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Experimental results from measurements performed during the 12 November 1966 total solar eclipse with a 4.28-cm radio polarimeter
Kaufmann P.; Matsuura O.T.; Dos Santos P.M. (1967)
Radio observations of the Sun with a 4.28-cm radio polarimeter were performed during the 12 November 1966 total solar eclipse at a site located near the city of Bagé, in the extreme south of Brazil. The solar activity during that period is discussed, giving additional data for the eclipse measurements themselves. The difference between radio and optical contacts indicated that there is a significant radio emission at a height near 0.12 solar radii over the photosphere, and the basic residual flux due to the contribution of the ring during the totality was found to be 12.2% of the total flux. An important "radio spot" was present near the center of the solar disk, contributing almost alone to the observed basic left-handed circularly polarized component of solar radiation. During totality no important residual polarization was found and if it still existed it is neglectable. © 1967.
Some results obtained with v.l.f. atmospherics measurements at São Paulo, Brazil
Kaufmann P.; Lopes W.; Schaal R.E. (1967)
Analysis of 10 months of v.l.f. atmospherics noise level fluctuations during 1963 has been done. The measurements have been performed with rather simple equipment and some interesting results were obtained concerning daily variations as a function of solar zenithal angles, and a number of effects peculiar to sunrise and sunset are discussed. Emphasis is placed on an understandable confusion which arises when attempting to study v.l.f. propagation through the ionosphere from atmospherics activity, since a certain number of randomly occurring features are difficult to determine. © 1967.
V.L.F. propagation across the geomagnetic anomaly during S.I.D.s
Kaufmann P.; Schaal R.E.; Lopes W.; Arakaki L. (1967)
A number of S.I.D.s (sudden ionospheric disturbances) has been selected and analysed, in order to find some compatibility with the general form of the theory of waveguide mode propagation in an Earth-ionosphere spherical waveguide having an upper boundary characterized by a conductivity parameter derived from an exponential model. The v.l.f. (very low frequency) transmissions were received at a site located near the center of the South Atlantic Geomagnetic Anomaly, all of them crossing the region of the equatorial electrojet-and the results show that the general formulation may be used if the daytime upper boundary is less than 65 km. On the other hand the peculiar physical conditions found in the upper atmosphere along such paths possibly have an important influence on its shape and on the considered waveguide configuration, and they must be considered for getting a better understanding of the S.I.D. effects. Further experiments are suggested, emphazising the need of a more accurate knowledge of the dependence of the ionospheric parameter L on frequency. © 1967.
Solar corona at centimetre wavelengths
Kaufmann P.; Matsuura O.T. (1968)
DETAILED spectral information on the Sun in the range of wavelengths from near 3 cm to 21 cm was obtained on November 12, 1966, when total solar eclipse measurements were being made. Several observers, using accurate equipment, reported the residual solar emission during totality, and these data were used in a discussion of the cm-wavelength solar corona. In order to have some uniformity in the analysis, we first established a smoothed total solar flux spectrum for the period of November 11, 12 and 13 (as shown by Kaufmann1). The residuals, in percentages, uncorrected for the active regions present in the solar disk, were then transformed into flux units and are shown in Table 1. © 1968 Nature Publishing Group.
A partial solar eclipse observed at 100-cm wavelength on 12 November 1966
Kaufmann P.; Matsuura O.T.; Dos Santos P.M.; Monno M. (1968)
Polarization bursts in the sun observed at microwave frequencies
Kaufmann P.; Matsuura O.T.; Mascaro A.C.M.; Mendes A.M. (1968)
There are microwave bursts not observable in the total flux from the Sun, but only in circular polarization. The production of these events in the Sun requires equivalent changes of the magnetic field imposed on the emission regions during the bursts. © 1968 Nature Publishing Group.
