar Optical Telescope (SOT) on the Hinode spacecraft.  We sharpened
the images by convolving them with the inverse-point-spread function of the 
SOT Ca II filter, and we are able to see some of the spicules originating on 
the disk just inside the limb.  Bright points are frequently at the root of the disk spicules. These 
``Ca II brightenings'' scuttle around at ~few x 10 km/s, live for ~100 sec, and may be what are 
variously known as ``H_{2V} grains,'' ``K_{2V} grains,'' or "K_{2V} bright points.''  When 
viewed extending over the limb, some of the spicules appear to expand horizontally or spit into 
two or more components, with the horizontal expansion or splitting velocities reaching  ~50 
km/s.  This work was funded by NASA's Science Mission Directorate through the Living With a 
Star Targeted Research and Technology Program, the Supporting Research and Program, the 
Heliospheric Guest Investigator Program, and the Hinode project. 
https://ntrs.nasa.gov/search.jsp?R=20100024132 2019-08-30T09:49:37+00:00Z
Solar Polar Spicules Observed with
Hinode
Alphonse C. Sterling1
 and Ronald L. Moore
NASA/MSFC/NSSTC, Huntsville, Alabama, USA
and
Craig E. DeForest
Southwest Research Institute, Boulder, Colorado, USA
'Currently at: JAXA/ISAS, Sagamihara, Japan
Overview
We examine solar polar region spicules using high-cadence Ca II data
from the Solar Optical Telescope (SOT) on the Hinode spacecraft. We
sharpened the images by convolving them with the inverse-point-spread
function of the SOT Ca ii filter, and we are able to see some of the spicules
originating on the disk just inside the limb. Bright points are frequently at
the root of the disk spicules. These “Ca II brightenings” scuttle around at
few x 10 km/s, live for — 100 sec, and may be what are variously known as
“H grains,” “K grains,” or “K bright points.” When viewed extending2V g	 ,	 2V g	 ,	 2V	 g p	 g
over the limb, some of the spicules appear to expand horizontally or spit
into two or more components, with the horizontal expansion or splitting
velocities reaching — 50 km s -1 . A full report of this work appears in
Sterling, Moore, & DeForest (2010) .
This work was funded by NASA’s Science Mission Directorate through
the Living With a Star Targeted Research and Technology Program, the
Supporting Research and Program, the Heliospheric Guest Investigator
Program, and the Hinode project.
The Data
We assembled a 70-min long movie of Ca ii images from the Hinode
Solar Optical Telescope (SOT), taken at the north solar limb on 2007 July
25. During this period the cadence was very high, at 10 sec. We selected a
30" x 30" sub-FOV from the SOT images for detailed analysis.
The images making up the movie were convolved with an inverse point
spread function (PSF) for the SOT broad band filter. This function was
provided by one of us (CED), and was produced by the method described in
DeForest et al. (2009), with ǫ = 0.03. The PSF itself is circularly symmetric,
and was derived by DeForest by hand-fitting the falloff curve of brightness
inside the lunar limb during the 2007 January eclipse. Employing this
convolution improves contrast and small-feature detectability in the SOT
images. In particular it improves visibility of the roots of some spicules on
the disk just inside the limb.
Overall Appearance
There is an overall “haze” extending from the solar surface up to
— 6000 km (8"), that may itself be largely or totally composed of spicules.
Projected on this are thin, discrete, dynamic spicule features. Figure 1a
shows the full field of view of our study, and the haze of the spicules.
In the movie constructed from the images, one obvious spicule dynamic
is their lateral swaying, which De Pontieu et al. (2007a) interpreted as a
response to Alfve´n waves. There is also a strong upward motion apparent in
the spicules themselves, with downward motion not obvious; rather, most of
the spicules appear to fade rather than fall back to the Sun. Velocities of
the spicules we observe are frequently — 50—150 km s -1 . These velocities
and fading properties are consistent with what De Pontieu et al. (2007b)
identified as “Type II” spicules.
The disk is filled with dynamic, transient features that we call “Ca II
brightenings.” They are of size — 1" with lifetimes of a few x100 sec, and
many have horizontal velocities of a few x 10 km s -1 . These may be what are
variously nown as “H	 rains ” “K	 rains ” or “K bright points” e.y	 2V g	 ,	 2V g	 ,	 2V	 g 	 (e.g.,
Sivaraman et al. 2000; Nindos & Zirin 1998; de Wijn et al. 2008; Rutten &
Uitenbroek 1991); those features have been discussed in terms of acoustic
shocks (e.g. Kalkofen 2007; Reardon et al. 2008), and also as a manifestation
of the magnetic field (e.g., de Wijn et al. 2008).
