Солнечно-земная физика, 2016, том 2, № 1
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Состав редколлегии журнала
Editorial Board
Жеребцов Г.А., академик —
главный редактор, ИСЗФ СО РАН
Zherebtsov G.A., Academician, Editor-in-Chief,
ISTP SB RAS
Степанов А.В., чл.-корр. РАН —
заместитель главного редактора, ГАО РАН
Stepanov A.V., Corr. Member of RAS,
Deputy Editor-in-Chief, GAO RAS
Потапов А.С., д-р физ.-мат. наук —
заместитель главного редактора, ИСЗФ СО РАН
Potapov A.S., D.Sc. (Phys.&Math),
Deputy Editor-in-Chief, ISTP SB RAS
Члены редколлегии
Members of the Editorial Board
Алтынцев А.Т., д-р физ.-мат. наук, ИСЗФ СО РАН
Altyntsev A.T., D.Sc. (Phys.&Math.), ISTP SB RAS
Мордвинов А.В., д-р физ.-мат. наук, ИСЗФ СО РАН
Mordvinov A.V., D.Sc. (Phys.&Math.), ISTP SB RAS
Максимов В.П., д-р физ.-мат. наук, ИСЗФ СО РАН
Maksimov V.P., D.Sc. (Phys.&Math.), ISTP SB RAS
Леонович А.С., д-р физ.-мат. наук, ИСЗФ СО РАН
Leonovich A.S., D.Sc. (Phys.&Math.), ISTP SB RAS
Тащилин А.В., д-р физ.-мат. наук, ИСЗФ СО РАН
Tashchilin A.V., D.Sc. (Phys.&Math.), ISTP SB RAS
Перевалова Н.П., д-р физ.-мат. наук, ИСЗФ СО РАН
Perevalova N.P., D.Sc. (Phys.&Math.), ISTP SB RAS
Белан Б.Д., д-р физ.-мат. наук, ИОА СО РАН
Belan B.D., D.Sc. (Phys.&Math.), IAO SB RAS
Муллаяров В.А., канд. физ.-мат. наук, ИКФИА СО РАН
Mullayarov V.A., C.Sc. (Phys.&Math.), IKFIA SB RAS
Деминов М.Г., д-р физ.-мат. наук, ИЗМИРАН
Deminov M.G., D.Sc. (Phys.&Math.), IZMIRAN
Обридко В.Н., д-р физ.-мат. наук, ИЗМИРАН
Obridko V.N., D.Sc. (Phys.&Math.), IZMIRAN
Гульельми А.В., д-р физ.-мат. наук, ИФЗ РАН
Guglielmi A.V., D.Sc. (Phys.&Math.), IPE RAS
Трошичев О.А., д-р физ.-мат. наук, ААНИИ
Troshichev O.A., D.Sc. (Phys.&Math.), AARI
Ермолаев Ю.И., д-р физ.-мат. наук, ИКИ РАН
Yermolaev Yu.I., D.Sc. (Phys.&Math.), IKI RAS
Мареев Е.А., чл.-корр. РАН, ИПФ РАН
Mareev E.A., Corr. Member of RAS, IAP RAS
Сафаргалеев В.В., д-р физ.-мат. наук, ПГИ РАН
Safargaleev V.V., D.Sc. (Phys.&Math.), PGI KSC RAS
Лазутин Л.Л., д-р физ.-мат. наук, НИИЯФ МГУ
Lazutin L.L., D.Sc. (Phys.&Math.), SINP MSU
Стожков Ю.И., д-р физ.-мат. наук, ФИАН
Stozhkov Yu.I., D.Sc. (Phys.&Math.), LPI RAS
Сомов Б.В., д-р физ.-мат. наук, ГАИШ МГУ
Somov B.V., D.Sc. (Phys.&Math.), SAI MSU
Лестер М., проф., Университет Лестера,
Великобритания
Lester M., Prof., University of Leicester, UK
Йихуа Йан, проф., Национальные астрономические обсерватории Китая, КАН, Пекин, Китай
Yan Yihua, Prof., National Astronomical Observatories, Beijing, China
Панчева Дора, проф., Национальный институт геодезии,
геофизики и географии БАН, София, Болгария
Pancheva D., Prof., Geophysical Institute, Bulgarian Academy of Sciences, Sofia, Bulgaria
Салахутдинова И.И., канд. физ.-мат. наук, ученый секретарь, ИСЗФ СО РАН
Salakhutdinova I.I., C.Sc. (Phys.&Math.), Scientific Secretary, ISTP SB RAS
Полюшкина Н.А., ответственный секретарь редакции, ИСЗФ
СО РАН
Polyushkina N.A., Executive Secretary of Editorial Board,
ISTP SB RAS
СОДЕРЖАНИЕ Мордвинов A.В., Певцов A.A., Бертелло Л., Петри Г.Дж.Д. Инверсия магнитного поля Солнца в 24-м цикле ……………………………………………………………………………………… 3–13 Прокопов П.А., Захаров Ю.П., Тищенко В.Н., Бояринцев Э.Л., Мелехов А.В., Пономаренко А.Г., Посух В.Г., Шайхисламов И.Ф. О возможности лабораторного моделирования процессов генерации альфвеновских возмущений в магнитных трубках в атмосфере Солнца ………………………... 14–23 Глоба М.В., Васильев Р.В., Кушнарев Д.С., Медведев А.В. Интерферометрические наблюдения мерцаний дискретного радиоисточника Лебедь-А на Иркутском радаре некогерентного рассеяния ……………………………………………………………………………………………………… 24–31 Макаров Г.А. Северо-южная асимметрия геомагнитной активности и электрическое поле солнечного ветра ………………........................................................................................................................ 32–35 Перевалова Н.П., Едемский И.К., Тимофеева О.В., Каташевцева Д.Д., Полякова А.С. Динамика возмущенности полного электронного содержания в высоких и средних широтах по данным GPS …………………………………………………………………………………………………………. 36–43 Руденко Г.В., Дмитриенко И.С. Проникновение внутренних гравитационных волноводных мод в верхнюю атмосферу ……………………………………………………………………………….. 44–55 Германенко А.В., Балабин Ю.В., Гвоздевский Б.Б., Щур Л.И. Природа вариаций гаммаизлучения во время осадков ……………………………………………………………………………… 56–63 Гечайте И., Погорельцев А.И., Угрюмов А.И. Влияние Арктического колебания на температурный режим восточной части Балтийского региона ………………………………………………… 64–70 Кобелев П.