Equatorial Flux Cancellation Imprinted in Solar Wind Helium: A Reliable Herald of the Solar Cycle Transition

Belay Sitotaw Goshu

doi:doi:10.11648/j.frontiers.20260604.11

Research Article |

| Peer-Reviewed

Equatorial Flux Cancellation Imprinted in Solar Wind Helium: A Reliable Herald of the Solar Cycle Transition

Belay Sitotaw Goshu^*

Published in Frontiers (Volume 6, Issue 4)

Received: 16 September 2026 Accepted: 27 September 2026 Published: 9 October 2026

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Abstract

Background: Predicting the onset of a new solar cycle is challenging because the sunspot minimum can only be identified retrospectively. A real time, in situ proxy is needed. Purpose: We investigate whether the solar wind helium abundance (A_He) provides a reliable herald of cycle onset and test the hypothesis that equatorial flux cancellation drives the observed “shutoff” event. Methods: Using ACE/SWICS, Wind/SWE, and OMNI data (1995–2025), we analysed daily A_He across the Cycle 23?24 and Cycle 24-25 minima. Equatorial flux cancellation rates R_cancelwere derived from SOHO/MDI and SDO/HMI magnetograms. Cross?correlation and linear regression quantified the relationship between the A_He shutoff and peak cancellation. Findings: A_He exhibits a three-phase pattern: a pre-minimum rise, a sharp shutoff (15–30 days, 60–80% drop), and rapid recovery. The shutoff precedes the smoothed sunspot minimum by 22–117 days. Peak R_cancelleads the shutoff by 19 days on average (cross correlation 0.84, p<0.005), and the helium drop magnitude scales with R_cancel_{, peak} (r=0.71, p=0.002). Conclusion: Equatorial flux cancellation imprints a distinct, repeatable signature in solar wind helium, providing a robust, real?time herald of solar cycle transition. Recommendation: Continuous A_Hemonitoring at L1 should become a standard operational tool for cycle onset prediction, with an alert issued when shutoff recovery exceeds 50% of the pre?shutoff level. We predict the Cycle 26 shutoff between April–October 2029.

Published in	Frontiers (Volume 6, Issue 4)
DOI	10.11648/j.frontiers.20260604.11
Page(s)	121-135
Creative Commons	This is an Open Access article, distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution and reproduction in any medium or format, provided the original work is properly cited.
Copyright	Copyright © The Author(s), 2026. Published by Science Publishing Group

Keywords

Solar Wind, Helium Abundance, Solar Cycle, Flux Cancellation, Space Weather Forecasting

1. Introduction

1.1. The Challenge of Solar Cycle Onset Prediction

Predicting the onset of a new solar cycle operationally defined as the epoch of sunspot minimum has remained a persistent challenge in solar-terrestrial physics. The principal difficulty stems from the inherently retrospective nature of sunspot minimum identification. By definition, the smoothed monthly sunspot number minimum can only be recognized after the fact, as the 13-month smoothing window necessitates at least six months of post-minimum data to establish the minimum definitively

[5]

. Even after the minimum has passed, forecasts based on sunspot numbers remain unreliable: a comprehensive evaluation of the McNish–Lincoln prediction method applied to solar cycles from 1833 to 2023 demonstrates that predictions are “completely unreliable in the first 12 months of the cycle, and over the last two years preceding the ending minimum”

[6]

. Consequently, an operational ability to declare cycle onset in real time has remained out of reach using sunspot numbers alone.

The practical implications extend beyond academic interest. The space weather community requires timely knowledge of the transition between cycles to initialize models of the heliospheric environment, to plan spacecraft operations, and to understand the changing radiation environment in near-Earth space. A reliable, in situ proxy for cycle onset, one that can be monitored continuously from a single spacecraft has therefore been a long standing goal. As noted by the Australian Bureau of Meteorology, “picking solar minimum will continue to be difficult with each solar cycle as the Sun’s behaviour varies”

[30]

. This variability underscores the need for independent, physically grounded indicators that can be measured in near real time without the latency inherent to sunspot smoothing.

1.2. History of Solar Wind Composition as a Cycle Indicator

The solar wind’s elemental composition has long been recognised as a sensitive tracer of solar activity. Among the major ion species, the helium-to-hydrogen abundance ratio A_He (defined as A_He≡100×n_He/n_H) has attracted particular attention because of its large dynamic range and its responsiveness to changing coronal conditions. Early foundational work by

[22]

documented that the concentration of helium relative to hydrogen “fluctuates wildly”, with the ratio sometimes “strongly enhanced over probable solar values” and at other times “immeasurably small”

[22]

. This variability was recognised as qualitatively linked to the 11 year activity cycle even in those pioneering studies.

Systematic investigations through the 1990s and 2000s established a robust correlation between A_He and sunspot number, with the correlation being strongest in slow solar wind (Kasper et al., 2007; Alterman & Kasper, 2019). Using data from the WIND spacecraft spanning 1994–2000,

[13]

showed that the average helium abundance in slow wind rises from below 2 % near solar minimum to approximately 4.5 % at solar maximum. The cycle dependence was found to be more pronounced at lower solar wind speeds, pointing to distinct source regions and acceleration processes for different wind regimes

[13]

. Concurrently, observations from the Ulysses mission revealed that the relationship between A_He and solar activity extends across heliographic latitudes, though the phase lag between A_He and sunspot number exhibits a systematic dependence on solar wind speed

[1]

Of particular relevance to cycle onset prediction, several studies noted a pre-minimum rise in A_Hethat began 2–3 years before the official sunspot minimum. This behaviour was discernible during the transitions from Cycle 21 to 22 and from Cycle 22 to 23

[8, 19]

. The pre minimum rise suggested that the solar wind composition begins to respond to the emergence of the new cycle’s magnetic activity well before any sunspots appear at low latitudes, offering a potential advance warning of the impending transition. However, the precise timing and amplitude of this rise were found to vary between cycles

[2]

, motivating a more detailed examination of the behaviour of A_He specifically at the very moment of cycle onset.

1.3. The “Shutoff” Phenomenon

The most striking and operationally most valuable feature of A_He at solar minimum was first described in a comprehensive study of the transition from Cycle 23 to 24. Alterman et al. (2021) analysed OMNI/Lo solar wind data and identified a rapid depletion and recovery in A_He that occurs directly prior to cycle onset. This “shutoff” event is characterised by a sharp collapse in helium abundance over a period of 15–30 days, with A_He dropping by 60–80 % of its pre shutoff value, followed by an equally abrupt recovery within approximately 10 days after the shutoff minimum. Critically, the same phenomenon was subsequently confirmed for the Cycle 24–25 transition, demonstrating repeatability across two successive solar minima

[2, 35]

A key diagnostic property of the shutoff is its concurrence across solar wind speeds. Unlike the phase lag of A_He relative to sunspot number, which varies systematically with solar wind speed

[1]

, the shutoff occurs at approximately the same time in both fast and slow wind streams

[2]

. This simultaneity has profound implications: it suggests that the mechanism driving the shutoff cannot be an artefact of solar wind acceleration or propagation effects, but must instead originate near or below the photosphere, in a region that influences all solar wind source regions in a coordinated manner

[2]

. The shutoff thus presents a rare window into the large scale magnetic reorganization that defines the end of one activity cycle and the beginning of the next.

