[SADXA] SADXA NOV MEETING - 2nd Half Presentation - UPDATE: 40m Solar Noon DX - SUMMARY

[W7EXG (Bill)]

SADXA -- Nov 21st MEETING -- 2nd HALF PRESENTATION 

TITLE: 40m Daytime DX - The Propagation Corridor
	UPDATE FOCUS: 40m DX @ SOLAR NOON

NOTE: This topic was originally presented in its entirety to SADXA in
1/17/19, and a revised version to CADXA on Oct. 3rd, 2019. 

AUTHOR/PRESENTER: Bill Davis - W7EXG
          
NOTE: TIMELY UPCOMING 40m DX DAYTIME EVENT:

With the Visible Solar Sun Spot Number currently at 0, and the Measured
Average Solar Flux Index at 67.4 for October 2019, we are fast approaching a
rare 40m RF propagation event in the Northern Hemisphere during the 2019
December Solstice time period.  A 40m daytime DX window will occur; lasting
almost the entire day - and for several weeks about the Dec. 21st Solstice.
40m DX at Solar Noon is possible in the US during this time period. This 40m
Solar Noon event will be highlighted and will be the focus in this UPDATE
presentation. It is hoped some SADXA members will take up the upcoming 40m
Solar Noon DX Challenge - with possibly a first!! 

SUMMARY

NOTE: Initially, a brief overview of the 40m DAYTIME DX concept will be
provided to refresh memories and update those who did not attend the
original presentations. 

Many have noted that 40m DX often occurs during the day, either sometime
before sunset or sometime after sunrise.  This research presented here was
my attempt to both qualitatively and quantitatively define the boundaries of
these 40m daytime DX propagations. 

A 40m DX daytime propagation corridor will be defined as a 40m DX day region
adjacent to the terminator, and having a corridor width. This corridor width
will be defined between the terminator and an E layer electron density
boundary -- where EMUF = 7 MHz. (EMUF = Maximum Usable Frequency of the E
layer)

The 7 MHz 40m signals will pass through the E layer in this corridor, since
7 MHz > EMUF in this corridor region. 

The corridor width is a function of E layer ionization and thus the Solar
Flux magnitude. The present lowest solar flux provides the greatest 40m DX
daytime corridor width, and also provides the lowest D absorption loss in
this region. 

The seasonal variations of the 40m DX daytime propagation corridor will be
illustrated to follow the seasonal terminator variations. 

During the December Solstice, the Solar Noon northern terminator boundary
will be shown to be only about 1100 miles from the northern US boundary with
Canada. This is the ONLY seasonal timeframe, when most of the US area is in
the 40m DX daytime propagation corridor and occurs during most of the day,
including Solar Noon. 

Ionograms are used to define EMUF vs Time for Dec. 21st, 2018, including
from the Austin, TX RF sounding site (30.4 deg lat). This Austin EMUF data
demonstrates the corridor width extends over the entire US, and as far South
as at least 30 deg - at Solar Noon.

Finally, several 40m DX daytime propagation corridor examples are presented
during December Solstice 2018, using computer Screen Captures of actual 40m
DX paths (CW skimmers) from DXMAPS.com website. Solar Noon 40m DX paths will
be highlighted for the US and New Zealand, during the December and June
Solstice respectively.  

A challenge will be set forth for any SADXA member to log the first (ever?)
40m SOLAR NOON DX QSO during this December Solstice. Guidelines will be
given to help optimize success. I am defining Solar Noon as (+/-) 1 hour
about Tucson's solar noon -> (12:21pm MST @ 12/21, for example). 

END