[Ips-hf-warning] ASWFC HF DEPRESSION WARNING issued 2334 UT on 12 Sep 2023 [SEC=OFFICIAL]

[rwc]

SUBJ: ASWFC HF RADIO COMMUNICATIONS WARNING 23/90
ISSUED AT 2331UT/12 SEPTEMBER 2023
BY THE AUSTRALIAN SPACE WEATHER FORECASTING CENTRE.

Depressions of 15-20% have been observed after local dawn this morning 
for the southern Australian region following overnight G1 activity. 
Depressed conditions may persist into early in the UT day on 
13-Sep, then MUFs are expected to recover as geomagnetic activity 
has abated. Northern Australian region MUFs are expected to remain 
near normal.

DEGRADED HF PROPAGATION CONDITIONS EXPECTED FOR EARLY IN UT 
DAY 13 SEPTEMBER 2023 FOR SOUTHERN AUSTRALAIN REGION.
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
_____________________________________________________________
13 Sep:   80   -15%/normal      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