Characteristics Of Whistlers Research Articles

An assessment of whistlers generated from tree-like gigantic jets

The characteristics of whistlers generated from an observed gigantic jet (GJ) are assessed and possible locations to detect these waves are deduced. Modeling is based on disturbances in the electric field, as measured by NCKU ELF/VLF station, associated with a tree-like GJ event over typhoon Lionrock. The power spectrum of GJ differs from that of common cloud-to-ground lightning; therefore, this study also investigates differences between GJ-generated signals and common lightning-generated whistlers. Detectability is evaluated by considering the absorption of amplitudes resulted from collisional damping associated with the propagation of generated waves. Our results show that in the ionosphere the waves are subject to greater attenuation as the frequency increases; however, a reversal occurs at lower frequencies of a few hundred Hz. The calculated waveforms show that the whistlers generated by the tree-like GJs are preceded by small fluctuations at high frequencies generated by the initiating lightning. Overall, the amplitudes increase with the passage of time; however, they are more randomly-distributed over time for whistlers generated from common lightning. The amplitudes decrease again when lower-frequency components below a few hundred Hz arrive. The amplitudes drop to the order of 1 mV/m as the waves propagate in the ionosphere, which puts them within a range detectable by the instruments on most satellites. Based on the locations of tree-like GJ events observed by ISUAL (Imager of Sprites and Upper Atmospheric Lightning), regions of the western and southeastern Pacific Ocean, as well as northern Africa region are the most likely locations to detect these whistlers.

Study of Duct Characteristics Deduced from Low Latitude Ground Observations of Day-Time Whistler at Jammu

Propagation characteristics of low latitude whistler duct characteristics have been investigated based on day-time measurements at Jammu. The morphogical characteristics of low latitude whistlers are discussed and compared with characteristics of middle and high latitude whistlers. The Max. electron density (Nm) at the height of the ionosphere obtained from whistler dispersion comes out to be higher than that of the background which is in accordance with the characteristics of whistler duct. The equivalent width is found to be close to the satellite observations and the characteristics of whistler duct in low latitude ionosphere are similar to those in middle and high latitude ionosphere. The width of ducts estimated from the diffuseness of the whistler track observed during magnetic storm is found to lie in the range of 50 - 200 Km.

Some new possibilities for diagnosing the magnetosphere based on whistler characteristics

Different types of natural electromagnetic emissions are generated in the Earth’s electronic radiation belts. The conditions for generation of these emissions depend on the plasma parameters, geometry of the system, wave transfer processes, and regularities of particle accumulation and precipitation from the magnetic trap. Effective interaction between waves and particles can often be described by the plasma magnetospheric maser theory. A plasma magnetospheric maser actually operates in several main regimes. These regimes are responsible for the generation of VLF emissions with different frequency spectrum dynamics. The regimes replace each other as a result of variations in the local and global characteristics of the magnetosphere. For example, the cyclotron generation dynamics largely depends on the the source power of energetic particles. Several new methods for diagnosing the near-Earth plasma can be implemented if the plasma magnetospheric maser theory is known.

Characteristics of whistler ducts recorded at Gulmarg

Morphological features of whistlers recorded at low latitude ground station Gulmarg (geomag. lat., 24‡ 26′N) are studied to deduce information about ducts. The morphological characteristics of low latitude whistlers are discussed and compared with the characteristics of middle and high latitude whistlers. The maximum electron density (N m ) at the height of the ionosphere obtained from whistler dispersion comes out to be higher than that of the background, which is in accordance with the characteristics of the whistler duct. The equivalent width of the whistler duct at the maximum height of its path is found to be close to the value obtained from satellite observations. The characteristics of whistler ducts in low latitude ionosphere are similar to those in middle and high latitude ionosphere. The width of ducts estimated from the diffuseness of the whistler track observed during magnetic storm is found to lie in the range of 50–200 km.

Propagation characteristics of whistler waves in the Jovian ionosphere and magnetosphere

The purpose of this paper is to carry out extensive reexamination of the propagation characteristics of unducted whistlers in the Jovian magnetosphere. In addition to the previous work on the dispersion of whistlers, our emphasis is placed on the detailed study of their amplitude variations in order to investigate the plasma structure of the magnetosphere and characteristics of causative lightning discharges. The two‐dimensional ray‐tracing computations are used as before to investigate magnetospheric whistler propagation paths, but with the first attempt of estimating the whole attenuation factors (polarization effect, focusing/defocusing and interactive damping (Landau and cyclotron)). The total attenuation due to three effects is estimated, which is compared with the amplitude of whistlers observed by the Voyager spacecraft. The following conclusions are reached. (1) Some bias in magnetospheric plasma density is required to explain the high‐frequency cutoff of whistlers, (2) the magnetospheric temperature is about 20 eV for the interpretation of low‐frequency cutoff of whistlers, and (3) estimated total radiated power per flash is about 4.5×106 W(0∼20 kHz) on the assumption of unducted propagation and nearly the same even in the case of ducted propagation.

