[Ips-hf-warning] ASWFC HF DEPRESSION WARNING issued 2205 UT on 19 Apr 2024 [SEC=OFFICIAL]

[rwc]

SUBJ: ASWFC HF RADIO COMMUNICATIONS WARNING 24/38
ISSUED AT 2205UT/19 APRIL 2024
BY THE AUSTRALIAN SPACE WEATHER FORECASTING CENTRE.

A recent CME arrival has caused a G3 geomagnetic storm. As a 
result of this, maximum usable frequencies for HF radio are expected 
to become depressed by 25-30% over 19-21 Apr, tending back to 
near predicted values by the end of the period. HF radio conditions 
are expected to be degraded, especially at high latitudes over 
this period.

DEGRADED HF PROPAGATION CONDITIONS EXPECTED
FROM 19-21 APRIL 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
_____________________________________________________________
19 Apr:  135          -25%      2  4  6  8  8 12 16 16
20 Apr:  120          -30%      2  4  6  6  8 12 16 16
21 Apr:  125   normal/-30%      2  4  6  6  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