Note: This page contains sample records for the topic ionospheric plasma convection from Science.gov.
While these samples are representative of the content of Science.gov,
they are not comprehensive nor are they the most current set.
We encourage you to perform a real-time search of Science.gov
to obtain the most current and comprehensive results.
Last update: August 15, 2014.
1

Effects of Ionospheric Conductivity on Convective Flow of Plasma in the Magnetosphere  

Microsoft Academic Search

Convective flow of plasma in the magnetosphere is apparently driven by the interaction between the solar wind and the magnetosphere, but the flow pattern is regulated by the ionosphere and by pressure gradients in the magnetospheric plasma. The equations for conservation of ionospheric currents are used here to deduce theoretical flow patterns. The currents caused by the pressure of magnetospheric

R. A. Wolf

1970-01-01

2

New SuperDARN Radar Capabilities for Observing Ionospheric Plasma Convection and ITM Coupling in the Mid-Latitude Ionosphere  

NASA Astrophysics Data System (ADS)

Within the past year the first pair of SuperDARN radars funded under the NSF MSI program has become operational at a site near Hays, Kansas. The fields of view of the co-located radars are oriented to provide common-volume observations with two existing radars in Virginia (Wallops, Blackstone) and two MSI radars under construction in Oregon (Christmas Valley). The emerging mid-latitude radar chain will complement the existing SuperDARN coverage at polar cap and auroral latitudes within North America. The mid-latitude radars observe the expansion of auroral effects during disturbed periods, subauroral polarization streams, and small-scale ionospheric irregularities on the nightside that open a window on the plasma drifts and electric fields of the quiet-time subauroral ionosphere. They also measure neutral winds at mesospheric heights and the propagation of ionospheric disturbances due to the passage of atmospheric gravity waves. The new radar capabilities provide unprecedented views of ITM processes in the subauroral ionosphere with applications to studies of ionospheric electric fields, ion-neutral coupling, atmospheric tides and planetary waves, ionospheric plasma structuring and plasma instability. In this talk we describe the new capabilities and the potential for providing large-scale context for related ITM measurements over North America. We present the first high-resolution two-dimensional maps of ionospheric plasma convection at mid-latitudes as generated from common-volume observations with the Hays and Blackstone radars.

Ruohoniemi, J. M.; Baker, J. B.; Greenwald, R. A.; Clausen, L. B.; Shepherd, S. G.; Bristow, W. A.; Talaat, E. R.; Barnes, R. J.

2010-12-01

3

Analytical Study of High-Latitude Plasma Convection in the Ionosphere  

NASA Astrophysics Data System (ADS)

This thesis carries out an analytical study and computer modeling on a global scale of plasma convection, as well as electric fields and currents, in the high latitude ionosphere. The imposed drivers include a cross-cap potential which corresponds to the fairly uniform dawn to dusk electric field inside the polar cap and an idealized sheet-like region II current, plus the polar cap field-aligned current (FAC) systems which simulate the observed NBZ and cusp currents. The electric potential associated with these drivers is derived analytically, and the equipotential contours depict the plasma convection pattern in the high latitude ionosphere under the MHD approximation. Starting from the primary output of the convection potential, the electric field is calculated, the height-integrated currents are determined via Ohm's law, and the region I current is determined via current continuity. In conjunction with the calculations, a graphics package is developed through which the analytical results of the ionospheric convection contours, the vector representation of the electric fields, height-integrated horizontal currents, and the convection flow can be visualized along with a quantitative representation of the FACs. The analytical model is very flexible in that the input variables have been parameterized conveniently. A graphics routine has also been designed to show any of the vector quantities along an arbitrary track across the polar cap or within a certain area of interest for the purpose of comparison of calculated results with observational data from satellite and radar measurements. We conclude that many features of the observed convection patterns may be directly attributed to FAC configurations. The observed Interplanetary magnetic fields (IMF) related convection features can be reproduced in our modeling by imposing FACs corresponding to the IMF situations and deriving convection patterns via the superposition of all of the FAC contributions. While the polar cap driver may play an important role in the convection poleward of the auroral zone, the auroral driver dominates the convection patterns in the sub-auroral region.

Zhang, Ling

1993-01-01

4

Strong IMF By-Related Plasma Convection in the Ionosphere and Cusp Field-Aligned Currents Under Northward IMF Conditions  

NASA Technical Reports Server (NTRS)

We present in this paper an investigation of IMF-By related plasma convection and cusp field-aligned currents using FAST data and AMIE model during a prolonged interval with large positive IMF By and northward Bz conditions (By/Bz much greater than 1). Using the FAST single trajectory observations to validate the global convection patterns at key times and key locations, we have demonstrated that the AMIE procedure provides a reasonably good description of plasma circulations in the ionosphere during this interval. Our results show that the plasma convection in the ionosphere is consistent with the anti-parallel merging model. When the IMF has a strongly positive By component under northward conditions, we find that the global plasma convection forms two cells oriented nearly along the Sun-earth line in the ionosphere. In the northern hemisphere, the dayside cell has clockwise convection mainly circulating within the polar cap on open field lines. A second cell with counterclockwise convection is located in the nightside circulating across the polar cap boundary, The observed two-cell convection pattern appears to be driven by the reconnection along the anti-parallel merging lines poleward of the cusp extending toward the dusk side when IMF By/Bz much greater than 1. The magnetic tension force on the newly reconnected field lines drives the plasma to move from dusk to dawn in the polar cusp region near the polar cap boundary. The field-aligned currents in the cusp region flow downward into the ionosphere. The return field-aligned currents extend into the polar cap in the center of the dayside convection cell. The field-aligned currents are closed through the Peterson currents in the ionosphere, which flow poleward from the polar cap boundary along the electric field direction.

Le, G.; Lu, G.; Strangeway, R. J.; Pfaff, R. F., Jr.; Vondrak, Richard R. (Technical Monitor)

2001-01-01

5

Travelling convection vortices in the ionosphere map to the central plasma sheet  

NASA Astrophysics Data System (ADS)

We investigate the magnetospheric domain responsible for the generation of ionospheric travelling convection vortices (TCV) by comparing the location of the TCV to the locations of the low-altitude particle-precipitation boundaries deduced from the DMSP satellite measurements. For three very well documented TCV events we are able to identify suitable satellite passes, in the sense that for each event we can identify two to three passes occurring close to the TCV observation in both time and space. In all three cases the comparisons place the TCV centres at or equatorward of the central plasma sheet/boundary plasma sheet precipitation boundary. Thus our results indicate that the field-aligned currents related to the TCV originate in the plasma sheet rather than at the magnetopause or in the low-latitude boundary layer, as previous studies suggest. Acknowledgements. We gratefully appreciate the on-line DMSP database facility at APL (Newell et al., 1991) from which this study has benefited greatly. We wish to thank E. Friis-Christensen for his encouragement and useful discussions. A. Y. would like to thank the Danish Meteorological Institute, where this work was done, for its hospitality during his stay there and the Nordic Baltic Scholarship Scheme for its financial support of this stay. Topical Editor K.-H. Glassmeier thanks M. J. Engebretson and H. Lhr for their help in evaluating this paper.--> Correspondence to: A. Yahnin-->

Yahnin, A.; Moretto, T.

1996-10-01

6

Ionospheric convection signatures and magnetic field topology  

NASA Technical Reports Server (NTRS)

A statistical study of signatures of the high-latitude ionospheric convection pattern and the simultaneously observed energetic electron precipitation is presented. Most often found are convection cells in which the sunward flowing region contains auroral particle precipitation but the antisunward flowing region does not. However, observations also show the frequent occurrence of convection cells in which neither the antisunward nor the sunward flowing plasma region contains auroral particle precipitation. These findings may appear within the dawnside or duskside convection pattern and strongly suggest that such convection cells may be associated with open magnetic field lines that thread the magnetotail lobes.

Coley, W. R.; Heelis, R. A.; Hanson, W. B.; Reiff, P. H.; Sharber, J. R.

1987-01-01

7

Polar-cap plasma convection measurements and their relevance to the real-time modeling of the high-latitude ionosphere  

SciTech Connect

Plasma-convection measurements, using Digisonde ionospheric sounders, were conducted. The plasma convection or ionospheric-drift measurements conducted at Thule and Qaanaaq during campaigns from Winter 1983/84 to present provide evidence, that antisunward convection dominates in the polar cap with velocities typical between 300 and 900 m.sec. Drift shears were observed during periods of arc-transition (quiet magnetic conditions). Observations of the plasma drift at Goose Bay show a drift reversal from westward to eastward around midnight CGLT. Observations at Argentia, typically a suboval/trough station, provide evidence under magnetically disturbed conditions for the midnight reversal of the antisunward flow pattern. However, the data are less consistent under magnetically quiet conditions. The proximity of the station to the boundary between corotating and convecting plasma may at times affect the consistency of the measurements. Recent theoretical calculations of electron density profiles within the high-latitude/polar-cap ionosphere demonstrate that the diurnal foF2 variation observed at Thule, is controlled by the plasma-convections pattern and the associated drift velocities. The model calculations for Bz < 0 and Bz. approx. 0 show factor 2 to 3 differences in Nmax over Thule, supporting the stated importance of convection pattern and velocity measurements for the modelling of the high-latitude ionosphere.

Not Available

1987-05-07

8

The excitation of plasma convection in the high-latitude ionosphere  

SciTech Connect

Recent observations of ionospheric flows by ground-based radars, in particular by the European Incoherent Scatter (EISCAT) facility using the Polar experiment, together with previous analyses of the response of geomagnetic disturbance to variations of the interplanetary magnetic field (IMF), suggest that convection in the high-latitude ionosphere should be considered to be the sum of two intrinsically time-dependent patterns, one driven by solar wind-magnetosphere coupling at the dayside magnetopause, the other by the release of energy in the geomagnetic tail (mainly by dayside and nightside reconnection, respectively). The flows driven by dayside coupling are largest on the dayside, where they usually dominate, are associated with an expanding polar cap area, and are excited and decay on {approximately} 10-min time scales following southward and northward turnings of the IMF, respectively. The latter finding indicates that the production of new open flux at the dayside magnetopause excites magnetospheric and ionospheric flow only for a short interval, {approximately} 10 min, such that the flow driven by this source subsequently decays on this time scale unless maintained by the production of more open flux tubes. Correspondingly, the flows excited by the release of energy in the tail, mainly during substorms, are largest on the nightside, are associated with a contracting polar cap boundary, and are excited on {approximately} 1-hour time scales following a southward turn of the IMF. In general, the total ionospheric flow will be the sum of the flows produced by these two sources, such that due to their different response times to changes in the IMF, considerable variations in the flow pattern can occur for a given direction and strength ofthe IMF. Consequently, the ionospheric electric field cannot generally be regarded as arising from a simple mapping of the solar wind electric field along open flux tubes.

Lockwood, M. (Rutherford Appleton Lab., Chilton (England)); Cowley, S.W.H.; Freeman, M.P. (Imperial College, London (England))

1990-06-01

9

Relationship of Topside Ionospheric Ion Outflows to Auroral Forms and Precipitation, Plasma Waves, and Convection Observed by Polar  

NASA Technical Reports Server (NTRS)

The POLAR satellite often observes upflowing ionospheric ions (UFIs) in and near the aurora] oval on southern perigee (approx. 5000 km altitude) passes. We present the UFI features observed by the thermal ion dynamics experiment (TIDE) and the toroidal imaging mass angle spectrograph (TIMAS) in the dusk-dawn sector under two different geomagnetic activity conditions in order to elicit their relationships with auroral forms, wave emissions, and convection pattern from additional POLAR instruments. During the active interval, the ultraviolet imager (UVI) observed a bright discrete aurora on the duskside after the substorm onset and then observed a small isolated aurora form and diffuse auroras on the dawnside during the recovery phase. The UFIs showed clear conic distributions when the plasma wave instrument (PWI) detected strong broadband wave emissions below approx. 10 kHz, while no significant auroral activities were observed by UVI. At higher latitudes, the low-energy UFI conics gradually changed to the polar wind component with decreasing intensity of the broadband emissions. V-shaped auroral kilometric radiation (AKR) signatures observed above -200 kHz by PWI coincided with the region where the discrete aurora and the UFI beams were detected. The latitude of these features was lower than that of the UFI conics. During the observations of the UFI beams and conics, the lower-frequency fluctuations observed by the electric field instrument were also enhanced, and the convection directions exhibited large fluctuations. It is evident that large electrostatic potential drops produced the precipitating electrons and discrete auroras, the UFI beams, and the AKR, which is also supported by the energetic plasma data from HYDRA. Since the intense broadband emissions were also observed with the UFIs, the ionospheric ions could be energized transversely before or during the parallel acceleration due to the potential drops.

Hirahara, M.; Horwitz, J. L.; Moore, T. E.; Germany, G. A.; Spann, J. F.; Peterson, W. K.; Shelley, E. G.; Chandler, M. O.; Giles, B. L.; Craven, P. D.; Pollock, C. J.; Gurnett, D. A.; Pickett, J. S.; Persoon, A. M.; Scudder, J. D.; Maynard, N. C.; Mozer, F. S.; Brittnacher, M. J.; Nagai, T.

1998-01-01

10

Ionospheric convection associated with discrete levels of particle precipitation  

Microsoft Academic Search

A precipitation index is described which quantifies the intensity and spatial extent of high-latitude particle precipitation based on observations made along individual satellite passes. By sorting plasma-convection data according to this index, average patterns of the ionospheric convection electric field were derived from a data set consisting of five years' observations by the Millstone Hill radar. Reference to the instantaneous

J. C. Foster; J.M. Holt; R. G. Musgrove; D. S. Evans

1986-01-01

11

Observation of interplanetary magnetic field and of ionospheric plasma convection in the vicinity of the dayside polar cleft  

NASA Technical Reports Server (NTRS)

Dayside ionosphere convection at high latitudes has been examined during a series of experiments using the Sondrestrom radar together with ancillary observations of the interplanetary magnetic field (IMF) by the IMP-8 spacecraft. The radar experiments obtained a latitude coverage of 67.6 to 81.3 deg Lambda and a temporal resolution of between 14 to 25 minutes. A total of 17 rotations through the dayside cleft region during April, June and July, 1983 have been examined. The observations show two convection cells with sunward flow at lower latitudes and antisunward flow at higher latitudes. The flow commonly rotates through a 180 deg angle resulting in the predominant appearance of east-west flows. Rapid temporal variations in the convection velocities are frequently observed. Many of the high latitude variations in convection velocity appear to be directly related to variations in the IMF By component, with eastward (westward) velocity associated with negative (positive) By. This is strong evidence for a direct electrical coupling between the solar wind and dayside high latitude ionosphere.

Clauer, C. R.; Banks, P. M.; Smith, A. Q.; Jorgensen, T. S.; Friis-Christensen, E.; Vennerstrom, S.; Wickwar, V. B.; Kelly, J. D.; Doupnik, J.

1984-01-01

12

Ionospheric convection driven by NBZ currents  

NASA Technical Reports Server (NTRS)

Computer simulations of Birkeland currents and electric fields in the polar ionosphere during periods of northward IMF were conducted. When the IMF z component is northward, an additional current system, called the NBZ current system, is present in the polar cap. These simulations show the effect of the addition of NBZ currents on ionospheric convection, particularly in the polar cap. When the total current in the NBZ system is roughly 25 to 50 percent of the net region 1 and 2 currents, convection in the central portion of the polar cap reverses direction and turns sunward. This creates a pattern of four-cell convection with two small cells located in the polar cap, rotating in an opposite direction from the larger cells. When the Birkeland currents are fixed (constant current source), the electric field is reduced in regions of relatively high conductivity, which affects the pattern of ionospheric convection. Day-night asymmetries in conductivity change convection in such a way that the two polar-cap cells are located within the large dusk cell. When ionospheric convection is fixed (constant voltage source), Birkeland currents are increased in regions of relatively high conductivity. Ionospheric currents, which flow horizontally to close the Birkeland currents, are changed appreciably by the NBZ current system. The principal effect is an increase in ionospheric current in the polar cap.

Rasmussen, C. E.; Schunk, R. W.

1987-01-01

13

Ionospheric convection associated with discrete levels of particle precipitation  

SciTech Connect

A precipitation index is described which quantifies the intensity and spatial extent of high-latitude particle precipitation based on observations made along individual satellite passes. By sorting plasma-convection data according to this index, average patterns of the ionospheric convection electric field were derived from a data set consisting of five years' observations by the Millstone Hill radar. Reference to the instantaneous precipitation index, and the average patterns keyed to it, provides a means of characterizing the global precipitation and convection patterns throughout an event.

Foster, J.C.; Holt, J.M.; Musgrove, R.G.; Evans, D.S.

1986-07-01

14

Ionospheric convection response to changing IMF direction  

NASA Technical Reports Server (NTRS)

By combining ground-based and satellite-based measurements of ionospheric electric fields, conductivities and magnetic perturbations, it was possible to examine the characteristics of instantaneous, ionospheric convection patterns associated with changing directions of the interplanetary magnetic field (IMF). In response to a rapid southward-to-northward turning of the IMF on July 23, 1983, the ionospheric convection reconfigured over a period of 40 minutes. The configuration changed from a conventional two-cell pattern to a contracted four-cell pattern, with reversed convection cells in the high-latitude dayside, associated with a strong potential drop of about 75 kV. Later, in response to a gradual rotation of the IMF from the +Z through the -Y toward the -Z direction, the nightside cells disappeared and the dawn cell in the reversed pair wrapped around and displaced the dusk cell until a conventional two-cell pattern was reestablished, largely in accord with the qualitative model of Crooker (1988). The results suggest that multiple cells can arise as a result of strong southward to northward transitions in the IMF. They appear to persist for sometime thereafter.

Knipp, D. J.; Richmond, A. D.; Emery, B.; Crooker, N. U.; De La Beaujardiere, O.; Evans, D.

1991-01-01

15

Effects of gravity wave dissipation on the thermosphere and ionosphere from deep convection: Excitation of secondary gravity waves, and large-scale changes to the background neutral wind, temperature, plasma frequency, and TEC  

NASA Astrophysics Data System (ADS)

In this talk, we discuss how the propagation and dissipation of gravity waves in the thermosphere affect both the thermosphere and ionosphere. We then discuss the propagation and dissipation of gravity waves excited by deep convection. We show that secondary gravity waves are excited by both the body forcing and the heating/cooling which accompany the dissipation of these gravity waves in the thermosphere. We show new global simulation results which model the gravity wave effects in the thermosphere and ionosphere from deep convection over the entire Earth for a 13 day period during the recent extreme solar minimum. We find that large-scale changes in the background neutral wind, temperature, plasma frequency, and TEC accompany the dissipation of these convectively-generated gravity waves.

Vadas, S. L.; Liu, H.

2012-12-01

16

Mapping ionospheric convection patterns to the magnetosphere  

SciTech Connect

While convection patterns in the high-latitude ionosphere are usually presented in a corotating frame of reference, those of the magnetosphere are given in inertial coordinates. In the corotating representation the convection throat, which is frequently associated with the cusp, opens between 1000 and 1100 MLT. Cusp precipitation, however, centers about noon. The authors find that transforming the convection patterns of Heppner and Maynard (hereinafter H-M) into inertial coordinates aligns the throat region with local noon. They present projections of the H-M patterns to the magnetosphere in both corotating and inertial coordinates using the magnetic field model of Tsyganenko. In inertial coordinates the mapped H-M convection throat opens at noon. Consistent with predictions of the Rice convection model for magnetospheric electric fields late in the substorm cycle, only a small fraction of the equipotential contours penetrate to the subsolar region. This suggests that a significant portion of flux tube merging occurs on magnetic field lines whose equatorial mapping is on the flanks of the magnetosphere. Nonconjugacy between the mapping of H-M patterns for both positive and negative interplanetary magnetic field B{sub Y}, especially in the 1400-1600 LT sector, may explain the B{sub Y} dependence of the electron precipitation {open_quotes}hot spot{close_quotes} discovered by Evans. A separate lobe cell is not required to explain the central, equipotential contours of the large convection cell. 31 refs., 3 figs.

Maynard, N.C.; Denig, W.F.; Burke, W.J. [Hanscom Air Force Base, MA (United States)] [Hanscom Air Force Base, MA (United States)

1995-02-01

17

Observations of an enhanced convection channel in the cusp ionosphere  

SciTech Connect

Transient or patchy magnetic field line merging on the dayside magnetopause, giving rise to flux transfer events (FTEs), is thought to play a significant role in energizing high-latitude ionospheric convection during periods of southward interplanetary magnetic field. Several transient velocity patterns in the cusp ionosphere have been presented as candidate FTE signatures. Instrument limitations, combined with uncertainties about ionospheric signature of FTEs have yet to be presented. This paper describes combined observations by the PACE HF backscatter radar and the DMSP F9 polar-orbiting satellite of a transient velocity signature in the southern hemispheric cusp. The prevailing solar wind conditions suggest that it is the result of enhanced magnetic merging at the magnetopause. The satellite particle precipitation data associated with the transient are typically cusplike in nature. The presence of spatially discrete patches of accelerated ions at the equatorward edge of the cusp is consistent with the ion acceleration that could occur with merging. The combined radar line-of-sight velocity data and the satellite transverse plasma drift data are consistent with a channel of enhanced convection superposed on the ambient cusp plasma flow. This channel is at least 900 km in longitudinal extent but only 100 km wide. It is zonally aligned for most of its extent, except at the western limit where it rotates sharply poleward. Weak return flow is observed outside the channel. These observations are compared with and contrasted to similar events seen by the EISCAT radar and by optical instruments. 30 refs., 2 figs.

Pinnock, M.; Rodger, A.S.; Dudeney, J.R. (Natural Environment Research Council, Cambridge (United Kingdom)); Baker, K.B.; Neweli, P.T.; Greenwald, R.A. (Johns Hopkins Univ., Laurel, MD (United States)); Greenspan, M.E. (Boston Univ., MA (United States))

1993-03-01

18

Studies of ionospheric plasma and electrodynamics and their application to ionosphere-magnetosphere coupling  

SciTech Connect

The contribution of the Dynamics Explorer (DE) program to the study of small-scale structure in the equatorial ionospheric number density and the bulk motion of the plasma in the equatorial ionosphere is considered. DE results have helped elucidate the role of E region and F region winds in decreasing the magnitude of variations in the east-west plasma drift at night, as a function of magnetic flux tube apex height, with increasing height above the altitude of the peak F region concentration. Other results concern the ionospheric convection pattern at high latitudes during periods of southward IMF, the magnetosphere/solar-wind interaction that may be involved in the production of the convection pattern, and the characteristics of the high-latitude ionospheric plasma motion during periods of northward IMF. 41 references.

Heelis, R.A.

1988-05-01

19

Convection surrounding mesoscale ionospheric flow channels  

NASA Astrophysics Data System (ADS)

We evaluate data from the European Incoherent Scatter (EISCAT) Svalbard radar (ESR) and Defense Meteorological Satellite Program (DMSP) spacecraft coupled with data from the Super Dual Auroral Radar Network (SuperDARN) polar cap convection patterns in order to study how the ionospheric convection evolves around a sequence of transient, mesoscale flow channel events in the duskside of the cusp inflow region. On a northwestward convection background for the interplanetary magnetic field (IMF) BY positive and BZ negative, a sequence of three eastward flow channels formed over the course of 1 hour in response to three sharp IMF rotations to IMF BY negative and IMF BZ positive. The first and third channels, due to IMF BY negative periods of 13 min and >30 min, respectively, develop in a similar manner: they span the entire ESR field of view and widen poleward with increasing time elapsed since their first appearance until the IMF rotates back. The convection patterns are consistent with the line-of-sight data from the ESR and DMSP within a 10 min adaption time. The flow lines form a twin-vortex flow, with the observed channel being the twin vortices' center flow. The fitting algorithm was pushed to its limits in terms of spatial resolution in this study. During portions of the channel events, the suggested twin-cell flow is not in agreement with our physical interpretation of the flow channels being reconnection events because cell closure is suggested across an anticipated nonreconnecting open-closed boundary. For these segments, we present simulated patterns which have been arrived at by a combination of looking at the raw data and examining the fitted convection patterns.

Rinne, Y.; Moen, J.; Baker, J. B. H.; Carlson, H. C.

2011-05-01

20

Ionospheric plasma cloud dynamics  

NASA Technical Reports Server (NTRS)

Measurements of the thermospheric neutral wind and ionospheric drift made at Eglin AFB, Florida and Kwajalein Atoll are discussed. The neutral wind measurements at Eglin had little variation over a period of four years for moderate magnetic activity (Kp 4); the ionospheric drifts are small. Evidence is presented that indicates that increased magnetic activity has a significant effect on the neutral wind magnitude and direction at this midlatitude station. The neutral wind at dusk near the equator is generally small although in one case out of seven it was significantly larger. It is described how observations of large barium releases can be used to infer the degree of electrodynamic coupling of ion clouds to the background ionosphere. Evidence is presented that indicates that large barium releases are coupled to the conjugate ionosphere at midlatitudes.

1976-01-01

21

South Pole electric field responses to overhead ionospheric convection  

Microsoft Academic Search

Moau_rements of the vertical atmospheric electric field (E) at the South Pole between 1982 and 1986 have been analyzed, and the results reveal an important component due to magnetospheric-ionospheric coupling processes. The results are consistent with the theoretical expectation that the ionospheric convection potential patterns in the polar caps, as measured by satellites, are superimposed on the otherwise nearly uniform

B. A. Tinsley; Weiping Liu; R. P. Rohrbaugh; M. W. Kirkland

1998-01-01

22

South Pole electric field responses to overhead ionospheric convection  

Microsoft Academic Search

Measurements of the vertical atmospheric electric field (Ez) at the South Pole between 1982 and 1986 have been analyzed, and the results reveal an important component due to magnetospheric-ionospheric coupling processes. The results are consistent with the theoretical expectation that the ionospheric convection potential patterns in the polar caps, as measured by satellites, are superimposed on the otherwise nearly uniform

B. A. Tinsley; Weiping Liu; R. P. Rohrbaugh; M. W. Kirkland

1998-01-01

23

Model of the high-latitude ionospheric convection pattern  

Microsoft Academic Search

Mathematical expressions have been constructed that allow the large-scale global convection characteristics of the high-latitude ionosphere to be reproduced. The model contains no discontinuities in the ion convection velocity and as such should be useful in F region chemical models. The number of variables in the model allow such features as the dayside throat and the Harang discontinuity to be

R. A. Heelis; J. K. Lowell; R. W. Spiro

1982-01-01

24

Ionospheric convection at Casey, a southern polar cap station  

NASA Astrophysics Data System (ADS)

A digital ionosonde (Digisonde Portable Sounder 4) located at Casey, Antarctica (66.3S, 110.5E, -80.8 corrected geomagnetic latitude) has been operational since early 1993 and has accumulated 3 years of plasma drift measurements, providing an excellent data set for studying the characteristics of ionospheric convection flow at a southern polar cap station. The purpose of this study is to investigate the influence of the IMF on the F region ionospheric convection over Casey and to compare it to the Heppner-Maynard satellite-derived electric field models. We find clear dependencies in the drift on the sign and strength of the IMF By and Bz components and with Kp. Antisunward flow dominates during Bz south conditions, turning to have a sunward component around noon when Bz is northward. The By component causes the entire convection system to rotate and distorts the dayside flow in the proximity of the throat, with a dawnward (duskward) component for By negative (positive). Comparison with the Bz south Heppner-Maynard BC, DE, and A patterns is favorable at most times, although we predict a rounder, more dominant dusk (dawn) cell and a smaller crescent-shaped dawn (dusk) cell for By<0 (By>0). There is a dependence on Kp when Bz is south in both the model and the drifts, flow directions becoming more antisunward and velocities becoming higher on the dayside as Kp increases. This implies the polar cap is expanding under conditions of enhanced reconnection. When Bz is north, the F region drift agreement with the BCP(P) and DEP(P) models is excellent on the dawn (dusk) side for By<0 (By>0) but diverges on the opposite side as the pattern flow lines twist sunward. Separation of the drifts into Bz weakly (<3nT) and strongly (>3nT) northward cases did not reveal any appreciable difference in the observed drift velocities.

Smith, P. R.; Dyson, P. L.; Monselesan, D. P.; Morris, R. J.

1998-02-01

25

Ionospheric convection during different phases of magnetospheric substorms  

NASA Technical Reports Server (NTRS)

Observations of ionospheric convection flows at a range of local times during the various phases of the substorm cycle are reported on with the aim of investigating the convection behavior during a range of times and phases. The ionospheric flow observations are from the EISCAT and DMSP satellites. The substorm phases are identified from energetic particle measurements from geosynchronous satellites. The growth phase convection indicates an initial expansion of the polar cap. There is an unexplained poleward motion of the flow reversal boundary (FRB). It is concluded that this motion does not necessarily provide a true representation of the balance between reconnection at the dayside and in the tail. The expansion phase flows do not show any evidence for tail reconnection until late in the phase. The convection during the recovery phase is indicative of tail reconnection as there is evidence that there is only a lobe cell driving convection on the dayside.

Lester, M.; Fox, N. J.; Reeves, G. D.; Hairston, M.

1996-01-01

26

Polar Cap Potential Saturation and Ionospheric Convection Patterns during Superstorms  

NASA Astrophysics Data System (ADS)

Five super intense magnetic storms (with minimum Dst < -200 nT) were examined to investigate the relationship between polar cap potential (PCP) saturation and ionospheric convection patterns. A quantitative method was used to determine whether or not PCP was saturated by applying both linear and nonlinear (exponential) fits for each event. The results showed that PCP saturation occurred for two of five. The two events with saturation had distorted ionospheric convection patterns (D-CONV) with asymmetric vortices, while for the other three events without PCP saturation had well-known standard convection (S-CONV) with quasi-symmetric twin vortices. The authors conclude that sporadic midnight sector substorm electric fields may contribute to the asymmetric convection patterns and PCP saturation, in agreement with previous speculations. Further analyses are needed to confirm this hypothesis.t;

Du, A.; Sun, W.; Tsurutani, B.

2012-12-01

27

Plasma interactions in Titan's ionosphere  

NASA Astrophysics Data System (ADS)

The Cassini mission has collected vast amounts of in situ data within the ionosphere of Saturn's moon Titan and has shown the complexity of the interaction of Saturn's magnetospheric plasma with Titan. Models of the interactions have been created; however, none have been able to completely describe the observed phenomena. Most notably, modeled electron densities are much larger than the electron densities observed by instruments aboard the Cassini spacecraft. This thesis will explore the possible causes of this discrepancy between measured and modeled electron densities using models calculating the production of ions due to solar photons and magnetospheric electrons precipitating down magnetic field lines and into the ionosphere, temperature calculations of the thermal electron population (electrons with energies less than 2 eV), and chemical reactions in the ionosphere. The results of these models will be compared to data collected by instruments aboard Cassini. Modeled ion production rates and thermal electron temperature profiles will be shown to be in good agreement with ion production rates derived from data collected by the Ion -- Neutral Mass Spectrometer (INMS) and electron temperatures measured by the Radio and Plasma Wave Science -- Langmuir Probe above 1000 km. Modeled ion mass spectra will be generated near the ionospheric peak and will be compared with the INMS measured mass spectra to examine the effects of chemical loss processes on the ion densities. From this analysis it will be shown that the overabundance of modeled electrons is not caused by over production of ions and that chemical loss processes, predominantly the electron dissociative recombination coefficient of HCNH+, need to be reexamined. After the model has been proven to reproduce accurate profiles of ion production and temperature, ion production profiles will be generated using solar photons and magnetospheric electron fluxes for four canonical cases detailed in the work of Rymer et al. [2009] and a globally averaged model of the neutral densities based on INMS neutral measurements from more than 30 flybys of Titan. These generic profiles can be combined to predict ionospheric observations made by the Cassini spacecraft for a variety of solar zenith angles and magnetospheric conditions.

Richard, Matthew Scott

28

Plasma Temperatures in the Ionosphere of Saturn  

Microsoft Academic Search

Using a one-dimensional version of the Saturn Thermosphere Ionosphere Model (STIM), we perform calculations of the ion and electron temperatures in the ionosphere of Saturn. There are no direct measurements of plasma temperatures in Saturn's atmosphere published to date, but they are often estimated from the topside plasma scale heights of radio occultation measurements of electron density. Based on Pioneer,

Luke Moore; M. Galand; M. Mendillo; I. Mller-Wodarg

2007-01-01

29

The relationship between ionospheric convection and magnetic activity  

SciTech Connect

In this paper, the authors show that there is a significant relationship between magnetic activity and the high-latitude ionospheric convection electric fields. In particular, when the westward electrojet is much stronger than the eastward electrojet, as occurs during magnetospheric substorms, the electric field patterns show subtle, but important, changes from the configurations that are obtained under more quiet conditions. The substorm differences are detected primarily near midnight, where there is an enhanced westward electric field associated with a penetration of the positive-potential, dawn convection cell into the negative, dusk convection cell. The peak value of the positive potential also increases during substorms and its location shifts closer to midnight, while the negative cell remains relatively constant. These results were obtained through the use of a procedure that uses electric field measurements from the DE 2 satellite to derive maps of the locations of the convection reversal boundaries, and functions for the distribution of the electric potential around these boundaries. This was accomplished for several sets of data that were grouped according to the interplanetary magnetic field and geomagnetic activity. Further refinements in the authors' analysis procedure are possible. The results could be used to produce more accurate maps of ionospheric convection. They also show that distortions of the electric field patterns near midnight are simply the result of polarization electric fields around conductivity enhancements. The distorted electric fields satisfy the condition that the ionospheric Hall current be divergence-free. 23 refs., 9 figs.

Shue, J.H.; Weimer, D.R. (Univ. of Alaska, Fairbanks, AK (United States))

1994-01-01

30

Ground-based studies of ionospheric convection associated with substorm expansion  

SciTech Connect

The instantaneous patterns of electric fields and currents in the high-latitude ionosphere are deduced by combining satellite and radar measurements of the ionospheric drift velocity, along with ground-based magnetometer observations for October 25, 1981. For this purpose, an updated version of the assimilative mapping of ionospheric electrodynamics technique has been used. These global patterns are unobtainable from any single data set. The period under study was characterized by a relatively stable southward interplanetary magnetic field (IMF), so that the obtained electric field patterns do reflect, in general, the state of sustained and enhanced plasma convection in the magnetosphere. During one of the satellite passes, however, an intense westward electrojet caused by a substorm intruded into the satellite (DE 2) and radar (Chatanika, Alaska) field of view in the premidnight sector, providing a unique opportunity to differentiate the enhanced convection and substorm expansion fields. The distributions of the calculated electric potential for the expansion and maximum phases of the substorm show the first clear evidence of the coexistence of two physically different systems in the global convection pattern. The changes in the convection pattern during the substorm indicate that the large-scale potential distributions are indeed of general two-cell patterns representing the southward IMF status, but the night-morning cell has two positive peaks, one in the midnight sector and the other in the late morning hours, corresponding to the substorm expansion and the convection enhancement, respectively. 40 refs., 12 figs., 1 tab.

Kamide, Y. [Nagoya Univ., Toyokawa (Japan)]|[National Center for Atmospheric Research, Boulder, CO (United States); Richmond, A.D.; Emery, B.A.; Hutchins, C.F. [National Center for Atmospheric Research, Boulder, CO (United States); Ahn, B.H. [National Center for Atmospheric Research, Boulder, CO (United States)]|[Kyungpook National Univ., Taegu (Korea, Democratic People`s Republic of); Beaujardiere, O. de la [Stanford Research Institute International, Menlo Park, CA (United States); Foster, J.C. [Massachusetts Institute of Technology, Cambridge, MA (United States); Heelis, R.A. [Univ. of Texas at Dallas, Richardson, TX (United States); Kroehl, H.W. [National Geophysical Data Center, Boulder, CO (United States); Rich, F.J. [Hanscom Air Force Base, MA (United States)] [and others

1994-10-01

31

Can the ionosphere regulate magnetospheric convection?  

Microsoft Academic Search

Following a southward shift of the interplanetary magnetic field, which implies enhanced reconnection at the nose of the magnetosphere, the magnetopause shrinks from its ChapmanFerraro equilibrium position. If the convective return of magnetic flux to the magnetopause equaled the reconnection rate, the magnetopause would not shrink. Consequently, there is a delay in the development of magnetospheric convection following the onset

F. V. Coroniti; C. F. Kennel

1973-01-01

32

A three-dimensional diffusion/convection model of the large scale magnetic field in the Venus ionosphere  

NASA Technical Reports Server (NTRS)

A three-dimensinal diffusion/convection model of the dayside Venus ionosphere magnetic field was developed on the basis of previously published one-dimensional diffusion/convection models, and assuming that the field and flow at the upper boundary (in the magnetic barrier) as well as the ionospheric plasma velocity are known. The results indicate that the low-altitude magnetosheath field draping may be distorted by the interaction with the ionosphere in such a manner that there is an apparent 'focusing' of the field toward the subsolar point, caused by the shear in the horizontal velocity between the magnetosheath and ionospheric flows. A comparison of published magnetic-field observations with the present results indicates that the simple nesting of external and internal velocity fields may be a good approximation to global plasma flows near Venus under normal conditions.

Luhmann, J. G.

1988-01-01

33

Studies of plasma irregularities and convection in the polar ionosphere using HILAT, SABRE and EISCAT. Interim report, 1 Feb 88-31 Mar 89  

SciTech Connect

A statistical study of the F-region main ionospheric trough has been undertaken with EISCAT common programme data to assess the possibility that the trough region is a perferential region for the generation of E-region irregularities. Three years of CP-3 data from EISCAT formed the basis of this study. Backscatter observed by the coherent radar, SABRE, was also utilized to study the occurrence of irregularities in the E-region. On 26 out of the 36 days when the trough was observed by EISCAT, SABRE observed coherent backscatter. Although this percentage seems high, there was no consistent relationship between the latitude of the trough minimum and the latitude of peak backscatter intensity. A case study involving a four day run of EISCAT in September 1986 indicates that the trough latitude can be affected by changes in the interplanetary magnetic field north-south components. On two days rapid decreases in the latitude of the trough were related to a southward turning of the IMF and the onset of backscatter. The high percentage of occurrence of backscatter is believed to be caused by enhanced convection.

Jones, T.B.; Lester, M.; Wilkinson, A.J.

1989-08-21

34

Global flow patterns and ionospheric convection in Jupiter's magnetosphere  

NASA Astrophysics Data System (ADS)

The size and configuration of Jupiter's magnetosphere is controlled by the ambient solar wind conditions, Jupiter's strong rotation and intrinsic magnetic field and the plasma sources internal to the magnetosphere. We will examine the relative importance of each of these factors using our 3D global magnetohydrodynamic (MHD) model of the Jovian magnetosphere. This model uses adaptive mesh refinement (AMR) to model the global Jovian system, including the mass loading region near Io's orbit. The inner boundary of the MHD model, at 3 R_J, is coupled to a height integrated ionospheric electric potential model. We will present results of the coupled model and show similarities and differences to other planetary magnetospheres. We will show that Jupiter's magnetosphere without mass loading and rotation is Earth-like in all but size. Adding rotation determines, to a large extent, the flow pattern in the magnetosphere. The addition of mass loading, although extremely important, does not change the character or topology of the magnetospheric convection but instead modifies the locations of magnetospheric features such as the bow shock, the magnetopause and the location of reconnection sites. In addition, we will show how features like the magnetospheric "wings" [Song, ASR, 2001] at the Earth are manifest and modified in the magnetosphere of Jupiter.

Hansen, K. C.; de Zeeuw, D. L.; Gombosi, T. I.; Ridley, A. J.; Toth, G.; Sokolov, I.

2003-04-01

35

The response of the large scale ionospheric convection pattern to changes in the IMF and substorms - Results from the SUNDIAL 1987 campaign  

NASA Astrophysics Data System (ADS)

Multipoint observations of ionospheric convection, made during the SUNDIAL 1987 campaign (May 29 to June 8) which included two intervals of variable IMF Bz and By and several substorms, are used to examine the response of the ionospheric convection in the postdusk and midnight sectors to changes in the IMF Bz component, as well as the effect of substorms on ionospheric convection. It was found that the primary ionospheric effect of a change in the IMF from positive Bz to negative Bz is an enhancement in plasma flow magnitude. The response time of the ionospheric convection to each southward turning varies from 15 min near 1800 MLT to 30 min near 2100 MLT and close to one hour near midnight. During one of the substorms, which consisted of several intensifications, the nightside flow reversal moved progressively to earlier local times in response to each substorm intensification.

Lester, M.; de La Beaujardiere, O.; Foster, J. C.; Freeman, M. P.; Luehr, H.; Ruohoniemi, J. M.; Swider, W.

1993-07-01

36

Extension of convection modeling into the high-latitude ionosphere - Some theoretical difficulties  

NASA Technical Reports Server (NTRS)

The Rice Convection Model (RCM) is extended and merged with empirical models so as to cover the entire high-latitude ionosphere with the aim of providing precipitation and electric field inputs for ionosphere and thermosphere modelers and producing a model in which the boundaries of the precipitation and electric field patterns maintain physically consistent relationships to each other. The computed auroral electron energy flux, plotted as a function of latitude, exhibited an exaggerated two-peak structure. When no floor was placed under the precipitation rate, the minimum between the two peaks was much too deep to be consistent with typical observations. The regions of excessively weak precipitation map to equatorial distances of 15-35 RE and thus to the regions of the plasma sheet that were not included in previous self-consistent convection calculations.

Wolf, R. A.; Spiro, R. W.; Rich, F. J.

1991-01-01

37

Ionospheric convection during the magnetic storm of 20-21 March 1991  

NASA Technical Reports Server (NTRS)

We report on the response of high-latitude ionospheric convection during the magnetic storm of March 20-21 1990. IMP-8 measurements of solar wind plasma and interplanetary magnetic field (IMF), ionospheric convection flow measurements from the Wick and Goose Bay coherent radars, EISCAT, Millstone Hill and Sondrestorm incoherent radars and three digisondes at Millstone Hill, Goose Bay and Qaanaaq are presented. Two intervals of particular interest have been indentified. The first starts with a storm sudden commencement at 2243 UT on March 20 and includes the ionospheric activity in the following 7 h. The response time of the ionospheric convection to the southward tuning of the IMF in the dusk to midnight local times is found to be approximately half that measured in a similar study at comparable local times during more normal solar wind conditions. A subsequent reconfiguration of the nightside convection pattern was also observed, although it was not possible to distinguish between effects due to possible changes in B(sub y) and effects due to substorm activity. The second interval, 1200-2100 UT 21 March 1990, included a southward turning of the IMF which resulted in the B(sub z) component becoming -10 nT. The response time on the dayside to this change in the IMF at the magnetopause was approximately 15 min to 30 min which is a factor of approximately 2 greater than those previously measured at higher latitudes. A movement of the nightside flow reversal, possibly driven by current systems associated with the substorm expansion phases, was observed, implying that the nightside convection pattern can be dominated by substorm activity.

Taylor, J. R.; Yeoman, T. K.; Lester, M.; Buonsanto, M. J.; Scali, J. L.; Ruohoniemi, J. M.; Kelly, J. D.

1994-01-01

38

A multi-ring ionospheric plasma probe  

NASA Technical Reports Server (NTRS)

An ionospheric plasma probe was constructed which consists of a long cylinder with the end facing the flow closed by an end plate made up of multiple annular rings and a center disk. A theoretical argument is given which yields the plasma potential and electron temperature in terms of known plasma parameters and the currents to the various rings of the end plate. This probe was successfully operated in an ionospheric flow simulation facility and the resulting plasma potential is in excellent agreement with the traditional Langmuir analysis (1.22 volts).

Sheldon, J. W.

1972-01-01

39

Plasma conductivity for Comet Halley ionosphere  

SciTech Connect

Observational as well as semitheoretical magnetic field profiles have been used to derive self-consistently the plasma conductivity profiles for the ionosphere of Comet Halley. The characteristic diffusion length for the field, according to the present model, is about 28 km; this is in very good agreement with the Giotto spacecraft observations. It is shown that ideal MHD as well as constant conductivity models are not appropriate for the study of dynamical structure of the Halley's ionosphere. 11 references.

Buti, B.; Eviatar, A.

1989-01-01

40

A Power Model for Plasma Convection.  

National Technical Information Service (NTIS)

A model for simulating the convection of plasma microstructure has been constructed. Labeled 'striation convection,' the procedure is based on the conservation of the square of plasma density or 'plasma power'. The model is driven by a previously develope...

J. B. Workman S. Y. F. Chu J. R. Ferrante

1979-01-01

41

Interhemispheric asymmetry of the high-latitude ionospheric convection pattern  

NASA Technical Reports Server (NTRS)

The assimilative mapping of ionospheric electrodynamics technique has been used to derive the large-scale high-latitude ionospheric convection patterns simultaneously in both northern and southern hemispheres during the period of January 27 to 29, 1992. When the interplanetary magnetic field (IMF) B(sub z) component is negative, the convection patterns in the southern hemisphere are basically the mirror images of those in the northern hemisphere. The total cross-polar cap potential drops in the two hemispheres are similar. When B(sub z) is positive and absolute value of B(sub y) greater than B(sub z), the convection configurations are mainly determined by B(sub y) and they may appear as normal 'two-cell' patterns in both hemispheres much as one would expect under southward IMF conditions. However, there is a significant difference in the cross-polar-cap potential drop between the two hemispheres, with the potential drop in the southern (summer) hemisphere over 50% larger than that in the northern (winter) hemisphere. As the ratio of absolute value of B(sub y)/B(sub z) decreases (less than one), the convection configuration in the two hemispheres may be significantly different, with reverse convection in the southern hemisphere and weak but disturbed convection in the northern hemisphere. By comparing the convection patterns with the corresponding spectrograms of precipitating particles, we interpret the convection patterns in terms of the concept of merging cells, lobe cells, and viscous cells. Estimates of the ' merging cell' potential drops, that is, the potential ascribed to the opening of the dayside field lines, are usually comparable between the two hemispheres, as they should be. The 'lobe cell' provides a potential between 8.5 and 26 kV and can differ greatly between hemispheres, as predicted. Lobe cells can be significant even for southward IMF, if absolute value of B(sub y) greater than the absolute value of B(sub z). To estimate the potential drop of the 'viscous cells,' we assume that the low-latitude boundary layer is on closed field lines. We find that this potential drop varies from case to case, with a typical value of 10 kV. If the source of these cells is truly a viscous interaction at the flank of the magnetopause, the process is likely spatially and temporally varying rather than steady state.

Lu, G.; Richmond, A. D.; Emery, B. A.; Reiff, P. H.; Beaujardiere, O. De LA; Rich, F. J.; Denig, W. F.; Kroehl, H. W.; Lyons, L. R.; Ruohoiemi, J. M.

1994-01-01

42

Three-dimensional ionospheric plasma circulation  

Microsoft Academic Search

Examination of the ion drift velocity vector measured on the DE2 spacecraft reveals the significance of ionospheric flows both perpendicular and parallel to the magnetic field at high latitudes. During periods of southward directed interplanetary magnetic field the familiar two-cell convection pattern perpendicular to the magnetic field is associated with field-aligned motion predominantly upward in the dayside auroral zone and

R. A. Heelis; W. R. Coley; M. Loranc; M. R. Hairston

1992-01-01

43

Formation of Striations in Ionospheric Plasma Clouds  

Microsoft Academic Search

It is suggested that a low-frequency 'gradient drift' instability may be important for the formation of striations in barium ion clouds released in the ionosphere above the E layer. The theory predicts that the trailing edge (with respect to the neutrals) of the plasma cloud will be unstable while the leading edge is stable, in qualitative agreement with observations. The

Lewis M. Linson; Joseph B. Workman

1970-01-01

44

Observations of ionospheric convection vortices - Signatures of momentum transfer  

NASA Technical Reports Server (NTRS)

Several classes of traveling vortices in the dayside ionospheric flow have been detected and tracked using the Greenland magnetometer chain. One class observed during quiet times consists of a continuous series of vortices moving generally antisunward for several hours at a time. Assuming each vortex to be the convection pattern produced by a small field aligned current moving across the ionosphere, the amount of field aligned current was found by fitting a modeled ground magnetic signature to measurements from the chain of magnetometers. The calculated field aligned current is seen to be steady for each vortex and neighboring vortices have currents of opposite sign. Low altitude DMSP observations indicate the vortices are on field lines which map to the inner edge of the low latitude boundary layer. Because the vortices are conjugate to the boundary layer, repeat in a regular fashion and travel antisunward, it is argued that this class of vortices is caused by surface waves at the magnetopause. No strong correlations between field aligned current strength and solar wind density, velocity, or Bz is found.

Mchenry, M. A.; Clauer, C. R.; Friis-Christensen, E.; Kelly, J. D.

1988-01-01

45

An ionospheric travelling convection vortex event observed by ground-based magnetometers and by VIKING  

SciTech Connect

This paper reports the ground based observation of an ionospheric travelling convection vortex event, which was observed in coincidence with observation of the VIKING spacecraft passing through closed field lines which map to this region. The spacecraft saw electric and magnetic signatures which were consistent with it having passed through field aligned current tubes, oppositely directed. This is the first such simultaneous observation and supports the theoretical models which relate such ionospheric travelling convection vortex events to field aligned currents.

Vogelsang, H.; Voelker, H. (Univ. of Goettingen (Germany)); Luehr, H. (Technical Univ., Braunschweig (Germany)); Woch, J. (Swedish Institute of Space Physics, Kiruna (Sweden)); Boesinger, T. (Univ. of Oulu (Finland)); Potemra, T.A. (Johns Hopkins Univ., Laurel, MD (United States)); Lindqvist, P.A. (Royal Institute of Technology, Stockholm (Sweden))

1993-11-05

46

Interplanetary magnetic field effects on high latitude ionospheric convection  

NASA Technical Reports Server (NTRS)

Relations between the electric field and the electric current in the ionosphere can be established on the basis of a system of mathematical and physical equations provided by the equations of current continuity and Ohm's law. For this reason, much of the synthesis of electric field and plasma velocity data in the F-region is made with the aid of similar data sets derived from field-aligned current and horizontal current measurements. During the past decade, the development of a self-consistent picture of the distribution and behavior of these measurements has proceeded almost in parallel. The present paper is concerned with the picture as it applies to the electric field and plasma drift velocity and its dependence on the interplanetary magnetic field. Attention is given to the southward interplanetary magnetic field and the northward interplanetary magnetic field.

Heelis, R. A.

1985-01-01

47

Characteristics of ionospheric convection and field-aligned current in the dayside cusp region  

NASA Technical Reports Server (NTRS)

The assimilative mapping of ionospheric electrodynamics (AMIE) technique has been used to estimate global distributions of high-latitude ionospheric convection and field-aligned current by combining data obtained nearly simultaneously both from ground and from space. Therefore, unlike the statistical patterns, the 'snapshot' distributions derived by AMIE allow us to examine in more detail the distinctions between field-aligned current systems associated with separate magnetospheric processes, especially in the dayside cusp region. By comparing the field-aligned current and ionospheric convection patterns with the corresponding spectrograms of precipitating particles, the following signatures have been identified: (1) For the three cases studied, which all had an IMF with negative y and z components, the cusp precipitation was encountered by the DMSP satellites in the postnoon sector in the northern hemisphere and in the prenoon sector in the southern hemisphere. The equatorward part of the cusp in both hemispheres is in the sunward flow region and marks the beginning of the flow rotation from sunward to antisunward. (2) The pair of field-aligned currents near local noon, i.e., the cusp/mantle currents, are coincident with the cusp or mantle particle precipitation. In distinction, the field-aligned currents on the dawnside and duskside, i.e., the normal region 1 currents, are usually associated with the plasma sheet particle precipitation. Thus the cusp/mantle currents are generated on open field lines and the region 1 currents mainly on closed field lines. (3) Topologically, the cusp/mantle currents appear as an expansion of the region 1 currents from the dawnside and duskside and they overlap near local noon. When B(sub y) is negative, in the northern hemisphere the downward field-aligned current is located poleward of the upward current; whereas in the southern hemisphere the upward current is located poleward of the downward current. (4) Under the assumption of quasi-steady state reconnection, the location of the separatrix in the ionosphere is estimated and the reconnection velocity is calculated to be between 400 and 550 m/s. The dayside separatrix lies equatorward of the dayside convection throat in the two cases examined.

Lu, G.; Lyons, L. R.; Reiff, P. H.; Denig, W. F.; Beaujardiere, O. De LA; Kroehl, H. W.; Newell, P. T.; Rich, F. J.; Opgenoorth, H.; Persson, M. A. L.

1995-01-01

48

Nowcasting convection velocity in the high-latitude ionosphere using statistical models  

NASA Astrophysics Data System (ADS)

The Weimer and IZMEM statistical convection models are driven with a time series of interplanetary magnetic field (IMF) measurements made onboard the Wind spacecraft. The model outputs are used to infer the ionospheric convection velocity at Casey, Antarctica (80.8S geomagnetic latitude), and then compared with measurements of Doppler velocity made using a Digisonde, and measurements of F-region convection implied by a collocated magnetometer. During a single, representative campaign interval, 13-17 February 1996, the Weimer model explained 19% (42%) of the variation in Doppler speed (direction) observed by the Digisonde, and 21% (14%) of the equivalent convection components observed by the magnetometer. This compares with IZMEM which explained 16% (46%) of the variation in Doppler speed (direction) observed by the Digisonde, and 34% (32%) of the equivalent convection components observed by the magnetometer. In general, there was better agreement between convection direction than convection speed. Some of the disagreement was probably due to differences between the IMF measured by Wind located ~170 RE upstream in the solar wind and the IMF actually arriving at the magnetopause. However, the results of this study do show that measurements of ionospheric velocity using different experimental techniques need heavy averaging to identify a common component of velocity controlled by the IMF vector. The present time series approach was also used to estimate 16+/-5 min as the time required for the ionospheric convection to reconfigure in response to IMF changes occurring at the magnetopause.

Parkinson, M. L.; Smith, P. R.; Dyson, P. L.; Morris, R. J.

1999-07-01

49

On the control of magnetospheric convection by the spatial distribution of ionospheric conductivities  

Microsoft Academic Search

Using the linear approximation of the motions of the magnetospheric ring current inner edge, a self-consistent, semianalytical model is developed of its coupling to the ionosphere via field-aligned currents, its reaction to an externally imposed dawn-to-dusk potential drop across the magnetospheric cavity, and its effect on the shielding of convection electric field from midlatitudes. The spatial distribution of ionospheric conductivities

Catherine Senior; Michel Blanc

1984-01-01

50

A plasma temperature anomaly in the equatorial topside ionosphere  

Microsoft Academic Search

A study of the thermal structure of the low-latitude (30N to 30S) ionosphere under equinoctial conditions at low, medium, and high solar activity has been carried out using the Sheffield University plasmasphere-ionosphere model (SUPIM) and Hinotori satellite observations. The study reveals the existence of an anomaly in the plasma (electron and ion) temperature in the topside ionosphere during the evening-midnight

N. Balan; K.-I. Oyama; S. Fukao; S. Watanabe; M. A. Abdu

1997-01-01

51

A quantitative deconstruction of the morphology of high-latitude ionospheric convection  

NASA Astrophysics Data System (ADS)

We present an analysis of ionospheric convection data derived from velocity measurements made by the Super Dual Auroral Radar Network (SuperDARN). Our analysis uses an established technique for combining the network data to produce maps of large-scale convection by fitting a spherical harmonic expansion of the ionospheric electric potential to the radar measurements. We discuss how the basis functions of the spherical harmonic expansion describe different characteristic elements of the ionospheric convection pattern and show how their associated coefficients can be used to quantify the morphology of the convection, much like the total transpolar voltage is used to quantify its strength, in relation to upstream interplanetary magnetic field conditions and associated magnetospheric activity. We find that 2/3 of the voltage associated with the typical convection pattern is described by a simple twin vortex basis function. The magnitude of the twin vortex is strongly dependent on IMF BZ and the degree of its (typically westward) rotation is weakly dependent on IMF BY. The remaining 1/3 of the total voltage is associated with deviations from the basic twin vortex pattern, introduced by the addition of other basis functions, such as IMF BY associated dusk-dawn asymmetries, nightside convection features associated with tail activity, and reverse high-latitude convection cells associated with intervals of IMF BZ > 0.