Spicules on the Disk Just Inside the
Limb
When we can identify spicules originating on the disk just inside the
limb, they frequently appear to have Ca ii brightenings at their bases.
Moreover, in several cases the appearance is as though the spicule emanates
from where Ca ii brightenings come close together, and then disappear as
the spicule takes off. Figure 1b—1f shows one example of the apparent
coalescence of bright points and the concurrent or subsequent ejection of
a spicule. Figure 2 shows a second example, where Ca ii brightenings
come together, and this time create a “curtain” of spicules, as the Ca ii
brightenings that came together disappear.
Table 1 presents a summary of the circumstances for six specific cases of
Ca ii brightenings (CBs) at the base of spicules from our study.
Splitting Spicules Above the Limb
A second aspect apparent in the Ca ii movie is that many spicules
expand or split into two or more spicules, after being ejected as what appears
to be a single spicule. Figure 3 shows an example.
Table 2 lists several cases of splitting or breaking-up spicules. Some
events are rather complex. For example events 6 and 7 seem to be
coordinated, with both seemingly-separate spicules “fraying” into two
or more components each at the same time; the close coordination and
breakup of these spicules suggests that both spicules could be part of a
single collimated structure some 2" wide, that breaks apart by expanding
outward horizontally. Before breaking up, the eastern spicule travels upward
at — 115 km s-1 . Several of the Table 2 events (events 1, 3, 4, 6, and 7)
are initially very thin (<150 km) and perhaps even unresolved by SOT,
as they jet upward. They then expand laterally into two or more strands
while fading, and at the same time or shortly afterwards their upward
motion seems to slow or stop. Event 2 is a fainter and broader object that
moves more slowly and goes to higher altitudes than most others. Event 5
seems to be a compact structure moving upward, with two legs spreading
out beneath it. Suematsu et al. (2008) described multi-threaded structure
in spicules from Hinode observations, and much earlier Tanaka (1974)
observed twinning in mottles; what we see here may be the same or a similar
phenomena.
Discussion
Close examination of high-cadence Ca ii images from Hinode/SOT,
enhanced using the PSF deconvolution technique, shows hitherto un-
discussed aspects of polar limb spicules. When viewed just inside the
limb, many spicules emanate from Ca ii brightenings, and sometimes from
apparently coalescing Ca ii brightenings. When viewed above the limb,
some spicules split into two or more components as they fade. We have not
however so far been able to follow an individual spicule that emanates from
Ca ii brightenings, and then subsequently spits into two or more spicules as
it fades. Therefore we cannot rule out the possibility that we are observing
two or more different types of ejective phenomena.
If the Ca ii brightenings are acoustic shocks, it is hard to understand
how the energy from acoustic shocks could be directly converted to spicules
of such high velocities, based on model calculations (e.g. Hollweg 1982;
Sterling & Mariska 1990; De Pontieu et al. 2004) (although some of the
assumptions going into the earlier models should be reconsidered in light of
newer data). If these brightenings represent different magnetic elements, the
merging of the brightenings could correspond to magnetic cancelation and
reconnection, and this could result in a corresponding deposition of thermal
energy in the low atmosphere, perhaps somehow creating the spicules (e.g.,
Sterling et al. 1991; Shibata et al. 2007).
Observations of splitting spicules suggest another possibility: a spicule
eruption could be a miniature filament eruption with the Ca ii brightenings
being produced early in the eruption. Consistent with this idea, the motion
of the splitting spicules is reminiscent of the spreading of the legs of filament
eruptions, and the expansion of the erupting filament in the onsets of coronal
mass ejections (CME) ( e.g., Hirayama 1974; Moore et al. 2001). That is,
spicules themselves may frequently be magnetic eruptions, similar to CMEs,
occurring on a much smaller size scale and occurring much more frequently
(Moore et al. 1977; Moore 2001). Such a scenario could perhaps explain why
the Ca ii brightenings often appear to move rapidly toward and collide with
each other. This apparent movement could reflect the onset of eruption (e.g.,
Sterling et al. 2007), with the apparent “collision” location corresponding to
flare loops, which would only be bright for a very short time due to the small
scale-size of the putative erupting region. Innes et al. (2009) present another
example of mini-CME-like events. Their features are longer-lived and of
lower velocity than our features. But they observed an on-disk coronal hole
in EUV, while we observed the Ca ii limb, and so we cannot draw simple
conclusions about the possible relationship with our observations. Much
more detailed examination of spicule data is needed to sort out the actual
eruption mechanism, and their connection with other solar features.
