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1

Observations of equatorial plasma bubbles using broadcast VHF radio waves  

Microsoft Academic Search

The propagation of VHF radio waves affected by field-aligned irregularities within equatorial plasma bubbles is examined. Continuous observation of VHF radio waves at Tateyama, Japan, shows that broadcast radio waves transmitted from Southeast Asia propagate to Japan. Using a ray-tracing calculation combined with a model of scattering by field-aligned irregularities, we determined scatter points suitable for the reception of these

H. Nakata; I. Nagashima; K. Sakata; Y. Otsuka; Y. Akaike; T. Takano; S. Shimakura; K. Shiokawa; T. Ogawa

2005-01-01

2

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

3

Seeding of equatorial plasma bubbles with electric fields from an Es-layer instability  

Microsoft Academic Search

Evidence is presented that supports the suggestion by Tsunoda (2006) that a polarization electric field, if generated by a sporadic-E (Es) layer instability (Cosgrove and Tsunoda, 2002), should map to the base of the F layer and seed equatorial plasma bubbles. Seeding, which leads to bubble development, seems to be a four-step process operating in the bottomside F layer: (1)

Roland T. Tsunoda

2007-01-01

4

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

5

On the Spatial Relationship of 1-Meter Equatorial Spread-F Irregularities and Plasma Bubbles.  

National Technical Information Service (NTIS)

A radar experiment was conducted on 18 August 1978 at Kwajalein Atoll, Marshall Islands, to investigate the spatial relationship of 1-m equatorial spread-F irregularities to plasma bubbles (localized depletions in F-layer plasma density). East-west scans ...

R. T. Tsunoda

1979-01-01

6

Long-lasting daytime equatorial plasma bubbles observed by the C/NOFS satellite  

NASA Astrophysics Data System (ADS)

We report the first observations of long-lasting daytime equatorial plasma bubbles with the Communication/Navigation Outage Forecasting System (C/NOFS) satellite. The most unusual features of the plasma bubbles are the persistence from the post-midnight sector through the afternoon sector and the extremely long lifetime of 12 h. In one case, the plasma bubbles were generated at 02:00-03:00 LT near the end of the main phase of a moderate magnetic storm and detected by C/NOFS over eight successive orbits, and the decrease of the ion density inside the bubbles was still as large as ~30% at 14:00-15:00 LT. In another case, one group of plasma bubbles was generated near the sunset terminator and existed over the entire nighttime until the post-sunrise sector (06:00-08:00 LT), and another group of plasma bubbles was first detected at 04:00-06:00 LT and lasted until ~11:00 LT. The latter group of bubbles occurred following a sharp northward turning of the interplanetary magnetic field (IMF) near the end of the main phase of a weak magnetic storm, and the overshielding electric field caused by the IMF northward turning and the storm time disturbance dynamo might both have contributed to the generation of the bubbles. The plasma bubbles reached 800 km or higher in altitude during daytime. The high altitudes may be critical for the long lifetime of the bubbles: the photo-ionization rate decreases rapidly with altitude. The photo-ionization process may take a long time to produce enough new plasma particles to fill the daytime bubbles at high altitudes.

Huang, Chao-Song; La Beaujardiere, O.; Roddy, P. A.; Hunton, D. E.; Ballenthin, J. O.; Hairston, M. R.

2013-05-01

7

Spatial relationship of 1-m equatorial spread F irregularities and plasma bubbles  

Microsoft Academic Search

A radar experiment was conducted on August 18, 1978, at Kwajalein Atoll, Marshall Islands, to investigate the spatial relationship of 1-m equatorial spread F irregularities to plasma bubbles (localized depletions in F layer plasma density). East-west scans were made with Altair, an incoherent scatter radar, to spatially map (1) the backscatter produced by field-aligned irregularities and (2) the electron density

Roland T. Tsunoda

1980-01-01

8

Spatial relationship of equatorial plasma bubbles and field-aligned irregularities observed with an all-sky airglow imager and the Equatorial Atmosphere Radar  

Microsoft Academic Search

We report, for the first time, simultaneous two-dimensional observations of 630-nm airglow depletions and radar backscatter from field-aligned irregularities (FAI) associated with equatorial plasma bubbles. Spatial distributions of backscatter were obtained by performing east-west scans with the 47-MHz Equatorial Atmosphere Radar (EAR) in West Sumatra, Indonesia. A 630-nm airglow depletion, caused by a plasma bubble, was simultaneously observed with an

Y. Otsuka; K. Shiokawa; T. Ogawa; T. Yokoyama; M. Yamamoto; S. Fukao

2004-01-01

9

On the spatial relationship of 1-m equatorial spread F-irregularities and plasma bubbles  

NASA Astrophysics Data System (ADS)

A radar experiment was conducted on August 18, 1978, at Kwajalein Atoll, Marshall Islands, to investigate the spatial relationship of 1-m equatorial spread F irregularities to plasma bubbles (localized depletions in F layer plasma density). East-west scans were made with Altair, an incoherent scatter radar, to spatially map (1) the backscatter produced by field-aligned irregularities and (2) the electron density distribution of the background F layer. Plasma bubbles were spatially mapped for the first time with an incoherent scatter radar. By assuming invariance along the magnetic field lines (over distances of less than 100 km) we show that 1-m field-aligned irregularities are directly related to plasma bubbles.

Tsunoda, R. T.

1980-01-01

10

Nonlinear evolution of equatorial spread F. 3. Plasma bubbles generated by structured electric fields  

SciTech Connect

Observations have shown that in some cases equatorial spread F (ESF) irregularities including plasma bubbles are related to temporal and spatial structures of electric fields. It has been conjectured that the electric field structures may be responsible for production of ESF bubbles. The authors present here numerical results of electric field effects in nonlinear evolution of ESF. In their simulations the authors have modeled electric field structures in both time and space. It is found that the temporal structures, including the prereversal enhancement, of the eastward electric field cause motion of the F layer in the vertical direction, but they cannot produce spatial structures of F region plasma. In contrast, plasma bubbles are produced when spatial structures of electric field are used as input in the simulations. The spatially irregular electric fields initiate plasma perturbations in the bottomside F region, then the perturbations are amplified by the Rayleigh-Taylor instability and evolve into topside plasma bubbles. It is concluded that spatial structures of electric field are needed for seeding of ESF bubbles. It is shown also that electric fields generated by E region gravity waves can result in production of F region bubbles. 45 refs., 8 figs.

Huang, Chao-Song; Kelley, M.C. [Cornell Univ., Ithaca, NY (United States)

1996-01-01

11

Optical observations of the growth and day-to-day variability of equatorial plasma bubbles  

Microsoft Academic Search

A new narrow-field ionospheric imaging system, the Portable Ionospheric Camera and Small-Scale Observatory, has been installed at the Cerro Tololo Inter-American Observatory near La Serena, Chile (geographic 30.17S, 289.19E; geomagnetic 16.72S, 0.42E). We present observations of the naturally occurring nightglow emission at 630.0 nm on three consecutive nights demonstrating the day-to-day variability in the occurrence of equatorial plasma bubbles or

J. J. Makela; E. S. Miller

2008-01-01

12

Optical observations of the growth and day-to-day variability of equatorial plasma bubbles  

Microsoft Academic Search

A new narrow-field ionospheric imaging system, the Portable Ionospheric Camera and Small-Scale Observatory, has been installed at the Cerro Tololo Inter-American Observatory near La Serena, Chile (geographic 30.17S, 289.19E geomagnetic 16.72S, 0.42E). We present observations of the naturally occurring nightglow emission at 630.0 nm on three consecutive nights demonstrating the day-to-day variability in the occurrence of equatorial plasma bubbles or

J. J. Makela; E. S. Miller

2008-01-01

13

Effect of magnetic activity on plasma bubbles over equatorial and low-latitude regions in East Asia  

NASA Astrophysics Data System (ADS)

The dependence of plasma bubble occurrence in the eveningside ionosphere, with magnetic activity during the period years 2001-2004, is studied here based on the TEC observations gathered by ground-based GPS receivers which are located in the equatorial and low-latitude regions in East Asia. The observed plasma bubbles consist of the plasma-bubble events in the equatorial (stations GUAM, PIMO and KAYT), and low-latitude regions (stations WUHN, DAEJ and SHAO). It is shown that most equatorial plasma-bubble events commence at 20:00 LT, and may last for >60 min. The magnetic activity appears to suppress the generation of equatorial plasma bubbles with a time delay of more than 3 h (4-9 h). While in the low-latitude regions, most plasma-bubble events commence at about 23:00 LT and last for <45 min. The best correlation between Kp and low-latitude plasma-bubble occurrence is found with an 8-9 h delay, a weak correlation exists for time delays of 6-7 h. This probably indicates that over 3 h delayed disturbance dynamo electric fields obviously inhibit the development of plasma bubbles in the pre-midnight sector.

Li, G.; Ning, B.; Liu, L.; Wan, W.; Liu, J. Y.

2009-01-01

14

Are plasma bubbles a prerequisite for the formation of broad plasma depletions in the equatorial F region?  

NASA Astrophysics Data System (ADS)

of broad plasma depletions (BPDs) at night in the equatorial F region is understood in association with plasma bubbles. However, we report BPDs that do not show a connection with bubbles. The characteristics of BPDs are investigated using the observations of the Communication/Navigation Outage Forecasting System (C/NOFS) satellite on 31 December 2008, 28 July 2010, and 1 February 2011. On those days, BPDs are detected in the longitude regions where C/NOFS did not detect bubbles prior to the detection of BPDs. The coincident C/NOFS and radar observations over Jicamarca in Peru show the occurrence of BPDs at the time when backscatter echoes are absent and at the height below backscatter echoes. These observations indicate that bubbles are not a prerequisite for those BPDs. The detections of those BPDs can be explained by the uplift of the equatorial F region peak height above the satellite orbit.

Kil, Hyosub; Lee, Woo Kyoung

2013-07-01

15

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

16

Seeding of equatorial plasma bubbles with electric fields from an Es-layer instability  

NASA Astrophysics Data System (ADS)

Evidence is presented that supports the suggestion by Tsunoda (2006) that a polarization electric field, if generated by a sporadic-E (Es) layer instability (Cosgrove and Tsunoda, 2002), should map to the base of the F layer and seed equatorial plasma bubbles. Seeding, which leads to bubble development, seems to be a four-step process operating in the bottomside F layer: (1) amplification of seed perturbations in a region of westward-drifting plasma, which is found below the velocity-shear node; (2) upward transference of this modulation through a rotational velocity shear to eastward-drifting plasma; (3) further seed amplification, when the F layer begins to descend; and (4) bubble growth from the seed via the Rayleigh-Taylor instability. The time available for interaction between F-region plasma and elongated channels of enhanced polarization electric field (the latter formed by the mentioned instability) appears to be crucial for seed amplification. The need for a descending F layer to increase interaction time with the eastward-drifting plasma is appealing because plasma bubbles display a propensity to appear after, and not during, the postsunset rise of the F layer. Although plausible, the need for Es presence, perhaps low solar activity, and a multistep process suggest that this mechanism may be a more occasional contributor than the collisional-shear instability (Hysell and Kudeki, 2004).

Tsunoda, Roland T.

2007-06-01

17

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

18

Equatorial plasma bubbles studied using African slant total electron content observations  

NASA Astrophysics Data System (ADS)

Equatorial plasma bubbles (EPBs) are field-aligned depletions of F-region ionospheric plasma density that grow from irregularities caused by the generalized Rayleigh-Taylor instability mechanism in the postsunset equatorial sector. Although they have been studied for some decades, they continue to be an important subject of both experimental and theoretical investigations because of their effects on trans-ionospheric radio communications. In this work, calibrated data of slant total electron content (sTEC) taken every 10 min from EGNOS System Test Bed Brazzaville (Congo), Douala (Cameroon), Lome (Togo) and N'Djamena (Chad), and International GNSS Service Ascension Island, Malindi (Kenya), and Libreville (Gabon), stations are used to detect plasma bubbles in the African equatorial region during the first 6 months of 2004. To identify these irregularities, the trend of every curve of sTEC against time is subtracted from the original data. The size of the EPBs is estimated by measuring its amplitude in the de-trended time variation of sTEC.