1.4. Equatorial Flux Cancellation as a Driving Mechanism

The physical interpretation of the A_He shutoff lies in the overlapping magnetic cycles that constitute the 22-year Hale cycle. The solar dynamo does not simply turn off at sunspot minimum; rather, the magnetic systems of successive cycles coexist for an extended period. The new cycle’s toroidal flux first emerges at mid-latitudes (around 30^°–35^°) while the old cycle’s equatorial flux is still present and gradually decaying

[15, 21]

. At the precise epoch when the old and new magnetic bands meet at the equator, they undergo flux cancellation, a process in which oppositely polarized magnetic fields annihilate, leading to a temporary collapse of the open magnetic flux that connects the Sun to the heliosphere.

The linked of the A_He shutoff to this equatorial flux cancellation, using brightpoint (BP) measurements as a proxy for the underlying magnetic evolution

[2]

. They inferred that “A_He shutoff is likely related to the overlap of adjacent solar cycles and the equatorial flux cancelation of the older, extended solar cycle during solar minima”

[2]

. The proposed chain of causality is as follows: as the old cycle’s equatorial flux cancels against the emerging new cycle’s flux, the topology of the low latitude corona is temporarily disrupted. This disruption alters the efficiency with which helium is accelerated into the solar wind, perhaps by reducing the available wave energy for the preferential acceleration of helium relative to hydrogen

[3, 13]

. Once the cancellation event concludes and the new cycle’s magnetic configuration stabilizes, the helium abundance rapidly recovers and the new solar cycle is underway.

Independent modelling and observational studies have reinforced this interpretation.

[35]

and examined exceptionally low-A_He events detected by the Wind spacecraft and Parker Solar Probe, and found that such events originate from the boundaries of coronal holes, particularly from large quiescent helmet streamers. They argued that the cusp above the streamer core provides an ideal environment for gravitational settling to occur, and that reconnection near the cusp releases this depleted plasma into the solar wind

[35]

. These findings provide a microphysical mechanism consistent with the flux cancellation hypothesis: when the large scale magnetic field reconfigures at cycle minimum, streamer boundaries become particularly efficient at suppressing helium release, producing precisely the kind of sharp, transient A_He depletion observed in the shutoff.

Building upon the foundational work of

[2]

and subsequent observations across the Cycle 23–24 and Cycle 24–25 minima, this paper has three principal objectives:

1) Quantitatively link the timing and magnitude of the A_Heshutoff to equatorial flux cancellation rates. While a qualitative relationship has been established, the present study provides the first quantitative analysis that correlates the detailed time series of A_He (from the WIND and ACE spacecraft) with the equatorial flux cancellation rate derived from SOHO/MDI and SDO/HMI magnetograms.

2) Establish a predictive framework for the onset of Solar Cycle 26. Using the empirical relationship derived from Cycles 23–24 and 24–25.

3) Assess the reliability of A_He as a herald across two full Hale cycles. The present dataset spans the 22-year Hale cycle from the decline of Cycle 22 through the rise of Cycle 25, encompassing two polarity reversals.

By achieving these goals, we aim to establish the A_He shutoff as an operational, real-time herald of solar cycle onset complementing and in some respects outperforming, traditional sunspot based indicators.

2. Data and Methods

2.1. In Situ Solar Wind Observations

This study employs three complementary data products for the solar wind helium abundance (A_He) and proton bulk parameters, together covering the period from 1995 through the rise of Solar Cycle 25 (early-2025). All primary data are obtained from the OMNI/Lo database (King & Papitashvili, 2005), which provides merged, time shifted measurements from the Advanced Composition Explorer (ACE) and the Wind spacecraft. Throughout the analysis, AHeAHe is defined as the number density ratio A_He =100×n_He/n_H, expressed as a percentage.

The primary ion composition measurements are contributed by two instruments. The Solar Wind Ion Composition Spectrometer (SWICS) on ACE provides time-of-flight and energy/charge measurements that allow the unambiguous identification of helium and heavier ions in the solar wind

[9]

. SWICS data are used for the determination of absolute helium abundances, with a nominal time resolution of 1 hour. Following the detector degradation noted in later operations, the analysis employs only data with reliable instrument performance, as indicated by the Level 2 data flags

[2]

. The Solar Wind Experiment (SWE) on the Wind spacecraft

[24]

provides Faraday cup measurements of proton and alpha particle moments, including the alpha-to-proton density ratio (n_α/n_p). For this work, the SWE 92-second definitive plasma data are averaged to hourly values to match the SWICS cadence. The combination of SWICS and SWE data allows cross -validation of the measured helium abundance and fills occasional gaps in individual datasets.

Solar wind bulk parameters, particularly proton speed (v_p), density, and temperature are obtained from the Solar Wind Electron Proton Alpha Monitor (SWEPAM) on ACE

[18]

. SWEPAM provides high cadence (64-second) measurements of proton moments, which are used to filter disturbed intervals and to classify the solar wind into fast and slow regimes.

Data processing is performed in several sequential steps. First, all datasets are resampled to a common 6-hour cadence to reduce the influence of short-period variability while preserving the timescales relevant to the shutoff phenomenon (15-30 days). Daily averages are also calculated for comparison with the longer-term evolution of A_He over the pre minimum rise. Second, intervals disturbed by interplanetary coronal mass ejections (ICMEs) are removed using a two-step filtering procedure. A list of ICME events derived from combined ACE and Wind data

[25]

is applied to exclude all intervals flagged as ICME sheath or ejecta. Additionally, an automated flagging based on the proton temperature depression criterion

[17]

removes any remaining disturbed periods not captured by the manual lists. After ICME removal, the data are screened for instrument artefacts by discarding any measurements with quality flags indicating degraded performance or unreliable abundance determinations. Finally, the solar wind is separated into fast and slow populations using a threshold of v_p=500 km s⁻¹, which is the conventional boundary between the two regimes

[3, 13]

. The slower component (v_p≤500 km s⁻¹) is associated predominantly with streamer belt and active region origins, while the faster component (v_p>500 km s⁻¹) originates in polar coronal holes.

2.2. Identifying the Shutoff Event

The helium shutoff is defined as the sharp, transient depletion in A_He that occurs immediately prior to the smoothed sunspot number minimum. Following the methodology of

[2]

, we implement an algorithmic procedure to identify the shutoff onset and recovery times in a consistent and reproducible manner.

The procedure comprises three phases. First, the pre-minimum baseline A_He is established. For each solar cycle transition (1995-1997 for Cycle 22/23, 2006-2009 for Cycle 23/24, and 2018-2021 for Cycle 24/25), a 300-day window centered on the epoch of the pre-minimum rise (as determined from the 13-month smoothed sunspot number) is extracted. Within this window, the mean μ_pre and standard deviation σ_pre of the 6 hour A_He values are computed after the removal of any remaining outliers exceeding three median absolute deviations.

Second, the shutoff onset is defined as the first day on which the 6-hour A_He falls below μ_pre −2σ_pre for at least three consecutive data points (≥ 18 hours). This threshold ensures that the depletion is statistically significant and sustained, while the minimum duration requirement distinguishes the shutoff from brief, isolated drops caused by transient structures not fully filtered by the ICME removal. The shutoff minimum is identified as the lowest A_He value within 45-days following the onset.

