Solar Cycle 24 is the 24th solar cycle since 1755, when recording of solar sunspot activity began.[1][2] It is the current solar cycle, and began on 8 January 2008.[3] The cycle continues to fall below predictions and is currently exhibiting 50% lower sunspot activity than predicted in May 2009.
Contents |
It is predicted that Solar Cycle 24 will peak in May 2013 with about 58[4] sunspots. This would make it the least active cycle since solar cycle 6, which ended in the year 1823.
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.[5][6] A 20-fold increase in particle counts that penetrate the Earth's magnetic field may be expected.[7]
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.[8]
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.[9]
On August 1, 2010, scientists at the Harvard-Smithsonian Center for Astrophysics (CfA) observed a series of four large CMEs emanating from the Earth-facing hemisphere by analyzing images recorded at NASA's Solar Dynamics Observatory. The observed velocities of the ejecta varied between 670,560 m/s and 1,118,000 m/s (metre per second), and were expected to reach the Earth's geomagnetic field sometime between August 4 and early August 5. As of 05:00 UTC August 4, the estimated time of arrival of the series was as follows:
All four ejections were described as large and, according to scientists, possessed enough energy to cause aurorae to be observed by naked eye in non-polar regions.[11] According to reports, aurorae would be visible at night toward the poleward horizon in temperate latitudes between 45° to 50°, and near overhead in regions closer to the poles.[12] The initial coronal mass ejection of August 1 originated from a sunspot designated Sunspot 1092, which was large enough to be seen without the aid of a solar telescope.[13] Aside from the visual effects of this CME series, scientists warned that electric impulses caused by disruptions in the magnetic field due to the ionized particles may damage infrastructure such as power grids and telephone lines not adequately protected against induced magnetic current. It has also been reported that several Earth-orbiting satellites may be in similar danger.[11] According to Leon Golub, an astronomer at CfA:
This eruption is directed right at us and is expected to get here early in the day on August 4. It's the first major Earth-directed eruption in quite some time. When such an expulsion reaches Earth, it interacts with the planet's magnetic field and can create a geomagnetic storm. Solar particles stream down the field lines toward Earth's poles. Those particles crash with atoms of nitrogen and oxygen in the atmosphere, which then glow like little neon signs. Sky watchers in the northern U.S. and other countries should look toward the north late Tuesday or early Wednesday for rippling "curtains" of green and red light.[14]
In the early morning hours of August 4, 2010 aurorae occurred in the northern hemisphere that were visible at latitudes as far south as Michigan and Wisconsin in the United States, and Ontario, Canada near latitude 45° North (see image at right). European observers reported sightings as far south as Denmark near latitude 56° North. The aurorae were reportedly green in color due to the interaction of the solar particles with oxygen atoms in the relatively denser atmosphere of southern latitudes.[15] This, however, was only the first wave of solar wind; the third and last was expected for the evening of August 5,[16] but missed Earth entirely.
Sunspot group 1158 produces an X class solar flare, the first of its kind since December 2006.
In early August, three sunspots unleashed M class flares, with the highest being M9.3.[17][18] On the night of August 5th, auroras were reported as far south as Oklahoma and Alabama. The storm was the biggest since October 2003. The storm also created a G4 out of 5 geomagnetic storm, enough to make power outages. In the southern hemisphere, auroras could have been seen as far north as South Africa, Southern Chile and Southern Australia.
Sunspot 1283 erupted with an M5.3 solar flare on September 5, just after 8 p.m. EDT (00 UTC)[19]
Just 22 hours later, NASA says, an X2.1 class solar flare – some four times stronger than the earlier flare – erupted from the same sunspot region. The second flare peaked on September 6 at 6:20 p.m. EDT (22:20 UTC)[20]
A day later, a third (slightly weaker) X1.8-class event on flare erupted from sunspot 1283 on September 7 at 6:38 p.m. EDT.(22:38 UTC).
An Aurora alert was issued for September 8-11. An X class flare can cause a "strong" radio blackout, categorized as R3, has the potential to cause about an hour-long blackout. [21]
Then on September 24, a large X2 flare erupted out of sunspot 1302. The flare was not earth directed. On the next day, a M7 flare was unleashed out of the same sunspot. [22]
On October 22, 2011, the sun unleashed a M1 flare, this time, was heading towards Mars.[23]
Solar activity increased again in late-December, with the sun unleashing M-flares. The most intense flare was an M4 flare at 18:16 UTC on December 25.[24]
|
|||||||||||||||||||||||||||||||