Chorus, hiss, and other audio-frequency emissions at stations of the whistlers-east network

Laaspere, T.; Morgan, M. G.; Johnson, W. C.

doi:10.1109/proc.1964.3368

Cited by 30 publications

(21 citation statements)

References 20 publications

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“…The broad peak we observe centered on 9 hours MLT at high latitudes does not seriously disagree with this, and a slight discrepancy may be expected due to the effect reported by Laaspere, et al [1964], who find that disturbed day chorus peaks earlier than quiet day chorus. The 9 hours MLT result for the position o f the diurnal maximum is consistent with the results of a 1963 ground station study by…”

contrasting

confidence: 74%

VLF emissions during magnetic storms and their association with 40-keV electrons

Cauffman¹,

Gurnett²

1969

J. Geophys. Res.

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During a sudden-commencement magnetic storm the VLF emission called polar chorus characteristically appears a t the onset of the storm, may increase in upper frequency extept to Q, 5 kHz, may change from spike to burst structure (normal chorus), and occurs over the greatest area on the fourth day of the storm, subsequently fades into low frequency, spike-structure polar chorus again and eventually disappears into the ELF hiss band generally present. Chorus occurrence shows symmetry about the 9:00 -21:OO magnetic local time meridian with a large maximum in magnetic morning and a -smaller maximum in magnetic evening. Figure 1 shows examples of VLF hiss, polar chorus with an ELF hiss band, and normal chorus. Five sudden-commencement magnetic storms and one "quiet time'' were chosen for study from the Injun 3 data 10 on the basis of the quantity and quality of data available. [Lincoln, 1964a and b], and indicates the number of MLT-INV sectors of each period for which data were assembled and analyzed.The method of data analysis is straightforward.Satellite orbit plots such as that shown in Figure 1 were used to select sectors for which data were available during each day of the storm. Using a Rayspan spectrum analyzer, frequency-time spectrograms such as that shown in Figure 1 were produced for all passes through these sectors. A visual analysis was made of the types of VLF emissions observed each day in the spectrograms of each sector. (1) ELF hiss is present in most sectors most of the time, including pre-storm times.( 2 ) VLF h i s s is present occasionally with no apparent tempor pattern. burst-type chorus and spike-type chorus.burst-type, possibly periodic chorus is generally observed from the second through the fourth days of a storm, after which the chorus returns to lower frequencies, reverts to spike structure, and eventually fades into the ELF hiss background normally present.

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contrasting

confidence: 74%

VLF emissions during magnetic storms and their association with 40-keV electrons

Cauffman¹,

Gurnett²

1969

J. Geophys. Res.

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“…The two principal synoptic programs are the Whistlers-'West networ]" [Helliwell andCarpenter, 1961 , 1962a], operated by Stanford University, and the WhistlersEast network [Laaspere, Morgan, and Johnson, 1962], operated by Dartmouth College.…”

Section: Field Operationsmentioning

confidence: 99%

“…Whistler occurrence data covering five years of () bserva tions in the Whistlers-East network and at a number of other stations were analyzed statistically by Laaspere, Morgan, and Johnson [1962]. It was found that most diurnal whistler curves can be considered to be variations of one basic form which shows three peaks superimposed on a broad nighttime maximum.…”

Section: Dispersion Theorymentioning

confidence: 99%

“…a diffu siv e equilibrium distribution , i.e., hydrostatIcally supported bu t constrain ed by the ~arth 's magn etic field. For ions the m ean fr ee pn.th l S short enough so that the concep t of an ionexosphere is not applicable [Johnson , 1962] . While the diffusive equilibriurn distribution of an ionic sp ecies ,~as gen~]"ally con~id ered to be go:v:erned by a scale h eJght t WICe t hat of t h e cOl"l"espondmg neutral sp ecies, it was pointed out by Mange [1960Mange [ 1961] that t his con cept is not justified for a minor ' ion in tbe presen ce of other ions.…”

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confidence: 99%

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URSI National Committee Report, XIV General Assembly, Tokyo, September 1963: Commission 4. Magnetospheric Radio (8 Sections)

