oler@HG.ULeth.CA (oler, CARY OLER) (06/16/91)
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POTENTIAL SEVERE GEOMAGNETIC STORM WARNING
01:00 UT, 16 JUNE
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WARNINGS ISSUED OR IN PROGRESS:
- POTENTIAL MINOR TO MAJOR GEOMAGNETIC STORM WARNING
- POTENTIAL MAJOR SOLAR FLARE WARNING (PROTON)
- SATELLITE PROTON AND PCA EVENT ALERT
ATTENTION:
The major class X12/3B flare of 15 June is expected to produce a minor
to major geomagnetic storm. The interplanetary shockwave from this flare is
expected to intercept the Earth late in the UT day of 16 June or early in the
UT day of 17 June. Minor to major geomagnetic storming is expected to
develop. We are predicting estimated planetary magnetic A-indices of 53 for
17 June, followed by a decrease to approximately 24 for 18 June.
To aid in the interpretation of the risks involved, the following
probability chart for geomagnetic activity in each of the six main categories
follows below. The prediction is based on expected activity levels for the
next four days (to 19 June).
GEOMAGNETIC ACTIVITY PREDICTION FOR JUNE 16 - JUNE 19
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| Activity | Day1 | Day2 | Day3 | Day4 |
|--------------|------|------|------|------|
| Quiet | 10% | 05% | 10% | 15% |
| Unsettled | 40% | 10% | 25% | 40% |
| Active | 40% | 20% | 35% | 40% |
| Minor Storm | 10% | 30% | 25% | 05% |
| Major Storm | 00% | 30% | 05% | 00% |
| Severe Storm | 00% | 05% | 00% | 00% |
|=====================|======|======|======|
| A-Index : | 17 | 53 | 24 | 15 |
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So for example, Day 2 represents June 17. On this day, there is a 05%
probability for quiet geomagnetic conditions, a 10% chance for unsettled
conditions, a 20% chance for active conditions, a 30% chance for both minor
and major storm conditions, and a 05% chance for severe storm conditions. On
this day, the A-index is expected to reach 53 (which is officially a
low-intensity major storm). However, there are equal probabilities for minor
to major storming. Taken together, there is a 60% probability for minor to
major storming, or a 50% probability for active to minor storming, or a
35% probability for major to severe storming. However, since there is only a
05% chance for a severe geomagnetic storm, conditions are likely to remain
below severe storm levels. So from this chart, Day 2 will be the most
disturbed day, with only a 15% probability for quiet to unsettled conditions.
If used properly, this prediction chart can provide valuable information
on potential activity. You should use it in making your own judgements
regarding the potential activity on these days.
A Low Latitude Auroral Activity Watch has been issued for the UT day of
17 June. Conditions may become favorable for low-latitude auroral activity
on this day.
HF propagation conditions will be poor on 17 June, provided an
interplanetary shock arrives as expected. If a shock fails to arrive,
conditions will continue at fair to good. Near complete absorption of radio
signals will continue over the next several days over polar paths.
There may be an opportunity for some VHF backscatter communications on
the UT day of 17 June, provided we are affected by todays major flare. If we
are not, no backscatter or other VHF anomalies are likely to be observed.
Conditions are expected to improve on 18 June.
PLEASE SEND ANY REPORTS OF DEGRADED RADIO PROPAGATION CONDITIONS, SIGHTINGS
OF AURORAL ACTIVITY, VHF BACKSCATTER COMMUNICATIONS OR OTHER ANOMALIES TO:
OLER@HG.ULETH.CA (INTERNET), OLER@ALPHA.ULETH.CA (USENET), OR (SNAIL-MAIL)
TO: SOLAR TERRESTRIAL DISPATCH, P.O. BOX 357, STIRLING, ALBERTA, CANADA,
T0K 2E0. PLEASE INCLUDE THE DATE AND TIME (LOCAL AND UT) OF THE OBSERVATION,
THE APPROXIMATE LATITUDE/LONGITUDE OF THE OBSERVATION LOCATION, AND A BRIEF
DESCRIPTION OF THE PHENOMENA OBSERVED. WE THANK ALL THOSE WHO TAKE THE TIME
TO SEND IN OBSERVATIONAL REPORTS.
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