Grocott, A.; Milan, S. E.; Imber, S. M.; Lester, M.; Yeoman, T. K.

2012-05-01

52

Structuring of the ionospheric convection flows associated with enhanced solar wind ULF fluctuations  

NASA Astrophysics Data System (ADS)

Recent studies have shown that, regardless of the orientation of the interplanetary magnetic field, high level of ULF wave activity in the solar wind can substantially enhance the ionospheric convection, suggesting that the ULF fluctuations may also be an important contributor to the coupling of the solar wind to the magnetosphere-ionosphere system. The convection enhancements associated with enhanced solar wind ULF power may be related to structuring of the ionospheric flow patterns. In order to have a more accurate understanding of the ionospheric response to the ULF power, our study will focus on both qualitative and quantitative evaluation of the structuring of the polar cap convection. Potential convection maps constructed from SuperDARN radar observations can be used for identification of characteristic features of the convection flow speed associated with solar wind ULF power. Additionally, we can utilize data from a network of ground magnetometers, which can, due to the continuous availability of high latitude station data, facilitate the evaluation of the flow patterns and thus help in the evaluation of the features that are identified from radar observations.

Pinto, V. A.; Kim, H.; Ruohoniemi, J. M.; Lyons, L. R.

2012-12-01

53

Interhemispheric Conjugacy of High-Latitude Ionospheric Convection Determined From DMSP IMF-Dependent Models  

NASA Astrophysics Data System (ADS)

In this study we report on a series of new ionospheric convection models constructed from the DMSP thermal ion drift measurements for both the northern and southern polar regions and for the summer, winter, and equinox. Applying the regression analysis technique to the IMF and DMSP data, we first obtained four basic elements of the convection response on 1-nT changes in the corresponding IMF component: (a) the two-cell, ``quasi-viscous'' convection (i.e., for IMF ~0 (b) the lobe convection cell controlled by the IMF azimuthal component; (c) the merging two-cell convection driven by the IMF southward orientation; and (d) the near-pole, two-cell ``reverse'' convection caused by the northward IMF. Then we fitted the obtained distributions of regression coefficients by the spherical harmonics; the resulting DMSP-based ionospheric convection model (DICM) is fully parameterized by the IMF strength and direction. After comparisons with other available high-latitude convection patterns organized by the IMF ``clock-angle'', we concluded that DICM shows all expected features of the solar wind-magnetosphere-ionosphere coupling. A new element in our model is its ``quasi-viscous'' term, which has not been yet obtained in any other satellite or radar-based ionospheric convection studies. Another new elements are the DICM seasonal dependence and interhemispheric symmetry/asymmetry features; for example, we found that the summer cross-polar potentials are 10-15% smaller than the winter potentials. The latter is in agreement with the seasonal dependence of field-aligned currents and with the voltage-current relationship required for the proper magnetosphere-ionosphere coupling. The obtained results justify a need in developing a unified approach for the modeling of high-latitude ionospheric convection from various data sources (i.e., from ground magnetometers, radars, digisondes, and satellite observations) allowing seemliness data assimilation in various ``space weather'' applications. The new models can be run on-line at the SPRL Web site http://www.sprl.umich.edu/mist/.

Papitashvili, V. O.; Rich, F. J.

2001-12-01

54

Plasma convection with parallel electric field in the RCM  

NASA Astrophysics Data System (ADS)

Inner magnetospheric convection, driven ultimately by the interaction of the solar wind with Earth's magnetosphere, sets up a system of region-2 field-aligned currents via pressure gradients. In regions of upward field-aligned currents, the physics of magnetosphere-ionosphere coupling dictates presence of field-aligned potential drops that act to accelerate energetic electrons precipitating into the upper atmosphere. Although it is assumed that this phenomenon is important inside the region of discrete aurora, in fact some of the upward currents associated with the westward-travelling substorm current wedge are found deeper in the magnetosphere, in the region normally characterized by the diffuse aurora. The Rice Convection Model (RCM) treats plasma drifts, electric fields, and field-aligned currents in the inner magnetosphere self-consistently in the slow flow approximation under the assumption of isotropic pitch-angle distribution. The RCM can trace plasma distribution during geomagnetic active times by applying time dependent boundary conditions with an optional depleted channel around midnight on the RCM high latitude boundary. We present a generalized version of the Knight relation that takes into account the non-Maxwellian nature of particle population carrying the field-aligned currents and discuss the implementation of this modified relation into the RCM. We use event simulations to evaluate the role of parallel electric field on the ring current, the field-aligned currents, and the auroral and ionospheric-current signatures of the substorm current wedge.

Song, Y.; Sazykin, S.; Wolf, R.; Toffoletto, F.

2009-12-01

55

Coordinated stable auroral red arc observations: Relationship to plasma convection  

NASA Astrophysics Data System (ADS)

During the March 20-22, 1990, magnetic storm, Millstone Hill radar and DMSP satellite observations detailed the conditions surrounding the occurrence of a SAR arc which was observed continuously through an 8-hour interval from dusk till past midnight in the North American sector. All-sky imaging with a 630.0-nm imager continually monitored the two-dimensional position and magnitude of the SAR arc emission while radar scans and satellite overflights measured magnetospheric inputs and ionospheric response. The arc was colocated with a deep, narrow plasma trough and a region of enhanced westward plasma convection of similar width situated immediately equatorward of the low-latitude extend to plasma sheet particle precipitation. A region of low-energy ion precipitation was observed at the equatorward edge of the SAR arc during a period of spatial/temporal coincident satellite/radar observations near the Millstone Hill longitude. The width of the SAR arc and related phenomena was of the order of 2, and the ~200-R emission was associated with an electron temperature of ~3500K and a 10reduction of plasma density at an altitude of 450 km. The best-fit model for the emission intensities of both the SAR arc and the background airglow suggests that either the electron temperature at the center of the SAR arc was somewhat higher than observed by the radar (~4000K), or the neutral densities, [O2] and [O], were increased by factors of 2 and 4, respectively, with respect to the MSIS values. The ionospheric trough and a colocated region of enhanced sunward convection (500-1700 ms-1) were observed in conjugate hemispheres throughout the local time range 18-02 MLT. The convection feature seen in association with the SAR arc had many of the characteristics of a subauroral iondrifts (SAID) event; we report here the first long-duration observations of a colocated SAID/SAR arc event. A narrow ionospheric trough developed during the interval when the SAID velocity was >1000 ms-1 and was accompanied by a weak (100 R) 630.0-nm emission. As the velocity fell to ~700 ms-1, the density in the trough recovered somewhat, and the arc intensity rose to ~300 R above background. This brighter period of the SAR arc occurred within a fossil trough/SAID. We conclude that there is a close spatial and temporal association among these three types of subauroral low-altitude phenomena-the SAR arc, the SAID event, and the fossil (convection-related) trough-and that this is indicative of the interrelationship of the magnetospheric processes and boundaries which are involved in their formation.

Foster, J. C.; Buonsanto, M. J.; Mendillo, M.; Nottingham, D.; Rich, F. J.; Denig, W.

1994-06-01

56

Ionospheric physics  

SciTech Connect

Advances in all areas of ionospheric research are reviewed for the 1987-1990 time period. Consideration is given to the equatorial ionosphere, the midlatitude ionosphere and plasmasphere, the auroral ionosphere, the polar ionosphere and polar wind, ionospheric electrodynamic inputs, plasma waves and irregularities, active experiments, ionospheric forecasting, and coupling the ionosphere with other regions.

Sojka, J.J. (USAF, Geophysics Laboratory, Hanscom AFB, MA (United States))

1991-01-01

57

Cassini measurements of cold plasma in the ionosphere of Titan.  

PubMed

The Cassini Radio and Plasma Wave Science (RPWS) Langmuir probe (LP) sensor observed the cold plasma environment around Titan during the first two flybys. The data show that conditions in Saturn's magnetosphere affect the structure and dynamics deep in the ionosphere of Titan. The maximum measured ionospheric electron number density reached 3800 per cubic centimeter near closest approach, and a complex chemistry was indicated. The electron temperature profiles are consistent with electron heat conduction from the hotter Titan wake. The ionospheric escape flux was estimated to be 10(25) ions per second. PMID:15894529

Wahlund, J E; Bostrm, R; Gustafsson, G; Gurnett, D A; Kurth, W S; Pedersen, A; Averkamp, T F; Hospodarsky, G B; Persoon, A M; Canu, P; Neubauer, F M; Dougherty, M K; Eriksson, A I; Morooka, M W; Gill, R; Andr, M; Eliasson, L; Mller-Wodarg, I

2005-05-13

58

Application of spherical cap harmonic analysis to plasma convection mapping at high latitudes  

NASA Astrophysics Data System (ADS)

The primary goal of this work is to develop, validate, and apply a new technique for mapping the high-latitude ionospheric plasma flow (convection pattern) from velocity measurements routinely performed by the Super Dual Auroral Radar (SuperDARN) network of high frequency (HF) radars. The currently employed FIT technique relies heavily on assumptions that are not always justifiable. A spherical cap harmonic analysis (SCHA) technique, traditionally used in handling geomagnetic field data, is introduced for mapping the high-latitude ionospheric convection pattern based on SuperDARN velocity measurements. The SCHA technique does not require contributions from a statistical model which is dependent on the magnitude and orientation of the interplanetary magnetic field (IMF), and does not confine the high-latitude flows to a specific region based on magnetic latitude. Several steps are taken to validate the SCHA convection mapping technique. First, it is demonstrated that the SCHA technique can reproduce an arbitrary pattern based on simulated data modified by a random noise component. SCHA maps of the global scale plasma flow pattern for various IMF conditions are next shown to be consistent with expectations for patterns reported in the literature. SCHA maps are compared to ion drifts measured by the Defense Meteorological Satellite Program (DMSP) satellites and with convection vectors inferred by merging SuperDARN measurements at beam crossings. The SCHA technique is shown to perform comparably to the FIT technique over regions of good data coverage. The SCHA technique provides a better representation of the ionospheric convection pattern for regions with limited data coverage and over regions of highly variable flow, particularly near the equatorward edge of the mapping region. SCHA analysis of SuperDARN data to create convection maps is expanded to include magnetometer measurements of the perturbation magnetic field. Plasma flow is determined from magnetometer data by combining the equivalent current determined from the external component of the perturbation magnetic field with a model of the ionospheric conductivity. The SCHA technique is used to investigate the reconfiguration of the convection pattern and changes to the cross polar-cap potential (CPCP) associated with a sudden transition in the vertical component of the IMF from stable positive to stable negative values. For such events, the FIT technique might misrepresent the convection pattern if the fitting is dominated by the a-priori statistical convection model. Both magnetometer and SuperDARN data sets are examined. The IMF transition wavefront impinges upon the magnetosphere near the 10 MLT sector; perturbations are clearly seen on the dayside with a 10 minute delay on the nightside. This translates into a dayside-to-nightside progression of the ionospheric response observed in the magnetic perturbations and SuperDARN velocities, contrary to what was reported for a number of other events in the literature. The foci of the new dawn and duskside convection cells are shown to steadily shift toward the dayside (over a period of 10-12 minutes, beginning 4-6 minutes after the onset of the ionospheric response) and do not 'snap' to their final position. Once the convection foci reach a final location, the overall convection pattern enhances for a period of 25 minutes. These results support the idea that the ionospheric convection response to a southward turning of the IMF is a two-stage process; (1) an initial dayside-to-nightside progression of the observed ionospheric response and a reconfiguration of the convection pattern, and (2) the subsequent intensification of the convection pattern. An additional investigation is performed to determine whether the polar cap north (PCN) magnetic index is satisfactory for estimating the CPCP and average cross polar cap flow velocity (CPCV). A roughly linear increase of both the CPCP and CPCV with PCN is found for 0 ? PCN ? 4, with a tendency for saturation for PCN > 4. The CPCP calculated using the SCHA-technique i

Fiori, Robyn A. D.

59

Excitation of Alfvn vortices in the ionosphere by the magnetospheric convection  

NASA Astrophysics Data System (ADS)

We analyze conditions for excitation of ULF waves in the ionospheric Alfvn resonator (IAR), taking into account the altitude-inhomogeneous profile of the magnetospheric convection velocity. This profile is formed as a result of interaction of the convective flow with the neutral atmosphere at altitudes 90 150 km. ULF waves comprise oblique Alfvn waves, trapped into the IAR, and ionospheric drift waves, which are in resonance with them. These waves together form strongly anisotropic, closed current loops, whose scale along the magnetic field greatly exceeds their transverse scale, i.e., lz ? l?, and can be considered Alfvn vortices. Within the framework of the proposed model of the ionosphere, we study the instability threshold and the amplitude growth rate of the Alfvn vortices as functions of different parameters (wave vector k22A5, angle between the wave vector and the convection velocity, ratio of the Alfvn-wave and Pedersen conductivities, etc.). Some estimates are given in application to the observed small-scale field-aligned currents in the auroral ionosphere.

Despirak, I. V.; Lubchich, A. A.; Trakhtengerts, V. Yu.

2008-05-01

60

Excitation of Alfven vortices in the ionosphere by the magnetospheric convection  

NASA Astrophysics Data System (ADS)

Excitation of ULF waves due to the positive feedback instability is considered in Ionospheric Alfvn Resonator (IAR) taking into account an inhomogeneous profile of velocity of the magnetospheric convection. This profile is formed by interaction of the convective flow with the neutral atmosphere at heights 90--150~km. ULF waves include oblique Alfvn waves, trapped in IAR, and drift ionospheric waves, which are in a resonance with each other. These waves together form strongly anisotropic closed current loops with the scale along the magnetic field l\\| ~ 1000~km and with the scale l\\perp ~ 1~km across the magnetic field and can be considered as Alfvn vortices. The instability threshold and the growth rate are investigated as functions of different parameters (wave vector k\\perp, angle between the wave vector and convection velocity, ratio of Alfvn wave and Pedersen conductivities) in a model of ionosphere close to the real one. Possible acceleration mechanisms of electrons by oblique Alfvn waves and the role of energetic electron precipitation in the feedback instability development are discussed. Some estimations are given in application to observed short-scale field- aligned currents and auroral arcs in the auroral ionosphere.

Trakhtengerts, V. Y.

2007-12-01

61

Evolution of high latitude ionospheric convection associated with substorms: Multiple radar observations  

NASA Astrophysics Data System (ADS)

The work presented in this dissertation concerns evolution of the high latitude ionospheric convection and the relevant current systems associated with substorms, with emphasize on these features near the nightside Harang reversal region. Three different types of radars, including the Super Dual Auroral Radar Network (SuperDARN) coherent-scatter radars, the new advanced modular incoherent-scatter radar at Poker Flat (PFISR), and the Sondrestrom incoherent-scatter radar (ISR), have been utilized. Observations from those radars, together with those from complementary instruments, including satellites and other ground-based instruments, have revealed fundamental new understand of the ionospheric electrodynamic properties associated with substorms. By using the SuperDARN and the PFISR radars, we found that the auroral activity at substorm onset is located in the center of the Harang reversal, which represents a key region in the magnetospheric and ionospheric convection and is part of the Region 2 system. We have also shown that nightside convection flows exhibit repeatable, distinct variations at different locations relative to the substorm-related auroral activity. Taking advantage of the simultaneous flow and ionization measurements from PFISR, a current closure relation has been found between the Region 2 and the substorm field-aligned current systems. These observations demonstrate a strong coupling between the Region 2 system and the substorm dynamics. This study sheds new light on the substorm-related magnetosphere-ionosphere coupling and contributes to the building of a holistic picture of the substorm dynamics. The third radar has been used to study the dayside ionospheric convection response to the external soar wind and IMF driving and its role in substorm dynamics. The results have been applied to study substorm triggering and in the future could be used to study the relation between the external driving and the formation of the Harang reversal.

Zou, Shasha

62

Large-scale Ionospheric Disturbances due to the Dissipation of Convectively-generated Gravity Waves over Brazil  

NASA Astrophysics Data System (ADS)

Dissipation of convectively generated gravity waves (GWs) over Brazil can cause large-scale perturbations of plasma drift and plasma density in the ionosphere by changing the wind dynamo and transport. We find that the circulation cells and the secondary GWs from the wave dissipation modify both the amplitude and direction of the EB plasma drifts. Near the geomagnetic equator, the magnitude of the pre-reversal enhancement (PRE) can be modulated. Because the tropospheric deep convective systems persist from the afternoon until midnight, the modification of the vertical drift near the geomagnetic equator of the upward drift persists till midnight. The largest changes of the wind-driven currents can occur either in the E or F region, and are determined by the magnitudes of the wind perturbations, and electric conductivities and their perturbations. The contributions to the plasma transport changes are from advection by the neutral winds along field lines, plasma drifts, and ambipolar diffusion, in the order of their relative significance in the numerical results.

Liu, H.; Vadas, S. L.

2012-12-01

63

Control parameters for polar ionospheric convection patterns during northward interplanetary magnetic field  

SciTech Connect

Using the DE 2 electric field data from 191 dawn-dusk passes, the authors have sought parameters that distinguish between the various polar ionospheric convection patterns for northward IMF. The passes were divided into the daytime and nightime sectors, and categorized the convection into three convection patterns for each sector by focusing on flow having a horizontal scale of > 150 km. The three daytime sector patterns are convection of reverse polarity, i.e., sunward at the highest latitudes and antisunward on both sides of the sunward flow region, irregular convection having a single antisunward flow region at the highest latitude, which is similiar to the pattern for southward IMF. The IMF clock (B{sub y}/B{sub z}) angle, the Earth`s dipole tilt angle, and the IMF B{sub x}/B{sub z} angle measured from the dipole axis are the patterns that cause the difference in the three convection pattern. In the nighttime sector three similar convection patterns are identified. The occurrence of these patterns is controlled by the IMF clock angle. Thus, the convection pattern for northward IMF is very sensitive to the direction of the IMF. The magnetospheric sources for the convection patterns are discussed. 18 refs., 5 fig.

Taguchi, S.; Hoffman, R.A. [NASA Goddard Space Flight Center, Greenbelt, MD (United States)] [NASA Goddard Space Flight Center, Greenbelt, MD (United States)

1996-03-15

64

Plasma motion in the Venus ionosphere - Transition to supersonic flow  

NASA Technical Reports Server (NTRS)

A remarkable feature of the ionosphere of Venus is the presence of nightward supersonic flows at high altitude near the terminator. In this paper it is shown that the relatively high pressure dayside plasma wells up slowly, and at high altitude it is accelerated horizontally through a relatively constricted region near the terminator toward the low-density nightside. In effect, the plasma flows through a 'nozzle' that is first converging, then diverging, permitting the transition to supersonic flow. The model plasma accelerates to supersonic speeds, reaching sonic speed just behind the terminator. The ion transport rates are sufficient to produce and maintain the nightside ionosphere.

Whitten, R. C.; Barnes, A.; Mccormick, P. T.

1991-01-01

65

Radio Pumping of Ionospheric Plasma with Orbital Angular Momentum  

Microsoft Academic Search

Experimental results are presented of pumping ionospheric plasma with a radio wave carrying orbital angular momentum (OAM), using the High Frequency Active Auroral Research Program (HAARP) facility in Alaska. Optical emissions from the pumped plasma turbulence exhibit the characteristic ring-shaped morphology when the pump beam carries OAM. Features of stimulated electromagnetic emissions (SEE) that are attributed to cascading Langmuir turbulence

T. B. Leyser; L. Norin; M. McCarrick; T. R. Pedersen; B. Gustavsson

2009-01-01

66

Large scale patterns of auroral ionospheric convection observed with the Chatanika radar  

SciTech Connect

Ionospheric convection at auroral latitudes has been examined during a series of long duration experiments with the Chatanika, Alaska, incoherent scatter radar. These experiments have been carefully designed to obtain maximum latitudinal coverage (56 /sup 0/..lambda.. to 75 /sup 0/..lambda..) while maintaining a temporal resolution of 30 min in order to resolve the effects of individual substorms on the convection pattern. Design criteria for the experiments are described together with presentation of observational data acquired during 400 hr of radar operations during various levels of geophysical disturbance. The data accentuate the repeatability of the gross features of the auroral convection and its basic conformity to the two0cell pattern predicted from the large-scale magnetospheric circulation. For moderate to active geomagnetic conditions uniform sunward convection with velocities of 800 to 1200 m/s spans the 62 /sup 0/..lambda.. to 72 /sup 0/..lambda.. latitude band at both dawn and dusk. In quieter circumstances the sunward convection continues in this region, but has smaller speeds and is centered at higher latitudes. Little evidence of a throat in the dayside convection pattern is seen at latitudes below 75 /sup 0/..lambda.. except in very disturbed circumstances. During several experiments coordinated operation of the Chatanika and Millstone Hill, Massachusetts, radars permitted the simultaneous observation of the auroral convection pattern at two different local times. substorms affect the convection at all local times and appears to generally enhance the rate of convection without seriously changing its direction. Near midnight, latitudinal displacements and expansions of the convection pattern during substorms may result in a local rotation or reversal of the direction of convection, while near dawn and dusk, convection velocities are enhanced and the region of sunward flow expands to lower latitudes.

Foster, J.C.; Doupnik, J.R.; Stiles, G.S.

1981-12-01

67

Plasma effects of active ion beam injections in the ionosphere at rocket altitudes  

NASA Technical Reports Server (NTRS)

Data from ARCS rocket ion beam injection experiments are primarily discussed. There are three results from this series of active experiments that are of particular interest in space plasma physics. These are the transverse acceleration of ambient ions in the large beam volume, the scattering of beam ions near the release payload, and the possible acceleration of electrons very close to the plasma generator which produce intense high frequency waves. The ability of 100 ma ion beam injections into the upper E and F regions of the ionosphere to produce these phenomena appear to be related solely to the process by which the plasma release payload and the ion beam are neutralized. Since the electrons in the plasma release do not convect with the plasma ions, the neutralization of both the payload and beam must be accomplished by large field-aligned currents (milliamperes/square meter) which are very unstable to wave growth of various modes.

Arnoldy, R. L.; Cahill, L. J., Jr.; Kintner, P. M.; Moore, T. E.; Pollock, C. J.

1992-01-01

68

Some aspects of modelling the high-latitude ionospheric convection from Cluster/Edi data  

NASA Astrophysics Data System (ADS)

Measurements onboard Cluster satellites are briefly described, which form the base for determining the intensity and direction of the electric field in the magnetosphere. The aim of this paper is to describe (1) the methodology of calculating the potential distribution at the ionospheric level and the results of constructing spatiotemporal convection patterns for different orientations of the IMF vector in the GSM YZ plane; (2) derivation of basic convection patterns (BCPs), which allow to deduce the statistical ionospheric convection pattern at high latitudes for any IMF Bz and By values (statistical convection model) using different sets of independent data; (3) the consequences of enlarging the amount of data used for analysis; (4) the results of potential calculations with various orders of the spherical harmonics describing them; (5) determination of the cross-polar cap potential with different IMF sector widths (? from 45 down to 10); (6) the results of our trials to determine the contribution of the IMF Bx component to the convection pattern.

Frster, M.; Feldstein, Y. I.; Gromova, L. I.; Dremukhina, L. A.; Levitin, A. E.; Haaland, S. E.

2013-01-01

69

Relationship of solar wind parameters to continuous, dayside, high latitude traveling ionospheric convection vortices  

NASA Technical Reports Server (NTRS)

The results of a statistical study of the occurrence of steady traveling ionospheric convection vortices are presented. The upstream solar wind parameters observed by the IMP 8 spacecraft are studied as well. It is suggested that this class of pulsations is most likely to be detected post local noon and when the solar wind speed is low. A correlation between the frequency of dayside pulsations and the solar wind speed is found.

Mchenry, Mark A.; Clauer, C. Robert; Friis-Christensen, Eigil

1990-01-01

70

Average patterns of precipitation and plasma flow in the plasma sheet flux tubes during steady magnetospheric convection  

NASA Technical Reports Server (NTRS)

Average patterns of plasma drifts and auroral precipitation in the nightside auroral zone were constructed during a steady magnetospheric convection (SMC) event on February 19, 1978. By comparing these patterns with the measurements in the midtail plasma sheet made by ISEE-1, and using the corresponding magnetic field model, the following features are inferred: (1) the concentration of the earthward convection in the midnight portion of the plasma sheet (convection jet); (2) the depleted plasma energy content of the flux tubes in the convection jet region; and (3) the Region-1 field-aligned currents generated in the midtail plasma sheet. It is argued that these three elements are mutually consistent features appearing in the process of ionosphere-magnetosphere interaction during SMC periods. These configurational characteristics resemble the corresponding features of substorm expansions (enhanced convection and 'dipolarized' magnetic field within the substorm current wedge) and appear to play the same role in regulating the plasma flow in the flux tubes connected to the plasma sheet.

Sergeev, V. A.; Lennartsson, W.; Pellinen, R.; Vallinkoski, M.; Fedorova, N. I.

1990-01-01

71

Spatial Distribution of Ionospheric Plasma and Field Structures in the High-Latitude F Region  

NASA Technical Reports Server (NTRS)

Ion density and velocity measurements from the Dynamics Explorer 2 (DE 2) spacecraft are used to obtain the average magnetic local time versus invariant latitude distribution of irregularities in the high-latitude F region ionosphere. To study the small-scale structure and its relationship to background conditions in the ionosphere, we have formed a reduced database using 2-s (approx. = 16 km) segments of the ion density and velocity data. The background gradients associated with each 2-s segment and the spectral characteristics, such as power at 6 Hz (approx. = 1.3 km) and spectral index, are among the reduced parameters used in this study. The relationship between the observed plasma structure and its motion is complex and dependent on the externally applied fields as well as locally generated plasma structure. The evolution of plasma structures also depends critically on the conductivity of the underlying ionosphere. Observations indicate an enhancement of irregularity amplitudes in two spatially isolated regions in both the ion density and the velocity. Convective properties seem to play a more important role in winter hemisphere where smaller-scale structures are maintained outside the source regions. (Delta)V irregularity amplitudes are enhanced in the cusp and the polar cap during northward interplanetary magnetic field regardless of season. The power in (Delta)V is usually higher than that associated with local polarization electric fields, suggesting that the observed structure in (Delta)N/N is strongly influenced by (Delta)V structure applied to large density gradients.

Kivanc, O.; Heelis, R. A.

1998-01-01

72

Contribution of low-energy ionospheric protons to the plasma sheet  

NASA Technical Reports Server (NTRS)

The magnetospheric transport of low-energy ionospheric ions is examined by means of three-dimensional particle codes. Emphasis is placed on the behavior of polar wind and cleft originating protons. It is demonstrated that, via nonadiabatic motion inside the neutral sheet, these ions can significantly contribute to the populations of the plasma sheet. The importance of this contribution is found to depend critically upon the dynamics of particles originating from the highest latitudes, as these possibly have access to the distant tail. Hence it is shown that polar wind H(+) expelled into the magnetosphere at very low energies (in the electron volt range) preferentially feed the plasma sheet during quiet times, experiencing accelerations up to several kiloelectron volts upon return into the inner magnetosphere. In contrast, during disturbed times, the intensifying magnetospheric convection confines this population to low L shells where it travels in a nearly adiabatic manner. As for the protons originating from the cleft fountain, the simulations reveal that they can be transported up to the vicinity of the distant neutral line in the nightside sector. Via interaction with the neutral sheet, these ionospheric ions are rapidly raised to the characteristic plasma sheet energy range. The density levels contributed by these populations are quite substantial when compared to those measured in situ. These simulations establish an active role of low-energy ionospheric ions in the overall magnetospheric dynamics.

Delcourt, D. C.; Moore, T. E.; Chappell, C. R.

1994-01-01

73

Tamao travel time of sudden impulses and its relationship to ionospheric convection vortices  

NASA Astrophysics Data System (ADS)

We have examined the propagation of sudden impulses (SI) by an MHD numerical simulation in the three-dimensional magnetosphere to assess the precision of the Tamao travel time approximation and the dynamic properties of preliminary impulses (PI). The results show that the propagation of SI signals is strongly influenced by the inhomogeneous Alfvn velocity profile, and the region of high Alfvn velocity immediately outside the plasmasphere allows the signals to reach ionospheric altitudes in the shortest time possible. At the ionospheric altitude, the simulated arrival time of the PI, defined by the first peak in wave amplitude, is in extremely good agreement with Tamao's prediction throughout the range of invariant latitudes connected to the outer magnetosphere. The arrival time at invariant latitudes within the plasmasphere, however, is slightly earlier than Tamao's prediction because of the fact that the impulse deviates from a point source as it arrives at the plasmapause. In contrast, the onset time of the PI, which corresponds to the first deflection in the magnetic field, varies little with invariant latitude, consistent with the well-established observations of the nearly simultaneous PI onset without the need to invoke the Earth-ionosphere waveguide model. Our simulation also shows that the differentiation in PI arrival time strongly influences the evolution of the ionospheric convection vortices. The twin vortices first appear slightly above the latitude connected to the plasmapause, and they move poleward because of the late arrival of impulse signals at higher latitudes. Another pair of vortices appears later at plasmaspheric latitudes owing to the delay of signals by the dense plasmasphere. Our results not only provide quantitative assessment on the Tamao path, which can benefit future development in travel time magnetoseismology, but they also demonstrate the evolution of PI-induced ionospheric convection vortices by incorporating the propagation characteristics of MHD waves.

Chi, P. J.; Lee, Dong-Hun; Russell, C. T.

2006-08-01

74

Small-scale plasma, magnetic, and neutral density fluctuations in the nightside Venus ionosphere  

SciTech Connect

Pioneer Venus orbiter measurements have shown that coherent small-scale waves exist in the electron density, the electron temperature, and the magnetic field in the lower ionosphere of Venus just downstream of the solar terminator (Brace et al., 1983). The waves become less regular and less coherent at larger solar zenith angles, and Brace et al. suggested that these structures may have evolved from the terminator waves as they are convected into the nightside ionosphere, driven by the day-to-night plasma pressure gradient. In this paper the authors describe the changes in wave characteristics with solar zenith angle and show that the neutral gas also has related wave characteristics, probably because of atmospheric gravity waves. The plasma pressure exceeds the magnetic pressure in the nightside ionosphere at these altitudes, and thus the magnetic field is carried along and controlled by the turbulent motion of the plasma, but the wavelike nature of the thermosphere may also be coupled to the plasma and magnetic structure. They show that there is a significant coherence between the ionosphere, thermosphere, and magnetic parameters at altitudes below about 185 km, a coherence which weakens in the antisolar region. The electron temperature and density are approximately 180{degree} out of phase and consistently exhibit the highest correlation of any pair of variables. Waves in the electron and neutral densities are moderately correlated on most orbits, but with a phase difference that varies within each orbit. The average electron temperature is higher when the average magnetic field is more horizontal; however, the correlation between temperature and dip angle does not extend to individual wave structures observed within a satellite pass, particularly in the antisolar region.

Hoegy, W.R.; Brace, L.H.; Kasprazak, W.T. (NASA Goddard Space Flight Center, Greenbelt, MD (United States)); Russell, C.T. (Univ. of California, Los Angeles (United States))

1990-04-01

75

Dawn/Dusk Auroras and Propagating Convection Disturbances: Ionospheric Effects of Increasing Solar Wind Ram Pressure  

NASA Astrophysics Data System (ADS)

A dawn/dusk auroral event that occurred on June 27, 1997 has been studied using observations from the WIND and POLAR spacecraft, Antarctic all-sky images, and Greenland magnetometers. The aurora was caused by a gradual (T ~ 90 min), intense (Pram ~ 11 nPa) solar wind ram pressure (\\varrho V2) pulse. Auroral intensities on both dawn and dusk flanks of the auroral oval increased linearly with the pressure increase. The aurora occurred in both diffuse and discrete forms. The energy deposition flux into discrete auroras was calculated to be increased by a factor of ~5 when the ram pressure increased by a factor of ~2 during the event. Propagating convection disturbances in the ionosphere were also detected within the auroras. The convection disturbances appeared in the magnetograms as ~20 min period and ~100 nT amplitude pulsations, which propagated antisunward at a speed of ~11 km/s. This ionospheric speed mapped to the magnetosheath flow speed very well. Mechanisms of the ionospheric responses are suggested to be some form of viscous interaction that occurs on the magnetopause boundary layer (such as the Kelvin-Helmholtz instability) and adiabatic compression.

Zhou, X.; Tsurutani, B. T.; Mende, S. B.; Frey, H. U.; Watermann, J. F.; Sibeck, D. G.; Arballo, J. K.

2001-12-01

76

Large-scale ionospheric disturbances due to the dissipation of convectively-generated gravity waves over Brazil  

NASA Astrophysics Data System (ADS)

In a companion paper, we show that large-scale secondary gravity waves and circulation cells are created by the body forces generated by the dissipation of convectively generated gravity waves over Brazil on 01 October 2005. In this paper, we show that these fluid perturbations cause large-scale perturbations of the plasma drift and plasma density in the ionosphere by changing the wind dynamo and transport. These fluid perturbations modify both the amplitude and direction of the plasma drifts. Near the geomagnetic equator, the magnitude of the pre-reversal enhancement can be increased or weakened, depending on the location and local time. Because the circulation cells persist from late afternoon through midnight, the modulation of the vertical drift near the geomagnetic equator persists until midnight. The largest changes of the wind-driven currents can occur either in the E or F region and are determined by the magnitudes of the wind perturbations, conductivities, and conductivity perturbations. The contributions to the plasma transport changes are from advection by the neutral winds along field lines, plasma drifts, and ambipolar diffusion, in the order of their relative significance in the numerical results.

Liu, H.-L.; Vadas, S. L.

2013-05-01

77

Unusual ionospheric plasma density enhancements during high-power ionospheric pumping at EISCAT  

NASA Astrophysics Data System (ADS)

Ionospheric pumping experiments using the EISCAT HF facility at high powers up to 1GW effective radiated power have been executed in 2011 and 2012. Analysis of the UHF incoherent scatter radar ion-line data show apparently large (up to double) plasma density enhancements above the HF reflection altitude. The UHF radar plasma-line data are consistent with the pump-induced electron temperature enhancements derived from the UHF radar ion-line data, but not the large plasma density enhancements. We show that horizontal transport, field-aligned diffusion, temperature-dependent chemical effects and pump-induced ionisation are not likely explanations.

Kosch, M. J.; Senior, A.; Bryers, C.; Rietveld, M. T.; Xu, B.; Wu, J.; Pedersen, T.

2012-12-01

78

A statistical study of the ionospheric convection response to changing interplanetary magnetic field conditions using the assimilative mapping of ionospheric electrodynamics technique  

Microsoft Academic Search

We examine 65 ionospheric convection changes associated with changes in the Y and Z components of the interplanetary magnetic field (IMF). We measure the IMF reorientations (for all but six of the events) at the Wind satellite. For 22 of the events the IMF reorientation is clearly observed by both Wind and IMP 8. Various methods are used to estimate

A. J. Ridley; Gang Lu; C. R. Clauer; V. O. Papitashvili

1998-01-01

79

Interplanetary magnetic field control of the ionospheric field-aligned current and convection distributions  

NASA Astrophysics Data System (ADS)

Patterns of the high-latitude ionospheric convection and field-aligned current (FAC) are a manifestation of the solar wind-magnetosphere-ionosphere coupling. By observing them we can acquire information on magnetopause reconnection, a process through which solar wind energy enters the magnetosphere. We use over 10 years of magnetic field and convection data from the CHAMP satellite and Super Dual Auroral Radar Network radars, respectively, to display combined distributions of the FACs and convection for different interplanetary magnetic field (IMF) orientations and amplitudes. During southward IMF, convection follows the established two-cell pattern with associated Region 1 and Region 2 FACs, indicating subsolar reconnection. During northward IMF, superposed on a weak two-cell pattern there is a reversed two-cell pattern with associated Region 0 and Region 1 FACs on the dayside, indicating lobe reconnection. For dominant IMF Bx, the sign of Bz determines whether lobe or subsolar reconnection signatures will be observed, but Bx will weaken the signatures compared to pure northward or southward IMF. When the IMF rotates from northward to duskward or dawnward, the distinct reversed and forward two-cell patterns start to merge into a distorted two-cell pattern. This is in agreement with the IMF By displacing the reconnection location from the open lobe field lines to closed dawn or dusk field lines, even though IMF Bz>0. As the IMF continues to rotate southward, the distorted pattern transforms smoothly to that of the symmetric two-cell pattern. While the IMF direction determines the configuration of the FACs and convection, the IMF amplitude affects their intensity.

Juusola, L.; Milan, S. E.; Lester, M.; Grocott, A.; Imber, S. M.

2014-04-01

80

The response of the large scale ionospheric convection pattern to changes in the IMF and substorms - Results from the SUNDIAL 1987 campaign  

Microsoft Academic Search

Multipoint observations of ionospheric convection, made during the SUNDIAL 1987 campaign (May 29 to June 8) which included two intervals of variable IMF Bz and By and several substorms, are used to examine the response of the ionospheric convection in the postdusk and midnight sectors to changes in the IMF Bz component, as well as the effect of substorms on

M. Lester; O. de La Beaujardiere; J. C. Foster; M. P. Freeman; H. Luehr; J. M. Ruohoniemi; W. Swider

1993-01-01

81

The effects of interplanetary magnetic field orientation on dayside high-latitude ionospheric convection  

NASA Technical Reports Server (NTRS)

The Atmosphere Explorer C data base of Northern Hemisphere ionospheric convection signatures at high latitudes is examined during times when the interplanetary magnetic field orientation is relatively stable. It is found that when the interplanetary magnetic field (IMF) has its expected garden hose orientation, the center of a region where the ion flow rotates from sunward to antisunward is displaced from local noon toward dawn irrespective of the sign of By. Poleward of this rotation region, called the cleft, the ion convection is directed toward dawn or dusk depending on whether By is positive or negative, respectively. The observed flow geometry can be explained in terms of a magnetosphere solar wind interaction in which merging is favored in either the prenoon Northern Hemisphere or the prenoon Southern Hemisphere when the IMF has a normal sector structure that is toward or away, respectively.

Heelis, R. A.

1984-01-01

82

Stimulated plasma instability and nonlinear phenomena in the ionosphere  

NASA Astrophysics Data System (ADS)

Several hundred topside ionograms were used to study simulated wave-particle interactions in the ionosphere. The study combined the benefits of high-frequency-resolution Alouette 2 analog sounder data with advanced digital graphics techniques. The study shows that the sounder phase can cause significant plasma heating when the plasma parameter is confined to specific ranges. The observations support the Harris instability generation process and the nonlinear Landau damping maintaining process for long-duration diffuse resonances. The observations also suggest that the so-called Q resonances have characteristics which imply that generation processes in a sounder-stimulated plasma turbulence may be involved.

Benson, R. F.

1982-12-01

83

Plasma motion in the Venus ionosphere: Transition to supersonic flow  

SciTech Connect

A remarkable feature of the ionosphere of Venus is the presence of nightward supersonic flows at high altitude near the terminator. In general the steady flow of an ideal gas admits a subsonic-supersonic transition only in the presence of special conditions, such as a convergence of the flow followed by divergence, or external forces. In this paper, the authors show that the relatively high pressure dayside plasma wells up slowly, and at high altitude it is accelerated horizontally through a relatively constricted region near the terminator toward the low-density nightside. In effect, the plasma flows through a nozzle that is first converging, then diverging, permitting the transition to supersonic flow. Analysis of results from previously published models of the plasma flow in the upper ionosphere of Venus shows how such a nozzle is formed. The model plasma does indeed accelerate to supersonic speeds, reaching sonic speed just behind the terminator. The computed speeds prove to be close to those observed by the Pioneer Venus orbiter, and the ion transport rates are sufficient to produce and maintain the nightside ionosphere.

Whitten, R.C.; Barnes, A. (NASA Ames Research Center, Moffet Field, CA (USA)); McCormick, P.T. (Santa Clara Univ., CA (USA))

1991-07-01

84

Ionosphere.  

National Technical Information Service (NTIS)

Significant new studies of the ionosphere have occurred very recently. One line of research has involved precise measurements of the arctic and antarctic ionosphere (in the high latitudes). As a result, new models of the ionosphere based on changes in tim...

G. J. Gassmann

1972-01-01

85

The response of ionospheric convection in the polar cap to substorm activity  

NASA Astrophysics Data System (ADS)

We report multi-instrument observations during an isolated substorm on 17 October 1989. The European Incoherent Scatter (EISCAT) radar operated in the SP-UK-POLI mode measuring ionospheric convection at latitudes 71 deg Lambda - 78 deg Lambda. Sub-Auroral Magnetometer Network (SAMNET) and the EISCAT Magnetometer Cross provide information on the timing of substorm expansion phase onset and subsequent intensifications, as well as the location of the field aligned and ionospheric currents associated with the substorm current wedge. Interplanetary Monitoring Platform-8 (IMP-8) magnetic field data are also included. Evidence of a substorm growth phase is provided by the equatorward motion of a flow reversal boundary across the EISCAT radar field of view at 2130 MLT, following a southward turning of the interplanetary magnetic field (IMF). We infer that the polar cap expanded as a result of the addition of open magnetic flux in the tail lobes during this interval. The flow reversal boundary, which is a lower limit to the polar cap boundary, reached an invariant latitude equatorward of 71 deg Lambda by the time of the expansion phase onset. We conclude that the substorm onset region in the ionosphere, defined by the westward electrojet, mapped to a part of the tail radially earthward of the boundary between open and closed magnetic flux, the distant neutral line. Thus the substorm was not initiated at the distant neutral line, although there is evidence that it remained active during the expansion phase.

Lester, M.; Lockwood, M.; Yeoman, T. K.; Cowley, S. W. H.; Luehr, H.; Bunting, R.; Farrugia, C. J.

1995-02-01

86

The response of ionospheric convection in the polar cap to substorm activity  

NASA Technical Reports Server (NTRS)

We report multi-instrument observations during an isolated substorm on 17 October 1989. The European Incoherent Scatter (EISCAT) radar operated in the SP-UK-POLI mode measuring ionospheric convection at latitudes 71 deg Lambda - 78 deg Lambda. Sub-Auroral Magnetometer Network (SAMNET) and the EISCAT Magnetometer Cross provide information on the timing of substorm expansion phase onset and subsequent intensifications, as well as the location of the field aligned and ionospheric currents associated with the substorm current wedge. Interplanetary Monitoring Platform-8 (IMP-8) magnetic field data are also included. Evidence of a substorm growth phase is provided by the equatorward motion of a flow reversal boundary across the EISCAT radar field of view at 2130 MLT, following a southward turning of the interplanetary magnetic field (IMF). We infer that the polar cap expanded as a result of the addition of open magnetic flux in the tail lobes during this interval. The flow reversal boundary, which is a lower limit to the polar cap boundary, reached an invariant latitude equatorward of 71 deg Lambda by the time of the expansion phase onset. We conclude that the substorm onset region in the ionosphere, defined by the westward electrojet, mapped to a part of the tail radially earthward of the boundary between open and closed magnetic flux, the distant neutral line. Thus the substorm was not initiated at the distant neutral line, although there is evidence that it remained active during the expansion phase.

Lester, M.; Lockwood, M.; Yeoman, T. K.; Cowley, S. W. H.; Luehr, H.; Bunting, R.; Farrugia, C. J.

1995-01-01

87

Measuring ionospheric electron density using the plasma frequency probe  

NASA Technical Reports Server (NTRS)

During the past decade, the plasma frequency probe (PFP) has evolved into an accurate, proven method of measuring electron density in the ionosphere above about 90 km. The instrument uses an electrically short antenna mounted on a sounding rocket that is immersed in the plasma and notes the frequency where the antenna impedance is large and nonreactive. This frequency is closely related to the plasma frequency, which is a direct function of free electron concentration. The probe uses phase-locked loop technology to follow a changing electron density. Several sections of the plasma frequency probe circuitry are unique, especially the voltage-controlled oscillator that uses both an electronically tuned capacitor and inductor to give the wide tuning range needed for electron density measurements. The results from two recent sounding rocket flights (Thunderstorm II and CRIT II) under vastly different plasma conditions demonstrate the capabilities of the PFP and show the importance of in situ electron density measurements of understanding plasma processes.

Jensen, Mark D.; Baker, Kay D.

1992-01-01

88

The ionosphere as a fully adequate source of plasma for the earth's magnetosphere  

Microsoft Academic Search

A series of recent measurements of the outflow of ionization from the ionosphere have further heightened the awareness of the strength of the ionospheric source of magnetospheric plasmas. In this paper the ionospheric contribution of the polar wind and cleft ion fountain at energies less than 10 eV has been added to the previously measured sources; this total ion outflow

C. R. Chappell; T. E. Moore; J. H. Jr. Waite

1987-01-01

89

Spherical cap harmonic analysis of Super Dual Auroral Radar Network (SuperDARN) observations for generating maps of ionospheric convection  

Microsoft Academic Search

A spherical cap harmonic analysis (SCHA) technique is introduced for mapping the 2-D high-latitude ionospheric convection pattern based on Super Dual Auroral Radar Network (SuperDARN) velocity measurements. The current method for generating such maps is the FIT technique which generates global-scale maps over the entire convection region. This is accomplished by combining observations with a statistical model to prevent unphysical

R. A. D. Fiori; D. H. Boteler; A. V. Koustov; G. V. Haines; J. M. Ruohoniemi

2010-01-01

90

Neutral beam injection and plasma convection in a magnetic field  

SciTech Connect

Injection of a neutral beam into a plasma in a magnetic field has been studied by means of numerical plasma simulations. It is found that, in the absence of a rotational transform, the convection electric field arising from the polarization charges at the edges of the beam is dissipated by turbulent plasma convection, leading to anomalous plasma diffusion across the magnetic field. The convection electric field increases with the beam density and beam energy. In the presence of a rotational transform, polarization charges can be neutralized by the electron motion along the magnetic field. Even in the presence of a rotational transform, a steady-state convection electric field and, hence, anomalous plasma diffusion can develop when a neutral beam is constantly injected into a plasma. Theoretical investigations on the convection electric field are described for a plasma in the presence of rotational transform. 11 refs., 19 figs.

Okuda, H.; Hiroe, S.

1988-06-01

91

The status of observations and theory of high latitude ionospheric and magnetospheric plasma turbulence  

Microsoft Academic Search

A review is given for the current status of both observations and theory of high latitude ionospheric plasma turbulence. The principal purpose of this review is to draw connections between the existing body of experimental evidence of fluid-like plasma turbulence in the ionosphere and the predictions of various fluid plasma models which have been proposed to describe the dynamics of

Paul M. Kintner; Charles E. Seyler

1985-01-01

92

Radio Pumping of Ionospheric Plasma with Orbital Angular Momentum  

SciTech Connect

Experimental results are presented of pumping ionospheric plasma with a radio wave carrying orbital angular momentum (OAM), using the High Frequency Active Auroral Research Program (HAARP) facility in Alaska. Optical emissions from the pumped plasma turbulence exhibit the characteristic ring-shaped morphology when the pump beam carries OAM. Features of stimulated electromagnetic emissions (SEE) that are attributed to cascading Langmuir turbulence are well developed for a regular beam but are significantly weaker for a ring-shaped OAM beam in which case upper hybrid turbulence dominates the SEE.

Leyser, T. B. [Swedish Institute of Space Physics, Box 537, SE-751 21 Uppsala (Sweden); Norin, L. [Department of Physics and Astronomy, Uppsala University, Box 515, Uppsala SE-751 20 (Sweden); McCarrick, M. [BAE SYSTEMS Advanced Technologies, 1250 24th St, NW, Suite 850, Washington, D.C. (United States); Pedersen, T. R. [Air Force Research Laboratory, Hanscom Air Force Base, Massachusetts 01731 (United States); Gustavsson, B. [Department of Physics and Technology, University of Tromsoe, N-9037 Tromsoe (Norway)

2009-02-13

93

Response time of the polar ionospheric convection pattern to changes in the north-south direction of the IMF  

Microsoft Academic Search

A three-day period from January 27 through January 29, 1992 is analyzed using one minute resolution solar wind data from the IMP-8 satellite and the ionospheric convection pattern data derived from the four operational DMSP satellites. During this period there were several clear reversals of the sign of the z component of the interplanetary magnetic field (IMF) which is known

Marc R. Hairston; Roderick A. Heelis

1995-01-01

94

Response time of the polar ionospheric convection pattern to changes in the north-south direction of the IMF  

SciTech Connect

A three-day period from January 27 through January 29, 1992 is analyzed using one minute resolution solar wind data from the IMP-8 satellite and the ionospheric convection pattern data derived from the four operational DMSP satellites. During this period there were several clear reversals of the sign of the z component of the interplanetary magnetic field (IMF) which is known to have a direct effect on the convection patterns observed in the polar ionosphere. Polar convection patterns observed by the frequent passes of four DMSP satellites are examined following each sign change to determine the time lag between the change in the IMF at the magnetopause and the establishment of a new global convection signature in the ionosphere. After removing the transit time for the IMF to travel from the position of the IMP-8 satellite to the magnetopause, a further time lag of about 17 to 25 minutes is observed for the five cases where the IMF turned from northward to southward. A longer lag of between 28 and 44 minutes is observed for the two cases where the IMF turned from southward to northward. These lags are interpreted as the inertial response time of the ionosphere in reacting to the change in the IMF. 16 refs., 4 figs.

Hairston, M.R.; Heelis, R.A. [Univ. of Texas at Dallas, Richardson, TX (United States)] [Univ. of Texas at Dallas, Richardson, TX (United States)

1995-03-01

95

Response of the ionospheric convection pattern to a rotation of the interplanetary magnetic field on January 14, 1988  

Microsoft Academic Search

Ionospheric convection signatures observed over the polar regions are provided by the DMSP F8 satellite. The authors consider five passes over the southern summer hemisphere during a time when the z component of the interplantary magnetic field was stable and positive and the y component changed slowly from positive to negative. Large-scale regions of sunward flow are observed at very

J. A. Cumnock; R. A. Heelis; M. R. Hairston

1992-01-01

96

Response of the ionospheric convection pattern to a rotation of the interplanetary magnetic field on January 14, 1988  

Microsoft Academic Search

Ionospheric convection signatures observed over the polar regions are provided by the DMSP F8 satellite. We consider five passes over the Southern summer Hemisphere during a time when the z component of the interplanetary magnetic field was stable and positive and the y component changed slowly from positive to negative. Large-scale regions of sunward flow are observed at very high

J. A. Cumnock; R. A. Heelis; M. R. Hairston

1992-01-01

97

The interplanetary electric field, cleft currents and plasma convection in the polar caps  

NASA Astrophysics Data System (ADS)

The relationship between the pattern of plasma convection in the polar cleft and the dynamics of the interplanetary electric field (IEF) is examined theoretically. It is shown that owing to the geometrical properties of the magnetosphere, the East-West component of the IEF will drive field-aligned currents which connect to the ionosphere at points lying on either side of noon, while currents associated with the North-South component of the IEF will connect the two polar caps as sheet currents, also centered at 12 MLT. In order to describe the consequences of the Interplanetary Magnetic Field (IMF) effects upon high-latitude electric fields and convection patterns, a series of numerical simulations was carried out. The simulations were based on a solution to the steady-state equation of current continuity in a height-integrated ionospheric current. The simulations demonstrate that a simple hydrodynamical model can account for the narrow 'throats' of strong dayside antisunward convection observed during periods of southward interplanetary IMF drift, as well as the sunward convection observed during periods of strongly northward IMF drift.

Banks, P. M.; Clauer, C. R.; Araki, T.; St. Maurice, J. P.; Foster, J. C.

1984-12-01

98

Self-focusing instability in ionospheric plasma with thermal conduction  

SciTech Connect

In this communication, an expression for the growth rate of self-focusing instability in the ionospheric plasma has been derived after taking finite thermal conduction into account. The instability arises on account of the depletion of electrons from regions where the irradiance of the perturbation is large. In contrast to earlier work, an appropriate energy balance equation for electrons and ions and the proper dependence of thermal conductivity on electron temperature have been used. The dependence of the growth rate of the filamentation instability on the background irradiation, thermal conductivity, and the wave number of transverse perturbation has been investigated. The mid-latitude daytime ionospheric model of Gurevich has been used for numerical computations, corresponding to a height of 200 km. The gradient of irradiance perturbations is assumed to be along the magnetic field of the Earth. The numerical results have been illustrated graphically and discussed.

Sodha, Mahendra Singh; Sharma, Ashutosh; Verma, M. P.; Faisal, Mohammad [Disha Academy of Research and Education, Disha Crown, Katchna Road, Shankar Nagar, Raipur 492 007, Chattisgarh (India); Ramanna Fellowship and DST Project Programme, Department of Education Building, Lucknow University, Lucknow 226 007 (India)

2007-05-15

99

Plasma density observations from the Dynamic Ionosphere Cubesat Experiment (DICE)  

NASA Astrophysics Data System (ADS)

The Dynamic Ionosphere Cubesat Experiment (DICE) was launched into an eccentric low Earth orbit on October 28, 2011 on a NASA rocket from Vandenburg Air Force Base. DICE consists of two identical 1.5U CubeSats with a mission objective to study and characterize geomagnetic Storm Enhanced Density (SED) bulge and plume by multipoint measurements. Each identical spacecraft carries two Langmuir probes to measure in-situ plasma densities, electric field probes to measure in-situ DC and AC electric fields, and a magnetometer to measure in-situ DC and AC magnetic fields. This work presents Langmuir probe data from both the CubeSats as they follow each other. The two Langmuir probes are deployed 180 degrees apart on 10cm long scissor booms from the top and bottom of the CubeSats. The probes are primarily operated in the ion saturation region as fixed bias probes to give relative plasma densities, but periodically swept (every 100 seconds) to give absolute plasma density and temperature. The derived densities will be compared to International Reference Ionosphere as well as other models.; Comparison of relative plasma density derived from two fixed bias Langmuir probes (DCP+ and DCP-) on DICE with IRI model.

Barjatya, A.; Swenson, C.; Fish, C. S.; Crowley, G.; Pilinski, M.; Azeem, S. I.; Neilsen, T. L.

2012-12-01

100

A Miniature Sweeping Impedance Probe for Ionospheric Plasma Diagnostics  

NASA Astrophysics Data System (ADS)

The impedance of a probe immersed in ionospheric plasma at radio frequencies is an important technique for determining absolute electron density. Building on 50 years of history in developing and flying RF probes for plasma diagnostics at Utah State, a new SIP (Sweeping Impedance Probe) design has been completed which will obtain qualitative improvement over previous instruments in terms of accuracy and sweep rate. This instrument will provide a continuous measurement of the plasma impedance magnitude and phase with an expected accuracy of 1% and 1 degree respectively over the 1 to 20 MHz range. This new SIP will be launched in January 2014 onboard the Auroral Spatial Structures Probe (ASSP) NASA sounding rocket mission using a short monopole probe. The rocket apogee of 600 km will allow the characterization of the plasma in the E and F layers at auroral latitudes and the study of short term and spatial variations along the high-altitude profile of the sounding rocket. Although this SIP design has been developed for a sounding rocket, it can be optimized and miniaturized for Cubesat's and included along other ionospheric diagnostic instruments such as double and Langmuir probes. This presentation is focused on the overall design of the instrument, the tests results for the ASSP instrument and conceptual designs for future CubeSat mission similar to the NSF DICE mission.

