In this work, we concentrate in the analysis of radio slowly drifting fine structures associated with solar flares recorded in the frequency range of (1000 - 2500) MHz by the Brazilian Solar Spectroscope (BSS), in regular operation at National Institute of Space Research (INPE) - Brazil. The main morphological aspects of each fine structure are narrow-band of about 5 - 10 MHz and small duration of the order of 50 milliseconds. The majority of these fine structures are observed over a time interval of a couple of minutes before the maximum of the associated flare, in the impulsive phase. However, some observations during the gradual decay phase are also reported. They drift towards lower frequencies, with slow rates typically of about of 10 - 100 MHz s-1 Estimated velocities of the exciter from the negatively drifting structures suggest that the shock-like exciter is propagating in the higher chromosphere. Than, those fine structures are interpreted as a possible signature in decimetric emissions from the chromospheric evaporation phenomenon. Details of these observations and their interpretation in terms of the plasma emission produced by accelerated particles and the chromospheric evaporation front is presented.

Brazilian Solar Spectroscope (BSS), operating in the frequency range of (1000 ¡ 2500) MHz with high time and frequency resolutions, has observed various fine structures showing intensity variations as functions of time and frequency. Here we are reporting radio bursts observed by BSS, from August to October/2001, exhibiting fine structures with total duration of the order of 300 ms, covering a frequency range of ~ 200 MHz. These characteristics are similar to those of the narrow band type III bursts observed above 1000 MHz. Hence these fine structures are variants of decimetric narrow band type III-like bursts. The fine structures observed exhibit variation of intensity as a function of frequency and curvatures in the frequency-time plane. These fine structures are explained as a propagation effect. We suggest that these structures are the signatures of the chromospheric density inhomogeneities lying in the line-of-sight path between the observer and the radio source. If the emitted frequencies are lower than the plasma frequency of the inhomogeneity, there will be absorption over a certain band, corresponding to the dimension of the inhomogeneity. The curved like structures are due to lower group velocities of the lower frequencies in the density inhomogeneities. The estimated scale sizes of the irregularities obtained are of the order of 10¹ - 10(4) km. Thus an alternative method to total solar eclipse observation is suggested for investigations of chromospheric density irregularities.

On 30th June 1989 high sensitivity-spectral resolution observations of solar radio bursts were carried out in the frequency range of 18 - 23 GHz. The burst observed at 17:46 UT was different from the 60 bursts observed so far in the sense that it exhibited a frequency fine structure superimposed on the ongoing burst in its rising phase, i.e. an additional enhancement of the flux density of the order of 10 SFU, observed only in the 21 and 22 GHz frequency channels, lasting for about 4 s. Interaction of an emerging loop with an adjacent loop accelerated particles in that loop from which the broadband burst was emitted due to the gyrosynchrotron emission. The observed fine structure is interpreted as due to thermal gyro-emission at 6th harmonic of the gyrofrequency originated from a hot kernel with short lifetime located at the top of emerging loop. We derived the hot kernel source parameters, th e temperature as 8 <FONT FACE="Symbol">´</font>10(7) K, the magnetic field as <img src="http:/img/fbpe/bjp/v29n3/510i1.gif" alt="510i1.gif (46 bytes)"> 1250 G and the density as <img src="http:/img/fbpe/bjp/v29n3/510i1.gif" alt="510i1.gif (46 bytes)"> 5 ×10(12) cm-3.