VLF Phase Research Articles

The impact of PMSE and NLC particles on VLF propagation

Abstract. PMSE or Polar Mesosphere Summer Echoes are a well-known phenomenon in the summer northern polar regions, in which anomalous VHF/UHF radar echoes are returned from heights ~85km. Noctilucent clouds and electron density biteouts are two phenomena that sometimes occur together with PMSE. Electron density biteouts are electron density depletion layers of up to 90%, which may be several kms thick. Using the NOSC Modefndr code based on Wait's modal theory for subionospheric propagation, we calculate the shifts in received VLF amplitude and phase that occur as a result of electron density biteouts. The code assumes a homogeneous background ionosphere and a homogeneous biteout layer along the Great Circle Path (GCP) corridor, for transmitter receiver path lengths in the range of 500–6000km. For profiles during the 10h about midnight and under quiet geomagnetic conditions, where the electron density at 85km would normally be less than 500el/cc, it was found that received signal perturbations were significant, of the order of 1–4dB and 5–40° of phase. Perturbation amplitudes increase roughly as the square root of frequency. At short range perturbations are rather erratic, but more consistent at large ranges, readily interpretable in terms of the shifts in excitation factor, attenuation factor and v/c ratios for Wait's modes. Under these conditions such shifts should be detectable by a well constituted experiment involving multiple paths and multiple frequencies in the north polar region in summer. It is anticipated that VLF propagation could be a valuable diagnostic for biteout/PMSE when electron density at 85km is under 500el/cc, under which circumstances PMSE are not directly detectable by VHF/UHF radars. Key words. Electromagnetism (wave propagation) – Ionosphere (polar ionosphere) – Radioscience (ionospheric propagation)

Solar flare induced ionospheric D-region enhancements from VLF phase and amplitude observations

Ionospheric perturbations due to solar flares, measured at VLF in both phase and amplitude on long subionospheric paths, are used to determine the accompanying D-region electron density enhancements as a function of the flare X-ray fluxes measured by the GOES satellites. The electron densities are characterised by the two traditional parameters, H′ and β (being measures of the ionospheric height and the rate of increase of electron density with height, respectively), found by computational modelling of the observed phases and amplitudes using the NOSC Earth-ionosphere waveguide programs (LWPC and ModeFinder) over a wide range of VLF frequencies, 10.2– 24.8 kHz , along a number of transequatorial paths across the Pacific Ocean to Dunedin, New Zealand. The transmitters monitored include Omega Japan, Omega Hawaii, NPM in Hawaii, and NLK near Seattle, USA, for which the paths range in length from 8.1 to 12.3 Mm . The observations include flares up to a magnitude of about X5 (5×10 −4 W m −2 at 0.1– 0.8 nm ). These gave VLF phase delay reductions of up to about 52 μs and amplitude enhancements up to nearly 10 dB for the 12.3 Mm NLK to Dunedin path on 24.8 kHz which corresponded, under low to medium solar cycle conditions (1994–1998), to a reduction in H′ from about 71 km down to about 58 km and an increase in β from about 0.39 km −1 up to a definite ‘saturation’ level of about 0.52 km −1 . These experimentally determined values of H′ and β were then used in LWPC to predict flare-induced VLF phase and amplitude perturbations over a wider range of frequencies than were actually available for observation.

VLF phase and amplitude: daytime ionospheric parameters

Experimental observations of the daytime variations of VLF phase and amplitude over a variety of long subionospheric paths have been found to be satisfactorily modelled with a D-region ionosphere, described by the two traditional parameters, H′ and β (being measures of the ionospheric height and the rate of increase of electron density with height, respectively). This VLF radio modelling uses the NOSC Earth–ionosphere waveguide programs but with an experimentally deduced dependence of these two ionospheric parameters on solar zenith angle. Phase and amplitude measurements from several VLF Omega and MSK stations were compared with calculations from the programs LWPC and Modefinder using values of H′ and β determined previously from amplitude only data. This led to refined curves for the diurnal variations of H′ and β which, when used in these programs, give not only calculated amplitudes but also, for the first time, calculated phase variations that agree well with a series of observations at Dunedin, New Zealand, of VLF signals from Omega Japan, Omega Hawaii, NPM (Hawaii) and NLK (Seattle) covering a frequency range of 10–25 kHz.

