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Polar coronal holes in the solar activity cycle
Accepted Manuscript Polar Coronal Holes in the Solar Activity Cycle N.N. Stepanian, N.I. Shtertser PII: DOI: Reference:
S0273-1177(14)00309-3 http://dx.doi.org/10.1016/j.asr.2014.05.018 JASR 11804
To appear in:
Advances in Space Research
Received Date: Revised Date: Accepted Date:
10 February 2014 15 May 2014 18 May 2014
Please cite this article as: Stepanian, N.N., Shtertser, N.I., Polar Coronal Holes in the Solar Activity Cycle, Advances in Space Research (2014), doi: http://dx.doi.org/10.1016/j.asr.2014.05.018
This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Polar Coronal Holes in the Solar Activity Cycle N.N. Stepanian, N.I. Shtertser Crimean Astrophysical Observatory, Taras Shevchenko National University of Kyiv, Nauchny, Crimea, Ukraine, [email protected]
Abstract: The area of coronal holes, located at solar latitudes of more than 60 degrees, is compared with the evolution of the large-scale magnetic fields on the Sun’s surface. We found a decrease in the area of the coronal holes as well as growth of their low-latitude boundaries in connection with a reversal of the polar magnetic field. Keywords: coronal holes; polar magnetic field. In the paper by Webb et al. (1984) concerning cycles 19-21, and in the paper by Stepanian (1993) on cycles 21-22, it was shown that after the reversal of the polar fields coronal holes (hereinafter CHs) in structures of the background fields with a new polar field appear at high latitudes with delay of 5 to 20 rotations of the Sun after the polarity reversal. In these papers, the magnetic fields are determined from H-alpha maps (McIntosh et al., 1991). An example of such maps is given in Figure 1.
We continued this research on materials related to cycles 22-23 for Carrington rotations CR 1799 – CR 1987 (1989 – 2002 years). For subsequent solar rotations we used observations of HeI 1083 nm line performed at CrAO. Synoptic maps constructed from these observations are available on the website of the Laboratory of Solar Physics of the Research Institute “Crimean Astrophysical Observatory” http://solar.crao.crimea.ua/data/synoptic_maps An example of such map is given in Figure 2. Magnetic field in the regions of observed CHs are taken from Stepanian et al. (2013). Synoptic maps of the radial component of the solar magnetic field Br with a resolution of latitude 10 degrees were constructed in this study. They are based on daily magnetograms of the photospheric magnetic field obtained by the magnetographs KPNO and SOLIS (NSO, USA) and were published on the site http://spaceweather.com from 1975 to 2013 (Carrington rotation CR 1625-CR 2135).
In all the synoptic maps we have considered CHs located above 60 degrees latitude in both hemispheres. All the CHs are divided into two types: polar CHs that reach the pole, and CHs that do not reach the pole. The latter are called sporadic. We have determined latitudinal and longitudinal intervals for all of them, in which CHs are located, along with the sums of all CHs’ areas in each rotation. The calculation is carried out separately for northern and southern hemispheres. Changing with the times the total area of these CHs presented for N hemisphere in the maxima of 22 and 23 cycles on the top panel of Figure 3 and Figure 4 . The calculation included the areas of both polar and sporadic CHs. A sign of the area characterizes the sign of the magnetic field in CHs. In the same time scale in the lower panels there are changes over time of
the area of 10-degree latitude intervals with a center ϕ = 75° occupied by “+” field in N hemisphere. They clearly demonstrate the process of polarity reversal of the polar fields. Graphs are taken from the paper by Stepanian et al. (2013). By reverse polarity, as well as in the paper by Stepanian et al. (2013), we mean the process of changing a sign of the polar field. More precisely, the change in area of the latitudinal zone occupied predominantly by “+” field (S + field ≥ 80%), or “−” field (S + field ≤ 20%) into the preferred field of the opposite sign. Figures 3 (Cycle 22) and 4 (Cycle 23):
Figures 3 and 4 show that in all the cases during polarity reversals, covering 30-40 solar rotations, there is time interval when CHs are absent, Sholes = 0. Starts and durations of polarity reversal processes and intervals of CH absence are shown in Table 1. Columns 1 and 2 give the start and duration of polarity reversals for 75 degrees north and south latitudes in cycles 22 and 23. Columns 4 and 5 give the start and duration of the interval without polar CHs. Time is expressed in Carrington rotations.
