Analysis of changes to propagation and refraction height on specific paths induced by the 14 October 2023 eclipse

Signal and noise levels, alongside precise frequency and frequency spread measurements were collected by over 20 WsprDaemon stations prior to, during, and after the October 2023 eclipse using FST4W digital mode. By combining fortuitous home locations with eclipse-specific portable operations, augmented with multiband transmitters at selected sites, the group has gathered a rich data set over 3.5 MHz to 28 MHz. Path geometry includes along- and across-eclipse, from 10s km to over 5000 km. Different geometries, path lengths and frequencies have enabled quantitative analysis of eclipse-induced propagation changes. Reduced D region absorption resulted in 7-9 dB increase in propagated-in noise on 7 MHz at KPH/KFS. The triangular form of the noise anomaly contrasted with a flat-topped +13-15 dB signal level anomaly on 3.57 MHz on a 466 km path. Reduced F2 layer critical frequency (foF2) resulted in several phenomena on 14 MHz identified via frequency spread changes. Two-hop propagation reverted to one-hop on an 1808 km path. On a 1055 km path one-hop changed to an above-the-basic MUF mode - two-hop sidescatter - with signal levels 30 dB lower. Reduced foF2 affected two-hop along-eclipse paths of 4400 km to 5000 km from Costa Rica to Nevada and California on 28 MHz. At ca. 4400 km signals were lost twice, as the second hop, then the first, were affected, with recovery between. Signals at 5000 km were not completely lost. Simple ray-trace modelling to match the observations suggested effective sunspot number (SSNe) had dropped from 125 to ~70. As stations were GPS-disciplined or GPS-aided precise Doppler shift measurements at two-minute intervals with 0.1 Hz resolution were obtained. On a 545 km path Doppler shift at 3.57 MHz, 7 MHz and 10.14 MHz were converted to path velocities and, integrated back and forward in time from a single F2 layer height from the Pt. Arguello ionosonde, gave a credible diurnal profile of refraction height. Compared to 15th October the 14th showed a triangular-shaped height anomaly with a maximum of +33 km. These and other results illustrate the effectiveness of path-specific analysis of FST4W data for eclipse studies.