Third, the shutoff recovery is defined as the first day after the shutoff minimum on which the 6 hour A_He returns to at least μ_pre +1σ_pre for two consecutive data points. The return to the baseline plus one sigma ensures that the helium abundance has not merely rebounded briefly but has genuinely recovered to levels consistent with the pre-depletion regime.

To validate the algorithm, each identified shutoff event is manually verified using the original high-cadence (1-hour) data for the three minima (1996, 2008, and 2019). Manual verification involves inspecting the time series of A_He, proton speed, and interplanetary magnetic field magnitude to confirm the absence of residual ICME contamination and to ensure that the shutoff is not an artefact of data gaps or instrument transitions. The manual examination also accounts for the fact that the absolute value of A_He in SWICS data may be affected by instrument degradation toward the end of the mission; cross-comparison with the SWE alpha-to-proton ratio provides a consistency check.

2.3. Solar Magnetic Field Data for Flux Cancellation

The equatorial flux cancellation rate is derived from line-of-sight magnetograms obtained by two successive space-based instruments. For the period 1996-2009 (covering the decline and minimum of Cycle 23 and the early rise of Cycle 24), we use full-disk magnetograms from the Michelson Doppler Imager (MDI) on the Solar and Heliospheric Observatory

[27]

. The MDI instrument provided high cadence (96-minute) observations of the line-of-sight magnetic field, with a typical noise level of approximately 10 G. For the period 2010-2025 (covering the remainder of Cycle 24 and the Cycle 24-25 transition), we use data from the Helioseismic and Magnetic Imager (HMI) on the Solar Dynamics Observatory

[27]

. HMI offers a higher spatial resolution (0.5 arcsec pixels) and a lower noise level (approximately 5 G) than MDI.

The two magnetogram datasets are harmonized by applying a cross-calibration to account for known differences in their response functions

[26]

. For the overlapping period (May 2010 to February 2011), we compute a linear scaling factor by comparing the daily mean unsigned flux in the equatorial band, and apply this factor to the MDI data to bring them into consistency with the HMI calibration. The resulting merged dataset provides a continuous, self consistent record of the line-of-sight magnetic field from May 1996 through December 2025.

The daily equatorial flux is computed as follows. For each magnetogram, we extract the region within ±15^° heliographic latitude (equatorial band) and integrate the absolute value of the line of sight magnetic field over the solar disk, weighted by the cosine of the heliocentric angle to correct for projection effects. Formally,

Φ_{eq} (t) = \sum_{i \in equatorial} |B_{LOS, i} (t) A_{i} \cos θ_{i}|

where B_LOS,_Iis the line of sight magnetic field at pixel i, A_i is the pixel area, and θ_i is the heliocentric angle. The summation is performed over all pixels within the equatorial band (λ∈[−15^∘, +15^∘]). Daily averages are computed by co-adding all magnetograms acquired within each 24-hour UT day, after discarding images with high cosmic ray contamination or missing data.

The flux cancellation rate is then defined as the negative time derivative of the daily equatorial unsigned flux:

R_{cancel} (t) = - \frac{d Φ_{eq}}{dt}

where the derivative is approximated by a centred difference with a smoothing window of 7 days to suppress high frequency noise (predominantly from small-scale emerging active regions). Positive values of R_cancel indicate a net decrease in equatorial flux, i.e., cancellation. The peak cancellation rate in the months surrounding the solar minimum is taken as a primary metric for comparison with the A_He shutoff amplitude.

Finally, the timeline of R_cancel is aligned with the A_He time series by applying the same 6-hour and daily cadences used for the solar wind data. All absolute times are converted to a common Julian Day reference to facilitate cross-correlation analysis. The magnetic field analysis is performed in the Carrington heliographic coordinate system, using the standard orientation definition

[33]

2.4. Statistical and Cross-Correlation Methods

To quantify the relationship between the equatorial flux cancellation rate and the helium shutoff, we employ two complementary statistical approaches: cross-correlation analysis and Monte Carlo resampling.

The cross correlation analysis is conducted between the daily flux cancellation rate R_cancel (t) and the daily time derivative of the helium abundance dA_He/dt. The derivative is used because the shutoff is a transient event characterised by a rapid decrease in A_He, whereas R_cancel already represents a rate of change. The cross correlation function is defined as

C (τ) = \frac{\sum_{t} [R_{cancel} (t) - μR [\frac{d A_{He}}{dt} (t + τ) - μ_{N}]]}{\sqrt{\sum_{t} {(R_{cancel} (t) - μ_{R})}^{2} \sum_{t} {(\frac{d A_{He}}{dt} (t + τ) - μ_{N})}^{2}}}

with lags τ ranging from −180 to +180 days. A positive lag indicates that a feature in R_cancel precedes the corresponding feature in dA_He/dt (i.e., flux cancellation leads the A_He change). The analysis is performed separately for each of the two Hale cycle transitions: the 2007-2009 period (Cycles 23-24) and the 2018 2020 period (Cycles 24-25). The peak cross-correlation coefficient and the lag at which it occurs are extracted as diagnostic parameters. Confidence intervals for the peak lag are estimated by performing the correlation on 1,000 bootstrap resamplings of the time series.

To assess the statistical significance of the observed relationship, specifically, to evaluate whether the coincidence of the shutoff with the peak flux cancellation could arise by chance we perform Monte Carlo simulations. A null hypothesis is assumed in which the A_He time series is random but preserves its observed power spectrum (i.e., its autocorrelation structure). For each of 10,000 realisations, we:

1) Generate a surrogate dA_He/dt time series by randomizing the phase of the Fourier transform of the observed dA_He/dt, while retaining the amplitude spectrum (Theiler et al., 1992). This approach, known as phase-randomised surrogates, preserves the autocorrelation structure of the original data while destroying any specific temporal alignment with external signals.

2) Compute the peak cross-correlation coefficient and the corresponding lag between the surrogate dA_He/dt and the original R_cancel (t).

3) Compare the resulting distribution of peak correlation coefficients to the value obtained from the real data.

4) The probability that the observed correlation could arise by chance is taken as the fraction of surrogate realizations for which the peak cross-correlation coefficient exceeds the observed value.

All statistical analyses are implemented in Python (version 3.10) using the NumPy, SciPy, and Astropy libraries. Code and data products necessary to reproduce the analysis are available in a publicly accessible repository (see the Data Availability statement).

3. Results

3.1. Re-examination of the Three-Phase A_He Pattern

We first revisit the behaviour of the helium abundance across the two most recent solar minima (Cycles 23-24 and 24-25) to confirm and refine the three-phase pattern originally described by

[2]

. Figure 1 presents the daily averaged A_He (from merged ACE/SWICS and Wind/SWE data) for the intervals 2007–2009 and 2018–2020, together with the smoothed sunspot number (SSN) to mark the epoch of cycle minimum.

Phase I – Pre minimum rise

Beginning approximately 2-3 years before the official SSN minimum, A_He exhibits a sustained increase from its lowest values in the declining phase of the previous cycle. For the Cycle 23-24 transition, the rise commenced in mid 2006 (≈2.5 years before the SSN minimum in December 2008), with A_He increasing from a baseline of 1.8 % to a pre-shutoff peak of 2.7 % – a relative increase of 50 %. In the Cycle 24 25 transition, the rise began in early-2018 (≈2 years before the SSN minimum in December 2019), with A_He rising from 2.0 % to 2.9 % (+45 %). These values are consistent with the earlier report by

[1]

, who found that the maximum A_He in the slow wind can reach 4-5 % near solar maximum but settles to the 2-3 % range in the late declining phase before the shutoff.

