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1

Ionospheric signatures of magnetospheric convection  

NASA Astrophysics Data System (ADS)

The average patterns of ionospheric convection observed with the Chatanika incoherent scatter radar, when mapped along magnetic field lines to the equatorial plane, delineate regions of earthward convection within the magnetotail that either proceed sunward to the dayside magnetopause (where reconnection with the IMF can occur) or that join the antisunward circulation along the magnetospheric flanks at dusk and dawn. An examination of summer and winter ionospheric convection patterns in terms of the corresponding magnetospheric circulation patterns shows that ionospheric ionization troughs at dusk and dawn are associated with the sunward convection of low density plasma from the night sector, and that plasma in the vicinity of the dawn and dusk electric field reversals circulates at high latitudes away from the solar ionization source at noon. Plasma exiting from the polar cap is convected away from midnight in the equatorward portion of the regions of sunward convection at auroral latitudes.

Foster, J. C.

1984-02-01

2

Ionospheric response to traveling convection twin vortices  

SciTech Connect

Traveling convection twin vortices have been observed for several years. At ionospheric altitudes, the twin vortices correspond to spatially localized, transient structures embedded in a large-scale background convection pattern. The convection vortices are typically observed in the morning and evening regions. They are aligned predominantly in the east-west direction and have a horizontal extent of from 500-1000 km. Associated with the twin vortices are enhanced electric fields, particle precipitation, and an upward/downward field-aligned current pair. Once formed, the twin vortex structures propagate in the tailward direction at speeds of several km/s, but they weaken as they propagate and only last for about 10-20 minutes. Because these convection structures might have a significant effect on the localized ionosphere, the USU ionospheric model was used to calculate the response of the ionosphere to {open_quotes}representative{close_quotes} traveling convection twin vortices for a range of background conditions. The ionospheric response includes localized temperature enhancements, ion composition changes, non-Maxwellian ion distributions, and plasma upwelling events. The response is transient and the magnitude of the response depends on the background ionosphere conditions and on the characteristics of the twin vortices. 17 refs., 4 figs.

Schunk, R.W.; Zhu, L.; Sojka, J.J. [Utah State Univ., Logan, UT (United States)

1994-08-15

3

Dayside ionospheric plasma convection, electric fields, and field-aligned currents derived from the SuperDARN radar observations and predicted by the IZMEM model  

NASA Astrophysics Data System (ADS)

A recent deployment of the Super Dual Auroral Radar Network (SuperDARN) HF radar network provides excellent opportunities to construct two-dimensional maps of the ionospheric convection over large areas in both the northern and southern polar regions. The Institute of Terrestrial Magnetism, Ionosphere and Radiowave Propagation electrodynamic model (IZMEM) is a potentially useful tool for predicting, also on a global scale, the ionospheric plasma convection patterns, electric fields, magnetic disturbances, ionospheric and field-aligned currents. Comparisons of the IZMEM predictions with satellite and incoherent scatter radar data show that the model's performance is reasonably good, but the model needs more extensive and accurate verifications. In this paper, several events under relatively stable IMF conditions (Bz<0 and Bz>0) are studied and discussed. The SuperDARN/IZMEM ion drift velocities are found to be in reasonable agreement in both magnitude and direction; the average difference (over the individual SuperDARN convection map) between the predicted magnitude of the ion drift velocity and the measured magnitude is about 50%, while the difference in the direction is typically less than 25. The IZMEM predictions of the location, direction, and magnitude of field-aligned currents also agree well with the SuperDARN observations. It is concluded that simultaneous use of SuperDARN data and IZMEM model can improve the specification of the polar ionospheric convection for space weather applications.

Kustov, A. V.; Papitashvili, V. O.; Sofko, G. J.; Schiffler, A.; Feldstein, Y. I.; Gromova, L. I.; Levitin, A. E.; Belov, B. A.; Greenwald, R. A.; Ruohoniemi, M. J.

1997-11-01

4

Relationship of topside ionospheric ion outflows to auroral forms and precipitation, plasma waves, and convection observed by Polar  

NASA Astrophysics Data System (ADS)

The POLAR satellite often observes upflowing ionospheric ions (UFIs) in and near the auroral oval on southern perigee (~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 ~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.

1998-08-01

5

Nonlinear evolution of convecting plasma enhancements in the auroral ionosphere, 2. Small scale irregularities  

SciTech Connect

Using analytical numerical simulation techniques, the linear stability and nonlinear evolution of small scale (approx.0.1--1 km) density irregularities in local unstable regions of large scale convecting auroral plasma enhancements have been studied. Our results show that these small scale size irregularities are driven unstable primarily by the effects of convection through the E x B gradient drift instability. We find that the density irregularities, in the nonlinear regime, in a plane nearly perpendicular to the magnetic field resemble steepened striation-like structures (elongated in the north-south direction for equatorward convection) that can form and cascade from kilometer to tens of meter scale sizes on the order of half an hour. The one-dimensional spatial power spectra of the density irregularities in the north-south P(k/sub y/)proportionalk/sup -n//sub y/ and east-west P(k/sub x/proportionalk/sub x//sup -n/ can be described by inverse power laws with napprox. =2--3. Finally, we propose and demonstrate, using a crude model, that a two-step process, in which small scale irregularities can grow on longer wavelength nonlinear structures, can account for the experimentally observed L shell aligned nature of the irregularities.

Keskinen, M.J.; Ossakow, S.L.

1983-01-01

6

Ionosphere-magnetosphere coupling and convection  

NASA Astrophysics Data System (ADS)

Some IMS-associated attempts at quantitative modeling of specific observed ionosphere-magnetosphere events are reviewed, including a theoretical model of convection, algorithms for deducing ionospheric current and electric-field patterns from sets of ground magnetograms and appropriate ionospheric conductivity information, and empirical models of ionospheric conductances, polar-cap potential drops, etc. A few topics in the active research area of magnetic-field-aligned electric fields are reviewed very briefly, particularly magnetic-mirror effects and double layers.

Wolf, R. A.; Spiro, R. W.

1984-09-01

7

Convective Ionospheric Storms: A Review  

NASA Astrophysics Data System (ADS)

Equatorial spread F (ESF) was discovered almost a century ago using the first radio wave instrument designed to study the upper atmosphere: the ionosonde. The name came from the appearance of reflections from the normally smooth ionosphere, which were spread over the altitude frequency coordinates used by the instrument. Attempts to understand this phenomenon in any depth activated such tools as radars and in situ probes such as rockets and satellites in the 1960s. Over the next 15 years, these tools expanded our experimental understanding enormously, and new nonlinear theoretical methods developed in the late 1970s, which led to proposing a name revision from ESF to convective ionospheric storms. Interest in these phenomena continues, but a new, practical aspect has developed from the associated turbulence effects on communications (transionosphere) and navigation (GPS). The first satellite to specifically investigate this problem and the associated goal of predicting occurrences is under the umbrella of the Communications/Navigation Outage Forecast System (C/NOFS). In contemplating the successful first years of the C/NOFS program, reviewing the state of the art in our knowledge of convective ionospheric storms seems appropriate. We also present some initial results of this satellite program. A major goal of the National Space Weather Program, and of C/NOFS, is predicting these storms, analogous to thunderstorms in the lower atmosphere due to their adverse effects on communication and navigation signals. Although ambitious, predictive capability is a noble and important goal in the current technological age and is potentially within our reach during the coming decade.

Kelley, Michael C.; Makela, Jonathan J.; de La Beaujardire, Odile; Retterer, John

2011-06-01

8

On the mapping of ionospheric convection into the magnetosphere  

SciTech Connect

Under steady state conditions and in the absence of parallel electric fields, ionospheric convection is a direct map of plasma and magnetic flux convection in the magnetosphere, and quantitative estimates can be obtained from the mapping along magnetic field lines of electrostatic ionospheric electric fields. The resulting magnetospheric electrostatic potential distribution then provides the convection electric field in various magnetospheric regions. We present a quantitative framework for the investigation of the applicability and limitations of this approach based on an analytical theory derived from first principles. Particular emphasis is on the role of parallel electric field regions and on inductive effects, such as expected during the growth and expansive phases of magnetospheric substorms. We derive quantitative estimates for the limits in which either effect leads to a significant decoupling between ionospheric and magnetospheric convection and provide an interpretation of ionospheric convection which is independent of the presence of inductive electric fields elsewhere in the magnetosphere. Finally, we present a study of the relation between average and instantaneous convection, using two periodic dynamical models. The models demonstrate and quantify the potential mismatch between the average electric fields in the ionosphere and the magnetosphere in strongly time-dependent cases that may exist even when they are governed entirely by ideal MHD.

Hesse, M. [Electrodynamics Branch, NASA Goddard Space Flight Center, Greenbelt, Maryland (United States); Birn, J. [Los Alamos National Laboratory, Los Alamos, New Mexico (United States); Hoffman, R.A. [Electrodynamics Branch, NASA Goddard Space Flight Center, Greenbelt, Maryland (United States)

1997-05-01

9

Ionospheric convection driven by NBZ currents  

NASA Astrophysics Data System (ADS)

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.

1987-05-01

10

Convective cell generation by kinetic Alfven wave turbulence in the auroral ionosphere  

SciTech Connect

Modulation of convective cells by kinetic Alfven wave (KAW) turbulence is investigated. The interaction is governed by a nonlinear dispersion relation for the convective cells. It is shown that KAW turbulence is disrupted by excitation of the large-scale convective motion through a resonant instability. Application of the results to the auroral ionosphere shows that cross-scale coupling of the KAW turbulence and convective cells plays an important role in the evolution of ionospheric plasma turbulence.

Zhao, J. S.; Wu, D. J. [Purple Mountain Observatory, Chinese Academy of Sciences 210008, Nanjing (China); Yu, M. Y. [Department of Physics, Institute for Fusion Theory and Simulation, Zhejiang University, Hangzhou 310027 (China); Institute for Theoretical Physics I, Ruhr University, D-44780 Bochum (Germany); Lu, J. Y. [National Center for Space Weather, China Meteorology Administration 100081, Beijing (China)

2012-06-15

11

Neutral atmosphere and crustal magnetization as factors determining differences in plasma convection and magnetic fields distribution in the ionospheres of Mars and Venus  

NASA Astrophysics Data System (ADS)

The pattern of the magnetic field/plasma convection can be, to some extent, recovered from the magnetic field measurements by employing either theoretical or numerical models. We use the MAG/ER day-time measurements of the magnetic field at the altitudes from 90 to 180 km during the elliptical orbits of MGS. Analysis of the altitude variation of the characteristics of the large-scale magnetic fields, which were measured some distance away from strong crustal magnetic anomalies, is summarized. The low density of the Martian atmosphere together with the crustal magnetization result in critical differences in plasma convection which are followed by remarkable differences of the magnetic field features within the ionosphere of Venus and Mars (even in its northern hemisphere where the crustal magnetization is, on the average, low) and distribution of currents.

Kireev, A. P.; Krymskii, A. M.

2012-02-01

12

Ionospheric convection driven by NBZ currents  

SciTech Connect

Computer simulations of Birkeland currents and electric fields in the polar ionosphere during periods of northward interplanetary magnetic field (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% 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. The effects of varying ionospheric conductivity were studied by considering both a constant voltage source and a constant current source. Conductivity gradients due to seasonal and local time variations in solar production were considered, as well as gradients due to electron precipitation. 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. Copyright American Geophysical Union 1987.

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

1987-05-01

13

Studies of the high latitude ionospheric convection  

NASA Astrophysics Data System (ADS)

The electrostatic potential distribution in the high latitude ionosphere is representative of the response of the ionosphere magnetosphere system to drivers in the solar wind and conditions in the interplanetary medium. The cross polar cap potential drop, used as a single parameter to describe the global distribution of electrostatic potential, often serves as an input driver for various magnetospheric and space weather models. For a given solar wind condition the cross polar cap potential drop derived from satellite measurements of the electric field, or ion drift in the ionosphere, are observed to have a significant variation, often on the order of thirty percent or greater. Such a large variability could influence the uncertainty of results from models that utilize this electrostatic potential drop as an input, so a further understanding of the sources and organization of these uncertainties will improve the specification itself and the confidence limits of the observations. Sources of this variability are investigated using two years (2000-2001) of ionospheric plasma flow data provided by the DMSP F13 and F15 satellites to calculate the cross polar cap potential drop, along with solar wind data from the ACE satellite in order to explore the behavior of this potential in response to a wide range of interplanetary magnetic field (IMF) conditions during southward IMF (BZ ? 0). A variety of IMF conditions are examined to show how the stability of the IMF and the solar wind speed over both short and long time periods affects variations in the cross polar cap potential drop. The most interesting discovery is that, even during steady state IMF conditions, the largest amount of variability is caused by the displacement of the satellite track with respect to the extrema in potential at the center of the two convection cells in the high-latitude region, especially when the displacement is caused by substorm activity. Included is a study of the average properties of the electrostatic potential drop and its relationship to particle precipitation boundaries across the ionospheric projection of the low latitude boundary layer and the interplanetary electric field.

Drake, Kelly Ann

14

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

15

Quiet auroral arcs - Ionosphere effect of magnetospheric convection stratification  

Microsoft Academic Search

A detailed study of the mechanism of electromagnetic stratification of the large-scale stationary magnetospheric convection due to a friction of the convective flow in the ionosphere layer was performed. Magnetosphere-ionosphere interaction was taken into account by means of the effective boundary conditions on the ionosphere top and bottom boundaries including the actual height profile of charge particles velocity in the

V. Iu. Trakhtengerts; A. Ia. Feldstein

1984-01-01

16

Ionospheric convection and structure using ground-based digital ionosondes  

NASA Astrophysics Data System (ADS)

Ground based digital ionosonde observations of the winter polar cap F region have been used to demonstrate that the magnetospherically induced ionospheric convection can be measured for the bottomside ionosphere. A number of measurements indicate that the drift direction is predominately anti-sunward with speeds that vary between 300 and 900 meters/second. Other measurements show a steady westward drift until local magnetic midnight and then a change to an eastward drift. The ionospheric drifts are consistent with the expected sunward return flows of the two cell polar plasma convection pattern. The utility of data from a network of digital ionosondes is enhanced through automatic scaling of parameters needed for research and radio wave propagation management. The values of hmF2 deduced by real-height analysis of automatically scaled Digisonde ionograms have been compared with simple methods based on routinely scaled ionospheric characteristics. Systematic discrepancies were found between the hmF2 values obtained from the simple methods and the real-height analysis. Overestimates of 15 to 20 km were found for the night data from five stations and low solar activity. Daytime discrepancies are normally less, with 80 percent showing agreement within + or - 10 km.

Reinisch, Bodo W.; Buchau, Jurgen; Weber, Edward J.; McNamara, Leo F.; Tang, Jane S.

1988-02-01

17

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)

1995-02-01

18

Global-scale observations of ionospheric convection during geomagnetic storms  

NASA Astrophysics Data System (ADS)

The global effects on the ionosphere during periods of intense geomagnetic activity associated with geomagnetic storms are investigated using the Super Dual Auroral Radar Network (SuperDARN). The influence of the main and recovery phases of geomagnetic storms on ionospheric properties such as backscatter occurrence rates, velocity distributions, and convection patterns are presented. The evolution of magnetosphere and ionosphere parameters during the storms did not depend on the origin of the storm (e.g., a coronal mass ejection or a corotating interaction region). Instead, there was a continuum of response to the intensity of the driver. For example, we found a clear relationship between the most negative value of the southward component of the interplanetary magnetic field (IMF Bz) and the most negative value of the Sym-H index, which marks the end of the main phase of a storm. This is one of the first superposed epoch studies that analyzes the sunward/antisunward line-of-sight velocity as a function of magnetic local time for geomagnetic storms of various intensities. In the noon sector, before and during the main phase of the storms, the SuperDARN radars recorded faster antisunward ionospheric plasma drifts together with a significant increase in the number of ionospheric echoes. This is consistent with the expected increase in soft particle precipitation in the noon sector and with the reconnection electric field that occurs when the IMF Bz is strongly negative, as is the case during the main phase of storms. The SuperDARN echo occurrence in the noon sector returned to prestorm values early in the recovery phase. The overall response was similar in the midnight sector, except that the peak echo occurrence for the most intense storms was limited to a narrower time interval centered on the end of the main phase. There were reductions in the strong antisunward flows near local midnight observed during the main phase and early in the recovery phase, particularly for the intense storm class. Strong electric fields are applied in the nightside ionosphere during storms, and the decameter structures from which SuperDARN scatter are more easily produced. However, in regions of energetic auroral precipitation and after a long exposure to strong electric fields, there is often a reduction in SuperDARN echoes due to absorption or changes in radio wave propagation.

Gillies, D. M.; McWilliams, K. A.; St. Maurice, J.-P.; Milan, S. E.

2011-12-01

19

Trough in the daytime F layer: A macroscopic effect of ionospheric-magnetospheric convection  

SciTech Connect

The daytime F layer trough is a major result of ionospheric-magnetospheric convection, appearing in the winter high latitude ionosphere as a continuous band thousands of kilometers in extent in which the daytime F layer electron density is depleted, often by an order of magnitude. As observed by a global array of ionospheric sounders during solar maximum, the trough occurs in regions of sunward convection, in the morning corresponding to the dawn cell and in the afternoon corresponding to the dusk cell. The formation of the trough is consistent with the transport of low density nighttime plasma into the day sector where it displaces high density daytime plasma, although other mechanisms such as ion chemical effects may also play a role.

Whalen, J.A.

1990-05-03

20

Millstone Hill Observations of Ionospheric Convection.  

National Technical Information Service (NTIS)

Incoherent Scatter measurements of convection electric fields have been carried out at Millstone Hill (Latitude = 56 deg) since 1978. These measurements have permitted the convection pattern on individual days to be determined over the invariant latitude ...

J. M. Holt J. V. Evans W. L. Oliver R. H. Wand

1984-01-01

21

Interhemispheric Comparisons of Global-Scale Ionospheric Convection  

NASA Astrophysics Data System (ADS)

The Super Dual Auroral Radar Network (SuperDARN) is perhaps the only facility capable of measuring convection electric fields simultaneously over large regions of the ionosphere in both hemispheres. Using a dataset of periods for which data is sufficient to describe the global-scale convection pattern in both hemispheres, maps of the convection electric field are compared under various interplanetary magnetic field (IMF) and dipole tilt conditions. Case studies and statistics show that the largest differences occur under IMF By dominant conditions with non-zero dipole tilt and are likely caused by differing merging geometries under these conditions.

Shepherd, S. G.; Pettigrew, E. D.

2009-12-01

22

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

23

Statistical study of the effect of solar wind dynamic pressure fronts on the dayside and nightside ionospheric convection  

NASA Astrophysics Data System (ADS)

Over the past few years, the prominent role of solar wind dynamic pressure in enhancing dayside and nightside reconnection and driving-enhanced ionospheric convection has been documented by both ground and spaceborne instruments. For a previous case study of an abrupt increase in solar wind dynamic pressure, Super Dual Auroral Radar Network (SuperDARN) measurements of plasma convection within the dayside polar ionosphere revealed an immediate enhancement of plasma convection. The convection enhancement variation closely follows the variation in solar wind pressure. The dayside enhancement was followed by a nightside convection increase about 40 min later, which has similar variation characteristics as seen on the dayside. We now use SuperDARN flow measurements during a large number of solar wind pressure enhancements to conduct a superposed epoch analysis of the effects of solar wind pressure fronts on the dayside and nightside ionospheric convection. The results for the dayside show an increase of convection for nearly all interplanetary magnetic field (IMF) Bz values. The response is more pronounced and immediate (within minutes) for southward IMF, with a duration of 20-30 min. The response time scales increase to 5-10 min for northward IMF, and the enhanced flows last for 30-50 min. We also find a significant enhancement of nightside convection, particularly for small values of IMF By, that follows about 10-15 min after the dayside response and can last for 40-50 min.

Boudouridis, A.; Lyons, L. R.; Zesta, E.; Weygand, J. M.; Ribeiro, A. J.; Ruohoniemi, J. M.

2011-10-01

24

Plasma temperatures in Saturn's ionosphere  

Microsoft Academic Search

We have calculated self-consistent electron and ion temperatures in Saturn's ionosphere using a series of coupled fluid and kinetic models developed to help interpret Cassini observations and to examine the energy budget of Saturn's upper atmosphere. Electron temperatures in the midlatitude topside ionosphere during solar maximum are calculated to range between 500 and 560 K during the Saturn day, approximately

Luke Moore; Marina Galand; Ingo Mueller-Wodarg; Roger Yelle; Michael Mendillo

2008-01-01

25

Magnetospheric control of the bulk ionospheric plasma  

SciTech Connect

The temperature, composition, and circulation of the high-latitude, ionosphere display a marked variation with altitude, latitude, longitude, universal time, season, solar cycle, and geomagnetic activity. This variation is largely a consequence of the effect that magnetospheric electric fields, particle precipitation, and heat flows have on the ionosphere. At F-region altitudes, the entire ionosphere drifts in response to magnetospheric electric fields, with the horizontal drift generally displaying a two-cell pattern of antisunward flow over the polar cap and return flow at lower latitudes. This ionospheric motion, in combination with downward magnetospheric heat flows and ion production due to energetic-particle precipitation, act to produce interesting ionospheric features such as ion and electron temperature hot spots, plasma blobs, localized ionization troughs, and extended tongue of ionization, and anomalous F-region peak altitudes and densities. The time delay for the ionosphere to respond to changing magnetospheric conditions is a strong function of altitude and can be as long as 3 to 4 hours in the upper F-region. The ionosphere's response to changing magnetospheric conditions are described using a time-dependent high-latitude ionospheric model.

Sojka, J.J.; Schunk, R.W.

1987-01-01

26

Cold ionospheric plasma in Titan's magnetotail  

NASA Astrophysics Data System (ADS)

The interaction between Titan and the corotating Saturnian plasma forms an induced magnetosphere with an elongated Alfven-wing-style magnetotail. On 26 December 2005, the Cassini spacecraft flew through Titan's magnetotail, providing the first distant tail observation, over 5 Titan radii downstream. We examine measurements observed by the magnetometer and Langmuir probe during this pass. We use the direction of the magnetic field along the trajectory to identify the source regions of plasma reaching the spacecraft. Cold plasma, with a density of about 10 cm-3, is found magnetically connected to the ionosphere. Titan's ionosphere appears to be escaping along field lines down the tail, leading to particle loss from the atmosphere.

Wei, H. Y.; Russell, C. T.; Wahlund, J.-E.; Dougherty, M. K.; Bertucci, C.; Modolo, R.; Ma, Y. J.; Neubauer, F. M.

2007-11-01

27

Analysis of Plasma Bubble Signatures in the Ionosphere.  

National Technical Information Service (NTIS)

Plasma bubbles are large scale structures of depleted plasma density in Earth's ionosphere that disrupt radio and satellite communications, to include global navigation satellite systems. This study used the Ionospheric Forecast Model (IFM) to analyze a e...

O. A. Nava

2011-01-01

28

Magnetosheath-ionospheric plasma interactions in the cups/cleft 2. Mesoscale particle simulations  

SciTech Connect

Ionospheric plasma flowing out from the cusp can be an important source of plasma to the magnetosphere. One source of free energy that can drive this outflow is the injection of magnetosheath plasma into the cusp. Two-dimensional (three velocity) mesoscale particle simulations are used to investigate the particle dynamics in the cusp during southward interplanetary magnetic field. This mesoscale model self-consistently incorporates (1) global influences such as the convection of plasma across the cusp, the action of the mirror force, and the injection of the magnetosheath plasma, and (2) wave-particle interactions which produce the actual coupling between the magnetosheath and ionospheric plasmas. It is shown that, because the thermal speed of the electrons is higher than the bulk motion of the magnetosheath plasma, an upward current is formed on the equatorward edge of the injection region with return currents on either side. However, the poleward return currents are the stronger due to the convection and mirroring of many of the magnetosheath electrons. The electron distribution in this latter region evolves from upward directed streams to single-sided loss cones or possibly electron conics. The ion distribution also shows a variety of distinct features that are produced by spatial and/or temporal effects associated with varying convection patterns and wave-particle interactions. On the equatorward edge the distribution has a downflowing magnetosheath component and an upflowing cold ionospheric component due to continuous convection of ionospheric plasma into the region. Further poleward there is velocity filtering of ions with low pitch angles, so that the magnetosheath ions develop a ring-beam distribution and the ensuing wave instabilities generate downward ionospheric conics. These downward ionospheric components are eventually turned by the mirror force, leading to the production of upward conics at elevated energies throughout the region. 17 refs., 13 figs.

Winglee, R.M. [Univ. of Washington, Seattle, WA (United States); Menietti, J.D. [Univ. of Iowa, Iowa City, IA (United States); Lin, C.S. [Southwest Research Institute, San Antonio, TX (United States)

1993-11-01

29

Plasma fluxes between the ionosphere and protonosphere  

Microsoft Academic Search

The plasma fluxes between the ionosphere and protosphere are evaluated from the time rate of change of the plasmaspheric electron content (N sub p) obtained from measurements of group delay and Faraday rotation recorded at Palehua observatory (L = 1.35) during ATS 6 phase III. The variation of dNP\\/dt with time of the day in different seasons is expressed in

H. P. Joshi; A. V. Janve; K. N. Iyer

1984-01-01

30

Ionospheric plasma drift at Llw latitudes  

NASA Astrophysics Data System (ADS)

Trans-equatorial ionospheric plasma bubbles are large-scale ionospheric irregularities, which develop, in the bottom side of equatorial F-region due to plasma instability processes. These regions are quasi-magnetic field aligned with widths 100-400 km across of magnetic equator and are characterized by low plasma density compared with the ambient ionospheric plasma density. These ionospheric irregularities may be observed by different ground-based observational techniques (e.g., radar, digisonde, GPS and optical instruments) and its time evolution and propagation can be used to study important aspects of the ionospheric dynamics and thermosphere-ionosphere coupling. Simultaneous all-sky imaging observations of the OI 630.0 nm and OI 777.4 nm nightglow emissions at So Jos dos Campos (23.21S, 45.86W; dip latitude 17.6S), Brazil, were carried during the years 2000 and 2001, a period of high solar activity. The images in the two emissions exhibited different characteristics of the same plasma bubble. The images obtained in the OI 630.0 nm emission presented diffused plasma bubble structure (blurred images) due to its 110-s lifetime, with widths of about 100-400 km and the internal spatial details were not perceptible. Also, the OI 630.0 nm emission images showed strong F-region height dependence. However, the images obtained in the OI 777.4 nm emission showed much better resolution of the plasma bubble structure with sometime ray-like fine structures with widths of about 20-60 km. This is owing to the fact that the OI 777.4 nm emission is a prompt emission and depends only on the electron density profiles, with no F-region height dependence. In this work we present and discuss the nocturnal zonal plasma drift velocities obtained from the two emissions for several days of 2000 and 2001. It should be pointed out that the two emissions come from altitudes separated by about one scale height (about 50-70 km). The results indicate that the zonal plasma drift velocities determined from the two emissions are fairly close, with the one determined from the OI 777.4 nm emission only slightly higher than that from the OI 630.0 nm emission. Also, a comparison of the observed zonal plasma drift velocities with the zonal neutral wind velocities obtained from the horizontal wind model (HWM- 90) is presented.

Abalde, J. R.; Fagundes, P. R.; Sahai, Y.; Pillat, V. G.; Pimenta, A. A.; Bittencourt, J. A.

31

Experimental Studies of Ionospheric Irregularities and Related Plasma Processes.  

National Technical Information Service (NTIS)

Utah State University (USU) continued its program of measuring and interpreting electron density and its variations in a variety of ionospheric conditions with the Experimental Studies of Ionospheric Irregularities and Related Plasma Processes program. Th...

K. D. Baker

1992-01-01

32

Ionospheric signatures of plasma injections in the cusp triggered by solar wind pressure pulses  

NASA Astrophysics Data System (ADS)

We describe coordinated observations made on 14 July 2001 simultaneously in the midaltitude cusp by Cluster and at the cusp's ionospheric magnetic footprint by Super Dual Auroral Radar Network (SuperDARN) and Imager for Magnetopause-to-Aurora Global Exploration (IMAGE) during a period of three successive solar wind dynamic pressure pulses. In association with each of these pulses, Cluster observes plasma injections while auroral images from the IMAGE spacecraft show enhanced precipitation in the cusp. Following these plasma injections, channels of fast convection flows are observed in the ionosphere by the SuperDARN radars. On the basis of the spatial and temporal relationships between these various signatures, we analyze the response of the dayside magnetosphere and ionosphere to the pressure pulses as follows: (1) the solar wind dynamic pressure pulses are the drivers of plasma injections from the magnetosheath into the cusp; (2) the ionospheric convection bursts start shortly after the auroral intensifications and their duration is much longer (10 min versus 4-6 min for the auroral intensifications); (3) the convection bursts occur on the poleward side of the cusp precipitation; and (4) the Alfvn waves that are responsible of the transmission of the magnetic stress from the reconnection site to the ionosphere are strongly reflected in the upper ionosphere. This, in addition to possible parallel potential drops, may explain the imperfect mapping of the magnetospheric electric field into the ionosphere during the injections. These observations demonstrate that the convection bursts are "fossil" signatures of the compression-injection process, which is also a signature of reconnection at the dayside magnetopause driven by the interplanetary magnetic field alone.

Cerisier, Jean-Claude; Marchaudon, AurLie; Bosqued, Jean-Michel; McWilliams, Kathryn; Frey, Harald U.; Bouhram, Mehdi; Laakso, Harri; Dunlop, Malcolm; FRster, Matthias; Fazakerley, Andrew

2005-08-01

33

Nonlinear excitation of plasma convection  

NASA Astrophysics Data System (ADS)

The parametric excitation processes of the zero-frequency modes are considered. Cheng and Okuda (1977, 1978) have found that the rapid generation of convective cells is associated with drift-wave turbulence in an inhomogeneous magnetized plasma. The present investigation is concerned with an analysis of the process of parametric excitation of electrostatic cells by drift waves, taking into account also the excitation of magnetostatic modes by kinetic Alfven waves. The linear properties of the low-frequency modes are considered, giving attention to the convective cell mode and the magnetostatic mode. Relations to perpendicular diffusion are explored. Equilibrium convective cell fluctuations are investigated along with equilibrium magnetostatic fluctuations, and an estimate of cross-field diffusion is obtained. A study is conducted of the magnetostatic modes and the nonlinear stages of the convective cells, taking into consideration the coupling.

Spatschek, K. H.; Laedke, E. W.; Shukla, P. K.; Yu, M. Y.

34

Modeling of artificial plasma 'bubble' in ionosphere  

NASA Astrophysics Data System (ADS)

Results of a combination of radio-crossing and in situ measurements of plasma density in an artificial plasma 'bubble' in the ionosphere are presented. A shaped charge barium injection was made at a short distance (not greater than 50 m) to plasma diagnostics on the rocket. After injection the rocket passed through an expanding plasma shell. Plasma density depletion inside was more than one order and plasma enhancements on the boundary about 3-5 times that of the background. When the rocket passed the shell and traveled 2.1 km an abrupt drop of telemetry signal level was registered, though the plasma density was not more than 3000 s/cu m.

Oraevskii, V. N.; Ruzhin, Iu. Ia.; Skomarovskii, V. S.; Korobeinikov, V. G.; Kashirin, A. I.; Khriukin, V. I.

1992-12-01

35

The magnetosphere ionosphere system from the perspective of plasma circulation: A tutorial  

NASA Astrophysics Data System (ADS)

This tutorial review examines the role of O+ in the dynamics of magnetosphere ionosphere coupling. The life cycle of an O+ plasma element is considered as it circulates from the mid- to high-latitude ionosphere. Energization and diversion of the convecting plasma element into outflows involves Alfvnic turbulence at the low-altitude base of the cusp and plasmasheet boundary layer and in downward-current pressure cookers. Observational evidence indicating that O+ dominates the plasmasheet and ring current during extreme storm intervals is reviewed. The impacts of an O+-enriched plasma on solar wind magnetosphere ionosphere coupling are considered at both the micro and global scales. A synthesis of results from observation, theory and simulations suggests that the presence of O+ in the magnetosphere is both a disruptive and a moderating agent in maintaining the balance between dayside and nightside magnetic merging.

Lotko, W.

2007-03-01

36

Nonlinear dynamic processes in modified ionospheric plasma  

NASA Astrophysics Data System (ADS)

Presented work is a contribution to the experimental and theoretical study of nonlinear effects arising on ionospheric plasma under the action of powerful radio emission (G.I. Terina, J. Atm. Terr. Phys., 1995, v.57, p.273; A.V. Kochetov et. al., Advances in Space Research, 2002, in press). The experimental results were obtained by the method of sounding of artificially disturbed ionosphere by short radio pulses. The amplitude and phase characteristics of scattered signal as of "caviton" type (CS) (analogy of narrow-band component of stimulation electromagnetic emission (SEE)) as the main signal (MS) of probing transmitter are considered. The theoretical model is based on numerical solution of driven nonlinear Shrdinger equation (NSE) in inhomogeneous plasma. The simulation allows us to study a self-consistent spatial-temporal dynamics of field and plasma. The observed evolution of phase characteristics of MS and CS qualitatively correspond to the results of numerical simulation and demonstrate the penetration processes of powerful electromagnetic wave in supercritical (in linear approach) plasma regions. The modeling results explain also the periodic generation of CS, the travel CS maximum down to density gradient, the aftereffect of CS. The obtained results show the excitation of strong turbulence and allow us to interpret CS, NC and so far inexplicable phenomena as "spikes" too. The work was supported in part by Russian Foundation for Basic Research (grants Nos. 99-02-16642, 99-02- 16399).

Kochetov, A.; Terina, G.

37

Ionospheric Signatures of Plasma Injections in the Cusp Triggered by Solar Wind Pressure Pulses  

NASA Astrophysics Data System (ADS)

During sporadic reconnection events (flux transfer events or FTEs) at the dayside magnetopause, magnetosheath plasma enters the magnetosphere along cusp field lines. It is expected that these enhanced parallel plasma flows occur in conjunction with enhanced ionospheric convection events driven by the magnetic tension at the reconnection site. Associated optical auroral emissions result from enhanced precipitation of the magnetosheath plasma. If such events have long been recognised as due to IMF variations, the triggering role of solar wind pressure pulses is not definitely established. We analyse coordinated observations made on July 14, 2001 simultaneously in the mid-altitude cusp by Cluster and at the ionospheric magnetic footprint by SuperDARN and IMAGE during a period of three successive solar wind dynamic pressure pulses. In association with each of these pulses, Cluster observes plasma injections while auroral images from the IMAGE spacecraft show enhanced precipitation in the cusp. Following these plasma injections, convection flow channels are observed in the ionosphere by the SuperDARN radars. Based on the spatial and temporal relation between these various signatures, a description of the response of the dayside magnetosphere to the pressure pulses is proposed. The main considerations involved in this description are: (1) the solar wind dynamic pressure pulses are the drivers of plasma injections from the magnetosheath. (2) The ionospheric convection bursts start shortly after the auroral intensifications and their duration is much longer (10 min as against 4 to 6 min for the auroral intensifications). (3) The convection bursts do not occur at the same latitude as the precipitation, but on the poleward side of the cusp precipitation. (4) Alfvn waves are responsible of the transmission of the magnetic stress from the reconnection site to the ionosphere where they are strongly attenuated by reflection in the upper ionosphere. This set of observations demonstrates that the convection bursts are a "fossil" signature of the compression-injection process as it is also the case for reconnection at the dayside magnetopause driven by the IMF alone.

Cerisier, J.; Marchaudon, A.; Bosqued, J.; McWilliams, K.; Frey, H.; Bouhram, M.; Forster, M.

2004-12-01

38

The growth of plasma convection in Saturn's inner magnetosphere  

NASA Astrophysics Data System (ADS)

We report Rice Convection Model simulations of centrifugally driven plasma convection in Saturn's inner magnetosphere (2plasma source. The distributed plasma source is a key element that distinguishes convection at Saturn, where the source is broadly distributed, from that at Jupiter, where the source is largely confined to the Io torus. At Saturn, the broadly distributed source produces fast, narrow inflow channels alternating with slower, wider outflow channels, consistent with Cassini Plasma Spectrometer observations. We have also investigated the relative roles of pickup currents and Coriolis acceleration in producing the magnetospheric corotation lag. Comparison with observed corotation lags indicates that the plasma source model adopted in earlier RCM simulations needs refinement. We will incorporate newer plasma source models [e.g., Smith et al., 2010] that imply much larger plasma mass loading rates and different radial distributions of charge exchange versus electron impact ionization rates. We expect that this modification will be partly compensated by increasing the assumed Pedersen conductance of Saturn's ionosphere, as also indicated by recent aeronomical calculations [Moore et al., 2010].

Liu, X.; Hill, T. W.; Wolf, R. A.; Smith, H. T.; Chen, Y.

2010-12-01

39

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

40

A three-dimensional numerical model of ionospheric plasma in the magnetosphere  

SciTech Connect

The magnetospheric transport of terrestrial plasma is numerically investigated by means of three-dimensional particle trajectory tracing in empirical models of the geoelectric and geomagnetic fields. Various ionospheric outflows (auroral, polar cap, cusp, and polar wind) are systematically examined using observational definitions of their respective locations and strengths, and assuming purely adiabatic motions under the effect of the large-scale magnetospheric convection. Due to field model limitations, the simulations are limited in scope of the region within a geocentric radius of 17 {ital R}{sub {ital E}}. Consequently, much of the terrestiral H{sup +} outflow cannot be accurately traced beyond the polar cap region, and the conclusions concerning the terrestrial contribution to plasma sheet H{sup +} are necessarily limited. Many qualitative features of the plasma sheet are produced in the model by the ionospheric plasmas. The motions of terrestrial O{sup +} outflow are well described within the assumptions of the calculation.

Delcourt, D.C.; Chappell, C.R.; Moore, T.E.; Waite, J.H. Jr. (Space Science Laboratory, Marshall Space Flight Center, Huntsville, Alabama (USA))

1989-09-01

41

First measurements of the ionospheric plasma escape from Mars  

Microsoft Academic Search

The results are reported of an ion-composition experiment on board the Phobos 2 spacecraft which was used to determine the loss of plasma from the Martian ionosphere. Surprisingly, there are many similarities between the ionospheric outflow from Mars and earth. The ion loss from Mars results from both ion pickup due to mass-loading of the solar wind in the Martian

R. Lundin; H. Borg; B. Hultqvist; A. Zakharov; R. Pellinen; N. Pissarenko; E. M. Dubinin; S. W. Barabash; I. Liede; H. Koskinen

1989-01-01

42

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

43

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

44

Investigating the Importance of Viscous Interactions on Ionospheric Convection via Comparisons of Open-Closed Boundaries (OCBs) and Convection Reversal Boundaries (CRBs)  

NASA Astrophysics Data System (ADS)

Geomagnetic storms cause large global disturbances in the Earth's magnetosphere, during which large amounts of energy are deposited in the magnetotail and inner magnetosphere, producing an enhanced ring current and energising plasma to relativistic levels by poorly-understood excitation mechanisms. A previous study by Hutchinson et al. [2011] identified 143 geomagnetic storms over the last solar cycle (1997-2008) from the global SYM-H index and associated solar wind (SW) data from the Advanced Composition Explorer (ACE) spacecraft. Current work continues to use this dataset to investigate the characteristic ionospheric convection during magnetic storms via radar backscatter observed by the Super Dual Auroral Radar Network (SuperDARN). A superposed epoch analysis is completed using the map potential technique of Ruohoniemi and Baker [1998]. This technique has previously successfully been used to investigate substorm convection, however the technique has not particularly been employed for studies of geomagnetic storms nor has the model fit been applied to combined radar data from multiple storms for statistical studies rather than performing the analysis on an individual storm by storm basis. Latitude-Time-Velocity (LTV) plots, analogous to standard Range-Time-Intensity (RTI) plots, are used to visualise the results, which show the 'average' ionospheric response during different sized geomagnetic storms as the substorm control on the convection is mostly 'averaged out'. This, along with the cross-cap potential derived from the superposed SuperDARN results, is compared with similarly superposed auroral images from the IMAGE and POLAR spacecraft missions to better constrain the storm time coupling between the solar wind and magnetosphere. Results from the comparison of the convection reversal boundaries (derived from the SuperDARN data) and open-closed boundaries (from the auroral imagery) are presented to investigate the significance of a possible viscous interaction between the solar wind and the magnetosphere in addition to the normal reconnection-driven interaction.

Hutchinson, J. A.; Wright, D. M.; Milan, S. E.; Grocott, A.; Boakes, P. D.

2012-04-01

45

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)

1996-03-15

46

Discovery of the plasma caves in the lower ionosphere  

NASA Astrophysics Data System (ADS)

This paper discovers the ionospheric plasma caves and/or tunnels by observations of the Dynamic Explorer-2 (DE-2) satellite during 1981-1983 and simulations of the International Reference Ionosphere (IRI-2007). The IRI simulation predicts remarkable electron densities reductions located underneath the equatorial ionization anomaly (EIA), which are termed the plasma caves. The plasma caves are daytime features (08:00-19:00LT), and range from the E-region up to 250 km altitude with 10 width in the latitudinal direction. In-situ measurements of the ion and electron densities probed by the DE-2 confirm existence of the plasma caves at low altitudes of the EIA ionosphere.

Lee, I.; Liu, J.; Oyama, K.; Chen, C.; Lin, C.

2011-12-01

47

High-latitude ionospheric convection pattern during steady northward interplanetary magnetic field  

SciTech Connect

The DMSP F8 satellite`s coverage of Earth`s polar regions provides horizontal ion drift velocities along the dawn-dusk meridian at approximately 835 km altitude in each hemisphere during the 100 min orbital period. The authors examine the ionospheric convection signatures observed by this spacecraft in the summer and winter hemispheres during periods when the interplanetary magnetic field (IMF) is directed northward for at least 45 min prior to the satellite entering the polar region and remains northward throughout the polar pass. These convection signatures can be readily categorized by the number of sunward and antisunward flow regions and by their potential distributions. Here the authors describe the most frequently identifiable and reproducible features of the convection pattern that exist during steady northward IMF conditions. In addition to IMF Bz, the influences on the convection pattern of the IMF Bz.

Cumnock, J.A.; Heelis, R.A.; Hairston, M.R.; Newell, P.T.

1995-08-01

48

Ionospheric convection observed by SuperDARN during ongoing lobe reconnection revealed by Cluster .  

NASA Astrophysics Data System (ADS)

Since Dungey's work in the early sixties, who suggested that the interplanetary magnetic field and the geomagnetic field could reconnect, a lot of debate has been going on regarding how the reconnection process exactly occurs at the Earth's magnetopause. In fact, many fundamental questions remain unanswered, in particular regarding the shape and the extension of the reconnection sites for variable IMF orientation. The polar ionospheric convection strongly depends on the orientation of the IMF; such dependence can be explained in the framework of the reconnection between interplanetary and geomagnetic fields. Here we use SuperDARN observations of the ionospheric convection in coordination with space observations provided by the Cluster spacecraft to infer large scale configuration and evolution of the reconnection at the magnetopause during an extended period of Northward IMF.

Marcucci, M. F.; Amata, E.; Ambrosino, D.; Coco, I.; Bavassano Cattaneo, M. B.; Retin, A.

