Hercules A

Hercules A
Radio-Optical View of the Galaxy Hercules A - Many thanks to: NASA, ESA, S. Baum and C. O'Dea (RIT), R. Perley and W. Cotton (NRAO/AUI/NSF), and the Hubble Heritage Team (STScI/AURA)

Tuesday, January 29, 2013

About interference fringes and modulation lanes in Io-B spectra

I am thinking and reading about interesting features in Jovian decametric spectra, sometimes seen in the Paris Observatory Nancay Station Archive. The following references may be of interest:


Imai Riihimaa Reyes Carr 2002:
"Measurement of Jupiter's decametric radio source parameters by the modulation lane method"

5 citations to this paper at:

"In previously published works we have developed a model to explain the production of modulation lanes in the dynamic spectra of Jupiter's decametric emission. In this paper we use the model with newly available data to test the model and to measure emission source and beam parameters. Some of the data were wideband, providing for the first time the opportunity to verify the accuracy of the model in fitting the considerable lane curvature exhibited in such a case. Relatively precise measurements of the cone half-angle of hollow-cone beam and other source and beam parameters of Io-B radiation were also made possible by the wideband data. Narrowband data enabled us to measure for the first time the beam cone half-angle for non-Io-A radiation. The measured cone half-angles for the two sources were both within ~2° or 3° of 60°. This measurement is consistent with the long-held idea that the sources Io-B, Io-A, and non-Io-A are due to the same rotating hollow-cone beam and that the only difference between the latter two is the intensification of Io-A radiation by the connection with Io in comparison with that of non-Io-A. We also measured the cone half-angle for S bursts and found it to be less than that of the much more common L bursts."

I display above a copy of Fig. 2 in this paper, and an image quoting a portion of Section 2, about interference fringes.


Imai Garcia Reyes Imai Thieman 2011:
"A Model of Jupiter's Decametric Radio Emissions as a Searchlight Beam"

"It has long been recognized that there is a marked long-term periodic variation in Jupiter's integrated radio occurrence probability. The period of the variation is on the order of a decade. Carr et al. [1970] showed that such variations are closely correlated with Jovicentric declination of the Earth (DE). The range of the smoothed variation of DE is from approximately +3.3 to -3.3 degrees. This DE effect was extensively studied and confirmed by Garcia [1996]. It shows that the occurrence probability of the non-Io-A source is clearly controlled by DE at 18, 20, and 22 MHz during the 1957-1994 apparitions. We propose a new model to explain the DE effect. This new model shows that the beam structure of Jupiter radio emissions, which has been thought of like a hollow-cone, has a narrow beam like a searchlight, which can be explained by assuming that the three dimensional shape of the radio source expands along the line of the magnetic field. If we consider the sizes of the radio coherent region are 1000 m along Jupiter's magnetic field line and 200 m along the latitudinal direction, the equivalent beam pattern is 1 degree wide along Jupiter's magnetic field line and 5 degrees in latitude. As the searchlight beam is fixed with Jupiter's magnetic field, the pure geometrical effect of DE can be explained by this searchlight beam model."