scholarly journals Correspondence between the ULF wave power spatial distribution and auroral oval boundaries

2016 ◽  
Vol 2 (2) ◽  
pp. 35-45 ◽  
Author(s):  
Ольга Козырева ◽  
Olga Kozyreva ◽  
Вячеслав Пилипенко ◽  
Vyacheslav Pilipenko ◽  
Марк Энгебретсон ◽  
...  
Keyword(s):  
Spatial Distribution ◽  
Spectral Power ◽  
Recovery Phase ◽  
Temporal Variations ◽  
Auroral Oval ◽  
Wave Power ◽  
Observational Result ◽  
Ulf Wave ◽  
Image Satellite ◽  
Magnetospheric Field

The location of the auroral oval boundaries has been mapped onto the Pc5 wave power spatial distribution. The poleward and equatorward boundaries of auroral oval are estimated using either the BAS database based on UV observations of the aurora by the IMAGE satellite or the OVATION model based on the DMSP particle data. The epicenter of the spectral power of broadband fluctuations in the Pc5 band during storm growth phase is mapped inside the auroral oval. During the storm recovery phase, the spectral power of narrowband Pc5 waves, both in the morning and dusk sector, is mapped inside the auroral oval or around its equatorward boundary. This observational result confirms the effects earlier reported: the spatial/temporal variations of the Pc5 wave power in the morning/pre-noon sector are closely related to the location of the auroral electrojet and magnetospheric field-aligned currents. At the same time, narrowband Pc5 waves demonstrate typical resonant features in the amplitude-phase latitudinal structure. Thus, the location of the auroral oval (or its equatorward border) is the preferred latitude of magnetospheric field-line Alfven resonator excitation. This effect is not taken into account by modern theories of ULF Pc5 waves, but it could be significant for development of more adequate models.

scholarly journals Correspondence between the ULF wave power spatial distribution and auroral oval boundaries

2016 ◽  
Vol 2 (2) ◽  
pp. 46-65 ◽  
Author(s):  
Ольга Козырева ◽  
Olga Kozyreva ◽  
Вячеслав Пилипенко ◽  
Vyacheslav Pilipenko ◽  
Марк Энгебретсон ◽  
...  
Keyword(s):  
Spatial Distribution ◽  
Spectral Power ◽  
Recovery Phase ◽  
Temporal Variations ◽  
Auroral Oval ◽  
Wave Power ◽  
Observational Result ◽  
Equatorward Boundary ◽  
Image Satellite ◽  
Magnetospheric Field

The world-wide spatial distribution of the wave power in the Pc5 band during magnetic storms has been compared with auroral oval boundaries. The poleward and equatorward auroral oval boundaries are estimated using either the British Antarctic Survey database containing IMAGE satellite UV observations of the aurora or the OVATION model based on the DMSP particle data. The “epicenter” of the spectral power of broadband Pc5 fluctuations during the storm growth phase is mapped inside the auroral oval. During the storm recovery phase, the spectral power of narrowband Pc5 waves, both in the dawn and dusk sectors, is mapped inside the auroral oval or around its equatorward boundary. This observational result confirms previously reported effects: the spatial/temporal variations of the Pc5 wave power in the morning/pre-noon sector are closely related to the dynamics of the auroral electrojet and magnetospheric field-aligned currents. At the same time, narrowband Pc5 waves demonstrate typical resonant features in the amplitude-phase latitudinal structure. Thus, the location of the auroral oval or its equatorward boundary is the preferred latitude for magnetospheric field-line Alfven resonator excitation. This effect is not taken into account by modern theories of ULF Pc5 waves, but it could be significant for the development of more adequate models.

scholarly journals Correspondence between the latitudinal ULF wave power distribution and auroral oval in conjugate ionospheres

