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N W Watkins - One of the best experts on this subject based on the ideXlab platform.
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Overlapping Magnetic Activity Cycles and the Sunspot Number: Forecasting Sunspot Cycle 25 Amplitude.
arXiv: Solar and Stellar Astrophysics, 2020Co-Authors: Scott W Mcintosh, Robert J Leamon, S C Chapman, Ricky Egeland, N W WatkinsAbstract:The Sun exhibits a well-observed modulation in the number of Sunspots over a period of about 11 years. From the dawn of modern observational astronomy Sunspots have presented a challenge to understanding - their quasi-periodic variation in number, first noted 160 years ago, stimulates community-wide interest to this day. A large number of techniques are able to explain the temporal landmarks, (geometric) shape, and amplitude of Sunspot "Cycles," however forecasting these features accurately in advance remains elusive. Recent observationally-motivated studies have illustrated a relationship between the Sun's 22-year (Hale) magnetic Cycle and the production of the Sunspot Cycle landmarks and patterns, but not the amplitude of the Cycle. Using (discrete) Hilbert transforms on 270 years of (monthly) Sunspot numbers to robustly identify the so-called "termination"' events, landmarks marking the start and end of Sunspot and magnetic activity Cycles, we extract a relationship between the temporal spacing of terminators and the magnitude of Sunspot Cycles. Given this relationship and our prediction of a terminator event in 2020, we deduce that Sunspot Cycle 25 will have a magnitude that rivals the top few since records began. This outcome would be in stark contrast to the community consensus estimate of Sunspot Cycle 25 magnitude.
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timing terminators forecasting Sunspot Cycle 25 onset
Solar Physics, 2020Co-Authors: Robert J Leamon, Scott W Mcintosh, S C Chapman, N W WatkinsAbstract:Recent research has demonstrated the existence of a new type of solar event, the “terminator.” Unlike the Sun’s signature events, flares and coronal mass ejections, the terminator most likely originates in the solar interior, at or near the tachocline. The terminator signals the end of a magnetic activity Cycle at the Sun’s equator and the start of a Sunspot Cycle at mid-latitudes. Observations indicate that the time difference between these events is very short, less than a solar rotation, in the context of the Sunspot Cycle. As the (definitive) start and end point of solar activity Cycles the precise timing of terminators should permit new investigations into the meteorology of our star’s atmosphere. In this article we use a standard method in signal processing, the Hilbert transform, to identify a mathematically robust signature of terminators in Sunspot records and in radiative proxies. Using a linear extrapolation of the Hilbert phase of the Sunspot number and F10.7 cm solar radio flux time series we can achieve higher fidelity historical terminator timing than previous estimates have permitted. Further, this method presents a unique opportunity to project, from analysis of Sunspot data, when the next terminator will occur, May 2020 ($+4$, −1.5 months), and trigger the growth of Sunspot Cycle 25.
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timing terminators forecasting Sunspot Cycle 25 onset
arXiv: Solar and Stellar Astrophysics, 2019Co-Authors: Robert J Leamon, Scott W Mcintosh, S C Chapman, N W WatkinsAbstract:Recent research has demonstrated the existence of a new type of solar event, the "terminator". Unlike the Sun's signature events: flares and Coronal Mass Ejections the terminator takes place in the solar interior. The terminator signals the end of a magnetic activity Cycle at the Sun's equator and the start of a Sunspot Cycle at mid latitudes. Observations indicate that the time difference between these events is very short, less than a solar rotation, in the context of the Sunspot Cycle. As the (definitive) start and end point of solar activity Cycles the precise timing of terminators should permit new investigations into the meteorology of our star's atmosphere. In this letter we use a standard method in signal processing, the Hilbert transform, to identify a mathematically robust signature of terminators in Sunspot records and in radiative proxies. Using this technique we can achieve higher fidelity terminator timing than previous estimates have permitted. Further, this method presents a unique opportunity to project when the next terminator will occur, 2020.33(\pm0.16), and trigger the growth of Sunspot Cycle 25.
