Evolution of Peripheral Active Region Upflows over the Solar Cycle

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Evolution of Peripheral Active Region Upflows over the Solar Cycle
Evolution of Peripheral Active Region
Upflows over the Solar Cycle
D. Baker1, D. Weston1, J. L. Culhane1,
L. van Driel-Gesztelyi1,2,3 S. Dacie1, S. Yardley1, L.K. Harra1
1University
College London, Mullard Space Science Laboratory, Dorking, UK.
2Observatoire de Paris, LESIA, UMR 8109 (CNRS), Paris, France.
3Konkoly Observatory of the Hungarian Academy of Sciences, Budapest, Hungary.
Hinode XRT/EIS Discovery of Persistent AR Upflows
•
XRT upflow seen (Sakao et. al., 2007); EIS observed upflow at ~ 50 km/s (Harra et al., 2008)
- persistent upflows at AR peripheries with temperatures: 1 MK ≤ Te ≤ 2.5 MK (Doschek et al., 2008)
- morphology differs from fan-loops where plasma downflows with Te ~ 0.6 MK (Warren et al., 2011)
- upflows mainly originate at sites of Quasi-Separatrix Layers (QSLs) (Baker et al., 2009, van DrielGesztelyi et al./ 2012, Démoulin et al., 2013)
•
Possibility of contribution to Slow Solar Wind led to considerable interest
- current observations suggest a 25% (Sakao et al., 2007) to 80% (Brooks et al., 2015) contribution
2
- uncertainty about outflow paths and no long-term data available
Selected ARs and their Solar Cycle Range
Active
Region* +
AR10926
AR10961
AR10978
AR10996
AR11032
AR11034
AR11035
AR11039
AR11043
AR11108
AR11120
AR11150
AR11271
AR11374
AR11459
AR11553
AR11576
AR11785
AR11909
AR12119
Date
12-JAN-2006
1-JUL-2007
12-DEC-2007
21-MAY-2008
20-NOV-2009
5-DEC-2009
15-DEC-2009
30-DEC-2009
2-FEB-2010
2-SEP-2010
5-NOV-2010
1-FEB-2011
21-AUG-2011
13-DEC-2011
20-APR-2012
9-AUG-2012
25-SEP-2012
8-JUL-2013
3-DEC-2013
20-JUL-2014
Latitude
(deg.)
-9.6
-9.4
-8.6
9.7
20.1
21.0
30.8
-27.7
24.8
29.9
38.6
-20.4
17.0
-17.3
-16.6
-22.4
-19.6
-10.2
17.5
-21.2
* Total of 20 ARs observed
+ Small sample: work will continue with
increased number of ARs
Cycle
Year
10.6
11.2
11.6
12.1
1.9
2.0
2.0
2.0
2.1
2.7
2.8
3.1
3.6
4.0
4.3
4.7
4.7
5.5
5.9
6.6
Purpose of Study
•
Examine variation of AR upflow properties and
the possibility of outflow during the solar cycle
- preliminary results presented
Cycle 23
START
Cycle 24
END
3
Latitudes of Selected ARs vs Years from Cycle Start
•
Total of 20 ARs studied: 4 from Cycle 23 and 16 from Cycle 24
•
Multi-cycle plot format from Hathaway – Living Reviews in Solar Physics, with ARs from
12 different solar cycles
- 20 ARs (cycles 23/24) from present study displayed on plot by black triangles
•
Data in later plots are displayed with respect to time in years from cycle start time
24 23
4
Magnetic Connectivity Changes through the Solar Cycle
AR 11120 (5-NOV-2010)
•
AR 11576 (25-SEP-2012)
Upflow properties may depend on external magnetic connectivities of the AR
- AR 11120 is a comparatively simple region with connections to QS and CH magnetic structures
- AR 11576 is a complex region with connections to other AR structures
• Studies of ARs throughout a cycle allow the impact of different magnetic connectivities on upflows to
be examined
5
Measured AR 11459 Upflow Parameters
•
•
Intensity, flow and non-thermal velocities were obtained from the Fe XII/195.12 Å line profile
Electron densities were obtained principally from the Fe XIII (I203.80Å /I202.04Å) line ratio with the