Г., Абунин А.А., Абунина M.А., Преображенский М.С., Смирнов Д.В., Луковникова А.А. Барометрический эффект нейтронной компоненты космических лучей на антарктической станции «Мирный» с учетом ветра ………………………………………………………………… 71–75 Янчуковский В.Л., Григорьев В.Г., Крымский Г.Ф., Кузьменко В.С., Молчанов А.Д. Приемные векторы мюонного телескопа станции космических лучей «Новосибирск» ………………………… 76–87 CONTENTS Mordvinov A.V., Pevtsov A.A., Bertello L., Petrie G.J.D. The reversal of the Sun’s magnetic field in cycle 24 ……………………………………………………………………………………………………... 3–13 Prokopov P.A., Zakharov Y.P., Tishchenko V.N., Boyarintsev E.L., Melekhov A.V., Ponomarenko A.G., Posukh V.G., Shaikhislamov I.F. On the possibility for laboratory simulation of generation of Alfven disturbances in magnetic tubes in the solar atmosphere ……………………………………………………… 14–23 Globa M.V., Vasilyev R.V., Kushnaryov D.S., Medvedev A.V. Interferometric observation of Cygnus-А discrete radiosource scintillations at Irkutsk Incoherent Scatter radar ………………………..…………... 24–31 Makarov G.A. North-south asymmetry of geomagnetic activity and solar wind electric field ……… 32–35 Perevalova N.P., Edemsky I.K., Timofeeva O.V. Katashevtseva D.D., Polyakova A.S. Dynamics of disturbance level of total electron content at high and middle latitudes according to GPS data ……………… 36–43 Rudenko G.V., Dmitrienko I.S. Penetration of internal gravity waveguide modes into the upper atmosphere ……………………………………………………………………………………………………. 44–55 Germanenko A.V., Balabin Yu.V., Gvozdevsky B.B., Schur L.I. Nature of gamma radiation variations during atmospheric precipitations …………………………………………………………….......…. 56–63 Gecaite I., Pogoreltsev A.I., Ugryumov A.I. Arctic Oscillation impact on thermal regime of the Baltic region Eastern part ……………………………………………………………………………………...….. 64–70 Kobelev P.G., Аbunin А.А., Аbunina M.А., Preobrajenskiy M.S., Smirnov D.V., Lukovnikova А.А. A wind effect of neutron component of cosmic rays at Antarctic station “Mirny” ……………………….. 71–75 Yanchukovsky V.L., Grigoryev V.G., Krymsky G.F., Kuzmenko V.S., Molchanov A.D. Receiving vectors of muon telescope of cosmic ray station “Novosibirsk” ………………………………………….. 76–87
Солнечно-земная физика. 2016. Т. 2, № 1
Solar-Terrestrial Physics. 2016. Vol. 2 Iss. 1
3
УДК 523.98
Поступила в редакцию 07.12.2015
DOI 10.12737/16356
Принята к публикации 29.01.2016
ИНВЕРСИЯ МАГНИТНОГО ПОЛЯ СОЛНЦА В 24-м ЦИКЛЕ
THE REVERSAL OF THE SUN’S MAGNETIC FIELD IN CYCLE 24
A.В. Мордвинов
Институт солнечно-земной физики СО РАН,
Иркутск, Россия, avm@ iszf.irk.ru
A.A. Певцов
Национальная солнечная обсерватория США,
Санспот, Нью-Мексико, США, pevtsov@noao.edu
Л. Бертелло
Национальная солнечная обсерватория США,
Тусон, Аризона, США, lbertello@nso.edu
Г.Дж.Д. Петри
Национальная солнечная обсерватория США,
Тусон, Аризона, США, gpetrie@noao.edu
A.V. Mordvinov
Institute of Solar-Terrestrial Physics SB RAS
Irkutsk, Russia, avm@ iszf.irk.ru
A.A. Pevtsov
National Solar Observatory, Sunspot,
New Mexico 88349, USA, pevtsov@noao.edu
L. Bertello
National Solar Observatory,
Tucson, Arizona, USA, lbertello@nso.edu
G.J.D. Petrie
National Solar Observatory,
Tucson, Arizona, USA, gpetrie@noao.edu
Аннотация. Анализ синоптических данных, полученных с помощью векторного спектромагнитографа (VSM) оптических долговременных исследований Солнца (SOLIS) и НАСА/НСО спектромагнитографа на вакуумном телескопе обсерватории
Китт-Пик, показывает, что инверсия магнитных полей на Солнце обнаруживают элементы стохастического процесса, который может включать развитие
особых структур всплывающего магнитного потока
и асимметрию активности северного и южного полушарий. Присутствие таких неоднородностей делает
моделирование и прогнозирование переполюсовок
полярного поля крайне затруднительными, если вообще возможными. В классической модели цикла
солнечной активности униполярные магнитные области (УМО) с полями преимущественно хвостовой
полярности двигаются по направлению к полюсу
благодаря меридиональным потокам и диффузии.
УМО постепенно приводят к исчезновению полярного магнитного поля предыдущего цикла и к формированию полярного поля противоположной полярности. Однако мы показываем, что эту детерминистскую картину может легко изменить развитие
мощного центра активности, или всплывание сверхбольшой активной области, или образование
«стратегически расположенной» корональной дыры.