Portillo, A.; Herraiz, M.; Radicella, S. M.; Ciraolo, L.

2008-04-01

19

Equatorial plasma bubbles/range spread F irregularities and the QBO  

SciTech Connect

This paper reports on a study of plasma bubbles or spread F irregularities, observed at equatorial observation stations, looked at in conjunction with measures of the quasi biennial oscillation (QBO) of the mean lower stratospheric winds. Plasma bubbles and spread F irregularities are thought to be different manifestations of the same basic event, distinguished mainly by the observational method. For the case of range spread F events, ionosonde data has revealed in the past daily and seasonal variations, effects due to the solar cycle, and dependence upon the geomagnetic field and longitudinal location. These relationships have been shown to be statistical in nature, so the authors have looked for other relationships which might be more relational in nature. When correlation with QBO phase variations are investigated, there is an observed increase or decrease in the range spread F, dependent upon whether the QBO is in an easterly or westerly phase, and observed in the American sector or Indian/East African sector.

Chen, P.R. (Chinese Academy of Sciences, Beijing (China))

1993-11-05

20

Comparison of zonal neutral winds with equatorial plasma bubble and plasma drift velocities  

NASA Astrophysics Data System (ADS)

A one-year dataset spanning March 2011 to March 2012 of coincident observations of nighttime thermospheric zonal neutral winds, equatorial plasma bubble (EPB) velocities, and zonal plasma drifts is used to examine the relationship between the thermosphere and the ionosphere near the geomagnetic equator over Peru. Thermospheric neutral winds are determined by using a bistatic Fabry-Perot interferometer (FPI) experiment located at Merihill and Nazca in Peru. The ambient plasma drift velocities were obtained using the incoherent scatter radar at the Jicamarca Radio Observatory in Peru. The EPB zonal velocities were estimated utilizing images of the OI 630.0 nm emission recorded by a narrow-field optical imaging system at the Cerro Tololo Inter-American Observatory in Chile. The joint analysis of these datasets illustrates that the nighttime and night-to-night variations in the zonal neutral winds, EPB velocities, and plasma drifts are well correlated. This consistent result of the local time variations of the neutral winds with that of EPB and plasma drifts illustrates that the F-region dynamo is, in general, fully activated. However, at times, the magnitude of the EPB velocities and the plasma drifts are different from the neutral winds. It is plausible that such a difference is due either to the effect of polarization electric fields developed inside the EPB or due to the latitudinal gradient of the neutral winds and EPB velocity measurements since the EPB velocities are estimated at a higher latitude, corresponding to an apex altitude of ~400 km, than the wind estimates, which derive from an apex altitude of ~250 km.

Chapagain, Narayan P.; Fisher, Daniel J.; Meriwether, John W.; Chau, Jorge L.; Makela, Jonathan J.

2013-04-01

21

Coordinated UV imaging of equatorial plasma bubbles using TIMED/GUVI and DMSP/SSUSI  

NASA Astrophysics Data System (ADS)

Coincident and near-coincident Global Ultraviolet Imager (GUVI) and Special Sensor Ultraviolet Spectrographic Imager (SSUSI) plasma bubble images provide a unique opportunity to image the evolution of a single feature over a large longitude and time range. SSUSI and GUVI are currently the only two UV imagers that can provide low-Earth orbit measurements capable of reconstructing a multidimensional electron density map. New imaging techniques applied to years of UV data provide a powerful tool for observing and understanding ionospheric electron density and equatorial plasma bubbles. GUVI, launched on board the TIMED satellite in December 2001, and SSUSI on board the DMSP F16 satellite launched in October 2003 have several overlapping years of observations of the nightside ionosphere. The low-Earth orbit of the DMSP and TIMED satellites allows for tomographic reconstruction of altitude versus longitude bubble cross sections from UV disk images. GUVI is at an altitude of 625 km in an orbit that precesses through all local solar times in just 60 days, and SSUSI is at an altitude of 830 km in a fixed 0800/2000 local solar time orbit. We have developed a technique for tomographic retrievals of electron density maps from GUVI observations. We are able to produce three-dimensional maps of ionospheric electron density. We discuss the adaptation of the tomographic imaging technique to SSUSI data and present initial results. Electron density reconstructions are accompanied by discussion and analysis of plasma bubble drift rates and the morphology and time changes in the tilt of the bubbles as they drift through the ionosphere.

Comberiate, Joseph; Paxton, Larry J.

2010-10-01

22

Generation and characteristics of equatorial plasma bubbles detected by the C/NOFS satellite near the sunset terminator  

NASA Astrophysics Data System (ADS)

We present the observations of equatorial plasma bubbles in the evening sector by the Communication/Navigation Outage Forecasting System (C/NOFS) satellite during 2011. We illustrate with a few examples the overall properties of the equatorial ionosphere as the solar activity approached maximum. C/NOFS was often below the F peak and this allowed us to examine the early phases of irregularity formation. We show examples when C/NOFS detected a continuous generation of plasma bubbles near the sunset terminator over eight successive orbits (12 h). A clear prereversal enhancement of upward plasma drift occurred between 18:00 and 19:00 LT when plasma bubbles were detected by C/NOFS, and the peak value of the upward ion drift at or near the magnetic equator was 40-70 m s-1. In some cases, C/NOFS was well below the F peak and detected wide regions with very low plasma density over 3000 km in longitude in the evening sector, and plasma bubbles were generated within the low-density region. C/NOFS also detected simultaneous existence of plasma bubbles between 19:00 and 03:00 LT, corresponding to a longitudinal coverage of 12,000 km. Significant differences in the characteristics of plasma bubbles between periods of low and high solar activity are identified. Large plasma bubbles occur in the midnight-dawn sector at low solar activity but in the evening sector at high solar activity. The lifetime of plasma bubbles is long (7 h or longer) at low solar activity but is short (3 h) at high solar activity. Broad plasma depletions occur near dawn at low solar activity, but wide low-density regions with multiple plasma bubbles occur in the evening sector at high solar activity.

Huang, Chao-Song; de La Beaujardiere, O.; Roddy, P. A.; Hunton, D. E.; Ballenthin, J. O.; Hairston, M. R.

2012-11-01

23

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.

24

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

25

Global Ultraviolet Imager equatorial plasma bubble imaging and climatology, 20022007  

Microsoft Academic Search

A comprehensive database of plasma bubble reconstructions is under development, with results reported here from more than 5 years of Global Ultraviolet Imager (GUVI) data. Climatological statistics of plasma bubble occurrence from this database are presented, including the effects of longitudinal, seasonal, geomagnetic, and solar cycle variations on plasma bubble occurrence. The relationship between the latitudinal separation and peak electron

Joseph Comberiate; Larry J. Paxton

2010-01-01

26

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

27

Comparison of nighttime zonal neutral winds and equatorial plasma bubble drift velocities over Brazil  

NASA Astrophysics Data System (ADS)

We present results from the first extended period of coincident observations of thermospheric zonal neutral winds and equatorial plasma bubble (EPB) zonal drift velocities over northeastern Brazil during the October to December months of 2009 and 2010. The EPB zonal drift velocities are estimated utilizing images of the O I 630.0 nm emissions recorded by a wide-angle imaging system at Cajazeiras. Thermospheric neutral wind estimates are based upon common volume observations made by a bistatic Fabry-Perot interferometer (FPI) experiment using FPIs located at Cajazeiras and Cariri in Brazil observing the Doppler shift of the O I 630.0 nm emission. The results illustrate a similar pattern of nighttime and night-to-night variations in the zonal neutral winds and EPB zonal drift velocities. In general, the geomagnetic zonal neutral winds and the EPB velocities show an excellent agreement illustrating that the F region dynamo is fully developed. However, in the early evening hours the EPB zonal speed is slower than that of the background winds on several occasions. We conclude that this indicates that during the bubble evolution period in the early evening the F region dynamo is not fully activated.

Chapagain, Narayan P.; Makela, Jonathan J.; Meriwether, John W.; Fisher, Daniel J.; Buriti, Ricardo A.; Medeiros, Amauri F.

2012-06-01

28

Optical observations of the development of secondary instabilities on the eastern wall of an equatorial plasma bubble  

Microsoft Academic Search

Optical evidence is presented for the growth of a local secondary plasma instability on the eastern wall of an equatorial plasma bubble observed from the Haleakala Volcano, Hawaii (geographic: 20.71 N, 203.83 E; geomagnetic: 21.31 N, 271.45 E). Typically, only the western wall of depletions at tropical latitudes are susceptible to secondary structuring. This event occurs during a minor geomagnetic

J. J. Makela; M. C. Kelley; M. J. Nicolls

2006-01-01

29

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 irregularities (ERI) disruption and valley region irregularities (VRI) generation are associated with the development of post-sunset equatorial plasma bubble (EPB) structures. It is suggested that the electric field coupling from the unstable equatorial F region to low-latitude E and valley region could trigger and inhibit the occurrence of irregularities, depending on the polarity of the polarization electric field associated with the bifurcation of equatorial plasma bubbles. The mapping of upward/eastward and downward/eastward electric field associated with the west-tilted and east-tilted bubble structures, may be responsible for the disruption of E region irregularities, and the generation of valley region irregularities, respectively. However, more observations from multi instruments will be required to confirm such a scenario that the multi bifurcated EPBs play crucial roles for the simultaneous occurrence of low latitude ERI disruption and VRI generation.

Ning, B.; Li, G.; Hu, L.

2011-12-01

30

On the nature of low-latitude Es influencing the genesis of equatorial plasma bubble  

NASA Astrophysics Data System (ADS)

The potential influence of the postsunset low-latitude sporadic E (Es) on the genesis of equatorial plasma bubble (EPB) has been investigated using observations made with the Gadanki radar and two ionosondes, one located at the magnetic equator providing the F layer characteristics and another at magnetically low-latitude providing the Es parameters. Observations revealed that the occurrence of EPB was associated with either the disruption of Es or presence of nonblanketing-type Es or intermittently occurring blanketing Es at low-latitude. In contrast, when blanketing Es occurred for a relatively long duration in the sunset hours, EPB did not occur. Model computation clearly reveals that the growth of the Rayleigh-Taylor instability depends very much on the thickness, height, and shape of electron density profile of the Es layer. The above findings thus suggest that low-latitude Es variability plays decisive role on the day-to-day variability of EPB through the growth rate of the Rayleigh-Taylor instability.

Joshi, L. M.; Patra, A. K.; Pant, T. K.; Rao, S. V. B.

2013-01-01

31

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

32

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

33

Equatorial ionospheric bubble precursor  

Microsoft Academic Search

A time-dependent nonlinear three-dimensional model for the evolution of the equatorial bottomside lower ionosphere in the presence of dissipating gravity waves has been developed. From the numerical solution of the model, it is found that large bottomtype F-region ionospheric density perturbations and electric fields can be driven by dissipating gravity waves from tropospheric sources. The spatial distribution of the ionospheric

M. J. Keskinen

2010-01-01

34

Distributions of TEC Fluctuations and Losses of Lock Associated with Equatorial Plasma Bubbles  

NASA Astrophysics Data System (ADS)

Equatorial plasma bubbles (EPBs) are local depletions of the electron density in the ionosphere. Due to field-aligned irregularities (FAIs) with various spatial scales, EPBs affect wide-band radio waves and cause scintillations in GPS navigation system. Strong scintillation can cause a GPS receiver to lose lock on GPS signals because of rapid variations of signal amplitude and phase, and limit the availability of carrier phase measurements. Since the scintillation is caused by Fresnel diffraction, the spatial scale of FAIs that causes the scintillation of GPS signals is about 2-300 m. Therefore, loss of phase lock (LOL) on GPS signals is a reference of hundred-meter-scale FAIs. As EPBs are also associated with fluctuations of the total electron content (TEC), the enhancement of Rate of TEC change index (ROTI) occurs around EPBs. Assuming that the altitude of the ionosphere is about 400 km, the velocity of the pierce point of the GPS radio wave at the ionospheric altitude is approximately 70 m/s around the zenith. Thus, ROTI averaged during 5 minutes is a reference of ten-kilometer-scale fluctuations. In this study, we analyzed LOL and 5-min. ROTI associated with EPBs to examine the spatial and temporal scales of electron density disturbances associated with EPBs. We selected 11 EPBs from 630-nm airglow images obtained by all-sky imager at Sata, Japan, in 2001. LOL and ROTI are obtained from GPS data from GPS Earth Observation Network (GEONET) of Japan, which consists of more than 1000 GPS receivers. As a result, it is shown that both LOL and the enhancement of ROTI are observed in 8 events out of 11 events. The distributions of LOL are approximately consistent with the areas in which the ionospheric electron density is depleted. The enhancements of ROTI are observed in the vicinities of EPBs. The enhancement of ROTI expands especially in the west side of EPBs. After the EPBs pass through, therefore, LOLs are vanished but the enhancements of ROTI last a while. This result shows that the hundred-meter-scale irregularities are distributed within EPBs while the ten-kilometer-scale disturbances are located around EPBs. Such huge EPBs as to be observed in Japan will appear in solar maximum periods. Therefore it is important to prepare against the next solar maximum by examining characteristics of the EPBs. Fortunately, LOL and the enhancement of ROTI are treated as indicators of these huge EPBs since most of the EPBs are associated with them. Examinations of these EPBs must be progressed further.