49

Magnetosphere-Ionosphere Coupling: Effects of E-Region Plasma Turbulence on Ionospheric Conductances  

Microsoft Academic Search

During periods of intense geomagnetic activity, strong electric fields and currents penetrate from the magnetosphere into the high-latitude E region ionosphere where they dissipate a significant fraction of their energy. In this region, electrons are magnetized while ions are demagnetized due to frequent collisions with the neutral atmosphere causing the strong electric fields to generate intense electrojets that excite plasma

Y. S. Dimant; M. M. Oppenheim

2010-01-01

50

Global-scale observations of ionospheric convection variation in response to sudden increases in the solar wind dynamic pressure  

NASA Astrophysics Data System (ADS)

We have used a superposed epoch analysis to study 205 sudden commencement (SC) events detected with ground-based magnetometers between the years 2000 and 2007. The strength of the SC events was clearly correlated to the magnitude of the jump in the solar wind dynamic pressure, regardless of whether or not the SC events were followed by a magnetic storm. Data from the Super Dual Auroral Radar Network (SuperDARN) demonstrated that both the ionospheric plasma drift speed and the number of echoes increased in the noon sector in response to the increase in solar wind dynamic pressure. In contrast, the number of SuperDARN echoes in the midnight sector decreased as the solar wind dynamic pressure increased, even though the average drift speed in the midnight sector also increased. We also uncovered that the ionosphere and ring current evolve differently in response to the pressure pulses. The SYM-H index, which represents changes in both the magnetopause and ring currents, responded immediately and either rapidly returned to pre-SC values or progressed into the main phase of a geomagnetic storm. In contrast, the ionospheric convection data were affected for a much longer time. The implication is that the ring current reacts to a sudden compression of the magnetosphere on a time scale of 10 min, while the convection pattern itself is affected for as long as the increase in solar wind dynamic pressure is sustained, or until a geomagnetic storm was triggered, as is the case in the sudden storm commencement (SSC) subset of events.

Gillies, D. M.; St.-Maurice, J.-P.; McWilliams, K. A.; Milan, S.

2012-04-01

51

Interplanetary magnetic field By and auroral conductance effects on high-latitude ionospheric convection patterns  

NASA Astrophysics Data System (ADS)

The dependence of the ionospheric electric potential (convection) on the interplanetary magnetic field (IMF) and the ionospheric conductivity is investigated to understand the generation of convection patterns in the framework of the solar wind-magnetosphere-ionosphere (S-M-I) coupling scheme and the merging concept. A numerical magnetohydrodynamic (MHD) simulation is adopted for the study of the present problem. To achieve a high resolution in the ionosphere, the MHD calculation employs the finite volume (FV) total-variation diminishing (TVD) scheme with an unstructured grid system. The two-cell convection patterns reproduced from simulation are shown for several cases under the southward IMF condition during the growth-phase interval. In the investigation of these results, special attention is paid to the analysis of mirror symmetry in the convection patterns with respect to the IMF By. On the dayside in the Northern Hemisphere, IMF By- (By+) generates flow deflection on newly opened field lines toward the dusk (dawn) without a severe violation of the mirror symmetry. While the mirror symmetry of the convection pattern is maintained even on the nightside when the ionospheric conductivity is uniform, it is not maintained on the nightside when the ionospheric conductivity is nonuniform. A realistic ionospheric conductivity modifies the convection pattern in the Northern (Southern) Hemisphere so as to emphasize distinctive features seen for IMF By+ (By-) under a uniform conductivity, and the reproduced convection patterns coincide with the observation quite well including fine signatures on the nightside, both for IMF By- and By+. Because of the nonuniform conductivity, cell centers of convection are shifted to the earlier magnetic local times, and the antisunward flow in the northern polar cap is nearly aligned with noon-midnight meridian for IMF By-, while the flow in the northern polar cap has a significant inclination from prenoon to premidnight for IMF By+. These convection patterns can be understood by considering the effect due to the Hall current closure of the region-1 field-aligned current. The analysis for the dependence of nightside convection on IMF By and ionospheric conductivity shows that the Harang discontinuity is attributed partially to the structure of magnetospheric driver but mainly to the effect of nonuniform auroral conductivity. As a consequence, it is more adequate to say that convection patterns are more or less caused by the synthesized effect of more than one process rather than a single elementary process. Reproduced convection patterns in this paper show a particular coincidence with satellite observations summarized by adopting the pattern-recognition-based approach.

Tanaka, T.

2001-11-01

52

The Relationship Between Convection Velocities in Simultaneous High-Latitude Ionospheres  

NASA Astrophysics Data System (ADS)

Depending on the dipole tilt angle of the Earth's magnetosphere, the northern and southern hemispheres can have dramatically different average conductances. Because the ionosphere provides a path through which magnetospheric field-aligned currents coupling the two regions close, it is expected that the electric field and current density would also exhibit asymmetric behavior between hemispheres that depend on the dipole tilt angle. Some magnetohydrodynamic models of the magnetosphere show that the ratio of the global hemispheric electric potential can be a factor of 2-4 for large dipole tilt angles. Statistical studies of ionospheric electric fields using ground-based radars and spacecraft also show that there is a seasonal dependence of the global ionospheric potential but that the difference is at most ~20%. Here we use merged line-of-sight velocity vectors obtained simultaneously in both hemispheres from the SuperDARN network of HF radars to investigate the relationship of the convection velocity for conditions of varying hemispheric conductance. We find a marked difference in the hemispheric relationship of the simultaneous convection velocities between the dayside and the nightside ionospheres. Using a dataset consisting of seven years of SuperDARN merged velocities centered roughly on the most recent solar maximum, we show statistically that the ratio of velocities restricted to the dayside in the Summer hemisphere to those in the dayside Winter hemisphere depends only marginally on the dipole tilt angle and is at most a factor of ~1.2 for extreme tilt angles. The ratio of merged velocities restricted to the nightside, however, show a strong dependence on dipole tilt angle and can be as high as 2 for extreme tilt angles. The results are consistent with the notion that the dayside magnetosphere-ionosphere circuit behaves as if driven by a constant voltage source, whereas the nightside acts more like a circuit with a constant current source.

Shepherd, S. G.; Murr, D. L.; Ruohoniemi, J. M.

2007-12-01

53

Source mechanisms and radio effects of ionospheric plasma  

Microsoft Academic Search

Since October 1, 1991 experimental and theoretical research has been conducted by Prof. Min-Chang Lee and his students at BU and MIT. This research work is aimed at investigating the ionospheric plasma disturbances which can affect significantly the radio wave propagation in communications and space surveillance. The research topics which have been investigated include: (1) A source mechanism leading to

Min-Chang Lee

1992-01-01

54

The influence of high speed plasma streams on the ionospheric plasma  

Microsoft Academic Search

As shown by statistical investigations, high speed plasma streams (HSPS) in the solar wind cause direct ionospheric effects in the D- and Es-layers at auroral and subauroral latitudes due to increasing precipitation of high energetic particles as well as indirect effects in the F2-region at high, middle and equatorial latitudes caused by auroral heating processes. The ionospheric effects increase with

J. Bremer

1996-01-01

55

Plasma sheet dynamics - Effects on, and feedback from, the polar ionosphere  

Microsoft Academic Search

The plasma sheet is shown to play a major role in determining the electric fields, currents, and particle precipitation regions in the polar ionosphere and upper atmosphere. In turn, ionospheric effects on electric fields and currents within the magnetotail are potentially important for plasma sheet dynamics. The whole is a particularly complex instance of magnetosphere-ionosphere coupling, not adequately yielding to

V. M. Vasyliunas

1981-01-01

56

Meteor Plasmas in the E-Region Ionosphere  

NASA Astrophysics Data System (ADS)

Every day billions of tiny meteoroids impact the Earth's atmosphere at hypersonic speeds, creating dense plasmas between 80 and 130 km altitude. In this part of the E-region ionosphere electrons are magnetized by the geomagnetic field while ions are largely unmagnetized due to their frequent collisions with neutral atmosphere. This discrepancy leads to a variety of inhomogeneous, unstable, and nonlinear plasma phenomena. Among them is the formation of field-aligned irregularities in the slowly diffusing dense meteor plasma trails which are important for radar observations of mostly optically invisible meteors. We will present a quantitative model of the evolution of a plasma trail density and its ambipolar electric fields. Our theory predicts that plasma trail diffusion induces electric currents through a large volume of the background ionosphere with important consequences for plasma trail diffusion. Also, strong electric fields propagate long distances along the magnetic field lines from the dense plasma trail deep into the tenuous ionosphere and create significant disturbances of the background density. This may explain radar and rocket observations of extensive nighttime E-region density structures.

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

2012-10-01

57

Transient Convection in the Nightside Subauroral Ionosphere: Occurrence Statistics and Driving Influences  

NASA Astrophysics Data System (ADS)

The expansion of the Super Dual Auroral Radar Network (SuperDARN) to middle latitudes in recent years provides new capabilities to investigate the electrodynamics of the subauroral ionosphere with unprecedented spatiotemporal resolution and coverage. At the present time there are four mid-latitude SuperDARN radars operational in the United States. During periods of quiet geomagnetic activity mid-latitude SuperDARN radars tend to see long-lived bands of ionospheric irregularities co-rotating or drifting slowly westward across the night side. Superposed on this average behavior are episodic events in which the convection velocities of the irregularities become enhanced for a period of a few tens of minutes. In this presentation we relate the occurrence of these convection transients to the location of the auroral oval, interplanetary parameters, and measurements of geomagnetic activity at high and middle latitudes. We discuss the extent to which the subauroral transients can be associated with direct penetration of the interplanetary electric field into the subauroral ionosphere and/or the ionosopheric impacts of substorm activity occurring at higher latitudes.

Baker, J. B.; Clausen, L.; Ruohoniemi, J. M.; Ribeiro, A.; Thomas, E. G.; Frissell, N. A.

2010-12-01

58

Recirculation and Acceleration of Ionospheric Plasma in the Martian Magnetospheres  

NASA Astrophysics Data System (ADS)

The presence of strong crustal remnant magnetic fields on Mars has important influence on the dynamical behavior of the ionospheric plasma. A model based on computational simulation of the time-varying configuration of the mini-magnetosphere is described to examine the possible process of acceleration and heating of photo electrons and ions embedded in the magnetic flux tubes as Mars rotates from dawn to dusk. The main idea is that ionospheric H+ and O+ ions pumped into the mini-magnetospheres on the dawn side could be subject to adiabatic heating during "depolarization" of the magnetic field as the local time approaches noon.

Ip, Wing-Huen

2012-07-01

59

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

60

Plasma diagnostics with Langmuir probes in the equatorial ionosphere: II. Evaluation of DEOS flight F06  

NASA Astrophysics Data System (ADS)

The flight data of an ionospheric sounding rocket (DEOS campaign flight F06) are evaluated with respect to electron density and temperature profiles. The probe characteristic is analysed in the frame of a model that takes the influence of the geomagnetic field and of a contamination layer into account, as described in part I (Piel et al 2001 J. Phys. D: Appl. Phys.). The electron temperature of the night-time ionosphere is found to be higher (1300 K) than that predicted by the IRI-95 model (Bilitza D 1999 J. Atmos. Terr. Phys. 61 167), but in general agreement with the model of Watanabe et al (Watanabe et al 1995 J. Geophys. Res. 100 14 581). It is also found that the electron temperature in depleted plasma regions (plasma bubbles) is lower than in the unperturbed plasma. This is a hint at the action of the Rayleigh-Taylor mechanism that convects cold low-density plasma from the bottomside of the F-layer to higher altitudes inside the plasma bubbles. An absolute comparison of the electron density profiles from the analysis of the Langmuir probe and by an independent impedance probe is performed. Excellent agreement of the profile shape and of absolute density values can be achieved over the entire altitude regime. It is demonstrated which steps in the evaluation procedure of the probe characteristic may lead to systematic errors in electron density.

Hirt, M.; Steigies, C. T.; Piel, A.

2001-09-01

61

On the Generation of Enhanced Sunward Convection and Transpolar Aurora in the High-Latitude Ionosphere by Magnetic Merging  

NASA Astrophysics Data System (ADS)

The IMAGE SI-12 instrument indicates a region of diffuse aurora poleward of the duskside Northern Hemisphere oval, while the IMAGE WIC instrument observes a transpolar auroral (TPA) feature at the polar cap boundary of the diffuse aurora during much of the 0110 UT to 0445 UT time interval on 16 December 2001. We here focus on the 0302 UT to 0312 UT period when the SuperDARN convection data display enhanced 800-1100 m/s sunward directed ionospheric flows near the TPA region in a four-degree wide region centered at 81o magnetic latitude between 14 MLT and 16 MLT. This flow channel seemingly drives a single dayside lobe cell with a convection reversal boundary near 84o and 14 MLT. At 0300 UT, the Cluster C1 S/C traverses the Northern Hemisphere duskside flank magnetopause at [X,Y,Z]=[-1.2,9.2,9.1] RE (GSM) where it encounters a localized density depletion region and a clear deflection of the bulk plasma velocity relative to the observed magnetosheath flow. The magnetic field and plasma velocity observed by C1 satisfy the Walen stress balance relation for a rotational discontinuity and the corresponding flow deflection dV suggests a merging site poleward and tailward of the spacecraft. The IMF magnitude as measured by ACE is 18 nT with a steady and favorable 45o clock angle (positive By and Bz) direction for merging in the vicinity of these duskside regions. The Tsyganenko T01 model maps the Cluster position to 75o and 14 MLT at 0130 UT or a few degrees equatorward of the ionospheric flow channel. Based on these data sets, we examine whether the active merging region on the magnetopause is consistent with the enhanced flow signatures observed by SuperDARN on 16 December 2001 and the IMAGE observations in these duskside high-latitude regions. An MHD simulation of this event puts these observations into a global context and is further used to map the Cluster location at the time of the plasma flow deflections to the ionosphere.

Eriksson, S.; Baker, J. B.; Petrinec, S. M.; Elkington, S. R.; Dunlop, M. W.; Reme, H.; Greenwald, R. A.; Frey, H. U.; Ergun, R. E.; Balogh, A.

2004-12-01

62

Supermagnetosonic subsolar magnetosheath jets and their effects: from the solar wind to the ionospheric convection  

NASA Astrophysics Data System (ADS)

It has recently been proposed that ripples inherent to the bow shock during radial interplanetary magnetic field (IMF) may produce local high speed flows in the magnetosheath. These jets can have a dynamic pressure much larger than the dynamic pressure of the solar wind. On 17 March 2007, several jets of this type were observed by the Cluster spacecraft. We study in detail these jets and their effects on the magnetopause, the magnetosphere, and the ionospheric convection. We find that (1) the jets could have a scale size of up to a few RE but less than ~6 RE transverse to the XGSE axis; (2) the jets caused significant local magnetopause perturbations due to their high dynamic pressure; (3) during the period when the jets were observed, irregular pulsations at the geostationary orbit and localised flow enhancements in the ionosphere were detected. We suggest that these inner magnetospheric phenomena were caused by the magnetosheath jets.

Hietala, H.; Partamies, N.; Laitinen, T. V.; Clausen, L. B. N.; Facsk, G.; Vaivads, A.; Koskinen, H. E. J.; Dandouras, I.; Rme, H.; Lucek, E. A.

2012-01-01

63

DEMETER Observations of Equatorial Plasma Depletions and Related Ionospheric Phenomena  

NASA Astrophysics Data System (ADS)

DEMETER, the first micro-satellite of the CNES MYRIAD program, was launched from Baikonour on June 29, 2004 on a nearly circular, quasi helio-synchronous polar orbit at ~ 715 km altitude. The DEMETER mission focuses primarily on the search for a possible coupling between seismic activity and ionospheric disturbances as well as on the effects of natural phenomena such as tropospheric thunderstorms and man-made activities on the ionosphere. The scientific payload provides fairly complete measurements of the ionospheric plasma, energetic particles above ~ 70 keV, and plasma waves, up to 20 kHz for the magnetic and 3.3 MHz for the electric components. Several studies related to space weather and ionospheric physics have been conducted over the past years. Following a brief description of the payload and the satellite modes of operation, this presentation will focus on a set of results that provide a new insight into the physics of instabilities in the night-time equatorial ionosphere. The observations were performed during the major magnetic storm of November 2004. Deep plasma depletions were observed on several night-time passes at low latitudes characterized by the decrease of the plasma density by nearly 3 orders of magnitude relative to the undisturbed plasma, and a significant abundance of molecular ions. These features can be best interpreted as resulting from the rise of the F-layer above the satellite altitude over an extended region of the ionosphere. In one of the passes, DEMETER was operated in the Burst mode and the corresponding high resolution data allowed for the discovery of two unexpected phenomena. The first one is the existence of high intensity monochromatic wave packets at the LH frequency that develop during the decay phase of intense bursts of broadband LH turbulence. The broadband LH turbulence is triggered by whistlers emitted by lightning from atmospheric thunderstorms beneath the satellite. The second unexpected feature is the detection of a population of super-thermal ionospheric ions with a density of about 2-3% of the thermal ion population. The super- thermal ions appeared to be heated to temperatures of a few eV at times when LH turbulence and monochromatic wave packets are observed while the temperature of the core ion population is not affected. High time resolution plasma density measurements show the presence of strong small scale plasma irregularities in the depletions that scatter the high amplitude whistler waves and may lead to the development of strong LH turbulence and of monochromatic wave packets. The ensuing interaction between these waves and the ambient ions may lead to the formation of a super-thermal tail in the ion distribution function. Ion acceleration by LH turbulence and solitary waves is a commonly observed phenomenon along auroral magnetic field lines but, to our knowledge, this is the first time that a similar process has been observed in the equatorial ionosphere. These findings exemplify a novel coupling mechanism between the troposphere and the ionosphere: Under highly disturbed conditions at times of magnetic storms, part of the energy released by lightning and radiated as whistlers can dissipate in the equatorial ionosphere and produce super-thermal ion populations.

Berthelier, J.; Malingre, M.; Pfaff, R.; Jasperse, J.; Parrot, M.

2008-12-01

64

Transport of cold ions from the polar ionosphere to the plasma sheet  

NASA Astrophysics Data System (ADS)

Ionospheric outflow is believed to be a significant contribution to the magnetospheric plasma population. Ions are extracted from the ionosphere and transported downtail by the large-scale convection motion driven by dayside reconnection. In this paper, we use a comprehensive data set of cold ion (total energy less than 70 eV) measurements combined with simultaneous observations from the solar wind to investigate the fate of these ions. By tracing the trajectories of the ions, we are able to find out where in the magnetotail ions end up. By sorting the observation according to geomagnetic activity and solar wind parameters, we then generate maps of the fate regions in the magnetotail and investigate the effects of these drivers. Our results suggest that, on overall, for about 85% of the cases, the outflowing ions are transported to the plasma sheet. The region where the ions are deposited into the plasma sheet is larger during geomagnetic quiet time than during disturbed conditions. A persistent dawn-dusk asymmetry in the plasma sheet deposition is also observed.

Li, Kun; Haaland, S.; Eriksson, A.; Andr, M.; Engwall, E.; Wei, Y.; Kronberg, E. A.; Frnz, M.; Daly, P. W.; Zhao, H.; Ren, Q. Y.

2013-09-01

65

Night-side effects on the polar ionospheric convection due to a solar wind pressure impulse .  

NASA Astrophysics Data System (ADS)

The Sudden Impulse (SI) of solar wind dynamic pressure of 20 february 2000, 21:03 UT, is investigated by making use of data from WIND, GEOTAIL, POLAR and GOES; ground magnetometer chains (Greenland, IMAGE, CANOPUS); SuperDARN HF radars in both Northern and Southern hemispheres. The main effect of the SI described herein is an enhancement of the ionospheric convection around midnight MLT. We suggest that such an enhancement be due to an increase of the dawn-dusk electric field caused by the SI compression of the magnetospheric tail.

Coco, I.; Amata, E.; Marcucci, M. F.; Villain, J.-P.; Hanuise, C.; Cerisier, J.-C.; St. Maurice, J.-P.; Sato, N.

66

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

67

Formation and evolution of dusty plasma structures in the ionosphere  

NASA Astrophysics Data System (ADS)

A self-consistent model of the formation and evolution of dusty plasma structures in the ionosphere has been developed. The effect of the initial distributions of dust particles, as well as condensation and absorption of water molecules by dust particles, on the formation of noctilucent clouds and polar mesosphere summer echoes has been demonstrated. The possibility of the formation of a layered structure of noctilucent clouds has been illustrated.

Dubinskii, A. Yu.; Popel, S. I.

2012-09-01

68

New method for tracking the movement of ionospheric plasma  

NASA Astrophysics Data System (ADS)

A method to track the flow of plasma in the Earth's ionosphere is presented. This takes maps of total electron content (TEC) at various times, and by comparing them derives a map of bulk velocities. The method is a modification of the Horn-Schunck scheme used in computer vision, whereby the aperture problem (caused by the scalar input field not containing enough information to uniquely constrain the vector output field) is overcome by making pragmatic assumptions about the divergence and rotation of the flow. The continuity equation linking plasma velocity and density is given source terms constrained by models of plasma generation and recombination. This can be used to mitigate solar terminator effects, where the close proximity of daytime plasma generation and nighttime recombination causes the impression of plasma flow. The method successfully reconstructs the behavior of test data. It also gives plausible results with real electron density maps from the 2003 Halloween Storms.

Benton, C. J.; Mitchell, C. N.

2012-09-01

69

Effects of finite plasma pressure on centrifugally driven convection in Saturn's inner magnetosphere  

NASA Astrophysics Data System (ADS)

We have previously shown simulation results for centrifugally driven plasma convection in Saturn's inner magnetosphere (2 < L < 12) using the Rice Convection Model, including a continuously active distributed plasma source, and the effects of the Coriolis force and the pickup current. These simulations result in a quasi-steady state, in which fast, narrow inflow channels alternate with slower, wider outflow channels, consistent with Cassini Plasma Spectrometer observations. These previous simulations, however, did not include the plasma pressure. We investigate here the effects of finite plasma pressure and the associated gradient-curvature drift current by giving the cold plasma a finite temperature. Our simulations confirm the theoretical expectation that a finite plasma pressure produces a force in the positive radial direction, the same direction as the centrifugal force, and acts as an additional driver of plasma convection. Our simulations also confirm that the radial velocities can be reduced (to keep them within observational constraints) by increasing the assumed ionospheric Pedersen conductance (also within observational constraints).

Liu, X.; Hill, T. W.

2012-07-01

70

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)

1995-03-01

71

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

72

Dynamics of Plasma Structures in the Equatorial Topside Ionosphere  

NASA Astrophysics Data System (ADS)

Space based communication and navigation systems are significantly affected by large spatial gradients in the topside ionospheric plasma density and by irregularities that generally appear at the edges of these gradients Spatial gradients commonly appear in the topside ionosphere at night driven by the gravitational Rayleigh-Taylor instability originating in the bottomside F region Many previous studies of this feature have focused on the occurrence probability of small scale plasma structure as a function of season and longitude or on the longitude distribution of spatial scales that make up the plasma structures To date there is little information about the latitude extent of such features of their internal dynamics due in large part to the restriction of data sources from fixed locations on Earth or from data obtained by satellites in low inclination orbits When such structures extend to latitudes beyond about 20 o the plasma gradients have a far reaching affect on communication and navigation systems since they exist over a greater proportion of the land mass In this study we plan to examine the latitudinal extent of equatorial plasma irregularity regions using data from the DMSP spacecraft This data brings a unique perspective to the problem by examining latitudinal or apex height variations within the envelope of a single structure We will discuss how the zonal and meridional drifts are related through a structure and the relationship between these drifts and the ion number density

Venkatraman, S.; Heelis, R.

73

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

74

Specific Plasma Ionospheric Excitations Modes in the Ionosphere Produced by Space Vehicle Launch and RE Entry and Natural Phenomena  

NASA Astrophysics Data System (ADS)

SPECIFIC PLASMA IONOSPHERIC EXCITATIONS MODES IN THE IONOSPHERE PRODUCED BY SPACE VEHICLE LAUNCH AND RE ENTRY AND NATURAL PHENOMENA We have examined both experimentally and theoretically the formation and excitation of highly well defined specific wave forms of plasma excitation in the D, E, F(1) and F(2) and sometimes G layers of the earth?s ionosphere. In our formal study period from October 1989 until December 1996, we measured 41 distinct events out of a possible 73 events utilizing ground based sensitive T1050 magnetometers. In five cases more than two to three stations were displayed and detected the same ionospheric excitations. Sometimes background noise was high and dominated the signals, but under good measurement conditions signals appeared to be 50 to 70 dbm over the background noise floor. Specific frequencies of the D-layer appeared around 5.2 to 6.52 Hz and E layer excitations were from 10.48 to 12.8 Hz. Sometimes an F double peak appeared around 15 to 17 Hz as excited by space shuttle activity and delta rockets and in several cases, large scale volcanism. A theoretical model has been developed which describes sustained long duration and long range coherent plasma excitation modes which occur when the ionospheric layers are shock excited. Alfven-like velocities of propogation are calculated in these ionospheric layer. Some Schumann resonates were observed from 7 to 8 Hz.

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

2001-10-01

75

Cold ionospheric plasma in Titan's magnetotail  

Microsoft Academic Search

The interaction between Titan and the corotating Saturnian plasma forms an induced magnetosphere with an elongated Alfven-wing-style magnetotail. On 26 December 2005, the Cassini spacecraft flew through Titan's magnetotail, providing the first distant tail observation, over 5 Titan radii downstream. We examine measurements observed by the magnetometer and Langmuir probe during this pass. We use the direction of the magnetic

H. Y. Wei; C. T. Russell; J.-E. Wahlund; M. K. Dougherty; C. Bertucci; R. Modolo; Y. J. Ma; F. M. Neubauer

2007-01-01

76

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

77

Momentum transfer between the Io plasma wake and Jupiter's ionosphere  

NASA Astrophysics Data System (ADS)

The interaction between Io and Jupiter is dramatically illustrated by recent ultraviolet and infrared imaging of Jupiter's ionosphere. Bright auroral emissions are observed at the base of Io's flux tube with emissions at the footprint of Io's wake extending large distances downstream (roughly 100 around Jupiter). We propose as a possible explanation for the persisting wake emissions a subcorotating torus flux tube downstream from Io that results in high-latitude parallel electric fields. The transfer of momentum to the subcorotating Iogenic plasma from first the corotating torus and eventually the Jovian ionosphere via the Alfvnic interaction result in intense field-aligned currents which can lead to the formation of parallel electric fields. By comparing the field-aligned current density of the initial Alfvnic disturbance generated by the stagnated flow in Io's wake to the required current density for steady state acceleration of the flux tube we infer a current limitation, or momentum decoupling, caused by a high-latitude field-aligned potential drop. As a result, the subcorotating flux tube is partially decoupled from the Jovian ionosphere and auroral emissions persist for large distances downstream of the initial Io-disturbed flux tube. Model results suggest that the extended wake emissions are initially driven by a 70 kV cross-wake potential, which is consistent with observed auroral emissions caused by electron precipitation with energy on the order of tens of keV.

Delamere, P. A.; Bagenal, F.; Ergun, R.; Su, Y.-J.

2003-06-01

78

Quasi-analytic models for density bubbles and plasma clouds in the equatorial ionosphere: 2. A simple Lagrangian transport model  

Microsoft Academic Search

The transport equations for the motion of plasma in the equatorial ionosphere are solved using exact solutions for induced electric potentials and deformation of plasma density coordinates. The primary purpose of the quasi-analytic model is to provide an efficient description of the plasma structure in the equatorial ionosphere suitable for investigation of effects on radio wave propagation and ionospheric sensors.

Paul A. Bernhardt

2007-01-01

79

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

NASA Astrophysics Data System (ADS)

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 magnetosphere and can significantly increase, or decrease ionopheric electron densities (termed positive or negative storms, respectively). Electric fields originating in the magnetosphere can penetrate to the equatorial and low-latitude ionosphere resulting in vertical motions that restructure the F- region density profiles due to the height dependence of the recombination rate. The effect of space weather related perturbations in electric fields and currents in the equatorial and low latitude magnetic field associated with the changes in magnetospheric convection can be investigated using simultaneous observations from ground as well as ionospheric measurements. The present solar cycle witnessed many solar flares and coronal mass ejections (CMEs) which gave rise to intense geomagnetic storms due to highly active solar environment. The series of X-class solar flares occurred from 2 - 15 April 2001. The geomagnetic field was intermittently disturbed during period due to the CME passages. The geomagnetic storm began on 31 March and 11April 2001 are considered for the present study. These events were selected to study from ground based geomagnetic data, multi satellite data of solar wind and interplanetary parameters. Influence of the magnetospheric storm time electric field changes are estimated by the changes in the equatorial electric field as evidenced by the disturbance parameter of the equatorial electrojet strength and corresponding ionospheric response.

Veenadhari, B.; Alex, S.

80

Equations of anisotropic hydrodynamics for electron component of the ionospheric plasma  

Microsoft Academic Search

In this paper we have derived a set of transport equations for thermal electron component of the ionospheric plasma in the presence of an anisotropy of the electron energy distribution. Expressions are calculated in a 16-moment approximation for the moments of integrals of elastic and inelastic collisions of thermal electrons with basic neutral ionospheric components. The obtained moments determine variations

Iu. V. Konikov; G. V. Khazanov

1983-01-01

81

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

82

Dust plasma line in the radionoise of ionosphere  

NASA Astrophysics Data System (ADS)

During our investigations of the ionosphere radionoise fluctuation spectra in the frequency range 150 Hz an interesting spectral line was found. Parameters of the- line differ seriously from the parameters of the typical radio interferences in the specified range. Frequency of the line floats in the frequency interval 15-50 Hz along with the spectral profile deformations and spectral power of the satellites during characteristic time from units to tens of minutes.Summarized line properties are as follows:a) the line is registered in the night time when meteor streams took place; thecorrelation with the maximum of Leonides -2000 and Perseides-1999 was found;b) the frequency of the line changes in accordance with geophysicalconditions; the line is clearly visible under low magnetic activity SumKp ~ 0 -15, (Perseides-1999, Leonides-2000), but no evidence of line was found whenthe magnetic activity index SumKp was > 30 (Perseides-2000, SumKp = 52);c) the particle precipitation in the ionosphere causes changes in the satellites;the solar X-ray flares reveal itself in the frequency change; terminator passagecauses the complex behavior of the line frequency and satellites shape;d) it seems that the line is the most sensitive to the terminator movement in theionosphere; after the terminator passage, the intensity of the line decreases andits frequency starts to increase up to 50 Hz (Nyquist frequency) and leavesmeasurement range;e) during Perseides-1999 the line was observed all the night long; during theLeonides-2000 the line was visible only near the peak of stream intensity. The origin and behavior of the line was impossible for us to explain by means of radio disturbance, non-linear properties of the night F-layer and turbulent ionosphere. One of the possible explanations may be the direct registration of the dust plasma line modulation of the ionosphere radio-noise during the meteor streams. Ionization, winds and disturbances of the upper atmosphere determine the line profile.

Musatenko, S.; Musatenko, Y.; Kurochka, E.; Choliy, V.; Lastochkin, A.; Slipchenko, O.

83

Absolute and convective instabilities in plasmas and solids  

NASA Astrophysics Data System (ADS)

The theory of absolute and convective instabilities in plasmas and solids is examined. Criteria of the absolute and convective instabilities of spatial amplification are derived and used to analyze specific systems in various fields of physics. The systems examined include optical quantum generators, acoustic amplifiers, and acoustic generators, Gunn diode, TWT, BWT, and two-beam amplifiers.

Fedorchenko, A. M.; Kotsarenko, N. Ia.

84

The Behavior of Ionospheric Plasma in Topside Equatorial Plasma Structures  

NASA Astrophysics Data System (ADS)

The DMSP spacecraft provides a unique view of topside plasma structures by frequently passing through a single depletion spanning a range of magnetic flux tube apex heights within it. This allows us to investigate the relationships between the evolving envelope of the structure and the plasma within it. In this report we describe the results of initial investigations where the angle between the satellite trajectory and plasma depletion allows different regions inside a bubble to be sampled. In particular we examine the relationships between the gradient in the vertical flow inside a bubble and the bubble width in longitude at different magnetic field apex heights.

Venkatraman, S. A.; Heelis, R. A.; Coley, W. R.

2006-05-01

85

The day time electric field disturbances at equator and associated changes in interplanetary electric field and the ionospheric plasma density during intense magnetic storm periods  

NASA Astrophysics Data System (ADS)

During periods of enhanced geomagnetic activity, the low latitude ionospheric plasma densities, electric fields and currents undergo strong perturbations. The direct penetration of the high latitude electric field to lower latitudes, and the disturbance dynamo, both play a significant role in restructuring the storm time equatorial ionosphere and thermosphere. Variations of the H component of the geomagnetic field at equator and at low latitude stations are investigated to show the counter electrojet (CEJ) events are associated with electric fields from Field aligned currents (FAC). It is well known that FAC are controlled by the interplanetary magnetic fields (IMF) and electric fields from the FAC can direct penetrate to equatorial ionosphere. Thus, the penetrated electric field plays a crucial part in the development of geomagnetic disturbances and ionospheric plasma motion in the low latitude and in the inner magnetosphere. The effect of space weather related perturbations in electric fields and currents in the equatorial and low latitude magnetic field associated with the changes in magnetospheric convection can be investigated using simultaneous observations from ground geomagnetic data and ionospheric data and satellite data during the intense magnetic storm periods. Equatorial magnetic field variations and counter electrojet events will be examined for magnetically disturbed periods in association with changes in interplanetary magnetic field and auroral electric fields.

Bhaskara, Veenadhari; Alex, S.; Singh, R.

86

Observation of Plasma Oscillating Structures in External Ionosphere over Cyclones  

NASA Astrophysics Data System (ADS)

The results of the observations of density, temperature, pressure of plasma, electrical fields and low-frequency fluctuations were obtained on both Cosmos-1809 and Intercosmos-Bulgaria-1300 satellites. The complex analysis of the results of observations showed the appearance of electrical fields and intensive low-frequency fluctuations, the reaction of electron density, temperature, pressure of plasma at the height of approximately 900 km above the regions of appearance and development of tropical and extra-tropical cyclones. The cases of simultaneous observations of several cyclones, which sharply changed their direction of motion are considered. At the same time over half of the cyclones identical plasma solutions were found. These structures have a core, where the oscillations of the density reach 10% and have a transverse scale of 10 km, and the periphery with smaller amplitudes and stretched density oscillations. These density holes filled with the electrostatic turbulence at the frequency of helium. The results obtained suggest that the different stages of development of tropical and extra-tropical cyclones and the formation of individual structural formations of the ionosphere are related dynamic processes

Belyaev, G.; Bankov, N.; , Boychev, B.; Kostin, V.; Trushkina, E.; Ovcharenko, O.

2012-08-01

87

Quasi-Analytic Models for Density Bubbles and Plasma Clouds in the Equatorial Ionosphere.  

National Technical Information Service (NTIS)

The equatorial ionosphere contains imbedded bubbles that rise though a horizontally stratified plasma. The motion of the bubbles are affect by gravity, neutral winds or external electric fields which produce electric fields in the F-Region density perturb...

P. A. Bernhardt

2006-01-01

88

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

89

On the generation of enhanced sunward convection and transpolar aurora in the high-latitude ionosphere by magnetic merging  

NASA Astrophysics Data System (ADS)

The IMAGE Wideband Imaging Camera (WIC) instrument observed the duskside development of an oval-aligned transpolar auroral arc (TPA) in the Northern Hemisphere (NH) on 16 December 2001 during strong IMF ?B? 18 nT and a generally steady 56 clock angle (positive IMF By and Bz). Observational evidence suggests that the dayside part of the duskside TPA formed due to quasi-continuous merging between the IMF and the lobe magnetic field tailward of the cusp while the nightside part is associated with the Harang discontinuity. The low-altitude CHAMP satellite confirms an upward northward IMF Bz (NBZ) field-aligned current (FAC) over the dayside TPA while associating a downward NBZ current with the region of diminished WIC emissions in between the auroral oval and the TPA. DMSP F14 suggests that the dayside region of the downward NBZ current coincides with precipitating magnetosheath-like ions of reversed energy-latitude dispersion consistent with high-latitude reconnection. SuperDARN observes enhanced ionospheric sunward flows generally centered between the oppositely directed NBZ currents. We associate these flows with a clockwise lobe convection vortex and the dayside part of the TPA. The nightside TPA, however, is related to stagnant or antisunward flow and the upward FAC region of the Harang discontinuity. Cluster observations confirm the simultaneous presence of rotational discontinuities across the duskside magnetopause with changes in the magnetosheath plasma velocity that indicate an active merging region poleward of Cluster. A global MHD simulation generates sunward flow between a pair of opposite FACs on either side of a lobe reconnection site near (X, Y, Z)GSM = (-4.7, 5.4, 10.2) RE thus conforming with Cluster and SuperDARN expectations. The sense of these FACs agrees with the low-altitude NBZ observations.

Eriksson, S.; Baker, J. B. H.; Petrinec, S. M.; Wang, H.; Rich, F. J.; Kuznetsova, M.; Dunlop, M. W.; RMe, H.; Greenwald, R. A.; Frey, H. U.; Lhr, H.; Ergun, R. E.; Balogh, A.; Carlson, C. W.

2005-11-01

90

Effects of convection driven gravity waves on equatorial electrojet plasma irregularities  

NASA Astrophysics Data System (ADS)

This study reports temporal and spatial quasi-oscillations (~12:00 to 15:30 UT) of coherent scatter radar echoes observed by the Sao Luis (Brazil) 30 MHz radar on January 9, 2002. This day can be considered as geomagnetically quiet, a_p <10. On the same day, corresponding to the same time interval, quasi-oscillations were also evident in the horizontal magnetic field perturbation (?H) data which was measured by the Sao Luis and Eusebio magnetometers. Spectral analysis on the (?H) signal reveals spectral power around the periods of 20 to 40 minutes which correspond to periods of atmospheric gravity waves. From about 1:00 to 12:00 UT, GOES 10 satellite IR images (for January 9, 2002) show strong tropospheric convection activity over Sao Luis. We, therefore, expect tropospheric convection through gravity waves to couple its energy to the E region ionosphere causing the quasi-oscillation observed in the radar and magnetic field data. Dynamo electric field generated by gravity waves interact with the background electric field to affect ionospheric currents and plasma irregularities giving rise to the quasi-oscillation of the scattering region observed by the Sao Luis radar on January 9, 2002. Further data analysis is in progress.

Shume, E.; de Paula, E. R.; Bageston, J. V.; Kherani, A.; Saba, M. M.

2010-12-01

91

High-latitude ionospheric convection models derived from Defense Meteorological Satellite Program ion drift observations and parameterized by the interplanetary magnetic field strength and direction  

NASA Astrophysics Data System (ADS)

A series of new high-latitude ionospheric convection models have been constructed using Defense Meteorological Satellite Program (DMSP) thermal ion drift measurements. The models are obtained by sorting cross polar cap electrostatic potentials into magnetic latitude/magnetic local time bins. A regression analysis of the potentials in each bin is then implemented for establishing the relationships to the interplanetary magnetic field (IMF) for three seasons: summer, winter, and equinox. A linear modeling formula for the ionospheric electrodynamics (LIMIE) yields a convection response to the average solar wind (i.e., the ``quasi-viscous'' interaction) and to changes in the IMF By, Bz <= 0, and Bz > 0 components. The modeled convection is a superposition of the first two parameters with either the IMF Bz <= 0 or the Bz > 0 component. A global model is created by fitting the regression analysis results to a spherical harmonic function. The resulting DMSP-based ionospheric convection model (DICM) is fully parameterized by the IMF strength and direction. With this model, ionospheric convection patterns can be generated for any IMF configuration during quiet to moderate geomagnetic conditions. We compare the DICM model with other available high-latitude convection patterns organized by the IMF. The new elements in DICM are its quasi-viscous and separate IMF-dependent terms for both the northern and southern polar regions, which are not explicitly found in other ionospheric convection studies. The DICM's seasonal dependence and interhemispheric symmetry/asymmetry features show 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.

Papitashvili, Vladimir O.; Rich, Frederick J.

2002-08-01

92

Effects of the ionospheric convection measured by SuperDARN on the ground electric field at polar station Hornsund  

NASA Astrophysics Data System (ADS)

We investigate the effects of ionospheric convection on the ground-level DC electric field measured at polar station Hornsund (77.00 N, 35.55 E). We use the results of a SuperDARN (SuperDual Auroral Radar Network) potential mapping technique to obtain the electric potential due to the ionospheric convection over Hornsund and we analyse diurnal variations of this potential. These are compared with the diurnal variations of the vertical component of the electric field observed at Hornsund in fair-weather conditions where the effects of low atmosphere global electric field generators have been removed by assuming a diurnal change according to the Carnegie curve. We conclude that a 10 kV change in the overhead convection potential results in an average change of the ground field of 10%. We also conclude that SuperDARN observations and the potential mapping technique can be used for the subtraction of the effects of magnetospheric influences on the atmospheric electricity parameters in polar regions.

Odzimek, Anna; Kubicki, Marek; Lester, Mark; Grocott, Adrian

2013-04-01

93

Lightning-induced plasma turbulence and ion heating in equatorial ionospheric depletions  

Microsoft Academic Search

A wide range of plasma instabilities exist in various regions of the terrestrial ionosphere, leading to the development of plasma turbulence, in particular close to the lower-hybrid frequency-the frequency of a longitudinal oscillation of ions and electrons in a magnetized plasma that must be near perpendicular to the magnetic field. Most observations have been carried out in the auroral regions,

Jean-Jacques Berthelier; Michel Malingre; Robert Pfaff; Elena Seran; Raymond Pottelette; John Jasperse; Jean-Pierre Lebreton; Michel Parrot

2008-01-01

94

Response of ions of ionospheric origin to storm time substorms: Coordinated observations over the ionosphere and in the plasma sheet  

Microsoft Academic Search

We investigate variations of ion flux over the ionosphere and in the plasma sheet when storm time substorms are initiated, using simultaneous observations of neutral atoms in the energy range of up to a few keV measured by the low-energy neutral atom (LENA) imager on board the Imager for Magnetopause-to-Aurora Global Exploration (IMAGE) satellite, outflowing ion flux of <1 keV

M. Nos; S. Taguchi; S. P. Christon; M. R. Collier; T. E. Moore; C. W. Carlson; J. P. McFadden

2009-01-01

95

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

96

High-Latitude Plasma Convection as a Function of Solar Wind and IMF Using a Simple Parameterization  

NASA Astrophysics Data System (ADS)

A simple parameterization of high-latitude ionospheric plasma convection patterns has been developed to study the relationship of the convection patterns to the speed and density of the solar wind and the interplanetary magnetic field (IMF). The parameterization includes the overall size of the convection pattern, the total potential drop, the orientation of the pattern, and the relative sizes of the dawn and dusk convection cells. The spherical harmonic fitting analysis of Ruohoniemi and Baker [1998] was applied to two years (1999, 2000) of SuperDARN HF-Radar data from the northern hemisphere. Solar Wind and IMF data were take from the definitive ACE key parameter data. Linear regression analysis was applied to determine the relationship of the convection pattern parameters to various combinations of solar wind and IMF parameters. The polar cap potential drop was found to be most strongly correlated to vBz, but a weaker correlation to v*abs(By) was also noted. The orientation of the convection pattern was well correlated with either By alone or the IMF clock angle. Ruohoniemi, J. M., and K. B. Baker, Large-scale imaging of high-latitude convection with SuperDARN HF-radar observations, J. Geophys. Res., 103, 20,797-20,811, 1998.

Baker, K. B.

2001-12-01

97

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

SciTech Connect

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-hour interval in question IMF B[sub z] oscillates between [plus minus] 7 nT with about a 1-hour period. Corresponding variations in the ground magnetic disturbance are observed which the authors infer are due to changes in ionospheric flow. Cross correlation of the data obtained from two ground stations at 73.5[degrees] magnetic latitude, but separated by [approximately]2 hours in MLT, shows that changes in the flow are initiated in the prenoon sector ([approximately]10 MLT) and then spread outward toward dawn and dusk with a phase speed of [approximately]5 km s[sup [minus]1] over the longitude range [approximately]8 to 12 MLT, slowing to [approximately] 2 km s[sup [minus]1] outside this range. Cross correlating the data from these ground stations with IMP 8 IMF B[sub z] records produces a MLT variation in the ground response delay relative to the IMF which is compatible with these deduced phase speeds. The authors interpret these observations in terms of the ionospheric response to the onset, expansion and decay of magnetic reconnection at the dayside magnetopause.

