oler@HG.ULeth.CA (oler, CARY OLER) (06/16/91)
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LOW LATITUDE AURORAL ACTIVITY WATCH
ISSUED: 02:45 UT, 16 JUNE
VALID: 17 JUNE
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ATTENTION:
The major class X12/3B flare of 15 June is expected to produce a minor
to major geomagnetic storm. An accompanying minor to major auroral storm is
also anticipated for 17 June. The auroral activity may be sufficient to be
observed over the central to southerly middle latitudes. There will be a
slim chance for lower latitude auroral activity.
To aid in interpreting the probabilities, the following probability
chart has been made available.
VISIBLE AURORAL ACTIVITY PREDICTION FOR NORTH AMERICA JUNE 16 - JUNE 19
NOTE: The days given below are UT days. Day 1 corresponds to the UT day of
16 June. For North America, Day 1 begins at 18:00 MDT, 19:00 CDT, etc, on 15
June. Day 2 begins at 18:00 MDT, 19:00 CDT, etc, on 16 June. Take this into
consideration when interpreting the chart below. The chart represents
the expected probabilities for observing visible auroral activity (during the
night hours), under a dark sky with good atmospheric conditions. Use the
appropriate section of the chart corresponding to your latitude.
The latitude boundaries are defined (approximately) as follows:
NORTHERN HEMISPHERE SOUTHERN HEMISPHERE
High latitudes >= 55 deg. N. | High latitudes >= 55 deg. S.
Middle latitudes >= 40 < 55 deg. N. | Middle latitudes >= 35 < 55 deg. S.
Low latitudes < 40 deg. N. | Low latitudes < 35 deg. S.
These are not precise boundaries because auroral activity is more closely
associated with geomagnetic latitude than with geographic latitude.
Nevertheless, the geographical latitude boundaries given above are good
approximations and are used in the chart below.
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| Latitude |Intensity| Day1 | Day2 | Day3 | Day4 |
|----------------|---------|------|------|------|------|
| |High | 00% | 75% | 30% | 05% |
| High Latitude |Moderate | 15% | 20% | 40% | 30% |
| |Low | 45% | 05% | 30% | 55% |
| |Not Visbl| 40% | 00% | 00% | 10% |
|----------------|---------|------|------|------|------|
| |High | 00% | 70% | 15% | 00% |
|Northerly Middle|Moderate | 05% | 20% | 40% | 20% |
| |Low | 40% | 10% | 40% | 40% |
| |Not Visbl| 55% | 00% | 05% | 40% |
|----------------|---------|------|------|------|------|
| |High | 00% | 20% | 05% | 00% |
| Central Middle |Moderate | 00% | 30% | 20% | 00% |
| |Low | 10% | 40% | 40% | 30% |
| |Not Visbl| 90% | 10% | 35% | 70% |
|----------------|---------|------|------|------|------|
| |High | 00% | 05% | 00% | 00% |
|Southerly Middle|Moderate | 00% | 15% | 05% | 00% |
| |Low | 00% | 30% | 20% | 05% |
| |Not Visbl| 100% | 50% | 75% | 95% |
|----------------|---------|------|------|------|------|
| |High | 00% | 00% | 00% | 00% |
| Northerly Low |Moderate | 00% | 05% | 05% | 00% |
| |Low | 00% | 35% | 10% | 00% |
| |Not Visbl| 100% | 60% | 85% | 100% |
|----------------|---------|------|------|------|------|
| |High | 00% | 00% | 00% | 00% |
| Central Low |Moderate | 00% | 00% | 00% | 00% |
| |Low | 00% | 30% | 10% | 00% |
| |Not Visbl| 100% | 70% | 90% | 100% |
|----------------|---------|------|------|------|------|
| |High | 00% | 00% | 00% | 00% |
| Southerly Low |Moderate | 00% | 00% | 00% | 00% |
| |Low | 00% | 10% | 05% | 00% |
| |Not Visbl| 100% | 90% | 95% | 100% |
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For example, the probability for observing auroral activity over the
southerly middle latitudes (near the 40N latitude boundary) on Day 2 (or
17 June, UT time) is as follows. There is a 05% chance for observing
high-intensity auroral activity over these regions on 17 June, a 15%
probability for observing moderate levels of activity, a 30% probability for
observing low levels of activity, and a 50% chance for being unable to
observe any auroral activity at all. Taken together, there is a 45%
probability for observing low to moderate auroral activity, a 20% probability
for observing moderate to high auroral activity, and an 80% probability that
activity will either be not visible or of low intensity on 17 June.
This chart is designed to give the observer all of the information
needed to make judgemental decisions. Using this chart, the observer will
know exactly what the forecasters believe may happen and whether there is a
high or low confidence in predicting specific levels of activity for specific
regions.
The UT day of 17 June (or, for North American observers, the local
evening hours of 16 June) is expected to provide the highest probabilities
for observing auroral activity over the lower latitudes. Lunar phase will
not interfere with attempts to view auroral activity.
This is expected to be the last opportunity to view flare-induced
auroral activity before Region 6659 departs around the west limb.
Photographic observers in the middle to low latitudes where auroral
activity is difficult to spot may want to take long-exposure photographs of
the northern to northeastern horizon even if auroral activity does not become
optically visible with the unaided eye. Often, long-exposure photographs
taken without optical confirmation yield positive results.
For any of you who obtain optical or photographic confirmation of
auroral activity (particularly over the lower latitudes), please send a note
to: oler@hg.uleth.ca, or to: oler@alpha.uleth.ca, or write to: Solar
Terrestrial Dispatch, Box 357, Stirling, Alberta, Canada, T0K 2E0. We are
interested in obtaining photographic copies of auroral activity viewed over
areas where it is normally not seen. We thank all those who take the time to
send in confirmation (or non-confirmation) reports.
** End of Watch **