Spatial characteristics of wave-like structures in diffuse aurora obtained using optical observations

Abstract. We present the results of a statistical study using optical images from ALIS (Auroral Large Imaging System) to investigate the spatial and temporal variations of structures in diffuse aurora. Analysis of conjugate Reimei data shows that such fine structures are a result of modulation of high-energy precipitating electrons. Pitch angle diffusion into the loss cone due to interaction of whistler mode waves with plasma sheet electrons is the most feasible mechanism leading to high-energy electron precipitation. This suggests that the fine structure is an indication of modulations of the efficiency of the wave–particle interaction. The scale sizes and variations of these structures, mapped to the magnetosphere, can give us information about the characteristics of the modulating wave activity. We found the scale size of the auroral stripes and the spacing between them to be on average 13–14 km, which corresponds to 3–4 ion gyro radii for protons with an energy of 7 keV. The structures move southward with a speed close to zero in the plasma convection frame.

Download Full-text

The generation of Ganymede's diffuse aurora through pitch angle scattering

Annales Geophysicae ◽

10.5194/angeo-35-239-2017 ◽

2017 ◽

Vol 35 (2) ◽

pp. 239-252

Author(s):

Arvind K. Tripathi ◽

Rajendra P. Singhal ◽

Onkar N. Singh II

Keyword(s):

Electron Temperature ◽

Pitch Angle ◽

Atomic Oxygen ◽

Particle Interaction ◽

Distribution Functions ◽

Dissociative Excitation ◽

Kappa Distribution ◽

Loss Cone ◽

Whistler Mode ◽

Whistler Mode Waves

Abstract. Diffuse auroral intensities of neutral atomic oxygen OI λ1356 Å emission on Ganymede due to whistler mode waves are estimated. Pitch angle diffusion of magnetospheric electrons into the loss cone due to resonant wave–particle interaction of whistler mode waves is considered, and the resulting electron precipitation flux is calculated. The analytical yield spectrum approach is used for determining the energy deposition of electrons precipitating into the atmosphere of Ganymede. It is found that the intensities (4–30 R) calculated from the precipitation of magnetospheric electrons observed near Ganymede are inadequate to account for the observational intensities (≤ 100 R). This is in agreement with the conclusions reached in previous works. Some acceleration mechanism is required to energize the magnetospheric electrons. In the present work we consider the heating and acceleration of magnetospheric electrons by electrostatic waves. Two particle distribution functions (Maxwellian and kappa distribution) are used to simulate heating and acceleration of electrons. Precipitation of a Maxwellian distribution of electrons can produce about 70 R intensities of OI λ1356 Å emission for electron temperature of 150 eV. A kappa distribution can also yield a diffuse auroral intensity of similar magnitude for a characteristic energy of about 100 eV. The maximum contribution to the estimated intensity results from the dissociative excitation of O2. Contributions from the direct excitation of atomic oxygen and cascading in atomic oxygen are estimated to be only about 1 and 2 % of the total calculated intensity, respectively. The findings of this work are relevant for the present JUNO and future JUICE missions to Jupiter. These missions will provide new data on electron densities, electron temperature and whistler mode wave amplitudes in the magnetosphere of Jupiter near Ganymede.

Download Full-text

A study of fine structure of diffuse aurora with ALIS-FAST measurements

Annales Geophysicae ◽

10.5194/angeo-26-3185-2008 ◽

2008 ◽

Vol 26 (11) ◽

pp. 3185-3195 ◽

Cited By ~ 20

Author(s):

T. Sergienko ◽

I. Sandahl ◽

B. Gustavsson ◽

L. Andersson ◽

U. Brändström ◽

...