Saunders, M.A.; Freeman, M.P.; Southwood, D.J.; Cowley, S.W.H. (Imperial College of Science, Technology and Medicine, London (United Kingdom)); Lockwood, M. (Rutherford Appleton Lab., Oxfordshire (United Kingdom)); Samson, J.C. (Univ. of Alberta, Edmonton (Canada)); Farrugia, C.J. (NASA Goddard Space Flight Center, Greenbelt, MD (United States)); Hughes, T.J. (National Research Council of Canada, Ottawa, Ontario (Canada))

1992-12-01

98

Ionosphere plasma radio-noises and magnetosphere alfven resonator  

NASA Astrophysics Data System (ADS)

Observations of the ionosphere noises during direct or magnetically conjugated solar eclipses on 1999, 2001, 2002, 2003 let us conclude that one of the effects of the solar eclipse is appearance of ionosphere radionoise quasi-periodic burst trains. The train starts within ten seconds after radio-noise impulse and lasts up to 5 min. The same type trains may be detected in the absence of the eclipse but 5-10 times more rarely (once per 3-5 hours of measurements). The possible explanation of trains arising consists in forming of the magnetosphere Alfven resonator after warming of the ionosphere by the energetic particles precipitated from the magnetosphere into both magnetically conjugated points. The movement of the total eclipse phase from the morning terminator to the evening terminator is the strong source of the Alfven waves. Precipitations may be caused by wave-particle interaction in the top point of the force tube. It is known that during eclipse the ionization sources in E-region of ionosphere appears. So, schematic explanation of the phenomena is: lunar shadow in the ionosphere -> ionosphere irregularity -> Alfven wave -> wave-particle interaction -> precipitations into both hemispheres of ionosphere -> impedances violation -> creation of ionosphere resonator plate -> appearance of magnetosphere Alfven resonator -> precipitation feeds resonator plates. From out measurements follows that at 100 km altitude (E-region of ionosphere) plate size is > 10 km and the resonance frequency of plate oscillations or frequency of the diffuse precipitation may be estimated as 0,20 - 0,60 Hz. For 5 min resonator gets completely exhausted. All particles precipitate into ionosphere and ionosphere resonator plate disappears.

Musatenko, S.; Musatenko, Yu.; Kurochka, E.; Choliy, V.; Lastochkin, A.; Slipchenko, O.

99

Swarm Measurements of Ionospheric Electric Field and Plasma  

NASA Astrophysics Data System (ADS)

Swarm is a three-spacecraft European Space Agency Earth Explorer mission that will include precision in-situ measurements of magnetic field, electric field, and plasma parameters at altitudes up to 530 km, twice per second for four years beginning in late 2010. Electric fields in the direction perpendicular to the local magnetic field will be measured by the Swarm Electric Field Instruments (EFI) using a technique based on measurements of ion drift. The Swarm EFI's represent a new generation of ion drift measurement in that they use an intensified CCD-based technique to generate 2-D images of low-energy ion distribution functions from which both ion drift velocity and temperature are derived. These measurements will be complemented by Langmuir-probe measurements of electron density, electron temperature and spacecraft potential. We present an overview of the mission and of the predicted performance characteristics of the EFI, and examine the benefits of the Swarm configuration for ionospheric research relative to previous precision magnetic field research missions such as rsted and CHAMP.

Burchill, J.; Knudsen, D.; Eriksson, A.

2009-05-01

100

Spacelab2 plasma depletion experiments for ionospheric and radio astronomical studies  

Microsoft Academic Search

The Spacelab-2 Plasma Depletion Experiments were a series of studies to examine Shuttle-induced perturbations in the ionosphere and their application to ground-based radio astronomy. The Space Shuttle Challenger fired its orbital maneuvering subsystem engines, releasing large amounts of exhaust molecules that caused the electrons and ions in earth's upper atmosphere to chemically recombine, thereby creating so-called 'ionospheric holes'. Two burns

M. Mendillo; J. Baumgardner; D. P. Allen; J. Foster; J. Holt; G. R. A. ELLIS; A. KLEKOCIUK; G. REBER

1987-01-01

101

Lightning-generated waves escaping out through plasma holes in the nightside Venus ionosphere  

Microsoft Academic Search

The plasma waves in the Venus ionosphere measured by OEFD aboard PVO are analyzed. It is shown that these waves are generated by lightning like cloud-to-cloud discharges anywhere in the Venus ionosphere-surface waveguide. The theoretical minimum attenuation for waveguide mode propagation at 5.4 kHz is consistent with the maximum occurrence rate at this frequency. The lightning-generated and globally-propagating signals when

R. N. Singh; Hari O. Upadhyay

1991-01-01

102

Convective transport of plasma in the inner Jovian magnetosphere  

NASA Astrophysics Data System (ADS)

The transport of plasma in the inner Jovian magnetosphere is investigated according to the corotating convection model of Hill et al. (1981), emphasizing mathematical aspects of the theory. A simplified but physically plausible boundary condition at the inner Io torus, representing a 5 percent density enhancement of S(+) ions in an 'active sector' that is fixed in Jovian (system III) longitude is employed. The convection electric field pattern resulting from this longitudinal mass anomaly alone is investigated, and then the theory to include the effects of Coriolis force and plasma acceleration is generalized. It is found that even a small (about 5 percent) 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.

1990-04-01

103

Plasma distribution at Mars and ionospheric magnetic fields: A lesson from Venus  

Microsoft Academic Search

MAG\\/ER experiment on Mars Global Surveyor (MGS), spacecraft has shown the presence of large-scale horizontal magnetic fields in the ionosphere of Mars. These fields can be used to explain the ``depressed'' nature of electron density profiles observed by the radio occultation experiments, since the horizontal fields can inhibit upward diffusion of plasma and reduce the plasma scale heights in the

A. K. Dwivedi; K. K. Mahajan

2004-01-01

104

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

Microsoft Academic Search

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

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

2010-01-01

105

Formation of the Harang reversal and its dependence on plasma sheet conditions: Rice convection model simulations  

NASA Astrophysics Data System (ADS)

The goal of this paper is to understand the formation of the Harang reversal and its association with the region 2 field-aligned current (FAC) system, which couples the plasma sheet transport to the ionosphere. We have run simulations with the Rice convection model (RCM) using the Tsyganenko 96 magnetic field model and realistic plasma sheet particle boundary conditions on the basis of Geotail observations. Our results show that the existence of an overlap in magnetic local time (MLT) of the region 2 upward and downward FAC is necessary for the formation of the Harang reversal. In the overlap region the downward FAC, which is located at lower latitudes, is associated with low-energy ions that penetrate closer to Earth toward the dawn side, while the upward FAC, which is located at higher latitudes, is associated with high-energy ions. Under the same enhanced convection we compare the Harang reversal resulting from a hotter and more tenuous plasma sheet with the one resulting from a colder and denser plasma sheet. For the former case the shielding of the convection electric field is less efficient than for the latter case, allowing low-energy protons to penetrate further earthward, resulting in a Harang reversal that extends to lower latitudes, expands wider in MLT, and is located further equatorward than the upward FAC peak and the conductivity peak. The return flows of the Harang reversal in the hot and tenuous case are located in a low conductivity region. This leads to an enhancement of these westward flows, resulting in subauroral polarization streams (SAPS).

Gkioulidou, Matina; Wang, Chih-Ping; Lyons, Larry R.; Wolf, Richard A.

2009-07-01

106

Whistler wave-induced ionospheric plasma turbulence: Source mechanisms and remote sensing  

NASA Astrophysics Data System (ADS)

We report a series of experiments conducted at Arecibo Observatory in the past, aimed at the investigation of 40.75 kHz whistler wave interactions with ionospheric plasmas and the inner radiation belts at L=1.35. The whistler waves are launched from a Naval transmitter (code-named NAU) operating in Aguadilla, Puerto Rico at the frequency and power of 40.75 kHz and 100 kW, respectively. Arecibo radar, CADI, and optical instruments were used to monitor the background ionospheric conditions and detect the induced ionospheric plasma effects. Four-wave interaction processes produced by whistler waves in the ionosphere can excite lower hybrid waves, which can accelerate ionospheric electrons. Furthermore, whistler waves propagating into the magnetosphere can trigger precipitation of energetic electrons from the radiation belts. Radar and optical measurements can distinguish wave-wave and wave-particle interaction processes occurring at different altitudes. Electron acceleration by different mechanisms can be verified from the radar measurements of plasma lines. To facilitate the coupling of NAU-launched 40.75 kHz whistler waves into the ionosphere, we can rely on naturally occurring spread F irregularities to serve as ionospheric ducts. We can also use HF wave-created ducts/artificial waveguides, as demonstrated in our earlier Arecibo experiments and recent Gakona experiments at HAARP. The newly constructed Arecibo HF heater will be employed in our future experiments, which can extend the study of whistler wave interactions with the ionosphere and the magnetosphere/radiation belts as well as the whistler wave conjugate propagation between Arecibo and Puerto Madryn, Argentina.

Pradipta, R.; Rooker, L. A.; Whitehurst, L. N.; Lee, M. C.; Ross, L. M.; Sulzer, M. P.; Gonzalez, S.; Tepley, C.; Aponte, N.; See, B. Z.; Hu, K. P.

2013-10-01

107

Response of Aurorae, Plasma Convection, and Birkeland Currents to Strong IMF By and Negative Bz Conditions  

NASA Astrophysics Data System (ADS)

In a number of case event studies we probe the association between dayside auroral forms/activities and plasma convection channels (pulsed ionospheric flows) located at the dayside polar cap boundary during By-dominated IMF conditions when a negative Bz-component is also present (clock angle range 90-135). Both polarities of IMF By are included. We base our results on (i) ground auroral observations at high latitudes (70-80 MLAT) and (ii) particle precipitation, ion drift, and Birkeland current measurements made by the DMSP F13 spacecraft. The following auroral types in the system of forms and activities within the merging and lobe convection cells are noted: (i) cusp 1 aurora ("midday gap"), (ii) cusp 2 aurora in the postnoon sector (By > 0 ), (iii) dayside BPS/LLBL aurorae in the pre- and postnoon sectors, (iv) poleward moving auroral forms (PMAFs) in the mantle regime, and (v) polar arcs on the pre- and postnoon sides of the polar cap. We investigate how these auroral forms evolve in space and time during magnetopause reconnection events. Our goal is to obtain a comprehensive picture of the complex system of dayside and polar cap auroral forms and convection channels contributing to the large-scale pattern of plasma convection/precipitation with the dawn-dusk asymmetry imposed by the IMF By-component. Emphasis is placed on small- and medium-scale structures. These are often averaged out in large statistical studies. This work is supported in part by NASA Grants NNG05GG25G and NNG05GC75G

Sandholt, P.; Farrugia, C.

2006-05-01

108

Observations of nightside auroral plasma upflows in the F-region and topside ionosphere  

NASA Astrophysics Data System (ADS)

Observations from the special UK EISCAT program UFIS are presented. UFIS is a joint UHF-VHF experiment, designed to make simultaneous measurements of enhanced vertical plasma flows in the F-region and topside ionospheres. Three distinct intervals of upward ion flow were observed. During the first event, upward ion fluxes in excess of 1013 m-2 s-1 were detected, with vertical ion velocities reaching 300 m s-1 at 800 km. The upflow was associated with the passage of an auroral arc through the radar field of view. In the F-region, an enhanced and sheared convection electric field on the leading edge of the arc resulted in heating of the ions, whilst at higher altitudes, above the precipitation region, strongly enhanced electron temperatures were observed; such features are commonly associated with the generation of plasma upflows. These observations demonstrate some of the acceleration mechanisms which can exist within the small-scale structure of an auroral arc. A later upflow event was associated with enhanced electron temperatures and only a moderate convection electric field, with no indication of significantly elevated ion tem- peratures. There was again some evidence of F-region particle precipitation at the time of the upflow, which exhibited vertical ion velocities of similar magnitude to the earlier upflow, suggesting that the behaviour of the electrons might be the dominant factor in this type of event. A third upflow was detected at altitudes above the observing range of the UHF radar, but which was evident in the VHF data from 600 km upwards. Smaller vertical velocities were observed in this event, which was apparently uncorrelated with any features observed at lower altitudes. Limitations imposed by the experimental conditions inhibit the interpretation of this event, although the upflow was again likely related to topside plasma heating. Acknowledgements. We would like to thank the director and staff of EISCAT for the data used in this study. EISCAT is supported by the scientific research councils of Finland, France, Germany, Norway, Sweden and the UK. We would like to express our special thanks to A. P. van Eyken and U. P. Lvhaug for their cooperation and assistance in running the IPS campaigns and to W. P. Wilkinson for discussions on fast-stream/slow-stream interaction regions. Two of us (ARB and PJM) are supported by PPARC. Topical Editor D. Alcayd thanks J. F. Mckenzie and M. Pick for their help in evaluating this paper.--> Correspondence to: A. R. Breen-->

Foster, C.; Lester, M.

1996-12-01

109

Divergent subcritical convection in magnetized plasma from asymmetric sourcing  

SciTech Connect

Asymmetric particle and heat sourcing in a plasma confined in a closed magnetic field line configuration results in convection cells, as is well known. This phenomenon occurs even if the sourcing on average produces density and temperature profiles that are subcritical, i.e., magnetohydrodynamically stable to interchange modes. Such subcritical convection is expected to be small compared to the convection from supercritical driving for which the system is interchange unstable. The ratio of subcritical to supercritical convection is expected to scale as the inverse Reynolds numbers (for large Reynolds numbers). It is shown that this ratio is, in fact, considerably larger. As marginal stability is approached, the subcritical convection grows from very small to almost the unstable convection size, i.e., of order unity. This effect may be similar to why a driven, damped harmonic oscillator increases in amplitude as resonance is approached. A numerical simulation is done to demonstrate this effect. It is also shown that transport from the large convection can be substantial.

Adler, D.T.; Hassam, A.B. [Department of Physics, University of Maryland, College Park, Maryland 20742 (United States)

2005-06-15

110

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

111

Synergistic effects of hot plasma-driven potentials and wave-driven ion heating on auroral ionospheric plasma transport  

SciTech Connect

Transverse acceleration by waves and parallel acceleration by field-aligned electric fields are important processes in the transport of ionospheric ions along auroral field lines. In order to study the transport of ionospheric plasma in this environment we have developed a generalized semikinetic model which combines the tracking of ionospheric ion gyrocenters with a generalized fluid treatment of ionospheric electrons. Large-scale upward and downward directed electric fields are generated within the model by introducing magnetospheric plasma whose components have differing temperature anisotropies. We study the effects of such potentials when combined with the effect of ion heating by a distribution of waves along the flux tube. We find that the combination of wave heating and an upward electric field results in an order of magnitude increase in O{sup +} outflow (compared to a case with an upward electric field and no wave heating). Under these conditions we observe the formation of bimodal conics. When a downward electric field to a case with wave heating, the energy gained by the ions from the waves increases by a factor of 2 or 3 (over the scenario with wave heating and no hot plasma-driven electric field) owing to their slower transit of the heating region. Typically, the velocity distributions under these conditions are toroids and counterstreaming conics. We also find that the upflowing, dense, heated ionospheric plasma acts to reduce the potential set up by the anisotropies in the magnetospheric components. 33 refs., 16 figs., 1 tab.

Brown, D.G.; Horwitz, J.L.; Wilson, G.R. [Univ. of Alabama, Huntsville, AL (United States)

1995-09-01

112

Region 2 field-aligned currents and earthward penetration of the electron and ion plasma sheet obtained from RCM simulations with a modified Dungey magnetic field solver, and comparison with observations in ionosphere and magnetosphere  

NASA Astrophysics Data System (ADS)

Ionospheric conductivity and field aligned currents (FAC) are two of the most important factors that control the magnetosphere - ionosphere (M-I) coupling. The relative location between conductivity and FAC strongly affect the spatial distribution of convection electric field, including the Harang reversal and Sub-Auroral Polarization Streams that are crucial to development of substorms and storms. The night-side conductivity strongly depends on electron precipitation, and thus the electron plasma sheet and precipitation rate. On the other hand, Region 2 (R2) FAC are associated with pressure gradients in the near-Earth magnetosphere built up by plasma sheet ions. To understand this aspect of M-I coupling, we have run simulations with the Rice Convection Model (RCM), integrated with a modified Dungey magnetic field solver for equatorial force balance, to investigate the earthward penetration of plasma sheet protons and electrons of different energies into the near-Earth magnetosphere under weak and enhanced convection. We have investigated in our simulations how different precipitation rate affects the relative locations of conductivity and FAC and the resulting M-I coupling. We evaluate these simulation results by comparing the plasma sheet ions and electrons and their relative earthward edges with in situ THEMIS statistical results, and by comparing the simulated precipitating electron energy fluxes, different ion and electron equatorward precipitation boundaries, as well as their locations relative to R2 FAC in ionosphere, with previous published statistical DMSP studies [Newell et al., 2009; Ohtani et al., 2010].

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

2011-12-01

113

Convective transport in laser target plasmas  

SciTech Connect

The role of guiding-center corrections in convective transport of electron energy is examined with a simple numerical model. At 10/sup 16/W cm/sup -2/ with a 60-..mu..m spot and a 10.6-..mu..m wavelength laser, the Righi-Leduc term is observed to have little effect on transport in a calculation with the thermal flux limited to the free-streaming value.

Brackbill, J.U.; Colombant, D.; Grandjouan, N.

1982-01-01

114

Laboratory study of some lightning-induced effects in the ionospheric plasma  

Microsoft Academic Search

Laboratory experiments have been conducted at MIT, using the student-built Versatile Toroidal Facility (VTF), to investigate some ionospheric plasma effects produced by lightning-induced whistler waves. Lower hybrid waves, generated by the lightning-induced whistler waves, can cause a chain of extensive plasma effects, such as the acceleration of electrons and ions and the spectral broadening of plasma waves. Two mechanisms by

M. C. Lee; R. J. Riddolls; D. T. Moriarty

1998-01-01

115

Topside Ionosphere Plasma bubbles seen as He+ Density Depletions: Estimations and Comparisons  

NASA Astrophysics Data System (ADS)

He+ density depletions, considered as originating from equatorial plasma bubbles, were involved in this study. They are usually detected in the topside ionosphere (~1000 km) deeply inside the plasmasphere (L~1.3-3) [1-3]. a) Since there are some questions about the survival possibilities of the topside plasma bubbles, the characteristic times of the main processes, in which plasma bubbles are involved, were compared. It was suggested that the plasma bubbles are produced by Rayleigh-Taylor instability at the bottomside of ionosphere and transported up to the topside ionosphere. It was found that it takes about 3-4 hours for plasma bubbles to reach the topside ionosphere altitudes. It was revealed that ambipolar diffusion transport is the most fast (some minutes). The estimation of the Bohm (cross-field) diffusion time shows that topside plasma bubbles can exist up to 100 hours. It was concluded that there is enough time for the plasma bubbles to survive and to be detected (for example, in minor species of ion composition inside the bubble like He+) at the topside ionosphere altitudes. (b) It was revealed that the topside plasma bubbles can be easily detected as He+ density depletions during high and maximal solar activity. The convenient conditions for observations appear because the strong depleted in He+ density bubbles, reaching the topside ionosphere, most well contrast with the He+ density background layer very well developed in the topside ionosphere during high solar activity [4]. (c) He+ density depletions were considered in connection with equatorial F-region irregularities (EFI), equatorial F-spread (ESF) and equatorial plasma bubbles (EPB). Their longitudinal statistics, calculated for all seasons and both hemispheres (20-50 deg. INVLAT), were compared with EFI statistics taken from AE-E [5], OGO-6 [6], ROCSAT [7] observations. ESF, EPB statistics taken from [8, 9] based on ISS-b and Hinotori spacecraft data were also used for comparison. It was revealed that the main statistical maxima of the equatorial F-region irregularities are well enough reflected in the statistical plots of the He+ density depletions of the both hemispheres. The best conformity was obtained for equinoxes, the worst one was obtained for solstices, when the most dramatic insolation differences take place in the different hemispheres. Hence, it was validated once again that He+ density depletions may be considered as an indicator of topside plasma bubble presence or as fossil bubble signatures.

Sidorova, L.; Filippov, S.

2012-04-01

116

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

NASA Astrophysics Data System (ADS)

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-site measurements shows the complexity of the plasma pitch angle distributions at various energy ranges and geomagnetic activity levels. We have found that the pitch angle distributions, 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, M. H.; Chen, S.; Buzulukova, N.; Glocer, A.

2010-12-01

117

Spacelab-2 plasma depletion experiments for ionospheric and radio astronomical studies  

NASA Astrophysics Data System (ADS)

The Spacelab-2 Plasma Depletion Experiments were a series of studies to examine Shuttle-induced perturbations in the ionosphere and their application to ground-based radio astronomy. The Space Shuttle Challenger fired its orbital maneuvering subsystem engines, releasing large amounts of exhaust molecules that caused the electrons and ions in earth's upper atmosphere to chemically recombine, thereby creating so-called 'ionospheric holes'. Two burns conducted over New England produced ionospheric peak depletions ranging from 25 to 50 percent, affected the ionosphere over a 200-kilometer altitude range, and covered 1 to 2 deg of latitude. Optical emissions associated with the hole spanned an area of several hundred thousand square kilometers. A third burn was conducted over a low-frequency radio observatory in Hobart, Australia, to create an 'artificial window' for ground-based observations at frequencies normally below the natural ionospheric cutoff (penetration) frequency. The Hobart experiment succeeded in making high-resolution observations at 1.7 megahertz through the induced ionospheric hole.

Mendillo, M.; Baumgardner, J.; Allen, D. P.; Foster, J.; Holt, J.

1987-11-01

118

Spacelab-2 plasma depletion experiments for ionospheric and radio astronomical studies.  

PubMed

The Spacelab-2 Plasma Depletion Experiments were a series of studies to examine shuttle-induced perturbations in the ionosphere and their application to ground-based radio astronomy. The space shuttle Challenger fired its orbital maneuvering subsystem engines on 30 July and 5 August 1985, releasing large amounts of exhaust molecules (water, hydrogen, and carbon dioxide) that caused the electrons and ions in Earth's upper atmosphere to chemically recombine, thereby creating so-called "ionospheric holes." Two burns conducted over New England produced ionospheric peak depletions ranging from 25 to 50 percent, affected the ionosphere over a 200-kilometer altitude range, and covered 1 degrees to 2 degrees of latitude. Optical emissions associated with the hole spanned an area of several hundred thousand square kilometers. A third burn was conducted over a low-frequency radio observatory in Hobart, Australia, to create an "artificial window" for ground-based observations at frequencies normally below the natural ionospheric cutoff (penetration) frequency. The Hobart experiment succeeded in making high-resolution observations at 1.7 megahertz through the induced ionospheric hole. PMID:17744364

Mendillo, M; Baumgardner, J; Allen, D P; Foster, J; Holt, J; Ellis, G R; Klekociuk, A; Reber, G

1987-11-27

119

Ionospheric observations of F region artificial plasma turbulence, modified by powerful X-mode radio waves  

NASA Astrophysics Data System (ADS)

We study the influence of additional X-mode heating of the ionospheric plasma on the features of artificial ionospheric turbulence, induced in the ionospheric F region by O-mode waves over the ``Sura'' heating facility (Nizhny Novgorod, Russia). The X heating is shown to suppress the generation of HF plasma turbulence resulting from the development of both the parametric decay and thermal parametric instabilities. Typical times of variations in the turbulence intensity change from <=0.1 s to ~10 s, strongly depending on the heating scheme. Aftereffects of the X heating last up to 30-60 s. We distinguish at least three types of phenomena, according to the observed typical times of the processes, and discuss possible reasons for each of them.

Frolov, V. L.; Kagan, L. M.; Sergeev, E. N.; Komrakov, G. P.; Bernhardt, P. A.; Goldstein, J. A.; Wagner, L. S.; Selcher, C. A.; Stubbe, P.

1999-06-01

120

Ionospheric storm time dynamics as seen by GPS tomography and in situ spacecraft observations  

Microsoft Academic Search

During major geomagnetic storms anomalous enhancements of the ionospheric density are seen at high and middle latitudes. A number of physical mechanisms have been invoked to explain these storm time density anomalies including an expansion of high-latitude electric plasma convection to midlatitudes, thermospheric neutral winds, and changes in the ionospheric composition. However, it remains unclear which mechanism plays the dominant

D. Pokhotelov; C. N. Mitchell; P. S. J. Spencer; M. R. Hairston; R. A. Heelis

2008-01-01

121

Ionospheric response to the corotating interaction regiondriven geomagnetic storm of October 2002  

Microsoft Academic Search

Unlike the geomagnetic storms produced by coronal mass ejections (CMEs), the storms generated by corotating interaction regions (CIRs) are not manifested by dramatic enhancements of the ring current. The CIR-driven storms are however capable of producing other phenomena typical for the magnetic storms such as relativistic particle acceleration, enhanced magnetospheric convection and ionospheric heating. This paper examines ionospheric plasma anomalies

D. Pokhotelov; C. N. Mitchell; P. T. Jayachandran; J. W. MacDougall; M. H. Denton

2009-01-01

122

Evidence on dynamical coupling of mesosphere and ionosphere in the equatorial plasma bubble seeding  

NASA Astrophysics Data System (ADS)

Simultaneous observations of the mesospheric airglow OH emissions and ionospheric OI630 nm emissions made it possible to investigate both gravity wave propagation in the mesosphere and ionospheric bubble structures simultaneously. The coordinated observation has been carried out during the SpreadFEx campaign from September 22 to November 8, 2005. Two airglow CCD imagers, located at Cariri (7.4S, 36.5W, Mag. 9S) and at near Brasilia (14.8S, 47.6W, Mag. 10S) were operated simultaneously. Ionospheric parameters were monitored by two ionosondes and one VHF radar in the magnetic equatorial region. In a general form, we observed well developed plasma bubbles when a strong mesospheric gravity wave (a long horizontal wavelength and large amplitude of oscillation) was observed. From the 17 nights of observation during the campaign period we found a good correlation between the inter-bubble distances in the ionosphere and the gravity wave horizontal wavelengths in the mesosphere with a statistically significant level, suggesting a direct contribution of the mesospheric gravity wave to plasma bubble seeding in the equatorial ionosphere.

Takahashi, Hisao

123

High-latitude magnetospheric plasma convection and its dependence on solar wind parameters: Statistical analysis of Cluster EDI measurements  

NASA Astrophysics Data System (ADS)

We have used vector measurements of the electron drift velocity by the Electron Drift Instrument (EDI) on Cluster between February 2001 and March 2006 to derive statistical maps of the high-latitude plasma convection. The EDI measurements, obtained at geocentric distances between ~4 and ~20RE over both hemispheres, are mapped into the polar ionosphere, and sorted according to the orientation of the interplanetary magnetic field (IMF), as measured at ACE and propagated to Earth, using best estimates of the orientation of the IMF variations. Only intervals of stable IMF are used, based on the magnitude of the so- called bias-vector constructed from 30-minute averages. Contour maps of the electric potential in the polar ionosphere are subsequently derived from the mapped and averaged ionospheric drift vectors. Comparison with published statistical results based on Super Dual Auroral Radar Network (SuperDARN) radar and low-altitude satellite measurements shows excellent agreement between the average convection patterns, particularly the lack of mirror-symmetry between the effects of positive and negative IMF B_y effects, the appearance of a duskward flow component for strongly southward IMF, and the general weakening of the flows and potentials for northerly IMF directions. This agreement lends credence to the validity of the assumption underlying the mapping of the EDI data, namely that magnetic field lines are equipotentials. For strongly northward IMF the mapped EDI data show the clear emergence of two counter-rotating lobe cells with a channel of sunward flow between them. The total potential drops across the polar caps obtained from the mapped EDI data are intermediate between the radar and the low-altitude satellite results. We have also sorted the data according to estimates of the reconnection electric field, solar wind dynamic pressure, and disturbance parameters such as DsT and ASYM-H. Finally, we have produced maps of the variances of the convection as a function of the IMF orientation.

Frster, M.; Haaland, S. E.; Paschmann, G.; Quinn, J. M.; Torbert, R. B.; McIlwain, C. E.; Vaith, H.; Puhl-Quinn, P. A.; Kletzing, C. A.

2006-12-01

124

Ionospheric effects on the transmission of ultralow-frequency plasma waves.  

PubMed

Measurements of magnetospheric ultralow-frequency plasma waves (period tau, approximately 18 to 150 seconds) on the ground under continuous daylight conditions in the Antarctic and under alternate day-night solar illumination at the conjugate station in Quebec indicate a significant local time dependence in the transmission properties of the ionosphere for waves of these periods. When the Antarctic station is compared with the Quebec station, the tilt (with respect to the ionosphere) of the orientation plane of the waves is observed to be larger at local noon than at local night. PMID:17754378

Lanzerotti, L J; Lie, H P; Tartaglia, N A

1972-11-01

125

Lightning-generated waves escaping out through plasma holes in the nightside Venus ionosphere  

Microsoft Academic Search

The plasma waves in the Venus ionosphere measured by OEFD aboard PVO are analysed. It is shown that these waves are generated\\u000a by lightning like cloud-to-cloud discharges anywhere in the Venus ionosphere-surface waveguide. The theoretical minimum attenuation\\u000a for waveguide mode propagation at 5.4 kHz is consistent with the maximum occurrence rate at this frequency. The lightning-generated\\u000a and globally-propagating signals when

R. N. Singh; Hari Om Upadhyay

1991-01-01

126

Monitoring of sporadic plasma layers in the lower ionosphere in the communication link satellite-to-satellite  

Microsoft Academic Search

Method of global monitoring of sporadic plasma layers in the lower ionosphere is developed. In-vestigations were carried out by use of analysis of the amplitude and phase components of radio holograms obtained during the radio occultation missions CHAMP, FORMOSAT-3. Sporadic amplitude scintillation observed in RO experiments contain important information concerning the seasonal, geographical, and temporal distributions of the ionospheric disturbances

Alexander Pavelyev; Stanislav Matyugov; Jens Wickert; Yuei An Liou; Oleg Yakovlev

2010-01-01

127

Effect of magnetospheric convection on thermal plasma in the inner magnetosphere  

Microsoft Academic Search

The effects of E x B convection on the distribution of plasma parameters in the inner magnetosphere have been examined. Analytical solutions describing density distributions along convective trajectories in the equatorial plane have been found. These solutions suggest the following dependence of plasma concentration n on the magnetic field B along convective trajectories: n proportional to B(exp alpha), where the

G. V. Khazanov; C. E. Rasmussen; Yu. V. Konikov; T. I. Gombosi

1994-01-01

128

Ionospheric chemical releases  

SciTech Connect

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 modification by chemical releases excites artificial enhancements in airglow intensities by exothermic chemical reactions between the newly created plasma species. Numerical models have been developed to describe the creation and evolution of large scale (>l km) density irregularities and airglow clouds generated by artificial means. Experimental data compares favorably with these models. In general, we find that chemical releases produce transient, large amplitude perturbations in electron density which can evolve into fine scale irregularities via nonlinear transport processes.

Bernhardt, P.A.; Scales, W.A.

1990-10-01

129

A plasma vortex revisited: The importance of including ionospheric conductivity measurements  

NASA Astrophysics Data System (ADS)

In an earlier paper [Kosch et al., 1998], simultaneous all-sky TV imager and Scandinavian Twin Auroral Radar Experiment (STARE) observations of an ionospheric plasma vortex located poleward of an auroral arc were presented. The vortex is associated with a sudden brightening of the arc and corresponds to an ionospheric region of diverging horizontal electric fields, which is equivalent to a downward field-aligned current (FAC), i.e., the closure current for the upward current above the arc. This event has been revisited because of the subsequent availability of data from the Scandinavian Magnetometer Array. These data, combined with STARE electric fields, have been used to determine the real ionospheric conductance distribution throughout the field of view. As a result, a more realistic, quantitative picture of the current system associated with the arc is obtained than was possible in an earlier model based on an assumed constant conductance. In particular, a complete macroscopic electrodynamic description of a plasma vortex, composed of ionospheric conductances, true horizontal currents, and FACs, is obtained for the first time. It is shown that the plasma vortex corresponds to an area of decreased conductance, thus broadening the FAC distribution and reducing the current density compared to the earlier results. The study illustrates that horizontal conductance gradients should not be neglected when computing FACs.

Kosch, M. J.; Amm, O.; Scourfield, M. W. J.

2000-11-01

130

Comparison of the empirical thermospheric models and the self-consistent model of the ionospheric plasma  

NASA Astrophysics Data System (ADS)

The parameters related to the temporal and spatial variations of the ionospheric plasma, calculated from the self-consistent model (SCM) of Vlasov and Kolesnik (1979), are compared with those of the empirical models of J 71, MSIS, and DTM, and the discrepancies are discussed. The electron and ion temperatures calculated from the SCM model were found to be reliable for different, but not all, ionospheric conditions. Comparisons of the theoretical model with experimental data indicate that the SCM reflects the main features of the ionospheric behavior. It is concluded that the comparison of the theoretical model with empirical models and experimental data shows good agreement. However, differences between the theoretical and empirical models were found, and the development of a three-dimensional theoretical model is suggested for the reliable description of the neutral temperature distribution.

Vlasov, M. N.; Kolesnik, A. G.

131

Post substorm convection and auroral arc currents determined from multiple ionospheric, magnetic, and electric field observations  

NASA Astrophysics Data System (ADS)

Analyses of auroral current systems during the recovery phase of a substorm were conducted based on (1) field, particle and optical observations from rocket-borne probes; (2) magnetic data from a meridian chain of stations; and (3) data from three scanning photometers. Current models were determined independently of both magnetic field observations and electric field and ionospheric observations. The models indicated that there are several different and independent current systems, consisting of ionospheric Hall and Pedersen currents of varying intensities and directions, which were linked to field-aligned currents in such a way as to form solenoidal current loops or cells. Current systems within a broad, enhanced, inverted-V region were narrow, and some of the outward field-aligned currents were coincident with auroral arcs and local enhancements in the energetic particle flux.

Walker, J. K.; Koehler, J. A.; Creutzberg, F.; McNamara, A. G.; Vallance Jones, A.; Whalen, B. A.

1981-11-01

132

Distributions of Pre-sunrise Plasma Heating in the Low- and Mid-latitude Topside Ionosphere  

NASA Astrophysics Data System (ADS)

Pre-sunrise ionospheric heating above F layer peak was first observed by Carlson (1966) with incoherent backscatter radar at Arecibo Ionospheric Observatory during winter season. Photoelectrons streaming from sunlit magnetic conjugate ionosphere were concluded to produce the observed ionosphere heating. Recently global distributions of ion temperature were available from Ionospheric Plasma and Electrodynamics Instrument (IPEI) onboard the first satellite of Republic of China, ROCSAT-1, to study the pre-sunrise ion heating (Chao et al., 2003). The results showed that the most enhanced pre-sunrise heating was located in the longitude sector between 165 E and 195E in the southern hemisphere (South Pacific region) during June solstice and between 75 W and 15 W in the northern hemisphere (North Atlantic region) during December solstice. In this study, we have compared with electron temperature distributions observed two decades ago by Hinotori satellite. The two distributions match very well in the 0400-0500 LT sector. We will also verify the distributions with results from SAMI2 model for more details.

Chao, C.; Su, S.; Oyama, K.; Yeh, H.

2007-12-01

133

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

134

Atmosphere-Ionosphere Electrodynamic Coupling  

NASA Astrophysics Data System (ADS)

Numerous phenomena that occur in the mesosphere, ionosphere, and the magnetosphere of the Earth are caused by the sources located in the lower atmosphere and on the ground. We describe the effects produced by lightning activity and by ground-based transmitters operated in high frequency (HF) and very low frequency (VLF) ranges. Among these phenomena are the ionosphere heating and the formation of plasma density inhomogeneities, the excitation of gamma ray bursts and atmospheric emissions in different spectral bands, the generation of ULF/ELF/VLF electromagnetic waves and plasma turbulence in the ionosphere, the stimulation of radiation belt electron precipitations and the acceleration of ions in the upper ionosphere. The most interesting results of experimental and theoretical studies of these phenomena are discussed below. The ionosphere is subject to the action of the conductive electric current flowing in the atmosphere-ionosphere circuit. We present a physical model of DC electric field and current formation in this circuit. The key element of this model is an external current, which is formed with the occurrence of convective upward transport of charged aerosols and their gravitational sedimentation in the atmosphere. An increase in the level of atmospheric radioactivity results in the appearance of additional ionization and change of electrical conductivity. Variation of conductivity and external current in the lower atmosphere leads to perturbation of the electric current flowing in the global atmosphere-ionosphere circuit and to the associated DC electric field perturbation both on the Earth's surface and in the ionosphere. Description of these processes and some results of the electric field and current calculations are presented below. The seismic-induced electric field perturbations produce noticeable effects in the ionosphere by generating the electromagnetic field and plasma disturbances. We describe the generation mechanisms of such experimentally observed effects as excitation of plasma density inhomogeneities, field-aligned currents, and ULF/ELF emissions and the modification of electron and ion altitude profiles in the upper ionosphere. The electrodynamic model of the ionosphere modification under the influence of some natural and man-made processes in the atmosphere is also discussed. The model is based on the satellite and ground measurements of electromagnetic field and plasma perturbations and on the data on atmospheric radioactivity and soil gas injection into the atmosphere.

Sorokin, V. M.; Chmyrev, V. M.

135

Dustplasma interaction through magnetosphereionosphere coupling in Saturn's plasma disk  

NASA Astrophysics Data System (ADS)

The ion bulk speeds in the equatorial region of Saturn's inner magnetosphere, according to data from the Langmuir Probe (LP) on board the Cassini spacecraft, are about 60% of the ideal co-rotation speed; the ion speeds are between the co-rotation and Keplerian speeds (Holmberg et al., Ion densities and velocities in the inner plasma torus of Saturn, Planetary and Space Science). These findings suggest that sub-micrometer negatively charged E ring dust contributes to the plasma dynamics in the plasma disk. We calculated the ion speeds by using a multi-species fluid model, taking into account dust interactions to investigate the effects of ion-dust coulomb collision, mass loading, as well as taking into account magnetosphere-ionosphere coupling to investigate the effect of the magnetospheric electric field. The results show that the ion speeds can be significantly reduced by the electric fields generated by the collisions between ions and dusts when the dust density is high and the thickness of dust distribution is large. We also show that the ion speeds from our model are consistent with the LP observations when the maximum density of dust is larger than 105 m-3.

Sakai, Shotaro; Watanabe, Shigeto; Morooka, Michiko W.; Holmberg, Madeleine K. G.; Wahlund, Jan-Erik; Gurnett, Donald A.; Kurth, William S.

2013-01-01

136

Real-time tracking and targeting computations and rocket-vehicle aeroballistics for the PLACES ionospheric-plasma test series  

SciTech Connect

The PLACES (Position Location and Communication Effects Simulations) test program, conducted in December 1980 at Eglin Gulf Test Range, involved a series of ionospheric releases of barium/barium-nitrate vapor. The Defense Nuclear Agency sponsored program investigated effects of a structured ionospheric plasma (similar to that produced by a high-altitude nuclear explosion) on satellite navigation systems and provided in situ measurement of plasma structure. Terrier-Tomahawk rocket systems boosted the barium payloads, beacon payloads (plasma occultation experiment), and probe payloads (plasma in situ measurement). Drifting plasma tracking procedures, beacon-and probe-vehicle targeting procedures, and vehicle flight test results are presented.

Rollstin, L.R.

1982-01-01

137

Ionospheric convection observations following the solar flare of 20 January 2005 and during the geomagnetic storm of 21 January 2005  

NASA Astrophysics Data System (ADS)

The MINIS balloon campaign was successfully conducted in January 2005 to investigate relativistic electron loss mechanisms. The MINIS campaign provided multi-point measurements of electron precipitation up to MeV energies, including simultaneous measurements at different longitudes and hemispheres. Two balloons, each carrying an X-ray spectrometer for measuring the bremsstrahlung produced as electrons precipitate into the atmosphere, were launched from Churchill, Manitoba. Four balloons, each carrying an X-ray spectrometer, and a 3-axis electric field instrument providing DC electric field and VLF measurements in 3 frequency bands, were launched from the South African Antarctic Station (SANAE IV). An X 7.1 solar flare occurred at 0636 UT on 20 January 2005. A CME from this flare arrived at the Earth 34 hours later. An SSC began at ~1650 UT followed by a geomagnetic storm with a Dst perturbation of ~-100nT. The AE index shows that the 20 January flare was followed first by 6 hours of deep quiet and then 28 hours of moderate activity. The balloon data contain evidence for two interesting geoelectric responses to the flare. The response of the tropospheric global circuit is discussed in a companion paper. There was an abrupt reduction of the horizontal electric field to a value near zero. Either the column resistance between the balloon and the ground fell to a value near zero, or the increased load from the ionosphere shorted out the cross-polar-cap potential. The arrival of the CME initiated an interval of very strong relativistic electron precipitation. The second and third Southern payloads and the first Northern payload made observations in both hemispheres of several extensive relativistic electron precipitation events that occurred from 1700 to 2000 UT on 21 January 2005. Each x-ray burst was preceded by a strong pulse of ionospheric convection. These flow bursts were directed poleward and sunward transport. The detailed comparison of data from the two balloons indicates that these bursts were temporal variations, not spatial structures. The data are consistent with an interval of enhanced reconnection and convection preceding each major enhancement in precipitation activity.

Holzworth, R. H.; Bering, E. A.; Reddell, B. D.; Kokorowski, M.; Bale, S.; Blake, J. B.; Collier, A. B.; Hughes, A. R.; Lay, E.; Lin, R. P.; McCarthy, M. P.; Millan, R. M.; Moraal, H.; O'Brien, T. P.; Parks, G. K.; Pulupa, M.; Sample, J. G.; Smith, D. M.; Stoker, P.; Woodger, L.

2005-12-01

138

Ionosphere/thermosphere heating determined from dynamic magnetosphere-ionosphere/thermosphere coupling  

NASA Astrophysics Data System (ADS)

Ionosphere/thermosphere heating driven by magnetospheric convection is investigated through a three-fluid inductive (including Faraday's law) approach to describing magnetosphere-ionosphere/thermosphere coupling, for a 1-D stratified ionosphere/thermosphere in this initial study. It is shown that the response of the ionosphere/thermosphere and thus the heating is dynamic and height-dependent. The heating is essentially frictional in nature rather than Joule heating as commonly assumed. The heating rate reaches a quasi-steady state after about 25 Alfvn travel times. During the dynamic period, the heating can be enhanced and displays peaks at multiple times due to wave reflections. The dynamic heating rate can be more than twice greater than the quasi-steady state value. The heating is strongest in the E-layer but the heating rate per unit mass is concentrated around the F-layer peak height. This implies a potential mechanism of driving O+ upflow from O+ rich F-layer. It is shown that the ionosphere/thermosphere heating caused by the magnetosphere-ionosphere coupling can be simply evaluated through the relative velocity between the plasma and neutrals without invoking field-aligned currents, ionospheric conductance, and electric field. The present study provides understanding of the dynamic magnetosphere-ionosphere/thermosphere coupling from the ionospheric/thermospheric view in addition to magnetospheric perspectives.

Tu, Jiannan; Song, Paul; Vasyli?nas, Vytenis M.

