[HCDX] Tropical Band Aurora Propagation

[W5USM@xxxxxxx]

The July 16 major geomagnetic storm again renewed an observation to share and 
ask whom has noted similar phenomena.

I suspect that under certain geomagnetic conditions the auroral oval may to 
some degree cause a focusing or ducting of 90, 75 and 60 tropical band 
signals over what are essentially east/west paths from my 33 degree north 
latitude. 

The same may be true, too, on higher frequency bands though I haven't 
explored much above 5100 kHz. 

The phenomena manifests in enhanced signal levels with little or no auroral 
audio demodulation from stations within a generally specific geographical 
area.

The observation July 16 began approximately 0800UT and extended past local 
sunrise fade out or sign-off of Solomon Island SIBC, 5020 kHz, Papua New 
Guinea NBC, 4890, and other PNG 90 and 60 meter stations commonly reported.

SIBC at 11,785 km and 270 degrees and NBC at 12,975 km and 276 degrees were 
at signal levels +40 dB or more above seasonal normals and rivaled the 
strength at their annual best.  Nearly all 90 meter PNG outlets were 
enhanced, but by only some +12 to +18 dB so the affect was decidedly more 
pronounced on 60 meter outlets.
The 4809 kHz outlet faded 50 plus minutes after my sunrise which is typical 
of local winter time fade.

Signals from the Aussie 2310, 2325 and 2485 stations were depressed.  Their 
azimuth heading is similar to Solomon and PNG Islands, but they are some 
2,500 km further from Dallas, TX.

Referring to the real-time auroral oval display on the Internet, the Dallas 
to Solomon/PNG path skirted just below the oval.  The Dallas to RRI path led 
through the oval and as expected, no RRIs, Asians nor subcontinent stations 
were heard. 

Given these parameters, I am suspicious of a focusing or ducting anomaly 
mechanism.

Comments of similar observations shall be appreciated.  Use your own judgment 
whether to post to the group of direct; not everyone is interested in 
propagation.

73 from Bill Smith, W5USM
 "Shortwave  Since  1950"
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