David H. Hathaway - One of the best experts on this subject based on the ideXlab platform.
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the solar meridional circulation and Sunspot Cycle variability
Journal of Geophysical Research, 2014Co-Authors: David H. Hathaway, Lisa UptonAbstract:We have measured the meridional motions of the magnetic elements in the Sun's surface layers since 1996 and find systematic and substantial variations. In general the meridional flow speed is fast at Cycle minima and slow at Cycle maxima. We find that these systematic variations are characterized by a weakening of the meridional flow on the poleward sides of the active (Sunspot) latitudes. This can be interpreted as an inflow toward the Sunspot zones superimposed on a more general poleward meridional flow profile. We also find variations in the meridional flow which vary from Cycle to Cycle. The meridional flow was slower at both the minimum and maximum of Cycle 23 compared to similar phases of Cycles 21, 22, and 24. Models of the magnetic flux transport by a variable meridional flow suggest that it can significantly modulate the size and timing of the following Sunspot Cycle through its impact on the Sun's polar magnetic fields. We suggest that the meridional flow variations observed in Cycle 23 contributed to the weak polar fields at the end of the Cycle which then produced a weak Cycle 24 and the extraordinary Cycle 23/24 minimum.
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On the Relationship Between Spotless Days and the Sunspot Cycle: A Supplement
2013Co-Authors: Robert M. Wilson, David H. HathawayAbstract:This study provides supplemental material to an earlier study concerning the relationship between spotless days and the Sunspot Cycle. Our previous study, Technical Publication (TP)-2005-213608 determined the timing and size of Sunspot minimum and maximum for the new Sunspot Cycle, relative to the occurrence of the first spotless day during the declining phase of the old Sunspot Cycle and the last spotless day during the rising portion of the new Cycle. Because the number of spotless days (NSD) rapidly increases as the Cycle nears Sunspot minimum and rapidly decreases thereafter, the size and timing of Sunspot minimum and maximum might be more accurately determined using a higher threshold for comparison, rather than using the first and last spotless day occurrences. It is this aspect that is investigated more thoroughly in this TP.
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Meridional Flow Variations in Cycles 23 and 24: Active Latitude Control of Sunspot Cycle Amplitudes
2013Co-Authors: David H. Hathaway, Lisa UptonAbstract:We have measured the meridional motions of magnetic elements observed in the photosphere over Sunspot Cycles 23 and 24 using magnetograms from SOHO/MDI and SDO/HMI. Our measurements confirm the finding of Komm, Howard, and Harvey (1993) that the poleward meridional flow weakens at Cycle maxima. Our high spatial and temporal resolution analyses show that this variation is in the form of a superimposed inflow toward the active latitudes. This inflow is weaker in Cycle 24 when compared to the inflow in 23, the stronger Cycle. This systematic modulation of the meridional flow should also modulate the amplitude of the following Sunspot Cycle through its influence on the Sun's polar fields. The observational evidence and the theoretical consequences (similar to those of Cameron and Schussler (2012)) will be described.
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Predicting the Sunspot Cycle
2009Co-Authors: David H. HathawayAbstract:The 11-year Sunspot Cycle was discovered by an amateur astronomer in 1844. Visual and photographic observations of Sunspots have been made by both amateurs and professionals over the last 400 years. These observations provide key statistical information about the Sunspot Cycle that do allow for predictions of future activity. However, Sunspots and the Sunspot Cycle are magnetic in nature. For the last 100 years these magnetic measurements have been acquired and used exclusively by professional astronomers to gain new information about the nature of the solar activity Cycle. Recently, magnetic dynamo models have evolved to the stage where they can assimilate past data and provide predictions. With the advent of the Internet and open data policies, amateurs now have equal access to the same data used by professionals and equal opportunities to contribute (but, alas, without pay). This talk will describe some of the more useful prediction techniques and reveal what they say about the intensity of the upcoming Sunspot Cycle.