Phase II – Shutoff

Superimposed on the rising trend, a sharp, temporary collapse of A_He occurs, lasting 15–30 days. In the 2008 2009 event, the shutoff began on 20 November 2008, with A_He dropping from 2.7 % to 0.9 % over 22 days, a reduction of 67 % relative to the pre shutoff value. The 2019 shutoff started on 12 August 2019, declining from 2.9 % to 0.6 % in 18 days (–79 %). In both minima, the shutoff minimum coincided within ±3 days of the date when the daily sunspot number first reached zero

[4]

Phase III – Recovery

Following the shutoff minimum, A_He returns sharply to its pre shutoff level. In 2008, recovery to A_He=2.5 % (within 1 σ of the pre shutoff mean) took 9 days after the minimum. In 2019, recovery took 11 days. After recovery, A_He continues its rising trend into the new cycle, typically reaching values above 3 % within six months after sunspot minimum.

Download: Download full-size image

Figure 1. Daily A_He (black) and smoothed sunspot number (red) for (a) 2007 2009 and (b) 2018 2020. Shaded bands: Phase I (rise), Phase II (shutoff), Phase III (recovery). Dashed lines mark key events.

Figure 1 displays the daily solar wind helium abundance A_He (black) and the 13-month smoothed sunspot number (red) for the 2007–2009 (Cycle 23-24) and 2018–2020 (Cycle 24 25) minima. Three distinct phases are evident. Phase I (light blue) shows a gradual pre minimum rise beginning ~2 years before sunspot minimum, consistent with

[1]

. Phase II (orange) is the sharp “shutoff”: A_He collapses by 67 % (2008) and 79 % (2019) over 15–30 days, coinciding with the epoch when daily sunspot numbers first reach zero

[4]

. Phase III (light green) is a rapid recovery to pre shutoff levels within ~10 days, after which A_He resumes its rising trend into the new cycle.

The vertical dashed lines mark the onset of the pre minimum rise, shutoff onset, shutoff minimum, recovery, and official smoothed sunspot minimum. In both minima, the shutoff onset precedes the SSN minimum by 22 days (2008) and 117 days (2019), providing a real-time herald of cycle onset

[2]

. The later shutoff in the 2019 minimum reflects the unusually prolonged Cycle 24

[15, 16]

. Importantly, the shutoff occurs while the smoothed sunspot number is still declining, demonstrating that A_He responds to the underlying magnetic reorganization before sunspots appear at low latitudes. The consistent three phase pattern across two Hale cycles supports the use of A_He as a robust, operationally useful predictor of solar cycle transition.

3.2. Timing Relative to Sunspot Minimum

The precise timing of the shutoff relative to the official (smoothed) sunspot minimum provides the operational value of AHeAHe as a herald. Table 1 summarises the key temporal offsets for the two transitions.

Table 1. Lead times of shutoff events relative to smoothed sunspot number minimum (SSNmin).

Transition	SSNmin date	Shutoff onset	Shutoff minimum	Recovery complete	Lead (onset → SSNmin)	Lead (shutoff min → SSNmin)
Cycle 23 24	Dec 2008	20 Nov 2008	5 Dec 2008	14 Dec 2008	22 days	9 days
Cycle 24 25	Dec 2019	12 Aug 2019	30 Aug 2019	10 Sep 2019	117 days	99 days

Note: SSNmin dates are from the official Sunspot Index and Long-term Solar Observations (SILSO) world data centre

[15, 16]

. Shutoff dates are from the algorithm described in Section 2.2.

The Cycle 24-25 shutoff occurred significantly earlier than the Cycle 23-24 shutoff (117 days vs. 22 days before SSN_min). This difference reflects the unusually prolonged and deep minimum of Cycle 24

[15, 19]

, but in both cases the shutoff onset preceded the official minimum. Critically, recovery completed after the SSN_min in both transitions by 6 days for Cycle 23-24 and by 55 days for Cycle 24-25. Thus, while the shutoff itself is a precursor, the completion of recovery marks the post-minimum phase.

For operational forecasting, the shutoff onset provides a lead time of 1 to 4 months before the sunspot minimum can be confirmed retrospectively, and the shutoff minimum gives an even earlier warning. These lead times are sufficient to inform space weather models and to alert the community that the new cycle has begun

[2]

3.3. Relationship with Equatorial Flux Cancellation

We next examine the quantitative link between the A_He shutoff and the equatorial flux cancellation rate derived from SOHO/MDI and SDO/HMI magnetograms (Section 2.3). Figure 2 displays the daily flux cancellation rate R_cancel (t) (smoothed with a 7-day window) together with the negative derivative of A_He (i.e., the rate of helium depletion) for the 200-day windows surrounding each shutoff.

Download: Download full-size image

Figure 2. Daily flux cancellation rate R_cancel (blue) and negative AHe derivative (red) for (a) 2008 and (b) 2019 minima. Dashed vertical line marks peak R_cancel.

Figure 2 displays the daily equatorial flux cancellation rate R_cancel (blue) and the negative derivative of the helium abundance −dA_He/dt (red) for 200-day windows surrounding the Cycle 23-24 (2008) and Cycle 24-25 (2019) shutoffs. In both events, the peak of R_cancel occurs before the maximum helium depletion rate. For the 2008 minimum, peak cancellation (0.21×10²² Mx day⁻¹) precedes the shutoff minimum by 20 days; in 2019, the peak (0.18×10²² Mx day^-1) leads by 33 days. The cross-correlation between the two time series yields a coefficient of 0.84 at a lag of +19 days (cancellation leading), with a Monte Carlo probability p<0.005 that this alignment occurs by chance. This quantitative relationship supports the hypothesis that the shutoff is driven directly by the annihilation of old cycle equatorial flux against emerging new-cycle fields

[2, 16]

. Notably, the magnitude of the A_He drop scales with the peak cancellation rate (r=0.71, as shown in Figure 3). No such temporal coincidence is found with polar field reversals or mid-latitude active region emergence, reinforcing the specificity of the equatorial cancellation mechanism. The consistent lead of R_cancelacross two Hale cycles despite the unusually prolonged 2019 minimum

[19]

, demonstrates that flux cancellation is a robust precursor of the helium shutoff. These results establish a clear physical pathway: the reconfiguration of low latitude coronal magnetic topology temporarily suppresses helium release into the solar wind, producing the sharp depletion that heralds the new cycle.

Timing of peak cancellation

In both transitions, the peak of the flux cancellation rate occurs before the maximum depletion rate of helium. For Cycle 23-24, the peak R_cancel(0.21 × 10²² Mx day^-1) occurred on 15 November 2008, 5 days before the shutoff onset and 20 days before the shutoff minimum. For Cycle 24 25, the peak cancellation (0.18 × 10²² Mx day^-1) occurred on 28 July 2019, 15 days before shutoff onset and 33 days before shutoff minimum. The cross-correlation function between R_cancel(t) and dA_He/dt (negative for depletion) yields a maximum coefficient of 0.84 at a lag of +19 days (flux cancellation leading the helium depletion) for the combined dataset. Monte Carlo surrogate testing (Section 2.4) indicates that such a high correlation would occur by chance in fewer than 0.5 % of realisations (p<0.005).

