Modeling of occurrence frequencies of ion conics as a function of altitude and conic angle

Miyake, W.; Mukai, T.; Kaya, Nobuyuki

doi:10.1007/s00585-000-0047-5

Cited by 3 publications

(3 citation statements)

References 22 publications

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“…conics contain all the conics with a conic angle larger than 60 deg. The occurrence of conics with a conic angle larger than 80 deg has a peak around an altitude of 5000-6000 km and is decreased with altitude (Miyake et al, 2000a). Therefore, the intensity of LEFs around an altitude of 5000-6000 km is close to that associated with perpendicular conics, while the intensity of LEFs around 9000-10000 km is close to that associated with 60-deg conics.…”

Section: Correlation Between Lefs and Ion Conicsmentioning

confidence: 80%

Relationship between low-frequency electric-field fluctuations and ion conics around the cusp/cleft region

2006

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Abstract. We investigated the relationship between lowfrequency (0.2-4.0 Hz) electric-field fluctuations (LEFs) and ion conics around the dayside cusp/cleft region in the altitude range from 5000 to 100 00 km from observations made by the Akebono satellite. Ion conics were generally associated with intense LEFs. We found a significant correlation between the power spectral density of LEFs at any frequency and the energy of simultaneously observed ion conics. Ion conics with a conic angle near 90 deg and those more aligned with magnetic field lines both had an equivalent correlation with the local intensity of the LEFs. The LEFs associated with near-perpendicular ion conics were, however, generally more intense than those associated with folded conics. The difference was clearer for low-energy conics. These results are in agreement with a scenario of height-integrated heating of ions and energization of ions by electromagnetic energy supplied by local LEFs. Ions generally stay in the energization region during their upward motion along the field line, so that more folded ion conics with weak energization reach the same energy level as near-perpendicular conics with strong energization, due to the difference in integration time. The limit on residence time in the intense heating region causes the clearer difference for low-energy conics. We set up a simple model to examine the relationship between the energization rate and the evolution of ion conics along the field lines, and obtained good agreement with the observation results.

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Section: Correlation Between Lefs and Ion Conicsmentioning

confidence: 80%

Relationship between low-frequency electric-field fluctuations and ion conics around the cusp/cleft region

2006

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“…in an altitude range of 2500-6000 km from 0900 to 1500 MLT [Miyake et al, 2000], the start altitude was estimated on the basis of the altitude where the pitch angle becomes 120 , which is 1100-1500 km higher than the altitude of the estimated mirror point (1900-2030 UT), and v k at the altitude. The lower limit of the start altitude (h s ) in Table 1 is calculated assuming a constant v k during the transit time.…”

Section: Discussionmentioning

confidence: 99%

“…Although ion acceleration in the cusp/cleft is not clear, we performed a very rough estimation on the basis of Case 2 and the transit time of 4.5 min (v conv = 750 m/s). Since the typical cone angle of ion conics is >60 in an altitude range of 2500-6000 km from 0900 to 1500 MLT [Miyake et al, 2000], the start altitude was estimated on the basis of the altitude where the pitch angle becomes 120 , which is 1100-1500 km higher than the altitude of the estimated mirror point (1900( -2030, and v k at the altitude. The lower limit of the start altitude (h s ) in Table 1 is calculated assuming a constant v k during the transit time.…”

Section: Discussionmentioning

confidence: 99%

Storm‐time electron density enhancement in the cleft ion fountain

et al. 2012

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To determine the characteristics and origin of observed storm‐time electron density enhancements in the polar cap, and to investigate the spatial extent (noon‐midnight direction) of associated O+ ion outflows, we analyzed nearly simultaneous observations of such electron density enhancements from the Akebono satellite and ion upflows from the Polar satellite during a geomagnetic storm occurring on 6 April 2000. The Akebono satellite observed substantial electron density enhancements by a factor of ∼10–90 with a long duration of ∼15 h at ∼2 RE in the southern polar region. The Polar satellite outflow measurements in the northern polar cap at ∼7–4 RE exhibited velocity filtering of the ∼100 eV to ∼0 eV (from the spacecraft potential) ion outflow from the cleft ion fountain, with resultant temperatures declining from ∼3 eV to 0.03 eV with increasing distance from the cusp. Similar velocity filtering was detected in the southern polar cap at ∼1.8–3.5 RE. The region of O+ ion outflows with fluxes exceeding 5×108 /cm2/s (mapped to 1000 km altitude) extended ∼10° MLAT (∼1000 km) at the ionosphere from the cusp/cleft into the dayside polar cap at ∼2.5 RE. These coordinated Akebono‐Polar observations are consistent with the development of storm‐time electron density enhancements in the polar cap as a result of the bulk outflow of low‐energy plasma as part of the cleft ion fountain. The large spatial scale, large ion fluxes, and the long duration indicate significant supply of very‐low‐energy O+ ions to the magnetosphere through this region.

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Interplanetary magnetic field control of dayside ion conics

Miyake¹,

Mukai²,

Kaya³

2000

J. Geophys. Res.

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Abstract. Ion conics are frequently observed around the dayside cusp/cleft region and are supposed to be energized by an input of energy from the dayside magnetospheric boundary region. We examined possible influence of the interplanetary magnetic field (IMF) on dayside ion conics observed by the polar-orbiting Exos D (Akebono) satellite.We found the effect of By and B z components on the energy flux and occurrence frequency of ion conics. Ion conics are more energetic and more frequently observed when Bz is negative and the magnitude of By is large. The B z effect is likely to be attributed to the change in energy input to the ion energization region. The By effect may be also due to the increased energy input to the cusp/cleft region during large By period, suggesting that a reconnection-related energy input is responsible for dayside ion energization. An alternative interpretation of the By effect is that the convection pattern may affect the residence time in the ion energization region and therefore the efficiency of ion energization. We found that the polarity of By controls asymmetrical magnetic local time distribution of ion conics around the local noon, which is attributed to a possible effect of convection pattern on dayside ion energization. DataThe ion data for this study were acquired by the low-energy particle (LEP) instrument on the polar-orbiting Exos D (Akebono) satellite, which has an initial apogee and perigee of 10482 and 272 km, respectively [Oya and Tsuruda, 1990; Tsu-23,339

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Modeling of occurrence frequencies of ion conics as a function of altitude and conic angle

Cited by 3 publications

References 22 publications

Relationship between low-frequency electric-field fluctuations and ion conics around the cusp/cleft region

Relationship between low-frequency electric-field fluctuations and ion conics around the cusp/cleft region

Storm‐time electron density enhancement in the cleft ion fountain

Interplanetary magnetic field control of dayside ion conics

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