Solar activity went from low to high this week. Activity was
dominated by Region 4455, which produced frequent C-class flares
alongside three significant flare events: an M9.3/Sf on June 1; as
well as an M7.7/1b and an X1.0/1n on June 3.
There are eight numbered regions on the visible disk. Region 4455
remains complex, maintaining its anti-Hale configuration and
displaying a newly developed delta structure. Continuous flux
emergence and spot growth with penumbral development were observed
just ahead of its mature, positive polarity lead spot. Regions 4458
and 4459 both showed growth and consolidation, with Region 4459
showing rapid spot development in its trailing area and gaining a
mixed-polarity gamma configuration. Region 4461 also showed flux
emergence driving a gamma configuration, though extreme
foreshortening near the limb limits high-confidence analysis of its
overall complexity. Region 4462 consolidated and showed increased
separation between its poles. The remaining regions were stable or in
decline.
Several eruptive events occurred during the reporting period. An
M9.3/Sf flare June 1 was accompanied by wideband radio emissions,
including a Type IV radio sweep with an estimated shock velocity of
253 km/s, and a 10.7-cm radio burst. An associated coronal mass
ejection (CME) became visible in LASCO C2 imagery on June 2. While
faint in coronagraph imagery, GOES/SUVI imagery implies a partial to
full halo profile, and COR2 triangulation confirms an Earth-directed
component. Modeling indicates this event is the most Earth-directed
CME of the period’s events.
The M7.7/1B flare on June 3 was accompanied by wideband radio
emissions, including a Type IV sweep, a Type II sweep with an
estimated shock velocity of 313 km/s, and a prominent three-minute
10.7-cm radio burst. The associated CME was first seen in LASCO C2 on
June 3. GOES/SUVI 304 imagery shows much of the ejecta was deflected
significantly northward by an adjacent positive polarity coronal
hole. STEREO COR2 imagery and modeling shows that, while it retains
an Earth-directed glancing component, it is the least
directly-targeted event of the period.
Solar activity is expected to be at moderate to high levels through
June 6. M-class (R1-R2/minor-moderate) flaring remains likely, with a
slight chance for X-class (R3/strong or greater) events, primarily
due to the eruptive capabilities of Regions 4455, 4458, and 4459.
Solar wind parameters continued to be slightly elevated with
conditions reflecting possible embedded transient influences. Wind
speeds held steady near 400 km/s for most of the period before a
distinct increase to near 450 km/s late in the period. The phi angle
showed a distinct transition into the positive (away from the Sun)
sector late in the period.
Mild enhancements are expected early on June 4 under the initial
onset of positive polarity high-speed stream (+CH HSS) influences.
Conditions will escalate dramatically mid-to-late on June 4 with the
arrival of the multiple June 3 CMEs. These significant enhancements
are expected to persist through June 5 with elevated conditions
persisting through June 6.
Weekly Commentary on the Sun, the Magnetosphere, and the Earth’s
Ionosphere, June 4, 2026, by F. K. Janda, OK1HH:
On May 28, a large sunspot group, AR 4455, began to emerge on the
northeastern limb of the solar disk. Its activity had already been
monitored in the preceding days by the Solar Orbiter spacecraft,
while we were also aware of it thanks to helioseismological
observations. In the first days of June, AR 4455 gradually grew,
while its configuration pointed to future growth in eruptive
activity. A series of moderately energetic eruption eruptions on June
2 turned out to be precursors. The main event, featuring four
energetically significant eruptions, took place on June 3, with at
least two of them accompanied by a coronal mass ejection (CME), while
at least one of which was headed directly toward Earth.
These lines you are currently reading are being written on June 4 at
around 16:00 UT, just before more than one particle cloud is expected
to hit Earth, marking the start of a geomagnetic disturbance. The
disturbance is expected to intensify on June 5 and is likely to
continue, albeit with lower intensity, on June 6.
The latest development in solar activity therefore differs
significantly from what we witnessed in May, during the previous
solar rotation, when solar activity was low and the magnetosphere
remained calm in the following days.
Conclusion: Ionospheric propagation conditions during the first
weekend of June will be variable and generally poor, with low MUF
values. Although a noticeable improvement is expected in the coming
days due to increased solar activity, another geomagnetic disturbance
can be expected as early as June 10. The only certainty is change!
The Predicted Planetary A Index for June 6 to June 12 is 8, 5, 5, 5,
5, 30, and 25 with a mean of 11.9. The Predicted Planetary K Index is
3, 2, 2, 2, 2, 6, and 5 with a mean of 3.1. 10.7 centimeter flux is
125, 125, 120, 120, 130, 135, and 135 with a mean of 127.1.
For more information concerning shortwave radio propagation, see
and the ARRL Technical Information
Service web page at, http://arrl.org/propagation-of-rf-signals. For
an explanation of numbers used in this bulletin, see
. Information and
tutorials on propagation can be found at, .
Also, check this:
https://bit.ly/3Rc8Njt
“Understanding Solar Indices” from September 2002 QST.