Nakata, H.; Kikuchi, H.; Tsugawa, T.; Otsuka, Y.; Takano, T.; Shimakura, S.; Shiokawa, K.; Ogawa, T.

2009-12-01

35

Coordinated UV imaging of equatorial plasma bubbles using TIMED\\/GUVI and DMSP\\/SSUSI  

Microsoft Academic Search

Coincident and near-coincident Global Ultraviolet Imager (GUVI) and Special Sensor Ultraviolet Spectrographic Imager (SSUSI) plasma bubble images provide a unique opportunity to image the evolution of a single feature over a large longitude and time range. SSUSI and GUVI are currently the only two UV imagers that can provide low-Earth orbit measurements capable of reconstructing a multidimensional electron density map.

Joseph Comberiate; Larry J. Paxton

2010-01-01

36

Electric field observations of equatorial bubbles  

SciTech Connect

The authors present here results from the double floating probe experiment carried on the San Marco D satellite, with emphasis on the observations of large incremental changes in the convective electric field vector at the boundary of equatorial plasma bubbles. This study concentrates on isolated bubble structures in the upper ionospheric F region and divides these observed bubble encounters into two types, type 1 (live bubbles) and type 2(dead bubbles). Type 1 bubbles show varying degrees of plasma density depletion and upward velocities ranging from 100 to 1,000 m/s. Type 2 bubbles show plasma density depletion but no appreciable upward convection. Both types of events are often surrounded by a halo of plasma turbulence extending considerably outside the region's plasma depletion. Most type 1 events show some evidence for local continuity in the eastward (y) electric current, where the y component of the observed electric field (E{sub y}) shows hyperbolic correlation with the plasma density (n), as dictated by horizontal current continuity. This model stresses the importance of including magnetic field aligned currents in deriving the electric potential equation from the divergence equation {del} {times} j = 0. All of the type 1 (live) events examined exhibit a striking and systematic lack of conservation of the vertical component (x) of the electric field vector (E{sub x}) on crossing these structures. This lack of conservation of E{sub x} is of the order of 1.5 mV/m from west to east, directly implying that type 1 bubbles are not steady state plasma structures. A straightforward interpretation of this jump phenomenon in E{sub x} leads to the conclusion that the walls of most of the type 1 bubbles are collapsing inward at the rate of some 50 m/s.

Aggson, T.L. (NASA Goddard Space Flight Center, Greenbelt, MD (United States)); Maynard, N.C. (Air Force Geophysics Lab., Hanscom AFB, MA (United States)); Hanson, W.B. (Univ. of Texas, Dallas (United States)); Saba, J.L. (ST Systems Corp., Lanham, MD (United States))

1992-03-01

37

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

38

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

39

Electron density and electron temperature in the valley between the equatorial E and F regions during the presence of plasma bubbles - Some recent rocket observations  

NASA Astrophysics Data System (ADS)

Rocket measurements of electron density and electron temperature made from Brazil show that the electron density and electron temperatures in the valley region between the equatorial E and F regions get modified during the onset of plasma bubbles. During one of the launches the Langmuir probe measured abnormally large electron temperatures below the F-region just before the onset of plasma bubbles but temperatures became normal soon after the onset of bubbles. Recently a Brazilian VS-30 rocket was launched from the equatorial rocket launching station CLBI in Natal, Brazil carrying a Langmuir probe operated alternately in swept and constant bias modes to measure both electron temperature and electron density respectively. The ground equipments operated before and during the rocket launch clearly showed the presence of plasma bubbles above the F-region. At the time of launch the bubble activity was at its peak. The electron density and temperature height profiles could be estimated from the LP data up to the rocket apogee altitude of 139km. These profiles are compared with model electron density and temperature profiles as well as with electron density and temperature profiles observed during other rocket launches under conditions of no plasma bubbles in the F-region.

Muralikrishna, Polinaya; Batista, Inez S.; Domingos, Sinval; Goreti dos Santos Aquino, Maria

2012-07-01

40

Equatorial plasma bubble zonal velocity using 630.0 nm airglow observations and plasma drift modeling over Ascension Island  

NASA Astrophysics Data System (ADS)

We present OI (630.0 nm) airglow image data from Ascension Island (geographic: 7.9S, 14.4W dip latitude: 16S) in the southern Atlantic Ocean taken with the Utah State University all-sky CCD camera during 20 March to 7 April 1997 in order to study plasma bubbles occurring in the low-latitude nighttime ionosphere. The initial plasma bubble onset occurs in the early evening hours at 19:15-20:00 LST and is followed by eastward propagation with an average speed of 90-120 m/s prior to local midnight, rapidly decreasing around the midnight and postmidnight periods. The Ascension results are compared with similar observations from Christmas Island in order to examine the longitudinal variations of EPB development and propagation. The observed EPB velocities from Ascension Island are also compared with the results of a plasma drift model. In a case study during the night of 4-5 April, the velocity reveals unusual latitudinal shear, up to 0.12 m/s/km, with a reversal to westward flow at low latitudes while eastward flow is maintained at higher latitudes. Consequently, the bubble rotates counterclockwise and tilts eastward, significantly away from alignment with the geomagnetic field lines. The westward reversal of the drift motion near the geomagnetic equator is most likely the result of a reversal in the F region dynamo or from a large increase in the altitude of the shear node in the F region plasma drift at the geomagnetic equator.

Chapagain, Narayan P.; Taylor, Michael J.; Makela, Jonathan J.; Duly, Timothy M.

2012-06-01

41

Equatorial plasma depletions with large upward plasma flow over 3800 km in longitude near dawn: C/NOFS observations and model simulations  

NASA Astrophysics Data System (ADS)

A spectacular phenomenon in the equatorial ionosphere near dawn is the occurrence of plasma depletions in which the plasma density is reduced by 1-3 orders of magnitude over thousands of kilometers in longitude, and the plasma flow is strongly upward over the entire depletion region. This phenomenon is observed repeatedly by the Communication/Navigation Outage Forecasting System (C/NOFS) satellite during deep solar minimum. A series of plasma bubbles is first detected by C/NOFS over a longitudinal range of 3300-3800 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 exists for more than 7 hours, and the bubbles do not become dead/fossil bubbles when they reach dawn sector. The observations clearly show the evolution from multiple plasma bubbles into broad depletions. We propose that the broad plasma depletions with large upward plasma flow result from merging of multiple equatorial plasma bubbles. We 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.

Huang, C.; de la Beaujardiere, O.; Retterer, J. M.; Roddy, P.; Hunton, D. E.; Ballenthin, J.; Pfaff, R. F.

2011-12-01

42

Irregularity decay in an isolated plasma bubble  

NASA Astrophysics Data System (ADS)

Complex signal scintillation observations of an isolated and decaying equatorial plasma bubble are described. Multiple scans through the bubble made from the Air Force Geophysics Laboratory Airborne Ionospheric Observatory, show evolution of irregularity energy over a broad range of scale sizes. At wavelengths larger than about 4 km, the energy remains nearly constant with time. At shorter scale sizes, the spectrum maintains an approximate law form (f-n) and n increases with time. This behavior suggests that the effective cross-field diffusion rate in the F region depends on scale size. Such a dependence has recently been predicted theoretically and is the result of magnetic field line coupling to the E layer.

Livingston, R. C.; Vickrey, J. F.

1984-05-01

43

Model computations of radio wave scintillation caused by equatorial ionospheric bubbles  

Microsoft Academic Search

In situ data measured on board AE satellites and rockets reveal spiky and wedgelike electron density structures inside the equatorial ionospheric bubbles. Two models are constructed to simulate the initial stage and fully developed stage of a bubble. Effects of radio propagation through such bubbles are simulated by solving the parabolic equation numerically. The results show that even though the

A. W. Wernik; C. H. Liu; K. C. Yeh

1980-01-01

44

Space-based ultraviolet optical signatures of simulated equatorial ionospheric bubbles  

NASA Astrophysics Data System (ADS)

Space-based ultraviolet (UV) optical signatures of equatorial ionospheric bubbles have been computed from a first-principles time-dependent physical mesoscale ionospheric simulation model. We find that for nadir-viewing geometry, extreme UV signatures at 911 of equatorial ionospheric bubble structures contain large bite-outs in intensity, are structured over tens of kilometers scales, and are distinctly different from the signatures of the quiet ionosphere.

Keskinen, M. J.; Dymond, K. F.; Ossakow, S. L.

2001-12-01

45

Large-scale quasiperiodic plasma bubbles: C/NOFS observations and causal mechanism  

NASA Astrophysics Data System (ADS)

Large-scale periodic plasma bubbles are often observed by ionospheric radars and satellites. The seeding effect of atmospheric gravity waves has been widely used to explain the generation of periodic plasma bubbles. However, it has not been well understood where the seeding process occurs and how a series of plasma bubbles is triggered. In this study, we present the observations of equatorial plasma bubbles by the Communication/Navigation Outage Forecasting System (C/NOFS) satellite. We show examples of quasiperiodic plasma bubbles in the post-midnight sector, with nearly equal distance of 800-1000 km between adjacent bubbles, in 2008 under deep solar minimum conditions. The bubble chain covered a longitudinal range of ~7000 km between 00:00 and 04:00 LT. Quasiperiodic plasma bubbles were also measured by C/NOFS in the evening sector in 2011 during the ascending phase of the solar activity, and the longitudinal distance between adjacent bubbles was ~500 km. We propose a causal mechanism to explain the generation of quasiperiodic plasma bubbles. In this scenario, atmospheric gravity waves are generated near the sunset terminator and initiate the Rayleigh-Taylor instability there. The spatial (longitudinal) periodicity of plasma bubbles is determined by the temporal periodicity of the seeding gravity waves. A period of 15-30 min of the seeding gravity waves corresponds to a longitudinal separation of 500-1000 km between adjacent bubbles. This mechanism provides a reasonable explanation of the observed quasiperiodic plasma bubbles.

Huang, Chao-Song; La BeaujardiRe, O.; Roddy, P. A.; Hunton, D. E.; Ballenthin, J. O.; Hairston, M. R.; Pfaff, R. F.

2013-06-01

46

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

47

Plasma bubble detection in the DEMETER micro-satellite data  

NASA Astrophysics Data System (ADS)

The occurrence of plasma bubbles is the most important phenomenon that affects the night time equatorial ionosphere resulting in strong and localized drops of the plasma density with often very sharp boundaries. Besides its own interest for ionospheric physics this phenomenon is also of significant practical importance since it disrupts HF communication and GPS signal reception. In the frame of a French ANR funded project to model the rise and development of plasma bubbles we have searched for specific disturbances of the low latitude ionosphere that might be considered as "precursors" of plasma bubbles, possibly leading, under favourable conditions, to an instable ionosphere. To this aim, we have manually selected and classified typical events observed on data from two instruments on board the DEMETER satellite, IAP (Plasma analyzer) and ISL (Langmuir probe experiment). We present in this poster the various types of events and show that one of them appears to be associated with the later occurrence of plasma bubbles. From the first list of events recorded during an ~ 18 month period we will discuss in detail the plasma disturbances and present initial results of a statistical study.