Martin-Hidalgo, J.; Swenson, C.

2013-12-01

101

Relation Between Ionospheric Plasma Irregularities at High Latitudes and Auroral Phenomena  

NASA Astrophysics Data System (ADS)

Ionospheric irregularities at low-latitudes, known as equatorial plasma bubbles, tend to occur preferably at post-sunset hours when the vertical plasma velocity during the pre-reversal enhancement is particularly strong. Recently, significant occurrence rates of plasma irregularities have also been reported in the high-latitude regions. Their generation mechanisms are quite different and at present still not fully understood. As these irregularities tend to cluster in three prominent regions of the polar area - cusp, polar cap, and pre-midnight substorm onset sector - we investigate their characteristics for these regions separately. One suggestion for high-latitude irregularity generation is ionisation by soft electron precipitations. These beams of soft electrons are commonly accompanied by bursts of small-scale field-aligned currents (FAC). In a superposed epoch analysis we investigate the relation between the occurrences of plasma irregularities and collocated small-scale FACs. In the cusp, a clear coincidence of the two phenomena is observed. Conversely, in the polar cap small-scale FACs are not so frequent. Therefore we suggest a transport of the irregularities from the cusp region into the polar cap by the general anti-sunward plasma convection pattern. In order to discuss possible relations between plasma irregularities detected in the pre-midnight sector and substorm phases we also compare the event times with the substorm catalogue of Frey and Mende (2006).

Ritter, P.; Park, J.; Luhr, H.

2012-12-01

102

Ionospheric and Birkeland current distributions for northward interplanetary magnetic field - Inferred polar convection  

NASA Astrophysics Data System (ADS)

A comprehensive analysis of the total vector magnetic disturbance field is presented. The analysis is based on satellite observations of the magnetic disturbance field over the polar regions during a strong northward-moving interplanetary magnetic field IMF. Specific attention is given to a determination of northward (NBZ) currents which accompany Birkeland currents. A Fourier technique is used to derive the physical parameters ionospheric system during two days of strong IMF activity, January 3, 1980 and November 11, 1979. The system shows a W-shaped pattern with an antisunward current over the magnetic pole and return currents on either side. It is shown that the antisunward orientation of the system implies the presence of sunward convection. Suggestions are given for multicell patterns over the polar regions for northward IMF during an IMF sign change.

Zanetti, L. J.; Potemra, T. A.; Bythrow, P. F.; Iijima, T.; Baumjohann, W.

1984-09-01

103

On Plasma Instabilities in the Polar Cap Ionosphere  

NASA Astrophysics Data System (ADS)

Plasma instabilities in the polar ionosphere cause the otherwise uniform plasma to develop inhomogeneous magnetic field-aligned structures over scale sizes from tens of km to meters. Radio waves propagating through these irregularities will experience strong scintillation, which disrupts VHF, UHF and GNSS navigation systems. At longer wavelengths (HF and VHF) the same plasma irregularities will also backscatter radio waves. In this presentation we describe efforts that are currently ongoing at Svalbard to study both the cause and effect of these irregularities. We present data from EISCAT, SuperDARN, ground-based optics, and in-situ sounding rockets. We also present initial results from a new receiver network that we are installing around Svalbard to monitor the impact on GNSS navigation systems.

Oksavik, K.; Moen, J. I.; Van Der Meeren, C.; Lester, M.

2012-12-01

104

Transverse ion heating in multicomponent plasmas. [in ionosphere  

NASA Technical Reports Server (NTRS)

A new mechanism is proposed for plasma modes which can occur only in a multicomponent plasma and not in pure electron-ion plasma. The addition of ions creates a new instability near the ion-ion hybrid mode whose frequency is adequate for the wave to interact with oxygen ions. To study heating of ions (such as ionospheric oxygen ions) in presence of auroral electrons, several numerical simulations were carried out using a one-dimensional electrostatic code in a magnetic field. It was found that in the presence of electrons drifting along auroral field lines into the ionosphere, the ion-ion hybrid mode can be driven unstable when the electron drift speed is too small to excite the lower hybrid instability. Since the ion-ion mode has a smaller frequency than that of the lower hybrid waves, it can couple to the heavy ions, resulting in a substantial heating of heavy ions; on the other hand, because of their frequencies, the lower hybrid waves can accelerate only light ion species.

Ashour-Abdalla, M.; Okuda, H.; Kim, S. Y.

1987-01-01

105

Solar Wind Driven Plasma Fluxes from the Venus Ionosphere  

NASA Astrophysics Data System (ADS)

SOLAR WIND DRIVEN PLASMA FLUXES FROM THE VENUS IONOSPHERE H. Prez-de-Tejada (1), R. Lundin (2), H. Durand-Manterola (1), S. Barabash (2), T. L. Zhang (3), J. A., Sauvaud (4), and M. Reyes-Ruiz (5) 1 - Institute of Geophysics, UNAM, Mxico, D. F. 2 - Swedish Institute of Space Physics, Kiruna, Sweden 3 - Space Research Institute, Graz, Austria 4 - CESR, Toulouse, France 5 - Institute of Astronomy, UNAM, Ensenada, Mxico Measurements conducted with the ASPERA-4 instrument and the magnetometer of the Venus Express spacecraft show that the kinetic pressure of planetary O+ ion fluxes measured in the Venus wake can be significantly larger than the local magnetic pressure and, as a result, those ions are not being driven by magnetic forces but by the kinetic energy of the solar wind. Beams of planetary O+ ions with those properties have been detected in several orbits of the Venus Express through the wake as the spacecraft traverses by the noon-midnight plane along its near polar trajectory. The momentum flux of the O+ ions leads to superalfvenic flow conditions. It is suggested that such O+ ion beams are produced in the vicinity of the magnetic polar regions of the Venus ionosphere where the solar wind erodes the local plasma leading to plasma channels that extend downstream from those regions.

Perez De Tejada, H. A.; Lundin, R. N.; Zhang, T.; Sauvaud, J. A.; Reyes-Ruiz, M.

2012-12-01

106

Intercomparison among plasma wake models for plasmaspheric and ionospheric conditions  

NASA Technical Reports Server (NTRS)

The angular distributions of ions in the wake of a body moving through a space plasma computed from three different models are compared in order to investigate wake current depletion ratios under conditions simulating the topside ionosphere and plasmasphere. Results demonstrate the importance of taking into account the thermal flux at low Mach numbers and the angular acceptance of ion detectors in making theory-experiment comparisons. For all models considered, gradients in the angular variations of the fluxes are shown to be steeper near the wake-ambient interface than closer to the maximum rarefaction region.

Samir, U.; Comfort, R. H.; Wright, K. H., Jr.; Stone, N. H.

1987-01-01

107

Ionospheric chemical releases  

NASA Technical Reports Server (NTRS)

Ionospheric plasma density irregularities can be produced by chemical releases into the upper atmosphere. F-region plasma modification occurs by: (1) chemically enhancing the electron number density; (2) chemically reducing the electron population; or (3) physically convecting the plasma from one region to another. The three processes (production, loss, and transport) determine the effectiveness of ionospheric chemical releases in subtle and surprising ways. Initially, a chemical release produces a localized change in plasma density. Subsequent processes, however, can lead to enhanced transport in chemically modified regions. Ionospheric modifications by chemical releases excites artificial enhancements in airglow intensities by exothermic chemical reactions between the newly created plasma species. Numerical models were developed to describe the creation and evolution of large scale density irregularities and airglow clouds generated by artificial means. Experimental data compares favorably with theses models. It was found that chemical releases produce transient, large amplitude perturbations in electron density which can evolve into fine scale irregularities via nonlinear transport properties.

Bernhardt, Paul A.; Scales, W. A.

1990-01-01

108

Plasma bubbles in the topside ionosphere: solar activity dependence  

NASA Astrophysics Data System (ADS)

The present study deals with the He+ density depletions, observed during a high solar activity at the topside ionosphere heights. There are the indications that plasma bubbles, produced by Rayleigh-Taylor instability at the bottomside of ionosphere, could rise up to the topside ionosphere and plasmasphere. Maryama and Matuura (1984), using ISS-b spacecraft data (high solar activity - F10.7=200, 1978-80), have seen the plasma bubbles in Ne density over equator at 1100 km heights in 46 cases in 1700 passes (3%). However, there is distinctly another picture in He+ density depletions according to ISS-b spacecraft data for the same period. They occur in the topside ionosphere over low- and middle- latitudinal regions (L=1.3-3) in 11% of the cases (Karpachev, Sidorova, 2002; Sidorova, 2004, 2007). The detailed study of the He+ density depletion characteristics was done. It was noted that the He+ density depletions are mostly seen in the evening-night sector (18-05 LT) from October till May. It was like to the peculiarities of the Equatorial Spread-F (ESF), usually associated with plasma bubble. The monthly mean He+ density depletion statistics, plotted in LT versus month, was compared with the similar plots for ESF statistics, obtained by Abdu and colleagues (2000) from ground-based ionograms over Brazilian regions for the period of the same solar activity. It was revealed good enough correlation (R=0.67). Also depletion values as function of LT were compared with the vertical plasma drift velocity variations, obtained for the same period from AE-E spacecraft and IS radar (Jicamarca) data. Striking similarity in development dynamics was revealed for the different seasons. It was concluded, that the He+ density depletions should be considered as originating from equatorial plasma bubbles. It seems the plasma bubbles, reaching the topside ionosphere altitudes, are mostly seen not in electron density but in He+ density as depletions. According to publications, many cases of the He+ density depletions were revealed on OGO-4, OGO-6, Oreol-1 and DE-2 spacecraft data. The most of these cases occur during high and maximal solar activity periods, when the He+ density layer is very well developed at the topside ionosphere heights (Wilford et al., 2003). Using the model of the plasma bubble formation as suggested by Woodman and La Hoz (1976), it was shown that the topside plasma bubbles, seen in He+ density, are rather typical phenomena for the topside ionosphere for high solar activity epoch. REFERENCE Abdu, M.A., J.H.A. Sobral, I.S. Batista, Equatorial spread F statistics in the american longitudes: some problems relevant to ESF description in the IRI scheme, Adv. Space Res., vol. 25, pp. 113-124, 2000. Karpachev, A.T. and L.N. Sidorova, Occurrence probability of the light ion trough and subtrough in ??+ density on season and local time, Adv. Space Res., vol. 29, pp. 999-1008, 2002. Maryama, T. and N. Matuura, Longitudinal variability of annual changes in activity of equatorial spread F and plasma bubbles, J. Geophys. Res., 89(A12), 10,903-10,912, 1984. Sidorova, L.N., He+ density topside modeling based on ISS-b satellite data, Adv. Space Res., vol. 33, pp. 850-854, 2004. Sidorova, L.N., Plasma bubble phenomenon in the topside ionosphere, Adv. Space Res., Special issue (COSPAR), doi: 10.1016/j.asr.2007.03.067, 2007. Wilford, C.R., R.J. Moffett, J.M. Rees, G.J. Bailey, Comparison of the He+ layer observed over Arecibo during solar maximum and solar minimum with CTIP model results, J. Geophys. Res., vol. 108, A12, pp. 1452, doi:10.1029/2003JA009940, 2003. Woodman, R.F. and C. La Hoz, Radar observations of F-region equatorial irregularities, J. Geophys. Res., vol. 81, pp. 5447-5466, 1976.

Sidorova, L.

2009-04-01

109

Response of the Large Scale Ionospheric Convection Pattern to Changes in the IMF and Substorms: Results from the SUNDIAL 1987 Campaign.  

National Technical Information Service (NTIS)

This paper reports multi-point observations of ionospheric convection made during the SUNDIAL 1987 campaign. Two specific intervals of varying interplanetary magnetic field, which also include several substorms, have been identified for detailed study. Th...

H. Luhr J. C. Foster M. Lester M. P. Freeman O. De La Beaujardiere

1993-01-01

110

Magnetosphere-Ionosphere Coupling through Plasma Turbulence in Electrojet  

NASA Astrophysics Data System (ADS)

Field-aligned currents enter the high latitude E-region ionosphere from the magnetosphere causing cross-field electric fields and currents. During periods of intense geomagnetic activity, these fields induce the formation of strong electrojets, plasma instabilities, and turbulence. This turbulence gives rise to intense anomalous electron heating and nonlinear transport which significantly affects the E-region conductivity. Electrojet conductivities play an important role in the Magnetosphere-Ionosphere system. These conductivities determine the polar-cap potential saturation level and the evolution of field-aligned currents. Quantitative understanding of turbulent conductivities and energy conversion issues is important to accurately model magnetic storms and substorms essential for Space Weather predictions. We will present results of recent theoretical efforts of global energy flow, along with results of 2D and 3D fully kinetic, particle-in-cell, simulations. These simulations reproduce many of the observational characteristics of radar signals and provide information useful in accurately modeling plasma turbulence. They demonstrate the significant progress we have made simulating physical processes in E-region electrojets.

Dimant, Y. S.; Oppenheim, M. M.

2009-11-01

111

Measuring ionospheric electron density using the plasma frequency probe  

SciTech Connect

During the past decade, the plasma frequency probe (PFP) has evolved into an accurate, proven method of measuring electron density in the ionosphere above about 90 km. The instrument uses an electrically short antenna mounted on a sounding rocket that is immersed in the plasma and notes the frequency where the antenna impedance is large and nonreactive. This frequency is closely related to the plasma frequency, which is a direct function of free electron concentration. The probe uses phase-locked loop technology to follow a changing electron density. Several sections of the plasma frequency probe circuitry are unique, especially the voltage-controlled oscillator that uses both an electronically tuned capacitor and inductor to give the wide tuning range needed for electron density measurements. The results from two recent sounding rocket flights (Thunderstorm II and CRIT II) under vastly different plasma conditions demonstrate the capabilities of the PFP and show the importance of in situ electron density measurements of understanding plasma processes. 9 refs.

Jensen, M.D.; Baker, K.D. (Utah State University, Logan (United States))

1992-02-01

112

Annual and solar cycle dependencies of SuperDARN scatter occurrence and ionospheric convection measurements  

NASA Astrophysics Data System (ADS)

The Super Dual Auroral Radar Network (SuperDARN) provides a long term data series which enables investigations of the coupled magnetosphere-ionosphere system. The network has been in existence essentially since 1995 when 6 radars were operational in the northern hemisphere and 4 in the southern hemisphere. We have been involved in an analysis of the data over the lifetime of the project and present results here from two key studies. In the first study we calculated the amount of ionospheric scatter which is observed by the radars and see clear annual and solar cycle variations in both hemispheres. The recent extended solar minimum also produces a significant effect in the scatter occurrence. In the second study, we have determined the latitude of the Heppner-Maynard Boundary (HMB) using the northern hemisphere SuperDARN radars. The HMB represents the equatorward extent of ionospheric convection for the interval 1996 - 2011. We find that the average latitude of the HMB at midnight is 61 magnetic latitude during solar the maximum of 2003, but it moves significantly poleward during solar minimum, averaging 64 latitude during 1996, and 68 during 2010. This poleward motion is observed despite the increasing number of low latitude radars built in recent years as part of the StormDARN network, and so is not an artefact of data coverage. We believe that the recent extreme solar minimum led to an average HMB location that was further poleward than the previous solar cycle. We have also calculated the Open-Closed field line Boundary (OCB) from auroral images during a subset of the interval (2000 - 2002) and find that on average the HMB is located equatorward of the OCB by ~7o. We suggest that the HMB may be a useful proxy for the OCB when global images are not available. The work presented in this paper has been undertaken as part of the European Cluster Assimilation Technology (ECLAT) project which is funded through the EU FP7 programme and involves groups at Leicester, Helsinki, Uppsala, FMI, Graz and St. Petersburg. The aim of the project is to provide additional data sets, primarily ground based data, to the Cluster Active Archive, and its successor the Cluster Final Archive, in order to enhance the scientific productivity of the archives.

Lester, M.; Imber, S. M.; Milan, S. E.

2012-12-01

113

Applications of numerical codes to space plasma problems  

NASA Technical Reports Server (NTRS)

Solar wind, earth's bowshock, and magnetospheric convection and substorms were investigated. Topics discussed include computational physics, multifluid codes, ionospheric irregularities, and modeling laser plasmas.

Northrop, T. G.; Birmingham, T. J.; Jones, F. C.; Wu, C. S.

1975-01-01

114

Plasma turbulence in the equatorial ionospheric F region  

NASA Astrophysics Data System (ADS)

Equatorial spread F is a spectacular phenomenon in which the equatorial region ionosphere is reshaped after sunset. The plasma instabilities responsible for equatorial spread F are fascinating since they occur on time scales ranging from seconds to hours and length scales from centimeters to tens of kilometers. The plasma irregularities that occur in the F region also influence the performance and reliability of space borne and ground based electronic systems and may cause the disruption of satellite operations, communications, navigation, and electrical power distribution grids, leading to potentially broad economic losses. The ionospheric model equations that describe these plasma instabilities display different dynamical behavior based on the value of the ion-neutral collision frequency. The transition occurs at the so-called inertial regime of the ionosphere, where the model equations are similar to the Navier Stokes equations except applied to inhomogeneous fluids. A general analytic solution does not exist for these nonlinear equations; however, a numerical model is developed by maintaining charge neutrality in the vicinity of a circular bubble rising from the collisional to the inertial regime. Using this model, we are able to determine the location of the inertial regime as a function of local time, longitude, season, and solar cycle. The model results determine that the regime occurs generally from about 2000 and 2100 local time and 500-900 km apex height. Also, the model predicts that solar minimum periods are generally more conducive for inertial effects than solar maximum periods. Time series analysis performed on Dynamics Explorer II ion density data show that a turbulent cascade form in the inertial regime predicted by the model. Intermediate scale density power spectra all obey k-5/3 spectra scaling when measured in altitude and local time windows predicted by our model as failing within the inertial regime. Meanwhile, density power spectra for data lying outside the inertial regime take on a range of power laws between k-0.75 and k-2.2 . Applying a wavelet transform, we are able to show that large depletions are necessary for inertial regime flows to exist.

McDaniel, Rickey Dale

115

Plasma Oscillations of charged Dust in the Ionosphere  

NASA Astrophysics Data System (ADS)

The significant maximum near 28-30 Hz was found in Fourier spectrums of the ionosphere radionoise at l=2m on August 12, 1999. At night the frequency of the maximum was slowly changing from 20 to 50 Hz (50 Hz is Nyquist frequency). Additional experiments (some of them were taken during Perseids, Orionids, Leonids and Geminids meteor beams) lead us to the conclusion that the observed line is the line of ionospheric dusty plasma because its intensity becomes more stronger at the presence of the meteor shower. In the night time the charge of the dust grains is negative (10e) and under the quiet heliogeomagnetic conditions (SKp20) the line frequency is in the range of 10-50 Hz. During the magnetic storm the charges of the grains may grow substantially (~100e) and line frequency goes beyond the Nyquist frequency. In the daytime the charges on the grains are formed owing to the solar ultraviolet ionisation. The charge is positive and relatively high (~100-1000e) and the line frequency is out of detectable range (100-300 Hz). The only evident recharger is the solar terminator.

Musatenko, S. I.; Musatenko, Y. S.; Maksymenko, O. V.; Kurochka, E. V.; Choly, V. Y.; Lastochkin, A. V.

2003-04-01

116

Solar wind-driven plasma fluxes from the Venus ionosphere  

NASA Astrophysics Data System (ADS)

conducted with the ASPERA-4 instrument and the magnetometer of the Venus Express spacecraft show that the kinetic pressure of planetary O+ ion fluxes measured in the Venus wake can be significantly larger than the local magnetic pressure, and as a result, those ions are not solely being driven by magnetic forces but also by the kinetic energy of the solar wind. Beams of planetary O+ ions with those properties have been detected in several orbits of the Venus Express through the Venus wake as the spacecraft traverses by the noon-midnight plane along its near-polar trajectory. The momentum flux of the O+ ions leads to superalfvenic flow conditions. It is suggested that such O+ ion beams are produced in the vicinity of the magnetic polar regions of the Venus ionosphere where the solar wind erodes the local plasma leading to plasma channels that extend downstream from those regions. The distribution of the number of cases where superalfvenic and subalfvenic conditions are measured along the Venus Express trajectory leads to dominant values when the total kinetic plasma pressure (including that of the solar wind protons) and the magnetic pressure are comparable, thus suggesting a possible equipartition of energy between the plasma and the magnetic field.

Prez-de-Tejada, H.; Lundin, R.; Durand-Manterola, H.; Barabash, S.; Zhang, T. L.; Sauvaud, J. A.; Reyes-Ruiz, M.

2013-12-01

117

Statistical parameters of nonisothermal lower ionospheric plasma in the electrically active mesosphere  

Microsoft Academic Search

The large V\\/m electric fields inherent in the lower mesosphere play an essential role in lower ionospheric electrodynamics. They must be the cause of large variations in the electron temperature and the electron collision frequency and consequently of the transition of the ionospheric plasma in the lower part of the D region into a nonisothermal state. This study is based

S. I. Martynenko; V. T. Rozumenko; O. F. Tyrnov; A. H. Manson; C. E. Meek

2005-01-01

118

Stimulated electromagnetic emissions by high-frequency electromagnetic pumping of the ionospheric plasma  

Microsoft Academic Search

A high frequency electromagnetic pump wave transmitted into the ionospheric plasma from the ground can stimulate electromagnetic radiation with frequencies around that of the ionospherically reflected pump wave. The numerous spectral features of these stimulated electromagnetic emissions (SEE) and their temporal evolution on a wide range of time scales are reviewed and related theoretical, numerical, and simulation results are discussed.

T. B. Leyser

2001-01-01

119

A climatological assessment of ionospheric travelling convection vortices using an automatic detection algorithm  

NASA Astrophysics Data System (ADS)

Analysis of geomagnetic variometer data from the Greenland magnetometer array shows signatures of localized ionospheric travelling convection vortices (TCVs), which are commonly believed to be generated by compression or decompression of the magnetopause by changes in the solar wind dynamic pressure, flux transfer events, or magnetospheric Kelvin-Helmholtz instabilities. We present an algorithm for automatic detection of TCVs in Greenland magnetic data which is based on the short-time-average through long-time-average trigger (STA/LTA), an algorithm broadly used in weak-motion seismology. Results of their climatological assessment of their occurrence properties are discussed. In this paper, three years of magnetometer data, from 2010 to 2013, collected at twelve stations at the West coast of Greenland are analysed and TCV events are classified with respect to their intensity, duration and time of occurrence. Subsequently, they are correlated with values of the interplanetary magnetic field (IMF), solar wind velocity and geomagnetic indices. The results indicate that TCVs occur usually around magnetic local noon with a typical duration of approximately 15 to 30 minutes. TCV detection is clearly facilitated during times of low geomagnetic background activity.

Kotsiaros, S.; Stolle, C.; Friis-Christensen, E. A.; Matzka, J.

2013-12-01

120

Ionospheric convection response to slow, strong variations in a Northward interplanetary magnetic field: A case study for January 14, 1988  

NASA Technical Reports Server (NTRS)

We analyze ionospheric convection patterns over the polar regions during the passage of an interplanetary magnetic cloud on January 14, 1988, when the interplanetary magnetic field (IMF) rotated slowly in direction and had a large amplitude. Using the assimilative mapping of ionospheric electrodynamics (AMIE) procedure, we combine simultaneous observations of ionspheric drifts and magnetic perturbations from many different instruments into consistent patterns of high-latitude electrodynamics, focusing on the period of northward IMF. By combining satellite data with ground-based observations, we have generated one of the most comprehensive data sets yet assembled and used it to produce convection maps for both hemispheres. We present evidence that a lobe convection cell was embedded within normal merging convection during a period when the IMF B(sub y) and B(sub z) components were large and positive. As the IMF became predominantly northward, a strong reversed convection pattern (afternoon-to-morning potential drop of around 100 kV) appeared in the southern (summer) polar cap, while convection in the northern (winter) hemisphere became weak and disordered with a dawn-to-dust potential drop of the order of 30 kV. These patterns persisted for about 3 hours, until the IMF rotated significantly toward the west. We interpret this behavior in terms of a recently proposed merging model for northward IMF under solstice conditions, for which lobe field lines from the hemisphere tilted toward the Sun (summer hemisphere) drape over the dayside magnetosphere, producing reverse convection in the summer hemisphere and impeding direct contact between the solar wind and field lines connected to the winter polar cap. The positive IMF B(sub x) component present at this time could have contributed to the observed hemispheric asymmetry. Reverse convection in the summer hemisphere broke down rapidly after the ratio absolute value of B(sub y)/B(sub z) exceeded unity, while convection in the winter hemisphere strengthened. A dominant dawn-to-dusk potential drop was established in both hemispheres when the magnitude of B(sub y) exceeded that of B(sub z) with potential drops of the order of 100 kV, even while B(sub z) remained northward. The latter transition to southward B(sub z) produced a gradual intensification of the convection, but a greater qualitative change occurred at the transition through absolute value of B(sub y)/B(sub z) = 1 than at at the transition through B(sub z) = 0. The various convection patterns we derive under northward IMF conditions illustrate all possibilities previously discussed in the literature: nearly single-cell and multicell, distorted and symmetric, ordered and unordered, and sunward and antisunward.

Knipp, D. J.; Emery, B. A.; Richmond, A. D.; Crooker, N. U.; Hairston, M. R.; Cumnock, J. A.; Denig, W. F.; Rich, F. J.; De La Beaujardiere, O.; Ruohoniemi, J. M.

1993-01-01

121

The influence of IMF on the lower ionosphere plasma in high and middle latitudes  

NASA Technical Reports Server (NTRS)

As shown by ground-based absorption measurements, the lower ionospheric plasma is markedly controlled by the structure of the IMF. Whereas in high auroral and subauroral latitudes this effect is very pronounced, in midlatitudes its influence is less important. A comparison of these results with satellite data of the IMF and the solar wind speed confirms the important role of these components, not only during special events but also for the normal state of the ionospheric D region plasma.

Bremer, J.

1989-01-01

122

Electron temperature enhancements in nighttime equatorial ionosphere under the occurrence of plasma bubbles  

NASA Astrophysics Data System (ADS)

Simultaneous in-situ measurements of electron density and temperature in the nighttime equatorial region were performed by a rocket experiment launched under solar minimum and geomagnetic quiet conditions from the station of Alcntara (2.24S; 44.24W), Brazil, on Dec. 18, 1995, 21:17 LT. These measurements detected during the upleg flight a large overheated area around the base of density profile. The presence of plasma bubbles was revealed during the downleg phase, as well as temperature enhancements detected preferentially at altitudes where plasma depletions are found. It was assumed that the region traversed by the rocket during the downleg was preceded before the bubble's onset by a large overheating as observed during the upleg flight. Analyzing this framework under the light of the Global Self-Consistent Model of the Thermosphere, Ionosphere and Protonosphere (GSM TIP), as well as a 2D numerical code that simulate the growth of an instability and the evolution of thermal energy inside a bubble, we found that despite an overheated area in the F-region bottomside can disturb the electron density profile around the altitude interval where such heat is deposited, it seems not have a direct influence over parameters responsible for the bubble onset. Additionally, the phenomenon of the intra-bubble thermal enhancement could be formed due to the convection of hot-electron fluid transported from the overheated region surrounding the base of the F-region to upper altitudes by the underlying mechanism of bubble generation.

de Meneses, F. C.; Klimenko, M. V.; Klimenko, V. V.; Alam Kherani, E.; Muralikrishna, P.; Xu, Jiyao; Hasbi, A. M.

2013-10-01

123

Injun 5 observations of magnetospheric electric fields and plasma convection  

NASA Technical Reports Server (NTRS)

Recent measurements of magnetospheric electric fields with the satellite Injun 5 have provided a comprehensive global survey of plasma convection at low altitudes in the magnetosphere. A persistent feature of these electric field observations is the occurrence of an abrupt reversal in the convection electric field at auroral zone latitudes. The plasma convection velocities associated with these reversals are generally directed east-west, away from the sun on the poleward side of the reversal, and toward the sun on the equatorward side of the reversal. Convection velocities over the polar cap region are normally less than those observed near the reversal region. The electric field reversal is observed to be coincident with the trapping boundary for electrons with energies E greater than 45 keV.

Gurnett, D. A.

1971-01-01

124

Ionospheric traveling convection vortices observed near the polar cleft - A triggered response to sudden changes in the solar wind  

NASA Technical Reports Server (NTRS)

Analysis of 20-second resolution magnetometer data from an array of temporary stations operated around Sondre Stromfjord, Greenland, during the summer of 1986 shows the signatures of localized ionospheric traveling convection vortices. An example of an isolated event of this kind observed near 08 local time is presented in detail. This event consists of a twin vortex pattern of convection consistent with the presence of two field-aligned current filaments separated by about 600 km in the east-west direction. This system of currents is observed to move westward (tailward) past the array of stations at about 4 km/sec. The event is associated with relative quiet time ionospheric convection and occurs during an interval of northward IMF. It is, however, associated with a large fluctuation in both the Z and Y components of the IMF and with a large sudden decrease in the solar wind number density. The propagation of the system is inconsistent with existing models of FTE current systems, but nevertheless appears to be related to a readjustment of the magnetopause boundary to a sudden change in the solar wind dynamic pressure and/or to a change in reconnection brought about by a sudden reorientation of the IMF.

Friis-Christensen, E.; Vennerstrom, S.; Mchenry, M. A.; Clauer, C. R.

1988-01-01

125

Penetration of the convection and overshielding electric fields to the equatorial ionosphere during a quasiperiodic DP 2 geomagnetic fluctuation event  

NASA Astrophysics Data System (ADS)

The convection electric field penetrates to the equatorial ionosphere with no significant shielding during DP 2 fluctuation events with periods of 30-60 min (Nishida, 1968) and even during the main phase of a storm that continues over several hours (Huang et al., 2007). On the other hand, shielding becomes effective in 20 min during the substorm growth phase (Somayajulu et al., 1987), and in 1 h during the main phase of a storm (Kikuchi et al., 2008a). To clarify the relative contributions of the convection and shielding electric fields at middle to equatorial latitudes, we analyzed an equatorial DP 2 fluctuation event of 30 min duration, using magnetometer data, Super Dual Auroral Radar Network (SuperDARN) convection maps, and electric potentials calculated with the comprehensive ring current model (CRCM). The equatorial DP 2 fluctuations were found to be caused by alternating eastward electrojets (e-EJ) and westward electrojets (w-EJ) in the equatorial ionosphere, which were caused by the southward and northward interplanetary magnetic field, respectively. Using the SuperDARN convection map, we further show that the e-EJ is associated with large-scale two-cell convection vortices, while the w-EJ accompanies reverse flow vortices equatorward of the two-cell vortices. With the aid of the CRCM, we suggest that the reverse flow vortices were associated with the region 2 field-aligned currents (R2 FACs) that caused overshielding at the equator. We think it reasonable that the overshielding electric field could appear at middle to equatorial latitudes irrespective of the period of fluctuations as the region 1 FACs decrease their intensity. This scenario well explains both DP 2 fluctuations with periods of 30-60 min and continuous penetration for several hours during the main phase of storms.

Kikuchi, T.; Ebihara, Y.; Hashimoto, K. K.; Kataoka, R.; Hori, T.; Watari, S.; Nishitani, N.

2010-05-01

126

Direct evidence of double-slope power spectra in the high-latitude ionospheric plasma  

NASA Astrophysics Data System (ADS)

We report direct observations of the double-slope power spectra for plasma irregularities in the F layer of the polar ionosphere. The investigation of cusp irregularities ICI-2 sounding rocket, which was launched into the polar cusp ionosphere, intersected enhanced plasma density regions with decameter-scale irregularities. Density measurements at unprecedented high resolution with multi-Needle Langmuir Probes allowed for a detailed study of the plasma irregularities down to kinetic scales. Spectral analysis reveals double-slope power spectra for regions of enhanced fluctuations associated mainly with density gradients, with the steepening of the spectra occurring close to the oxygen gyrofrequency. These findings are further supported with the first results from the ICI-3 rocket, which flew through regions with strong precipitation and velocity shears. Previously, double-slope spectra have been observed in the equatorial ionosphere. The present work gives a direct evidence that the double-slope power spectra can be common in the high-latitude ionosphere.

Spicher, A.; Miloch, W. J.; Moen, J. I.

2014-03-01

127

Convective transport of plasma in the inner Jovian magnetosphere  

SciTech Connect

The authors investigate the transport of plasma in the inner Jovian magnetosphere according to the corotating convection model of Hill et al. (1981), emphasizing mathematical aspects of the theory. They employ a simplified but physically plausible boundary condition at the inner Io torus, representing a 5% density enhancement of S{sup +} ions in an active sector that is fixed in Jovian (system 3) longitude. They first investigate the convection electric field pattern resulting from this longitudinal mass anomaly alone, and then generalize the theory to include the effects of Coriolis force and plasma acceleration. They find that even a small ({approximately}5%) longitudinal asymmetry of the inner torus produces a convection system capable of removing torus plasma from the magnetosphere on a time scale of order one month.

Liu, W.W.; Hill, T.W. (Rice Univ., Houston, TX (United States))

1990-04-01

128

SuperDARN observations of quasi-stationary mesoscale convection vortices in the dayside high-latitude ionosphere  

NASA Astrophysics Data System (ADS)

During the past few years of SuperDARN observations, mesoscale (500-1000 km diameter) clockwise-sense convection vortices which do not show significant movement in any direction have been observed in the postnoon sector. These convection vortices or small convection cells are herein named quasi-stationary convection vortices (QSCVs). In this paper, a statistical study of 28 QSCVs is presented, using Saskatoon-Kapuskasing radar data from the period October 1993 to March 1997. These QSCVs occur in the magnetic latitude interval 72-81 between 1430 and 1630 magnetic local time (MLT) and are centered near the western end of the afternoon convection cell. The QSCVs occur mainly during southward interplanetary magnetic field (IMF) but sometimes for northward IMF. They appear at lower latitudes as the IMF Bz becomes more negative; they occur at higher latitudes and earlier local times for positive IMF By and at lower latitudes and later local times for negative IMF By. All the QSCVs appear to be associated with large-amplitude fluctuations either in the IMF or in the solar wind pressure, or in both. It is found that the time of the ionospheric convection change in response to the fluctuations in the IMF and solar wind pressure at the magnetopause is about 6-9 min. The observations have shown some evidence that the termination of the vortex is caused also by large changes in the IMF and/or solar wind pressure. The lifetime of the QSCVs is typically 10-20 min, but it can be as long as 50 min. The QSCVs have clockwise rotational sense and are closely associated with the region 1 field-aligned currents. Unlike traveling convection vortices, the QSCVs do not appear to be related to any instability at the magnetopause or low-latitude boundary layer. The large fluctuations in the solar wind pressure and IMF seem to be likely initiating mechanisms for the QSCVs.

Huang, Chao-Song; Sofko, George J.; McWilliams, Kathryn A.; Bristow, William A.; Greenwald, Ray A.; Kelley, Michael C.

1998-12-01

129

Grid-Sphere Electrodes for Contact with Ionospheric Plasma  

NASA Technical Reports Server (NTRS)

Grid-sphere electrodes have been proposed for use on the positively biased end of electrodynamic space tethers. A grid-sphere electrode is fabricated by embedding a wire mesh in a thin film from which a spherical balloon is formed. The grid-sphere electrode would be deployed from compact stowage by inflating the balloon in space. The thin-film material used to inflate the balloon is formulated to vaporize when exposed to the space environment. This would leave the bare metallic spherical grid electrode attached to the tether, which would present a small cross-sectional area (essentially, the geometric wire shadow area only) to incident neutral atoms and molecules. Most of the neutral particles, which produce dynamic drag when they impact a surface, would pass unimpeded through the open grid spaces. However, partly as a result of buildup of a space charge inside the grid-sphere, and partially, the result of magnetic field effects, the electrode would act almost like a solid surface with respect to the flux of electrons. The net result would be that grid-sphere electrodes would introduce minimal aerodynamic drag, yet have effective electrical-contact surface areas large enough to collect multiampere currents from the ionospheric plasma that are needed for operation of electrodynamic tethers. The vaporizable-balloon concept could also be applied to the deployment of large radio antennas in outer space.

Stone, Nobie H.; Poe, Garrett D.

2010-01-01

130

a Study of Plasma Convection in the Compact Auburn Torsatron.  

NASA Astrophysics Data System (ADS)

Density measurements in toroidal plasmas on the Compact Auburn Torsatron (CAT) typically show the plasma density to be lower in the core of the plasma than in the outer regions. These so-called hollow density profiles are observed in most stellarator plasmas generated by electron cyclotron resonant breakdown. A study performed on the Interchangeable Modular Stellarator (IMS) suggested that steady state electric fields can account for outward cross -field plasma convection leading to hollow density profiles. The dissertation is motivated by previous work on IMS. The goal of the dissertation is to investigate the importance of steady-state poloidal electric fields to the apparent convection that gives rise to hollow density profiles in stellarator plasmas. Plasma generated in CAT is of relatively low density and temperature, and it is possible to measure the plasma potential, density, electron temperature and pressure everywhere in the steady-state plasma using emissive and Langmuir probes. The two-dimensional plasma potential and temperature, density and pressure profiles in the poloidal plane are measured directly in CAT. Normally, in Electron Cyclotron Resonant Heating (ECRH)-generated discharges, the plasma density profiles tend to be flat or somewhat hollow. By changing the neutral pressure and magnetic field (which moves the location of the resonant layer for ECRH), both hollow and peaked density profiles can be obtained under different conditions. Measurements of the plasma potential and pressure have been made in both first and second harmonic ECR-generated plasmas. From these 2-D potential measurements, the 2-D electrical field (in a poloidal plane) can be obtained. The results are used to calculate cross field particle flux values by making use of the magnetic flux surfaces measured by electron beam mapping. The flux-averaged radial plasma flow velocity measured by this technique is compared with numerically modeled density profile with a diffusion equation. While convective cells are observed in the plasma, the net effect of the steady-state electric fields provide sufficient convection to produce the hollow density profiles. The convection theory has difficulty in explaining the peak profiles seen in CAT.

Zhang, Qiqun

131

Plasma heating, electric fields and plasma flow by electron beam ionospheric injection  

NASA Technical Reports Server (NTRS)

The electric fields and the floating potentials of a Plasma Diagnostics Payload (PDP) located near a powerful electron beam injected from a large sounding rocket into the auroral zone ionosphere have been studied. As the PDP drifted away from the beam laterally, it surveyed a region of hot plasma extending nearly to 60 m radius. Large polarization electric fields transverse to B were imbedded in this hot plasma, which displayed large ELF wave variations and also an average pattern which has led to a model of the plasma flow about the negative line potential of the beam resembling a hydrodynamic vortex in a uniform flow field. Most of the present results are derived from the ECHO 6 sounding rocket mission.

Winckler, J. R.; Erickson, K. N.

1990-01-01

132

Dayside ionospheric convection changes in response to long-period interplanetary magnetic field oscillations - Determination of the ionospheric phase velocity  

NASA Astrophysics Data System (ADS)

Ground magnetic field perturbations recorded by the CANOPUS magnetometer network in the 7 to 13 MLT sector are used to examine how reconfigurations of the dayside polar ionospheric flow take place in response to north-south changes of the IMF. During the 6-h interval in question, IMF Bz oscillates between +/- 7 nT with about a 1-h period. Corresponding variations in the ground magnetic disturbance are observed which we infer are due to changes in ionospheric flow. Cross correlation of the data obtained from two ground stations at 73.5 deg magnetic latitude, but separated by about 2 hours in MLT, shows that changes in the flow are initiated in the prenoon sector (about 10 MLT) and then spread outward toward dawn and dusk with a phase speed of about 5 km/s over the longitude range about 8 to 12 MLT, slowing to about 2 km/s outside this range. Cross correlating the data from these ground stations with IMP 8 IMF Bz records produces a MLT variation in the ground response delay relative to the IMF which is compatible with these deduced phase speeds.

Saunders, M. A.; Freeman, M. P.; Southwood, D. J.; Cowley, S. W.; Lockwood, M.; Samson, J. C.; Farrugia, C. J.; Hughes, T. J.

1992-12-01

133

The response of plasma density to breaking inertial gravity wave in the lower regions of ionosphere  

NASA Astrophysics Data System (ADS)

We present a three-dimensional numerical study for the E and lower F region ionosphere coupled with the neutral atmosphere dynamics. This model is developed based on a previous ionospheric model that examines the transport patterns of plasma density given a prescribed neutral atmospheric flow. Inclusion of neutral dynamics in the model allows us to examine the charge-neutral interactions over the full evolution cycle of an inertial gravity wave when the background flow spins up from rest, saturates and eventually breaks. Using Lagrangian analyses, we show the mixing patterns of the ionospheric responses and the formation of ionospheric layers. The corresponding plasma density in this flow develops complex wave structures and small-scale patches during the gravity wave breaking event.

Tang, Wenbo; Mahalov, Alex

2014-04-01

134

Interhemispheric contrasts in the ionospheric convection response to changes in the interplanetary magnetic field and substorm activity: a case-study  

NASA Astrophysics Data System (ADS)

Interhemispheric contrasts in the ionospheric convection response to variations of the interplanetary magnetic field (IMF) and substorm activity are examined, for an interval observed by the Polar Anglo-American Conjugate Experiment (PACE) radar system between ~1600 and ~2100 MLT on 4 March 1992. Representations of the ionospheric convection pattern associated with different orientations and magnitudes of the IMF and nightside driven enhancements of the auroral electrojet are employed to illustrate a possible explanation for the contrast in convection flow response observed in radar data at nominally conjugate points. Ion drift measurements from the Defence Meteorological Satellite Program (DMSP) confirm these ionospheric convection flows to be representative for the prevailing IMF orientation and magnitude. The location of the fields of view of the PACE radars with respect to these patterns suggest that the radar backscatter observed in each hemisphere is critically influenced by the position of the ionospheric convection reversal boundary (CRB) within the radar field of view and the influence it has on the generation of the irregularities required as scattering targets by high-frequency coherent radar systems. The position of the CRB in each hemisphere is strongly controlled by the relative magnitudes of the IMF Bz and By components, and hence so is the interhemispheric contrast in the radar observations.

Shand, B. A.; Yeoman, T. K.; Lewis, R. V.; Greenwald, R. A.; Hairston, M. R.

1998-07-01

135

The Ionospheric Bubble Index deduced from magnetic field and plasma observations onboard Swarm  

NASA Astrophysics Data System (ADS)

In the post-sunset tropical ionospheric F-region plasma density often exhibits depletions, which are usually called equatorial plasma bubbles (EPBs). In this paper we give an overview of the Swarm Level 2 Ionospheric Bubble Index (IBI), which is a standard scientific data of the Swarm mission. This product called L2-IBI is generated from magnetic field and plasma observations onboard Swarm, and gives information as to whether a Swarm magnetic field observation is affected by EPBs. We validate the performance of the L2-IBI product by using magnetic field and plasma measurements from the CHAMP satellite, which provided observations similar to those of the Swarm. The L2-IBI product is of interest not only for ionospheric studies, but also for geomagnetic field modeling; modelers can de-select magnetic data which are affected by EPBs or other unphysical artifacts.

Park, J.; Noja, M.; Stolle, C.; Lhr, H.

2013-11-01

136

Mapping ionospheric convection response to IMF B(sub y) negative and B(sub z) positive conditions  

NASA Technical Reports Server (NTRS)

We have used the Assimilative Mapping of Ionospheric Electrodynamics (AMIE) procedure to derive electric potential patterns for a period of strong and slowly varying northward Interplanetary Magnetic Field (IMF). Using these patterns we offer some insight into high-latitude convection response to differing IMF conditions between the hours of 0850 and 1720 UT on 14 January 1988. We introduce a newly assimilated data set, Defense Meteorological Satellite Program (DMSP) ion drift measurements, as a means of mapping electric fields in polar regions. Also, for the first time we map both southern and northern hemisphere convection flows. We show that significantly different convection patterns are simultaneously possible in the two polar caps when B(sub z) is positive and that asymmetries in these patterns are influenced by the strength of B(sub y) and B(sub x). When the ratio absolute value of B(sub y)/B(sub z) exceeds unity the polar cap convection increases and changes from sunward to anti-sunward for B(sub z) positive conditions.

Knipp, D. J.; Emery, B. A.; Richmond, A. D.; Hairston, M. R.

1994-01-01

137

Equatorial plasma convection from global simulations of the Earth's magnetosphere  

Microsoft Academic Search

The convection of plasma in the closed field region of the Earth's magnetosphere is an important consequence and a diagnostic of the coupling of solar wind momentum and energy into the magnetosphere. In the outer regions the nature of the flow can help to distinguish between different coupling processes; for example, between (1) a global reconnection process between closed geomagnetic

C. M. Mobarry; J. A. Fedder; J. G. Lyon

1996-01-01

138

The ionosphere as a fully adequate source of plasma for the earth's magnetosphere  

NASA Technical Reports Server (NTRS)

The ionospheric contribution of the polar wind and cleft ion fountain at energies less than 10 eV has been added to previously measured sources; this total ion outflow has then been used to calculate the resulting ion density in the different internal regions of the earth's magnetosphere: plasmasphere, plasma trough, plasma sheet, and magnetotail lobes. Using estimated volumes for these regions and an ion residence time characteristic of each region, it is found that the observed magnetospheric densities can be attained in all cases with no contribution from the solar wind plasma. In the case of the plasma sheet the ionospherically supplied density is more than enough to match the observations and even suggests an invisible component of low-energy plasma (less than 10 eV) which has never been observed. A detailed comparison between the calculated ionospheric source effects in the plasma sheet and those recently measured by ISEE shows excellent agreement and suggests a direct polar low-energy ion source for the plasma sheet which has remained unmeasured because of spacecraft potential effects. Although the solar wind is clearly the earth's magnetospheric energy source and energetic solar wind ions are observed in the magnetosphere, these calculations suggest the possibility that the ionospheric source alone is sufficient to supply the entire magnetospheric plasma content under all geomagnetic conditions.

Chappell, C. R.; Moore, T. E.; Waite, J. H., Jr.

1987-01-01

139

Behavior of thermal plasma in the ionosphere and magnetosphere  

NASA Technical Reports Server (NTRS)

Models of ion flow in the topside ionosphere were developed. These models took both H(+) and O(+) into account and permitted various parameter studies to be made affecting H(+) escape in polar winds. Extensive computer programs were written to display the measured electron density profiles in ways useful to geophysical analysis. The relationship between the location of the plasmapause as it is found in the equatorial plane and the location of the ionospheric trough was also investigated.

Banks, P. M.; Doupnik, J. R.

1973-01-01

140

SuperDARN convection and Sondrestrom plasma drift  

NASA Astrophysics Data System (ADS)

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.

Xu, L.; Koustov, A. V.; Thayer, J.; McCready, M. A.

2001-07-01

141

Modeling of the Convection and Interaction of Ring Current, Plasmaspheric and Plasma Sheet Plasmas in the Inner Magnetosphere  

NASA Technical Reports Server (NTRS)

Distinctive sources of ions reside in the plasmasphere, plasmasheet, and ring current regions at discrete energies constitute the major plasma populations in the inner/middle magnetosphere. They contribute to the electrodynamics of the ionosphere-magnetosphere system as important carriers of the global current system, in triggering; geomagnetic storm and substorms, as well as critical components of plasma instabilities such as reconnection and Kelvin-Helmholtz instability at the magnetospheric boundaries. Our preliminary analysis of in-situ measurements shoves the complexity of the plasmas pitch angle distributions at particularly the cold and warm plasmas, vary dramatically at different local times and radial distances from the Earth in response to changes in solar wind condition and Dst index. Using an MHD-ring current coupled code, we model the convection and interaction of cold, warm and energetic ions of plasmaspheric, plasmasheet, and ring current origins in the inner magnetosphere. We compare our simulation results with in-situ and remotely sensed measurements from recent instrumentation on Geotail, Cluster, THEMIS, and TWINS spacecraft.

Fok, Mei-Ching; Chen, Sheng-Hsien; Buzulukova, Natalia; Glocer, Alex

2010-01-01

142

Response time of the polar ionospheric convection pattern to changes in the north-south direction of the IMF. Scientific report No. 1  

SciTech Connect

A three day period from January 27 through January 29, 1992 is analyzed using one minute resolution solar wind data from the IMP8 satellite and the ionospheric convection pattern data derived from the four operational DMSP satellites. During this period there were several clear reversals of the sign of the z component of the interplanetary magnetic field (IMF) which is known to have a direct effect on the convection patterns observed in the polar ionosphere. Polar convection patterns observed by the frequent passes of four DMSP satellites are examined following each sign change to determine the time lag between the change in the IMF at the magnetopause and the establishment of a new global convection signature in the ionosphere. After removing the transit time for the IMF to travel from the position of the IMP-8 satellite to the magnetopause, a further time lag of about 17 to 25 minutes is observed for the five cases where the IMF turned from northward to southward. A longer lag of between 28 and 44 minutes is observed for the two cases where the IMF turned from southward to northward. These lags are interpreted as the inertial response time of the ionosphere in reacting to the change in the IMF.

Hairston, M.R.; Heelis, R.A.

1995-03-01

143

Simulations of plasma structure evolution in the high-latitude ionosphere  

NASA Technical Reports Server (NTRS)

The Naval Research Laboratory has recently developed a two-dimensional inertial, electrostatic code which has been successfully applied to the development and evolution of ionospheric structure driven by plasma instabilities. This code models the ionosphere and magnetosphere as a set of horizontal two-dimensional layers which are coupled by the vertical magnetic field lines at high latitudes. It is shown that the development of instability-generated structure can be strongly dependent on this coupling. For example, the influence of magnetospheric coupling on the E x B gradient drift instability is to retard the instability's growth and to isotropize density irregularities. The influence of ionospheric coupling on the Kelvin-Helmholtz instability is to retard its growth and to suppress vortex formation. This paper presents the results of numerical simulations of these instabilities and discusses their application to high-latitude ionospheric structure.

Huba, J. D.; Keskinen, M. J.; Fedder, J. A.; Mitchell, H. G.; Satyanarayana, P.

1988-01-01

144

Response of the ionospheric convection pattern to a rotation of the interplanetary magnetic field on January 14, 1988  

NASA Technical Reports Server (NTRS)

Ionospheric convection signatures observed over the polar regions are provided by the DMSP F8 satellite. We consider five passes over the Southern summer Hemisphere during a time when the z component of the interplanetary magnetic field was stable and positive and the y component changed slowly from positive to negative. Large-scale regions of sunward flow are observed at very high latitudes consistent with a strong z component. When By and Bz are positive, but By is greater than Bz, strong evidence exists for dayside merging in a manner similar to that expected when Bz is negative. This signature is diminished as By decreases and becomes smaller than Bz, resulting in a four-cell convection pattern displaced toward the sunward side of the dawn-dusk meridian. In this case the sign of By affects the relative sizes of the two highest-latitude cells. In the Southern Hemisphere the duskside high-latitude cell is dominant for By positive and the dawnside high-latitude cell is dominant for By negative. The relative importance of possible electric field sources in the low-latitude boundary layer, the dayside cusp, and the lobe all need to be considered to adequately explain the observed evolution of the convection pattern.

Cumnock, J. A.; Heelis, R. A.; Hairston, M. R.

1992-01-01

145

A comparison of plasma waves produced by ion accelerators in the F-region ionosphere  

NASA Technical Reports Server (NTRS)

Ion beams injected into the ionosphere are known to produce waves related to the normal modes of the plasma. The spectra of plasma waves produced during four sounding rocket experiments are examined. The experimental conditions were somewhat different during each experiment. The accelerated ion was either Xe(+) or Ar(+) and the experimental geometry, described by the separation vector between the plasma wave receiver and the ion accelerator, was either parallel or perpendicular to the geomagnetic field.

Kintner, P. M.; Labelle, J.; Scales, W.; Erlandson, R.; Cahill, L. J., Jr.

1986-01-01

146

Ionospheric signatures of a plasma sheet rebound flow during a substorm onset  

NASA Astrophysics Data System (ADS)

Magnetic reconnection in Earth's magnetotail produces fast earthward flows in the plasma sheet. Tailward flows are often observed associated with the earthward flows. Both return flow vortices at the flanks of an earthward flow channel and rebound of the earthward flow from the intense dipolar magnetic field of the inner magnetosphere have been shown to explain tailward flows observed near Earth. We combine plasma sheet measurements from Cluster with conjugate ground-based magnetic and auroral data to examine the development of earthward and tailward flow signatures during a substorm onset. We show for the first time observations of ionospheric signatures that appear to be associated with rebound flows. Because of the highly dynamic magnetotail configuration, special care is taken with the satellite footprint mapping. The ionospheric footprints produced by the event oriented AM02 model drift equatorward and poleward in response to tail magnetic field stretching and dipolarization, respectively. The footprint motion matches that of the ambient ionospheric structures, and the plasma flow measured by Cluster agrees with that inferred from the conjugate ionospheric observations, confirming the validity of the AM02 mapping. The ionospheric signatures of fast earthward flows during a substorm onset are shown to resemble the known signatures of quiet-time flows, including equatorward propagating auroral streamers inside a channel of enhanced poleward equivalent current. However, the large-scale dipolarization results in additional poleward expansion of the signatures, as has been predicted by simulations.

Juusola, L.; Kubyshkina, M.; Nakamura, R.; PitkNen, T.; Amm, O.; Kauristie, K.; Partamies, N.; RMe, H.; Snekvik, K.; Whiter, D.

2013-01-01

147

Observations of ionospheric ion flow and related convective electric fields in and near an auroral arc  

Microsoft Academic Search

determine the ion bulk flow velocity, temperature, and density. It is shown that the ion flow velocity is highly correlated with energetic electron precipitation. The convective component (perpendicular to the local magnetic field B) was found to be large (equivalent electric field z  100-200 mV\\/m) poleward of a series of poleward expanding arcs. Inside the arc the convective flow

B. A. Whalen; D. W. Green; I. B. McDiarmid

1974-01-01

148

Noinlinear, Coherent, Collective, Resonant Plasma Propagation Modes in the Ionosphere  

NASA Astrophysics Data System (ADS)

We theoretically describe the complex media of the ionospheric resonance system in which we consider longitudinal as well as transverse components of electric and magnetic fields resulting from natural and man-made sources of excitation. The properties of the ionosphere, as a cool, ionized medium, can sustain plasmon and ion acoustic excitation modes, which appear to explain certain of its unique observed properties. These properties involve collective, coherent resonant states that are sustained over long propagation distances and also over relatively long temporal periods with low dispersive losses. Long range and relatively long-lived shock excitation modes are examined which produced by natural and/or man-made phenomena, such as solar flare and other activity.(1) Characteristic frequencies of resonant excitation of the ionospheric layers have been characterized, and we also calculate the speed of some of the unique velocities of signal propagations in these specific ionospheric layers. The characteristics of the micro pulsations in the magnetosphere are also characterized. (1) E.A. Rauscher and W.L Van Bise, Bull. Am. Phys. Soc. EB01, 1300(2002)

van Bise, W. L.; Rauscher, E. A.

