Deuteron whistler and trans-equatorial propagation of the ion cyclotron whistler

New ion cyclotron whistlers which have the asymptotic frequency of one half the local proton gyrofrequency, $\text{G}{}_{\mathrm{p}}\text{2}$, and the minimum (or equatorial) proton gyrofrequency, G_pm, along the geomagnetic field line passing through the satellite have been found in the low-latitude topside ionosphere from the spectrum analysis of ISIS VLF electric field data received at Kashima, Japan. Ion cyclotron whistlers with asymptotic frequency of G_pm or $\text{G}{}_{\mathrm{pm}}\text{2}$ are observed only in the region of $\text{B}{}_{\mathrm{m}}\text{>}\text{B}\text{2}$ or rarely $\text{B}{}_{\mathrm{m}}\text{>}\text{B}\text{4}$, where B is the local magnetic field and B_m is the mini magnetic field along the geomagnetic field line passing through the satellite.The particles with one half the proton gyrofrequency may be the deuteron or alpha particle. Theoretical spectrograms of the electron whistlers (R-mode) and the ion cyclotron whistlers (L-mode) propagating along the geomagnetic field lines are computed for the appropriate distributions of the electron density and the ionic composition, and compared with the observed spectrograms.The result shows that the ion cyclotron whistler with the asymptotic frequency of $\text{G}{}_{\mathrm{p}}\text{2}$ is the deuteron whistler, and that the ion cyclotron whistlers with the asymptotic frequency of G_pm or $\text{G}{}_{\mathrm{pm}}\text{2}$ are caused by the trans-equatorial propagation of the proton or deuteron whistler from the other hemisphere.     

Role of geomagnetic disturbance on whistler occurrence at a low latitude station

In this paper, we report the results derived from a statistical analysis of whistlers recorded at Varanasi during the period January 1990–December 1999. The monthly occurrence rate shows a maximum during January to March. In order to study the role of geomagnetic disturbance on the whistler occurrence rate, we have used the K_P index and its variation. It is found that the occurrence probability monotonically increases with ∑K_P (daily sum) values. It is found that, when ∑K_P>20, the occurrence rate is greater than the average value, in good agreement with results reported by other workers. In addition, we also present the probability of the observation of whistlers during weak/intense geomagnetic storms and also during the main phase and recovery phase of geomagnetic storms.     

VLF goniometer observations at halley bay,Antarctica—II. Magnetospheric structure deduced from whistler observations

On 26 July 1967, a magnetically quiet day (ΣK_p = 12?) with high whistler activity at Halley Bay, it was found possible, by measurement of whistler nose-frequency and dispersion and the bearings of the whistler exit points, to make a detailed study of the magnetospheric structure associated with the whistler ducts.During the period 0509–2305 UT most of the exit points of whistlers inside the plasmasphere were situated along a strip about 100km wide passing through Halley Bay in an azimuthal direction 30°E of N between 57° and 62° invariant latitude. A mechanism which can give rise to such a well-defined locus which co-rotates with the Earth is not clear. Nevertheless, it does appear that the locus coincides with the contour of solar zenith angle 102° at 1800 UT 25 July. This was also the time of occurrence of a sub-storm and it is suggested that the magnetospheric structure was initiated by proton precipitation along the solar zenith angle 102° contour.At mid-day knee-whistlers observed outside the plasmapause had exit points which were closely aligned along an L-shell at an invariant latitude of 62.5°. They exhibited a marked variation (~ 3:1) in electron tube content over about 12° of invariant longitude and a drift of about 8 msec^?1 to lower L-shells.Throughout the period of observation the plasmapause lay about 2° polewards of the mean position found by Carpenter (1968) for moderately disturbed days.     

A whistler study of plasmapause motion in the vicinity of sanae,Antarctica

For 4 months of synoptic records whistlers have been analyzed in two groups, high latitude (HL) whistlers with f_n?8 kHz and low latitude (LL) whistlers with f_n?8 kHz. A decrease in percentage occurrence of HL whistlers with increasing K_p is interpreted as being due to equatorwards movement of the plasmapause in the vicinity of SANAE, Antarctica (L=4). The diurnal variation in HL and LL whistler occurrence reveals an average behaviour of the plasmapause, namely, an equatorwards movement beginning at around 2000 LT followed by a return movement from 0400 LT to 0800 LT.     

An evaluation of duct-life times from low latitude ground observations of whistlers

On certain occasions, whistler rate occurrences at Gulmarg (24°N geomagnetic) and Naini Tal (19°N geomagnetic) are found to exhibit some periodicity. Power spectrum analyses of the occurrence rates yield a dominant period of about 1 hr. It is suggested that this period is an indication of the duct-life times at low L-values. Dispersion analyses of the whistlers have qualitatively confirmed the existence of separate ducts during the period of observation. It is pointed out that power spectrum analyses may not be applicable to whistler data corresponding to high L-values.     