Numerical simulation of LEP Trimpis observed at Poitiers, France, on signals from VLF transmitters

Transient amplitude and phase perturbations on subionospheric VLF signals, known as the Trimpi effect, are caused by the scattering of VLF radiation from localized ionization enhancements in the nighttime D-region. The patches of ionization are due to precipitation from the radiation belts of keV electrons, that is induced by lightning-generated whistlers.This work is concerned with the numerical simulation of such VLF perturbations, termed LEP (lightning-induced electron precipitation) or classic Trimpis. Two different codes are used to compute the VLF propagation in the Earth-ionosphere waveguide in the presence of a D-region inhomogeneity. The first is based on mode theory, and the second on the FDTD (finite-difference time-domain) method. Both codes are two-dimensional and, therefore, relevant only to LEP events lying on the transmitter-receiver great circle path (TRGCP). A method of simulation is proposed to interpret quantitatively VLF amplitude and phase changes in terms of the approximate location and size of the associated ionospheric perturbation along the TRGCP. The method is applied to LEP Trimpis observed at Poitiers ( L = 2) on signals from the NAA and GQD transmitters. Results are discussed in the light of the information that may be deduced from the high-resolution analysis of VLF temporal signatures. A sequence of simultaneous LEP Trimpis observed at Poitiers on three widely separated transmission paths is studied; two alternative interpretations are proposed.

Multi-instrument coincident detection of sprites

This paper describes the instrumentation used for sprite detection during two campaigns near Darwin, Australia, in 1997 and 1998. The sprites (large electrical luminous discharges above thunderstorms) are detected by both ‘direct’ (optical) and ‘indirect’ (radio frequency) methods. The optical detectors consist of (i) two intensified video capture systems that are capable of capturing and storing only video frames containing sprites, and (ii) up to four photometers whose outputs are monitored so that only events defined as significant are captured. The radio-frequency detectors consist of (i) four-channel sferic detectors operating in the VLF region and (ii) one or more AbsPAL VLF phase and amplitude loggers. All detectors use GPS receivers for timing reference, which allows post-capture comparison of all events with high accuracy.

Logarithmic decay and Doppler shift of plasma associated with sprites

VLF phase and amplitude perturbations in ‘early/fast Trimpis’ have been observed simultaneously on two or more transmitters at two or more receiver sites and simultaneously with sprites observed optically in Colorado. In all cases the early/fast Trimpis could apparently be resolved into two components: the RORD (rapid onset, rapid decay) component coincident with the sprite and a ‘classic Trimpi’ component having the slower onset and decay of Trimpis generally thought to be caused by whistler-induced electron precipitation from the radiation belts. The phase and amplitude perturbations can decay at very different rates, and even change in sign from positive to negative perturbation (‘overshoot’) during decay. This implies a spatial separation between the rapid decay plasma responsible for the RORD and the slow decay plasma responsible for the classic Trimpi component of up to a few tens of km. This is much less than the expected separation of sprite plasma and electron precipitation plasma induced by the same cloud–ground lightning. The discovery of very strong early/fast Trimpis in the tropics (Darwin, Australia), where electron precipitation is unlikely, which showed similar effects like overshoot but much more clearly, caused an examination of recent Colorado data of high resolution. The Colorado Trimpis, which are clearly associated with sprites, show the same features as the Darwin Trimpis where optically detected sprites were not available. Both can be explained in terms of sprite plasma decaying from the bottom up without recourse to electron precipitation.

Are VLF rapid onset, rapid decay perturbations produced by scattering off sprite plasma?

Rapid onset, rapid decay perturbations (RORDs) of subionospheric VLF propagation require highly localized or laterally structured plasma at low altitudes to explain the wide angle scattering observed and the rapid decay. Simultaneous occurrence of RORDs and red sprites, illustrated by a single event here, together with VLF phase and group delay measurements from a pair of spaced receivers suggest that RORDs are produced by scattering from conducting columns at the position and with the lateral shape of the sprite. The sprite luminosity decays much faster than the RORDs which depend on the sprite conductivity and so plasma density. Plasma is also produced near the sprite plasma by energetic electrons precipitated from the magnetosphere by ducted whistlers and after the expected whistler and electron propagation delay. This whistler‐induced electron precipitation (WEP) plasma produces wide angle VLF scattering similar to that by sprite plasma, implying similar lateral fine structure. This suggests that the processes leading to sprites also produce whistler ducts in the magnetosphere.