Onishi, T.; Nguyen, C.-T.; Berthelier, J.-J.

2012-04-01

48

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

49

Seasonal/longitudinal variations of the topside plasma bubbles occurrence  

NASA Astrophysics Data System (ADS)

The present study deals with the seasonal and longitudinal (s/l) variations of the plasma bubble occurrence probability. Topside ionosphere plasma bubbles, seen as He+ density depletions of the topside ionosphere ( 1000 km) deeply inside the plasmasphere (L 1.3-3) (Sidorova, Adv. Space Res., 2004, 2007), are considered. He+ density depletions were obtained from ISS-b space-craft data (1978-80, F10.7 200) for the post-sunset hours under winter, summer and equinoctial condition in the interval of 25 -50 INVLAT for Southern and Northern hemispheres. The ob-tained statistics were compared with the s/l statistics of the equatorial F-region irregularities (EFI), based on the AE-E (McClure et al., JGR, 1998), OGO-6 (Basu et al., Radio. Sci., 1976) and ROCSAT (Su et al., JGR, 2006) data. Moreover, ESF and RSF (range spread-F) statistics, obtained (Maruyama and Matuura, JGR, 1980, 1884) from ISS-b data, and plasma bubble statistics, obtained (Watanabe and Oya, JGG, 1986) from Hinotori data (1981, 650 km), were taken for comparison. EFI, ESF (RSF) and plasma bubble statistics were obtained above the equatorial region within 20 DIPLAT under the same solar activity conditions. It was revealed that the main statistical maxima of the mentioned above equatorial F-region irregularities are well enough reflected in the s/l statistical plots of the He+ density depletions of the both hemispheres. The best conformity was obtained during the equinox periods, the worst one -during solstice periods, when the most dramatic insolation differences take place for the different hemispheres.

Sidorova, Larisa

50

Diagnostics of Microwave Bubble Plasma in Liquid  

NASA Astrophysics Data System (ADS)

Plasma production in the liquid phase has attracted much attention due to its potential applications such as biomedical or environmental processes. As a new technique, we have developed bubble plasma production in liquid with use of pulsed microwave from a slot antenna, and have succeeded in decomposing harmful chemicals such as trichloroethylene (TCE). In this work, optical emission and absorption spectroscopies were adopted to diagnose the microwave bubble plasma. OES result indicated strong OH emission from the plasma, suggesting production of reactive OH radical in the bubble plasma from water vapor. Furthermore, plasma density of the bubble plasma was investigated by time-resolved Stark broadening spectroscopy. To give insight into the reactive species in the liquid phase, plasma-treated water was investigated with UV/VIS optical absorption spectroscopy and a chemical reagent that is sensitive to hydrogen peroxide. From these measurements, existence of hydrogen peroxide in the liquid phase was confirmed.

Toyoda, Hirotaka; Sugiura, Hiroyasu; Saito, Ryota; Ishijima, Tatsuo

2008-10-01

51

Equatorial bubbles as observed with GPS measurements over Pune, India  

Microsoft Academic Search

Ionospheric total electron content (TEC) and scintillations have been recorded continuously since April 2003 using a dual-frequency GPS receiver at Pune, India (geographic latitude 19.1N, longitude 74.05E 24N dip), situated in between the magnetic equator and the northern crest of the equatorial anomaly. The TEC often shows bite-outs when severe amplitude scintillations are observed on the GPS L1 carrier level.

A. DasGupta; A. Paul; S. Ray; A. Das; S. Ananthakrishnan

2006-01-01

52

Equatorial bubbles as observed with GPS measurements over Pune, India  

Microsoft Academic Search

Ionospheric total electron content (TEC) and scintillations have been recorded continuously since April 2003 using a dual-frequency GPS receiver at Pune, India (geographic latitude 19.1N, longitude 74.05E; 24N dip), situated in between the magnetic equator and the northern crest of the equatorial anomaly. The TEC often shows bite-outs when severe amplitude scintillations are observed on the GPS L1 carrier level.

A. DasGupta; A. Paul; S. Ray; A. Das; S. Ananthakrishnan

2006-01-01

53

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

54

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

55

Vortex bubble formation in pair plasmas.  

PubMed

It is shown that delocalized vortex solitons in relativistic pair plasmas with small temperature asymmetries can be unstable for intermediate intensities of the background electromagnetic field. Instability leads to the generation of ever-expanding cavitating bubbles in which the electromagnetic fields are zero. The existence of such electromagnetic bubbles is demonstrated by qualitative arguments based on a hydrodynamic analogy, and by numerical solutions of the appropriate nonlinear Schrdinger equation with a saturating nonlinearity. PMID:23944600

Berezhiani, V I; Shatashvili, N L; Mahajan, S M; Aleksi?, B N

2013-07-18

56

Equatorial F-Region plasma depletion drifts: latitudinal and seasonal variations  

NASA Astrophysics Data System (ADS)

The equatorial ionospheric irregularities have been observed, in the past few years, by different techniques (e.g. ground-based radar, digisonde, GPS, optical instruments and in situ satellite and rocket instrumentation) and its time evolution and propagation characteristics can be used to study important aspects of ionospheric dynamics and thermosphere-ionosphere coupling. At present, one of the most powerful optical techniques to study the large-scale ionospheric irregularities is the all-sky imaging photometer system, which normally measures the strong F-region nightglow 630 nm emission from atomic oxygen. The monochromatic OI 630 nm emission images usually show quasi north-south magnetic field aligned intensity depletion bands, which are the bottomside optical signatures of large-scale F-region plasma irregularities (also called plasma bubbles). The zonal drift velocities of the plasma bubbles can be inferred from the space-time displacement of the dark structures (low intensity regions) seen on the images. In this study, images obtained with an all-sky imaging photometer, using the OI 630 nm nightglow emission, from Cachoeira Paulista (22.7 S, 45 W, 15.8 S dip latitude), Brazil, have been used to determine the nocturnal monthly and latitudinal variation characteristics of the zonal plasma bubble drift velocities in the low latitude (16.7S to 28.7S) region. The east and west walls of the plasma bubble show a different evolution with time. The method used here is based on the western wall of the bubble, which presents a more stable behavior. Also, the observed zonal plasma bubble drift velocities are compared with the thermospheric zonal neutral wind velocities obtained from the HWM-90 model to investigate the thermosphere-ionosphere coupling. Salient features from this study are presented and discussed.

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

2003-04-01

57

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

58

Storm-enhanced plasma density (SED) features, auroral and polar plasma enhancements, and rising topside bubbles of the 31 March 2001 superstorm  

NASA Astrophysics Data System (ADS)

This study focuses on the 31 March 2001 superstorm's evening and nighttime sectors. We specified forward fountain circulation and equatorial ionization anomaly (EIA), storm-enhanced density (SED) plume plasma flows, auroral zones, polar cap regions, and traveling ionospheric disturbances (TIDs). These permitted analyzing low-latitude plasma structures, and middle- and high-latitude plasma buildups. Results reveal significant low-latitude plasma structuring around Ancon due to topside rising bubbles during the initial phase under disturbance conditions. The deep equatorial plasma depletion, appearing over the Pacific during the main phase, is an EIA-trough-bubble structure. Topside bubbles and TID-related drift perturbations structured SED plume plasma. Plasma distribution maximized when TIDs were in phase with fountain circulation and SED plume plasma flows, and equatorward wind surges maintained high plasma densities. Plasma density and plasma flow measurements demonstrate the SED plume plasma's poleward migration through the auroral zone into the polar region and the maintenance and increase of auroral and polar enhancements forming a polar tongue of ionization (TOI). Our results contradict previous studies on this superstorm reporting the suppression of bubble formation over Ancon and the absence of TOI and explaining the development of equatorial depletion with no E B drift action. Our results oppose the current hypothesis that plasma enhancements are transported over many hours into the polar region. Indeed, SED plume plasma (produced by plasmaspheric detachment processes) creates multiple downward plasma flows (stretching from the midlatitude trough's equatorward edge to the polar cap region) that in turn create plasma buildups at various latitudes where flow stagnates.

Horvath, Ildiko; Lovell, Brian C.

2011-04-01

59

Day-to-day variability in the development of plasma bubbles associated with geomagnetic disturbances  

NASA Astrophysics Data System (ADS)

The development of equatorial ionospheric irregularities into large-scale ionospheric plasma bubbles continues to be an active area for scientific investigations. In this paper, we present simultaneous OI 630.0-nm emission all-sky imaging observations carried out at the Astrophysics National Laboratory (LNA), Brazopolis (22.5S, 45.6W, altitude 1860 m) and ionospheric sounding observations carried out at Palmas (10.2S, 48.2W located close to the magnetic equator) and Sao Jose dos Campos (23.2S, 45.9W located under the southern crest of equatorial ionospheric anomaly, close to Brazopolis), Brazil, to study the day-to-day variability in the development of ionospheric plasma bubbles during both geomagnetically disturbed and quiet periods in September-October 2002. Also, we present simultaneous complementary phase fluctuation (ROT) data obtained from the global position system (GPS) meridional chain operated by the Brazilian Institute of Geography and Statistic (IBGE). On the three nights studied in the present investigation (one geomagnetically quiet and two geomagnetically disturbed), it has been observed that the geomagnetic disturbances, during this spring equinox period, have a strong effect on the generation and development of ionospheric plasma bubbles.

Abalde, J. R.; Sahai, Y.; Fagundes, P. R.; Becker-Guedes, F.; Bittencourt, J. A.; Pillat, V. G.; Lima, W. L. C.; Candido, C. M. N.; de Freitas, T. F.

2009-04-01

60

Day-to-day variability in the development of plasma bubbles associated with geomagnetic disturbances  

NASA Astrophysics Data System (ADS)

The development of equatorial ionospheric irregularities into large-scale ionospheric plasma bubbles continues to be an active area for scientific investigations. In this paper we present simultaneous ionospheric sounding observations carried out at Palmas (10.2 S, 48.2 W; located close to the magnetic equator) and Sao Jose dos Campos (23.2 S, 45.9 W; located under the southern crest of equatorial ionospheric anomaly), and OI 630.0 nm emission all-sky imaging observations carried out at the Astrophysics National Laboratory (LNA), Brazopolis (22.5 S, 45.6 W, altitude 1860 m; located close to Sao Jose dos Campos), Brazil, to study the day-to-day variability in the development of ionospheric plasma bubbles during geomagnetic disturbance in September - October, 2002. Also, we present simultaneous complementary vertical total electron content (VTEC) and phase fluctuation data obtained from the GPS (Global Position System) meridional chain operated by Brazilian Network for Continuous Monitoring (RBMC). On the four nights studied in the present investigation (one geomagnetically quiet and three geomagnetically disturbed) it has been observed that the geomagnetic disturbances, during this spring-equinox period, show strong effect on the generation and development of ionospheric plasma bubbles.

Abalde Guede, Jose Ricardo; Abalde Guede, Jose Ricardo; Sahai, Yogeshwar; Fagundes, Paulo Roberto; Becker-Guedes, Fabio; Bittencourt, Jose A.; Pillat, Valdir G.; Lima, Washington L. C.; Nicoli Candido, Claudia Maria

61

Spread F plasma bubble vertical rise velocities determined from spaced ionosonde observations  

SciTech Connect

Systematic time differences in the onsets of spread F events in the ionograms are observed between the magnetic equatorial station Fortaleza (4/sup 0/S, 38/sup 0/W, dip latitude 1.8/sup 0/S) and the low-latitude station Cachoeira Paulista (23/sup 0/S, 45/sup 0/W, dip latitude 14/sup 0/S), two stations in Brazil, located at close-by magnetic meridional planes (actually some 12/sup 0/ of magnetic longitude apart). On the assumption, justified from different experimental observations, that the spread F irregularities occur in strongly field-aligned plasma bubbles that extend several degrees on either side of the magnetic equator, and rise up in vertically elongated columns over the magnteic equator, we have related the observed time differences in the onsets of spread F events at the two stations to the plasma bubble vertical rise velocities of the plasma bubbles so determined are found to be well within the values measured by VHF radar and satellite techniques, and further show, at times, good correlations with the amplitude of the prereversal peak in the vertical drift velocities and the heights of the evening equatorial F layer. Possible implications of these results are discussed.

