Relations between turbulent regions of interplanetary magnetic field and Jovian decametric radio wave emissions from the main source

Jovian decametric radio wave emissions that were observed at Goddard Space Flight Center, U.S.A. for a period from 1 October to 31 December, 1974 and data obtained at Mt Zao observatory, Tohoku University, Japan, for a period from 14 July to 6 December, 1975 have been used to investigate the relationship of the occurrence of the Jovian decametric radio waves (JDW), from the main source, to the geomagnetic disturbance index, ΣK_p. The dynamic cross-correlation between JDW and ΣK_p indicates an enhanced correlation for certain values of delay time. The delay time is consistent with predicted values based on a model of rotating turbulent regions in interplanetary space associated with two sector boundaries of the interplanetary magnetic field, i.e. the rotating sector boundaries of the interplanetary magnetic field first encounter the Earth's magnetosphere producing the geomagnetic field disturbances, and after a certain period, they encounter the Jovian magnetosphere. There are also cases where the order of the encounter is opposite, i.e. the sector boundaries encounter first Jovian magnetosphere and encounter the Earth's magnetosphere after a certain period.     

Harmonic components of decametric solar radio bursts

Type-IIIb, IIId, and III solar decametric radio bursts, being distinguished by the typical negative drift rate of their dynamic spectra, are compared. Observational data were obtained with a UTR-2 antenna during the period 1973–1982. During the analysis of the bursts of all these spectral varieties, the frequency drift time (drift delay) was measured in the ranges 25 to 12.5 MHz, 25 to 20 MHz, and 12.5 to 10 MHz. Durations of type-III bursts were determined at the harmonically-related frequencies of 25 and 12.5 MHz; radio source locations were also used.It is shown that these decametric bursts are distinctly divided into two groups: (1)type-IIIb chains of simple stria bursts and also normal type-III storm bursts observed at central regions constitute a group of events with a fast drifting spectrum; (2) type-III bursts from type-IIIb-III pairs and the limb variant of normal III bursts, as well as peculiar type-IIId chains of diffuse striae and related chains with an echo component, constitute a second group of events with comparatively slow drift rates.The first group of the phenomena is associated with the fundamental F frequency and the second one, with the harmonic H of the coronal plasma frequency. The results of the present investigation agree well with earlier conclusions on the harmonic origin of decametric chains and type-III bursts. Measurements of drift delays in narrow frequency ranges, an octave apart, as well as type-III burst durations at harmonically-related frequencies confirm the existence of both F and H components in the solar radiation. The essential result of 10 years of decametric observations is that the frequency drift rates and durations are rather stable parameters for the various type-III bursts and stria-burst chains. The stability characterizes some unspecified conditions of burst generation in the middle corona.     

Fine structure of decametric type II radio bursts

We have performed a comparative analysis of the fine structure of two decametric type II bursts observed on July 17 and August 16, 2002, with the 1024-channel spectrograph of the UTR-2 radio telescope in the frequency range 18.5–29.5 MHz and with the IZMIRAN spectrograph in the frequency range 25–270 MHz. The August 16 burst was weak, ～2–5 s.f.u., but exhibited an unusual fine structure in the form of broadband fibers (Δf _e > 250–500 kHz) that drifted at a rate characteristic of type II bursts and consisted of regular narrow-band fibers (Δf _e > 50–90 kHz at 24 MHz) resembling a rope of fibers. The July 17 burst was three orders of magnitude more intense (up to 4500 s.f.u. at 20 MHz) and included a similar fiber structure. The narrow fibers were irregular and shorter in duration. They differed from an ordinary rope of fibers by the absence of absorption from the low-frequency edge and by slow frequency drift (slower than that of a type II burst). Both type II bursts were also observed in interplanetary space in the WIND/WAVES RAD2 spectra, but without any direct continuation. Analysis of the corresponding coronal mass ejections (CMEs) based on SOHO/LASCO C2 data has shown that the radio source of the type II burst detected on August 16 with UTR-2 was located between the narrow CME and the shock front trailing behind that was catching up with the CME. The July 17 type II fiber burst also occurred at the time when the shock front was catching up with the CME. Under such conditions, it would be natural to assume that the emission from large fibers is related to the passage of the shock front through narrow inhomogeneities in the CME tail. Resonant transition radiation may be the main radio emission mechanism. Both events are characterized by the possible generation of whistlers between the leading CME edge and the shock front. The whistlers excited at shock fronts manifest themselves only against the background of enhanced emission from large fibers (similar to the continuum modulation in type IV bursts). The reduction in whistler group velocity inside inhomogeneities to 760 km s^?1 may be responsible for the unusually low drift rate of the narrow fibers. The magnetic field inside inhomogeneities determined from fiber parameters at 24 MHz is ～0.9 G, while the density should be increased by at least a factor of 2.     

