Topband: Bad 160m Conditions

[kq2m at kq2m.com]

Fabulous explanation - Thank you Frank!

73

Bob, KQ2M


On 2023-01-09 01:27, Frank W3LPL wrote:
> 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