On the possible influence of seismic activity on the propagation of magnetospheric whistlers at low latitudes

The purpose of this paper is to examine the possible seismic influence on the propagation of magnetospheric whistlers at low latitudes on the basis of long-term data observed at Sugadaira (geomagnetic latitude 25°N) during 1970–1978 and at Sakushima (24°) during 1980–1982. It is found from statistical analysis of the Sugadaira data that anomalous whistlers whose dispersion value is greater than twice the typical value, exhibit a substantial increase in occurrence during seismic activity in the geographic longitude sector of 100°E–160°E, and this association becomes more enhanced when we take the occurrence of any whistlers (short, long and/or anomalous) during the summer time (June–August). Finally, with increasing anomaly (that is, anomalous dispersions and summertime), we have found an exceedingly high statistical correlation between the summertime anomalous whistlers at Sakushima and the seismic activity satisfying the above condition. We have studied whistler characteristics for all earthquakes. These studies have indicated that a considerable number of cases of earthquakes are of a type such that several earthquakes occur successively; and, correspondingly, we observed an enhanced occurrence of anomalous whistlers during such prolonged seismic activities. Several isolated and intense earthquakes are characterized by the appearance of anomalous whistlers prior to and after the earthquake. In conclusion, we claim that whistlers with anomalous dispersions are likely to be closely correlated with earthquakes occurring in the relevant longitude range, but we cannot make any definite statement on the use of low-latitude whistlers as precursors of earthquakes and further detailed studies are obviously required on this subject. Some possible mechanisms of the earthquake-associated effect causing whistler propagation are discussed.

Comment on “Is Venus alive?”

The June 3, 1986 issue of Eos contains a Forum by Harry Taylor (National Aeronautics and Space Administration Goddard Space Flight Laboratory, Greenbelt, Md.) with a report on his latest speculations regarding Venus lightning and on his interpretation of certain measurements from the plasma wave investigation on the Pioneer Venus Orbiter. The same views have also been announced as recent discoveries by Taylor and an associate in interviews in Science News (April 5, 1986) and in New Scientist (May 15, 1986). In fact, many of the statements and interpretations in Taylor's letter (and in the interviews) are demonstrably wrong, and I want to correct the record for Eos readers.Taylor's discussion refers to a number of Pioneer Venus publications that appeared in various journals between 1979 and 1986. In these papers, my colleagues and I identified as whistler mode plasma waves certain low‐frequency impulses detected with an electric antenna at low altitudes during the Venus night. These Venus noise bursts have all the characteristics of whistlers from lightning, and this connection was discussed in all of the published papers.

Intensity and polarization characteristics of whistlers deduced from multi‐station observations

Whistlers recorded at four stations along the geomagnetic meridian near Roberval, Canada, on July 23, 1979, have been analyzed. They showed a spatial attenuation rate as high as ∼6 dB/100 km, which is appreciably larger than previous theoretical predictions. The wave polarization of these whistlers was also analyzed; the wave polarization was a maximum (right handed) at the station where wave intensity was a maximum. The wave polarization was also right handed at a station distant from the wave exit region. The locations of the wave exit region inferred from the intensity maximum were compared with the L values of the whistler paths derived from the dispersion analysis. We obtained a consistent relation between them when uncertainties in the dipole field model are taken into account.

Experimental study of the relationship between the propagation distance and the polarization characteristics of whistlers

AbstractWideband (0‐8 kHz) measurements were performed for VLF whistlers at Moshiri (geomag. lat. 35°N) in Hokkaido in January, 1983 to investigate the relationship between polarization characteristics of whistlers and their propagation distance after the ionospheric transmission in the Earth‐ionosphere waveguide. the phase differences of the two signals of whistlers detected by orthogonal (E‐W and N‐S) loop antennas have been measured and the following results found: (1) the polarization of whistlers which penetrate the ionosphere close to the observing station is righthanded over a wide frequency range; and (2) some whistlers are found to have propagated over a distance of ∼1500 km. These whistlers exhibit a right‐handed polarization at some frequencies and a left‐handed polarization at other frequencies. However, the averaging of the observed polarizations over a wide frequency results in a nearly linear polarization; this agrees qualitatively with previous theoretical calculations by Crary.

Whistler mode plasma waves observed on electron Echo 2

Observations of whistler-mode waves associated with beams of electrons injected into the ionosphere are reported. The measurements are from the plasma-wave experiments carried on the Electron Echo 2 sounding rocket launched on September 24, 1972. Over 2000 electron injections were made with durations of 8 ms and 64 ms and pitch angles from 0 to 180 deg. The electric field receivers carried on the ejected nose cone observed strong whistler waves in the range from less than 100 kHz up to the electron cyclotron frequency of 1400 kHz. The whistler characteristics fall into four distinct types depending on pitch angle and gun energy. Both frequency and amplitude showed strong dependence on time from the start of the pulse and pitch angle. Cases of enhancement at the leading edge of a gun pulse, growth during a pulse, and echoes after the end of a pulse were all observed.