From the comparison of data given in the table it is obvious that intervals of absence of CHs in cycle 22 begin later than the start of polarity reversal in 10 rotations and end simultaneously with the end of polarity reversal. In cycle 23, CHs disappear when the polarity reversal starts and appear a few rotations later than the end of polarity reversal. The sign of the field in CHs, which appear after the polarity reversal, changes into the opposite one. Consider the behavior of the low-latitude boundaries of the polar CHs before and after the polarity reversals. Figures 5 and 6 show variations over time of latitude intervals for polar CHs in the northern and southern hemispheres. Polar CHs having a positive (“+”) magnetic field are marked with black filled squares; CHs with a negative magnetic field (“-”) are marked with empty circles.
Figures 5 and 6 clearly shows that after the polarity reversal polar fields cover a large latitudinal zone. As the new polarity reversal approaches, this latitudinal zone becomes narrower, the lower boundary of CHs approaches the pole, an interval without CHs appears. Sporadic CHs appear at the end of the period without polar CHs. After the change of the sign of the polar field, CHs appear in a large latitudinal interval.
Conclusion A common feature for polarity reversals in cycles 19-23 is the presence of intervals from 5 to 20 Carrington rotations in which polar CHs are absent. Before the reversal polarity of polar fields the low-latitude boundaries of CHs approach the pole. The duration of intervals without CHs and the time of their occurrence vary from cycle to cycle and are different at the solar poles of the same cycle. As to cycles 19-21, when the magnetic field was determined from Halpha observations, we cannot conclude with certainty about the process of repeated shorttime polarity reversals since H-alpha observations often do not determine rapid variations of the magnetic field. References
McIntosh P.S.; Willock E.C.; Thompson R.J. Atlas of stack plots derived from synoptic charts. / 1991, Report BAG 101 NGDC. Stepanian N. N.; Akhtemov Z. S.; Fainshtein V. G.; Rudenko G. V. The height stratification of solar magnetic fields in cycles 21-23 / 2013, Bull. of the Crimean Astrophys. Observatory, Vol. 109, No. 1. pp. 115-123. Stepanian N.N. Coronal holes and phone magnetic field at the Sun / 1993, “Solar Cycle” Collection of scientific papers, St. Petersburg, Russia, pp. 44-55 (in Russian). Webb D.F.; Davis J.M.; McIntosh P.S./ Observations of the reapperance of Polar Coronal Holes and the Reversal of the Polar Magnetic Field./ 1984, Solar Phys., Vol. 92, pp. 109-132. Figure Legend Figure 1: Example of the synoptic map of the Kitt Peak Observatory. Figure 2: Synoptic map of the RI “Crimean Astrophysical Observatory”. Dark regions correspond to the brightness at the center of HeI 1083 nm line I ≤ 1.03 In, where In = normalized brightness equal to one. Figure 3: Changes in areas of CHs (top panels) and percentage of area of the 10-degree latitudinal zone with a center at 75°, occupied by “+” magnetic field (bottom panel), for the northern hemisphere during the polarity reversal in solar cycle 22. Figure 4: The same as in Figure 3 for cycle 23. Figure 5: Change of latitude intervals occupied by polar CHs in the northern hemisphere. Squares refer to CHs, having the magnetic field of “+” sign, empty circles – CHs with the negative magnetic field. Figure 6: Change of latitude intervals occupied by polar CHs in the southern hemisphere.