Keyword(s):

Fine Structure ◽

Pitch Angle ◽

Internal Gravity Wave ◽

Auroral Zone ◽

Loss Cone ◽

Optical Instruments ◽

The North ◽

Whistler Mode Waves ◽

Diffuse Aurora ◽

Auroral Arcs

Abstract. We present results of an investigation of the fine structure of the night sector diffuse auroral zone, observed simultaneously with optical instruments (ALIS) from the ground and the FAST electron spectrometer from space 16 February 1997. Both the optical and particle data show that the diffuse auroral zone consisted of two regions. The equatorward part of the diffuse aurora was occupied by a pattern of regular, parallel auroral stripes. The auroral stripes were significantly brighter than the background luminosity, had widths of approximately 5 km and moved southward with a velocity of about 100 m/s. The second region, located between the region with auroral stripes and the discrete auroral arcs to the north, was filled with weak and almost homogeneous luminosity, against which short-lived auroral rays and small patches appeared chaotically. From analysis of the electron differential fluxes corresponding to the different regions of the diffuse aurora and based on existing theories of the scattering process we conclude the following: Strong pitch angle diffusion by electron cyclotron harmonic waves (ECH) of plasma sheet electrons in the energy range from a few hundred eV to 3–4 keV was responsible for the electron precipitation, that produced the background luminosity within the whole diffuse zone. The fine structure, represented by the auroral stripes, was created by precipitation of electrons above 3–4 keV as a result of pitch angle diffusion into the loss cone by whistler mode waves. A so called "internal gravity wave" (Safargaleev and Maltsev, 1986) may explain the formation of the regular spatial pattern formed by the auroral stripes in the equatorward part of the diffuse auroral zone.

Download Full-text

Dayside Diffuse Aurora and the Cold-Plasma Structuring: A Brief Review

Frontiers in Astronomy and Space Sciences ◽

10.3389/fspas.2021.725677 ◽

2021 ◽

Vol 8 ◽

Author(s):

De-Sheng Han

Keyword(s):

Cold Plasma ◽

Particle Interaction ◽

Resonance Energy ◽

Hot Electrons ◽

Loss Cone ◽

Wave Particle Interaction ◽

Central Plasma ◽

Cold Plasmas ◽

Diffuse Aurora ◽

Local Noon

Diffuse aurora is generated by the precipitation of hot electrons from the central plasma sheet due to wave-particle interaction. Near magnetic local noon (MLN), the diffuse aurora was often observed in structured forms, such as in stripy or patchy. In the magnetosphere, when the hot electrons meet with a cold plasma structure, the threshold of resonance energy for the electrons in the cold plasma region can be lowered, leading to more electrons being involved in the wave-particle interaction and being scattered into the loss cone. As a result, stronger diffuse aurora can be produced in the correspondent region. Based on this mechanism, the structured dayside diffuse auroras have been suggested to correspond to the cold plasma structures in the dayside outer magnetosphere. This brief review focuses on showing that 1) the stripy diffuse auroras observed near MLN are specifically informative, 2) there are two types of diffuse aurora near MLN, which may correspond to cold plasmas originating from inside and outside the magnetosphere, respectively, and 3) we can study the inside-outside coupling by using the interaction between diffuse and discrete auroras observed near MLN.

Download Full-text

Formfactors of Relativistic Composite Particle Interactions in Unified Nonlinear Spinorfield Models

Zeitschrift für Naturforschung A ◽

10.1515/zna-1985-0717 ◽

1985 ◽

Vol 40 (7) ◽

pp. 752-773

Author(s):

H. Stumpf

Keyword(s):

Composite Particle ◽

Particle Interaction ◽

High Energy ◽

Field Theories ◽

Quantum Field Theories ◽

Statistical Interpretation ◽

Quantum Field ◽

Mapping Procedure ◽

Effective Dynamics ◽

Rough Approximation

Unified nonlinear spinorfield models are self-regularizing quantum field theories in which all observable (elementary and non-elementary) particles are assumed to be bound states of fermionic preon fields. Due to their large masses the preons themselves are confined and below the threshold of preon production the effective dynamics of the model is only concerned with bound state reactions. In preceding papers a functional energy representation, the statistical interpretation and the dynamical equations were derived and the effective dynamics for preon-antipreon boson states and three preon-fermion states (with corresponding anti-fermions) was studied in the low energy limit. The transformation of the functional energy representation of the spinorfield into composite particle functional operators produced a hierarchy of effective interactions at the composite particle level, the leading terms of which are identical with the functional energy representation of a phenomenological boson-fermion coupling theory. In this paper these calculations are extended into the high energy range. This leads to formfactors for the composite particle interaction terms which are calculated in a rough approximation and which in principle are observable. In addition, the mathematical and physical interpretation of nonlocal quantum field theories and the meaning of the mapping procedure, its relativistic invariance etc. are discussed.