2002-04-01

149

Simultaneous observations of convective ionospheric storms: ROCSAT-1 and ground-based imagers  

Microsoft Academic Search

The irregularities that occur in the postsunset equatorial ionosphere are one of the most spectacular effects of space weather. They occur over many decades of scale sizes and can cause scintillation of signals transmitted on a wide range of frequencies used by satellite communication and navigation systems, rendering such systems inoperable for a period of time. In the near future,

J. J. Makela; M. C. Kelley; S.-Y. Su

2005-01-01

150

Eastward propagation of a plasma convection enhancement following a southward turning of the interplanetary magnetic field  

SciTech Connect

On October 27th 1984, high-latitude ionospheric convection was observed by the European incoherent scatter (EISCAT) radar. For a nine-hour period, simultaneous observations of the interplanetary magnetic field (IMF) were obtained sunward of the Earth's bow shock. During this period, the IMF abruptly turned southward, having previously been predominantly northward for approximately three hours, and a strong enhancement in convection was observed 11 +- 1 minutes later. Using the very high time resolution of the EISCAT data, it is shown that the convection enhancement propagated eastward, around the afternoon magnetic local time sector, at a speed of the order of 1 kms/sup -1/. These results are interpreted in terms of the effects of an onset of steady IMF-geomagnetic field merging and are the first to show how a new pattern of enhanced convection is established in the high latitude ionosphere.

Lockwood, M.; van Eyken, A.P.; Bromage, B.J.I.; Willis, D.M.; Cowley, S.W.H.

1986-01-01

151

Observations of plasma line splitting in the ionospheric incoherent scatter spectrum.  

PubMed

Wide-bandwidth ionospheric incoherent scatter (IS) spectra obtained using the Arecibo IS radar show the occurrence of a split in the plasma line (i.e., two plasma lines) when the plasma frequency is close to the second harmonic of the electron gyrofrequency. This split is predicted in the IS theory for a magnetized plasma, but observations have never been reported. Here we present the experimental results and theoretical calculations supporting the observations. These results may assist in understanding the behavior of Langmuir waves in the magnetized plasma and are a validation of what historically was a somewhat controversial aspect of the IS theory. PMID:18352291

Bhatt, Asti N; Nicolls, Michael J; Sulzer, Michael P; Kelley, Michael C

2008-02-01

152

Tomographic imaging and characterization of ionospheric equatorial plasma irregularities with the Global Ultraviolet Imager  

NASA Astrophysics Data System (ADS)

This dissertation develops a technique for reconstructing multidimensional images of the electron density of the Earth's ionosphere using spectroscopic measurements obtained from the Global Ultraviolet Imager (GUVI). This work combines a novel image processing approach, models of GUVI observations as tomographic reconstruction problems, and new studies of equatorial plasma irregularities and the global F-region ionosphere. The image processing component of the research involves the development of a computationally efficient, edge-preserving regularization technique incorporating projection on convex sets (POCS) in order to solve the limited-angle tomographic image reconstruction problem. The algebraic reconstruction technique was specifically tailored to reconstruct the shapes of plasma irregularities while also recovering the altitude and longitude profile of the background ionosphere, all using data with a low signal-to-noise ratio. GUVI observation geometry is discretely modeled and a linear algebraic relationship is derived between GUVI brightness measurements and ionospheric electron density values. The specific formulation of the problem varies to accommodate the physics of different latitude regions of the ionosphere in order to allow the three-dimensional observation geometry to be cast as a two-dimensional limited-angle tomography problem. The experimental aspect explores the equatorial plasma bubble imaging capabilities of this technique and its scientific impact. Retrievals of altitude and longitude profiles allow for characterization of plasma bubbles based on their structure and depth of depletion. This information can then be used in coordinated studies of plasma bubbles with groundbased imaging systems. These coordinated studies both serve to validate the reconstructed images and to provide complementary information for a more complete understanding of plasma bubble events.

Comberiate, Joseph Michael

153

Yosemite Conference on Ionospheric Plasma in the Magnetosphere: Sources, Mechanisms and Consequences, meeting report  

NASA Technical Reports Server (NTRS)

The sixth biennial Yosemite topical conference and the first as a Chapman Conference was held on February 3 to 6, 1986. Due to the recent changes in our perception of the dynamics of the ionospheric/magnetospheric system, it was deemed timely to bring researchers together to discuss and contrast the relative importance of solar versus terrestrial sources of magnetospheric plasma. Although the solar wind was once thought to dominate the supply of plasma in the Earth's magnetosphere, it is now thought that the Earth's ionosphere is a significant contributor. Polar wind and other large volume outflows of plasma have been seen at relatively high altitudes over the polar cap and are now being correlated with outflows found in the magnetotail. The auroral ion fountain and cleft ion fountain are examples of ionospheric sources of plasma in the magnetosphere, observed by the Dynamics Explorer 1 (DE 1) spacecraft. The conference was organized into six sessions: four consisting of prepared oral presentations, one poster session, and one session for open forum discussion. The first three oral sessions dealt separately with the three major topics of the conference, i.e., the sources, mechanisms, and consequences of ionospheric plasma in the magnetosphere. A special session of invited oral presentations was held to discuss extraterrestrial ionospheric/magnetospheric plasma processes. The poster session was extended over two evenings during which presenters discussed their papers on a one-on-one basis. The last session of the conferences was reserved for open discussions of those topics or ideas considered most interesting or controversial.

Gallagher, D. L.; Burch, J. L.; Klumpar, D. M.; Moore, T. E.; Waite, J. H., Jr.

1987-01-01

154

A PLASMA INSTABILITY RESULTING IN FIELD-ALIGNED IRREGULARITIES IN THE IONOSPHERE  

Microsoft Academic Search

A theory of the two-stream ion wave instability in a plasma is developed ; that takes into account both the effect of collisions of the ions and electrons ; with neutral particles and the presence of a uniform magnetic field. Applying ; the results to the ionosphere, it is found that irregularities of ionization ; density should arise spontaneously in

D. T. Farley; D. T. Jr

1963-01-01

155

Maintenance of the Venus nightside ionosphere: Electron precipitation and plasma transport  

Microsoft Academic Search

Suprathermal integral electron spectra between 5 and 45 eV measured by the Pioneer Venus orbiter RPA are presented for the Venus nightside ionosphere. The observed integral electron flux is relatively constant with time and altitude. The simultaneously measured plasma density is much more variable and not correlated with the electron flux. For a typical electron spectrum the ionization rates and

K. Spenner; W. C. Knudsen; R. C. Whitten; P. F. Michelson; K.L. Miller; V. Novak

1981-01-01

156

A plasma flow vortex in the magnetotail and its related ionospheric signatures  

NASA Astrophysics Data System (ADS)

We presented a large-scale plasma flow vortex event that occurred on 1 March 2009 observed by Time History of Events and Macroscale Interactions during Substorms (THEMIS) satellites. During the interval, THEMIS satellites were located in the premidnight region between 11 and 16 RE downtail. Dawnward-earthward plasma flows were seen initially in the magnetotail, followed by duskward-tailward flows. This suggests that a clockwise plasma flow vortex (seen from above the equatorial plane) was observed on the dawn side of the plasma sheet. Furthermore, high energy (>1 keV) electrons were observed. Auroral images at 427.8 nm and THEMIS white light all-sky imager (ASI) at Fort Smith showed a discrete auroral patch formed at the poleward of the auroral oval, it then intensified. It extended eastward and equatorward first and followed by westward motion to form the clockwise auroral vortex. The auroral feature corresponded to the ionospheric signatures of the plasma flow vortex in the magnetotail when the Alfvn transit time between the magnetotail and the ionosphere was taken into account. We suggest that the large-scale clockwise plasma flow vortex in association with the high energy (>1 keV) electrons on the dawn side of the plasma sheet generated a downward field-aligned current (FAC) that caused the related ionospheric signatures. The plasma flow vortex had rotational flow speeds of up to 300 km s-1. The current density associated with the plasma flow vortex was estimated at 2.0 ?A m-2, mapped to the ionosphere.

Tang, C. L.

2012-03-01

157

Plasma convection and ion beam generation in the plasma sheet boundary layer  

NASA Technical Reports Server (NTRS)

Because of the dawn-dusk electric field E(dd), plasma in the magnetotail convects from the lobe toward the central plasma sheet (CPS). In the absence of space or velocity diffusion due to plasma turbulence, convection would yield a steady state distribution function f = V exp (-2/3) g(v exp 2 V exp 2/3), where V is the flux tube volume. Starting with such a distribution function and a plasma beta which varies from beta greater than 1 in the CPS to beta much smaller than 1 in the lobe, the evolution of the ion distribution function was studied considering the combined effects of ion diffusion by kinetic Alfven waves (KAW) in the ULF frequency range (1-10 mHz) and convection due to E(dd) x B drift in the plasma sheet boundary layer (PSBL) and outer central plasma sheet (OCPS). The results show that, during the early stages after launching the KAWs, a beamlike ion distribution forms in the PSBL and at the same time the plasma density and temperature decrease in the OCPS. Following this stage, ions in the beams convect toward the CPS resulting in an increase of the plasma temperature in the OCPS.

Moghaddam-Taaheri, E.; Goertz, C. K.; Smith, R. A.

1991-01-01

158

Radial convection of plasma structures in a turbulent rotating magnetized plasma column  

Microsoft Academic Search

The turbulent regime of the rotating magnetized plasma column in the Mistral device has been studied. The structures inside the turbulence move on average along a spiral trajectory. These long-lived structures are convected in the background plasma to the walls contributing to a large extent both to particle and to energy transport. Without drift induced by the curvature and the

Claudia Riccardi; Ruggero Barni; Thiery Pierre; Alexandre Escarguel; Didier Guyomarc'h

2003-01-01

159

The Dayside Ionospheric "Superfountain" (DIS), plasma transport and other consequences  

NASA Astrophysics Data System (ADS)

Prompt penetration electric fields (PPEFs) and the consequential dayside ionospheric superfountain (DIS) are reviewed. An example of O+ uplift to ~840 km altitude at ~0940 local time (DMSP F15) during the superstorm of 30 October 2003 is illustrated. The SAMI-2 model is modified to incorporate intense superstorm electric fields. With an inclusion of a ~4 mV/m eastward electric field, SAMI-2* modeling results show many of the expected DIS effects.

Tsurutani, B. T.; Saito, A.; Verkhoglyadova, O. P.; Mannucci, A. J.; Abdu, M. A.; Araki, T.; Gonzalez, W. D.; Iijima, B. A.; Lakhina, G. S.; McCreadie, H.; Sobral, J. H. A.; Tsuda, T.; Yumoto, K.; Vasyliunas, V. M.

160

Modeling the low-latitude ionospheric electron density and plasma turbulence in the November 2004 storm period  

Microsoft Academic Search

The storm period of 812 November 2004 offers an opportunity for insight into the phenomena of low-latitude ionospheric structure during geomagnetically disturbed times because of the strength of the disturbances, the timing of the storms, and the instrumentation that was operating during the interval. We will take advantage of these factors to model the ambient ionosphere and the plasma turbulence

J. M. Retterer; Ronald Ilma; M. C. Kelley; Jorge L. Chau; C. E. Valladares; L. C. Gentile; K. Groves

2010-01-01

161

Modeling the low-latitude ionospheric electron density and plasma turbulence in the November 2004 storm period  

Microsoft Academic Search

The storm period of 8-12 November 2004 offers an opportunity for insight into the phenomena of low-latitude ionospheric structure during geomagnetically disturbed times because of the strength of the disturbances, the timing of the storms, and the instrumentation that was operating during the interval. We will take advantage of these factors to model the ambient ionosphere and the plasma turbulence

J. M. Retterer; Ronald Ilma; M. C. Kelley; Jorge L. Chau; C. E. Valladares; L. C. Gentile; K. Groves

2010-01-01

162

Kinetic modeling of O(+) upflows resulting from E x B convection heating in the high-latitude F region ionosphere  

NASA Technical Reports Server (NTRS)

We report here the results of modeling work aimed at understanding the development of ionospheric O(+) field-aligned upflows that develop in response to high-latitude E x B drift induced frictional heating. The model used is a collisional semikinetic model which includes ion-neutral resonant charge exchange and polarization collisions as well as Coulomb self-collisions. It also includes the process of chemical removal of O(+) as well as all of the macroscopic forces: ambipolar electric, gravity, magnetic mirror, and centripetal. Model results show the development of several types of non-Maxwellian velocity distributions including toroids at low altitude, distributions with large heat flow in the perpendicular component at intermediate altitudes, and distributions with a separate upflowing population or upward superthermal tail at high altitudes. Whenever the convection electric field increases from a small value (less than 25 mV/m) to a large value (100-200 mV/m) in 6 min or less large upflows develop with parallel drift speeds which peak (below 1000 km) at values between 500 m/s and 2 km/s, parallel fluxes which peak between 6.0 x 10(exp 8) and 3.2 x 10(exp 9)/sq cm/s, and parallel per particle heat flows which peak between 8.0 x 10(exp -9) and 8.0 x 10(exp -8) ergs cm/s. The higher values in these ranges occur for a cooler neutral atmosphere, with a larger convection electric field that is turned on quickly. The model produces field-aligned O(+) flow speeds that are larger than those produced by a 20-moment generalized transport model but smaller then those produced by an isotropic hydrodynamic model for comparable values of the convection turn on times. The model results compare favorably with some topside satellite and radar data.

Wilson, G. R.

1994-01-01

163

Climatology of Ionospheric Plasma Irregularities at High Latitudes, as Observed by CHAMP  

NASA Astrophysics Data System (ADS)

Ionospheric irregularities at low-latitudes, also known as equatorial plasma bubbles, have been investigated before, but no comparable effort has been made at high latitudes. In this study we demonstrate clear diamagnetic signatures of high-latitude ionospheric irregularities as observed by the CHAMP satellite. Each detected magnetic event is verified by linear correlation with electron density variation. We present a climatology of these irregularity signatures for the years 2001-2010. The occurrence rate of ionospheric irregularities generally peaks along the auroral oval in both hemispheres. Highest occurrence frequencies are found at the dayside cusp and in the pre-midnight ionosphere. The occurrence rate increases with solar and auroral activity. The region of high occurrence rate expands equatorward with increasing auroral activity. Occurrence probabilities are higher in local winter than in local summer. The overall occurrence rate is smallest around June solstice and largest around December solstice. Our observed climatology of diamagnetic signatures is in reasonable agreement with previously reported scintillations statistics. The ionospheric irregularities are generally accompanied by bursts of small-scale field-aligned currents (FACs), and are collocated with Region 1 FACs. Based on all our observations we make suggestions on the generation mechanism.

Luhr, H.; Park, J.; Ehrlich, R.; Ritter, P.

2012-12-01

164

Magnetosphere-ionosphere coupling and scale breaking of a plasma cloud in the magnetosphere  

NASA Astrophysics Data System (ADS)

The goal of this paper is to deliver a long-missing interpretation of a central issue of the NASA-MPE barium injection experiment performed in September 1971. It pertains to the interaction with the ionosphere. Observations of the cloud's motion revealed no obvious sign of such interaction. The barium vapor was released from a Scout rocket at an altitude of 31,000 km above South America during late evening hours and was observed for more than 4000 s. The barium plasma split into several field-parallel streaks which moved for a long time as if subject to constant acceleration as viewed from the inertial frame of the rocket at release. This means that no reflection of energy due to a mismatch of ionospheric conductivity and the characteristic impedance of an impinging Alfvn wave was observed. It is this finding that has never been properly interpreted. Furthermore, after a careful assessment of the barium cloud properties and environmental parameters, we find a theoretical coupling time to the ambient flow which turns out to be substantially longer than observed. Although this appears to indicate that some interaction with the ionosphere occurred, we can rule out multiple wave reflections during the observed acceleration phase. Discarding other possibilities, we interpret the observed motions as sign of perfect matching of the momentum and energy flux into the ionosphere with the rate of dissipation. This is achieved during the initial phase by scale breaking of the cloud into streaks with narrow widths which allow parallel potential drops along the Alfvn wings because of the waves' inertial nature and inside the lower ionosphere owing to the finite parallel resistivity, thereby greatly reducing the effective Pedersen conductivity. The significance of this finding goes beyond understanding the barium injection experiment. It sheds light on how magnetospheric plasma irregularities can share momentum and energy with the ionosphere in an optimized fashion.

Haerendel, Gerhard; Mende, Stephen B.

2012-09-01

165

Comparison of the USU GAIM ionospheric plasma densities with Arecibo ISR observations  

NASA Astrophysics Data System (ADS)

Physics-based data assimilation models of the ionosphere were developed at Utah State University as the central part of a DoD MURI funded program called GAIM (Global Assimilation of Ionospheric Measurements). Recently, the Air Force Weather Agency (AFWA) has selected one of the USU GAIM models for its operational use and the same model will also be implemented at the Community Coordinated Modeling Center (CCMC) for scientific studies. The selected model is based on a physics-based model of the ionosphere and a Gauss-Markov Kalman Filter (GMKF) as a basis for assimilating a diverse set of real-time (or near real-time) observations. The physics-based model is the Ionospheric Forecast Model (IFM), which accounts of five ion species and covers the E-region, F-region and the topside from 90 to 1400 km altitude. Within the GMKF, the IFM derived ionospheric densities constitute a background density field on which perturbations are superimposed based on the available data and their errors. In the current configuration the GMKF assimilates slant TEC from a variable number of ground GPS sites, bottom-side Ne profiles from a variable number of ionosondes, in situ Ne from four DMSP satellites, and nighttime line-of-sight UV radiances measured by satellites. In the current application of the model the ionospheric plasma densities at F region heights obtained from our GAIM model will be compared with observed plasma densities from the Arecibo incoherent scatter radar. The emphasis of this comparison is on the observed and modeled day-to-day variability over Arecibo and its spatial extend as specified by the global and regional GAIM model. The comparison will cover several periods of Arecibo observations with both small and large day-to-day variability.

Scherliess, L.; Schunk, R. W.; Sojka, J. J.; Thompson, D. C.; Zhu, L.

2005-05-01

166

Basic Features of E B Convection Nonlinearity in Tokamak Plasmas  

NASA Astrophysics Data System (ADS)

Basic features of E B convection nonlinearity in tokamak plasmas, especially, large-scale coherent structures, are studied on the basis of both the model of three coupled modes and the model of four coupled modes. The difference of our models with the most existing models is that we deal with a linearly unstable system such as the ion-temperate-gradient (ITG) driven turbulence in tokamaks. Two types of coherent structure are identified with spatio-temporal characteristics called a zonal flow (ZF), and an oscillating shearing flow (OSF), respectively. At the same time, the anomalous heat fluxes in the system are analyzed in some details. Results show that the two types of coherent structure play different roles in both the plasma turbulent fluctuations and the related anomalous transports. Moreover, only the large-scale coherent structure with zero frequency, namely, the zonal flow, can suppress the turbulent fluctuations effectively and hence benefits tokamak plasma confinements.

Peng, Xiaodong; Qiu, Xiaoming; Wang, Gang

2012-04-01

167

Plasma irregularities in the D-region ionosphere in association with sprite streamer initiation  

NASA Astrophysics Data System (ADS)

Sprites are spectacular optical emissions in the mesosphere induced by transient lightning electric fields above thunderstorms. Although the streamer nature of sprites has been generally accepted, how these filamentary plasmas are initiated remains a subject of active research. Here we present observational and modelling results showing solid evidence of pre-existing plasma irregularities in association with streamer initiation in the D-region ionosphere. The video observations show that before streamer initiation, kilometre-scale spatial structures descend rapidly with the overall diffuse emissions of the sprite halo, but slow down and stop to form the stationary glow in the vicinity of the streamer onset, from where streamers suddenly emerge. The modelling results reproduce the sub-millisecond halo dynamics and demonstrate that the descending halo structures are optical manifestations of the pre-existing plasma irregularities, which might have been produced by thunderstorm or meteor effects on the D-region ionosphere.

Qin, Jianqi; Pasko, Victor P.; McHarg, Matthew G.; Stenbaek-Nielsen, Hans C.

2014-05-01

168

Io's atmosphere and ionosphere - New limits on surface pressure from plasma models  

NASA Technical Reports Server (NTRS)

The paper studies charge particle impact as a mechanism for the production of Io's ionosphere. Pioneer 10 thermal plasma measurements and magnetospheric plasma models which explain the observed spatial distribution of neutral hydrogen and sodium atoms in the vicinity of Jupiter's satellite Io imply electron fluxes of about 10 to the 10th/sq cm/s. The fluxes and the temperature (about 100 eV) of this plasma suggest that electron impact ionization is the dominant process in forming the ionosphere of Io. It is found that the surface number density of the neutral species required to match the observed electron density profiles is about 10 to the 9th/cu cm or less. This value is two orders of magnitude lower than previous estimates.

Johnson, T. V.; Matson, D. L.; Carlson, R. W.

1976-01-01

169

Plasma irregularities in the D-region ionosphere in association with sprite streamer initiation.  

PubMed

Sprites are spectacular optical emissions in the mesosphere induced by transient lightning electric fields above thunderstorms. Although the streamer nature of sprites has been generally accepted, how these filamentary plasmas are initiated remains a subject of active research. Here we present observational and modelling results showing solid evidence of pre-existing plasma irregularities in association with streamer initiation in the D-region ionosphere. The video observations show that before streamer initiation, kilometre-scale spatial structures descend rapidly with the overall diffuse emissions of the sprite halo, but slow down and stop to form the stationary glow in the vicinity of the streamer onset, from where streamers suddenly emerge. The modelling results reproduce the sub-millisecond halo dynamics and demonstrate that the descending halo structures are optical manifestations of the pre-existing plasma irregularities, which might have been produced by thunderstorm or meteor effects on the D-region ionosphere. PMID:24806314

Qin, Jianqi; Pasko, Victor P; McHarg, Matthew G; Stenbaek-Nielsen, Hans C

2014-01-01

170

Linking Plasma Conditions in the Magnetosphere with Ionospheric Signatures  

NASA Technical Reports Server (NTRS)

Modeling of the full magnetosphere, ring current and ionosphere system has become an indispensable tool in analyzing the series of events that occur during geomagnetic storms. The CCMC has a full model suite available for the magnetosphere, together with visualization tools that allow a user to perform a large variety of analyses. The January, 21, 2005 storm was a moderate-size storm that has been found to feature a large penetration electric field and unusually large polar caps (low-latitude precipitation patterns) that are otherwise found in super storms. Based on simulations runs at CCMC we can outline the likely causes of this behavior. Using visualization tools available to the online user we compare results from different magnetosphere models and present connections found between features in the magnetosphere and the ionosphere that are connected magnetically. The range of magnetic mappings found with different models can be compared with statistical models (Tsyganenko) and the model's fidelity can be verified with observations from low earth orbiting satellites such as DMSP and TIMED.

Rastaetter, Lutz; Kozyra, Janet; Kuznetsova, Maria M.; Berrios, David H.

2012-01-01

171

Recent and planned observations of thermal plasma in magnetosphere-ionosphere coupling using thermal plasma imaging  

NASA Astrophysics Data System (ADS)

Thermal plasma imaging (TPI) is a technique developed over the past fifteen years, beginnning with the Freja Cold Plasma Analyzer. TPI generates high-resolution, 2-D (angle/energy) representations of charged particle distribution functions in the thermal (0-20 eV) or suprathermal (0-200 eV) energy ranges. This talk will review results from a series of sub-orbital flights of TPI instruments, and will preview capabilities and studies planned for the ePOP Suprathermal Electron Imager and the Swarm Electric Field Instruments. The enhanced Polar Outflow Probe, planned for launch in 2009, will study polar ion outflow and the mechanisms that cause it, including ambipolar electric fields driven by photoelectrons and/or soft electron precipitation. The Swarm EFIs are TPI-based instruments that will measure electric fields through ion drifts during a four-year mission that will begin in 2010. These measurements combined with Swarm's precision magnetic field measurements will provide an unprecedented view of electrodynamic coupling and energy transfer between the ionosphere, thermosphere and magnetosphere.

Knudsen, David

172

Space weather. Ionospheric control of magnetotail reconnection.  

PubMed

Observed distributions of high-speed plasma flows at distances of 10 to 30 Earth radii (R(E)) in Earth's magnetotail neutral sheet are highly skewed toward the premidnight sector. The flows are a product of the magnetic reconnection process that converts magnetic energy stored in the magnetotail into plasma kinetic and thermal energy. We show, using global numerical simulations, that the electrodynamic interaction between Earth's magnetosphere and ionosphere produces an asymmetry consistent with observed distributions in nightside reconnection and plasmasheet flows and in accompanying ionospheric convection. The primary causal agent is the meridional gradient in the ionospheric Hall conductance which, through the Cowling effect, regulates the distribution of electrical currents flowing within and between the ionosphere and magnetotail. PMID:25013068

Lotko, William; Smith, Ryan H; Zhang, Binzheng; Ouellette, Jeremy E; Brambles, Oliver J; Lyon, John G

2014-07-11

173

First storm-time plasma velocity estimates from high-resolution ionospheric data assimilation  

NASA Astrophysics Data System (ADS)

This paper uses data assimilation to estimate ionospheric state during storm time at subdegree resolution. We use Ionospheric Data Assimilation Four-Dimensional (IDA4D) to resolve the three-dimensional time-varying electron density gradients of the storm-enhanced density poleward plume. By Estimating Model Parameters from Ionospheric Reverse Engineering (EMPIRE), we infer the three-dimensional plasma velocity from the densities. EMPIRE estimates of ExB drift are made by correcting the Weimer 2000 electric potential model. This is the first time electron densities derived from GPS total electron content (TEC) data are being used to estimate field-aligned and field-perpendicular drifts at such high resolution, without reference to direct drift measurements. The time-varying estimated electron densities are used to construct the ionospheric spatial decorrelation in vertical total electron content (TEC) on horizontal scales of less than 100 km. We compare slant TEC (STEC) estimates to actual STEC GPS observations, including independent unassimilated data. The IDA4D density model of the extreme ionospheric storm on 20 November 2003 shows STEC delays of up to 210 TEC units, comparable to the STEC of the GPS ground stations. Horizontal drifts from EMPIRE are predicted to be northwestward within the storm-enhanced density plume and its boundary, turning northeast at high latitudes. These estimates compare favorably to independent Assimilative Mapping of Ionospheric Electrodynamics-assimilated high-latitude ExB drift estimates. Estimated and measured Defense Meteorological Satellite Program in situ drifts differ by a factor of 2-3 and in some cases have incorrect direction. This indicates that significant density rates of change and more accurate accounting for production and loss may be needed when other processes are not dominant.

Datta-Barua, Seebany; Bust, Gary S.; Crowley, Geoff

2013-11-01

174

Ionospheric plasma temperatures during 1976-2001 over Millstone Hill  

NASA Astrophysics Data System (ADS)

Incoherent scatter measurements have been made since the 1960s over Millstone Hill. Zenith antenna data since 1976 and steerable antenna data since 1980 are now available through the WWW-based Madrigal database system. By analyzing this large volume of data in a systematic way, this paper provides an updated climatology of the ionospheric temperature over Millstone Hill, including diurnal variations, solar activity dependences, and the electron density Ne and electron temperature Te relationship. The daytime Te in the F2-layer is found to increase with the increasing solar activity in summer, and to decrease in winter. The inverse correlation between Ne and Te prevails in winter and equinox but is much less pronounced or even disappears in summer. Based on the database, Millstone Hill incoherent scatter radar models are established, and compared with the latest International Reference Model.

Zhang, Shun-Rong; Holt, John M.

175

Convective Coupling Between the Lower Atmosphere and the Thermosphere/Ionosphere  

NASA Astrophysics Data System (ADS)

In this talk, I discuss recent research relating the coupling of the lower and upper atmosphere via gravity waves (GWs) generated by deep convective plumes. These gravity waves are excited by the convective overshoot. Those GWs which reach the thermosphere tend to dissipate at z=120-220 km. Because of wind filtering in the lower thermosphere, they are oriented in a certain direction when they deposit their momentum in the thermosphere. This deposition of momentum accelerates the neutral fluid in the thermosphere horizontally, and is dubbed a thermospheric "body force". We discuss a case study here involving a convective plume in Brazil on 01 Oct, 2005. We find that this body force is quite large spatially, and has a large amplitude of ~ 1 m/s2. It excites large scale secondary gravity waves with horizontal waveslengths of 2000 km and horizontal phase speeds of 500 m/s. These secondary GWs propagate up to at least z=420 km, and propagate globally on the nightside to the north and south poles after 4-6 hours. These secondary GWs propagate in all directions except that perpendicular to the force direction. Additionally, large-scale LSTIDs are created which "follow" the GWs around the globe. Finally, large "mean" neutral winds and wind shear are created in the body force region, which dissipate after 4 hours. This new mechanism for the generation of large-scale GWs during geomagnetically quiet times agrees well with existing observations.

Vadas, S. L.

2009-05-01

176

Processes accompanying the charging of dust grains in the ionospheric plasma  

NASA Astrophysics Data System (ADS)

The influence of the neutral component of the dusty ionospheric plasma on the process of dust grain charging is analyzed. Microscopic ion fluxes onto a dust grain are calculated with allowance for the interaction with the neutral components of the ionospheric plasma for both negatively and positively charged dust grains. For the latter case, which takes place in the presence of intense UV or X-ray solar radiation, the electron heating caused by the photoelectric effect is also investigated. It is found that the efficiency of electron heating depends on the density of neutral particles. The altitudes at which these effects appreciably influence the charging of different types of nano- and microscale dust grains are determined. It is shown that these effects should be taken into account in describing noctilucent clouds, polar mesosphere summer echoes, and physical phenomena involving grains of meteoric origin.

Kopnin, S. I.; Morzhakova, A. A.; Popel, S. I.; Shukla, P. K.

2011-08-01

177

Plasma inhomogeneities and radiowave scattering in experiments with electron pulses in the ionosphere  

NASA Astrophysics Data System (ADS)

The absorption of telemetry radiosignals at frequencies of 250 and 75 MHz, transmitted from rockets, was observed in the ARAKS and Zarnitza 2 rocket experiments, respectively, with electron pulses in the ionosphere. The signals were registered with ground receivers. Four cases of complete signal absorption on the propagation path were observed in the ARAKS experiment. The radio absorption at frequencies substantially higher than the plasma and upper hybrid frequencies can be related to wave scattering by plasma inhomogeneities. It has been indicated that plasma inhomogeneities were generated when electrostatic oscillations damped in the region with decreased plasma density at a decrease in the natural oscillation phase volume in the frequency-wave vector space with decreasing plasma density. The observed radio absorption could be related to reflectionless wave scattering in an inhomogeneous plasma structure.

Izhovkina, N. I.; Erokhin, N. S.; Mikhailovskaya, L. A.

2014-01-01

178

Radial Convection of Plasma Structures in a Turbulent Rotating Magnetized-Plasma Column  

Microsoft Academic Search

The turbulent regime of a rotating magnetized plasma column has been studied. The detection and the spatiotemporal analysis of structures by means of conditional sampling techniques is performed. Because of the overall rotation and centrifugal effects, the structures inside the turbulence move on average along a spiral trajectory leading to a net radial convection of the charged particles to the

Th. Pierre; A. Escarguel; D. Guyomarc'h; R. Barni; C. Riccardi

2004-01-01

179

Scintillations, plasma drifts, and neutral winds in the equatorial ionosphere after sunset  

Microsoft Academic Search

An equatorial campaign was conducted during September 25 to October 7, 1994, to investigate the neutral and plasma dynamics in the equatorial ionosphere after sunset in relation to the day-to-day variability of the occurrence of equatorial spread F (ESF). The campaign was organized under the auspices of National Science Foundation's Multi-Instrumented Studies of the Equatorial Thermosphere Aeronomy program (MISETA), which

S. Basu; E. Kudeki; C. E. Valladares; E. J. Weber; H. P. Zengingonul; S. Bhattacharyya; R. Sheehan; M. A. Biondi; H. Kuenzler; J. Espinoza

1996-01-01

180

Space Weather Event Modeling of Plasma Injection Into the Inner Magnetosphere with the Rice Convection Model  

NASA Astrophysics Data System (ADS)

The inner magnetosphere modeling is an important component of the magnetosphere simulation frameworks with significant implications for space weather and a. principle methodology to understand the magnetospheric response to changes in the solar wind. The thesis shows our efforts in constructing and validating the contemporary Rice Convection Model (RCM) code and its interface as a next-generation code to predict electric fields, field-aligned currents, and energetic particle fluxes in the inner magnetosphere and subauroral ionosphere during geomagnetic disturbed times. The RCM was used to simulate the geomagnetic storms with fixed boundary conditions of time-dependent Tsyganenko-Mukai boundary conditions. This work shows the results of two extremely- strong storm events with significant interchange motion. The ring current injection predicted by the RCM is shown to be overestimated, consistent with the previous results of overestimating particle fluxes by the RCM. This effect is magnified here since the southward component of interplanetary magnetic field is very strong reaching about 50 nT. Time-dependent Borovsky's boundary condition is implemented and used to alleviate the huge pressure and get better tendency of ring current energy calculated by the Dessler-Parker-Sckopke relation. This work also describes a new module of generalized Knight's relation to compute the parallel potential drops from the calculated field-aligned currents through Vasyliunas equation. It gives different ionospheric conductance and plasma drift signatures particularly around the midnight. The inclusion of parallel electric fields will replace the treatments of energy flux in the substorm simulations since that the Hardy normalization cannot perform the desired function during the substorm expansion phase and the energy flux floor gives arbitrary enhanced the precipitating energy flux and ionospheric conductances at high latitude especially for the westward clectrojet around the midnight. Since the original Knight's relation gives too large field-aligned potential drop, the modified Knight's relation is applied and implemented successfully into the RCM. Therefore, the RCM is capable of real time event simulation including strong geomagnetic storms and magnetospheric substorms, although full validation of model predictions with typical observations remains to be done.

Song, Yang

181

2-dimensional FDTD simulations of plasma wave propagations in the ionosphere  

NASA Astrophysics Data System (ADS)

We developed a 2-dimensional FDTD simulation code which can treat wave propagations in magnetized plasma. Though we need to perform full particle simulations in order to recognize accurate characteristics of waves propagating in space plasma, FDTD simulations can be performed with much less computer resources than those necessary for full particle simulations, in memories as well as cpu times. Since space plasma is magnetized, it is necessary to incorporate the dielectric tensor with anisotropy and dispersibility in FDTD simulation code, in order to calculate the electromagnetic field in space plasma. We use PLRC method to formulization FDTD scheme to reduce numerical errors. In FDTD simulations, it is essential that how to realize an effective absorbing boundary. We developed PML absorbing boundary condition with anisotropy and dispersibility, and succeeded to realize very effective absorbind boundary. According to the rocket observations, we can receive MF radio wave above the dense ionospheric layer whose density is larger than those corresponding to cutoff frequency of MF radio wave. We consider that this is because the thickness of the ionopheric layer is smaller than the wavelength of MF radio wave, the density of ionospheric layer is not constant in the horizontal plane. We have been analyzing the characteristics of MF wave propagation in the ionospher with Full-wave method. In the Full-wave method, since the electron density profile is assumed to change in one-dimensional corrsponding to the alititude, we can only treat one-dimensional electron density profiles. In this study, therefore, we performed a series of FDTD simulations of MF wave propagations in ionospheres with several types of electron density distributions in the horizontal plane, such as electron dense cloud, sporadic layer, etc., and studied the relation between spatial scale of ionospheric layer and MF radio wavelength. In addition, we performed a FDTD simulation of MF radio wave propagations with the ionospheric layer model which is estimated by Full-wave analysis of S-310-37 sounding rocket observations. S-310-37 sonding rocket was launched at USC (Uchinoura Space Center, Kagoshima) in Jan. 2007. We are going to compare FDTD simulation results, Full-wave analysis and rocket observations, and study the influence of electron density profile on the propagation characterictics of MF radio wave in the ionosphere.

Miyake, T.; Yoshino, S.; Okada, T.; Ishisaka, K.

2007-12-01

182

SuperDARN observations of an unusually contracted ionospheric convection pattern during the recent deep solar minimum  

NASA Astrophysics Data System (ADS)

We present a long term study, from 1995 - 2011, of the latitude of the Heppner-Maynard Boundary (HMB) determined using the northern hemisphere SuperDARN radars. The HMB represents the equatorward extent of ionospheric convection. We find that the average latitude of the HMB at midnight is 61 magnetic latitude during the solar maximum of 2003, but it moves significantly poleward during solar minimum, averaging 64 latitude during 1996, and 68 during 2010. This poleward motion is observed despite the increasing number of low latitude radars built in recent years as part of the StormDARN network, and so is not an artefact of data coverage. We believe that the recent extreme solar minimum lead to an average HMB location that was further poleward than previous solar cycles. We also calculated the open-closed field line boundary (OCB) from auroral images during the years 2000-2002 and find that on average the HMB is located equatorward of the OCB by ~6. We suggest that the HMB may be a useful proxy for the OCB when global auroral images are not available.

Imber, S. M.; Milan, S. E.; Lester, M.

2012-04-01

183

Understanding Substorms from the Auroral Ionosphere to the Distant Plasma Sheet  

NASA Technical Reports Server (NTRS)

The global polar UVI images have been correlated with observations from the ground, ionosphere, geomagnetic tail between 10-20 earth radii and the interplanetary space. One of the objectives of our study is to better understand the connection among many complex phenomena occurring close to Earth and those in the near--earth plasma sheet. We have examined the details of how the auroral and polar cap boundaries at different local times behave in relation to variations occurring in the solar wind, ionosphere and plasma sheet during substorms. We have also compared locations of boundaries deduced from images to electron flux "boundaries" observed by polar orbiting spacecraft. Our results indicate that the ionospheric dynamics is important and polar cap and auroral oval boundaries expand and contract in a complicated but systematic way. These variations are correlated to solar wind parameters and growth and recovery phenomena in the plasma sheet. These results can be interpreted in terms of directly driven and/or unloading substorm processes.

Parks, G. K.; Brittnacher, M.; Chen, L.; Chua, D.; Elsen, R.; Fillingim, M.; McCarthy, M.; Wilber, M.; Germany, G.; Spann, J.; Lin, R. P.

1998-01-01

184

Titan's plasma environment and ionosphere during the T85/T42/T32 magnetosheath encounters (Invited)  

NASA Astrophysics Data System (ADS)

During the T85 flyby we observe the highest electron number densities ever reported from the ionosphere of Titan as measured by RPWS/LP. The measured density reached 4310 cm-3, which is at least 500 cm-3 higher than ever observed before, and at least 50 % above the average density for similar solar zenith angles. The peak of the ionospheric density is not reached on this flyby, making the maximum measured density a lower limit. Furthermore, we observe that Titan was located in the magnetosheath of Saturn for at least 2 h 45 min before the actual flyby. This long-term exposure to magnetosheath plasma and crossings of the magnetopause and bow shock might be the reason why the peak ionospheric electron density during T85 rise to the maximum recorded. We propose that enhanced fluxes of solar wind protons precipitating and causing particle impact ionoisation is the physical explanation for the extreme densities during T85. Measurements by RPWS/LP indicate from several flybys (T83-T91) that the electron density in the peak region of Titan's ionosphere (950-1100 km) has increased by about 15-30% during the last 2 years. Furthermore, the peak ionospheric density is found at lower altitudes, though the flyby geometry often affords only the inference of an upper-limit. The increase is most likely a response to the rising toward a new solar max with increasing EUV flux. Still, T85 stands out in terms of extreme densities. We compare the ionospheric structure and plasma environment of Titan during the T85 flyby to that of the previous T32/T42 magnetosheath encounter. T32 showed no apparent increased density in the peak region but that flyby occurred during the solar minimum era and close to the terminator plane of Titan. T42 on the other hand showed high electron densities despite the solar minimum conditions, but occurred at low solar zenith angles, where the ionospheric density normally is higher compared to high solar zenith angles. Orbital geometry and Cassini MAG measurements during the T85 magentosheath encounter.

Edberg, N. J.; Andrews, D. J.; Shebanits, O.; Agren, K.; Wahlund, J.; Opgenoorth, H. J.; Garnier, P.; Roussos, E.; Cravens, T.; Badman, S. V.; Modolo, R.; Bertucci, C.; Dougherty, M. K.

2013-12-01

185

Plasma waves near the double resonance layer in the ionosphere  

Microsoft Academic Search

Dispersion properties of plasma waves with frequencies ? close to the upper hybrid frequency ?u and the multiple electron cyclotron frequency n?Be (double resonance) are considered for an inhomogeneous plasma with opposite gradients of the electron density and magnetic field magnitude. We show that a region of possible solutions of the dispersion relation decreases in real space as well as

S. M. Grach; B. Thid; T. B. Leyser

1994-01-01

186

Magnetosphere-ionosphere interactions: Near Earth manifestations of the plasma universe  

NASA Technical Reports Server (NTRS)

As the universe consists almost entirely of plasma, the understanding of astrophysical phenomena must depend critically on the understanding of how matter behaves in the plasma state. In situ observations in the near Earth cosmical plasma offer an excellent opportunity of gaining such understanding. The near Earth cosmical plasma not only covers vast ranges of density and temperature, but is the site of a rich variety of complex plasma physical processes which are activated as a results of the interactions between the magnetosphere and the ionosphere. The geomagnetic field connects the ionosphere, tied by friction to the Earth, and the magnetosphere, dynamically coupled to the solar wind. This causes an exchange of energy an momentum between the two regions. The exchange is executed by magnetic-field-aligned electric currents, the so-called Birkeland currents. Both directly and indirectly (through instabilities and particle acceleration) these also lead to an exchange of plasma, which is selective and therefore causes chemical separation. Another essential aspect of the coupling is the role of electric fields, especially magnetic field aligned (parallel) electric fields, which have important consequences both for the dynamics of the coupling and, especially, for energization of charged particles.

Faelthammar, Carl-Gunne

1986-01-01

187

Near Synchronous Plasma Structuring in the Middle and Equatorial Ionosphere During Intense Magnetic Storms  

NASA Astrophysics Data System (ADS)

Near simultaneous formation of plasma density structures in the ionosphere at middle and equatorial latitudes during intense magnetic storms is investigated. The magnetic storms of July 15, 2000, March 30-31, 2001 and October 29 - 31, 2003 are studied. These storms are characterized by minimum SYM-H (1-min Dst) values of -350 nT, -420 nT and -400 nT respectively. The evolution of plasma density structures in the midlatitude and the equatorial ionosphere is investigated by measuring amplitude scintillation of satellite signals at 250 MHz and L-band, phase fluctuations of GPS signals and by detecting equatorial plasma bubbles with DMSP satellites. It is shown that at the time of the fast rate of change of SYM-H, an impulsive onset of scintillation occurs at Hanscom AFB, a sub-auroral station, and the associated plasma structures in the equatorial ionosphere are observed in the specific longitude sector for which the early evening period corresponds to the time of rapid SYM-H variation, as shown earlier for moderate storms (Basu et al., JGR, 2001). From continuous measurements of scintillation of signals from geostationary satellites and phase fluctuations of GPS signals, it is found that the onset of equatorial plasma structures is delayed by about 20 minutes from the onset of midlatitude scintillation. This delay is discussed in the framework of instantaneous storm-time electric field penetration from high latitudes to middle to equatorial latitudes and the instability growth time of sub-km scale irregularities. It is also shown that during intense storms, the equatorward neutral wind can cause the post-sunset plasma drift in the equatorial region to be as large as 200 m/sec in the westward direction in contrast to the quiet time drift of 100 m/sec in the eastward direction.

Basu, S.; Groves, K. M.; MacKenzie, E.; Keskinen, M. J.; Rich, F.

2004-12-01

188

The ionosphere of Venus - Observations and their interpretation  

NASA Technical Reports Server (NTRS)

The implications of Soviet and U.S. observations of the Venus ionosphere's density, temperature, composition, motion, and magnetic structure are discussed, in view of the strong influence exerted on nearly all ionospheric parameters by the solar wind. The IMF conveys solar wind pressure to the ionosphere, compressing, accelerating, heating and removing plasma, forming the ionopause and inducing a nightward convection of plasma. Within the ionosphere, the main electron density peak is at an altitude of about 140 km on the day side, and is believed to be formed by local production and loss analogous to the earth's E region. Throughout most of the ionosphere, the nightward ion flow is primarily driven by the day-to-night pressure gradient, and electron precipitation also contributes to the nightside ionization. The lower atmosphere is dominated by O2(+), except at the lowest altitudes at night, where NO(+) and CO2(+) become significant ions.

Brace, L. H.; Taylor, H. A., Jr.; Gombosi, T. I.; Kliore, A. J.; Knudsen, W. C.; Nagy, A. F.

1983-01-01

189

Plasma bubbles and irregularities in the equatorial ionosphere  

Microsoft Academic Search

Using the Atmosphere Explorer satellite AE-C, we observe large-scale (10- to >200-km) irregular biteouts of up to three orders of magnitude in the ion concentration N in the nighttime equatorial F region associated with small-scale inhomogeneities in N. Similar phenomena were reported by Hanson and Sanatani but without the more complete plasma diagnostics present on AE. Simultaneous plasma velocity observations

J. P. McClure; W.B. Hanson; J. H. Hoffman

1977-01-01

190

August 28, 1978, Storm 1. GEOS 2 observations of the initial magnetopause crossings and STARE observations near the ionospheric convection reversal  

SciTech Connect

During the postdawn period on August 28, 1978, from approx.0750 to 0830 magnetic local time, the magnetopause moved several earth radii inward to less than 6.6 R/sub E/, where it remained until approx.1120 MLT. As the magnetopause approached the earth, the poleward boundary of the westward auroral electrojet moved southward to geomagnetic latitudes less than 66/sup 0/. Fortuitously, the geostationary satellite GEOS 2 was located in this morning sector during this entire period, and experienced a series of magnetopause crossings. In quiet periods GEOS 2 was conjugate to that area of the lower E region which constituted the field-of-view of the Scandinavian Twin Auroral Radar Experiment (STARE) radars. This paper compares the magnetospheric satellite and ionospheric radar observations. The combined observations suggest that, near the dawnside magnetopause, large-scale merging was occurring, while in the ionosphere, the convection reversal region and poleward portion of the auroral zone underwent major equatorward shifts and featured prominent sunward moving ULF pulsations. Between the magnetopause and ionosphere a large increase in the ring current accompanied the equatorward shift of the convection reversal.

Sofko, G.J.; Korth, A.; Kremser, G.

1985-02-01

191

Comparison of the ionospheric plasma turbulence over seismic and equatorial regions.  

NASA Astrophysics Data System (ADS)

Many strong earthquakes which are objects of interest in investigations of the changes registered in the electric field in the ELF frequency range (1 Hz - 1250 Hz) in the ionospheric plasma, occurs in the equatorial region. In order to determine, if the observed disturbances are connected with the coupling between the ground and the ionosphere in the seismic active region, it is necessary to analyse and compare plasma instability phenomena occurring in the equatorial F-region ionosphere and are known as equatorial spread F (ESF) to changes before earthquakes because their character is very similar. The aim of this paper is the analysis of changes in the electromagnetic ELF field, registered by the French micro-satellite DEMETER over epicentres of three selected strong earthquakes with magnitude bigger than 6, which took place in: Sichuan, Chile and Haiti. A comparison between those cases and changes observed by the same satellite over the equatorial region in the similar time of year is presented. The analysis of the data, was conducted with the Fourier, wavelet and bispectral methods. The last one gives answer to question, whether the changes localized with the spectral analysis are nonlinear. Further processing consists the determination of the power spectrum and its slope, which allows to determine the type of turbulence which was inducted by the three wave interaction. The last stage of the presented research, was finding the characteristic remarks of changes, by calculation of the probability density function (PDF) and calculation of its characteristic values such as kurtosis and skewness.

Kosciesza, M.; Blecki, J.; Parrot, M.; Wronowski, R.

2012-04-01

192

The Skylab barium plasma injection experiments. I - Convection observations  

NASA Technical Reports Server (NTRS)

Two barium-plasma injection experiments were carried out during magnetically active periods in conjunction with the Skylab 3 mission. The high-explosive shaped charges were launched near dawn on November 27 and December 4, 1973, UT. In both cases, the AE index was near 400 gammas, and extensive pulsating auroras covered the sky. The first experiment, Skylab Alpha, occurred in the waning phase of a 1000-gamma substorm, and the second, Skylab Beta, occurred in the expansive phase of an 800-gamma substorm. In both, the convection was generally magnetically eastward, with 100-km-level electric fields near 40 mV/m. However, in the Alpha experiment the observed orientation of the barium flux tube fit theoretical field lines having no parallel current, but the Beta flux-tube orientation indicated a substantial upward parallel sheet current.

Wescott, E. M.; Stenbaek-Nielsen, H. C.; Davis, T. N.; Peek, H. M.

1976-01-01

193

Excitation and diagnosis of cascading Langmuir waves in ionospheric plasmas at Gakona, Alaska  

NASA Astrophysics Data System (ADS)

Ionospheric plasma heating experiments were conducted at Gakona, Alaska to investigate cascading spectra of Langmuir wave turbulence, excited by parametric instabilities diagnosed by Modular UHF Ionospheric Radar (MUIR). This work is aimed at testing the recent theory of Kuo and Lee (2005 J. Geophys. Res. 110 A01309) that addresses how the cascade of Langmuir waves can distribute spatially via the resonant and non-resonant decay processes. The non-resonant cascade proceeds at the location where parametric decay instability (PDI) or oscillating two-stream instability (OTSI) is excited and severely hampered by the frequency mismatch effect. By contrast, the resonant cascade, which takes place at lower matching heights, has to overcome the propagation loss of the Langmuir pump waves in each cascade step. Our experimental results have corroborated these predictions about the generation of cascading Langmuir waves by the HAARP heater.

Burton, L. M.; Cohen, J. A.; Pradipta, R.; Labno, A.; Lee, M. C.; Batishchev, O.; Rokusek, D. L.; Kuo, S. P.; Watkins, B. J.; Oyama, S.

2008-12-01

194

Equatorial ionospheric vertical plasma drift model over the Brazilian region  

Microsoft Academic Search

Comparison between equatorial inospheric F region vertical plasma drift from satellite measurements (Fejer et al., 1995), for the Brazilian longitude sector, and the drifts derived from ionosonde measurements around sunset shows significant differences on the prereversal peak behavior during solstices of high solar activity periods. Using ionosonde measurements around sunset and satellite measurements at other local times, we constructed an

I. S. Batista; R. T. de Medeiros; M. A. Abdu; J. R. de Souza; G. J. Bailey; E. R. de Paula

1996-01-01

195

Studies of HF-induced Strong Plasma Turbulence at the HAARP Ionospheric Observatory  

NASA Astrophysics Data System (ADS)

High power HF transmitters may induce a number of plasma instabilities in the interaction region of overdense ionospheric plasma. We report results from our recent experiments using over one gigawatt of HF power (ERP) to generate and study strong Langmuir turbulence (SLT) and particle acceleration at the HAARP Observatory, Gakona, Alaska. Among the effects observed and studied in UHF radar backscatter are: SLT spectra including the outshifted plasma line or free-mode, appearance of a short timescale ponderomotive overshoot effect, collapse, cascade and co-existing spectra, control of artificial field-aligned irregularities (AFAI), the aspect angle dependence of the plasma line spectra, and suprathermal electrons. Mapping the intensity of SLT versus pointing angle, we have discovered a number of regions of strong interaction displaced from the primary HF interaction region. Stimulated electromagnetic emission (SEE) measurements complement radar measurements. Experimental results are compared to previous high latitude experiments and predictions from recent modeling efforts.

Sheerin, J. P.; Adham, N.; Roe, R. G. E.; Keith, M. R.; Watkins, B. J.; Bristow, W. A.; Bernhardt, P. A.; Selcher, C. A.

2010-11-01

196

The Ionospheric Convection and Birkeland Current Response to an Impulse in the Interplanetary Magnetic Field BY Component  

NASA Astrophysics Data System (ADS)

When the interplanetary magnetic field (IMF) is dawnward or duskward, magnetic merging between the IMF and the geomagnetic field occurs near the cusp on the dayside flanks of the magnetosphere. During these intervals, sunward flow channels on open field lines with velocities in excess of 2 km/s are generated in the polar ionosphere, which can deposit large amounts of energy into the cusp-region thermosphere. In this study, we analyze an interval on 5 April 2010 where there was a strong dawnward impulse in the IMF, followed by a gradual decay in IMF magnitude at constant clock angle. Data from ground based radars and the DMSP spacecraft were assimilated to investigate the global convection pattern during this interval, and data from the Active Magnetospheric and Planetary Electrodynamics Response Experiment (AMPERE) were used to investigate the associated Field-Aligned Current (FAC) system. Additionally, data from AMPERE and the Sondrestrom Incoherent Scatter Radar were used to investigate the time response of the flow channel and its associated FAC pair. We find that there is a delay of approximately 1.25 hours between the arrival of the dawnward IMF impulse at the magnetopause and the speed of the flow channel and strength of the FACs flanking it. In addition to correlation between the dawnward component of the IMF and the flanking FAC strength, we also find that there is inverse correlation between the flanking FAC strength and both the SYM-H index and Solar Wind Alfvenic Mach Number. No statistically significant correlation is found between the flanking FAC strength and solar wind dynamic pressure.

Wilder, F. D.; Eriksson, S.; Korth, H.; Baker, J. B.; Hairston, M. R.; Heinselman, C. J.; Anderson, B. J.

2013-05-01

197

Slow ions in plasma wind tunnels. [satellite-ionosphere interaction  

NASA Technical Reports Server (NTRS)

One of the limitations of simulation experiments for the study of interaction between a satellite and its space environment is the background of slow ions in the plasma chamber. These ions appear to be created by charge exchange between the beam ions and residual neutral gas and may affect measurements of the current and potential in the wake. Results are presented for a plasma wind tunnel experiment to study the effect of slow ions on both the ion and electron current distribution and the electron temperature in the wake of a body in a streaming plasma. It is shown that the effect of slow ions for beam ion density not exceeding 3 is not significant for measurements of ion current variations in the wake zone. This is not the case when studies are aimed at the quantitative examination of electron current and temperature variations in the near wake zone. In these instances, the measurements of electron properties in the wake should be done at very low system pressures or over a range of system pressures in order to ascertain the influence of slow ions.

Oran, W. A.; Stone, N. H.; Samir, U.

1976-01-01

198

On the equatorial transport of Saturn's ionosphere as driven by a dust-ring current system  

NASA Technical Reports Server (NTRS)

The diurnal modulation of the dust ring current of Saturn's D-ring causes field-aligned Birkeland currents to flow near the dawn and dusk terminators and close across the midlatitude ionosphere. One consequence of this current system is the establishment of a global convection pattern in the equatorial outer ionosphere. Outward motion of the dayside ionospheric plasma as well as the corresponding absorption effect of the inner ring system might be one physical cause of the depletion of the ionospheric content of Saturn.

Ip, W.-H.; Mendis, D. A.

1983-01-01

199

Ionospheric Observation Activities Report.  

National Technical Information Service (NTIS)

Space plasma physics research, particularly high latitude ionospheric phenomena and phenomena related to the interaction of the ionosphere with the magnetosphere and with the neutral atmosphere is summarized. Experiments using sounding rockets, the Viking...

1984-01-01

200

Ionospheric nf sub H resonances: Frequency shifts versus plasma conditions  

NASA Technical Reports Server (NTRS)

The Alouette 2 resonances observed near the harmonics of the electron cyclotron frequency f sub H reveal frequency shifts (relative to the n(f sub H) values derived from model field calculations) which can be interpreted in terms of plasma wave dispersion effects. These effects are observed on the 2(f sub H) resonance when it is near the resonance observed close to the upper hybrid frequency f sub T. The observations suggest that an oblique echo model may be required to give a proper interpretation of the 2(f sub H) resonance. Cyclotron damping can be ignored only when the angle between the propagation vector and the direction perpendicular to the earth's magnetic field B is less than a few degrees for the 2(f sub H) wave, and less than a few tenths of a degree for the n(f sub H) waves with n 2. The negative offset of the absolute value of B inferred from the plasma resonance observations is consistent with expectations based on recent OGO 3 and OGO 5 rubidium magnetometer observations at higher altitudes in the equatorial regions.