Table 1: The reversal of the Polar Magnetic Field at Latitude 75° and Intervals of Lack of Polar Coronal Holes Cycle, Start of reversals Duration of Start of the Duration of Hemisphere polarity reversals interval without the interval polar CHs without polar CHS 22, N 1810 45 1820 23 22, S 1825 30 1832 25 23, N 1960 20 1960 15 23, S 1963 22 1964 25
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S0273-1177(14)00309-3 http://dx.doi.org/10.1016/j.asr.2014.05.018 JASR 11804
To appear in:
Advances in Space Research
Received Date: Revised Date: Accepted Date:
10 February 2014 15 May 2014 18 May 2014
Please cite this article as: Stepanian, N.N., Shtertser, N.I., Polar Coronal Holes in the Solar Activity Cycle, Advances in Space Research (2014), doi: http://dx.doi.org/10.1016/j.asr.2014.05.018
This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Polar Coronal Holes in the Solar Activity Cycle N.N. Stepanian, N.I. Shtertser Crimean Astrophysical Observatory, Taras Shevchenko National University of Kyiv, Nauchny, Crimea, Ukraine, [email protected]
Abstract: The area of coronal holes, located at solar latitudes of more than 60 degrees, is compared with the evolution of the large-scale magnetic fields on the Sun’s surface. We found a decrease in the area of the coronal holes as well as growth of their low-latitude boundaries in connection with a reversal of the polar magnetic field. Keywords: coronal holes; polar magnetic field. In the paper by Webb et al. (1984) concerning cycles 19-21, and in the paper by Stepanian (1993) on cycles 21-22, it was shown that after the reversal of the polar fields coronal holes (hereinafter CHs) in structures of the background fields with a new polar field appear at high latitudes with delay of 5 to 20 rotations of the Sun after the polarity reversal. In these papers, the magnetic fields are determined from H-alpha maps (McIntosh et al., 1991). An example of such maps is given in Figure 1.
We continued this research on materials related to cycles 22-23 for Carrington rotations CR 1799 – CR 1987 (1989 – 2002 years). For subsequent solar rotations we used observations of HeI 1083 nm line performed at CrAO. Synoptic maps constructed from these observations are available on the website of the Laboratory of Solar Physics of the Research Institute “Crimean Astrophysical Observatory” http://solar.crao.crimea.ua/data/synoptic_maps An example of such map is given in Figure 2. Magnetic field in the regions of observed CHs are taken from Stepanian et al. (2013). Synoptic maps of the radial component of the solar magnetic field Br with a resolution of latitude 10 degrees were constructed in this study. They are based on daily magnetograms of the photospheric magnetic field obtained by the magnetographs KPNO and SOLIS (NSO, USA) and were published on the site http://spaceweather.com from 1975 to 2013 (Carrington rotation CR 1625-CR 2135).
In all the synoptic maps we have considered CHs located above 60 degrees latitude in both hemispheres. All the CHs are divided into two types: polar CHs that reach the pole, and CHs that do not reach the pole. The latter are called sporadic. We have determined latitudinal and longitudinal intervals for all of them, in which CHs are located, along with the sums of all CHs’ areas in each rotation. The calculation is carried out separately for northern and southern hemispheres. Changing with the times the total area of these CHs presented for N hemisphere in the maxima of 22 and 23 cycles on the top panel of Figure 3 and Figure 4 . The calculation included the areas of both polar and sporadic CHs. A sign of the area characterizes the sign of the magnetic field in CHs. In the same time scale in the lower panels there are changes over time of
the area of 10-degree latitude intervals with a center ϕ = 75° occupied by “+” field in N hemisphere. They clearly demonstrate the process of polarity reversal of the polar fields. Graphs are taken from the paper by Stepanian et al. (2013). By reverse polarity, as well as in the paper by Stepanian et al. (2013), we mean the process of changing a sign of the polar field. More precisely, the change in area of the latitudinal zone occupied predominantly by “+” field (S + field ≥ 80%), or “−” field (S + field ≤ 20%) into the preferred field of the opposite sign. Figures 3 (Cycle 22) and 4 (Cycle 23):
Figures 3 and 4 show that in all the cases during polarity reversals, covering 30-40 solar rotations, there is time interval when CHs are absent, Sholes = 0. Starts and durations of polarity reversal processes and intervals of CH absence are shown in Table 1. Columns 1 and 2 give the start and duration of polarity reversals for 75 degrees north and south latitudes in cycles 22 and 23. Columns 4 and 5 give the start and duration of the interval without polar CHs. Time is expressed in Carrington rotations.
