Long-term solar activity studies using microwave imaging observations and prediction for cycle 25

Gopalswamy, N.; Mäkelä, P.; Yashiro, S.; Akiyama, S.

doi:10.1016/j.jastp.2018.04.005

Cited by 37 publications

(20 citation statements)

References 59 publications

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“…This result is consistent with that obtained by Gopalswamy et al (2018). In addition, the slope of the plot becomes moderate or flat at higher T b .…”

Section: Correlation Between Polar Brightening and Polar Solar Windsupporting

confidence: 92%

Comparative Study of Microwave Polar Brightening, Coronal Holes, and Solar Wind over the Solar Poles

Fujiki

Shibasaki²,

Yashiro

et al. 2019

Sol Phys

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We comparatively studied the long-term variation in polar brightening observed with the Nobeyama Radioheliograph, the polar solar wind velocity with interplanetary scintillation observations at the Institute for Space-Earth Environmental Research, and the coronal hole distribution computed by potential field calculations of the solar corona using synoptic magnetogram data obtained at Kitt Peak National Solar Observatory. First, by comparing the solar wind velocity (V ) and the brightness temperature (T b ) in the polar region, we found good correlation coefficients (CCs) between V and T b in the polar regions, CC = 0.91 (0.83) for the northern (southern) polar region, and we obtained the V -T b relationship as V =12.6 (T b -10 667) 1/2 + 432. We also confirmed that the CC of V -T b is higher than those of V -B and V -B/f , where Fujiki et al.B and f are the polar magnetic field strength and magnetic flux expansion rate, respectively. These results indicate that T b is a more direct parameter than B or B/f for expressing solar wind velocity. Next, we analyzed the long-term variation of the polar brightening and its relation to the area of the polar coronal hole (A). As a result, we found that the polar brightening matches the probability distribution of the predicted coronal hole and that the CC between T b and A is remarkably high, CC = 0.97. This result indicates that the polar brightening is strongly coupled to the size of the polar coronal hole. Therefore, the reasonable correlation of V -T b is explained by V -A. In addition, by considering the anticorrelation between A and f found in a previous study, we suggest that the V -T b relationship is another expression of the Wang-Sheeley relationship (V -1/f ) in the polar regions.

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“…This result is consistent with that obtained by Gopalswamy et al (2018). In addition, the slope of the plot becomes moderate or flat at higher T b .…”

Section: Correlation Between Polar Brightening and Polar Solar Windsupporting

confidence: 92%

Comparative Study of Microwave Polar Brightening, Coronal Holes, and Solar Wind over the Solar Poles

Fujiki

Shibasaki²,

Yashiro

et al. 2019

Sol Phys

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“…Similarly, using the brightness temperature of the 17 GHz microwave emission as a proxy for the field strength, Gopalswamy et al (2018) found that the correlation between this proxy and the sunspot number is maximal for time shifts of $ 4-6 years (depending on cycle and hemisphere). Their forecast for Cycle 25 is a smoothed SSN of 89 for the S hemisphere and 59 for the N hemisphere (the latter being a lower bound as the proxy had not reached its maximum at the time of publication).…”

Section: Extending the Range Of The Polar Precursor: Early Forecasts mentioning

confidence: 99%

Solar cycle prediction

Petrovay

2020

Living Rev Sol Phys

200

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A review of solar cycle prediction methods and their performance is given, including early forecasts for Cycle 25. The review focuses on those aspects of the solar cycle prediction problem that have a bearing on dynamo theory. The scope of the review is further restricted to the issue of predicting the amplitude (and optionally the epoch) of an upcoming solar maximum no later than right after the start of the given cycle. Prediction methods form three main groups. Precursor methods rely on the value of some measure of solar activity or magnetism at a specified time to predict the amplitude of the following solar maximum. The choice of a good precursor often implies considerable physical insight: indeed, it has become increasingly clear that the transition from purely empirical precursors to model-based methods is continuous. Model-based approaches can be further divided into two groups: predictions based on surface flux transport models and on consistent dynamo models. The implicit assumption of precursor methods is that each numbered solar cycle is a consistent unit in itself, while solar activity seems to consist of a series of much less tightly intercorrelated individual cycles. Extrapolation methods, in contrast, are based on the premise that the physical process giving rise to the sunspot number record is statistically homogeneous, i.e., the mathematical regularities underlying its variations are the same at any point of time, and therefore it lends itself to analysis and forecasting by time series methods. In their overall performance during the course of the last few solar cycles, precursor methods have clearly been superior to extrapolation methods. One method that has This article is a revised version of

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“…This unusual behavior has drawn the attention of researchers worldwide who have attempted to predict the amplitude of solar cycle 25 (Bhowmik & Nandy, 2018;Cameron et al, 2016;Gopalswamy et al, 2018;Hathaway & Upton, 2016;Iijima et al, 2017;Janardhan et al, 2015;Jiang et al, 2018;Kakad et al, 2017;Kirov et al, 2018;Macario-Rojas et al, 2018;Pesnell & Schatten, 2018;Petrovay et al, 2018;Sarp et al, 2018;Upton & Hathaway, 2014, 2018. The different estimates of SSN in V1.0 and V2.0 for the amplitude of cycle 25 by different researchers along with the ratio of peak SSN of cycle 25 to cycle 24 are summarized in Table 1.…”

Section: Introductionmentioning

confidence: 99%

Another Mini Solar Maximum in the Offing: A Prediction for the Amplitude of Solar Cycle 25

Janardhan

Ananthakrishnan

2020

JGR Space Physics

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We examine the temporal changes in both solar polar magnetic field (PMF) at latitudes ≥45° and heliospheric magnetic field (HMF) at 1 AU during solar cycles 21–24 with emphasis on the recent activity changes after July 2015, the so called “mini solar maximum” of cycle 24. While unsigned PMF shows solar cycle modulations in cycles 21 and 22, it shows an anti‐correlation with solar cycle variation in cycle 24. In addition, the floor level of the HMF (of 4.6 nT), that is, the value that the HMF returns to at each solar minimum, is breached about 2 years prior to cycle 24 minimum, indicating a reduced HMF floor level of 3.2 ± 0.5 nT in the upcoming cycle 24 minimum. In light of the change of unsigned PMF and the availability of a revised smoothed sunspot number (SSN V2.0) after July 2015, we revisit the correlation of unsigned PMF and HMF at solar minimum. The correlation is used to estimate values of the HMF at the cycle 24 minimum and the amplitude of the upcoming cycle 25. The updated prediction is 134 ± 11 or 131 ± 11 on the revised SSN V2.0 scale assuming the cycle 24 minimum to occur in 2020 or 2021, respectively. The SSN values indicate that the cycle 25 will be stronger than cycle 24 and a little weaker than cycle 23, even if the current solar cycle minimum occurs in 2021 instead of 2020. This implies that we will witness another mini solar maximum in the upcoming cycle 25.

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Long-term solar activity studies using microwave imaging observations and prediction for cycle 25

Cited by 37 publications

References 59 publications

Comparative Study of Microwave Polar Brightening, Coronal Holes, and Solar Wind over the Solar Poles

Comparative Study of Microwave Polar Brightening, Coronal Holes, and Solar Wind over the Solar Poles

Solar cycle prediction

Another Mini Solar Maximum in the Offing: A Prediction for the Amplitude of Solar Cycle 25

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