Ionospheric radio wave absorption in the auroral zone and the interplanetary magnetic field sector structure

We have considered the character of radio wave absorption variations in the auroral zone, depending on the relative number of sunspots over a 11-yr cycle and on a interplanetary magnetic field (IMF) sector polarity, by using observations carried out at Murmansk, by the Al method, at noon throughout 1959 to 1967. It was shown that the abnormal absorption occurrence frequencies as well as the background absorption values are generally bigger in the case of the IMF directed away from the Sun. The difference, caused by IMF sector polarity, of both values is subject to regular quasi-two-year variations.     

Short-lived Jovian decametric events observed with an acousto-optical radio spectrograph

S-bursts and other short-lived events in Jupiter's decametric radio spectra are studied with an acousto-optical radio spectrograph (AORS) and a charge-coupled device (CCD) readout. The lifetimes of regular S-bursts are of the order of tens of milliseconds. Lifetimes of S-bursts that occur in quasi-periodic trains are mostly below 20 ms. Short-lived bursts that do not seem to drift in frequency are also observed. Such bursts (nondrift bursts) may occur in S-trains and at the vertex of tilted-V patterns. The vertex bursts have lifetimes comparable to those of the S-train bursts. Preliminary measurements of the risetimes of bursts indicate that a significant proportion of the vertex bursts exhibit risetimes of less than 2 ms.     

Auroral boundary variations and the interplanetary magnetic field

This paper describes a DMSP data set of 150 auroral images during magnetically quiet times which have been analyzed in corrected geomagnetic local time and latitudinal coordinates and fit to offset circles. The fit parameters R (circle radius) and (X, Y) (center location) have been compared to the hourly interplanetary magnetic field (IMF) prior to the time of the satellite scan of the aurora. The results for variation of R with B_z, agree with previous works and generally show about a 1° increase of R with increase of southward B_z by 1 nT. The location of the circle center also has a clear statistical shift in the Southern Hemisphere with IMF B_y such that the southern polar cap moves towards dusk (dawn) with B_y > (B_y < 0).     

Estimate of an environmental magnetic field of fast radio bursts

Fast radio bursts(FRBs) are a type of newly-discovered transient astronomical phenomenon.They have short durations, high dispersion measures and a high event rate. However, due to unknown distances and undetected electromagnetic counterparts at other wavebands, it is difficult to further investigate FRBs. Here we propose a method to study their environmental magnetic field using an indirect method.Starting with dispersion measures and rotation measures(RMs), we try to obtain the parallel magnetic field component ■ which is the average value along the line of sight in the host galaxy. Because both RMs and redshifts are now unavailable, we demonstrate the dependence of ■ on these two separate quantities.This result, if the RM and redshift of an FRB are measured, would be expected to provide a clue towards understanding an environmental magnetic field of an FRB.     

Polarization of Jovian decametric radiation

Decametric radiation from Jupiter impinging on the Earth's ionosphere is not in a magnetoionic base mode. If one assumes, as most researchers in the field do, that the radiation is generated at Jupiter in the extraordinary base mode, one must conclude that coupling has occurred somewhere near Jupiter. It is shown here that coupling does not occur in Jupiter's ionosphere but further out in the Jovian magnetosphere. The lack of observed Faraday rotation within Jupiter's ionosphere and magnetosphere cannot be used to rule ou ta hot, dense ionosphere and magnetosphere as was suggested previously. It is also shown that the radiation emerging from Jupiter should be elliptically polarized with an axial ratio varying between 0.4 and 0.9. The orientation of the polarization ellipse varies as a function of emitting longitude.     

Locations of Jovian decametric radiation sources

The location of the Jovian decametric radiation main source is determined to be the south magnetic pole while the location of the early source is found to be near the north magnetic pole, with an equal contribution from a region near the south magnetic pole. The results are based on calculations of the region observable from the Earth (ROE) for Jovian decametric radio waves that are emitted in the direction ± 10° centered on the direction perpendicular to the Jovian magnetic field and based on a Pioneer 11 model of the field at the level of the topside region of the Jovian ionosphere. Ground-based observations of the occurrence frequency of the decametric radiation as a function of Jovian longitude, which indicate a remarkable asymmetry between the early and main sources, agree with the calculated ROE area that varies as a function of CML observed from the Earth. The observations support a recent theory for the origin of the decametric radiation which is based on a wave-mode conversion from plasma waves into electromagnetic waves.     

