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POST CME EVENTS: COOL JETS AND CURRENT SHEET EVOLUTION
A. Bemporad, G. Poletto, S. T. Suess
POST CME EVENTS: COOL JETS AND
CURRENT SHEET EVOLUTION
A. Bemporad1, G. Poletto2, S. T. Suess3
1Astronomy
& Space Science Dept., University of Firenze, L.go E. Fermi 2, 50125 Firenze, Italy
- Arcetri Astrophysical Observatory, L.go E. Fermi 5, 50125 Firenze, Italy
3NASA Marshall Space Flight Center, Mailstop SD50, Huntsville, AL, USA
2INAF
IAU Symposium 226
Coronal and Stellar Mass Ejections
September 13-17, 2004 – Beijing, China
POST CME EVENTS: COOL JETS AND CURRENT SHEET EVOLUTION
A. Bemporad, G. Poletto, S. T. Suess
Summary:
We present here an analysis of the SOHO/UVCS, LASCO, EIT and
Ulysses/SWOOPS, SWICS observations of a CME on November 26-27,
2002. The talk will be organized as follows:
• The coronal morphology evolution during and after the CME as seen by
LASCO.
• SOHO/UVCS observations.
• UVCS data analysis and interpretation.
• Ulysses/SWOOP & SWICS data.
• Conclusions.
IAU Symposium 226
Coronal and Stellar Mass Ejections
September 13-17, 2004 – Beijing, China
POST CME EVENTS: COOL JETS AND CURRENT SHEET EVOLUTION
A. Bemporad, G. Poletto, S. T. Suess
The CME as seen by LASCO:
Beginning of UVCS
observations
LASCO/C2
(2002/11/26, 00:06 11/29, 23:06 UT)
LASCO/C3
(2002/11/26, 00:18 11/29, 22:18 UT)
IAU Symposium 226
Coronal and Stellar Mass Ejections
September 13-17, 2004 – Beijing, China
POST CME EVENTS: COOL JETS AND CURRENT SHEET EVOLUTION
A. Bemporad, G. Poletto, S. T. Suess
SOHO/UVCS observations:
Slit position:
Latitude: 27°N
Height: 1.7 Rsun
Time interval:
11/26, 18:39  11/29, 02:56
Main spectral lines
observed:
• Fe XVIII l974.9, Fe XV l481.4,
Si XII ll499.4 - 520.7, Ca XIV
l943.6
• O VI ll1031.9 – 1037.6, Lyb
l1025.7, Lyg l972.5, C III l977.0
IAU Symposium 226
Coronal and Stellar Mass Ejections
September 13-17, 2004 – Beijing, China
POST CME EVENTS: COOL JETS AND CURRENT SHEET EVOLUTION
A. Bemporad, G. Poletto, S. T. Suess
SOHO - Ulysses quadrature observations:
• A SOHO – Ulysses
quadrature occurs twice a
year (D simbols) when the
angle between the SOHO
Line of Sight (LOS) and
the radial from the Sun to
Ulysses is ~ 90°.
• In this geometry, the
same plasma studied with
remote sensing technique
by UVCS is observed later
in situ by Ulysses.
IAU Symposium 226
Coronal and Stellar Mass Ejections
September 13-17, 2004 – Beijing, China
POST CME EVENTS: COOL JETS AND CURRENT SHEET EVOLUTION
A. Bemporad, G. Poletto, S. T. Suess
SOHO: remote sensing observations
IAU Symposium 226
Coronal and Stellar Mass Ejections
September 13-17, 2004 – Beijing, China
POST CME EVENTS: COOL JETS AND CURRENT SHEET EVOLUTION
A. Bemporad, G. Poletto, S. T. Suess
UVCS data: the “cool” plasma jets
EIT images show recursive
ejection of plasma from the
Chromosphere at latitudes
between ~ 35°N and 55°N.
These jets, expected to have
a plasma temperature lower
than the ~106 K Corona, show
emission in UVCS data from
neutral H (Lyb and Lyg) and
the C III ion (Tmax= 8 104 K).
Doppler line shifts indicate a
plasma vLOS up to 250 km/s.
The same jets are also visible
in the LASCO/C2 images as
an increase in the white light
intensity.
SOHO/EIT He II 304 difference images
IAU Symposium 226
Coronal and Stellar Mass Ejections
September 13-17, 2004 – Beijing, China
POST CME EVENTS: COOL JETS AND CURRENT SHEET EVOLUTION
A. Bemporad, G. Poletto, S. T. Suess
UVCS data: emission from high temperature plasma
Between the latitude of ~ 15°N and
30°N, UVCS data show emission
from the Fe XVIII ion (Tmax ~ 6 106
K);
the main emission is centered at
~ 23°N (bin #35). Such temperatures are unusually high even for
Active Regions.