An estimate of the duct life time from low latitude ground observations of whistlers at Varanasi

The observed periodicity in the whistler occurrence rate recorded at our low latitude ground station at Varanasi (geomagnetic latitude, 14°55'N) is interpreted in terms of duct life time at lowL values. Power spectrum analysis of the whistler data yields a period of about 50 min for the growth and decay of ducts. Further dispersion analysis of the whistlers has qualitatively confirmed the existence of separate ducts during the period of observations.     

Characteristics of whistler ducts recorded at Gulmarg

Morphological features of whistlers recorded at low latitude ground station Gulmarg (geomag. lat., 24 26N) 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.     

A summary of whistlers observed by Voyager 1 at Jupiter

The Voyager 1 observations of whistlers at Jupiter are summarized in order to provide a basis for further analyses of the density profile of the Io plasma torus as well as to support studies of atmospheric lightning at Jupiter. All the whistlers detected by Voyager I fell into three general regions in the torus at radial distances ranging between 5 and 6R_J. An analysis of the broadband wave amplitudes measured by the Voyager 1 plasma wave instrument and estimates of the peak whistler amplitudes imply that the grouping of whistlers was due to variations in the sensitivity of the receiver to the whistlers and not to variations in the source or propagation paths of the whistlers. The whistler dispersions are presented in statistical form for each of the three groups of events and analyzed in view of the structure of the Io plasma torus as determined by plasma measurements. The results of these analyses give source locations for the whistlers at the foot of the magnetic field lines threading the torus in both hemispheres and over a range of longitudes.     

Generation of intermediate drift bursts in solar type IV radio continua through coupling of whistlers and Langmuir waves

The possible generation of intermediate drift bursts in type IV dm continua through coupling between whistler waves, traveling along the magnetic field, and Langmuir waves, excited by a loss-cone instability in the source region, is elaborated. We investigate the generation, propagation and coupling of whistlers. It is shown that the superposition of an isotropic background plasma of 10⁶K and a loss-cone distribution of fast electrons is unstable for whistler waves if the loss-cone aperture 2α is sufficiently large (sec α?4); a typical value of the excited frequencies is 0.1 ω _ce (ω _ce is the angular electron cyclotron frequency). The whistlers can travel upwards through the source region of the continuum along the magnetic field direction with velocities of 21.5–28 v _A (v _A is the Alfvén velocity). Coupling of the whistlers with Langmuir waves into escaping electromagnetic waves can lead to the observed intermediate drift bursts, if the Langmuir waves have phase velocities around the velocity of light. In our model the instantaneous bandwith of the fibers corresponds to a frequency of 0.1–0.5 ω _ce and leads to estimates of the magnetic field strength in the source region. These estimates are in good agreement with those derived from the observed drift rate, corresponding to 21.5–28 v _A, if we use a simple hydrostatic density model.     

Magnetospheric electric field from low latitude whistlers during magnetic storm

An attempt has been made to estimate the east-west component (E_w) of the magnetospheric equatorial electric field near L = 1.12 during a magnetic storm period from the whistlers observed at our low latitude ground station, Nainital (geomag.lat. 19°1'N), on March 25, 1971 in the 0130–0500 IST sector. The method of measuring E_w from the observed cross L-motions of whistler ducts within the plasmasphere, indicated by changes in nose frequency of whistlers, has been outlined. The nose frequencies of non-nose whistlers under consideration have been deduced from Dowden-Allcock linear Q-technique. The variation of ($\text{?}{}_{\mathrm{n}}\text{)}{}^{\mathrm{<mtext>2</mtext><mtext>3</mtext>}}$ with local time has been shown, the slope of which can be directly related to the convection electric field. The estimated equatorial electric field at L? 1.12 is in the range 0.1–0.5 mV m^?1 (in the 0130–0500 IST sector) during a storm period, which is in agreement with the results reported by earlier workers. The departure from a dipole field and the contribution of an induced electric field from the temporal changes have been discussed. The importance of an electric field study has been indicated.     

Forecasting the intensity of solar proton events from the time characteristics of solar microwave bursts

A survey of the main characteristics of solar microwave bursts in relation to their usefulness for indicating the intensity of associated solar proton emissions suggests that time parameters give much better results than intensity or spectrum parameters. In particular, best results are obtained by using the effective, or mean, burst duration defined by $$T_M = 1/P_{max} \int_0^T {P(t)dt} $$ where T is the overall burst duration, P is the power density at time T, and P _max is the maximum power density. For proton energies > 10 MeV the proton flux N _p is given approximately by N _p = 0.034 T _M ³ particles ster^?1 cm^?2 s^?1, where T _m is in minutes, with a correlation factor of 0.8. Corresponding coefficients have been derived for a number of energy ranges. Using this parameter solar proton warnings and intensity estimates can be made with observations at only one frequency, preferably in the range 5–20 GHz.     

