scholarly journals A modeling study of ionospheric F2-region storm effects at low geomagnetic latitudes during 17-22 March 1990

2006 ◽  
Vol 24 (3) ◽  
pp. 915-940 ◽  
Author(s):  
A. V. Pavlov ◽  
S. Fukao ◽  
S. Kawamura
Keyword(s):  
Magnetic Field ◽  
Electric Field ◽  
Neutral Wind ◽  
Geomagnetic Equator ◽  
Equatorial Anomaly ◽  
Vibrationally Excited ◽  
Plasma Drift ◽  
Time Period ◽  
Field Lines

Abstract. We have presented a comparison between the modeled NmF2 and hmF2, and NmF2 and hmF2, which were observed in the low-latitude ionosphere simultaneously by the Kokubunji, Yamagawa, Okinawa, Manila, Vanimo, and Darwin ionospheric sounders, by the middle and upper atmosphere (MU) radar during 17-22 March 1990, and by the Arecibo radar for the time period of 20-22 March 1990. A comparison between the electron and ion temperatures measured by the MU and Arecibo radars and those produced by the model of the ionosphere and plasmasphere is presented. The empirical zonal electric field, the meridional neutral wind taken from the HWM90 wind model, and the NRLMSISE-00 neutral temperature and densities are corrected so that the model results agree reasonably with the ionospheric sounder observations, and the MU and Arecibo radar data. It is proved that the nighttime weakening of the equatorial zonal electric field (in comparison with that produced by the empirical model of Fejer and Scherliess (1997) or Scherliess and Fejer (1999)), in combination with the corrected wind-induced plasma drift along magnetic field lines, provides the development of the nighttime enhancements in NmF2 observed over Manila during 17-22 March 1990. As a result, the new physical mechanism of the nighttime NmF2 enhancement formation close to the geomagnetic equator includes the nighttime weakening of the equatorial zonal electric field and equatorward nighttime plasma drift along magnetic field lines caused by neutral wind in the both geomagnetic hemispheres. It is found that the latitudinal positions of the crests depend on the E×B drift velocity and on the neutral wind velocity. The relative role of the main mechanisms of the equatorial anomaly suppression observed during geomagnetic storms is studied for the first time in terms of storm-time variations of the model crest-to-trough ratios of the equatorial anomaly. During most of the studied time period, a total contribution from meridional neutral winds and variations in the zonal electric field to the equatorial anomaly changes is larger than that from geomagnetic storm disturbances in the neutral temperature and densities. Vibrationally excited N2 and O2 promote the equatorial anomaly enhancement during the predominant part of the studied time period, however, the role of vibrationally excited N2 and O2 in the development of the equatorial anomaly is not significant. The asymmetries in the neutral wind and densities relative to the geomagnetic equator are responsible for the north-south asymmetry in NmF2 and hmF2, and for the asymmetry between the values of the crest-to-trough ratios of the Northern and Southern Hemispheres. The model simulations provide evidence in favor of an asymmetry in longitude of the energy input into the auroral region of the Northern Hemisphere on 21 March 1990.

scholarly journals Comparison of the measured and modeled electron densities, and electron and ion temperatures in the low-latitude ionosphere during 19-21 March 1988

2004 ◽  
Vol 22 (8) ◽  
pp. 2747-2763 ◽  
Author(s):  
A. V. Pavlov ◽  
S. Fukao ◽  
S. Kawamura
Keyword(s):  
Geomagnetic Latitude ◽  
Neutral Wind ◽  
Relative Role ◽  
Geomagnetic Equator ◽  
Quiet Time ◽  
Equatorial Anomaly ◽  
Latitude Dependence ◽  
The North ◽  
Mu Radar ◽  
Time Period