Radiation characteristics of quasi-periodic radio bursts in the Jovian high-latitude region

Ulysses had a “distant encounter” with Jupiter in February 2004. The spacecraft passed from north to south, and it observed Jovian radio waves from high to low latitudes (from +80° to +10°) for few months during its encounter. In this study, we present a statistical investigation of the occurrence characteristics of Jovian quasi-periodic bursts, using spectral data from the unified radio and plasma wave experiment (URAP) onboard Ulysses. The latitudinal distribution of quasi-periodic bursts is derived for the first time. The analysis suggested that the bursts can be roughly categorized into two types: one having periods shorter than 30 min and one with periods longer than 30 min, which is consistent with the results of the previous analysis of data from Ulysses’ first Jovian flyby [MacDowall, R.J., Kaiser, M.L., Desch, M.D., Farrell, W.M., Hess, R.A., Stone, R.G., 1993. Quasi-periodic Jovian radio bursts: observations from the Ulysses radio and plasma wave. Experiment. Planet. Space Sci. 41, 1059-1072]. It is also suggested that the groups of quasi-periodic bursts showed a dependence on the Jovian longitude of the sub-solar point, which means that these burst groups are triggered during a particular rotational phase of the planet. Maps of the occurrence probability of these quasi-periodic bursts also showed a unique CML/MLAT dependence. We performed a 3D ray tracing analysis of the quasi-periodic burst emission to learn more about the source distribution. The results suggest that the longitudinal distribution of the occurrence probability depends on the rotational phase. The source region of quasi-periodic bursts seems to be located at an altitude between 0.4 and 1.4 Rj above the polar cap region (L>30).     

Influence of a solar active region on the interplanetary magnetic field

The interplanetary magnetic field has been mapped between 0.4 and 1.2 AU in the ecliptic plane, extrapolating from satellite measurements at 1 AU. The structure within sectors and the evolution of sectors are discussed. The development of a solar active region appears to produce magnetic loops in the interplanetary medium that result in the formation of a new sector.     

A stability analysis of the spiral sector transition region in the interplanetary magnetic field

We use a four-layer model in a stability analysis of the ME type spiral sector transition in the interplanetary magnetic field. Our results show that (1) three kinds of large-scale waves may be excited in the region and for all three, there exists a low-frequency cut-off. (2) In all three, the rate of growth of instability increases with k; in Model A only, the rate of growth has a maximum and a minimum. (3) As the angle between k and the solar wind velocity vector $\text{V}{}_{\mathrm{q}}$ increases, the cut-off frequency increases, and the excitation of waves gets more and more difficult, until it becomes impossible when k is perpendicular to $\text{V}{}_{\mathrm{q}}$. (4) when the angle between k and $\text{V}{}_{\mathrm{q}}$ is 75°, waves with a wavelength of 5 × 10⁴ km and a phase velocity of 340 km/s may be excited; this agrees with the observations by Voyager 1 at the Earth's magnetopause. Hence we deduce that waves in the spiral sector transition region may be a source that triggers off the Kelvin-Helmholtz instability of the magnetopause.     

A search for compact decametric radio sources in supernova remnants using the interplanetary scintillation technique

Interplanetary scintillation observations of eleven supernova remnants and the pulsar J1939+2134, around which the existence of a supernova remnant remains obscure, were carried out with the largest in the world decameter radio telescope UTR-2 at 20, 25 and 30 MHz to determine if any of them contain compact radio sources with the angular size θ<5″. The sample included the young Galactic remnants and the other powerful SNRs. The interplanetary scintillations of the compact radio source in the Crab Nebula associated with the well-known pulsar J0534+2200 and the pulsar J1939+2134 were observed. Apart from the Crab Nebula, we have not detected a compact radio source in supernova remnants with the angular size θ<5″ and the flux density more than 10 Jy. The observations do not confirm the existence of the low frequency compact source in Cassiopeia A that has remained controversial.     

The dependence of Jupiter's decametric emissions on the Jovian magnetic latitude of Io

The present analysis confirms the contention that the majority of Jupiter's decametric radio emissions occur when Io is above the northern magnetic hemisphere of Jupiter. However, a substantial portion of the non-Io-related component of source A was found to occur when Io was above southern magnetic latitudes of Jupiter.     

A theory of Jovian shadow bursts

The shadow events in the dynamic spectra of Jovian decametric emission are explained as the result of interaction between electron bunches responsible for S and L emissions. The relevant dispersion relation is derived for the fast extraordinary mode in the cold magnetospheric plasma in the presence of S and L electron bunches. The growth rate of the synchrotron maser instability is studied in the presence and absence of S-electrons. It is shown that the synchrotron maser instability responsible for L-emission can be temporarily quenched by the invasion of S-electrons, thereby stopping the L-emission. The theory accounts for various observed features of the shadow events.     