Whistlers in the solar corona and their relevance to fine structures of type IV radio emission

This short report concerns a general consideration of whistler manifestations in fine structures, including possible trajectories of obliquely propagating whistlers, the role of quasilinear diffusion and an interpretation of new observations. A whistler ray tracing and kinetic whistler growth rates under arbitrary angles to the magnetic field in the solar corona were calculated. Different regimes of a whistler instability yield divers elements of fine structures: different stripes in emission and absorption or millisecond pulsations, moreover, zebra-stripes can convert into fiber bursts and inversely. A new explanation of low-frequency absorption in fibers is proposed: it is connected with an attenuation of plasma-wave instability due to the fast electron diffusion by whistlers. Rope-like chains of fiber bursts are explained by a periodic whistler instability in a magnetic reconnection region.     

Role of “Core” and “Halo” solar electrons in ionization of the interstellar medium

The probability of the interstellar wind atoms (H and He) to survive ionization by solar wind electrons is presented. For the first time a dual temperature electron distribution is used to model the effects of “core” (10 eV) and “halo” (60 eV) solar electrons on the probabilities. Survival probability distributions as a function of helicocentric distance were calculated for variations in the electron temperature, solar radiation force, and the interstellar wind flow velocity. These probabilities are important in determining the radial density distributions of the interstellar atoms. It has been found that the interstellar wind has a distinctively higher probability of surviving “halo” rather than “core” electron ionization only at heliocentric distances, ρ, smaller than about 0.5 a.u. For distances larger than 0.5 a.u., the probabilities of surviving “halo” electrons are close to the probabilities of surviving “core” electrons. Also, the probabilities for both “core” and “halo” electrons are relatively insensitive to changes in u_∞ (interstellar wind velocity at infinity), μ (the solar ratio of radiation to gravitational force) and α (a model parameter for solar electron temperature) for ρ > 0.5. For distances smaller than that, the sensitivity increases significantly.     

Geoactive zones in the solar wind

Three parameters of the solar wind, proton number density n, Z-component of frozen-in magnetic field, in solar ecliptic coordinates and magnetic field variability ΔB, may be called geoactive parameters since each of them is responsible for a certain phase or stage of a geomagnetic storm.An undisturbed solar corpuscular stream differs from the quiet solar wind mainly in higher bulk velocity v; other parameters, in particular, n, Z and ΔB, are not enhanced in the stream. However, the examination of a number of geomagnetic storms shows that v is not a geoactive parameter. Hence the corpuscular stream itself is not more geoactive than the quiet solar wind.The retarding of corpuscular stream by the quiet solar wind results in various plasma deformations (compression, torsion, shear). This, in turn, leads to the creation, in the stream and ambient quiet solar wind, of geoactive zones. Each zone is characterized by the enhancement of some geoactive parameter. The entry of the Earth into a geoactive zone causes a corresponding phase or stage of a geomagnetic storm.The concept of geoactive zones is applied to the analysis of the geomagnetic storm of 8–10 July 1966.     

Parallel electric field-induced instability in the magnetospheric ion-electron plasma

A complete dispersion relation for a whistler mode wave propagation in an anisotropic warm ion-electron magnetoplasma in the presence of parallel electric field using the dispersion relation for a circularly polarized wave has been derived. The dispersion relation includes the effect of anisotropy for the ion and electron velocity distribution functions. The growth rate of electron-ion cyclotron waves for different plasma parameters observed atL = 6.6R _E has been computed and the results have been discussed in detail in the light of the observed features of VLF emissions and whistlers. The role of the combination of ion-cyclotron and whistler mode electromagnetic wave propagation along the magnetic field in an anisotropic Maxwellian weakly-ionized magnetoplasma has been studied.     

A Study of the Solar Proton Flux Model

The solar proton event (SPE) may become a serious threat to the cosmonautical activities of human beings, so the prediction of the flux of solar protons within a certain period has important guiding significance for the projection of the anti-radiation solidification of space vehicles. On the basis of a statistical analysis of the data of SPEs in the 20th to 23rd cycles of solar activity, a new model of solar proton fluxes with E > 10 MeV and E > 30 MeV is established. In comparison with the JPL model, which is frequently adopted in the present aerospace engineering, the influence factor of solar activity on the occurrence of proton events is introduced, and it can be used to estimate the proton fluxes under various levels of solar activity. The results can better match the characteristics of the distribution of proton events.     

