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A Statistical Study about Transequatorial loops

Jie ChenNational Astronomical Observatories

Chinese Academy of Sciences

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Transequatorial Loops(TELs) have relation to some solar physics phenomena

• They may be relevant to solar dynamo model (Babcock,1961)

• The evolution of TELs reflects magnetic reconnection (Tsuneta, 1996)

• The disappearance or brighten of TELs has relation to CME or flare eruption (Khan et al.2000; Glover et al.)

• Active regions which have the same chirality are more easily to form TELs (Canfield et al.1996; Farnik et al.1999; Pevtsov 2000)

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Our Work

Data Base and Observation• Whole YOHKOH/SXT data set (1991 October--2

001 December)• SOHO/MDI and Kitt Peak full disk longitude mag

netograms• We choose the images which are most clear and

close to the middle of solar disk• Find 356 TELs

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Category

• According to the magnetic polarities that TELs connect the regions in photosphere: PTEL, FTEL

PTEL

SPTEL

FTEL

SFTEL

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According to the numbers of TELs that the same region connected and magnetic polarities, we can classify TELs to SPTEL, SFTEL; DTELsA, DTELsB, DTELsC

DTELsA

DTELsB

DTELsC

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TEL (number)

356 100%

PTEL 229 64%

FTEL 127 36%

TEL CLASSIFICATION

STEL DTELsSPTEL SFTEL DTELsA DTELsB DTELsC120 32 145 41 18

79% 21% 71% 20% 9%

152 204

43% 57%

Statistical Results

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Discussion

• About bipolar group, the leading polarity is more compact and lives longer than the following polarity, the preceding polarity is more easy to form TELs than the following polarity, so PTEL has a larger proportion than FTEL

• When the two active regions both are mature, then the following polarity has the same probability with the leading polarity, so DTELsA has a larger ratio

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solar cycle 22

TEL 148 100%

PTEL 91 61%

FTEL 57 39%

solar cycle 23

TEL 208 100%

PTEL 138 66%

FTEL 70 34%

Preference Independent of Solar Cycle

During solar cycle 22, in the northern hemisphere, the leading polarity is negative; during solar cycle 23, magnetic polarity is reversed

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A: TELs number in different years B: the percent is TELs to sunspot number C: PTEL number in different years D: FTEL number in different years

TELs number has the same trend with solar cycle

The ratio of TELs to sunspot number is about 10%

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Some Parameters about TELs

• Separation: the footpoints distance between regions that TELs connected (Chase et al.,1977; Farnik et al.1999; Pevtsov, 2000 &2004)

• Tilt Angle: the angle between TELs and equator (P

evtsov 2004)• Asymmetry in Latitude: the footpoints asymmetry i

n latitude of TELsThese parameters reflect the properties of TELs and

maybe have relation with solar dynamoThrough compute flux-weighted center of the magne

tic polarities, we calculate these parameters

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Separation

Mean value is about 270 (similar to Pevtsov(2000) result)

It decreases from the minimum of solar cycle to maximum, this result is consistent to radial magnetic field variation following solar cycle

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Tilt angle

When the north footpoint is to the west of south footpoint, the angle is less than 900; reverse, it is more than 900

Mean value is about 900

Tilt angle value in different years

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Asymmetry in Latitude

Mean value is 0.6

Asymmetry in latitude is different in different years

If the latitude value in northern hemisphere is larger than it is in southern hemisphere, the result is more than 0; reverse, it is less than 0

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　 separation

tilt angl

e

asymmetry in latitude

total average

26.9 89.3 0.6

solar cycle 22

21.8 93.9 -0.2

solar cycle 23

30.5 86.0 1.2

Three Parameters are All Different in Different Solar Cycle

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Result

1.About TELs, PTEL has a preference and this result is independent of solar cycle

2.TELs number variation following solar cycle and the ratio of TELs to sunspot number is about 10%

3. Separation, Tilt Angle, Asymmetry in Latitude is different in different solar cycle

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Thank you!