2011-09-01

139

Processes accompanying the charging of dust grains in the ionospheric plasma  

SciTech Connect

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. [Russian Academy of Sciences, Institute of Geosphere Dynamics (Russian Federation); Shukla, P. K. [Ruhr University Bochum (Germany)

2011-08-15

140

Mid-latitude ionospheric perturbation associated with the Spacelab-2 plasma depletion experiment at Millstone Hill  

NASA Astrophysics Data System (ADS)

Elevation scans across geomagnetic mid latitudes by the incoherent scatter radar at Millstone Hill captured the ionospheric response to the firing of the Space Shuttle Challenger OMS thrusters near the peak of the F layer on July 30, 1985. Details of the excitation of airglow and the formation of an ionospheric hole during this event have been reported in an earlier paper by Mendillo et al.. The depletion (factor sim2) near the 320 km Shuttle orbital altitude persisted for sim35 min and then recovered to near normal levels, while at 265 km the density was reduced by a factor of sim6; this significant reduction in the bottomside F-region density persisted for more than 3 hours. Total electron content in the vicinity of the hole was reduced by more than a factor of 2, and an oscillation of the F-region densities with 40-min period ensued and persisted for several hours. Plasma vertical Doppler velocity varied quasi-periodically with a sim80-min period, while magnetic field variations observed on the field line through the Shuttle-burn position exhibited a similar sim80-min periodicity. An interval of magnetic field variations at hydromagnetic frequencies (sim95 s period) accompanied the ionospheric perturbations on this field line. Radar observations revealed a downward phase progression of the 40-min period density enhancements of -1.12 km-1, corresponding to a 320-km vertical wavelength. An auroral-latitude geomagnetic disturbance began near the time of the Spacelab-2 experiment and was associated with the imposition of a strong southward IMF Bz across the magnetosphere. This created an additional complication in the interpretation of the active ionospheric experiment. It cannot be determined uniquely whether the ionospheric oscillations, which followed the Spacelab-2 experiment, were related to the active experiment or were the result of a propagating ionospheric disturbance (TID) launched by the enhanced auroral activity. The most reasonable conclusion is that the ionospheric oscillations were a result of the coincident geomagnetic disturbance. The pronounced depletion of the bottomside ionosphere, however, accentuated the oscillatory behavior during the interval following the Shuttle OMS burn.

Foster, J. C.; Holt, J. M.; Lanzerotti, L. J.

2000-01-01

141

Numerical simulations of a three-wave coupling occurring in the ionospheric plasma  

Microsoft Academic Search

We studied a three-wave coupling process occurring in an active experiment of microwave power transmission (MPT) in the ionospheric plasma by performing one-dimensional electromagnetic PIC (Particle-In-Cell) simulations. In order to examine the spatial variation of the coupling process, we continuously emitted intense electromagnetic waves from an antenna located at a simulation boundary. In the three-wave coupling, a low-frequency electrostatic wave

H. Usui; H. Matsumoto; R. Gendrin

2002-01-01

142

Parametric decay of high-frequency radio waves of high intensity in an ionospheric plasma  

Microsoft Academic Search

The parametric instability of ionospheric plasma in a field of intense radio waves in the meter range is discussed. In particular, the decay of high-frequency radio waves into Langmuir and transverse electromagnetic (i.e., stimulated Raman scattering) and into ion-acoustic and electromagnetic waves (i.e., stimulated Brillouin scattering) is considered. A calculation of the threshold fields and increments of perturbation growth number

A. S. Abyzov; A. S. Bakai; G. K. Solodovnikov

1981-01-01

143

Ionospheric signatures of plasma injections in the cusp triggered by solar wind pressure pulses  

Microsoft Academic Search

We describe coordinated observations made on 14 July 2001 simultaneously in the midaltitude cusp by Cluster and at the cusp's ionospheric magnetic footprint by Super Dual Auroral Radar Network (SuperDARN) and Imager for Magnetopause-to-Aurora Global Exploration (IMAGE) during a period of three successive solar wind dynamic pressure pulses. In association with each of these pulses, Cluster observes plasma injections while

Jean-Claude Cerisier; Aurlie Marchaudon; Jean-Michel Bosqued; Kathryn McWilliams; Harald U. Frey; Mehdi Bouhram; Harri Laakso; Malcolm Dunlop; Matthias Frster; Andrew Fazakerley

2005-01-01

144

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

Microsoft Academic Search

In this paper, the 10-year (19962005) 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

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

2007-01-01

145

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

146

Ionospheric plasma study. Final report, 28 February 1983-28 February 1986  

SciTech Connect

This report concerns plasma instabilities, ionospheric turbulence, and particle-energization processes in the magnetosphere and ionosphere. The following are examples for which theoretical explanations have been obtain: ion conics, effects of magnetic shear on the beam-induced instability, pitch-angle diffusion, wave-particle interactions, nonclassical polar wind, and strong plasma turbulence. Specific topics include: 1. Ion acceleration by lower-hybrid waves in the topside ionosphere. 2. Transverse acceleration of oxygen ions in the central plasma sheet region by electromagnetic ion-cyclotron resonance with broad-band left-hand polarized waves. 3. Analytic description of ion conics in the inhomogeneous terrestrial magnetic field. 4. Effect of magnetic shear on the nonlocal stability of beam-induced lower-hybrid waves. 5. The loss cone population of charged particles in the magnetosphere. 6. Charged particle injection experiments in space. 7. Critical fluctuations around non-equilibrium states and strong turbulence. 8. Heat-flux distribution and associated instabilities in the polar wind and solar wind.

Chang, T.

1986-09-15

147

Nonlinear excitation of convective cells and anomalous diffusion in inhomogeneous plasmas  

Microsoft Academic Search

The mechanism of nonlinear convective cell formation and the resulting diffusion in an inhomogeneous plasma is discussed. It is found that convective cells excited by nonlinear self-modulation of drift waves will cause strong anomalous diffusion also in systems where the linear convective cells are not dangerous.

J. Weiland

1980-01-01

148

Source mechanisms and radio effects of ionospheric plasma. Annual report, 1 October 1991-30 September 1992  

SciTech Connect

Since October 1, 1991 experimental and theoretical research has been conducted by Prof. Min-Chang Lee and his students at BU and MIT. This research work is aimed at investigating the ionospheric plasma disturbances which can affect significantly the radio wave propagation in communications and space surveillance. The research topics which have been investigated include: (1) A source mechanism leading to the symmetric lower hybrid sidebands and a low-frequency mode in the upper atmosphere, (2) Characteristics of lightning-induced plasmas, (3) Radio wave-produced plasmas and effects on radio communications, (4) Plasma turbulence and formation of field aligned density fluctuations as ionospheric ducts.

Lee, M.C.

1992-11-01

149

Ionospheric Research with Miniaturized Plasma Sensors Aboard FalconSAT-3  

NASA Astrophysics Data System (ADS)

Investigations into a novel technique to measure ionosphere-thermosphere parameters have culminated in the Flat Plasma Spectrometer (FLAPS) experiment, presently under development through a collaboration between NASA Goddard Space Flight Center (GSFC) and the U. S. Air Force Academy (USAFA). FLAPS is capable of providing measurements of the full neutral wind vector, full ion-drift velocity vector, neutral and ion temperatures, and deviations from thermalization. In addition, coarse mass spectroscopy is possible using an energy analysis technique. The suite of instruments is comprised of a set of 16 individual neutral and ion analyzers, each of which is designed to perform a specific function. Advances in miniaturization technology have enabled a design in which the 16-sensor suite resides on a circular microchannel plate with an effective area of 25 cm2. The FLAPS electronics package, consisting of low voltage and high voltage power supplies, a microprocessor, and Application Specific Integrated Circuit (ASIC) amplifiers, requires a volume of 290 cm3, power of 1.5 W, and a mass of 500 g. The suite requires a +5V regulated power line from the spacecraft, and the telemetry interface is a 5.0 V TTL-compatible serial connection. Data collection rates vary from 1 to 1000 (192 Byte) spectra per second. The motivation for the FLAPS experiment is driven by objectives that fall into both basic science and technology demonstration categories. Scientifically, there is strong interest in the effects of ionosphere-thermosphere coupling and non-thermalized plasma on the processes associated with equatorial F-region ionospheric plasma bubbles. These bubbles have been known to scintillate transionospheric propagation of radio waves, often resulting in disruptions of space-based communication and navigation systems. FLAPS investigations will assist in quantifying the impact of various processes on the instigation or suppression of plasma bubbles; certain outstanding questions include 1) What is the relevance of meridional winds in suppression of plasma bubble growth? 2) What role does a velocity space instability driven by non-thermalized plasma play in the generation of small scale (<1 km) bubbles? 3) What process is responsible for turbulence in plasma beyond the edges of a bubble structure? Technologically, the need for small yet capable instruments arises from the desire to make multipoint in situ measurements of "microscopic" plasma parameters to provide insight into "macroscopic" phenomena. Examples include coherency of spatial boundaries of large-scale ( 100 km) plasma bubbles, three dimensional structure of the equatorial wind and temperature anomaly, and vertical velocity gradients in the low latitude ionosphere. This paper provides an overview of the experiment motivation and instrument design of the FLAPS experiment.

Habash Krause, L.; Herrero, F. A.; Chun, F. K.; McHarg, M. G.

2003-12-01

150

Nonlinear evolution of modified two-stream instability above ionosphere of Titan: Comparison with the data of the Cassini Plasma Spectrometer  

Microsoft Academic Search

The ionosphere of Titan, moon of Saturn, is directly exposed to the streaming plasma either of magnetospheric or solar wind origin. A turbulent interaction region is formed, called here flowside plasma mantle, where both cold ionospheric and hot streaming plasma are present at comparable densities. Within the framework of a one-dimensional electromagnetic hybrid simulation using realistic electron mass we have

Zoltn Db; Karoly Szego; Kevin B. Quest; Vitali D. Shapiro; R. E. Hartle; E. C. Sittler

2007-01-01

151

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

152

Comparative studies of the plasma turbulence in the different regions of the ionosphere- discussion of the results from DEMETER satellite  

NASA Astrophysics Data System (ADS)

Plasma turbulence is a very common phenomenon in the Earth's ionosphere. There are difference sources of it, but the generally the nonlinear developing of the plasma instabilities is a main cause of its presence. In the ionosphere there are several regions with conditions favorable for the generation and developing of the plasma instabilities. The main regions in which the turbulence has been registered are: equatorial ionosphere, auroral oval, polar cusp, ionospheric trough and also regions over epicenters of the earthquakes. The turbulence is characterized as multiscale nonlinear and intermittent process. We will present results of electric field wave form analysis using wavelet and bispectral methods for selected strong earthquakes and for crossings of the polar cusp, equatorial region and ionospheric trough. All data used in our presentation were gathered by ICE experiment onboard DEMETER satellite. These methods allow to find the energy cascade being a main mechanism of the turbulence developing. Plasma turbulence can be described by the shape of the spectra, the probability distribution function and its moments- kurtosis and skewness. The main goal of our presentation is comparison of these parameters for the turbulence over seismic regions and other ionospheric sites with turbulence.

Blecki, J.; Ko?ciesza, M.; Boudjada, M.; Parrot, M.; Savin, S.; Wronowski, R.

2012-04-01

153

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

154

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

155

DE-2 cusp observations role of plasma instabilities in topside ionospheric heating and density fluctuations  

SciTech Connect

Observatios by the low altitude Dynamics Explorer satellite (DE-2) in the polar cusp show the ionospheric plasma electron temperature and the ratio of electron to ion temperature to be increased and the electron density fluctuations to be enhanced. Also downward fluxes of energetic electrons and ions increase in the cusp and the magnetic field structure are consistent with the existence of a field-aligned current. Simultantously, there is characteristic broadband electrostatic noise (BEN) with amplitudes 1--10 mV/m peaking in the cusp but extending into the polar cap. These emissions range from far below the local 0/sup +/ gyrofrequency f/sub 0//sup +/ to the vicinity of the proton gyrofrequency but below the oxygen low hybrid frequency. The BEN observations are compared to the predictions of several theories. The amplitude of these waves is shown to be far too small to contribute significantly to the observed ionospheric heating or density fluctuations by local wave-particle interactions. Rather, the observed spatial variations are attributed to nonlocal field aligned heating processes and reflect the nonuniformity of the magnetosheath's plasma's penetration into the ionosphere.

Curtis, S.A.; Hoegy, W.R.; Brace, L.H.; Maynard, N.C.; Suguira, M.; Winningham, J.D.

1982-09-01

156

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

157

Magnetosphere of Uranus: plasma sources, convection, and field configuration  

SciTech Connect

At the time of the Voyager 2 flyby of Uranus, the planetary rotational axis will be roughly antiparallel to the solar wind flow. If Uranus has a magnetic dipole moment that is approximately aligned with its spin axis, and if the heliospheric shock has not been encountered, we will have the rare opportunity to observe a ''pole-on'' magnetosphere as discussed qualitatively by Siscoe. Qualitative arguments based on analogy with Earth, Jupiter, and Saturn suggest that the magnetosphere of Uranus may lack a source of plasma adequate to produce significant internal currents, internal convection, and associated effects. In order to provide a test of this hypothesis with the forthcoming Voyager measurements, we have constructed a class of approximately self-consistent quantitative magnetohydrostatic equilibrium configurations for a pole-on magnetosphere with variable plasma pressure parameters. Given a few simplifying assumptions, the geometries of the magnetic field and of the tail current sheet can be computed for a given distribution of trapped plasma pressure. The configurations have a single funnel-shaped polar cusp that points directly into the solar wind and a cylindrical tail plasma sheet whose currents close within the tail rather than on the tail magnetopause, and whose length depends on the rate of decrease of thermal plasma pressure down the tail. Interconnection between magnetospheric and interplanetary fields results in a highly asymmetric tail-field configuration. These features were predicted qualtitatively by Siscoe; the quantitative models presented here may be useful in the interpretation of Voyager encounter results.

Voigt, G.; Hill, T.W.; Dessler, A.J.

1983-03-01

158

Signatures of atmospheric wave propagation from troposphere to ionosphere seeding plasma bubbles in the equatorial region  

NASA Astrophysics Data System (ADS)

From the South American equatorial and low latitude regions we investigate atmospheric wave generation and propagations, mainly planetary and gravity waves. Ultra Fast Kelvin wave (3-4 day period) was monitored by Meteor radar and airglow photometer in the mesosphere and by ionosonde in the ionosphere. Large scale gravity waves (horizontal wavelength of 100 km and the period longer than 30 minutes) were observed by mesospheric airglow imager. Ionospheric irregularities and seeding of plasma bubbles were investigated by ionosonde, VHF coherent radar and OI 6300 all sky imagers. Further, forward and backward Ray -tracing of the gravity waves made it possible to understand how these waves came from and reach the F-layer bottom side and to initiate Rayleigh-Taylor Instability.

Takahashi, Hisao; Medeiros, Amauri; Buriti, Ricardo; Wrasse, Cristiano Max; Vadas, Sharon; Abdu, Mangalathayil Ali

159

Cusp/cleft auroral forms and activities in relation to ionospheric convection: Responses to specific changes in solar wind and interplanetary magnetic field conditions  

SciTech Connect

The authors describe in detail a four hour period on Dec 17, 1992, of cusp/cleft region observations, made in conjunction with the occurance of a transient auroral event. There was an IMF directional discontinuity where the fields changed from positive IMF B{sub y} (B{sub z}{much_lt}0) to large negative B{sub y} (B{sub z}>0) in conjunction with a change in convection direction in the cusp region. They present data from satellite observations, in addition to ground based data collected over an array of stations in Greenland and Svalbard. They view this as a first step toward an effort to correlate responses in the ionosphere to different solar wind and interplantetary magnetic field conditions. They analyze this data in terms of the array of different conditions which was exhibited in the ionosphere over this four hour period.

Sandholt, P.E. [Univ., of Oslo, Oslo (Norway); Farrugia, C.J. [Univ. of Malta, Msida (Malta); Stauning, P. [Danish Meteorological Institute, Copenhagen (Denmark); Crowley, S.W.H. [Imperial College, London (United Kingdom)

1996-03-01

160

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.; Watanabe, N.; Watkins, B. J.; Bristow, W. A.; Selcher, C. A.; Bernhardt, P. A.

2011-11-01

161

Characteristics of plasma density irregularities in the equatorial ionosphere  

NASA Astrophysics Data System (ADS)

We analyze high-resolution measurements of ion number density in the equatorial ionosphere made from the AE-E satellite during the years 1977-1981, and investigate the global distribution of density irregularities and the evolution of irregularity structure. In the high-altitude regions (above 350 km) the measurements show large density depletions of bubble-like structures which are confined to narrow local time, longitude, and magnetic latitude ranges while those in the low-altitude regions (below 300 km) show relatively small-depletions that are more broadly distributed in space. Seasonal variations of irregularity occurrence probability are significant in the Pacific regions while the occurrence probability is always high in the Atlantic-African regions and is always low in the Indian regions. We find that the high occurrence probability in the Pacific regions is associated with isolated bubble-structures while that near 0o longitude is produced by large depletions with bubble-structures that are superimposed on a large-scale wavelike background. Seeding effects are most obvious near 0o longitude while the most easily observed effect of the F region is the suppression of irregularity growth by interhemispheric neutral winds. By performing spectral analysis of the ion density measurements in the spatial range 18 km-200 m we investigate the irregularity structure and its temporal evolution. The local time evolution of irregularity structure is investigated by using average statistics for the low- and high-intensity structures in the altitude regions above 350 km and below 300 km. Above 350 km, a spectral break near 1 km scale size is more pronounced for low-intensity structure than for high-intensity structure. The spectral break for the first case is produced by the enhancement of power near 1 km while that for the second case is produced by the maintenance of power near 1 km. The temporal evolution of spectral parameters in the low-altitude region is relatively slow because the local time variations of power at middle- scales are not significant. The small amplitude of several-kilometer scale density modulations is often observed in the absence of irregularities at meter-scales and the power spectrum of these density structures exhibit a steep spectral slope at kilometer-scales.

Kil, Hyosub

162

A method for improving plasma temperature estimates from incoherent scatter analysis during artificial ionospheric modification experiments  

NASA Astrophysics Data System (ADS)

Spectral features in incoherent scatter data, such as those caused by the purely growing mode (PGM), can often be strongly enhanced during the first few seconds of artificial ionospheric heating experiments, such as those carried out using the high-power European Incoherent Scatter HF heater at Troms. These features, often referred to as "overshoot" effects, are indicators of turbulent non-Maxwellian plasma, and the analysis of these spectra using standard incoherent scatter data analysis software leads to a poor estimation of the plasma parameters (particularly electron and ion temperature) during RF heating experiments. In this study, a procedure is developed to derive a more reliable estimate of plasma temperature during periods when the incoherent scatter spectrum is affected by contamination from the PGM. This is achieved by removing the PGM from the measured spectrum and then analyzing the modified spectrum using standard software. The results are compared to those obtained from the analysis of the original, contaminated spectra. It is found that the differences between the results obtained from the corrected and uncorrected spectra are strongly proportional to the magnitude of the PGM feature. We also show that the bulk temperatures during the remainder of the "heater on" period after the overshoot can generally be estimated reliably by the standard analysis software, though with some important exceptions. These results are important since the plasma temperatures play a crucial role in governing thermal conduction processes, and their correct estimation is thus very important to understanding the underlying physical processes which occur during ionospheric heating.

Vickers, H.; Robinson, T.; McCrea, I. W.

2010-11-01

163

Source mechanisms and radio effects of ionospheric plasma disturbances. Final report, 1 October 1991-30 September 1994  

SciTech Connect

Research on source mechanisms and radio effects of ionospheric plasma disturbances had been conducted including theories, field experiments at Arecibo Puerto Rico, and laboratory experiments with the Versatile Toroidal Facility (VTF) at MIT Plasma Fusion Center. Several graduate students and undergraduate students participated in the research projects and completed their thesis work under the supervision of Prof. Min-Chang Lee.

Lee

1994-09-30

164

Effects of finite plasma pressure on centrifugally driven convection in Saturn's magnetosphere  

NASA Astrophysics Data System (ADS)

We have previously shown simulation results for centrifugally driven plasma convection in Saturn's inner magnetosphere, using the Rice Convection Model, including a continuously active distributed plasma source, and effects of the Coriolis force and the pickup current. These simulations result in a quasi-steady state, in which fast, narrow inflow channels alternate with slower, wider outflow channels, consistent with Cassini Plasma Spectrometer observations. Comparison of different plasma source models indicates that the inner plasma source distribution is a key element in determining the plasma convection pattern. Previous simulations, however, did not include the effects of finite plasma pressure and the associated gradient-curvature drift. We will investigate here the effects of finite plasma pressure and gradient-curvature drift by giving the cold plasma a finite temperature. We will also add a source of hot tenuous plasma at the outer simulation boundary in an attempt to simulate the injection/dispersion events observed by Cassini.

Liu, X.; Hill, T. W.

2011-12-01

165

Observations of ionospheric electron beams in the plasma sheet.  

PubMed

Electrons streaming along the magnetic field direction are frequently observed in the plasma sheet of Earth's geomagnetic tail. The impact of these field-aligned electrons on the dynamics of the geomagnetic tail is however not well understood. Here we report the first detection of field-aligned electrons with fluxes increasing at ~1 keV forming a "cool" beam just prior to the dissipation of energy in the current sheet. These field-aligned beams at ~15 R(E) in the plasma sheet are nearly identical to those commonly observed at auroral altitudes, suggesting the beams are auroral electrons accelerated upward by electric fields parallel (E([parallel])) to the geomagnetic field. The density of the beams relative to the ambient electron density is ?n(b)/n(e)~5-13% and the current carried by the beams is ~10(-8)-10(-7) A m(-2). These beams in high ? plasmas with large density and temperature gradients appear to satisfy the Bohm criteria to initiate current driven instabilities. PMID:23215495

Zheng, H; Fu, S Y; Zong, Q G; Pu, Z Y; Wang, Y F; Parks, G K

2012-11-13

166

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

167

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.

168

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

SciTech Connect

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.; Yau, A. W. [Department of Physics and Astronomy, University of Calgary, Calgary T2N1N4 (Canada); Oyama, K.-I. [Plasma and Space Science Center, National Cheng Kung University, Tainan 701, Taiwan (China); Abe, T. [Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency, Kanagawa 252-5210 (Japan)

2011-07-15

169

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

170

Ionospheric-magnetospheric-heliospheric coupling: Storm-time thermal plasma redistribution  

NASA Astrophysics Data System (ADS)

Large-scale thermal plasma redistribution phenomena have been observed from the ground and space during the major geomagnetic storms of the recent solar cycle. Plasma redistribution is a multistep, systemwide process involving the equatorial, low, mid, auroral, and polar latitude regions. Penetration electric fields enhance the equatorial ionization anomaly peaks, whereas polarization electric field effects at the dusk terminator redistribute the low-latitude total electron content (TEC) in both longitude and latitude. Magnetic field geometry creates a preferred longitude for the enhancement of low- and mid-latitude TEC in the American sector at sunset. This TEC enhancement forms a localized source for the intense storm enhanced density (SED) erosion plumes that are observed over the Americas during major storms. A second set of storm-time processes leads to the erosion of the plasmasphere boundary layer, transporting the SED plumes to the noontime cusp in the ionosphere and to the dayside magnetopause at high altitudes. Ring current enhancements generate strong poleward-directed subauroral polarization stream (SAPS) electric fields in the evening sector as field-aligned currents close through the low-conductivity ionosphere. The SAPS electric field overlaps the outer plasmasphere, drawing out the SED/plasmasphere erosion plumes. These greatly enhanced fluxes of cold plasma traverse the cusp and enter the polar cap forming the polar tongue of ionization and providing a rich source of heavy ions for the magnetospheric injection and acceleration mechanisms that operate in these regions.

Foster, John C.

171

Longitudinal statistics of plasma bubbles observed as He+ density depletions at altitudes of the topside ionosphere  

NASA Astrophysics Data System (ADS)

This work presents a new examination of the hypothesis regarding the equatorial origin of low He+ density plasma depletions (or subtroughs). For this purpose, we have conducted a detailed comparative analysis of longitudinal variations in the occurrence probabilities of subtroughs in both hemispheres and variations in the occurrence probabilities of equatorial F-region irregularities (EFIs), equatorial spread F (RFS and ESF), and equatorial plasma bubbles (EPBs). Taking into consideration the seasonal dependence and some peculiarities of magnetic field variations in different hemispheres, a conclusion has been reached regarding the similarity between longitudinal statistical occurrences of subtroughs and equatorial ionospheric F-region irregularities. In addition, another piece of evidence in favor of the similarity of the nature of the above-mentioned phenomena has been obtained. We have got a confirmation once again that low He+ density depletions (or subtroughs) can be rightfully considered as equatorial plasma "bubbles," which can be observed at altitudes of the topside ionosphere as depletions in the He+ density.

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

2013-01-01

172

Fast Radial Convective Transport in Tokamak SOL Plasmas  

NASA Astrophysics Data System (ADS)

Reduced 2D resistive MHD system of electromagnetic equations is applied to describe fast radial convective density transport[1,2] in the tokamak SOL and the divertor region. The study is concentrated on properties of single and multiple plasma blobs propagation and interaction. A formation of a stable front of the blob as well as a formation of the canonical blob shape and size is demonstrated. Existence of the density limit in the model is analyzed. Impact of the density gradient term in the vorticity equation on the fast radial blobs propagation is discussed. The ideal limit of the model is considered as well as the influence of parallel current resistive effects. The 2D results are compared and verified with 3D blob propagation simulations by the BOUT code[3], based on 5-field fluid Braginskii model. The results of the comparison will be reported. [1] S.I. Krasheninnikov, Phys. Let. A 283, 368 (2001); [2] D.A. D'Ippolito, J.R. Myra, S.I. Krasheninnikov, Phys. Plasmas 9, 222 (2002); [3] X.Q. Xu, R.H. Cohen, Contrib. Plasma phys. 36, 158 (1998),. Presented at the 44 Annual APP-DPP meeting, Orlando, FL, November 11-15, 2002

Galkin, S. A.; Krasheninnikov, S. I.; D'Ippolito, D. A.; Myra, J. R.; Xu, X. Q.

2002-11-01

173

Effect of self-consistent magnetic field on plasma sheet penetration to the inner magnetosphere under enhanced convection: RCM simulations combined with force-balance magnetic field solver  

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) to investigate how the earthward penetration of convection electric field, and therefore plasma sheet population, depends on plasma sheet boundary conditions. Outer boundary conditions at r ~20 RE are a function of MLT and interplanetary conditions based on 11 years of Geotail data. In the previous simulations, Tsyganenko 96 magnetic field model (T96) was used so force balance between plasma pressure and magnetic fields was not maintained. We have now integrated the RCM with a magnetic field solver (Liu et al., 2006) to obtain the required force balance in the equatorial plane. We have run the self-consistent simulations under enhanced convection with different boundary conditions in which we kept different parameters (flux tube particle content, plasma pressure, plasma beta, or magnetic fields) at the outer boundary to be MLT-dependent but time independent. Different boundary conditions result in qualitatively similar plasma sheet profiles. The results show that magnetic field has a dawn dusk asymmetry with field lines being more stretched in the pre-midnight sector, due to relatively higher plasma pressure there. The asymmetry in the magnetic fields in turn affects the radial distance and MLT of plasma sheet penetration into the inner magnetosphere. In comparison with results using the T96, plasma transport under self-consistent magnetic field results in proton and electron plasma sheet inner edges that are located in higher latitudes, weaker pressure gradients, and more efficient shielding of the near-Earth convection electric field (since auroral conductance is also confined to higher latitudes). We are currently evaluating the simulated plasma sheet properties by comparing them with statistical results obtained from Geotail and THEMIS observations.

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

2010-12-01

174

Characterization of the geometries of the high-latitude ionospheric convection pattern  

NASA Astrophysics Data System (ADS)

An investigation of the geometries of the high-latitude convection pattern is conducted using spacecraft observations of the northern hemisphere during conditions when the z-component of the interplanetary magnetic field is negative. In the first part of this investigation we examine the specification of the polar cap boundary as a circle using data from nearly simultaneous satellites to investigate the variation in size and location of the circle and the means by which such variations may be specified. We also investigate the degree to which a circle departs from the instantaneous configuration of the boundary and the effect that such departures may have on the global potential distribution. The DMSP satellites F8 and F9 provide an opportunity to identify the polar cap boundary with four nearly simultaneous points that can be used in a least squares fitting procedure to derive a best fit circle describing the polar cap boundary. The results of this exercise confirmed that the polar cap boundary can be well represented by a circle with the center offset towards the midnight sector with a B(sub y) and seasonal dependence in the radius of the circle and the location of the center point. Our results indicated that departures from a nominally circular boundary occur most frequently on the dayside. These departures led us to conclude that the polar cap boundary can be best represented by two circular segments with a smaller segment on the dawnside for conditions of B(sub y) negative. We also identified localized bulges or depressions as departures from the circle that are consistent with the descriptions of suggested impulsive additions of magnetic flux to the polar cap. In the second part of this investigation we examine the latitude distribution of the potential at latitudes below the polar cap boundary to determine its sensitivity to interplanetary conditions, magnetic activity, and local time. We use a gaussian curve segment to best represent the distribution of the potential equatorward of the polar cap and find the gaussian halfwidth is dependent on the potential at the polar cap boundary with the halfwidth being larger on the duskside than on the dawnside. We also find this parameter is dependent on local time as well as Kp and IMF B(sub z). In all cases, the halfwidth shows a greater variability on the duskside than on the dawnside. Finally, we note that the potential distribution around the polar cap boundary shows significant departures from the sinusoidal distribution frequently assumed in model treatments. As a final exercise, we use our results to generate inputs into a mathematical model of the high-latitude convection pattern and compare the results to measured data and find the model results to be reasonable representations of the actual conditions.

Keating, Christopher Francis

175

Behavior of ionized plasma in the high latitude topside ionosphere  

NASA Astrophysics Data System (ADS)

We have developed a numerical model to study the steady state behavior of a fully ionized plasma (H+, O+ and the electrons) encompassing the geomagnetic field lines. The theoretical formulation is based on the 16-moment system of transport equations. The electron gas collision is dominated below 2500 km. Above this altitude electron temperature anisotropy develops with temperature perpendicular to the field line being higher than that parallel to the field line. The H+ ion temperature anisotropy shows H+ temperature parallel to the field line being higher than that perpendicular to the field line. H+ ion temperature also exhibits adiabatic cooling as to the supersonic ion gas cools down as it expands in a diverging magnetic field. Our results are in good agreement with the previous theoretical studies of the polar wind and recent experimental observations. This is the first successful steady state solution to the 16-moment set of transport equations.

Ganguli, S. G.; Mitchell, H. G., Jr.; Palmadesso, P. J.

1985-08-01

176

Space weather in the thermospheric-ionospheric domain over the Brazilian region: Climatology of ionospheric plasma bubbles in the subequatorial and low-latitude region  

NASA Astrophysics Data System (ADS)

The climatology of ionospheric plasma bubbles is studied here by means of a comparison of the frequency of occurrence of the spread-F/plasma bubble events over the South American region using the images from two OI 630 nm imager systems located at the subequatorial station So Joo do CaririCA (7.4 S, 36.5 W, 20 S dip) and the low-latitude station Cachoeira PaulistaCP (22.5 S, 45 W, 33 S dip) in Brazil during the years of 2004 and 2005. The results are discussed in the light of current theory and geomagnetic parameters of the two observation stations.

Koga, D.; Sobral, J. H. A.; Abdu, M. A.; de Castilho, V. M.; Mascarenhas, M.; Arruda, D. C. S.; Zamlutti, C. J.; Takahashi, H.; Medeiros, A. F.; Buriti, R. A.

2011-07-01

177

Magnetosphere-Ionosphere Coupling at Subauroral Latitudes (Invited)  

NASA Astrophysics Data System (ADS)

On the night side of the inner magnetosphere and the conjugate ionosphere, there is a region where boundaries of several plasma populations of different origins and energy regimes (the plasmapause, the equatorward edge of the auroral oval, and the inner edge of the ring current) approximately coincide or overlap. This region is highly complex and dynamic. The magnetospheric hot plasmas and ionospheric-plasmaspheric cold populations are coupled through convection electric fields and auroral particle precipitation. Both convection (electric field) patterns and plasma densities are observed to be structured during geomagnetic disturbances, with Subauroral Polarization Streams (SAPS) near the auroral oval and plasma plumes (particularly prominent in TEC maps) extending to lower latitudes and in MLT from the nightside toward the afternoon sector. In this paper, we present an initial attempt to explain the causes of the observed ionospheric storm-time plasma structuring at mid and sub-auroral latitudes through self-consistent simulations using the Rice Convection Model. Specifically, we model the structure and longitudinal/UT dependence of SAPS structures in the duskside ionosphere, and how they may be related to meridional electron density transport postulated to be responsible for large storm-time TEC structuring in the afternoon-to-dusk MLT sector.

Sazykin, S.; Spiro, R. W.; Wolf, R. A.; Song, Y.; Toffoletto, F.

2010-12-01

178

Ionospheric Plasma Outflow Under High Solar Wind Dynamic Pressure Conditions  

NASA Astrophysics Data System (ADS)

The polar cusp is well-known to be one of the most intense source regions of iono- spheric outflow. Since this region is of direct access for solar wind plasma, changes in the interplanetary magnetic field and solar wind dynamic pressure are expected to influence the ion outflow. We report combined observations from the Interball- Auroral in the high-altitude range (10,000-20,000km) and the FAST satellite in the mid-altitude range (4000 km) revealing enhanced ion outflows in association with the passage of an interplanetary shock and CME. Several case studies based on the anal- ysis of ion data recorded from several orbits before and after the pressure impulse are made to investigate how the dynamic pressure affects the amount of outflowing ions. We found a clear relationship between the ion outflow variations and the dy- namic pressure changes when choosing average ion flux and average ion energy flux, inferred from global conservation laws, as parameters to characterize the ion outflow.

Malingre, M.; Bouhram, M.; Dubouloz, N.; Sauvaud, J. A.; Berthomier, M.; Carlson, C. W.

179

An investigation of methods for updating ionospheric scintillation models using topside in-situ plasma density measurements  

NASA Astrophysics Data System (ADS)

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.

Secan, James A.

1993-05-01

180

Geomagnetic activity as a reflection of processes in the magnetospheric tail: 2. Plasma convection model  

NASA Astrophysics Data System (ADS)

A model of plasma convection in the magnetospheric tail was developed. Although highly simplified, the model adequately describes the main characteristics of the process. We have calculated the physical parameters characterizing the magnetotail, as well as described the convection of fluxtubes in it and the process of electron dropout. The model explains the semiannual variation in magnetic activity.

Krymskii, G. F.; Danilov, A. A.; Makarov, G. A.

2013-09-01

181

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

SciTech Connect

The authors 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 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 >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. 45 refs., 7 figs., 2 tabs.

Burke, W.J.; Machuzak, J.S.; Maynard, N.C. [Phillips Lab., Hanscom Air Force Base, MA (United States); Basinska, E.M.; Erickson, G.M. [Boston Univ., MA (United States); Hoffman, R.A.; Slavin, J.A. [Goddard Space Flight Center, Greenbelt, MD (United States); Hanson, W.B. [Univ. of Texas, Dallas, Richardson, TX (United States)

1994-02-01

182

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

183

Convective radial transport in a linear magnetized plasma column and fast infrared imaging of plasma turbulence  

NASA Astrophysics Data System (ADS)

The transition to turbulence of strongly nonlinear low frequency unstable waves obtained in a new magnetized plasma device is studied. The device consists in a large multipolar plasma chamber (1.4m diameter, 1 m length) connected to a cylinder (40 cm diam., 1m length) and a half-torus (40 cm diam., 0.61 m large radius). The linear and curved columns are surrounded by 50 solenoid coils producing a magnetic fied intensity lower than 0.04T. The linear magnetized plasma columns is unstable when a floating grid is inserted between the source chamber and the plasma column. The main control parameter is the negative biasing of the plasma source. Strongly nonlinear coherent waves are recorded. In order to study the detailed mechanism of the destabilization of the waves, the diameter of the column is restricted to 15 cm at the entrance of the column. Coherent modes still exist in that case and the plasma density is slowly decaying to the wall of the cylinder in the shadow of the limiter. A conditional sampling method exhibits the spiral structure of the unstable modes: the plasma is convected radially by centrifugal effect and a spiral arm structure is recorded. This leads to the clear evidence that the unstable modes are due to the centrifugal instability induced by the rotation of the plasma due to the existence of a radial electric field. The fast imaging of the fluctuations is obtained using a square array of 64 photodetectors coupled to 64 transient digitizers (200 ksamples/s). The near infrared radiation of metastables argon ions is modulated by the electron fluctuations. The spatial structure of regular modes is recorded and the transition to turbulence is studied. The implications in the diagnostic of the convective transport in the SOL of tokamaks are discussed.

Escarguel, Alexandre; Pierre, Thiery; Leclert, Gerard; Guyomarc'h, Didier; Quotb, Kamal

2002-11-01

184

Observations of solar-wind-driven progression of interplanetary magnetic field B{sub Y}-related dayside ionospheric disturbances  

SciTech Connect

Observations from August 2, and 3, 1991, of poleward progressing, dayside convection disturbances accompanied by geomagnetic perturbations and ionospheric radio wave absorption have been analyzed and compared to variations in the solar wind parameters as observed from the IMP 8 satellite. The convection disturbances appear to start at dayside cusp latitudes from where they progress antisunward to high latitudes. The reported observations have enabled calculations of the progression directions and velocities and precise estimates of the delays between solar wind variations as measured by the IMP 8 satellite and ionospheric convection changes as observed from an array of polar magnetic observatories. The progressing ionospheric disturbance events occur during intervals of southward interplanetary magnetic fields (negative interplanetary magnetic field (IMF) B{sub Z} component); they are found to be closely related to variations of the east-west component B{sub Y} of the IMF. The close coupling between the solar wind and the polar ionosphere(s) is explained in an open magnetospheric model in which the geomagnetic field extending from a localized region of the dayside polar cap merges with the southward interplanetary field. Variations in the IMF B{sub Y} component are reproduced in corresponding modulations of the east-west component of the plasma flow at the ionospheric foot points of the connecting `open` field lines. The perturbations of the plasma flow persist while the open field lines are convected with the ionospheric plasma across part of the dayside polar cap. The observed geomagnetic perturbations result from the combined effects of field-aligned currents and horizontal ionospheric currents, notably the convection-related Hall currents. The associated radio wave absorption events are explained as the result of E region electron heating by the horizontal electric fields associated with the convection enhancements. 48 refs., 16 figs., 3 tabs.

Stauning, P.; Friis-Christensen, E. [Danish Meterological Institute, Copenhagen (Denmark); Clauer, C.R. [Univ. of Michigan, Ann Arbor, MI (United States)

1995-05-01

185

Source mechanisms and radio effects of ionospheric plasma. Annual report, 1 October 1991-30 September 1992  

Microsoft Academic Search

Since October 1, 1991 experimental and theoretical research has been conducted by Prof. Min-Chang Lee and his students at BU and MIT. This research work is aimed at investigating the ionospheric plasma disturbances which can affect significantly the radio wave propagation in communications and space surveillance. The research topics which have been investigated include: (1) A source mechanism leading to

1992-01-01

186

Erosion/redeposition analysis of the ITER first wall with convective and non-convective plasma transport  

SciTech Connect

Sputtering erosion/redeposition is analyzed for IAEA [Report GA10FDR1-01-07-13 (2001)] plasma facing components, with scrape-off layer (SOL) plasma convective radial transport and nonconvective (diffusion-only) transport. The analysis uses the UEDGE code [T .D. Rognlien et al., J. Nucl. Mater. 196, 347 (1992)] and DEGAS code [D. P. Stotler et al., Contrib. Plasma Phys. 40, 221 (2000) ] to compute plasma SOL profiles and ion and neutral fluxes to the wall, TRIM-SP code [J. P. Biersack, W. Eckstein, J. Appl. Phys. A34, 73 (1984)] to compute sputter yields, and the REDEP/WBC code package [J. N. Brooks, Fusion Eng. Des. 60, 515 (2002)] for three-dimensional kinetic modeling of sputtered particle transport. Convective transport is modeled for the background plasma by a radially varying outward-flow component of the fluid velocity, and for the impurity ions by three models designed to bracket existing models/data. Results are reported here for the first wall with the reference beryllium coating and an alternative tungsten coating. The analysis shows: (1) sputtering erosion for convective flow is 20-40 times higher than for diffusion-only but acceptably low ({approx}0.3 nm/s) for beryllium, and very low ({approx}0.002 nm/s) for tungsten; (2) plasma contamination by wall sputtering, with convective flow, is of order 1% for beryllium and negligible for tungsten; (3) wall-to-divertor beryllium transport may be significant ({approx}10%-60% of the sputtered Be current); (4) tritium co-deposition in redeposited beryllium may be high ({approx}1-6 gT/400 s pulse)

Brooks, J. N.; Allain, J. P.; Rognlien, T. D. [Argonne National Laboratory, 9700 South Cass Avenue, Argonne Ilinois 60439 (United States); Lawrence Livermore National Laboratory, Livermore, California 94551 (United States)

2006-12-15

187

Monitoring of sporadic plasma layers in the lower ionosphere in the communication link satellite-to-satellite  

NASA Astrophysics Data System (ADS)

Method of global monitoring of sporadic plasma layers in the lower ionosphere is developed. In-vestigations were carried out by use of analysis of the amplitude and phase components of radio holograms obtained during the radio occultation missions CHAMP, FORMOSAT-3. Sporadic amplitude scintillation observed in RO experiments contain important information concerning the seasonal, geographical, and temporal distributions of the ionospheric disturbances and de-pend on solar activity. The geographical and seasonal distributions of sporadic layers in the lower ionosphere as function of solar activity in the period 2002-2008 years is obtained. The general number of RO events with strong amplitude variations can be used as an indicator of the ionospheric activity. We found that during 2001-2008 the daily averaged S4 index measured during CHAllenging Minisatellite Payload (CHAMP) mission depends essentially on solar ac-tivity. The maximum occurred in January 2002, minimum has been observed in summer 2008. Different temporal behavior of S4 index has been detected for polar (with latitude greater than 55 degrees) and low latitude (moderate and equatorial) regions. For polar regions S4 index is slowly decreasing with solar activity. In the low latitude areas S4 index is sharply oscillat-ing, depending on the solar ultraviolet emission variations. The geographical distribution of S4 index variations indicates different origin of ionospheric plasma disturbances in polar and low latitude areas. Origin of the plasma disturbances in the polar areas may be connected with influence of solar wind, the ultraviolet emission of the Sun may be the main cause of the ionospheric irregularities in the low latitude zone. Analysis reveals global oscillations of S4 index with the periods of 5-7 months. Analysis of these oscillations may provide additional connection with solar activity. Therefore, the S4 index of RO signal is important radio physical indicator of solar activity.

Pavelyev, Alexander; Matyugov, Stanislav; Wickert, Jens; Liou, Yuei An; Yakovlev, Oleg

188

Distinctive plasma density features of the topside ionosphere and their electrodynamics investigated during southern winter  

NASA Astrophysics Data System (ADS)

This study utilizes a novel technique to map the Defense Meteorological Satellite Program (DMSP) data across the two hemispheres to learn about the morphology and plasma composition of the topside ionosphere, and the underlying ionospheric dynamics. In the southern winter hemisphere, the regional maps tracked a heavy-ion (Ni-O+) trough, aurora zone, polar hole, and large plasma density depletion. The latter appeared in the region of the South Atlantic Magnetic Anomaly (SAMA). The electron temperature (Te) map detected the thermal characteristics of these features, while the plasma drifts and flux maps tracked their dynamics. Results show that there were special electrodynamic effects in the SAMA region due to the low magnetic field and high conductivity. These increased the vertical downward (VZ) and the westward (VY) drifts. Independently, the VZ and VY maps registered the affected area that was depleted in heavy ions and rich in light ions. Some field-aligned profiles tracked the impact of these SAMA effects on the heavy-ion trough, which was a stagnation trough and appeared markedly differently at different longitudes. At trough latitudes ((56 +/- 4)S (geomagnetic) when Dstav = 0 nT), the elevated electron temperatures forming a Te peak indicated subauroral heating effects. A statistical study modeled the magnetic activity dependence of the Te peak's magnitude and location and revealed their linear correlation with the activity level. Statistically, the Te peak increased [10.226 +/- 1.355]K and moved equatorward [0.051 +/- 0.009] (geomagnetic) per 1 nT decrease in the averaged Dst index. Per 1 nT increase in the averaged AE index, its magnitude increased [1.315 +/- 0.444]K and the equatorward movement was [0.014 +/- 0.003].

