Pitch-angle scattering of energetic protons in the magnetotail current sheet as the dominant source of their isotropic precipitation into the nightside ionosphere

Сергеев, В. А.; Sazhina, Elena; Tsyganenko, N. A.; Lundblad, J.Å.; Søraas, F.

doi:10.1016/0032-0633(83)90103-4

Cited by 281 publications

(327 citation statements)

References 16 publications

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“…Because of the restricted local time of these bursts near the midnight sector and the fact that the large-timescale bursts tend to occur near the edge of the outer radiation belt (Figures 1 and 2), these precipitation bands can also relate to the breakdown in adiabatic motions in a region where the gyroradii of the electrons are comparable to the curvature of magnetic field lines [e.g., Sergeev et al, 1983]. SAMPEX observation of these bursts in the midnight sector include significant contribution from the trapped population owing to the orbit characteristic.…”

Section: Discussionmentioning

confidence: 99%

SAMPEX observations of precipitation bursts in the outer radiation belt

Nakamura¹,

Isowa²,

Kamide³

et al. 2000

J. Geophys. Res.

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Abstract. The occurrence frequency of precipitation bursts of > 1 MeV electrons in the outer radiation belt is examined using data from the SAMPEX satellite. Electron burst characteristics shown in this paper include the dependence of the precipitation on magnetic local time, radial distance and geomagnetic activity. Precipitation bursts with timescales < 1 s, i.e., microbursts, are studied in detail, including their dependence on the phases of geomagnetic storms. It is found that precipitation bursts occur typically in the region between L = 4 and L = 6. Microbursts tend to occur at L lower than the bursts with timescales of several tens of seconds. The number of observed microbursts significantly increases during storms, appearing mainly in the morning sector early in the recovery phase of storms. These findings suggest that the microbursts may be due to interactions with electron whistler waves, which take place near the dawnside plasmapause in the density irregularities that are perhaps created in the "recovering" plasmasphere. The prevalence of bursty precipitation indicates that this enhanced loss component of the relativistic electron flux should be taken into account in any quantitative model of relativistic electron acceleration processes.

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Section: Discussionmentioning

confidence: 99%

SAMPEX observations of precipitation bursts in the outer radiation belt

Nakamura¹,

Isowa²,

Kamide³

et al. 2000

J. Geophys. Res.

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“…0148-0227/97/96JA-02797509.00 95 gies higher than a critical one has been investigated by various authors [e.g., Imhof et al, 1977;Sergeev et al, 1983]. Popielawska et al [1985] and Sergeev and Malkov [1988] used various magnetosphere models including that of Tsyganenko [1987] to test whether it is possible to use these models to reproduce the observed sharp decrease of threshold energy with increasing L. The isotropy boundary was typically at higher latitudes than presented in previous experimental papers and was generally less steep in the profile of threshold energy versus L. Further calculations with refined models of Tsyganenko [1989] were performed by Popielawska and Zwolakowska [1991].…”

Section: Paper Number 96ja02797mentioning

confidence: 99%

“…Under these conditions one would not expect trapping to exist [e.g., Sergeev et al, 1983], and consequently the pitch angle distributions at low satellite altitudes would be nearly isotropic over the upper hemisphere at energies such that the gyroradii are sut•iciently large. This phenomenon is illustrated in Figure 1 in which the energy spectra measured at one position of the UARS satellite at different pitch angles are plotted.…”

