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Solar cycle 22
The Sun, with some sunspots visible, during solar cycle 22 (1992).
Sunspot data
Start dateSeptember 1986
End dateAugust 1996
Duration (years)9.9
Max count212.5
Max count monthNovember 1989
Min count13.5
Spotless days309
Cycle chronology
Previous cycleSolar cycle 21 (1976-1986)
Next cycleSolar cycle 23 (1996-2008)

Solar cycle 22 was the 22nd solar cycle since 1755, when extensive recording of solar sunspot activity began.[1][2] The solar cycle lasted 9.9 years, beginning in September 1986 and ending in August 1996. The maximum smoothed sunspot number observed during the solar cycle was 212.5 (November 1989), and the starting minimum was 13.5.[3] During the minimum transit from solar cycle 22 to 23, there were a total of 309 days with no sunspots.[4][5][6]

March 1989 geomagnetic storm

[edit]
Main article: March 1989 geomagnetic storm
Artist's depiction of solar wind colliding with Earth's magnetosphere.

During March 1989, a severe geomagnetic storm caused the collapse of Hydro-Québec's electricity transmission system. The geomagnetic storm causing this event was itself the result of a Coronal Mass Ejection on March 9, 1989.[7] A few days before, on March 6, 1989, a very large X15 solar flare also occurred.[8] At 2:44 am on March 13, 1989, a severe geomagnetic storm struck Earth.[9][10] The storm began on Earth with extremely intense auroras at the poles. The aurora could be seen as far south as Texas.[11] As this occurred during the Cold War, many worried that a nuclear first-strike might be in progress.[11] Others considered the intense auroras to be associated with the Space Shuttle mission STS-29, which had been launched on March 13 at 9:57:00 AM.[12] The burst caused short-wave radio interference, including the disruption of radio signals from Radio Free Europe into Russia. It was initially believed that the signals had been jammed by the Soviet government.

As midnight came and went, invisible electromagnetic forces were staging their own pitched battle in a vast arena bounded by the sky above and the rocky subterranean reaches of the Earth. A river of charged particles and electrons in the ionosphere flowed from west to east, inducing powerful electrical currents in the ground that surged into many natural nooks and crannies.[11]

Some satellites in polar orbits lost control for several hours. GOES weather satellite communications were interrupted causing weather images to be lost. NASA's TDRS-1 communication satellite recorded over 250 anomalies caused by the increased particles flowing into its sensitive electronics.[11] The Space Shuttle Discovery was having its own mysterious problems. A sensor on one of the tanks supplying hydrogen to a fuel cell was showing unusually high pressure readings on March 13. The problem went away just as mysteriously after the solar storm subsided.

The variations in the Earth's magnetic field also tripped circuit breakers on Hydro-Québec's power grid. The utility's very long transmission lines and the fact that most of Quebec sits on a large rock shield prevented current flowing through the Earth, finding a less resistant path along the 735 kV power lines.[13]

The James Bay network went offline in less than 90 seconds, giving Quebec its second massive blackout in 11 months.[14] The power failure lasted 9 hours and forced the company to implement various mitigation strategies, including raising the trip level, installing series compensation on ultra high voltage lines and upgrading various monitoring and operational procedures. Other utilities in North America, the UK, Northern Europe and elsewhere implemented programs to reduce the risks associated with geomagnetically induced currents.[13]

Since 1995, geomagnetic storms and solar flares have been monitored from the Solar and Heliospheric Observatory (SOHO) joint-NASA-European Space Agency satellite.

