| 1. |
- Han, D. -S, et al.
(författare)
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Coordinated observations of two types of diffuse auroras near magnetic local noon by Magnetospheric Multiscale mission and ground all-sky camera
- 2017
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Ingår i: Geophysical Research Letters. - : American Geophysical Union (AGU). - 0094-8276 .- 1944-8007. ; 44:16, s. 8130-8139
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Tidskriftsartikel (refereegranskat)abstract
- Structured diffuse auroras are often observed near magnetic local noon (MLN), but their generation mechanisms are poorly understood. We have found that two types of structured diffuse auroras with obviously different dynamical properties often coexist near MLN. One type usually drifts from low to high latitude with higher speed and shows pulsation. The other type is always adjacent to the discrete aurora oval and drifts together with nearby discrete aurora with much lower speed. Using coordinated observations from MMS and ground all-sky imagers, we found that the two types of diffuse auroras are well correlated with number density increase of O+ (from the ionosphere) and of He2+ (from magnetosheath) ions, respectively. These observations indicate that mangetosheath particles penetrated into the magnetosphere also can play an important role for producing the dayside diffuse aurora. In addition, for the first time, electron cyclotron harmonic waves are observed associated with dayside diffuse aurora.
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| 2. |
- Li, J., et al.
(författare)
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Zipper-like" periodic magnetosonic waves : Van Allen Probes, THEMIS, and magnetospheric multiscale observations
- 2017
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Ingår i: Journal of Geophysical Research - Space Physics. - : AMER GEOPHYSICAL UNION. - 2169-9380 .- 2169-9402. ; 122:2, s. 1600-1610
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Tidskriftsartikel (refereegranskat)abstract
- An interesting form of "zipper-like" magnetosonic waves consisting of two bands of interleaved periodic rising-tone spectra was newly observed by the Van Allen Probes, the Time History of Events and Macroscale Interactions during Substorms (THEMIS), and the Magnetospheric Multiscale (MMS) missions. The two discrete bands are distinct in frequency and intensity; however, they maintain the same periodicity which varies in space and time, suggesting that they possibly originate from one single source intrinsically. In one event, the zipper-like magnetosonic waves exhibit the same periodicity as a constant-frequency magnetosonic wave and an electrostatic emission, but the modulation comes from neither density fluctuations nor ULF waves. A statistical survey based on 3.5 years of multisatellite observations shows that zipper-like magnetosonic waves mainly occur on the dawnside to noonside, in a frequency range between 10 f(cp) and f(LHR). The zipper-like magnetosonic waves may provide a new clue to nonlinear excitation or modulation process, while its cause still remains to be fully understood.
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| 3. |
- Bortnik, J., et al.
(författare)
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An Observation Linking the Origin of Plasmaspheric Hiss to Discrete Chorus Emissions
- 2009
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Ingår i: Science. - : American Association for the Advancement of Science (AAAS). - 0036-8075 .- 1095-9203. ; 324:5928, s. 775-778
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Tidskriftsartikel (refereegranskat)abstract
- A long-standing problem in the field of space physics has been the origin of plasmaspheric hiss, a naturally occurring electromagnetic wave in the high-density plasmasphere (roughly within 20,000 kilometers of Earth) that is known to remove the high-energy Van Allen Belt electrons that pose a threat to satellites and astronauts. A recent theory tied the origin of plasmaspheric hiss to a seemingly different wave in the outer magnetosphere, but this theory was difficult to test because of a challenging set of observational requirements. Here we report on the experimental verification of the theory, made with a five-satellite NASA mission. This confirmation will allow modeling of plasmaspheric hiss and its effects on the high-energy radiation environment.
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| 4. |
- Nishimura, Y., et al.