Abdu, M.A.; de Medeiros, R.T.; Sobral, J.H.A.; Bittencourt, J.A.

1983-11-01

62

Cluster and Double Star multipoint observations of a plasma bubble  

Microsoft Academic Search

Depleted flux tubes, or plasma bubbles, are one possible explanation of bursty bulk flows, which are transient high speed flows thought to be responsible for a large proportion of flux transport in the magnetotail. Here we report observations of one such plasma bubble, made by the four Cluster spacecraft and Double Star TC-2 around 14:00 UT on 21 September 2005,

A. P. Walsh; A. N. Fazakerley; A. D. Lahiff; M. Volwerk; A. Grocott; M. W. Dunlop; A. T. Y. Lui; L. M. Kistler; M. Lester; C. Mouikis; Z. Pu; C. Shen; J. Shi; M. G. G. T. Taylor; E. Lucek; T. L. Zhang; I. Dandouras

2009-01-01

63

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

64

Further results referring to the neutral density depletions attributed to plasma bubbles  

NASA Astrophysics Data System (ADS)

The interaction between the ionized and neutral components of the upper atmosphere (ion drag, air drag) is not limited to the large-scale motions, but it works also among the small-scale motions. This is demonstrated by neutral density depletions (NDD) revealed by us in the neutral density measurements of great time resolution of the San Marco V satellite. The morphological and statistical investigations indicate that NDDs and plasma bubbles have similar characteristics. On the other hand, according to modelling, depletions of the total neutral density discovered by us below a height of about 350 km (collision-dominated case) in the vicinity of the equator might be really due to equatorial plasma bubbles. The relation of the NDDs to plasma bubbles (ion density depletions) is studied partly by direct comparison and modelling, partly indirectly by the distribution of the occurrence of NDDs according to local solar time, to season, to height and to longitude. All of them are arguing in favour of the plasma bubble origin of the NDDs.

Bencze, P.; Almr, I.; Ills-Almr, E.

2000-10-01

65

Plasma and Magnetic Periodicities in Saturn's Equatorial Ring Current  

NASA Astrophysics Data System (ADS)

Using data taken by the Cassini MAG instrument in 2005 and 2006, we apply the spectrum analysis technique adopted by Gurnett et al. [2007], which fits a sine wave to the normalized SKR amplitude, iteratively sweeping the period to determine the period(s) for which the sine fit has its maximum amplitude. We find that the amplitude of the magnetic pressure variation in the equatorial plane between 6 and 15 Rs maximizes at the SLS4 South frequency, with a secondary maximum that falls near the SLS4 North frequency. We also identify weak but consistent signatures of both the SLS4N frequency and the SLS4S frequency in the total ion pressure in Saturn's equatorial region. In this presentation we expand our initial study to include the more recent equatorial orbits in 2009-2010. This interval is of particular interest, as it coincides with the equinox and subsequent "cross-over" of the SLS North and South frequencies, as reported by Gurnett et al. [2009] and Lamy [2010]. We report an anti-phase relationship between variations in thermal plasma pressure and magnetic pressure, assuming that both rotate at the SLS4 South rate. We will examine whether the amplitude of the periodic signal in the magnetic pressure and RPWS electron density varies with local time.

Ramer, K. M.; Kivelson, M. G.; Sergis, N.; Khurana, K. K.; Walker, R. J.; Persoon, A. M.

2011-12-01

66

Features of highly structured equatorial plasma irregularities deduced from CHAMP observations  

NASA Astrophysics Data System (ADS)

In this study five years of CHAMP (Challenging Mini-satellite Payload) fluxgate magnetometer (FGM) data is used to investigate the characteristics of Equatorial Plasma Bubbles (EPBs). We filtered the FGM data by using band-passes with four different cut-off periods to get the EPBs with different maximum spatial scale sizes in the meridional plane ranging from 76-608 km. Associated with the EPB observations at about 400 km, the typical altitude of CHAMP during the year 2000-2005, we also investigate the post-sunset equatorial vertical plasma drift data from ROCSAT-1 (Republic of China Satellite 1). Since the height of the F-layer is highly correlated with the vertical plasma drift and solar flux, we sorted the ROCSAT-1 data into different groups by F10.7. From the integrated vertical drift we have estimated the post-sunset uplift of the ionosphere. By comparing the properties of EPB occurrence for different scale sizes with the global distribution of plasma vertical uplift, we have found that EPBs reaching higher altitudes are more structured than those which are sampled by CHAMP near the top side of the depleted fluxtube. Such a result is in accord with 3-D model simulations (Aveiro and Hysell, 2010). Small-scale EPB structures are observed by CHAMP when the irregularities reach apex heights of 800 km and more. Such events are encountered primarily in the Brazilian sector during the months around November, when the post-sunset vertical plasma drift is high.

Xiong, C.; Lhr, H.; Ma, S. Y.; Stolle, C.; Fejer, B. G.

2012-08-01

67

Plasma formation inside deformed gas bubbles submerged in water  

NASA Astrophysics Data System (ADS)

Plasma formation in liquids produces highly reactive products that may be desirable for a variety of applications, including water purification and waste processing. The direct ignition of plasma in these environments, however, is limited by the large breakdown strength of liquids, which imposes severe voltage and energy requirements on the design of practical devices. One way to address this issue is by first igniting plasma in gas bubbles injected into the water. These bubbles provide an environment with higher reduced electric field (E/N) that is more suitable for plasma formation. If the same bubbles can be excited into strong distortions of their shape and volume, then it is possible to further alter E/N, both by field enhancement at the bubble's highly distorted dielectric interface (via E) and by fluctuations in its internal gas pressure (via N). This principle is investigated by trapping a single bubble at the node of a 26.4 kHz underwater acoustic field and driving it into violent oscillations using an A.C electric field. A third high voltage needle is placed nearby and used to ignite plasma in the bubble at various points during its oscillation. The bubble response is captured using a high speed camera capable of up to 30,000 frames per second.

Sommers, Bradley; Foster, John

2012-10-01

68

Three-dimensional numerical simulation of equatorial F region plasma irregularities with bottomside shear flow  

Microsoft Academic Search

A three-dimensional numerical simulation of plasma density irregularities in the postsunset equatorial F region ionosphere leading to equatorial spread F (ESF) is described. The simulation advances the plasma number density and electrostatic potential forward in time by enforcing the constraints of quasi-neutrality and momentum conservation. The magnetic field lines are not modeled as equipotentials. Simulations are performed for cases with

H. C. Aveiro; D. L. Hysell

2010-01-01

69

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

70

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.

71

Magnetic Bubble Formation Produced by an Expanding Laser Plasma.  

National Technical Information Service (NTIS)

A magnetic depleted bubble resulting from the expansion of a laser-generated debris plasma into a low density magnetized background plasma is observed. A compressed magnetic field propagates slightly ahead of the debris plasma and has a thickness on the o...

S. T. Kacenjar B. H. Ripin J. A. Stamper J. Grun E. A. McLean

1984-01-01

72

Plasma core at the center of a sonoluminescing bubble  

NASA Astrophysics Data System (ADS)

Considering high temperature and pressure during single bubble sonoluminescence collapse, a hot plasma core is generated at the center of the bubble. In this paper a statistical mechanics approach is used to calculate the core pressure and temperature. A hydrochemical model alongside a plasma core is used to study the bubble dynamics in two host liquids of water and sulfuric acid 85 wt % containing Ar atoms. Calculation shows that the extreme pressure and temperature in the plasma core are mainly due to the interaction of the ionized Ar atoms and electrons, which is one step forward to sonofusion. The thermal bremsstrahlung mechanism of radiation is used to analyze the emitted optical energy per flash of the bubble core.

Bemani, F.; Sadighi-Bonabi, R.

2013-01-01

73

Mathematical modeling of plasma drifts over equatorial low latitude regions  

NASA Astrophysics Data System (ADS)

This paper presents a mathematical model to simulate ionospheric plasma drifts at equatorial low latitude regions by coupling of E- and F-regions. The governing non-linear differential equations (of elliptic and parabolic nature) are solved numerically through finite-difference schemes and obtained neutral winds and electric fields. The temperature and electron density profiles are generated utilizing MSIS-86 atmospheric model. The continuity equation is employed to obtain night-time E-region density profile using measured ionograms at Trivandrum (India). The computed vertical and zonal plasma drifts are comparable with measured Jacamarca plasma drifts with little variations during noon and evening times. The plasma drifts at Trivandrum (8.5 N, 76.5 E, dip 0.5 N) are compared with those of Jicamarca (12 S, 76.9 W, dip 2 N). Neutral wind simulations of present model agree well with those of horizontal wind model (HWM-93). The post-sunset enhancement and its reversal are also discussed.

Sundaresan, S.; Nageswara Rao, B.

2010-09-01

74

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.

75

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

76

Seasonal and longitudinal variations of equatorial plasma depletions  

NASA Astrophysics Data System (ADS)

In this work, we examine the seasonal and longitudinal variation of equatorial plasma depletions. Due to their three-dimensional structure, we also refer to them as, equatorial topside channels. All channels are found to be comprised of contiguous simple-channel scale (<150 km longitudinal width) substructure. We interpret the substructure as parallel rising channels of depleted plasma. Three classes of structure are identified, based on the width of the channel and the number of internal simple channels. Within a given longitude region, there is comparatively little seasonal variation in the relative numbers of each channel class or their large-scale characteristics. However, we find significant longitudinal variations in all parameters. Superscale (500--1000 km zonal width) channels are found to predominate in Atlantic-African sector, while simple (50--150 km) and mesoscale (200--500) channels dominate in the Pacific. Atlantic-African channels are on average more highly depleted than Pacific channels, and a superscale background oscillation is most often seen in the Atlantic-African sector. We find evidence that the presence or absence of seeds contributes to the occurrence frequency of channels in a given longitude. Additionally, we find that the preponderance of superscale channels in the Atlantic-African sector leads to a higher penetration rate of channels into the topside. This result clarifies past observations which noted greater topside activity in the African sector. Our finding of the ubiquity of bottomside structure, with the result that all channels are comprised of 50--150 km substructure, leads us to conclude that the bottomside is often pre-seeded with simple-scale size structure.

Hei, Matthew A.

77

Observations and modeling of the coupled latitude-altitude patterns of equatorial plasma depletions  

Microsoft Academic Search

The equatorial ionosphere is host to the most dramatic and enigmatic plasma instability mechanism in the geospace environment. Equatorial spread F (ESF) was discovered in early ionosonde measurements and interpreted theoretically using Rayleigh-Taylor theory. Subsequent diagnostic and modeling advances have improved substantially our understanding of ESF onset and evolution and its associated effects on the ionosphere throughout the low-latitude domain.

Michael Mendillo; Eftyhia Zesta; Sheela Shodhan; Peter J. Sultan; Richard Doe; Yogeshwar Sahai; Jeffrey Baumgardner

2005-01-01

78

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

79

Oscillating plasma bubbles. IV. Grids, geometry, and gradients  

NASA Astrophysics Data System (ADS)

Plasma bubbles are created in an ambient plasma. The bubble is formed inside a cavity bounded by a negatively biased grid. Ions are injected through the grid and neutralized by electrons from either the background plasma or an internal electron emitter. The external electron supply is controlled by the grid bias relative to the external plasma potential. When the electron flux is restricted to the ion flux, the sheath of the bubble becomes unstable and causes the plasma potential to oscillate near the ion plasma frequency. The exact frequency depends on the net space charge density in the bubble sheath. The frequency increases with density and grid voltage, provided the grid forms a parallel equipotential surface. The present investigation shows that when the Debye length becomes smaller than the grid openings the electron flux cannot be controlled by the grid voltage. The frequency dependence on grid voltage and density is modified creating frequency and amplitude jumps. Low frequency sheath oscillations modulate the high frequency normal oscillations. Harmonics and subharmonics are excited by electrons in an ion-rich sheath. When the plasma parameters vary over the bubble surface, the sheath may oscillate at different frequencies. A cavity with two isolated grids has been used to investigate anisotropies of the energetic electron flux in a discharge plasma. The frequency dependence on grid voltage is entirely different when the grid controls the energetic electrons or the bulk electrons. These observations are important to several fields of basic plasma physics, such as sheaths, sheath instabilities, diagnostic probes, current, and space charge neutralization of ion beams.