VLF remote sensing of the auroral electrojet

We investigate a new potential technique to determine the position of the auroral electrojet from ground‐based VLF amplitude and phase measurements. The chief advantage of this technique over conventional ground magnetometer measurements is that it can provide data on a continental scale with a small number of receiving stations and with a minimum of data processing. At the edge of the auroral zone, where the electrojet current system flows, high‐energy (E > 300 keV) precipitating electrons cause local electron density enhancements in the ionosphere which cause phase and amplitude perturbations in VLF waves propagating in the Earth‐ionosphere waveguide. Continuous measurements of the amplitude and phase of signals from the Omega North Dakota VLF transmitter were made in Nome, Alaska. Using a two‐dimensional model of VLF propagation which accounts for ionospheric disturbances caused by the electron precipitation associated with the electrojet, the amplitude and phase signatures of electrojet incursion across each propagation path were predicted. Seventeen nights of simultaneous VLF amplitude and phase data and ground magnetometer data were examined and catalogued based on the degree of temporal correlation between the two data sets and the degree to which the VLF events matched the propagation simulations. Of the nights exhibiting activity, more than 60% exhibited excellent correlation between the magnetometer and VLF events, and the majority of these showed good agreement with the model results. An additional estimate of the electrojet position was provided for one of the studied nights by field‐aligned current measurements from the Freja satellite. A comparison of these independent means of determining the electrojet position shows that they are in good agreement for the night examined.

The Use of a GPS-Equipped Aircraft as a Mobile Platform to Study the Propagation of Omega Navigation Signals

The almost complete constellation of GPS satellites now provides excellent positional information for aircraft, with typical worst-case errors of the order of 100 metres. The low frequency waves used for Omega navigation have wavelengths of the order of 30 kilometres and thus, even in an aircraft moving at varying speeds up to around 500 km per hour, it is now a simple matter to measure VLF phase with a significance at the 1 degree level. This paper describes the use of GPS to provide accurate positional information to VLF receivers located on aircraft of the Royal New Zealand Airforce (RNZAF) en-route to Antarctica. The marked phase irregularities on signals from La Reunion and Argentina, observed north of the icecap in earlier studies using aircraft fitted with inertial navigation systems, have been confirmed and described with much greater precision. Smaller phase anomalies have also been observed on signals from Omega Australia and Omega Hawaii, whilst flying directly over the Antarctic icecap. The latter signal was previously regarded as unperturbed and used in earlier studies as a phase reference. Small-scale periodic variations of phase and amplitude have also been recorded on signals propagating from Omega Australia. These variations are considered to be caused by the reflection of the VLF waves at discontinuities in the height (e.g. mountains) or the lower boundary conductivity of the Earth-ionosphere waveguide. Reflections of smaller amplitude have also been observed flying over the open ocean before reaching Antarctica.

Size and location of lightning-induced ionisation enhancements from measurement of VLF phase and amplitude perturbations on multiple antennas

A 600-km array of five Trimpi receivers (“elements”) has been set up in New Zealand broadside to the VLF (22.3 kHz) transmitter, NWC, some 6000 km west, with element separations varying from 8 km to 550 km. Although such a five-element array is inadequate for imaging of lightning-induced ionisation enhancements (LIEs) by VLF holography, or inverse scattering, estimates of LIE size and location can be made if the shape and form of the LIE can be guessed or assumed, with even fewer elements. With five elements, tests of the assumed model can be made as well. Owing to its transform properties, the simplest model to use for scattering inversion is the Gaussian LIE distribution. For this model, and for single mode propagation, an inversion process is derived here for the full range of LIE and path dimensions, ranging from those for which the receiver is in the diffraction far field to those in which “geometric optics” dominate. This inversion process has some validity for small LIEs of other shapes of simple form. For more extreme models, the dominance of geometry or diffraction can usually be established in individual cases which then allows simple scaling procedures to be used in scattering inversion. Some 70 Trimpi events were observed on all five elements during a single night in July. 1991 (late winter). These were used to determine LIE location and size, and to test the applicability of various LIE models. It was found that most LIEs that night occurred over the Tasman Sea near the great circle from the VLF transmitter, NWC, to Wellington, generally some 500 to 2000 km from Wellington, and with north-south dimensions of 100–250 km. Much longer east-west dimensions (oriented towards NWC) are suggested to account for the very strong Trimpis observed. While about half of these LIEs that night could have had a smooth lateral spread (e.g., Gaussian), the remainder required varying degrees of fine structure, from “flat” or Butterworth LIEs to multiple LIEs as might be expected from multiduct whistlers, to explain the observed diffraction pattern exhibiting maxima and minima as well as the wide angular range over which simultaneous Trimpis were observed.