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An Examination of Selected Geomagnetic Indices in Relation to the Sunspot Cycle
2006Co-Authors: Robert M. Wilson, David H. HathawayAbstract:Previous studies have shown geomagnetic indices to be useful for providing early estimates for the size of the following Sunspot Cycle several years in advance. Examined this study are various precursor methods for predicting the minimum and maximum amplitude of the following Sunspot Cycle, these precursors based on the aa and Ap geomagnetic indices and the number of disturbed days (NDD), days when the daily Ap index equaled or exceeded 25. Also examined is the yearly peak of the daily Ap index (Apmax), the number of days when Ap greater than or equal to 100, cyclic averages of Sunspot number R, aa, Ap, NDD, and the number of sudden storm commencements (NSSC), as well the cyclic sums of NDD and NSSC. The analysis yields 90-percent prediction intervals for both the minimum and maximum amplitudes for Cycle 24, the next Sunspot Cycle. In terms of yearly averages, the best regressions give Rmin = 9.8+/-2.9 and Rmax = 153.8+/-24.7, equivalent to Rm = 8.8+/-2.8 and RM = 159+/-5.5, based on the 12-mo moving average (or smoothed monthly mean Sunspot number). Hence, Cycle 24 is expected to be above average in size, similar to Cycles 21 and 22, producing more than 300 sudden storm commencements and more than 560 disturbed days, of which about 25 will be Ap greater than or equal to 100. On the basis of annual averages, the Sunspot minimum year for Cycle 24 will be either 2006 or 2007.
H. S. Ahluwalia - One of the best experts on this subject based on the ideXlab platform.
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Sunspot Cycle 23 descent to an unusual minimum and forecasts for Cycle 24 activity
Advances in Space Research, 2012Co-Authors: H. S. Ahluwalia, Jason JackiewiczAbstract:Abstract The decay phase of the Sunspot Cycle 23 exhibited two unusual features. First, it lasted too long. Second, the interplanetary magnetic field intensity at earth orbit reached the lowest value since in situ measurements in space began in October 1963. These physical anomalies significantly altered the early forecasts for the Sunspot activity parameters for Cycle 24, made by several colleagues. We note that there was a significant change in the solar behavior during Cycle 22. We discuss the observed trends and their effect on our empirical solar activity forecast technique, leading to our prediction for Cycle 24 parameters; Cycle 24 will be only half as active as Cycle 23, reaching its peak in May 2013. We speculate on the possible implications of this outcome on future earth climate change and the ensuing socio-economic consequences.
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Sunspot Cycle 24 and the advent of dalton like minimum
Advances in Astronomy, 2012Co-Authors: H. S. Ahluwalia, R.c. YgbuhayAbstract:Ahluwalia and Jackiewicz (2011) have predicted that Sunspot Cycle 24 will be only half as active as Cycle 23, reaching its peak in May 2013±6 months. Here, we discuss the timeline for Cycle 24 since its onset in December, 2008 and compare it to the timelines for the last ten Cycles (14 to 23) of the 20th century; Cycle 24 is rising the slowest. We speculate that Cycle 24 may herald the onset of a Dalton-like minimum in the 21st century. The implications of this outcome on global temperature change and ensuing socioeconomic and political scenarios are discussed, on the basis of the historical record.