A.C.S. and R.L.M. were supported by funding from NASA’s Office
of Space Science through the Solar Physics Supporting Research and
Technology Program and the Sun-Earth Connection Guest Investigator
Program. We thank Drs. T. E. Berger, T. D. Tarbell, and D. M. Zarro for
useful discussions and assistance. Hinode is a Japanese mission developed
and launched by ISAS/JAXA, with NAOJ as domestic partner and NASA
and STFC (UK) as international partners. It is operated by these agencies
in co-operation with ESA and NSC (Norway).
Table 1: Ca ii Brightenings (CBs) at Spicule Bases
Event Location CB Start Time CB Interaction Time CB Lifetime (s) a CB Velocity b Spicule Notes
1 19.5,938.0 07:04:56 07:06:32 144 15 At	 least	 one	 set	 of
CBs.	 Spicule	 velocity:
— 40 km s-1—100 km s-1.
2 5.0,938.0 — 07:06:22 07:08:48 — 288 25 Curtain of short spicules,
hard to trace above the
limb.
3 17.0,939.0 07:07:58 07:10:12 268 50 Ejection appears to “sweep
up” a — 5"circular radius
of CBs by 07:12:36 UT.
Spicule material flows up
at — 60kms-1.
4 1.5,938.0 G— 07:13:05 07:13:34(?) — 124 40 Clear spicule ejected at e.g.
07:13:24, but CB collision
not so obvious.
5 1.5,938.0 6—07:15:19 07:16:36(?) — 182 30 Clear spicule visible at e.g.
07:16:36, repetition of pre-
vious.	 Initial spicule ve-
locity —	 40 until about
07:17:14 UT, then at least
85 km s -1 . Again CB col-
lision not so obvious.
6 22.5,940.0 07:26:11 07:27:27 — 115 15 Clear spicule ejected.
aTime from appearance to disappearance of Ca ii brightenings (CBs).
bVelocities estimates from horizontal displacements, and uncertainties are — a factor of two.
–— 11 –—
Table 2: Splitting Spicules List.
Event	 Location	 Start Time Time to breakup (s) a Spicule Vel (km s -1 ) Split Vel (km s -1 ) Notes
1 20.0,942.0 07:01:44 6—48 170 f 50 45 f 10 Comes out as single strand,
blows apart into two or
more strands.	 Diffuse top
makes upward velocity un-
certain.
2 8.5,950.5 607:26:20 > 106 40 f 10 45 f 10 Different from most others:
Initially	 faint,	 slow,	 tall,
never narrow; starts broad
and gets broader (— 4").
3 18.5,943.0 07:27:46 104 220 f 70 37 f 12 Fig. 3 event.	 Faint exten-
sions appear early, making
velocities hard to measure
precisely.
4 9.5,950.5 07:33:32 >—38 70 f 15 27 f 10 Single	 strand,	 expands
while fading into diffused
structure.
5 20.0,947.0 07:41:21 48 120 f 30 50 f 15 Faint.	 Plug at top, with
two legs below.
6 18.5,944.0 07:49:30 67 130 f 20 55 f 30 Perhaps part of Event 7.
7 21.0,944.5 07:49:49 48 67 f 10 60 f 15 Perhaps part of Event 6.
'Time from when spicule is first visible until it starts to expand or split.
–12 –
REFERENCES
DeForest, C. E., Martens, P. C. H., & Wills-Davey, M. J. 2009, ApJ, 690, 1264
De Pontieu, B., Erd’elyi, R., & James, S. P. 2004, Nature, 430, 536
De Pontieu, B., Erd’elyi, R., & De Moortel, I. 2005, ApJ, 624, L61
De Pontieu, B., et al. 2007a, PASJ, 59, S655
De Pontieu, B. et al. 2007b, Science, 318, 1574.
de Wijn, et al. 2008, ApJ, 684, 1469
Hirayama, T. 1974, Sol. Phys., 34, 323
Hollweg, J. V. 1982, ApJ, 257, 345
Kalkofen, W. 2007, ApJ, 671, 2154
Innes, D. E., Genetelli, A., Attie, R., & Potts, H. E. 2009, A&A, 495, 319
Moore, R. 2001, in Encyclopedia of Astronomy and Astrophysics, ed. P. Murdin (Bristol: Inst. of
Phys. Publ.), 2691
Moore, R. L., Tang, F. Bohlin, J. D., & Golub, L. 1977, ApJ, 218, 286
Moore, R. L., Sterling, A. C., Hudson, H. S., & Lemen, J. R. 2001, ApJ, 552, 833
Nindos, A., & Zirin, H. 1998, Sol. Phys., 179, 253
Reardon, K. P., Lepreti, F., Carbone, V., & Vecchio, A. 2008, ApJ, 683, 207
Rutten, R. J., & Uitenbroek, H. 1991, Sol. Phys., 134, 15
Shibata, K., et al. 2007, Science, 318, 1591S
Sivaraman, K. R., et al. 2000, A&A, 363, 279
Sterling, A. C., & Mariska, J. T. 1990, ApJ, 349, 647
–13 –
Sterling, A. C., et al., 1991, ApJ, 381, 313
Sterling, A. C., Harra, L. K., & Moore, R. L. 2007, ApJ, 669, 1359
Sterling, A. C., Moore, R. L., & DeFores t, C. E. 2010, ApJ, 714, L1
Suematsu, Y., et al. 2008, ASP Conference Series, 397, 27S
Tanaka, K. 1974, IAUS, 56, 239
This manuscript was prepared with the AAS LATEX macros v5.2.