Stenzel, R. L.; Urrutia, J. M.

2012-08-01

80

Dynamics and interactions of pulsed laser generated plasma bubbles in dusty plasma liquids  

NASA Astrophysics Data System (ADS)

The plasma bubble with dust particle depletion can be generated by a nano-second laser pulse focused on one of the dust particles suspended in a strongly coupled dusty plasma liquid. The bubble dynamics at different time scales, including the initial forming and later traveling stages are investigated. In the first stage, dust particles are pushed outward by the outward ion flow associated with the plume generated by the more intensed plasma. The bubble then travels downward at a speed about 60 mm/s associated with a surrounding dipole-like dust flow field. Two bubbles can also be simultaneously generated at different locations by separated laser pulses to study their interactions. Strong coupling is observed between two vertical bubbles. However, two horizontal bubbles are weakly coupled. The possible mechanism is discussed.

Chu, Hong-Yu; Liao, Chen-Ting; Lin, I.

2005-10-01

81

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

82

Laser-Induced Plasma In a Water Bubble  

SciTech Connect

In this work we present a theoretical study concerning the Laser Induced Breakdown Spectroscopy (LIBS) in water. The strong influence of chemical processes on the fluid dynamic expansion has been investigated. To this aim a fluid dynamic code has been developed and coupled with a chemical model, considering the plasma inside the bubble in local thermodynamic equilibrium (LTE)

Casavola, A.; Pesce, L. [Dipartimento di Chimica, Universita di Bari (Italy); Colonna, G. [CNR-IMIP, Bari section (Italy); Capitelli, M. [Dipartimento di Chimica, Universita di Bari (Italy); CNR-IMIP, Bari section (Italy)

2005-05-16

83

Modulation of equatorial electrojet plasma waves by overshielding electric field during geomagnetic storms  

NASA Astrophysics Data System (ADS)

This brief report presents daytime 30 MHz radar observations of equatorial electrojet plasma irregularities in So Lus, Brazil, during the 10 January 2002, 4 September 2002, and 6 November 2001 geomagnetic storms. Modulation of equatorial electrojet plasma waves by the overshielding electric field is detected by the radar during the January and September storm events. The depressions of radar echo intensity observed by the So Lus radar during the 10 January and 4 September 2002 storms are caused by inhibition of large-, medium-, and short-scale electrojet plasma waves by the overshielding electric field. Corresponding to the depressions of the radar echoes, counter equatorial electrojets were observed by ground-based magnetometer in So Lus. The influences of disturbance dynamo, undershielding, and overshielding electric fields on the equatorial electrojet irregularities and current have been evident on the 6 November 2001 radar and magnetic field data. This study demonstrates the control of the equatorial electrojet plasma waves (growth and suppression) by the interplanetary magnetic field and also the coupling between the high-latitude and equatorial ionospheres.

Shume, E. B.; de Paula, E. R.; Abdu, M. A.

2011-08-01

84

Zonal Distribution of Plasma Bubble Occurrence Studied with Ground-based GPS Receiver Networks  

NASA Astrophysics Data System (ADS)

Zonal distribution of plasma bubble occurrence was investigated with ground-based GPS receiver networks between India and Guam. Total Electron Content (TEC) measurement by a ground-based GPS receiver can observe spatial and temporal variations of plasma bubble activity in its field-of-view of 700km. To increase its field-of-view, plasma bubbles were back-traced to the location where they were generated with three assumptions for their generation time, drift velocity, and decay of their activity. The "back-trace" method makes possible to reveal the zonal distribution of plasma bubble activity for wider than 2,000km in the zonal direction from single ground-based GPS receiver. In this study, zonal distribution of plasma bubble activity was investigated for wider than 10,000km from 60E to 150E using 11 ground-based GPS receivers data in 2003. 1,585 of plasma bubbles were detected, which were almost all of the plasma bubbles appeared in the are and in the period. The estimated plasma bubble distribution using GPS network was consistent with that measured by the FORMOSAT-1 satellite. Statistical study was done for the zonal width of plasma bubble and intervals between plasma bubbles. It was found that more than 60% out of 1,585 plasma bubbles had shorter zonal width than 150km. It was also found that more than 80% of intervals of plasma bubbles had shorter length than 350km. Plasma drift velocity shear and atmospheric gravity wave could control the zonal distribution of plasma bubbles.

Nishioka, M.; Saito, A.; Tsugawa, T.

2009-05-01

85

Radar interferometric imaging of field-aligned plasma irregularities in the equatorial electrojet  

Microsoft Academic Search

A multiple-receiver radar technique for imaging the spatial distribution of ionospheric plasma irregularities is introduced and demonstrated with equatorial electrojet data obtained at the Jicamarca Radio Observatory. The images obtained with a few seconds time resolution enable the monitoring of the temporal evolution of the irregularity structures within the radar field of view. Daytime electroject images contain signatures of localized

Erhan Kudeki; Fahri Surucu

1991-01-01

86

Bubbles  

NASA Astrophysics Data System (ADS)

Vanitas vanitatum et omnia vanitas: bubbles are emptiness, non-liquid, a tiny cloud shielding a mathematical singularity. Born from chance, a violent and brief life ending in the union with the (nearly) infinite. But a wealth of phenomena spring forth from this nothingness: underwater noise, sonoluminescence, boiling, and many others. Some recent results on a ``blinking bubble'' micropump and vapor bubbles in sound fields are outlined. The last section describes Leonardo da Vinci's observation of the non-rectlinear ascent of buoyant bubbles and justifies the name Leonardo's paradox recently attributed to this phenomenon.

Prosperetti, Andrea

2004-06-01

87

Electrical coupling of the E and F regions and its effects on plasma bubble: A study using all-sky imaging in the OI 630 nm emission  

NASA Astrophysics Data System (ADS)

One of the manifestations of the depleted magnetic flux tubes in the nighttime equatorial ionospheric F layer is a reduction in the OI 630 nm emission nightglow intensity as compared with the surrounding regions. As these depleted flux tubes rise through the F layer in the magnetic equator region, their bottomside feet migrate poleward, sometimes reaching dip latitudes of over 20^o. During this stage, the vertical motion is driven by the gravitational Rayleigh-Taylor mechanism, and the depleted flux tubes can reach well over 1500 km apex height at the magnetic equator. In this work, observations of the OI 630 nm emission nightglow intensity images using a ground-based all-sky system, recently conducted at Cachoeira Paulista (latitude 22.7^oS, longitude 45^oW, altitude 550 m, dip latitude 17.9^oS, declination 20.5^oW), have been used to study the electro-dynamical processes required to describe the evolution/modulation of the plasma bubbles. It is observed that the time required for full development of the plasma bubbles during the months of October and March takes about 30-40% more time to achieve full development stage than during the months of November to February. Qualitatively, this can be understood in terms of the shorting effect of the background plasma, by which a given current is being driven by a smaller electric field, which in turn means smaller plasma velocities. Since the conductivity along magnetic field lines is extremely high, these electric fields may also depend on the dynamics of plasma far from the equatorial region, but connected to the equatorial region by magnetic field lines. We investigated the role of E region sunset (latitudinal gradient in the E region conductivity) in the evolution/modulation of the plasma bubbles by determining the local solar time at the dip equator when the conjugate E layers enter in darkness.

Pimenta, A.; Fagundes, P.; Bittencourt, J.; Sahai, Y.; Takahashi, H.

2003-04-01

88

Comparison of Nighttime Zonal Neutral Winds and Plasma Bubble Drift Velocities over Brazil  

NASA Astrophysics Data System (ADS)

We present the first simultaneous measurements of equatorial thermospheric neutral wind measurements and plasma bubble (EPB) zonal speeds over northeastern Brazil during September-December 2009 and 2010. The wind data are obtained from a bi-static Fabry-Perot interferometer experiment measuring the Doppler shift of the 630.0-nm spectral emission. The FPIs are located at Cajazeiras (6.86S, 38.56W) and Cariri (7.38S, 36.53W). The EPB zonal speed, which is assumed to be equal to the drift of the background plasma, is measured using images of the 630.0-nm emission obtained from a wide-angle imaging system collocated with the FPI at Cajazeiras. In general, the simultaneous measurement of the zonal neutral wind and the EPB zonal speed show excellent agreement. However, the EPB zonal speed is slower than that of the wind motion in the early evening hours on several occasions, suggesting the F-region dynamo is not fully activated.

Chapagain, N. P.; Makela, J. J.; Meriwether, J. W.; Buriti, R. A.; Medeiros, A.

2011-12-01

89

Design and Construction of the Plasma Bubble Expansion Experiment  

NASA Astrophysics Data System (ADS)

We will present the design and construction of a new compact coaxial magnetized plasma gun and its associated hardware systems. The plasma gun will be used for experimental studies of ``magnetic bubble'' expansion into a pre-existing lower density background plasma on the HELCAT facility at UNM. These experiments will address key nonlinear plasma physics issues pertinent to plasma models of the formation and evolution of extra-galactic radio lobes. The gun will be powered by a 120?F 10kV ignitron-switched capacitor bank. High pressure gas, controlled by a gas valve system, will be puffed into an annular gap between inner and outer coaxial electrodes. An applied high voltage ionizes the gas and creates a radial current sheet. The 100kA discharge current generates toroidal flux, and an external magnet will provide poloidal ``bias'' flux. This poster will describe in detail the design and construction of the various power systems for the new plasma gun source.

Zhang, Y.; Lynn, A. G.; Hsu, S. C.; Gilmore, M.; Watts, Christopher

2007-11-01

90

Micro Dynamics of Pulsed Laser Induced Bubbles in Dusty Plasma Liquids  

NASA Astrophysics Data System (ADS)

We experimentally study the micro dynamics of the laser induced plasma bubble in a dusty plasma liquid formed by negatively charged dust particles suspended in a low pressure rf Ar glow discharge. The plume from the ablation of the suspended dust particles pushes away dust particle and generates a dust-free plasma bubble. It then travels downward. The spatio-temporal evolution of the dust density fluctuation surrounding the bubble is monitored by directly tracking dust motion through optical video microscopy. The micro dynamics of the bubble associated dust acoustic type solitary oscillation in the wake field is investigated and discussed.

Teng, Lee-Wen; Tsai, Chen-Yu; Tseng, Yu-Ping; I, Lin

2008-09-01

91

OGO 6 measurements of supercooled plasma in the equatorial exosphere  

Microsoft Academic Search

Plasma measurements performed on Ogo 6 reveal T\\/sub e\\/ and T\\/sub i\\/ ; values that on occasion appear to be well below the expected neutral gas ; temperature. The phenomenon is observed only at night above 500 km near the ; magnetic equator. It is suggested that the expansion cooling of the plasma is ; accomplished by downward motions of

W.B. Hanson; A.F. Nagy; R. J. Moffett

1973-01-01

92

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

93

Searching for quark-gluon plasma (QGP) bubble effects at RHIC\\/LHC  

Microsoft Academic Search

Since the early eighties, we have shared with van Hove the following view: If a quark-gluon plasma were produced in high energy heavy ion colliders, then its hadronization products would likely come from small bubbles of plasma localized in phase space. We develop a model based on HIJING, to which we added a ring of adjoining multiple bubbles in the

S. J. Lindenbaum; R. S. Longacre; M. Kramer

2003-01-01

94

Characterization of single and colliding laser-produced plasma bubbles using Thomson scattering and proton radiography  

NASA Astrophysics Data System (ADS)

Time-resolved measurements of electron and ion temperatures using Thomson scattering have been combined with proton radiography data for comprehensive characterization of individual laser-produced plasma bubbles or the interaction of bubble pairs, where reconnection of azimuthal magnetic fields occurs. Measurements of ion and electron temperatures agree with lasnex simulations of single plasma bubbles, which include the physics of magnetic fields. There is negligible difference in temperatures between a single plasma bubble and the interaction region of bubble pairs, although the ion temperature may be slightly higher due to the collision of expanding plasmas. These results are consistent with reconnection in a ?8 plasma, where the release of magnetic energy (<5% of the electron thermal energy) does not appreciably affect the hydrodynamics.

