The solar cycle (or solar magnetic activity cycle) is the periodic change in the sun’s activity (including changes in the levels of solar radiation and ejection of solar material) and appearance (visible in changes in the number of sunspots, flares, and other visible manifestations). Solar cycles have a duration of about 11 years. They have been observed (by changes in the sun’s appearance and by changes seen on Earth, such as auroras) for hundreds of years. Solar variation causes changes in space weather and to some degree weather and climate on Earth. It causes a periodic change in the amount of irradiation from the Sun that is experienced on Earth. It is one component of solar variation, the other being aperiodic fluctuations.
A compilation of significant solar events during Solar Cycle 24 by SolarWatcher.
Solar Cycle 24 is the 24th solar cycle since 1755, when recording of solar sunspot activity began. It is the current solar cycle, and began on 8 January 2008, but there was minimal activity through early 2009.
NASA predicts that solar cycle 24 will peak in early or mid 2013 with about 59 sunspots. This would make it the least active cycle in the past one hundred years. The International Space Environment Service predicts the cycle to peak at 90 sunspots in May 2013.
Prior to the minima between the end of Solar Cycle 23 and the beginning of Solar Cycle 24, there were essentially two competing theories about how strong Solar Cycle 24 would be. The two camps could be distinguished by those believing the Sun retained a long memory (Solar Cycle 24 would be active) or whether it had a short memory (Solar Cycle 24 would be quiet). Prior to 2006, the difference was very drastic with a minority set of researchers predicting “the smallest solar cycle in 100 years.” Another group of researchers, including those at NASA, were predicting that it “looks like its going to be one of the most intense cycles since record-keeping began almost 400 years ago.”
The delayed onset of high latitude spots indicating the start of Solar Cycle 24 led the “active cycle” researchers to revise their predictions downward and the consensus by 2007 was split 5-4 in favor of a smaller cycle. Consensus is now a small cycle as Solar Cycles are much more predictable 3 years after minima.
According to NASA, the intensity of geomagnetic storms during Solar Cycle 24 may be elevated in some areas where the Earth’s magnetic field is weaker than expected. This fact was discovered by the THEMIS spacecraft in 2008.A 20-fold increase in particle counts that penetrate the Earth’s magnetic field may be expected. Solar Cycle 24 has been the subject of various hypotheses and commentary pertaining to its potential effects on Earth.
While acknowledging that the next solar maximum will not necessarily produce unusual geomagnetic activity, astrophysicist Michio Kaku has taken advantage of the media focus on the 2012 phenomenon to draw attention to the need to develop strategies for coping with the terrestrial damage that such an event could inflict. He asserts that governments should ensure the integrity of electrical infrastructures, so as to prevent a recurrence of disruption akin to that caused by the solar storm of 1859.
The current solar cycle is currently the subject of research, as it does not appear to be generating sunspots in the manner which would be expected. Sunspots did not begin to appear immediately after the last minimum (in 2008) and although they started to reappear in late 2009, they are at significantly lower than anticipated. (Wiki)
On April 19, 2012, the National Astronomical Observatory of Japan predicted that the Sun’s magnetic field will assume a quadrupole configuration in Solar Cycle 24. Generally speaking, the solar magnetic field has a bipolar configuration; like a bar magnet, for example, the Sun’s south and north polar regions have a positive and negative polarity structure respectively.
The Sun’s polar magnetic field is considered to be the origin of sunspots which are known to be the source of solar activity. That behavior will be very important in forecasting solar activity in the future. In the past, polarity reversal was observed by solar telescopes on the ground. Consequently, only the average strength and polarity of the magnetic fields was found due to the lack resolution, and it was not possible to know what was occurring in the solar polar region.
Based on observations conducted with high spatial resolution and high-precision polarimetry of the Solar Optical Telescope (SOT) aboard the “Hinode” satellite in September of 2007, magnetic field patches, which were broad and spotty, with a magnetic field strength comparable to sunspots, were discovered for the first time, scattered in the solar polar region. (Reference: Press release “‘Hinode’ discovered strong magnetic field patches in the Sun’s polar region.”)
Since that, the “Hinode” satellite has been conducting polar observation regularly for four years, during which solar activity passed the solar minimum and has been increasing. As a result, it was discovered during observations conducted in January 2012 that the north polar magnetic field was dwindling close to almost zero, one year earlier than expected. That is to say, the number of magnetic field patches, which play the role of magnetic field spots in the north polar region, decreased rapidly and spots of opposite polarity emerged at low latitudes. Consequently, it is considered that there is a large scale disappearance of the opposite polarity magnetic field and polarity reversal occurring in the north polar region of the sun.
According to these observations, the north polar magnetic field is forecast to shift from negative to positive polarity soon. On the other hand, surprisingly, the “Hinode” has confirmed that there are few signs of polarity reversal in the south polar field, and it is steadily maintaining positive polarity. Generally speaking, the solar magnetic field has a bipolar configuration; like a bar magnet, for example, the sun’s south and north polar regions have a positive and negative polarity structure respectively. However, according to observations by “Hinode,” it is assumed that the solar magnetic field will be a quadrupole structure, where both the north and south have positive polarity. Numerical calculations are being performed to understand the structure of the solar magnetic field based on the “Hinode” observation data.
Solar polar observation is extremely important for forecasting solar activity in the future. The solar minimum, which is the period from the end of the previous solar activity cycle to the beginning of the current cycle, has continued longer than expected (An ordinary solar cycle is approximately 11 years, while the current cycle is 12.6 years). (Hinode)
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