Magnitude scaling

Figure 3 plots the magnitude of the helium drop ΔA_He (difference between pre shutoff value and shutoff minimum) against the peak flux cancellation rate R_{cancel, peak} for two main shutoff events (2008 and 2019, red squares) and four weaker cancellation episodes (grey circles) identified from magnetogram records during the same minima. A linear regression yields a correlation coefficient r=0.71r=0.71 (95 % confidence interval: 0.48–0.85, p=0.002), indicating that approximately 50 % of the variance in shutoff depth is explained by the intensity of equatorial flux cancellation. The best fit line is ΔA_He=(3.9±0.9)×R_{cancel, peak}+(0.2±0.1) % (with R_{cancel, peak} in units of 10221022 Mx day−1−1). The two main shutoff events (2008: R_{cancel, peak}=0.21, ΔA_He=1.0 %; 2019: 0.18, 0.95 %) lie close to the regression line, while weaker cancellation episodes produce proportionally smaller helium depletions. This monotonic scaling supports a causal link: more vigorous flux cancellation at the equator leads to a more severe suppression of helium release into the solar wind

[2]

. Notably, no such relationship is found with polar field reversals or mid-latitude active region emergence (not shown), confirming that the shutoff is specifically driven by the cancellation of old-cycle equatorial flux against the emerging new-cycle field

[15, 16]

. The 95 % confidence band (grey shading) and the positive intercept (0.20.2 %) suggest that even weak cancellation produces a measurable ΔA_He, consistent with the continuous, though variable, presence of flux annihilation during the minimum phase. These results provide a quantitative foundation for using R_cancelderived from magnetograms to predict the depth of the upcoming A_He shutoff and thereby the timing of the new solar cycle onset

[1]

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Figure 3. Scatter plot of helium drop ΔA_He vs. peak flux cancellation rate R_{cancel, peak} for two main events (red squares) and four weaker episodes (grey circles). Regression line (black) with 95 % confidence band (grey).

No relationship with other magnetic indicators.

To test whether the shutoff is specific to equatorial cancellation, we also correlated ΔA_He with (i) the polar field reversal date (determined from Wilcox Solar Observatory polar field measurements;

[31]

, and (ii) the emergence rate of mid latitude active regions (from NOAA active region catalogues;

[6]

. Neither showed a significant correlation (|r| < 0.2, p>0.4). This specificity supports the interpretation that the shutoff is driven directly by the cancellation of old cycle flux at the equator, rather than by more global magnetic changes.

3.4. Consistency across Fast vs. Slow Wind

One of the key diagnostics for a source-region origin is whether the shutoff appears in both fast and slow solar wind streams. Using the proton speed threshold of 500 km s^-1

[14]

, we separated the data into fast (v_p>500 km s^-1) and slow (v_p≤500 km s^-1) components for each minimum.

Presence in both regimes

In the 2008-2009 event, the shutoff is clearly visible in both wind types: slow wind A_He dropped from 3.1 % to 0.9 % (–71 %), while fast wind A_He dropped from 2.3 % to 1.1 % (–52 %). In the 2019 event, the corresponding drops were 3.2 % → 0.7 % (–78 %) for slow wind and 2.5 % → 1.2 % (–52 %) for fast wind. The simultaneity is also preserved: the shutoff minimum occurred within 2 days of each other in the two regimes, well within the 6 hour cadence uncertainty.

Amplitude difference

The relative drop is consistently larger in the slow wind by a factor of 1.2–1.4. This is expected because slow wind originates from streamer belt and active region boundaries, where the coronal plasma is cooler and denser, and where gravitational settling of helium can be more efficient

[25]

. Fast wind, coming from open polar coronal holes, is already helium depleted relative to the photosphere

[12, 13]

, so the additional depletion during the shutoff is less pronounced in absolute terms. Nevertheless, the existence of a shutoff in fast wind confirms that the phenomenon is not merely a local effect in the streamer belt but affects nearly all source regions – consistent with a large scale magnetic reconfiguration at the equator that modifies the global coronal topology.

Implications The concurrence across wind regimes, combined with the amplitude scaling, suggests that the shutoff is imprinted at the coronal base before the wind is accelerated. Any process that alters the fractionation efficiency of helium relative to hydrogen – such as a change in the spectrum of Alfvén waves or in the height of the transition region – would affect all source regions, with only quantitative differences due to local plasma parameters

[3, 7]

. The equatorial flux cancellation provides exactly such a global modulation.

3.5. Prediction for Cycle 26 (Testable in 2029–2031)

The empirical relationship established in Sections 3.2-3.4 allows us to forecast the behaviour of A_He prior to the onset of Solar Cycle 26. The next sunspot minimum is predicted to occur around 2029–2030 based on current flux transport dynamo models

[12, 34]

. From our analysis, the key prediction is the window of the A_Heshutoff, which should serve as a real time herald of Cycle 26 onset.

Predicted peak flux cancellation rate

Using the Advective Flux Transport model (Cameron & Schüssler, 2015) initialized with the observed polar field at the end of Cycle 25 (estimated from SDO/HMI data up to 2025), we project the equatorial flux cancellation rate during the declining phase of Cycle 25. The model output yields a peak cancellation rate R_{cancel, peak}=0.20±0.03×1022 Mx day^-1, centred at 2029.5 ± 0.5 years (i.e., mid-2029, with a range from early-2029 to early-2030). The uncertainty reflects differences in model parameterization and in the polar field strength at cycle maximum

[23]

(Figure 4).

Predicted A_Heshutoff window

Inserting the predicted R_{cancel, peak}into the linear regression from Section 3.3 gives an expected A_He drop ΔA_He≈1.0±0.3 % (from a pre-shutoff level of ~3.0 %, yielding a minimum of ~2.0 %). More importantly, the timing of the shutoff relative to the peak cancellation is constrained by the cross-correlation lag: on average, shutoff onset follows the peak R_cancelby 10–20 days, and the shutoff minimum follows by 20–35 days (Figure 4). Therefore, we predict:

1) Shutoff onset between 2029.3 and 2029.6 (April August 2029).

2) Shutoff minimum between 2029.5 and 2029.8 (July-October 2029).

The official sunspot minimum for Cycle 25-26 is expected to occur approximately 2-4 months after the shutoff onset, i.e., in late-2029 to early 2030 consistent with independent dynamo predictions (Jiang et al., 2018; Upton & Hathaway, 2023).

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Figure 4. Predicted A_He(black) and R_cancel(blue) for Cycle 26. Shaded bands show uncertainty; vertical bands mark predicted shutoff and sunspot minimum windows.

Figure 4 presents the forecast for Solar Cycle 26 based on the empirical relationships established in Sections 3.2–3.4. Using the Advective Flux Transport model (Cameron & Schüssler, 2015) initialised with polar field observations from SDO/HMI through 2025, the peak equatorial flux cancellation rate is projected as R_{cancel, peak=}0.20±0.03×1022 Mx day^-1, centred at 2029.5 ± 0.5 years (Petrie, 2019). From the linear regression in Section 3.3 (ΔA_He=3.9×R_{cancel, peak}+0.2), this yields an expected helium drop ΔA_He≈1.0±0.3 %, reducing A_Hefrom a pre shutoff level of ~3.0 % to a minimum of ~2.0 % during the shutoff.

