[Ips-hf-warning] IPS HF COMMS WARNING

[rwc]

SUBJ: IPS HF RADIO COMMUNICATIONS WARNING 04/48
ISSUED AT 10/0036Z NOVEMBER 2004
BY THE AUSTRALIAN SPACE FORECAST CENTRE.

DEGRADED HF PROPAGATION CONDITIONS EXPECTED
FROM 10-11 NOVEMBER 2004
SEVERELY DEPRESSED IONOSPHERIC CONDITIONS EXPECTED
FOR 10 NOVEMBER. EXPECTED SHOCK ARRIVAL ON 11 
NOVEMBER AND SIMILAR DEPRESSED CONDITIONS AS A RESULT
ARE EXPECTED ON 11 NOVEMBER AND POSSIBLY THE 12 NOVEMBER.

IF COMMS DIFFICULTIES EXPERIENCED TRY A LOWER FREQUENCY BAND
FOLLOW ON HF WARNING FROM HF WARNING: 47
_____________________________________________________________

SOLAR ACTIVITY FORECAST       HF COMMS FADEOUTS             
10 Nov:  Moderate to high     Probable             
11 Nov:  Moderate to high     Probable             

HF COMMUNICATIONS FORECAST (AUSTRALIAN/NEW ZEALAND REGION)
                                   FREQUENCY BANDS  
       T-index  MUFs          2  4  6  8 12 16 22 26
_____________________________________________________________
10 Nov  20     -30%/normal    2  4  6  6  8 12 16 16 
11 Nov  20     normal/-30%    2  4  6  6  8 12 16 16 


An IPS MUF depression HF Warning and IPS shortwave fadeout 
HF Warning are both current. Shortwave fadeouts degrade 
lower shortwave radio frequencies first (through increased 
ionospheric absorption) and the usual strategy during shortwave 
fadeouts is to try a higher frequency. In contrast, during 
periods of ionospheric MUF depression, the upper frequencies 
are degraded first and the usual strategy is to use a 
lower frequency. 

If a shortwave fadeout occurs during a period when ionospheric 
MUFs are depressed the available HF bandwidth will be "squeezed", 
with increased absorption raising the lowest usable frequency 
and the ionospheric depression lowering the highest usable 
frequency. Under such conditions it is suggested that the 
HF communicator operates on the highest usable frequency, 
even though this may well be in fact lower than what is normally 
supported for that particular circuit.

IPS Radio and Space Services      | email: asfc at ips.gov.au
PO Box 1386                       | WWW: http://www.ips.gov.au
Haymarket NSW 1240  AUSTRALIA     | FTP: ftp://ftp.ips.gov.au 
tel: +61 2 9213 8010              | fax: +61 2 9213 8060 

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