Rosenberg, M. J.; Ross, J. S.; Li, C. K.; Town, R. P. J.; Sguin, F. H.; Frenje, J. A.; Froula, D. H.; Petrasso, R. D.

2012-11-01

95

Three-dimensional numerical simulation of equatorial F region plasma irregularities with bottomside shear flow  

NASA Astrophysics Data System (ADS)

A three-dimensional numerical simulation of plasma density irregularities in the postsunset equatorial F region ionosphere leading to equatorial spread F (ESF) is described. The simulation advances the plasma number density and electrostatic potential forward in time by enforcing the constraints of quasi-neutrality and momentum conservation. The magnetic field lines are not modeled as equipotentials. Simulations are performed for cases with no background winds, with no background electric field or gravity, and with winds, a background electric field, and gravity all working in concert. The first run produced generalized Rayleigh Taylor (GRT) instability, and the second produced collisional shear instability (CSI). The combined run produced an instability which developed into an intense ESF event more quickly and with more realistic characteristics than the other two. Simulation results are compared with incoherent and coherent scatter radar data from the magnetic equator. A number of signature ESF characteristics are shown to be reproduced by the simulation.

Aveiro, H. C.; Hysell, D. L.

2010-11-01

96

Response to ''Comment on 'Scalings for radiation from plasma bubbles''' [Phys. Plasmas 18, 034701 (2011)  

SciTech Connect

In the preceding Comment, Corde, Stordeur, and Malka claim that the trapping threshold derived in my recent paper is incorrect. Their principal argument is that the elliptical orbits I used are not exact solutions of the equation of motion in the fields of the bubble. The original paper never claimed this--rather I claimed that the use of elliptical orbits was a reasonable approximation, which I based on observations from particle-in-cell simulations. Integration of the equation of motion for analytical expressions for idealized bubble fields (either analytically [I. Kostyukov, E. Nerush, A. Pukhov, and V. Seredov, Phys. Rev. Lett. 103, 175003 (2009)] or numerically [S. Corde, A. Stordeur, and V. Malka, ''Comment on 'Scalings for radiation from plasma bubbles,' '' Phys. Plasmas 18, 034701 (2011)]) produces a trapping threshold wholly inconsistent with experiments and full particle-in-cell (PIC) simulations (e.g., requiring an estimated laser intensity of a{sub 0{approx}}30 for n{sub e{approx}}10{sup 19} cm{sup -3}). The inconsistency in the particle trajectories between PIC and the numeric model used by the comment authors arises due to the fact that the analytical fields are only approximately true for ''real'' plasma bubbles, and lack certain key features of the field structure. Two possible methods of resolution to this inconsistency are either to find ever more complicated but accurate models for the bubble fields or to find approximate solutions to the equations of motion that capture the essential features of the self-consistent electron trajectories. The latter, heuristic approach used in my recent paper produced a threshold that is better matched to experimental observations. In this reply, I will also revisit the problem and examine the relationship between bubble radius and electron momentum at the point of trapping without reference to a particular trajectory.

Thomas, A. G. R. [Centre for Ultrafast Optical Science, University of Michigan, Ann Arbor, Michigan 48109 (United States)

2011-03-15

97

Coordinated airborne and satellite measurements of equatorial plasma depletions  

Microsoft Academic Search

A series of experiments was conducted in December 1979 to investigate the structure of plasma depletions in the low latitude, nightime ionosphere. The measurements included all sky imaging photometer (ASIP), ionosonde and amplitude scintillation observations from the AFGL Airborne Ionospheric Observatory (AIO), and in situ ion density measurements from the Atmosphere Explorer (AE-E) Bennett Ion Mass Spectrometer (BIMS). The AIO

E. J. Weber; H. C. Brinton; J. Buchau; J. G. Moore

1982-01-01

98

Nonlinear evolution of equatorial spread F 4. Gravity waves, velocity shear, and day-to-day variability  

Microsoft Academic Search

Production and evolution of plasma bubbles seeded by gravity waves in the equatorial F region are studied under different conditions using a computer simulation. The problem of day-to-day variability in the occurrence of equatorial spread F (ESF) is discussed. It is shown that gravity waves over a wide range of amplitude and wavelength are a very effective seed mechanism for

Chao-Song Huang

1996-01-01

99

Equatorial aeronomy; International Symposium, 8th, San Miguel de Tucuman, Argentina, Mar. 21-27, 1990, Selected Papers  

NASA Astrophysics Data System (ADS)

Progress in the understanding of the complex processes controlling the coupling of the different regions in the low latitude and equatorial atmosphere is reviewed. Topics under consideration include early incoherent scatter observations at Jicamarca, low latitude electrodynamic plasma drifts, the equatorial spread-F and neutral atmospheric turbulence, rocket observations in the equatorial electrojet, solar activity effects on an equatorial plasma bubble zonal velocity and its latitude gradient as measured by airglow scanning photometers, zonal irregularity drifts and neutral winds measured near the magnetic equator in Peru, multiple beam observations of midlatitude ionospheric disturbances by the MU radar, and in situ measurement of an ionospheric plasma density by two different techniques.

Fejer, B. G.; Anderson, D. N.; Fukao, S.; Abdu, M. A.

1991-08-01

100

Bubbles  

NASA Astrophysics Data System (ADS)

``Vanitas vanitatum et omnia vanitas": bubbles are emptiness, non-liquid, a tiny cloud shielding a mathematical singularity. Born from chance, a violent and brief life ending in the union with the (nearly) infinite. But a wealth of phenomena spring forth from this nothingness: underwater noise, sonoluminescence, boiling, many others. Ultimately, diffusive processes govern much of the physics, and the difference between the diffusivity of heat and dissolved gases in ordinary liquids holds the key to the striking differences between gas and vapor bubbles.

Prosperetti, Andrea

2002-11-01

101

Electromagnetic Analysis of ITER Diagnostic Equatorial Port Plugs During Plasma Disruptions  

SciTech Connect

ITER diagnostic port plugs perform many functionsincluding structural support of diagnostic systems under high electromagnetic loads while allowing for diagnostic access to the plasma. The design of diagnostic equatorial port plugs (EPP) are largely driven by electromagnetic loads and associate responses of EPP structure during plasma disruptions and VDEs. This paper summarizes results of transient electromagnetic analysis using Opera 3d in support of the design activities for ITER diagnostic EPP. A complete distribution of disruption loads on the Diagnostic First Walls (DFWs), Diagnostic Shield Modules (DSMs) and the EPP structure, as well as impact on the system design integration due to electrical contact among various EPP structural components are discussed.

Y. Zhai, R. Feder, A. Brooks, M. Ulrickson, C.S. Pitcher and G.D. Loesser

2012-08-27

102

Kinetic Theory of Equilibrium Axisymmetric Collisionless Plasmas in Off-equatorial Tori around Compact Objects  

NASA Astrophysics Data System (ADS)

The possible occurrence of equilibrium off-equatorial tori in the gravitational and electromagnetic fields of astrophysical compact objects has been recently proved based on non-ideal magnetohydrodynamic theory. These stationary structures can represent plausible candidates for the modeling of coronal plasmas expected to arise in association with accretion disks. However, accretion disk coronae are formed by a highly diluted environment, and so the fluid description may be inappropriate. The question is posed of whether similar off-equatorial solutions can also be determined in the case of collisionless plasmas for which treatment based on kinetic theory, rather than a fluid one, is demanded. In this paper the issue is addressed in the framework of the Vlasov-Maxwell description for non-relativistic, multi-species axisymmetric plasmas subject to an external dominant spherical gravitational and dipolar magnetic field. Equilibrium configurations are investigated and explicit solutions for the species kinetic distribution function are constructed, which are expressed in terms of generalized Maxwellian functions characterized by isotropic temperature and non-uniform fluid fields. The conditions for the existence of off-equatorial tori are investigated. It is proved that these levitating systems are admitted under general conditions when both gravitational and magnetic fields contribute to shaping the spatial profiles of equilibrium plasma fluid fields. Then, specifically, kinetic effects carried by the equilibrium solution are explicitly provided and identified here with diamagnetic energy-correction and electrostatic contributions. It is shown that these kinetic terms characterize the plasma equation of state by introducing non-vanishing deviations from the assumption of thermal pressure.

Cremaschini, Claudio; Kov?, Ji?; Slan, Petr; Stuchlk, Zden?k; Karas, Vladimr

2013-11-01

103

Electron trajectories and betatron oscillation in the wake bubble in laser-plasma interaction  

SciTech Connect

The trajectories of electrons originating from different initial locations in the unperturbed plasma during the interaction of an ultraintense laser with underdense plasma in the bubble regime are followed by particle-in-cell simulation. It is found that plasma electrons initially aligned with the rim of the laser focal spot contribute most to the bow wave in front of the bubble and those aligned with the lateral bubble sheath edge contribute most to the self-injection at the back of the bubble. A scaling law between the transverse electric and magnetic fields for the case where there are many electrons in the bubble is given and discussed in terms of betatron oscillations of the injected electrons.

Wu Haicheng; Xie Baisong [Key Laboratory of Beam Technology and Materials Modification of the Ministry of Education, Beijing Normal University, Beijing 100875 (China); College of Nuclear Science and Technology, Beijing Normal University, Beijing 100875 (China); Liu Mingping; Hong Xueren; Zhangshan [College of Nuclear Science and Technology, Beijing Normal University, Beijing 100875 (China); Yu, M. Y. [Institute for Fusion Theory and Simulation, Zhejiang University, Hangzhou 310027, China and Institut fuer Theoretische Physik I, Ruhr-Universitaet Bochum, D-44780 Bochum (Germany)

2009-07-15

104

Bubble Bubble  

NSDL National Science Digital Library

With magic bubble solution, a boy discovers that he can blow any kind of bubble imaginable: a kangaroo, a bird, a car, or a boat. Mercer Mayer's colorful illustrations enliven this engaging tale of mysterious bubbles.

Mayer, Mercer

2009-11-11

105

Comment on ''Scalings for radiation from plasma bubbles''[Phys. Plasmas 17, 056708 (2010)  

SciTech Connect

Thomas has recently derived scaling laws for x-ray radiation from electrons accelerated in plasma bubbles, as well as a threshold for the self-injection of background electrons into the bubble [A. G. R. Thomas, Phys. Plasmas 17, 056708 (2010)]. To obtain this threshold, the equations of motion for a test electron are studied within the frame of the bubble model, where the bubble is described by prescribed electromagnetic fields and has a perfectly spherical shape. The author affirms that any elliptical trajectory of the form x{sup '2}/{gamma}{sub p}{sup 2}+y{sup '2}=R{sup 2} is solution of the equations of motion (in the bubble frame), within the approximation p{sub y}{sup '2}/p{sub x}{sup '2}<<1. In addition, he highlights that his result is different from the work of Kostyukov et al. [Phys. Rev. Lett. 103, 175003 (2009)], and explains the error committed by Kostyukov-Nerush-Pukhov-Seredov (KNPS). In this comment, we show that numerically integrated trajectories, based on the same equations than the analytical work of Thomas, lead to a completely different result for the self-injection threshold, the result published by KNPS [Phys. Rev. Lett. 103, 175003 (2009)]. We explain why the analytical analysis of Thomas fails and we provide a discussion based on numerical simulations which show exactly where the difference arises. We also show that the arguments of Thomas concerning the error of KNPS do not hold, and that their analysis is mathematically correct. Finally, we emphasize that if the KNPS threshold is found not to be verified in PIC (Particle In Cell) simulations or experiments, it is due to a deficiency of the model itself, and not to an error in the mathematical derivation.

