[Ips-dsgr] ASWFC Daily Report - 20 September 26 issued 2330 UT on 20 Sep 2026 [SEC=OFFICIAL]
Australian Space Weather Forecasting Centre
aswfc at bom.gov.au
Mon Sep 21 09:30:50 AEST 2026
SUBJ: ASWFC DAILY SOLAR AND GEOPHYSICAL REPORT
ISSUED AT 2330UT/20 SEPTEMBER 2026
FROM THE AUSTRALIAN SPACE WEATHER FORECASTING CENTRE
SUMMARY FOR 20 SEPTEMBER AND FORECAST FOR 21 SEPTEMBER - 23 SEPTEMBER
STATUS INDICATORS SOL:GREEN MAG:** YELLOW ** ION: GREEN
ASWAS SCALE DESCRIPTION: https://bit.ly/3lmaMBx
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1A. SOLAR SUMMARY
Activity 20 Sep: R0
Flares: none.
Observed 10.7 cm flux/Equivalent Sunspot Number for 20 Sep: 101/49
1B. SOLAR FORECAST
21 Sep 22 Sep 23 Sep
Activity R0, chance of R1 R0, chance of R1 R0, chance of R1
Fadeouts None expected None expected None expected
10.7cm/SSN 105/54 105/54 100/48
COMMENT: Solar flare activity was at the R0 level on 20-Sep,
with a C3.7 flare from Active Region (AR) 4534 (N07W04, beta-gamma-delta)
being the largest observed. This region is the most magnetically
complex of four numbered and one unnumbered active sunspot regions
currently on the visible solar disk. AR 4534 has shown significant
growth since appearing on the disk, but remains small overall.
AR 4532 (S05W50, beta) has exhibited some mild growth over the
same period, and also remains small. Recently numbered AR 4535
has begun to rotate onto the front side of the solar disk at
N11E75, and currently appears to exhibit an alpha magnetic classification.
An unnumbered region has appeared at N03E15, showing some growth
over the past UT day, and exhibiting a beta magnetic classification.
The remaining region, AR 4533 (S12E64, alpha) has remained stable
since rotating onto the front side of the disk. Solar flare activity
is forecast at the R0 level, with a chance of R1 over 21-23 Sep,
due to the recent growth of AR 4534, as well as recent eastern-limb
flare activity likely originating from AR 4535. Solar radiation
storm conditions were at the S0 level on 20-Sep, with the solar
proton flux consistent with background levels. S0 solar radiation
storm conditions are forecast over 21-23 Sep. No Earth-directed
coronal mass ejections (CMEs) were observed over the past UT
day. A low-velocity, north-directed CME was visible in SOHO/LASCO
from 19/2200UT. This event was observed to originate on the far
side of the solar surface, and is not geoeffective. The solar
wind environment trended towards ambient conditions over 20-Sep,
with the solar wind speed declining from 400-425 km/s early in
the UT day to be currently at 355-365 km/s. The interplanetary
magnetic field strength (IMF, Bt) was stable over the UT day,
peaking at 5 nT. The north-south component (Bz) ranged between
-4 and +3 nT over the same period. The solar wind speed is expected
to remain at background levels over 21-22 Sep, before rising
late on 22-Sep as the Earth begins to connect with a coronal
hole high speed wind stream. The solar wind speed will continue
to rise on 23-Sep due to this high speed wind stream.
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2A. MAGNETIC SUMMARY
Geomagnetic field for Australian Region 20 Sep: G0
Estimated Indices 20 Sep : A K
Australian Region 2 11200001
Cocos Island 1 21100000
Darwin 3 12200002
Townsville 2 12200011
Learmonth 1 11100001
Alice Springs 1 01200001
Gingin 1 11100001
Canberra 1 01200001
Kennaook Cape Grim 2 12200001
Hobart 2 12200001
Estimated Antarctic Regional K Indices 20 Sep :
Casey 6 33310001
Mawson 21 53321006
Observed Regional daily pc3 Indices 20 Sep :
Darwin 0 (Quiet)
Townsville 0 (Quiet)
Learmonth 0 (Quiet)
Alice Springs 0 (Quiet)
Gingin 0 (Quiet)
Canberra 0 (Quiet)
Pc3 pulsations are high frequency (10-45 second period) variations
of the Earths magnetic field. Daily pc3-indices are the daily sum
of 20 minute pc3-indices for that station and have been shown to be
well correlated with rejection of high resolution aeromagnetic
survey flight-line data.
