[Ips-hf-warning] IPS HF COMMS WARNING

[rwc]

SUBJ: IPS HF RADIO COMMUNICATIONS WARNING 03/81
ISSUED AT 30/2158Z OCTOBER 2003
BY THE AUSTRALIAN SPACE FORECAST CENTRE.

Due to an earlier than expected arrival of a CME a 
major geomagnetic storm started  in the late hours 
of the UT day 30 October. Strong depressions and 
degradations may now be expected almost the whole 
day on 31 October (UT-day). 

DEGRADED HF PROPAGATION CONDITIONS EXPECTED
FROM 30 OCTOBER 2003 TO 01 NOVEMBER 2003
IF COMMS DIFFICULTIES EXPERIENCED TRY A LOWER FREQUENCY BAND
FOLLOW ON HF WARNING FROM HF WARNING: 80
_____________________________________________________________

SOLAR ACTIVITY FORECAST       HF COMMS FADEOUTS             
30 Oct:  high                 Probable             
31 Oct:  high                 Probable             
01 Nov:  high                 Probable             

HF COMMUNICATIONS FORECAST (AUSTRALIAN/NEW ZEALAND REGION)
                                   FREQUENCY BANDS  
       T-index  MUFs          2  4  6  8 12 16 22 26
_____________________________________________________________
30 Oct    30   -15% to -25%   2  4  6  8 12 16 16 22 
31 Oct    10   -40% to -25%   2  4  6  8  8 12 16 16 
1 Nov    40    -20% to -10%   2  4  6  8 12 16 22 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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