Re: [IRCA] the big black absorptive cloud

[Nick Hall-Patch <nhp@xxxxxxxx>]

At 14:40 03/11/2007, you wrote:
>Hi Nick,
>where do you find info about this cloud? I also noticed the same 
>wipeout here. Everything looked excellent still at 1200.


I wish I knew, Mauno; I was joking at the time, but it seems to be a 
very real phenomenon, and one which, to my limited knowledge, still 
doesn't really have an observable solar / geomagnetic parameter 
associated with it.   What has changed since a day or two ago which 
has caused all long distance signal strengths to deteriorate so markedly?

(forgive me, as I suspect you already know all the following) This 
deterioration (not always so sudden as today) was I believe initially 
described as the "mid-winter anomaly" in DX club literature in the 
sixties, and was applied to the general drop off of trans-Atlantic 
signal strengths observed as mid-winter approached, after the glory 
days of September and October.  This is an unfortunate term, because 
the same term is also used in academic literature to describe a 
daytime phenomenon of winter-time excessive absorption of signals in 
the D region, which doesn't seem to carry over to night, at least 
according to theory; I don't think I've ever seen empirical data on 
this.  To confuse the issue further, there also appears to be 
something called a "winter anomaly" associated with the F2 layer, and 
they don't appear related.

At one time, some thought stratospheric warming was associated with 
this, but Carl Leutzselschwab, K9LA, the 160m propagation expert, 
pretty much debunked that in a couple of articles.

I banged on about the MWA a couple of years back on the 
coastalroundtable group, but didn't get much interest at the time 
from other than John Bryant.  There are a number of references on the 
daytime winter anomaly, which you probably already have,  but 
nighttime winter anomaly conditions on medium wave just don't seem to 
have been researched particularly so far as I can tell.   So we're 
left with my not so mythical "big black absorptive cloud".



best wishes,

Nick










>I received this from NOAA:
>Space Weather Message Code: ALTEF3
>Serial Number: 1397
>Issue Time: 2007 Nov 03 0505 UTC
>ALERT: Electron 2MeV Integral Flux exceeded 1000pfu
>Threshold Reached: 2007 Nov 03 0500 UTC
>Station: GOES12
>Observed Yesterday: Yes
>Yesterday Maximum 2MeV Flux: 4620 pfu
>
>73, Mauno
>
>----- Original Message ----- From: "Nick Hall-Patch" <nhp@xxxxxxxx>
>To: "Mailing list for the International Radio Club of America" 
><irca@xxxxxxxxxxxxxxxx>
>Sent: Saturday, November 03, 2007 4:22 PM
>Subject: [IRCA] the big black absorptive cloud
>
>
>>
>>>   As for this morning, don't ask!   A COMPLETE wipe-out.  Not a
>>>single audio heard between 13:47 and 14:05....first time this
>>>season.  Doesn't look good, I'm afraid!  ...........Walt.
>>
>>Glad it's not just me.   I shouldn't have mentioned that (not so
>>mythical?) absorptive cloud in the ionosphere, because it seems to
>>have arrived over the Pacific Ocean this morning, there being no
>>indication of geomagnetic activity on the NOAA site, just K-indices
>>of zero and one overnight.
>>
>>audio traces on 612, 747 and 774 by 1420UT, just a few weak 
>>carriers otherwise.
>>
>>Nick
>>
>>
>>
>>
>>****************************************************************************
>>Nick Hall-Patch
>>Victoria, B.C.
>>Canada
>>
>>****************************************************************************
>>
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>>

****************************************************************************
Nick Hall-Patch
Victoria, B.C.
Canada

**************************************************************************** 

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