Statistical Feature Recognition for Multidimensional Solar Imagery

A maximum a posteriori (MAP) technique is developed to identify solar features in cotemporal and cospatial images of line-of-sight magnetic flux, continuum intensity, and equivalent width observed with the NASA/National Solar Observatory (NSO) Spectromagnetograph (SPM). The technique facilitates human understanding of patterns in large data sets and enables systematic studies of feature characteristics for comparison with models and observations of long-term solar activity and variability. The method uses Bayes’ rule to compute the posterior probability of any feature segmentation of a trio of observed images from per-pixel, class-conditional probabilities derived from independently-segmented training images. Simulated annealing is used to find the most likely segmentation. New algorithms for computing class-conditional probabilities from three-dimensional Gaussian mixture models and interpolated histogram densities are described and compared. A new extension to the spatial smoothing in the Bayesian prior model is introduced, which can incorporate a spatial dependence such as center-to-limb variation. How the spatial scale of training segmentations affects the results is discussed, and a new method for statistical separation of quiet Sun and quiet network is presented.     

Plasmasphere response to the onset of quiet magnetic conditions: Plasma convection patterns

A whistler study has been made of plasma convection within the plasmasphere during a transition from steady moderate geomagnetic activity to quiet conditions. Continuous whistler data recorded at Sanae, Antarctica (L= 3.98) for the period 0400 UT, 10 July to 0400 UT, 11 July 1973 have been analyzed in 15 min intervals.This study has revealed two distinct bulges in the plasmasphere centred on 1700 and 0100 UT. The bulges appear to result from the outward flow of plasma rather than the addition of new plasma. We tentatively interpret the late bulge at 0100 UT as being the duskside bulge of earlier studies rotated into the midnight region. In this bulge, plasma above L = 3.8 appears to convect outwards to form the bulge whereas plasma at lower L-values is relatively undisturbed. For the early bulge (1700 UT) the plasma convection pattern is similar over all observable L-values and closely reflects the shape of the estimated plasmapause in that region. Comparison of the bulges, with those obtained by Carpenter (1966) suggests that the onset of quiet conditions results in a general displacement of the bulges in an eastward direction by about 3 hr.     

Conjugate measurements of VLF transmitter signals at middle latitude (L = 1.93)

Whistler-mode signals were measured at the conjugate point (L = 1.93) in South Australia of the VLF transmitter in Eastern U.S.S.R. The intensity of whistler-mode signals increased usually at sunset and occasionally at sunrise, and was moderate during night-time. By means of the calculation of the wave attenuation in the lower ionosphere, the result may be interpreted in terms of different mechanisms of propagation in the magnetosphere and transmission out of the ionosphere: spatially coherent propagation in a field-aligned duct and transmission out of the duet onto the ground at sunset and sunrise; and spatially incoherent propagation and transmission at night. A high correlation was found between the occurrence probability of the 14.881 kHz whistler-mode signals and the occurrence number of whistlers, which may suggest that the occurrence of whistlers is controlled predominantly by propagation conditions.     

Enhanced energetic electron intensities at 100 km altitude and a whistler propagating through the plasmasphere

During the flight of a Petrel rocket, instrumented by the SRC Radio and Space Research Station with Geiger counters and launched westwards from South Uist, Outer Hebrides, Scotland (L=3.38), a transient increase was observed in the intensity of energetic electrons having pitch angles between 60 and 120°. The increase, by a factor of 20 above the quasi-steady intensity observed throughout the remainder of the flight, occurred in 0.8 sec and was simultaneous for both >45 keV and >110 keV electrons. Recorded ～0.5 sec later, on the ground, was a two-hop whistler. During the enhanced electron intensity event, the entire duration of which was ～6 sec, the four-, six- and eight-hop whistlers were also received. From an analysis of the whistlers' spectrogram, it is concluded that the whistlers were ducted through the magnetosphere along the L=3.3 ±0.1 field line; the electron density in the equatorial plane is found to be 330 ±10 cm^?3, a value characteristic of conditions within the plasmapause. It is suggested that these temporally and/or spatially associated phenomena, rather than arising by a chance coincidence, were the result of a gyroresonant interaction between energetic electrons and whistler mode waves moving in opposite directions. For gyroresonance on this field line at the equator, the parallel component of energy of the electrons is 25 keV at 3 kHz in the whistler band, or 100 keV at 1 kHz below it. It is suggested that a magnetospheric event occurred, causing both sudden enhanced electron precipitation and favourable conditions for the propagation and/or amplification of whistlers. A possible explanation is that energetic electrons, having a sufficiently anisotropic distribution function and associated with those injected during an earlier auroral substorm, become unstable via the transverse resonance instability when they drift into the plasmasphere, a region of high density thermal plasma.