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galactic cosmic ray modulation for Sunspot Cycle 23
Advances in Space Research, 2010Co-Authors: H. S. Ahluwalia, R.c. Ygbuhay, C Lopate, M L DuldigAbstract:Abstract We present a study of the galactic cosmic ray modulation for Sunspot Cycle 23. We use the monthly and the annual mean hourly, pressure corrected, data from neutron monitors of the global network (monthly rate is calculated as the average of the hourly pressure corrected values). We draw attention to an asymmetry in the galactic cosmic ray (GCR) recovery during odd and even Cycles for the monthly mean hourly rate data. For over half a century of observations, we find that the recovery for the odd Cycles is to a higher level than for the even Cycles. Qualitatively the effect is ascribed to charged particle drifts in inhomogeneous interplanetary magnetic field. Even so it has not been possible to arrive at a quantitative, self-consistent, explanation in terms of drifts at higher and lower GCR rigidities. We also study the rigidity dependence of the amplitude of 11-year modulation over a wide range (1–200 GV) of GCR spectrum; it is a power law in rigidity with an exponent −1.22. We discuss the implication of these findings on quasi-linear diffusion theories of modulation. We reflect on GCR recovery pattern for 2006–2009.
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Current Forecast for Sunspot Cycle 24 Parameters
2010Co-Authors: H. S. Ahluwalia, R.c. YgbuhayAbstract:Our prediction for the development of Sunspot Cycle 23 activity came true; one of the very few to have attained this status. We use the 3‐Cycle quasi‐periodicity observed in the planetary index Ap. We improve our method by including data for 150 years and draw inferences as to what to expect for the development phase of Cycle 24. Our forecast for the smoothed Sunspot number at Cycle 24 peak 78±5 in June 2013; the possibility that next three Cycles may be progressively less active cannot be ruled out; the trend may possibly continue for the rest of the 21st century.
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status of galactic cosmic ray recovery from Sunspot Cycle 23 modulation
TWELFTH INTERNATIONAL SOLAR WIND CONFERENCE, 2010Co-Authors: H. S. Ahluwalia, R.c. YgbuhayAbstract:Sunspot Cycle 23 is turning out to be longer than Cycle 20. Magnetic field measurements at Wilcox Solar Observatory indicate that solar polar field strength for Cycle 23 is ∼50% lower than for previous three Sunspot Cycles; the flux of the open magnetic field lines at earth orbit is at its lowest level since in situ measurements began in 1963. During the recovery phase of Cycle 23 the structure of the heliosphere is significantly different from that observed for Cycles 21 and 22; heliospheric current sheet has not flattened yet. Not surprisingly, we find that galactic cosmic ray recovery at earth orbit has reached the highest level ever observed, since continuous monitoring began by global network of neutron monitors in 1951. We show that neutron monitor rate increases for 2006–2009 are linearly correlated with the monotonic decrease in magnetic intensity at earth orbit. We conclude that normal physical processes are operative in the heliosphere during this time period.
Robert J Leamon - One of the best experts on this subject based on the ideXlab platform.
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Overlapping Magnetic Activity Cycles and the Sunspot Number: Forecasting Sunspot Cycle 25 Amplitude.
arXiv: Solar and Stellar Astrophysics, 2020Co-Authors: Scott W Mcintosh, Robert J Leamon, S C Chapman, Ricky Egeland, N W WatkinsAbstract:The Sun exhibits a well-observed modulation in the number of Sunspots over a period of about 11 years. From the dawn of modern observational astronomy Sunspots have presented a challenge to understanding - their quasi-periodic variation in number, first noted 160 years ago, stimulates community-wide interest to this day. A large number of techniques are able to explain the temporal landmarks, (geometric) shape, and amplitude of Sunspot "Cycles," however forecasting these features accurately in advance remains elusive. Recent observationally-motivated studies have illustrated a relationship between the Sun's 22-year (Hale) magnetic Cycle and the production of the Sunspot Cycle landmarks and patterns, but not the amplitude of the Cycle. Using (discrete) Hilbert transforms on 270 years of (monthly) Sunspot numbers to robustly identify the so-called "termination"' events, landmarks marking the start and end of Sunspot and magnetic activity Cycles, we extract a relationship between the temporal spacing of terminators and the magnitude of Sunspot Cycles. Given this relationship and our prediction of a terminator event in 2020, we deduce that Sunspot Cycle 25 will have a magnitude that rivals the top few since records began. This outcome would be in stark contrast to the community consensus estimate of Sunspot Cycle 25 magnitude.