Benson, R. F.

1971-01-01

201

Storm-induced plasma stream in the low-latitude to midlatitude ionosphere  

NASA Astrophysics Data System (ADS)

Geomagnetic disturbances from 7 to 12 November 2004 were quite intense, and the maximum excursion of Dst reached -374 nT. Unusual ionospheric phenomena have been observed around the world that have been associated with successive magnetic storms during this period. The ionospheric total electron content (TEC) was increased at the longitudes of Japan within a short time after sunset on 8 November, from 20 TEC units at 1830 JST to 97 TEC units at 2015 JST (JST = UT + 9 h), where 1 TEC unit = 11016 el/m2. The enhanced TEC was significant over Hokkaido (43N), and the center of the enhanced region was well within the plasmasphere as an L value of approximately 1.5. The drift velocity of the plasma in the density-enhanced region measured by the Defense Meteorological Satellite Program (DMSP) satellite was westward with a peak value of 250 m/s in the Earth's frame, demonstrating a positive correlation between density and drift velocity. A similar TEC event was observed after sunset on 10 November: TEC was enhanced, from 15 TEC units at 1830 JST to 45 TEC units at 2030 JST. During the second event, the ionosphere was highly structured and the rate of the TEC index (ROTI) increased. The two-dimensional map of a ROTI-enhanced region exhibited the west to northwest transportation of plasma in which density irregularities were entrained. A physical mechanism is proposed to explain these disturbances, i.e., storm-induced plasma stream, which is different from a phenomenon called storm-enhanced density at midlatitudes.

Maruyama, Takashi; Ma, Guanyi; Tsugawa, Takuya

2013-09-01

202

UCB current detector experiment on Swedish auroral payloads. [ionospheric current and plasma flow measurements  

NASA Technical Reports Server (NTRS)

A split Langmuir probe has been developed to make in situ measurements of ionospheric current density and plasma bulk flow. The probe consists of two conducting elements that are separated by a thin insulator that shield each other over a 2 pi solid angle, and that are simultaneously swept from negative to positive with respect to the plasma. By measuring the current to each plate and the difference current between plates, information is obtained on the plasma's current density, bulk flow, electron temperature, and density. The instrument was successfully flown twice on sounding rockets into auroral events. Measurement data indicate that the total auroral current configuration is composed of several alternating east and west electrojets associated with several alternating up and down Birkeland currents.

Mozer, F.

1974-01-01

203

A global analysis of the electrodynamic interactions between a space station and the ionospheric plasma environment  

NASA Technical Reports Server (NTRS)

A general analysis of the electrodynamic interactions between a space station with two biased platforms and the ionospheric plasma is presented. This problem can be separated into a far-field problem, concerned with the electromagnetic interference surrounding the entire space station, and a near-field problem, concentrated on the interactions in the vicinity of the biased platforms. The far-field problem is solved by application of plasma fluid theory. The space station will generate a radiation field composed mainly of the Alfven waves. This far-field radiation depends on the details of the near-field current collection. Computer particle simulations were performed in the near-field of the biased platform to study the plasma flow field, the sheath structure and the current collection. Approximate analytical solutions to the near-field are also obtained. The far-field and near-field solutions are coupled to provide a global description of the electrodynamic interactions.

Wang, J.; Hastings, D. E.

1991-01-01

204

Near-simultaneous plasma structuring in the midlatitude and equatorial ionosphere during magnetic superstorms  

NASA Astrophysics Data System (ADS)

Near simultaneous formation of ionospheric plasma density structures at middle and equatorial latitudes during the intense magnetic storms of October 29-31, 2003, July 15, 2000, and March 30-31, 2001 is investigated. The evolution of these structures is explored by measuring amplitude scintillation of satellite signals at 250 MHz, determining zonal irregularity drifts and by detecting equatorial plasma bubbles with DMSP satellites. During abrupt decreases of SYM-H (1-minute resolution Dst) that signify the penetration of high latitude electric fields, an impulsive onset of scintillation occurs at Hanscom AFB (HAFB), a sub-auroral location, as well as in the equatorial region where the early evening period corresponds to the time of scintillation onset at midlatitudes. The onset of equatorial scintillation is delayed from that at midlatitudes by about 20 minutes which can be accounted for by considering instantaneous electric field penetration and plasma instability growth time of equatorial irregularities.

Basu, S.; Basu, Su.; Groves, K. M.; MacKenzie, E.; Keskinen, M. J.; Rich, F. J.

2005-04-01

205

Suprathermal plasma analyzer for the measurement of low-energy electron distribution in the ionosphere  

NASA Astrophysics Data System (ADS)

It is commonly believed that an energy transfer from thermal to suprathermal electrons (ionosphere. However, observation of electron energy spectrum in this energy range is quite limited because of technical difficulties of measurement. We have developed an instrument to measure electron energy distribution from thermal to suprathermal energy continuously with high-energy resolution of about 0.15 eV. The measurement principle is based on the combination of a retarding potential analyzer with a channel electron multiplier (CEM) and the Druyvesteyn method, which derives energy distribution from the current-voltage characteristics. The capability of detecting plasma space potential enables absolute calibration of electron energy. The instrument with a small vacuum pump, which is required for the CEM to work in low-vacuum region, was first successfully tested by a sounding rocket S-310-37 in the ionospheric E region. The instrument is expected to provide new opportunities to measure energy distribution of thermal and non-thermal electrons in low-density plasma, where a Langmuir probe cannot measure electron temperature because of low plasma density.

Shimoyama, M.; Oyama, K.-I.; Abe, T.; Yau, A. W.

2011-07-01

206

Suprathermal plasma analyzer for the measurement of low-energy electron distribution in the ionosphere.  

PubMed

It is commonly believed that an energy transfer from thermal to suprathermal electrons (ionosphere. However, observation of electron energy spectrum in this energy range is quite limited because of technical difficulties of measurement. We have developed an instrument to measure electron energy distribution from thermal to suprathermal energy continuously with high-energy resolution of about 0.15 eV. The measurement principle is based on the combination of a retarding potential analyzer with a channel electron multiplier (CEM) and the Druyvesteyn method, which derives energy distribution from the current-voltage characteristics. The capability of detecting plasma space potential enables absolute calibration of electron energy. The instrument with a small vacuum pump, which is required for the CEM to work in low-vacuum region, was first successfully tested by a sounding rocket S-310-37 in the ionospheric E region. The instrument is expected to provide new opportunities to measure energy distribution of thermal and non-thermal electrons in low-density plasma, where a Langmuir probe cannot measure electron temperature because of low plasma density. PMID:21806205

Shimoyama, M; Oyama, K-I; Abe, T; Yau, A W

2011-07-01

207

Monitoring ionospheric plasmas in space weather context via DSLP observations on board Proba-2  

NASA Astrophysics Data System (ADS)

The experiment Dual Segmented Langmuir Probe (DSLP) on board Proba-2 spacecraft (ESA) provides a long-term continual survey of basic plasma properties measured in situ in the dawn and dusk sectors of the upper terrestrial ionosphere. DSLP observations are acquired by two identical segmented spherical Langmuir probes representing a novel approach to a well developed plasma diagnostic technique. Starting its nominal operations in May 2010 almost four years of regular observations are currently being available providing a substantial data set for monitoring observed ionospheric disturbances and irregularities in view of potential space weather drivers. Here we present initial DSLP data scientific applications including seasonal or immediate variations of derived plasma properties in comparison with possible effects of sudden solar events or long term trends in the overall solar activity. In addition we present an on-line data archive build on complete DSLP data set where all raw measurements are routinely being processed into calibrated higher level data products derived from the PDS and CDF standards and made available throughout web interface.

Travnicek, Pavel; Stverak, Stepan; Hercik, David; Pavelka, Roman

2014-05-01

208

Zonal drift velocities of the ionospheric plasma bubbles over brazilian region using oi630nm airglow digital images  

NASA Astrophysics Data System (ADS)

The zonal drift velocities of the ionospheric plasma bubbles over the Brazilian region are analyzed in this study that is based on OI630nm airglow digital images. These digital images were obtained by an all-sky imager system between October 1998 and August 2000, at Cachoeira Paulista (22.5S, 45W), a low latitude region. In this period, 138 nights of OI 630 nm airglow experiments were carried out of which 30 nights detected the ionospheric plasma bubbles. These 30 nights correspond to magnetically quiet days (?K_P<24+) and were grouped according approximately to their season. KEY WORDS: Imager System, Ionospheric Plasma Bubbles, Zonal drift velocities, OI630nm.

Arruda, D. C. S.; Sobral, J. H. A.; Abdu, M. A.; Castilho, V. M.; Takahashi, H.

209

Large-scale imaging of high-latitude convection with Super Dual Auroral Radar Network HF radar observations  

Microsoft Academic Search

The HF radars of the Super Dual Auroral Radar Network (SuperDARN) provide measurements of the E x B drift of ionospheric plasma over extended regions of the high- latitude ionosphere. With the recent augmentation of the northern hemisphere component to six radars, a sizable fraction of the entire convection zone (approximately one-third) can be imaged nearly instantaneously (-2 min). To

J. M. Ruohoniemi; K. B. Baker

1998-01-01

210

Ionospheric plasma bubble zonal drift over the tropical region: a study using OI 630 nm emission all-sky images  

NASA Astrophysics Data System (ADS)

With the advances in all-sky imaging technology for nightglow emission studies, the F-region OI 630 nm emission has become an important tool for ionospheric/ thermospheric coupling studies. At tropical regions, the all-sky imaging observations of the OI 630 nm emission show quasi north-south aligned intensity depletion bands, which are the optical signatures of large scale Fregion plasma- irregularities (plasma bubbles). By observing the motion of the intensity depleted bands it is possible to infer the ionospheric plasma bubble zonal velocity. All-sky images from So Joo do Cariri (7.4S, 36.5W), and Cachoeira Paulista (22.7S, 45W), Brazil, between December 1999 and February 2000 (summer in the southern hemisphere) are analysed in order to investigate the nocturnal and latitudinal behavior of the ionospheric plasma bubble zonal drifts. The data set included 16 nights from So Joo do Cariri (equatorial region) and 24 nights from Cachoeira Paulista (low latitude). An interesting characteristic observed is significant latitudinal variations in the ionospheric plasma bubble zonal drifts in the tropical region between 20:00-22:00 local time. The averaged result of the latitudinal analyses has revealed two peaks in the ionospheric plasma bubble zonal drifts. One peak is located near the magnetic equator (~150 m/s), occurring between 21:00 and 22:00 LT. Another peak in the ionospheric plasma bubble zonal drifts is located at approximately 18 S latitude (~140 m/s), occurring between 20:00 and 22:00 LT. The valley in the latitudinal variations is located approximately near 10S (~120 m/s) and this reduction in the ionospheric plasma bubble zonal drift is attributed to a reduction in the zonal neutral wind. A comparison of the observed latitudinal variations in the ionospheric plasma bubble zonal drifts with the zonal winds obtained from the HWM-90 model reveals a good agreement. We find that the increase in electron density within the Equatorial Anomaly was sufficient to account for the observed reduction in the zonal winds. The observed development and motion of the nighttime F-region irregularities in the tropical region are presented and discuss ed in this work.

Pimenta, A.; Bittencourt, J.; Fagundes, P.; Sahai, Y.; Buriti, R.; Takahashi, H.; Taylor, M.

211

Self-Consistent Magnetosphere-Ionosphere Coupling and Associated Plasma Energization Processes  

NASA Technical Reports Server (NTRS)

Magnetosphere-Ionosphere (MI) coupling and associated with this process electron and ion energization processes have interested scientists for decades and, in spite of experimental and theoretical research efforts, are still ones of the least well known dynamic processes in space plasma physics. The reason for this is that the numerous physical processes associated with MI coupling occur over multiple spatial lengths and temporal scales. One typical example of MI coupling is large scale ring current (RC) electrodynamic coupling that includes calculation of the magnetospheric electric field that is consistent with the ring current (RC) distribution. A general scheme for numerical simulation of such large-scale magnetosphere-ionosphere coupling processes has been presented earlier in many works. The mathematical formulation of these models are based on "modified frozen-in flux theorem" for an ensemble of adiabatically drifting particles in the magnetosphere. By tracking the flow of particles through the inner magnetosphere, the bounce-averaged phase space density of the hot ions and electrons can be reconstructed and the magnetospheric electric field can be calculated such that it is consistent with the particle distribution in the magnetosphere. The new a self-consistent ring current model has been developed that couples electron and ion magnetospheric dynamics with calculation of electric field. Two new features were taken into account in addition to the RC ions, we solve an electron kinetic equation in our model, self-consistently including these results in the solution. Second, using different analytical relationships, we calculate the height integrated ionospheric conductances as the function of precipitated high energy magnetospheric electrons and ions as produced by our model. This results in fundamental changes to the electric potential pattern in the inner magnetosphere, with a smaller Alfven boundary than previous potential formulations would predict but one consistent with recent satellite observations. This leads to deeper penetration of the plasma sheet ions and electrons into the inner magnetosphere and more effective ring current ions and electron energization.

Khazanov, G. V.; Six, N. Frank (Technical Monitor)

2002-01-01

212

Ionospheric plasma escape by high-altitude electric fields: Magnetic moment ''pumping''  

SciTech Connect

Measurements of electric fields and the composition of upward flowing ionospheric ions by the Viking spacecraft have provided further insight into the mass dependent plasma escape process taking place in the upper ionosphere. The Viking results of the temperature and mass-composition of individual ion beams suggest that upward flowing ion beams can be generated by a magnetic moment ''pumping'' mechanism caused by low-frequency transverse electric field fluctuations, in addition to a field aligned ''quasi-electrostatic'' acceleration process. Magnetic moment ''pumping'' within transverse electric field gradients can be described as a conversion of electric drift velocity to cyclotron velocity by the inertial drift in time-dependent electric field. This gives an equal cyclotron velocity gain for all plasma species, irrespective of mass. Oxygen ions thus gain 16 times as much transverse energy as protons. In addition to a transverse energy gain above the escape energy, a field-aligned quasi-electrostatic acceleration is considered primarily responsible for the collimated upward flow of ions. The field-aligned acceleration adds a constant parallel energy to escaping ionospheric ions. Thus, ion beams at high altitudes can be explained by a bimodal acceleration from both a transverse (equal velocity) and a parallel (equal energy) acceleration process. The Viking observations also show that the thermal energy of ion beams, and the ion beam width are mass dependent. The average O/sup +//H/sup +/ ''temperature ratio has been found to be 4.0 from the Viking observations. This is less than the factor of 16 anticipated from a coherent transverse electric field acceleration but greater than the factor of 1 (or even less than 1) expected from a turbulent acceleration process. /copyright/ American Geophysical Union 1989

Lundin, R.; Hultqvist, B.

1989-06-01

213

Ionospheric irregularities  

Microsoft Academic Search

Extensive experimental and theoretical research has been performed in the last decade to study ionospheric irregularities. These studies have shown that plasma instabilities play a major role in the generation of the irregularities. In this work we describe in detail the recent experimental studies of the E and F region irregularities and also the extensive work on plasma instability theories

B.G. Fejer; M. C. Kelley

1980-01-01

214

Convections  

NSDL National Science Digital Library

This experiment demonstrates convection, the fundamental reason we have weather. Explore what happens when cold ice hits a tub of warm water. This activity guide includes a step-by-step instructional video.

Center, Saint L.

2013-01-30

215

Plasma bubble registration at altitudes of the topside ionosphere: Numerical evaluations  

NASA Astrophysics Data System (ADS)

The possibility of registering a plasma bubble at altitudes of the topside ionosphere based on its minor species He+ were studied. The characteristic times of the main aeronomic and electrodynamic processes, in which a bubble and its ion component He+ are involved, were calculated and compared. The recombination processes of helium ions in a bubble, the vertical transfer of a plasma bubble as a whole, and the diffusion transfer of the plasma bubble minor constituent (He+) were considered. The characteristic times of ambipolar and transverse (Bohm) diffusion were calculated when the diffusion transfer was estimated. The effect of the photoionization processes on plasma bubble dissipation were estimated based on the He+ bubble ion component. It was shown that the bubble filling characteristic time with an average He+ depletion to the He+ ambient density is 24 h. It was concluded that such a prolonged bubble lifetime makes it possible to register a plasma bubble reliably over approximately two days. However, it has been noted that only a residual plasma bubble structure, i.e., its trace visible in He+ ions, will apparently be registered during most prolonged observations.

Sidorova, L. N.; Filippov, S. V.

2014-05-01

216

Auroral ionospheric signatures of the plasma sheet boundary layer in the evening sector  

NASA Technical Reports Server (NTRS)

We report on particles and fields observed during Defense Meteorological Satellite Program (DMSP) F9 and DE 2 crossings of the polar cap/auroral oval boundary in the evening magnetic local time (MLT) sector. Season-dependent, latitudinally narrow regions of rapid, eastward plasma flows were encountered by DMSP near the poleward boundary of auroral electron precipitation. Ten DE 2 orbits exhibiting electric field spikes that drive these plasma flows were chosen for detailed analysis. The boundary region is characterized by pairs of oppositely-directed, field-aligned current sheets. The more poleward of the two current sheets is directed into the ionosphere. Within this downward current sheet, precipitating electrons either had average energies of a few hundred eV or were below polar rain flux levels. Near the transition to upward currents, DE 2 generally detected intense fluxes of accelerated electrons and weak fluxes of ions, both with average energies between 5 and 12 keV. In two instances, precipitating ions with energies greater than 5 keV spanned both current sheets. Comparisons with satellite measurements at higher altitudes suggest that the particles and fields originated in the magnetotail inside the distant reconnection region and propagated to Earth through the plasma sheet boundary layer. Auroral electrons are accelerated by parallel electric fields produced by the different pitch angle distributions of protons and electrons in this layer interacting with the near-Earth magnetic mirror. Electric field spikes driving rapid plasma flows along the poleward boundaries of intense, keV electron precipitation represent ionospheric responses to the field-aligned currents and conductivity gradients. The generation of field-aligned currents in the boundary layer may be understood qualitatively as resulting from the different rates of earthward drift for electrons and protons in the magnetotail's current sheet.

Burke, W. J.; Machuzak, J. S.; Maynard, N. C.; Basinska, E. M.; Erickson, G. M.; Hoffman, R. A.; Slavin, J. A.; Hanson, W. B.

1994-01-01

217

Magnetospheric convection in the nondipolar magnetic field of Uranus  

NASA Technical Reports Server (NTRS)

A method for determining the magnetospheric convection electric field, using simple analytic approximations under the assumption of uniform ionospheric conductivity, is described and applied to Uranus. Magnetic field models including quadrupole and octupole moments are used to determine the shape of the polar caps and the mapping of the electric field and parallel currents between ionosphere and magnetosphere. The model predictions are compared with plasma data taken by Voyager 2 in the inner Uranian magnetosphere.

Selesnick, Richard S.

1988-01-01

218

Ionospheric plasma bubble zonal drifts over the tropical region: a study using OI 630nm emission all-sky images  

NASA Astrophysics Data System (ADS)

In tropical regions, all-sky imaging observations of the OI 630nm emission show quasi north-south aligned intensity depletion bands, which are the optical signatures of large-scale F-region plasma irregularities (plasma bubbles). By observing the west-east motion of the intensity depleted bands it is possible to infer the ionospheric plasma bubble zonal velocity. All-sky images from Sa~o Joa~o do Cariri (7.4S, 36.5W) and from Cachoeira Paulista (22.7S, 45.0W), Brazil, between December 1999 and February 2000 (summer in the southern hemisphere), are analyzed in order to investigate the nocturnal and latitudinal behavior of the ionospheric plasma bubble zonal drift velocities. The data set included 12 nights from Sa~o Joa~o do Cariri (equatorial region) and 12 nights from Cachoeira Paulista (low latitude). An interesting characteristic observed is the significant latitudinal variations in the ionospheric plasma bubble zonal drifts in the tropical region, between 20:00-22:00 local time. The average result of the latitudinal analyses has revealed two peaks in the ionospheric plasma bubble zonal drift velocities. One peak is located near the magnetic equator (~160m/s), occurring between 21:00 and 22:00 LT, and another peak is located at approximately 19S latitude (~150m/s), occurring between 20:00 and 22:00 LT. The valley in the latitudinal variations is located approximately near 10S(~120m/s) and this reduction in the ionospheric plasma bubble zonal drifts is attributed to a reduction in the zonal neutral wind velocities. A comparison of the observed latitudinal variations in the ionospheric plasma bubble zonal drifts with the zonal winds obtained from the HWM-90 model reveals good agreement. We find that the increase in electron density within the Equatorial Ionospheric Anomaly was sufficient to account for the observed reduction in the zonal wind velocities. The observed development and motion of the nighttime F-region irregularities in the tropical region are presented and discussed in this paper.

Pimenta, A. A.; Bittencourt, J. A.; Fagundes, P. R.; Sahai, Y.; Buriti, R. A.; Takahashi, H.; Taylor, M. J.

2003-07-01

219

New ISTP Solar Max: A Multi-Spacecraft Study of the Flow of Ionospheric Plasma  

NASA Technical Reports Server (NTRS)

The unique instrumentation on the Polar satellite combined with the simultaneous measurement of different parts of the magnetosphere with multiple satellites make possible the study of magnetospheric processes in a special way. In particular, the study of the ionospheric supply of plasma to the magnetosphere can by accomplished to give important results on the plasmas which drive the dynamics of the magnetosphere. This study concentrated on the period of September to December, 2001 in which the Polar orbit had precessed to the point that the line of apsides was near the equatorial plane. This unique orbital configuration enabled the TIDE instrument to measure outflowing ions across the polar cap and then transit the magnetotail lobes and observe the dramatic change in plasma characteristics as the satellite entered the plasma sheet. Contact was made with investigators on the Cluster and Geotail satellite missions and corresponding time frames were studied in the data. There were two approximate conjunctions between Polar and Geotail and data were compared to look for features which might be related. The higher energy concentration of the Geotail instrument made direct comparisons with TIDE difficult, and the Cluster measurements did not surface any cases that corresponded closely in space and time. There were, however, many interesting aspects of the Polar orbits which permitted the observation of the changing ionospheric outflowing plasma characteristics. As in earlier measurements, the ionospheric plasma could be seen flowing up the magnetic field lines out of the northern and southern polar caps. Its energy suggested a polar wind origin energized by the centrifugal acceleration of flow through the polar cusp. The roughly 10eV ions then moved out into the lobes of the magnetotail where they could be seen flowing toward the plasma sheet in both the northern and southern magnetotail lobes. There was also a double field-aligned region of warm ions observed just outside the plasmasphere, stretching toward the auroral zone and inner plasma sheet boundary. Upon entering the plasma sheet, the plasma energy jumped from 10 s of eV to greater than 1 keV. The single field aligned flows transitioned to highly variable spatially choppy energized ion distributions with a variety of pitch angle configurations. This pattern was quite repeatable in all of the Polar orbits that were examined and are compatible with the source of ions being the polar wind which is then energized to 10 s of eV by the centrifugal acceleration. These modestly energized polar wind ions are then carried to the magnetotail where they are substantially energized by the curvature drift-induced movement across the cross-tail potential of the magnetotail. This latter drift energizes the ions to the energies typically found in the plasma sheet. Subsequent drift and energization can cause the ions to become part of the ring current. The results of this study were presented at the Spring AGU meeting in 2002 and the GEM meeting in June 2003. They are the foundation for a paper that has been submitted by Matthew Huddleston to the Journal of Geophysical Research in December 2003. This work was part of the thesis that Matthew completed in finishing his Ph.D. in Physics at Vanderbilt University.

Chappell, Charles R.

2003-01-01

220

Theory and Observations of Plasma Waves Excited Space Shuttle OMS Burns in the Ionosphere  

NASA Astrophysics Data System (ADS)

Measurements of artificial plasma turbulence were obtained during two Shuttle Exhaust Ionospheric Turbulence Experiments (SEITE) conducted during the flights of the Space Shuttle (STS-127 and STS-129). Based on computer modeling at the NRL PPD and Laboratory for Computational Physics & Fluid Dynamics (LCP), two dedicated burns of the Space Shuttle Orbital Maneuver Subsystem (OMS) engines were scheduled to produce 200 to 240 kg exhaust clouds that passed over the Air Force Research Laboratory (AFRL) Communications, Navigation, and Outage Forecast System (C/NOFS) satellite. This operation required the coordination by the DoD Space Test Program (STP), the NASA Flight Dynamics Officer (FDO), the C/NOFS payload operations, and the C/NOFS instrument principal investigators. The first SEITE mission used exhaust from a 12 Second OMS burn to deposit 1 Giga-Joules of energy into the upper atmosphere at a range of 230 km from C/NOFS. The burn was timed so C/NOFS could fly though the center of the exhaust cloud at a range of 87 km above the orbit of the Space Shuttle. The first SEITE experiment is important because is provided plume detection by ionospheric plasma and electric field probes for direct sampling of irregularities that can scatter radar signals. Three types of waves were detected by C/NOFS during and after the first SEITE burn. With the ignition and termination of the pair of OMS engines, whistler mode signals were recorded at C/NOFS. Six seconds after ignition, a large amplitude electromagnetic pulse reached the satellite. This has been identified as a fast magnetosonic wave propagating across magnetic field lines to reach the electric field (VEFI) sensors on the satellite. Thirty seconds after the burn, the exhaust cloud reach C/NOFS and engulfed the satellite providing very strong electric field turbulence along with enhancements in electron and ion densities. Kinetic modeling has been used to track the electric field turbulence to an unstable velocity distribution produced after the supersonic exhaust molecules charge exchanged with ambient oxygen ions. Based on the success of the first SEITE mission, a second dedicated burn of the OMS engine was scheduled to intercept the C/NOFS satellite, this time at an initial range of 430 km. The trajectory of this exhaust cloud was not centered on the satellite so the turbulent edge was sampled by the C/NOFS instruments. The electromagnetic pulse and the in situ plasma turbulence was recorded during the second SEITE experiment. A comparison of the data from the two OMS burns shows that a wide range of plasma waves are consistently produced with rocket engines are fired in the ionosphere.

Bernhardt, P. A.; Pfaff, R. F.; Schuck, P. W.; Hunton, D. E.; Hairston, M. R.

2010-12-01

221

Decrease of auroral intensity associated with reversal of plasma convection in response to an interplanetary shock as observed over Zhongshan station in Antarctica  

NASA Astrophysics Data System (ADS)

We examined temporal variations of a dayside aurora and corresponding ionospheric plasma convection observed by an all-sky camera (ASC) and the Super Dual Auroral Radar Network (SuperDARN) over Zhongshan (ZHS), located at -74.5 in magnetic latitude (MLAT) in Antarctica, during a geomagnetic sudden commencement (SC) event that occurred on 27 May 2001. Simultaneous ASC observations at South Pole (SP, -74.3 MLAT) were also analyzed. During the SC time, ZHS and SP were located in the postnoon (1610 MLT) and prenoon (1100 MLT) sectors, respectively. Before the SC onset (1458UT), the ASC at ZHS observed an auroral arc with moderate intensity in the poleward direction of the field of view (FOV), and the SuperDARN radar detected sunward ionospheric plasma flow over ZHS. Just after the SC onset, the auroral intensity over ZHS decreased rapidly and the direction of the plasma flow was reversed to antisunward. Decrease of auroral intensity and reversal of the associated plasma convection in response to a sudden increase of the solar wind dynamic pressure at the early stage of a SC event has never been reported before. We suggest that these observational results were generated by a downward field-aligned current (FAC) and are consistent with a physical model of SC. The model predicts the appearance of a pair of FACs flowing downward (upward) in the postnoon (prenoon) sector at the very beginning of the SC, which is also supported by our observations. Consistence of the detailed observations with the model will be discussed in the paper, and we argue that here we present the first optical observational evidence supporting the validity of the model.

Liu, J. J.; Hu, H. Q.; Han, D. S.; Araki, T.; Hu, Z. J.; Zhang, Q. H.; Yang, H. G.; Sato, N.; Yukimatu, A. S.; Ebihara, Y.

2011-03-01

222

The thresholds of ionospheric plasma instabilities pumped by high-frequency radio waves at EISCAT  

NASA Astrophysics Data System (ADS)

We test the existing theories regarding the thresholds for the parametric decay instability (PDI), the oscillating two-steam instability (OTSI), and the thermal parametric instability (TPI) using the European Incoherent Scatter (EISCAT) facility's ionospheric heater. In these processes, the pump wave can couple to various electrostatic waves in the F layer ionosphere, which can be observed using the EISCAT UHF radar (PDI and OTSI) or by HF radar (TPI). On 19 October 2012, the heater power was stepped from 0.5 MW to 100 MW effective radiated power in seven steps using a 1 min on, 1 min off cycle. We use an electric field model, taking into account D region absorption, to compare theory with our observations. In all three cases, we find good agreement. In addition, the growth of striations formed during the TPI causes anomalous absorption of the heater wave, which we observe as decreased UHF ion line and plasma line backscatter power. We show evidence that heating for a prolonged period of time reduces the UHF ion line intensity throughout the experiment.

Bryers, C. J.; Kosch, M. J.; Senior, A.; Rietveld, M. T.; Yeoman, T. K.

2013-11-01

223

Extreme longitudinal variability of plasma structuring in the equatorial ionosphere on a magnetically quiet equinoctial day  

NASA Astrophysics Data System (ADS)

We investigate the extreme longitudinal variability of equatorial scintillation under quiet magnetic conditions during 22-23 March 2002. Scintillation Network Decision Aid (SCINDA) observations show intense activity in the South American-Atlantic sector during local evening hours, whereas an absence of scintillation is seen in the far east Asian sector. Ground- and space-based measurements from SCINDA, the Global Ultraviolet Imager (GUVI), TOPEX, and a chain of GPS receivers are used in combination with the Utah State University Global Assimilation of Ionospheric Measurements (USU-GAIM) model to explore the relationship between the large-scale ionization distribution and small-scale irregularities at low latitudes in both the scintillating and nonscintillating longitude sectors. Our analysis shows that there are significant differences in the evolution of the ionization distributions during the evening hours, which are likely the result of differences in the daytime and postsunset vertical plasma drift in the two sectors. This study demonstrates the importance of USU-GAIM as a new tool for investigating longitudinal as well as day-to-day variability that is observed in the large-scale distribution of the ionosphere and how this relates to the occurrence of scintillation.

McDonald, Sarah E.; Basu, Sunanda; Basu, Santimay; Groves, Keith M.; Valladares, Cesar E.; Scherliess, Ludger; Thompson, Donald C.; Schunk, Robert W.; Sojka, Jan J.; Zhu, Lie

2006-12-01

224

Enhanced nonlinear interaction of powerful electromagnetic waves with ionospheric plasma near the second electron gyroharmonic  

SciTech Connect

Plasma experiments in which a powerful electromagnetic pump wave is transmitted into the ionosphere from the ground give access to a rich range of phenomena, including gyroharmonic effects when the pump frequency is near an harmonic of the ionospheric electron gyrofrequency. For pump frequencies close to the second gyroharmonic, experiments show a strong enhancement, as observed in radar scatter from pump-induced geomagnetic field-aligned density striations and optical emissions. This is in contrast to the case at the third harmonic and higher at which most of the effects are instead suppressed. We show theoretically that electrostatic oscillations can be localized in density inhomogeneities associated with small scale striations. The localized field is a mixture of the electron Bernstein and upper hybrid modes when the pump frequency is near the second gyroharmonic. The coupling of the modes is enabled by a symmetry feature of the linear electron Bernstein and upper hybrid dispersion properties that occur only near the second gyroharmonic. Electron acceleration inside the density inhomogeneities by localized azimuthal electrostatic oscillations is more efficient near the second gyroharmonic than at higher frequencies, consistent with the observed enhancements.

Istomin, Ya. N. [P. N. Lebedev Physical Institute, Leninsky Prospect 53, 119991 Moscow (Russian Federation)] [P. N. Lebedev Physical Institute, Leninsky Prospect 53, 119991 Moscow (Russian Federation); Leyser, T. B. [Swedish Institute of Space Physics, Box 537, SE-751 21 Uppsala (Sweden)] [Swedish Institute of Space Physics, Box 537, SE-751 21 Uppsala (Sweden)

2013-05-15

225

Energetic O+ and H+ Ions in the Plasma Sheet: Implications for the Transport of Ionospheric Ions  

NASA Technical Reports Server (NTRS)

The present study statistically examines the characteristics of energetic ions in the plasma sheet using the Geotail/Energetic Particle and Ion Composition data. An emphasis is placed on the O+ ions, and the characteristics of the H+ ions are used as references. The following is a summary of the results. (1) The average O+ energy is lower during solar maximum and higher during solar minimum. A similar tendency is also found for the average H+ energy, but only for geomagnetically active times; (2) The O+ -to -H+ ratios of number and energy densities are several times higher during solar maximum than during solar minimum; (3) The average H+ and O+ energies and the O+ -to -H+ ratios of number and energy densities all increase with geomagnetic activity. The differences among different solar phases not only persist but also increase with increasing geomagnetic activity; (4) Whereas the average H+ energy increases toward Earth, the average O+ energy decreases toward Earth. The average energy increases toward dusk for both the H+ and O+ ions; (5) The O+ -to -H+ ratios of number and energy densities increase toward Earth during all solar phases, but most clearly during solar maximum. These results suggest that the solar illumination enhances the ionospheric outflow more effectively with increasing geomagnetic activity and that a significant portion of the O+ ions is transported directly from the ionosphere to the near ]Earth region rather than through the distant tail.

Ohtani, S.; Nose, M.; Christon, S. P.; Lui, A. T.

2011-01-01

226

Plasma wave turbulence due to the wake of an ionospheric sounding rocket  

NASA Astrophysics Data System (ADS)

In the ionosphere, a rarefied plasma region called "plasma wake" is formed behind a sounding rocket. Based on a one-dimensional Vlasov-Maxwell simulation, it was suggested that electron distribution functions in the plasma wake behind spacecraft are different from the Maxwell-Boltzmann distribution function [Singh et al., 1987]. Thus, plasma waves are expected to be generated in the wake of a sounding rocket. Some studies reported plasma waves around the wake of artificial satellites [Keller et al., 1997] and solar system bodies such as Moon [Nakagawa et al., 2003]. Yamamoto (2000) is the first study that focused on plasma waves induced by sounding rockets on the basis of the results of several rocket experiments. He compared the observed wave frequency with the electron number density in the wake and indicated plasma waves could be generated inside the rocket wake. In order to investigate the properties of the waves in more detail (e.g. spin-phase dependence, generation mechanism, etc.), we are now analyzing the data of electron number density and electric fields of plasma waves in mid-latitude ionosphere by an impedance probe and a plasma wave receiver, which were installed on the sounding rocket S-520-26. In the analysis, we have found plasma waves in a frequency range of 1.3-2.4 MHz (hereinafter called Group-A) as well as those in a frequency range between 0.02 MHz to about 0.6 fce (Group-B), and those in a frequency range from about 0.5 fce to 0.9 fce (Group-C), where fce is the electron cyclotron frequency deduced from the IGRF model. The Group-A emissions are similar to the waves observed in previous studies [Yamamoto, 2000]. Comparison with the data of the impedance probe has suggested the Group-A waves are short-wavelength electrostatic waves including upper-hybrid resonance (UHR) mode waves and electrostatic electron cyclotron harmonic (ESCH) waves. On the other hand, the Group-B and Group-C waves are whistler mode waves. Besides, the analysis with the rocket attitude data has clarified that the Group-A emissions are enhanced when the antenna element pointed in the directions of 320-20 and 150-250 in spin-phase angle while that the Group-B waves have been observed clearly when the antenna element pointed to 50-110 and 200-300, and that the Group-C waves are found in 90-160. The spin-phase dependences suggest inhomogeneous distributions of the occurrence regions of plasma instabilities with respect to the wake structure, or anisotropy of the wave propagation in plasma. In order to discuss the generation mechanism of the observed plasma waves, we have performed numerical calculations of linear growth rate of plasma waves by assuming anisotropic velocity distribution functions with an electron beam or temperature anisotropy. As a result, we could confirm positive linear growth rates in wave numbers and frequency ranges of UHR mode waves, ESCH waves, and electrostatic whistler mode waves. Actual distribution functions around the rocket wake, however, might not be simple as we assumed. Therefore, further studies with using Vlasov-Maxwell simulation will be needed.

Endo, K.; Kumamoto, A.; Ono, T.; Katoh, Y.

2013-12-01

227

Relationship between the spatial structure of the polar ionosphere and the precipitation of auroral protons  

NASA Astrophysics Data System (ADS)

The effect of the precipitation of auroral protons (APs) on the formation of the spatial structure of the high-latitude ionosphere is analyzed on the basis of a model of convecting ionospheric plasma. Calculations that account for both electron and proton precipitations are compared with those that account only for electron precipitations. It is shown that APs lead to significant changes in the formation of the spatial distribution of electron temperature and density below 250 km.

Krivilev, V. N.; Mingalev, V. S.; Buianova, T. V.; Mingaleva, G. I.

1985-12-01

228

Modeling polar cap F-region patches using time varying convection  

NASA Technical Reports Server (NTRS)

Creation of polar cap F-region patches are simulated for the first time using two independent physical models of the high latitude ionosphere. The patch formation is achieved by temporally varying the magnetospheric electric field (ionospheric convection) input to the models. The imposed convection variations are comparable to changes in the convection that result from changes in the B(y) IMF component for southward IMF. Solar maximum-winter simulations show that simple changes in the convection pattern lead to significant changes in the polar cap plasma structuring. Specifically, in winter, as enhanced dayside plasma convects into the polar cap to form the classic tongue-of-ionization the convection changes produce density structures that are indistinguishable from the observed patches.

Sojka, J. J.; Bowline, M. D.; Schunk, R. W.; Decker, D. T.; Valladares, C. E.; Sheehan, R.; Anderson, D. N.; Heelis, R. A.

1993-01-01

229

Convection-driven delivery of plasma sheet material to the inner magnetosphere.  

NASA Astrophysics Data System (ADS)

We present data from the MENA instrument onboard the IMAGE satellite taken during a period of enhanced convection on 26 June 2001. During the interval, MENA observes energetic neutral atoms (ENAs) in the magnetotail and an Earthwards-propagating enhancement in their flux, at the same time as the convection strength increases (as measured by the Kp and MBI indices). Data from the magnetospheric plasma analyser (MPA) instrument onboard satellites in geosynchronous orbit indicate that enhanced ion and electron fluxes at plasma sheet energies (~1-45 keV) are detected at the same time as enhanced ENA flux are observed at the satellite location. We interpret the results as a convection-driven delivery of plasma sheet material, the ENA signature of which we observe with IMAGE/MENA. We use the rate of the propagation of the ENA enhancement to infer the speed of the plasma sheet delivery to the inner magnetosphere.

Denton, M. H.; Thomsen, M. F.; Lavraud, B.; Skoug, R. M.; Henderson, M. G.; Funsten, H. O.; Jahn, J.; Pollock, C. J.; Weygand, J.

2005-12-01

230

Causal link of the wave-4 structures in plasma density and vertical plasma drift in the low-latitude ionosphere  

NASA Astrophysics Data System (ADS)

We investigate the annual and local time variations of the wave-4 structures in the plasma density and vertical drift in the low-latitude F region by analyzing the measurements from the first Republic of China satellite (ROCSAT-1) and conducting simulations with the Global Ionosphere and Plasmasphere (GIP) model. The GIP model uses apex magnetic coordinates with International Geomagnetic Reference Field (IGRF) for magnetic field, neutral wind from HWM-07, and thermospheric parameters from the NRLMSISE-00 model. In order to understand how the vertical drifts relate to the longitudinal structure of the topside ionosphere, we apply the equatorial vertical drifts observed from ROCSAT-1 to drive the GIP model. The model well reproduces the longitudinal structure in electron density, and the magnitudes of electron density are comparable with ROCSAT-1 measurement at 600 km. The ROCSAT-1 observations of the vertical drift and plasma density show maximum amplitudes of their wave-4 components in July-September and minimum amplitudes in December-February. An eastward shift of the wave-4 components with increasing local time is observed in both the density and the vertical drift. The GIP model density showed similar annual and local time variations of the wave-4 component. Since the model uses the observed equatorial vertical E B drift as an input, the results indicate the vertical drifts are essential in the formation and evolution of the longitudinal wave-4 density structure. The amplitude of the eastward propagating diurnal tide (DE3) at 110 km shows similar annual and local time variations as the F region parameters, supporting the link between the DE3 tide, vertical E B drift, and F region plasma density on a global scale.

Fang, T.-W.; Kil, H.; Millward, G.; Richmond, A. D.; Liu, J.-Y.; Oh, S.-J.

2009-10-01

231

Modeling Storm-Time Ionospheric Dynamics with RCM-SAMI3: Progress and Challenges  

NASA Astrophysics Data System (ADS)

Modeling large-scale dynamics of the terrestrial ionosphere during geomagnetic disturbances requires a first-principles approach as the physics of the cold ionospheric plasma and the hot magnetospheric particle populations are strongly interwoven, primarily through electric fields and particle precipitation. To address this challenge, we previously created the RCM-SAMI3 coupled model of the ionosphere and the inner magnetosphere. The Rice Convection Model (RCM) is used to simulate the magnetospheric particle distribution function and associated field-aligned currents and electric fields, and to estimate auroral electron precipitation into the ionosphere; SAMI3 evolves the three-dimensional ionospheric plasma distribution and computes the conductance tensor for the RCM. Magnetospheric processes taking place outside the modeling region are represented in the RCM by time-dependent boundary conditions on plasma fluxes, electric fields, and also magnetic field guided by observations. In this paper, we present the most recent developments of the coupled model, namely, extending the ionospheric modeling region all the way from the geomagnetic equator to the poles, including the effects of auroral precipitation on ionospheric electrodynamics, and accounting for longitudinal variations in the terrestrial intrinsic magnetic field. We use numerical simulations of the coupled inner magnetosphere-ionosphere system during active periods (both event simulations and idealized cases) with RCM-SAMI3. Our main goal is to determine capabilities and shortcomings of the model by analyzing storm-time response of the ionospheric electron densities and ground-based magnetic field perturbations.

Sazykin, S.; Huba, J. D.; Spiro, R. W.; Wolf, R. A.; Toffoletto, F.

2012-12-01

232

Ionospheric electron-content measurements during the second space-plasma negative-ion experiment (SPINEX-2)  

NASA Technical Reports Server (NTRS)

The second space-plasma negative-ion experiment (SPINEX-2), a chemical-release active experiment to investigate negative-ion effects in the ionospheric F region, is described by Mendillo et al. (1982). This paper describes the electron-content measurements in somewhat more detail than would be appropriate there. The circumstances of the experiment, particularly the use of a vehicle with a very high spin rate, presented some unusual challenges during interpretation of the electron-content data. These are described. The resulting profiles show clearly that the chemical release caused a very significant 'hole' in the ionosphere. Under certain fairly realistic assumptions, the actual number of free electrons removed from the region of the peak of the ionospheric F layer is estimated to be about 4 x 10 to the 25th. The same assumptions lead to a simple radial distribution of the depleted region about the rocket trajectory in the neighborhood of the release.

Fulford, J. A.; Macdougall, J. W.; Forsyth, P. A.; Mendillo, M.; Bernhardt, P. A.

1987-01-01

233

Plasma wave turbulence due to the wake of an ionospheric sounding rocket  

NASA Astrophysics Data System (ADS)

A sounding rocket moving in the ionosphere generally interacts with surrounding plasma. Because this affects in-situ measurement data, it is very important to understand the physics of the interaction between the ionosphere and a moving vehicle. For instance, a rarefied plasma region called "plasma wake" is formed behind a sounding rocket. Several previous studies based on rocket experiments have suggested that upper-hybrid resonance (UHR) mode waves are excited in a rocket wake. A wake turbulence model has been proposed as a possible explanation for the waves where two stream instability occurs in the wake center owing to the incident plasma flow from the both sides of the wake edges. Thus, plasma waves are generated and have been observed by the wave receivers onboard the rockets. Plasma waves in a wake have been reported not only around sounding rockets but also around solar system bodies such as Moon. As for a rocket wake, the generation mechanism of the waves has been investigated by using wave receivers with time resolutions worse than 500 msec. They are, however, not enough for detailed investigations about the plasma wave generations and propagations. To discuss the properties of the plasma waves caused around a rocket wake, we have analyzed the data of electric fields and electron number density in the S-520-26 sounding rocket experiment, which was performed at Uchinoura, Japan, on January 12, 2012. The rocket reached an altitude of 298 km, and the data has been obtained four or five times in one spin period of the rocket by using a newly developed digital plasma wave monitor and an impedance probe, whose time resolutions are about 260 msec. In the observation, enhancement of plasma waves has been observed in two frequency ranges from 0.02 to 0.9 MHz (LF range), and from 1.3 to 2.4 MHz (MF range). The frequency range of the MF emissions is around the UHR frequency, which is determined based on the IGRF magnetic field model and electron number density measured by the impedance probe. However, the lowest frequency of the emissions is almost the same as the Z-mode cutoff frequency, particularly in higher altitude range than 280 km. The wave spectra are similar to those observed by the previous studies. The frequency range of the LF emissions is found to be that of whistler mode branch. Based on the rocket attitude, it is suggested that the electric fields of the LF and MF emissions are nearly perpendicular and parallel to the wake structure, respectively. If we can assume that the observed waves are generated around the rocket, they have to be electrostatic waves because the wave length should be shorter than the size of the disturbed region. We have performed calculations of plasma dispersion relations with assuming some anisotropic velocity distribution functions of electrons expected around the wake, and deduced the linear growth rates, group velocities, etc. We compare the observational results with calculated ones, and discuss the generation mechanisms of the plasma waves.

Endo, Ken; Kumamoto, Atsushi; Oya, Hiroshi; Ono, Takayuki; Katoh, Yuto

2013-04-01

234

The flow of plasma in the solar terrestrial environment  

NASA Technical Reports Server (NTRS)

The scientific goals of the program are outlined, and some of the papers submitted for publication within the last six months are briefly highlighted. Some of the topics covered include ionosphere-magnetosphere coupling, polar cap arcs, polar wind, convection vortices, ionosphere-plasmasphere coupling, and the validity of macroscopic plasma flow models.

Schunk, R. W.; Birmingham, T. J.

1992-01-01

235

Convection of Plasmaspheric Plasma into the Outer Magnetosphere and Boundary Layer Region: Initial Results  

NASA Technical Reports Server (NTRS)

We present initial results on the modeling of the circulation of plasmaspheric- origin plasma into the outer magnetosphere and low-latitude boundary layer (LLBL), using a dynamic global core plasma model (DGCPM). The DGCPM includes the influences of spatially and temporally varying convection and refilling processes to calculate the equatorial core plasma density distribution throughout the magnetosphere. We have developed an initial description of the electric and magnetic field structures in the outer magnetosphere region. The purpose of this paper is to examine both the losses of plasmaspheric-origin plasma into the magnetopause boundary layer and the convection of this plasma that remains trapped on closed magnetic field lines. For the LLBL electric and magnetic structures we have adopted here, the plasmaspheric plasma reaching the outer magnetosphere is diverted anti-sunward primarily along the dusk flank. These plasmas reach X = -15 R(sub E) in the LLBL approximately 3.2 hours after the initial enhancement of convection and continues to populate the LLBL for 12 hours as the convection electric field diminishes.

Ober, Daniel M.; Horwitz, J. L.; Gallagher, D. L.

1998-01-01

236

Effect of tail plasma sheet conditions on the penetration of the convection electric field in the inner magnetosphere: RCM simulations with self-consistent magnetic field  

NASA Astrophysics Data System (ADS)

Transport of plasma sheet particles into the inner magnetosphere is strongly affected by the penetration of the convection electric field, which is the result of the large-scale magnetosphere ionosphere electromagnetic coupling. This transport, on the other hand, results in plasma heating and magnetic field stretching, which become very significant in the inner plasma sheet (inside 20 RE). We have previously run simulations with the Rice Convection Model (RCM), using the Tsyganenko 96 magnetic field model, to investigate how the earthward penetration of electric field depends on plasma sheet conditions. Outer proton and electron sources at r ~20 RE, are based on 11 years of Geotail data, and realistically represent the mixture of cold and hot plasma sheet population as a function of MLT and interplanetary conditions. We found that shielding of the inner magnetosphere electric field is more efficient for a colder and denser plasma sheet, which is found following northward IMF, than for the hotter and more tenuous plasma sheet found following southward IMF. Our simulation results so far indicate further earthward penetration of plasma sheet particles in response to enhanced convection if the preceding IMF is southward, which leads to weaker electric field shielding. Recently we have integrated the RCM with a magnetic field solver to obtain magnetic fields that are in force balance with given plasma pressures in the equatorial plane. We expect the self-consistent magnetic field to have a pronounced dawn dusk asymmetry due to the asymmetric inner magnetospheric pressure. This should affect the radial distance and MLT of plasma sheet penetration into the inner magnetosphere. We are currently using this force-balanced and self-consistent model with our realistic boundary conditions to evaluate the dependence of the shielding timescale on pre-existing plasma sheet number density and temperature and to more quantitatively determine the correlation between the plasma sheet conditions and spatial distribution of the penetrating particles. Our results are potentially crucial to understanding the contribution of plasma sheet penetration to the development of the storm-time ring current.

Gkioulidou, M.; Wang, C.; Lyons, L. R.; Wolf, R.

2009-12-01

237

Cold streams of ionospheric oxygen in the plasma sheet during the CDAW-6 event of March 22, 1979  

NASA Technical Reports Server (NTRS)

During magnetospheric substorm events, the plasma and ion composition experiments in the ISEE-1 and 2 satellites detected cold ionospheric O+ streams, moving tailwards in the near Earth magnetotail. Flow is parallel to the magnetic field lines, with drift velocity in agreement with the electric field topology obtained by mapping the model ionospheric field along the magnetic field lines. Fluctuations of the flow velocity of the streams can be related to magnetotail movements. Oscillations of the flow direction and speed with periods ranging from 5 to 10 min that suggest the presence of waves are observed. The streams are observed at all distances between 15 and 6 Re from the Earth. When averaged over 360 deg, the streams show up as a low energy peak, superimposed on the distribution of isotropic plasma sheet ions. This double-peak structure of the energy spectrum seems typical of the disturbed plasma sheet.

Orsini, S.; Amata, E.; Candidi, M.; Balsiger, H.; Stokholm, M.; Huang, C. Y.; Lennartsson, W.; Lindqvist, P. A.

1983-01-01

238

Cold streams of ionospheric oxygen in the plasma sheet during the CDAW 6 event of March 22, 1979  

NASA Technical Reports Server (NTRS)

During magnetospheric substorm events, the plasma and ion composition experiments in the ISEE-1 and 2 satellites detected cold ionospheric O+ streams, moving tailwards in the near earth magnetotail. Flow is parallel to the magnetic field lines, with drift velocity in agreement with the electric field topology obtained by mapping the model ionospheric field along the magnetic field lines. Fluctuations of the flow velocity of the streams can be related to magnetotail movements. Oscillations of the flow direction and speed with periods ranging from 5 to 10 min that suggest the presence of waves are observed. The streams are observed at all distances between 15 and 6 Re from the earth. When averaged over 360 deg, the streams show up as a low energy peak, superimposed on the distribution of isotropic plasma sheet ions. This double-peak structure of the energy spectrum seems typical of the disturbed plasma sheet.

Orsini, S.; Amata, E.; Candidi, M.; Balsiger, H.; Stokholm, M.; Huang, C.; Lennartsson, W.; Lindqvist, P.-A.

1985-01-01

239

Large-Scale 2D and 3D Simulations of Plasma Turbulence in the Lower Ionosphere  

NASA Astrophysics Data System (ADS)

For five decades, radars and rockets have observed plasma turbulence in the weakly ionized, highly collisional plasma of the E-region ionosphere. This turbulence is caused by the Farley-Buneman, gradient drift, and thermal instabilities. In the high-latitude electrojet, during strong magnetospheric perturbations (storms and sub-storms), radars have observed anomalous electron heating (AEH) caused by turbulent electric fields. We will present results of recent 2D and 3D fully kinetic, particle-in-cell, simulations that reproduce many of the observational characteristics of radar signals. As predicted by theory, the 3D simulations show the development of waves having a turbulent electric field with a small component parallel to the geomagnetic field. This field component is mainly responsible for the majority of AEH. For the first time, we can now quantify this effect using accurate simulations. These simulations provide information useful in accurately modeling plasma turbulence and demonstrate the significant progress we have made simulating physical processes in E-region electrojets.

Dimant, Y. S.; Oppenheim, M. M.

2008-11-01

240

Ionospheric Modeling: Coupling to the Inner and Outer Magnetosphere  

NASA Astrophysics Data System (ADS)

The Naval Research Laboratory has developed a comprehensive 3D model of the earth's ionosphere: SAMI3 (Sami3 is Also a Model of the Ionosphere). SAMI3 models the plasma and chemical evolution of seven ion species (H+, He+, N+, O+, N2+, NO2+ and O2+). The complete ion temperature equation is solved for three ion species (H+, He+ and O+) as well as the electron temperature equation. Ion inertia is included in the ion momentum equation for motion along the geomagnetic field. In addition, the E B drift motion of the plasma is included for both zonal electric fields (vertical drifts) and meridional electric fields (zonal drifts). The neutral species are specified using the empirical NRLMSISE00 model that is based on MSIS86 and the HWM model. SAMI3 uses a nonorthogonal, nonuniform, fixed grid. The code is fully parallelized using the Message Passing Interface (MPI) method. The code has been recently upgraded to provide global coverage of the ionosphere ( 89 magnetic latitude) within the context of a single model. The code has been self-consistently electrodynamically coupled to the Rice Convection Model (RCM) and partially coupled to the LFM magnetosphere model. We report results of ionospheric dynamics associated with electrodynamic forcing by the inner and outer magnetosphere, e.g., the convection of plasma across the polar cap, the impact of storm-time penetration electric fields on the low- to mid-latitude ionosphere. Research supported by ONR.

Huba, J. D.

2007-05-01

241

Ionospheric Modeling: Coupling to the Inner and Outer Magnetosphere  

NASA Astrophysics Data System (ADS)

The Naval Research Laboratory has developed a comprehensive 3D model of the earth's ionosphere: SAMI3 (Sami3 is Another a Model of the Ionosphere). SAMI3 models the plasma and chemical evolution of seven ion species (H+, He+, N+, O+, N2+, NO2+ and O2+). The complete ion temperature equation is solved for three ion species (H+, He+ and O+) as well as the electron temperature equation. Ion inertia is included in the ion momentum equation for motion along the geomagnetic field. In addition, the E B drift motion of the plasma is included for both zonal electric fields (vertical drifts) and meridional electric fields (zonal drifts). The neutral species are specified using the empirical NRLMSISE00 model that is based on MSIS86 and the HWM model. SAMI3 uses a nonorthogonal, nonuniform, fixed grid. The code has been recently upgraded to provide global coverage of the ionosphere ( 89 magnetic latitude) within the context of a single model. The code has been self-consistently electrodynamically coupled to the Rice Convection Model (RCM) and to the Lyon/Fedder/Mobarry (LFM) magnetosphere model. We report results of ionospheric dynamics associated with electrodynamic forcing by the inner and outer magnetosphere, e.g., the convection of plasma across the polar cap, the impact of storm-time penetration electric fields on the low- to mid-latitude ionosphere, and sub-auroral polarization streams. Research supported by ONR and NASA.