At this latitude the Fe XVIII line
intensity increases reaching its
maximum on November 27, at
~ 14:00 UT (i.e. about 21h after
the initiation of the CME), then
decreases, while Fe XV intensity
increases continuously.
IAU Symposium 226
Coronal and Stellar Mass Ejections
September 13-17, 2004 – Beijing, China
POST CME EVENTS: COOL JETS AND CURRENT SHEET EVOLUTION
A. Bemporad, G. Poletto, S. T. Suess
UVCS data analysis: plasma temperature determination
In coronal conditions, the electron density Ne is low
enough that the lines form by electron collisional
excitation followed by spontaneous emission. The line
intensity Iline is thus:
where nel /nH is the elemental abundance relative to H and
ne is the local electron density.
G(Te) is the contribution function defined as:
where nion /nel is the ionic fraction which is a function of the
electron temperature Te , Bline is the branching ratio for
the line transition and qline is the electron excitation rate.
The emissivity e can be defined as
Fe X, Fe XV and Fe XVIII Emissivities from the CHIANTI
spectral code (v. 4.01, computed with the ionization
equilibria of Mazzotta et al., 1998).
Assuming the ratio between intensities of spectral lines from different
ions of the same element to be equal to the ratio between their
emissivities; this ratio depends only on the electron temperature Te ,
hence the observed ratio gives an estimate for Te .
IAU Symposium 226
Coronal and Stellar Mass Ejections
September 13-17, 2004 – Beijing, China
POST CME EVENTS: COOL JETS AND CURRENT SHEET EVOLUTION
A. Bemporad, G. Poletto, S. T. Suess
UVCS data analysis: temperature at ~ 23°N of latitude
cooling
In this work Te has been estimated from the
observed ratio between the Fe XV and Fe XVIII
spectral lines.
From this ratio we estimate that, at the
beginning of our observations and at a
latitude of ~ 23°N, Te was higher than 8.7 106
IAU Symposium 226
Coronal and Stellar Mass Ejections
September 13-17, 2004 – Beijing, China
POST CME EVENTS: COOL JETS AND CURRENT SHEET EVOLUTION
A. Bemporad, G. Poletto, S. T. Suess
UVCS data: interpretation
• CME models predict that, after the eruption of the flux
rope (top panel) and the formation of the current sheet
below the expanding bubble, magnetic reconnection,
starting from the chromospheric level, relaxes the open
configuration into a closed .
• Magnetic reconnection heats plasma converting magnetic
energy into kinetic and thermal energies.
• The heated plasma in the closed loops is expected to cool
down via radiative and conductive cooling.
Are we looking at the top of the loops
or at the Current Sheet?
(from J. Lin et al., 2004, ApJ, 602, 422)
IAU Symposium 226
Coronal and Stellar Mass Ejections
September 13-17, 2004 – Beijing, China
POST CME EVENTS: COOL JETS AND CURRENT SHEET EVOLUTION
A. Bemporad, G. Poletto, S. T. Suess
The rising of reconnecting loops:
If we were looking at the top of a newly reconnecting
loop system, we would expect a vrise of ~ 100 km/s.
vNorth ≃ 2.3 km/s ; vSouth ≃ 1.3 km/s
(EIT Fe XII images)
IAU Symposium 226
Coronal and Stellar Mass Ejections
September 13-17, 2004 – Beijing, China
POST CME EVENTS: COOL JETS AND CURRENT SHEET EVOLUTION
A. Bemporad, G. Poletto, S. T. Suess
The cooling of reconnecting loops:
Order of magnitude estimates of the
conductive and radiative cooling time for
a semi – circular loop of height of 0.7 Rsun
shows that the loops cool mainly by
conduction over times on the order of 1h.
cooling
We concluded that we are observing
a CURRENT SHEET.
IAU Symposium 226
Coronal and Stellar Mass Ejections
September 13-17, 2004 – Beijing, China
POST CME EVENTS: COOL JETS AND CURRENT SHEET EVOLUTION
A. Bemporad, G. Poletto, S. T. Suess
The Current Sheet and the rising neutral point
• Over the past few years UVCS has found
evidence of current sheet (see for instance
Ko et al. 2003): long lasting, narrow, hot
regions were prominent in the Fe XVIII line.
• A long lasting current sheet in the aftermath
of fast CMEs (v0 flux rope = 1000 km/s) has also
been predicted on the basis of theoretical
arguments by J. Lin 2002.
Our Current Sheet last more than 2 days and
the CME front speed is about 480 km/s.