August 1989 geomagnetic storm

[edit]

In August 1989, another geomagnetic storm affected microchips, leading to a halt of all trading on Toronto's stock market.[15] This geomagnetic storm was caused by a very large X20 solar flare on August 16, 1989, which was even stronger than the X15 flare from March 6, 1989, referred above.[8]

Sunquakes discovered

[edit]

"Sunquakes" caused by solar flares were first observed during this cycle. These are running acoustic waves, as opposed to the standing waves that constitute the material of helioseismology. The flare impulse launches these waves from the photosphere, and they arc deeply into the interior of the Sun before refracting back to the surface to appear as faint ripples, expanding radially away from the flare some tens of minutes later. The flare in which these waves were first observed, SOL1996-07-09, occurred more than three years after the last previous major event.[16]

See also

[edit]

References

[edit]
Revisions and contributorsEdit on WikipediaRead on Wikipedia

Solar cycle 22

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Solar cycle 22 was the twenty-second recorded solar cycle since systematic sunspot observations began in 1755, spanning from the minimum in September 1986 to the subsequent minimum in August 1996, with a duration of approximately 10 years.[1] It featured a notably rapid ascent phase, rising from minimum to maximum in just 38 months, the second-shortest such rise among all recorded cycles.[2] The cycle reached its peak in November 1989, achieving a maximum smoothed international sunspot number of 212.5, making it one of the strongest modern solar cycles and ranking among the top ten overall in terms of sunspot activity.[1] This period of heightened solar activity was characterized by intense phenomena, including a high number of solar flares, coronal mass ejections, and solar proton events, with six major proton events exceeding thresholds observed during the cycle—levels reminiscent of the exceptionally active cycle 19.[3] One of the most significant events was the severe geomagnetic storm of March 13, 1989, triggered by a coronal mass ejection, which caused widespread auroral displays and led to a major power blackout affecting 6 million people in Quebec, Canada, for up to 9 hours due to induced currents overwhelming the electrical grid.[4][5] Observations during cycle 22, supported by missions like the Solar Maximum Mission, provided key insights into solar irradiance variations and ultraviolet emissions, revealing cycle amplitudes in spectral irradiance that influenced atmospheric and space weather studies.[6] Overall, the cycle's vigor contributed substantially to understanding the 11-year solar oscillation and its impacts on Earth's magnetosphere and technology-dependent infrastructure.[7]

Overview

Duration and Phases

Solar cycle 22 officially began in September 1986, marked by the onset of rising sunspot activity following the minimum of solar cycle 21, with a smoothed minimum sunspot number of 13.5 indicating a low-activity baseline.[1] The cycle concluded in August 1996, as it transitioned into the minimum preceding solar cycle 23.[1] Overall, the cycle spanned 9.9 years, which is shorter than the typical 11-year average for solar cycles.[2] The cycle progressed through distinct phases, beginning with a rising phase from 1986 to 1989, during which sunspot emergence accelerated over approximately 38 months.[2] This led into the maximum phase in late 1989 to early 1990, characterized by the period of peak solar activity.[1] The subsequent declining phase, from 1990 to 1996, featured a gradual reduction in activity, culminating in an extended minimum with 309 spotless days during the transition to the next cycle.[8]

Sunspot Progression and Peak

Solar cycle 22 exhibited a rapid ascent in sunspot activity following the minimum in September 1986, with the smoothed international sunspot number rising from 13.5 to a peak of 212.5 in November 1989.[1] This marked one of the strongest cycles in recorded history, surpassing the average intensity and ranking third among modern cycles, behind only cycles 19 and 21 in terms of maximum amplitude.[1] The cycle's progression reflected the typical waxing and waning of solar magnetic activity, but with notable vigor during its ascending and maximum phases. The monthly sunspot number reached a high of 284.5 in June 1989, amid significant variability that saw fluctuations of over 50 units between consecutive months around the peak period.[9] Annual mean sunspot numbers illustrate the cycle's trajectory, starting low at the minimum and climbing steeply before a gradual decline:
YearAnnual Mean Sunspot Number
198614.8
198733.9
1988123.0
1989211.1
1990191.8
1991203.3
1992133.0
199376.1
199444.9
199525.1
199611.6
Data from SIDC version 2.0 series.[10] By 1996, activity had waned to near-minimum levels, signaling the transition to cycle 23. Over the full cycle, observers recorded approximately 12,000 individual sunspots, underscoring the cycle's robust output compared to quieter periods.[11] The decline phase featured 309 spotless days during the minimum transition to cycle 23, a relatively deep quiet interval that highlighted the cycle's complete evolution from high activity to dormancy.[12] Sunspot distribution displayed mild hemispheric asymmetry, with the northern hemisphere contributing more prominently near the peak.[13]

