[Ips-hf-warning] ASWFC HF DEPRESSION WARNING issued 2310 UT on 05 Mar 2023 [SEC=OFFICIAL]

[rwc]

SUBJ: ASWFC HF RADIO COMMUNICATIONS WARNING 23/27
ISSUED AT 2307UT/05 MARCH 2023
BY THE AUSTRALIAN SPACE WEATHER FORECASTING CENTRE.

A coronal hole wind stream is inducing mild geomagnetic activity 
and subsequently southern region Australia ionospheric MUFs are 
depressed 15-20% after local dawn this morning. Depressed MUFs 
for the southern Australian region are expected for the local 
day 06-07 Mar. Northern Australian region MUFs are expected to 
remain be near predicted monthly values to enhanced by up to 
20% and for HF communication within this region HF communicators
should use a T-index of 110.

DEGRADED HF PROPAGATION CONDITIONS EXPECTED
FROM 06-07 MARCH 2023 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
_____________________________________________________________
06 Mar:  50         -20%        2  4  6  8  8 12 16 16
07 Mar:  70   -20%/normal       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