NOTE: Indices may have been generated from data obtained in
cooperation with the following organisations: Geoscience Australia,
University of Newcastle Space Physics Group, Australian Government
Antarctic Division and International Center for Space Weather
Science and Education, Japan.
Estimated AFr/Ap Indices 20 Sep : A
Fredericksburg 6
Planetary 6
Observed AFr/Ap Indices 19 Sep : A K
Fredericksburg 6
Planetary 7 2321 2222
2B. MAGNETIC FORECAST
Date Ap Conditions
21 Sep 4 G0
22 Sep 7 G0
23 Sep 18 G0, chance of G1
COMMENT: Geomagnetic conditions in the Australian region were
at the G0 level over 20-Sep, with G0 conditions also recorded
at the planetary scale. Mostly G0 conditions were reported in
the Antarctic region, with some G1-G2 intervals observed at Mawson.
G0 conditions are forecast over 21-23 Sep, with a chance of G1
on 23-Sep due to high speed wind stream effects of an equatorial
coronal hole.
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3A. GLOBAL HF PROPAGATION SUMMARY
Latitude Band
Date Low Middle High
20 Sep Normal Normal Normal-fair
PCA Event : No event.
3B. GLOBAL HF PROPAGATION FORECAST
Latitude Band
Date Low Middle High
21 Sep Normal Normal Normal
22 Sep Normal Normal Normal-fair
23 Sep Normal-fair Normal-fair Normal-fair
COMMENT: Global high-frequency (HF) radio propagation conditions
on 20-Sep were mostly normal, with some normal-fair conditions
observed in high-latitude northern hemisphere regions at the
beginning of the UT day. Some mild degradations were also observed
at mid-latitude European sites at the end of the UT day. Global
HF propagation conditions are forecast to be mostly normal over
21-22 Sep, with some mild degradations possible on 23-Sep due
to forecast geomagnetic activity.
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4A. AUSTRALIAN REGION IONOSPHERIC SUMMARY
Date T index
20 Sep 60
Observed Australian Regional MUFs
Cocos Island Region:
No data available during local day.
No data available during local night.
Niue Island Region:
Enhanced by 20% during local day.
Enhanced by 15% during local night.
Northern Australian Region:
Near predicted monthly values.
Southern Australian Region:
Near predicted monthly values.
Antarctic Region (Casey/Davis/Mawson):
Near predicted monthly values over the UT day.
Monthly T index:
Month T index
Aug 66
Sep 62
Oct 60
4B. AUSTRALIAN REGION IONOSPHERIC FORECAST
Date T index MUFs
21 Sep 60 Near predicted monthly values
22 Sep 60 Near predicted monthly values
23 Sep 55 Near predicted monthly values
COMMENT: Maximum Usable Frequencies (MUFs) in the Australian
region were mostly near predicted monthly values over UT day
20-Sep, with enhancements of 15-20% observed at Niue Island.
Mild spread-F was observed at Perth and Hobart. MUFs are forecast
to remain near predicted monthly values over 21-22 Sep, with
some mild depressions of up to 10% possible on 23-Sep due to
forecast geomagnetic activity.
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5. SPACE ENVIRONMENT SUMMARY
GOES satellite data for 19 Sep
Daily Proton Fluence >1 MeV: 2.4E+05
Daily Proton Fluence >10 MeV: 2.0E+04
Daily Electron Fluence >2 MeV: 3.10E+07 (normal fluence)
Electron Fluence Daily Deep Dielectric Discharge Probability: 5%
Fluence (flux accumulation over 24hrs)/ cm2-ster-day.
X-ray background: B2.6
Solar Wind Day Averaged Data for 19 Sep
Speed: 426 km/sec Density: 3.8 p/cc Temp: 106000 K Bz: 0 nT
(Courtesy Space Weather Prediction Center, Boulder USA)
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Australian Space Weather Forecasting Centre
Bureau of Meteorology
ASWFC at bom.gov.au
www.bom.gov.au | www.sws.bom.gov.au
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