Fe XII (I186.87Å /I195.12Å) and Fe XIV (I264.79Å /I274.20Å) ratios also being used
- plasma temperatures were obtained from appropriate line ratios
- parameters measured for all 20 ARs
6
7
•
Parameter values for leading and following polarities plotted against years into the solar cycle
-
values are the means of the top 10% from the distributions for each upflow region
no obvious cycle-related trends detected
slight tendency for end-of-cycle ARs to have upflows with higher VDoppler and VNT values
observations confirm that highest VDoppler values match lowest intensities
larger sample size is needed
8
Total Mx vs NT Vel Leading
2E+22
•
1.8E+22
1.6E+22
VNT shows positive correlation
with total magnetic flux (MX)
- valid for leading and following
polarities
1.4E+22
1.2E+22
1E+22
Total MX
8E+21
Linear (Total MX)
6E+21
4E+21
y = 3E+20x - 2E+21
R² = 0.1815
2E+21
0
0
10
20
VNT
30
40
50
Total Mx vs NT Vel Following
•
2E+22
1.8E+22
1.6E+22
1.4E+22
1.2E+22
1E+22
Total MX
8E+21
Linear (Total MX)
Higher magnetic flux provides
greater free energy
- resulting reconnection and MHD
waves lead to increased VNT
6E+21
4E+21
y = 3E+20x ‐ 1E+21
R² = 0.2169
2E+21
0
0
10
20
30
40
50
60
9
NT Velocity vs Doppler Velocity (Leading)
•
50
45
40
VNT
35
30
- reason not clear
- due to small sample?
Nonthermal Velocity (Leading)
25
Linear (Nonthermal Velocity
(Leading))
20
15
Weak negative correlation
between VDoppler and VNT for
leading polarity
10
‐25
‐20
‐15
‐10
y = 0.4743x + 40.528
R² = 0.0225
5
VDoppler
0
‐5
0
NT Velocity vs Doppler Velocity (Following)
•
60
50
40
VNT
NT Velocity (Following)
30
Linear (NT Velocity (Following))
Strong positive correlation
between VDoppler and VNT for
following polarity
- agrees with previous EIS
results for ARs
20
10
VDoppler
‐25
‐20
‐15
‐10
y = ‐1.9372x + 8.2954
R² = 0.6822
0
‐5
0
10
PFSS Magnetic Field Modelling for the Active Regions
•
PFSS Models were constructed for all 20 ARs in the sample
- example for AR 11120 (5-NOV-2010) shows no open field in the AR neighbourhood
- for AR 11039 open associated negative polarity field is shown in purple
•
Only seven of the 20 ARs had access to neighbouring open field lines
•
Multi-stage reconnection pathways can provide access to open field (Mandrini et al., 2014)
11
Summary
•
Total of 20 ARs selected from Cycles 23 and 24 for interval JAN-2006 to JUL-2014
•
Measured upflow parameters (I, vDoppler, vNT,Te,ne) showed no strong cycle dependence for
either leading or following magnetic polarities
•
Relation between vDoppler and, vNT shows:
- weak –ve correlation for leading polarity
- strong +ve correlation for following polarity; agrees with previous EIS AR study results
•
Upflow regions had access to open magnetic fields for only seven of the 20 ARs
12
Future Work
•
Results must be obtained for a larger AR sample with a broader range of magnetic
configurations
•
These should include in particular network and CH as well as other AR connections to further
analyse cycle dependence
•
For vDoppler and, vNT correlation sign difference between leading and following polarities
must be confirmed
•
A subset of any future AR sample that are at a similar stage of development should be studied
•
Upflow contribution to the slow solar wind should be assessed
13

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