The apparent sky temperatures and tropospheric absorption on solar radiation at 7 GHz1
Matsuura O.T.; Kaufmann P. (1968)
The effect of a total solar eclipse on long path VLF transmission
Kaufmann P.; Schaal R.E. (1968)
The effects of the total solar eclipse of 12 November 1966 on VLF transmissions at 26·1 kHz transmitted from NPM, Hawaii, and received at São Paulo, are presented. The eclipse occurred during the sunrise transition period, making the data interpretation rather difficult. There was a clearly-marked change of phase, corresponding to a maximum delay of 12·3 sec. © 1968.
Some characteristics of an S-component of solar radiation identified on November 1966 eclipse at 4.28-cm wavelength
Kaufmann P. (1968)
A strong S-component of solar radiation was identified during the total solar eclipse of November 12, 1966. Its characteristics, as measured at 4.28 cm, were studied in terms of flux and polarization, and its spectral features were derived by the use of data from other observatories. The whole source presented approximately the typical characteristics suggested by some authors in the last few years, and further it has been shown that it could be resolved into at least two enhanced regions, one showing unpolarized radiation with a brightness temperature Tb≈ 1.2 × 106 °K, and the other showing 50% of left-handed circularly polarized radiation, with Tb≈ 0.7 × 106 °K. The source's overall characteristics favour the presence of non-thermal absorption at the emitting regions. © 1968 D. Reidel Publishing Company.
A magnetohydrodynamic approach for interpreting solar polarization bursts at 7 GHz
Matsuura O.T. (1969)
A magnetohydrodynamic (MHD) approach is presented that appears to be comprehensive for the interpretation of the recently discovered microwave solar events, in which only the degree of circular polarization changes, without any increase in the output of the total solar flux. On the basis of this explanation experimental evidence is suggested for Alfvén waves, in relation to the velocity fields in the solar chromosphere. © 1969 D. Reidel Publishing Company.
Some relationships between solar X-ray bursts and SPA's produced on VLF propagation in the lower ionosphere
Kaufmann P.; Paes de Barros M.H. (1969)
This paper discusses SPA's measured at long VLF propagation paths in the lower ionosphere and their association with solar X-ray bursts observed by USNRL satellites in the 0-3 Å, 0-8 Å and 8-20 Å bands. Excellent correlations were found between the SPA importances (in degrees per Mm) and the logarithm of the X-ray burst peak intensities. A hardening of the X-ray burst spectra is evident for increasing importance of SPA's; the threshold energy required for the occurrence of such anomalies was estimated, it is 4.3×10-5 ergs cm-2 sec-1 in the main ionizing band of 0-3 Å. It was also possible to derive the effective recombination coefficient at the normal D-region height of 70 km, this being αr≈6×10-6 cm3 sec-1; furthermore ion production rates were estimated during SPA's at heights below the reference level. © 1969 D. Reidel Publishing Company.
Some peculiar tropospheric and ground effects on solar noise radio measurements at 7 GHz
Matsuura O.T.; Kaufmann P.; dos Santos P.M.; Fanto P. (1969)
It has been studied statistically the incidence of solar radio flux fluctuations in nearly 1000 hr of continuous observations at 7 GHz, and shown that some tropospheric phenomena can be analysed by this method. Of the fluctuations 93 per cent were coincident with the presence of CL clouds whose borders seem to be the major factors responsible for reflecting a portion of the incoming rays, producing interference fringes at the observer's site. Absorption effects were also sometimes observed, and small effects in polarization were qualitatively characterized. Such events could be easily confused with the "fluctuation" type solar bursts, and the present results emphasize the need of improved criteria for the analysis of very small solar events, that do exist at microwave wavelengths. Further work was developed on steady troposphere attenuation at larger zenithal angles, and on ground contribution at solar onset times. © 1969.
Unpolarized impulsive solar bursts observed at 7 GHz
Kaufmann P. (1969)
The occurrence of very faintly polarized, or unpolarized impulsive bursts observed at 7 GHz is discussed. It appears that some of them show a peculiar spectral peak somewhere between 5 GHz and 7 GHz. Possible interpretations are suggested, emphasizing the need to associate to the burst the state of polarization of the S-component in which it occurred. © 1969 D. Reidel Publishing Company.