Huba, J. D.; Slinker, S.; Joyce, G.; Sazykin, S.; Wolf, R.; Spiro, R.

2007-12-01

242

Recent Advances in Mid-latitude Ionosphere/Thermosphere Science  

NASA Astrophysics Data System (ADS)

One of the original reasons for building a National Ionospheric Observatory (now the National Astronomy and Ionospheric Center or NAIC) near Arecibo, Puerto Rico was the location, which is in the best behaved region of the ionosphere. At 30 magnetic latitude and 19 geographic latitude, it is well equatorward of the auroral and sub-auroral zones and poleward of the equatorial anomalies most of the time. The island thus has some of the best weather and space weather on the planet. However, similar to an occasional hurricane striking the island, the ionosphere overhead has occasional ionospheric and thermospheric disturbances. Some of these space weather phenomena, e.g., mesoscale TIDs and unstable sporadic E layers, are endemic to the region and, prior to the advent of airglow imagers and GPS networks, were difficult to visualize using radiowave data alone. Other weather events are caused by infringement on this zone from processes in more active weather regions. For example, neutral waves launched from the auroral oval (large scale TIDs) pass through the region; electric fields penetrate from the solar wind and create both plasma uplifts, causing positive ionospheric storms, and stormenhanced density plumes, coursing through the region. From the south, convective equatorial ionospheric storms create plasma bubbles that can reach mid-latitudes. Examples of data obtained during these phenomena, and possibly more, will be presented and discussed in light of our present understanding.

Kelley, Michael

243

Convective Velocity Reversal Caused by Turbulence Transition in Tokamak Plasma  

NASA Astrophysics Data System (ADS)

Particle transport has been studied in the Tore Supra tokamak by using modulated ion cyclotron resonance heating to generate perturbations of density and temperature. For the first time, a reversal of the particle convective velocity and a strong increase in the turbulent particle flux have been clearly observed. When the mixed critical gradient ?c=R/LT+4(R /Ln)=22 is exceeded, the particle flux increases sharply and the convective velocity reverses from inward to outward. These observations are in agreement with quasilinear, gyrokinetic calculations. The critical gradient corresponds to a transition from an instability driven by the ion temperature gradient to the onset of another instability caused by trapped electrons.

Zhong, W. L.; Zou, X. L.; Bourdelle, C.; Song, S. D.; Artaud, J. F.; Aniel, T.; Duan, X. R.

2013-12-01

244

Yearly variations of global plasma densities in the topside ionosphere at middle and low latitudes  

NASA Astrophysics Data System (ADS)

In this paper, the 10-year (1996-2005) measurements of total ion density (Ni) from the Defense Meteorological Satellite Program (DMSP) spacecraft at 0930 and 2130 LT have been analyzed to investigate the yearly variations of global plasma densities in the topside ionosphere at magnetic latitudes from 60S to 60N. Results indicate that there are strong yearly variations in the DMSP Ni at 840 km. The annual components of longitude-averaged Ni dominate at most latitudes with maxima around the June solstices in the Northern Hemisphere and the December solstice in the Southern Hemisphere. In contrast, seasonal anomaly (maxima Ni around the December solstice) exists in the northern equatorial zone. Moreover, the differences in Ni at the two solstices are not symmetrical about the magnetic equator, being generally higher in the Southern Hemisphere than in the Northern Hemisphere. Conjugate-averaged Ni is substantially greater at the December solstice than at the June solstice. This annual asymmetry is modulated by solar activity effect and has latitudinal and longitudinal structures. The longitude effects of the annual asymmetry depend on local time, being stronger in the evening sector than in the morning sector. The solstice differences and annual asymmetry are more marked with increasing solar activity. The annual asymmetry appears not only in the rising phase of the solar cycle but also in the declining phase. Thus the solar condition differences between the two solstices do not account for the Ni asymmetry. The concentration of neutral oxygen [O], provided from the NRLMSIS model, shows a similar pattern of annual and hemispheric asymmetries. Moreover, effects of the HWM model neutral winds are also constituent with the change patterns of Ni. Therefore, considering the principal processes in the topside ionosphere, the changes of [O] and the rates of thermospheric winds should contribute to the annual asymmetry in Ni at 840-km altitude.

Liu, Libo; Zhao, Biqiang; Wan, Weixing; Venkartraman, S.; Zhang, Man-Lian; Yue, X.

2007-07-01

245

Diurnal transport effects on the F-region plasma at Chatanika under quiet and disturbed conditions  

Microsoft Academic Search

High latitude ionospheric model predictions are compared with the diurnal variations of plasma convection velocities and electron densities observed at Chatanika, Alaska, on geomagnetically quiet and disturbed days near equinox. Since the time-dependent variation of the magnetospheric electric field was not known, plasma drift velocities and ion densities are calculated for two different convection-precipitation models, each of which corresponds to

J. Murdin; J. J. Sojka; R. W. Schunk

1984-01-01

246

Model of the high-latitude ionospheric convection pattern during southward interplanetary magnetic field using DE 2 data  

NASA Technical Reports Server (NTRS)

Data from the polar-orbiting satellite DE 2 are used to calculate one-dimensional electrostatic potential distributions across the polar cap region. Using passes that lie within + or - 3 hours MLT of the dawn-dusk line, various parameters of the polar potential distribution (location and magnitude of the maxima and minima, location of the zero potential point, etc.) are analyzed in relation to each other and to the IMF. The resulting dependences are used to derive a two-dimensional model of the distribution of the electrostatic potential in the high-latitude ionosphere during times of southward IMF. This model can be generated using as inputs either the ionospheric potential parameters or, based on the relationships analyzed here, the IMF conditions. The capabilities of the resulting mathematical model are illustrated, and the importance of retaining a flexibility in the model to accommodate individual observations is emphasized.

Hairston, M. R.; Heelis, R. A.

1990-01-01

247

Equivalent circuit simulation of spectra registered with cylindrical dipole antenna in ionospheric electron plasma  

NASA Astrophysics Data System (ADS)

Tubular and wire antennas have been employed since an advent of in situ measurements in space. It is generally accepted that they are well suited to recipe electromagnetic radiation from remote sources as well as divers local plasma emissions. In many cases electron plasma may be resolved into relatively cold and dense main component, characterized by plasma frequency fn and more energetic minor components. Based on dispersion relation of electron cold magnetoplasma or low temperature isotropic plasma one may expect plasma emission within upper hybrid band (max(fc,fn),fu=sqrt(fc*fc+fn*fn)) or slightly above plasma frequency fn, respectively. In dependence on characteristics of minority population, incoherent Cerenkov emission, quasi thermal emission or convective instabilities were invoked. With aid of quasi thermal noise spectroscopy, large sets of core and halo densities and temperatures were derived from spectra registered in solar wind. On the other hand, despite numerous reports on permanent reception of upper hybrid emissions within plasma sphere, there were no convincing reports on parameters of suprathermal population derived from wave data. Frequently, spectral structures assigned to upper hybrid band emissions were broader than calculated band (max(fc,fn), fu), what called for importance of propagation and warm magnetoplasma effects but upper hybrid band falls into broad local minimum in passive mode spectra from the ISS-b satellite and the upper hybrid frequency falls into local minimum in passive mode spectra registered at middle and low latitudes on the Alouette-2 satellite. We show that spectra recorded in plasmas like that inside a plasma sphere may be qualitatively influenced by transfer function of equivalent input circuit. Usually, transfer function is invoked to estimate amplitude corrections on frequencies greater than plasma frequency. In that case, a stray capacitance acts as a voltage divider. In cold m gnetoplasma, antenna is inductive in some banda below upper hybrid frequency. Stray capacitance and antenna inductance, provide possibility for parallel resonance in input circuit. Solely due to dependence of transfer function on equivalent circuit impedances, white noise spectrum on antenna terminals may show up as highly variable banded structure. We show consistency between computed transfer functions and spectra registered in frequency range .1- 10MHz on the ACTIVE, APEX and CORONAS satellites. Identical tubular monopoles were employed as dipole antenna elements, but nominal input resistances ranged from low to high. Characteristic magnetoplasma frequencies were calculated with local plasma frequency derived from impedance measurements, topside sounder data and electron beam induced spectra. If plasma is sufficiently dense, distinct emission in the (fn,fu) band do not show up in passive mode spectra.

Kiraga, A.

248

Computer simulations of finite plasma streams convected across a magnetized vacuum  

SciTech Connect

A two-dimensional electrostatic particle-in-cell code is used to simulate the convection of a finite stream of initially neutral plasma across a uniform magnetic field. The simulations show that the stream loses momentum with distance as a result of two erosion mechanisms that have greater effects for denser plasmas: (1) erosion of the charge layers at the sides of the stream as a result of velocity shear and (2) erosion of the head of the stream as a result of charge separation where ions travel ahead of the electrons. The electron charge layer exhibits a velocity shear that excites the diocotron instability. This instability occurs earlier for denser plasmas but it does not appear when the length of the stream is shorter than four wavelengths. The charge separation at the head of the stream causes the eroded plasma to drift with a sheared velocity. A flutelike instability develops at the head of the plasma stream for sufficiently dense plasmas. The simulations show that the plasma is eroded faster by the head erosion mechanism. Electric field fringe effects cause the plasma head to broaden and the tail of the plasma to narrow. The simulations show that although the plasma configuration is changed a great deal by erosion and fringe effects, the stream is convected across the magnetic field with a constant velocity for sufficiently dense plasmas and with a velocity that approaches the injection for denser plasmas. The simulations also show that the convection velocity for a partially and for a completely eroded plasma is the same.

Galvez, M.; Gisler, G.; Barnes, C. (Los Alamos National Laboratory, Los Alamos, New Mexico 87545 (US))

1989-12-01

249

Magnetosphere-ionosphere connection in 3D-force balanced magnetic field configurations driven by empirical plasma sheet pressure under different geomagnetic conditions  

NASA Astrophysics Data System (ADS)

The magnetic field configuration is crucial to plasma sheet dynamics and M-I coupling. More accurate evaluation of its role requires a configuration in force balance with plasma pressure, which cannot be provided by current empirical models. In this study we established 3D force-balanced magnetic field and investigated the characteristics of field configuration and the magnetosphere-ionosphere connection for different Kp levels and solar wind dynamic pressure (PSW). We first constructed an empirical equatorial plasma pressure model using THEMIS and Geotail data, which was then used as the pressure constraint in the Zaharia [2008] magnetic field solver to obtain 3D magnetic field. The model results show that larger convection electric field during higher Kp drives plasma sheet further earthward, resulting in a substantial pressure increase near the Earth, while magnetosphere compression during higher PSW mainly enhances pressure in the tail plasma sheet. Comparing the magnetic field response to the pressure change due to increasing PSW, the Kp associated pressure increase causes the perpendicular current density (J?) peak and associated Region-2 field-aligned currents (FACs) to move deeper earthward, the magnetic field to decrease further in the near-Earth region, and field lines to stretch more significantly. The model magnetic field and its changes with Kp and PSW are found to agree fairly well with THEMIS and Geotail observations. Furthermore, we estimated the ion isotropic boundary (IB) caused by current sheet scattering for different particle energies. The IB equatorial locations match well with the earthward boundary of isotropic ions observed by THEMIS. We found that the IB is located around the transition region of dipolar to tail-like magnetic field and is close to the inner edge of Region-2 FAC. In the ionosphere, the latitudes of the IB are lower at midnight than at dawn/dusk. The IB latitudes decrease with increasing ion energy as well as with increasing Kp and PSW. These features are consistent with the IB latitudes observed by FAST satellite.

Yue, C.; Wang, C.; Zaharia, S. G.; Donovan, E.; Lyons, L. R.

2013-12-01

250

Ionospheric climatology over Brazil: Zonal plasma velocities from experimental observations and theoretical validations  

NASA Astrophysics Data System (ADS)

We present model calculations and experimental estimations of the zonal drift velocities over Brazil. The latter ones are derived from plasma bubbles signatures on OI6300 ? airglow images A obtained at the conjugate stations Boa Vista - BV (Geogr. 2.8N, 60.7W, dip angle: 22.0N ) and Campo Grande - CG (Geogr. 20.5S, 54.7W, dip angle: 22.32S) during the Conjugate Points Experiment COPEX carried out in Brazil between October and November 2002. Simultaneous velocities as derived by VHF and GPS techniques are also presented and compared. The theoretical ambient plasma zonal velocities were calculated using the formulations by Haerendel et al. (1992) and Eccles (1998) for which the input parameters were based on the available empirical models for zonal electric field (Scherliess and Fejer, 1999), horizontal winds (HWM- 1993), neutral constituents (MSIS-1990) and ionospheric parameters (IRI-2001). The model results show reasonable correlation coefficients between observed and predicted values. However relatively large discrepancies of magnitudes are found between them.

Sobral, Jos

251

Recovery of the Nonmonotonic Altitude Profile of the Plasma Frequency Based on the Ionospheric Oblique Sounding Data  

NASA Astrophysics Data System (ADS)

We propose a method and an algorithm for recovery of the nonmonotonic altitude profile of the plasma frequency using the model data on oblique sounding of a spherically layered isotropic ionosphere in the piecewise-quasiparabolic approximation of the altitude profile of the electron number density. The algorithm has been tested with a fairly complex ionosphere model allowing for the E, F1, and F2 layers and the E-F1 interlayer valley. This method was used to recover the effective altitude profile of the plasma frequency at the midpoints of the Khabarovsk-Tory, Magadan-Tory, Norilsk-Tory, and Usolie-Tory paths from the experimental ionograms having a gap in the single-hop mode traces.

Mikhailov, S. Ya.; Grozov, V. P.

2013-12-01

252

Convective velocity reversal caused by turbulence transition in tokamak plasma.  

PubMed

Particle transport has been studied in the Tore Supra tokamak by using modulated ion cyclotron resonance heating to generate perturbations of density and temperature. For the first time, a reversal of the particle convective velocity and a strong increase in the turbulent particle flux have been clearly observed. When the mixed critical gradient ?c=R/L(T)+4(R/L(n))=22 is exceeded, the particle flux increases sharply and the convective velocity reverses from inward to outward. These observations are in agreement with quasilinear, gyrokinetic calculations. The critical gradient corresponds to a transition from an instability driven by the ion temperature gradient to the onset of another instability caused by trapped electrons. PMID:24483800

Zhong, W L; Zou, X L; Bourdelle, C; Song, S D; Artaud, J F; Aniel, T; Duan, X R

2013-12-27

253

First CLUSTER plasma and magnetic field measurements of flux transfer events in conjunction with their ionospheric flow signatures  

NASA Astrophysics Data System (ADS)

The launch of the Cluster satellite constellation allows, amongst other things, the study of the small-scale spatio-temporal structures in the near-Earth geospace. We present a case study of the high-altitude northern hemispheric cusp by the Cluster-II spacecraft constellation under southward IMF conditions. During this interval Cluster traversed the northern hemispheric dayside region and crossed the magnetopause close to the noon-midnight meridian, and observed both the plasma and magnetic field observations of transient reconnection for a number of hours. Throughout this interval, the ionospheric footprint of the spacecraft maps into the Canadian sector of the Earth's ionosphere into the Saskatoon and Kapuskasing HF radars fields-of-view. This SuperDARN HF radar pair observe the ionospheric flows generated by this transient reconnection during this interval at approximately the same magnetic latitude and local time. The calculated orientation of the reconnected flux tubes is found to be in accordance with the prevailing IMF conditions and the direction of motion of the excited ionospheric flows. We discuss these observations in terms of transient magnetic flux transfer and in terms of the size and location of the active reconnection X-line at the low-latitude magnetopause.

Rae, I. J.; Taylor, M. G.; Lavraud, B.; Cowley, S. W.; Lester, M.; Fenrich, F. R.; Fazakerley, A.; Rème, H.; Sofko, G.; Balogh, A.

2001-12-01

254

Dust-plasma interaction through the magnetosphere-ionosphere coupling in Saturn's inner magnetosphere  

NASA Astrophysics Data System (ADS)

A few hundred eV ion observations by the particle detectors on the Cassini spacecraft showed that the plasma speeds in the Saturn's inner magnetosphere are close to the ideal co-rotation speed around 5 Rs and gradually become 70--80% of the ideal co-rotation speed at 7 Rs. On the other hand, the Cassini observation using the Langmuir Probe (LP) showed that the ion bulk speeds are close to Keplerian in the E ring. The E ring of Saturn consists of small (micron- and nano- meter sized) dust grains. These dusts are negatively charged inside 7 Rs and expected to contribute to the electro dynamics in the plasma disk. Near Enceladus, which is a major source of the E ring dusts, the electron densities are significantly smaller than the ion densities and the ion speeds are near Keplerian. Recently the Cassini Plasma Spectrometer (CAPS) has also observed that the sub-co-rotation speed of the ions slows down to 50-80% of the ideal co-rotation speed. We investigated statistically the ion bulk speeds in the equatorial region of the inner magnetosphere using the LP onboard the Cassini spacecraft from February 2005 to October 2008 (Rev003--087). The LP observations showed that the ion speeds are about 60% of the ideal co-rotation speed at 5 Rs. Beyond 7 Rs the ion speed values are spread toward the ideal co-rotation speed. This may come from that the sub-micron sized negatively charged E ring dust contributes to the plasma dynamics in the plasma disk. We have also calculated the ion speeds using the multi-component MHD equations including dust to investigate the effect of the ion-dust coulomb collision and the mass loading. Our model shows that the ion-dust collision can reduce the ion acceleration by the co-rotation electric field when the ion-dust collision frequency is comparable to the ion cyclotron frequency, and that the ions significantly slow down from co-rotation speed by mass loading. The ion-dust collision and the mass loading generate currents and magnetopheric electric fields in the inner magnetosphere, i.e. a magnetosphere-ionosphere (M-I) coupling. The magnetosperic electric fields based on the M-I coupling reduce the co-rotation electric fields in the inner magnetosphere and can slow the ion speeds. We attribute the ion speeds with about 60% of the ideal co-rotation speed at 5 Rs to coming from the M-I coupling through the dust-plasma interaction in the inner magnetosphere.

Sakai, S.; Watanabe, S.; Morooka, M.; Holmberg, M.; Wahlund, J.

2011-12-01

255

Thermosphere-Ionosphere-Magnetosphere Coupling and Mass Outflow - the Magnetosphere/Ionosphere Perspective (Invited)  

NASA Astrophysics Data System (ADS)

Global scale models of the solar wind-magnetosphere-ionosphere interaction have long established history of including magnetosphere-ionosphere coupling through the electrodynamic coupling. Typically this coupling includes closure of field aligned currents from the magnetosphere in the electrostatic ionosphere with the conductances being modified by particle precipitation processes. Recent advances in simulation technology, namely multi-fluid MHD, allow the scope of MI coupling in simulations to include mass outflows from the thermosphere-ionosphere into the magnetosphere. Multiple approaches to addressing this challenge have been developed. In one approach empirical parametrization of the outflow characteristics, namely velocity and flux, are used to include high intensity sources such as the auroral zone and cusp. Another approach starts by modeling the plasma flow along a single field line and then expands to include multiple field lines convecting over the polar cap. In both approaches the ionospheric outflow has profound effects on the state of the magnetosphere. Generally speaking it improves agreement with Dst observations, alters the cross polar cap potential, and can fundamentally alter the evolution of the modeled magnetospheric state. Initial indications from some of the model efforts show that including this plasma source may also alter the solar wind-magnetosphere interaction. While significant advances on including these effects in global scale models has been accomplished many challenges remain.

Wiltberger, M. J.

2010-12-01

256

Ionospheric plasma escape by high-altitude electric fields: Magnetic moment pumping  

NASA Astrophysics Data System (ADS)

Viking results of the temperature and mass-composition of individual ion beams suggest that upward flowing ion beams can be generated by a magnetic moment pumping mechanism caused by low-frequency transverse electric field fluctuations, in addition to a field aligned quasi-electrostatic acceleration process. Magnetic moment pumping within transverse electric field gradients can be described as a conversion of electric drift velocity to cyclotron velocity by the inertial drift in a time-dependent electric field. This gives an equal cyclotron velocity gain for all plasma species irrespective of mass. Oxygen ions thus gain 16 times higher transverse energy as compared to protons. In addition to a transverse energy gain above the escape energy, a field aligned quasi-electrostatic acceleration is considered primarily responsible for the collimated upward flow of ions. The field aligned acceleration adds a constant parallel energy to escaping ionospheric ions. Thus, ion beams at high altitudes can be explained by a bimodal acceleration from both a transverse (equal velocity) and a parallel (equal energy) acceleration process. The Viking observations also show that the thermal energy of ion beams, and the ion beam width are mass dependent. The average O+/H+ temperature ratio is found to be 4.0 from the Viking observations. This is less than the factor of 16 anticipated from a coherent transverse electric field acceleration but greater than the factor of 1 (or even less than 1) expected from a turbulent acceleration process.

Lundin, Richard; Hultqvist, Bengt

1989-01-01

257

Plasma impedance probe and time-correlated electron saturation current fluctuation diagnostics on the TEPCE cubesat project with application for ionospheric studies*  

NASA Astrophysics Data System (ADS)

A multipoint measurement of ionospheric irregularities is possible using the Tethered Electrodynamic Propulsion Cubesat Experiment (TEPCE). This project is designed to demonstrate propulsion of a tethered satellite due to the Lorentz force acting along the current carrying tether as it crosses the Earth's magnetic field. The two cubesat end masses have plasma diagnostics to characterize the ionospheric conditions during operations. A plasma impedance probe diagnostic is designed to perform an absolute measurement of the electron density, while an electron saturation current diagnostic provides a continuous, although relative, electron density measurement. The electron saturation current measurements from the two end masses will be time correlated, thus allowing the possibility of characterizing fluctuations in the ionospheric electron density at a wave number determined by the 1km tether length and directed mostly perpendicular to the magnetic field. Such measurements could provide valuable insight into F-region instabilities (spread-F) associated with ionospheric storms. *Research supported by the Office of Naval Research

Cothran, C. D.; Amatucci, W. E.; Gatling, G.; Coffey, S.

2011-12-01

258

Evidence of auroral oval TEC enhancement and simultaneous plasma patch break-off events in the Arctic and Antarctic ionosphere during the initial phase of a geomagnetic storm event at equinox, 26 September 2011  

NASA Astrophysics Data System (ADS)

A moderate geomagnetic storm during 26-27 September 2011 instigated ionospheric TEC responses in the high latitude regions, imaged in this dual-hemispheric study using the ionospheric reconstruction tool MIDAS (Multi-Instrument Data Analysis System). This case study showcases the current capabilities of GPS inversion tomography at high latitudes, given the improvement in ground-based receiver distribution in the polar reaches during the last decade. Several interesting features of the high latitude response are highlighted. During the initial phase of the storm (Dst+ increase signature), a ring feature in the TEC was imaged around the position of the Arctic auroral oval that persisted for over an hour. Verification of the auroral oval position and incident particle precipitation was provided by the SSUSI ultra-violet imager and SSJ/4 spectrometer on-board the polar-orbiting DMSP satellites. Shortly after the ring feature dissipated, two consecutive and defined plasma patch break-off events occurred within the North American sector, with anti-sunward convection then circulating the TEC enhancements over Greenland and Iceland. Apparent during the main phase of the storm (Dst- signature), these break-off events were likely triggered by switching periods of the interplanetary magnetic field (IMF) from southward (Bz-) to northward (Bz+) under constant By+ conditions projected at the magnetopause. A coincident patch break-off event was imaged in the Antarctic in the local dawn-noon sector; this simultaneity may be attributed to the more balanced incidence angle of the IMF during equinox upon the Northern and Southern hemispheres. Finally, the ionospheric trough was identified over Scandinavia and Europe as a clear band of depletion between the storm-enhanced dayside electron density and expansion of the auroral zone during the main phase of the storm. This study demonstrates that, in combination with other instruments, GPS tomography has become a useful tool providing a unique view on the physical processes occurring in the Arctic and Antarctic ionospheres.

Kinrade, Joe; Mitchell, Cathryn; Paxton, Larry; Bust, Gary

2013-04-01

259

Convective Dust Clouds Driven by Thermal Creep in a Complex Plasma  

SciTech Connect

Steady-state clouds of microparticles were observed, levitating in a low-frequency glow discharge generated in an elongated vertical glass tube. A heated ring was attached to the tube wall outside, so that the particles, exhibiting a global convective motion, were confined vertically in the region above the location of the heater. It is shown that the particle vortices were induced by the convection of neutral gas, and the mechanism responsible for the gas convection was the thermal creep along the inhomogeneously heated tube walls. The phenomenon of thermal creep, which commonly occurs in rarefied gases under the presence of thermal gradients, should generally play a substantial role in experiments with complex plasmas.

Mitic, S.; Suetterlin, R.; Hoefner, A. V. Ivlev H.; Thoma, M. H.; Zhdanov, S.; Morfill, G. E. [Max-Planck-Institut fuer extraterrestrische Physik, D-85741 Garching (Germany)

2008-12-05

260

Convective dust clouds driven by thermal creep in a complex plasma.  

PubMed

Steady-state clouds of microparticles were observed, levitating in a low-frequency glow discharge generated in an elongated vertical glass tube. A heated ring was attached to the tube wall outside, so that the particles, exhibiting a global convective motion, were confined vertically in the region above the location of the heater. It is shown that the particle vortices were induced by the convection of neutral gas, and the mechanism responsible for the gas convection was the thermal creep along the inhomogeneously heated tube walls. The phenomenon of thermal creep, which commonly occurs in rarefied gases under the presence of thermal gradients, should generally play a substantial role in experiments with complex plasmas. PMID:19113560

Mitic, S; Stterlin, R; Hfner, A V Ivlev H; Thoma, M H; Zhdanov, S; Morfill, G E

2008-12-01

261

Ionospheric Alfvn resonator revisited: Feedback instability  

Microsoft Academic Search

The theory of ionospheric Alfvn resonator (IAR) and IAR feedback instability is reconsidered. Using a simplified model of the topside ionosphere, we have reanalyzed the physical properties of the IAR interaction with magnetospheric convective flow. It is found that in the absence of the convective flow the IAR eigenmodes exhibit a strong damping due to the leakage of the wave

Oleg A. Pokhotelov; V. Khruschev; M. Parrot; S. Senchenkov; V. P. Pavlenko

2001-01-01

262

Ionospheric modification induced by high-power HF transmittersA potential for extended range VHF-UHF communications and plasma physics research  

Microsoft Academic Search

When the ionized upper atmosphere of the earth is illuminated by high-power HF radio waves at appropriate frequencies, the temperature of electrons in the ionosphere can be raised substantially. In addition, radio waves with sufficient energy cause parametric instabilities that generate a spectrum of intense plasma waves. Observations of these phenomena have produced new understanding of plasma processes. One consequence

W. F. Utlaut

1975-01-01

263

Ionospheric plasma flow over large high-voltage space platforms. I - Ion-plasma-time scale interactions of a plate at zero angle of attack. II - The formation and structure of plasma wake  

NASA Technical Reports Server (NTRS)

The paper presents the theory and particle simulation results for the ionospheric plasma flow over a large high-voltage space platform at a zero angle of attack and at a large angle of attack. Emphasis is placed on the structures in the large, high-voltage regime and the transient plasma response on the ion-plasma time scale. Special consideration is given to the transient formation of the space-charge wake and its steady-state structure.

Wang, J.; Hastings, D. E.

1992-01-01

264

The orientation of Titan's dayside ionosphere and its effects on Titan's plasma interaction  

NASA Astrophysics Data System (ADS)

A hybrid particle code has been used to examine how Titan's interaction with Saturn's magnetosphere is effected by the orientation of the dayside ionosphere with respect to the incident magnetospheric flow. The hybrid code self-consistently includes a version of Titan's ionosphere represented by 7 generic ion species, over 40 ion-neutral chemical reactions, ion-neutral collisions and Hall and Pederson conductivities. Emphasis is placed on what effects the orientation angle has on the ion loss rates, ion densities, and the electric and magnetic fields. The results are analyzed and regardless of the orientation angle the ionosphere is found to be within photochemical equilibrium below 1200 km altitude. The ion loss rates and field structures also show little dependence on the orientation of the dayside ionosphere. It is found to first order illumination angle does not have a significant effect on these features of the Titan interaction.

Ledvina, S. A.; Brecht, S. H.; Cravens, T. E.

2012-02-01

265

Parametric Instabilities and Ionospheric Modification  

Microsoft Academic Search

Parametric instabilities, excited in the ionosphere by high-power HF transmitters with a frequency below the maximum ionospheric plasma frequency, produce nonlinear energy absorption and enhanced scattering of electromagnetic radiation, which has been detected by the Arecibo Thomson scatter radar. This paper reviews and extends both the linear and nonlinear saturation theory of parametric instabilities within the ionospheric context. The new

F. W. Perkins; C. Oberman; E. J. Valeo

1974-01-01

266

Spatial distribution of ionospheric plasma and field structures in the high-latitude F region  

Microsoft Academic Search

Ion density and velocity measurements from the Dynamics Explorer 2 (DE 2) spacecraft are used to obtain the average magnetic local time versus invariant latitude distribution of irregularities in the high-latitude F region ionosphere. To study the small-scale structure and its relationship to background conditions in the ionosphere, we have formed a reduced database using 2-s (~16 km) segments of

. Kivan; R. A. Heelis

1998-01-01

267

Radiative divertor plasmas with convection in DIII-D  

SciTech Connect

The radiation of divertor heat flux on DIII-D is shown to greatly exceed the limits imposed by assumptions of energy transport dominated by electron thermal conduction parallel to the magnetic field. Approximately 90% of the power flowing into the divertor is dissipated through low Z radiation and plasma recombination. The dissipation is made possible by an extended region of low electron temperature in the divertor. A one-dimensional analysis of the parallel heat flux finds that the electron temperature profile is incompatible with conduction dominated parallel transport. Plasma flow at up to the ion acoustic speed, produced by upstream ionization, can account for the parallel heat flux. Modeling with the two-dimensional fluid code UEDGE has reproduced many of the observed experimental features.

Leornard, A.W. [General Atomics, San Diego, CA (United States); Porter, G.D.; Wood, R.D. [Lawrence Livermore National Lab., CA (United States)] [and others

1998-01-01

268

The Role of Ionospheric Outflow Preconditioning in Determining Storm Geoeffectiveness  

NASA Astrophysics Data System (ADS)

It is now well accepted that ionospheric outflow plays an important role in the development of the plasma sheet and ring current during geomagnetic storms. Furthermore, even during quiet times, ionospheric plasma populates the magnetospheric lobes, producing a reservoir of hydrogen and oxygen ions. When the Interplanetary Magnetic Field (IMF) turns southward, this reservoir is connected to the plasma sheet and ring current through magnetospheric convection. Hence, the conditions of the ionosphere and magnetospheric lobes leading up to magnetospheric storm onset have important implications for storm development. Despite this, there has been little research on this preconditioning; most global simulations begin just before storm onset, neglecting preconditioning altogether. This work explores the role of preconditioning in determining the geoeffectiveness of storms using a coupled global model system. A model of ionospheric outflow (the Polar Wind Outflow Model, PWOM) is two-way coupled to a global magnetohydrodynamic model (the Block-Adaptive Tree Solar wind Roe-type Upwind Scheme, BATS-R-US), which in turn drives a ring current model (the Ring current Atmosphere interactions Model, RAM). This unique setup is used to simulate an idealized storm. The model is started at many different times, from 1 hour before storm onset to 12 hours before. The effects of storm preconditioning are examined by investigating the total ionospheric plasma content in the lobes just before onset, the total ionospheric contribution in the ring current just after onset, and the effects on Dst, magnetic elevation angle at geosynchronous, and total ring current energy density. This experiment is repeated for different solar activity levels as set by F10.7 flux. Finally, a synthetic double-dip storm is constructed to see how two closely spaced storms affect each other by changing the preconditioning environment. It is found that preconditioning of the magnetospheric lobes via ionospheric outflow greatly influences the geoeffectiveness of magnetospheric storms.

Welling, D. T.; Liemohn, M. W.; Ridley, A. J.

2012-12-01

269

Electric fields and electrostatic potentials in the high latitude ionosphere  

NASA Technical Reports Server (NTRS)

Recent interpretive studies of electric field-driven ionospheric plasma convection data from the AE-C satellite are described, where the instruments employed include an ion drift meter and an ion-retarding potential analyzer. Electrostatic potential curves are derived from ion drift velocity measurements for high-latitude segments of the satellite's orbit. The potential curves are shown to be useful in determining the character of the global electrostatic potential pattern, with emphasis on the separation of convective cells. Results are given for six orbits, with attention to the mid-day auroral region.

Banks, P. M.; Saint Maurice, J.-P.; Heelis, R. A.; Hanson, W. B.

1981-01-01

270

Rice Convection Model simulation of the substorm-associated injection of an observed plasma bubble into the inner magnetosphere: 2. Simulation results  

NASA Astrophysics Data System (ADS)

We present results from a Rice Convection Model simulation of the early expansion phase of a substorm that occurred 22 July 1998. The theoretical basis of the simulation is the idea that the plasma injected into the inner magnetosphere during a substorm primarily consists of a low-content plasma bubble, which is made up of flux tubes with lower values of the entropy parameter PV 5/3 than their neighbors. As discussed in an accompanying paper, to simulate this event, we carefully tailor model inputs to fit Geotail observations of the bubble at X GSM ? -9 R E . We find that both potential and induction electric fields play important roles in transporting and energizing the particles during the event. The potential electric field associated with Birkeland currents that flow along the east and west sides of the bubble (i.e., the substorm current wedge) is characterized by a localized strengthening of the westward auroral ionospheric electric field within the bubble, as well as the production of a region of enhanced westward flow just Equatorward of the diffuse electron aurora. The inner edge of the modeled plasma sheet assumes a dented-in form that is similar in shape to the injection boundary proposed many years ago on observational grounds. Flux tubes that are pushed earthward ahead of the bubble at onset form a sharp pressure peak near local midnight and geosynchronous orbit, and the particles on those tubes contribute significantly to the injection of particles into the inner magnetosphere.

Zhang, J.-C.; Wolf, R. A.; Spiro, R. W.; Erickson, G. M.; Sazykin, S.; Toffoletto, F. R.; Yang, J.

2009-08-01

271

Ionospheric modification by high power radio waves  

Microsoft Academic Search

Investigations using powerful, high frequency (HF) radio waves to temporarily modify the ionosphere are reviewed. Studies of the natural upper atmosphere have been conducted using these controlled, active experiments by observing the ionospheric response to HF induced perturbations. Other basic physics investigations have examined the ionosphere and its properties and behavior as a plasma. Topics examined include ionospheric heating, parametric

L. M. Duncan; W. E. Gordon

1982-01-01

272

Current leakage for low altitude satellites - Modeling applications. [simulation of high voltage solar cell array in ionospheric plasma environment  

NASA Technical Reports Server (NTRS)

To simulate the behavior of a high voltage solar cell array in the ionospheric plasma environment, the large (90 ft x 55 ft diameter) vacuum chamber was used to measure the high-voltage plasma interactions of a 3 ft x 30 ft conductive panel. The chamber was filled with Nitrogen and Argon plasma at electron densities of up to 1,000,000 per cu cm. Measurements of current flow to the plasma were made in three configurations: (a) with one end of the panel grounded, (b) with the whole panel floating while a high bias was applied between the ends of the panel, and (c) with the whole panel at high negative voltage with respect to the chamber walls. The results indicate that a simple model with a constant panel conductivity and plasma resistance can adequately describe the voltage distribution along the panel and the plasma current flow. As expected, when a high potential difference is applied to the panel ends more than 95% of the panel floats negative with respect to the plasma.

Konradi, A.; Mccoy, J. E.; Garriott, O. K.

1979-01-01

273

Numerical simulation of magnetospheric convection including the effect of field-aligned currents and electron precipitation  

Microsoft Academic Search

Early results of a new self-consistent fluid model are presented for steady convection of the plasma from the geomagnetic tail through the Earth's inner magnetosphere below 10 Earth radii (RE), including its coupling with the ionosphere. This model computes the transport of both the ion and electron fluids and constitutes an important improvement of the fluid numerical model of Fontaine

Christophe Peymirat; Dominique Fontaine

1994-01-01

274

A method for determining the drift velocity of plasma depletions in the equatorial ionosphere using far-ultraviolet spacecraft observations  

NASA Astrophysics Data System (ADS)

The Far-Ultraviolet Imager (IMAGE-FUV) on board the NASA IMAGE satellite has been used to observe plasma depletions in the nightside equatorial ionosphere. Observations from periods around spacecraft apogee, during which equatorial regions are visible for several hours, have allowed the velocity of these plasma depletions to be determined. A new method for determining the velocity of these depletions using an image analysis technique, Tracking Of Airglow Depletions (TOAD), has been developed. TOAD allows the objective identification and tracking of depletions. The automation of this process has also allowed for the tracking of a greater number of depletions than previously achieved without requiring any human input, which shows that TOAD is suitable for use with large data sets and for future routine monitoring of the ionosphere from space. Furthermore, this automation allows the drift velocities of each bubble to be determined as a function of magnetic latitude, which will give us the capability of retrieving geophysically important parameters such as the electric field, which are believed to vary rapidly with magnetic latitude.

Park, S. H.; England, S. L.; Immel, T. J.; Frey, H. U.; Mende, S. B.

2007-11-01

275

Plasma convection in the nightside magnetosphere of Saturn determined from energetic ion anisotropies  

NASA Astrophysics Data System (ADS)

The Cassini Ion and Neutral Camera measures intensities of hydrogen and oxygen ions and neutral atoms in the Saturnian magnetosphere and beyond. We use the measured intensity spectrum and anisotropy of energetic hydrogen and oxygen ions to detect, qualify, and quantify plasma convection. We find that the plasma azimuthal convection speed relative to the local rigid corotation speed decreases with radial distance, lagging the planetary rotation rate, and has no significant local time dependences. Plasma in the dusk-midnight quadrant sub-corotates at a large fraction of the rigid corotation speed, with the primary velocity being azimuthal but with a distinct radially outward component. The duskside velocities are similar to those obtained from earlier orbits in the midnight-dawn sector, in contrast to the depressed velocities measured at Jupiter using Energetic Particles Detector measurements on the Galileo spacecraft in the dusk-midnight quadrant. We find significant radial outflow in most of the nightside region. The radial component of the flow decreases with increasing local time in the midnight-dawn sector and reverses as dawn is approached. This and previous results are consistent with a plasma disk undergoing a centrifugally induced expansion as it emerges into the nightside, while maintaining partial rotation with the planet. The magnetodisk expansion continues as plasma rotates across the tail to the dawnside. We do not see evidence in the convection pattern for steady state reconnection in Saturn's magnetotail. The outermost region of the magnetodisk, having undergone expansion upon emerging from the dayside magnetopause confinement, is unlikely to recirculate back into the dayside. We conclude that plasma in the outer magnetodisk [at either planet] rotates from the dayside, expands at the dusk flank, but remains magnetically connected to the respective planet while moving across the tail until it interacts with and is entrained into the dawnside magnetosheath flow. This interaction causes plasma in the outer magnetospheric regions of Jupiter and Saturn to decouple from the planet and exhaust tailward down a dawnside low latitude boundary layer. Magnetospheric plasma will also interact with the dayside magnetosheath plasma, moving across the boundary [enhanced by shear instability] and into the magnetosheath, where it is lost to the magnetosphere with the magnetosheath flow.

Kane, M.; Mitchell, D. G.; Carbary, J. F.; Krimigis, S. M.

2014-02-01

276

Ionospheric plasma turbulence over region of 2006 Iran, 2005 Lake Tanganyika and 2010 New Britain Region earthquakes.  

NASA Astrophysics Data System (ADS)

We report the results of the observation of ELF plasma turbulence registered by DEMETER satellite in the ionosphere over epicenter region of three earthquakes. First one took place on 2nd of February 2005 in Lake Tanganyika Region with magnitude 6.9. Second was earthquake with magnitude 6.1 in Iran on 31st March 2006. The last one took place on 4th of August 2010 in New Britain Region with magnitude 7.0. Obtained results we compare with data gathered during corresponding time and region with quiet seismic conditions. To study this turbulent processes we apply Fourier, wavelet, bispectral analysis and statistical description with use of kurtosis and skewness of the electric field fluctuations. These registrations are correlated with the plasma parameters measured onboard DEMETER satellite and with geomagnetic indices.

Kosciesza, Malgorzata; Blecki, Jan; Wronowski, Roman; Parrot, Michel

2013-04-01

277

Effects of ionospheric conductance in high-latitude phenomena  

NASA Astrophysics Data System (ADS)

In this thesis, the relationship between several high-latitude phenomena and the ionospheric conductance in both hemispheres is studied theoretically and experimentally. Theoretically, the high-latitude electrodynamics is studied by considering currents in the magnetosphere-ionosphere system resulting from the ionospheric sheet current redistribution between the conjugate ionospheres. It is shown that strong flow between the conjugate ionospheres, the interhemispheric currents (IHC), can be set up if the conductance distribution is asymmetric in the conjugate ionospheric regions. Such conditions are typical for solstices owing to the differences in the solar illumination. Analytical and numerical modeling shows that IHCs can appear in the regions of strong conductance gradient, more specifically around the solar terminator line, and that the intensity of the IHCs can be comparable to the intensity of the well known Region 1/Region 2 currents. The effect of IHC excitation on observable magnetic perturbations on the ground is investigated. It is shown that in the vicinity of the solar terminator line, the pattern of magnetic perturbation can be such that an apparent equivalent current vortex can be detected. In addition, strong conductance gradients are shown to affect significantly the quality of the ionospheric plasma flow estimates from the ground-based magnetometer data. Experimentally, the effect of the nightside ionospheric conductance on occurrence of substorms, global storm sudden commencement and radar auroras is investigated. To characterize substorm occurrence, new parameters, the derivatives of the classical AE and AO indices, are introduced. It is shown that the seasonal and diurnal variations of these parameters are controlled by the total nightside ionospheric conductance in the conjugate regions. The substorm onsets preferentially occur at low levels of the total conductance, which is consistent with the idea of the substorm triggering through the magnetosphere-ionosphere feedback instability. It is hypothesized that the total conductance affects the global storm onsets as well. To check this idea, the 33-year sudden storm commencement (SSC) data are considered. The semiannual, annual, semidiurnal, and diurnal variations in the SSC occurrence rate are found to be significant and these components exhibit a strong relationship with the total conductance of the high-latitude ionospheres. Finally, the SuperDARN midnight echo occurrence is shown to correlate, for some radars, with the total conductance minima and presumably with electric field maxima, which is consistent with general expectation that the F-region irregularities occur preferentially during times of enhanced electric fields. The gradients of the high-latitude conductance can also lead to significant errors in the plasma convection estimates from the ground-based magnetometers, and to investigate this effect a statistical assessment of the difference between the true plasma convection (SuperDARN) and the magnetometer-inferred equivalent convection direction is performed. The largest differences are found for the transition region between the dark and sunlit ionospheres and in the midnight sector where strong conductance gradients are expected due to particle precipitation. Consideration of regular conductance gradients due to solar illumination improves the agreement between the radar and magnetometer data. Finally, an attempt is made to demonstrate the effects of conductance upon the properties of traveling convection vortices (TCVs). Joint SuperDARN and magnetometer data reveal that there is resemblance between the magnetometer and radar inferred TCV images on a scale of thousands of kilometers. However, on a smaller scale of hundreds of kilometers, significant differences are observed.

Benkevitch, Leonid

278

The access of dayside ionospheric O + ions to the plasma sheet during the september 24-25, 1998 magnetic storm  

NASA Astrophysics Data System (ADS)

We have investigated the population of the magnetosphere by ionospheric O + ions from the dayside during the first 8 h of the September 24-25, 1998 magnetic storm by tracing ion trajectories from the ionosphere in time-dependent electric and magnetic fields obtained from a three-dimensional global magnetohydrodynamic (MHD) simulation of the magnetosphere during this storm event. The MHD simulation used WIND data upstream of Earth as input for this storm that began at 2345 UT on September 24, 1998, when a magnetic cloud impacted Earth's magnetosphere. Ions were launched from both hemispheres on the dayside, in a region extending from 11 to 13 MLT and from 70 to 85 invariant latitude at five minute intervals, beginning 2 h before storm onset and extending to 8 h after the storm commenced. Ions were launched with energies that reflected the effects of ion energization along field lines during this event (e.g. [Cladis, J.B., Collin, H.L., Lennartsson, O.W., Moore, T.E., Peterson, W.K., Russell, C.T., 2000. Observations of centrifugal acceleration during compression of magnetosphere. Geophys. Res. Lett. 27, 915.]), as these effects were not a priori included in the MHD simulation of the event. The ion launch rate was dynamically normalized to observations by using the [Pollock Jr., C.J., Chappell, C.R., Gurnett, D.A., 1990. A survey of upwelling ion event characteristics. J. Geophys. Res. 95, 18-969.] and [Moore, T.E., Peterson, W.K., Russell, C.T., Chandler, M.O., Collier, M.R., Collin, H.L., Craven, P.D., Fitzenreiner, R., Giles, B.L., Pollock, C.J., 1999. Ionospheric mass ejection in response to a CME. Geophys. Res. Lett. 26, 2339.] relationship between the standard deviation of solar wind dynamic pressure and dayside O + outflow. We found that ionospheric O + ions had access to the plasma sheet beyond a radial distance of 10 RE before the storm, but gained access to the near-Earth region and partial ring current soon after the sudden commencement. In addition, significant changes to the magnetospheric configuration caused by the variations in solar wind dynamic pressure, most notably the two pressure peaks at 2345 and 0145 UT resulted in a relative absence of O + ions from the magnetotail extending from 0140 to 0300 UT. After 0300 UT, and for the next hour, the O + density in the plasma sheet increased to >1 cm -3, and O + was more abundant in the magnetotail compared even to the period immediately following the storm commencement.

Peroomian, Vah; El-Alaoui, Mostafa; Abdalla, Maha Ashour; Zelenyi, Lev M.

2006-01-01

279

Numerical modeling of the large-scale neutral and plasma responses to the body forces created by the dissipation of gravity waves from 6 h of deep convection in Brazil  

NASA Astrophysics Data System (ADS)

We study the response of the thermosphere and ionosphere to gravity waves (GWs) excited by 6 h of deep convection in Brazil on the evening of 01 October 2005 via the use of convective plume, ray trace, and global models. We find that primary GWs excited by convection having horizontal wavelengths of ?H70-300 km, periods of 10-60 min, and phase speeds of cH50-225 m/s propagate well into the thermosphere. Their density perturbations are ?'/?15- 25% at z150 km and are negligible at z>300 km. The dissipation of these GWs creates spatially and temporally localized body forces with amplitudes of 0.2- 1.0 m/s2at z120-230 km. These forces generate two counter-rotating circulation cells with horizontal velocities of 50-350 m/s. They also excite secondary GWs; those resolved by our global model have ?H4000-5000 km and cH500-600 m/s. These secondary GWs propagate globally and have ?'/?10- 25% and 5-15% at z=250 and 375 km, respectively. These forces also create plasma perturbations of foF2'0.2-1.0 MHz, TEC'0.4- 1.5 TECU (total electron content unit, 1TECU =1016 elm-2), and hmF2'5-50 km. The large-scale traveling ionospheric disturbances (LSTIDs) induced by the secondary GWs have amplitudes of foF2'0.2-0.5 MHz, TEC'0.2- 0.6 TECU, and hmF2'5-10 km. In a companion paper, we discuss changes to the prereversal enhancement and plasma drift from these forces.

Vadas, S. L.; Liu, H.-L.

2013-05-01

280

Convective amplification of a three-wave parametric instability in inhomogeneous plasma  

SciTech Connect

The three-wave parametric instability in inhomogeneous plasma is revisited and the inconsistency of the convective amplification in previous literatures is resolved. By employing multiple methods, the amplification factor of the decay mode due to the inhomogeneity is confirmed as A=??{sub 0}{sup 2}/(v{sub g1x}v{sub g2x}?{sup ?}), which is independent of the linear damping rate of the decay mode, where ?{sub 0} is the nonlinear growth rate in homogeneous plasma, v{sub g1x} and v{sub g2x} are the group velocities in the x direction of the two decay modes and ?{sup ?} is the derivative of the wavevector mismatch of the three coupled waves due to the plasma inhomogeneity.

Zhao, Aihui; Gao, Zhe [Department of Engineering Physics, Tsinghua University, Beijing 100084 (China)] [Department of Engineering Physics, Tsinghua University, Beijing 100084 (China)

2013-11-15

281

Plasma convection in Saturn's outer magnetosphere determined from ions detected by the Cassini INCA experiment  

NASA Astrophysics Data System (ADS)

The Ion and Neutral Camera (INCA), one of three sensors comprising the Magnetospheric Imaging Instrument (MIMI) on the Cassini spacecraft, measures intensities of hydrogen and oxygen ions and neutral atoms in the Saturnian magnetosphere. The measured intensity spectrum and anisotropy of hot hydrogen and oxygen ions may be used to deduce the spectral parameters and the velocity of the ion population. The anisotropies are frequently convective in nature, allowing for the determination of a bulk velocity. Under the ``frozen in'' assumption, this is also the velocity of the cold plasma of magnetospheric ions. Initial analysis of selected measurements of nightside ion populations with strong anisotropies indicates nearly rigid corotation of magnetospheric plasma interior to Titan's orbit. Beyond this distance, these measurements infer that the plasma maintains at best a constant rotation velocity, falling farther behind the rigid corotation rate at increasing distance.

Kane, M.; Mitchell, D. G.; Carbary, J. F.; Krimigis, S. M.; Crary, F. J.

2008-02-01

282

Investigation of methods for updating ionospheric scintillation models using topside in situ plasma density measurements. Final report, 1 May 1990-30 April 1993  

SciTech Connect

Modern military communication, navigation, and surveillance systems depend on reliable, noise free transionospheric radio-frequency channels and can be severely impacted by small-scale electron-density irregularities in the ionosphere. This report summarizes the results of a three year investigation into the methods for updating ionospheric scintillation models using observations of ionospheric plasma-density irregularities measured by the DMSP Scintillation Meter (SM) sensor. Results are reported from the analysis of data from a campaign conducted in January 1990 near Tromso, Norway, in which near coincident in-situ plasma-density and transionospheric scintillation measurements were made. Estimates for the level of intensity and phase scintillation on a transionospheric UBF radio link in the early-evening auroral zone were calculated from DMSP SM data and compared to the levels actually observed. Results are also presented from a comparison with scintillation observations made with a coincident DNA Polar BEAR satellite pass. Ionosphere, Ionospheric Scintillation, Radiowave Scintillation, Defense Meteorology Satellite Program (DMSP).

Secan, J.A.

1993-05-01

283

In situ measurements of ionospheric plasma turbulence over five frequency decades: Heritage flight of the Plasma Local Anomalous Noise Experiment (PLANE)  

NASA Astrophysics Data System (ADS)

Observations of ionospheric plasma density and frequency-dependent broadband plasma turbulence made during the heritage flight of the Plasma Local Anomalous Noise Experiment (PLANE) are presented. Rather than record high frequency time series data, the experiment was designed to record Power Spectral Distributions (PSDs) in five decadal frequency bins with upper limits ranging from 1.0 Hz to 10 kHz. Additionally, PLANE was designed distinguish turbulence in the ambient plasma from that local to the spacecraft. The instrument consists of two retarding potential analyzers (RPAs) connected together via a feedback loop to force one analyzer into the I-V trace retardation region at all times. Fluctuations in this measurement are believed to be ambient only as the RPA's voltage would be too high for locally turbulent plasma to surmount the potential barrier, which is nominally at ram energy. The instrument requires pointing along the spacecraft's ram velocity vector to make this measurement, thus requiring stabilization in pitch and yaw. During PLANE's heritage flight, though the satellite's attitude control system failed early in the mission, plasma data were collected during opportune times in which the instrument rotated into and out of the ram. Observations of plasma density and PSDs of high frequency plasma turbulence were recorded on several occasions. Additionally, a plasma source onboard the satellite was used to generate artificial plasma turbulence, and the PLANE data observed periodic structure presumably associated with the rotation of the spacecraft during these source firings. A brief comparison with other high frequency in situ plasma instruments is presented.

Habash Krause, L.; Enloe, C. L.; McHarg, M. G.

2013-12-01

284

Detection of energetic hydrogen molecules in Jupiter's magnetosphere by Voyager 2 - Evidence for an ionospheric plasma source  

NASA Technical Reports Server (NTRS)

The discovery of energetic (approximately 1 MeV/nuc) H3 and H2 molecules in Jupiter's magnetosphere is reported. The data, obtained with the LECP instrument on Voyager 2, showed these molecules to be present throughout the magnetosphere and as far as 180 Jupiter radii from the planet, in the 'magnetospheric wind' region. Although the relative abundances of H3 and H2 do not show a monotonic trend with distance from Jupiter, the intervals of highest abundance were found in the outer magnetosphere. As an example, in the radial range 51-56 Jupiter radii, of the dayside magnetosphere, the abundances of H3 and H2 (0.60-0.95 MeV/nuc) were about 20 and 13-25% that of He, respectively, and the He abundance was about 1-2% that of H. Since H3(+) is expected to be an important constituent of Jupiter's ionosphere, the data provide strong evidence that, in addition to Io, the ionosphere may be an important local plasma source for the Jovian energetic particles. The measurements reported may represent the first detection in nature of molecules at energies as high as 1 MeV/nucleon.

Hamilton, D. C.; Gloeckler, G.; Krimigis, S. M.; Bostrom, C. O.; Armstrong, T. P.; Axford, W. I.; Fan, C. Y.; Hunten, D. M.; Lanzerotti, L. J.

1980-01-01

285

The Response of the Thermosphere and Ionosphere to Magnetospheric Forcing  

NASA Astrophysics Data System (ADS)

During the past six years, rapid advances in three observational techniques (ground-based radars, optical interferometers and satellite-borne instruments) have provided a means of observing a wide range of spectacular interactions between the coupled magnetosphere, ionosphere and thermosphere system. Perhaps the most fundamental gain has come from the combined data-sets from the NASA Dynamics Explorer (DE) Satellites. These have unambiguously described the global nature of thermospheric flows, and their response to magnetospheric forcing. The DE spacecraft have also described, at the same time, the magnetospheric particle precipitation and convective electric fields which force the polar thermosphere and ionosphere. The response of the thermosphere to magnetospheric forcing is far more complex than merely the rare excitation of 1 km s-1 wind speeds and strong heating; the heating causes large-scale convection and advection within the thermosphere. These large winds grossly change the compositional structure of the upper thermosphere at high and middle latitudes during major geomagnetic disturbances. Some of the major seasonal and geomagnetic storm-related anomalies of the ionosphere are directly attributable to the gross wind-induced changes of thermospheric composition; the mid-latitude ionospheric storm `negative phase', however, is yet to be fully understood. The combination of very strong polar wind velocities and rapid plasma convection forced by magnetospheric electric fields strongly and rapidly modify F-region plasma distributions generated by the combination of local solar and auroral ionization sources. Until recently, however, it has been difficult to interpret the observed complex spatial and time-dependent structures and motions of the thermosphere and ionosphere because of their strong and nonlinear coupling. It has recently been possible to complete a numerical and computational merging of the University College London (UCL) global thermospheric model and the Sheffield University ionospheric model. This has produced a self-consistent coupled thermospheric--ionospheric model, which has become a valuable diagnostic tool for examining thermospheric--ionospheric interactions in the polar regions. In particular, it is possible to examine the effects of induced winds, ion transport, and the seasonal and diurnal U.T. variations of solar heating and photoionization within the polar regions. Polar and high-latitude plasma density structure at F-region altitudes can be seen to be strongly controlled by U.T., and by season, even for constant solar and geomagnetic activity. In the winter, the F-region polar plasma density is generally dominated by the effects of transport of plasma from the dayside (sunlit cusp). In the summer polar region, however, an increase in the proportion of molecular to atomic species, created by the global seasonal circulation and augmented by the geomagnetic forcing, controls the plasma composition and generally depresses plasma densities at all U.Ts. A number of these complex effects can be seen in data obtained from ground-based radars, Fabry--Perot interferometers and in the combined DE data-sets. Several of these observations will be used, in combination with simulations using the UCL--Sheffield coupled model, to illustrate the major features of large-scale thermosphere--ionosphere interactions in response to geomagnetic forcing. The past decade has seen a major improvement in the quality and quantity of experimental data available to study the thermosphere and ionosphere and their response to magnetospheric forcing. Earlier, large measured changes of individual parameters were difficult to place in a global or large-scale perspective. However, a clear picture of the distinction between the solar and geomagnetic forcing processes has emerged from the combined data-sets available from spacecraft such as the Dynamics Explorers, and from ground-based radar and optical observations of the polar thermosphere. A first experimental view of the strong coupling between the thermosphere and ionosp

Rees, D.; Fuller-Rowell, T. J.