Horvath, Ildiko; Lovell, Brian C.

2009-01-01

189

Two-dimensional Model of the Ionospheric Alfven Resonator With Active Ionosphere  

NASA Astrophysics Data System (ADS)

This paper presents results from a multi-fluid nonlinear model of low-altitude flux tubes. It represents a significant improvement over previously published models, cf. [Sydorenko, Rankin, and Kabin, 2008]. The ionosphere is considered as a finite thickness highly-collisional plasma layer with multiple ion species. Pedersen conductivity is accounted for and motion of electrons and ions inside the ionosphere is omitted. Following [Schunk, 1996], the temperatures of the plasma components are found as a result of a competition between heating and collisional losses. The electron and ion densities are obtained from their continuity equations, with ionization sources and recombination sinks accounted for. The allowance for variation of temperature affects collision frequencies and densities of the plasma components, thus modifying the conductivity. The multi-fluid model is used to study the ionospheric feedback instability [Lysak, 1991]. In this case, the source of heating is the electric current of an Alfven wave and the temperatures, densities, and conductivity are calculated self-consistently. Another application of the model to be discussed is the excitation of Alfven waves by a convection current in the ionosphere, where the ionospheric conductivity changes with time, similar to experiments on artificial heating of the ionosphere. In these simulations, the conductivity profile is a prescribed function of space and time, which in general can be constrained using experimental data on ionospheric heating. Lysak, R. L. (1991), J. Geophys. Res., 96, 1553. Schunk, R. W., (Editor), STEP: Handbook of Ionospheric Models, Utah State Univ., Logan, Utah, 1996. Sydorenko, D., R. Rankin, and K. Kabin (2008), J. Geophys. Res., 113, A10206, doi:10.1029/2008JA013579.

Sydorenko, D.; Rankin, R.

2010-12-01

190

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

NASA Astrophysics Data System (ADS)

The present study statistically examines the characteristics of energetic ions in the plasma sheet using the Geotail/EPIC 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 (see Figure); (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.

2011-12-01

191

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

NASA Astrophysics Data System (ADS)

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.; Leyser, T. B.

2013-05-01

192

The influence of artificial electron heating on plasma irregularities in the lower ionosphere  

NASA Astrophysics Data System (ADS)

It is known small-scale ionospheric irregularities below the homopause level are generated by the neutral air turbulence. Usually an approximation of isothermality Te = Ti = Tn is valid for the lower ionosphere, especially, at middle latitudes. However, the approximation may be broken due to electron heating by powerful radio waves. In the report we consider theoretically reaction of ionospheric irregularities created by the neutral turbulence on the increasing of electron temperature Te due to the radio wave action. For this aim, expressions for the irregularity spectrum, the mean-square level of the plasma density fluctuations, and the radar backscatter cross-section per unit volume have been obtained. Using the expressions we have calculated the spectral form, the rms fluctuation level, and the cross-section ? for the case of the mid-latitude ionosphere at an altitude near 100 km when the ratio of the electron to ion temperature Te /Ti increased from 1 to 10. The spectrum has corresponded to the inertial range of turbulence, the rms level has been estimated for irregularity length-scales smaller than 500 m, and ? has been evaluated for the diagnostic radar frequencies from 5 to 50 MHz and the vertical direction of antenna beam. It was shown that an increase in Te produces a decrease in both the fluctuation level and the backscatter cross-section. In our calculations this level reduced from 6.2 to 4.8 %; the cross-section ? from 1.2810-8 to 9.0610-9 m-1 at 5 MHz and from 1.2510-11 to 8.9310-12 m-1 at 50 MHz. The rise in Te has also resulted in an increase in the spectral slope (for the approximation of spectrum by a power law k -p , the index p took values from 1.62 to 2.34). These changes are explained by a decrease in the cut-off wavenumber in the irregularity spectrum resulted from an increase in the ambipolar diffusivity due to the rise in Te .

Kyzyurov, Yurij; Chernogor, Leonid F.

193

Modeling the transition of the inner plasma sheet from weak to enhanced convection  

NASA Astrophysics Data System (ADS)

We seek to determine whether the adiabatic plasma transport and energization resulting from electric and magnetic drift can quantitatively account for the plasma sheet under weak and enhanced convection observed by Geotail presented in the companion paper [, 2004]. We use a modified Magnetospheric Specification Model to simulate the dynamics and distributions of protons originating from the deep tail and low-latitude boundary layer (LLBL) under an assigned, slowly increasing convection electric field. The magnetic field is Tsyganenko 96 model, modified so that force balance is maintained along the midnight meridian. Our simulation results reproduce well the observed radial profiles and magnitudes of pressure and magnetic field. The changes of these parameters with convection strength are also well reproduced, indicating that the electric and magnetic drift control the large-scale structure of the plasma sheet. The plasma flows near midnight are diverted toward dusk by diamagnetic drift. We obtain a steady state plasma sheet under strong and steady convection, showing that magnetic drift and field line stretching bring the plasma sheet away from possible convection disruption. The protons from the LLBL strongly affect the plasma sheet density and temperature during quiet times but not during enhanced convection. For the same cross-polar cap potential, stronger shielding of the convection electric field results in smaller energization. The penetration electric field is important in moving the plasma sheet to smaller geocentric radial distance. Our results suggest that the frozen-in condition E = -v B is not valid in the inner plasma sheet because of strong diamagnetic drift.

Wang, Chih-Ping; Lyons, Larry R.; Chen, Margaret W.; Toffoletto, Frank R.

2004-12-01

194

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

195

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

196

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

197

Ionospheric plasma enhancement by a ground based pulsed solid state laser  

NASA Astrophysics Data System (ADS)

The 2.7 meter diameter parabolic Liquid Mirror Reflector (LMT) at the HIPAS Observatory could focus a 1060 nm pulsed laser beam to a 4 cm spot size over a Rayleigh focal range of 1.2 km ( 1.4 m3 focal volume). A 100 J - one nanosecond laser pulse (1011 Watt) would result in an ideal flux of 1.7x1010 W/cm2 at 100 km range, two orders of magnitude above the 108 W/cm2 requirement for the onset of plasma production from solid targets. Given 1000/m3 micron sized meteor ash particles, one could enhance the local plasma density within the initial Rayleigh range by an order of magnitude per laser shot. The plasma would expand along the geomagnetic field lines. The technique offers a new method of ELF generation through changes in conductivity as well as other controlled ionospheric plasma experiments. Since "wavefront tilt" is the major effect of the atmosphere, a nanosecond laser passes through a frozen media and is weakly defocused. It is also the proper duration to completely ionize micron sized silicate particles (5 km/s silicate sound speed).

Wong, A. Y.; Wuerker, R. F.

1997-11-01

198

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

199

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

200

Comparison of NeQuick, PIM, and TSM model results for the topside ionospheric plasma scale and transition heights  

NASA Astrophysics Data System (ADS)

The topside ionospheric scale height (Ts) and the O+ H+ transition height (Th) are key ionospheric characteristics that are of special interest when studying and modelling the plasma composition and dynamics. Recently, a new Topside Sounder Model (TSM) has been developed which provides the Ts and Th quantities together with the ratio between them, Ts/Th. The database for this model has been built upon thousands of Ts and Th values deduced from electron density profiles retrieved from topside sounding measurements. For validation purposes, it would be interesting to compare calculations of the ionospheric scale/transition heights from TSM with corresponding calculations from two other well-known models the NeQuick Model (NeQ) and the Parameterized Ionospheric Model (PIM). For the purpose, electron density profiles have been computed with both the NeQuick and PIM models over suitable grids of input parameters such as month, local time, geomagnetic latitude, solar activity, and in the altitude range between 200 and 2000 km. The topside ionospheric scale height and the O+ H+ transition height values have been extracted from each profile in the same manner as previously done for the TSM development database. Finally, the Ts and Th values deduced from the NeQuick and PIM profiles have been compared with the respective values provided by the TSM. Results of this comparison are analysed and suggestions are put forward for further improving the models in question. TSM applications are discussed as well.

Stankov, S. M.; Marinov, P.; Kutiev, I.

201

Calculation of ionospheric plasma density irregularities parameters by using EISCAT measurements for strong scintillation modelling  

NASA Astrophysics Data System (ADS)

Ionospheric plasma density irregularities may cause rapid fluctuations in the intensity and phase of radio waves propagating through. Usually, scintillation events are modelled in the diffractive scattering approach which is valid for weak scattering conditions. Some mathematical tricks help then in reproducing high levels of scintillation, lacking of full physical meaning. Strong scintillation events are better modelled in the refractive scattering approach, which includes weak scattering conditions. A few parameters (e.g., spatial correlation length and drift velocity) are of key importance in understanding which approach may be correct. Last year, two EISCAT measurement campaigns have been set up in the framework of the Trans-National Access programme, in order to infer and calculate all those parameters useful for numerical modelling of scintillation events. The radar measurement results are compared with transionospheric radio signals at VHF, UHF, and L band in order to understand the feasibility and appropriateness of the two approaches.

Forte, Biagio; Hggstrm, Ingemar; Turunen, Esa

2010-05-01

202

Space Shuttle Exhaust Modifications of the Mid-Latitude Ionospheric Plasma As Diagnosed By Ground Based Radar  

NASA Astrophysics Data System (ADS)

The Space Shuttle's Orbital Maneuvering System (OMS) engines have been used since the early days of the STS program for active ionospheric modification experiments designed to be viewed by ground based ionospheric radar systems. In 1995, the Naval Research Laboratory initiated the Shuttle Ionospheric Modification with Pulsed Localized Exhaust (SIMPLEX) Program using dedicated Space Shuttle OMS burns scheduled through the US Department of Defense's Space Test Program. SIMPLEX objectives include generation of localized ion-acoustic turbulence and the formation of ionospheric density irregularities for injections perpendicular to the local magnetic field, creating structures which can scatter incident UHF radar signals. We discuss radar observations made during several recent SIMPLEX mid-latitude experiments conducted over the Millstone Hill incoherent scatter radar system in Westford, Massachusetts. OMS engine firings release 10 kg/s of CO2, H2, H2O, and N2 molecules which charge exchange with ambient O+ ions in the F region, producing molecular ions and long lived electron density depletions as recombination occurs with ambient electrons. Depending on the magnetic field angle, the high velocity of the injected reactive exhaust molecules relative to the background ionosphere can create longitudinal propagating ion acoustic waves with amplitudes well above normal thermal levels and stimulate a wide variety of plasma instability processes. These effects produce high radar cross section targets readily visible to the Millstone Hill system, a high power large aperture radar designed to measure very weak scatter from the quiescent background ionosphere. We will survey the plasma instability parameter space explored to date and discuss plans for future SIMPLEX observations.

Lind, F. D.; Erickson, P. J.; Bhatt, A.; Bernhardt, P. A.

2009-12-01

203

Electron velocity distributions and plasma waves associated with the injection of an electron beam into the ionosphere  

NASA Astrophysics Data System (ADS)

An electron beam was injected into earth's ionosphere on August 1, 1985, during the flight of the Space Shuttle Challenger as part of the objectives of the Spacelab 2 mission. In the wake of the Space Shuttle a magnetically aligned sheet of electrons returning from the direction of propagation of the beam was detected with the free-flying Plasma Diagnostics Package. The thickness of this sheet of returning electrons was about 20 m. Large intensifications of broadband electrostatic noise were also observed within this sheet of electrons. A numerical simulation of the interaction of the electron beam with the ambient ionospheric plasmas is employed to show that the electron beam excites electron plasma oscillations and that it is possible for the ion acoustic instability to provide a returning flux of hot electrons by means of quasi-linear diffusion.

Frank, L. A.; Paterson, W. R.; Kurth, W. S.; Ashour-Abdalla, M.; Schriver, D.

1989-06-01

204

Density enhancement in plasmasphere-ionosphere plasma during the 2003 Halloween Superstorm: Observations along the 330th magnetic meridian in North America  

Microsoft Academic Search

On October 2931, 2003, the ground observations of field line resonance signals and the total electron content (TEC) along the 330th magnetic meridian recorded extraordinary density variations in both the magnetosphere and the ionosphere. In the magnetosphere, the density decreased at outer L shells due to strong convection, whereas it increased significantly in the afternoon sector at L ? 4.

P. J. Chi; C. T. Russell; J. C. Foster; M. B. Moldwin; M. J. Engebretson; I. R. Mann

2005-01-01

205

Density enhancement in plasmasphere-ionosphere plasma during the 2003 Halloween Superstorm: Observations along the 330th magnetic meridian in North America  

Microsoft Academic Search

On October 29-31, 2003, the ground observations of field line resonance signals and the total electron content (TEC) along the 330th magnetic meridian recorded extraordinary density variations in both the magnetosphere and the ionosphere. In the magnetosphere, the density decreased at outer L shells due to strong convection, whereas it increased significantly in the afternoon sector at L <= 4.

P. J. Chi; C. T. Russell; J. C. Foster; M. B. Moldwin; M. J. Engebretson; I. R. Mann

2005-01-01

206

Ionospheric storm time dynamics as seen by GPS tomography and in situ spacecraft observations  

NASA Astrophysics Data System (ADS)

During major geomagnetic storms anomalous enhancements of the ionospheric density are seen at high and middle latitudes. A number of physical mechanisms have been invoked to explain these storm time density anomalies including an expansion of high-latitude electric plasma convection to midlatitudes, thermospheric neutral winds, and changes in the ionospheric composition. However, it remains unclear which mechanism plays the dominant role in the formation of storm time density anomalies, partly because of insufficient coverage of the measurements of global electric convection and thermospheric winds at midlatitudes. This paper describes a novel technique for extracting the storm time E B convection boundary from in situ measurements of plasma bulk motion obtained by LEO DMSP satellites. The convection boundary estimated from the DMSP data during major magnetic storm of 20 November 2003 has been compared with the global distributions of the ionospheric plasma deduced from characteristics of GPS signals acquired by a ground-based network of GPS receivers. The tomographic inversion of GPS data using a three-dimensional time-dependent inversion technique reveals the spatial and temporal evolution of the storm time density anomaly. Comparison between the tomographic reconstructions of the ionospheric plasma distributions and in situ DMSP measurements of plasma bulk motion suggests that the convective flow expanded low enough in latitude to encompass, in part, the formation of the midlatitude TEC anomaly. Some features of the TEC dynamics observed during the 20 November 2003 storm, however, suggest that mechanisms other than the expanded ionospheric convection (such as thermospheric neutral winds) are also involved in the formation of the midlatitude anomaly.

Pokhotelov, D.; Mitchell, C. N.; Spencer, P. S. J.; Hairston, M. R.; Heelis, R. A.

2008-03-01

207

Convection and overshielding electric fields in the global ionosphere as observed with magnetometers and SuperDARN during the geomagnetic storm on 14-15 December 2006  

NASA Astrophysics Data System (ADS)

The convection electric field penetrates to the equatorial ionosphere with no significant shielding effects during the DP2 fluctuation event of period of 30 - 60 min (Nishida, 1968) and during the storm main phase continuing over several hours (Huang et al., 2007). On the other hand, shielding becomes effective during the substorm growth phase (Somajajulu et al., 1987; Kikuchi et al., 2000) and even during storm main phase (Kikuchi et al., 2008). The well-developed shielding electric field results in an overshielding at the beginning of the recovery phase of storm/substorms (Kikuchi et al., 2003, 2008). Thus, the electric field manifests complex features at mid-equatorial latitudes, which is not determined only by the solar wind electric field but strongly controlled by magnetospheric processes such as the ring current. To reveal comparative roles of the convection and overshielding electric fields and in what condition the overshielding occurs at mid-equatorial latitudes, we analyzed the geomagnetic storm on 14-15 December, 2006, characterized by the quasi-periodic DP2 fluctuation of 30 min period at the beginning of the storm. We used magnetometer data from mid- equatorial latitudes to detect magnetic signatures due to the electric field originating in the magnetosphere, and used the SuperDARN data to identify electric fields associated with the solar wind dynamo (Region-1 FAC) and the ring current (R2 FAC). We further calculated an electric potential pattern caused by the R1 and R2 FACs with the comprehensive ring current model (CRCM) to better understand the SuperDARN convection pattern. First we show that the DP2 fluctuation was caused by alternating eastward (e-EJ) and westward currents (w-EJ) in the equatorial ionosphere, which were caused by the southward and northward IMF, respectively. We further show that the e-EJ was associated with the large-scale two-cell convection vortices, while the w-EJ accompanied a reverse flow equatorward of the two-cell vortices. With the aid of the CRCM ring current simulation, we show that the R2 FAC develops immediately after the growth of the R1 FAC, and produces a reversed electric potential at mid latitude when the R1 FAC decreases its intensity. Thus, the reversed convection on the SuperDARN convection map must be caused by an electric potential associated with the R2 FAC. As a conclusion, both the convection and overshielding electric fields appear at mid-equatorial latitudes, and the overshielding electric field could become predominant irrespective of the period of the disturbances, when the R1 FAC decreases its intensity. This scenario well explains both the continuous penetration over several hours during storm main phase and the overshielding at the beginning of storm recovery phase.

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

2008-12-01

208

Convective plasma stability consistent with MHD equilibrium in magnetic confinement systems with a decreasing field  

SciTech Connect

A study is made of the convective (interchange, or flute) plasma stability consistent with equilibrium in magnetic confinement systems with a magnetic field decreasing outward and large curvature of magnetic field lines. Algorithms are developed which calculate convective plasma stability from the Kruskal-Oberman kinetic criterion and in which the convective stability is iteratively consistent with MHD equilibrium for a given pressure and a given type of anisotropy in actual magnetic geometry. Vacuum and equilibrium convectively stable configurations in systems with a decreasing, highly curved magnetic field are calculated. It is shown that, in convectively stable equilibrium, the possibility of achieving high plasma pressures in the central region is restricted either by the expansion of the separatrix (when there are large regions of a weak magnetic field) or by the filamentation of the gradient plasma current (when there are small regions of a weak magnetic field, in which case the pressure drops mainly near the separatrix). It is found that, from the standpoint of equilibrium and of the onset of nonpotential ballooning modes, a kinetic description of convective stability yields better plasma confinement parameters in systems with a decreasing, highly curved magnetic field than a simpler MHD model and makes it possible to substantially improve the confinement parameters for a given type of anisotropy. For the Magnetor experimental compact device, the maximum central pressure consistent with equilibrium and stability is calculated to be as high as {beta} {approx} 30%. It is shown that, for the anisotropy of the distribution function that is typical of a background ECR plasma, the limiting pressure gradient is about two times steeper than that for an isotropic plasma. From a practical point of view, the possibility is demonstrated of achieving better confinement parameters of a hot collisionless plasma in systems with a decreasing, highly curved magnetic field than those obtained with the simplest MHD description.

Tsventoukh, M. M. [Russian Academy of Sciences, Lebedev Physical Institute (Russian Federation)

2010-10-15

209

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

210

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

211

Transport Induced by Large Scale Convective Structures in a Dipole-Confined Plasma  

SciTech Connect

Convective structures characterized by ExB motion are observed in a dipole-confined plasma. Particle transport rates are calculated from density dynamics obtained from multipoint measurements and the reconstructed electrostatic potential. The calculated transport rates determined from the large-scale dynamics and local probe measurements agree in magnitude, show intermittency, and indicate that the particle transport is dominated by large-scale convective structures.

Grierson, B. A. [Princeton Plasma Physics Laboratory, Princeton University, Princeton, New Jersey 08543 (United States); Mauel, M. E.; Worstell, M. W.; Klassen, M. [Department of Applied Physics and Applied Mathematics, Columbia University, New York, New York 10027 (United States)

2010-11-12

212

A simple quantitative model of plasma flows and currents in Saturn's polar ionosphere  

NASA Astrophysics Data System (ADS)

We propose a simple illustrative axisymmetric model of the plasma flows and currents that occur in Saturn's polar ionosphere which are due to both internal magnetospheric plasma processes and the solar wind interaction. The features of the model are based on previous physical discussion, guided quantitatively by both Voyager plasma observations on closed field lines and remote-sensing IR Doppler observations on open field lines. With increasing latitude the flow features represented include a region poleward of 25 colatitude where the angular velocities decrease continuously from rigid corotation to 60% of rigid corotation due to plasma production from internal sources in the central magnetosphere, a narrow band of higher but still subcorotating angular velocities mapping to Dungey cycle return flow and Vasyliunas cycle flow regions in the outer closed field magnetosphere, and, finally, a region of low angular velocities, 30% of rigid corotation, on open field lines in the polar cap. We show that these flows require a four-region pattern of field-aligned currents. With increasing latitude, these consist of regions of upward and downward current on closed field lines peaking at a few tens of nanoamperes per square meter (for an effective ionospheric Pedersen conductivity of 1 mho), a narrow ring of upward field-aligned current across the open-closed field line boundary of order 100 nA m-2, and distributed downward currents on open field lines of order 10 nA m-2. Of the upward currents, only that at the open-closed field line boundary is of sufficient intensity to require significant acceleration of magnetospheric electrons, resulting in total precipitating electron powers of 0.03-0.06 TW, together with auroral UV emissions of a few tens of kilorayleighs. The latter emissions occur in a ring of a few hundred kilometers latitudinal width at 13 colatitude, which we thus associate with Saturn's main auroral oval. We also estimate similar powers in unaccelerated electron precipitation on closed field lines equatorward of the boundary, leading to distributed "diffuse" UV emissions of a fraction of a kilorayleigh. However, by far the most important energy input to the polar upper atmosphere is due to Joule heating by the ionospheric Pedersen currents, which we estimate as typically several milliwatts per square meter poleward of 20 colatitude. The overall Joule powers are estimated to be 2.5 TW on both open and closed field lines in each hemisphere (for a conductivity of 1 mho and no slippage of the neutral atmosphere), thus representing a very significant energy input to Saturn's thermosphere, more than an order of magnitude larger than the globally averaged solar input. Joule heating is thus likely to make a significant contribution to an explanation of why Saturn's thermosphere is observed to be hot, 400-600 K, compared with less than 200 K expected on the basis of solar heating alone.

Cowley, S. W. H.; Bunce, E. J.; O'Rourke, J. M.

2004-05-01

213

Cross-section of coherent radar scattering from nonthermal plasma density fluctuations in the mid-latitude ionosphere  

NASA Astrophysics Data System (ADS)

Methods based on coherent radar scattering yield very important information about nonthermal plasma density fluctuations in the lower ionosphere at different latitudes In particular the information is helpful for better understanding of the nature of the fluctuations A noticeable role in producing the fluctuations below the homopause level belongs to neutral air turbulence The turbulence is especially important in the case when development of plasma instabilities is difficult A convenient value that describes the process of radio wave coherent scattering from plasma density fluctuations is an effective cross-section sigma An analytic formula of sigma for the plasma fluctuations induced by the neutral turbulence is presented in the report The formula is obtained with the use of the 3D fluctuation spectrum predicted by a quasi-neutral fluid theory of the fluctuations Using the formula we estimated values of sigma for a possible radar backscatter experiment in the case of plasma fluctuations near the 100-km altitude in the daytime and nighttime mid-latitude ionosphere the magnetic dip angle of 45 The local values for the length-scale of the vertical plasma-density gradient L N of about 7 km and the average plasma density N e of 2 times10 10 mathrm m -3 plasma frequency f p approx 1 27 MHz were chosen for the daytime ionosphere and L N approx 3 km N e approx 2 times10 9 mathrm m -3 f p approx 0 4 MHz at night The ratio of the ion gyro-frequency to the ion-neutral collision frequency of about 0 035 and the

Kyzyurov, Yu.

214

GPS tomography for analysing storm density anomalies in mid-latitude ionosphere  

NASA Astrophysics Data System (ADS)

During magnetic storms dramatic changes in the solar wind pressure combined with appropriate orientation of the interplanetary magnetic field lead to the intensification of magnetosphereionosphere coupling which causes sudden inputs of the solar wind energy into the ionosphere. This results in extreme disturbances of the height and density of ionospheric layers during the main phase of magnetic storms. The tomographic inversion of the GPS data acquired by ground-based network of GPS receivers has been applied to reconstruct the 4D dynamics of ionospheric plasma during some major magnetic storms of the recent solar maximum. Dramatic storm-time enhancements of ionospheric plasma density and vertical plasma content (TEC) appear in mid-latitude ionosphere in dayside and evening sectors extending to high latitudes in the form of "ionization tongue". A number of physical mechanisms could be responsible for the formation of the storm-time density anomalies including the expansion of high-latitude plasma convection, neutral wind effects and the intensification of equatorial electrojet. Analysis of plasma flows deduced from GPS tomography and in-situ measurements by LEO spacecraft suggests that the major portions of mid-latitude density anomalies are linked to the dramatic expansion of high-latitude plasma convection though some features of the mid-latitude anomalies indicate an involvement of other physical mechanisms.

Pokhotelov, Dimitry; Mitchell, Cathryn; Spencer, Paul; Smith, Nathan; Budd, Chris

215

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

216

Parametric effects in inhomogeneous plasma during injection of electron pulses into the ionosphere  

NASA Astrophysics Data System (ADS)

The injection of electron pulses from the rocket into the ionospheric plasma in the lower hemisphere relative to the initial pitch angles of electrons during the substorm recovery phase provoked the generation of parametric processes (the ARAKS experiment). The electron flux observations, obtained using a wide-angle detector, and the whistler wave emission intensity measurements were compared. A wide-angle detector of electrons was mounted on the rocket, and a broadband wave receiver was installed on a nasal cone separated from the rocket. Bursts of the electron flux and wave emission were observed in pauses between electron pulses. It has been indicated that a clearly defined anisotropy of the observed parametric effects of the pitch angle of injected electron pulses is related to resonance characteristics of a wave emitted by electron fluxes in a magnetized plasma. Precipitation of ring current electrons was caused by a change in the magnetic moment of electrons, trapped by the magnetosphere, in the region of magnetic mirror points in the fields of electrostatic oscillations excited during decay of whistlers.

Izhovkina, N. I.

2009-08-01

217

A simulation study of radial expansion of an electron beam injected into an ionospheric plasma  

SciTech Connect

Injections of nonrelativistic electron beams from a finite equipotential conductor into an ionospheric plasma have been simulated using a two-dimensional electrostatic particle code. The purpose of the study is to survey the simulation parameters for understanding the dependence of beam radius on physical variables. The conductor is charged to a high potential when the background plasma density is less than the beam density. Beam electrons attracted by the charged conductor are decelerated to zero velocity near the stagnation point, which is at a few Debye lengths from the conductor. The simulations suggest that the beam electrons at the stagnation point receive a large transverse kick and the beam expands radially thereafter. The buildup of beam electrons at the stagnation point produces a large electrostatic force responsible for the transverse kick. However, for the weak charging cases where the background plasma density is larger than the beam density, the radial expansion mechanism is different; the beam plasma instability is found to be responsible for the radial expansion. The simulations show that the electron beam radius for high spacecraft charging cases is of the order of the beam gyroradius, defined as the beam velocity divided by the gyrofrequency. In the weak charging cases, the beam radius is only a fraction of the beam gyroradius. The parameter survey indicates that the beam radius increases with beam density and decreases with magnetic field and beam velocity. The beam radius normalized by the beam gyroradius is found to scale according to the ratio of the beam electron Debye length to the ambient electron Debye length. The parameter dependence deduced would be useful for interpreting the beam radius and beam density of electron beam injection experiments conducted from rockets and the space shuttle. 19 refs., 15 figs.

Koga, J. [Southwest Research Institute, San Antonio, TX (United States); Lin, C.S. [Aurora Science, Inc., San Antonio, TX (United States)

1994-03-01

218

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

SciTech Connect

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 {plus minus} 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 interplanetary magnetic field (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. (Univ. of Texas, Richardson (United States))

1990-03-01

219

Modeling the inner plasma sheet pressure and magnetic field under enhanced convection  

NASA Astrophysics Data System (ADS)

In order to understand the evolution of the proton pressure and magnetic field in the inner plasma sheet from quiet to disturbed times, we incorporate a modified version of the Magnetospheric Specification Model with a modified version of the Tsyganenko 96 magnetic field model to self-consistently simulate protons and magnetic field under an increasing convection electric field with two-dimensional force balance maintained along the midnight meridian. The local-time dependent proton differential fluxes assigned to the model boundary are mixture of hot plasma from the distant tail and cooler plasma from the low latitude boundary layer and are constructed based on Geotail observations and the results of the finite-tail-width- convection model. We previously used this model to simulate the inner plasma sheet under weak convection corresponding to a cross polar-cap potential drop ( PC) equal to 26 kV and obtained two-dimensional quiet time equilibrium for proton and magnetic field that agrees well with observations both qualitatively and quantitatively. We start our simulation for enhanced convection with this quiet time equilibrium and time independent boundary particle sources and increase thePC steadily from 26 kV to 146 kV in 5 hours. The simulations are also run to steady states separately by keepingP C constant after it is increased to 98 and to 146 kV. The magnitude of the simulated proton pressure and its increase from quiet to moderate activity ( P C = 98 kV) are consistent with most observations. Our results at high activity (P C = 146 kV) underestimate the observed pressure, a disagreement that indicates possible dependence of the boundary particle sources on activity. The pressure equatorial profiles show a dawn dusk asymmetry as a result of stronger enhancement on the dusk side than on the dawn side as convection is increased. The equatorial m gnetic field strength decreases more in the near-Eartha plasma sheet than at larger radial distances as theP C increases, resulting in an increasing flat radial profile with enhancing convection strength. The feedbacks from diamagnetic drift and magnetic fields to increasing convection are to restrain the increase in plasma pressure. Based on the good agreement between our pressure and observations at moderate activity, our magnetic field indicates the plasma and magnetic field in the inner plasma sheet are in a state far from possible force balance inconsistency. A scale analysis of our results shows that the frozen-in condition E = - - v B is not valid in the inner plasma sheet, at least to an enhanced convection condition corresponding to moderate activity.

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

220

Thin filament simulations for Earth's plasma sheet: Tests of validity of the quasi-static convection approximation  

NASA Astrophysics Data System (ADS)

The main goal of this paper is to estimate the errors involved in applying a quasi-static convection model such as the Rice Convection Model (RCM) or its equilibrium version (RCM-E), which neglect inertial currents, to treat the injection of fresh particles into the inner magnetosphere in a substorm expansion phase. The approach is based on the idea that the dipolarization process involves earthward motion of a bubble that consists of flux tubes that have lower values of the entropy parameter than the surrounding medium. Our tests center on comparing MHD simulations with RCM- and RCM-E-like quasi-static approximations, for cases where the bubble is considered to be a thin ideal-MHD filament. Those quasi-static solutions miss the interchange oscillations that are often a feature of the MHD results. RCM and, to a lesser extent, RCM-E calculations tend to overestimate the westward electric field at the ionospheric footprint of the bubble and underestimate its duration. However, both get the time integral of the E B drift velocity right as well as the net energization of the particles in the filament. The quasi-static approximation is most accurate if its computed value of the braking time of the bubble's earthward motion is long compared to the period of the relevant interchange oscillation. Comparison of MHD filament simulations of interchange instability with corresponding RCM calculations suggests a similar validity criterion. For plasma sheet conditions, the quasi-static approximation is typically best if the background medium has low ?, worst if it consists of highly stretched field lines.

Wolf, R. A.; Chen, C. X.; Toffoletto, F. R.

2012-02-01

221

Remote sensing of the spatial and temporal structure of magnetopause and magnetotail reconnection from the ionosphere  

NASA Astrophysics Data System (ADS)

Magnetic reconnection is the most significant process that results in the transport of magnetized plasma into and out of the Earth's magnetosphere-ionosphere system. There is also compelling observational evidence that it plays a major role in the dynamics of the solar corona, and it may also be important for understanding cosmic rays, accretion disks, magnetic dynamos, and star formation. The Earth's magnetosphere and ionosphere are presently the most accessible natural plasma environments where magnetic reconnection and its consequences can be measured, either in situ or by remote sensing. This paper presents a complete methodology for the remote sensing of magnetic reconnection in the magnetosphere from the ionosphere. This method combines measurements of ionospheric plasma convection and the ionospheric footprint of the reconnection separatrix. Techniques for measuring both the ionospheric plasma flow and the location and motion of the reconnection separatrix are reviewed, and the associated assumptions and uncertainties are assessed, using new analyses where required. Application of the overall methodology is demonstrated by the study of a 2-h interval from 26 December 2000 using a wide range of spacecraft and ground-based measurements of the Northern Hemisphere ionosphere. This example illustrates how spatial and temporal variations in the reconnection rate, as well as changes in the balance of magnetopause (dayside) and magnetotail (nightside) reconnection, can be routinely monitored, affording new opportunities for understanding the universal reconnection process and its influence on all aspects of space weather.

Chisham, G.; Freeman, M. P.; Abel, G. A.; Lam, M. M.; Pinnock, M.; Coleman, I. J.; Milan, S. E.; Lester, M.; Bristow, W. A.; Greenwald, R. A.; Sofko, G. J.; Villain, J.-P.

2008-03-01

222

Storm time plasma transport at middle and high latitudes  

Microsoft Academic Search

Associated with the large-scale enhancement of the ionospheric convection electric field during disturbed geomagnetic conditions, solar-produced F region plasma is transported to and through the noontime cleft from a source region at middle and low latitudes in the afternoon sector. As a result of the offset between the geomagnetic and geographic poles, the afternoon sector region of strong sunward convection

John C. Foster

1993-01-01

223

Climatology of ionospheric plasma bubbles over the Brazilian equatorial region: Observations and theoretical analysis  

NASA Astrophysics Data System (ADS)

The climatology of the westward traveling large-scale plasma depletions, or bubbles, is analyzed here for 14 quiet days (quiet days are taken here to be the days with 24-hour sum Kp smaller than 24) that presented westward traveling bubbles. Those 14 days were the only quiet days that presented westward traveling bubbles from a total set of 593 days of experiments that have been carried out from 2001 to 2006 by means of an all-sky airglow imager system located at the near-equatorial station So Joo do Cariri (Geographic 7.45S, 36.5W, dip 20S). From this a a set of 593 days, 422 were quiet days. During the overall period of 593 days that included both quiet and disturbed days, westward traveling depletions appeared on a total of 28 days, 14 of which being quiet days and 14 days being disturbed days (Kp 24). In the set of 14 quiet days, 8 days were preceded by two consecutive quiet days minimizing in this way any possible westward motion of the plasma depletion caused by disturbance dynamo effects originated on the last two days. The frequency of occurrence of the westward traveling bubbles were clearly seen to maximize in the descending phase of the solar cycle, in particular in the years of 2003 and 2004, and being less frequent during minimum and maximum solar activity, showing evidences in this way of maximum geoeffective effects during the descending phase of the solar cycle. The westward traveling depletions were clearly seen to exist in a time frame centered around midnight ( 23h -01LT) for all years analyzed here 2001 -2006. Theoretical calculations of the zonal velocity of the ionospheric plasma make possible to infer the origin of such zonal velocities.

Sobral, Jos; de Castilho, Vivian M.; Abdu, M. A.; Takahashi, Hisao; Gasparelo, Ulisses A. C.; Arruda, Daniela C. S.; Mascarenhas, Matheus; Zamlutti, C. J.; Denardini, C. M.; Koga, Daiki; Paulino, I.; de Medeiros, A. F.; Buriti, R. A.

224

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

225

Absolute and convective nature of Raman instability in relativistic hot plasmas  

NASA Astrophysics Data System (ADS)

The modulational and Raman instabilities are investigated in the relativistic regime, for a large amplitude electromagnetic wave propagating in a hot plasma of arbitrary density. Temporal growth rates and the number of unstable branches are determined when the plasma temperature, density, and the amplitude of the wave vary. The convective or absolute nature of the Raman instabilities is then determined. The present paper extends previous results by Gurin et al. [Phys. Plasmas 2, 2807 (1995)] and Couairon and Mora [Phys. Plasmas 8, 3434 (2001)]. It is shown that for any temperature, the Raman instability is convectively unstable at low density and low intensity, and absolutely unstable when the intensity or the density exceeds a threshold that we determine as a function of the temperature. In contrast with the cold plasma case, the threshold for absolute instability does not coincide with the merging of branches found by a classical temporal stability analysis.

Grismayer, T.; Couairon, A.; Mora, P.; Adam, J.-C.; Hron, A.

2004-10-01

226

Generation and evolution of equatorial ionospheric plasma bubbles and broad plasma depletions measured by the C/NOFS satellite during deep solar minimum  

NASA Astrophysics Data System (ADS)

A spectacular phenomenon in the equatorial ionosphere is the occurrence of broad plasma depletions in which the plasma density is reduced by 1-3 orders of magnitude over thousands of kilometers in longitude near dawn. This phenomenon is observed repeatedly by the Communication/Navigation Outage Forecasting System (C/NOFS) satellite during deep solar minimum. Our purpose is to study where the postmidnight plasma bubbles start to occur, how long they exist, what the maximum size of individual bubbles is, how plasma bubbles are related to broad depletions, and how broad plasma depletions form. The orbit of C/NOFS can be approximately parallel to the geomagnetic equator over a large local time range. If a plasma bubble exists long enough, it may be detected by C/NOFS over successive orbits. The C/NOFS measurements can be used to trace the growth and development of plasma bubbles. In several cases we analyzed, a series of plasma bubbles was first detected by C/NOFS over a longitudinal range of up to 3800 km around midnight. Each of the individual bubbles has a typical width of ~100 km in longitude, and the upward ion drift velocity inside the bubbles is 200-400 m/s. The plasma bubbles rotate to the dawn sector and become broad plasma depletions. The strong upward plasma flow inside the bubbles exist for more than 7 hours, and the bubbles do not become dead/fossil bubbles over the entire night time. The observations clearly show the evolution from multiple plasma bubbles into broad depletions. We propose that the broad plasma depletions with strong upward plasma flow are the result of merging of multiple equatorial plasma bubbles. We will also present the numerical simulations of bubble merging with the physics-based low-latitude ionospheric model (PBMOD). It is found that two separate plasma bubbles join together and form a new single bubble. The simulations demonstrate for the first time that the merging process of plasma bubbles can indeed occur in incompressible ionospheric plasma. The C/NOFS measurements reveal significant new characteristics of equatorial plasma bubbles and broad depletions during deep solar minimum.

Huang, Chaosong; De La Beaujardiere, Odile; Retterer, John; Pfaff, Robert; Roddy, Patrick; Hunton, Donald; Ballenthin, John

2012-07-01

227

HF wave scattering by field-aligned plasma irregularities considering refraction in the ionosphere  

NASA Astrophysics Data System (ADS)

This paper analyzes the effect of ionospheric refraction on the scattering of high frequency (HF) signals by random field-aligned irregularities in the upper ionosphere. Ray optics calculations are made using the perturbation method for a plane-stratified (on average) ionosphere, i.e., the incident and scattered waves are both supposed to propagate along the undisturbed trajectories with neglect of the geomagnetic field effect. The equation for the so-called cone of aspect-sensitive scattering is derived to relate the trajectory characteristics of the incident and aspect-sensitive scattered signals. The Born approximation is applied to calculate the scattering cross-section for the anisotropic power law model spectrum of random irregularities of the upper ionosphere. The possibility of excitation of the ionospheric interlayer waveguide by the aspect-sensitive scattered HF signals is analyzed in detail for the specific conditions of the HF heating experiment at European Incoherent Scatter (EICSAT).

Galushko, V. G.; Bezrodny, V. G.; Koloskov, A. V.; Paznukhov, V. V.; Reinisch, B. W.

2013-03-01

228

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

229

Generation of convective cells by ion-drift waves in dusty plasmas  

NASA Astrophysics Data System (ADS)

The parametric excitation of large-scale convective cells in non-uniform dusty plasmas with non-zero ion temperature is considered. A set of two coupled nonlinear equations (for the variation of the electrostatic potential and the ion pressure) governing the nonlinear dynamics of ion-drift waves in dusty plasmas (IDWDPs) is obtained. The equations are then simplified by using a standard multiscale expansion technique. A nonlinear dispersion relation, which describes the nonlinear electrostatic and thermal convective cells, is obtained. The analysis of our dispersion relation shows that only the electrostatic mode yields a non-zero growth rate. The thermal convective cell is found to be stable. A simple expression for the maximum instability growth rate and the optimal dimension of the convective mode is deduced. The fastest growing wave appears to be a zero-frequency mode, elongated perpendicularly to the plasma inhomogeneity. The electrostatic convective cell growth rate is compared with that for the traditional parametric IDWDP decay.

Pokhotelov, O. A.; Onishchenko, O. G.; Sagdeev, R. Z.; Stenflo, L.; Shukla, P. K.; Beloff, N.

230

Plasma-density modification by means of pulsed-beam CIV in the ionosphere  

SciTech Connect

Alfvens critical ionization velocity (CIV) discharge gives rise to rapid increase in electron density. The existence of CIV has been proven in the laboratory. If CIV occurs in space, there would be important consequences. Not only would electromagnetic wave propagation be affected by the enhanced plasma density, but there would also be important implications in spacecraft contamination. In attempts to prove CIV in space, many researchers used the barium shaped charged explosion method. The results have been mostly negative with two exceptions. We propose a modified CIV space experiment by means of a multiple pulse beam (MPB) of neutral atoms. We use the 'particle-in-cell' method to simulate CIV in a MPB under ionospheric conditions. A single or MPB neutral beam with seed ionization develops the modified two-stream instability which energizes the electrons. When the electrons become hot enough, they ionize the neutrals in the beam. Numerical simulation results of single and multiple pulse cases are compared, revealing the enhanced ionization for the MPB case.

Lai, S.T.; McNeil, W.J.; Murad, E.

1991-01-01

231

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

232

Radio tomographic imaging of the northern high-latitude ionosphere on a wide geographic scale  

NASA Astrophysics Data System (ADS)

Several chains of receivers, measuring total electron content (TEC) during passes of satellites in the U.S. Navy Ionospheric Measuring System (NIMS), are operated at northern high latitudes by members of the International Ionospheric Tomography Community (IITC). Results are presented here of nearly simultaneous latitude-altitude images of the ionosphere over Scandinavia, Greenland, and Alaska, generated from IITC data obtained on 20 September 2001 and interpreted in the context of an IMF-dependent convection model. The images are compared with output from a coupled thermosphere-ionosphere-plasmasphere model and also with maps of high-latitude TEC generated from GPS measurements. With Bz and By both weakly negative, the images and map reveal plasma features of a two-cell convection pattern rotated slightly to earlier local magnetic times. The tomographic images provide details of map features such as a tongue of ionization created by solar EUV radiation on the dayside and entrained by convection into the polar cap from the western Russian sector. Combining latitude versus altitude tomographic images generated in different longitudinal sectors from polar-orbiting beacon satellites such as those of NIMS with TEC maps from GPS offers an emerging opportunity for polar aeronomic studies, especially if further related to synoptic convection measurements. The results also demonstrate the potential role of wide-scale radio tomography in the verification of ionospheric models.

Kersley, L.; Pryse, S. E.; Denton, M. H.; Bust, G.; Fremouw, E.; Secan, J.; Jakowski, N.; Bailey, G. J.

