Major Flare Watch Evaluation

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 their interpretation. 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 to over 200 solar observers and mission 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.