Astronomy and Astrophysics – Astrophysics
Scientific paper
Dec 2009
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2009agufmsh41b1645i&link_type=abstract
American Geophysical Union, Fall Meeting 2009, abstract #SH41B-1645
Astronomy and Astrophysics
Astrophysics
[6954] Radio Science / Radio Astronomy, [7509] Solar Physics, Astrophysics, And Astronomy / Corona, [7514] Solar Physics, Astrophysics, And Astronomy / Energetic Particles, [7534] Solar Physics, Astrophysics, And Astronomy / Radio Emissions
Scientific paper
Type-I burst is one of the solar radio phenomena observed in meter wave length. Micro-type-III burst is observed in the hectometric and kilometric wavelength ranges. Daily variations of type-I and micro-type-III bursts activities correlate well. These two bursts are usually observed with active regions but not associated with solar flares. These two bursts are relatively weak but occur more frequently than strong flare related bursts. These characteristics suggest that there are some frequent and small-scale energy release processes in the solar corona. Although type-I and micro-type-III bursts are thought to be emitted by non-thermal electrons in the corona, the electron acceleration processes have not been understood enough. In this study, several observations are performed to understand the relationship between type-I and micro-type-III which may have an important clue for revealing their electron acceleration processes. An observation of type-I burst was performed using a ground-based radio telescope of Tohoku University named Iitate Planetary Radio Telescope (IPRT). A physical aperture of the solar observation system of the IPRT is about 512 square meters and it has high sensitivity in the meter wave range. The data observed with WAVES onboard the WIND spacecraft was used to identify micro-type-III. From the data analyses for the IPRT and WAVES, following results are suggested: [1] The intensity of the observed type-I bursts enhanced when the individual burst element of micro-type-III occurred. This observation result suggests that type-I burst and micro-type-III burst are made by electrons which have a same origin. [2] Micro-type-III burst is thought to be emitted on open field lines. On the other hand, type-I burst is known to be generated by the non-thermal electrons trapped in a closed loop. Considering these ideas, particle acceleration region of the observed two bursts are suggested to be located in closed loop regions next to open field lines. [3] The micro-type-III bursts were always emitted in lower frequency than the type-I bursts and there was a frequency gap between these two bursts. Since they are thought to be emitted around the local plasma frequency, frequency gap means electron density gap around their source regions. The type-I bursts are emitted in closed magnetic loops and the electron density at the source regions is higher than surrounding corona. On the other hand, the micro-type-III bursts are emitted along open field lines so the electron densities at their source regions are relatively low because coronal plasma flows out to the interplanetary space. Therefore the frequency gap between the type-I and micro-type-III bursts is explained by this electron density gap around the source regions.
Iwai K.
Misawa Hiroaki
Morioka Akira
Tsuchiya Fuminori
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