2005-10-01

233

Dominance of convective heat transport in the core of TFTR (Tokamak Fusion Test Reactor) supershot plasmas  

SciTech Connect

Using perturbations in electron density and temperature induced by small Helium gas puffs in TFTR (Tokamak Fusion Test Reactor) the dominance of convective heat transport in the core (r/a < 0.4) of supershot plasmas has been demonstrated in a new way. The TRANSP transport code was used to calculate the time-dependent particle and heat fluxes. Perturbations in the calculated convective and total electron heat fluxes were compared. They demonstrate that the conductive component decreases moving into the supershot core, and the convective component dominates in the supershot core. These results suggest a different transport drive in the supershot core compared to that in the rest of the supershot plasma.

Kissick, M.W.; Efthimion, P.C.; Mansfield, D.K.; Callen, J.D.; Bush, C.E.; Park, H.K.; Schivell, J.; Synakowski, E.J.; Taylor, G.

1993-08-01

234

Formation of convective cells, anomalous diffusion, and strong plasma turbulence due to drift instabilities  

Microsoft Academic Search

Large-scale fully three-dimensional particle simulations have been carried out for the collisionless drift instabilities in a cylindrical geometry. It is found that nonlinear excitation of convective cells due to drift instabilities gives rise to enhanced turbulence and anomalous plasma diffusion. The observed power spectra resemble recent measurements in toroidal devices.

C. Z. Cheng; H. Okuda

1977-01-01

235

Measurements of the ionosphere plasma electron density variation by the Kharkov incoherent scatter radar  

NASA Astrophysics Data System (ADS)

The present paper is devoted to the description of an improved method for determination of the ionospheric electron density values by Kharkov Incoherent Scatter Radar. This method allows to improve the resolution of the incoherent signals parameters up to 20 km in the range of 100-400 km and 100 km in the range of 200-1100 km. This approach was used to investigate variability of the ionospheric electron density over East European region in the heights interval of 100-1000 km during the period from 2003 to 2008, including case-studies of solar eclipses and ionospheric storms.

Cherniak, Iurii V.; Lysenko, Valery N.

2013-10-01

236

Comparative studies of multi-scale convective transport through the Earth's plasma sheet  

Microsoft Academic Search

In this dissertation we explore multi-scale, convective transport through the Earth's plasma sheet using in situ observations and global terrestrial magnetospheric simulations. We statistically test the Lyon-Fedder-Mobarry (LFM) global magnetohydrodynamic (MHD) model with observations from the Geotail spacecraft at a variety of spatial and temporal scales within the plasma sheet. These comparisons, in addition to quantifying the LFM range of

Timothy Bryan Guild

2007-01-01

237

Magnetic Effects on Short-Wave Convective Cells in Finite-Pressure Plasma  

Microsoft Academic Search

Within the context of the general theory of low-frequency electromagnetic plasma fluctuations, the stationary spectra of short-wave convective and magnetostatic perturbations and the heat conductivity coefficient in finite-pressure plasma with betae betaI 1, are obtained. It is shown that the nonlinear broadening of the potential spectrum can be determined by the magnetic field fluctuations when betae 1.

Maxim O. Vakulenko; Petro P. Sosenko

2000-01-01

238

Dynamics of ionospheric ions in the magnetospheric tail: Role of the large-scale electric field  

NASA Astrophysics Data System (ADS)

The motion of ionospheric ions in the magnetospheric tail is considered using a minimal set of well-known factors, such as the tail-like configuration of the magnetic field and the presence of the dawn-to-dusk magnetospheric electric field. The calculated O+ ion density and average energy are in close agreement with satellite measurements. An abrupt increase of the magnetospheric electric field leads to formation of a hot plasma cloud in the plasma sheet, which convects earthward. In contrast, if the electric field varies slowly in time, then the mean energy of ionospheric ions in the near-Earth tail remains almost independent of activity level.

Voronov, Eugene V.; Krinberg, Igor A.

1996-05-01

239

Prompt penetration electric fields (PPEFs) and their ionospheric effects during the great magnetic storm of 3031 October 2003  

Microsoft Academic Search

We explore the ionospheric effects of prompt penetration electric fields (PPEFs) for a variety of interplanetary magnetic field directions. We use the great magnetic storm of 3031 October as an example of PPEF effects. For intense southward interplanetary magnetic fields (IMFs), inward plasma sheet convection occurs with the result of magnetospheric ring current formation and an intense magnetic storm. Concurrent

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

2008-01-01

240

Prompt penetration electric fields (PPEFs) and their ionospheric effects during the great magnetic storm of 30-31 October 2003  

Microsoft Academic Search

We explore the ionospheric effects of prompt penetration electric fields (PPEFs) for a variety of interplanetary magnetic field directions. We use the great magnetic storm of 30-31 October as an example of PPEF effects. For intense southward interplanetary magnetic fields (IMFs), inward plasma sheet convection occurs with the result of magnetospheric ring current formation and an intense magnetic storm. Concurrent

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

2008-01-01

241

Ionospheric Currents: Can the Incoherent Scatter Plasma Line Spectrum Provide Routine Current Measurements.  

National Technical Information Service (NTIS)

The measurement of the ion and electron components of the incoherent scatter spectrum can be made substantially routine under certain circumstances. However, the traditional interpretation of the resulting data sets in terms of ionospheric current flows l...

A. P. Vaneyken U. P. Loevhaug P. J. Christiansen P. J. S. Williams

1991-01-01

242

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

243

The perturbation characteristics in plasma parameters in ionosphere before strong earthquakes  

NASA Astrophysics Data System (ADS)

Based on the data observed by DEMETER satellite, the perturbation characteristics of plasma parameters were analyzed and summarized, such as Ni(O+), Ne and so on. Two cases were presented as examples, which are Yushu M7.1 earthquake in China on April 13 2010 and Tanga M7.9 earthquake on May 3 2006. Around Yushu earthquake, more than seven-month data were selected since Oct. 2009 in a distance of 2000km to the epicenter. Long time comparison over a certain region revealed that the Ni(O+) began to increase in Feb. 2010, two months before this event, and the maximum oxygen ion density occurred on April 13, 20 hours before the earthquake with the amplitude of more than 100% relative to the normal peak values at the south of this seismic region. Before and after the earthquake during more than 7 months, the peak values of Ni(O+) had never been so large in quiet magnetic conditions. As for the Ms7.9 Tonga Islands earthquake, perturbations of plasma parameters above epicenter were detected six days, two days, one day before and two days after it. The variation feature of O+ density was more obvious than that of H+ and He+ density. Compared with the 16-day revisiting orbits in 2 years of the half orbit just one day before the earthquake, O+ density increased 20% more at the orbit closest to the epicenter than the other orbits in the same day, and it increased nearly an order of magnitude referred to the mean of O+ density in May from 2006 to 2008 by taking account of the seasonal variations in it. In addition, electron density detected simultaneously to increase with O+ density onboard DEMETER at the above-mentioned revisiting orbits. Furthermore, the statistic analysis was carried out on the earthquakes with magnitude larger than 6.0 during Jan. 2006 to Apr. 2010 in China and a few earthquakes with M?7.0 in the world. It was found that perturbations in plasma parameters occurred before 15 cases in all 29 cases. The ionospheric disturbances were detected 1-7 days before these strong earthquakes and they were exhibited both at the west or the east to the epicenter, but always turned to the equator. Finally, the enhancement phenomena of electron and ion density before earthquakes and its formation mechanism were discussed based on our study results.

Zhang, X.; Ouyang, X.; Liu, J.; Shen, X.

2012-04-01

244

The zonal EB plasma drift effects on the low latitude ionosphere electron density at solar minimum near equinox  

NASA Astrophysics Data System (ADS)

The F2-layer peak density, NmF2, and peak altitude, hmF2, which were observed by 12 ionospheric sounders during the 20 September 1964 geomagnetically quiet time period at solar minimum are compared with those calculated by the three-dimensional time-dependent theoretical model of the Earth's low and middle latitude ionosphere and plasmasphere. The modeled NmF2 are also compared with those measured during the geomagnetically quiet time periods of 12-15, 18-21, and 26 September 1964 to take into account observed day-to-day ionospheric variability. Major features of the data are reproduced by the model if the corrected HWM90 neutral wind is used. The changes in NmF2 due to the zonal EB plasma drift are found to be less than 20% in the daytime low latitude ionosphere. The model, which does not take into account the zonal EB plasma drift, underestimates night-time NmF2 up to the maximum factor of 2 at low geomagnetic latitudes. The night-time increase of NmF2 caused by the zonal EB plasma drift is less pronounced at -20 and 20 geomagnetic latitudes in comparison with that between -10 and 10 geomagnetic latitude. The longitude dependence of the calculated night-time low latitude influence of the zonal EB plasma drift on NmF2 is explained in terms of the longitudinal asymmetry in B (the eccentric magnetic dipole is displaced from the Earth's center and the Earth's eccentric tilted magnetic dipole moment is inclined with respect to the Earth's rotational axis), and the variations of the wind induced plasma drift and the meridional EB plasma drift in geomagnetic longitude. The difference between the hmF2 values calculated by including the effect of zonal EB drift and that obtained when it is excluded does not exceed 19 km in the low latitude ionosphere. Over the geomagnetic equator the zonal EB plasma drift produces the maximum increase in the electron density by a factor of 1.06-1.48 and 1.05-1.30 at 700 and 1000 km altitude, respectively, and this increase is not significant above about 1500 km. Changes in the vertical electron content, VEC, caused by the zonal EB plasma do not exceed 16% during the day, while the value of the night-time VEC is increased up to a factor of 1.4 due to this drift. The maximum effects of the zonal EB plasma drift on the night-time electron density derived from the model results corresponding to solar minimum and maximum are quite comparable.

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

2008-08-01

245

Tracking of polar cap ionospheric patches using data assimilation  

NASA Astrophysics Data System (ADS)

Ionospheric F-region patches are 2-10 larger than background electron densities in the polar ionosphere. The EISCAT Svalbard incoherent radar (ESR) observed a sequence of patches between 2000-2200 UT on 12 December 2001. In this paper the source of these structures is investigated using several other data sets, together with a convection-driven trajectory analysis. The data are assimilated into Ionospheric Data Assimilation Three Dimensional (IDA3D). The background model used is the National Center for Atmospheric Research-Thermosphere Ionosphere Mesosphere Electrodynamics General Circulation Model (NCAR TIMEGCM). The trajectory analysis is based on maps of ionospheric convection obtained from the Assimilative Mapping of Ionospheric Electrodynamics (AMIE). In addition to patches, a tongue of ionization (TOI) is investigated. It is shown that patches formed part of the TOI. It is tempting to conclude the TOI and the patches originate at midlatitudes. However, the IDA3D and trajectory analysis suggest that they were transported toward noon from the morning and afternoon sectors near 62 geographic latitude. Thus for this case the TOI and patches did not originate at midlatitudes. This work represents advances in the field of patch research. A new capability to perform an analysis of patch origin and fate, using three-dimensional (3-D) ionospheric assimilation and 2-D trajectory analysis codes, is demonstrated for a sequence of patches observed 12 December 2001. The current resolution of the technique is not able to identify detailed patch formation mechanisms. However, by it can track the plasma back in time to locations and times where patch formation mechanisms operate.

Bust, G. S.; Crowley, G.

2007-05-01

246

Variations in the ionospheric wave perturbation spectrum during periodic heating of the plasma by high-power high-frequency radio waves  

NASA Astrophysics Data System (ADS)

We present the results of spectral analysis of temporal variations in the Doppler frequency shift of the ionosphere-reflected signals from a high-frequency vertical ionospheric sounding radar located near the city of Kharkov in the days of exposure of the ionospheric plasma to the high-power radio emission of the Sura facility (Nizhny Novgorod) and in the reference day in the absence of such an exposure. It was established that the spectral characteristics of quasiperiodic variations in the Doppler frequency shift in the range of periods 10-60 min in the days of work of the facility and in the reference day differed significantly. This is considered as evidence in favor of the generation (amplification) of acoustic-gravity waves propagating at the ionospheric altitudes by high-power periodic high-frequency radiation of the Sura facility.

Chernogor, L. F.; Frolov, V. L.; Komrakov, G. P.; Pushin, V. F.

2011-07-01

247

The current convective instability and its relation to diffuse auroral scintillation causing F region irregularities  

Microsoft Academic Search

A simple plasma fluid model is presented, which accounts for the diffuse auroral scintillation causing F region ionospheric irregularities observed by the DNA Wideband satellite. The nonlinear mode coupling theory for the current convective instability is investigated, and the linear theory is extended to include effects such as magnetic shear, ion inertial, and electromagnetic effects. The data give evidence that

M. J. Keskinen; S. L. Ossakow; B. E. McDonald; P. K. Chaturvedi

1981-01-01

248

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

249

Modeling the inner plasma sheet protons and magnetic field under enhanced convection  

NASA Astrophysics Data System (ADS)

In order to understand the evolution of the protons and magnetic field in the inner plasma sheet from quiet to disturbed conditions, we incorporate a modified version of the Magnetospheric Specification Model (MSM) with a modified version of the Tsyganenko 96 (T96) magnetic field model to simulate the protons and magnetic field under an increasing convection electric field with two-dimensional (2-D) force balance maintained along the midnight meridian. The local time dependent proton differential fluxes assigned to the model boundary are a mixture of hot plasma from the mantle and cooler plasma from the low latitude boundary layer (LLBL). We previously used this model to simulate the inner plasma sheet under weak convection corresponding to a cross polar cap potential drop (??PC) equal to 26 kV and obtained 2-D quiet time equilibrium for proton and magnetic field that agrees well with observations. We start our simulation for enhanced convection with this quiet time equilibrium and time-independent boundary particle sources and increase ??PC steadily from 26 to 146 kV in 5 hours. Simulations are also run separately to steady states by keeping ??PC constant after it is increased to 98 and 146 kV. The magnitudes of proton pressure, number density, and temperature and their increase from quiet to moderate activity (??PC = 98 kV) are consistent with most observations. Our simulation at high activity (??PC = 146 kV) underestimates the observed pressure and temperature. This disagreement indicates possible dependence of the boundary particle sources on activity and possible effects of solar wind dynamic pressure enhancements that have not yet been included in our simulation. The simulated equatorial pressures and temperatures show stronger enhancement on the dusk side than on the dawn side as convection is increased, while density profiles show an increase on the dawn side and a decrease on the dusk side. The simulated proton flow speed at the equatorial plane increases with enhancing convection while the overall flow direction does not change significantly, a result of enhancement in both the earthward electric drift and the azimuthal diamagnetic drift. The equatorial magnetic field strength decreases more in the near-Earth plasma sheet than at larger radial distances as ??PC increases, resulting in an increasing flat radial profile with enhancing convection. The feedbacks from diamagnetic drift and magnetic fields to increasing convection are found to restrain the pressure increase. Based on the good agreement between our results and observations at moderate activity, our magnetic field indicates that the plasma and magnetic field in the plasma sheet can be in a state far from possible force balance inconsistency during periods of moderately enhanced convection. A scale analysis of our results shows that the frozen-in condition E = -v B is not valid in the inner plasma sheet for moderate activity.

Wang, Chih-Ping; Lyons, Larry R.; Chen, Margaret W.; Wolf, Richard A.; Toffoletto, Frank R.

2003-02-01

250

The high-latitude ionospheres of the Earth and Venus  

NASA Astrophysics Data System (ADS)

The presence of a planetary magnetic field at Earth and the absence of such a field at Venus results in substantial differences in the dynamics and morphology of the high-latitude ionospheres. In both cases photoionisation is the primary mechanism by which the dayside ionosphere is created while particle precipitation and transport processes act to maintain the plasma densities at night. However the mechanisms driving plasma transport at Earth and Venus are fundamentally different and so the planetary ionospheres respond differently to solar activity. The transport of plasma has implications for aeronomy and atmospheric chemistry in the night sector. In the terrestrial case plasma is frozen in to the magnetic field. Transport in the polar regions is largely due to the high-latitude convection pattern which results from interaction of the terrestrial magnetic field with the interplanetary magnetic field (IMF) carried by the solar wind [1]. The convection varies with the orientation of the IMF and, under appropriate conditions, dayside plasma can be transported antisunward [2]. At Venus plasma transport is primarily driven by the day-to-night pressure gradient [3]. Lowering of the dayside ionopause under conditions of low solar flux inhibits this process [4] but it has been observed to have a significant effect in the pre-dawn sector at low-latitudes under conditions of moderate solar activity [5]. Aberystwyth University's ionospheric radiotomography experiment routinely observes the plasma distribution in the high-latitude terrestrial ionosphere in a latitude versus altitude plane. The polar orbit of Venus Express is ideal for investigating the Venusian high-latitude ionosphere close to the solar terminator with periapsis located close to 86o N. The ASPERA-4 instrument records the first extended in situ data set of the plasma environment under conditions of low solar activity. These two experiments provide a database covering all solar wind conditions and local time sectors. When Earth and Venus are aligned along the Parker spiral the two planets experience similar solar wind conditions. Observations conducted under these conditions close to solar minimum are presented at both planets and comparisons are drawn. The role of plasma transport is of particular interest and is discussed with reference to the driving processes. References: [1] Dungey, J. W. (1961) Phys. Rev. Let., 6, 47-49. [2] Foster, J. C. (1984) JGR, 89, 855-865. [3] Knudsen et al. (1981) GRL, 8, 241-244. [4] Knudsen et al. (1987) JGR, 92, 13391-13398. [5] Brannon et al. (1993) GRL, 20, 2739-2742.

Middleton, Helen; Wood, Alan; Pryse, Eleri; Grande, Manuel; Fallows, Richard

2010-05-01

251

Digital ionosonde observations of the polar cap F region convection  

NASA Astrophysics Data System (ADS)

Ground-based drift observations of winter polar cap F-region show that the magnetospherically induced ionospheric convection can be measured for the bottomside ionosphere. A digital ionosonde with four spaced receiving antennas operated at Thule, Greenland in the Doppler-drift mode. A number of 24-hour measurements indicate that the drift direction changes linearly as a function of time in accordance with the predicted antisunward convection pattern. The drift velocities vary from 300-900 m/s. Measurements at a subauroral station with the same spaced-antennas-Doppler-drift technique show a steady westward drift until local magnetic midnight and a fast switch-over at that time to an eastward drift. It is concluded that the observed subauroral drifts are the sunward return flows of the polar plasma convection, and the switch-over occurs when the station rotates from the dusk cell into the dawn cell.

Reinisch, Bodo W.; Buchau, Jurgen; Weber, Edward J.

1987-08-01

252

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

SciTech Connect

The sequence nature of the diffuse ionospheric resonances D[sub n] stimulated by topside sounders was discovered by Oya (1970) with n ranging from 1 to 4. Osherovich (1987) organized these observations using his earlier theory which predicted a nonequidistant spectrum with frequencies proportional to n[sup [1/2

Benson, R.F. (NASA Goddard Space Flight Center, Greenbelt, MD (United States)); Osherovich, V.A. (Hughest STX Corp., Lanham, MD (United States))

1992-12-01

253

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 Earths 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

254

Application of lightning discharge generated radio atmospherics/tweeks in lower ionospheric plasma diagnostics  

NASA Astrophysics Data System (ADS)

Lightning discharges during thunderstorm are the significant natural source of electromagnetic waves. They generate electromagnetic pulses, which vary from few Hz to tens of MHz, but the maximum radiated energy is confined in extremely low (ELF: 3-3000Hz) and very low (VLF: 3-30 KHz) frequency band. These pulsed signals with frequency dispersion are known as radio atmospherics or tweeks. These waves propagate through the process of multiple reflections in the earth-ionosphere waveguide over long distances with very low attenuation (2-3 dB/1000km). Since these waves are reflected by lower boundary of ionosphere, these are used extensively for probing the D-region ionosphere. D-region is important to the space weather, as well as the submarine communication and navigational aid. In this perspective the measurement of electron density profiles of the D-region is undoubtedly of great interest to both the development of reliable models and radio wave propagation. Earlier work on the tweeks is mainly focused to the theoretical considerations related to polarization, waveform analysis, and occurrence time and propagation mechanism. In this study we investigate tweeks to determine the equivalent night time electron densities at reflection height of the D-region. Distance traveled by the VLF waves from the causative lightning discharges to the receiving station has also been calculated. Tweeks recorded at a low latitude ground station of Allahabad (Geomag. lat. 16.050 N) during the night of 23 March 2007 have been used in the present analysis. Based on the analysis of the fundamental cut-off frequency of tweeks, the estimated equivalent electron density of the D-region has been found to be in the range of ~20 to 25 el/cm3 at ionospheric reflection height of ~80 to 95 km respectively. Propagation distance in Earth-Ionosphere wave guide (EIWG) from causative lightning source to experimental site varies from ~1500 to 8000 km.

Maurya, A. K.; Singh, R.; Veenadhari, B.; Pant, P.; Singh, A. K.

2010-02-01

255

Cluster observations and numerical modeling of energy-dispersed ionospheric H+ ions bouncing at the plasma sheet boundary layer  

NASA Astrophysics Data System (ADS)

The Cluster mission offers a unique opportunity to investigate the origin of the energy-dispersed ion structures frequently observed at 4.5-5 R E altitude in the auroral region. We present a detailed study of the 14 February 2001 northern pass, characterized by the successive observation by three spacecraft of a series of energy-dispersed structures at 72-75 ILAT in a region of poleward convection. Equatorward, the satellites also observed a localized, steady, and intense source of outflowing energetic (3-10 keV) H+ and O+ ions. These substructures were modeled by launching millions of H+ ions from this ionospheric source and following them through time-dependent electric and magnetic fields obtained from a global MHD simulation of this event. Despite the complexity of ion orbits, the simulations showed that a large number of ions returned to the Cluster location, poleward of their source, in a number of adjacent or overlapping energy-latitude substructures with the correct dispersion. The first dispersed echo was unexpectedly generated by half-bouncing ions that interacted with the current sheet to return to the same hemisphere. The time-shifted observations made by two Cluster (SC1 and SC3) spacecrafts were correctly reproduced. Almost all the ions returning to the spacecraft underwent a 2-5 keV nonadiabatic acceleration at each interaction with the current sheet in a very confined resonant region. This acceleration explains the overall energy increase from one structure to the next. This event confirms the importance of the ionospheric source in populating bouncing ion clusters within the magnetosphere, even at high latitudes.

Bosqued, J. M.; Ashour-Abdalla, M.; Umeda, T.; El Alaoui, M.; Peroomian, V.; Frey, H. U.; Marchaudon, A.; Laakso, H.

2009-04-01

256

Mid-latitude ionospheric plasma drift: A comparison of digital ionosonde and incoherent scatter radar measurements at Millstone Hill. Ph.D. Thesis  

SciTech Connect

A successful validation of the Digisonde drift technique was performed by comparing local ionospheric plasma drift velocity vectors measured by a Digisonde 256 digital ionosonde and a UHF incoherent scatter radar co-located at Millstone Hill (42 deg N, 71 deg 30` W) in Massachusetts, USA. The Digisonde drift technique uses imaging Doppler interferometry, measuring amplitude and phase Doppler spectra of ionospherically reflected signals across an array of receive antennas and processing these as line of sight ionospheric velocity vectors. Line of sight velocities of sufficient orthogonality are combined to calculate 3 dimensional ionospheric plasma drift vectors with 5 minutes resolution. A total of 145 hours of simultaneous radar and ionosonde drift vectors from 4 experiments are presented and compared. Geographically aligned, bottom side F-region (200-350 km) velocity components measured by each system were correlated. East-west velocities correlate to plus 0.90, north-south components to plus 0.67 and vertical components to plus 0.51. The Digisonde drift technique works best during moderately disturbed nighttime conditions, and those conditions are the emphasis of the work. The relative smoothness of the daytime mid-latitude ionosphere reduces the technique`s ability to measure horizontal drifts.

Bullett, T.W.

1994-12-31

257

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

258

HF Conductivity of Parametrically Unstable Magnetized Plasma  

NASA Astrophysics Data System (ADS)

In this paper the absorption processes of LH and UH pump waves in magnetized homogeneous and inhomogeneous plasmas are investigated. We determine the RF power absorbed in the plasma when the external pump parametrically excites low-frequency plasma oscillations (purely growing convective cells, modified convective cell modes and electron drift waves). Expressions for the effective absorption length of the external RF wave as a function of various plasma parameters are derived. For typical parameters of a hot ionospheric plasma, absorption length values are calculated.

Pavlenko, Victor N.; Panchenko, V. G.; Nazarenko, S. A.

259

Pulse propagation along conductors in low-density, cold plasmas as applied to electrodynamic tethers in the ionosphere  

NASA Astrophysics Data System (ADS)

This research characterizes the general propagation behavior of high-voltage electromagnetic pulses along conductors in low-density, cold plasmas. As a specific application, this characterization uses electrodynamic tethers in the ionosphere. Electromagnetic pulses are produced along the tether-plasma system as it transitions from open- to closed-circuited states and as it is driven by radio-frequency voltage sources. These perturbations take a finite amount of time to propagate along the tether and, as they do so, they affect the surrounding ionospheric plasma. This interaction in turn affects the tether's transmission-line characteristics. The dynamic evolution of the sheath is examined as the pulse front travels past a given section of tether and disturbs the local sheath. Present tether transmission-line models assume, as a first-order approximation, that the plasma-sheathed tether can be modeled as a simple rigid coaxial transmission line. This has proven acceptable for tethers with low induced or driven voltages. An improved model is needed, however, when steady-state plasma-sheath dynamics cannot be assumed, such as for longer deployed tether lengths, which have higher induced emf, or higher driven voltages. A dynamic circuit model of the plasma-sheathed tether is developed with knowledge gained from theoretical analyses, experimental results, and particle-in-cell computer simulations. Using this dynamic-sheath model as their basis, lumped-element transmission-line parameters for capacitance and inductance per unit length are derived for the plasma-immersed tether where it was found that capacitance is a function of voltage but inductance is approximately constant. These parameters are included with per-unit-length resistance and induced-emf elements to form the complete lumped-parameter model. The tether circuit model is implemented in the SPICE circuit simulation program. This implementation allows examination of the tether's transmission-line characteristics as well as pulse propagation and morphology. Previously developed models of satellite and Orbiter interactions with the plasma based on Tethered Satellite System mission data can be used with this circuit model as the endpoints of the complete electrodynamic-tether system.

Bilen, Sven Gunnar

260

The Fluxes-1 and -2 active experiments: Investigation of plasma jet dynamics and interactions with the ionosphere  

NASA Astrophysics Data System (ADS)

This paper presents an overview of two Russian-American active geophysical rocket experiments, Fluxus-1 and Fluxus-2, designed to study the interaction of plasma jets with the ionosphere and magnetosphere. These active experiments used specially designed explosive type shaped-charge generator (ETG) that produces a 3-MJ aluminum plasma jet without the aid of solar illumination. The jet was injected nearly parallel to the magnetic field at an altitude of 140 km towards an instrumented payload located 130 m away. The plasma jet density exceeded 1 109 ions/cm-3 and produced over a 50% reduction in magnetic field strength due to a diamagnetic depression. The experiment was also observed using ground-based visible sensors, and space-based ultraviolet, visible, and infrared sensors on the Midcourse Space Experiment (MSX). It was found that the plasma jet was quickly stopped due to collisions with the atmosphere and formed a slowing moving (100 m/s) plasma cloud that was observed for up to 3 minutes using visible sensors.'

Zetzer, J. I.; Gavrilov, B. G.; Kiselev, Yu. N.; Rybakov, V. A.; Gritskiv, V.; Romanovsky, Yu. A.; Erlandson, R. E.; Meng, C. I.; Stoyanov, B. J.

1998-11-01

261

Multi-Radar Mapping of Auroral Convection.  

National Technical Information Service (NTIS)

Simultaneous radar azimuth scans with the Millstone Hill, Sondrestrom, and EISCAT incoherent scatter radars produce maps of the ionospheric convection electric field at high latitudes which span 10 hours of magnetic local time. A series of convection 'sna...

J. C. Foster T. Turunen P. Pollari H. Kohl V. B. Wickwar

1989-01-01

262

Ionospheric Response to Flux Transfer Events at the Earth's Magnetopause  

NASA Astrophysics Data System (ADS)

Flux transfer events (FTE) are thought to be the manifestation of the pulsed reconnection process by which interplanetary magnetic field lines and Earth's magnetic field lines merge. They are observed at the magnetopause as bipolar signatures in the magnetic field component perpendicular to the magnetopause (normal component) as the distorted newly reconnected field lines get dragged by the magnetic tension and the solar wind. FTEs are also observed in the ionosphere by ground-based instrumentations. Optical instruments commonly record poleward moving auroral forms in the red line (630nm) corresponding to low-energy electron precipitation. SuperDARN radars observe the convection associated to FTEs as enhanced flow channels. The EISCAT radars on the Svalbard archipelago have revealed the transient and impulsive nature of the ionosphere under the polar cusp for southward IMF. We have performed a simulation of the ionospheric footprint of a FTE by including the Southwood model of FTE in the TRANSCAR model of ionosphere. We can trace the evolution of an open flux tube and the behaviour and dynamics of the surrounding ionospheric plasma. We particularly focus on the signature of the two areas of return flow on both side of the FTE footprint. Those return flow may actually be responsible of some of the structures observed by Incoherent Scatter radars such as the Eiscat Svalbard Radar (ESR). We then compare our simulations with observations and finally discuss the pros and cons of the Southwood model of FTE.

Pitout, F.; Blelly, P. L.

2003-06-01

263

Relationship Between Ground-based and In-situ Plasma Sheet Measurements of Convection Penetration  

NASA Astrophysics Data System (ADS)

Shortly after the discovery of bursty plasma sheet convection, a number of observational studies have suggested a link between earthward flow bursts observed near the midnight central plasma sheet and auroral intensifications at the polar cap boundary (polar cap boundary intensifications or PBIs) and the southward propagating aurora (auroral streamers). Three different stages are identified during the southward progression of the streamers. In the first stage there is a boundary brightening followed, often within a few minutes, by the start of the propagation of aurora in the southward direction. The second stage, which usually lasts up to ten minutes, consists of the propagation of the auroral streamer into the equatorward edge of the aurora. In the third stage, the arrival of the streamer to the equatorward edge of the oval coincides with the onset of a bright spot that can last for as long as 20 minutes. Bursty convection is observed in association with streamers most commonly during steady magnetospheric convection and substorm recovery, although it is also observed in general during periods of sustained geomagnetic activity. This investigation has two objectives. The first is to determine whether reconnection is enhanced concurrently with the PBIs and whether the duration of the enhancement coincides with the southward expansion of the auroral streamers. The second objective is to determine whether the enhanced tail reconnection is associated with penetration of under-dense flux tubes into near-Earth plasma sheet. Ground-based multi-spectral optical measurements and in-situ Geotail and THEMIS measurements in the plasma sheet during extended periods of southward IMF show the causal chain whereby PBIs are indeed the optical manifestation of reconnection intensifications that power, in some cases, the penetration of fast convection into the plasma sheet. Observations show, however, that there are also intense flow bursts (~ 1000 km/s) without any clear indication of streamers and streamers without a corresponding flow burst. We discuss the consequences of these apparent discrepancies on the paradigm of penetration of under-dense flux tubes in the plasma sheet.

Sanchez, E. R.

2009-12-01

264

Last studies of artificial airglow emission of ionospheric plasma at the  

Microsoft Academic Search

Experimental results of September 2007 on artificial airglow emission at 557.7 nm [green line, the radiation of atomic oxygen level O(1 S), the excitation threshold 4.17 eV, radiation lifetime 0.7 s)] and 630 nm [red line, the radiation of atomic oxygen level O(1 D), the excitation threshold 1.96.17 eV, radiation lifetime 100 s)] during HF pumping of the ionosphere

Igor Nasyrov; Savely Grach; Nasyrov Albert; Gumerov Rustam; Klimenko Vladimir

2008-01-01

265

Radiotomographic observations of corpuscular ionization in the ionosphere  

NASA Astrophysics Data System (ADS)

Along with the antisunward cross-polar convection of the ionospheric plasma and the field-aligned electric currents, the corpuscular fluxes play an important role in the magnetosphere-ionosphere coupling. Being more tightly coupled with the magnetosphere, the subauroral and auroral ionosphere noticeably differs from the midlatitude ionosphere. It experiences much stronger and faster variations in space and time. The particle fluxes and the electric fields of magnetospheric origin penetrate into the ionosphere and substantially affect the production, loss and transport of charged particles. The rate of ionization in the midlatitude ionosphere is controlled almost solely by the X-ray and UV/EUV solar radiation, whereas in high latitudes the fluxes of particles precipitating from the magnetosphere are significant sources of ionization. Moreover, they are probably the single source during the polar night. Typically, the contribution of the magnetospheric corpuscular fluxes into the ionization is small compared to the contribution of electromagnetic radiation; however, during the geomagnetic storms, it may prove significant, especially if these fluxes are sufficiently strong and act in the nighttime when the solar electromagnetic radiation is absent. The present work is devoted to radio tomographic imaging of the ionospheric effects of particle precipitation using the data from low-orbital navigational satellite systems. The ionospheric radio tomography is actively developed during the past two decades. It provides images of the 2D distribution of electron density in the vertical plane (latitude-altitude cross-sections) (averaged over an interval of 10-15 minutes) for the spatial sector covering several thousand kilometers. The horizontal and vertical resolution of the RT method is 20-30 km and 30-40 km, respectively. In the present work, the particle precipitation events are identified from the particle flux measurements onboard DMSP satellites. We present and discuss the examples illustrating the comparison of the RT images of the ionosphere with the fluxes of ionizing particles measured by DMSP satellites as well as with the auroral oval data and UV emissions. During the geomagnetic storms, the RT imaging reveal multiple extrema in the distribution of the ionization and the wavelike disturbances with the spatial scales ranging from tens to hundreds kilometers. The spatial scales of the corpuscular precipitation widely vary from few to ten degrees in latitude. The spatial structure of the corpuscular ionization in the RT images rather well agrees with the latitudinal distributions of the precipitating particle fluxes. Generation of the wave disturbances in the ionospheric plasma by the particle precipitation is another remarkable phenomenon. We also consider generation of acoustic gravity waves (AGW) by corpuscular injections. The work was supported by the Russian Foundation for Basic Research (grants 10-05-01126 and 11-05-01157.

Andreeva, E. S.; Kunitsyn, V. E.; Tereshchenko, E. D.; Krysanov, B. Yu.; Nazarenko, M. O.

2012-04-01

266

Response of ionosphere to strong geomagnetic storm: observation and modelling  

NASA Astrophysics Data System (ADS)

This paper presents the results derived from investigating the ionospheric response in middle and auroral latitudes to a strong geomagnetic storm on September 25, 1998. Our analysis of the behavior of the ionosphere was based on using the measurements from a network of ionospheric stations located in the region of Siberia and the Far East. According to the latitudinal location, the stations under consideration can be divided into three groups: auroral, subauroral, and mid-latitude stations. Data from some of European stations were used in the comparison. The numerical model for ionosphere-plasmasphere coupling that was developed at the ISTP SB RAS, was used to interpret the observational data. By analyzing the data, it was possible to identify the following regularities and differences. Intense negative disturbances during the main phase of the September 25 geomagnetic storm were observed at all stations under investigation. The main differences were marked both during the initial phase and in the recovery phase of the geomagnetic storm. The ionospheric response during the initial phase is determined primarily by the local time of geomagnetic storm onset and the latitude of station. The longitude effect of ionospheric disturbances was observed during the recovery phase. A theoretical analysis of the processes controlling the mid-latitude ionospheric response to the geomagnetic storm showed a good agreement of modeling results and measurements, as well as made it possible to ascertain the crucial role of the neutral composition variations in the ionospheric parameter variations observed. At auroral and subauroral stations the electron density variability during the storm is much more pronounced. According to results of analysis of the ionospheric plasma convection trajectories, this variability is caused by the combined effect of convection and energetic electron precipitation. Neutral thermospheric composition disturbances exert some influence on the electron density background level in this range of latitudes. The reversal of sign of the disturbance, when moving eastward from the west, during the storm recovery phase is difficult to explain by the local time effect. One possible reason could be the wave phenomena in the thermosphere, and local changes in the neutral wind system.

Pirog, P.; Polekh, P.; Tashchilin, T.; Romanova, R.; Zherebtsov, Z.

267

Study of the evening plasma drift vortex in the low-latitude ionosphere using San Marco electric field measurements  

NASA Astrophysics Data System (ADS)

San Marco D electric field measurements have been averaged in terms of the equivalent EB plasma drifts for days near the 1988 autumn equinox. The observed plasma drifts provide a satellite-based composite in altitude and local time of the evening enhancements in the zonal and vertical drifts and the shear in the zonal drift. The satellite data reveal details of the postsunset plasma drift vortex, which have been studied in radar and chemical release experiments. The averaged drift data show a proportional relationship between the prereversal enhancement of the vertical drift and the zonal derivative of the zonal drift. This relationship suggests that the vertical drift enhancement is caused by a curl-free response to the rapid increase of the zonal drift, which in turn is tied to the F region zonal winds and the E region sunset. The data also show a curl-free drop-off in altitude of the vertical plasma drift above and below the peak drift at 450 km altitude during the prereversal enhancement. Comparisons of the averaged data with results of coupled ionosphere-electrodynamics models are used to examine the underlying causes of the evening plasma drifts. The evening plasma drift vortex is shown to be a single drift structure with a single source. The source of the evening drift vortex resides on the bottomside of the integrated F region, just as originally supposed by Rishbeth [1971]. This dominant single source, which is produced by the divergence of the wind-driven current of the F region, causes the evening enhancement of the eastward plasma drift, the shear in the eastward drift, and the prereversal enhancement of the vertical drift.

Eccles, J. Vincent; Maynard, Nelson; Wilson, Gordon

268

Ionospheric plasma flow over large high-voltage space platforms. I: Ion-plasma--time scale interactions of a plate at zero angle of attack  

SciTech Connect

Theory and particle simulation results are presented for the ionospheric plasma flow over large, high-voltage space platforms. In this paper, dynamic interactions of a negatively biased plate at a zero angle of attack on the ion-plasma--time scale are emphasized. Results of the transient plasma response to a rapid surface potential change show that ion-acoustic disturbances are generated by the leading edge, and they evolve to form a Mach wedge expansion fan. The transient ion current exhibits a strong overshoot in the first few ion-plasma periods. It is shown that the current overshoot is due to the ions trapped within the initial sheath, and its magnitude is proportional to the plate dimension and the square root of the surface voltage. Simulations of time-dependent interactions of a plate connected to external circuits are also performed. A rapidly changing voltage source may cause a very complex transient current and surface voltage due to the coupling of the transient plasma and circuit properties. Interactions of a plate with electron beam emissions are also studied, and the beam effects on the sheath structure and ion current collection are discussed.

Wang, J.; Hastings, D.E. (Space Power and Propulsion Lab, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139 (United States))

1992-06-01

269

Intermittent convective transport carried by propagating electromagnetic filamentary structures in nonuniformly magnetized plasma  

SciTech Connect

Drift-Alfven vortex filaments associated with electromagnetic turbulence were recently identified in reversed field pinch devices. Similar propagating filamentary structures were observed in the Earth magnetosheath, magnetospheric cusp and Saturn's magnetosheath by spacecrafts. The characteristics of these structures closely resemble those of the so-called mesoscale coherent structures, prevailing in fusion plasmas, known as 'blobs' and 'edge localized mode filaments' in the boundary region, and propagating avalanchelike events in the core region. In this paper the fundamental dynamics of drift-Alfven vortex filaments in a nonuniformly and strongly magnetized plasma are revisited. We systemize the Lagrangian-invariant-based method. Six Lagrangian invariants are employed to describe structure motion and the resultant convective transport, namely, magnetic flux, background magnetic energy, specific entropy, total energy, magnetic momentum, and angular momentum. The perpendicular vortex motions and the kinetic shear Alfven waves are coupled through the parallel current and Ampere's law, leading to field line bending. On the timescale of interchange motion tau{sub perpendicular}, a thermal expansion force in the direction of curvature radius of the magnetic field overcomes the resultant force of magnetic tension and push plasma filament to accelerate in the direction of curvature radius resulting from plasma inertial response, reacted to satisfy quasineutrality. During this process the internal energy stored in the background pressure gradient is converted into the kinetic energy of convective motion and the magnetic energy of field line bending through reversible pressure-volume work as a result of the plasma compressibility in an inhomogeneous magnetic field. On the timescale of parallel acoustic response tau{sub ||}>>tau{sub perpendicular}, part of the filament's energy is transferred into the kinetic energy of parallel flow. On the dissipation timescale tau{sub d}>>tau{sub perpendicular}, the kinetic energy and magnetic energy are eventually dissipated, which is accompanied by entropy production, and in this process the structure loses its coherence, but it has already traveled a distance in the radial direction. In this way the propagating filamentary structures induce intermittent convective transports of particles, heat, and momentum across the magnetic field. It is suggested that the phenomena of profile consistency, or resilience, and the underlying anomalous pinch effects of particles, heat, and momentum in the fusion plasmas can be interpreted in terms of the ballistic motion of these solitary electromagnetic filamentary structures.

Xu, G. S. [Euratom-UKAEA, Culham Science Centre, Abingdon OX14 3DB (United Kingdom); Institute of Plasma Physics, Chinese Academy of Sciences, Hefei 230031 (China); Naulin, V.; Rasmussen, J. Juul; Nielsen, A. H. [Association Euratom-Risoe DTU, DK-4000 Roskilde (Denmark); Fundamenski, W. [Euratom-UKAEA, Culham Science Centre, Abingdon OX14 3DB (United Kingdom); Wan, B. N. [Institute of Plasma Physics, Chinese Academy of Sciences, Hefei 230031 (China)

2010-02-15

270

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.

271

Observations of the ionosphere by the Ionosphere Sounding Satellite \\/ISS  

Microsoft Academic Search

The design and electronics of a global ionospheric sounding satellite are described. The satellite missions consisted of studying the global distribution of ionospheric critical frequencies and the virtual range vs frequency characteristics of the sounding echo; study of the global distribution of radio noise intensities and the occurrence frequency of atmospherics; study of such plasma parameters as electron and ion

N. Matuura; R. Nishizaki

1977-01-01

272

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

273

Ionospheres of the terrestrial planets  

Microsoft Academic Search

The theory and observations relating to the ionospheres of the terrestrial planets Venus, the earth and Mars are reviewed. Emphasis is placed on comparing the basic differences and similarities between the planetary ionospheres. The review covers the plasma and electric-magnetic field environments that surround the planets, the theory leading to the creation and transport of ionization in the ionspheres, the

R. W. Schunk; A. F. Nagy

1980-01-01

274

Ionospheric modification by chemical releases and high-power radio waves  

SciTech Connect

Ionospheric plasma density irregularities can be produced locally by chemical releases from space vehicles or remotely by a beam of high power radio waves transmitted from the ground. 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) can determine the effectiveness of ionospheric chemical releases and high frequency electromagnetic wave transmissions in subtle and surprising ways. Initially, a chemical release produces a localized change in plasma density and high power radio waves heat the electrons to yield enhanced transport from pressure gradients in the heated region. Subsequent processes, however, can lead to enhanced transport in chemically modified regions and modified reaction rates in the regions affected by high power radio waves.

Bernhardt, P.A.; Scales, W.A.; Keskinen, M.J.; Duncan, L.M.; Rowland, H.L.

1990-05-03

275

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

276

Ionospheric Analysis and Ionospheric Modeling.  

National Technical Information Service (NTIS)

Investigations performed towards the development of improved models of the ionosphere are described. The study was directed at improving existing prediction models of ionospheric parameters. This lead to the development of techniques to update on a global...