1989-06-01

286

Reviewing the Mechanisms Underlying the Pre-reversal Enhancement of the Vertical Plasma Drift in the Low Latitude Ionosphere  

NASA Astrophysics Data System (ADS)

The evening pre-reversal enhancement (PRE) of the zonal electric field and the corresponding vertical plasma drift in the low-latitude ionosphere is an important feature in determining the structure and stability of the ionosphere. There are three competing theories of the cause of the PRE; curl free response [Eccles, 1998a and Rishbeth, 1972], off-equator Hall current divergence [Farley et al., 1986]; and equatorial electrojet current divergence [Harendel and Eccles, 1992]. We review these theories of the PRE cause in the context of field-line-integrated electrodynamics model and then examine the viability of each proposed cause using simplified electrodynamics simulations. While all three physical theories are real physical processes occurring in the evening low latitude ionosphere, we demonstrate that the PRE arises primarily from a curl-free response to the rapid temporal evolution of the vertical electric field as proposed by Eccles [1998a] in support of a short comment by Rishbeth [1972] within his paper on the F region dynamo. The curl-free effect magnitude has three components: (1) the exchange of the dominance of the E region dynamo to the F region dynamo as the E region Pedersen conductivity in conjugant hemispheres decay around sunset, (2) the acceleration of the F region zonal neutral wind as the ion-neutral drag diminishes around sunset, and (3) the apex altitude range of operation of the F region dynamo current. The maximum PRE magnitude occurs at E region sunset when the integrated E region Pedersen conductivities of both hemispheres decrease to less than the integrated F region Pedersen conductivity. The mechanism proposed by Farley et al. [1986] is examined. While the off-equator gradient of the Hall currents can affect the zonal electric field near sunset, it only provides a modest adjustment to the PRE magnitude. The Farley mechanism is limited due to the slow acceleration of the zonal neutral wind prior to E region sunset. It is also demonstrated that the magnitude of the PRE in response to the curl-free effect is affect only very slightly by conductivity conditions within the equatorial electrojet (EEJ). While the EEJ is the most important path of zonal current in the low-latitude ionosphere it is more of a passive load on the F region dynamo electromotive presence. However, the EEJ does dominate the electric field structure below the field-line integrated bottomside F region as presented by Haerendel and Eccles [1992]. These results suggest that the prediction of the PRE magnitude requires accurate knowledge of the decay of the E regions of both hemispheres and of the magnitude and acceleration of the zonal neutral wind in the F region near E region sunset. Eccles, J. V. (1998), A simple model of low-latitude electric fields, J. Geophys. Res., 103, 26,699-26,708. Farley, D. T., E. Bonelli, B.G. Fejer, and M. F. Larsen (1986), The pre-reversal enhancement of the zonal electric field in the equatorial ionosphere, J. Geophys. Res., 91, 13,723-13,728. Haerendel, G. and J. V. Eccles (1992), The Role of the equatorial electrojet in the evening ionosphere, J. Geophys. Res., 97, 1181-1192. Rishbeth, H. (1971), Polarization fields produced by winds in the equatorial F-region, Planet. Space Sci. (19) 357-369.

Eccles, J. V.; St-Maurice, J.; Schunk, R. W.

2013-12-01

287

Planetary ionospheres  

NASA Technical Reports Server (NTRS)

An analogy is drawn between the Eath's ionosphere and the existence of ionospheres around other planets or natural satellites. An ionosphere is defined as a series of layers (D, E, E1, F2) and their characteristics are discussed. Emphasis is on the role of solar wind impacting with the potential ionosphere and the subsequent chemical and diffusion processes that can be observed. Data from the MARINER and PIONEER space programs are cited concerning measured electron density and ionospheric refractivity of extraterrestrial ionospheres, then an attempt is made to model these atmospheres based on Earth ionosphere theory.

Bauer, S. J.

1977-01-01

288

Electric Field and Plasma Density Observations of Irregularities and Plasma Instabilities in the Low Latitude Ionosphere Gathered by the C/NOFS Satellite  

NASA Technical Reports Server (NTRS)

The Vector Electric Field Investigation (VEFI) on the C/NOFS equatorial satellite provides a unique data set which includes detailed measurements of irregularities associated with the equatorial ionosphere and in particular with spread-F depletions. We present vector AC electric field observations gathered on C/NOFS that address a variety of key questions regarding how plasma irregularities, from meter to kilometer scales, are created and evolve. The talk focuses on occasions where the ionosphere F-peak has been elevated above the C/NOFS satellite perigee of 400 km as solar activity has increased. In particular, during the equinox periods of 2011, the satellite consistently journeyed below the F-peak whenever the orbit was in the region of the South Atlantic anomaly after sunset. During these passes, data from the electric field and plasma density probes on the satellite have revealed two types of instabilities which had not previously been observed in the C/NOFS data set: The first is evidence for 400-500km-scale bottomside "undulations" that appear in the density and electric field data. In one case, these large scale waves are associated with a strong shear in the zonal E x B flow, as evidenced by variations in the meridional (outward) electric fields observed above and below the F-peak. These undulations are devoid of smaller scale structures in the early evening, yet appear at later local times along the same orbit associated with fully-developed spread-F with smaller scale structures. This suggests that they may be precursor waves for spread-F, driven by a collisional shear instability, following ideas advanced previously by researchers using data from the Jicamarca radar. A second result is the appearance of km-scale irregularities that are a common feature in the electric field and plasma density data that also appear when the satellite is near or below the F-peak at night. The vector electric field instrument on C/NOFS clearly shows that the electric field component of these waves is strongest in the zonal direction. These waves are strongly correlated with simultaneous observations of plasma density oscillations and appear both with, and without, evidence of larger-scale spread-F depletions. These km-scale, quasi-coherent waves strongly resemble the bottomside, sinusoidal irregularities reported in the Atmosphere Explorer satellite data set by Valladares et al. and are believed to cause scintillations of VHF radiowaves. We interpret these new observations in terms of fundamental plasma instabilities associated with the unstable, nighttime equatorial ionosphere.

Pfaff, Robert F.; Freudenreich, H.; Rowland, D.; Klenzing, J.; Liebrecht, C.

2012-01-01

289

The plasma environment, charge state, and currents of Saturn's C and D rings  

NASA Technical Reports Server (NTRS)

The charge state and associated currents of Saturn's C an D rings are studied by modeling the flow of ionospheric plasma from the mid- to low-latitude ionosphere to the vicinity of the rings. It is found that the plasma density near the C and D rings, at a given radial location, will experience a one to two order of magnitude diurnal variation. The surface charge density (SCD) of these rings can show significant radial and azimuthal variations due mainly to variation in the plasma density. The SCD also depends on structural features of the rings such as thickness and the nature of the particle size distribution. The associated azimuthal currents carried by these rings also show large diurnal variations resulting in field-aligned currents which close in the ionosphere. The resulting ionospheric electric field will probably not produce a significant amount of plasma convection in the topside ionosphere and inner plasmasphere.

Wilson, G. R.

1991-01-01

290

The effect of longitudinal conductance variations on the ionospheric prompt penetration electric fields  

NASA Astrophysics Data System (ADS)

Ionospheric prompt penetration electric fields of magnetospheric origin, together with the atmospheric disturbance dynamo, represent the most important parameters controlling the storm-time dynamics of the low and mid-latitude ionosphere. These prompt penetration fields result from the disruption of region-2 field-aligned shielding currents during geomagnetically disturbed conditions. Penetration electric fields con- trol, to a large extent, the generation and development of equatorial spread-F plasma instabilities as well as other dynamic space weather phenomena in the ionosphere equatorward of the auroral zone. While modeling studies typically agree with average patterns of prompt penetration fields, experimental results suggest that longitudinal variations of the ionospheric con- ductivities play a non-negligible role in controlling spread-F phenomena, an effect that has not previously been modeled. We present first results of modeling prompt pene- tration electric fields using a version of the Rice Convection Model (RCM) that allows for longitudinal variations in the ionospheric conductance tensor. The RCM is a first- principles numerical ionosphere-magnetosphere coupling model that solves for the electric fields, field-aligned currents, and particle distributions in the ionosphere and inner/middle magnetosphere. We compare these new theoretical results with electric field observations.

Sazykin, S.; Wolf, R.; Spiro, R.; Fejer, B.

291

Numerical simulation of plasma transport in Saturn's inner magnetosphere using the Rice Convection Model  

NASA Astrophysics Data System (ADS)

We use the Rice Convection Model to simulate plasma transport in Saturn's inner magnetosphere, 2 < L < 12, where L = equatorial distance in planetary radii. By incorporating a continuously active distributed plasma source derived from neutral cloud modeling, the simulation shows alternating longitudinal sectors ("fingers") of inflow and outflow. Their initial development confirms the retarding effects of the Coriolis force and the pickup current. In their further nonlinear development, the inflow fingers become much narrower in longitude than the outflow ones, which may explain a previously unexplained feature of the Cassini Plasma Spectrometer (CAPS) observations. Our analysis confirms that the narrower inflowing fingers have much larger radial speeds than the broader outflowing sectors. We analyze the corotation lag and find that in the innermost region (L < 5) the pickup current is the major driver of the corotation lag, but in the more distant region (L > 5) both the pickup current and the Coriolis acceleration contribute significantly to the corotation lag. We compare our simulation results with observational results from CAPS data. For the radial flow component, the simulation results fit observations reasonably well. In the azimuthal component, there are significant differences in the magnitude and radial structure of the corotation lag, which may provide guidance for future refinement of the plasma source model.

Liu, X.; Hill, T. W.; Wolf, R. A.; Sazykin, S.; Spiro, R. W.; Wu, H.

2010-12-01

292

A model of the plasma flow and current in Saturn's polar ionosphere under conditions of strong Dungey cycle driving  

NASA Astrophysics Data System (ADS)

We propose a simple model of the flow and currents in Saturn's polar ionosphere. This model is motivated by theoretical reasoning, and guided quantitatively by in situ field and flow data from space missions, ground-based IR Doppler measurements, and Hubble Space Telescope images. The flow pattern consists of components which represent (1) plasma sub-corotation in the middle magnetosphere region resulting from plasma pick-up and radial transport from internal sources; (2) the Vasyliunas-cycle of internal plasma mass-loss down the magnetospheric tail at higher latitudes; and (3) the polar Dungey-cycle flow driven by the solar wind interaction. Upstream measurements of the interplanetary magnetic field (IMF) indicate the occurrence of both extended low-field rarefaction intervals with essentially negligible Dungey-cycle flow, and few-day high-field compression regions in which the Dungey-cycle voltage peaks at a few hundred kV. Here we model the latter conditions when the Dungey-cycle is active, advancing on previous axi-symmetric models which may be more directly applicable to quiet conditions. For theoretical convenience the overall flow pattern is constructed by adding together two components - a purely rotational flow similar to previous axi-symmetric models, and a sun-aligned twin vortex representing the dawn-dusk asymmetry effects associated with the Vasyliunas-and Dungey-cycle flows. We calculate the horizontal ionospheric current associated with the flow and the field-aligned current from its divergence. These calculations show that a sheet of upward-directed field-aligned current flows at the boundary of open field lines which is strongly modulated in local-time by the Dungey-cycle flows. We then consider implications of the field-aligned current for magnetospheric electron acceleration and aurorae using two plasma source populations (hot outer magnetospheric electrons and cool dense magnetosheath electrons). Both sources display a strong dawn-dusk asymmetry in the accelerating voltages required and the energy fluxes produced, resulting from the corresponding asymmetry in the current. The auroral intensities for the outer magnetosphere source are typically ~50 kR at dawn and ~5 kR at dusk, in conformity with recent auroral observations under appropriate conditions. However, those for the magnetosheath source are much smaller. When the calculated precipitating electron energy flux values are integrated across the current layer and around the open closed field line boundary, this yields total UV output powers of ~10 GW for the hot outer magnetosphere source, which also agrees with observations.

Jackman, C. M.; Cowley, S. W. H.

2006-05-01

293

Characteristics of nocturnal ionospheric zonal plasma drift velocities determined from OI 630.0 nm and 777.4 nm all sky imaging observations  

NASA Astrophysics Data System (ADS)

In the Brazilian sector, mostly during the period from October to March, the equatorial and low latitude Fregions present quasi north-south magnetic field- aligned large-scale ionospheric irregularities, which are one of the most remarkable features of these regions of the upper atmosphere. These ionospheric irregularities may be observed by different observational techniques (e.g., radar, digisonde, GPS and optical instruments) and its time evolution and propagation can be used to study important aspects of ionospheric dynamics and thermosphere-ionosphere coupling. Simultaneous observations of the OI 630.0 nm and 777.4 nm nightglow emissions using all-sky imaging systems at So Jos dos Campos (23.21o S, 45.86o W; dip latitude 17.6o S), Brazil, have been used to determine the nighttime variations of zonal plasma bubble drift velocities. The OI 630.0 nm and 777.4 nm emissions come from altitudes of about 250 km and 350 km, respectively. The optical signatures of the OI 777.4 nm emission are more closely related to the actual ionospheric plasma bubble structures, owing to the fact that it is a prompt emission and depends only on the electron density profiles, with no F-region height dependence. On the other hand, the OI 630.0 nm emission comes from the bottomside of the F layer with a strong F region height dependence and shows- blurred images due to its 110-s lifetime. The all-sky imaging systems used in the present studies have CCDs, with high quantum efficiency which provide excellent capabilities for quantitative measurements of faint and low contract emissions. Both the emissions (OI 630.0 nm and 777.4 nm) show quasi north-south aligned intensity depletion bands, which are the optical signatures of large scale F-region plasma bubbles. Thus, it is possible to infer the nocturnal ionospheric zonal plasma drift velocities by just following the space-time displacements of the intensity-depleted bands seen in the images. The nocturnal zonal plasma drift velocities obtained from the two emissions are presented and discussed in this communication. Also, a comparison of the observed zonal plasma drift velocities with the zonal neutral wind velocities obtained from the horizontal wind model (HWM- 90) are presented.

Abalde, J.; Pimenta, A.; Fagundes, P.; Sahai, Y.; Bittencourt, J.

294

Survey and prediction of the ionospheric scintillation using data mining techniques  

Microsoft Academic Search

Irregularly structured ionospheric regions may cause amplitude and phase fluctuations of radio signals. Such distortion is called ionospheric scintillation. These ionospheric irregularities occur as part of depleted plasma density regions that are generated at the magnetic equator after sunset by equatorial ionospheric plasma instability mechanism. Also known as ionospheric bubbles, they drift upward to high altitudes at the equator and

L. F. C. Rezende; E. R. de Paula; S. Stephany; I. J. Kantor; M. T. A. H. Muella; P. M. de Siqueira; K. S. Correa

2010-01-01

295

Plasma Convection in the Magnetotail of Saturn and a Comparison to Jupiter  

NASA Astrophysics Data System (ADS)

On numerous orbits that explored the dusk side magnetotail during 2009-2010, the Ion and Neutral Camera (INCA) instrument on the Cassini spacecraft has detected fluxes of hot ions. We have analyzed ion data during this period and found that plasma in the dusk-midnight quadrant sub-corotates, albeit at a large fraction of the rigid corotation speed, with the primary velocity being azimuthal but with a distinct outward component. The velocities, measured beyond ~20 Rs, are similar to those obtained from earlier orbits in the midnight-dawn sector, in contrast to the depressed velocities measured at Jupiter in the dusk-midnight quadrant, using Energetic Particles Detector (EPD) measurements on the Galileo spacecraft. These INCA data at Saturn along with previous results are consistent with a plasma disk undergoing a centrifugally induced expansion as it emerges into the night side, while maintaining partial rotation with the planet. From earlier and present Saturn studies, the magnetodisk expansion continues as plasma rotates across the tail to the dawn side. In neither magnetotail do we see evidence for steady state reconnection, despite the significant asymmetry in the convection velocity at Jupiter. We have noted previously that in the outer regions of the night side magnetodisk, equatorial plasma azimuthal speeds plateau (as a function of radial distance) at both Jupiter and Saturn, at distances in the night side beyond the magnetopause standoff distance. The outermost region of the magnetodisk, having undergone expansion upon emerging from the day side magnetopause confinement, is unlikely to recirculate back into the dayside. We present a scenario in which plasma confined in a magnetodisk (at either planet) emerges from the day side, expands at the dusk flank, but continues moving around the planet, across the tail, and loses mass at its outer edges primarily near the dawn flank of the magnetotail. The Kelvin-Helmholtz instability provides vorticies to enhance plasma reconnection and diffusion to transport mass down the tail and out of the system.

Kane, M.; Mitchell, D. G.; Carbary, J. F.; Krimigis, S. M.

2010-12-01

296

Electromechanical feedback processes in the ionosphere. Final technical report, 1 December 1984-31 May 1988  

SciTech Connect

The general goals were to provide a better understanding of observed neutral and plasma structures in the upper atmosphere, and to define appropriate parameterizations for the neutral-plasma interactions governing these structures in comprehensive numerical models of the thermosphere and ionosphere. A convection model was utilized to investigate the electrodynamic coupling between the magnetosphere and thermosphere including the effects of neutral winds, and noting the change in electric fields penetrating to low latitudes due to the wind effects. A unique aspect of the study is that the high-latitude convection-driven winds are included self-consistently and interactively; that is, a steady-state wind parameterization was derived analytically in terms of the electric potential, which is in turn included in a closed-loop calculation for the electric potential itself. An analogous study was performed for the thermosphere-ionosphere system, wherein the balance height of the F layer was expressed analytically in terms of the meridional neutral wind, and the two parameters allowed to evolve self-consistently within dynamical calculations representing magnetically disturbed and quiet conditions in the thermosphere. In another series of calculations, plasma structures unique to the equatorial ionosphere were modeled analytically and incorporated into a numerical solution of the neutral dynamics to demonstrate the controlling influence of the ionosphere on the equatorial thermosphere.

Forbes, J.M.

1988-08-31

297

Temperature structure of plasma bubbles in the low latitude ionosphere around 600 km altitude  

Microsoft Academic Search

The electron temperature inside plasma bubbles at a height of 600 km was first measured by means of Japan's seventh scientific satellite Hinotori which is an equator orbiting satellite with an inclination of 31 deg. During the period between June 1981 and February 1982, 724 plasma bubbles were detected and studied. The electron temperature inside the plasma bubbles is either

K.-I. Oyama; K. Schlegel; S. Watanabe

1988-01-01

298

High latitude field aligned light ion flows in the topside ionosphere deduced from ion composition and plasma temperatures  

NASA Technical Reports Server (NTRS)

Using a comprehensive ionospheric data set comprised of all available ion composition and plasma temperature measurements from satellites, the vertical distributions of ion composition and plasma temperatures are defined from middle latitudes up into the polar cap for summer conditions for altitudes below about 1200 km. These data are sufficient to allow a numerical estimation of the latitudinal variation of the light ion outflows from within the plasmasphere to the polar wind regions. The altitude at which significant light ion outflow begins is found to be lower during solar minimum conditions than during solar maximum. The H(+) outward speeds are of the order of 1 km/s near 1100 km during solar maximum but attain several km/s speeds for solar minimum. He(+) shows a similar altitude development of flow but attains polar cap speeds much less than 1 km/s at altitudes below 1100 km, particularly under solar maximum conditions. Outward flows are also found in the topside F-region for noontime magnetic flux tubes within the plasmasphere.

Grebowsky, J. M.; Hoegy, W. R.; Chen, T. C.

1993-01-01

299

High-order stimulated ionospheric diffuse plasma resonances - Significance for magnetospheric emissions  

NASA Technical Reports Server (NTRS)

The paper presents Alouette 2/ISIS 1 data which furnish evidence for the stimulation of high-order D(n) resonances (n greater than 4) by topside sounders, confirming the prediction of Osherovich (1990) based on an analogy with naturally occurring narrowband magnetospheric emissions. The results indicate that observations of stimulated ionospheric emissions and naturally occurring magnetospheric emissions can be used as complementary data sets to address such fundamental questions as the nature of the excitation mechanism for these emissions and the nature of the waves (i.e., whether the waves predominantly electrostatic or with a significant magnetic component present), and the question of the dominance among the Dn, Dn(+), and Dn(-) resonances and the conditions required for all three to be present at the same time.

Benson, Robert F.; Osherovich, Vladimir A.

1992-01-01

300

High-order stimulated ionospheric diffuse plasma resonances - Significance for magnetospheric emissions  

NASA Astrophysics Data System (ADS)

The paper presents Alouette 2/ISIS 1 data which furnish evidence for the stimulation of high-order D(n) resonances (n greater than 4) by topside sounders, confirming the prediction of Osherovich (1990) based on an analogy with naturally occurring narrowband magnetospheric emissions. The results indicate that observations of stimulated ionospheric emissions and naturally occurring magnetospheric emissions can be used as complementary data sets to address such fundamental questions as the nature of the excitation mechanism for these emissions and the nature of the waves (i.e., whether the waves predominantly electrostatic or with a significant magnetic component present), and the question of the dominance among the Dn, Dn(+), and Dn(-) resonances and the conditions required for all three to be present at the same time.

Benson, Robert F.; Osherovich, Vladimir A.

1992-12-01

301

A high-latitude, low-latitude boundary layer model of the convection current system  

SciTech Connect

Observations suggest that both the high- and low-latitude boundary layers contribute to magnetospheric convection, and that their contributions are linked. In the interpretation pursued here, the high-latitude boundary layer (HBL) generates the voltage while the low-latitude boundary layer (LBL) generates the current for the part of the convection electric circuit that closes through the ionosphere. This paper gives a model that joins the high- and low-latitude boundary layers consistently with the ionospheric Ohm's law. It describes an electric circuit linking both boundary layers, the region 1 Birkeland currents, and the ionospheric Pedersen closure currents. The model works by using the convection electric field that the ionosphere receives from the HBL to determine two boundary conditions to the equations that govern viscous LBL-ionosphere coupling. The result provides the needed self-consistent coupling between the two boundary layers and fully specifies the solution for the viscous LBL-ionosphere coupling equations. The solution shows that in providing the current required by the ionospheric Ohm's law, the LBL needs only a tenth of the voltage that spans the HBL. The solution also gives the latitude profiles of the ionospheric electric field, parallel currents, and parallel potential. It predicts that the plasma in the inner part of the LBL moves sunward instead of antisunward and that, as the transpolar potential decreases below about 40 kV, reverse polarity (region 0) currents appear at the poleward border of the region 1 currents. A possible problem with the model is its prediction of a thin boundary layer ({approximately}1000 km), whereas thicknesses inferred from satellite data tend to be greater.

Siscoe, G.L. (Univ. of California, Los Angeles (USA)); Lotko, W.; Sonnerup, B.U.O. (Dartmouth College, Hanover NH (USA))

1991-03-01

302

Detection of long-living neutral hydrated clusters in laboratory simulation of ionospheric D region plasma  

NASA Astrophysics Data System (ADS)

The existence of hydrated cluster ions is known through in situ measurements in the D region of the ionosphere and laboratory simulation experiments. A series of experiments were conducted at Sagamihara, Japan with the intention of detecting some of the ions which, although predicted, had eluded detection in laboratory simulation. The other motivation was to look for heavier ions in laboratory simulations in conditions close to those in the D region. With the availability of better ion mass spectrometers, these could supposedly be detected by rocket measurements. Results of these experiments point to a new aspect, namely, the production of a neutral hydrated cluster molecule, which (a) has ionization potential of less than 10.2 eV, (b) has lifetimes in excess of 90 min, and (c) is formed within a limited pressure range. As this neutral cluster molecule has a mass number of 102, most probably it is NO?(H2O)4. A number of other important ions, which were detected earlier in laboratory experiments, were also seen in our data. These include NO+(H2O)n, NO+(H2O)nX, NO2+(H2O)n, H3O+(H2O)n, H3O+(H2O)nX, and O2+(H2O)n series. A few clusters {36+(H3O+OH), 60+(NO+NO) and 63+(NO+HO2)} and molecular ions {29+(N2H+), 33+(HO2+) and 43+(N3H+)} were also detected in these experiments. It was also found that, like the earlier experiments, the concentration of most of the hydrated ions showed an oscillatory behavior. The ion formation was observed only within a limited pressure range, which corresponds to the 50 to 100 km altitude range of the ionosphere.

Sinha, H. S. S.; Oyama, Koh-Ichiro; Watanabe, S.

2013-01-01

303

A diagnostic tool for the study of stochastic properties of density striations excited by powerful electromagnetic waves in the ionospheric plasma  

NASA Astrophysics Data System (ADS)

Powerful electromagnetic waves illuminating the ionospheric plasma generate small-scale density irregularities elongated in the direction of the geomagnetic field. Stochastic motion of these irregularities results in fluctuations of HF radio signals backscattered by the illuminated region. Observations of the full wave form of the radio signals make it possible to reconstruct the distribution function of the irregularities over their velocities. An experiment with such a reconstruction is proposed.

Puchkov, V. A.

2013-11-01

304

The impact of gravity waves rising from convection in the lower atmosphere on the generation and nonlinear evolution of equatorial bubble  

Microsoft Academic Search

The nonlinear evolution of equatorial F-region plasma bubbles under varying ambient ionospheric conditions and gravity wave seeding perturbations in the bottomside F-layer is studied. To do so, the gravity wave propagation from the convective source region in the lower atmosphere to the thermosphere is simulated using a model of gravity wave propagation in a compressible atmosphere. The wind perturbation associated

E. Alam Kherani; M. A. Abdu; E. R. de Paula; D. C. Fritts; J. H. A. Sobral; F. C. de Meneses Jr.

2009-01-01

305

Dayside ionospheric processes and their effect on O+ escape  

NASA Astrophysics Data System (ADS)

It is well known that O+ escape from the ionosphere is a multi-stage process where upwelling thermal (less than 1 eV) O+ ions are energized above escape velocity (10 eV) by various processes above the ionosphere. There has been, however, relatively little investigation of the relative importance of ionospheric processes such as photoionization, convection, motion of the neutral atmosphere, and particle precipitation in determining the magnitude and local time distribution of escaping O+ ions. We use a recently developed large-scale database of upwelling thermal O+ ions observed on the DMSP satellites at 850 km during quiet geomagnetic conditions and the FLIP ionospheric code to investigate the relative importance of these processes in the dayside high latitude ionosphere. Observations have established that the escaping flux of energetic O+ ion outflow associated with the dayside cusp is shifted dawnward from noon where the precipitation of low energy electrons and wave power are at their dayside maxima. The magnitude of the dawnward shift is generally larger than the well-documented, convection-driven, shift in the local time of the cusp as a function of the magnitude and direction of the Y component of the interplanetary magnetic field. Modeling using the FLIP code shows that the dawnward shift is the result of the history of the thermal plasma on magnetic field lines as they rotate into and out of darkness producing a maximum upwelling flux shortly after dawn. The combination of a dawn focused source population and noon focused energization region results in a net dawnward shift in the dayside maximum of escaping energetic O+ during the geomagnetically quiet conditions considered. Our model results also suggest that neutral winds influence the location of the dayside local time maximum of upwelling O+ more than electron precipitation.

(Bill) Peterson, W. K.; Richards, Phil; Redmon, Rob; Andersson, Laila

2012-07-01

306

Plasma modifications induced by an X-mode HF heater wave in the high latitude F region of the ionosphere  

NASA Astrophysics Data System (ADS)

We presented experimental results of strong plasma modifications induced by X-mode powerful HF radio waves injected towards the magnetic zenith into the high latitude F region of the ionosphere. The experiments were conducted in 2009-2011 using the EISCAT Heating facility, UHF incoherent scatter radar and the EISCAT ionosonde at Troms, Norway; and the CUTLASS SuperDARN HF coherent radar at Hankasalmi, Finland. The results showed that the X-mode HF pump wave can generate strong small-scale artificial field aligned irregularities (AFAIs) in the F region of the high-latitude ionosphere. These irregularities, with spatial scales across the geomagnetic field of the order of 9-15 m, were excited when the heater frequency (fH) was above the ordinary-mode critical frequency (foF2) by 0.1-1.2 MHz. It was found that the X-mode AFAIs appeared between 10 s and 4 min after the heater is turned on. Their decay time varied over a wide range between 3 min and 30 min. The excitation of X-mode AFAIs was accompanied by electron temperature (Te) enhancements and an increase in the electron density (Ne) depending on the effective radiated power (ERP). Under ERPs of about 75-180 MW the Te enhances up to 50% above the background level and an increase in Ne of up to 30% were observed. Dramatic changes in the Te and Ne behavior occurred at effective radiated powers of about 370-840 MW, when the Ne and Te values increased up to 100% above the background ones. It was found that AFAIs, Ne and Te enhancements occurred, when the extraordinary-mode critical frequency (fxF2) lied in the frequency range fH-fce/2?fxF2?fH+fce/2, where fce is the electron gyrofrequency. The strong Ne enhancements were observed only in the magnetic field-aligned direction in a wide altitude range up to the upper limit of the UHF radar measurements. In addition, the maximum value of Ne is about 50 km higher than the Te enhancement peak. Such electron density enhancements (artificial ducts) cannot be explained by temperature-dependent reaction rates. They can be attributed to HF-induced ionization production by accelerated electrons. The possible mechanisms for plasma modifications induced by powerful X-mode HF radio waves were discussed.

Blagoveshchenskaya, N. F.; Borisova, T. D.; Yeoman, T. K.; Rietveld, M. T.; Hggstrm, I.; Ivanova, I. M.

2013-12-01

307

Stimulated Electromagnetic Emission Indicator of Glow Plasma Discharges from Ionospheric HF Wave Transmissions with HAARP  

NASA Astrophysics Data System (ADS)

High power radio waves resonantly interact with to accelerate electrons for production of artificial aurora and plasma clouds. These plasma clouds are formed when the HF frequency is tuned near a harmonic of the electron cyclotron frequency. At a narrow band resonance, large electrostatic fields are produced below the F-layer and the neutral atmosphere breaks down with a glow plasma discharge. The conditions for this resonance are given by matching the pump wave frequency and wave-number with the sum of daughter frequencies and wave-numbers for several plasma modes. The most likely plasma mode that accelerates the electrons is the electron Bernstein wave in conjunction with an ion acoustic wave. Both upper hybrid and whistler mode waves are also possible sources of electron acceleration. To determine the plasma process for electron acceleration, stimulated electromagnetic emissions are measured using ground receivers in a north-south chain from the HAARP site. Recent observations have shown that broad band spectral lines downshifted from the HF pump frequency are observed when artificial plasma clouds are formed. For HF transmissions are the 2nd, 3rd, and 4th gyro harmonic, the downshifted indicators are found 500 Hz, 20 kHz, and 140 kHz, respectively, from the pump frequency. This Indicator Mode (IM) anticipates that a plasma layer will be formed before it is recorded with an ionosonde or optical imager.

Bernhardt, P. A.; Scales, W.; Briczinski, S. J.; Fu, H.; Mahmoudian, A.; Samimi, A.

2012-12-01

308

Observations of the response time of high-latitude ionospheric convection to variations in the interplanetary magnetic field using EISCAT and IMP8 data  

Microsoft Academic Search

We have combined 300 h of tristatic mea- surements of the field-perpendicular F region iono- spheric flow measured overhead at Troms by the EISCAT UHF radar, with simultaneous IMP-8 mea- surements of the solar wind and interplanetary magnetic field (IMF) upstream of the Earth's magnetosphere, in order to examine the response time of the ionospheric flow to changes in the

H. Khan; S. W. H. Cowley

1999-01-01

309

a Study of the Ionospheric Signature of Ion Supply from the Ionosphere to the Magnetosphere.  

NASA Astrophysics Data System (ADS)

Recent studies have demonstrated the importance of the ionosphere as a source of magnetospheric plasma; in particular, the observations of upwelling ions (UWI) by the DE-1 Retarding Ion Mass Spectrometer have illustrated the significance of low-energy ion supply to the magnetosphere. The composition of the UWI implies an ionospheric source, and the Dynamics Explorer dual satellite mission provides an opportunity to search for the ionospheric signature of UWI. Magnetometer data from both satellites is used to determine magnetic conjunctions of the satellites; these conjunctions are searched for correlated observations of UWI and upward flowing thermal ion (UFI) events. Four cases of correlated observations are presented as proof of that the UFI are indeed the ionospheric signature of UWI; it is found from these examples that the events are associated with intense field-aligned currents at both satellites and with anti-sunward convection, enhanced fluxes of low-energy precipitating electrons from the boundary plasma sheet, and upward thermal ion fluxes in excess of 10^9 cm^{-2 } s_{-1} at DE-2. Analysis of the Retarding Potential Analyzer data indicate that UFI events are characterized by the largest ion temperatures observed in the high-latitude ionosphere and by a composition dominated by O^+ and molecular ions. One UFI event was encountered in three consecutive passes by DE-2 during a three-hour period; the region sampled supplied in excess of 10^ {28} ions to altitudes above about 900 km during this period. These fluxes are in excess of the ionospheric sources required for UWI and charge exchange, so not all of the ions observed in an UFI are given escape energy but instead must comprise a downward return flow in the polar cap. While UWI are primarily a dayside phenomena, UFI are found in all local time sectors sampled by DE-2. A morphological study of thermal ion vertical drifts above an invariant latitude of 50^circ reveals a separation of vertical drifts into distinct regions according to the drift direction. The separation is clearly present for drift speeds in excess of 100 ms^ {-1}; the downward drifts are found in the polar cap while the upward drifts are found in a region that corresponds to the statistical location of the auroral oval and the field-aligned current systems. The occurrence probabilities of drifts above 100ms^{ -1} at all local times increase with altitude and magnetic activity; the occurrence probabilities on the dayside are generally greater than the corresponding values on the nightside. The results of this study are in qualitative agreement with the results of outflow studies using DE-1 instrumentation and with computer simulations of ion injection into the magnetosphere. The results of this work demonstrate that the ionosphere is an adequate source of the ion outflows observed in the magnetosphere, and that a three-dimensional plasma convection pattern is essential to a description of high-latitude ionospheric plasma transport.

Loranc, Mark Andre Peter

310

On the expansion of ionospheric plasma into the near-wake of the Space Shuttle Orbiter  

NASA Technical Reports Server (NTRS)

During the Spacelab 2 mission, while the Plasma Diagnostics Package was attached to the Remote Manipulator System, differential ion vector measurements were obtained in the near wake at a distance of 4-5 Shuttle radii. The Orbiter's wake was found to fill in at a much faster rate than can be explained by simple thermal motion. The measurements strongly suggest that filling of the Orbiter's wake is produced by the process of 'collisionless plasma expansion into a vacuum' and that, for oblique angles of the magnetic field and velocity vectors, the near wake plasma depletion a few radii downstream is not sensitive to the body scale size.

Stone, N. H.; Wright, K. H., Jr.; Samir, U.; Hwang, K. S.

1988-01-01

311

Macroscopic time and altitude distribution of plasma turbulence induced in ionospheric modification experiments  

SciTech Connect

This is the final report of a three-year Laboratory-Directed Research and Development (LDRD) project at the Los Alamos National Laboratory (LANL). This research concentrated on the time dependence of the heater, induced-turbulence, and electron-density profiles excited in the ionosphere by a powerful radio-frequency heater wave. The macroscopic density is driven by the ponderomotive pressure and the density self-consistently determines the heater propagation. For typical parameters of the current Arecibo heater, a dramatic quasi-periodic behavior was found. For about 50 ms after turn-on of the heater wave, the turbulence is concentrated at the first standing-wave maximum of the heater near reflection altitude. From 50--100 ms the standing-wave pattern drops by about 1--2 km in altitude and the quasi-periodicity reappears at the higher altitudes with a period of roughly 50 ms. This behavior is due to the half-wavelength density depletion grating that is set up by the ponderomotive pressure at the maxima of the heater standing-wave pattern. Once the grating is established the heater can no longer propagate to higher altitudes. The grating is then unsupported by the heater at these altitudes and decays, allowing the heater to propagate again and initiate another cycle. For stronger heater powers, corresponding to the Arecibo upgrade and the HAARP heater now under construction, the effects are much more dramatic.

Rose, H.; Dubois, D.; Russell, D. [Lodestar Research Corp., Boulder, CO (United States); Hanssen, A. [Univ. of Tromsoe (Norway)

1996-03-01

312

Direct measurements of ion drift velocity in the upper ionosphere during a magnetic storm. Part 1: Experiment description and some results of measurements during magnetically quiet time  

Microsoft Academic Search

In October-November 1967, asymmetry of the free-stream flow of ambient ionospheric plasma around a satellite caused mainly by the plasma drift or convection under action of the dc electric field was measured onboard the Cosmos-184 Satellite. Geometry and reduction techniques for these measurements from a satellite oriented along the velocity vector were considered. The deviations of the satellite orientation relative

Y. I. Galperin; V. N. Ponomarev; A. G. Zosimova

1973-01-01

313

Adiabatic Betatron deceleration of ionospheric charged particles: a new explanation for (i) the rapid outflow of ionospheric O ions, and for (ii) the increase of plasma mass density observed in magnetospheric flux tubes during main phases of geomagnetic s  

NASA Astrophysics Data System (ADS)

Using European arrays of magnetometers and the cross-phase analysis to determine magnetic field line resonance frequencies, it has been found by Kale et al. (2009) that the plasma mass density within plasmaspheric flux tubes increased rapidly after the SSC of the Hallowe'en 2003 geomagnetic storms. These observations tend to confirm other independent experimental results, suggesting that heavy ion up-flow from the ionosphere is responsible for the observed plasma density increases during main phases of geomagnetic storms. The aim of our contribution is to point out that, during main phases, reversible Betatron effect induced by the increase of the southward Dst-magnetic field component (|? Bz|), diminishes slightly the perpendicular kinetic energy (W?) of charged particles spiraling along field lines. Furthermore, due to the conservation of the first adiabatic invariant (? = Wm/ Bm) the mirror points of all ionospheric ions and electrons are lifted up to higher altitudes i.e. where the mirror point magnetic field (Bm) is slightly smaller. Note that the change of the mirror point altitude is given by: ? hm = -1/3 (RE + hm) ? Bm / Bm. It is independent of the ion species and it does not depend of their kinetic energy. The change of kinetic energy is determined by: ? Wm = Wm ? Bm / Bm. Both of these equations have been verified numerically by Lemaire et al. (2005; doi: 10.1016/S0273-1177(03)00099-1) using trajectory calculations in a simple time-dependant B-field model: i.e. the Earth's magnetic dipole, plus an increasing southward B-field component: i.e. the Dst magnetic field whose intensity becomes more and more negative during the main phase of magnetic storms. They showed that a variation of Bz (or Dst) by more than - 50 nT significantly increases the mirror point altitudes by more than 100 km which is about equal to scale height of the plasma density in the topside ionosphere where particles are almost collisionless (see Fig. 2 in Lemaire et al., 2005). From these theoretical results we infer that all ionospheric electrons and ions species (including the O+ ions) experience an outward flow along geomagnetic field lines whose angle of dip is not too large. Since above 500 km altitude the various ions densities decrease almost exponentially with altitude with characteristic scale heights (Hions) of the order of 100 km or less, the main phase uplift of all mirror points increases the local mass density all along these field lines. This changes the plasmaspheric concentrations of the O+ ions as well as of others heavy ions in the topside ionosphere and plasmasphere. We will outline experimental tests to check this new hypothesis and physical mechanism to enhance the plasma mass density during the main phases of geomagnetic storms. A subsequent decrease of the plasma ion mass density is expected following the geomagnetic storm event, due to inverse Betatron effect during the recovery phase, and due to the effect of gravity pulling the heavier ions back to lower altitudes.

Lemaire, Joseph; Pierrard, Viviane; Darrouzet, Fabien

2013-04-01

314

Solar zenith angle dependence of the plasma density and temperatures in the polar ionosphere and magnetosphere during geomagnetically quiet periods at solar maximum  

NASA Astrophysics Data System (ADS)

The electron density in the polar region is one of the most important parameters in under-standing the acceleration mechanisms of outflowing ions and plasma supply from the ionosphere toward the magnetosphere. However, the lack of observations above the polar ionosphere, es-pecially in an altitude range of 1000-4000 km, has made it difficult to clarify how strongly the solar radiation influences the electron density in the polar magnetosphere and ion accel-eration between the polar ionosphere and magnetosphere. In order to quantitatively evaluate the contribution of solar radiation to the electron density in the polar topside ionosphere and magnetosphere, we have investigated the solar zenith angle (SZA) dependence of the electron density profile in the polar cap during geomagnetically quiet periods. The electron density data used in the present study are obtained from 63 months of plasma wave observations by the Akebono satellite in an altitude range of 500-10,500 km, where observations have been limited, at solar maximum (monthly-averaged F10.7 larger than 170). Electron density profiles at low altitudes are well fitted by quasi-hydrostatic equilibrium functions, while those at higher altitudes are well described by power law functions. In the quasi-hydrostatic equilibrium func-tions, we used a constant temperature, and altitude dependence of the gravitational force and magnetic field strength are taken into account. A clear transition of the density profile is identified at about 2000 km altitude above an SZA of about 110 degrees. The largest variation in the fitted electron density with SZA is identified at 2100 km altitude, where the electron density varies by a factor of 88 from 1.25*104 cm-3 at an SZA of 50 degrees to 1.43*102 cm-3 at an SZA of 130 degrees in the polar cap. Above 5800 km altitude, the variation in the fitted electron density is limited within a factor of 20. The electron density and scale height decrease drastically with increasing SZA in an SZA range of 90-120 degrees. The sum of the ion and electron temperatures estimated from the scale height at an SZA of 120 degrees (3600 K) is less than half of that at an SZA of 90 degrees (8200 K). Furthermore, in order to compare the change in the ionospheric plasma temperature with that obtained by the Akebono satellite, we have investigated the SZA dependence of the electron and ion temperatures in the topside ionosphere using 19 months of data derived from EISCAT Svalbard Radar (ESR), located at an invariant latitude of 75.2 degrees, in an altitude range of 300-1100 km during geomagnetically quiet periods at solar maximum. The electron (ion) temperature above about 300 (600) km altitude decreases most drastically with increasing SZA in an SZA range of 80-110 degrees, which is near the terminator in the ionosphere. Although the SZA range of the drastic temperature change was about 10 degrees lower than that derived by the Akebono data, the drastic decrease in the ionospheric temperatures strongly suggests the dominant role of heating and photo-ionization processes by solar radiation in determining the electron density up to about 2000 km in the polar cap during geomagnetically quiet peri-ods, while the ionospheric control of the electron density gradually diminishes with increasing altitude above about 2000 km altitude.

Kitamura, Naritoshi; Terada, Naoki; Ogawa, Yasunobu; Nishimura, Yukitoshi; Ono, Takayuki; Shinbori, Atsuki; Kumamoto, Atsushi

315

The SuperDARN Data System: An established, Internet Based, Data Access Tool for Ionospheric Physics  

NASA Astrophysics Data System (ADS)

The Super Dual Auroral Radar Network (SuperDARN) is an international network of High Frequency Radars that operate in the Northern and Southern Polar regions in the study of Ionospheric Plasma Convection. Through the SuperDARN web-site hosted at APL (http://superdarn.jhuapl.edu), the network has developed a set of sophisticated, Internet based, data access and analysis tools. The network has also successfully developed real-time data streaming from the Northern Hemisphere radar chain and acts as a space-weather monitor for Ionospheric Convection. Recent work has involved incorporating measurements from a variety of other instruments into the system. The techniques developed for the SuperDARN project can easily be extended to the wider Space Physics Community.

Barnes, R. J.; Greenwald, R. A.; Ruohoniemi, M.

2003-12-01

316

Investigation of methods for updating ionospheric scintillation models using topside in-situ plasma-density measurements. Rept. for 1 May 90-30 Apr 91  

SciTech Connect

Modern military communication, navigation, and surveillance systems depend on reliable, noise-free transionospheric radio-frequency channels. They can be severely impacted by small-scale electron-density irregularities in the ionosphere, which cause both phase and amplitude scintillation. Basic tools used in planning and mitigation schemes are climatological in nature and thus may greatly over- and under-estimate the effects of scintillation in a given scenario. This report summarizes the results of the first year of a three-year investigation into the methods for updating ionospheric scintillation models using observations of ionospheric plasma-density irregularities measured by DMSP Scintillation Meter (SM) sensor. Results are reported from the analysis of data from a campaign conducted in January 1990 near Tromso, Norway, in which near coincident in-situ plasma-density and transionospheric scintillation measurements were made. Estimates for the level of intensity and phase scintillation on a transionospheric UHF radio link in the early-evening auroral zone were calculated from DMSP SM data and compared to the levels actually observed.

Secan, J.A.

1991-05-15

317

Observations of Substorms from the Auroral Ionosphere to the Distant Plasma Sheet  

NASA Technical Reports Server (NTRS)

We have been studying how substorms work by examining the global polar Ultraviolet Imager (UVI) images in correlation with observations from the ground, interplanetary space and the geomagnetic tail between 10-20 earth radii. One of the objectives of our study is to better understand the connection among many complex phenomena going on close to Earth and those in the distant plasma sheet. We have studied, for example, how the aurora[ and polar cap boundaries at different local times behave in relation to variations observed in the solar wind and plasma sheet during substorms. Preliminary results indicate that the polar cap and auroral oval boundaries expand and contract in a complicated but systematic way. These variations are correlated to solar wind parameters, and thinning and recovery phenomena in the plasma sheet. These results will be presented and interpreted in terms of directly driven and/or unloading substorm processes.

Parks, G.; Brittnacher, M.; Chen, L.; Chua, D.; Elsen, R.; Fillingim, M.; McCarthy, M.; Germany, G.; Spann, J.

1998-01-01

318

Characterizing ISS Charging Environments with On-Board Ionospheric Plasma Measurements  

NASA Technical Reports Server (NTRS)

Charging of the International Space Station (ISS) is dominated by interactions of the biased United States (US) 160 volt solar arrays with the relatively high density, low temperature plasma environment in low Earth orbit. Conducting surfaces on the vehicle structure charge negative relative to the ambient plasma environment because ISS structure is grounded to the negative end of the US solar arrays. Transient charging peaks reaching potentials of some tens of volts negative controlled by photovoltaic array current collection typically occur at orbital sunrise and sunset as well as near orbital noon. In addition, surface potentials across the vehicle structure vary due to an induced v x B (dot) L voltage generated by the high speed motion of the conducting structure across the Earth's magnetic field. Induced voltages in low Earth orbit are typically only approx.0.4 volts/meter but the approx.100 meter scale dimensions of the ISS yield maximum induced potential variations ofapprox.40 volts across the vehicle. Induced voltages are variable due to the orientation of the vehicle structure and orbital velocity vector with respect to the orientation of the Earth's magnetic field along the ISS orbit. In order to address the need to better understand the ISS spacecraft potential and plasma environments, NASA funded development and construction of the Floating Potential Measurement Unit (FPMU) which was deployed on an ISS starboard truss arm in August 2006. The suite of FPMU instruments includes two Langmuir probes, a plasma impedance probe, and a potential probe for use in in-situ monitoring of electron temperatures and densities and the vehicle potential relative to the plasma environment. This presentation will describe the use of the FPMU to better characterize interactions of the ISS with the space environment, changes in ISS charging as the vehicle configuration is modified during ISS construction, and contributions of FPMU vehicle potential and plasma environment measurements to investigations of on-orbit anomalies in ISS systems.

Minow, Jospeh I.; Craven, Paul D.; Coffey, Victoria N.; Schneider, Todd A.; Vaughn, Jason A.; Wright Jr, Kenneth; Parker, Paul D.; Mikatarian, Ronald R.; Kramer, Leonard; Hartman, William A.; Alred, John W.; Koontz, Steven L.

2008-01-01

319

A study of the cleft region using synoptic ionospheric plasma data obtained by the polar orbiting satellites Aeros-B and Isis-2  

NASA Technical Reports Server (NTRS)

The concentrations of O(+) and NO(+) in the dayside high-latitude cleft region of the ionosphere are investigated based on synoptic particle and plasma measurements obtained by the polar orbiting Aeros-B and Isis-2 satellites. At a time when the orbital planes of the satellites are almost at right angles to each other, three maxima in ion temperature are observed, with two of them accompanied by an increased electron temperature and electron density irregularities, and the density of the molecular ions NO(+) and O2(+) is found to increase at the expense of O(+) density. Results are discussed in terms of a theory relating perpendicular electric fields to oxygen atom reaction rates. Systematic analysis of the Aeros data base reveals 14 additional instances of O(+) to NO(+) conversion, with a large variety of forms and structures reflecting the complex structure and dynamics of the high-latitude dayside ionosphere.

Kist, R.; Klumpar, D.

1980-01-01

320

Electron content of the ionosphere and the plasma sphere on the basis of ATS-6-Data, NNSS-data, and ionograms. [Navy Navigation Satellite System  

NASA Technical Reports Server (NTRS)

The reported investigation takes into account data obtained with the aid of the geostationary satellite ATS-6, the satellites of the U.S. navy navigation system (NNSS) at an altitude between 900 and 1200 km, and the satellites ISIS 1 and ISIS 2. The altitude range between ground and ATS-6 is divided into two regions, including the 'ionosphere', involving the region with an upper limit of 2000 km, and the 'plasma sphere', involving the region above an altitude of 2000 km. Data concerning the electron content obtained from different sources are compared, taking into account discrepancies between ionogram-derived values and values computed on the basis of satellite measurements. Attention is also given to the vertical electron content of the ionosphere on the basis of a combination of data obtained with the aid of the ATS-6 and the NNSS.

Leitinger, R.; Hartmann, G. K.; Davies, K.

1976-01-01

321

Mid-latitude ionospheric plasma temperature climatology and model based on Saint Santin incoherent scatter radar data from 1966-1987  

NASA Astrophysics Data System (ADS)

Zhang and Holt (2003, Ionospheric plasma temperatures during 1976-2001 over Millstone Hill, Adv. Space Res.) have reported the ionospheric plasma temperature variation based on incoherent scatter radar (ISR) observations between 1976 and 2001 at Millstone Hill, a typical sub-auroral mid-latitude site in North America. The French Saint Santin ISR, with a geographic latitude slightly higher but an apex latitude 7 degress lower than Millstone, collected bistatic and quadristatic measurements for 2 solar cycles beginning in September 1965.A database of these data from 1966 and 1987 has been used in this study in order to establish the mid-latitude ionospheric climatology, in particular that of the upper atmosphere thermal status, as well as empirical models for space weather applications. This paper presents, in comparison with the Millstone results, the variation of ion and electron temperature (Ti and Te) with solar activity, season, time of the day, and altitude. It is found that the F2 region Te at St Santin is not as high as in Millstone between May and September, when electron density (Ne) is relatively higher. The midday Te increases below 300 km with F107, as at Millstone Hill. However, above 300 km it tends to decrease with F107 at St Santin and increases between May and September at Millstone Hill. Ti between 250-350 km peaks not in summer but around May. Based on this database, Saint Saintin ionospheric models for Ne, Te, and Ti have also been created using a bin-fit technique similar to that used for the Millstone Hill models. Comparisions with corresponding IRI predications indicate good agreement in Ti at high solar activity, and IRI tends to give Te above the F2 peak higher than both the Saint Santin and Millstone Hill models.

Zhang, S. R.; Holt, J. M.; Zalucha, A. M.; Amory-Mazaudier, C.

322

Space weather effects on low latitude geomagnetic field and ionospheric plasma response  

Microsoft Academic Search

Space weather disturbances caused by enhanced stream of solar plasma during solar flares and Coronal Mass ejections (CMEs) are known to disrupt communications, endanger satellite payloads and introduce severe errors in a variety of tracking and positioning systems. The phenomena known as geomagnetic storms are the most obvious features of space weather disturbances. Magnetic storms are fundamental disturbances in the

B. Veenadhari; S. Alex

2006-01-01

323

Electron density and electron neutral collision frequency in the ionosphere using plasma impedance probe measurements  

Microsoft Academic Search

Swept Impedance Probe measurements in a sporadic E layer observed during the Sudden Atomic Layer (SAL) sounding rocket mission are analyzed to obtain absolute electron densities and electron neutral collision frequencies accurately. Three sets of upleg and downleg impedance data are selected for the analysis. Initial estimates of the plasma parameters are obtained through a least mean square fit of

E. Spencer; S. Patra; T. Andriyas; C. Swenson; J. Ward; A. Barjatya

2008-01-01

324

Ionospheric beam-plasma interactions: production of quasi-mode in the ion density  

NASA Astrophysics Data System (ADS)

New observations by the Poker Flat Incoherent Scatter Radar (PFISR) of the recently discovered coherent echoes [Akbari et al., 2012, 2013] suggest that the underlying beam-plasma instability occurs in a different parameter regime. These observations show simultaneous enhancements of the ion-acoustic (IA) spectrum, as well as the up- and down-shifted plasma-line spectra; the filled-in nature of these IA spectra is the subject of this study. High time-resolution measurements reveal that the IA spectrum consists of discrete peaks at frequencies less than the expected frequency of the ion-acoustic resonant mode. The superposition of these peaks will appear as a filled-in spectrum when the spectrum is averaged over many radar pulses. These peaks are the signature of non-resonant, low frequency wave modes, or quasi-modes of the plasma with subsonic speeds. Such quasi-modes can be produced by different regimes of the beam-plasma instability, as described by the Zakharov system of equations, namely the supersonic and subsonic modulational instabilities and the modified parametric decay instability. The subsonic modulational instability appears as a natural and well suited candidate due to its subsonic nature and the wavenumber range of the resulting turbulence. The drive responsible for the instability is generally assumed to be soft precipitations, i.e. electron beam of energy less than 500 eV. Such electron beam directly interacts with large-scale Langmuir waves, i.e. with small wavenumbers due to the matching resonance condition. According to Bragg scattering theory, IS radar only senses electrostatic waves at a single wavenumber. Therefore, observation of the turbulence by PFISR requires also a mechanism capable of transferring the energy to waves with larger wavenumber visible by the radar. Modulational instabilities and cavitating Langmuir turbulence are examples of such mechanisms. The results presented here are of great importance in the fundamental context of beam-plasma interactions.

Akbari, H.; Semeter, J. L.; Guio, P.

