On 24 November 2012, an interval of polar cap patches was identified by an all‐sky airglow imager located near the dayside cusp. During the interval, the successive appearance of poleward moving ...auroral forms (PMAFs) was detected, which are known to represent ionospheric manifestations of pulsed magnetic reconnections at the dayside magnetopause. All of the patches observed during the interval appeared from these transient auroral features (i.e., there was a one‐to‐one correspondence between PMAFs and newly created baby patches). This fact strongly suggests that patches can be directly and seamlessly created from a series of PMAFs. The optical intensities of the baby patches were 100–150 R, which is slightly lower than typical patch luminosity on the nightside and may imply that PMAF‐induced patches are generally low density. The generation of such patches could be explained by impact ionization due to soft particle precipitation into PMAFs traces. In spite of the faint signature of the baby patches, two coherent HF radars of the SuperDARN network observed backscatter echoes in the central polar cap, which represented signatures of plasma irregularities associated with the baby patches. These indicate that patches created from PMAFs have the potential to affect the satellite communications environment in the central polar cap region.
Key Points
Simultaneous observations of PMAF and polar cap patches near the cusp
Patches are directly and seamlessly produced from PMAF
PMAF‐generated patches are low density but accompanied by irregularities
Past satellite observations in the polar region at about 4,000 km altitude have reported lower hybrid waves (LHWs) and their harmonics, but the excitation mechanism of the harmonic LHWs has not yet ...been clarified. We perform one‐dimensional, electromagnetic, full particle‐in‐cell simulations by setting parameter values in the ranges observed by the satellite. The results from the two runs, that is, for ωpe/Ωe = 0.1 and 0.2, show that the energetic ions can generate the harmonic LHWs in both cases. However, in the former case, more harmonic LHWs with larger amplitudes are created and stronger background‐ion acceleration is observed. Thus, our present simulations have solved a previously unsolved problem, revealing the possibility that harmonic LHWs are involved in ion acceleration phenomena commonly observed in the polar region, such as ion outflow.
Plain Language Summary
The lower hybrid waves (LHWs), which can be excited by high‐energy ions with an anisotropic velocity distribution, are often observed in the polar region of the Earth's magnetosphere. Recently, increasing attention has been paid to the harmonics of the LHWs, which have been occasionally reported in the Earth's magnetosphere, but their excitation mechanism remains unclear. In this letter, we perform one‐dimensional, electromagnetic, particle‐in‐cell simulations to investigate the development of the LHWs and their harmonic waves. The simulations are based on the observation of harmonic LHWs in the polar region of the Earth's magnetosphere. We have demonstrated that high‐energy ions with a ring‐like velocity distribution can generate the LHWs and their harmonic waves, and background ions are strongly accelerated when harmonic LHWs are strongly excited. Thus, our simulations have solved a previously unsolved problem, revealing the possibility that the harmonic LHWs are involved in ion acceleration phenomena commonly observed in the polar region, such as ion outflow.
Key Points
The harmonic structure of lower hybrid waves (LHWs) was reported at 4,000 km altitude in the polar region, but its excitation mechanism remains unclear
We have demonstrated that ring‐like energetic ions can generate the harmonic structure of LHWs
The ion acceleration can be strongly enhanced when the harmonic LHWs can be strongly excited
In the cusp region, a significantly enhanced thermospheric mass density is commonly observed around 400 km altitude. Despite a number of studies, the enhancement mechanism has not been fully ...characterized. In order to determine how the Joule heating and resultant mass density enhancements are generated in the F region of the ionosphere during a few hours after the Alfvén resonator modes are set up, we have developed a new efficient method to calculate Alfvén waves. In this method, the Fourier transform was used, and Alfvén waves were solved as frequency‐domain boundary value problems. We employed a two‐dimensional local model and performed five modeling runs. The result from the modeling runs shows that the Alfvén resonator modes generate significant neutral upwelling at ∼300 km altitude, which creates a “cell” of the neutral mass density enhancement at altitudes centered between 350 and 400 km. This cell becomes evident roughly 1 hr after the Alfvén resonator modes are set up, and this region continues to exist stably for 2 more hours. A fractional mass density enhancement at 400 km altitude 3 hr after the Alfvén resonator modes having an Alfvénic field‐aligned current of 20 μAm−2 $\mu \mathrm{A}{\mathrm{m}}^{-2}$ at the top boundary are set up reaches ∼30%, which is consistent with the result obtained from satellite observations. In terms of the Poynting flux, this corresponds to ∼20 mWm−2, which is also consistent with previous satellite observations.
