There's some confusion about the effects of increasing solar activity on 160 meter DX propagation.
160 meter DX propagation is often badly affected by nighttime propagation degradations, especially as Solar Cycle 25 becomes much more active from now through solar maximum in about 2024-2025 and as it slowly declines to current ionization levels through about 2027-2028. Solar flares have no know impact on 160 meter DX propagation. Solar flares produce electromagnetic radiation that travels from sun to Earth at the speed of light - in about 8 minutes. Solar flare electromagnetic radiation (mostly X-rays) affects only the sunlit side of the earth and ionosphere. There are no known physical processes that extend solar flare effects into the night time ionosphere. While solar flares have no relevance to 160 meter DX propagation, solar flares often occur coincident with (but are not caused by) coronal mass ejections that can cause severe post-midnight absorption in the D region on propagation paths that cross the auroral oval (e.g., North America to northern Europe and Asia). CMEs cause the auroral oval to dip to much lower latitudes causing post-midnight increased D region absorption on propagation paths crossing lower latitudes. Unrelated to CMEs, coronal hole high speed stream effects also cause increased D region absorption in the post-midnight auroral oval and occur very frequently compared to geo-effective CMEs (thankfully most CMEs never strike the Earth or its magnetosphere, they usually miss our tiny planet). But what about 160 meter absorption usually present much earlier in the night, from sunset through midnight and later? The E region usually retains enough ionization to degrade 160 meter night time propagation especially during the more active years of the solar cycle. The ionized night time E region causes increased absorption at the bottom of the E region (just above the D region) and blankets propagation that would otherwise pass through the E region to the F region. Blanketing causes many shorter hops that suffer increased loss from multiple lossy passes through the ionized E region. 73 Frank W3LPL _________________ Searchable Archives: http://www.contesting.com/_topband - Topband Reflector
