Three‐dimensional modeling of the electromagnetic characteristics of equatorial plasma depletions

Dao, E. V.; Seyler, C. E.; Kelley, M. C.

doi:10.1002/jgra.50216

Cited by 16 publications

(29 citation statements)

References 29 publications

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“…It is quite obvious from that figure that the magnetic activity varies synchronously in all three components. Such a close relation between small-scale plasma structures and Alfvén wave activity is also suggested by the model of Dao et al [1]. This can be regarded as a justification for our approach to use the occurrence of intermediate-scale plasma irregularities for identifying Alfvén wave events.…”

Section: Discussionsupporting

confidence: 79%

“…These are interpreted as signatures of Alfvén waves (e.g., [2,8,9]) associated with field-aligned currents. Such Alfvén waves are transient features with a lifetime of several tens of seconds (see [1]). If they are observed over longer periods, there has to be an exciting mechanism triggering them again and again.…”

Section: Introductionmentioning

confidence: 99%

“…In spite of the many indications for the electromagnetic nature of EPB there is a lack of systematic studies about EPB Alfvén wave characteristics. Recently Dao et al [1] developed a highresolution 3D-model of ionospheric plasma instabilities. These authors managed to resolve the full range of electric and magnetic field variations resulting from density depletion, current divergence and Alfvén wave propagation.…”

Section: Introductionmentioning

confidence: 99%

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AlfvÃ©n wave characteristics of equatorial plasma irregularities in the ionosphere derived from CHAMP observations

et al. 2014

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We report magnetic field observations of the components transverse to the main field in the frequency range 1-25 Hz from times of equatorial plasma irregularity crossings. These field variations are interpreted as Alfvénic signatures accompanying intermediate-scale (150 m-4 km) plasma density depletions. Data utilized are the high-resolution CHAMP magnetic field measurements sampled at 50 Hz along the north-south satellite track. The recorded signals do not reflect the temporal variation but the spatial distribution of Alfvénic signatures. This is the first comprehensive study of Alfvénic signatures related to equatorial plasma bubbles that covers the whole solar cycle from 2000 to 2010. A detailed picture of the wave characteristics can be drawn due to the large number (almost 9000) of events considered. Some important findings are: Alfvénic features are a common feature of intermediate-scale plasma structures. The zonal and meridional magnetic components are generally well correlated suggesting skewed current sheets. The sheets have an orientation that is on average deflect by about 32 • away from magnetic east toward upward or downward depending on the hemisphere. We have estimated the Poynting flux flowing into the E region. Typical values are distributed over the range 10 −8 -10 −6 W/m 2 . Large Poynting fluxes are related to steep spectra of the Alfvénic signal, which imply passages through regularly varying electron density structures. No dependence of the Poynting flux level on solar activity has been found. But below a certain solar flux value (F10.7 < 100 sfu) practically no events are detected. There is a clear tendency that large Poynting flux events occur preferably at early hours after sunset (e.g., 20:00 local time). Toward later times the occurrence peak shifts successively toward lower energy levels. Finally we compare our observations with the recently published results of the high-resolution 3-D model simulations by Dao et al. [1]. Keywords: equatorial ionosphere, topside ionosphere, plasma waves and instabilities, plasma irregularities, plasma depletions www.frontiersin.org August 2014 | Volume 2 | Article 47 | 1 PHYSICS Lühr et al. Alfvénic signatures of plasma irregularities

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Section: Discussionsupporting

confidence: 79%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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AlfvÃ©n wave characteristics of equatorial plasma irregularities in the ionosphere derived from CHAMP observations

et al. 2014

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“…For the interpretation of these narrow solitary plasma depletions in the context of EPB evolution it would be helpful to make use of high-resolution 3-D bubble simulations. The model of Dao et al [12] may be regarded as a promising step in that direction.…”

Section: Discussionmentioning

confidence: 99%

“…In spite of their impressive results these models are not able to resolve density structures smaller than 10 km. Important progress in that respect has been achieved by the high-resolution 3-D model of Dao et al [12]. These authors managed to go down to sub-kilometer scales and resolve temporal variations to fractions of a millisecond.…”

