[Ips-hf-warning] ASWFC HF DEPRESSION WARNING issued 0030 UT on 30 Sep 2025 [SEC=OFFICIAL]

[Australian Space Weather Forecasting Centre]

SUBJ: ASWFC HF RADIO COMMUNICATIONS WARNING 25/87
ISSUED AT 0027UT/30 SEPTEMBER 2025
BY THE AUSTRALIAN SPACE WEATHER FORECASTING CENTRE.

Southern Australian region MUFs are depressed 15-30% after local 
dawn this morning following overnight G1 geomagnetic activity 
associated with a prolonged interval of southward interplanetary 
magnetic field (IMF) conditions. Northern Australian region MUFs 
are 15-20% enhanced after local dawn this morning morning. The 
southward IMF conditions appear to have ended and southern Australian 
region MUFs are expected to gradually recover today.

DEGRADED HF PROPAGATION CONDITIONS EXPECTED
FOR 30 SEPTEMBER 2025 FOR SOUTHERN AUS/NZ REGION ONLY.
IF COMMS DIFFICULTIES EXPERIENCED TRY A LOWER FREQUENCY BAND
_____________________________________________________________

HF COMMUNICATIONS FORECAST (SOUTHERN AUSTRALIAN/NEW ZEALAND REGION)
  Southern Australia                 FREQUENCY BANDS
       T-index      MUFs        2  4  6  8 12 16 22 26
_____________________________________________________________
30 Sep:   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