Abstract. We have presented a comparison between the modeled NmF2 and hmF2, and NmF2 and hmF2 which were observed at the equatorial anomaly crest and close to the geomagnetic equator simultaneously by the Akita, Kokubunji, Yamagawa, Okinawa, Chung-Li, Manila, Vanimo, and Darwin ionospheric sounders and by the middle and upper atmosphere (MU) radar at Shigaraki (34.85°N, 136.10°E, Japan) during the 19-21 March 1988 geomagnetically quiet time period at moderate solar activity near approximately the same geomagnetic meridian of 201°. A comparison between the electron, Te, and ion, Ti, temperatures measured by the MU radar and those produced by the model of the ionosphere and plasmasphere is presented for 19-21 March 1988. It is shown that there is a large disagreement between the measured and modeled hmF2 from about 07:00 UT to about 11:00 UT if the equatorial ExB drift given by Scherliess and Fejer (1999) is used. The required equatorial upward ExB drift is weaker from 03:14 UT to 11:14 UT than that given by Scherliess and Fejer (1999) for the studied time period. The required modification of the ExB drift weakens the effect of the fountain in NmF2 bringing the modeled and measured hmF2 and NmF2, into reasonable agreement. The depth of the equatorial NmF2 trough in the calculated NmF2 is approximately consistent with the measured depth if the modified equatorial ExB drift is used. It has been found that the north-south asymmetries in the observed NmF2 and hmF2 about the geomagnetic equator are mainly caused by the asymmetry in the neutral wind about the geomagnetic equator. In the Northern Hemisphere, the meridional neutral wind taken from the HWW90 wind model and the NRLMSISE-00 atomic oxygen density are corrected so that the model results agree with the ionospheric sounders and MU radar observations. A theory of the primary mechanisms causing the latitude dependence of the morning and evening peaks in Te is developed. The latitude dependence of the magnitudes of these peaks in Te is interpreted in terms of the corresponding dependence of the electron density. The relative role of the ExB drift and the plasma drift caused by the neutral wind in the formation and the dependence of the magnitudes of the morning and evening electron temperature peaks on the geomagnetic latitude is studied.

scholarly journals The role of electric field, peripheral chains, and magnetic effects on significant 1H upfield shifts of the encapsulated molecules in chalcogen-bonded capsules

2021 ◽  
Vol 23 (35) ◽  
pp. 19647-19658
Author(s):  
Demeter Tzeli ◽  
Ioannis D. Petsalakis ◽  
Giannoula Theodorakopoulos ◽  
Faiz-Ur Rahman ◽  
Yang Yu ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Electric Field ◽  
Chemical Shifts ◽  
Electric Field Effects ◽  
Magnetic Effects ◽  
Field Effects ◽  
Equal Importance

Significant 1H upfield chemical shifts of the guests in the capsules are consequences of polarizability of chalcogens, electric field effects and peripheral chains. The effects of the electric field and of magnetic field are of equal importance.

scholarly journals Mapping of steady-state electric fields and convective drifts in geomagnetic fields – Part 1: Elementary models

2016 ◽  
Vol 34 (1) ◽  
pp. 55-65 ◽  
Author(s):  
A. D. M. Walker ◽  
G. J. Sofko
Keyword(s):  
Magnetic Field ◽  
Steady State ◽  
Electric Field ◽  
Electric Fields ◽  
Magnetic Field Line ◽  
Geomagnetic Field ◽  
Geomagnetic Field Models ◽  
Spatial Derivatives ◽  
Field Lines ◽  
The Magnetic Field

Abstract. When studying magnetospheric convection, it is often necessary to map the steady-state electric field, measured at some point on a magnetic field line, to a magnetically conjugate point in the other hemisphere, or the equatorial plane, or at the position of a satellite. Such mapping is relatively easy in a dipole field although the appropriate formulae are not easily accessible. They are derived and reviewed here with some examples. It is not possible to derive such formulae in more realistic geomagnetic field models. A new method is described in this paper for accurate mapping of electric fields along field lines, which can be used for any field model in which the magnetic field and its spatial derivatives can be computed. From the spatial derivatives of the magnetic field three first order differential equations are derived for the components of the normalized element of separation of two closely spaced field lines. These can be integrated along with the magnetic field tracing equations and Faraday's law used to obtain the electric field as a function of distance measured along the magnetic field line. The method is tested in a simple model consisting of a dipole field plus a magnetotail model. The method is shown to be accurate, convenient, and suitable for use with more realistic geomagnetic field models.

scholarly journals A Look into Students' Interpretation of Electric Field Lines

2017 ◽  
pp. 342-364
Author(s):  
Esmeralda Campos ◽  
Genaro Zavala
Keyword(s):  
Magnetic Field ◽  
Electric Field ◽  
Random Sample ◽  
Qualitative Approach ◽  
Undergraduate Level ◽  
Field Lines