Мы показываем, что активность, имеющая место в
24 цикле, возможно, является результатом этой
хаотичности в эволюции поверхностного магнитного
поля Солнца.
Ключевые слова: солнечный цикл, солнечная
активность, магнитные поля, корональные дыры.
Abstract. Analysis of synoptic data from the Vector
Spectromagnetograph (VSM) of the Synoptic Optical
Long-term Investigations of the Sun (SOLIS) and the
NASA/NSO
Spectromagnetograph
(SPM)
at
the
NSO/Kitt Peak Vacuum Telescope facility shows that
the reversals of solar polar magnetic fields exhibit elements of a stochastic process, which may include the
development of specific patterns of emerging magnetic
flux, and the asymmetry in activity between northern
and southern hemispheres. The presence of such irregularities makes the modeling and prediction of polar field
reversals extremely hard if possible. In a classical model
of solar activity cycle, the unipolar magnetic regions
(UMRs) of predominantly following polarity fields are
transported polewards due to meridional flows and diffusion. The UMRs gradually cancel out the polar magnetic field of the previous cycle, and rebuild the polar
field of opposite polarity setting the stage for the next
cycle. We show, however, that this deterministic picture
can be easily altered by the developing of a strong center of activity, or by the emergence of an extremely
large active region, or by a ‘strategically placed’ coronal
hole. We demonstrate that the activity occurring during
the current cycle 24 may be the result of this randomness in the evolution of the solar surface magnetic field.
Keywords: Solar cycle, sunspot activity, magnetic
fields, coronal holes.
1.
INTRODUCTION
The Babcock–Leighton mechanism [Babcock, 1961;
Leighton, 1969] outlines a basic picture of cyclic
changes of the Sun’s magnetic fields. First, the solar
cycle starts from a poloidal field defined by the magnetic
field confined in the polar areas of the Sun. Then, differential rotation converts this poloidal field into a to-
roidal configuration, giving rise to the emergence of
active regions in the photosphere. As the solar cycle
progresses, the magnetic field of active regions is dispersed by turbulent convection and meridional flow.
These transport mechanisms lead to the accumulation of
magnetic flux of trailing polarity of decaying active regions at high solar latitudes, eventually reversing the po
A.В. Мордвинов, A.A. Певцов, Л. Бертелло, Г.Дж.Д. Петри
A.V. Mordvinov, A.A. Pevtsov, L. Bertello, G.J.D. Petrie
4
larity of the polar fields and building the next solar cycle.
This concept led to the development of a distinct family
of flux-transport numerical models that employ the Sun’s
differential rotation, supergranular diffusion and the meridional flows, to successfully represent many properties
of observed long-term evolution of large-scale magnetic
fields [DeVore et al., 1985; Wang et al., 1989].
The flux transport models were also extensively
used to study effects of various parameters on the evolution of polar magnetic field and the solar cycle [Jiang et
al., 2013]. For example, Baumann et al. [2004] have
shown that the active region tilt described by Joy’s law
[Pevtsov et al., 2014], the diffusion and the rate of flux
emergence have significant effect on the polar magnetic
field. The speed of the meridional flow was found to affect
the strength of solar cycle with slower meridional flow
resulting in weaker solar cycles [Zhao et al., 2014]. Despite
recent improvements, several questions remain open about
flux transport models including the role of the not-well
known variations in the speed of the meridional flow and
scatter in orientation of active regions (Joy’s law).
Both observations and numerical simulations indicate the importance of polar field as a predictor for
strength of future solar cycle [e.g., Upton and Hathaway, 2014]. On the other hand, the observational evidence of the importance of active region tilts on the
strength of the solar cycle is inconclusive. The initial
report by Dasi-Espuig et al. [2010] about finding a relation between the mean active regions tilt of a given cycle and the strength of next cycle was questioned by
Ivanov [2012]; McClintock, Norton [2013], and later,
the results were revised by Dasi-Espuig et al. [2013].
Pevtsov et al. [2014] also argued that a relationship between the current surface activity (including active region tilt, flux emergence etc.) and the strength of the
polar field may be complicated by a prior state of the
polar field. For example, a strong surface activity may not
necessary lead to a stronger polar field if it has a significant polar field of opposite polarity to cancel out.
On the other hand, even a relatively modest surface
activity may result in a strong polar field if the polar
field of the previous cycle is weak. The question of the
polar field strengths dependence on history is a longstanding issue in flux-transport research. For example,
in their long-term flux-transport simulations Schrijver et al.
[2002] found that the polar fields did not reverse during
every cycle, e.g., a weak cycle would often fail to reverse strong polar fields. They suggested that this problem could be overcomed if the polar fields decayed
away on timescales of 5–10 years. This idea of radial
diffusion is not widely accepted now. Wang et al.
[2002] showed that polar field reversals could be maintained if the surface flow speeds were systematically
higher in large-amplitude cycles than in weak ones.
Whatever this or other mechanisms can explain the
complicated relationships between succeeding activity
cycles of different amplitudes and polar field strengths
is still the subject of debate.
The evolution of the polar magnetic field (and its reversal) in the current solar cycle 24 has been recently
studied by several researchers [Mordvinov, Yazev,
2014; Sun et al., 2015; Petrie, Ettinger, 2015; Tlatov et
al., 2015]. Still, a complete understanding of the processes affecting the recent polar field reversal is missing. This justifies additional studies of the peculiarities
of current solar cycle and its polar field reversals. In our
study, we use a combination of synoptic observations
and numerical modeling as described in detail in Sections 2–5. Our findings are discussed in Section 6.
2.
