When was the last sunspot minimum

In the absence of the shielding more rays reaching the Earth and forming high clouds in the atmosphere, it is leading to the cooling, according to Zarkhova. The possible decrease in temperatures has led to people, even some scientists, to predict that the solar minimum cooling might cause a Little Ice Age and offset the rising temperatures due to global warming.

In February , it released a statement that dispelled the fact that there would be any major effect on global temperature rise due to greenhouse gas emissions due to human activities. It said even during a Grand Solar Minimum, the decrease in climate forcing would only be worth as much as three years of carbon dioxide growth in the atmosphere.

NASA also said the impact of global warming would be six times greater than the cooling caused by the Grand Solar Minimum, and that even if the period lasted for a century, the planet would continue to warm. Scientists takes six months to a year to just decide upon what exactly is happening in the Sun from observations. For instance, on May 29, a NASA spacecraft observed a family of sunspots that were associated with the biggest solar flare since October The solar flare observed by NASA is not big enough to be dangerous, but it could signal the beginning of the 25th solar cycle.

But scientists can only be sure about this in hindsight, after observations have been made for at least six months to one year. In fact, the scientists had gathered at that meeting to precisely predict the next solar maximum with the help of 60 prediction models.

The meeting was important as governments and private companies would need to be informed to shield their equipments and installations from deadly solar flares. The newest models among these resemble modern climate prediction models using physics-based simulations of the Sun to predict how it will evolve and how it will impact solar activity. Even with state-of-the-art models and top scientists reviewing them, the only conclusion that could be drawn was that Sun will attain a peak sunspot range of , and that this will happen sometime between and , during the 25th cycle.

Analysis determines we are in Solar Cycle September 15, - The solar minimum between Solar Cycle 24 and 25 - the period when the sun is least active - happened in December , when the month smoothed sunspot number fell to 1. We are now in Solar Cycle 25 with peak sunspot activity expected in , the panel said. Solar Cycle 24 was average in length, at 11 years, and had the 4th-smallest intensity since regular record keeping began with Solar Cycle 1 in It was also the weakest cycle in years.

Solar maximum occurred in April with sunspots peaking at for the solar cycle, well below average, which is This resulted in solar maximum having fewer sunspots than if the two hemispheres were in phase. Solar Cycle 25 For the past eight months, activity on the sun has steadily increased, indicating we transitioned to Solar Cycle The obtained data for — CE are, in general, consistent with the previously obtained annual and 5-year resolution data, as shown in Fig.

Carbon record and the reconstructed cosmic ray and solar activity cycles around the onset of the Maunder Minimum. Red and gray lines are the high-precision data and their uncertainty ranges.

Blue and gray lines are respectively the data and their uncertainty ranges obtained by Stuiver et al. Daily sunspot groups by Vaquero et al. The black curves in Fig. In Fig. Note that the height of reconstructed sunspot cycle maximum in Fig. The variability of reconstructed GCR intensity in Fig. Although the number of sunspot data is limited around this period, we noticed that the evolution of reconstructed solar cycles is consistent with the observational records of sunspot groups in terms of the relative amplitudes and the timing of the cycle minima, especially for the first two sunspot cycles since telescopic observations began Fig.

Recently, there have also been several researches reconstructing sunspot butterfly diagram for this period 29 , 30 , 31 , 32 , According to those reconstructions, high-latitude sunspots, which can be the sign of the arrival of new solar cycle, had started to appear around the end of CE and CE.

The sunspot cycle minima reconstructed based on carbon are in CE and CE, which are consistent with the reconstructed butterfly diagram.

Note that some of the high-latitude sunspots may start to appear a few months earlier than the actual onset of solar cycle i. For the pre-telescopic era, historical aurorae records can be used to examine the validity of solar cycles reconstructed by carbon Note, however, that peaks in auroral activity may lag sunspot cycle maxima by a few years The minima of reconstructed solar cycles shown in Fig.

Carbon record with improved precision achieved in this study allowed us to discuss the length of each solar cycle. We found that the solar cycle that started around CE lasted about 5 years, much shorter than the mean length of solar cycles.

However, the subsequent cycle shows a distinct lengthening, suggesting that this cycle was lengthened to about 16 years, approximately 5 years longer than the average. Note that the mean cycle length since CE is The subsequent cycle then seems to be about 11 years.

