[Ips-hf-warning] ASWFC HF DEPRESSION WARNING issued 0320 UT on 28 Dec 2022 [SEC=OFFICIAL]

[rwc]

SUBJ: ASWFC HF RADIO COMMUNICATIONS WARNING 22/106
ISSUED AT 0318UT/28 DECEMBER 2022
BY THE AUSTRALIAN SPACE WEATHER FORECASTING CENTRE.

Southern Australian region MUFs have not recovered as expected 
today, with depressions of up to 20% observed at 03UT on 28-Dec 
at Perth, Canberra and Hobart. Depressed conditions for the southern 
Australian region are now expected to persist. Northern Australian 
region ionospheric frequencies of support are currently near 
normal.

DEGRADED HF PROPAGATION CONDITIONS EXPECTED
FOR 28 DECEMBER 2022 FOR SOUTHERN AUSTRALIAN REGION ONLY.
IF COMMS DIFFICULTIES EXPERIENCED TRY A LOWER FREQUENCY BAND
_____________________________________________________________

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

Note:
An SWS MUF depression HF Warning and SWS 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