On the slow rise phase of eruptive
solar prominences
Nandita Srivastava
Udaipur Solar Observatory, Physical Research Laboratory, Udaipur
Contributions by
Vishal Joshi, Physical Research Laboratory, Ahmedabad
Sara F. Martin, Helio Research, La Crescenta, USA
IHY, Nov. 27-Dec. 1, 2006, Bangalore
Outline of the talk
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•
•
•
Introduction
Observations & Data Analysis
Results
Plan for new observations at Udaipur Solar
observatory
INTRODUCTION: ERUPTIVE FILAMENTS & CMEs
1. CMEs accelerate faster than associated erupting prominences seemed to imply
that CMEs could be the cause of erupting filaments (Hundhausen, Sime and
Low 1990).
2. Erupting filaments could result either from weakening of the overlying corona
or from the build-up of filament magnetic fields (Kuperus and Raadu, 1974).
3. Neither CMEs nor erupting filaments causes the other but both have a
common cause from large scale evolving magnetic features (Feynman and
Hundhausen 1994) or from reconnection of large-scale coronal magnetic fields
(Schmieder et al. 2002).
There is an extremely close relationship between erupting filaments
and CMEs
Pre-eruptive and eruptive
stages in the life of a filament:
1. Activation of filaments
2. Slow rise
3. Acceleration to higher speeds
4. Eruptive process over in several hours
5. Often twisting of the prominence observed
6. Many times, associated CME observed.
FILAMENT ACTIVATION AS PRECURSORS TO CMEs?
While several models have been proposed to explain how CMEs are triggered
(e.g. van Ballegooijen and Martens 1989, Martens and Kuin 1989, Forbes and
Isenberg 1991, Antiochos et. al. 1999, Krall et. al 2000, Amari et al. 2000, Linker
et al. 2001, Sturrock et. al 2002, Low and Zhang 2002, Fan and Gibson 2004)
None of these models specifically address filament activation.
Activation can occur an hour before the onset of a CME and involves
generation of flows and heating.
Relatively long term activation implies that it is governed by convective
motions of photosphere. Both demand additional energy.
Rising motion, oscillation or other related activation phenomena may
help understanding the eruptive phase.
Some filaments exhibit within a few hours to a day before their eruption
known as “short-term” rise.
Some filaments also reveal a slow increase in height beginning many days
prior to their eruption –”long term” rise.
Filippov and Den (2000, 2001) offer evidence of a critical height related to
the vertical gradient of the local magnetic field; thus every filament would
have its own critical height and would erupt when this height is exceeded.
Critical height of stable filament
equilibrium hc versus observed
prominence height above the limb
hp. The dotted line corresponding
to equality of these quantities is the
stability boundary. The solid
circles correspond to the filaments
which safely passed the west limb.
The open circles correspond to the
filaments which disappeared from
the disk.
Estimation of height
• Technique proposed by d’Azambuja and d’Azambuja
(1948) : Involves calculation of the tilt of the filament to
the vertical direction, width of the filament and its
heliographic coordinates.
Large errors if the angle between the line-of-sight and
plane of filament is small; projected width calculation.
• Vrsnak et al. (1998, 1999): Determine the rotation rate of
the Sun using filament as tracers and compare with the
known solar rotation rate. The difference gives the
height.
• Engvold & PROM team members (Nov. 2006) –
Proposed on investigating if all the filaments rise slowly.working on an improved technique.
Objective & Introduction
• Study of the pre-eruptive phase helps in understanding the trigger
mechanism of the associated CME. This is also useful for space weather
prediction.
• Studies in H-alpha have been made by several authors in the past.
Tandberg-Hanssen (1980), Kahler (1988), Filippov and Den (2001, 2002,
2003).
New observations available with EIT (304 A) on SoHO.
Estimate the range of heights above the solar surface at which
eruptive prominences attain maximum acceleration and
velocity.