DESCRIPTION OF DATA
We use line-of-sight observations in the photospheric
spectral lines of FeI 630.15–630.25 nm taken by the
Vector Spectromagnetograph (VSM) of the synoptic
optical long-term investigation of the Sun (SOLIS) facility [Keller et al., 2003; Balasubramaniam and
Pevtsov, 2011] to investigate solar activity during the
declining phase of cycle 23 and current cycle 24 (August 2003 – present). For early cycles we employ similar data taken by the NASA/NSO Spectromagnetograph
(SPM) at the NSO/Kitt Peak Vacuum Telescope [Jones
et al., 1992] from February 1974 to August 2003.
The butterfly diagram shown in Figure 1 represent
the long-term variations of large-scale magnetic field
with time and latitude. It is formed from the daily fulldisk magnetograms as described in Petrie [2012]. Here
we summarize the method. For each sky image, all pixels with central meridian distance 30° or less are binned
into 180 equal-size bins in sine (latitude) and the average of each bin is taken. This process produces a 180element array in sine (latitude) for each image. We
combine these along a time axis to form the twodimensional space-time maps shown in the Figure.
In the construction of the butterfly diagrams, two
corrections are applied: The longitudinal field measurements are used to derive data for the radial field
component, and poorly observed and unobserved fields
near the poles are estimated so that data are provided for
all latitudes at all times. The radial field component is
derived from the longitudinal measurements by assuming
that the photospheric field is approximately radial, dividing by the cosine of the heliocentric angle ρ (the angle
between the line of sight and the local solar radial vector).
Because the solar rotation axis is tilted at an angle of
7.25° with respect to the ecliptic plane, the fields near
the solar poles are observed with very large viewing
angles and are not observed at all for six months at a
time. Also the noise level is inflated near the poles by
the radial field correction described above. For these
reasons, locations in the butterfly diagram nearest the
poles are filled using estimated values for these fields.
These estimates are based on a combination of direct
field measurements, annual averages of high-latitude
fields, and a polynomial fit across the pole for each image, calculated assuming symmetry about the pole. Finally the butterfly diagram is smoothed using a 27-day
boxcar filter. White vertical stripes correspond to missing observations.
3.
ACTIVITY AT THE END
OF CYCLE 23 AND BEGINNING
OF SOLAR CYCLE 24
The current cycle 24 started after a deep and prolonged
minimum which ended in late 2008 – early 2009 [Bertello
Инверсия магнитного поля Солнца в 24-м цикле
The reversal of the Sun’s magnetic field in cycle 24
5
et al., 2011]. During that minimum, the Sun’s polar magnetic flux was significantly reduced, compared to the previous three cycles, and the background (non-polar) magnetic fields were very weak (Figure 1). There was no overlap between low-latitude activity of the preceding cycle 23
(see Figure 1, years 2006–2008) and higher latitude sunspot activity of cycle 24 (Figure 1, years 2010–2011). The
earliest signs of cycle 24 activity can be identified at Carrington Rotation (CR) 2076, approximately at 40° N latitude near the head of black arrow No. 5 in Figure 1.
From cycle 20 to cycle 23, Figure 1 shows a pattern
of increasing gap between neighboring cycles as well as
the increasing length of periods between polar field reversals in each hemisphere. For example, for the northern pole, the periods between polar field reversals were
3701 days (cycles 21–22), 3771 days (cycles 22–23),
and 5191 days (cycles 23–24). For the southern pole,
there were 3991 days (cycles 21–22), 3141 days (cycles
22–23), and 5021 days (cycles 23–24), accordingly. While
at first glance it might appear that there is some correlation
between the period of polar field reversals and the length of
the following cycle, the statistics is very small; it could be
just a simple consequence that the length of solar cycle
together with the gap between cycles will approximately
define the periods between polar field reversals. The small
brown triangles mark the time of polar field reversals derived from WSO observations.
Figure 1 also demonstrates the uncertainty in determining the polar field reversals. Small brown triangles
at the top and bottom edges of color panel mark the location of polar field reversals derived from Wilcox Solar Observatory (WSO) observations. While in some
instances the location of triangles is in agreement with
transition from one polarity field to the other as shown
in the super synoptic map (e.g., сycles 21 and 23, in the
northern hemisphere, and cycle 21 in southern hemisphere), in other instances, the agreement is not very
good (e.g., сycles 22–24 in the southern hemisphere).
Such disagreement may reflect a specifics of supermaps
construction (e.g., averaging, or by the technique used
to fill the polar field gaps) as well as the interpretation
of direct observations of polar fields (e.g., smoothing
the polar field measurements and estimating the polar
fields for periods when either N or S poles are not observable from Earth).
The north-south asymmetry in magnetic activity can
be identified in all cycles shown in Figure 1, but it is
more pronounced in cycle 23. At the beginning of cycle 24,
the hemispheric asymmetry may appear switching to
favor the northern hemisphere (compare active regions
activity in two hemispheres in 2011–2014), but later
increase in sunspot activity in the southern hemisphere
swung the asymmetry back to the southern hemisphere
(Figure 1). The hemispheric asymmetry can be clearly
seeing in the sunspot activity (Figure 1, panels a, b). For
example, total area of sunspots in the northern hemisphere (AN) peaks around year 2000, and it declines to
its minimum in late 2006 (line plot at the top of Figure 1).
By comparison, the total sunspot area in the southern
hemisphere (AS) reaches maximum in year 2002, and
then it steady declines to its minimum late in 2008 (line
plot at the bottom of Figure 1).
The solar cycle minimum lasts from about mid-2007
till late-2009 in the northern hemisphere, and from mid
2008 till early 2010 in the southern hemisphere. In cycle
24, the sunspot activity appears peaking in late 2011–
2012 in the northern hemisphere, while sunspot activity
in the southern hemisphere exhibits a peak in 2014. It is
interesting to note that the cycle maxima in sunspot activity in two hemispheres were shifted by about two
years in cycle 23 (with activity in southern hemisphere
lasting longer). However, at the beginning of cycle 24,
the phase shift between the two hemispheres was only
about a few months (with the northern hemisphere leading in its activity). By the time of cycle 24 maximum,
the difference in cycle maxima between the two hemispheres is again about two years, with activity in the
southern hemisphere lasting longer.