(författare)
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Estimation of magnetic field mapping accuracy using the pulsating aurora-chorus connection
- 2011
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Ingår i: Geophysical Research Letters. - 0094-8276 .- 1944-8007. ; 38, s. L14110-
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Tidskriftsartikel (refereegranskat)abstract
- Although magnetic field models are widely used in magnetosphere-ionosphere coupling studies to perform field-line mapping, their accuracy has been difficult to estimate experimentally. Taking advantage of the high correlation between lower-band chorus and pulsating aurora, we located the THEMIS spacecraft footprint within similar to km accuracy and calculated the differences from mappings given in widely-used Tsyganenko models. Using 13 conjunctions of the THEMIS spacecraft and ground-based imagers, we found that the Tsyganenko model footprints were located within 1 degrees-2 degrees magnetic latitude and 0.1-0.2 h magnetic local time of our derived footprint. The deviation between the footprints has a consistent dependence on geomagnetic activity. Our results showed that the real magnetic field tends to be less stretched than that in the Tsyganenko models during quiet times and comparable to or more stretched during disturbed times. This approach can be used to advance modeling of field lines that connect to the near-Earth plasma sheet.
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| 5. |
- Nishimura, Y., et al.
(författare)
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Identifying the Driver of Pulsating Aurora
- 2010
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Ingår i: Science. - : American Association for the Advancement of Science (AAAS). - 0036-8075 .- 1095-9203. ; 330:6000, s. 81-84
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Tidskriftsartikel (refereegranskat)abstract
- Pulsating aurora, a spectacular emission that appears as blinking of the upper atmosphere in the polar regions, is known to be excited by modulated, downward-streaming electrons. Despite its distinctive feature, identifying the driver of the electron precipitation has been a long-standing problem. Using coordinated satellite and ground-based all-sky imager observations from the THEMIS mission, we provide direct evidence that a naturally occurring electromagnetic wave, lower-band chorus, can drive pulsating aurora. Because the waves at a given equatorial location in space correlate with a single pulsating auroral patch in the upper atmosphere, our findings can also be used to constrain magnetic field models with much higher accuracy than has previously been possible.
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| 6. |
- Nishimura, Y., et al.
(författare)
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Multievent study of the correlation between pulsating aurora and whistler mode chorus emissions
- 2011
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Ingår i: Journal of Geophysical Research. - 0148-0227 .- 2156-2202. ; 116, s. A11221-
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Tidskriftsartikel (refereegranskat)abstract
- A multievent study was performed using conjugate measurements of the Time History of Events and Macroscale Interactions during Substorms (THEMIS) spacecraft and an all-sky imager during periods of intense lower-band chorus waves. The thirteen identified cases support our previous finding, based on two events, that the intensity modulation of lower-band chorus near the magnetic equator is highly correlated with quasiperiodic pulsating auroral emissions near the spacecraft's magnetic footprint, indicating that lower-band chorus is the driver of the pulsating aurora. Furthermore, we identified a fortuitous measurement made simultaneously by two THEMIS spacecraft with small spatial separation. The two spacecraft were found to be located in a single pulsating chorus patch and the spacecraft footprints were in the same pulsating auroral patch when intense chorus bursts were measured simultaneously, whereas only one of the spacecraft's footprints was in a patch when the other spacecraft did not detect intense chorus. On the basis of this event, we can estimate the pulsating chorus patch size by mapping the pulsating auroral patches from the ionosphere toward the magnetic equator, giving a roughly circular region of similar to 5000 km diameter for corresponding azimuthally elongated patches with similar to 100 km size in the ionosphere. Using a ray-tracing-based calculation of the divergence of chorus raypaths from a point source, together with the corresponding resonant energies, we found that the chorus patch size is most probably not a result of ray divergence but a property of the wave excitation region.
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| 7. |
- Dimou, Konstantinos, et al.