Section: Introductionmentioning

confidence: 99%

Systematic study of intermediate-scale structures of equatorial plasma irregularities in the ionosphere based on CHAMP observations

Lühr¹,

Xiong²,

Park³

et al. 2014

Front. Physics

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Equatorial spread-F ionospheric plasma irregularities on the night-side, commonly called equatorial plasma bubbles (EPB), include electron density variations over a wide range of spatial scales. Here we focus on intermediate-scale structures ranging from 100 m to 10 km, which play an important role in the evolution of EPBs. High-resolution CHAMP magnetic field measurements sampled along north-south track at 50 Hz are interpreted in terms of diamagnetic effect for illustrating the details of electron density variations. We provide the first comprehensive study on intermediate-scale density structures associated with EPBs, covering a whole solar cycle from 2000 to 2010. The large number of detected events, almost 9000, allows us to draw a detailed picture of the plasma fine structure. The occurrence of intermediate-scale events is strongly favored by high solar flux. During times of F10.7 <100 sfu practically no events were observed. The longitudinal distribution of our events with respect to season or local time agrees well with that of the EPBs, qualifying the fine structure as a common feature, but the occurrence rates are smaller by a factor of 4 during the period 2000-2005. Largest amplitude electron density variations appear at the poleward boundaries of plasma bubbles. Above the dip-equator recorded amplitudes are small and fall commonly below our resolution. Events can generally be found at local times between 19 and 24 LT, with a peak lasting from 20 to 22 LT. The signal spectrum can be approximated by a power law. Over the frequency range 1-25 Hz we observe spectral indices between −1.4 and −2.6 with peak occurrence rates around −1.9. There is a weak dependence observed of the spectral index on local time. Toward later hours the spectrum becomes shallower. Similarly for the latitude dependence, there is a preference of shallower spectra for latitudes poleward of the ionization anomaly crest. Our data suggest that the generation of small plasma structures is part of the early stage EPB development, during times when the vertical plasma drift surpasses a certain threshold.

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Does a localized plasma disturbance in the ionosphere evolve to electrostatic equilibrium? Evidence to the contrary

Cosgrove

2016

JGR Space Physics

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Electrostatic equilibrium must be achieved through electromagnetic evolution. From an initial state with nonzero neutral wind localized along the geomagnetic field, and with all other plasma and electromagnetic perturbations initially zero, evolution progresses from plasma velocity to electric field to magnetic field, where the last step can launch an Alfvén wave that transmits the electromagnetic disturbance along geomagnetic field lines. Without the Alfvén wave the disturbance does not map along geomagnetic field lines, and there is no semblance of electrostatic equilibrium. This paradigm is essentially the traditional magnetosphere/ionosphere coupling paradigm, except addressed to smaller‐scale, local ionospheric phenomena. However, Alfvén waves have not been thoroughly studied in the context of the partially ionized, collisional ionospheric plasma, and so the full effects predicted by this modeling paradigm are not known. In this work we adopt the two‐fluid equations and investigate whether the ionosphere supports Alfvén‐type waves that can transmit disturbances along geomagnetic field lines and perform a wave analysis of the “lumped circuit” parameters normally used to characterize the ionosphere under electrostatic equilibrium. We find that under the wave analysis (1) the Pedersen conductivity is severely modified and has a negative real part at short wavelengths; (2) the mapping distance for electric fields is significantly modified, and there is a nonnegligible wavelength along the geomagnetic field; and (3) the load admittance seen by a localized dynamo is strongly reactive, causing a phase offset between electric field and current, as compared with that when the load is electrostatic.

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Three‐dimensional modeling of the electromagnetic characteristics of equatorial plasma depletions

Cited by 16 publications

References 29 publications

AlfvÃ©n wave characteristics of equatorial plasma irregularities in the ionosphere derived from CHAMP observations

AlfvÃ©n wave characteristics of equatorial plasma irregularities in the ionosphere derived from CHAMP observations

Systematic study of intermediate-scale structures of equatorial plasma irregularities in the ionosphere based on CHAMP observations

Does a localized plasma disturbance in the ionosphere evolve to electrostatic equilibrium? Evidence to the contrary

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