[Ips-hf-warning] ASWFC HF DEPRESSION WARNING issued 0644 UT on 17 Sep 2024 [SEC=OFFICIAL]

[Australian Space Weather Forecasting Centre]

SUBJ: ASWFC HF RADIO COMMUNICATIONS WARNING 24/104
ISSUED AT 0644UT/17 SEPTEMBER 2024
BY THE AUSTRALIAN SPACE WEATHER FORECASTING CENTRE.

Southern Australia regional MUFs were depressed by 15-25% early 
on UT day 17-Sep following geomagnetic storm activity, but have 
since recovered to near predicted monthly values. Northern Australian 
region MUFs have generally been near predicted monthly values 
on 17-Sep. Further periods of 15% depressions are possible over 
the remainder of 17-Sep and into 18-Sep due to the ongoing geomagnetic 
storm.

DEGRADED HF PROPAGATION CONDITIONS EXPECTED
FROM 17-18 SEPTEMBER 2024
IF COMMS DIFFICULTIES EXPERIENCED TRY A LOWER FREQUENCY BAND
_____________________________________________________________

HF COMMUNICATIONS FORECAST (AUSTRALIAN/NEW ZEALAND REGION)
                                   FREQUENCY BANDS
       T-index      MUFs        2  4  6  8 12 16 22 26
_____________________________________________________________
17 Sep:  100   normal/-15%      2  4  6  8 12 12 16 22
18 Sep:  100   normal/-15%      2  4  6  8 12 12 16 22

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