Solar Phenomena

Sunspots and Magnetic Activity

Solar cycle 22 exhibited notable north-south asymmetry in sunspot distribution, with the northern solar hemisphere dominating activity and hosting approximately 54% of the sunspots throughout the cycle.[14] This imbalance contributed to uneven magnetic activity between the hemispheres, influencing the overall evolution of solar phenomena during the cycle.[15] The asymmetry was particularly evident during the maximum phase, where northern hemisphere sunspots outnumbered those in the south, reflecting underlying dynamo processes that favored flux emergence in the north.[16] Prominent active regions exemplified the cycle's magnetic complexity, such as NOAA active region 5395 in March 1989, which emerged during the ascending phase and hosted multiple sunspot groups within a large complex.[17] This superactive region featured rapid evolution of magnetic elements, including the growth and decay of umbrae, and sustained high levels of activity over its disk passage, contributing to prolonged sunspot visibility and enhanced local magnetic fields.[18] Such complexes underscored the cycle's propensity for concentrated magnetic activity, often leading to regions capable of producing significant solar events. The evolution of the solar magnetic field during cycle 22 included the reversal of polar fields around 1989–1990, marking a key transition in the global dynamo.[19] This reversal occurred earlier and more abruptly in the northern hemisphere, beginning in early 1990 and completing by mid-1990, compared to the southern hemisphere where it started later in 1991 and finished by late that year, highlighting hemispheric asymmetry in field strength and timing.[19] The stronger northern reversal aligned with the overall northern dominance, as unipolar magnetic regions migrated poleward to facilitate the polarity flip. Sunspots in cycle 22 adhered to Spörer's law, emerging initially at high latitudes of approximately 35° in both hemispheres around 1986 before drifting equatorward to about 15° by the cycle's peak.[20] This latitudinal migration reflected the conveyor-belt model of the solar dynamo, with sunspot zones broadening and shifting progressively toward the equator as the cycle advanced. High magnetic flux emergence during the cycle served as a strength indicator, correlating with elevated peaks in the 10.7 cm radio flux exceeding 200 solar flux units (sfu), which measured the enhanced non-thermal emissions from active regions.[21]

Flares and Coronal Mass Ejections

Solar cycle 22 was marked by intense solar flare activity, with numerous X-class events characterized by peak soft X-ray fluxes exceeding 10^{-4} W/m². These flares originated from complex active regions and released vast amounts of energy, often in the form of electromagnetic radiation across X-ray, ultraviolet, and radio wavelengths. The cycle's heightened magnetic complexity led to a higher incidence of powerful eruptions compared to preceding cycles, contributing to significant solar phenomena observed throughout its duration.[2] One of the most intense flares of the cycle occurred on August 16, 1989, classified as an X20 event based on its extraordinary soft X-ray emission, making it one of the strongest recorded up to that time. This flare produced extreme levels of radiation, surpassing many historical benchmarks for X-ray intensity. Earlier in the cycle, on March 6, 1989, an X15-class flare erupted from active region 5395, releasing immense energy and triggering a massive coronal mass ejection that highlighted the region's prodigious activity. Active region 5395 alone generated 11 X-class flares over a 14-day period in March, underscoring the episodic peaks in flare productivity during the cycle.[22][23][2] The cycle featured over 100 X-class flares overall, with notable clustering during periods of maximum activity, such as the 11 events in March 1989 from a single active region. These bursts of flare frequency reflected the solar dynamo’s peak efficiency in generating twisted magnetic fields prone to reconnection. Major flares during the cycle were frequently associated with coronal mass ejections, many of which were high-speed events reaching velocities up to 2000 km/s or more, including full-halo CMEs that expanded symmetrically and were observable from Earth-directed perspectives. These halo CMEs often enveloped the coronagraph field of view, indicating their broad angular extent and potential for geoeffectiveness.[24][25][26] Solar cycle 22 produced numerous significant solar proton events, with integrated fluences surpassing 10^9 protons/cm² above 10 MeV in several cases, marking some of the highest particle outputs observed in modern records up to that cycle. These events stemmed primarily from the acceleration of protons in flare-related shocks or CME-driven interplanetary shocks, posing risks to high-altitude aviation and satellites. The cycle's proton activity was comparable to that of earlier intense periods, like solar cycle 19, emphasizing its status as one of the most prolific for energetic particle releases.[27] Major flares during the cycle frequently generated intense type II and type IV radio bursts, with type II emissions tracing shock propagation through the corona and type IV indicating persistent synchrotron radiation from flare-accelerated electrons trapped in magnetic structures. These bursts, often spanning decametric to metric wavelengths, led to widespread radio blackouts by overwhelming ionospheric absorption and enhancing noise levels, disrupting shortwave communications globally during peak events like those in March and August 1989.[28][29]