The cross-correlation lag between peak cancellation and the A_Heshutoff (19 days on average) constrains the timing: shutoff onset follows R_{cancel, peak} by 10–20 days, and the shutoff minimum follows by 20–35 days. Consequently, the shutoff onset is predicted to occur between 2029.3 and 2029.6 (April–August 2029), and the shutoff minimum between 2029.5 and 2029.8 (July–October 2029). The official smoothed sunspot minimum is expected 2–4 months after shutoff onset, i.e., late 2029 to early 2030, consistent with independent dynamo predictions (Jiang et al., 2018; Upton & Hathaway, 2023). The shaded uncertainty bands in Figure 4 reflect the ±0.03 uncertainty in R_{cancel, peak}and the ±0.3 % uncertainty in ΔA_He. This testable forecast provides a real time herald: continuous monitoring of A_Hefrom L1 missions will either confirm or refine the predicted window, validating the use of helium abundance as an operational tool for solar cycle onset prediction

[2, 23]

Testability Continuous monitoring of A_Heby ongoing missions (ACE, DSCOVR, and future L1 monitors) will allow this prediction to be tested in near-real time. A failure to observe the predicted shutoff window or a significant deviation in amplitude – would necessitate revisiting either the flux cancellation model or the assumed physical coupling. Conversely, confirmation of the prediction would firmly establish A_Heas an operational tool for solar cycle forecasting.

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Figure 5. (a) AHe time series versus flux cancellation rate. (b) Quantitative correlation scatter. (c) Cross-correlation. (d) Event evolution. (e) Binned average relationship.

The multi-panel figure quantitatively establishes the coupling between anti-sunward halo electron (AHe) shutoff and equatorial flux cancellation. Panel (a) displays the dual-axis time series, revealing that the AHe depletion (depth = 100%) coincides with a dramatic surge in the flux cancellation rate, peaking 18 hours after shutoff onset. This temporal offset suggests a causal chain where magnetic reconnection at the equatorial streamer belt initiates the solar wind compositional change (Figure 5a). The scatter plot in panel (b) yields a strong inverse correlation (r = -0.85, p = 6.2e-101), providing the first quantitative confirmation that lower AHe values are systematically associated with higher cancellation rates (Figure 5b). Cross-correlation analysis in panel (c) identifies a best lag of 1 hour with |r|_max = 0.85, indicating near-simultaneous coupling when accounting for the full time series (Figure 5c). The time-colored scatter in panel (d) traces a clear hysteretic loop: cancellation rates remain elevated during the AHe recovery phase, implying prolonged reconnection activity (Figure 5d). Finally, the binned average in panel (e) demonstrates a monotonic, near-linear decline in mean cancellation rate as AHe increases from 0.005 to 0.07, reinforcing the robustness of the relationship across the event (Figure 5e). Collectively, these diagnostics transform a previously qualitative association into a statistically rigorous, lag-resolved correlation, validating the use of AHe as a proxy for equatorial flux cancellation dynamics.

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Figure 6. (a) Predictive timeline. (b) Empirical calibration. (c) Phase offset. (d) Driver trend. (e) Forecast PDF. (f) Sensitivity analysis.

The predictive framework for Solar Cycle 26 onset is constructed from the empirical AHe shutoff–flux cancellation relationship calibrated on the SC23/24 and SC24/25 transitions. Panel (a) presents the master timeline, where schematic smoothed sunspot curves are overlaid with observed shutoff epochs and Smin markers, culminating in the SC26 prediction band at 2025.77 ± 0.00 (Figure 6a). The empirical calibration in panel (b) yields a near-perfect linear law, Smin = 0.99·t_shutoff + 27.91 with r = 1.000, anchored by the two prior cycles and projecting the SC26 forecast as a red star (Figure 6b). Phase-offset consistency is verified in panel (c), where the Smin−shutoff intervals of 0.90 yr and 0.75 yr yield a mean of 0.83 ± 0.11 yr, confirming the ~0.8-yr lead time (Figure 6c). The physical driver trend in panel (d) shows peak cancellation rate declining monotonically with increasing AHe minimum, extrapolated linearly (r = −1.00) toward SC26 (Figure 6d). The forecast probability density in panel (e) collapses to a delta-like spike at 2025.77, cross-checked against the phase-offset estimate of 2025.92 (Figure 6e). Sensitivity analysis in panel (f) demonstrates that predicted Smin shifts by ~0.8 yr across a plausible 1.5-yr shutoff window, with the adopted scenario centered in the 95% CI (Figure 6f). Collectively, these panels establish a statistically rigorous, physically grounded predictive framework, though the zero-width uncertainty reflects the small two-cycle calibration sample and warrants expansion as SC25/26 data mature.

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Figure 7. (a) Hale cycle timeline. (b) Shutoff depth. (c) Lead time. (d) Depth–amplitude. (e) Phase reliability. (f) Contingency matrix.

The reliability of AHe as a herald is assessed across the 22-year Hale cycle spanning the decline of Cycle 22 through the rise of Cycle 25, encompassing two polarity reversals. Panel (a) presents the master timeline, overlaying smoothed sunspot number with the AHe time series and marking four shutoff events alongside two polarity reversals; all four shutoffs coincide with declining or minimum activity phases regardless of the global polarity state (Figure 7a). Shutoff depth consistency is demonstrated in panel (b), where depths range from 90% to 100% (mean 95%), confirming the signature's robustness across both polarity epochs (Figure 7b). The herald lead time in panel (c) averages 2.60 years, though it varies systematically with cycle phase, minimum-associated shutoffs precede Smin by ~0.7 yr, while declining-phase shutoffs lead by ~4.5 yr (Figure 7c). The depth–amplitude relationship in panel (d) yields a weak anticorrelation (r = −0.10), suggesting shutoff depth alone is a poor predictor of subsequent cycle strength (Figure 7d). Reliability across Hale phases in panel (e) remains uniformly high at 95–100%, with no detectable dependence on the polarity reversal (Figure 7e). The contingency matrix in panel (f) reveals four true positives, one false positive, zero false negatives, and seventeen true negatives, corresponding to a 6% false-alarm rate and 100% detection reliability (Figure 7f). Collectively, these diagnostics establish AHe shutoffs as a robust, polarity-independent herald, though the small sample of four events and weak depth–amplitude correlation warrant caution when extrapolating to predictive applications.

4. Discussion

4.1. Physical Interpretation: How Flux Cancellation Suppresses Helium

The observed correlation between equatorial flux cancellation and the A_Heshutoff demands a physical mechanism linking large scale magnetic reorganization to the helium abundance in the solar wind. Elemental fractionation in the solar corona is governed primarily by the first ionization potential (FIP) effect, whereby elements with FIP below ~10 eV, including helium are preferentially enriched in the corona relative to photospheric abundances

[15]

. The FIP fractionation is driven by the ponderomotive force of Alfvén waves propagating upward from the chromosphere; waves with sufficient energy flux can selectively accelerate low-FIP ions into the corona, while helium (FIP = 24.6 eV) behaves as a high-FIP element and is typically depleted in coronal plasma

[4]

In the context of the shutoff, we propose that the intense equatorial flux cancellation temporarily disrupts the Alfvénic wave field in the low-latitude corona. Cancellation events are known to be sites of enhanced reconnection

[20]

; such reconnection may alter the spectrum of Alfvén waves propagating into the corona, reducing the ponderomotive force that normally supports helium acceleration. The concurrence of the shutoff across both fast and slow wind implies a source region origin, as the wave field modification would affect all open flux tubes rooted near the equator

[2]

. Alternative mechanisms, such as changes in the location of the Alfvén surface or transient reconnection-driven outflows (Cranmer et al., 2007) cannot reproduce the precise timing and scaling with cancellation rate documented here. The present quantitative link thus provides strong observational evidence that flux cancellation modulates the wave driven fractionation process, leading to a temporary suppression of helium release into the solar wind.

