[RSM] Propagation to Europe is Likely by Late October

[Cary Rubenfeld]

From: Frank Donovan <donovanf at starpower.net>
To: PVRC
Date: Fri, 9 Aug 2024 19:08:21 -0400 (EDT)

6 meter F2 propagation to Europe usually requires that
daily SFI exceed 200 for about a week from mid-October
through mid-February. A few isolated days exceeding
200 are not enough. March through mid-October are
unfavorable dates for 6 meter F2 propagation to Europe.

Its interesting to examine those rare dates when
daily SFI exceeds 300 even though its not needed
for reliable 6 meter F2 propagation to Europe.

Daily SFI has exceeded 300 during only about 100 days
since SFI measurements were first made in 1947, nearly
half of those days were during Solar Cycle 19 from
Nov 1956 through Aug 1959.

Daily SFI has exceeded 300 during only 29 days since 1959.
Three of those days occurred this week and we might get
a few more over the next few days.

SFI never exceeded 300 from February 1991 until
just a few days ago, Aug 7, 2024.

Solar Cycle 21 was favorable for 6 meter F2 propagation
to Europe from 1979 through late 1981 but only six days
had SFI exceeding 300, further evidence that SFI exceeding
300 is not needed for reliable 6 meter F2 propagation
to Europe.

Nov  8, 1979  310.1
Nov  9, 1979  314.4
Nov 10, 1979  367.0
Nov 11, 1979  325.7

Oct 16, 1981  302.4
Oct 17, 1981  302.9

Solar Cycle 22 was very favorable for F2 propagation
to Europe from 1989 to 1992. Cycle 22 had 21 days
with SFI exceeding 300, by far the most since
Solar Cycle 19.

Jun 13, 1989 319.2
Jun 14, 1989 327.2
Jun 15, 1989 334.7
Jun 16, 1989 320.9
Jun 17, 1989 303.7

Sep  7, 1989  303.4
Sep  8, 1989  302.1
Sep  9, 1989  311.5
Sep 19, 1989  303.3

Aug 22, 1990 322.8
Aug 23, 1990 322.7
Aug 24, 1990 329.2
Aug 25, 1990 303.9


Jan 28, 1991 313.8
Jan 29, 1991 344.5
Jan 30, 1991 359.2
Jan 31, 1991 348.6
Feb 1, 1991 307.3

Feb 22, 1991  302.6
Feb 23, 1991  311.5
Feb 22, 1991  313.1

*Adjusted SFI* is a better measure of *solar*
* activity*than observed SFI.

*Observed SFI* is a better measure of the intensity
*of ionizing radiation *affecting F2 region MUFs

www.ngdc.noaa.gov/stp/space-weather/solar-data/solar-features/solar-radio/noontime-flux/penticton/penticton_adjusted/listings/listing_drao_noontime-flux-adjusted_daily.txt

73
Frank
W3LPL