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timing terminators forecasting Sunspot Cycle 25 onset
Solar Physics, 2020Co-Authors: Robert J Leamon, Scott W Mcintosh, S C Chapman, N W WatkinsAbstract:Recent research has demonstrated the existence of a new type of solar event, the “terminator.” Unlike the Sun’s signature events, flares and coronal mass ejections, the terminator most likely originates in the solar interior, at or near the tachocline. The terminator signals the end of a magnetic activity Cycle at the Sun’s equator and the start of a Sunspot Cycle at mid-latitudes. Observations indicate that the time difference between these events is very short, less than a solar rotation, in the context of the Sunspot Cycle. As the (definitive) start and end point of solar activity Cycles the precise timing of terminators should permit new investigations into the meteorology of our star’s atmosphere. In this article we use a standard method in signal processing, the Hilbert transform, to identify a mathematically robust signature of terminators in Sunspot records and in radiative proxies. Using a linear extrapolation of the Hilbert phase of the Sunspot number and F10.7 cm solar radio flux time series we can achieve higher fidelity historical terminator timing than previous estimates have permitted. Further, this method presents a unique opportunity to project, from analysis of Sunspot data, when the next terminator will occur, May 2020 ($+4$, −1.5 months), and trigger the growth of Sunspot Cycle 25.
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timing terminators forecasting Sunspot Cycle 25 onset
arXiv: Solar and Stellar Astrophysics, 2019Co-Authors: Robert J Leamon, Scott W Mcintosh, S C Chapman, N W WatkinsAbstract:Recent research has demonstrated the existence of a new type of solar event, the "terminator". Unlike the Sun's signature events: flares and Coronal Mass Ejections the terminator takes place in the solar interior. The terminator signals the end of a magnetic activity Cycle at the Sun's equator and the start of a Sunspot Cycle at mid latitudes. Observations indicate that the time difference between these events is very short, less than a solar rotation, in the context of the Sunspot Cycle. As the (definitive) start and end point of solar activity Cycles the precise timing of terminators should permit new investigations into the meteorology of our star's atmosphere. In this letter we use a standard method in signal processing, the Hilbert transform, to identify a mathematically robust signature of terminators in Sunspot records and in radiative proxies. Using this technique we can achieve higher fidelity terminator timing than previous estimates have permitted. Further, this method presents a unique opportunity to project when the next terminator will occur, 2020.33(\pm0.16), and trigger the growth of Sunspot Cycle 25.
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deciphering solar magnetic activity i on the relationship between the Sunspot Cycle and the evolution of small magnetic features
The Astrophysical Journal, 2014Co-Authors: Scott W Mcintosh, Robert J Leamon, Xin Wang, Alisdair R Davey, R Howe, Larisza D Krista, A Malanushenko, Robert S Markel, J CirtainAbstract:Sunspots are a canonical marker of the Sun's internal magnetic field which flips polarity every ~22 yr. The principal variation of Sunspots, an ~11 yr variation, modulates the amount of the magnetic field that pierces the solar surface and drives significant variations in our star's radiative, particulate, and eruptive output over that period. This paper presents observations from the Solar and Heliospheric Observatory and Solar Dynamics Observatory indicating that the 11 yr Sunspot variation is intrinsically tied to the spatio-temporal overlap of the activity bands belonging to the 22 yr magnetic activity Cycle. Using a systematic analysis of ubiquitous coronal brightpoints and the magnetic scale on which they appear to form, we show that the landmarks of Sunspot Cycle 23 can be explained by considering the evolution and interaction of the overlapping activity bands of the longer-scale variability.
Dibyendu Nandy - One of the best experts on this subject based on the ideXlab platform.
