JOP143 Impulsive Flare Dynamics
Received: 20 April 2001

CONTACTS:

  Harry Warren [hwarren@cfa.harvard.edu]
  Tom Metcalf  [metcalf@lmsal.com]

INSTRUMENTS:

  TRACE, HESSI, MDI

SCIENCE OBJECTIVES:

  We propose a JOP to investigate the spatial and temporal
  relationships between non-thermal and thermal emission during the
  impulsive phase of solar flares using coordinated observations from
  TRACE, HESSI, and MDI. The primary goals of this JOP are [1] to
  understand the relationships between the footpoint hard x-ray
  emission, the UV flare ribbons, and the structure of the
  photospheric magnetic field, and [2] to understand the properties of
  hot thermal flare plasma (12-25 MK) and its relationship to both
  footpoint and coronal hard x-ray sources.

OBSERVATIONS:

  HESSI: HESSI observations simply consist of time-tagged photon
  events. Thus the observing parameters, such as integration time or
  energy resolution, are made during analysis and can be modified to
  optimize the data product of interest (such as an image, light
  curve, or spectrum) and no special observing sequences are
  required. Of primary interest to us will be HESSI's imaging
  capabilities and good energy resolution. 

  For objective [1] we will be interested in images at energies
  greater than ~25 keV so that the non-thermal footpoint emission can
  be identified.  For objective [2] we will particularly interested in
  HESSI images at 6-7 keV, where the Fe XXV resonance line will be an
  important contributor at high temperatures. For this objective we
  will also be interested in HESSI images at higher energies so that
  we can look for coronal (Masuda) hard x-ray sources and study the
  relationship between these sources and the hottest thermal flare
  plasma.

  TRACE: There will an observing mode for each objective

    [1] High-cadence UV observations which make use of the circular
    buffers. The HPW.flarewatch1600 sequence will provide 3s cadence
    data at full-resolution for about 8 minutes before the flare flag
    is triggered followed by 15 minutes of 2s cadence data. Partial
    fields of view (384"x384" pre-flare and 256"x256" during the
    response) are used to increase the cadence. The use of the
    automatic exposure control will minimize the number of saturated
    pixels. EUV images (primarily 171) will be taken in context. These
    data will allow us to correlate the location and evolution of the
    hard x-ray footpoint emission with the UV flare ribbons.

    [2] To study the formation and evolution of very high temperature
    (12-25 MK) thermal flare plasma we require high-cadence (10-20s)
    195 observations at full resolution.  Reading out only a
    sub-region of the CCD (384"x384") will improve the cadence. UV
    context images are desirable for alignment with photospheric
    magnetograms. The Fe XXIV emission imaged in the TRACE 195 channel
    will be compared with the HESSI 6-7 keV images.

  MDI: High-resolution or full-disk magnetograms depending on the
  location of the target. The MDI magnetograms will be used to study
  the relationship between the properties of the photospheric magnetic
  field, such as shear, and the location of the footpoint hard x-ray
  emission.

  Other Instruments: Collaboration with other instruments, such as
  Yohkoh, SoHO/CDS, or ground-based observatories, is highly
  desirable.

SCHEDULING:

  Since we are approaching the declining phase of the solar-cycle it
  will be important to seize any opportunity to observe the large,
  flaring active regions that appears.  Ideally, we would like to
  observe any active region with significant flare potential for 7 to
  14 days.

TARGET SELECTION:

  The TRACE target will be the active region selected by the Max
  Millennium Chief Observer at Big Bear Solar Observatory.