Relation between VLF phase deviations and solar X-ray fluxes during solar flares

Sudden phase anomalies (SPA's) observed in the phase of GBR 16 kHz VLF signals during the years 1977 to 1983 have been analysed in the light of their associated solar X-ray fluxes in the 0.5–4 A and 1–8 A bands. An attempt has been made to investigate the solar zenith angle (χ) dependence of the integrated solar X-ray flux for producing SPA's. It is deduced from the observations for χ < 81° that the phase deviation increases linearly as a whole with increasing solar X-ray fluxes in these two bands. The threshold X-ray flux needed to produce a detectable SPA effect has been estimated to be 1.6 × 10−4 ergcm−2 s−1 and 1.8 × 10−3 ergcm−2 s−1 in the 0.5–4 A and 1–8 A bands, respectively. For both bands the average cross section for all atmospheric constituents at a height of 70 km is almost equal to the absorption cross section for the 3 A X-ray emission.

Diurnal lower ionosphere electron density variations observed in the South Atlantic Geomagnetic Anomaly and sub-Antarctic region during the occurrence of the major PCA event of 4 August 1972

VLF phase and amplitude signals simultaneously received in Atibaia and Curitiba, both in Brazil, were analysed during the occurrence of the major proton flare event of 4 August 1972. Phase advances recorded in Stockholm (Sweden) and Inubo (Japan) were also included for comparison purposes. Particular attention was devoted to the NWC (Australia)-Atibaia (Brazil) propagation-path which passes through disturbed regions (geomagnetically), namely the sub-Antarctic region and the South Atlantic Geomagnetic Anomaly (SAGA), and which propagates completely in the southern hemisphere. Following the current mechanisms that allow charged particles to precipitate at low altitudes in the ionosphere ( Dregion), four regions were defined based on the most significant ‘ L’ value involved. By means of successive comparisons with low and mid latitude propagation paths, some parameters typical of the lower ionosphere were deduced for the southern hemisphere in association with PCA events detected in the polar caps. Fitting exponential models to the data analysed, daytime electron density profiles were obtained for different ‘ L’ values throughout the disturbed period.

Path‐dependent properties of subionospheric VLF amplitude and phase perturbations associated with lightning

A comprehensive study of lightning‐associated amplitude and phase perturbations on multiple VLF/LF signals (Trimpi events) observed at Stanford, California and at Palmer Station, Antarctica, has revealed a number of new properties that appear to be characteristic of the particular signal paths. (1) Signal amplitude changes are on the whole evenly distributed between enhancement and attenuation, but some individual signal paths have strong preferences for one or the other. (2) Phase changes on almost all paths show a strong preference for advancement, with phase retardation occurring rarely. (3) The range in size of amplitude and phase changes appears to be relatively constant for a given path, but it is found to vary between different paths. None of the existing models of the Trimpi effect are found to explain all of the observed new features. Instead, the new experimental findings provide an empirical framework to guide the evaluation of more sophisticated models. Analysis also indicates that the magnitudes of simultaneous amplitude and phase changes are only weakly correlated and that the recovery signatures of amplitude and phase events can be substantially different, with the signal amplitude generally recovering faster. This apparent independence of amplitude and phase perturbations is interpreted to result from the altitude distributed nature of the ionospheric disturbances.

VLF disturbances at the south atlantic magnetic anomaly following magnetic storms

Using VLF wave data from a trajectory confined within a low L-value portion of the South Atlantic Magnetic Anomaly (SAMA), in association with seven moderate to large geomagnetic storms during the period 1976–1981, a relationship between the amplitude of the VLF phase disturbance and the intensity of the geomagnetic storm was obtained. Furthermore, using X-ray data from balloon flights collected at the SAMA in 1981 we have also derived a relationship between the VLF phase disturbance amplitude and the precipitated electron flux obtained from the X-ray data. This latter result permits an estimation of precipitating electron fluxes at the SAMA during magnetic storms from VLF phase data.