2018 ◽  
Author(s):  
V.A. Martines-Bedenko ◽  
V.A. Pilipenko ◽  
M.D. Hartinger ◽  
M.J. Engebretson ◽  
D.A. Lorentzen ◽  
...  
Keyword(s):  
Power Distribution ◽  
Auroral Oval ◽  
Wave Power ◽  
Ulf Wave

scholarly journals Observations of an auroral streamer in a double oval configuration

2011 ◽  
Vol 29 (4) ◽  
pp. 701-716 ◽  
Author(s):  
O. Amm ◽  
R. Nakamura ◽  
T. Takada ◽  
K. Kauristie ◽  
H. U. Frey ◽  
...  
Keyword(s):  
Southern Hemisphere ◽  
Recovery Phase ◽  
Auroral Oval ◽  
Expansion Phase ◽  
Optical Instruments ◽  
Image Satellite ◽  
Bursty Bulk Flow ◽  
Polarization Electric Field ◽  
Late Evening ◽  
Eiscat Radar

Abstract. During the late evening and night of 14 September 2004, the nightside auroral oval shows a distinct double oval configuration for several hours after a substorm onset at ~18:45 UT. This structure is observed both by the IMAGE satellite optical instruments focusing on the Southern Hemisphere, and by the MIRACLE ground-based instrument network in Scandinavia. At ~21:17 UT during the recovery phase of the substorm, an auroral streamer is detected by these instruments and the EISCAT radar, while simultaneously the Cluster satellites observe a bursty bulk flow in the conjugate portion of the plasma sheet in the magnetotail. Our combined data analysis reveals significant differences between the ionospheric equivalent current signature of this streamer within a double oval configuration, as compared to previously studied streamer events without such a configuration. We attribute these differences to the presence of an additional poleward polarization electric field between the poleward and the equatorward portions of the double oval, and show with a simple model that such an assumption can conceptually explain the observations. Further, we estimate the total current transferred in meridional direction by this recovery phase streamer to ~80 kA, significantly less than for previously analysed expansion phase streamer events. Both results indicate that the development of auroral streamers is dependent on the ambient background conditions in the magnetosphere-ionosphere system. The auroral streamer event studied was simultaneously observed in the conjugate Northern and Southern Hemisphere ionosphere.

On the nature of ULF wave power during nightside auroral activations and substorms: 1. Spatial distribution

2011 ◽  
Vol 116 (A5) ◽  
Author(s):  
Kyle R. Murphy ◽  
I. Jonathan Rae ◽  
Ian R. Mann ◽  
David K. Milling
Keyword(s):  
Spatial Distribution ◽  
Wave Power ◽  
Ulf Wave

scholarly journals Reconnection electric field estimates and dynamics of high-latitude boundaries during a substorm

2009 ◽  
Vol 27 (5) ◽  
pp. 2157-2171 ◽  
Author(s):  
T. Pitkänen ◽  
A. T. Aikio ◽  
A. Kozlovsky ◽  
O. Amm
Keyword(s):  
Electric Field ◽  
Growth Phase ◽  
Continuation Method ◽  
Recovery Phase ◽  
Temporal Variations ◽  
Auroral Oval ◽  
Closed Field ◽  
Polar Cap ◽  
Vhf Radar ◽  
The North

