Temporal variation of particle precipitation in Erath's polar cap from DMSP observations

2021 ◽  
Author(s):  
Yanshi Huang ◽  
Shan Liang
Keyword(s):  
Impact Ionization ◽  
Temporal Variations ◽  
Particle Energy ◽  
Upper Atmosphere ◽  
Polar Cap ◽  
Polar Latitude ◽  
Line Region ◽  
Open Field Line ◽  
Low Energy Electron ◽  
Uniform Area

<p>Previous observations and simulations have shown that the low-energy electron precipitation in the cusp plays an important role in ionosphere and thermosphere through particle impact ionization and heating. In this study, we investigate the precipitating particles in the Earth's polar cap region, which is also an open-field line region as the cusp. In many numerical simulations of the upper atmosphere, the polar cap region is described as a uniform area with no spatial and temporal variations of the particle energy and fluxes. We analyze years of the particle observations from DMSP satellites to show the temporal variations of particle characteristics in the region poleward of 80 degree magnetic latitudes in this study. The results show the solar cycle, annual and seasonal variations of particle (electrons, ions) energy, number flux and energy flux in the polar cap. The results will be useful to improve the polar-latitude precipitating particle description in upper atmosphere modeling.</p>

scholarly journals Low-energy electron-impact ionization of helium

1998 ◽  
Vol 57 (5) ◽  
pp. R3161-R3164 ◽  
Author(s):  
Igor Bray ◽  
Dmitry V. Fursa ◽  
J. Röder ◽  
H. Ehrhardt
Keyword(s):  
Electron Impact ◽  
Impact Ionization ◽  
Electron Impact Ionization ◽  
Low Energy ◽  
Energy Electron ◽  
Low Energy Electron

scholarly journals Aurora and open magnetic flux during isolated substorms, sawteeth, and SMC events

2007 ◽  
Vol 25 (8) ◽  
pp. 1865-1876 ◽  
Author(s):  
A. D. DeJong ◽  
X. Cai ◽  
R. C. Clauer ◽  
J. F. Spann
Keyword(s):  
Magnetic Flux ◽  
Temporal Variations ◽  
Auroral Oval ◽  
Polar Cap ◽  
Expansion Phase ◽  
Magnetospheric Convection ◽  
Open Magnetic Flux ◽  
Open Flux ◽  
The Individual

Abstract. Using Polar UVI LBHl and IMAGE FUV WIC data, we have compared the auroral signatures and polar cap open flux for isolated substorms, sawteeth oscillations, and steady magnetospheric convection (SMC) events. First, a case study of each event type is performed, comparing auroral signatures and open magnetic fluxes to one another. The latitude location of the auroral oval is similar during isolated substorms and SMC events. The auroral intensity during SMC events is similar to that observed during the expansion phase of an isolated substorm. Examination of an individual sawtooth shows that the auroral intensity is much greater than the SMC or isolated substorm events and the auroral oval is displaced equatorward making a larger polar cap. The temporal variations observed during the individual sawtooth are similar to that observed during the isolated substorm, and while the change in polar cap flux measured during the sawtooth is larger, the percent change in flux is similar to that measured during the isolated substorm. These results are confirmed by a statistical analysis of events within these three classes. The results show that the auroral oval measured during individual sawteeth contains a polar cap with, on average, 150% more magnetic flux than the oval measured during isolated substorms or during SMC events. However, both isolated substorms and sawteeth show a 30% decrease in polar cap magnetic flux during the dipolarization (expansion) phase.

scholarly journals Multiscale modelling for tokamak pedestals

2018 ◽  
Vol 84 (2) ◽  
Author(s):  
I. G. Abel ◽  
A. Hallenbert
Keyword(s):  
First Principles ◽  
Detailed Comparison ◽  
Multiscale Approach ◽  
Systems Of Equations ◽  
Line Region ◽  
Open Field Line ◽  
Small Parameters ◽  
The Relationship ◽  
Kinetic Physics ◽  
Current Modelling

Pedestal modelling is crucial to predict the performance of future fusion devices. Current modelling efforts suffer either from a lack of kinetic physics, or an excess of computational complexity. To ameliorate these problems, we take a first-principles multiscale approach to the pedestal. We will present three separate sets of equations, covering the dynamics of edge localised modes (ELMs), the inter-ELM pedestal and pedestal turbulence, respectively. Precisely how these equations should be coupled to each other is covered in detail. This framework is completely self-consistent; it is derived from first principles by means of an asymptotic expansion of the fundamental Vlasov–Landau–Maxwell system in appropriate small parameters. The derivation exploits the narrowness of the pedestal region, the smallness of the thermal gyroradius and the low plasma$\unicode[STIX]{x1D6FD}$(the ratio of thermal to magnetic pressures) typical of current pedestal operation to achieve its simplifications. The relationship between this framework and gyrokinetics is analysed, and possibilities to directly match our systems of equations onto multiscale gyrokinetics are explored. A detailed comparison between our model and other models in the literature is performed. Finally, the potential for matching this framework onto an open-field-line region is briefly discussed.

scholarly journals The Infrared, Optical and Ultraviolet Properties of Active Nuclei

1984 ◽  
Vol 110 ◽  
pp. 73-83
Author(s):  
Marie-Helene Ulrich
Keyword(s):  
Energy Distribution ◽  
Temporal Variations ◽  
Optical Polarization ◽  
Broad Line ◽  
Continuum Spectrum ◽  
Broad Line Region ◽  
Line Region ◽  
The Continuum

We review the important properties of active nuclei, in particular (i) the optical polarization and its relation to the jets found by VLBI (ii) the energy distribution and the temporal variations of the continuum spectrum and (iii) the distribution of the matter in the broad line region.

