High‐Frequency Communications Response to Solar Activity in September 2017 as Observed by Amateur Radio Networks

Numerous solar flares and coronal mass ejection-induced interplanetary shocks associated with solar active region AR12673 caused disturbances to terrestrial high-frequency (HF, 3-30 MHz) radio communications from 4-14 September 2017. Simultaneously, Hurricanes Irma and Jose caused significant damage to the Caribbean Islands and parts of Florida. The coincidental timing of both the space weather activity and hurricanes was unfortunate, as HF radio was needed for emergency communications. This paper presents the response of HF amateur radio propagation as observed by the Reverse Beacon Network and the Weak Signal Propagation Reporting Network to the space weather events of that period.Distributed data coverage from these dense sources provided a unique mix of global and regional coverage of ionospheric response and recovery that revealed several features of storm time HF propagation dynamics. X-class flares on 6,7, and 10 September caused acute radio blackouts during the day in the Caribbean with recovery times of tens of minutes to hours, based on the decay time of the flare. A severe geomagnetic storm with Kp(max) = 8+ and SYM-H-min = -146 nT occurring 7-10 September wiped out ionospheric communications first on 14 MHz and then on 7 MHz starting at similar to 1200 UT 8 September. This storm, combined with affects from additional flare and geomagnetic activity, contributed to a significant suppression of effective HF propagation bands both globally and in the Caribbean for a period of 12 to 15 days. Plain Language Summary Radio communications using the high-frequency (HF) bands (3-30 MHz) is important for emergency communications because it is the only form of electronic communications that can travel over the horizon without relying on man-made infrastructure such as the Internet, satellite systems, or phone networks. This is possible because HF rays can be bent back to Earth by the ionosphere, an electrically charged layer of the upper atmosphere. Space weather events such as X-ray flares from the Sun and geomagnetic storms can alter the ionosphere to disrupt these communications. During September 2017, a significant number of solar flares and geomagnetic activity occurred.Simultaneously, major hurricanes, including Hurricane Irma and Hurricane Jose, caused situations in the Caribbean region requiring the use of emergency HF communications, often provided by ham (amateur) radio operators. This paper shows the impacts of these space weather disturbances on HF communications as observed by multiple ham radio monitoring systems.