Spot group area.
- Large spot group area is a necessary, but not sufficient, criterion for calling a MFW.
- Large spot group area is sufficient only in combination with one one of the Criteria #2 - 6 below.
- Current daily values of spot group areas (uh) are listed
on NOAA Space Weather Prediction Center
- Today's daily values are easily compared to yesterday's
through the today/yesterday values given on the "Today's NOAA Active
Regions" list below the images at solarmonitor.org.
- If there is reason to think that the group spot area might be growing
rapidly, check by making full-disk HMI intensity movies at the
SDO AIA/HMI Browse Data
page (Movies with every 5th image work well)
- N.B.: scatter in spot group area associated with flares of a given GOES class is an order of magnitude (Sammis, Tang & Zirin (2000)
Figure 2). Therefore, it's best not to take the current working definition of large spot group area too literally.
If ANY of the Criteria listed below are met, call a Major Flare Watch.
Criterion #1. A major
flare has occured on the disk
(if a region produced one big flare, it will probably produce
at least one more).
- If you are at a computer, you can check for recent flares using lists & GOES light curves at SolarSoft Latest Events
- If you have your cell phone with you, and you have signed up with
Spaceweathertext.com,
you can get text messages when X-flares occur 24/7.
Criterion #2. Large island delta configuration -
even better if the region is reversed polarity. Bright H-alpha plage
(much brighter than normal plage, perhaps twice that of the quiet
chromosphere) will
be present, typically obscuring umbrae or running along the polarity
inversion line.
-
Check for bright H-alpha (much brighter than normal plage) at GONG H-alpha Network which has better temporal coverage and continuity of intensity scale than the following alternate sites:
Criterion #3. Large beta-gamma-delta configuration with bright H-alpha plage and better still
if reversed polarity. Bright H-alpha along the neutral line is
needed.
Criterion #4. Elongated umbrae in pairs of opposite polarity in a large sunspot group, even if the umbrae are
not a delta configuration, if vector magnetograms reveal strong
shear along the strong-field part of the polarity inversion line.
- Check the same list of sites as #2.
-
Check for strong shear using SOLIS vector magnetograms from the
SOLIS Data
Information page .
On that page, under "VSM Data:", click on "Latest VSM Data".
On that page click
on the "Photosphere (630.2 nm) Vector Magnetic Field" full-disk
image, then click on the AR of interest.
Then click on the image labeled "LOS Magnetic Field", which shows the
transverse fields using arrows. The current working definition of
"strong shear" means that along the polarity inversion line both (1) the
maximum shear angle at somme point exceeds 85 degrees and
(2) the length of the portion of the PIL with strong
shear (shear angle > 80 degrees) exceeds 10,000 km (13"). Working
definition of the strong-field part of the polarity inversion line
means B_transverse at least 1000 Gauss (see arrow length scale).
- SOLIS vector magnetograms are available seven days per week, but
only when weather in Tucson is good.
Criterion #5. Emerging Flux Region (EFR) coming up within an existing large sunspot group if the leader spots
of the EFR are adjacent to the existing group's trailing spots
or vice-versa.
Criterion #6. Rapidly moving sunspots - sunspot(s) moving towards and/or
into an opposite polarity spot or parallel to the polarity inversion
line (shearing motion) in a large sunspot group.
If ANY of the Criteria listed below are met, call a Major Flare Watch.
Criterion #1. A major
flare has occured on the limb
(if a region produced one big flare, it will probably produce
at least one more).
- If you are at a computer, you can check for recent flares using lists & GOES light curves at
SolarSoft Latest Events
- If you have your cell phone with you, and you have signed up with
Spaceweathertext.com,
you will get text messages when M5 or greater flares occur 24/7.
Criterion #2.
A C or low M flare has been observed on the East limb (possibly
a partially occulted major flare on the back side), and
H-alpha images on the
GONG H-alpha website
(the H-alpha movies are particularly useful) or AIA images on the
SDO | DATA web page
indicate bright knots at the tops of post flare loops, and
EUVI/AIA 195 Stonyhurst Heliographic maps
on that same page show a large active region just over
the East limb.
Criterion #3.
A C or low M flare has been observed on the West limb (possibly
a partially occulted major flare on the back side), and
H-alpha images on the
GONG H-alpha website
or AIA images on the
SDO | DATA web page
indicate bright knots at the tops of post flare loops, and
a recent beta/gamma/delta magnetic classification and/or
a history of M flare activity before the associated region
rotated over the limb.
REFERENCE MATERIAL.