Space Weather Impacts

Geomagnetic Storms

Solar cycle 22 produced numerous geomagnetic storms of G3 (strong) intensity or greater, exceeding the frequency observed in average solar cycles due to heightened solar activity, including frequent coronal mass ejections (CMEs) and high-speed solar wind streams.[30] These storms were often triggered by preceding solar flares that launched CMEs toward Earth, with interplanetary causes such as high-speed solar wind streams reaching up to 800 km/s and sustained southward orientations of the interplanetary magnetic field (IMF) enhancing their geoeffectiveness by facilitating energy transfer into the magnetosphere.[31] The most intense event was the G5 (extreme) geomagnetic storm on March 13, 1989, initiated by a CME associated with an X15-class solar flare on March 9; it reached a minimum Dst index of -589 nT and represented the longest duration of severe storm conditions in the cycle, lasting over 24 hours at intense levels.[32] Auroral activity during this storm expanded dramatically to mid-latitudes, with displays visible as far south as Florida, Cuba, and Puerto Rico.[33] A major solar proton event on August 16, 1989, associated with an X20-class solar flare and CME from active region 5629, produced moderate geomagnetic disturbances (Dst ≈ -145 nT) and significant radiation effects, including single-event upsets that halted trading on the Toronto Stock Exchange for 90 minutes due to computer failures.[34] In October 1989, a series of G4-level storms from October 20–21, precursors to later "Halloween storms" in subsequent cycles, were triggered by multiple CMEs following an X13-class flare on October 19, with Dst minima of -202 nT and -268 nT, respectively, and notable impacts on ionospheric and auroral dynamics at high latitudes.[35]

Technological and Environmental Effects

One of the most significant technological impacts of Solar cycle 22 occurred during the March 1989 geomagnetic storm, when geomagnetically induced currents (GICs) overwhelmed the Hydro-Québec power grid in Canada, causing a complete blackout that lasted nine hours and affected six million people across the province.[36] The GICs, induced by rapid changes in Earth's magnetic field, saturated transformer cores and triggered protective relays, leading to cascading failures in the high-voltage transmission system.[37] This event resulted in estimated damages exceeding $2 billion, including direct costs from equipment damage and indirect losses from disrupted services such as water treatment and transportation.[38] Satellite operations faced substantial disruptions during the same March 1989 storm, with over 1,300 tracked space objects temporarily lost due to atmospheric drag and radiation effects, while specific satellites like TDRS-1 experienced single-event upsets that compromised attitude control and data relay functions.[39][40] In August 1989, an intense solar proton event (peak flux >10^4 pfu >10 MeV) associated with active region 5629 caused radiation-induced degradation to satellite electronics and solar arrays, accelerating wear equivalent to years of normal operation and forcing operational adjustments for affected spacecraft.[41] Communication systems were severely hampered, particularly high-frequency (HF) radio links in polar regions, which suffered blackouts lasting hours due to ionospheric disturbances that absorbed or scattered signals.[36] Early GPS navigation systems, operational since the mid-1980s, also encountered signal degradation from these ionospheric irregularities, leading to reduced accuracy in positioning for military and civilian users reliant on the nascent network.[42] Aviation operations were compelled to adapt to heightened radiation risks, with airlines such as Delta and United rerouting polar flights during the March and August 1989 storms to avoid exposure zones near the poles, where cosmic ray showers intensified; these diversions added millions in fuel costs and delays per event, averaging over $100,000 per rerouted flight.[5][43] Environmentally, the storms produced vivid auroral displays visible globally, extending as far south as the Caribbean and southern U.S. states like Texas and Florida, due to charged particles precipitating into the atmosphere over unusually wide latitudes.[33] Minor ionospheric scintillation further impacted aviation by causing signal fading in VHF communications and early satellite-based navigation over auroral zones.[44] The major storms of Solar cycle 22, such as the Quebec blackout and widespread disruptions, underscored critical vulnerabilities in power grids, satellite infrastructure, and communication networks.