2013-12-01

325

Effect of zonal E B plasma drift on electron density in the low-latitude ionospheric F region at a solar activity maximum near vernal equinox  

NASA Astrophysics Data System (ADS)

The variations in the density of the ionospheric F2 layer maximum ( NmF2) under the action of the zonal plasma drift perpendicularly to the magnetic ( B) and electric ( E) fields in the direction geomagnetic west-geomagnetic east have been studied using the three-dimensional nonstationary theoretical model of electron and ion densities ( N e and N i ) and temperatures ( T e and T i ) in the low-latitude and midlatitude ionospheric F region and plasmasphere. The method of numerical calculations of N e , N i , T e , and T i , including the advantages of the Lagrangian and Eulerian methods, is used in the model. A dipole approximation of the geomagnetic field ( B), taking into account the non-coincidence of the geographic and geomagnetic poles and differences between the positions of the Earths and geomagnetic dipole centers, is accepted in the calculations. The calculated NmF2 and altitudes of the F2 layer maximum ( hmF2) have been compared with these quantities measured at 16 low-latitude ionospheric sounding stations during the geomagnetically quiet period October 11-12, 1958. This comparison made it possible to correct the input model parameters: the NRLMSISE-00 model [O], the meridional component of the neutral wind velocity according to the HWW90 model, and the meridional component of the equatorial plasma drift due to the electric field specified by the empirical model. It has been indicated that the effect of the zonal E B plasma drift on NmF2 can be neglected under daytime conditions and changes in NmF2 and hmF2 under the action of this drift are insignificant under nighttime conditions north of 25 and south of -26 geomagnetic latitude. The effect of the zonal E B plasma drift on NmF2 and hmF2 is most substantial in the nightside ionosphere approximately from -20 to 20 geomagnetic latitude, and the neglect of this drift results in an up to 2.4-fold underestimation of NmF2. The found dependence of the effect of the zonal E B plasma drift on NmF2 and hmF2 on geomagnetic latitude is related to the longitudinal asymmetry of B, asymmetry of the neutral wind about the geomagnetic equator, and changes in the meridional E B plasma drift at a change in geomagnetic longitude.

Pavlov, A. V.; Pavlova, N. M.

2007-10-01

326

On the approach to forecasting polar ionospheric conditions  

NASA Technical Reports Server (NTRS)

The major properties of polar ionospheric main anomalous events are summarized. The monitoring of large scale features of the ionization distribution that are the projections of large scale structural characteristics of magnetospheric plasma on the upper ionosphere is suggested as a basic principle of polar ionospheric condition forecasting. It is concluded that the processes of the magnetosphere/ionosphere interaction appear to play a predominant role in the creation of the polar ionosphere.

Besprozvannaya, A. S.; Shirochkov, A. V.; Shchuka, T. I.

1979-01-01

327

Radar soundings of the ionosphere of Mars.  

PubMed

We report the first radar soundings of the ionosphere of Mars with the MARSIS (Mars Advanced Radar for Subsurface and Ionosphere Sounding) instrument on board the orbiting Mars Express spacecraft. Several types of ionospheric echoes are observed, ranging from vertical echoes caused by specular reflection from the horizontally stratified ionosphere to a wide variety of oblique and diffuse echoes. The oblique echoes are believed to arise mainly from ionospheric structures associated with the complex crustal magnetic fields of Mars. Echoes at the electron plasma frequency and the cyclotron period also provide measurements of the local electron density and magnetic field strength. PMID:16319123

Gurnett, D A; Kirchner, D L; Huff, R L; Morgan, D D; Persoon, A M; Averkamp, T F; Duru, F; Nielsen, E; Safaeinili, A; Plaut, J J; Picardi, G

2005-12-23

328

Electron thermal effect on linear and nonlinear coupled Shukla-Varma and convective cell modes in dust-contaminated magnetoplasma  

SciTech Connect

Linear and nonlinear properties of coupled Shukla-Varma (SV) and convective cell modes in the presence of electron thermal effects are studied in a nonuniform magnetoplasma composed of electrons, ions, and extremely massive and negatively charged immobile dust grains. In the linear case, the modified dispersion relation is given and, in the nonlinear case, stationary solutions of the nonlinear equations that govern the dynamics of coupled SV and convective cell modes are obtained. It is found that electrostatic dipolar and vortex street type solutions can appear in such a plasma. The relevance of the present investigation with regard to the Earth's mesosphere as well as in ionospheric plasmas is also pointed out.

Masood, W. [TPPD, PINSTECH, P. O. Nilore, Islamabad 44000, Pakistan and National Center for Physics (NCP), Islamabad 45320 (Pakistan); Mirza, Arshad M. [Department of Physics, Theoretical Plasma Physics Group, Quaid-i-Azam University, Islamabad 45320 (Pakistan)

2010-11-15

329

Electron density and electron neutral collision frequency in the ionosphere using plasma impedance probe measurements  

NASA Astrophysics Data System (ADS)

Swept Impedance Probe measurements in a sporadic E layer observed during the Sudden Atomic Layer (SAL) sounding rocket mission are analyzed to obtain absolute electron densities and electron neutral collision frequencies accurately. Three sets of upleg and downleg impedance data are selected for the analysis. Initial estimates of the plasma parameters are obtained through a least mean square fit of the measured impedance data against the analytical impedance formula ZB(f) of Balmain (1969). These initial parameters are used as a starting point to drive a finite difference computational model of an antenna immersed in a plasma called PF-FDTD. The parameters are then tuned until a close fit is obtained between the measured impedance data and the numerical impedance data calculated by the PF-FDTD simulation. The electron densities obtained from the simulation were close to those obtained from the IRI 2001 model. The electron neutral collision frequencies obtained from the more accurate PF-FDTD simulation were up to 20% lower than the values predicted by Balmain's formula. The obtained collision frequencies are also lower than the quiet time values predicted by Schunk and Nagy (2000) when used in conjunction with neutral densities and electron temperature from the Mass Spectrometer Incoherent Scatter Radar Extended-90 model.

Spencer, E.; Patra, S.; Andriyas, T.; Swenson, C.; Ward, J.; Barjatya, A.

2008-09-01

330

Coordinated ESR-Reimei observations of the cusp ionosphere  

NASA Astrophysics Data System (ADS)

The polar cusp, being the region where the magnetosheath plasma has a direct access to the magnetosphere and the polar ionosphere, is an interesting region to study, not only to understand how the coupling between the solar wind and the magnetosphere works, but also because at its footprint, interesting ionospheric phenomena occur: complex local electrodynamics, particle heating and outflow, etc. To study those phenomena, we have selected a few Reimei satellite overflights of the EISCAT Svalbard Radar (ESR) in the cusp region. These conjunctions allow us to directly compare precipitating magnetosheath particles and their effects on the dayside polar ionosphere. We present preliminary results of two of those conjunctions. The first case is characterized by an unusually strong zonal convection speed measured by the ESR at 08:25 UT on September 28, 2007. This strong plasma flow is believed to increase the ion temperature through frictional heating with the neutrals and drive ion outflow. However, we do not allays see very high ion temperature in our case, suggesting that Joule heating is not the unique source of ion outflow. In the second case around 08:11 UT on October 18, 2007, the conjunction occurs when the ESR is at the equatorward boundary of the cusp. Yet, the soft-electron precipitation is rather weak and as well as the electron temperature measured by the ESR. An interesting feature is that the particle sensor onboard Reimei observes a discontinuous cusp that we explain by the changes in the IMF orientation (given by Themis).

Pitout, F.; Ogawa, Y.; Ebihara, Y.; Asamura, K.; Hirahara, M.; Seki, K.

2010-12-01

331

A Dynamic Coupled Magnetosphere-Ionosphere-Ring Current Model  

NASA Astrophysics Data System (ADS)

In this thesis we describe a coupled model of Earth's magnetosphere that consists of the Lyon-Fedder-Mobarry (LFM) global magnetohydrodynamics (MHD) simulation, the MIX ionosphere solver and the Rice Convection Model (RCM). We report some results of the coupled model using idealized inputs and model parameters. The algorithmic and physical components of the model are described, including the transfer of magnetic field information and plasma boundary conditions to the RCM and the return of ring current plasma properties to the LFM. Crucial aspects of the coupling include the restriction of RCM to regions where field-line averaged plasma-beta =1, the use of a plasmasphere model, and the MIX ionosphere model. Compared to stand-alone MHD, the coupled model produces a substantial increase in ring current pressure and reduction of the magnetic field near the Earth. In the ionosphere, stronger region-1 and region-2 Birkeland currents are seen in the coupled model but with no significant change in the cross polar cap potential drop, while the region-2 currents shielded the low-latitude convection potential. In addition, oscillations in the magnetic field are produced at geosynchronous orbit with the coupled code. The diagnostics of entropy and mass content indicate that these oscillations are associated with low-entropy flow channels moving in from the tail and may be related to bursty bulk flows and bubbles seen in observations. As with most complex numerical models, there is the ongoing challenge of untangling numerical artifacts and physics, and we find that while there is still much room for improvement, the results presented here are encouraging. Finally, we introduce several new methods for magnetospheric visualization and analysis, including a fluid-spatial volume for RCM and a field-aligned analysis mesh for the LFM. The latter allows us to construct novel visualizations of flux tubes, drift surfaces, topological boundaries, and bursty-bulk flows.

Pembroke, Asher

332

Cross-B convection of artificially created, negative-ion clouds and plasma depressions - Low-speed flow  

NASA Technical Reports Server (NTRS)

A negative-ion, positive-ion plasma produced by the release of an electron attachment chemical into the F region becomes electrically polarized by collisions with neutrals moving across magnetic field lines. The resulting electric field causes E x B drift of the two ion species and the residual electrons. The cross-field flow of the modified ionosphere is computed using a two-dimensional numerical simulation which includes electron attachment and mutual neutralization chemistry, self-consistent electric fields, and three-species plasma transport. The velocity of the plasma is initially in the direction of the neutral wind because the negative-ion cloud is a Pedersen conductivity enhancement. As the positive and negative ions react, the Pedersen conductivity becomes depressed below the ambient value and the velocity of the plasma reverses direction. A plasma hole remains after the positive and negative ions have mutually neutralized. The E x B gradient drift instability produces irregularities on the upwind edge of the hole.

Bernhardt, Paul A.

1988-01-01

333

Cold plasma heating in the plasma sheet boundary layer - Theory and simulations  

NASA Technical Reports Server (NTRS)

Satellite observations in recent years have confirmed that the plasma sheet boundary layer is a permanent feature of the earth's magnetotail located between the lobe and central plasma sheet during both quiet and active magnetic periods. Distinct features of the boundary layer include field aligned ion beams and intense electrostatic emissions known as broadband electrostatic noise. Since the plasma sheet boundary layer is a spatial feature of the magnetotail, within it will occur thermal mixing of the resident warm boundary layer plasma with inflowing (convecting) cold ionospheric plasma. A theoretical study involving linear theory and nonlinear numerical particle simulations is presented which examines ion beam instabilities in the presence of a thermally mixed hot and cold background plasma. It is found that the free energy in the ion beams can heat the cool ionospheric plasma to ambient plasma sheet boundary layer temperatures via broadband electrostatic noise. These results, along with recent observational reports that ionospheric outflow can account for measured plasma sheet densities, suggest that the ionospheric role in plasma sheet dynamics and content may be as large as the solar wind.

Schriver, David; Ashour-Abdalla, Maha

1990-01-01

334

Waves generated in the vicinity of an argon plasma gun in the ionosphere  

NASA Technical Reports Server (NTRS)

Wave and particle observations were made in the close vicinity of an argon plasma gun carned to over 600 km altitude on a sounding rocket. The gun was carned on a subpayload, separated from the main payload early in the flight. Twelve-second argon ion ejections were energized alternately with a peak energy of 100 or 200 eV. They produced waves, with multiple harmonics, in the range of ion cyclotron waves, 10 to 1000 Hz at rocket altitudes. Many of these waves could not be identified as corresponding to the cyclotron frequencies of any of the ions, argon or ambient, known to be present. In addition, the wave frequencies were observed to rise and fall and to change abruptly during a 12-s gun operation. The wave amplitudes, near a few hundred Hertz, were of the order of O. 1 V/m. Some of the waves may be ion-ion hybrid waves. Changes in ion populations were observed at the main payload and at the subpayload during gun operations. A gun-related, field-aligned, electron population also appeared.

Cahill, L. J., Jr.; Arnoldy, R. L.; Lysak, R. L.; Peria, W.; Lynch, K. A.

1993-01-01

335

The response of the high-latitude dayside ionosphere to an abrupt northward transition in the IMF  

NASA Technical Reports Server (NTRS)

We examine the response of the high-latitude ionosphere in the prenoon sector to a northward turning of the IMF. The event was observed in the 11-13 UT interval on June 1, 1987, in the course of a multiday SUNDIAL campaign. The transition in the IMF was observed by the IMP-8 satellite which was located upstream of the earth at a distance of 36 Re. The ionospheric response in the 70-80 deg invariant latitude interval was monitored by two radars. The preexisting plasma convection observed by the radars exhibited large velocities (500-1000 m/s) and stable longterm trends, consistent with the inertial rotation of the convection pattern expected of the conditions then prevailing, B(z) less than 0, B(y) greater than 0. The plasma flow rapidly abated in response to the IMF transition. The electron density measurements made by radar in the meridional plane showed that the ionosphere had been rich in structure with the active deposition of ionization by particle precipitation. Subsequently it resembled an inactive, unstructured mid-latitude configuration. There was a dramatic decrease in the amount of backscatter observed by the HF radar. We analyze the times of transition in the various data sets and show that the ionosphere began to show the effects of the IMF transition about 2 min after its probable arrival at the magnetopause boundary.

Ruohoniemi, J. M.; Greenwald, R. A.; De La Beaujardiere, O.; Lester, M.

1993-01-01

336

The response of the high-latitude dayside ionosphere to an abrupt northward transition in the IMF  

NASA Astrophysics Data System (ADS)

We examine the response of the high-latitude ionosphere in the prenoon sector to a northward turning of the IMF. The event was observed in the 11-13 UT interval on June 1, 1987, in the course of a multiday SUNDIAL campaign. The transition in the IMF was observed by the IMP-8 satellite which was located upstream of the earth at a distance of 36 Re. The ionospheric response in the 70-80 deg invariant latitude interval was monitored by two radars. The preexisting plasma convection observed by the radars exhibited large velocities (500-1000 m/s) and stable longterm trends, consistent with the inertial rotation of the convection pattern expected of the conditions then prevailing, B(z) less than 0, B(y) greater than 0. The plasma flow rapidly abated in response to the IMF transition. The electron density measurements made by radar in the meridional plane showed that the ionosphere had been rich in structure with the active deposition of ionization by particle precipitation. Subsequently it resembled an inactive, unstructured mid-latitude configuration. There was a dramatic decrease in the amount of backscatter observed by the HF radar. We analyze the times of transition in the various data sets and show that the ionosphere began to show the effects of the IMF transition about 2 min after its probable arrival at the magnetopause boundary.

Ruohoniemi, J. M.; Greenwald, R. A.; de La Beaujardiere, O.; Lester, M.

1993-07-01

337

Observations of filamentary field-aligned current coupling between the magnetospheric boundary layer and the ionosphere  

NASA Technical Reports Server (NTRS)

A distinct class of dayside high-latitude magnetic pulsations can be identified from the spatial characteristics of the disturbance field. These pulsations exhibit traveling radial patterns such as would result from moving filaments of field-aligned current interacting with the ionosphere to produce cells of Hall current and vortexlike plasma flow. Time intervals containing a series of continuous multiple vortices are investigated here. The vortices occur on the boundary between sunward and antisunward ionospheric plasma convection. Low altitude DMSP satellite particle measurements indicate that the vortices are on magnetic field lines which map to the inner edge of the magnetospheric low latitude boundary layer. No repetitive solar wind disturbance (e.g., pressure variations) appears to be associated with the events, suggesting that the vortices are related to a local magnetospheric instability. No strong correlation between interplanetary field conditions and the detection of vortices is found.

Clauer, C. R.; Mchenry, M. A.; Friis-Christensen, E.

1990-01-01

338

Reverse convection  

SciTech Connect

A model of magnetospheric topology for periods when the interplanetary magnetic field (IMF) points northward indicates that reverse convection can readily occur when Earth's dipole or the IMF tilt toward or away from the Sun. In either case, all or part of one tail lobe drapes over the dayside, and the magnetopause merging voltage is applied directly to the ionosphere in that lobe only, to the center or nightside of the polar cap. The overdraped lobe forms layers both earthward and sunward of the magnetopause, similar to layers observed during periods of northward IMF. The model predicts two quasi-steady state patterns of reverse convection: (1) lobe cells in the polar cap of the overdraped lobe, generated by open-to-open flux transfer at the magnetopause and (2) merging cells in both polar caps, generated by closed-to-open flux transfer at the magnetopause and balanced open-to-closed transfer at an internal reconnection site, comparable to the tail merging site for southward IMF. The model also predicts transitional patterns of reverse convection for growing and shrinking polar caps in response to changes in dipole tilt and B[sub x] and in response to a sudden transition from southward to northward IMF. The model predicts theta aurora bar formation on the dawnside polar cap boundary when activation of the internal reconnection site ends polar cap growth. In this view the theta aurora becomes the northward IMF counterpart to substorms.

Crooker, N.U. (Univ. of California, Los Angeles (United States))

1992-12-01

339

Investigation of localized 2D convection mapping based on artificially generated Swarm ion drift data  

NASA Astrophysics Data System (ADS)

Ionospheric plasma flow is an indicator of the interconnection between the solar wind, interplanetary magnetic field (IMF), and Earths magnetosphere. Ionospheric convection has been mapped in the past using either a widespread data set for instantaneous convection mapping over a short time period or data from an instrument measuring convection in a spatially confined region over a long time period for the purpose of building a statistically averaged convection pattern. This study explores convection mapping using a spherical cap harmonic analysis (SCHA) technique within a localized spherical cap based on data that will be available from the Swarm three-satellite constellation. Convection is mapped in the vicinity of hypothetical Swarm satellite tracks where it is adequately constrained by data. By using statistical models to emulate Swarm measurements, we demonstrate that such mapping can be successful based on data from the Swarm A and Swarm B satellites. Convection is divided into well constrained and poorly constrained subsets to determine parameters characterizing goodness-of-fit based on known quantities. Using the subset of well constrained maps, it is determined that convection is best mapped for a spherical cap having an angular radius of ?c=10. The difference between the maximum mapped convection and the maximum velocity measured along the satellite track (?v) is introduced to evaluate goodness-of-fit. For the examples presented in this paper, we show that a threshold value of ?v=281 m/s successfully differentiates between well and poorly constrained maps 77.6% of the time. It is shown that convection can be represented over a larger region through the use of multiple spherical caps.

Fiori, R. A. D.; Boteler, D. H.; Koustov, A. V.; Knudsen, D.; Burchill, J. K.

2014-07-01

340

Comparison of Stimulated Electromagnetic Emissions from Long Time Langmuir and Upper Hybrid/Electron Bernstein Turbulence during Electromagnetic Pumping of the Ionospheric Plasma  

NASA Astrophysics Data System (ADS)

A powerful high frequency electromagnetic pump wave transmitted into the ionosphere from the ground excites plasma turbulence which causes electromagnetic radiation that can be detected on the ground. We report experimental results from using the EISCAT-Heating facility in Norway as the pump for the daytime ionospheric plasma, detection of the stimulated electromagnetic radiation, and probing of the Langmuir turbulence by the EISCAT-UHF and -VHF incoherent scatter radars. The long time scale frequency spectrum (several seconds integration time) of the radar scatter from near parallel to the geomagnetic field is compared to that of the stimulated electromagnetic emissions for different pump frequencies near the third electron gyro harmonic. It is found that the long time scale Langmuir turbulence which is strongly excited at the gyro harmonic as detected with the EISCAT-VHF radar does not cause significant electromagnetic radiation. This is contrary to the case of the upper hybrid/electron Bernstein turbulence excited at pump frequencies away from the gyro harmonic, which results in a rich spectrum of stimulated electromagnetic emissions. The experimental results appear to question our present understanding of the mechanisms for electromagnetic radiation from Langmuir turbulence.

Leyser, T. B.; Isham, B.; La Hoz, C.; Rietveld, M. T.; Hagfors, T.; Kofman, W.; Mishin, E.

2000-10-01

341

A method for determining the drift velocity of plasma depletions in the equatorial ionosphere using far-ultraviolet spacecraft observations: initial results  

NASA Astrophysics Data System (ADS)

The Far-Ultraviolet Imager (IMAGE-FUV) on-board the NASA IMAGE satellite has been used to observe plasma depletions in the nightside equatorial ionosphere. Observations from periods around spacecraft apogee, during which equatorial regions are visible for several hours, have allowed the velocity of these plasma depletions to be determined. A new method for determining the velocity of these depletions using an image analysis technique, Tracking Of Airglow Depletions (TOAD), has been developed. TOAD allows the objective identification and tracking of depletions. The automation of this process has also allowed for the tracking of a greater number of depletions than previously achieved without requiring any human input, which shows that TOAD is suitable for use with large data sets and for future routine monitoring of the ionosphere from space. Furthermore, this allows the drift velocities of each depletion to be determined as a function of magnetic latitude as well as local time. Previous ground-based airglow observations from a small number of locations have indicated that the drift velocities of depletions may vary rapidly with magnetic latitude. Here we shall present the first results from TOAD of this shear in drift velocities from our global sample of depletion drift velocities.

England, S. L.; Immel, T. J.; Park, S. H.; Frey, H. U.; Mende, S. B.

2007-12-01

342

Ionospheric research  

NASA Technical Reports Server (NTRS)

Data from research on ionospheric D, E, and F, regions are reported. Wave propagation, mass spectrometer measurements, and atmospheric reactions of HO2 with NO and NO2 and NH2 with NO and O2 are summarized.

1975-01-01

343

Ionospheric Research.  

National Technical Information Service (NTIS)

The report contains research directed toward the investigation of the lower ionosphere. Specific emphasis was placed on the design, conduction and analysis of rocket-borne A.C. conductivity probes and radio wave propagation experiments. These objectives h...

T. A. Seliga

1968-01-01

344

Ionosphere research  

NASA Technical Reports Server (NTRS)

A report is presented on on-going research projects in ionospheric studies. The topics discussed are planetary atmospheres, E and F region, D region, mass spectrometer measurements, direct measurements and atmospheric reactions.

1976-01-01

345

Diurnal transport effects on the F-region plasma at Chatanika under quiet and disturbed conditions  

NASA Technical Reports Server (NTRS)

High latitude ionospheric model predictions are compared with the diurnal variations of plasma convection velocities and electron densities observed at Chatanika, Alaska, on geomagnetically quiet and disturbed days near equinox. Since the time-dependent variation of the magnetospheric electric field was not known, plasma drift velocities and ion densities are calculated for two different convection-precipitation models, each of which corresponds to a different level of magnetic activity. Model calculations for the magnetically quiet day produced plasma drift velocities and electron densities that were in good agreement, both qualitatively and quantitatively, with the measurements. The two models have demonstrated the relative sensitivity of the high latitude ionosphere to different combinations of magnetospheric convection and induced vertical drifts associated with thermospheric winds.

Murdin, J.; Sojka, J. J.; Schunk, R. W.

1984-01-01

346

Solar zenith angle dependence of the plasma density and temperature in the polar ionosphere and magnetosphere during geomagnetically quiet periods at solar maximum  

NASA Astrophysics Data System (ADS)

Plasma density and temperature in the polar region are important parameters for acceleration of outflowing thermal energy ions (the so-called polar wind). In order to quantitatively evaluate the contribution of solar radiation to the electron density in the polar topside ionosphere and magnetosphere, we have investigated the solar zenith angle (SZA) dependence of the electron density profile in the polar cap during geomagnetically quiet periods. The electron density data used in the present study were obtained from 63 months of plasma wave observations by the Akebono satellite in an altitude range of 500-10,500 km at solar maximum (monthly-averaged F10.7 larger than 170). Electron density profiles at low altitudes were found to be well fitted by quasi-hydrostatic equilibrium functions, while those at higher altitudes were well described by power law functions. In the quasi-hydrostatic equilibrium functions, we used a constant temperature, and altitude dependence of the gravitational force and magnetic field strength were taken into account. A clear transition of the density profile is identified at about 2000 km altitude above an SZA of about 110 degrees. The largest variation in the fitted electron density with SZA is identified at 2100 km altitude, where the electron density varies by a factor of 88 from 1.25 10^4 cm^-3 at an SZA of 50 degrees to 1.43 10^2 cm^-3 at an SZA of 130 degrees in the polar cap. Above 5800 km altitude, the variation in the fitted electron density is limited within a factor of 20. The electron density and scale height decrease drastically with increasing SZA in an SZA range of 90-120 degrees. The sum of the ion and electron temperatures estimated from the scale height at an SZA of 120 degrees (3600 K) is less than half of that at an SZA of 90 degrees (8200 K). Furthermore, in order to compare the change in the ionospheric plasma temperature with that obtained by the Akebono satellite, we have investigated the SZA dependence of the electron and ion temperatures in the topside ionosphere using 19 months of data derived from EISCAT Svalbard Radar (ESR), located at an invariant latitude of 75.2 degrees, in an altitude range of 300-1100 km during geomagnetically quiet periods at solar maximum. The electron (ion) temperature above about 300 (600) km altitude decreases most drastically with increasing SZA in an SZA range of 80-110 degrees, which is near the terminator in the ionosphere. The drastic decrease in the ionospheric temperatures strongly suggests the dominant role of heating and photo-ionization processes by solar radiation in determining the electron density up to about 2000 km in the polar cap during geomagnetically quiet periods, while the ionospheric control of the electron density diminishes gradually with increasing altitude above about 2000 km altitude.

Kitamura, N.; Terada, N.; Ogawa, Y.; Ono, T.; Nishimura, Y.; Shinbori, A.; Kumamoto, A.

2010-12-01

347

HF modulated ionospheric currents  

NASA Astrophysics Data System (ADS)

The HAARP HF facility is used to modulate the components of the auroral electrojet that flow in the D-region of the ionosphere, creating ELF/VLF radiation which is then measured at a receiver co-located with the HAARP HF antenna. An HF heating model is coupled to a full wave plasma interaction FDTD code to determine the ELF/VLF response of the ionospheric plasma to the modulated HF stimulation. The predicted FDTD fields on the ground are found to be in remarkable agreement with those measured at a receiver co-located with HAARP. The FDTD code also predicts an upwardly propagating whistler mode that is tightly bound to the magnetic field lines.

Payne, J. A.; Inan, U. S.; Foust, F. R.; Chevalier, T. W.; Bell, T. F.

2007-12-01

348

Solar wind dynamic pressure forced oscillation of the magnetosphere-ionosphere coupling system: A numerical simulation of directly pressure-forced geomagnetic pulsations  

Microsoft Academic Search

We have investigated dynamical effects of an oscillating solar wind dynamic pressure (Psw) on the magnetosphere-ionosphere (M-I) system using a global magnetohydrodynamic (MHD) numerical simulation. We find that a directly Psw-forced pulsation on the ground is strongly controlled by the Psw-induced plasma convection patterns in the M-I system and the associated three-dimensional current system. When a sinusoidal Psw oscillation with

Tetsuo Motoba; Shigeru Fujita; Takashi Kikuchi; Takashi Tanaka

2007-01-01

349

Response of ionosphere and thermosphere during radial interplanetary magnetic field  

NASA Astrophysics Data System (ADS)

The configurations of ionosphere and thermosphere have been investigated by using high-resolution measurements of CHAMP satellite. During the period IMF By and Bz components are weak and Bx keeps pointing to the Earth for almost 10 hours. The geomagnetic indices Dst is about -40 nT and AE about 100 nT on average during the interest period. The CPCP (cross polar cap potential) output by AMIE and calculated from DMSP observations have average values of 15-20 kV. Obvious hemispheric differences are shown in the configurations of FACs on the dayside and nightside. In the south pole FACs diminish in intensity with magnitudes below 0.25 A/m2, the plasma convection retains its quiet time two cell flow pattern, and the air density is quiet low. However, there are obvious activities in the north cusp FACs. One pair of FACs emerges in the north cusp region, which shows opposite polarities to DPY FACs. The new type of currents is accompanied by sunward plasma flow channels. These ionospheric features might be manifestations of the magnetic reconnection processes occurring in the north magnetospheric flanks. The enhanced ionospheric current systems have deposited large amount of energies into the thermosphere, causing enhanced air densities in the cusp region, which subsequently propagate equatorward both on the dayside and nightside. Although the radial IMF is considered as geomagnetic quiet condition, the present study has demonstrated for the first time there are prevailing energy inputs from the magnetosphere to both the ionosphere and thermosphere in the polar cusp region.

Wang, Hui; Luehr, Hermann; Shue, Jihong

2014-05-01

350

Kinetic and thermodynamic properties of a convecting plasma in a two-dimensional dipole field  

NASA Technical Reports Server (NTRS)

Charged particle guiding center motion is considered in the magnetic field of a two-dimensional ('line') dipole on which is superimposed a small, static, perpendicular electric field. The parallel equation of motion is that of a simple harmonic oscillator for cos theta, the cosine of magnetic colatitude theta. Equations for the perpendicular electric and magnetic drifts are derived as well as their bounce-averaged forms. The latter are solved to yield a bounce-averaged guiding center trajectory, which is the same as that obtained from conversation of magnetic moment mu, longitudinal invariant J, and total (kinetic plus electrostatic) energy K. The algebraic simplicity of the trajectory equations is also manifest in the forms of the invariants. An interesting result is that guiding centers drift in such a way that they preserve the values of their equatorial pitch angles and (equivalently) mirror latitudes. The most general Maxwellian form of the equilibrium one-particle distribution function f is constructed from the invariants, and spatially varying density and pressure moments, parallel and perpendicular to the magnetic field, are identified. Much of the paper deals with the more restricted problem in which f is specified as a bi-Maxwellian over a straight line of finite length in the equatorial plane of the dipole and perpendicular to field lines. This might be thought of as specifying a cross-tail ion injection source; our formalism then describes the subsequent spatial development. The distribution away from the source is a scaled bi-Maxwellian but one that is cut off at large and small kinetic energies, which depend on position. Density and pressure components are reduced from the values they would have if the total content of individual flux tubes convected intact. The equatorial and meridional variations of density and pressure components are examined and compared systematically for the isotropic and highly anisotropic situations. There appears to be little qualitative difference due to anisotropy. An anisotropy measure is defined, and its spatial variation determined as a signature of possible MHD instability. Extreme values are found, larger than at the source, but the plasma beta in such regions is probably so low as to render the effect inconsequential energetically. Finally, the possible consequence of 'nonadia- batic' pressure profiles on electrostatic interchanges is considered, and a boundary delineating stabilizing and destabilizing regions determined.

Huang, T. S.; Birmingham, T. J.

1994-01-01

351

Persistent Longitudinal Variations of Plasma Density and DC Electric Fields in the Low Latitude Ionosphere Observed with Probes on the C/NOFS Satellite  

NASA Technical Reports Server (NTRS)

Continuous measurements using in situ probes on consecutive orbits of the C/N0FS satellite reveal that the plasma density is persistently organized by longitude, in both day and night conditions and at all locations within the satellite orbit, defined by its perigee and apogee of 401 km and 867 km, respectively, and its inclination of 13 degrees. Typical variations are a factor of 2 or 3 compared to mean values. Furthermore, simultaneous observations of DC electric fields and their associated E x B drifts in the low latitude ionosphere also reveal that their amplitudes are also strongly organized by longitude in a similar fashion. The drift variations with longitude are particularly pronounced in the meridional component perpendicular to the magnetic field although they are also present in the zonal component as well. The longitudes of the peak meridional drift and density values are significantly out of phase with respect to each other. Time constants for the plasma accumulation at higher altitudes with respect to the vertical drift velocity must be taken into account in order to properly interpret the detailed comparisons of the phase relationship of the plasma density and plasma velocity variations. Although for a given period corresponding to that of several days, typically one longitude region dominates the structuring of the plasma density and plasma drift data, there is also evidence for variations organized about multiple longitudes at the same time. Statistical averages will be shown that suggest a tidal "wave 4" structuring is present in both the plasma drift and plasma density data. We interpret the apparent association of the modulation of the E x B drifts with longitude as well as that of the ambient plasma density as a manifestation of tidal forces at work in the low latitude upper atmosphere. The observations demonstrate how the high duty cycle of the C/NOFS observations and its unique orbit expose fundamental processes at work in the low latitude, inner regions of geospace.

Pfaff, R.; Freudenreich, H.; Klenzing, J.; Rowland, D.; Liebrecht, C.; Bromund, K.; Roddy, P.

2010-01-01

352

Theory of imperfect magnetosphere-ionosphere coupling  

SciTech Connect

A theory of magnetosphere-ionosphere coupling in the presence of field-aligned potential drops is formulated within the framework of magnetohydrodynamic equations. Our formulation allows the magnetosphere as well as the ionosphere to respond self-consistently to the parallel potential drop along auroral field lines. Equipotential contours are distorted into a V-shaped structure near the convection reversal boundary and S-shaped on the equatorward side, each gives rise to an inverted V precipitation band. The loading effect of the imperfect coupling results in a valley in the electric field profile which occurs equatorward of the convection reversal boundary.

Kan, J.R.; Lee, L.C.

1980-09-01

353

Nighttime Ionosphere Tomographic Reconstruction Observatory  

NASA Astrophysics Data System (ADS)

Ionospheric irregularities, also known as ionospheric bubbles, are transient features of the low and middle latitude ionosphere with important implications for operational systems. Understanding irregularity formation, development, and evolution is vital for efforts within NASA and DoD to forecast scintillation. Irregularity structures have been studied primarily using ground-based systems, though some spaced-based remote and in-situ sensing has been performed. An ionospheric observatory aboard the International Space Station (ISS) would provide new capability to study low- and mid-latitude ionospheric structures on a global scale. By combining for the first time high-sensitivity in-track photometry with vertical ionospheric airglow spectrographic imagery, we demonstrate that high-fidelity optical tomographic reconstruction of bubbles can be performed from the ISS. Ground-based imagery can supplement the tomography by providing all-sky images of ionospheric structures (e.g. bubbles and TIDs) and of signatures of lower atmospheric dynamics, such as gravity waves, that may play a role in irregularity formation. The optical instrumentation can be augmented with additional sensors to provide measurements of scintillation and in situ plasma density, composition, and drifts.

Budzien, S. A.; Stephan, A. W.; Makela, J. J.; Chua, D. H.; Dymond, K.; Coker, C.; Chakrabarti, S.

2011-12-01

354

Fossil magnetic fields due to Titan's plasma interaction revisited:The role of the electric conductivities in the ionosphere and in Titan's interior  

NASA Astrophysics Data System (ADS)

The concept of fossil magnetic fields has been introduced into the physics of Titans plasma interaction a few years ago ( Neubauer et al.,J.geophys.Res.,2006) and has first been applied to Titan magnetic field data by Bertucci et al.(Science, 2008) .The concept is based on the idea that because of very low plasma velocities near Titan, magnetic flux tubes entering Titans near plasma environment through an upstream fiducial plane at approximately XTIIS= - 3 RTitan (say) can spend up to a few hours in Titans environment as intact structures until they reach their lowest altitude. Eventually they are flushed out of the system. We discuss an extension of this idea by allowing the flux tubes to enter the lower ionosphere, where the frozen-in -fields concept starts to break down and diffusion of magnetic fields becomes dominant due to the increasing resistivity. However, the age of a field line can still be defined by considering a discontinuity (e.g. magnetopause related) to enter Titans environment through the fiducial plane referred to above. The age is shown to reach a relative maximum of several hours inside the ionosphere. Even larger ages of ~ ten days can be reached if a conducting ocean exists below Titans subsurface and yet larger ones if a conducting core exists. We show that observations at low altitudes and/or in a corridor in the wake of Titan are needed for observations of these fields, which are within the reach of the Cassini flyby trajectories. However, the required special inflow conditions occur relatively rarely.

Neubauer, F. M.; Hoerdt, A.; Wennmacher, A.; Simon, S.; Bertucci, C.; Dougherty, M. K.

2010-12-01

355

Magnetospheric convection strength inferred from inner edge of the electron plasma sheet and its relation to the polar cap potential drop  

NASA Astrophysics Data System (ADS)

The sharp inner edge of the nightside electron plasma sheet observed by the THEMIS spacecraft is shown to provide a measure of the effective convection strength that transports plasma sheet plasma into the inner magnetosphere. The effective convection strength is characterized by the difference of potential between the magnetopause terminators at dawn and at dusk. We have surveyed inner boundary crossings of the electron plasma sheet measured by three THEMIS probes on orbits from Nov. 2007 to Apr. 2009. The values of the convection electric potential are inferred from the locations of the inner edge for different energy channels using a steady-state drift boundary model with a dipole magnetic field and a Volland-Stern electric field. When plotted against the solar wind electric field ( ), the convection electric potential is found to have a quasi-linear relationship with the driving solar wind electric field for the range of values tested (meaningful statistics only for Esw < 1.5 mV/m). Reasonably good agreement is found between the convection electric potential and the polar-cap potential drop calculated from model of Boyle et al. [1997] when the degree of shielding in the Volland-Stern potential is selected as gamma=1.5.

Jiang, F.; Kivelson, M. G.; Walker, R. J.; Khurana, K. K.; Angelopoulos, V.

2010-12-01

356

The effects of dynamic ionospheric outflow on the ring current  

NASA Astrophysics Data System (ADS)

The importance of ionospheric O+ on the development of the storm time ring current is recognized but not well understood. The addition of this outflow in global MHD models has the potential to change the magnetic field configuration, particle densities and temperatures, and the convection electric field. This makes including heavy ion outflow in ring current simulations difficult, as this addition cannot be easily decoupled from a host of other changes. This study attempts to overcome this problem by using three coupled models, PWOM, RIM, and BATS-R-US, to drive a ring current model, RAM-SCB. The differences in drivers when outflow is included and is not included are compared to see how outflow changes ring current input. It is found that including this outflow reduces the convection electric field, lowers the plasma sheet number density and temperature, and increases the complexity of the plasma sheet ion composition both temporally and spatially. These changes cause an overall reduction in ring current energy density. Further simulations that attempt to isolate these effects find that the most important change in terms of ring current development is the drop in convection electric field. Local time dependencies of O+ injections are found to be nontrivial as well. Capturing all of these effects requires a whole system, first-principles approach.

Welling, D. T.; Jordanova, V. K.; Zaharia, S. G.; Glocer, A.; Toth, G.

2011-02-01

357

Plasmapause Convects to the Magnetopause During Halloween Solar Storm  

NSDL National Science Digital Library

The plasmasphere is a region of ionospheric plasma which co-rotates with the Earth, carried by the magnetic field lines. The plasmapause marks the outer boundary of this region. This colder plasma is more easily moved by the electric fields created by strong solar storms. In the Halloween 2003 event, these fields convected some of the cold plasma out to the magnetopause (grey, semi-transparent surface) and reduced the size of the cold plasma region near the Earth. For this visualization, the 3-dimensional structure was constructed from the equatorial profile of the plasmapause (as measured by IMAGE-EUV data) by extending the region along field lines of a simple dipole field.

Bridgman, Tom; Williams, James; Shirah, Greg; Goldstein, Jerald

2004-12-15

358

Investigation of methods for improving models of ionospheric plasma-density irregularities and radio-frequency scintillation. Technical report  

SciTech Connect

Many modern military systems used for communications, command and control, navigation, and surveillance depend on reliable and relatively noise-free transmission of radiowave signals through the earth's ionosphere. Small-scale irregularities in the ionospheric density can cause severe distortion, known as radiowave scintillation, of both the amplitude and phase of these signals. The WBMOD computer program can be used to estimate these effects on a wide range of systems. The objective of this study is to investigate improvements to the WBMOD model based on extensive data sets covering both the equatorial and high-latitude regimes. This report summarizes the work completed during the second year, which include completion of the new models for the equatorial region and initial development of models for the high latitude (auroral and polar cap) region.

Secan, J.A.; Bussey, R.M.

1993-11-01

359

Solar zenith angle dependence of plasma density and temperature in the polar cap ionosphere and low-altitude magnetosphere during geomagnetically quiet periods at solar maximum  

NASA Astrophysics Data System (ADS)

We constructed an empirical model of the electron density profile with solar zenith angle (SZA) dependence in the polar cap during geomagnetically quiet periods using 63 months of Akebono satellite observations at solar maximum. The electron density profile exhibits a transition at 2000 km altitude only under dark conditions. The electron density and scale height at low altitudes change drastically, by factors of 25 (at 2300 km altitude) and 2.0, respectively, as the SZA increases from 90 to 120. The SZA dependence of the ion and electron temperatures is also investigated statistically on the basis of data obtained by the Intercosmos satellites and European Incoherent Scatter (EISCAT) Svalbard radar (ESR). A drastic change in the electron temperature occurs near the terminator, similarly to that in the electron density profile obtained by the Akebono satellite. The sum of the ion and electron temperatures obtained by the ESR (6500 K at 1050 km altitude under sunlit conditions and 3000 K at 750 km altitude under dark conditions) agrees well with the scale height at low altitudes obtained from the Akebono observations, assuming that the temperature is constant and that O+ ions are dominant. Comparisons between the present statistical results (SZA dependence of the electron density and ion and electron temperatures) and modeling studies of the polar wind indicate that the plasma density profile (especially of the O+ ion density) in the polar cap is strongly controlled by solar radiation onto the ionosphere by changing ion and electron temperatures in the ionosphere during geomagnetically quiet periods.

Kitamura, N.; Ogawa, Y.; Nishimura, Y.; Terada, N.; Ono, T.; Shinbori, A.; Kumamoto, A.; Truhlik, V.; Smilauer, J.

2011-08-01

360

RCM-E simulation of bimodal transport in the plasma sheet  

NASA Astrophysics Data System (ADS)

sheet transport is bimodal, consisting of both large-scale adiabatic convection and intermittent bursty flows in both earthward and tailward directions. We present two comparison simulations with the Rice Convection ModelEquilibrium (RCM-E) to investigate how those high-speed flows affect the average configuration of the magnetosphere and its coupling to the ionosphere. One simulation represents pure large-scale slow-flow convection with time-independent boundary conditions; in addition to the background convection, the other simulation randomly imposes bubbles and blobs through the tailward boundary to a degree consistent with observed statistical properties of flows. Our results show that the bursty flows can significantly alter the magnetic and entropy profiles in the plasma sheet as well as the field-aligned current distributions in the ionosphere, bringing them into much better agreement with average observations.

Yang, Jian; Wolf, Richard A.; Toffoletto, Frank R.; Sazykin, Stanislav; Wang, Chih-Ping

2014-03-01

361

The ionospheric outflow feedback loop  

NASA Astrophysics Data System (ADS)

Following a long period of observation and investigation beginning in the early 1970s, it has been firmly established that Earth's magnetosphere is defined as much by the geogenic plasma within it as by the geomagnetic field. This plasma is not confined to the ionosphere proper, defined as the region within a few density scale heights of the F-region plasma density peak. Rather, it fills the flux tubes on which it is created, and circulates throughout the magnetosphere in a pattern driven by solar wind plasma that becomes magnetically connected to the ionosphere by reconnection through the dayside magnetopause. Under certain solar wind conditions, plasma and field energy is stored in the magnetotail rather than being smoothly recirculated back to the dayside. Its release into the downstream solar wind is produced by magnetotail disconnection of stored plasma and fields both continuously and in the form of discrete plasmoids, with associated generation of energetic Earthward-moving bursty bulk flows and injection fronts. A new generation of global circulation models is showing us that outflowing ionospheric plasmas, especially O+, load the system in a different way than the resistive F-region load of currents dissipating energy in the plasma and atmospheric neutral gas. The extended ionospheric load is reactive to the primary dissipation, forming a time-delayed feedback loop within the system. That sets up or intensifies bursty transient behaviors that would be weaker or absent if the ionosphere did not strike back when stimulated. Understanding this response appears to be a necessary, if not sufficient, condition for us to gain accurate predictive capability for space weather. However, full predictive understanding of outflow and incorporation into global simulations requires a clear observational and theoretical identification of the causal mechanisms of the outflows. This remains elusive and requires a dedicated mission effort.

Moore, T. E.; Fok, M.-C.; Garcia-Sage, K.

2014-08-01

362

Temporal structure of the fast convective flow in the plasma sheet: Comparison between observations and two-fluid simulations  

NASA Astrophysics Data System (ADS)

The present study examines the temporal structure of the fast flow in the plasma sheet using both observations and simulations. The data analysis part adopts the strictest criterion ever for the satellite location so that selected flows are mostly convective. From Geotail measurements at X > -31 RE, 818 earthward-flow and 290 tailward-flow events are selected. Superposed epoch analyses are conducted with two different reference times: the start of the fast flow and the time of a sharp change in the Bz component. The results are summarized as follows: (1) The magnetic field becomes dipolar in the course of the fast earthward flow; (2) Sharp dipolarization tends to be preceded by a transient decrease in BZ, which starts along with the fast flow and is accompanied by an increase in the plasma density; (3) The corresponding signatures, albeit less clear, can also be found for the tailward flow; (4) Whereas the plasma density decreases in association with the fast flow irrespective of the flow direction (though, more gradually for the tailward flow), the ion temperature increases for the earthward flow and decreases for the tailward flow; (5) The plasma and total pressures decrease in the course of the fast flow, suggesting the reduction of the lobe field strength; (6) In general, magnetic field and plasma parameters change more gradually in time for the tailward flow than for the earthward flow. Those characteristics of the fast flow can be found irrespective of the X distance, even though the ambient magnetic field and plasma vary significantly between X = -5 and -31 RE. The near-Earth reconnection is inferred to be the responsible mechanism for most, if not all, flow events, and the difference between the earthward and tailward flows presumably reflects difference in downstream conditions. On the earthward side of the reconnection site, the flow needs to proceed against the rigid terrestrial magnetic field, whereas on the tailward side the flow does not have any obstruction once reconnection reaches the lobe magnetic field. This idea is consistent with the change of the magnetic inclination, which suggests that the plasma sheet becomes thicker and thinner in the course of the earthward and tailward flows, respectively. These observational results are compared with fast plasma flows modeled by two-fluid simulations of magnetic reconnection. A focus is placed on the reduction of BZ prior to dipolarization for the earthward flow (the precursory BZ increase for the tailward flow) since this is the new finding owing to our strict condition for the convective flow. It is found that the fragmentation of the current sheet and the formation of multiple neutral lines create signatures similar to the satellite observations. After multiple X lines form, one of them dominates and establishes the overall flow pattern associated with reconnection. Magnetic islands formed between the X lines are swept downstream by the reconnection process. The signature of this earthward convection of a magnetic island past a satellite at rest in the magnetotail is a strongly bipolar signature in Bz with a sudden enhancement in the density: Bz spikes negative and then positive in rapid succession, with a maximum in the density between these two spikes. It is therefore suggested that the temporal structure of the observed fast plasma flows contains information directly linked to their genesis.

Ohtani, Shin-Ichi; Shay, Michael A.; Mukai, Toshifumi

2004-03-01

363

a One-Dimensional Multi-Species MHD Model of the Ionospheres of Venus and Mars  

Microsoft Academic Search

The behavior of the ionospheric magnetic fields and ionospheric plasma of the dayside ionospheres of Venus and Mars was studied using a one-dimensional multi-species MHD model. The coupled continuity, momentum and Maxwell's equations were solved simultaneously for the major ions and for the magnetic field. In the ionosphere of Venus, the calculated magnetic field profiles were in good agreement with

Hiroyuki Shinagawa

1987-01-01

364

The plasma plumes of Europa and Callisto  

NASA Astrophysics Data System (ADS)

We investigate the proposition that Europa and Callisto emit plasma plumes, i.e., a contiguous body of ionospheric plasma, extended in the direction of the corotation flow, analogous to the plume of smoke emitted in the downwind direction from a smokestack. Such plumes were seen by Voyager 1 to be emitted by Titan. We find support for this proposition in published data from Galileo Plasma Science and Plasma Wave observations taken in the corotation wakes of both moons and from magnetometer measurements reported from near the orbit of, but away from, Europa itself. This lends credence to the hypothesis that the plumes escaping from the ionospheres of Europa and Callisto are wrapped around Jupiter by corotation, survive against dispersion for a fairly long time and are convected radially by magnetospheric motions. We present simple models of plume acceleration and compare the plumes of the Europa and Callisto to the known plumes of Titan.

Eviatar, Aharon; Paranicas, Chris

2005-11-01

365

Low- and mid-latitude ionospheric electric fields during the January 1984 GISMOS campaign  

NASA Technical Reports Server (NTRS)

The electrical coupling between the high-, middle-, and low-latitude ionospheres during January 17-19, 1984 is examined, using interplanetary and high-latitude magnetic field data together with F region plasma drift measurements from the EISCAT, Sondre Stromfjord, Millstone Hill, Saint-Santin, Arecibo, and Jicamarca incoherent scatter radars. The penetration both the zonal and meridional electric field components of high-latitude origin into the low-latitude and the equatorial ionospheres are studied. The observations in the postmidnight sector are used to compare the longitudinal variations of the zonal perturbation electric field with predictions made from global convection models. The results show that the meridional electric field perturbations are considerably more attenuated with decreasing latitude than the zonal fluctuations. It is concluded that variations in the meridional electric field at low latitudes are largely due to dynamo effects.

Fejer, B. G.; Kelley, M. C.; Senior, C.; De La Beaujardiere, O.; Lepping, R.

1990-01-01

366

Ionospheric scintillation  

Microsoft Academic Search

Available observations of ionospheric scintillation are analyzed to evaluate the adequacy of existing models used for the interpretation of scintillation data. The theoretical models are reviewed and the frequency and propagation geometry dependences predicted by the models are compared with the observations. The models were used to construct scintillation occurrence distribution functions which show that scintillation phenomena significantly affect the

R. K. Crane

1977-01-01

367

Ionospheric Research.  

National Technical Information Service (NTIS)

The Statement of Work for the research to be performed under Contract AF 19(628)-4050 called for research directed toward the investigation of the lower ionosphere. Specific emphasis was placed on the design, conduction and analysis of rocket-borne A. C. ...

T. A. Seliga

1967-01-01

368

Growth and maintenance of large-scale magnetic fields in the dayside Venus ionosphere  

NASA Astrophysics Data System (ADS)

Observations from the Pioneer Venus orbiter magnetometer reveal the presence of large-scale magnetic fields in the dayside ionosphere during or after periods of high solar wind dynamic pressure. Various hypotheses have been proposed concerning the spatial and temporal evolution of these field structures. The hypothesis that the field is produced by a diffusion/convection process rather than by currents driven by electric fields resulting from the solar wind interaction is examined. Dynamic pressure variations occur on various time scales at Venus, producing transient and quasi-steady magnetization features. A one-dimensional diffusion/convection calculation is performed, using typical ionopause field and pressure values for a variety of altitudes. The Venus ionopause is considered to be the altitude at which ionospheric thermal pressure is equal to the magnetosheath magnetic pressure, which in turn is well correlated with the normal component of solar wind dynamic pressure. A subsolar model of downward plasma velocity in the 140-290 km range is used. The calculated growth of the ionospheric magnetic field, and the resulting quasi-steady altitude profiles, compare favorably with the observed profiles. The majority of the observed magnetic structures are best explained as the quasi-steady effects of the prevailing solar wind dynamic pressure, which determines the altitude and magnetic field strength of the ionopause boundary.

Phillips, J. L.; Luhmann, J. G.; Russell, C. T.

1984-12-01

369

Initial Results From Coupling Magnetosphere, Inner Magnetosphere, Ionosphere, and Thermosphere Models  

NASA Astrophysics Data System (ADS)

The Center for Integrated Space Weather Modeling (CISM) is working on developing a comprehensive geospace model. The core of this models is composed of three components. The interaction between the magnetosphere and a solar wind is simulated by the Lyon-Fedder-Mobarry global magnetospheric (LFM) model. The inner magnetosphere is simulated by the Rice Convection Model (RCM). Response of the ionosphere-thermosphere system to magnetospheric driving is simulated by the Thermosphere Ionosphere Nested Grid (TING) Model. We begin with a brief discussion of these three models are coupled together. In the current configuration, the LFM acts and as an intermediary between the other geospace models. It determines the particle fluxes and electric field inputs to the TING model by using its inner magnetospheric state as modified by the Rice convection model. The LFM also supplies magnetic field and plasma information to the RCM. The RCM also needs ionospheric conductivity information which as passed to it from TING via the LFM. Next, we'll compare results from the individual models to results from the coupled model for an interval of steady southward IMF that includes a magnetospheric substorm. Finally, we'll address the need for measurements throughout the system to quantify the accuracy of the coupled model.

Wiltberger, M.; Toffoletto, F. R.; Lyon, J. G.; Sazykin, S.; Wang, W.

2005-12-01

370

Evidence for Corotating Convection in Saturn's Magnetosphere  

NASA Astrophysics Data System (ADS)

Saturn's magnetic field exhibits a high degree of azimuthal symmetry, yet the field and plasma signatures of the magnetosphere are modulated at a period close to that of planetary rotation. How, then, is a clear periodicity imposed on the magnetic field and plasma of the planetary magnetosphere? In this talk, Cassini magnetometer data are used to develop a scenario for the dynamics of the Saturn magnetosphere. The proposal is that mass transport, accomplished in the inner magnetosphere by interchange motion, feeds into the outer magnetosphere where ballooning driven by centrifugal stress leads to outward transport, field reconnection and plasma loss in a favored local time sector; flux is transported inward in other regions. The model is closely related to the concept of corotating convection proposed by Dessler, Hill, and co-workers for Jupiter. The proposed mechanism can be consistent with aspects of the empirical camshaft model introduced by Espinosa et al., 2003 to explain Pioneer and Voyager magnetometer data. Anomalous transport here proposed could originate from a localized ionospheric conductivity anomaly. The resulting cyclic stress modulates the current in the current sheet and can account for its north-south excursions. The convection patterns proposed also imply that corotating, field-aligned currents would be a basic feature of the Saturn system.

Kivelson, M. G.; Southwood, D. J.; Dougherty, M. K.

2006-05-01

371

A two-dimensional kinematic dynamo model of the ionospheric magnetic field at Venus  

SciTech Connect

The ionosphere of Venus was observed by the magnetometer on the Pioneer Venus Orbiter (PVO) to be permeated by a large-scale magnetic field for conditions of high solar wind dynamic pressure. The ionospheric conductivity is very high above 170 km and magnetic flux is carried by the plasma flow both vertically downward and in an antisunward direction. Ohmic dissipation of the electric current allows the magnetic field to diffuse for altitudes below 150-170 km. A number of one-dimensional kinematic dynamo and MHD models have been developed to explain the observed vertical magnetic field profiles, but did not include the effects of horizontal transport. The authors have constructed a two-dimensional kinematic dynamo model of the dayside ionospheric magnetic field at Venus in which the 2-D magnetic induction equation (i.e., magnetic diffusion-convection equation) is numerically solved using specified plasma velocities. The vertical velocity profile is taken from the one-dimensional MHD model of Shinagawa and Cravens (1988) and the horizontal velocities are adapted from published PVO retarding potential analyzer results (Knudsen et al., 1982). They demonstrate that the basic features of the vertical magnetic field profile, such as the presence of a magnetic layer at 170 km, remain unaltered by horizontal flow effects. However, they also show that horizontal plasma flow can strongly affect the magnetic field for altitudes above 300 km.

Cravens, T.E.; Wu, D. (Univ. of Kansas, Lawrence (USA)); Shinagawa, H. (Marshall Space Flight Center, Huntsville, AL (USA))

1990-11-01

372

Particle-in-cell simulation of incoherent scatter radar spectral distortions related to beam-plasma interactions in the auroral ionosphere  

NASA Astrophysics Data System (ADS)

An electrostatic parallel particle-in-cell (EPPIC) code that allows for particle beam injections and multiple boundary co