Location of lightning‐induced electron precipitation from measurement of VLF phase and amplitude perturbations on spaced antennas and on two frequencies

The phase and amplitude perturbations on a VLF subionospheric transmission can always be expressed in terms of a perturbation or echo phasor. It is believed that lightning‐induced electron precipitation (LEP) can produce a localized increase in ionization which acts as a scattering center and so echo source for subionospheric VLF waves. The phase of the echo relative to the direct signal will differ on spaced antennas if the angle of arrival of the two signals differ. Similarly, this relative phase will vary with frequency if the group delay of the signals differ. Thus measurement of these differences allows location of the scattering centers and so the LEP. Locations made show a significant grouping in a region where both the lightning intensity is high and the field line passes through the center of the inner radiation belt.

Local and long-distance effects of meteor showers in the low ionosphere

The effect of the Geminids and α Scorpiids meteor showers in the lower ionosphere have been observed using two different methods. Low ionosphere group heights, measured by a VLF ionosonde located in southern Brazil, indicated significant anomalous lowering of the effective reflection height which was in good correlation with the transit of the α Scorpiids stream. The group reflection coefficients also showed very pronounced correlated variations. The diurnal VLF phase variations over two long-distance propagation paths showed significant phase deviations from the average during the transits of the showers' radiants. Geomagnetic activity during the periods concerned was low and the results obtained using the two different techniques confirm the occurrence of changes in the physical conditions of the low ionosphere produced by meteor showers on local, as well as on long-distance, scales.

The diffraction of VLF radio waves by a patch of ionosphere illuminated by a powerful HF transmitter

At Skibotn in northern Norway, measurements have been made of the effect of powerful HF waves, from the heating facility at Ramfjordmoen, on the propagation of VLF waves from the Omega transmitter (12.1 kHz) near Aldra and on the 16.4‐kHz transmissions (JXN) at Helgeland. The HF beam was deflectable in a north‐south direction, which enabled it to intersect the VLF propagation path. The VLF amplitude and phase perturbations were found to oscillate about zero as the beam was scanned across the propagation path, and typical daytime amplitude and phase perturbations had maximum magnitudes of ∼0.1 dB and 0.5°. The maximum values appeared when the heated beam was symmetrically located across the VLF path. A study of the temporal variability of the amplitude and phase perturbations at a fixed‐beam deflection angle (38°S) showed that large enhancements of up to two orders of magnitude occurred in the amplitude and phase perturbations at times when the total received VLF field strength passed through a minimum. Maximum amplitude and phase perturbations of 6 dB and 50° were recorded during one such minimum in the total received signal. Theoretical computations are presented which evaluate the diffracting effect of a heated patch of auroral ionosphere on multimode propagation in the earth‐ionosphere waveguide. Computations of propagation under a series of ionospheres ranging from typical daytime to nighttime have been made, and the normal and enhanced amplitude and phase perturbations have been successfully modeled. Attempts at reproducing the perturbing effects of a mobile heated patch have not been nearly so successful, especially at large deflection angles.

Comment on “Modeling the ion chemistry of the D region: A case study based upon the 1966 total solar eclipse” by Sears et al.

