Topband: Update to the SFI predictions in my May QST Article

[donovanf at erols.com]

Hi Frank 


Its impossible to know at this early date if 2010 is a good solar flux 
index model for 2021 , it depends how optimistic you are. Hopefully 
we'll be able to make better judgements (guesses?) in about six months. 


For example: 


The solar flux index was mostly below 80 until February 2011, then 
suddenly jumped to mostly above 100 from March through August, 
and suddenly jumped again to 140 in September, but -- disappointingly -- 
stayed only at about 140 and occasionally a little higher for almost 
four years. 


Sudden jumps in SFI may happen this year -- or not -- its impossible 
to know. Be very skeptical of anyone who tries to convince you 
otherwise. That's why I very carefully crafted the wording in the 
paragraph in my article that addresses solar flux growth from 
2021 through 2023. 


This is excellent site toexamine historic SFI values. You can zoom 
the date range using the sliders in the graph. Its best to select 
logarithmic Y axis: 


https://lasp.colorado.edu/lisird/data/penticton_radio_flux 


Please don't forget to vote for your favorite May QST article here: 



http://www.arrl.org/cover-plaque-poll 


73 
Frank 
W3LPL 




----- Original Message -----

From: "Frank Stein" <fstein at ieee.org> 
To: "Frank Donovan W3LPL (Frank Donovan W3LPL)" <donovanf at erols.com> 
Sent: Thursday, April 22, 2021 1:46:26 PM 
Subject: Re:Update to the SFI predictions in my May QST Article 



Frank, 

Great article and appreciate the recent update. 

Would 2010 be the best proxy for what kind of propagation we might see this year? For example, if I look at your M/M results for 2010 ARRL DX-SSB contest, 80% of the contacts were to Europe and 40/20m were the key bands. 



Thanks, 

Frank 

W4TG 







On Thu, Apr 22, 2021 at 1:18 AM < donovanf at erols.com > wrote: 





The April 2021 NASA solar flux index forecast for solar cycle 25 
has been published, mostly advancing the predicted date for solar 
maximum to 2024. The SFI represented by the 50% percentile 
(green line) is similar to solar Cycle 24. A double peaked solar 
cycle -- similar to recent Solar Cycles 23 and 24 -- could delay 
solar maximum by a year or more. 


www.nasa.gov/sites/default/files/styles/full_width/public/thumbnails/image/apr2021f10_prd_plt.png?itok=B7vfEY7Y 


Slightly updated wording to my May QST article, 
unconstrained by QST page limits and reflecting the 
NASA's predicted 2024 solar maximum: 
, 
If the SFI persists below 90 through December 2021, then 
propagation should improve gradually until a solar maximum 
weaker than Cycle 24's arrives in 2024. 



If the SFI persists above 110 through December 2021, then 
propagation should improve rapidly until a solar maximum 
similar to Cycle 24's arrives in 2024. 



If the SFI persists above 125 through December 2021, then 
propagation is likely to improve more rapidly until a solar 
maximum stronger than Cycle 24's arrives in 2024. 


Don't forget to vote for your favorite May QST article here: 


http://www.arrl.org/cover-plaque-poll 


73 
Frank 
W3LPL 













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