[Ips-hf-warning] ASWFC HF DEPRESSION WARNING issued 0028 UT on 01 Oct 2025 [SEC=OFFICIAL]

[Australian Space Weather Forecasting Centre]

SUBJ: ASWFC HF RADIO COMMUNICATIONS WARNING 25/88
ISSUED AT 0026UT/01 OCTOBER 2025
BY THE AUSTRALIAN SPACE WEATHER FORECASTING CENTRE.

The southern Australian regional ionosphere has been depressed 
20-30% after local dawn this morning following G1 geomagnetic 
activity in the Australian region on 30-Sep. The planetary geomagnetic 
field reached G3 on 30-Sep. Southern Australian region MUFs are 
expected to be 15-20% depressed today, slowly recovering as the 
day progresses. Northern Australian regional MUFs are expected 
to remain near predicted monthly values to 15% enhanced.

DEGRADED HF PROPAGATION CONDITIONS EXPECTED
FOR 01 OCTOBER 2025
IF COMMS DIFFICULTIES EXPERIENCED TRY A LOWER FREQUENCY BAND
_____________________________________________________________

HF COMMUNICATIONS FORECAST (SOUTHERN AUSTRALIAN/NEW ZEALAND REGION ONLY)
                                   FREQUENCY BANDS
       T-index      MUFs        2  4  6  8 12 16 22 26
_____________________________________________________________
01 Oct:   50   -20%/normal      2  4  6  8  8 12 16 16

Note:
An ASWFC MUF depression HF Warning and ASWFC 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. 

In general use a lower frequency if you are having trouble
with your normal workable 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.

Australian Space Weather Forecasting Centre
Bureau of Meteorology
ASWFC at bom.gov.au
www.bom.gov.au | www.sws.bom.gov.au