Download Full-text

SuperDARN convection and Sondrestrom plasma drift

Annales Geophysicae ◽

10.5194/angeo-19-749-2001 ◽

2001 ◽

Vol 19 (7) ◽

pp. 749-759 ◽

Cited By ~ 21

Author(s):

L. Xu ◽

A. V. Koustov ◽

J. Thayer ◽

M. A. McCready

Keyword(s):

Reasonable Agreement ◽

Temporal Variations ◽

Line Of Sight ◽

Data Sets ◽

Plasma Convection ◽

Map Comparison ◽

Incoherent Scatter ◽

Plasma Drift ◽

End Products ◽

Strong Disagreement

Abstract. Plasma convection measurements by the Goose Bay and Stokkseyri SuperDARN radar pair and the Sondrestrom incoherent scatter radar are compared in three different ways, by looking at the line-of-sight (l-o-s) velocities, by comparing the SuperDARN vectors and corresponding Sondrestrom l-o-s velocities and by comparing the end products of the instruments, the convection maps. All three comparisons show overall reasonable agreement of the convection measurements though the data spread is significant and for some points a strong disagreement is obvious. The convection map comparison shows a tendency for the SuperDARN velocities to be often less than the Sondrestrom drifts for strong flows (velocities > 1000 m/s) and larger for weak flows (velocities < 500 m/s). On average, both effects do not exceed 35%. Data indicate that inconsistencies between the two data sets occur largely at times of fast temporal variations of the plasma drift and for strongly irregular flow ac-cording to the SuperDARN convection maps. These facts indicate that the observed discrepancies are in many cases a result of the different spatial and temporal resolutions of the instruments.Key words. Ionosphere (ionospheric irregularities; plasma convection; polar ionosphere)

Download Full-text

Optical observations of Very High Energy Sources from the Boyden Observatory

10.22323/1.241.0007 ◽

2016 ◽

Author(s):

Brian van Soelen ◽

Pieter Meintjes

Keyword(s):

High Energy ◽

Optical Observations ◽

Energy Sources ◽

Very High Energy ◽

Very High

Download Full-text

Simultaneous observations at different altitudes of ionospheric backscatter in the eastward electrojet

Annales Geophysicae ◽

10.1007/s00585-997-0055-9 ◽

1998 ◽

Vol 16 (1) ◽

pp. 55-68 ◽

Cited By ~ 12

Author(s):

S. E. Milan ◽

M. Lester

Keyword(s):

Spectral Characteristics ◽

Temporal Variations ◽

Approximate Determination ◽

Spectral Signature ◽

Plasma Convection ◽

Flow Angle ◽

F Region ◽

Ion Acoustic ◽

E Region ◽

Acoustic Speed

Abstract. A common feature of evening near-range ionospheric backscatter in the CUTLASS Iceland radar field of view is two parallel, approximately L-shell-aligned regions of westward flow which are attributed to irregularities in the auroral eastward electrojet region of the ionosphere. These backscatter channels are separated by approximately 100–200 km in range. The orientation of the CUTLASS Iceland radar beams and the zonally aligned nature of the flow allows an approximate determination of flow angle to be made without the necessity of bistatic measurements. The two flow channels have different azimuthal variations in flow velocity and spectral width. The nearer of the two regions has two distinct spectral signatures. The eastern beams detect spectra with velocities which saturate at or near the ion-acoustic speed, and have low spectral widths (less than 100 m s–1), while the western beams detect lower velocities and higher spectral widths (above 200 m s–1). The more distant of the two channels has only one spectral signature with velocities above the ion-acoustic speed and high spectral widths. The spectral characteristics of the backscatter are consistent with E-region scatter in the nearer channel and upper-E-region or F-region scatter in the further channel. Temporal variations in the characteristics of both channels support current theories of E-region turbulent heating and previous observations of velocity-dependent backscatter cross-section. In future, observations of this nature will provide a powerful tool for the investigation of simultaneous E- and F-region irregularity generation under similar (nearly co-located or magnetically conjugate) electric field conditions.Key words. Auroral ionosphere · Ionospheric irregularities · Plasma convection

