[Ips-hf-warning] IPS HF COMMS WARNING

[rwc]

SUBJ: IPS HF RADIO COMMUNICATIONS WARNING 03/75
ISSUED AT 24/2236Z OCTOBER 2003
BY THE AUSTRALIAN SPACE FORECAST CENTRE.


DEPRESSED AND DEGRADED HF PROPAGATION CONDITIONS EXPECTED
FOR FIRST HALF 25 OCTOBER 2003 DEPRESSIONS EXPECTED TO
BE MOSTLY CONFINED TO SOUTH OF BRISBANE. NORTHERN AUS
REGION COMMUNICATORS SHOULD USE A TINDEX OF 55.

IF COMMS DIFFICULTIES EXPERIENCED TRY A LOWER FREQUENCY BAND
FOLLOW ON HF WARNING FROM HF WARNING: 74
_____________________________________________________________

SOLAR ACTIVITY FORECAST       HF COMMS FADEOUTS             
25 Oct:  high                 Probable             

HF COMMUNICATIONS FORECAST (SOUTEHRN AUSTRALIAN/NEW ZEALAND REGION)
                                   FREQUENCY BANDS  
       T-index  MUFs          2  4  6  8 12 16 22 26
_____________________________________________________________
25 Oct   25    -15%           2  4  6  8 12 12 16 22 


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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