Solar cycle 24

Solar cycle 24
	ISES Solar Cycle 24 Sunspot Number Progression
Sunspot data
Start date	December 2008
End date	May 2020
Max count	81.8
Max count month	April 2014
Min count	2.2
Spotless days	489
Cycle chronology
Previous cycle	Solar cycle 23 (1996-2008)
Next cycle	Solar cycle 25 (2019-~2030)

Solar Cycle 24 was the most recent solar cycle, the 24th since 1755, when extensive recording of solar sunspot activity began.[1][2] It began in December 2008 with a smoothed minimum sunspot number of 2.2,[3] and ended in December 2019.[4] Activity was minimal until early 2010.[5][6] It reached its maximum in April 2014 with a 23 months smoothed sunspot number of 81.8.[7] This maximum value was substantially lower than other recent solar cycles, down to a level which had not been seen since cycles 12 to 15 (1878-1923).

NASA Solar Cycle 24 Sunspot Number Prediction

Predictions

Prior to the minimum between the end of Solar Cycle 23 and the beginning of Solar Cycle 24, two theories predicted how strong Solar Cycle 24 would be. One camp postulated that the Sun retained a long memory (Solar Cycle 24 would be active) while the other asserted that it had a short memory (quiet). Prior to 2006, the difference was substantial with a minority of researchers predicting "the smallest solar cycle in 100 years."[8] Another group of researchers, including one at NASA, predicted that it "looks like its going to be one of the most intense cycles since record-keeping began almost 400 years ago."[9]

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.[10] By 2012, consensus was a small cycle, as solar cycles are much more predictable 3 years after minima.

In May 2009 the NOAA Space Weather Prediction Center's Solar Cycle 24 Prediction Panel predicted the cycle to peak at 90 sunspots in May 2013.[11] In May 2012 NASA's expert David Hathaway predicted a peak in Spring of 2013 with about 60 sunspots.[12]

NASA funded and used Ken Schatten's physics-based models,[13] which utilized a solar Dynamo model, to accurately predict the low. This method used the correlation between solar magnetic field strength at solar minimum to sunspot number at solar maximum to accurately predict the peak solar flux of each of the last three solar cycles. Schatten's predictions become accurate as early as solar minima, 5–6 years before solar max.

Results

In early 2013, after several months of calm, it was obvious that the active 2011 was not a prelude to a widely predicted late 2012-early 2013 peak in solar flares, sunspots and other activity. This unexpected stage prompted some scientists to propose a "double-peaked" solar maximum, which then occurred. The first peak reached 99 in 2011 and the second peak came in early 2014 at 101.[14]

Speculation

The 2008 breach of Earth's magnetic shield

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.[15][16] A 20-fold increase in particle counts that penetrate the Earth's magnetic field may be expected.[17] 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 took 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 asserted that governments should ensure the integrity of electrical infrastructure, so as to prevent a recurrence of disruption akin to that caused by the solar storm of 1859.[18]

The current solar cycle is currently the subject of research, as it is not generating sunspots in the expected manner. Sunspots did not begin to appear immediately after the last minimum (in 2008) and although they started to reappear in late 2009, they were at significantly lower rates than anticipated.[19]

On April 19, 2012, the National Astronomical Observatory of Japan predicted that the Sun's magnetic field would assume a quadrupole configuration.[20]

Throughout 2012, NASA posted news releases discrediting the 2012 phenomenon and the so-called Mayan prophecy, delinking them from solar activity and space weather.[21][22]

Events

Solar flares by year
10 20 30 40 2008 2009 2010 2011 2012 2013 2014 2015 2016 2017 2018 2019 M5-M9 X1-X5 X5-X9

