The solar storms of August 1972 were a historically powerful series of solar storms with intense to extreme solar flare, solar particle event, and geomagnetic storm components in early August 1972, during solar cycle 20. The storm caused widespread electric- and communication-grid disturbances through large portions of North America as well as satellite disruptions. On 4 August 1972 the storm caused the accidental detonation of numerous U.S. naval mines near Haiphong, North Vietnam. The coronal mass ejection (CME)'s transit time from the Sun to the Earth is the fastest ever recorded.

The most significant detected solar flare activity occurred from 2 to 11 August. Most of the significant solar activity emanated from active sunspot region McMath 11976 (MR 11976; active regions being clusters of sunspot pairs). McMath 11976 was extraordinarily magnetically complex. Its size was large although not exceptionally so. McMath 11976 produced 67 solar flares (4 of these X-class) during the time it was facing Earth, from 29 July to 11 August. It also produced multiple relatively rare white light flares over multiple days. The same active area was long-lived. It persisted through five solar rotation cycles, first receiving the designation as Region 11947 as it faced Earth, going unseen as it rotated past the far side of the Sun, then returning Earthside as Region 11976, before cycling as Regions 12007, 12045, and 12088, respectively.

The 4 August flare was among the largest since records began. It saturated the Solrad 9 X-ray sensor at approximately X5.3 but was estimated to be in the vicinity of X20, the threshold of the very rarely reached R5 on the NOAA radio blackout space weather scale. A radio burst of 76,000 sfu was measured at 1 GHz. This was an exceptionally long duration flare, generating X-ray emissions above background level for more than 16 hours. Rare emissions in the gamma ray (${\displaystyle \gamma }$-ray) spectrum were detected for the first time, on both 4 and 7 August, by the Orbiting Solar Observatory (OSO 7). The broad spectrum electromagnetic emissions of the largest flare are estimated to total 1-5 x 10³² ergs in energy released.

The arrival time of the associated coronal mass ejection (CME) and its coronal cloud, 14.6 hours, remains the record shortest duration as of November 2023, indicating an exceptionally fast and typically an exceptionally geoeffective event (normal transit time is two to three days). A preceding series of solar flares and CMEs cleared the interplanetary medium of particles, enabling the rapid arrival in a process similar to the July 2012 solar storm. Normalizing the transit times of other known extreme events to a standard 1 AU to account for the varying distance of the Earth from the Sun throughout the year, one study found the ultrafast 4 August flare to be an outlier to all other events, even compared to the great solar storm of 1859, the overall most extreme known solar storm, which is known as the "Carrington Event". This corresponds to an ejecta speed of an estimated 2,850 km/s (1,770 mi/s).

The near Earth vicinity solar wind velocity may also be record-breaking and is calculated to have exceeded 2,000 km/s (1,200 mi/s) (about 0.7% of light speed). The velocity was not directly measurable as instrumentation was off-scale high. Analysis of a Guam magnetogram indicated a shockwave traversing the magnetosphere at 3,080 km/s (1,910 mi/s) and astonishing sudden storm commencement (SSC) time of 62 s. Estimated magnetic field strength of 73-103 nT and electric field strength of >200 mV/m was calculated at 1 AU.

Reanalysis based on IMP-5 (a.k.a. Explorer 41) space solar observatory data suggests that >10-MeV ion flux reached 70,000 particles·s^-1·sr^-1·cm^-2 (i.e. 70,000 particles per second, per steradian, per square centimeter; see Radiance) bringing it near the exceedingly rarely reached NOAA S5 level on the solar radiation scale. Fluxes at other energy levels, from soft to hard, at >1 MeV, >30 MeV, and >60 MeV, also reached extreme levels, as well as inferred for >100 MeV. The particle storm led to northern hemisphere polar stratospheric ozone depletion of about 46% at 50 km (31 mi) altitude for several days before the atmosphere recovered and which persisted for 53 days at the lower altitude of 39 km (24 mi).

The intense solar wind and particle storm associated with the CMEs led to one of the largest decreases in cosmic ray radiation from outside the Solar System, known as a Forbush decrease, ever observed. Solar energetic particle (SEP) onslaught was so strong that the Forbush decrease in fact partially abated. SEPs reached the Earth's surface, causing a ground level event (GLE).

The 4 August flare and ejecta caused significant to extreme effects on the Earth's magnetosphere, which responded in an unusually complex manner. The minimum disturbance storm time index (Dst) was only −154 nT, falling merely within the relatively common "intense" storm category. Initially an exceptional geomagnetic response occurred and some extreme storming occurred locally later (some of these possibly within substorms), but arrival of subsequent CMEs with northward oriented magnetic fields is thought to have shifted the interplanetary magnetic field (IMF) from an initial southward to northward orientation, thus substantially suppressing geomagnetic activity as the solar blast was largely deflected away from rather than toward Earth. An early study found an extraordinary asymmetry range of ≈450 nT. A 2006 study found that if a favorable IMF southward orientation were present that the Dst may have surpassed −1,600 nT, comparable to the 1859 Carrington Event, and a 2024 study found that such a storm could have produced a 774–775-scale solar particle event.