RE: [HCDX] MF/HF Radio Blackout

["Jan Alvestad" <Jan.Alvestad@xxxxxxxxxxxxxxxx>]

>   The latest partially geo-effective Coronal Mass Ejection 
> (CME) collided
> with Earth's magnetic field beginning at 0749 UTC this 
> morning 03/10/26. It

Thomas and others,

there's no such thing as a partially geo-effective CME. A CME
becomes geo-effective if it causes a geomagnetic disturbance.
What you probably meant to say was "partial halo CME". This
particular CME reached the Earth but did not cause any geomagnetic
disturbance (the interplanetary magnetic field was northwards all
the time until the arrival of the next CME, see below).

> was associated with a large M7.6 class solar flare from 
> Sunspot Group #10486
> that occurred on 03/10/24. However as the Bz component of the

The source of this CME was probably an event in region 10486 on
October 23. Another CME arrived later in the day and was associated
with a solar wind shock as observed by SOHO at 18:35 UTC. The
source of this CME was likely the M7 flare you referred to above.
This is a geo-effective CME and is currently causing unsettled to
minor storm conditions.

>   Now more bad news. A large filament eruption that occurred 
> beginning at
> 0106 UTC this morning in association with geo-effective 
> Sunspot Group #
> 10484, produced a geo-effective (squarely Earth directed) Coronal Mass
> Ejection and will impact Earth's magnetic field beginning 
> sometime on UTC
> 03/10/28.

Interesting. The prominence/filament eruption you refer to
was associated with a CME directed off the solar west limb. At
least that is what can be observed in SOHO/LASCO images. This
CME does not appear to be have any Earth directed parts.

>   Also another huge X1.3 class solar flare occurred beginning 
> at 0500 UTC
> this morning, in association with Sunspot Group #10486. It 
> also produced a
> geo-effective Coronal Mass Ejection that will impact Earth's 
> magnetic field
> sometime on UTC 03/10/27. This solar flare also caused a 
> strong MF/HF radio
> blackout in Asia, Australia and the Middle East.

Yes, this was a full halo CME and it could reach the Earth by late
October 27 or early October 28.

A long duration X1.2 proton flare in region 10484 at 18:19 UTC on
October 26 is another piece of bad propagation news. Not only will
the polar cap absorption event in progress limit HF propagation
over polar and near polar paths, but a CME associated with this
event could reach the Earth on October 28 and severely degrade
HF and LF propagation, particularly over high latitude paths.

Another X class proton flare from region 10484 anytime over the next
few days could limit propagation even over middle and low latitude
paths.

While not yet numbered by NOAA/SEC, STAR region S291 emerged 
very quickly on October 26 in the northeast quadrant and could soon
begin producing M class flares and contribute to an even higher
solar flux, perhaps to levels exceeding the previous high for
solar cycle 23.

Jan Alvestad
Solar Terrestrial Activity Report (http://www.dxlc.com/solar/)

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