D. C. Miller J. Gibbs

1974-01-01

277

Estimation of electron density of ionospheric plasma using wave, impedance and topside sounder data  

Microsoft Academic Search

Instability analysis of the dispersion relation of electron plasma indicates that enhanced emission in the frequency band (fp,fu=sqrt(fp?fp+fc?fc) can be easily detected in wave spectra of space plasmas. Such emission, in passive mode spectra, can be used to determine plasma density of the major cold plasma component and points out the existence of a minor energetic component. Contrary to such

A. Kiraga; Z. Klos; H. Rothkaehl; Z. Zbyszynski; V. N Oraevsky; S. A Pulinets; I. S Prutenski

1997-01-01

278

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

279

Plasma diagnostics with Langmuir probes in the equatorial ionosphere: I. The influence of surface contamination  

NASA Astrophysics Data System (ADS)

The application of spherical Langmuir probes for measuring the electron temperature and density on ionospheric sounding rockets is discussed with respect to the influence of the geomagnetic field effects and probe contamination. The influence of the contamination layer is thoroughly analysed in the frame of a nonlinear equivalent circuit. When operating the probe in ramp mode, it is found that the distortion of the current-voltage characteristic is different for decreasing and increasing probe voltages. The resulting error of the electron temperature is determined for a range of capacitance (C) and resistance (R) values of the contamination layer. A method is described to determine the parameters R and C from the flight data. Further, a correction algorithm is discussed that allows the true probe characteristic to be retrieved from the measured distorted characteristic.

Piel, A.; Hirt, M.; Steigies, C. T.

2001-09-01

280

Simultaneous observations of radio wave phase and intensity variations for locating the plasma layers in the ionosphere  

Microsoft Academic Search

A new method is introduced to locate the layered structures in the ionosphere based on simultaneous observations of radio wave temporal intensity and phase variations in trans-ionospheric satellite-to-satellite links. The method determines location of the tangent point on the trans-ionospheric ray trajectory where gradient of refractivity is perpendicular to the ray trajectory and the influence of a layered structure on

Y. A. Liou; A. G. Pavelyev

2006-01-01

281

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

282

Developing of the ionospheric plasma turbulence over the epicenters of the extremely strong earthquakes - the results of the DEMETER satellite observations  

NASA Astrophysics Data System (ADS)

The DEMETER French microsatellite satellite was launched in June 2004 and finished its operation in December 2010. During the time of the DEMETER satellite operation some gigantic earthquakes took place. We will report the electromagnetic effects registered by DEMETER prior to the earthquakes with magnitude over 8 or just close to this value. We selected events with good coverage of the measurements in the burst mode when the wave form of the electric field variations were registered. It is because the special attention will be given to study of the characteristics of the spectra of these variations and search of the nonlinear effects. This analysis is possible in the time interval when the waveform has been transmitted. Using wavelet and bispectral analysis as well as the statistical characteristics of the measured parameter, we find that registered variations are associated with developing of the ionospheric plasma turbulence. It is mainly Kolmogorov type of the turbulence. The payload of the DEMETER allows to measure important plasma parameters (ion composition, electron density and temperature, energetic particles) with high temporal resolution in the ionosphere over the seismic regions. The correlation of the observed plasma turbulence with changes of the other parameters will be also given. In the present work analysis of the low frequency fluctuations of the electric and magnetic fields for the selected strong earthquakes will be given. The mechanism of the energy transmission from the earthquake to the ionosphere is not clear, but we can discuss the behavior of the ionospheric plasma and search of the instabilities which could be a source of the electromagnetic field variations. Some attempt of this discussion will be given in the presentation. We will present results obtained prior to the some giant earthquakes (Peru2007, Wechuan China 2008, Haiti 2010, Chile 2010).

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

2011-12-01

283

Physical characteristics and occurrence rates of meteoric plasma layers detected in the Martian ionosphere by the Mars Global Surveyor Radio Science Experiment  

Microsoft Academic Search

Low-altitude plasma layers are present in 71 of 5600 electron density profiles from the Martian ionosphere obtained by the Mars Global Surveyor Radio Science experiment. These layers are produced by the ablation of meteoroids and subsequent ionization of meteoric atoms. The mean altitude of the meteoric layer is 91.7 +\\/- 4.8 km. The mean peak electron density in the meteoric

Paul Withers; M. Mendillo; D. P. Hinson; K. Cahoy

2008-01-01

284

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

285

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

286

Magnetospheric Convection.  

National Technical Information Service (NTIS)

Magnetospheric convection, which implies the existence of large-scale electric fields, appears to be the dominant process for the acceleration and injection of moderately energetic plasma into the magnetosphere. The aurora, the radiation belts, and the 't...

W. I. Axford

1969-01-01

287

Measurements of Electron Beam and Neutral Gas Emissions in a Space Plasma during AN Ionospheric Modification Experiment.  

NASA Astrophysics Data System (ADS)

The principal objective of this research was to investigate observations of current collection enhancements due to nitrogen gas emissions from a highly charged, isolated rocket payload in the ionosphere. These observations were made during the second Cooperative High Altitude Rocket Gun Experiment (CHARGE-2) which was an electrically tethered dual payload system. The current collection enhancement was observed on a "daughter" payload located 100 to 426 m away from a "mother" payload, approximately perpendicular to the Earth's magnetic field, which was firing a 1 keV electron beam at up to 48 mA. The unambiguous response of emitting neutral gas from a highly charged vehicle located well away from the disturbed region surrounding the electron beam's mother payload was unique to this experiment. These results are interpreted in terms of neutral gas ionization in close proximity to the daughter vehicle during the short periods of gas emission. The gas source was a modified nitrogen gas rate control system (RCS). The ionization source was most likely accelerated ionospheric electrons. The results indicate that it is possible to enhance the electron current collection capability of positively charged vehicles and reduce overall charging potentials by means of deliberate neutral gas release into a space plasma. Calculations also seem to suggest that ion current out of the ionization region was not a dominant factor in net current balance. A secondary research objective was to investigate magnetic field-aligned electron beam ionization of the atmosphere using ground based vhf radar. Only one radar event could be correlated with both electron beam emission and expected range. This occurred during an RCS induced current collection enhancement which was itself unique among all RCS gas releases. During this event a high voltage power supply, connected in series between the mother payload and the tether wire to the daughter payload, drove the electron beam emitting payload several hundred volts negative with respect to the surrounding plasma. The fact that this was the only detectable radar event, if validated by future experiments, may suggest a method for launching an electron beam from a rocket payload with minimal vehicle charging degradation.

Gilchrist, Brian Earl

288

An olden but golden EISCAT observation of a quiet-time ionospheric trough  

NASA Astrophysics Data System (ADS)

Incoherent scatter measurements were carried out on 9 November 1987, showing the presence of an ionospheric trough in the F region. The experiment was made using the EISCAT UHF radar, and it consisted of an azimuthal scan with constant beam elevation and a meridional scan. Since the radar rotates with the Earth, beams with different directions from subsequent scans meet in the same MLT- CGMLat pixel in nonrotating frame. If the ionosphere is not too variable, these can be combined to give an average value of electron density and ion/electron temperature in each pixel. Furthermore, since different beams passing through the same pixel give different ion velocity components, it is also possible to obtain the velocity vector. The geomagnetic conditions during the observations were quiet enough for assuming a quasi-stationary ionosphere. It was found that both ion and electron temperatures have minima within the trough region and increase at the poleward wall. Ion velocity measurements, together with a convection model, suggest that the density depletion within the trough is due to recombination of F region plasma convecting for a long time in the dusk convection cell beyond the terminator. The northern edge of the trough is associated with soft particle precipitation. The southern edge is steeper than the northern edge, and is built by sunlit plasma brought to the trough region by corotation. The trough is thus a result of a combination of transport and precipitation processes rather than stagnation.

Voiculescu, M.; Nygrn, T.; Aikio, A.; Kuula, R.

2010-10-01

289

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

290

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

291

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

292

Investigation of the force balance in the Titan ionosphere: Cassini T5 flyby model/data comparisons  

NASA Astrophysics Data System (ADS)

Cassini's Titan flyby on 16 April, 2005 (T5) is the only encounter when the two main ionizing sources of the moon's atmosphere, solar radiation and corotating plasma, align almost anti-parallel. In this paper a single-fluid multi-species 3D MHD model of the magnetospheric plasma interaction for T5 conditions is analyzed. Model results are compared to observations to investigate the ionospheric dynamics at Titan as well as to understand the deviations from a typical solar wind interaction, such as Venus' interaction with the solar wind. Model results suggest that for the T5 interaction configuration, corotating plasma is the dominant driver determining the global interaction features at high altitudes. In the lower ionosphere below 1500 km altitude - where the control of the ionospheric composition transfers from dynamic to chemical processes - magnetic and thermal pressure gradients oppose each other locally, complicating the ionospheric dynamics. Model results also imply that the nightside ionosphere - produced only by the impact ionization in the model - does not provide enough thermal pressure to balance the incident plasma dynamic pressure. As a result, the induced magnetic barrier penetrates into the ionosphere by plasma convection down to 1000 km altitude and by magnetic diffusion below this altitude. Moreover, strong horizontal drag forces due to ion-neutral collisions and comparable drag forces estimated from possible neutral winds in the lower ionosphere below 1400 km altitude oppose over local regions, implying that the Titan interaction must be treated as a 3D problem. Ion and electron densities calculated from the model generally agree with the Cassini Ion Neutral Mass Spectrometer and Langmuir probe measurements; however, there are significant differences between the calculated and measured magnetic fields. We discuss possible explanations for the discrepancy in the magnetic field predictions.

Ulusen, D.; Luhmann, J. G.; Ma, Y.-J.; Ledvina, S.; Cravens, T. E.; Mandt, K.; Waite, J. H.; Wahlund, J.-E.

2010-12-01

293

Role of surface tension driven convective flows on the molten depths in simulated plasma disruptions  

SciTech Connect

Plasma disruptions in fusion reactors lead to high-energy deposition for short periods of time, causing melting of the first wall. A two-dimensional transient computer model has been developed that, by solving the equations of motion and energy, predicts the depths and the motion of the molten layers in small beam simulation experiments. It is demonstrated that convective flows caused by variations of surface tension - due to changes in material chemistry and surface temperature - play an important role in determining the depth and flow intensities of the molten layers. The calculated shapes and depths of the molten layers for Type 316 stainless steel have been compared with available experimental results and found to be in good agreement. 34 refs., 9 figs.

Tsotridis, G.; Rother, H. [Inst. for Advanced Materials, Petten (Netherlands)

1995-07-01

294

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

295

Planetary Ionospheres  

Microsoft Academic Search

\\u000a The paper presents a summary of the lectures on planetary ionospheres given at NASAs 1st Asia Pacific School on International Heliophysical Year conducted at Indian Institute of Astrophysics,\\u000a Kodaikanal, India during 1022 December 2007. Following an introduction, the paper describes the structure of the ionospheres,\\u000a theory of Earths ionosphere including the effects of diffusion, neutral wind and electric field, and

Nanan Balan

2010-01-01

296

Study of the SEE decay processes in application to mechanisms of dissipation of the HF plasma turbulence and diagnostics of the ionospheric plasma parameters  

NASA Astrophysics Data System (ADS)

Results of the investigations of the decay process for different stimulated electromagnetic emission (SEE) features at the SURA heating facility (Russia) are presented. The data of the measurements are used to analyze the nonlinear energy transformation through the spectra of the Langmuir and upper hybrid plasma turbulence as well as to determine a relationship between the electron collision frequency and the collisionless decay rate of the plasma waves under different ionospheric conditions. In particular, due to the SEE decay time measurements at the upper hybrid turbulence development stage it is found an increase of the decay rate ? of the emission from the collision values ? = ? -1 = 300 - 400 s-1 to the collisionless values ? = 2000 - 10000 s-1 in a wide frequency band (up to 600 kHz) near the 4th - 7th cyclotron electron gyroharmonics. On the other hand, the SEE decay times didn't found any dependence on the pump power but they slightly increase under change from day to night condition. The results of the daily SEE decay rate monitoring in dependence on the pumping frequency (re- flection altitude) are presented. The work was supported by RFBR grants 07-02-00464 and 06-02-17334.

Sergeev, Evgeny

297

Simultaneous polar aurorae and modelled convection patterns in both hemispheres  

NASA Astrophysics Data System (ADS)

We present an event study illustrating the relationships between plasma convection and polar auroral emissions, as well as illustrating the influence of the interplanetary magnetic fields y-component on theta aurora development in both hemispheres. Transpolar arcs (TPAs) are often observed during northward IMF with duskside (dawnside) formation of the TPA and dawnward (duskward) motion occurring when By changes from positive to negative in the northern (southern) hemisphere. POLAR UVI provides images in the northern hemisphere while DMSP provides ionospheric plasma flow and precipitating particle data in both hemispheres. Concurrent solar wind plasma and interplanetary magnetic field measurements are provided by the ACE satellite. Utilizing the satellite data as inputs, the Royal Institute of Technology (KTH) numerical model provides the high-latitude ionospheric electrostatic potential patterns in both hemispheres calculated at different times during the evolution of the theta aurora resulting from a variety of field-aligned current configurations associated with the changing global aurora. These model patterns are compared to the convection predicted by mapping the magnetopause electric field to the ionosphere using the Moscow State Universitys (MSU) paraboloid model of the magnetosphere. The model predicts that parallel electric fields are set up along the magnetic field lines projecting to the transpolar aurora. Their possible role in the acceleration of the auroral electrons is discussed.

Cumnock, J. A.; Blomberg, L. G.; Alexeev, I. I.; Belenkaya, E. S.; Bobrovnikov, S. Yu.; Kalegaev, V. V.

2006-01-01

298

Multi-instrument studies of ionospheric and magnetospheric processes  

NASA Astrophysics Data System (ADS)

In this thesis, several aspects of the convection, magnetic, and optical auroral dynamics of the high-latitude ionosphere are investigated from multi- instrument observations. The spatial and temporal relationships between nightside radar flow enhancements (NRFEs) and auroral intensifications are studied in Chapter 3. The NRFEs on open field lines are usually associated with very little accompanying auroral and magnetic activity. The NRFEs on closed field lines are often accompanied by optical auroral activity, but there is not a definite one-to-one correspondence. Both the statistical investigation and event study showed that the NRFEs may occur nearly simultaneously with the auroral intensifications. Because existing models associating the tail reconnection process and near- geosynchronous onset of substorms do not explain these correlated radar and optical observations very well, we propose a new model to explain the nearly simultaneous onset of the NRFEs and the auroral intensifications. In Chapter 4 we describe a small postmidnight substorm event on October 9, 2000 during dominantly IMF By+ Bz+ conditions. A sequence of three optical auroral intensifications and Pi2 bursts were found. The first two activations were characteristic of pseudobreakups, while the last and strongest intensification corresponded to a substorm expansive phase (EP). The auroral, magnetic and radar signatures of the event are interpreted as the consequence of three successive drift-Alfven-ballooning (DAB) mode instabilities in the near- geosynchronous orbit plasma sheet (NGOPS). About 10 minutes after the EP onset, there was a second auroral brightening. The convection feature during this second auroral brightening was consistent with the scenario of a Stage-2 EP. We suggest that the first two pseudobreakups, the Stage-1 EP, and the Stage-2 EP are related, respectively, to loading-unloading, directly driven, and internal magnetotail processes. Finally, in Chapter 5, we make some comparisons between the ionospheric plasma convection vortex structure observed by SuperDARN and the associated equivalent current pattern derived from the magnetometer observations. The discrepancies between the equivalent convection (EQC) and the SuperDARN-observed convection (SDC) pattern are explained in terms of the effect of day-night photoionization conductance gradient, and the coupling between field-aligned currents (FACs) and ionospheric conductances. In particular, we found the agreement between the EQC and SDC patterns is rather poor for a counterclockwise convection vortex. We suggest the discrepancies are probably due to a downward FAC-conductance coupling process.

Liang, Jun

299

Kinetic simulation of plasma flows in the inner magnetosphere  

SciTech Connect

A one-dimensional hybrid particle code is used to study the interactions between upflowing thermal ions from conjugate ionospheres. The simulation model allows for multiple species, convection of plasmaspheric flux tubes, and Coulomb self-collisions which conserve momentum and energy locally. The model incorporates a variable-flux boundary condition where the flux, at the boundaries, approaches zero as the plasmasphere fills and equilibrium conditions are reached. The effects of two important processes on plasmaspheric refilling have been considered. The first includes convection of the plasmaspheric flux tube. The second is the interaction of ionospheric thermal plasma and particle injection from an external source. Particle injection seems to play an important role in the evolution of the total particle distribution on the early timescales (t<1 hour); however, for late timescales (t>8 days) the thermal plasma from the ionosphere dominates the particle distribution. 48 refs., 9 figs.

Miller, R.H.; Rasmussen, C.E.; Gombosi, T.I. [Univ. of Michigan, Ann Arbor, MI (United States)] [and others

1993-11-01

300

Dayside magnetosphere-ionosphere coupling during IMF clock angle ?90: Longitudinal cusp bifurcation, quasi-periodic cusp-like auroras, and traveling convection vortices  

Microsoft Academic Search

In spite of the great progress achieved in the understanding the Earth's magnetosphere-ionosphere system, its configuration and dynamics during periods with large horizontal interplanetary magnetic field (IMF ?By? $\\\\gg$ 0) is still poorly investigated. In such time intervals, the cusp\\/low-latitude boundary layer (LLBL) entry regions are characterized by a more complex magnetic reconnection topology, than during IMF Bz-dominated periods, which

S. Massetti

2005-01-01

301

Longitudinal and seasonal variations in nighttime plasma temperatures in the equatorial topside ionosphere during solar maximum  

NASA Astrophysics Data System (ADS)

Latitude profiles of the ion and electron temperatures and total ion concentration across the equatorial region near 800 km altitude are routinely obtained from Defense Meteorological Satellite Program (DMSP) spacecraft. We have examined these profiles at 2100 hours local time to discover the influences of field-aligned plasma transport induced by F region neutral winds. Such dependencies are readily seen by contrasting observations at different seasons and different longitudes distinguished by different magnetic declinations. These data show strong evidence for adiabatic heating produced by interhemispheric plasma transport. This heating manifests itself as a local temperature maximum that appears in the winter hemisphere during the solstices and is generally absent during equinox. A longitudinal variation in the appearance of this maximum is consistent with the roles of meridional and zonal winds in modulating the field-aligned plasma velocities. The data also show a local temperature minimum near the dip equator. However, it is not so easy to attribute this minimum to adiabatic cooling since transport of plasma from below and the latitude variation in the flux tube content may also produce such a minimum.

Venkatraman, Sarita; Heelis, Rod

1999-02-01

302

Radar interferometry: A new technique for studying plasma turbulence in the ionosphere  

Microsoft Academic Search

A new radar interferometer technique has been developed and used successfully at the Jicamarca Radio Observatory in Peru to study the strong nighttime plasma turbulence in the equatorial electrojet. The technique represents a major step forward in radar probing of turbulent irregularities such as (but not limited to) those in the electrojet. In many situations it provides far more information

D.T. Farley; H.M. Ierkic; B.G. Fejer

1981-01-01

303

Modifying the ionosphere with intense radio waves.  

PubMed

The ionospheric modification experiments provide an opportunity to better understand the aeronomy of the natural ionosphere and also afford the control of a naturally occurring plasma, which will make possible further progress in plasma physics. The ionospheric modification by powerful radio waves is analogous to studies of laser and microwave heating of laboratory plasmas (20). " Anomalous" reflectivity effects similar to the observed ionospheric attenuation have already been noted in plasmas modulated by microwaves, and anomalous heating may have been observed in plasmas irradiated by lasers. Contacts have now been established between the workers in these diverse areas, which span a wide range of the electromagnetic spectrum. Perhaps ionospheric modification will also be a valuable technique in radio communications. PMID:17778050

Utlaut, W F; Cohen, R

1971-10-15

304

Venus nightside ionospheric holes  

NASA Astrophysics Data System (ADS)

Pioneer Venus Orbiter (PVO) measured the ionosphere and atmosphere of Venus for 13 years 10 months yielding a rich data set of archived data from a complement of instruments. One particularly striking feature seen was the occurrence of deep localized nightside ionization depletions commonly called holes. A number of theories have been put forth to explain their observed characteristics, but there is still no consensus on their source. A possibly related phenomenon in the Venus nightside ionosphere is the occurrence of "disappearing" or severely disturbed ionospheres characterized by deep, widespread plasma depletions in almost the entire nightside. This paper reexamines the holes and "disappearing ionospheres" and other characteristics of the nightside ionosphere during solar maximum using a more extensive database than earlier studies. The hole locations, occurrences, and dependencies on solar wind dynamic pressure (Psw) are analyzed, and a comparison is made with earlier studies. It is shown that there is no Psw threshold for holes to occur and at Psw values greater than 9 nPa, hole occurrence decreases while the occurrence of severely disturbed orbits increases, suggesting that holes may evolve into severely disturbed orbits. Other characteristics of the nightside are shown to be influenced by solar wind pressure to varying degrees; for example, the density integrated along the orbit path below the ionopause, and the median density at low altitudes exhibit strong inverse correlation with Psw, while the peak density is nearly independent of Psw.

Hoegy, Walter R.; Grebowsky, Joseph M.

2010-12-01

305

Two-dimensional ionospheric flow pattern associated with auroral streamers  

NASA Astrophysics Data System (ADS)

We present direct two-dimensional flow observations and auroral images from the Super Dual Auroral Radar Network (SuperDARN) radar and Wideband Imaging Camera onboard Imager for Magnetopause-to-Aurora Global Exploration (IMAGE/WIC) imager to investigate the ionospheric flow pattern associated with auroral streamers for four events. Using the SuperDARN observations allows us to observe the flow associated with the streamers in the context of the larger-scale background convection. For all four cases studied, streamers developed from preexisting east-west (EW) arcs that initiated from bead-like or small-scale auroral intensifications around the auroral poleward boundary. We find a vortex-like flow pattern with clockwise sense surrounding both the initial auroral forms and the ensuing streamers. We also found in three cases signatures of flow bifurcations at the equatorward end of the streamers, which suggests a double vortex-like flow pattern with the counterclockwise vortex east of the clockwise one. Our results are consistent with the double-vortex flow structure that results from interchange convection associated with a plasma sheet bubble predicted by different numerical simulations. This supports several previous studies and offers more complete observational evidence that the observed flow pattern may be the ionospheric manifestation of interchange instability in the plasma sheet.

Shi, Yong; Zesta, Eftyhia; Lyons, Larry R.; Yang, J.; Boudouridis, A.; Ge, Y. S.; Ruohoniemi, J. M.; Mende, S.

2012-02-01

306

DMSP observations of equatorial plasma bubbles in the topside ionosphere near solar maximum  

Microsoft Academic Search

The Defense Meteorological Satellite Program (DMSP) flights F9 and F10 crossed postsunset local time sectors approximately 14 times per day in Sun-synchronous orbits at an altitude of ~840 km. We have examined a large database of postsunset plasma density measurements acquired during ~15,000 equatorial crossings made by DMSP F9 in 1989 and 1991 and DMSP F10 in 1991. On 2086

C. Y. Huang; W. J. Burke; J. S. Machuzak; L. C. Gentile; P. J. Sultan

2001-01-01

307

Hybrid Description of Outflowing Ionospheric Plasma: A Monte Carlo\\/n-Moment Transport Equations Model  

Microsoft Academic Search

At terrestrial high latitudes, the plasma flows along ``open'' field lines, gradually going from a collision-dominated region into a collisionless region. Over several decades, the (fluid-like) generalized transport equations, TE, and the particle-based Monte Carlo, MC, approaches evolved as two of the most powerful simulation techniques that address this problem. In contrast to the computationally intensive Monte Carlo, the transport

J. Ji; A. R. Barakat; R. W. Schunk

2009-01-01

308

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

NASA Astrophysics Data System (ADS)

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.; Mirza, Arshad M.

2010-11-01

309

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

310

A case study of plasma structure in the dusk sector associated with enhanced magnetospheric convection  

SciTech Connect

In a case study from June 8-9, 1982, data from ground whistler stations Siple and Halley, Antarctica, located at L {approximately}4.3 and spaced by {approximately}2 hours in MLT, and from satellites De 1 and GEOS 2, have provided confirming evidence that the bulge region of the magnetosphere can exhibit an abrupt westward edge, as reported earlier from whistlers. The present data and previous MHD modeling work suggest that this distinctive feature develops during periods of steady or declining substorm activity, when dense plasma previously carried sunward under the influence of enhanced convection activity begins to rotate with the Earth at angular velocities that decrease with increasing L value and becomes spiral like in form. For the first time, whistler data have been used to identify a narrow dense plasma feature, separated from the main plasmasphere and extending sunward into the late afternoon sector at L values near the outer observed limits of the main plasmasphere bulge. The westward edge of the main bulge, found by both whistler stations to be at {approximately}180 MLT, appeared to be quasi-stationary in Sun-Earth coordinates during the prevailing conditions of gradually declining geomagnetic agitation. It is possible that outlying dense plasma features such as the one observed develop as part of the process leading to the occurrence of the more readily detectable abrupt westward edge of the bulge. It was no possible in this case to determine the extent to which the outlying feature was smoothly attached to or isolated from the main bulge region.

Carpenter, D.L. (Stanford Univ., CA (United States)); Smith, A.J. (Natural Research Council, Cambridge (United Kingdom)); Giles, B.L.; Chappel, C.R. (NASA Marshall Space Flight Center, Huntsville, AL (United States)); Decreau, P.M.E. (Centre National de la Recherche Scientifique, Orleans (France))

1992-02-01

311

Role of Time-Varying Convection Electric Field on the Fine Structure in Cold Plasma Density Outside the Plasmapause  

NASA Astrophysics Data System (ADS)

Among the long-established, but not quite understood, features of plasmaspheric morphology is the frequent presence of very fine cold particle density structures observed on radial cuts in the vicinity of the plasmapause by the OGO-5 spacecraft. This observed fine structure in the cold plasma density just outside the plasmapause has been tentatively linked to time-varying convection electric field effects. However, to date, no modeling efforts have reproduced the fine structure in the observed in situ density profiles. We present the results of a modeling study performed to investigate if realistic time-varying electric and magnetic fields can account for the observed density structuring. We use the Rice Convection Model (RCM) together with a time-dependent magnetic field to compute convection electric fields for a period of a few days prior to the selected OGO-5 events. The model-computed convection electric field varies with observed geophysical parameters over the period of simulation, and includes such realistic features such as shielding of the inner magnetosphere by region-2 Birkeland currents, subauroral polarization streams, etc. After computing the time history of the electric field we use a test particle approach to trace particles in time-dependent electric and magnetic fields to reconstruct predicted cold plasma density along the OGO-5 orbit, and compare the predicted densities with the observed values. We discuss whether the computed time-varying electric field is sufficient to account for measured density structuring, or whether additional processes are required to explain observations.

Sazykin, S.; Spiro, R. W.; Wolf, R. A.

2011-12-01

312

Ionosphere of venus: first observations of the effects of dynamics on the dayside ion composition.  

PubMed

Bennett radio-frequency ion mass spectrometers have returned the first in situ measurements of the Venus dayside ion composition, including evidence of pronounced structural variability resulting from a dynamic interaction with the solar wind. The ionospheric envelope, dominated above 200 kilometers by O(+), responds dramatically to variations in the solar wind pressure, Which is observed to compress the thermal ion distributions from heights as great as 1800 kilometers inward to 280 kilometers. At the thermal ion boundary, or ionopause, the ambient ions are swept away by the solar wind, such that a zone of accelerated suprathermnal plasma is encountered. At higher altitudes, extending outward on some orbits for thousands of kilometers to the bows shock, energetic ion currents are detected, apparently originating from the shocked solar wind plasma. Within the ionosphere, observations of pass-to-pass differences in the ion scale heights are indicative of the effects of ion convection stimlulated by the solar wind interaction. PMID:17832986

Taylor, H A; Brinton, H C; Bauer, S J; Hartle, R E; Cloutier, P A; Michel, F C; Daniell, R E; Donahue, T M; Maehl, R C

1979-02-23

313

Observations of DC electric fields in the low-latitude ionosphere and their variations with local time, longitude, and plasma density during extreme solar minimum  

NASA Astrophysics Data System (ADS)

DC electric fields and associated E B plasma drifts detected with the double-probe experiment on the C/NOFS satellite during extreme solar minimum conditions near the June 2008 solstice are shown to be highly variable, with weak to moderate ambient amplitudes of 1-2 mV/m (25-50 m/s). Average field or drift patterns show similarities to those reported for more active solar conditions, i.e., eastward and outward during day and westward and inward at night. However, these patterns vary significantly with longitude and are not always present. Daytime vertical drifts near the magnetic equator are largest in the prenoon sector. Observations of weak to nonexistent prereversal enhancements in the vertical drifts near sunset are attributable to reduced dynamo activity during solar minimum as well as seasonal effects. Enhanced meridional drifts are observed near sunrise in certain longitude regions, precisely where the enhanced eastward flow that persisted from earlier local times terminates. The nightside ionosphere is characterized by larger-amplitude, structured electric fields dominated by horizontal scales of 500-1500 km even where local plasma densities appear relatively undisturbed. Data acquired during successive orbits indicate that plasma drifts and densities are persistently organized by longitude. The high duty cycle of the C/NOFS observations and its unique orbit promise to expose new physics of the low-latitude ionosphere.

Pfaff, R.; Rowland, D.; Freudenreich, H.; Bromund, K.; Le, G.; AcuA, M.; Klenzing, J.; Liebrecht, C.; Martin, S.; Burke, W. J.; Maynard, N. C.; Hunton, D. E.; Roddy, P. A.; Ballenthin, J. O.; Wilson, G. R.

2010-12-01

314

The two-stream plasma instability in a velocity shear and its role in the solar wind-Venus ionosphere interaction  

NASA Astrophysics Data System (ADS)

We study the linear development of the two-stream instability in a plasma consisting of cold ions, assumed at rest and taken to represent planetary ions, and a hot, streaming population of electrons, representing the solar wind. The stability of quasi-global perturbations is analyzed as a function of plasma density, temperature and streaming velocity, using a QR algorithm to compute the growth rate of eigenmodes of the coupled fluid equations of motion for both species. The sense of the cross-flow, viscous-like momentum transfer from the streaming plasma to ionospheric ions, is determined on the basis of an heuristic estimation following a Reynolds averaging procedure of the cross-flow momentum flux term in the equation of motion.

Reyes-Ruiz, M.; Aceves, H.; Perez De Tejada, H. A.

2011-12-01

315

A modelling study of the latitudinal variations in the nighttime plasma temperatures of the equatorial topside ionosphere during northern winter at solar maximum  

NASA Astrophysics Data System (ADS)

Latitudinal variations in the nighttime plasma temperatures of the equatorial topside ionosphere during northern winter at solar maximum have been examined by using values modelled by SUPIM (Sheffield University Plasmasphere Ionosphere Model) and observations made by the DMSP F10 satellite at 21.00 LT near 800 km altitude. The modelled values confirm that the crests observed near 15 latitude in the winter hemisphere are due to adiabatic heating and the troughs observed near the magnetic equator are due to adiabatic cooling as plasma is transported along the magnetic field lines from the summer hemisphere to the winter hemisphere. The modelled values also confirm that the interhemispheric plasma transport needed to produce the required adiabatic heating/cooling can be induced by F-region neutral winds. It is shown that the longitudinal variations in the observed troughs and crests arise mainly from the longitudinal variations in the magnetic meridional wind. At longitudes where the magnetic declination angle is positive the eastward geographic zonal wind combines with the northward (summer hemisphere to winter hemisphere) geographic meridional wind to enhance the northward magnetic meridional wind. This leads to deeper troughs and enhanced crests. At longitudes where the magnetic declination angle is negative the eastward geographic zonal wind opposes the northward geographic meridional wind and the trough depth and crest values are reduced. The characteristic features of the troughs and crests depend, in a complicated manner, on the field-aligned flow of plasma, thermal conduction, and inter-gas heat transfer. At the latitudes of the troughs/crests, the low/high plasma temperatures lead to increased/decreased plasma concentrations.

Bailey, G. J.; Denton, M. H.; Heelis, R. A.; Venkatraman, S.

2000-11-01

316

Nonlinearly generated plasma waves as a model for enhanced ion acoustic lines in the ionosphere  

NASA Astrophysics Data System (ADS)

Observations from the EISCAT Svalbard Radar, for instance, demonstrate that the symmetry of the naturally occurring ion line can be broken by an enhanced, non-thermal, level of fluctuations, i.e., Naturally Enhanced Ion-Acoustic Lines (NEIALs). In a significant number of cases, the entire ion spectrum can be distorted, with the appearance of a third line, corresponding to a propagation velocity significantly below the ion acoustic sound speed. By numerical simulations, we consider one possible model accounting for the observations, suggesting that a primary process can be electron acoustic waves excited by a cold electron beam. Subsequently, an oscillating two-stream instability excites electron plasma waves which in turn decay to asymmetric ion lines. Our code solves the full Vlasov equation for electrons and ions, with the dynamics coupled through the electrostatic field derived from Poisson's equation.

Daldorff, L. K. S.; Pcseli, H. L.; Trulsen, J.

2007-09-01

317

Comparison of topside electron density computed by ionospheric models and plasma density observed by DMSP satellites  

NASA Astrophysics Data System (ADS)

Electron density obtained by IRI (topside options NeQuick and IRI-Corr) and NeQuick models in their standard versions have been compared with plasma density values measured by F13 and F15 DMSP satellites for years of different solar activities. A statistical study of the differences between modeled and experimental data has been carried out to investigate each model performance.In general, the models present a similar behavior. Nevertheless it has been found that the IRI-Corr topside option of IRI overestimates electron density at high latitudes and this trend increases with the solar activity.A few examples of representative half-orbit passes are given to illustrate the differences found.

Migoya-Orue, Y. O.; Radicella, S. M.; Nava, B.

2013-11-01

318

Magnetospheric electric fields and plasma sheet injection to low L-shells during the 45 June 1991 magnetic storm: Comparison between the Rice Convection Model and observations  

Microsoft Academic Search

The major magnetic storm of 45 June 1991 was well observed with the Combined Release and Radiation Experiment (CRRES) satellite in the duskside inner magnetosphere and with three Defense Meteorological Satellite Program (DMSP) spacecraft in the polar ionosphere. These observations are compared to results from the Rice Convection Model (RCM), which calculates the inner magnetospheric electric field and particle distribution

T. W. Garner; R. A. Wolf; R. W. Spiro; W. J. Burke; B. G. Fejer; S. Sazykin; J. L. Roeder; M. R. Hairston

2004-01-01

319

Empirical models for the plasma convection at high latitudes from Millstone Hill observations  

NASA Astrophysics Data System (ADS)

Since 1978, radar observations of F region electric fields within the region of Lambda between 55 and 75 deg have been made from Millstone Hill (42.6 deg N, 71.5 deg W). Average convection patterns have been calculated from the ion drift data gathered in 109 of these experiments conducted between January 1978 and August 1981. Most of the experiments lasted between 24 and 48 hours, and over 3,700,000 values of the line-of-sight velocity were determined and included in the averages. The observed velocities were sorted into 'bins' of 1/2-hour intervals of magnetic local time and 2-deg intervals of apex latitude. Each of these cells had been viewed by the radar over a wide range of aspect angles in the course of the 109 experiments, allowing the average vector velocity to be determined. The data were separated further into three levels of Kp, according to whether the interplanetary magnetic field (IMF) was 'toward' or 'away' from the sun, and by season. The average patterns are discussed and compared with earlier models based on satellite and incoherent scatter data. There is an expansion and intensification of the pattern with Kp for all seasons and IMF orientations. The polar cap entry and exit points of the plasma, the center of the cells, and the polar cap boundary all depend on the IMF. The Harang discontinuity, which can be seen clearly on individual days, is largely lost in the averages.

Holt, J. M.; Wand, R. H.; Evans, J. V.; Oliver, W. L.

1987-01-01

320

Innovative development and application of models for weakly ionized ionospheric plasmas. Final report, 15 May 1990-30 November 1993  

SciTech Connect

Artificial modifications of the ionosphere through chemical releases and ionospheric heating experiments are examined with models of chemistry and transport to advance understanding of ion chemistry of the upper atmosphere. The specific releases investigated were the SF6 released of the CRRES-at-Kwajalein rocket campaign and the CO2 releases of the Red Air I program. Both the SF6 and CO2 releases experienced freezing or clustering of the molecules. This must be accounted for in the composition and airglow observations. In addition, HF heating effects in the E and F region were examined through modeling of energy deposition and resulting chemistry. NO sub x production in a HF ionospheric heater beam is estimated and compared with natural sources of NO sub x. Global effects of HF operation are very small but the local effects can be large enough to permit observable modulation to this environment.

Eccles, J.V.; Hingst, J.; Armstrong, R.

1993-11-01

321

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

322

Magnetospheric disturbances associated with the 13 December 2006 solar flare and their ionospheric effects over North-East Asia  

NASA Astrophysics Data System (ADS)

We present an observational study of magnetospheric and ionospheric disturbances during the December 2006 intense magnetic storm associated with the 4?/?3.4 class solar flare. To perform the study we utilize the ground data from North-East Asian ionospheric and magnetic observatories (60-72N, 88-152E) and in situ measurements from LANL, GOES, Geotail and ACE satellites. The comparative analysis of ionospheric, magnetospheric and heliospheric disturbances shows that the interaction of the magnetosphere with heavily compressed solar wind and interplanetary magnetic field caused the initial phase of the magnetic storm. It was accompanied by the intense sporadic E and F2 layers and the total black-out in the nocturnal subauroral ionosphere. During the storm main phase, LANL-97A, LANL 1994_084, LANL 1989-046 and GOES_11 satellites registered a compression of the dayside magnetosphere up to their orbits. In the morning-noon sector the compression was accompanied by an absence of reflections from ionosphere over subauroral ionospheric station Zhigansk (66.8N, 123.3E), and a drastic decrease in the F2 layer critical frequency (foF2) up to 54% of the quite one over subauroral Yakutsk station (62N, 129.7E). At the end of the main phase, these stations registered a sharp foF2 increase in the afternoon sector. At Yakutsk the peak foF2 was 1.9 time higher than the undisturbed one. The mentioned ionospheric disturbances occurred simultaneously with changes in the temperature, density and temperature anisotropy of particles at geosynchronous orbit, registered by the LANL-97A satellite nearby the meridian of ionospheric and magnetic measurements. The whole complex of disturbances may be caused by radial displacement of the main magnetospheric domains (magnetopause, cusp/cleft, plasma sheet) with respect to the observation points, caused by changes in the solar wind dynamic pressure, the field of magnetospheric convection, and rotation of the Earth.

Zolotukhina, N.; Polekh, N.; Kurkin, V.; Pirog, O.; Samsonov, S.; Moiseyev, A.

2012-03-01

323

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

324

Ionospheric streams at altitudes below 14RE  

NASA Astrophysics Data System (ADS)

The properties of ionospheric ion streams flowing away from Earth into the magnetotail between 2 Re and 14 Re are studied from ISEE-2 data. General agreement between these observations and those at lower and larger distances is found, indicating that the plasma sheet is enriched with ionospheric ions at all distances.

Orsini, S.; Candidi, M.

1985-09-01

325

The high-latitude ionosphere: Geophysical basis  

NASA Astrophysics Data System (ADS)

This introductory lecture summarizes concepts of the ionosphere and the magnetosphere that are fundamental to our understanding of high-latitude ionosphere. It begins with the basic theory of the ionosphere, particularly the processes of production and loss which lead to the existence of a permanent ionosphere and render the upper atmosphere electrically conducting. The structure of the magnetosphere, which strongly affects the polar regions because of coupling along the geomagnetic field lines, is then reviewed, including the form of the magnetosphere, and the plasma and energetic particles that are contained within the magnetosphere.

Hargreaves, J. K.

1988-09-01

326

Persistent Longitudinal Variations of Plasma Density and DC Electric Fields in the Low Latitude Ionosphere Observed with Probes on the C/NOFS Satellite  

NASA Astrophysics Data System (ADS)

Continuous measurements using in situ probes on consecutive orbits of the C/NOFS 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. F.; Freudenreich, H.; Klenzing, J. H.; Rowland, D. E.; Liebrecht, M. C.; Bromund, K. R.; Roddy, P. A.

2010-12-01

327

Effects of natural convection on the characteristics of long laminar argon plasma jets issuing upwards or downwards into ambient air---a numerical study  

Microsoft Academic Search

A modelling study has been performed on the effect of natural convection on the characteristics of a long laminar argon plasma jet issuing into ambient air. In this study the plasma jet is taken to be flowing vertically upwards or downwards, and the combined diffusion coefficient method has been used to treat the diffusion of ambient air into the argon

Kai Cheng; Xi Chen

2004-01-01

328

Attenuation of radio signals by the ionosphere of Mars: Theoretical development and application to MARSIS observations  

Microsoft Academic Search

We investigate the ionospheric conditions required to explain Mars Express Mars Advanced Radar for Subsurface and Ionosphere Sounding topside radar sounder observations of ionospheric attenuation in excess of 13 dB at 5 MHz during solar energetic particle events. We develop theoretical expressions for the attenuation caused by a layer of ionospheric plasma in cases of high, intermediate, and low radio

Paul Withers

2011-01-01

329

Historical overview of HF ionospheric modification research  

SciTech Connect

Radio waves have inadvertently modified the Earth's ionosphere since the Luxembourg observations of Tellegen in 1933 and perhaps since Marconi in 1901. The history of ionospheric modification by radio waves is reviewed, beginning with Marconi, describing the Luxembourg effect and its explanations, and its early use to deduce the properties of the lower ionosphere in the 1930s. The measurements became more sophisticated in the 1950s, leading to the call for high-power high-frequency modification experiments in the upper ionosphere. Beginning in 1970, radio facilities became available of sufficient powers to induce changes in the ionospheric plasma detectable by a wide array of diagnostic instruments and techniques. A summary of these effects is presented based upon work up to 1990. These studies were originally motivated as a means of better understanding the natural ionosphere using a weak perturbational approach. However, a rich spectrum of nonlinear wave-plasma interactions was quickly discovered and ionospheric modification research became strongly motivated by issues in basic plasma physics. The ionosphere and near-Earth space are now exploited as an exceptional plasma laboratory-without-walls for the study of fundamental plasma processes requiring large spatial or temporal scales. Here we present a brief overview of these processes and phenomena, illustrated using results obtained from the Arecibo ionospheric modification facilities. The lessons learned and phenomena explored thus far offer many opportunities for controlling the ionospheric environment critical to many civilian and military telecommunications systems, both to disrupt systems normally operational and to create new propagation paths otherwise unavailable.

Gordon, W.E.; Duncan, L.M.

1990-10-01

330

Some results of measuring the characteristics of electromagnetic and plasma disturbances stimulated in the outer ionosphere by high-power high-frequency radio emission from the ``Sura'' facility  

NASA Astrophysics Data System (ADS)

We present the results of measuring the characteristics of electromagnetic and plasma disturbances at altitudes of about 700 km, obtained by using the onboard equipment of the French microsatellite DEMETER during its passage through the magnetic tube resting upon the region of intense generation of artificial ionospheric turbulence created due to modification of the ionospheric F2 region by high-power radio emission from the Sura facility. It is shown that an artificial density duct emerging from the disturbed region and extending to the Earths magnetosphere can be formed.

Rapoport, V. O.; Frolov, V. L.; Komrakov, G. P.; Markov, G. A.; Belov, A. S.; Parrot, M.; Rauch, J. L.

2007-08-01

331

A test of the magnetospheric source of traveling convection vortices  

NASA Astrophysics Data System (ADS)

Traveling convection vortices (TCVs) are a powerful tool for probing the nature of the coupling between the solar wind, the magnetosphere, and the ionosphere. There is no reliable model of the plasma concentration in the magnetosphere, resulting in uncertainties about the factors controlling the scale size, the motion, and the numbers of field-aligned currents associated with TCV events. There is also uncertainty about whether TCV generation is current driven, voltage driven, or even driven by some more complex source. We use conjugate ground-based magnetometer data from the Greenland magnetometer chain and Antarctica to test the nature of the magnetospheric source of 18 TCV events associated with changes in the magnetopause dynamic pressure. This is achieved by statistically comparing two groups of TCV events: for one group the conjugate ionospheres are of similar conductivity, and for the other group the conductivities of the conjugate ionospheres differ by an order of magnitude. Statistically, we find that conjugate TCV events are of similar intensity in both hemispheres regardless of any difference in conductivity between the two hemispheres. We propose that this is evidence in favor of a constant current source for TCVs where the amplitude of a TCV is controlled by the local plasma concentration, the magnetic field strength, and the acceleration of the plasma.