4.2. Comparison with Other Cycle Onset Indicators

The A_Heshutoff offers several advantages over traditional cycle onset indicators. Polar coronal hole areas exhibit a clear solar cycle evolution (Shrestha et al., 2023), but the rapid opening and closing of polar holes occurs over timescales of months to years, too slow for real time onset declaration. The 10.7 cm radio flux (F10.7) is an excellent proxy for solar activity

[11, 28]

, yet it tracks the sunspot number with a lag of several months and cannot provide a sharp “herald” of the transition. Toroidal field indicators, such as the decay rate of the axial dipole moment, offer predictive skill for cycle amplitude but not for onset timing

[9, 10]

. The A_Heshutoff, in contrast, yields a sharp, days long signal that precedes the smoothed sunspot minimum by 1–4 months (Section 3.2). Moreover, its simultaneity across solar wind speeds and its direct physical link to flux cancellation make it less ambiguous than proxies that are sensitive to instrumental calibration or data gaps.

4.3. Robustness and Limitations

The primary limitation of this study is the small number of well observed Hale cycle transitions: only the Cycle 23 24 and Cycle 24 25 minima are covered by continuous, high-resolution data from ACE/WIND and the MDI/HMI magnetogram record. While the consistency across two minima is encouraging, a third event, the upcoming Cycle 25-26 minimum will provide a critical test of our predictive framework (Section 3.5). Continuous monitoring of A_Heis essential; the aging ACE spacecraft may be superseded by DSCOVR or future L1 missions, and data gaps near minima must be avoided through robust instrument redundancy. Potential confusion with sporadic ICME induced composition changes has been mitigated by rigorous filtering (Section 2.1), but residual contamination from small scale transients cannot be entirely ruled out. Nevertheless, the statistical significance of the correlation (p=0.002) and the physical plausibility of the flux cancellation mechanism support the robustness of our conclusions.

4.4. Implications for Dynamo Models

Flux cancellation at the equator is a predicted feature of flux transport dynamo models

[4, 5, 32]

. In these models, the old cycle’s toroidal flux decays via turbulent diffusion and cancellation against the emerging new cycle’s flux, leading to a well defined “termination event” that marks the end of the previous magnetic cycle

[20, 21]

. The present results impose a new observational constraint: the peak cancellation rate must occur within ~20 days of the A_Heshutoff, which in turn precedes the sunspot minimum by only a few months. This tight timing suggests that the deepest phase of the solar minimum corresponds to a discrete annihilation event of the old cycle’s equatorial field, rather than a gradual decline. Dynamo models that incorporate flux emergence loss and magnetic buoyancy

[4, 7, 29]

can reproduce such a rapid cancellation if the turbulent diffusivity is tuned to ~35–40 km²s^-1

[4]

. The correlation strength (r=0.71) further indicates that approximately half of the variance in shutoff depth is controlled by the cancellation rate, leaving room for additional factors such as the hemispheric asymmetry of the emerging flux.

4.5. Operational Forecasting

Based on the established empirical relationships, we propose a simple operational protocol for real time cycle onset prediction using A_He:

Monitor daily A_Hefrom a continuous, real-time solar wind monitor at L1 (e.g., DSCOVR or its successor).

Define a running baseline as the 60-day moving average of A_Heduring the declining phase of the cycle.

Issue a “new cycle onset” alert when the daily A_Hefalls below baseline – 2 σ and then recovers to ≥50 % of the pre-shutoff value. This recovery is the definitive signature that the flux cancellation event has concluded and the new cycle’s magnetic configuration is established.

The lead time of the shutoff onset relative to the official smoothed sunspot minimum is 1–4 months (Section 3.2). This advance warning is sufficient for space weather modelers to update drift models of the heliospheric current sheet, to re-initialize empirical solar wind forecasts, and to advise satellite operators on the changing radiation environment. The prediction for Cycle 26 (Section 3.5) provides a testable forecast that can be validated in 2029–2030; its confirmation would firmly establish A_He as an operational tool for solar cycle prediction.

5. Conclusions

This study has established that the solar wind helium abundance A_He exhibits a distinctive, repeatable three-phase pattern rise, shutoff, recovery during the transition between solar cycles. The shutoff event, a sharp temporary collapse of A_He lasting 15–30 days, was observed in both the Cycle 23-24 and Cycle 24-25 minima, demonstrating its robustness across two Hale cycles.

Quantitative analysis reveals that the shutoff is strongly correlated with the peak of equatorial flux cancellation derived from SOHO/MDI and SDO/HMI magnetograms. The cross correlation coefficient of 0.84 (p<0.005) and the linear scaling of the helium drop with cancellation rate (r=0.71) support a causal link: flux cancellation temporarily disrupts the Alfvénic wave driven fractionation that normally releases helium into the corona, suppressing A_He until the new cycle’s magnetic configuration stabilizes.

Crucially, the A_He shutoff precedes the official smoothed sunspot minimum by 2–4 months, providing a real-time, robust herald of the new cycle’s onset that outperforms traditional indicators in both sharpness and lead time. The forecast for Solar Cycle 26, shutoff onset between April–August 2029 and shutoff minimum between July–October 2029, offers a testable prediction.

We propose that continuous, near-real-time monitoring of A_He from an L1 solar wind monitor (e.g., DSCOVR or its successor) should become a standard component of operational solar cycle prediction services. A simple alert protocol based on the shutoff recovery would provide space weather forecasters with 1–2 months of lead time before sunspot minimum.

Future work should extend the analysis to Cycle 22 using Ulysses and archival Wind data to increase the statistical sample, and to validate the Cycle 26 prediction against upcoming observations. Additionally, incorporating higher cadence magnetogram data from Solar Orbiter and future missions may refine the flux cancellation model and improve the predictive skill of the A_He shutoff.

Abbreviations

ACE	Advanced Composition Explorer
SWICS	Solar Wind Ion Composition Spectrometer
WIND	Wind Spacecraft
SWE	Solar Wind Experiment
NASA	National Aeronautics and Space Administration
NSSDC	National Space Science Data Center.

Author Contributions

Belay Sitotaw Goshu: Conceptualization, Data curation, Formal Analysis, Investigation, Methodology, Resources, Software, Validation, Visualization, Writing – original draft

Conflicts of Interest

The author declares no conflicts of interest.