Section: Introductionmentioning

confidence: 99%

Characteristics of electrons at the trapping boundary of the radiation belt

Imhof¹,

Chenette²,

Gaines³

et al. 1997

J. Geophys. Res.

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Abstract. New measurements are presented of the L-dependent energy threshold for electron flux isotropy observed near midnight from low-altitude satellites. These data provide the basis for an important remote sensing of the geomagnetic field configurations near the outer edge of the radiation belt. The threshold energy for isotropy observed at low altitudes is interpreted as providing a measure of the effective scale length of inhomogeneity of the geomagnetic field near the equator at high altitude. The data presented were obtained with electron spectrometers on the UARS satellite providing flux and energy spectrum measurements for energies between 30 keV and 5 MeV simultaneously at a variety of pitch angles. On certain orbits the UARS satellite achieved fine L shell resolution and nearly simultaneous measurements at different local times. With this previously unavailable L shell resolution the threshold energy for isotropy versus L shell curves near midnight have shown slopes steeper than 20 MeV per unit L on 20% of the cases, using the International Geomagnetic Reference Field (IGRF) 85 magnetic field model. On 66% of the satellite passes the slopes at the two boundary crossings within 01 to 06 hours in magnetic local time and about 10 min in elapsed time were within a factor of 3 of each other. The L shell at which isotropy occurs above a given threshold energy is found to be generally lower and the slope steeper at times of high geomagnetic disturbance. For the analysis presented here, if isotropy occurs when the radius of field line curvature is less than 10 times the gyroradius of the particles, the scale lengths of inhomogeneities were always found to be less than 2900 km, and in 99% of the cases the scale lengths were greater than 73 km.

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“…However, in the regions where the particle gyroradius ρ becomes comparable to the magnetic curvature radius (R c ) and adiabatic approximation is violated, the pitch-angle scattering fills the loss cone and leads to particle precipitation into the ionosphere. For the protons with energies ranging between a few tens and 100 keV, the boundary between adiabatic and nonadiabatic particle motion occurs near the center of the tail current sheet on the nightside at r ∼ 6 − 9 Re (e.g., Sergeev and Tsyganenko, 1982;Shevchenko et al, 2010;Wang et al, 2012;Yue et al, 2014). Tailward of that boundary a strong current sheet scattering (CSS) provides the nearly isotropic proton angular distributions in the tail plasma sheet (e.g., Ganushkina et al, 2005;Yue et al, 2014) whose precipitation forms an extended isotropic proton precipitation region, the proton auroral oval (Sergeev et al, 1983;Donovan et al, 2003;Meurant et al, 2007).…”

Section: Introductionmentioning

confidence: 99%

Magnetospheric conditions near the equatorial footpoints of proton isotropy boundaries

et al. 2015

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Abstract. Data from a cluster of three THEMIS (Time History of Events and Macroscale Interactions during Substorms) spacecraft during February-March 2009 frequently provide an opportunity to construct local data-adaptive magnetospheric models, which are suitable for the accurate mapping along the magnetic field lines at distances of 6-9 Re in the nightside magnetosphere. This allows us to map the isotropy boundaries (IBs) of 30 and 80 keV protons observed by low-altitude NOAA POES (Polar Orbiting Environmental Satellites) to the equatorial magnetosphere (to find the projected isotropy boundary, PIB) and study the magnetospheric conditions, particularly to evaluate the ratio K IB (R c /r c ; the magnetic field curvature radius to the particle gyroradius) in the neutral sheet at that point. Special care is taken to control the factors which influence the accuracy of the adaptive models and mapping. Data indicate that better accuracy of an adaptive model is achieved when the PIB distance from the closest spacecraft is as small as 1-2 Re. For this group of most accurate predictions, the spread of K IB values is still large (from 4 to 32), with the median value K IB ∼ 13 being larger than the critical value K cr ∼ 8 expected at the inner boundary of nonadiabatic angular scattering in the current sheet. It appears that two different mechanisms may contribute to form the isotropy boundary. The group with K ∼ [4, 12] is most likely formed by current sheet scattering, whereas the group having K IB ∼ [12, 32] could be formed by the resonant scattering of low-energy protons by the electromagnetic ion-cyclotron (EMIC) waves. The energy dependence of the upper K limit and close proximity of the latter event to the plasmapause locations support this conclusion.We also discuss other reasons why the K ∼ 8 criterion for isotropization may fail to work, as well as a possible relationship between the two scattering mechanisms.

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Pitch-angle scattering of energetic protons in the magnetotail current sheet as the dominant source of their isotropic precipitation into the nightside ionosphere

Cited by 281 publications

References 16 publications

SAMPEX observations of precipitation bursts in the outer radiation belt

SAMPEX observations of precipitation bursts in the outer radiation belt

Characteristics of electrons at the trapping boundary of the radiation belt

Magnetospheric conditions near the equatorial footpoints of proton isotropy boundaries

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