Major Flare Watch Evaluation
From RHESSI Wiki
Introduction
Flares that produce gamma-ray lines are the highest priority target of the RHESSI Mission. Multi-wavelength imaging and spectroscopic observations from other spacecraft and ground-based observatories before, during and after such flares are crucial to the interpretation or the RHESSI data. To optimize such observations, the Max Millennium Chief Observers (MM_COs) [1] announce a Major Flare Watch when the probability of gamma-ray-producing flares is high. Such announcements [2] appear in the Max Millennium Messages of the Day [3], distributed worldwide to over 200 solar observers and mission operations planners through the self-subscribing MMmmotd mailing list and archive [4]. How well has this system worked? That's the subject of this Nugget.
Major Flare Watch Criteria
Throughout the RHESSI mission, the MM_COs have used a set of Major Flare Watch criteria that are an outgrowth of the classic "BEARALERTS - A Successful Flare Prediction System" [5] paper by Zirin and Marquette (1991):
- A major flare has occured (if a region produced one big flare, it will probably produce at least one more)
- Large island delta - opposite polarity umbrae within 2 heliographic degrees within a common penumbra (delta configuration) and, in addition, the delta surrounded by opposite polarity flux - even better if the region is reversed polarity. Bright H-alpha will be present.
- Large delta configuration with bright H-alpha plage and better still if reversed polarity. Bright H-alpha along the neutral line is needed.
- Elongated umbrae in pairs of opposite polarity even if the umbrae are not a delta configuration. Transverse magnetograms will reveal strong shear.
- Emerging Flux Region within an existing active region, if the leader spots of the EFR are adjacent to the existing region's trailing spots or vice-versa.
- Rapidly moving sunspots - sunspot(s) moving towards and/or into an opposite polarity spot.
Statistics for Daily Major Flare Watch Messages
We've had a look at all GOES X-ray flares recorded in the daily NOAA/NWS Space Weather Prediction Center events files from 26-Mar-2001 to 17-May-2010, inclusive. We then extracted the number of flares at or above a chosen GOES class within 24 hours of the Major Flare Watch UTC message issue times. The total number of flares at or above the same GOES class is extracted from the complete time range under consideration (26-Mar-2001 to 17-May-2010) allowing the percentage to be calculated. We also extract the number of flares found within each of the 220 MFW 24 hour periods, so the number of MFW messages that both successfully and unsuccessfully catch flares is extracted and the percentage of MFW messages which are successful is calculated.
It helps to look at these results in graphical form:
