Major Flare Watch Evaluation

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(What if MWF Periods Started/Ended Earlier?)
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== What if MWF Periods Started/Ended Earlier? ==
== What if MWF Periods Started/Ended Earlier? ==
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For practical reasons, it may be difficult for any given observatory or spacecraft to respond immediately to the declaration of a Major Flare Watch.  To consider the effect of delayed response, we identified all 33 periods of contiguous daily MFW messages between 1-Feb-2001 to 31-May-2010.  We then used the SWFC data to ask "What if these MFW periods had started one day earlier/later or ended one day earlier/later? The results are shown in Figure 2.
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For practical reasons, it may be difficult for any given observatory or spacecraft to respond immediately to the declaration of a Major Flare Watch.  To consider the effect of delayed response, we identified all 33 periods of contiguous daily MFW messages between 1-Feb-2001 to 31-May-2010.  We then used the NOAA/NWS data to ask "What if these MFW periods had started one day earlier/later or ended one day earlier/later? The results are shown in Figure 2.
[[Image:mmco_percent_periods_comp.jpeg|frameless|center|thumb|500px|'''Figure 2:''' Percentage of flares at or above a chosen GOES class within 24 hours of the Major Flare Watch UTC message issue times (24-hour MFW periods, aka MFWs) for 26-Mar-2001 to 17-May-2010, for various offsets in time of the start of the MFW period ]]
[[Image:mmco_percent_periods_comp.jpeg|frameless|center|thumb|500px|'''Figure 2:''' Percentage of flares at or above a chosen GOES class within 24 hours of the Major Flare Watch UTC message issue times (24-hour MFW periods, aka MFWs) for 26-Mar-2001 to 17-May-2010, for various offsets in time of the start of the MFW period ]]

Revision as of 19:51, 9 November 2010

Contents

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" paper by Zirin and Marquette (1991)[5]:

  1. A major flare has occured (if a region produced one big flare, it will probably produce at least one more)
  2. 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.
  3. Large delta configuration with bright H-alpha plage and better still if reversed polarity. Bright H-alpha along the neutral line is needed.
  4. Elongated umbrae in pairs of opposite polarity even if the umbrae are not a delta configuration. Transverse magnetograms will reveal strong shear.
  5. 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.
  6. 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 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.

Table 1: Number of flares at or above a chosen GOES class within 24 hours of the Major Flare Watch UTC message issue times (24-hour MFW periods, MFWs below) during the period 26-Mar-2001 to 17-May-2010

In graphical form (Figure 1), these results show that the percentage of all flares caught in MFWs by the MM_COs saturates at about 75% in the X-class range, which is roughly coincident with the occurence of gamma-ray lines observed by RHESSI (Shih et al., 2009) [6]

Figure 1: Percentage of flares at or above a chosen GOES class within 24 hours of the Major Flare Watch UTC message issue times (24-hour MFW periods, aka MFWs) for 26-Mar-2001 to 17-May-2010

What if MWF Periods Started/Ended Earlier?

For practical reasons, it may be difficult for any given observatory or spacecraft to respond immediately to the declaration of a Major Flare Watch. To consider the effect of delayed response, we identified all 33 periods of contiguous daily MFW messages between 1-Feb-2001 to 31-May-2010. We then used the NOAA/NWS data to ask "What if these MFW periods had started one day earlier/later or ended one day earlier/later? The results are shown in Figure 2.

Figure 2: Percentage of flares at or above a chosen GOES class within 24 hours of the Major Flare Watch UTC message issue times (24-hour MFW periods, aka MFWs) for 26-Mar-2001 to 17-May-2010, for various offsets in time of the start of the MFW period

NB: Success catching > X1 flares is independent of 1-day delays in MFW period start dates. Of course, if we could get a crystal ball, we would, so that we never had to implement the all-important first criterion in the list above.

Summary

Gamma-ray flares are a high-value target.   For reasons evident in Figure 1, let's identify them with GOES class > X1 (~ Shih et al., 2009) [7].    The data show that 220 MFW days were called over 9-plus years, < 7% of all available observing days   About 75% of all > X1 flares were caught.  This percentage is insensitive to 1-day delays.

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