The length of the cycle just before the Maunder Minimum again seems to be lengthened to be about 12—15 years. Extending the high-precision data, therefore, is needed to narrow the estimation range for this cycle. An important finding of this study is that the lengthening of solar cycle started three cycles before the onset of the Maunder Minimum.

In the framework of the flux transport dynamo model, which is known to reproduce several features of solar cycle, solar activity level is determined by either or both of two factors: dynamo excitation by the randomly determined tilt of sunspot pairs 37 and the change in the meridional circulation in the solar convection zone On the one hand, the flow speed of meridional circulation determines the cycle lengths 17 , although its structure is still controversial Under the condition the time-scale of turbulent diffusion of the magnetic field in the convection zone is relatively short, slow meridional circulation could cause a substantial loss of the magnetic field.

One possible interpretation of the multiple lengthened cycles before the Maunder Minimum is that the speed of meridional circulation was significantly slowed down to contribute to the reduction of the magnetic field that emerges on the solar surface as sunspots.

The reconstructed variation of cosmic rays in Fig. The absolute levels of sunspot activity over the subsequent two cycles needs to be determined through the ongoing efforts to discover additional historical records and to improve the methodology of reconstruction 31 ; however, the sunspot reconstructions during the recent decade have indicated a tendency of gradual reduction in the cycle amplitudes toward the Maunder Minimum 5 , 6 , 24 , 31 and are consistent with our results.

The long preparatory period observed at the Maunder Minimum is consistent with what was suggested for the Spoerer Minimum. On the other hand, only one cycle was lengthened before the onset of the Dalton Minimum, which was The Dalton Minimum is different from the Maunder and the Spoerer minima regarding its duration and depth.

We hypothesize that the lengthening of plural neighboring solar cycles, among which at least one cycle is several years longer than 11 years, could be a prerequisite for long-lasting sunspot disappearance. While the length of Solar Cycle 23 was Therefore, current declining tendency in solar activity is less likely to immediately result in a long-lasting sunspot disappearance.

We conclude, however, that the behavior of Solar Cycle 25 would be critically important to the later solar activity and that there remains the possibility that sunspots may disappear for decades in the case Solar Cycle 25 is substantially lengthened. Careful examinations of both the solar surface and the interior are needed throughout the Solar Cycle Our current understanding of solar dynamos will predict the change in meridional circulation only when a large-scale magnetic field is developed to disrupt the flow by the Lorentz force, angular momentum transport, or by the changing pressure balance due to the sunspot emergence However, the sunspot peak of the 16 year-long cycle is not outstandingly high; instead, the preceding cycle shows a significant enhancement in the magnetic activity.

The lagged reduction in the meridional circulation, therefore, is a theoretical challenge to be solved in the future. The data set that supports the findings of this study is listed in Table S1. We used the compact Accelerator Mass Spectrometer AMS installed at the Yamagata University 26 , 27 for the measurement of carbon content in tree rings.

We used two cedar tree samples for this study. This sample covers — CE and was previously used to reconstruct the solar cycles during the Maunder Minimum This tree covers — CE The trees were subdivided into blocks, and each of the annual tree rings was separated to produce graphite as the target material of AMS following the procedures presented by Moriya etal. We introduced into AMS three to four cathodes filled with graphite produced from each of the annual samples and ran the measurements for each target wheel for 14 cycles s for each cycle.

Then, if the conditions of cathodes and the AMS allowed it, we repeated the measurements twice 10—14 cycles. To reduce the systematic errors attributed to the instability of AMS and minimize the error bars of the carbon data, we treated each of the 14 cycles as completely different measurements.

Furthermore, we conducted delta 13C correction for every 0. Table S1 lists the high-precision data obtained from eight years of measurements from to The red circles in Fig. S1b show the weighted mean for all of the measurements.

The gray circles in Fig. S1a are the previously obtained biennial data using the Murou and Yaku cedar samples by Miyahara et al. S1b are the annual data previously obtained by Stuiver et al. The newly obtained high-resolution data are consistent with the IntCal13 data 22 and the annual data by Stuiver et al. Note that the long-term trend in the carbon content is attributed to the long-term variation of solar magnetic activity and the resultant increase of the carbon production rate.

Because of the cumulation of carbon in the atmosphere, it shows an upward trend while the solar magnetic activity is in a relatively weak condition. On the basis of the high-precision data as obtained above, we reconstructed the solar cycles around the onset of the Maunder Minimum.