The strongest flares of Solar Cycle 24 (above M5.0 class) and related events
Class	Year	Date	Sunspot region	Radio B.	SR Storm	CME	GM Storm
X9.33	2017	Sep 6	2673	R3	S1	Yes	-
X8.2	2017	Sep 10	2673	R3	S3	Yes	-
X6.9	2011	Aug 9	1263	R3	S1	Yes	-
X5.4	2012	Mar 7	1429	R3	S3	Yes	G3
X4.9	2014	Feb 25	1990	R3	S1	Yes	G2
X3.3	2013	Nov 5	1890	R3	-	Yes	-
X3.2	2013	May 14	1748	R3	-	Yes	-
X3.19	2014	Oct 24	2192	R3	-	No	-
X2.8	2013	May 13	1748	R3	-	Yes	-
X2.74	2015	May 5	2339	R3	-	Yes	-
X2.3	2013	Oct 29	1875	R3	-	Yes	-
X2.2	2011	Feb 15	1158	R3	-	Yes	G1
X2.2	2014	Jun 10	2087	R3	-	?	-
X2.2	2015	Mar 11	2297	R3	-	Yes	-
X2.2	2017	Sep 6	2673	R3	-	?	-
X2.1	2013	Oct 25	1882	R3	-	Yes	-
X2.1	2011	Sep 6	1283	R3	S1	Yes	G3
X2.0	2014	Oct 26	2192	R3	-	No	-
X2.0	2014	Oct 27	2192	R3	-	No	-
X1.9	2011	Nov 3	1339	R3	-	Yes	-
X1.9	2011	Sep 24	1302	R3	S1	Yes	G4
X1.8	2011	Sep 7	1283	R3	S1	Yes	G1
X1.8	2012	Oct 23	1598	R3	-	No	-
X1.8	2014	Dec 20	2242	R3	-	Yes	-
X1.7	2013	Oct 25	1882	R3	-	Yes	-
X1.7	2012	Jan 27	1402	R3	S2	Yes	-
X1.7	2013	May 13	1748	R3	-	Yes	-
X1.66	2014	Sep 10	2158	R3	S2	Yes	G3
X1.6	2014	Oct 22	2192	R3	-	No	-
X1.5	2011	Mar 9	1166	R3	-	Yes	G2
X1.5	2014	Jun 10	2087	R3	-	?	-
X1.4	2011	Sep 22	1302	R3	-	Yes	-
X1.4	2012	Jul 12	1520	R3	S1	Yes	G2
X1.3	2012	Mar 7	1430	R3	S3	No	-
X1.3	2014	Apr 25	2035	R3	-	?	-
X1.3	2017	Sep 7	2673	R3	S2	No	G4
X1.2	2014	Jan 7	1944	R3	S2	Yes	-
X1.2	2013	May 15	1748	R3	S1	Yes	G1
X1.1	2012	Mar 5	1429	R3	-	Yes	G2
X1.1	2012	Jul 6	1515	R3	S1	Yes	G1
X1.1	2013	Nov 8	1890	R3	-	Yes	-
X1.1	2013	Nov 10	1890	R3	-	Yes	-
X1.1	2014	Oct 19	2192	R3	-	No	-
X1.0	2013	Nov 19	1893	R3	S1	Yes	-
X1.0	2013	Oct 28	1875	R3	S1	Yes	-
X1.0	2014	Mar 29	2017	R3	-	?	-
X1.0	2014	Jun 11	2087	R3	-	?	-
X1.0	2014	Oct 25	2192	R3	-	No	-
M9.9	2014	Jan 1	1936	R2	-	Yes	-
M9.3	2013	Oct 24	1877	R2	-	Yes	-
M9.3	2011	Aug 4	1261	R2	S1	Yes	G4
M9.3	2011	Jul 30	1260	R2	-	No	-
M9.3	2014	Mar 12	1996	R2	-	?	-
M9.2	2015	Mar 7	2339	R2	-	Yes	-
M9.0	2012	Oct 20	1598	R2	-	Yes	-
M8.7	2012	Jan 23	1402	R2	S3	Yes	G1
M8.7	2014	Oct 22	2192	R2	-	No	-
M8.7	2014	Dec 17	2242	R2	-	Yes	-
M8.4	2012	Mar 10	1429	R2	-	Yes	-
M8.3	2010	Feb 12	1046	R2	-	Yes	-
M8.2	2015	Mar 3	2290	R2	-	Yes	-
M8.1	2017	Sep 8	2673	R2	-	?	-
M7.9	2012	Mar 13	1429	R2	S2	Yes	G2
M7.9	2014	Nov 5	2205	R2	-	Yes	-
M7.9	2015	Jun 25	2371	R2	S1	Yes	G2