Despite a relatively low amplitude in cycle 23, the
asynchronicity in sunspot activity between two hemispheres helped in maintaining a relatively high level of
magnetic activity during minimum of cycle 23. MuñozJaramillo et al. [2015] have shown that although the
minimum of cycle 23 was one of the lowest in recent
history, it did not reach the lowest possible limit because the activity in each hemisphere reached minimum
at different times. At the end of cycle 23, sunspot activity in the southern hemisphere lasted longer, as compared to the northern hemisphere.
In Figure 1b, inclined patterns show magnetic flux
transport from decaying activity complexes towards the
Sun’s poles. Zones of intense sunspot activity resulted
to extensive surges which reached the poles and led to
the polar field reversals [Mordvinov, Yazev, 2014; Sun
et al., 2015, Petrie, Ettinger, 2015; Petrie, 2015]. Black
arrows mark episodes of flux transport from decaying
active regions during the declining phase of cycle 23
and rising phase of cycle 24. To emphasize the appearance
of poleward surges, the magnetic flux is scaled between ±4
Gauss. With such scaling an unphysical negative-polarity
artifact appears prominent at the North Pole for 2015. It
looks comparable in strength to the polar fields generally,
but it is not. Our measurements indicate that the magnetic
flux in this polar area continues to be close to zero, with
mixed polarity but with a positive bias. The artefact vanished as soon as good September 2015 data became available (see Figure 17 [Petrie, 2015]).
Between about CR2045 through CR2070 (or for
about year and a half) sunspot activity was limited to the
southern hemisphere only. This extended activity may
helped the polar field in southern hemisphere to last
longer. Thus, for example, in addition to poleward surges of negative polarity magnetic field (e.g., No. 4 and 8
in Figure 1) that were working to reduce the positive
polarity flux in southern polar region, there were poleward
surges of positive polarity (e.g., No. 2, 6, and 10) that continued strengthening the existing polar field of previous
cycle. Similar behavior is observed in the northern hemisphere with surges of negative (No. 1, 5, and 9) and positive (No. 3, 7, 11) polarity field. Such sequential surges of
positive-negative polarity are not uncommon (see Figure 1,
years 1982–1986 southern hemisphere).
4.
ORIGIN OF POLEWARD SURGES
OF OPPOSITE POLARITY
Due to the preferred orientation of active regions
relative to the equator (Joy’s law), the following polarity magnetic field of dissipating active regions is trans-
A.В. Мордвинов, A.A. Певцов, Л. Бертелло, Г.Дж.Д. Петри A.V. Mordvinov, A.A. Pevtsov, L. Bertello, G.J.D. Petrie 6 Figure 1. Changes in sunspot areas in millionths of solar hemisphere for the northern (a) and southern (c) hemispheres. Evolution of the Sun’s magnetic fields from 1974 to 2015 (b). Blue/red halftones represent positive/negative polarity field. Numbered arrows mark position of poleward surges discussed in Section 4 ported poleward. According to Hale polarity rule, the active regions in northern hemisphere had negative (positive) trailing polarity in cycle 23 (24). The trailing polarity of active regions in the southern hemisphere was positive (negative) in cycle 23 (24). Thus, poleward surges No. 1, 7, and 11 (Figure 1b, northern hemisphere) and No. 2, 6, 12, and 14 (southern hemisphere) have polarity corresponding to normal Hale’s and Joy’s orientation of active regions in two cycles. Surges No. 3, 9, and 13 (Northern hemisphere) and No. 4, 8 and 10 (Southern hemisphere) have ‘abnormal’ polarity. To better understand the origin of each of these surges, we now provide a detailed description of their evolution. 4.1. Surge No. 10 Early indications of surge No. 10 development can be traced back to NOAA AR11089. This region was located in the southern hemisphere and had the leading flux of positive polarity (see, Figure 2). Thus, the magnetic field of this active region was oriented in agreement with the Hale polarity rule for solar cycle 24. However, by CR2100 (August 21, 2010 at central meridian) the tilt of the magnetic field of this region did not follow the Joy’s law. This non-Joy’s tilt was the result of a very specific evolution of active region. The region emerged from behind East limb on July 19–20, 2010 as a complex multi-sunspot region. The overall orientation of active region was in agreement with Joy’s law (leading polarity sunspots were located closer to the equator, and trailing polarity spots located father away from the equator, see Figure 2). As the region evolved, one of the sunspots of trailing polarity moved eastward from the main group, and dissipated rapidly. By July 23, this spot was reduced in size to a few small pores, which had completely vanished by mid-day July 24. The overall structure of active region got simplified, and by July 23, the active region could be best characterized as a typical bipolar region with two welldeveloped sunspots of opposite polarity and a few pores in between. The region’s tilt was in agreement with Joy’s law. After July 26, the sunspot of trailing polarity begins dissipating rapidly, and by early July 28, it is reduced to a few small pores. Then, in early July 28, a new bipolar region starts developing at the location of decaying flux of AR11089, and by July 29, this newly emerging flux appears as a bipolar group with small sunspots of leading and following polarity. The orientation of this region still follows the Joy’s law, by the tilt is smaller then the tilt of AR11089. By the time the region reaches the West limb (July 30–31), its leading polarity field combined the positive flux from its original (but significantly dissipated) leading sunspot and the leading polarity of newly emerged region. The trailing polarity is represented mostly by the flux of newly emerged region. As the result, the leading polarity flux is significantly larger in area as compared with the trailing flux. By its orientation, the magnetic flux now appears as having a non-Joy’s tilt, although in white light the active region still follows the Joy’s law in its orientation. One rotation later (CR2101), a new bipolar region developed at the exact location of dissipating remnants of AR11089. Leading and following polarity sunspots had a wide separation (about 15 degrees in longitude), and the region was oriented nearly
Инверсия магнитного поля Солнца в 24-м цикле
The reversal of the Sun’s magnetic field in cycle 24
7
Figure 2. Evolution of active region NOAA 11089 as seen in line-of-sight magnetograms (top) and broadband pseudocontinuum images (bottom) from SDO/HMI. White/black halftones correspond to magnetic field of positive/negative polarity.
