[Ips-hf-warning] ASWFC HF DEPRESSION WARNING issued 0219 UT on 19 Sep 2023 [SEC=OFFICIAL]

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SUBJ: ASWFC HF RADIO COMMUNICATIONS WARNING 23/95
ISSUED AT 0218UT/19 SEPTEMBER 2023
BY THE AUSTRALIAN SPACE WEATHER FORECASTING CENTRE.

A CME impact from 18/1300 UT has induced geomagnetic activity. 
This geomagnetic activity is expected to cause depressions to 
maximum usable frequencies (MUFs) for HF radio propagation. Degraded 
HF conditions are expected over 19-21 Sep. Conditions may begin 
to recover by 21-Sep. 

DEGRADED HF PROPAGATION CONDITIONS EXPECTED
FROM 19-21 SEPTEMBER 2023
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
_____________________________________________________________
19 Sep:   96   normal/-20%      2  4  6  8  8 12 16 16
20 Sep:   96   -15%/normal      2  4  6  8 12 12 16 22
21 Sep:   96   normal/-10%      2  4  6  8 12 16 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