Propagation of interplanetary shock waves by observations of type II solar radio bursts on IMP-6

A new interpretation of the low frequency type II solar radio bursts of 30 June 1971, and 7–8 August 1972 observed with IMP-6 satellite (Malitson et al., 1973a,b) is suggested. The analysis is carried out for two models of the electron density distribution in the interplanetary medium taking into account that N ~ 3.5 cm^?3 at a distance of 1 a.u. It is assumed that the frequency of the radio emission corresponds to the average electron density behind the shock front which exceeds the undisturbed electron density by the factor of 3. The radio data indicate essential deceleration of the shock waves during propagation from the Sun up to 1 a.u. The characteristics of the shock waves obtained from the type II bursts agree with the results of the in situ observations.     

Unified theory of the interplanetary magnetic field

A simple model is used to present a unified picture of the polarity pattern of the interplanetary magnetic field observed during the solar cycle. Emphasis in this paper is on the field near solar maximum. The heliographic latitude dependence of the dominant polarity of the interplanetary magnetic field is explained in terms of weak poloidal (dipolar) field sources in the sun's photosphere. Unlike the Babcock theory, the author hypothesizes that the dipolar field exists at equatorial latitudes (0–20°), too, (as well as in polar regions) and that the major source of the interplanetary magnetic field observed near the ecliptic plane is the dipolar field from equatorial latitudes. The polarity of the interplanetary field data taken in 1968 and in the first half of 1969 near solar maximum may possibly be explained in terms of a depression of the dipolar field boundary in space. The effect on the solar wind of the greater activity in the northern hemisphere of the sun that existed in 1968 and in the first half of 1969 is believed responsible for this hypothesized depression, especially near solar maximum, of the plane separating the + and - dipolar polarity below the solar equatorial plane in space. Predictions are made concerning the interplanetary field to be observed near the ecliptic plane in each portion of the next solar cycle.     

Comparison of the mean photospheric magnetic field and the interplanetary magnetic field

The mean photospheric magnetic field of the sun seen as a star has been compared with the interplanetary magnetic field observed with spacecraft near the earth. Each change in polarity of the mean solar field is followed about 4 1/2 days later by a change in polarity of the interplanetary field (sector boundary). The scaling of the field magnitude from sun to near earth is within a factor of two of the theoretical value, indicating that large areas on the sun have the same predominant polarity as that of the interplanetary sector pattern. An independent determination of the zero level of the solar magnetograph has yielded a value of 0.1±0.05 G. An effect attributed to a delay of approximately one solar rotation between the appearance of a new photospheric magnetic feature and the resulting change in the interplanetary field is observed.     

Power spectra of the interplanetary magnetic field

Power spectra based on Pioneer 6 interplanetary magnetic field data in early 1966 exhibit a frequency dependence of f ^–2 in the range 2.8 × 10^–4 to 1.6 × 10^–2 cps for periods of both quiet and disturbed field conditions. Both the shape and power levels of these spectra are found to be due to the presence of directional discontinuities in the microstructure (< 0.01 AU) of the interplanetary magnetic field. Power spectra at lower frequencies, in the range of 2.3 × 10^–6 to 1.4 × 10^–4 cps, reflect the field macrostructure (> 0.1 AU) and exhibit a frequency dependence roughly between f ^–1 and f ^–3/2. The results are related to theories of galactic cosmic-ray modulation and are found to be consistent with recent observations of the modulation.     

Observations of Jupiter's decametric radio emissions

Observations of the mean power of Jupiter's decametric radio emissions at six frequencies, 4.7, 15.7, 18.7, 21.5, 24.5 and 28.0 Mc/s, have been used to prepare histograms of relative power and probability of occurrence at each frequency.The variation of the mean flux density of the emissions was determined as a function of frequency, and was found to increase monotonically with decreasing frequency down to 4.7 Mc/s. The spectrum consists of two parts, one having a spectral index of −2.5 between 4.7 Mc/s and 20 Mc/s, and the other a spectral index of −13.7 between 24 and 30 Mc/s. The location of Jupiter's magnetic poles is discussed. The 4.7 Mc/s data is consistent with Jupiter's north magnetic pole being located near 175° system III longitude, while the higher frequency results indicate slightly lower longitudes. The data at 4.7, 15.7, 24.5 and 28.0 Mc/s was examined for influence of the Jovian Satellite Io and contour diagrams of the emission were plotted.