M7.7	2012	Jul 19	1520	R2	-	Yes	-
M7.6	2015	Sep 28	2422	R2	-	?	-
M7.6	2016	Jul 23	2567	R2	-	Yes	-
M7.4	2011	Sep 25	1302	R2	-	Yes	G1
M7.3	2014	Apr 18	2036	R2	S1	?	-
M7.3	2014	Oct 2	2173	R2	-	Yes	-
M7.3	2017	Sep 7	2673	R2	-	?	-
M7.2	2014	Jan 7	1944	R2	-	No	-
M7.1	2011	Sep 24	1302	R2	-	Yes	G4
M7.1	2014	Oct 27	2192	R2	-	?	-
M6.9	2012	Jul 8	1515	R2	S1	Yes	-
M6.9	2014	Dec 18	2241	R2	-	Yes
M6.7	2011	Sep 8	1283	R2	-	Yes	G1
M6.7	2014	Oct 27	2192	R2	-	?	-
M6.7	2016	Apr 18	2529	R2	-	Yes	-
M6.6	2011	Feb 13	1158	R2	-	Yes	-
M6.6	2011	Feb 18	1158	R2	-	No	-
M6.6	2014	Jan 30	1967	R2	-	Yes	-
M6.6	2014	Oct 28	2192	R2	-	?	-
M6.6	2015	Jun 22	2371	R2	S2	Yes	G4
M6.5	2013	Apr 11	1719	R2	S2	Yes	-
M6.5	2014	Apr 2	2027	R2	-	?	-
M6.5	2014	Jul 8	2113	R2	-	?	-
M6.5	2014	Nov 3	2205	R2	S1	Yes	-
M6.4	2010	Feb 7	1045	R2	-	Yes	-
M6.4	2013	Dec 31	1936	R2	-	Yes	-
M6.3	2013	Nov 1	1884	R2	-	Yes	-
M6.3	2012	Mar 9	1429	R2	-	Yes	G2
M6.1	2012	Jul 5	1515	R2	-	No	-
M6.1	2012	Jul 28	1532	R2	-	Yes	-
M6.1	2014	Dec 4	2222	R2	-	Yes	-
M6.0	2012	Nov 13	1613	R2	-	Yes	-
M6.0	2011	Aug 3	1261	R2	-	Yes	G4
M5.9	2013	Jun 7	1762	R2	-	Yes	-
M5.9	2014	Aug 24	2151	R2	-	?	-
M5.8	2011	Sep 24	1302	R2	-	?	-
M5.8	2015	Mar 9	2297	R2	-	Yes	-
M5.7	2012	May 10	1476	R2	-	Yes	-
M5.7	2013	May 3	1739	R2	-	Yes	-
M5.7	2014	Nov 16	2209	R2	-	?	-
M5.7	2017	Apr 2	2644	R2	-	No	-
M5.6	2012	Jul 2	1515	R2	-	Yes	-
M5.6	2015	Jan 13	2257	R2	-	No	-
M5.6	2015	Aug 24	2403	R2	-	?	-
M5.5	2012	Aug 18	1548	R2	-	No	-
M5.5	2015	Oct 2	2422	R2	-	?	-
M5.5	2016	Jul 23	2567	R2	-	Yes	-
M5.5	2017	Sep 4	2673	R2	-	?	-
M5.4	2010	Nov 6	1121	R2	-	?	-
M5.4	2014	Nov 6	2205	R2	-	?	-
M5.3	2011	Sep 6	1283	R2	-	Yes	G3
M5.3	2011	Mar 8	1165	R2	-	Yes	G1
M5.3	2012	Jul 4	1515	R2	-	Yes	-
M5.3	2014	May 8	2056	R2	-	?	G1
M5.3	2017	Apr 2	2644	R2	-	No	-
M5.2	2014	Feb 4	1967	R2	-	?	-
M5.1	2012	May 17	1476	R2	S2	Yes	-
M5.1	2013	Oct 28	1875	R2	-	Yes	-
M5.1	2014	Sep 28	2173	R2	-	Yes	-
M5.1	2015	Mar 10	2297	R2	-	Yes	-
Source: Solarham.com[23] and NOAA's SWPC.[24] The CME field indicates whether the solar flare hurled a CME (oriented or not to Earth). The Radio B./SR Storm/GM Storm fields indicate the NOAA scales of radio blackouts/solar radiation storms/geomagnetic storms, being G1 (minor), G2 (moderate), G3 (strong), G4 (severe) and G5 (extreme).