From the comparison of data given in the table it is obvious that intervals of absence of CHs in cycle 22 begin later than the start of polarity reversal in 10 rotations and end simultaneously with the end of polarity reversal. In cycle 23, CHs disappear when the polarity reversal starts and appear a few rotations later than the end of polarity reversal. The sign of the field in CHs, which appear after the polarity reversal, changes into the opposite one. Consider the behavior of the low-latitude boundaries of the polar CHs before and after the polarity reversals. Figures 5 and 6 show variations over time of latitude intervals for polar CHs in the northern and southern hemispheres. Polar CHs having a positive (“+”) magnetic field are marked with black filled squares; CHs with a negative magnetic field (“-”) are marked with empty circles.
Figures 5 and 6 clearly shows that after the polarity reversal polar fields cover a large latitudinal zone. As the new polarity reversal approaches, this latitudinal zone becomes narrower, the lower boundary of CHs approaches the pole, an interval without CHs appears. Sporadic CHs appear at the end of the period without polar CHs. After the change of the sign of the polar field, CHs appear in a large latitudinal interval.
Conclusion A common feature for polarity reversals in cycles 19-23 is the presence of intervals from 5 to 20 Carrington rotations in which polar CHs are absent. Before the reversal polarity of polar fields the low-latitude boundaries of CHs approach the pole. The duration of intervals without CHs and the time of their occurrence vary from cycle to cycle and are different at the solar poles of the same cycle. As to cycles 19-21, when the magnetic field was determined from Halpha observations, we cannot conclude with certainty about the process of repeated shorttime polarity reversals since H-alpha observations often do not determine rapid variations of the magnetic field. References
McIntosh P.S.; Willock E.C.; Thompson R.J. Atlas of stack plots derived from synoptic charts. / 1991, Report BAG 101 NGDC. Stepanian N. N.; Akhtemov Z. S.; Fainshtein V. G.; Rudenko G. V. The height stratification of solar magnetic fields in cycles 21-23 / 2013, Bull. of the Crimean Astrophys. Observatory, Vol. 109, No. 1. pp. 115-123. Stepanian N.N. Coronal holes and phone magnetic field at the Sun / 1993, “Solar Cycle” Collection of scientific papers, St. Petersburg, Russia, pp. 44-55 (in Russian). Webb D.F.; Davis J.M.; McIntosh P.S./ Observations of the reapperance of Polar Coronal Holes and the Reversal of the Polar Magnetic Field./ 1984, Solar Phys., Vol. 92, pp. 109-132. Figure Legend Figure 1: Example of the synoptic map of the Kitt Peak Observatory. Figure 2: Synoptic map of the RI “Crimean Astrophysical Observatory”. Dark regions correspond to the brightness at the center of HeI 1083 nm line I ≤ 1.03 In, where In = normalized brightness equal to one. Figure 3: Changes in areas of CHs (top panels) and percentage of area of the 10-degree latitudinal zone with a center at 75°, occupied by “+” magnetic field (bottom panel), for the northern hemisphere during the polarity reversal in solar cycle 22. Figure 4: The same as in Figure 3 for cycle 23. Figure 5: Change of latitude intervals occupied by polar CHs in the northern hemisphere. Squares refer to CHs, having the magnetic field of “+” sign, empty circles – CHs with the negative magnetic field. Figure 6: Change of latitude intervals occupied by polar CHs in the southern hemisphere.
Table 1: The reversal of the Polar Magnetic Field at Latitude 75° and Intervals of Lack of Polar Coronal Holes Cycle, Start of reversals Duration of Start of the Duration of Hemisphere polarity reversals interval without the interval polar CHs without polar CHS 22, N 1810 45 1820 23 22, S 1825 30 1832 25 23, N 1960 20 1960 15 23, S 1963 22 1964 25
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