[Ips-hf-warning] ASWFC HF DEPRESSION WARNING issued 2341 UT on 30 Dec 2022 [SEC=OFFICIAL]

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SUBJ: ASWFC HF RADIO COMMUNICATIONS WARNING 22/108
ISSUED AT 2339UT/30 DECEMBER 2022
BY THE AUSTRALIAN SPACE WEATHER FORECASTING CENTRE.

Southern Australian region MUFs expected to be depressed 10 to 
20% on 31-Dec due to mild overnight geomagnetic activity induced 
by a solar coronal hole wind stream. Northern Australian region 
MUFs expected to remain mostly near predicted monthly values, with
some initial mild depressions in ionospheric frequencies of support
early in the UT day, then recovering.

DEGRADED HF PROPAGATION CONDITIONS EXPECTED
FOR 31 DECEMBER 2022 FOR SOUTHERN AUSTRLAIAN 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
_____________________________________________________________
31 Dec:   45          -20%      2  4  6  8  8 12 16 16

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