Some center-limb statistical trends of impulsive solar bursts at 7 GHz
Matsuura O.T.; Nave M.F.F. (1970)
The more impulsive 7 GHz bursts seem to prefer the solar limb regions, while the degree of polarization decreases with increasing impulsivity. © 1970 D. Reidel Publishing Company.
Polarization changes with time during solar microwave impulsive bursts
Kaufmann P.; Matsuura O.T.; Dos Santos P.M. (1970)
The evolution with time of circular polarization π(t) from solar bursts at 7 GHz presents, in the majority of cases, a polarization degree peak before the maximum flux time. The subsequent evolution of π(t) is continuous and usually increasing. The changes could be caused by superimposed polarization effects, due to the fast emissive electrons (dominant in the first phase), and to the propagation effects caused by the coronal condensation where the event occurred (dominant in the second phase). In an approximate approach, π(t) is connected to the movement of the source in the second phase, being qualitatively sound, but limited to the lack of knowledge on acceleration processes and on magnetic field topology in the active region where the flares take place. © 1970 D. Reidel Publishing Company.
The correlation between sudden phase anomalies and solar microwave radio bursts
Kaufmann P.; Mendes A. (1970)
More than two hundred SIDs were observed as VLF phase anomalies (SPA) at times when measurements were being made of solar radio noise at 7 GHz. 99 per cent of the SPAs were correlated with microwave solar events. The SPAs are usually smooth and do not show structure corresponding to that in many of the associated radio bursts. A linear correlation coefficient of 0.6 was found between the mean flux of solar bursts and the 'importance' of the SPAs as measured in terms of the phase change divided by the length of the transmission path. The SPAs show only very small dependence on the solar zenithal angle. © 1970.
Changes in coronal condensations emission after solar bursts at microwaves
Kaufmann P.; Scalise Jr. E.; Santos P.M.D. (1970)
The amount of circular polarization of the total solar radio emission at 7 GHz present permanent changes after the occurrence of certain radio bursts associated with larger flares. For isolated S-components, associated with such flares the changes of the polarization degree ΔΠsranges between 0.004 to 0.1, and appears to be a function of the flare importance. A semi-qualitative interpretation associates ΔΠswith magnetic field reductions at the S-component, agreeing fairly well with a flare mechanism based on collisionless dissipation of magnetic energy, corresponding to energies in the range of 1030 to 1032 ergs, assuming an average model for the coronal condensations. © 1970 D. Reidel Publishing Company.
Ozone screening heights deduced from sunrise effects at very low frequencies
Schaal R.E.; Ananthakrishnan S. (1970)
During the period August-September of any year, the entire NAA-São Paulo path is illuminated almost simultaneously at sunrise, resulting in a sharp drop in the phase of the received signal. Using sunrise phase transitions and an assumed night-time reflection height of 90 km, an ozone screening height of 58 km was deduced. A calculation of the wavelength of the photo-detaching radiation, using this value of the screening height yielded a value of λ = 3015 A ̊. © 1970.
Observations with a 7 GHz polarimeter
Matsuura O.T.; Scalise Jr. E.; Dos Santos P.M.; Kaufmann P. (1970)
Night-time anomalies in very low frequency propagation produced by a galactic X-ray source at centaurus
Kaufmann P.; De Barros M.H.P.; Vianna E.N. (1970)
NIGHT-TIME propagation of very low frequency (VLF) waves in the terrestrial ionosphere shows considerable variability, both in phase and in amplitude, in comparison with the relatively stable daytime conditions. The night-time anomalies are not yet well understood, a number of them being associated with the presence of energetic particles originating from solar proton events 1. The explanation of others remains obscure. © 1970 Nature Publishing Group.

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