Title: SOLAR MICROWAVE DRIFTING SPIKES AND SOLITARY KINETIC ALFVEN WAVES
1SOLAR 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
2Motivations 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.
3DATA
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
4Data Analysis
- RCP LCP central frequencies
- Lifetime
- Relative bandwidth
- Drift rate
5Interpretation
- 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.
6Interpretation
Radiation generated by the Electron Cyclotron
MASER emission mechanism
7Theoretical structure of a SKAW
- Relative density
- Parallel electric field
- Electric potential
- Electron velocity inside a SKAW
8Derived 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
9Microwave 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