Abstract. The dynamics of the polar cap and the auroral oval are examined in the evening sector during a substorm period on 25 November 2000 by using measurements of the EISCAT incoherent scatter radars, the north-south chain of the MIRACLE magnetometer network, and the Polar UV Imager. The location of the polar cap boundary (PCB) is estimated from electron temperature measurements by the mainland low-elevation EISCAT VHF radar and the 42 m antenna of the EISCAT Svalbard radar. A comparison to the poleward auroral emission (PAE) boundary by the Polar UV Imager shows that in this event the PAE boundary is typically located 0.7° of magnetic latitude poleward of the PCB by EISCAT. The convection reversal boundary (CRB) is determined from the 2-D plasma drift velocity extracted from the dual-beam VHF data. The CRB is located 0.5–1° equatorward of the PCB indicating the existence of viscous-driven antisunward convection on closed field lines. East-west equivalent electrojets are calculated from the MIRACLE magnetometer data by the 1-D upward continuation method. In the substorm growth phase, electrojets together with the polar cap boundary move gradually equatorwards. During the substorm expansion phase, the Harang discontinuity (HD) region expands to the MLT sector of EISCAT. In the recovery phase the PCB follows the poleward edge of the westward electrojet. The local ionospheric reconnection electric field is calculated by using the measured plasma velocities in the vicinity of the polar cap boundary. During the substorm growth phase, values between 0 and 10 mV/m are found. During the late expansion and recovery phase, the reconnection electric field has temporal variations with periods of 7–27 min and values from 0 to 40 mV/m. It is shown quantitatively, for the first time to our knowledge, that intensifications in the local reconnection electric field correlate with appearance of auroral poleward boundary intensifications (PBIs) in the same MLT sector. The results suggest that PBIs (typically 1.5 h MLT wide) are a consequence of temporarily enhanced longitudinally localized magnetic flux closure in the magnetotail.

ULF Wave Power During Geomagnetic Storms and Implications for Radial Diffusion Processes

2021 ◽  
Author(s):  
Jasmine Sandhu ◽  
Jonathan Rae ◽  
John Wygant ◽  
Aaron Breneman ◽  
Sheng Tian ◽  
...  
Keyword(s):  
Statistical Analysis ◽  
Diffusion Coefficients ◽  
Radiation Belt ◽  
Geomagnetic Storms ◽  
Radial Diffusion ◽  
Ulf Waves ◽  
Wave Power ◽  
Outer Radiation Belt ◽  
Large Variability ◽  
Ulf Wave

<p>Ultra Low Frequency (ULF) waves drive radial diffusion of radiation belt electrons, where this process contributes to and, at times, dominates energisation, loss, and large scale transport of the outer radiation belt. In this study we quantify the changes and variability in ULF wave power during geomagnetic storms, through a statistical analysis of Van Allen Probes data for the time period spanning 2012 – 2019. The results show that global wave power enhancements occur during the main phase, and continue into the recovery phase of storms. Local time asymmetries show sources of ULF wave power are both external solar wind driving as well as internal sources from coupling with ring current ions and substorms.</p><p>The statistical analysis demonstrates that storm time ULF waves are able to access lower L values compared to pre-storm conditions, with enhancements observed within L = 4. We assess how magnetospheric compressions and cold plasma distributions shape how ULF wave power propagates through the magnetosphere. Results show that the Earthward displacement of the magnetopause is a key factor in the low L enhancements. Furthermore, the presence of plasmaspheric plumes during geomagnetic storms plays a crucial role in trapping ULF wave power, and contributes significantly to large storm time enhancements in ULF wave power.</p><p>The results have clear implications for enhanced radial diffusion of the outer radiation belt during geomagnetic storms. Estimates of storm time radial diffusion coefficients are derived from the ULF wave power observations, and compared to existing empirical models of radial diffusion coefficients. We show that current Kp-parameterised models, such as the Ozeke et al. [2014] model, do not fully capture the large variability in storm time radial diffusion coefficients or the extent of enhancements in the magnetic field diffusion coefficients.</p>

scholarly journals Field-aligned chorus wave spectral power in Earth's outer radiation belt

2015 ◽  
Vol 33 (5) ◽  
pp. 583-597 ◽  
Author(s):  
H. Breuillard ◽  
O. Agapitov ◽  
A. Artemyev ◽  
E. A. Kronberg ◽  
S. E. Haaland ◽  
...  
Keyword(s):  
Pitch Angle ◽  
Radiation Belt ◽  
Spectral Power ◽  
Peak Frequency ◽  
Wave Power ◽  
Outer Radiation Belt ◽  
Substantial Impact ◽  
Wide Range ◽  
Frequency Variations ◽  
Chorus Wave