On Electricity & Magnetism (EM) courses at undergraduate level, the concept of electric field poses one of the most relevant and basic topics, along with the concept of magnetic field. Professors and students may use different diagrams as a tool to visualize the electric field, such as vectors or electric field lines. The present study aims to identify how students interpret and use electric field lines as a tool or resource to describe the electric field. Two versions of a test with open-ended questions were administered in Spanish in a private Mexican university to a random sample of students taking the EM course, and were analyzed with a qualitative approach. It was found that students do not interpret electric field lines diagrams correctly, which may lead to misconceptions. Many students based their answers on the concepts of superposition, force and repulsion.

Theory and observations of switchbacks’ evolution in the solar wind

2021 ◽  
Author(s):  
Anna Tenerani ◽  
Marco Velli ◽  
Lorenzo Matteini
Keyword(s):  
Magnetic Field ◽  
Solar Wind ◽  
Radial Magnetic Field ◽  
Open Questions ◽  
Coronal Activity ◽  
Turbulent Heating ◽  
Field Lines ◽  
Radial Evolution ◽  
Field Correlation

<p>Alfvénic fluctuations represent the dominant contributions to turbulent fluctuations in the solar wind, especially, but not limited to, the fastest streams with velocity of the order of 600-700 km/s. Alfvénic fluctuations can contribute to solar wind heating and acceleration via wave pressure and turbulent heating. Observations show that such fluctuations are characterized by a nearly constant magnetic field amplitude, a condition which remains largely to be understood and that may be an indication of how fluctuations evolve and relax in the expanding solar wind. Interestingly, measurements from Parker Solar Probe have shown the ubiquitous and persistent presence of the so-called switchbacks. These are magnetic field lines which are strongly perturbed to the point that they produce local inversions of the radial magnetic field. The corresponding signature of switchbacks in the velocity field is that of local enhancements in the radial speed (or jets) that display the typical velocity-magnetic field correlation that characterizes Alfvén waves propagating away from the Sun. While there is not yet a general consensus on what is the origin of switchbacks and their connection to coronal activity, a first necessary step to answer these important questions is to understand how they evolve and how long they can persist in the solar wind. Here we investigate the evolution of switchbacks. We address how their evolution is affected by parametric instabilities and the possible role of expansion, by comparing models with the observed radial evolution of the fluctuations’ amplitude. We finally discuss what are the implications of our results for models of switchback generation and related open questions.</p>

scholarly journals Very High-Energy Emission from the Direct Vicinity of Rapidly Rotating Black Holes

Galaxies ◽  
2018 ◽  
Vol 6 (4) ◽  
pp. 122 ◽  
Author(s):  
Kouichi Hirotani
Keyword(s):  
Magnetic Field ◽  
Black Holes ◽  
Black Hole ◽  
Electric Field ◽  
Gamma Rays ◽  
Accretion Rate ◽  
High Energy ◽  
Relativistic Electrons ◽  
Field Lines ◽  
The Magnetic Field

When a black hole accretes plasmas at very low accretion rate, an advection-dominated accretion flow (ADAF) is formed. In an ADAF, relativistic electrons emit soft gamma-rays via Bremsstrahlung. Some MeV photons collide with each other to materialize as electron-positron pairs in the magnetosphere. Such pairs efficiently screen the electric field along the magnetic field lines, when the accretion rate is typically greater than 0.03–0.3% of the Eddington rate. However, when the accretion rate becomes smaller than this value, the number density of the created pairs becomes less than the rotationally induced Goldreich–Julian density. In such a charge-starved magnetosphere, an electric field arises along the magnetic field lines to accelerate charged leptons into ultra-relativistic energies, leading to an efficient TeV emission via an inverse-Compton (IC) process, spending a portion of the extracted hole’s rotational energy. In this review, we summarize the stationary lepton accelerator models in black hole magnetospheres. We apply the model to super-massive black holes and demonstrate that nearby low-luminosity active galactic nuclei are capable of emitting detectable gamma-rays between 0.1 and 30 TeV with the Cherenkov Telescope Array.

scholarly journals Mechanisms of the electron density depletion in the SAR arc region