(författare)
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Generic link layer : A solution for multi-radio transmission diversity in communication networks beyond 3G
- 2005
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Ingår i: VTC2005-FALL. - 0780391527 ; , s. 1672-1676
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Konferensbidrag (refereegranskat)abstract
- Communication systems beyond 3G (B3G) will consist of a mixture of radio access technologies. For such systems the challenge is to provide a multi-radio access architecture that facilitates the interconnection of heterogeneous radio access networks and supports efficiently the various services. Achieving this interconnection in a transparent way for users and services requires extensions at link layer level. The Generic Link Layer (GLL), as proposed in the context of the Ambient Networks (AN) project addresses this challenge. The principal role of GLL within the AN multi-radio access architecture is to integrate different Radio Access Technologies (RATs) at the link layer and to facilitate their efficient interworking. A feature that is enabled by the use of GLL is termed multi-radio transmission diversity (MRTD). It implies a well-defined split of a data-flow over the available RATs; the main benefits thereby are gain in user QoS, in spectral efficiency and in robustness. In this paper we give the system architecture and the GLL functions required for the realization of MRTD. Then, the specific scenario of cooperation between UMTS and IEEE 802.11 is discussed.
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| 8. |
- Li, Jinxing, et al.
(författare)
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Local Excitation of Whistler Mode Waves and Associated Langmuir Waves at Dayside Reconnection Regions
- 2018
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Ingår i: Geophysical Research Letters. - : American Geophysical Union (AGU). - 0094-8276 .- 1944-8007. ; 45:17, s. 8793-8802
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Tidskriftsartikel (refereegranskat)abstract
- In the Earth's dayside reconnection boundary layer, whistler mode waves coincide with magnetic field openings and the formation of the resultant anisotropic electrons. Depending on the energy range of anisotropic electrons, whistlers can grow at frequencies in the upper and/or lower band. Observations show that whistler mode waves modulate Langmuir wave amplitude as they propagate toward the X line. Observations of whistler mode wave phase and Langmuir waves packets, as well as coincident electron measurements, reveal that whistler mode waves can accelerate electrons via Landau resonance at locations where E(parallel to)is antiparallel to the wave propagation direction. The accelerated electrons produce localized beams, which subsequently drive the periodically modulated Langmuir waves. The close association of those two wave modes reveals the microscale electron dynamics in the exhaust region, and the proposed mechanism could potentially be applied to explain the modulation events observed in planetary magnetospheres and in the solar wind. Plain Language Summary The Sun's and Earth's magnetic field can merge and reconnect on dayside magnetopause. Using measurements from NASA's MMS spacecraft, we report that a class of electromagnetic wave, named whistler mode wave, coincides with the reconnected magnetic field lines. Besides, those whistlers are observed to modulate the electric field oscillations, known as Langmuir waves. Using high-resolution wave and particle measurements, we explain that the whistlers are locally excited when electrons from both sides of the magnetopause mix and form an unstable distribution. The modulated Langmuir waves are generated due to localized electron acceleration, which occurs when the velocity of electrons matches that of whistlers in the direction along the magnetic field. The whistler mode waves and associated Langmuir waves can be used as an additional tool to remotely sense the occurrence of magnetic reconnections.
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| 9. |
- Li, W., et al.
(författare)
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Global distribution of whistler-mode chorus waves observed on the THEMIS spacecraft
- 2009
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Ingår i: Geophysical Research Letters. - 0094-8276 .- 1944-8007. ; 36:9, s. L09104-
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Tidskriftsartikel (refereegranskat)abstract
- Whistler mode chorus waves are receiving increased scientific attention due to their important roles in both acceleration and loss processes of radiation belt electrons. A new global survey of whistler-mode chorus waves is performed using magnetic field filter bank data from the THEMIS spacecraft with 5 probes in near-equatorial orbits. Our results confirm earlier analyses of the strong dependence of wave amplitudes on geomagnetic activity, confinement of nightside emissions to low magnetic latitudes, and extension of dayside emissions to high latitudes. An important new finding is the strong occurrence rate of chorus on the dayside at L > 7, where moderate dayside chorus is present > 10% of the time and can persist even during periods of low geomagnetic activity.
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