Brown curve marks approximate location of magnetic neutral line. Letters P and N mark polarity (positive and negative) of leading and following parts of active region. Red oval outlines approximate location of new flux emergence at the tail of AR11089.
parallel to solar equator (possibly a very slight nonJoy’s orientation). Based on the appearance of magnetic
flux on sequential Carrington rotation maps, this complex evolution placed the leading polarity flux to higher
latitude and then the combined action of differential
rotation and meridional flow led to formation of a ‘tong’
of dissipating flux of positive polarity gradually transported towards southern polar region. The next solar
rotation (Figure 3b) shows dissipating remnants of active regions shown in Figure 2 developing a non-Joy’s
polarity orientation. The development of this surge continued as a new flux emerge in the same area further
strengthening the non-Joy’s orientation (Figure 3, c).
In addition to NOAA AR11089, development of active regions NOAA 11108 (CR2101, Sept. 22 2010,
Hale and Joy’s orientation), NOAA 11115 (CR2102,
Oct. 21, 2010, unipolar sunspot of positive polarity),
and NOAA 11126 (CR2103, Nov. 17, 2010, non-Hale
and non-Joy’s orientation) also contributed to formation
of poleward surge No. 10 although this contribution is
less clear. ARs 11108, 11115, and 11126 developed at
about the same latitudes (≈S30 deg), and their rotation
rate was about 4–5 % slower than typical rotation rate
for this latitude. However, three regions developed in
longitudes progressively shifted much farther eastward
from previous rotation to consider them as part of the
A.В. Мордвинов, A.A. Певцов, Л. Бертелло, Г.Дж.Д. Петри A.V. Mordvinov, A.A. Pevtsov, L. Bertello, G.J.D. Petrie 8 Figure 3. Evolution of magnetic flux at the source of poleward surge No. 10 over three solar rotations. Panel (a) shows portion of full disk VSM/SOLIS longitudinal magnetogram taken 24 July 2010, 19:21:41 UT, (b) — 21 August 2010, 21:45:05 UT, and (c) — 17 September 2010, 16:26:30 UT same center of activity (for example, a difference between location of AR11108 extrapolated to AR111026 time and actual location of this region is larger than 120 deg in longitude). The development of these three regions strengthens magnetic field of positive polarity in this general area, and this flux eventually contributes to tail of positive polarity that originated from NOAA AR10089. 4.2. Surge No. 13 This surge seems to develop starting from active region NOAA11417 (CR2120). There was a small coronal hole located south-west of that active region. On the next rotation, two new active regions (NOAA11432 and NOAA11433) developed east of decaying magnetic flux of AR11417. AR11432 was normal Hale’s and Joy’s region, but AR11433 was mostly unipolar (negative) polarity spot. Interaction between ARs 11432 and 11433 led to near dissipation of positive polarity field, and it strengthen the negative polarity flux. Coronal hole grew and extended to the west and north of these two ARs. Over the next several rotations, new active regions developed and dissipated to the east from this area, but the presence of the coronal hole helped retaining negative polarity field against dissipation. The emergence of active regions in this area was such that even development of a large active region 11476 in CR2123 did not change the balance of magnetic flux. It appears that the overall evolution led to positive field getting more fragmented and dispersed, while negative polarity field survived and contributed to the growth of area that still had coronal hole on some part of it. This evolution continues even after the coronal hole disappeared, and by CR2137-2139, a large area of negative polarity had extended to high latitudes, and it was later transported to the northern polar region. 4.3. Surges No. 4, 3, and 9 Surge No. 9 originated in a large active region of non-Joy’s orientation. The evolution of this surge was studied in detail (and modeled via a flux-transport modeling) by Yeates et al. [2015]. The reader is referred to this article for additional details about this surge. The origin of the poleward surge 4, which starts around CR2138 cannot be traced to a single active region or activity complex. Instead, it appears to be the result of evolution of several active regions spread over a broad range of longitudes. Based on visual inspection of daily magnetograms taken during CR2137-38, it appears that the number of regions during this period of time show non-Joy’s orientation in the southern hemisphere. As these regions evolve, the leading polarity field is transported to higher latitudes. Collectively, the surges from individual decaying regions contribute to what we see in supersynoptic map as poleward surge No. 4. The origin of surge No. 3 is similar to surge No. 4: it also originated as the result of collective action of several active regions, and the solar activity that took place around the start-time of that surge also exhibits an enhancement the fraction of active regions with non-Joy’s orientation. To verify the significance of active regions with non-Joy’s orientation in development of poleward surges of opposite polarity, we plotted a distribution of active region tilts. Data for this plot were taken from the data set described by Györi et al. [2011]. To study evolution of zonal magnetic flux in more detail we analyzed synoptic maps composed of highresolution SOLIS/VSM measurements. Figures 4, a, c show changes in sunspot areas in the northern and southern hemispheres. Figure 4, b shows a supersynoptic map composed of longitude averaged magnetic flux (in redto-blue palette). Small gaps in these measurements were filled with the use of SDO/HMI data. The zonal flux distribution is denoised using a wavelet decomposition
Инверсия магнитного поля Солнца в 24-м цикле
The reversal of the Sun’s magnetic field in cycle 24
9
Figure 4. Changes in sunspot areas for the northern (a) and southern (c) hemispheres. Time-latitude evolution of zonal magnetic flux is shown in red-to-blue (b); zones of intense sunspot activity and domains of non-Joy’s active region tilt are overplotted
in black and green colors
technique. This diagram shows global rearrangements
of solar magnetic flux in relation to sunspot activity in
the current cycle. Zones of intense sunspot activity are
shown in black (>70 millionths of the solar hemisphere). As a rule, surges of trailing polarities (marked
with solid arrows) originated after decay of long-living
activity complexes.