1996 ◽  
Vol 14 (2) ◽  
pp. 211-221 ◽  
Author(s):  
A. V. Pavlov
Keyword(s):  
Electric Field ◽  
Magnetic Storm ◽  
Electron Density ◽  
Drift Velocity ◽  
Recovery Phase ◽  
Electron Densities ◽  
Model Framework ◽  
Vibrationally Excited ◽  
Plasma Drift ◽  
Excited Nitrogen

Abstract. This study compares the measurements of electron density and temperature and the integral airglow intensity at 630 nm in the SAR arc region and slightly south of this (obtained by the Isis 2 spacecraft during the 18 December 1971 magnetic storm), with the model results obtained using the time dependent one-dimensional mathematical model of the Earth\\'s ionosphere and plasmasphere. The explicit expression in the third Enskog approximation for the electron thermal conductivity coefficient in the multicomponent mixture of ionized gases and a simplified calculation method for this coefficient presents an opportunity to calculate more exactly the electron temperature and density and 630 nm emission within SAR arc region are used in the model. Collisions between N2 and hot thermal electrons in the SAR arc region produce vibrationally excited nitrogen molecules. It appears that the loss rate of O+(4S) due to reactions with the vibrationally excited nitrogen is enough to explain electron density depression by a factor of two at F-region heights and the topside ionosphere density variations within the SAR arc if the erosion of plasma within geomagnetic field tubes, during the main phase of the geomagnetic storm and subsequent filling of geomagnetic tubes during the recovery phase, are considered. To explain the disagreement by a factor 1.5 between the observed and modeled SAR arc electron densities an additional plasma drift velocity ~–30 m s–1 in the ion continuity equations is needed during the recovery phase. This additional plasma drift velocity is likely caused by the transition from convecting to corotating flux tubes on the equatorward wall of the trough. The electron densities and temperatures and 630 nm integral intensity at the SAR arc and slightly south of this region as measured for the 18 December 1971 magnetic storm were correctly described by the model without perpendicular electric fields. Within this model framework the effect of the perpendicular electric field ~100 mv m–1 with a duration ~1 h on the SAR arc electron density profiles was found to be large. However, this effect is small if ~1–2 h have passed after the electric field was set equal to zero.

Preliminary investigation of the structure of the upper ionosphere as observed by the topside sounder satellite, Alouette

1964 ◽  
Vol 281 (1387) ◽  
pp. 464-487 ◽  
Keyword(s):  
Magnetic Field ◽  
Preliminary Investigation ◽  
Radiation Belts ◽  
Local Times ◽  
Topside Ionosphere ◽  
Equatorial Anomaly ◽  
Electron Distributions ◽  
Field Lines ◽  
Pass Through ◽  
Upper Ionosphere

Results are presented which illustrate the shape of the topside electron distributions at different local times and different latitudes. It is shown that the ionosphere appears to cool and contract during the night. The morphology and diurnal variation of the geomagnetic equatorial anomaly has been investigated; the structure of the equatorial topside ionosphere appears to be determined by the Earth’s magnetic field, and the geomagnetic anomaly is shown to exist in the topside only between 10.00 and 22.00 local time. Deductions about the composition or temperature of the atmosphere are shown to be complicated because diffusion occurs along field lines only and also because the temperature increases with height above ground. The scale height of the electron density distributions is found to increase with latitude, and it is shown that this effect is probably related to an increase of electron temperature with latitude. Five different localized phenomena have been observed in the ionosphere by the topside sounder, and three of these are shown to occur at the latitudes at which the magnetic field lines which pass through the hearts of the three radiation belts enter the Earth’s atmosphere. Other results are presented which also constitute important evidence that particles dumped from the radiation belts may be important sources of heat or ionization in the atmosphere. Observations made at sunrise and also during an eclipse indicate that the effects of electromagnetic movements and/or movements produced by temperature changes are very important in the upper ionosphere.

scholarly journals <i>F</i>-region ionospheric perturbations in the low-latitude ionosphere during the geomagnetic storm of 25-27 August 1987

2004 ◽  
Vol 22 (10) ◽  
pp. 3479-3501 ◽  
Author(s):  
A. V. Pavlov ◽  
S. Fukao ◽  
S. Kawamura
Keyword(s):  
Geomagnetic Latitude ◽  
Significant Inhibition ◽  
Geomagnetic Equator ◽  
Equatorial Anomaly ◽  
Plasma Drift ◽  
The North ◽  
Mu Radar ◽  
The Difference ◽  
Time Changes ◽  
South Asymmetry

