[600MRG] 630m WSPR Propagation Over a Typical Day: Six Regimes

[James Hollander]

Six-Regime 630m.  Second post.  73,  Jim H   W5EST   

II. POST-SR REGIME 
     The sun's ionizing radiation begins to bathe 630m signal rays at SR.  The ionization rate in the D-region now exceeds the recombination rate of electrons with their positive ions.  The electron concentration and its accompanying D-region absorption rapidly increase.  Ionization and recombination compete with each other.  A resulting equilibrium level of electron concentration increases as the sun's ionizing radiation ascends in elevation angle after SR.  Then the D-region becomes no longer nearly edge-on to the arriving SR solar ionizing radiation and is progressively less obliquely oriented to it.  A switch from F-region signal reflection to less-efficient D-region reflection around SR may also occur, see Note 1 later.
     Less-distant and stronger 630m stations' signals somewhat survive the rising D-region absorption for a while after SR--for longer times at a receiving station with a good antenna system and receiver.  Ionospheric convection and patches of varying electron concentration can cause SNR variations and WSPR reception gaps.  Generally, sky wave reception either suddenly or spottily ceases as the SNRs ultimately fall below the WSPR decodability threshold level (about -33dB) within about an hour after SR.  Ground wave reception continues through the day.

II.  630M DAYTIME REGIME
     Ionization and recombination of positive ions in the D-region compete and maintain a substantial equilibrium that establishes a relatively high daytime electron concentration and high D-region absorption at the low 630m frequency.  Solar flare events some days may deliver high intensity ionizing radiation that ionizes the D-region so intensively that it becomes somewhat more reflective at 630m. (The D-region is more capable of reflection at the low 630m frequency than at HF.)  During a big solar flare event, 630m daytime signals may be WSPR-decodable for hundreds of miles.  In the afternoon, conditions blend into the pre-SS regime next.