A location of active regions that disobey the Joy’s
law (colored in green) overplotted on the supersynoptic
map of magnetic flux. It appears that that the active regions deviating from Joy’s law are not located randomly
in latitude and time; there are large-scale patterns in
their distribution. For example, in 2013–2014, majority
of active regions in near-equatorial area had non-Joy’s
orientation (see large green area around years 2013 and
2014). Coherent areas of non-Joy’s tilts also present in
low latitude regions in late-2008-early 2009. The existence of such coherent areas contradicts a conventional
explanation that non-Joy’s tilts are the result of buffetings of magnetic flux tubes rising through the turbulent
convection zone.
For most poleward surges discussed in Section 4,
there is an area of non-Joy’s tilt at the time and latitude
when the surge had originated (see areas colored in
green near the beginning of poleward surges No. 3, 9,
13 (northern hemisphere) and surges No. 4 and 6
(Southern hemisphere). Surge No. 10 does not show
such association, which agrees with the description of
evolution of active region tilt in that area. The presence
of areas with non-Joy’s tilt at the beginning of most
surges indirectly supports the notion that majority of
poleward surges of opposite polarity field originates
from active regions with non-Joy’s tilt. These surges are
marked with dashed arrows.
4.4.
Surge No. 5
This surge that originates in near equatorial region
represents example when the magnetic field (of active
region’s leading polarity) crosses the equator, and is
gradually transported to the polar areas of opposite hemisphere. The magnetic flux in this surge was quite weak,
and it is not clear if this flux was eventually transported
all the way to the northern polar region. This example
suggests an interesting scenario that even if the sunspot
activity is limited to a single hemisphere, the polar field
in both hemispheres could still be created as it is the
case for ‘normal’ cycles. The validity of such scenario
depends on the interplay between the lifetime of decaying flux and the time it takes to transport it across equator to other hemisphere.
To further investigate this scenario for a crossequatorial transport of magnetic flux, we employed a simplified flux-transport model previously used by us to study
the effects of sunspot emergence and the dissipation on
detectability of solar differential rotation from sun-as-a-star
observations. For additional details about this model, see
Bertello, Pevtsov, and Pietarila [2012]. In the model, we
imitated the active regions using pairs of bipoles of differ
A.В. Мордвинов, A.A. Певцов, Л. Бертелло, Г.Дж.Д. Петри
A.V. Mordvinov, A.A. Pevtsov, L. Bertello, G.J.D. Petrie
10
ent size. The bipoles were ‘emerged’ at random longitudes
within the latitudinal range of about 5 degrees centered at
20 degrees of latitude in the southern hemisphere. All bipoles had fixed tilt relative to the equator, and their polarity
orientation corresponded to the Hale-Nicholson polarity
rule for the southern hemisphere in cycle 23.
The magnetic fluxes of bipoles were varied randomly within a preset range of fluxes. Test-runs of this
model indicated that some of the magnetic flux of leading polarity can be transported across the solar equator
as the result of active region growth (leading polarity is
moving away from the center of emerging activity region in westward and the equatorward directions, while
at the same time, the following polarity is moving slightly
eastward and poleward). The diffusion of magnetic field
also contributes to the cross-equatorial transport of magnetic flux. The simulations also showed that diffusion rate is
important in defining if any flux will survive as a coherent
structure by the time it is transported to the pole. Our findings from this model simulations are in agreement with
Cameron et al. [2013] results.
Running the model over the period of time corresponding to about 5 years, we were able to see a buildup of magnetic flux of opposite polarity in the northern
and the southern polar areas even though the sunspot
activity was limited to the southern hemisphere. Switching the polarity orientation of bipoles (Hale-Nicholson
polarity rule) from one cycle to the other, led to the reversal of polar fields in both hemispheres, as it would
for normal cycles (with the sunspot activity in both
hemispheres). As other example of transequatorial flux
transport we refer the reader to Pevtsov and Abramenko
[2010] who reported a case, when a coronal hole originating as an extension of a south polar coronal hole got
disconnected and was gradually transported to the polar
area in the northern hemisphere.
In the next section we study changes in cycleintegrated magnetic flux taking into account its prognostic importance. The polar field buildup quantifies the
efficiency of magnetic flux transport and characterizes
its north-south asymmetry in the current cycle.
5.
CYCLE-INTEGRATED
MAGNETIC FLUX
Solar and stellar dynamo are driven by convective
and shear flows in solar convective zone. If the cycleaverage properties of such flows do not change significantly from one cycle to the other, one could speculate
that the total magnetic flux produced during each solar
cycle should also show no significant variation from one
cycle to the other. In other words, the total magnetic
flux produced in cycle n, should be about the same as in
cycle n–1 or cycle n+1. If such cycle-integrated fluxinvariance existed, it would reveal itself in a correlation
between the length of solar cycle and its amplitude, i.e.,
high-amplitude cycles would tend to be shorter in duration, while the opposite would be true for cycles with
low amplitude. In fact, the international sunspot data do
show a presence of such correlation albeit with a significant scatter [e.g., see Figure 5 in Petrovay, 2010]. Linear fit to the data corresponds to
Acycle = (339.638 ± 85.273) – (20.988 ∓ 7.718) Lcycle,
where Lcycle is cycle length (years) and Acycle is its ampli
tude (units of the international sunspot index). If one
assumes that cycle 24 had reached its maximum, the
fitted linear function can be used to estimate the length
of cycle 24 as 12.3 years, which suggests that cycle 24
will reach its minimum in early 2021.
