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The Adjusted Solar Flux & the Start of Solar Cycle 25
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Abstract
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A “Solar Dynamo” (SODA) Index prediction of the amplitude of Solar Cycle 25 is described. The SODA Index combines values of the solar polar magnetic field and the solar spectral irradiance at 10.7 cm to create a precursor of future solar activity. The result is an envelope of solar activity that minimizes the 11-year period of the sunspot cycle. We show that the variation in time of the SODA Index is similar to several wavelet transforms of the solar spectral irradiance at 10.7 cm. Polar field predictions for Solar Cycles 21 – 24 are used to show the success of the polar field precursor in previous sunspot cycles. Using the present value of the SODA index, we estimate that the next cycle’s smoothed peak activity will be about 140±30 solar flux units for the 10.7 cm radio flux and a Version 2 sunspot number of 135±25. This suggests that Solar Cycle 25 will be comparable to Solar Cycle 24. The estimated peak is expected to occur near 2025.2±1.5 year. Because the current approach uses data prior to solar minimum, these estimates may improve as the upcoming solar minimum draws closer.
We present observational signatures of solar cycle 25 onset. Those signatures are visibly following a migratory path from high to low latitudes. They had starting points that are asymmetrically offset in each hemisphere at times that are 21-22 years after the corresponding, same polarity, activity bands of solar cycle 23 started their migration. Those bands define the so-called "extended solar cycle." The four magnetic bands currently present in the system are approaching a mutually cancelling configuration, and solar minimum conditions are imminent. Further, using a tuned analysis of the daily band latitude-time diagnostics, we are able to utilize the longitudinal wave number (m=1) variation in the data to more clearly reveal the presence of the solar cycle 25 bands. This clarification illustrates that prevalently active longitudes (different in each hemisphere) exist at mid-latitudes presently, lasting many solar rotations, that can be used for detailed study over the next several years with instruments like the Spectrograph on IRIS, the Spectropolarimeter on Hinode, and, when they come online, similar instruments on the Daniel K. Inouye Solar Telescope (DKIST) as we watch those bands evolve following the cancellation of the solar cycle 24 activity bands at the equator late in 2019.
In 1981, the production of the international Sunspot Number moved from the
Z\"{u}rich Observatory to the Royal Observatory of Belgium, marking a very
important transition in the history of the Sunspot Number. Those recent decades
are particularly important for linking recent modern solar indices and fluxes
and the past Sunspot Number series. However, large variations have been
recently identified in the scale of the Sunspot Number between 1981 and the
present.
Here, we reconstruct a new average Sunspot Number series $S_N$ using
long-duration stations between 1981 and 2015. We also extend this
reconstruction using long-time series from 35 stations over 1945-2015, which
includes the 1981 transition. In both reconstructions, we also derive a
parallel Group Number series $G_N$. Our results confirm the variable trends of
the Locarno pilot station. We also verify the scale of the resulting 1981-2015
correction factor relative to the preceding period 1945--1980. By comparing the
new $S_N$ and $G_N$ series, we find that a constant quadratic relation exists
between those two indices. This proxy relation leads to a fully constant and
cycle-independent $S_N/G_N$ ratio over cycles 19 to 23, with the exception of
cycle 24. We find a very good agreement between our reconstructed $G_N$ and the
new "backbone" Group Number but inhomogeneities in the original Group Number as
well as the $F_{10.7}$ radio flux and the American sunspot number $R_a$.
This analysis opens the way to the implementation of a more advanced method
for producing the Sunspot Number in the future. In particular, we identify the
existence of distinct subsets of observing stations sharing very similar
personal k factors, which may be a key element for building a future
multi-station reference in place of the past single pilot station.
To investigate the relation between observations of the 10.7 cm flux and the
international sunspot number so that a physical unit may be ascribed to
historical records, both polynomial and power law models are developed giving
the radio flux as a function of sunspot number and vice versa. Bayesian data
analysis is used to estimate the model parameters and to discriminate between
the models. The effect on the parameter uncertainty and on the relative
evidence of normalizing the measure of fit is investigated. The power law
giving flux as a function of sunspot number is found to be the most plausible
model and may be used to estimate the radio flux from historical sunspot
observations.