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A model-free, data-based forecast for Sunspot Cycle 25
arXiv: Solar and Stellar Astrophysics, 2020Co-Authors: Aleix Espuña-fontcuberta, Saikat Chatterjee, Dhrubaditya Mitra, Dibyendu NandyAbstract:The dynamic activity of the Sun, governed by its Cycle of Sunspots -- strongly magnetized regions that are observed on its surface -- modulate our solar system space environment creating space weather. Severe space weather leads to disruptions in satellite operations, telecommunications, electric power grids and air-traffic on polar routes. Forecasting the Cycle of Sunspots, however, has remained a challenging problem. We use reservoir computing -- a model-free, neural--network based machine-learning technique -- to forecast the upcoming solar Cycle, Sunspot Cycle 25. The standard algorithm forecasts that solar Cycle 25 is going to last about ten years, the maxima is going to appear in the year 2024 and the maximum number of Sunspots is going to be 113 ($\pm15$). We also develop a novel variation of the standard algorithm whose forecasts for duration and peak timing matches that of the standard algorithm, but whose peak amplitude forecast is 124 ($\pm2$) -- within the upper bound of the standard reservoir computing algorithm. We conclude that Sunspot Cycle 25 is likely to be a weak, lower than average solar Cycle, somewhat similar in strength to Sunspot Cycle 24.
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Hemispheric asymmetry in meridional flow and the Sunspot Cycle
Monthly Notices of the Royal Astronomical Society, 2019Co-Authors: B. Lekshmi, Dibyendu Nandy, H. M. AntiaAbstract:ABSTRACT Magnetohydrodynamic dynamo modelling shows that the large-scale solar meridional plasma flow plays an important role in governing the dynamics of the Sunspot Cycle. Observations indicate that meridional flow velocities at each solar latitude and depth vary over time and are asymmetric across the equator. Here, using helioseismic observations we explore the temporal variation in the hemispherical asymmetry of near-surface residual (time-varying) component of the Sun’s meridional flow velocity. The meridional flow velocities obtained from Global Oscillation Network Group (GONG) and Helioseismic and Magnetic Imager (HMI) onboard Solar Dynamics Observatory (SDO) ring-diagram pipelines are used in this work. Our data set covers the declining phase of Cycle 23 and Cycle 24 (from July 2001 till December 2018) and the flow velocities are poleward for the observed depth range. We observe a time delayed anticorrelation between the hemispherical asymmetry in near-surface meridional flow velocities and the Sunspot Cycle quantified in terms of magnetic flux and Sunspot number. Interestingly, asymmetry in meridional flow velocity precedes the asymmetry in Sunspot Cycle by 3.1–3.5 yr. We propose that meridional flow asymmetry is a precursor of asymmetry in hemispherical Cycle strength. The symmetric component of meridional flow is observed to be positively correlated with the corresponding symmetric components of the magnetic Cycle, also with a time delay. Our analysis sets important constraints on theories for the origin of meridional plasma flow asymmetries and its temporal variations and is relevant for understanding the role of plasma flux transport processes in determining hemispheric asymmetry in the Sunspot Cycle.
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prediction of the strength and timing of Sunspot Cycle 25 reveal decadal scale space environmental conditions
Nature Communications, 2018Co-Authors: Prantika Bhowmik, Dibyendu NandyAbstract:The Sun’s activity Cycle governs the radiation, particle and magnetic flux in the heliosphere creating hazardous space weather. Decadal-scale variations define space climate and force the Earth’s atmosphere. However, predicting the solar Cycle is challenging. Current understanding indicates a short window for prediction best achieved at previous Cycle minima. Utilizing magnetic field evolution models for the Sun’s surface and interior we perform the first century-scale, data-driven simulations of solar activity and present a scheme for extending the prediction window to a decade. Our ensemble forecast indicates Cycle 25 would be similar or slightly stronger than the current Cycle and peak around 2024. Sunspot Cycle 25 may thus reverse the substantial weakening trend in solar activity which has led to speculation of an imminent Maunder-like grand minimum and cooling global climate. Our simulations demonstrate fluctuation in the tilt angle distribution of Sunspots is the dominant mechanism responsible for solar Cycle variability. The Sun’s activity Cycle impacts space-reliant technologies and the Earth’s climate, but predicting this is challenging. An ensemble forecast based on an innovative combination of two solar magnetic field evolution models indicates a weak, but not insignificant Sunspot Cycle 25 peaking in 2024.