Based on direct measurements of solar magnetic
field by full disk longitudinal magnetographs operated
by the National Solar Observatory (the 512 channel
Diode Array Magnetograph (NSO-512) at the National
Solar
Observatory/Kitt
Peak
Vacuum
Telescope
(NSO/KPVT, 1974–1992), the NASA/NSO Spectromagnetograph at NSO/KPVT (SPM, 1992–2002), and
the Vector Stokes Magnetograph on Synoptic Optical
Long-term Investigations of the Sun (VSM/SOLIS,
2003-present), we find that the total flux observed in
cycles 21, 22, and 23 is about the same. Difference in
total cycle-integrated flux in cycles 21 and 22 is about
–7.5 % and in cycles 22 and 23 is about 1.7 %. Slightly
larger difference in pair of cycles 21–22 is due to lack
of observations from the first two years of cycle 21.
Thus, the direct magnetic field data also support the
notion that the cycle-integrated magnetic flux on the
Sun does not change significantly from one cycle to the
other. However, while this apparent agreement in total
cycle-integrated magnetic flux is intriguing, the speculation about the invariance of the cycle-integrated needs
further confirmation, e.g., via direct dynamo modeling
and analysis of other data sets such as WSO.
The integrated measurements of polar fields from
the Wilcox Solar Observatory (WSO) and the
SOLIS/VSM are shown in Figure 5. The data for this
plot were computed following the recipe provided at the
SOLIS web site at solis.nso.edu/0/vsm/vsm plrfield.html. The WSO data correspond to the line-ofsight flux, while the VSM magnetic field measurements
were converted to radial flux (normal to the local solar
surface) under the assumption that the photospheric
field is vertical. This and a significant difference in the
observational parameters between the two measurements can explain the difference in amplitudes of polar
flux from these two instruments.
Table 1 provides approximate dates of polar field
reversals derived from these two plots. Both WSO and
VSM data were filtered using a low-bandpass filter to
compensate for annual variations of observed polar
field, which occur due to change in visibility of two
poles with Earth orbital position. From these integrated
data, it appears that the magnetic field in the southern
hemisphere at 60–70° latitudinal range reversed its polarity in mid-2013. At higher latitudes (65–75°), the
reversal occurred in late 2013.
The polarity reversal in the northern hemisphere is
less clear: both WSO and VSM data indicate multiple
reversals that occurred in mid-2012, mid-2014 and perhaps, late 2014 – early 2015. Since the first reversal the
polar field in the northern hemisphere remained weak,
and it was practically fluctuating around zero. Only very
recently (CR2161), with the increase in sunspot activity
in the northern hemisphere we finally see a trend suggesting that the northern polar field is beginning to increase in amplitude (Figure 5, far right side of
SOLIS/VSM plot). We see this behavior to be the result
of a specific pattern of activity in the northern hemisphere.
Инверсия магнитного поля Солнца в 24-м цикле
The reversal of the Sun’s magnetic field in cycle 24
11
Figure 5. Comparison between SOLIS/VSM radial (top) and Wilcox LOS filtered polar measurements (bottom). Note the
different scales. Northern hemisphere measurements are shown in blue, while the southern values are shown in red. For the case
of SOLIS/VSM, measurements are shown for two different latitude bands: 60° to 70° (solid lines) and 65° to 75° (dashed lines).
The times of polar reversals are given in Table 1. The most recent plot of polar fields can be found at solis.nso.edu
Time of polar reversals from Wilcox and VSM photospheric measurements
Wilcox SOLIS/VSM
60–70° 65–75°
North
South
North
South
North
South
1st
06.15.2012
06.26.2013
05.14.2012
05.10.2013
12.31.2012
10.28.2013
2nd
03.03.2014
03.09.2014
05.19.2014
3rd
10.15.2014
02.15.2015
03.13.2015
6.
DISCUSSION AND SUMMARY
The recent development of the solar activity in the
current cycle made it evident that the north-south
asymmetry of sunspot activity resulted in asynchronous
reversal of the Sun’s polar field. We demonstrate the
well-defined surges of trailing polarities that reached the
Sun’s poles and led to the polar field reversals. We give
concrete examples to demonstrate that the regular polarfield build-up was disturbed by surges of leading polarities
resulted from violations of Joy’s law at lower latitudes.
During the declining phase of cycles 21 and 22, the
dissipating field of active regions continued strengthening the polar field. In these cycles, the decline in polar
field is clearly associated with a start of the next cycles.
In cycle 23, however, the polar magnetic field in the
northern hemisphere begun declining even before active
regions of a new cycle 24 had emerged in high latitudes.
This decline can be associated with poleward surge No.
3 (Figure 1), which originated from location of several
small active regions with non-Joy’s tilt. On the other
hand, the polar field in the southern hemisphere got a
slight boost, from surge No. 10. While this surge was
eventually the result of non-Joy’s orientation of corresponding magnetic flux, this abnormal orientation developed in course of a peculiar evolution of magnetic
flux in this active region as well as additional flux
emergence in this area in the following rotations.
In fact, Petrie and Ettinger [2015] found that poleward surges are almost always due to more than one
region, particularly the important surges. Generally the
high latitudes are occupied by decayed flux of both polarities from various regions at different stages of evolution. A surge develops when one polarity dominates
overall, and sometimes, but not always, the dominant
flux can be easily traced back to one, two, or a few major regions. After the first reversal, magnetic field in the
Northern hemisphere had experienced a brief reversal to
previous polarity state, which can be contributed to
poleward surge No. 13. This surge has also developed
as the result of a peculiar evolution and interaction be