SOLAR MICROWAVE DRIFTING SPIKES AND SOLITARY KINETIC ALFVEN WAVES

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SOLAR MICROWAVE DRIFTING SPIKES AND SOLITARY
KINETIC ALFVEN WAVES

• D. J. Wu, J. Huang, J. F. Tang, and Y. H. Yan
• The Astrophysical Journal, 665 L171L174, 2007
  August 20
• presented by
• Gelu M. Nita

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Motivations for selecting this paper

• Mechanisms driving eruptive phenomena and
  elementary processes occurring at the smallest
  coherent scales have been outstanding problems in
  solar physics.
• In this Letter, a novel kind of fine structures
  of solar radio bursts, solar microwave drifting
  spikes (SMDSs), is reported.
• The frequency range in which these structures
  were observed and the frequency and time
  resolutions of the observing instrument exactly
  match the observational abilities of the NJITs
  FST instrument.
• If proven correct, the interpretation presented
  in this Letter may provide diagnostics for some
  characteristic parameters of solar corona in the
  flaring region, which may be applied if similar
  events are observed by FST.

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DATA
Solar Broadband Radio Spectrometer (SBRS)
National Astronomical Observatories of China
(NAOC) 1.25 ms temporal resolution 4 MHz
frequency resolution 1.101.34 GHz freq.
range 2004 November 3 03257.5 to 032510.2
UT NOAA AR 10696 N09E45 65 individual SMDSs from
1.112 to 1.268 GHz
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Data Analysis

1. RCP LCP central frequencies
2. Lifetime
3. Relative bandwidth
4. Drift rate

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Interpretation

• The analysis shows that the SMDSs can be produced
  by a group of solitary kinetic Alfven waves
  (SKAWs) with small cross-field scales, in which
  the electrons in the SKAWs are accelerated
  self-consistently by the SKAW electric fields to
  tens of keV and trapped within the SKAW potential
  wells.
• It is these trapped electrons that trigger the
  SMDSs via the Electron Cyclotron Maser Emission
  (ECME) mechanism, and the frequency drifts of the
  SMDSs are attributed to the SKAW propagation
  along the magnetic field.
• The SKAWs are exact solutions of two-fluid
  equations for a low-? plasma and have been
  experimentally verified in the magnetosphere,
  where they accelerate auroral electrons to
  several keV.
• The authors believe the SMDSs represent a new
  observational signature of SKAWs in the solar
  atmosphere.

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Interpretation
Radiation generated by the Electron Cyclotron
MASER emission mechanism
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Theoretical structure of a SKAW

1. Relative density
2. Parallel electric field
3. Electric potential
4. Electron velocity inside a SKAW

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Derived parameters

• df/f gt local Alfven velocity vA6103 km/s
• longitudinal source size 4Km
• transversal source size 10m
• vA gt energy of trapped electrons 50 keV
• SKAW frequency 1.5103 Hz
• ltfgt gt mean source magnetic field Bs100G
• vA ,ltfgt gt plasma density n0 1.3109 cm-3
• n0 gt trapped electron density n0 1.3108 cm-3

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Microwave spikes observed by FSTDecember 06,
2006, 1941 UT
DATA Zoom in somewhere in the 1-1.5 GHz
range 1MHz frequency resolution 100??s
integration time 20ms time resolution PRELIMINARY
RESULTS ltdf/fgt(0.350.28) 20,000
spikes/minute! Spike lifetime lt20ms Almost 100
circular polarization No obvious drift