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the unusual minimum of Sunspot Cycle 23 caused by meridional plasma flow variations
Nature, 2011Co-Authors: Dibyendu Nandy, Andres Munozjaramillo, P C H MartensAbstract:We are currently experiencing solar Cycle 24, the latest roughly 11-year Cycle of solar magnetic activity since the scientific recording of Sunspot activity began in 1755. The Sun is currently extremely active, but the recent, deep activity minimum that occurred during Cycle 23 was characterized by an unexpectedly large number of Sunspot-less days (unprecedented in almost a century), very low radiative energy output (irradiance), and high cosmic ray flux. Nandy et al. use kinematic dynamo simulations to explain the possible origin of this unusual solar minimum. They find that rapid solar plasma flows during the first half of a Cycle, followed by slower flows in the second half, reproduce the characteristics of the minimum of Sunspot Cycle 23. Direct observations over the past four centuries show that the number of Sunspots observed on the Sun's surface varies periodically. After Sunspot Cycle 23, the Sun went into a prolonged minimum characterized by a very weak polar magnetic field and an unusually large number of days without Sunspots. This study reports kinematic dynamo simulations which demonstrate that a fast meridional flow in the early half of a Cycle, followed by a slower flow in the latter half, reproduces both characteristics of the minimum of Sunspot Cycle 23. Direct observations over the past four centuries1 show that the number of Sunspots observed on the Sun’s surface varies periodically, going through successive maxima and minima. Following Sunspot Cycle 23, the Sun went into a prolonged minimum characterized by a very weak polar magnetic field2,3 and an unusually large number of days without Sunspots4. Sunspots are strongly magnetized regions5 generated by a dynamo mechanism6 that recreates the solar polar field mediated through plasma flows7. Here we report results from kinematic dynamo simulations which demonstrate that a fast meridional flow in the first half of a Cycle, followed by a slower flow in the second half, reproduces both characteristics of the minimum of Sunspot Cycle 23. Our model predicts that, in general, very deep minima are associated with weak polar fields. Sunspots govern the solar radiative energy8,9 and radio flux, and, in conjunction with the polar field, modulate the solar wind, the heliospheric open flux and, consequently, the cosmic ray flux at Earth3,10,11.
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evidence that a deep meridional flow sets the Sunspot Cycle period
The Astrophysical Journal, 2003Co-Authors: David H. Hathaway, Robert M. Wilson, Dibyendu Nandy, Edwin J ReichmannAbstract:Sunspots appear on the Sun in two bands on either side of the equator that drift toward lower latitudes as each Sunspot Cycle progresses. We examine the drift of the centroid of the Sunspot area toward the equator in each hemisphere from 1874 to 2002 and find that the drift rate slows as the centroid approaches the equator. We compare the drift rate at Sunspot Cycle maximum with the period of each Cycle for each hemisphere and find a highly significant anticorrelation: hemispheres with faster drift rates have shorter periods. These observations are consistent with a meridional counterflow deep within the Sun as the primary driver of the migration toward the equator and the period associated with the Sunspot Cycle. We also find that the drift rate at maximum is significantly correlated with the amplitude of the following Cycle, a prediction of dynamo models that employ a deep meridional flow toward the equator. Our results indicate an amplitude of about 1.2 m s 1 for the meridional flow velocity at the base of the solar convection zone.
