Since the advent more than a century ago of communications using long conductors and wireless, space weather effects on technologies are found to be most pronounced during intervals of solar maximum. Current solar cycle 24 has been small in terms of solar activity and its effects on Earth. Sunspot numbers, F10.7 radio flux, and geomagnetic activity as compiled and reported by the NOAA Space Weather Prediction Center (SWPC; www.swpc.noaa.gov) all show this small activity. Both the F10.7 radio emissions and sunspot numbers are 20% to 25% below the maximum values obtained in cycle 23. In terms of effects on Earth, the smoothed monthly Ap index is about 8, nearly one third the maximum observed in cycle 23 (where peak values more than 20 were measured for several months in 2003 (www.swpc.noaa.gov/SolarCycle/)).
Nevertheless, solar activity during small cycles can still affect technologies, and there always remains the possibility of large events that will attract headline attention in the press. Those researchers still active can recall the large solar event of 4 August 1972, in the declining phase of cycle 20. Before coronal mass ejections were officially identified, the transit time of the disturbance to reach Earth was about 15 h, implying a solar wind speed of order 2500 km/s. The event, occurring while the Western Hemisphere was in daylight, produced power outages in Canada and the U.S. and the disruption of a major transcontinental telecommunications cable in Illinois.
Nearly 2 years ago the Sun produced an event that could have been as seriously disruptive of technologies as was the 1972 event, and as was the famous Carrington event of 1859—which was notable for its disruptions of the first electrical system, the telegraph. Baker and colleagues reported recently in this journal that a solar outburst on 23 July 2012 had all of the characteristics of an extreme event that could have serious consequences for electric power and communications systems (http://onlinelibrary.wiley.com/doi/10.1002/swe.20097/abstract). However, the event was aimed not at Earth but toward the STEREO A spacecraft, some 140° west of the Earth-Sun line. These authors concluded that this time Earth escaped a potentially serious encounter with solar wrath.
While large, potentially disruptive events rightly attract significant public interest, other solar activity can also produce detrimental effects on technologies. A recent example is the solar event of 25 April 2014. The X-rays from this class X1.3 solar storm in Region 2035 on the west limb reportedly produced high-frequency radio blackouts for about an hour across the Eastern Pacific Rim (SWPC Space Weather Message Code: SUMX01, Serial Number: 99, Issue Time: 25 April 2014 0048 UTC).
Thus, even in comparatively small solar activity cycles such as the current one, the Sun is capable of producing events with both more limited and larger impacts on technologies at Earth. Continued awareness and alertness to the space weather natural hazard is incumbent on system designers and operators, and on forecasters and modelers.