Compare the height and velocity profiles of the eruptive
prominence with that of the associated CME to understand
the basic driving mechanisms in both cases.
OBSERVATIONAL DATA & ANALYSIS
Data set : SoHO EIT HeII 304Å images & LASCO-C2 images
Criteria for selection of data : EIT (304 images) (60-80 x 103K)
Normal cadence: 1 frames every 6 hours
CME watch: 4-5 frames per hour
High cadence images: 8 frames or more per hour
Event Selection : 6 events of
near limb eruptive prominences
and associated CMEs
January 8, 2000
An eruptive prominence as observed in He 304 Å recorded on 8
January, 2000 by the EIT/SoHO telescope. No LASCO data was
available for this day therefore the association of the CME
cannot be confirmed.
Example: 8 January 2000 (event 2)
•2 point running average and 3 point
interpolation in height time data
• Differentiation using 3 point
Lagrangian interpolation.
Slow rise with linear fit
Slow rise with 2nd order fit
This event reveals 2 distinct phases.
The first phase marked by a slow or gradual
rise for several hours before the eruptive phase
reveals conspicuous acceleration.
Lower panel shows the blow-up of the heighttime plot of the slow rise phase. The curve is
fitted with 2nd order polynomial.
Here the prominence clearly rises with
acceleration of the order of ~ 8 cm s-2, in
contrast to prior studies which suggested a
slow rise with constant velocity (Sterling and
Moore 2003.)
Second example: 31st July 2003
Slow rise with linear fit
Slow rise with 2nd order fit
Eruption on 1 JULY 2000
Profiles similar to that slowly evolving gradual CMEs (Srivastava et al.
1999, 2000)
Measured parameters for eruptive prominences in He 304 Å
MAIN OR ERUPTIVE PHASE
Height range
For maximum
velocity
(R O)
Event
no.
Date
1
08-Jan-00
62
0.48
---
25
0.39
0.42
2
08-Jan-00
130
0.71
0.66
77
0.57
0.64
3
01-Jul-00
22
0.45
---
3
0.24
0.29
4
25-Oct-02
154
0.62
---
66
0.43
0.48
5
25-Oct-02
38
0.32
0.34
17
0.31
0.33
6
30-Jul-03
25
0.19
0.22
11
0.15
0.17
VELOCITY 20-150 km s -1
ACCELERATION 3-80 m s-2
Maximum
acceleration
(m/s2)
Height range
For maximum
acceleration.
(RO)
Maximum
Velocity
(km/s)
Measured parameters for the initial (Slow Rise) phase
Time
duration
(hours)
Maximum
height
(R0)
Event no.
Date
acceleration
(cm/s2)
1
08-Jan-00
7.7
3.81
0.21
2
08-Jan-00
7.2
8.10
0.12
3
01-Jul-00
Slow Rise not observed
4
25-Oct-02
4.2
6.2
0.11
5
25-Oct-02
4.8
1.2
0.04
6
30-Jul-03
11.8
6.59
0.13
SLOW RISE ~
4-12 cm s -2
IN THE
LOWER
CORONA
Measured parameters for the associated CMEs
Leading edge
core
Event no. Date
Average
Velocity
km/s
Acceleration
m/s2
Average
velocity
km/s
Acceleration
m/s2
3
01-Jul-00
204
---
191
---
5
25-Oct-02
344
16.2
218
16.8
RESULTS
1. Eruption occurs in 2 distinct phases for all the eruptive prominences studied here except
one case. The initial phase is characterised by slow rise for all the prominences. This
characteristic can be used as a precursor of prominence eruption which may help to
predict the occurrence of an associated CME.
2. Slow rise phase shows constant acceleration of 4- 12 cm s-2. This is in contrast to
previous works in which slow rise with constant velocity has been reported (Tandberg –
Hanssen et al. 1980; Sterling and Moore, 2005).
3. In the second phase, namely eruptive phase, prominences experience larger acceleration
upto 80 m s-2 achieving a velocity in the range 20-150 km s-1.