scholarly journals Inferring thermospheric composition from ionogram profiles: A calibration with the TIMED spacecraft

2019 ◽  
Author(s):  
Christopher J. Scott ◽  
Shannon Jones ◽  
Luke A. Barnard
Keyword(s):  
Dissociative Recombination ◽  
Temporal Variations ◽  
Molecular Ions ◽  
Upper Atmosphere ◽  
Global Network ◽  
G Factor ◽  
Satellite Drag ◽  
Important Region ◽  
Ion Production ◽  
Sensitive Function

Abstract. Measurements of thermospheric composition via ground-based instrumentation are challenging to make and so details about this important region of the upper atmosphere are currently sparse. We present a technique that deduces quantitative estimates of thermospheric composition from ionospheric data, for which there is a global network of stations. The visibility of the F1 peak in ionospheric soundings from ground-based instrumentation is a sensitive function of thermospheric composition. The ionospheric profile in the transition region between F1 and F2 peaks can be expressed by the G factor, a function of ion production rate and loss rates via ion-atom interchange reactions and dissociative recombination of molecular ions. This in turn can be expressed as the square of the ratio of ions lost via these processes. We compare estimates of the G factor obtained from ionograms recorded at Kwajalein (9° N, 167.2° E) for 25 times during which the TIMED spacecraft recorded approximately co-located measurements of the neutral thermosphere. We find a linear relationship between √G and the molecular: atomic composition ratio, with a gradient of 2.23 ± 0.17 and an offset of 1.66 ± 0.19. This relationship reveals the potential for using ground-based ionospheric measurements to infer quantitative variations in the composition of the neutral thermosphere. Such information can be used to investigate spatial and temporal variations in thermospheric composition which in turn has applications such as understanding the response of thermospheric composition to climate change and the efficacy of the upper atmosphere on satellite drag.

scholarly journals Coordinated Cluster, ground-based instrumentation and low-altitude satellite observations of transient poleward-moving events in the ionosphere and in the tail lobe

2001 ◽  
Vol 19 (10/12) ◽  
pp. 1589-1612 ◽  
Author(s):  
M. Lockwood ◽  
H. Opgenoorth ◽  
A. P. van Eyken ◽  
A. Fazakerley ◽  
J.-M. Bosqued ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Solar Wind ◽  
Propagation Delay ◽  
Polar Cap ◽  
F Region ◽  
Electrons And Ions ◽  
Transient Events ◽  
Low Energy Electron ◽  
Convection Patterns ◽  
Magnetopause Reconnection

Abstract. During the interval between 8:00–9:30 on 14 January 2001, the four Cluster spacecraft were moving from the central magnetospheric lobe, through the dusk sector mantle, on their way towards intersecting the magnetopause near 15:00 MLT and 15:00 UT. Throughout this interval, the EISCAT Svalbard Radar (ESR) at Longyearbyen observed a series of poleward-moving transient events of enhanced F-region plasma concentration ("polar cap patches"), with a repetition period of the order of 10 min. Allowing for the estimated solar wind propagation delay of 75 ( ± 5) min, the interplanetary magnetic field (IMF) had a southward component during most of the interval. The magnetic footprint of the Cluster spacecraft, mapped to the ionosphere using the Tsyganenko T96 model (with input conditions prevailing during this event), was to the east of the ESR beams. Around 09:05 UT, the DMSP-F12 satellite flew over the ESR and showed a sawtooth cusp ion dispersion signature that also extended into the electrons on the equatorward edge of the cusp, revealing a pulsed magnetopause reconnection. The consequent enhanced ionospheric flow events were imaged by the SuperDARN HF backscatter radars. The average convection patterns (derived using the AMIE technique on data from the magnetometers, the EISCAT and SuperDARN radars, and the DMSP satellites) show that the associated poleward-moving events also convected over the predicted footprint of the Cluster spacecraft. Cluster observed enhancements in the fluxes of both electrons and ions. These events were found to be essentially identical at all four spacecraft, indicating that they had a much larger spatial scale than the satellite separation of the order of 600 km. Some of the events show a correspondence between the lowest energy magnetosheath electrons detected by the PEACE instrument on Cluster (10–20 eV) and the topside ionospheric enhancements seen by the ESR (at 400–700 km). We suggest that a potential barrier at the magnetopause, which prevents the lowest energy electrons from entering the magnetosphere, is reduced when and where the boundary-normal magnetic field is enhanced and that the observed polar cap patches are produced by the consequent enhanced precipitation of the lowest energy electrons, making them and the low energy electron precipitation fossil remnants of the magnetopause reconnection rate pulses.Key words. Magnetospheric physics (polar cap phenomena; solar wind – magnetosphere interactions; magnetosphere – ionosphere interactions)

Low Energy Electron Impact Ionization and Fragmentation: Cyclobutanone

1973 ◽  
Vol 51 (4) ◽  
pp. 624-627 ◽  
Author(s):  
Graham Richard Branton ◽  
Claudio Kong Nam Pua
Keyword(s):  
Energy Distribution ◽  
Electron Impact ◽  
Mass Spectrometer ◽  
Ionization Energy ◽  
Impact Ionization ◽  
Electron Impact Ionization ◽  
Low Energy ◽  
Energy Electron ◽  
Low Energy Electron

Cyclobutanone is shown to yield both C3H6+ and C2H2O+ ions on fragmentation under electron impact in a mass spectrometer. Using the energy distribution difference (EDD) technique the ionization energy of cyclobutanone is found to be 9.58 eV and the appearance potentials of the C3H6+ and C2H2O+ ions are found to be 9.85 and 10.53 eV, respectively.

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