Decimetric dot-emissions arranged in zebras and fibers

H. Meszarosova$^1$, H.S. Sawant$^2$, M. Karlicky$^1$, F.C.R. Fernandes$^3$, J.R. Cecatto$^2$, M.C. de Andrade$^2$

$^1$Astronomical Institute of the ASCR, CZ-25165 Ondrejov, Czech Republic
$^2$National Space Research Institute (INPE), Sao Jose dos Campos, SP, Brazil
$^3$Institute of Research and Development (IPD - UNIVAP), Sao Jose dos Campos, SP, Brazil

For the first time, we have investigated statistically 20 groups of decimetric dot-emissions as fine structures of zebras and fibers observed during 1999-2001 years in frequency range 950-2600 MHz by Brazilian Solar Spectroscope (BSS). There are two types of dot-emissions: 1) dots arranged in zebras and 2) dots arranged in fibers. Also some of classical zebras and fibers consist of distinguishable dot-like structures. Common parameters of both classical and arranged dot-zebras are number of zebra lines (5) and time/frequency thickness of zebra dots (130 ms/14 MHz, respectively). Arranged dot-zebras have greater total zebra duration and bandwidth, frequency distance between two zebra lines and time distance between neighboring dots than the classical one (28 s and 312 MHz, 66 MHz and 107 ms) in comparison to (5 s and 178 MHz, 18 MHz and 14 ms), respectively. Common parameters of both classical and arranged dot-fibers are time distance between two fibers (470 ms), individual fiber bandwidth (180 MHz) and time/frequency thickness of fiber dots (130 ms/15 MHz, respectively). Arranged dot-fibers have smaller total fiber group duration and bandwidth, individual fiber duration but they have greater frequency distance between neighboring fiber dots than the classical one (14 s and 321 MHz, 552 ms and 14 MHz) in comparison to (47 s and 409 MHz, 3161 ms and 8 MHz), respectively. The similarity in morphology, in characteristic properties (electron density n = 4-16x10^9/cm^3 and coronal magnetic field B = 120-250 gauss) and observed continuous changes of dot-fibers into dot-zebras and vice versa are in favor of the same physical origin of these structures. We propose that the dots are generated when propagating packet of whistler waves incomes to the regions where upper-hybrid waves are generated due to the double plasma resonance. Furthermore, while the well-organized dots are generated at these double resonance regions in smoothed solar atmosphere, a chaotic behavior of dots can be caused by MHD turbulence at these regions.