Journal of Geophysical Research: Space PhysicsVolume 89, Issue A4 p. 2406-2408 CommentariesFree Access Comment on “Modeling the ion chemistry of the D region: A case study based upon the 1966 total solar eclipse” by Sears et al. M. A. Abdu, M. A. AbduSearch for more papers by this authorJ. H. A. Sobral, J. H. A. SobralSearch for more papers by this authorI. S. Batista, I. S. BatistaSearch for more papers by this author M. A. Abdu, M. A. AbduSearch for more papers by this authorJ. H. A. Sobral, J. H. A. SobralSearch for more papers by this authorI. S. Batista, I. S. BatistaSearch for more papers by this author First published: 1 April 1984 https://doi.org/10.1029/JA089iA04p02406AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL No abstract is available for this article. References Abdu, M. A., I. S. Batista, J. H. A. Sobral, Particle ionization rates from total solar eclipse rocket ion composition results in the south Atlantic geomagnetic anomaly, J. Geophys. Res., 84, 4328– 4334, 1979. Abdu, M. A., I. S. Batista, L. R. Piazza, O. Massambani, Magnetic storm associated particle precipitation in the south Atlantic anomaly: Evidence from VLF phase measurements, J. Geophys. Res., 86, 7533– 7542, 1981. Batista, I. S., M. A. Abdu, Magnetic storm associated delayed sporadic E enhancements in the Brazilian geomagnetic anomaly, J. Geophys. Res., 82, 4777– 4783, 1977. Gledhill, J. A., R. A. Hoffman, Nighttime observations of 0.2–25 keV electrons in the south Atlantic anomaly made by Atmospheric Explorer-C, J. Geophys. Res., 86, 6739– 6744, 1981. Lyons, L. R., A. D. Richmond, Low-latitude E region ionization by energetic ring current particles, J. Geophys. Res., 83, 2201, 1978. Mechtly, E. A., K. Seino, L. G. Smith, Lower ionosphere electron densities measured during the solar eclipse of November 12, 1966, Radio Sci., 4, 371– 375, 1969. Mizera, P. F., J. B. Blake, Observations of ring current protons at low latitude, J. Geophys. Res., 78, 1058, 1973. Narcisi, R. S., A. D. Bailey, L. E. Wlodyka, C. R. Philbrick, Ion composition measurements in the lower ionosphere during the November 1966 and March 1970 solar eclipse, J. Atmos. Terr. Phys., 34, 647– 658, 1972. Ogawa, T., T. Tohmatsu, Photoelectronic processes in the upper atmosphere, II, The hydrogen and helium ultraviolet glow as an origin of the nighttime ionosphere, Rep. Ionos. Space Res. Jpn., 20, 395– 417, 1966. Pfitzer, K. A., J. R. Winkler, Experimental observation of a large addition to the electron inner radiation belt after solar flare event, J. Geophys. Res., 73, 5899– 5797, 1968. Rees, M. H., Auroral ionization and excitation by incident energetic electrons, Planet. Space Sci., 11, 1209– 1218, 1963. Sears, R. D., M. G. Heaps, F. E. Niles, Modeling the ion chemistry of the D region: A case study based upon the 1966 total eclipse, J. Geophys. Res., 86, 10,073– 10,086, 1981. Tinsley, B. A., Evidence that the recovery phase ring current consists of helium ions, J. Geophys. Res., 81, 6193, 1976. Ulwick, J. C., Eclipse rocket measurements of charged particle concentration, J. Atmos. Terr. Phys., 34, 659– 665, 1972. Volume89, IssueA41 April 1984Pages 2406-2408 ReferencesRelatedInformation

An Investigation of Aging in a Quartz Crystal by VLF Phase Comparison Method

Abstmcf-The objective of the study presented here is the determination of aging characteristics of the local crystal which has been in continuous operation for fifteen years. To do this, the data accumulated since 1968, by phase comparison of the local crystal with the 16 kHz primary standard frequency emitted from Rugby, England, has been analyzed from the point of view of aging in the local crystal. The aging rate, which was parts in lo9 per day at the very early phase of operation of the local crystal, came down to parts in 10l2 per day at present. In this study an AT-cut rectangular quartz plate vibrating at 5 MHz is used. Since there is not a unique theory of aging in literature for crystal resonators, an attempt to explain the time dependence of the aging rate for the AT-cut crystal chips is made by making use of observed aging characteristics. It is believed that the study may help in the developments of nonaging quartz crystal units.

Quantitative study of substorm‐associated VLF phase anomalies and precipitating energetic electrons on November 13, 1979

The phase anomalies associated with substorms are observed on VLF signals propagating on transauroral paths (transmitters at OMEGA‐ALDRA (13.6 kHz), GBR (16.0 kHz), and OMEGA‐NORTH DAKOTA (13.6 kHz)) which were continually received at Inubo, Japan, during the events on November 13, 1979. Detailed comparisons are made between these phase anomalies and geomagnetic bays, and quantitative relations are obtained with precipitating energetic electrons (E &gt; 30, E &gt; 100, and E &gt; 300 keV) detected on board the TIROS‐N and NOAA 6 satellites. It is concluded that two types of VLF phase anomalies exist which, in turn, are associated with two phases in the history of energetic electron precipitation into the atmosphere. The first type of phase anomaly is associated with direct injection of energetic electrons into the outer magnetosphere and atmosphere which, in turn, is completely correlated in time with development of the auroral electrojet current system. The second type arises from energetic electrons which subsequently precipitate from a trapped electron population and has a delayed onset and prolonged duration. An excellent quantitative correlation is obtained between the logarithm of the electron flux and the magnitude of the phase anomaly on the OMEGA‐ALDRA signal. From the local time characteristics of this quantitative relation it is deduced that the electrons with E &gt; 300 keV are the main source of D region ionization responsible for the VLF phase anomaly.