–14 –
Fig. 1.— Frame a is from video 1a of Sterling, Moore, & DeForest (2010), showing Ca ii
spicules at the north polar limb. Boxes represent the fields of view (FOV) of closeups shown
in other figures: the small box on the right is the FOV for Figs. 1b—1f; the small box
of the left is the FOV for Fig. 2; and the large box is the FOV for Fig. 3. Figs. 1b—
1f are from video 1bf of Sterling, Moore, & DeForest (2010), and show merging of two
Ca ii brightenings in (b) and (c), and a spicule ejected after the merging and fading of the
brightenings in (d)—(f); this is event 1 of Table 1. In (d)—(f) other spicules are abundant,
forming a haze identifiable in the broader solar context in (a), and also there is at least one
other relatively prominent spicule visible in (b). But the arrows in (d)—(f) point out the
specific spicule apparently resulting from the interaction of the Ca ii brightenings of (b) and
(c), and this is better seen in video 1bf of Sterling, Moore, & DeForest (2010). For this
and all figures the color table is reversed, so that Ca ii brightenings on the solar disk appear
dark. North is up and West is to the right in this and all other figures of this Poster. A
weak radial filter was applied to this figure and to figure 2 to enhance the detail in the stills;
this results in an artifact of an intensity jump at the limb.
–15 –
Fig. 2.— Frame from video 2 of Sterling, Moore, & DeForest (2010), showing Ca ii bright-
enings coming together (a), resulting in spicular ejections (b), and leaving a void after the
brightenings and spicules have faded (c). This is event 2 in Table 1.
–16 –
Fig. 3.— Frame from video 3 of Sterling, Moore, & DeForest (2010), showing a spicule
ejected as a single strand (a), and splitting into two strands later (b). A spicule appears as a
single-jet structure when it is ejected at 07:01:44 UT. From about 07:02:22 UT however, this
single spicule “breaks up” into two structures, with one moving westward at — 45 km s-i.
This is event 1 of Table 2. The color table was changed from earlier figures to better show
above-the-limb features.
SOT Ca II: 25-Jul-2007 07:06:03 UT
944
942
i5 940
`m
Y
938
936
14	 16	 18	 20
X (arcsecs)
SOT Ca II: 25-Jul-2007 07:07:39 UT
944
22
942
i5 940
`m
Y
938
942
i5 940
`m
Y
938
936
14	 16	 18	 20
X (arcsecs)
SOT Ca II: 25-Jul-2007 07:07:48 UT
944
22
936
22	 14	 16	 18	 20
X (arcsecs)
SOT Ca II: 25-Jul-2007 07:07:58 UT
944
942
i5 940
`m
Y
938
942
i5 940
`m
Y
938
936
14 22
936
22	 1416	 18	 20
X (arcsecs)
16	 18	 20
X (arcsecs)
SOT Ca II: 25-Jul-2007 07:08:17 UT
944 (a)
942
940
938
936
2	 4	 6	 8	 10
X (arcsecs)
SOT Ca II: 25-Jul-2007 07:08:46 UT
944 (b)
942
940
938
936
2	 4	 6	 8	 10
X (arcsecs)
SOT Ca II: 25-Jul-2007 07:10:22 UT
944 (c)
942
940
938
936
2	 4	 6	 8	 10
X (arcsecs)
SOT Ca II: 25-Jul-2007 07:02:13 UT	 SOT Ca II: 25-Jul-2007 07:03:01 UT
954
952
950
U 948
Ui
>- 946
944
942
950
U 948
Ui
946
944
942
16	 18	 20	 22	 24	 26	 28
X (arcsecs)
16	 18	 20	 22	 24	 26	 28
X (arcsecs)
940
14
940
14
954
952


Solar Polar Spicules Observed with Hinode

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