Abstract. We have presented a comparison between the modeled NmF2 and hmF2, and NmF2 and hmF2 which were observed at the equatorial anomaly crest and close to the geomagnetic equator simultaneously by the Akita, Kokubunji, Yamagawa, Okinawa, Manila, Vanimo, and Darwin ionospheric sounders and by the middle and upper atmosphere (MU) radar (34.85° N, 136.10° E) during the 25-27 August 1987 geomagnetically storm-time period at low solar activity near 201°, geomagnetic longitude. A comparison between the electron and ion temperatures measured by the MU radar and those produced by the model of the ionosphere and plasmasphere is presented. The corrections of the storm-time zonal electric field, EΛ, from 16:30 UT to 21:00 UT on 25 August bring the modeled and measured hmF2 into reasonable agreement. In both hemispheres, the meridional neutral wind, W, taken from the HWW90 wind model and the NRLMSISE-00 neutral temperature, Tn, and densities are corrected so that the model results agree with the ionospheric sounders and MU radar observations. The geomagnetic latitude variations in NmF2 on 26 August differ significantly from those on 25 and 27 August. The equatorial plasma fountain undergoes significant inhibition on 26 August. This suppression of the equatorial anomaly on 26 August is not due to a reduction in the meridional component of the plasma drift perpendicular to the geomagnetic field direction, but is due to the action of storm-time changes in neutral winds and densities on the plasma fountain process. The asymmetry in W determines most of the north-south asymmetry in hmF2 and NmF2 on 25 and 27 August between about 01:00-01:30 UT and about 14:00 UT when the equatorial anomaly exists in the ionosphere, while asymmetries in W, Tn, and neutral densities relative to the geomagnetic equator are responsible for the north-south asymmetry in NmF2 and hmF2 on 26 August. A theory of the primary mechanisms causing the morning and evening peaks in the electron temperature, Te, is developed. An appearance, magnitude variations, latitude variations, and a disappearance of the morning Te peaks during 25-27 August are caused by variations in EΛ, thermospheric composition, Tn, and W. The magnitude of the evening Te peak and its time location are decreased with the lowering of the geomagnetic latitude due to the weakening of the effect of the plasma drift caused by W on the electron density. The difference between 25 August and 26-27 August in an appearance, magnitude and latitude variations, and a disappearance of the evening Te peak is caused by variations in W, the thermospheric composition, Tn, and EΛ.

scholarly journals Storm-time ring current: model-dependent results

2012 ◽  
Vol 30 (1) ◽  
pp. 177-202 ◽  
Author(s):  
N. Yu. Ganushkina ◽  
M. W. Liemohn ◽  
T. I. Pulkkinen
Keyword(s):  
Magnetic Field ◽  
Electric Field ◽  
Boundary Conditions ◽  
Electric Fields ◽  
Ring Current ◽  
Current Model ◽  
Current Data ◽  
Storm Events ◽  
Boundary Location ◽  
Field Lines

Abstract. The main point of the paper is to investigate how much the modeled ring current depends on the representations of magnetic and electric fields and boundary conditions used in simulations. Two storm events, one moderate (SymH minimum of −120 nT) on 6–7 November 1997 and one intense (SymH minimum of −230 nT) on 21–22 October 1999, are modeled. A rather simple ring current model is employed, namely, the Inner Magnetosphere Particle Transport and Acceleration model (IMPTAM), in order to make the results most evident. Four different magnetic field and two electric field representations and four boundary conditions are used. We find that different combinations of the magnetic and electric field configurations and boundary conditions result in very different modeled ring current, and, therefore, the physical conclusions based on simulation results can differ significantly. A time-dependent boundary outside of 6.6 RE gives a possibility to take into account the particles in the transition region (between dipole and stretched field lines) forming partial ring current and near-Earth tail current in that region. Calculating the model SymH* by Biot-Savart's law instead of the widely used Dessler-Parker-Sckopke (DPS) relation gives larger and more realistic values, since the currents are calculated in the regions with nondipolar magnetic field. Therefore, the boundary location and the method of SymH* calculation are of key importance for ring current data-model comparisons to be correctly interpreted.

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