The procedure is as follows: 1 construct model curves for sunspot cycle, 2 construct correspondent cosmic-ray variations, 3 solve the three-box carbon cycle model to derive the resultant atmospheric carbon variations, and 4 compare them with the high-precision carbon data. A straightforward way to reveal the decadal-scale variation of cosmic rays from the carbon data is to take the differentials of the annual data, solve the carbon cycle model with reverse time according to the carbon budget equation [Eq.

We, therefore, decided to solve the carbon cycle model forward with multiple scenarios of cosmic ray variations. We input the variation of carbon production rate equivalent to the synthetic cosmic ray variations into the carbon cycle model, and compared the resultant atmospheric carbon variation with the high-precision data. In this way, we determined the profile of cosmic ray variations that could well explain the observed carbon and then estimated the most probable variations for solar cycles.

First, we constructed a model curve for the sunspot cycle. Here, we used the sunspot data back to CE 5. By normalizing the sunspot cycles both by the peak numbers and cycle lengths, we averaged the 27 sunspot cycles since CE to construct a typical curve for the sunspot cycle. Then, we constructed synthetic curves for the sunspot cycle. We treated the following four parameters as variables: 1 sunspot number at the cycle maximum, 2 sunspot number at the cycle minimum, 3 cycle length, and 4 the length of the declining phase.

We constructed sunspot cycles with these parameters starting from the sunspot maximum cosmic-ray minimum and obtained the corresponding cosmic-ray variations, as described below. Second, we constructed a model curve for the cosmic-ray variation. Figure S2a indicates the sunspot numbers since 5 , as well as the neutron monitor data obtained at Oulu 44 and Climax Both of the data were normalized, and the Climax data were scaled to the Oulu neutron data Fig.

S2b to average the two series. The combined neutron monitor data Fig. S2c were then compared with the sunspot data. The solar magnetic polarity reverses at every maximum of sunspot decadal-scale cycle, and this polarity influences the trajectory of galactic cosmic rays in the heliosphere. The time profile of the cosmic ray variation, therefore, is dependent on the polarity of the Sun.

Figure S2d indicates the relationship between cosmic rays and the sunspot numbers for positive red circles and negative blue hexagrams polarities. On the basis of the relationship, we constructed a simple model red and blue lines to construct the curves of cosmic-ray cycles from the sunspot activity cycles.

For the positive polarity, we used the second-order approximation of the data. When solar activity is high, transient events such as solar coronal mass ejections significantly influence the reduction of cosmic rays on the Earth.

The influence of solar polarity, therefore, becomes small. On the basis of these two curves, we constructed time profiles of cosmic-ray variations which were used as input to the carbon cycle model.

Finally, we solved the carbon cycle model with multiple possible curves of cosmic-ray variations as input. We used the three-box carbon cycle model with carbon exchange rates presented by Roth and Joos As a setup, we constructed a long-term cosmic ray curve by taking 7-point moving averages of the 5-year resolution data of IntCal13 22 gray, thick line in Fig. S3a and by inversely solving the carbon cycle model.

Figure S3b shows the obtained long-term variation of cosmic rays. To this variation, we connected the synthetic curves of cosmic ray cycles starting around — CE to run the carbon cycle model. Previous study has suggested that carbon peak around — corresponds to solar cycle minimum of negative polarity It allows to estimate that carbon peaks around , , and CE as are seen in Fig.

S3a correspond to solar cycle minima of negative polarity, while the peaks around and correspond to positive polarity. Based on this estimation, we constructed synthetic cosmic-ray curves starting around — CE with negative polarity. We also assumed that the minimal length of the ascending phase of the solar cycle is 2 years. The limitations on the ascending and the declining phase of the cycles were determined based on the evolution of the sunspot cycles since CE Fig. We calculated atmospheric carbon content with the three-box carbon cycle model by inputting the scenarios with the above parameters in steps: 1 5, 2 5, 3 1 year, and 4 1 year.

Then, to examine the degree of coincidence between the modeled carbon and the measured ones blue and red lines in Fig. In this study, we made comparisons between the modeled and measured data for each cosmic-ray cycle, starting from sunspot maximum to the next maximum. We first conducted the calculation of chi-square values for the cycle starting around — CE Cycle 1.