The rising of the neutral point height p vs time
(from J. Lin 2002)
IAU Symposium 226
Coronal and Stellar Mass Ejections
September 13-17, 2004 – Beijing, China
POST CME EVENTS: COOL JETS AND CURRENT SHEET EVOLUTION
A. Bemporad, G. Poletto, S. T. Suess
Ulysses: in situ observations
IAU Symposium 226
Coronal and Stellar Mass Ejections
September 13-17, 2004 – Beijing, China
POST CME EVENTS: COOL JETS AND CURRENT SHEET EVOLUTION
A. Bemporad, G. Poletto, S. T. Suess
Ulysses data: the identification for the same hot plasma
observed in situ at ~ 4.3 AU.
• In order to identify the in situ observation interval
including the 26 November CME, we made a first
extrapolation back to the Sun using the average
solar wind speed of 431 km/s.
• Hence, because in general CMEs will slow as
they propagate into the interplanetary medium,
we assumed that the ICME propagated at half the
sum of the average solar wind speed plus the
initial speed of the CME from the LASCO/CME list.
The 26 November CME is identified as the plasma
observed at Ulysses on 14 – 15 December 2002
(DoY 348 – 349).
The solar wind speed measured by Ulysses/SWOOPS
(Solar Wind Observations Over the Poles of the Sun)
(From G. Poletto, S. T. Suess, A. Bemporad et al., ApJL 2004)
IAU Symposium 226
Coronal and Stellar Mass Ejections
September 13-17, 2004 – Beijing, China
POST CME EVENTS: COOL JETS AND CURRENT SHEET EVOLUTION
A. Bemporad, G. Poletto, S. T. Suess
Ulysses data: the identification for the same hot plasma
observed in situ at ~ 4.3 AU.
The Fe charge state percentage vs day of year in 2002 from Ulysses/SWICS
(Solar Wind Ionization state and Composition Spectrometer)
(From G. Poletto, S. T. Suess, A. Bemporad et al., ApJL 2004)
In between DoY 348 – 349 (bottom black bar) SWICS observed the highest charge state (Fe16+) reported
in the data (top red bars): this could be a benchmark case to relate the in situ freeze-in temperature to
temperature of the coronal source wich must have been about 9  106 K.
IAU Symposium 226
Coronal and Stellar Mass Ejections
September 13-17, 2004 – Beijing, China
POST CME EVENTS: COOL JETS AND CURRENT SHEET EVOLUTION
A. Bemporad, G. Poletto, S. T. Suess
Conclusions:
• Many cool jets are observed after the CME, not directly
correlated with the post – CME evolution.
• We identified the high temperature plasma as the current
sheet following a CME.
• Lifetime of the current sheet is longer than 2 days.
• Temperature of the current sheet is higher than of 8.7  106 K
and decreases in about 2 days down to 3.3  106 K.
• We presented for the first time evidence for the same hot
plasma after CME events, in both remote and in situ
observations.
IAU Symposium 226
Coronal and Stellar Mass Ejections
September 13-17, 2004 – Beijing, China
POST CME EVENTS: COOL JETS AND CURRENT SHEET EVOLUTION
A. Bemporad, G. Poletto, S. T. Suess
“Hot” and “cool” plasma distribution
• At the beginning of the UVCS
observations there is very little
emission in Fe XVIII and a diffuse
emission in O VI.
• In the following evolution the
peak of the Fe XVIII emission is
located between the two maxima
in the O VI emission.
The hot plasma is located in
between branches of cool plasma.
(From G. Poletto, S. T. Suess, A. Bemporad et al., ApJL 2004)
IAU Symposium 226
Coronal and Stellar Mass Ejections
September 13-17, 2004 – Beijing, China
POST CME EVENTS: COOL JETS AND CURRENT SHEET EVOLUTION
A. Bemporad, G. Poletto, S. T. Suess
tcooling ~ 2 hours
(T ~ 1.5  106 K → 6.0  104 K)
• Over the past few years UVCS has found evidence of
current sheet in the aftermath of CMEs (Ciaravella et al.
2002; Raymond et al. 2003; Ko et al. 2003): long lasting,
narrow, hot regions were prominent in the Fe XVIII line.
• Rising post CME loops was also observed by SOHO/EIT
and Yohkoh/SXT.
(not in scale)
IAU Symposium 226
Coronal and Stellar Mass Ejections
September 13-17, 2004 – Beijing, China
POST CME EVENTS: COOL JETS AND CURRENT SHEET EVOLUTION
A. Bemporad, G. Poletto, S. T. Suess
IAU Symposium 226
Coronal and Stellar Mass Ejections
September 13-17, 2004 – Beijing, China