Storm-time characteristics of low-latitude whistlers

Using the results from special observations, the storm-time effects on whistler characteristics at low latitudes were examined and found to agree with previous statistical studies. A short discussion is made on the link between spread-F irregularities and magnetospheric whistler ducts. The enhanced whistler activity is explained as a consequence of the stable whistler duct region during spread-F conditions.

Whistler modulational instability

Derivation of the modulational instability characteristics of whistlers in cold and hot plasmas. The cold-plasma analysis considers both ion motion and relativistic effects; the unstable band, with a growth rate proportional to (B/B sub zero)squared, is contiguous to Omega sub e/4 and, depending on the plasma density, lies above or below that frequency (Omega sub e is the electron cyclotron frequency of the static magnetic field; B and B sub zero are the whistler and static magnetic fields). In hot plasmas, stability occurs between Omega sub e/4 and Omega prime (less than Omega sub e), with Omega prime depending mainly on the mean energy and anisotropy of the energetic electron population; the complementary unstable band has a growth rate proportional to (B/B sub zero) to the 1/2 power. The relevance of the instability to whistlers in the magnetosphere is discussed.

Commission 8: Progress in Radio Noise of Terrestrial Origin

Since Commission 8 was only created on a provisional basis at the Munich General Assembly of URSI in 1966, and since also the U.S. National Committee does not maintain an organization for Commission 8 within the U.S.A., it seems appropriate for informative reasons to start this survey by listing the fields of scientific activity covered by the Commission. These are:1. Atmospherics, their source characteristics and location.2. Propagational influences on radio noise (with Commission 3).3. ELF noise from lightning (with Commission 4).4. Types of lightning flashes generating whistlers. Propagational effects, other than those in the whistler mode, influencing whistler characteristics (with Commission 4).5. Statistical properties of noise, noise interference with radio communications.6. Man‐made noise.This review will discuss work falling within the above fields of study carried out under U.S. auspices and described in 1966, 1967, and 1968. The survey will be confined to papers appearing in recognized journals and other sources of ready availability to which my attention has been drawn; reports of limited circulation and private information will not be considered.

A Study of Whistling Atmospherics. V. Dispersion

The dispersion characteristics of whistlers recorded at Brisbane, Adelaide, and Hobart, mainly during the lGY, are examined. The dispersion recorded at each station shows a wide range of values. Diurnal (10-15 st) and annual variations (20-25 si) are observed and correlations between dispersion and F. critical frequency and dispersion and magnetic disturbance are discussed. No association between dispersion and sunspot number was detected. The position of the "ionospheric sources" of the whistlers is of prime importance as dispersion varies with geomagnetic latitude. Much of the variation in dispersion observed by individual stations is believed to be due to their being able to "see" ionospheric sources up to 100 away.

Propagation characteristics of whistlers trapped in field-aligned columns of enhanced ionization

Evidence from whistlers shows that the outer ionosphere contains columns or ducts of enhanced ionization. The theory of propagation in these ducts shows an upper cutoff frequency at one-half the gyrofrequency. The average propagation velocity for whistlers trapped in the ducts can be approximated by assuming that the energy follows along the ionization maximum with wave normals aligned with the magnetic field.

Extension of nose whistler analysis

Recent work by Smith [1960] on the theory of nose whistlers suggests several methods of obtaining nose frequency and nose time delay information from ordinary whistlers: i.e., whistlers that do not exhibit a ‘nose’ on the spectrographic records. Since the nose frequency and time delay provide information on whistler path location and on electron density, and since ordinary whistlers occur far more frequently than do nose whistlers, such methods are potentially of great value as tools of research. The purpose of this letter is to outline one of several possible methods to obtain the nose frequency and the time delay to the nose when the nose is not directly observable. The method is based on the observation that the dispersion characteristics of whistlers are nearly independent of frequency and ionization distribution when normalized with respect to the nose frequency and the low frequency dispersion.

Solar activity and whistler dispersion

Since early 1956, the very-low-frequency phenomena known as whistlers have been observed regularly and simultaneously at several locations in North America and in New Zealand. Various whistler characteristics are tabulated and exchanged within the above network. One of the characteristics reported is the time-delay between the occurrence of the atmospheric “bonk” (Morgan and Dinger, 1956) from a nearby lightning flash and the arrival of the associated whistler which has made the double-transit journey through the outer ionosphere, being guided by the earth's magnetic field to the opposite hemisphere, and back again (Storey, 1953; Morgan and Allcock, 1956). Since a whistler consists of a falling tone, lasting for perhaps a second, the time-delays are measured from the bonk to the appearance of the highest audible component of the whistler, normally in the vicinity of 5 kc/sec.