Key Points
A new calculation method of Alfvén waves presented here allows us to capture spatially variable features in the cusp
Alfvén resonator modes generate significant neutral upwelling at ∼300 km altitude, and a cell of the neutral mass density enhancement is created at ∼400 km altitude
Alfvénic Poynting flux of roughly 20 mWm−2 can explain the average ∼30% increase in mass density fraction observed at 400 km altitude
On the equatorward side of the dayside cusp there often appear diffuse auroras. In this paper, we report north‐south aligned discrete aurora events and show the spatial relationships between the ...auroras and the plasma flow. Several events of the north‐south aligned discrete auroral structures were identified using an all‐sky imager at Longyearbyen, Svalbard, during the recovery of a moderately disturbed period on 8 December 2013. During a brief interval of the moderately disturbed period, the cusp shifted to higher latitudes; as a result, the field‐aligned beam of the EISCAT Svalbard Radar (ESR) passed through the northern portion of the north‐south aligned auroral structures. Simultaneous observations from the all‐sky imager and ESR reveal that enhancements in ion temperature (caused by fast ion flow) occurred near the eastward and westward boundaries of the north‐south aligned auroral structures. However, within the region of the most enhanced aurora, the ion temperature enhancements were moderately suppressed. These features indicate that the ion flow slows down in the region of electron precipitation responsible for north‐south aligned auroral structures. We can quantitatively interpret the slowdown of the flow as the reduction of the electric field due to the polarization effect in the north‐south aligned region of the increased Pedersen conductivity. It thus appears that the magnetospheric source of the north‐south aligned discrete auroras is a limited area embedded in the region of plasma flow toward the dayside magnetopause.
Key Points
First simultaneous observations of north‐south aligned discrete auroras equatorward of the cusp from an all‐sky imager and EISCAT are presented
A decrease in the elevated ion temperature is coincident with the north‐south aligned aurora
The plasma flow slows in the middle of the east‐west dimension of the north‐south aligned aurora
Edge of polar cap patches Hosokawa, K.; Taguchi, S.; Ogawa, Y.
Journal of geophysical research. Space physics,
April 2016, 2016-04-00, 20160401, Letnik:
121, Številka:
4
Journal Article
Recenzirano
Odprti dostop
On the night of 4 December 2013, a sequence of polar cap patches was captured by an all‐sky airglow imager (ASI) in Longyearbyen, Norway (78.1°N, 15.5°E). The 630.0 nm airglow images from the ASI of ...4 second exposure time, oversampled the emission of natural lifetime (with quenching) of at least ∼30 sec, introduce no observational blurring effects. By using such high‐quality ASI images, we succeeded in visualizing an asymmetry in the gradients between the leading/trailing edges of the patches in a 2‐D fashion. The gradient in the leading edge was found to be 2–3 times steeper than that in the trailing edge. We also identified fingerlike structures, appearing only along the trailing edge of the patches, whose horizontal scale size ranged from 55 to 210 km. These fingers are considered to be manifestations of plasma structuring through the gradient‐drift instability (GDI), which is known to occur only along the trailing edge of patches. That is, the current 2‐D observations visualized, for the first time, how GDI stirs the patch plasma and such a mixing process makes the trailing edge more gradual. This result strongly implies a close connection between the GDI‐driven plasma stirring and the asymmetry in the large‐scale shape of patches and then suggests that the fingerlike structures can be used as markers to estimate the fine‐scale structure in the plasma flow within patches.
Key Points
Fingerlike signatures of plasma instability are identified within polar cap patches
Gradient in the leading edge of patches is sharper than that in the trailing edge
Plasma mixing through the plasma instability determines the shape of patches
Prognostic scores have been developed to estimate the risk of recurrence and the probability of survival after nephrectomy for renal cell carcinoma (RCC). The use of these tools, despite being ...helpful to plan a customized schedule of follow-up, to the patient's tailored counselling and to select individuals who could potentially benefit from adjuvant treatment, currently is not routine, due to their relative complexity and to the lack of histological data (i.e. necrosis).
We developed a simple score called GRade, Age, Nodes and Tumor (GRANT) based on four easily obtained parameters: Fuhrman grade, age, pathological nodal status and pathological tumor size. Patients with 0 or 1 factor are classified as favorable risk, whereas patients with two or more risk factors as unfavorable risk. The large population of RCC patients from the ASSURE adjuvant trial was used as independent dataset for this external validation, to investigate the prognostic value of the new score in terms of disease-free survival and overall survival and to evaluate its possible application as predictive tool. Statistical analyses were carried out by the Department of Biostatistics & Computational Biology, Dana-Farber Cancer Institute (Boston, USA) for the ASSURE trial patients’ population.
The performance of the new model is similar to that of the already validated score systems, but its strength, compared with the others already available, is the ease and clarity of its calculation, with great speed of use during the clinical practice. Limitations are the use of the Fuhrman nuclear grade, not valid for rare histologies, and the TNM classification modifications over time.
The GRANT score demonstrated its potential usefulness for clinical practice.
NCT00326898.