Scientific Discoveries

Sunquakes

Sunquakes, seismic disturbances on the Sun's surface triggered by solar flares, were first observed during solar cycle 22 on July 9, 1996, in association with an X2.6-class flare originating from active region 7978. This event was detected using the Michelson Doppler Imager (MDI) aboard the Solar and Heliospheric Observatory (SOHO), which recorded p-mode oscillations manifesting as expanding ripples in the photospheric Doppler velocity. The flare, peaking at approximately 09:11 UT, marked the inaugural detection of flare-induced helioseismic activity, highlighting the dynamic coupling between solar surface events and subsurface responses.[45] The mechanism underlying this sunquake involves the impact of downward-propagating flare ribbons—energetic particle beams and plasma flows—striking the solar surface, thereby generating acoustic waves. Unlike the standing p-mode oscillations used in traditional helioseismology to probe the Sun's interior, these are running waves that propagate outward as coherent wavefronts. Key characteristics include initial propagation speeds ranging from 7 to 20 km/s, accelerating with distance due to decreasing atmospheric density, with visible energy ripples persisting for several hours and Doppler velocity amplitudes reaching up to 40 m/s. These features were captured in time-distance diagrams from MDI data, revealing a localized excitation source near the flare's hard X-ray footpoints. This discovery provided crucial evidence for the efficient transfer of flare-released magnetic energy into the solar interior via acoustic perturbations, validating theoretical models of flare reconnection and particle acceleration dynamics. The sunquake's total energy release was estimated to be about 40,000 times that of the 1906 San Francisco earthquake, underscoring the immense scale of solar seismic events.[46] This discovery of the first sunquake prompted further studies, with additional sunquakes detected in subsequent solar cycles, leading to refined numerical simulations that better modeled wave propagation and damping within the solar convection zone.[47]