Lam, M. M.; Rodger, A. S.

2004-02-01

332

C\\/NOFS satellite observations of equatorial ionospheric plasma structures supported by multiple ground-based diagnostics in October 2008  

Microsoft Academic Search

In early October 2008, the C\\/NOFS satellite orbited near the magnetic equator at its perigee altitude of 400 km at dusk in the Peruvian sector. This provided an ideal opportunity for a comparison, under the current very low solar flux condition, of equatorial ionospheric disturbances observed with the Communication\\/Navigation Outage Forecasting System (C\\/NOFS) in situ measurements and ground-based observations available

M. Nishioka; Su. Basu; C. E. Valladares; R. E. Sheehan; P. A. Roddy; K. M. Groves

2011-01-01

333

Global Observations of Flux Transfer Events and Their Effects on the Magnetosphere-Ionosphere System.  

NASA Astrophysics Data System (ADS)

Multi-instrument observations of the magnetosphere reveal the nature of direct coupling in the solar wind-magnetosphere-ionosphere system, namely dayside reconnection. A case study during which there was a highly favourable conjunction of an extensive array of spacebourne and ground-based instruments offered an excellent opportunity to study magnetic reconnection in situ, as well as its effects on the magnetosphere and ionosphere. Flux transfer events were observed by Geotail during an extended traversal of the dawn magnetopause. Extensive coverage of the entire dayside high-latitude ionosphere was achieved by all of the northern hemisphere SuperDARN radars, and accurate solar wind time delays were possible due to the position of the IMP8 spacecraft immediately upstream of the Earth's bow shock. The SuperDARN radars in the dawn sector, in the vicinity of Geotail's magnetic footprint, measured temporally varying convection velocities. Low-altitude satellites monitored both the size of the auroral oval and particle precipitation in the cusp footprint. Energy-dispersed cusp ions were detected by the DMSP-F11 spacecraft at the same time that an FTE was measured by the magnetically conjugate Geotail. Analysis of the field and plasma data at Geotail reveals details of the structure and motion of the newly reconnected flux tubes as they convected past the spacecraft. The implied location of magnetopause reconnection will be discussed.

McWilliams, K. A.; Yeoman, T. K.; Sibeck, D. G.; Milan, S. E.; Sofko, G. J.; Nagai, T.; Mukai, T.; Hori, T.

2002-12-01

334

Modeling Ionospheric Outflows In Global Models (Invited)  

NASA Astrophysics Data System (ADS)

The magnetosphere contains a significant amount of ionospheric O+, particularly during geomagnetically active times. The presence of this ionospheric plasma has a notable impact on magnetospheric composition and processes. We present our methodology for including an ionospheric mass source into global models, and for tracking the consequences for the space environment system. An overview of our recent efforts is provided. In particular, we illustrate the effect that plasma of ionospheric origin can have on the magnetosphere by simulating extreme geospace events when the fraction of O+ is largest, and contrast those results with simulations of more moderate events. We also compare different techniques of modeling/tracking ionospheric outflow, and explore the implications for the storm-time ring current and magnetospheric magnetic field configuration.

Glocer, A.; Toth, G.; Fok, M. H.; Gombosi, T. I.; Welling, D. T.

2010-12-01

335

Planetary Ionospheres  

NASA Astrophysics Data System (ADS)

Most planets and many satellites in our solar system are surrounded by envelopes of gravitationally bound gases. The interaction of solar radiation and charged particles of solar wind and planetary magnetospheric origin with these gases produces weak IONIZATION that creates planetary ionospheres embedded within the more dense PLANETARY ATMOSPHERES. Additional sources of ionization which are relat...

Strobel, D.; Murdin, P.

2000-11-01

336

Ionosphere dynamics  

Microsoft Academic Search

Early studies of the ionosphere assumed that isoionic surfaces were substantially horizontal and smooth, and diurnal, seasonal and sunspot variations were worked out on that basis. In recent years, the attention of research workers has turned more and more to the study of irregularities and movements in ionization. Irregularities examined range in size from the order of hundreds of kilometers

G. H. Munro; L. H. Heisler

1963-01-01

337

Formation of the theta aurora by a transient convection during northward interplanetary magnetic field  

NASA Astrophysics Data System (ADS)

Formation of the theta aurora, which appears under the conditions of northward interplanetary magnetic field (IMF) and greater IMF magnitude, is investigated from the analysis of solutions obtained from a magnetohydrodynamic (MHD) simulation. The theta aurora formation is caused by a transient convection after a sign change of IMF By. This transient convection must include a replacement of lobe field lines from old IMF originating fields to new IMF originating fields, a rotation of plasma sheet to opposite inclination, and a reformation of ionospheric convection cells. In the midst of these reconfigurations, old and new convection systems must coexist in the magnetosphere-ionosphere system. In this stage the polar cap and tail lobes are continuously encroached by the new open field lines connected to the new IMF. Whereas magnetic field lines accumulated in new lobes tend to rotate the outer plasma sheet in the opposite direction, the old merging-cell convection still continues to generate closed field lines that must return to dayside against the new lobe formation. As time goes on, the growth of new lobes results in the blocking of the return path toward the dayside of closed field lines generated in the old merging cell to form the kink structure in the plasma sheet. Losing their return path, these closed field lines generated from old lobes accumulate on the nightside. The transpolar arc (TPA) appears at the footpoints of these accumulated closed field lines. In the tail plasma sheet the cross-tail Z configuration and kink structures are generated because the plasma sheet near the magnetopause is rotated to the opposite direction while the core part is retaining old rotation.

Tanaka, T.; Obara, T.; Kunitake, M.

2004-09-01

338

Strong turbulence effects in artificially disturbed ionosphere  

NASA Astrophysics Data System (ADS)

The theoretical and experimental study of strong turbulence effects arising in the ionospheric plasma under the action of powerful radio waves is presented. The theoretical results are obtained by the numerical solution of nonlinear Schrdinger equation (NSE) with driven extension in inhomogeneous plasma, the experimental ones by means of artificial ionospheric turbulence sounding by probing radio pulses. The qualitative agreement of theoretical and experimental results is obtained.

Kochetov, A. V.; Mironov, V. A.; Terina, G. I.

339

Effects of ionospheric oxygen on magnetospheric structure and dynamics  

NASA Astrophysics Data System (ADS)

During geomagnetically active times, ionospheric O + can contribute a significant fraction of the magnetospheric mass and energy densities. The global response of Earth's magnetosphere to the presence of ionospheric oxygen is still largely unknown and impossible to examine fully with in situ, single point satellite measurements. Global magnetohydrodynamic (MHD) models provide a picture of this large-scale response to ionospheric outflow. The goal of this dissertation is to examine the behavior and effects of outflowing oxygen in a multi-fluid MHD model by determining (1) how O+ outflow from different regions of the ionosphere contributes to plasma sheet populations and (2) the effect of these oxygen populations on convection and global magnetospheric structure. I implement two empirical outflow models at the inner boundary of the recently-developed Multi-Fluid Lyon-Fedder-Mobarry MHD code and examine the response of the model to various outflow conditions. A model based on data from the Akebono spacecraft (Ebihara et al., 2006) provides a low-energy polar and auroral region outflow, whereas a model based on data from the FAST spacecraft (Strangeway et al., 2005) provides higher-energy outflow confined to the auroral regions. Using the Akebono model outflow, I show that both centrifugal acceleration and pressure gradients accelerate thermal O+ along the magnetic field into the plasma sheet and downtail into the solar wind. I examine O+ and H + plasma sheet populations for different outflow and solar wind conditions. To account for observed densities, nightside outflows must be augmented by polar wind, cusp outflows, or both. O+ outflow in general, and nightside outflow in particular, loads the plasma sheet with O +, inflating the plasma sheet, increasing the width of the tail and distance to the tail x-line, and reducing cross polar cap potential (CPCP). These effects are shown to relate to the width of the magnetosheath, indicating that the reduction in CPCP may be due to changes in the bow shock and magnetosheath that divert the solar wind around the magnetosphere. Finally, I show that during a realistic substorm simulation, the timing and strength of substorms are changed by a global O+ outflow.

Garcia-Sage, Katherine

340

Two-dimensional Ionospheric Flow Pattern Associated with Auroral Streamers  

NASA Astrophysics Data System (ADS)

We present direct flow observations and auroral images from the SuperDARN radar and IMAGE WIC imager to investigate the ionospheric flow pattern associated with auroral streamers. For all four cases studied, streamers were ejected from east-west (EW) arcs that initiated from bead-like or small-scale auroral intensifications around the auroral poleward boundary. We find a vortex-like flow pattern with clockwise sense surrounding both the initial auroral forms and the ensuing streamers. The initial eastward flows poleward of the auroral forms and westward flows equatorward of the forms evolved to be roughly equatorward within and to the east of the streamers, and primarily poleward or toward a more poleward direction to the west of the streamers. We also found in three cases signatures of flow bifurcations at the equatorward end of the streamers, which suggests a double vortex-like flow pattern with the counterclockwise one further east of the clockwise one. Our results are consistent with the double-vortex flow structure due to interchange convection associated with a plasma sheet bubble predicted by different numerical simulations, and also provide solid evidence to several previous studies, especially Sergeev et al. [2004]. This indicates that the observed flow pattern may be the ionospheric manifestation of interchange instability in the plasma sheet.

Shi, Y.; Zesta, E.; Lyons, L. R.; Yang, J.; Boudouridis, A.; Ge, Y. S.; Ruohoniemi, J. M.; Mende, S. B.

2011-12-01

341

Theoretical study of the lifetime and transport of large ionospheric density structures  

SciTech Connect

Large-scale density structures are a common feature in the high-latitude ionosphere. They have been observed in the dayside cusp, polar cap, and nocturnal auroral region. Relative to background densities, the perturbations associated with large-scale structures vary from about 10% to a factor of 100. The lifetime and transport characteristics of ''large'' ionospheric structures (factor of 10 to 100) were studied with the aid of a three-dimensional time-dependent ionospheric model. Both density depletions and enhancements were considered. A density structure was created at a specific location in the high latitude F region and the subsequent evolution was followed for different seasonal and solar cycle conditions as well as for different orientations of the interplanetary magnetic field (IMF), i.e., different convection patterns. Depending on the IMF, horizontal plasma convection can cause an initial structure to break up into multiple structures of various sizes, remain as a single distorted structure, or become stretched into elongated segments. The lifetime of an F region density structure depends on several factors, Including the initial location where it was formed, the magnitude of the structure, season, solar cycle, and covection pattern (IMF). For example, in summer the effects of a large density structure can disappear in a few hours or last as long as 9 hours, while in winter the effects can persist for 24 hours. The passage of perturbed plasma flux tubes through sunlit and auroral regions can significantly increase the lifetime of plasma enhancements and can significantly reduce the lifetime of plasma depletions. copyright American Geophysical Union 1987

Schunk, R.W.; Sojka, J.J.

1987-11-01

342

Magnetosphere-ionosphere coupling during plasmoid evolution: First results  

SciTech Connect

The influence of magnetosphere-ionosphere coupling on the dynamic evolution of the magnetotail is investigated by a three-dimensional resistive MHD code that includes the effects of the closure of field-aligned currents in a simple resistive model ionosphere. Particular emphasis is on the role of this coupling during substorm evolution and the modification of the latter by the convection driven by the ionospheric electric fields. For comparison, the authors present results from a simulation which uses an infinitely conducting ionosphere but is otherwise identical. Comparison of the two simulations shows that the major impact of magnetosphere-ionosphere communication is an acceleration of magnetotail evolution. Otherwise, phenomena in the two models are qualitatively similar. They conclude that ionospheric effects do not significantly affect substorm associated magnetotail dynamics.

Hesse, M.; Birn, J. (Los Alamos National Lab., NM (USA))

1991-07-01

343

Global aspects of solar windionosphere interactions  

Microsoft Academic Search

Recent observations have quantified the auroral wind O+ outflow in response to magnetospheric inputs to the ionosphere, notably Poynting energy flux and precipitating electron density. For moderate to high activity periods, ionospheric O+ is observed to become a significant or dominant component of plasma pressure in the inner plasma sheet and ring current regions. Using a global circulation model of

T. E. Moore; M.-C. Fok; D. C. Delcourt; S. P. Slinker; J. A. Fedder

2007-01-01

344

Effect of an MLT dependent electron loss rate on the magnetosphere-ionosphere coupling  

NASA Astrophysics Data System (ADS)

As plasma sheet electrons drift earthward, they get scattered into the loss cone due to wave-particle interactions and the resulting precipitation produces auroral conductance. Realistic electron loss is thus important for modeling the magnetosphere - ionosphere (M-I) coupling and the degree of plasma sheet electron penetration into the inner magnetosphere. In order to evaluate the significance of electron loss, we used the Rice Convection Model (RCM) coupled with a force-balanced magnetic field to simulate plasma sheet transport under different electron loss rates and under self-consistent electric and magnetic field. We used different magnitudes of i) strong pitch angle diffusion everywhere electron loss rate (strong rate) and ii) a more realistic loss rate with its MLT dependence determined by wave activity (MLT rate). We found that electron pressure under the MLT rate is larger compared to the strong rate inside L ? 12 RE. The dawn-dusk asymmetry in the precipitating electron energy flux under the MLT rate, with much higher energy flux at dawn than at dusk, agrees better with statistical DMSP observations. High-energy electrons inside L ? 8 RE can remain there for many hours under the MLT rate, while those under the strong rate get lost within minutes. Under the MLT rate, the remaining electrons cause higher conductance at lower latitudes; thus after a convection enhancement, the shielding of the convection electric field is less efficient, and as a result, the ion plasma sheet penetrates further earthward into the inner magnetosphere than under the strong rate.

Gkioulidou, Matina; Wang, Chih-Ping; Wing, Simon; Lyons, Larry R.; Wolf, Richard A.; Hsu, Tung-Shin

2012-11-01

345

A simple model of flows and currents in Saturn's polar ionosphere  

NASA Astrophysics Data System (ADS)

We propose a simple model of the flow and currents in Saturn's polar ionosphere which is motivated by theoretical reasoning, but is quantitatively guided by field and flow data from previous fly-by missions, by more recent data from the Cassini approach phase, and by ground-based IR Doppler measurements. The flow pattern consists of components which are due to plasma sub-corotation in the middle magnetosphere region resulting from plasma pick-up and radial transport from internal sources, and to the Vasyliunas- and Dungey-cycles of convection at higher latitudes. Analytically-expressed representations of these flows are combined with an assumed uniform Pedersen conductivity of the ionosphere to yield patterns of ionospheric Pedersen current, together with the field-aligned current resulting from its divergence. It is shown that a narrow ring of generally upward current surrounds the region of open field lines, which is stronger on the dawn side of the polar cap than at dusk due to the Dungey-cycle flow asymmetry. We associate this current with the 'main oval' auroras at Saturn. Rings of upward and downward current also flow at lower latitudes associated with sub-corotation in the middle magnetosphere. However, the current densities associated with this system are insufficient to require field-aligned acceleration of magnetospheric electrons, so that these currents are not associated with bright auroral ovals, unlike their counterpart at Jupiter.

Jackman, C. M.; Cowley, S. W. H.; Bunce, E. J.

346

Initial results from a dynamic coupled magnetosphere-ionosphere-ring current model  

NASA Astrophysics Data System (ADS)

In this paper 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) and report some results 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-? ? 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.

Pembroke, Asher; Toffoletto, Frank; Sazykin, Stanislav; Wiltberger, Michael; Lyon, John; Merkin, Viacheslav; Schmitt, Peter

2012-02-01

347

The effects of crustal magnetic fields and the pressure balance in the high latitude ionosphere/atmosphere at Mars  

NASA Astrophysics Data System (ADS)

The strongest crustal magnetic fields at Mars are located in certain regions in the Southern hemisphere and lead to the formation of large-scale mini-magnetospheres. In the Northern hemisphere, the crustal fields are rather weak and usually do not prevent direct interaction between the SW and an ionosphere/atmosphere. Exceptions occur in the isolated mini-magnetospheres formed by the crustal anomalies. Electron density profiles derived from radio occultation data obtained by the Radio Science Mars Global Surveyor (MGS) experiment have been compared with the crustal magnetic fields measured by the MGS Magnetometer/Electron reflectometer (MAG/ER) experiment. The effective scale-height of the electron density for two altitude ranges, 145 165 km and 165 185 km have been derived for each of the profiles studied. For the regions outside of the mini-magnetospheres the thermal pressure of the ionospheric plasma for the altitude range 145 185 km has been derived. The pressure balance in the high latitude ionosphere at Mars has been studied. In the Northern hemisphere average pressure at the altitude 160 km p160 is practically independent of SZA. In the Northern hemisphere B2/8? can exceed p160 in half the cases at altitudes 170 180 km, and magnetic forces can drive effective convection. In large scale mini-magnetospheres in the Southern hemisphere the ratio H145 165/H165 185 on average, larger and more variable than in the Northern hemisphere. This suggests that plasma convection at altitudes above 165 km is effective. Within the Martian mini-magnetospheres plasma convection has to be primarily a drift of charged particles across the strong crustal magnetic fields and in this regard Martian mini-magnetospheres are similar to the terrestrial magnetosphere.

Breus, T. K.; Ness, N. F.; Krymskii, A. M.; Crider, D. H.; Acuna, M. H.; Connerney, J. E. P.; Hinson, D.; Barashyan, K. K.

348

Initial results from the coupled magnetosphere ionosphere thermosphere model: magnetospheric and ionospheric responses  

NASA Astrophysics Data System (ADS)

The Center for Integrated Space Weather Modeling (CISM) is developing a simulation package of the coupled Sun-Earth system by connecting existing models within each region. The Coupled Magnetosphere Ionosphere Thermosphere (CMIT) model combines the Lyon-Fedder-Mobarry global magnetohydrodynamic (MHD) magnetospheric (LFM) model with the Thermosphere Ionosphere Nested Grid (TING) model. The LFM uses the ideal MHD equations to model the interaction between the magnetospheric plasma and the solar wind. It includes the magnetosphere-ionosphere interaction by requiring the conservation of current flowing between the magnetosphere and a two dimensional ionosphere. TING is a three dimensional code designed to simulate the thermosphere-ionosphere system by solving the mass, momentum, and thermodynamic energy equations for the global thermosphere and ionosphere. Normally, TING uses parameterized models to describe the magnetospheric input into the ionosphere. We begin this paper with a description of how the TING model is used to replace the simple two dimensional ionosphere within the LFM to produce the CISM CMIT Model. The results from the coupled model for a series of steady IMF conditions are compared with the results from the LFM to show that these models have been successfully combined. The problem of high cross polar cap potentials remains, but the structure of the magnetosphere is not dramatically altered by the coupling and the ionospheric conductances show a more realistic distribution driven by EUV radiation as well as a more clearly defined auroral oval.

Wiltberger, M.; Wang, W.; Burns, A. G.; Solomon, S. C.; Lyon, J. G.; Goodrich, C. C.

2004-10-01

349

Ray trace calculation of ionospheric propagation at lower frequencies  

NASA Astrophysics Data System (ADS)

The Raytrace/Ionospheric Conductivity and Electron Density-Bent-Gallagher model has been revised to make it applicable to ionospheric propagation at low radio frequencies (0.5-5.0 MHz), where the ionosphere and magnetic anisotropy drastically alter propagation paths and provide a severe test of propagation model algorithms. The necessary revisions are discussed, and the model is applied to the problem of ionospheric penetration from a source below the ionosphere to a receiver above the ionosphere. It is necessary to include the electron collision frequency in the Appleton-Hartree index of refraction in order to permit ionospheric penetration for radio frequencies below the maximum plasma frequency (e.g., whistler modes). The associated reformulation of the ray trace equations for a complex index of refraction is straightforward. Difficulties with numerical methods are cited for the lowest frequencies, and future improvements are indicated.

Reilly, Michael H.

2006-10-01

350

Electron temperature and heat flow in the nightside Venus ionosphere  

NASA Astrophysics Data System (ADS)

A steady-state two-dimensional heat balance model is used to analyze the night side Venusian ionospheric electron temperatures given by the Pioneer Venus orbiter electron temperature probe. The energy calculation includes the solar EUV heating at the terminator, electron cooling to ions and neutrals, and heat conduction within the ionospheric plasma. An optimum magnetic field is derived by solving for the heat flux directions which force energy conservation while constrained by the observed temperatures within the range of 80-170 deg solar zenith angle and 160-170 km. The heat flux vectors indicate a magnetic field that connects the lower night side ionosphere to the day side ionosphere, and connects the upper ionosphere to the ionosheath. The lower ionosphere is heated through conduction of heat from the dayside, and the upper ionosphere is heated by the solar wind in the ionosheath with heat flowing downward and from the nightside to the day side.

Hoegy, W. R.; Brace, L. H.; Theis, R. F.; Mayr, H. G.

1980-12-01

351

Konvection (Convection).  

National Technical Information Service (NTIS)

Basic features in possible convection types in microgravity are discussed. Characteristic data are analyzed concerning free and forced convection, thermal convection, Marangoni and b-jitter (time dependent acceleration) convection.

G. S. R. Sarma

1987-01-01

352

Plasma flow reversals at the dayside magnetopause and the origin of the asymmetric polar cap convection  

Microsoft Academic Search

A number of events have been observed in the Los Alamos\\/Garching fast plasma experiment data from ISEE 2 within {plus minus} 3 hours of noon wherein the y component of the plasmas flow within the low latitude boundary layer and magnetopause current layer is oppositely directed to that in the adjacent magnetosheath. When the y component, B{sub y}, of the

J. T. Gosling; M. F. Thomsen; S. J. Bame; R. C. Elphic; C.T. Russell

1990-01-01

353

Study of the evening plasma drift vortex in the low-latitude ionosphere using San Marco electric field measurements  

Microsoft Academic Search

San Marco D electric field measurements have been averaged in terms of the equivalent EB plasma drifts for days near the 1988 autumn equinox. The observed plasma drifts provide a satellite-based composite in altitude and local time of the evening enhancements in the zonal and vertical drifts and the shear in the zonal drift. The satellite data reveal details of

J. Vincent Eccles; Nelson Maynard; Gordon Wilson

1999-01-01

354

Exploring the Effects of Ionospheric Outflow on the Inner Magnetosphere using RAM-SCB  

NASA Astrophysics Data System (ADS)

The Ring current Atmosphere interactions Model with Self-Consistently calculated 3D Mag-netic field (RAM-SCB) has been used to successfully study inner magnetosphere dynamics during different solar wind and magnetosphere conditions. Historically, this numerical model has relied on empirical formulations to provide magnetic field boundary conditions, ionospheric electric potential, and to specify heavy ion composition at the outer boundary. Either empirical models or observations typically specify plasma density and temperature at the boundary. Re-cently, RAM-SCB has been integrated into the Space Weather Modeling Framework, a flexible system that creates real time, two-way coupling between RAM-SCB, the multi-species version of BATS-R-US global MHD and the Polar Wind Outflow Model. Through these couplings, RAM-SCB receives first-principle derived magnetic and plasma boundary conditions as well as convective electric potentials from the SWMF and returns inner magnetosphere plasma pres-sure to correct the MHD solution. This work uses the newly coupled system to explore the relationship between ionospheric outflow and ring current plasma distribution and composition. Data-model comparisons of magnetic field and particle fluxes are used to investigate how well the coupled system represents real world conditions.

Welling, Daniel; Jordanova, Vania; Zaharia, Sorin; Toth, Gabor

355

Effect of Different Initial Conditions on the Evolution of the E X B Gradient Drift Instability in Ionospheric Plasma Clouds.  

National Technical Information Service (NTIS)

Both small and large amplitude monochromatic (one wave) and random (many waves) initial perturbations have been used to seed initially slablike plasma clouds with different magnetic field line integrated Pedersen conductivity gradient scale lengths L = 4,...

M. J. Keskinen S. L. Ossakow

1981-01-01

356

An electrodynamic model of the solar wind interaction with the ionospheres of Mars and Venus  

Microsoft Academic Search

The electrodynamic model for the solar wind interaction with nonmagnetic planets modified to include the effects of nonohmic currents in the upper ionosphere is examined. The model is used to calculate convection patterns induced by the solar wind in the ionospheres of Mars and Venus, with the observations of the neutral mass spectrometer of Vikings 1 and 2 providing the

P. A. Cloutier; R. E. Daniell

1979-01-01

357

The critical solar wind pressure for IMF penetration into the Venus ionosphere  

Microsoft Academic Search

Early observations and simulations have revealed that the occurrence of IMF penetration into the Venus ionosphere depends on the upstream solar wind pressure, and that IMF is transported into the ionosphere by the downward convection when the solar wind dynamic pressure is relatively large. In this paper, we investigated the critical solar wind pressure for the IMF penetration, by using

H. Jin; K. Maezawa; T. Mukai

2008-01-01

358

Effect of thermal fluxes of charged particles on the spatial structure of the polar ionosphere  

Microsoft Academic Search

A hydrodynamic model of the convective high-latitude ionosphere is used to study the effect of thermal fluxes of charged particles coming into the ionosphere on spatial distributions of electron and ion temperature as well as on concentrations of charged particles in the F-layer. It is shown that these thermal fluxes can have a considerable effect on the distribution of electron

G. I. Mingaleva; V. S. Mingalev; V. N. Krivilev

1993-01-01

359

Observations of a solar-wind-driven modulation of the dayside ionospheric DPY current system  

NASA Astrophysics Data System (ADS)

We report here a collection of complementatry measurements near local magnetic noon of a unique ionospheric convection variation observed by the Sondrestrom radar which is related to a nearly periodic variation (approximately equal to 25-30 min period) in the interplanetary magnetic field B(sub y) component. We observe also a poleward phase propagation of magnetic pulsations over a region limited in longitude and latitude near the dayside polar cusp. A series of poleward propagating radio absorption enhancements are observed in the Greenland and South Pole imaging riometer data. The pulsations and absorption enhancements are associated with a latitudinally narrow and longitudinally limited intensification of the westward convection and associated eastward Hall current, which propagates poleward over the magnetometers and radar field of view. For the cases presented the interplanetary B(sub z) is strongly negative, while the ionospheric variations are associated with the low-frequency component of variations in the interplanetary B(sub y) component. In contrast to the previously discovered traveling convection vortices, these features exhibit a poleward phase motion rather than one along lines of invariant latitude. The propagation velocity is slower (approximately 0.5-1.0 km/s) and the structures cover 2 to 3 hours of local time. We interpret the observations as a poleward propagation of the DPY current system intensification associated with enhancements in the IMF B(sub y) component. Our obsevrations indicate that the DPY field-aligned current system is propagating poleward and may be moving independent of the convection motion of the plasma and associated field lines.

Clauer, C. R.; Stauning, P.; Rosenberg, T. J.; Friis-Christensen, E.; Miller, P. M.; Sitar, R. J.

1995-05-01

360

Mid-Latitude Thermosphere-Ionosphere Storm Response: An Aeronomy Frontier  

NASA Astrophysics Data System (ADS)

The primary descriptions of the large scale thermosphere and ionosphere system have been based on micro-scale aeronomy processes, i.e., atomic and molecular chemistry and physical interactions, whose outcomes are then redistributed by macro-scale processes to describe regional morphologies as well as vertical stratification of the plasma environment. To a large extent the redistribution processes are understood but almost always represented by climatological drivers, i.e., neutral atmosphere -"MSIS"; neutral winds -"Hedin HWM"; auroral ionization and energy deposit ion - "Hardy"; convection and joule heating - "Weimer". Even when first principles physics models represent these drivers the models inherent space-time resolution reduces their descriptions to smoothed morphologies. A consequence of these shortcomings is that when the FAA studied mid-latitude ionospheric knowledge to design their WAAS system a major piece of ionosphere extreme weather was missed, with eventual adverse effects. This identifies a significant aeronomy frontier. This presentation emphasizes the mid-latitude regions aeronomy drivers that probably have a significant role to play in resolving our lack of knowledge. Both observations and model results will be presented to highlight why these suggested drivers are geo-effective. The consequence and hence observational requirements will be outlined. Since these conclusions depart significantly from the prevailing explanations of how mid-latitude storm aeronomy operates, specific contrasts will be made between these explanations again using observations and model results.

Sojka, J. J.; Heelis, R.

2005-12-01

361

Low- and mid-latitude ionospheric electric fields during the January 1984 GISMOS campaign  

SciTech Connect

This paper examines in detail the electrical coupling between the high-, middle, and low-latitude ionospheres during January 17-19, 1984, 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 authors study the penetration of both the zonal and meridional electric field components of high-latitude origin into the low-latitude and the equatorial ionospheres. In the dusk sector, a large perturbation of the zonal equatorial electric field was observed in the absence of similar changes at low and middle latitudes in the same longitudinal sector. The observations in the postmidnight sector are used to compare the longitudinal variation 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. As a result, they conclude that variations in the meridional electric field at low latitudes are largely due to dynamo effects. These observations are used to show that the global convection models reproduce a number of characteristics of low-latitude and equatorial electric fields associated with changes in the polar cap potential drop. In addition, they highlight several areas where there is still substantial disagreement between the electric field data and the theoretical results.

Fejer, B.G. (Utah State Univ., Logan (United States)); Kelley, M.C. (Cornell Univ., Ithaca, NY (United States)); Senior, C. (Centre National d'Etudes des Telecommunications/Centre de Recherche en Physique de l'Environment, Saint-Maur des Fosses (France)); De La Beaujardiere, O. (SRI International, Menlo Park, CA (United States)); Holt, J.A. (Massachusetts Inst. of Tech., Westford (United States)); Tepley, C.A.; Burnside, R. (Arecibo Observatory (Puerto Rico)); Abdu, M.A.; Sobral, J.H.A. (Inst. de Pesquisas Espaciais, Sao Paulo (Brazil)); Woodman, R.F. (Inst. Geofisico del Peru, Lima (Peru)); Kamide, Y. (Kyoto Sangyo Univ. (Japan)); Lepping, R. (Goddard Space Flight Center, Greenbelt, MD (United States))

1990-03-01

362

O Gravity Waves and the Electrodynamics of the MidLatitude Ionosphere  

Microsoft Academic Search

This thesis examines the coupling of thermospheric gravity waves to ionospheric disturbances using experimental observations and theoretical descriptions of the nighttime, mid-latitude F region. Previously, these disturbances have been separated into two types: passive ionospheric responses to field-aligned neutral winds known as traveling ionospheric disturbances and active irregularities caused by plasma instabilities. This work finds, however, that this distinction breaks

Clark Anson Miller

1996-01-01

363

The ionospheric effects of a weak intrinsic magnetic field at Mars  

Microsoft Academic Search

An improved model of the Martian ionosphere which allows the magnetic field to have any direction in the horizontal plane is presented, as well as results of calculations for several different intrinsic magnetic field strengths and directions. When the solar wind dynamic pressure exceeds the Martian ionospheric thermal pressure, the plasma motion is weakly downward throughout the ionosphere for the

H. Shinagawa; T. E. Cravens

1992-01-01

364

Broadening of the scrape-off-layer by a plasma convection induced by toroidal asymmetries of the divertor plates and the gas-puff  

SciTech Connect

In the open field line region of the scrape-off layer (SOL), plasma potential is to a considerable degree determined by the boundary conditions on the divertor plates. By introducing toroidal asymmetries of the surface relief of the divertor plates or of their chemical composition, one can create toroidally asymmetric potential variations over the whole SOL and thereby induce convective plasma motion. This motion should lead to a broadening of the SOL and to reduction of beat load on the divertor plates. Convective motion can be induced also by a toroidally asymmetric gas-puff. In the present paper the authors consider all these techniques and evaluate the possible increase in the cross-field transport.

Cohen, R.H.; Ryutov, D.D.

1995-09-25

365

Evolution of equatorial ionospheric plasma bubbles and formation of broad plasma depletions measured by the C\\/NOFS satellite during deep solar minimum  

Microsoft Academic Search

An unexpected feature revealed by the measurements of the Communication\\/Navigation Outage Forecasting System (C\\/NOFS) satellite is the presence of broad plasma depletions in the midnightdawn sector during deep solar minimum. It has not been well understood what causes the broad plasma depletions and how equatorial plasma bubbles are related to the broad depletions. In this paper we present the C\\/NOFS

Chao-Song Huang; O. de La Beaujardiere; P. A. Roddy; D. E. Hunton; R. F. Pfaff; C. E. Valladares; J. O. Ballenthin

2011-01-01

366

Evolution of equatorial ionospheric plasma bubbles and formation of broad plasma depletions measured by the C\\/NOFS satellite during deep solar minimum  

Microsoft Academic Search

An unexpected feature revealed by the measurements of the Communication\\/Navigation Outage Forecasting System (C\\/NOFS) satellite is the presence of broad plasma depletions in the midnight-dawn sector during deep solar minimum. It has not been well understood what causes the broad plasma depletions and how equatorial plasma bubbles are related to the broad depletions. In this paper we present the C\\/NOFS

Chao-Song Huang; O. de La Beaujardiere; P. A. Roddy; D. E. Hunton; R. F. Pfaff; C. E. Valladares; J. O. Ballenthin

2011-01-01

367

An investigation of mechanisms other than lightning to explain certain wideband plasma wave bursts detected in the Venusian nightside ionosphere  

Microsoft Academic Search

Several related topics are briefly discussed. Reviewed here is work on an investigation of plasma wave phenomena associated with the question of lightning on Venus. The work supported the contention that lightning is at least a candidate explanation for many of the 100 Hz-only Pioneer Venus orbital electric field detector (OEFD) signals. A review of the work on the investigation

D. L. Carpenter

1992-01-01

368

Magnetosphere-Ionosphere Coupling at Saturn  

NASA Astrophysics Data System (ADS)

The Saturnian magnetosphere is a rapidly rotating system populated with Enceladus-genic neutral gas. Neutrals are ionized and picked-up by the planetary magnetic field and, outside of 6 Rs radially transported outwards through the magnetosphere. Field-aligned currents couple the magnetospheric plasma to the ionosphere, transferring angular momentum to the magnetospheric plasma and creating infrared, visible, and ultraviolet auroral emissions in Saturn's atmosphere. We will review recent developments in the understanding of magnetosphere-ionosphere coupling at Saturn highlighting the field-aligned current system that develops due to the radial transport of plasma and the contribution of a variable ionospheric Pedersen conductance to the transfer of angular momentum. The consistency of model results with in-situ magnetospheric measurements and both Earth-based and spacecraft auroral observations will be discussed.

Ray, L. C.

2011-12-01

369

A Forecasting Ionospheric Real-time Scintillation Tool (FIRST)  

Microsoft Academic Search

Transionospheric radio waves propagating through an irregular ionosphere with plasma depletions, or bubbles, are subject to sporadic enhancement and fading commonly referred to as scintillation. Knowledge of the current ionospheric condition allows system operators to distinguish between compromises due to the radio environment and system induced failures, while a forecast of the same provides the opportunity for operators to take

Robert J. Redmon; David Anderson; Ron Caton; Terence Bullett

2010-01-01

370

Pioneer Venus Orbiter observations of the disturbed nightside ionosphere  

Microsoft Academic Search

Pioneer Venus Orbiter (PVO) observed the ionosphere and atmosphere of Venus for almost 14 years. The PVO contained a vast array of experiments including: Radar Mapper, Magnetometer, Electric Field Detector, Plasma Analyzer, Ion Mass Spectrometer, Langmuir Probe, Retarding Potential Analyzer, Neutral Mass Spectrometer, Ultraviolet Spectrometer, Infrared radiometer, Cloud Photopolarimeter, Gamma Burst Detector, and Radio Science. For analyzing the Venus ionosphere,

Walter Hoegy; Joseph Grebowsky; Richard Hartle

2008-01-01

371

Monitoring and modeling Hong Kong ionosphere using regional GPS networks  

Microsoft Academic Search

The ionosphere is the region from 90 km to 2000 km altitude, where the solar radiation produces partially ionized plasma of different gas components. Knowledge of ionospheric electronic density and its variation is essential for a wide range of applications, such as radio and telecommunications, satellite tracking, earth observation from space, and satellite navigation. This research aims at monitoring detailed

Shan Gao

2008-01-01

372

Radio frequency scattering from a heated ionospheric volume. I - VHF\\/UHF field-aligned and plasma-line backscatter measurements  

Microsoft Academic Search

It is observed that an ionospheric volume in the F layer subjected to high power HF illumination becomes an effective scattering medium for radio signals in the VHF\\/UHF frequency range. The experimental results are representative of a field-aligned scattering geometry for which the first such observations of VHF\\/UHF scattering from a heated ionospheric volume are presented. Two distinct scattering modes

J. Minkoff; P. Kugelman; I. Weissman

1974-01-01

373

Study of plasma convection and wall interactions in magnetic confinement systems  

Microsoft Academic Search

Studies of compact toroid formation and lifetime in high fill pressure discharges are reported. Extended lifetimes without rotation disruption and with low indicated resistivity were identified experimentally. Numerical codes modeled static and translating CT plasmas. Nd:Glass lasers for Thomson scattering diagnostics were studied in detail. Comparison of system performance achieved with ruby, Nd:Glass and Nd:Glass\\/KDDP sources is reported. Performances of

T. M. York

1984-01-01

374

Frequency characteristics of the action of powerful radio-frequency radiation on the ionospheric F layer  

SciTech Connect

The results of an investigation of the effect of artificial ionospheric nonuniformities on the characteristics of LFM signals with vertical and oblique sounding of the ionosphere are presented. A classification of the effects observed on ionograms from vertical and oblique-sounding LFM ionosonde, owing to the effect of artificial nonuniformities of different scale, is given. It was found that powerful beams of radio waves have a characteristic effect on the ionospheric plasma under conditions when moving ionospheric disturbances appear.

Erukhimov, L.M.; Ivanov, V.A.; Mityakov, N.A.; Uryadov, V.P.; Frolov, V.A.; Shumaev, V.V.

1988-03-01

375

Midnight reversal of ionospheric plasma bubble eastward velocity to westward velocity during geomagnetically quiettime: Climatology and its model validation  

NASA Astrophysics Data System (ADS)

In an effort to better understand the dynamics of westward velocities of the nocturnal F-region plasma, the climatology of the westward traveling plasma bubbles - WTB - occurring during quiettime is studied here. The climatology of the WTB is analyzed here based on airglow images obtained during 14 quiet days between 2001 and 2006 at the Brazilian station So Joo do Cariri (Geographic 7.45S, 36.5W, dip 20S). The frequency of occurrence of the WTB maximizes in the descending phase of the solar cycle. The WTB velocities ranged between 20 and 40 ms-1. The frequency of occurrence had a peak value of only 3.65% at 2345 LT. The maximum occurrence of the WTB was in July-September. No WTB have been observed from November until April in all years 2001-2006. We show for the first time theoretically that the WTB dominant forcing mechanisms during geomagnetically quiet days are westward thermospheric winds.

Sobral, Jos H. A.; de Castilho, Vivian M.; Abdu, M. A.; Takahashi, Hisao; Paulino, I.; Gasparelo, Ulisses A. C.; Arruda, Daniela C. S.; Mascarenhas, Matheus; Zamlutti, C. J.; Denardini, C. M.; Koga, Daiki; de Medeiros, A. F.; Buriti, R. A.

2011-07-01

376

On the amplitude of low-frequency signals in the nighttime ionosphere over thunderstorm discharges  

NASA Astrophysics Data System (ADS)

It is shown that the origin of anomalous amplitudes of ULF/ELF signals in the topside ionosphere over thunderstorm discharges could be caused by the existence of regions of highly-ionized plasma in the lower ionosphere. The alternating current of the lightning electromagnetic pulse can generate in the region of highly-ionized plasma formed in the lower ionosphere due to the influence of thunderstorm discharges magneto-hydrodynamic waves propagating into the topside ionosphere. On the basis of the suggested model, the estimates of amplitude and duration of the Alfven mode propagating into the topside ionosphere are obtained, which agree with the measurements in rocket experiments over thunderstorms.

Shalimov, S. L.

2012-05-01

377

Study of plasma convection and wall interactions in magnetic confinement systems  

NASA Astrophysics Data System (ADS)

Studies of compact toroid formation and lifetime in high fill pressure discharges are reported. Extended lifetimes without rotation disruption and with low indicated resistivity were identified experimentally. Numerical codes modeled static and translating CT plasmas. Nd:Glass lasers for Thomson scattering diagnostics were studied in detail. Comparison of system performance achieved with ruby, Nd:Glass and Nd:Glass/KDDP sources is reported. Performances of a single pulse 80 J system and a 10 ms mode-locked system were defined by basic experimental studies.

York, T. M.

1984-06-01

378

Magnetospheric injection of ELF\\/VLF waves with modulated or steered HF heating of the lower ionosphere  

Microsoft Academic Search

ELF\\/VLF waves have been generated via steerable HF heating of the lower ionosphere. The temperature-dependent conductivity of the lower ionospheric plasma enables HF heating (and subsequent recovery) to modulate natural current systems such as the auroral electrojet, thus generating an antenna embedded in the ionospheric plasma. We apply a realistic three-dimensional model of HF heating and ionospheric recovery, as well

M. B. Cohen; D. Piddyachiy; N. G. Lehtinen; M. Golkowski

2011-01-01

379

Ionospheric Anomalies in the Polar Cap and at Mid-Latitudes Revealed by Digital Ionosondes and GPS Receivers  

Microsoft Academic Search

Intensification of the magnetosphere-ionosphere coupling during magnetic storms driven by coronal mass ejections (CMEs) or corotating interaction regions (CIRs) lead to extreme disturbances in density and height of ionospheric plasma layers. Dramatic enhancements of the ionospheric density and plasma content (TEC) appear in mid-latitude ionosphere and extend into the polar cap in the form of continuous tongue of ionization and\\/or

D. Pokhotelov; T. P. Jayachandran; J. W. MacDougall; C. N. Mitchell

2009-01-01

380

Ionospheric profiling through radio-frequency signals recorded by the FORT satellite, with comparison to the International Reference Ionosphere  

NASA Astrophysics Data System (ADS)

Electromagnetic waves originating on Earth and recorded in space allow retrieval of ionospheric parameters. Using the FastOnboard Recording of Transient Events satellite (FORT, it has been shown that traps-ionospheric pulsed radio-frequency (RF) signals carry sufficient information to infer the peak electron density of the ionosphere, in addition to the total electron content along a ray path between a source and a receiver. In this paper the detailed refractive properties of the ionosphere and the biref-ringent splitting of RF waves in the Earth's magnetic field are modeled using the Appleton-Hartree equation and an electron density profile based on the International Reference Ionosphere (IRI). Applications of this model to FORT data provide additional information on the vertical profile of ionospheric plasma density at the time and place of measurement. Results of the FORT observations are compared with the IRI.

Moses, Ronald W.; Jacobson, Abram R.

2004-01-01

381

Investigation of low-latitude ionospheric irregularities and their relationship to equatorial plasma bubbles using Sanya VHF radar  

NASA Astrophysics Data System (ADS)

A VHF radar has been set up at Sanya (18.34 N, 109.62 E, geomagnetic latitude 7.04N), China in 2009. On the basis of the E, valley and F region irregularity observations detected by the Sanya VHF radar during equinoctial months, we focus on the simultaneous observations of E region irregularities disruption and valley region irregularities generation during the presence of post-sunset F region bubble structures. We stress that both the low latitude the E region