2008

Solar flares in 2008[25]
0.5 1 1.5 2 2.5 3 Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec C M X

On January 4, 2008, a reversed-polarity sunspot appeared, presaging the arrival of Solar Cycle 24 -- though not marking its official beginning. It was high latitude (30° N) and magnetically reversed. NOAA named the spot AR10981, or sunspot 981 for short.[5]
Sunspot 1007 produced the first solar flare above the B-class on November 2, 2008.
Sunspot 1009 produced the first solar flare above the C-class, a C1.4, on December 11, 2008. Only a few sunspots were observed on the surface of the Sun throughout 2008. The smoothed monthly sunspot number reached a minimum in December 2008 (2.2), therefore an international panel of scientists declared that month as the beginning of Solar Cycle 24. [26]

2009

Solar flares in 2009[27]
2.5 5 7.5 10 12.5 15 Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec C M X

Solar activity remained extremely low throughout 2009. The observed monthly sunspots exceeded 10 only in December.

2010

Solar flares in 2010[28]
10 20 30 40 50 60 Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec C M X

January

Sunspot 1041 produced the first solar flare above the M-class, an M2.3 (followed by an M1.7 just seven hours after and by four consecutive M flares, the strongest reaching M3.4, the next day) on January 19, 2010.

February

Sunspot 1046 produced an M8.3-class flare on February 12, 2010. 9 M-class flares were unleashed by active regions 1045 and 1046 this month.

April

On April 5, 2010 the first coronal mass ejection (CME) of Solar Cycle 24 produced by a sunspot (but unrelated to flares; in fact, a single C-class X-ray flux event was registered this month) and causing a true geomagnetic storm was registered. The Kp index, which quantifies disturbances in the horizontal component of Earth's magnetic field, was 7 by then, so the geomagnetic storm reached a G3 (strong level) on the NOAA G-scale.

Multiple coronal mass ejections

On August 1–2, 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. They 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:

Wednesday, August 4 – 07:00 UTC
Wednesday, August 4 – 17:00 UTC
Thursday, August 5 – 00:00 UTC
Thursday, August 5 – 06:00 UTC[29]

All four ejections were described as large and, according to scientists, possessed enough energy to cause aurorae to be observed by the naked eye in non-polar regions.[30] 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.[31] 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.[32] 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 had also been reported that several Earth-orbiting satellites might have been in similar danger.[30] 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.[33]

Solar northern hemisphere during the first eruption as seen in extreme ultraviolet by the Solar Dynamics Observatory.
SDO multi-wavelength image of the August 1, 2010 event.

Solar flare

According to the Solar Dynamics Observatory, these CMEs were probably connected to a C3.2-class solar flare that peaked on August 1 at 08:26 UT. The origin of this blast was sunspot 1092. The connection between both events was established despite the ~400,000 km distance between them.[34]

Aurorae observations

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. 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.[35] This, however, was only the first wave of solar wind; the third and last was expected for the evening of August 5,[36] but missed Earth entirely. The geomagnetic storm reached a G2 (moderate) level on the NOAA scale.

Solar radiation storm

Unrelated to the multiple coronal mass ejections, some days after, on August 14, a C4.4-class flare produced the first solar radiation storm of Solar Cycle 24. The proton storm event was minor, rating at S1, and was easily absorbed by the ionosphere.

November

Active region 1121 emitted an M5.4 flare on November 6.[37]

December

The year 2010 ended up with 21 M-class solar flares.

2011

Solar flares in 2011[38]
50 100 150 200 Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec C M X

'Valentine’s Day' 2011 flare

Peaking at 01:56 UT on February 15, 2011, sunspot group 1158 produced an X2.2-class solar flare. Dubbed the Valentine's Day solar event by the scientific community, it was the first Solar Cycle 24 flare reaching X class level. In fact, it was the first of its class since December 2006. NOAA issued an R3 (strong) radio blackout alert pertaining this prominent x-ray flux event. In addition to flashing Earth with X and UV radiation, the explosion also hurled a CME in Earth's direction. The magnetosphere was impacted on February 18. The CME struck a minor G1-level geomagnetic storm.[39][40]
Shortly before, on February 13, sunspot 1158 had unleashed an M6.6-class solar flare. On February 18, the same active region produced another x-ray burst with the same strength.[41] 13 M-class bursts were registered in February 2011.

March

A CME exploded from the vicinity of sunspot 1164 during the late hours of March 7, 2011. It leapt away from the Sun traveling ~2200 km/s, making it the fastest CME since September 2005.
On March 9, active region 1166 erupted in an X1.5 flare. An R3-level radio blackout was reported. The related CME caused a G2 geomagnetic storm two days later.[42] 21 M-class flares were registered this month.

July

Sunspot 1260 produced an M9.3-class solar flare on July 30, 2011. Because of its brevity, the eruption did not hurl a substantial cloud of ionized material or CME toward Earth, so it was not geoeffective.[43]

The Aug 9, 2011 X6.9-class flare, taken by NASA's Solar Dynamics Observatory (SDO) in extreme UV light at 131 Angstroms.