The Solar Influences Data Analysis Center (SIDC) issued a new version (version 2) of the sunspot number data in July 2015. The 13-month smoothed monthly sunspot number from the new version is used for the first time to research the relations among the feature parameters of solar cycles under the bimodal distribution for the modern era cycles (10–23), and, their physical implications are discussed. These relations are utilized to predict the maximum amplitude of solar cycle 25. Cycle 25 is predicted to start in October 2020 and reach its maximum amplitude of 168.5±16.3 in October 2024, thus, it should be stronger than cycle 24 but weaker than cycle 23.
Over the last decade there has been mounting evidence that the strength of the Sun's polar magnetic fields during a solar cycle minimum is the best predictor of the amplitude of the next solar cycle. Surface flux transport models can be used to extend these predictions by evolving the Sun's surface magnetic field to obtain an earlier prediction for the strength of the polar fields, and thus the amplitude of the next cycle. In 2016, our Advective Flux Transport (AFT) model was used to do this, producing an early prediction for Solar Cycle 25. At that time, AFT predicted that Cycle 25 will be similar in strength to the Cycle 24, with an uncertainty of about 15% . AFT also predicted that the polar fields in the southern hemisphere would weaken in late 2016 and into 2017 before recovering. That AFT prediction was based on the magnetic field configuration at the end of January 2016. We now have 2 more years of observations. We examine the accuracy of the 2016 AFT prediction and find that the new observations track well with AFT's predictions for the last two years. We show that the southern relapse did in fact occur, though the timing was off by several months. We propose a possible cause for the southern relapse and discuss the reason for the offset in timing. Finally, we provide an updated AFT prediction for Solar Cycle 25 which includes solar observations through January of 2018.
Evidence strongly indicates that the strength of the Sun's polar fields near the time of a sunspot cycle minimum determines the strength of the following solar activity cycle. We use our Advective Flux Transport (AFT) code, with flows well constrained by observations, to simulate the evolution of the Sun's polar magnetic fields from early 2016 to the end of 2019 --- near the expected time of Cycle 24/25 minimum. We run a series of simulations in which the uncertain conditions (convective motion details, active region tilt, and meridional flow profile) are varied within expected ranges. We find that the average strength of the polar fields near the end of Cycle 24 will be similar to that measured near the end of Cycle 23, indicating that Cycle 25 will be similar in strength to the current cycle. In all cases the polar fields are asymmetric with fields in the south stronger than those in the north. This asymmetry would be more pronounced if not for the predicted weakening of the southern polar fields in late 2016 and through 2017. After just four years of simulation the variability across our ensemble indicates an accumulated uncertainty of about 15\%. This accumulated uncertainty arises from stochastic variations in the convective motion details, the active region tilt, and changes in the meridional flow profile. These variations limit the ultimate predictability of the solar cycle.
Source: WDC-SILSO, Royal Observatory of Belgium, Brussels". SILSO, World Data Center -Sunspot Number and Long-term Solar Observations
- K F Tapping
Tapping, K. F. 10.7 cm Solar Radio Flux. Space weather Volume 11, issue 7, 2013.
Pages 394-406 http://onlinelibrary.wiley.com/doi/10.1002/swe.20064/full
"Source: WDC-SILSO, Royal Observatory of Belgium, Brussels". SILSO, World Data
Center -Sunspot Number and Long-term Solar Observations, Royal Observatory of
Belgium, on-line Sunspot Number catalogue: http://www.sidc.be/SILSO/, 'year(s)-of-data, 1976 -2018'
"Source 10.7cm radio flux values (sfu): Penticton, B.C., Canada".
10.7cm radio flux values (sfu): Penticton, B.C., Canada
http://www.spaceweather.ca/solarflux/sx-5-mavg-en.php
"NOAA, SWPC Space Weather Operations (SWO)".
Source: Recent Solar Indices of Observed Monthly Mean Values:
ftp://ftp.swpc.noaa.gov/pub/weekly/RecentIndices.txt