Download Full-text

Ocean Zooglider: an autonomous vehicle for optical and acoustic sensing of zooplankton and suspended particles

10.5194/egusphere-egu21-8658 ◽

2021 ◽

Author(s):

Sven Gastauer ◽

Jeffrey S. Ellen ◽

Mark D. Ohman

Keyword(s):

Autonomous Navigation ◽

Adaptive Sampling ◽

Marine Mammals ◽

Imaging System ◽

Autonomous Vehicle ◽

Three Dimensional ◽

Marine Snow ◽

Seafloor Topography ◽

Optical Images ◽

Mission Duration

Zooglider is an autonomous buoyancy-driven ocean glider designed and built by the Instrument Development Group at Scripps. Zooglider includes a low power camera with a telecentric lens for shadowgraph imaging and two custom active acoustics echosounders (operated at 200/1000 kHz).&#160; A passive acoustic hydrophone records vocalizations from marine mammals, fishes, and ambient noise.&#160; The imaging system (Zoocam) quantifies zooplankton and &#8216;marine snow&#8217; as they flow through a sampling tunnel within a well-defined sampling volume. Other sensors include a pumped Conductivity-Temperature-Depth probe and Chl-a fluorometer.&#160; An acoustic altimeter permits autonomous navigation across regions of abrupt seafloor topography, including submarine canyons and seamounts. &#160;Vertical sampling resolution is typically 5 cm, maximum operating depth is ~500 m, and mission duration up to 50 days.&#160; Adaptive sampling is enabled by telemetry of measurements at each surfacing.&#160; Our post-deployment processing methodology classifies the optical images using advanced Deep Learning methods that utilize context metadata.&#160; Zooglider permits in situ measurements of mesozooplankton and marine snow - and their natural, three dimensional orientation - in relation to other biotic and physical properties of the ocean water column. &#160;Zooglider resolves micro-scale patches, which are important for predator-prey interactions and biogeochemical cycling.&#160;&#160;

Download Full-text

Radio Emission from Flares in Single Late-type Stars

International Astronomical Union Colloquium ◽

10.1017/s0252921100034485 ◽

1995 ◽

Vol 151 ◽

pp. 22-31

Author(s):

Arnold O. Benz

Keyword(s):

Radio Emission ◽

High Energy ◽

Primary Energy ◽

Relativistic Electrons ◽

Late Type ◽

Loss Cone ◽

Magnetically Trapped ◽

Stellar Flares ◽

Gyrosynchrotron Emission ◽

M Stars

AbstractRadio observations provide the most direct information on non-thermal electrons in stellar flares and in the coronae of late-type stars. Radio emissions of single main-sequence F, G, and of many K stars have recently been discovered, in addition to the well-known dwarf M stars. Their long-duration radio flares with low circular polarization, slow variations and broad bandwidth can be attributed to gyrosynchrotron emission of mildly relativistic electrons. The same holds for the low-level (‘quiescent’) radio emission. On the other hand, highly polarized radio flares of M stars have been interpreted by coherent emissions from loss-cone instabilities of magnetically trapped electrons. These conjectures are consistent with recent VLBI observations. The identification of the radio emission process allows to estimate the high-energy component of the flare and compare it to the total flare energy. The weakly polarized radio emission may serve as a proxy for hard X-ray signatures of relativistic electrons. The fraction of primary energy released into energetic electrons then appears to be large and similar to solar flares.

Download Full-text