To understand the features of the quasistatic field‐aligned currents (FACs) consisting of multiple mesoscale (∼10–100 km) upward and downward FAC regions in the duskside auroral oval, we examined the ...magnetic field data obtained through the constellation measurements of Swarm satellites for a duration of more than three years. We introduced a method of automated event identification and took the events in 577 satellite orbits that pass through the high‐latitude part of the 14–18 magnetic local time auroral oval. The results of the analysis reveal that the occurrence ratio of the FAC events increases with the IMF BZ, and that the event can be detected at a ratio exceeding 20% for BZ greater than 1 nT. This indicates that the quasistatic mesoscale FACs in the duskside sector are pertinent to a northward IMF condition and that they are not a simple remnant of the diminished Region 1. The results also show that the FAC density tends to increase with the solar wind proton density, implying that the latter is directly associated with FAC generation. The FAC events can occur in a wide range of solar zenith angles, that is, 65–135°, indicating that whether the ionosphere is sunlit or dark is not crucial for the appearance of the event. These results strongly suggest that multiple mesoscale FACs are produced in the low‐latitude boundary layer through a mechanism related to solar wind plasma entry processes that can be more easily attained as the northward component of the IMF increases.
Key Points
As the IMF BZ increases, mesoscale multiple quasistatic field‐aligned currents embedded in the diminished dusk Region 1/2 become prominent
The density of the mesoscale field‐aligned currents tends to increase with the solar wind proton density
The event appears regardless of whether the ionosphere is sunlit or dark
During northward interplanetary magnetic field (IMF), irregular magnetic perturbations were observed in the duskside aurora oval via Swarm satellites instead of large‐scale Region 1/2 magnetic ...perturbations. By taking advantage of Swarm constellation measurements, and their conjugate observations with an all‐sky imager on the ground, the features of the irregular magnetic perturbations were examined. Detailed analysis of the data from Swarm A and Swarm C for two events demonstrated that the irregular magnetic perturbations are a result of highly structured quasistatic field‐aligned currents (FACs), not dynamic Alfvén waves. The typical latitudinal size of the upward FACs is 20–30 km. In each region of the upward FACs, 630‐nm aurora emissions are relatively strong, indicating that the energy flux of precipitating electrons having energies of a few hundred electron volts is high in each of the upward FAC regions. The enhanced mesoscale auroras continued to exist for at least approximately 30 min. These indicate that the mesoscale FAC structures also have quasipersistent features. The precipitating particle data from the Defense Meteorological Satellite Program satellite, which passed through the field of view of the all‐sky imager, indicate that the source of the precipitating particles is the duskside low‐latitude boundary layer (LLBL). We suggest that the highly structured quasipersistent FACs flow along the magnetic field lines connected to the duskside LLBL where cold dense ions exist. The highly structured FACs in the duskside aurora oval are the phenomena that are pertinent to the magnetosphere for a northward IMF condition, not a simple remnant of the typical Region 1.
Key Points
Irregular magnetic perturbations occur in the dusk part of the auroral oval instead of Region 1/2 magnetic perturbations
The irregular magnetic perturbations are a result of highly structured quasistatic field‐aligned currents
The highly structured field‐aligned currents are the phenomena pertinent to the magnetosphere for a northward IMF condition
We describe herein the synthesis of solid Au@Pd and hollow AgPd nanoflowers displaying controlled sizes and compositions in order to investigate how their size, composition, and the presence of Au in ...the core of the nanoparticles influence their catalytic performance toward both liquid and gas-phase transformations. While the size and composition of Au@Pd and AgPd the nanoflowers could be controlled as function of growth time, their structure (solid or hollow) was dependent on the nature of the seeds employed for the synthesis, i.e., Au or Ag nanoparticles. Moreover, Au@Pd and AgPd nanoflowers were successfully supported onto commercial silica displaying truly uniform dispersion. The catalytic activities of Au@Pd and AgPd nanoflowers were investigated toward the 4-nitrophenol reduction and the benzene, toluene, and o-xylene (BTX) oxidation. The catalytic activities for the reduction of 4-nitrophenol decreased as follows: Au₅₈@Pd₄₂ > Au₂₇@Pd₇₃ > Ag₂₀Pd₈₀ and Ag₈Pd₉₂ > Au₁₂@Pd₈₈ > Ag₃₈Pd₆₂, suggesting that the Au core enhanced the catalytic activity relative to the hollow material when for Pd at.% was up to 80. Regarding the BTX oxidation, supported Au@Pd displayed higher catalytic activities than AgPd nanoflowers, also illustrating the role of the Au cores in the nanoflowers for improving catalytic performance. We believe these results may serve as a platform for the synthesis of Pd-based bimetallic nanomaterials that enable the correlation between these physical/chemical parameters and properties and thus optimized catalytic activities.
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