Abstract. Chorus-type whistler waves are one of the most intense electromagnetic waves generated naturally in the magnetosphere. These waves have a substantial impact on the radiation belt dynamics as they are thought to contribute to electron acceleration and losses into the ionosphere through resonant wave–particle interaction. Our study is devoted to the determination of chorus wave power distribution on frequency in a wide range of magnetic latitudes, from 0 to 40°. We use 10 years of magnetic and electric field wave power measured by STAFF-SA onboard Cluster spacecraft to model the initial (equatorial) chorus wave spectral power, as well as PEACE and RAPID measurements to model the properties of energetic electrons (~ 0.1–100 keV) in the outer radiation belt. The dependence of this distribution upon latitude obtained from Cluster STAFF-SA is then consistently reproduced along a certain L-shell range (4 ≤ L ≤ 6.5), employing WHAMP-based ray tracing simulations in hot plasma within a realistic inner magnetospheric model. We show here that, as latitude increases, the chorus peak frequency is globally shifted towards lower frequencies. Making use of our simulations, the peak frequency variations can be explained mostly in terms of wave damping and amplification, but also cross-L propagation. These results are in good agreement with previous studies of chorus wave spectral extent using data from different spacecraft (Cluster, POLAR and THEMIS). The chorus peak frequency variations are then employed to calculate the pitch angle and energy diffusion rates, resulting in more effective pitch angle electron scattering (electron lifetime is halved) but less effective acceleration. These peak frequency parameters can thus be used to improve the accuracy of diffusion coefficient calculations.

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.

On the interplay between solar wind parameters and ULF wave power as a function of geomagnetic activity at high‐ and mid‐latitudes

2021 ◽  
Author(s):  
Stavros Dimitrakoudis ◽  
Ian R. Mann ◽  
Georgios Balasis ◽  
Constantinos Papadimitriou ◽  
Anastasios Anastasiadis ◽  
...  
Keyword(s):  
Solar Wind ◽  
Geomagnetic Activity ◽  
Wave Power ◽  
Ulf Wave ◽  
Solar Wind Parameters

scholarly journals Ionospheric signatures during a magnetospheric flux rope event

2008 ◽  
Vol 26 (12) ◽  
pp. 3967-3977 ◽  
Author(s):  
L. Juusola ◽  
O. Amm ◽  
H. U. Frey ◽  
K. Kauristie ◽  
R. Nakamura ◽  
...  
Keyword(s):  
Flux Rope ◽  
Recovery Phase ◽  
Expansion Phase ◽  
Northern Fennoscandia ◽  
Ionospheric Region ◽  
Image Satellite ◽  
Imaging Camera ◽  
Flux Ropes ◽  
Field Aligned Current ◽  
Upward Current

Abstract. On 13 August 2002, during a substorm, Cluster encountered two earthward moving flux ropes (FR) in the central magnetotail. The first FR was observed during the expansion phase of the substorm, and the second FR during the recovery phase. In the conjugate ionospheric region in Northern Fennoscandia, the ionospheric equivalent currents were observed by the MIRACLE network and the auroral evolution was monitored by the Wideband Imaging Camera (WIC) on-board the IMAGE satellite. Extending the study of Amm et al. (2006), we examine and compare the possible ionospheric signatures associated with the two FRs. Amm et al. studied the first event in detail and found that the ionospheric footprint of Cluster coincided with a region of downward field-aligned current. They suggested that this region of downward current, together with a trailing region of upward current further southwestward, might correspond to the ends of the FR. Unlike during the first FR, however, we do not see any clear ionospheric features associated with the second one. In the GSM xy-plane, the first flux rope axis was tilted with respect to the y-direction by 29°, while the second flux rope axis was almost aligned in the y-direction, with an angle of 4° only. It is possible that due to the length and orientation of the second FR, any ionospheric signatures were simply mapped outside the region covered by the ground-based instruments. We suggest that the ground signatures of a FR depend on the orientation and the length of the structure.

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