Bauer¹,

Booker²,

Crichlow³

et al. 1964

J. RES. NATL. BUR. STAN. SECT. D. RAD. SCI.

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CompositionPri01" Lo 1961 it was gener ally accepted tha t the main cons Lituen t of the atmosph er e above 300 km was atomic oxygen up to a n altitude of about 1000 km and that at hi gh er altitudes hydroge n would predominate. Direct ex perim ental evid e nce for th e presen ce of neutral h ydroge n in the outer atmosph er e has come from t he high resolution Ly m an a spectrum obtained by Purcell a nd Tousey [1960]. From th e absorption core of th eir L ym an a spectrum , the total con ten t of hydrogen above the altitude of the rock et measurem ent has b ee n determin ed . John son [1961] has interpreted t his hyd roge n co ntent to be cLi stributed in t he form of n, "geocorona." The problenl of interpretation of the L y man a observations in terms of hydroge n and its location wi th r espect to the earth has r ecently b een r evi ewed in detail b y Donahue [1962]. The computation of the distribution of neutral h ydrogen is complicated by the fact that at magn etospheric levels "exospheri c" conditions prevail, i. e., the mean free path of neutral hydrogen is greater than the local scale height. Because of the escape of particles with high velocities, the velocity distribution is, strictly speaking, non-Maxwellian and the distribution of density with hei gh t does not follow t he simple h ydrostatic equation, but has to be computed by taking into account ballistic escape, b allistic r eentry a nd bound-orbiting particles. Such compu t a.tions have been mad e by bpik and Singer [1961] and by Johnson [1961]. Out to a geocentric distance of a bout two ear th r adii , a simple h y drostatic dis tri bution , however , stillreprese n ts fI, r easonably good n.p pro xi III ation .Photoionization and /or ch ar ge exchange with oxygen ion s of the neu tral hyd rogen of th e geocoron a lead to the protons constituting t h e " protonosph er e." rrhe ions fLt J1h1gn etospheric levels are distribu ted according t? a diffu siv e equilibrium distribution , i.e., hydrostatIcally supported bu t constrain ed by the ~arth 's magn etic field. For ions the m ean fr ee pn.th l S short enough so that the concep t of an ionexosphere is not applicable [Johnson , 1962] . While the diffusive equilibriurn distribution of an ionic sp ecies ,~as gen~]"ally con~id ered to be go:v:erned by a scale h eJght t WICe t hat of t h e cOl"l"espondmg neutral sp ecies, it was pointed out by Mange [1960Mange [ 1961] that t his con cept is not justified for a minor ' ion in tbe presen ce of other ions. The electric field which is set up to prevent further charge separation ' of electrons and ions diffu sing under gravity, and which is propor tional to t h e me}1n mass of the (s ingly charged) positive ions, ca uses the density of minor ligh t ions first to increase with alt it ud e until it b eco mes predominant, n.Iter whi ch it shows the llsual expon ential decrease with altitude according to n. scn.le h eigh t appr~aching twice that of t he conesponding n eutral constItu ent. S ubsequently to . Mange's independent derivation of the equation go...

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“…The origin of these very low frequency emissions is not yet understood, but it is thought that the production of VLF emissions lies in the interaction of charged particles with the plasma of the ionosphere or magnetosphere. Laaspere et al (1964) suggests that at middle and high latitudes the occurrence of VLF emissions appears to be controlled mainly by emission processes rather than by the subsequent propagation of the emitted waves through the magnetosphere and ionosphere. From the theoretical calculations of Cory (1962a, 1962b), Laschy (1965), and the satellite observations of Leiphart et al (1962) and Gurnett and O'brien (1964) on the absorption of VLF signals at high and middle latitude stations, it appears that the ionospheric absorption plays an important role in the observation of whistlers and VLF emissions on ground at low latitudes.…”

Section: Introductionmentioning

confidence: 99%

Absorption of Very Low Frequency Waves in the Whistler Mode Propagation at Low Latitudes

Somayajulu

Tantry

1967

J. geomagn. geoelec

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The absorption contributed by F-region though generally smaller than that contributed by D and E layers is never negligible and at times of high F-layer concentrations during the magnetic storms the F-layer absorption may even be dominant.The absorption of VLF waves is low at night and as such can not explain the low occurrence of whistlers during night time. However, when the angle between the magnetic field and the wave normal is taken into account it is found that the absorption index increases considerably and hence the whistler energy may not be received on the ground especially at geomagnetic latitudes below 15.Comparing the computed values of absorption of VLF waves by Altman and Cory at 40 geomagnetic latitude and Laschy at 55 latitude with our values, for low latitudes it is found that the absorption increases rapidly as the latitude decreases which is in conformity with the results of Helliwell and Altman and Cory.

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Chorus, hiss, and other audio-frequency emissions at stations of the whistlers-east network

Cited by 30 publications

References 20 publications

VLF emissions during magnetic storms and their association with 40-keV electrons

VLF emissions during magnetic storms and their association with 40-keV electrons

URSI National Committee Report, XIV General Assembly, Tokyo, September 1963: Commission 4. Magnetospheric Radio (8 Sections)

Absorption of Very Low Frequency Waves in the Whistler Mode Propagation at Low Latitudes

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