4. All prominences with height > 0.2 RO have an associated CME (Gilbert et. al. ApJ.
2000) . (Our study, one exceptional case)
5. The average maximum height of eruptive prominences observed in Hα as reported by
Gilbert et.al. 2000 is 1.45 RO. In our study, the maximum height range extends up to 1.8
RO. This suggests that EIT 304 A images can be used to trace prominences up to higher
altitude compared to Hα images.
Need for new observations at USO
•
•
Observations
with current
setup at
USO
Need for information on solar events
directed towards the earth
Provide quantitative inputs or new
parameters for improvement of space
weather prediction model.
Dual Beam Hα Doppler Systems for Observations of
Erupting Filaments at USO, Udaipur & Helio Research, USA
• Observations of the EFs against the solar disk is possible and their mass Doppler
shifted mass motions as well as motions in the plane of the sky are the best known
proxy for the occurrence of the CMEs.
• Observations of Doppler shifts increasing from 10-100 km s-1 and higher in
erupting filaments within 300 of the center of the solar disk can serve as promising
means of knowing that a CME is heading towards the Earth.
VERY FEW OBSERVATORIES REGULARLY OBSERVE DOPPLER SHIFTS IN
SOLAR FILAMENTS!
Our Proposal:
To construction of a new 1Å tunable filter which can be used both as a standalone filter and as a pre-filter for the ultra narrow band etalons in the imaging of
solar events in H-alpha.
Simultaneous recording of the Hα Doppler shifts in filaments with a tunable 1Å
filter along with our narrow band etalons (filters) for disk events. (a) more
complete recording of filaments and prominences with 1Å tunable filters (b)
extending the l-o-s velocity range of our current narrow-band (1/10 Å) filters.
Proposed Schematic drawing of dual beam Doppler System for USO
Two (1.4 Å) single period multilayer interference filters in
tandem with a Polaroid and
quarter-wave plate between the
two filters.
Tilting mechanism for tuning :
If the tilt is only a few
degrees, the pass-band
shifts in wavelength
proportional to the amount
of tilt with very minimal
broadening of the filter
profile.
The telecentric beam of light from the telescope enters the polarizing beam-splitter
through a 1Å tunable Hα interference pre-filter. One polarization which is reflected by
the beam splitter is selected for the lithium niobate etalon and is passed to CCD1. The
other polarization goes to a CCD2 after reflection from a diagonal mirror.
Images with 1 A filter as a
stand alone filter (Helio
Research)
Images several quiet and one active filament
all recorded on 2003 Jan 20
When activated, filaments, seen through this
filter, change from low contrast to high
contrast features.
Useful for Space weather
warning: The large change
in the contrast of active and
erupting filaments offers a
unique new opportunity to
experimentally
establish
thresholds and criteria for
future automated software
detection
of
activated
filaments.
Usefulness of Doppler data
Roll effect: Analysis of Doppler images in
various positions of the wing reveals
effects such as roll effect which otherwise
are not conspicuous in line-center images.
FP Tuning range -1.5 to +1.5 Å corresponds to Doppler velocity -75 to +75
km sec-1. With 1 A tunable filter this range would be increased to so that
Doppler velocity in the blue range increases to -150 to +150 km s-1.
Relating Ha Doppler observations to STEREO, EUVI and SoHO
EIT images at 304Å –Observational campaigns planned
(a) the 304Å images from 3 spacecraft (2 STEREO +SoHO) will better give
the large-scale overall 3-D motions of activations and eruptions while
information from our H-alpha Doppler images will better give 3-D
information on the fine structures such as counterstreaming, rolling motion,
spiraling motion, and many irregular motions.
(b) Temporal Advantage: Image cadence in EUVI is one image every 3
minutes. Image cadence in our system (for line center) would be every 40
seconds with other images every 4 sec in the different positions of the line.
THANK YOU!