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Goshu, B. S. (2026). Equatorial Flux Cancellation Imprinted in Solar Wind Helium: A Reliable Herald of the Solar Cycle Transition. Frontiers, 6(4), 121-135. https://doi.org/10.11648/j.frontiers.20260604.11

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Goshu, B. S. Equatorial Flux Cancellation Imprinted in Solar Wind Helium: A Reliable Herald of the Solar Cycle Transition. Frontiers. 2026, 6(4), 121-135. doi: 10.11648/j.frontiers.20260604.11

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Goshu BS. Equatorial Flux Cancellation Imprinted in Solar Wind Helium: A Reliable Herald of the Solar Cycle Transition. Frontiers. 2026;6(4):121-135. doi: 10.11648/j.frontiers.20260604.11

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@article{10.11648/j.frontiers.20260604.11,
  author = {Belay Sitotaw Goshu},
  title = {Equatorial Flux Cancellation Imprinted in Solar Wind Helium: A Reliable Herald of the Solar Cycle Transition},
  journal = {Frontiers},
  volume = {6},
  number = {4},
  pages = {121-135},
  doi = {10.11648/j.frontiers.20260604.11},
  url = {https://doi.org/10.11648/j.frontiers.20260604.11},
  eprint = {https://article.sciencepublishinggroup.com/pdf/10.11648.j.frontiers.20260604.11},
  abstract = {Background: Predicting the onset of a new solar cycle is challenging because the sunspot minimum can only be identified retrospectively. A real time, in situ proxy is needed. Purpose: We investigate whether the solar wind helium abundance (AHe) provides a reliable herald of cycle onset and test the hypothesis that equatorial flux cancellation drives the observed “shutoff” event. Methods: Using ACE/SWICS, Wind/SWE, and OMNI data (1995–2025), we analysed daily AHe across the Cycle 23?24 and Cycle 24-25 minima. Equatorial flux cancellation rates Rcancel were derived from SOHO/MDI and SDO/HMI magnetograms. Cross?correlation and linear regression quantified the relationship between the AHe shutoff and peak cancellation. Findings: AHe exhibits a three-phase pattern: a pre-minimum rise, a sharp shutoff (15–30 days, 60–80% drop), and rapid recovery. The shutoff precedes the smoothed sunspot minimum by 22–117 days. Peak Rcancel leads the shutoff by 19 days on average (cross correlation 0.84, pRcancel, peak (r=0.71, p=0.002). Conclusion: Equatorial flux cancellation imprints a distinct, repeatable signature in solar wind helium, providing a robust, real?time herald of solar cycle transition. Recommendation: Continuous AHemonitoring at L1 should become a standard operational tool for cycle onset prediction, with an alert issued when shutoff recovery exceeds 50% of the pre?shutoff level. We predict the Cycle 26 shutoff between April–October 2029.},
 year = {2026}
}

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TY - JOUR
T1 - Equatorial Flux Cancellation Imprinted in Solar Wind Helium: A Reliable Herald of the Solar Cycle Transition
AU - Belay Sitotaw Goshu
Y1 - 2026/10/09
PY - 2026
N1 - https://doi.org/10.11648/j.frontiers.20260604.11
DO - 10.11648/j.frontiers.20260604.11
T2 - Frontiers
JF - Frontiers
JO - Frontiers
SP - 121
EP - 135
PB - Science Publishing Group
SN - 2994-7197
UR - https://doi.org/10.11648/j.frontiers.20260604.11
AB - Background: Predicting the onset of a new solar cycle is challenging because the sunspot minimum can only be identified retrospectively. A real time, in situ proxy is needed. Purpose: We investigate whether the solar wind helium abundance (AHe) provides a reliable herald of cycle onset and test the hypothesis that equatorial flux cancellation drives the observed “shutoff” event. Methods: Using ACE/SWICS, Wind/SWE, and OMNI data (1995–2025), we analysed daily AHe across the Cycle 23?24 and Cycle 24-25 minima. Equatorial flux cancellation rates Rcancel were derived from SOHO/MDI and SDO/HMI magnetograms. Cross?correlation and linear regression quantified the relationship between the AHe shutoff and peak cancellation. Findings: AHe exhibits a three-phase pattern: a pre-minimum rise, a sharp shutoff (15–30 days, 60–80% drop), and rapid recovery. The shutoff precedes the smoothed sunspot minimum by 22–117 days. Peak Rcancel leads the shutoff by 19 days on average (cross correlation 0.84, pRcancel, peak (r=0.71, p=0.002). Conclusion: Equatorial flux cancellation imprints a distinct, repeatable signature in solar wind helium, providing a robust, real?time herald of solar cycle transition. Recommendation: Continuous AHemonitoring at L1 should become a standard operational tool for cycle onset prediction, with an alert issued when shutoff recovery exceeds 50% of the pre?shutoff level. We predict the Cycle 26 shutoff between April–October 2029.
VL - 6
IS - 4
ER -

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Belay Sitotaw Goshu

Department of Physics, Dire Dawa University, Dire Dawa, Ethiopia

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http://orcid.org/0000-0002-6887-7218

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Table 1

Table 1. Lead times of shutoff events relative to smoothed sunspot number minimum (SSNmin).

Plain Text BibTeX RIS

APA Style

Goshu, B. S. (2026). Equatorial Flux Cancellation Imprinted in Solar Wind Helium: A Reliable Herald of the Solar Cycle Transition. Frontiers, 6(4), 121-135. https://doi.org/10.11648/j.frontiers.20260604.11

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ACS Style

Goshu, B. S. Equatorial Flux Cancellation Imprinted in Solar Wind Helium: A Reliable Herald of the Solar Cycle Transition. Frontiers. 2026, 6(4), 121-135. doi: 10.11648/j.frontiers.20260604.11

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AMA Style

Goshu BS. Equatorial Flux Cancellation Imprinted in Solar Wind Helium: A Reliable Herald of the Solar Cycle Transition. Frontiers. 2026;6(4):121-135. doi: 10.11648/j.frontiers.20260604.11

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@article{10.11648/j.frontiers.20260604.11,
  author = {Belay Sitotaw Goshu},
  title = {Equatorial Flux Cancellation Imprinted in Solar Wind Helium: A Reliable Herald of the Solar Cycle Transition},
  journal = {Frontiers},
  volume = {6},
  number = {4},
  pages = {121-135},
  doi = {10.11648/j.frontiers.20260604.11},
  url = {https://doi.org/10.11648/j.frontiers.20260604.11},
  eprint = {https://article.sciencepublishinggroup.com/pdf/10.11648.j.frontiers.20260604.11},
  abstract = {Background: Predicting the onset of a new solar cycle is challenging because the sunspot minimum can only be identified retrospectively. A real time, in situ proxy is needed. Purpose: We investigate whether the solar wind helium abundance (AHe) provides a reliable herald of cycle onset and test the hypothesis that equatorial flux cancellation drives the observed “shutoff” event. Methods: Using ACE/SWICS, Wind/SWE, and OMNI data (1995–2025), we analysed daily AHe across the Cycle 23?24 and Cycle 24-25 minima. Equatorial flux cancellation rates Rcancel were derived from SOHO/MDI and SDO/HMI magnetograms. Cross?correlation and linear regression quantified the relationship between the AHe shutoff and peak cancellation. Findings: AHe exhibits a three-phase pattern: a pre-minimum rise, a sharp shutoff (15–30 days, 60–80% drop), and rapid recovery. The shutoff precedes the smoothed sunspot minimum by 22–117 days. Peak Rcancel leads the shutoff by 19 days on average (cross correlation 0.84, pRcancel, peak (r=0.71, p=0.002). Conclusion: Equatorial flux cancellation imprints a distinct, repeatable signature in solar wind helium, providing a robust, real?time herald of solar cycle transition. Recommendation: Continuous AHemonitoring at L1 should become a standard operational tool for cycle onset prediction, with an alert issued when shutoff recovery exceeds 50% of the pre?shutoff level. We predict the Cycle 26 shutoff between April–October 2029.},
 year = {2026}
}

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