🚀 go-pugleaf

>Path: infoac!unido!fauern!ira.uka.de!sol.ctr.columbia.edu!spool.mu.edu!sdd.hp.com!swrinde!ucsd!news-mail-gateway
>From: oler@HG.ULeth.CA (CARY OLER)
>Newsgroups: rec.radio.amateur.misc
>Subject: POTENTIAL GEOMAGNETIC STORM WARNING UPDATE - 23 APRIL
>Message-ID: <910422195813.26600691@HG.ULeth.CA>
>Date: 23 Apr 91 01:58:13 GMT
>Sender: daemon@ucsd.Edu
>Organization: UCSD Usenet Gateway
>Lines: 73


                /\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\

                        SOLAR TERRESTRIAL BULLETIN

                              23 April, 1991
                                 00:00 UT

                /\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\


Please note:  The Potential Geomagnetic Induced Current (GIC) Warning has
been replaced with a 'condition code' status, described as follows.  This
method will be employed in all future alerts and warnings.  It applies to
areas in the middle and high latitude regions, particularly within or
near the auroral zone.

          Condition:  GREEN - No GICs expected or possible.
                      AMBER - No GICs observed, but a risk exists.
                              Precautionary or preparatory actions warranted.
                        RED - GICs possible or observed.


POTENTIAL GEOMAGNETIC STORM WARNING UPDATE


Potential GIC Status: AMBER.

The following Warning remains IN EFFECT until 24:00 UT on 23 April:

   - POTENTIAL MINOR GEOMAGNETIC STORM WARNING.

The following Warnings have been CANCELLED:

   - POTENTIAL LOW LATITUDE AURORAL ACTIVITY WARNING (cancelled).
   - POTENTIAL MAJOR SOLAR FLARE WARNING (cancelled).


     An interplanetary shock has so far, failed to arrive from the major
X-class flare of 20 April.  We are still within the window and may
yet see some effects from this flare.  However, as time passes, the
probability for observing geomagnetic storming is decreasing.  The Potential
Geomagnetic Storm Warning will remain in effect until 24:00 UT on 23 April.
There is still a good possibility for increased geomagnetic activity from the
20 April major flare.

     Geomagnetic activity is not expected to be as strong as was first
predicted, because of the amount of time which is taking for the effects to
reach the Earth.  As a result, we have downscaled the potential geomagnetic
activity prediction to generally Minor Storm conditions, if a flare shock
arrives.  Geomagnetic activity likely will not reach major storm levels, and
may in fact only reach low-intensity minor storming.  The predicted planetary
A-index for 23 April is 30.  High latitudes could surpass A-indices of 40 if
a shock arrives.

     Low latitude auroral activity will likely not be observable.  Lunar
phase will begin hampering attempts to view auroral activity now, as well.
However, northerly middle and high latitudes could still witness moderate to
high levels of auroral activity if any flare effects arrive.

     HF propagation conditions could still see some moderate levels of
degradation, but conditions are no longer expected to be as poor as was first
predicted.

     A risk still exists for VHF auroral backscatter communications,
particularly over the northerly middle and high latitudes, provided
geomagnetic activity increases over the next 24 hours.

     If a shock fails to arrive within the next 18 to 24 hours, geomagnetic
and auroral activity will likely remain generally dormant.


**  End of Bulletin  **