The active region 1302, responsible for two X-class flares in Sep 22 and 24, 2011. Image taken that month by NASA's SDO.

August

On August 5, 2011, the combined cloud of three consecutive CMEs produced brilliant aurorae, reported as far south as Oklahoma and Alabama. The geomagnetic storm reached a G4 (severe) level, enough to create power outages. It was one of the strongest geomagnetic storms in years. In the southern hemisphere, aurorae could be seen as far north as South Africa, Southern Chile and Southern Australia. The CMEs were hurled by three M-class flares erupting in active sunspot 1261: M1.4 on August 2, M6.0 on August 3 and M9.3 on August 4.[44][45][46]

X6.9-class flare

On August 9 at 08:05 UT, sunspot 1263 produced a massive X6.9-class solar flare, the third X-flare of Solar Cycle 24 and the most powerful so far (as of May 2013). There was also a CME associated with this burst. Although the flare was not Earth-directed, radiation created waves of ionization in Earth's upper atmosphere, briefly disrupting communications at some VLF and HF radio frequencies. An R3-level (strong) radio blackout alert was issued. A proton event greater than 10 MeV (million electron volts) and exceeding 10 pfu (proton flux units) was also reported, so an S1-level solar radiation storm was also issued.[47]

September

Sunspot 1283 erupted with an M5.3-class solar flare on September 6 at 01:50 UT. An R2 (moderate) blackout radio alert was issued. The burst was Earth-directed. Just 21 hours later, an X2.1-class flare – some four times stronger than the earlier flare – erupted from the same sunspot region. NOAA detected an R3 (strong) radio blackout and an S1 (minor) solar radiation storm. The combined CMEs of these bursts arrived at Earth on September 9, provoking a G3 (strong) geomagnetic storm.

The next day, September 7, an X1.8-class solar flare erupted from sunspot 1283, producing an S1 solar radiation storm. A fourth flare, an M6-class, was ejected by the same sunspot on September 8.[48][49][50]

This sequence of flares produced waves of ionization in Earth's upper atmosphere, briefly altering the propagation of low-frequency radio signals around Earth. Moreover, the eruptions hurled clouds of plasma in its direction. CME impacts, strong geomagnetic storms and aurorae were registered from September 9 onwards.

Then, on September 22, an X1.4-class solar flare erupted out of sunspot 1302. An R3-level radio blackout was registered. The blast produced a significant CME, but was not Earth directed. Two days later, an X1.9-class flare, followed in the next 31 hours by a spectacular string of 14 M-class flares, the biggest being two M7 flares, was mostly unleashed out of the same sunspot. The first two explosions, X1.9 and M7.1, propelled a pair of closely spaced CMEs. A G4 (severe) geomagnetic storm was reported on September 26.[51][52]

In total, the Sun produced four X flares and 31 M flares in September 2011, one of the most active months of Solar Cycle 24 so far.

October

The Sun unleashed eight M-class flares this month, being the strongest the M3.9 event, followed by an Earth-directed CME, produced by sunspot 1305 on October 2. Just in the eve, sunspots 1302 and 1305 had emitted flares almost at the same time; the first event was a C-class and the second one reached a M1.2 category. This double eruption, which hurled a double CME as well, were particularly interesting as coincided with the arrival of a comet, discovered by amateur astronomers the previous day, that disintegrated in spectacular fashion when it plunged into the Sun. A very similar scenario happened on May 10–11, 2011.[53]

November

On November 3, 2011, active region 1339, one of the largest sunspots in years - 40,000 km wide and at least twice that in length - unleashed an X1.9-class solar flare. Waves of ionization in the upper atmosphere created an R3 (strong) radio blackout. The related CME was not headed for Earth.[54] 13 M-class flares were registered this month. November 2011 may be considered the most active month of the current Cycle 24 so far, as monthly sunspot count was nearly 100 (96.7) and the same went for the F10.7 Solar Flux (the radio emission from the Sun at a wavelength of 10.7 cm) that racked up a value of 153.1. However, these numbers are well below those of Cycle 23 at its peak. Cycle 23 peak sunspot count was 170 and its F10.7 was about 235.[55]

December

Solar activity increased again in late December, with the Sun unleashing eight M-flares. The most intense flare, produced by sunspot 1385, was an M4.0 event on December 25.[56] The year 2011 ended up with 111 M-class and 8 X-class solar flares.[57]