Solar Cycle 24

Solar Cycle 24
Name	Solar Cycle 24
Start	December 2008
End	December 2019
Smoothed sunspot max	116.4 (approx.)
Max date	April 2014
Preceding	Solar Cycle 23
Following	Solar Cycle 25

Solar Cycle 24 was the 24th numbered cycle in the modern series of solar activity records, spanning roughly from December 2008 to December 2019. The cycle exhibited unusually low activity compared with several 20th century cycles and produced a series of notable solar eruptions, geomagnetic storms, and research campaigns that involved major observatories and space agencies. Its development and consequences were monitored by institutions across multiple countries and influenced studies in heliophysics, space weather forecasting, and technological resilience.

Overview

Solar Cycle 24 began near the minimum following Solar Cycle 23 and reached its smoothed monthly sunspot maximum in April 2014 as measured by agencies such as National Oceanic and Atmospheric Administration and Royal Observatory of Belgium. The cycle featured a double-peaked maximum with activity modulated by magnetic polarity reversals observed by missions including Solar and Heliospheric Observatory, Solar Dynamics Observatory, and Parker Solar Probe precursor ground campaigns involving Big Bear Solar Observatory, Mauna Loa Observatory, and Mount Wilson Observatory. Forecasts and retrospective analyses were published by organizations like European Space Agency, NASA, National Science Foundation, and research groups at Stanford University and Harvard–Smithsonian Center for Astrophysics.

Solar Activity and Sunspot Number

Sunspot counts during the cycle were tracked with the international sunspot number produced by the World Data Center SILSO at the Royal Observatory of Belgium, with peak smoothed values near 116.4 and raw monthly peaks influenced by the dual-peak structure. The cycle’s amplitude was lower than the averages observed during intervals dominated by the Modern Maximum and contrasted with high-activity cycles such as Solar Cycle 19 and Solar Cycle 22. Measurements incorporated long-running datasets from the Greenwich Photo-heliographic Results, magnetograms from the Wilcox Solar Observatory, and helioseismic data from the Global Oscillation Network Group. Comparative analyses referenced reconstructions using cosmogenic isotopes archived at institutions like the Swiss Federal Institute of Technology Zurich and the University of Bern.

Major Events and Geomagnetic Impacts

Notable eruptive events during the cycle included powerful coronal mass ejections and X-class flares detected by instruments on Geostationary Operational Environmental Satellite platforms and the Reuven Ramaty High Energy Solar Spectroscopic Imager. The strong geomagnetic storm in March 2015 produced aurorae observed in regions monitored by the Alaska Volcano Observatory network and affected infrastructures overseen by agencies such as Federal Aviation Administration and Federal Energy Regulatory Commission. The November 2013 and September 2017 events produced fast halo CMEs tracked by the SOHO/LASCO coronagraph and led to geomagnetic alerts disseminated through services run by NOAA Space Weather Prediction Center and Met Office space weather operations. Spacecraft anomalies were reported by operators at Intelsat, Iridium Communications, and research teams managing JAXA missions during select disturbances.

Scientific Observations and Research

Research during and after the cycle advanced understanding of solar dynamo theory, flux transport, and polar field precursors through work by groups at University of Colorado Boulder, Max Planck Institute for Solar System Research, and University of California, Berkeley. Observational campaigns combined data from instruments on SDO/AIA, Hinode, and STEREO with ground-based spectroscopy at Kitt Peak National Observatory and Cerro Tololo Inter-American Observatory. Studies published by researchers affiliated with Princeton University and Columbia University explored connections between sunspot asymmetry, meridional flow variations, and the weak amplitude of the cycle, while model intercomparisons involved teams from NOAA, ESA, and the International Space Environment Service. Cross-disciplinary investigations linked solar forcing to upper-atmosphere responses monitored by NASA's TIMED mission and ionospheric studies by groups at University of Colorado's Laboratory for Atmospheric and Space Physics.

Societal and Technological Effects

Societal impacts included enhanced auroral visibility documented by observers at Greenland, Iceland, and high-latitude communities tracked by agencies such as National Science Foundation (United States). Technological effects encompassed radio blackouts affecting transpolar aviation routes coordinated with the International Civil Aviation Organization and satellite anomalies influencing operators like SES S.A. and Boeing satellite programs. Power grid operators, including those advised by North American Electric Reliability Corporation, incorporated lessons into resilience planning after geomagnetic-induced current assessments performed with research partners at Massachusetts Institute of Technology and Argonne National Laboratory.

Comparison with Other Solar Cycles

When compared to prominent cycles in the 20th century—such as Solar Cycle 19—this cycle was markedly weaker, aligning more closely with minima-era cycles and prompting comparisons to the Dalton Minimum in terms of reduced sunspot numbers. Its double-peaked structure resembled features seen in Solar Cycle 23 but differed in amplitude and timing from Solar Cycle 22 and Solar Cycle 21. Long-term context was provided by analyses of cosmogenic isotope records from Max Planck Institute for Chemistry and historical sunspot compilations curated by the Royal Observatory of Belgium and the World Data Center SILSO, informing projections made by modelers at National Centers for Environmental Prediction and academic teams worldwide.

Category:Solar cycles