Advances in Solar Physics

The launch of the Yohkoh satellite in August 1991 marked a pivotal advancement in solar observations during the maximum phase of Solar Cycle 22, providing the first high-resolution soft X-ray imaging of the solar corona.[48] This capability allowed detailed capture of flares and dynamic coronal structures, revealing mechanisms of magnetic reconnection through features such as X-ray jets, plasmoid ejections, and cusp-like configurations indicative of reconnection sites.[49] Yohkoh's instruments, including the Soft X-ray Telescope (SXT), demonstrated how reconnection drives explosive energy release in the corona, with observations showing plasma inflows and outflows consistent with theoretical models of magnetic field topology changes.[50] The Solar and Heliospheric Observatory (SOHO), launched in December 1995 toward the end of Solar Cycle 22, further revolutionized coronal and interior studies with its suite of instruments.[51] Early data from the Large Angle and Spectrometric Coronagraph (LASCO) provided unprecedented views of coronal mass ejections (CMEs), enabling the tracking of their initiation and propagation from the solar surface.[52] Complementing this, the Michelson Doppler Imager (MDI) delivered initial measurements of the Sun's interior dynamics and surface magnetic fields via helioseismology, which supported real-time monitoring of solar activity for space weather forecasting.[53] These observations during the cycle's declining phase laid the groundwork for understanding CME origins and solar oscillations. Studies of solar proton events (SPEs) during Solar Cycle 22, which included approximately 60 events above 10 MeV with several high-fluence examples exceeding 10,000 pfu, significantly advanced models of galactic cosmic ray modulation.[54] Analysis of these events, particularly the large-fluence ones associated with powerful flares and shocks, revealed enhanced heliospheric turbulence that suppresses cosmic ray fluxes more effectively than in prior cycles, refining drift and diffusion parameters in modulation theories.[55] For instance, the October 1989 event's prolonged high-energy proton emission highlighted shock acceleration efficiencies, improving predictions of Forbush decreases in cosmic ray intensity.[56] Data on polar field reversals during Solar Cycle 22, observed through magnetograms showing the northern reversal in 1989 and southern in 1990, refined Babcock-Leighton dynamo models by validating the role of surface flux transport in regenerating the poloidal field.[19] These observations demonstrated how decaying bipolar regions contribute to poleward flux migration, sustaining the 22-year Hale cycle through alpha-effect generation at mid-latitudes.[57] The cycle's strong polar fields at minimum provided quantitative constraints, enhancing model accuracy for predicting cycle amplitudes via poloidal-toroidal field conversions.[58] Observations of north-south hemispheric asymmetry in sunspot activity during Solar Cycle 22, where the northern hemisphere peaked earlier and stronger than the south, spurred theories on nonlinear dynamo effects such as alpha-quenching and meridional flow variations.[59] This asymmetry, persisting across the cycle, indicated dynamo saturation mechanisms that couple hemispheres through differential rotation and flux emergence irregularities, leading to models incorporating stochastic bipole tilts for realistic cycle irregularities. Such insights emphasized nonlinear feedback in the solar dynamo, explaining deviations from symmetric Hale cycle behavior.[60]

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  11. Sunspot Number | SIDC
  12. [PDF] Comparison of Solar Cycle 24 with 3 Previous Cycles in respect of ...
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  15. (PDF) N-S Asymmetry And Periodicity Of Daily Sunspot Number ...
  16. Superactive Region AR:5395 of SOLAR-CYCLE-22 - NASA/ADS
  17. Super Active Regions, X-ray Flares and Geo-magnetic Storm
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  19. The Solar Cycle | Living Reviews in Solar Physics
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  23. Evolutionary aspects and north-south asymmetry of soft X-ray flare ...
  24. Low Geo‐Effectiveness of Fast Halo CMEs Related to the 12 X ...
  25. Descriptive study of solar activity sudden increase and Halloween ...
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  28. Low-frequency solar radio type II bursts and their association with ...
  29. Magnetic Storms During the Space Age: Occurrence and Relation to ...
  30. Properties and Geoeffectiveness of Solar Wind High‐Speed ...
  31. A 21st Century View of the March 1989 Magnetic Storm - Boteler
  32. 25 Years Ago: Amazing Auroras from 1989's Great Solar Storm
  33. Solar flare impacts microchips, August 16, 1989 - EDN Network
  34. Global ionospheric effects of the October 1989 geomagnetic storm
  35. Space Weather and Safety
  36. [PDF] March 13, 1989 Geomagnetic Disturbance
  37. Lights Out - Canadian Underwriter
  38. Satellite Anomalies - SolarStorms.org
  39. [PDF] tdrs-1 single event upsets and the effect of the space environment
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  41. Space weather effects on technology
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  44. The Solar Minimum Active Region 7978, Its X2.6/1B Flare, CME, and ...
  45. Solar Flare Leaves Sun Quaking
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  51. The SOHO Mission: an Overview - NASA ADS
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  56. Solar Polar Fields and the 22-Year Activity Cycle - SpringerLink
  57. Can the long-term hemispheric asymmetry of solar activity result ...
  58. Predicting the amplitude and hemispheric asymmetry of solar cycle ...
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