OVIAN DECAMETER RADIO EMISSION: TO THE QUESTION ON THE SIZE OF SOURCES

Анотація

There are debated the questions on
size and properties of sources of Jupiter DAM radio
emission (JRE). The evolution and the parameters of
the sources in the DAM Io-B-storm of October 30,
2008, consisting of a large number of S-bursts, and
interspersed with L-bursts and N-bursts, are analyzed
in detail. It is shown that S-bursts in this storm
are most likely to occur in the northern hemisphere
of Jupiter at heights (0–0.2)R j and at longitudes
λ IIIs = (195–220) o (when Jupiter is deployed to the
observer CML = λ III = 130–160 o ). The onset of the
Io-B-storm is associated with sources at high altitudes,
and over time the sources drop down to Jupiter (as
the observed S-burst frequencies increase with time).
The possibility of the appearance of L- and N-bursts
on the background of S-bursts is discussed. L-bursts
can arise from the southern hemisphere of Jupiter, at
a height of 0.2R j . And N-bursts can most likely be
located in the northern hemisphere at λ IIIs = 66 o
at a height of 0.2R j . Using the spectral data on the
JRE from 30.10.08, the sizes (thickness and length)
of filament-like sources of JRE - electron beams were
determined, and the parameters of the MHD (Alfven)
waves that activating the JRE bursts. It is shown
that the L-radiation sources most likely appear to
be thin filaments elongated to magnetic field lines,
with a thickness of more then 10 km, and up to
2000 km in length. And the sources of S-radiation
look like links with filament-like emissions less than 1
km thick (10–100 strands in a bundle) and up to 300
km in length flying at a speed of (0.05–0.1) c away
from Jupiter . The observed A-wave velocities are
2–3 times slower than the A-wave velocity predicted
theoretically (about 0.001 c, in light velocity units).
Frequency (0.2–1 MHz) and temporal (up to 1 min)
diffraction modulation of "lanes" confirms the size of
the S-sources less than 200 km. Conclusions are made
about the theoretical prerequisites for the appearance
of S-bursts with observed parameters. Estimates of
the radiation intensity of S-sources indicate an addi-
tional increase in the radiation of the source near the
generation region; this indicates a non-homogeneous
structure of the environment in the active regions
of the Jupiter magnetosphere. The thin transverse
structure of the S-sources can be explained by the
mechanism of plasmas fluctuations with periods of
τ = τ ea = 10 ms, and with the peculiarities of the
bunches of plasma clots that lead to electron leakage
and to the emission of plasma plaits. The observed
deceleration of the MHD wave velocities can be
explained by the influence of the Io – Jupiter flow
tube.