Abstract
Using
Nobeyma radio heliographic
observations we have studied temporal
variations of a number
of sunspot-associated sources on the wave-length of 1.76 cm in
circularly polarized emission.
For all three cases of well-developed and rather stable sunspots we
found distinctly manifistated
nearly harmonic oscillation with the periods in the range of 150-190
seconds. In one case of
unstable and quickly developing active region the fluctuations seem to
be chaotic with no
dominating period of fluctuations.
This type of solar radio sources is generally accepted to be generated
by cyclotron emission of
thermal electrons in the magnetic tube of a sunspot penatrating the
solar corona. This implies the
presence of the magnetic field of about 2000 Gauss there. The observed
phenomenom
demonstrates the oscillation of the area and/or the temperature of the
gyroresonance region. A
model computations show that variations of the height of the CCTR with
the amplitude of the order
of ten km may be enough to produce the observed fluctuations. The
oscillations with the period
approximately equal to 3 minutes are well-knon phenomena in the
chromsphere above the
sunspots. We suggest that we have found the appearance of the 3-minute
oscillations of
sunspots in the radio emission.