Corde, S.; Stordeur, A.; Malka, V. [Laboratoire d'Optique Appliquee, ENSTA ParisTech-CNRS UMR7639-Ecole Polytechnique, Chemin de la Huniere, 91761 Palaiseau (France)

2011-03-15

106

Electrons trajectories around a bubble regime in intense laser plasma interaction  

NASA Astrophysics Data System (ADS)

Some typical electrons trajectories around a bubble regime in intense laser plasma interaction are investigated theoretically. By considering a modification of the fields and ellipsoid bubble shape due to the presence of residual electrons in the bubble regime, we study in detail the electrons nonlinear dynamics with or without laser pulse. To examine the electron dynamical behaviors, a set of typical electrons, which locate initially at the front of the bubble, on the transverse edge and at the bottom of the bubble respectively, are chosen for study. It is found that the range of trapped electrons in the case with laser pulse is a little narrower than that without laser pulse. The partial phase portraits for electrons around the bubble are presented numerically and their characteristic behaviors are discussed theoretically. Implication of our results on the high quality electron beam generation is also discussed briefly.

Lu, Ding; Zhao, Xue-Yan; Xie, Bai-Song; Ali Bake, Muhammad; Sang, Hai-Bo; Wu, Hai-Cheng

2013-06-01

107

Control of Plasma and Cavitation Bubble in Liquid-Phase Laser Ablation Using Supersonic Waves  

NASA Astrophysics Data System (ADS)

We examined the effects of a supersonic wave on laser-induced plasma and ablation-induced cavitation bubbles in liquid-phase laser ablation. The effect of the supersonic wave on laser-induced plasma was the change in the optical emission intensity. We observed an intense optical emission when the ablation target was irradiated with a laser pulse at a negative phase of the sound pressure of the supersonic wave. The effect of the supersonic wave on ablation-induced cavitation bubbles was the repetitive formation and collapse of the bubbles at the same frequency as the supersonic wave. The ablation-induced cavitation bubbles served as a ``seed'', and the repetitive formation and collapse of the cavitation bubbles were driven by the sound pressure of the supersonic wave.

Takada, Noriharu; Fujikawa, Akinori; Sasaki, Koichi

2011-12-01

108

Improvement of equatorial density distribution of the global core plasma model using GPS-derived TEC  

NASA Astrophysics Data System (ADS)

The global core plasma model (GCPM) is a realistic electron density model of the inner magnetosphere. By using long-term total electron content (TEC) data obtained from several GPS tracking stations along the equator and a low Earth orbit satellite, the accuracy of the GCPM equatorial density is examined. According to the statistical analysis of the GPS TEC, we found a remarkable feature in bias errors in the GCPM-derived TEC. Most of the errors are found to distribute in the topside ionosphere due to the simple representation of the density there.

Goto, Y.; Kasahara, Y.; Ide, T.

2012-04-01

109

Design of a Compact Coaxial Magnetized Plasma Gun for Magnetic Bubble Expansion Experiments  

Microsoft Academic Search

We will discuss the design of a compact coaxial magnetized plasma gun and its associated hardware systems in detail. The plasma gun will be used for experimental studies of magnetic bubble expansion into a lower pressure background plasma, as a model for extragalactic radio lobes. The gun is powered by an ignitron-switched capacitor bank. High-pressure gas will be puffed into

Yue Zhang; Alan G. Lynn; Scott C. Hsu; Hui Li; Wei Liu; Mark Gilmore; Christopher Watts

2008-01-01

110

Degradation of Perfluoro Compounds by Pulsed Plasmas within Bubbles in Water  

NASA Astrophysics Data System (ADS)

Perfluorooctanoic acid (PFOA) at a concentration of 500 mg/L in water was successfully degraded using pulsed plasmas generated inside oxygen or argon bubbles. 6 kV-200 ns pulsed voltages were applied to the water bubbles at repetition rates of 500?2000 Hz and pulse plasmas were generated along the inner surface of gas bubbles. After 120 min operation, almost half of the fluorine atoms were detached from PFOA molecules. The decomposition energy efficiency for PFOA obtained with oxygen was 140 mg/kWh which value was quite large as comparing to the values obtained with other chemical methods.

Sasaki, Keisuke; Hayashi, Ryuichi; Yasuoka, Koichi

111

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

112

Time-resolved OES measurement of microwave plasma produced inside controlled bubbles under water  

NASA Astrophysics Data System (ADS)

Plasma generation inside bubbles under liquid has been given much attention because of its potential industrial applications such as water purification, sterilization, materials processing and so on. In our previous study, we have demonstrated that liquid temperature and operating pressure have great influences on the plasma production and decomposition of organic solutes in de-ionized water. However, physical and chemical processes occurring inside the bubbles are still unclear because the plasma is not produced under well-defined experimental conditions. In this work, we have developed a microwave bubble plasma system where reproducible microwave plasma is produced inside size-controlled bubbles. With the aid of this system, temporal variations of He I emission from discharge gas and H or OH emission from water vapor are measured by time-resolved photon-counting technique. After the plasma ignition, He I intensity rapidly increases within less than 100 ns. However, OH and H intensities increase 1 ?s after the plasma ignition. This result suggests that the water vapor is produced by the plasma irradiation on the bubble surface.

Ishijima, Tatsuo; Suzuki, Haruka; Toyoda, Hirotaka

2011-11-01

113

Conjugate Point Equatorial Experiment (COPEX) campaign in Brazil: Electrodynamics highlights on spread F development conditions and day-to-day variability  

Microsoft Academic Search

A Conjugate Point Equatorial Experiment (COPEX) campaign was conducted during the OctoberDecember 2002 period in Brazil, with the objective to investigate the equatorial spread F\\/plasma bubble irregularity (ESF) development conditions in terms of the electrodynamical state of the ionosphere along the magnetic flux tubes in which they occur. A network of instruments, including Digisondes, optical imagers, and GPS receivers, was

M. A. Abdu; I. S. Batista; B. W. Reinisch; J. R. de Souza; J. H. A. Sobral; T. R. Pedersen; A. F. Medeiros; N. J. Schuch; E. R. de Paula; K. M. Groves

2009-01-01

114

Conjugate Point Equatorial Experiment (COPEX) Campaign in Brazil: Electrodynamics highlights on spread F development conditions and day-to-day variability  

Microsoft Academic Search

A conjugate point equatorial experiment (COPEX) campaign was conducted during October - December 2002 period in Brazil, with the objective to investigate the equatorial spread F\\/plasma bubble irregularity (ESF) development conditions in terms of the electrodynamical state of the ionosphere along the magnetic flux tubes in which they occur. A network of instruments including digisondes, optical imagers, and GPS receivers,

M. A. Abdu; I. S. Batista; B. W. Reinisch; J. R. de Souza; J. H. A. Sobral; T. R. Pedersen; A. F. Medeiros; N. J. Schuch; E. R. de Paula; K. M. Groves

2008-01-01

115

Conjugate Point Equatorial Experiment (COPEX) campaign in Brazil: Electrodynamics highlights on spreadFdevelopment conditions and day-to-day variability  

Microsoft Academic Search

A Conjugate Point Equatorial Experiment (COPEX) campaign was conducted during the October-December 2002 period in Brazil, with the objective to investigate the equatorial spread F\\/plasma bubble irregularity (ESF) development conditions in terms of the electrodynamical state of the ionosphere along the magnetic flux tubes in which they occur. A network of instruments, including Digisondes, optical imagers, and GPS receivers, was

M. A. Abdu; I. S. Batista; B. W. Reinisch; J. R. de Souza; J. H. A. Sobral; T. R. Pedersen; A. F. Medeiros; N. J. Schuch; E. R. de Paula; K. M. Groves

2009-01-01

116

Magnetic Bubble Expansion Experimental Investigation Using a Compact Coaxial Magnetized Plasma Gun  

NASA Astrophysics Data System (ADS)

The poster will first discuss the construction and improved design of a compact coaxial magnetized plasma gun. The plasma gun is used for experimental studies of magnetic bubble expansion into a lower pressure background plasma, which as a model for extragalactic radio lobes and solar coronal mass ejections. In this experiment, the plasma bubble's density, electron temperature, and propagation speed are measured by using a multiple-tipped langmuir probe. Also a three axis B-dot probe array is used to measure the magnetic field in three dimensions during the expansion process. In this poster experiment setup and data will be provided. Finally the comparison with the simulation result will be made.

Zhang, Yue; Lynn, Alan; Hsu, Scott; Li, Hui; Liu, Wei; Gilmore, Mark; Watts, Christopher

2009-11-01

117

Detection of an equatorial spread-F bubble by ground-based photometers and the San Marco 5 satellite  

Microsoft Academic Search

In the Fall of 1988, San Marco 5, instrumented with ion density and electric field experiments, made passes through the equatorial F-region in the Brazilian sector, where scanning photometers have been operated at Cachoeira Paulista, Brazil, for many years. We have cross-checked these large data sets and report here on one night of active spread-F with good data from both

J.-M. Jahn; J. La Belle; J. H. A. Sobral; T. L. Aggson; W. B. Hanson

1997-01-01

118

RCM-E simulation of ion acceleration during an idealized plasma sheet bubble injection  

NASA Astrophysics Data System (ADS)

In this paper, we investigate the role of plasma sheet bubbles in the ion flux variations at geosynchronous orbit during substorm injections by using the Rice Convection Model with an equilibrated magnetic field model (RCM-E). The bubble is initiated in the near-Earth plasma sheet with a localized reduction in entropy parameter PV5/3 following a substorm growth phase. In the expansion phase, characteristic features of substorm injections are reproduced; that is, there is a prominent dispersionless flux increase for energetic protons (>40 keV) and a flux decrease for lower-energy protons near midnight geosynchronous orbit while there is dispersive flux enhancement near the dusk sector. We find that the injection boundary is well coincident with the earthward boundary of the bubble, inside which the depletion of plasma content causes the magnetic field dipolarization, and in return, the magnetic field collapse energizes particles and alters the drift paths dramatically. Our results also show that a high-PV5/3 island is pushed ahead of the fast earthward propagating bubble, and a dipolarization front forms between them. Within the high-PV5/3 island, the diamagnetic effect makes the plasma pressure increase and the strength of the magnetic field decrease to a local minimum. We suggest that plasma sheet bubbles are elementary vehicles of substorm time particle injections from the main plasma sheet to the inner magnetosphere.

Yang, J.; Toffoletto, F. R.; Wolf, R. A.; Sazykin, S.

2011-05-01

119

Energy enhancement of proton acceleration in combinational radiation pressure and bubble by optimizing plasma density  

SciTech Connect

The combinational laser radiation pressure and plasma bubble fields to accelerate protons are researched through theoretical analysis and numerical simulations. The dephasing length of the accelerated protons bunch in the front of the bubble and the density gradient effect of background plasma on the accelerating phase are analyzed in detail theoretically. The radiation damping effect on the accelerated protons energy is also considered. And it is demonstrated by two-dimensional particle-in-cell simulations that the protons bunch energy can be increased by using the background plasma with negative density gradient. However, radiation damping makes the maximal energy of the accelerated protons a little reduction.

Bake, Muhammad Ali; Xie Baisong [Key Laboratory of Beam Technology and Materials Modification of the Ministry of Education, Beijing Normal University, Beijing 100875 (China); College of Nuclear Science and Technology, Beijing Normal University, Beijing 100875 (China); Shan Zhang [Department of Mathematics and Physics, Shijiazhuang Tiedao University, Shijiazhuang 050043 (China); Hong Xueren [College of Nuclear Science and Technology, Beijing Normal University, Beijing 100875 (China); College of Physics and Electronic Engineering, Northwest Normal University, Lanzhou 730070 (China); Wang Hongyu [Department of Physics, Anshan Normal University, Anshan 114005 (China); Shanghai Bright-Tech Information Technology Co. Ltd, Shanghai 200136 (China)

2012-08-15

120

Neutron imaging of inertial confinement fusion target plasmas using high-resolution gel bubble detectors  

SciTech Connect

Recently developed gel bubble detectors with higher detection efficiency look attractive for high-resolution neutron imaging of inertial confinement target plasmas. Bubble detectors can detect neutrons with a spatial resolution as small as 5 {mu}m. By allowing high-resolution imaging of National Ignition Facility (NIF) and Laser MegaJoule (LMJ) Facility targets without the need for {>=}25 m line-of-sight paths, bubble detectors should allow views in multiple and orthogonal directions from the target. Earlier proof-of-principle tests on OMEGA were limited by the very low (8x10{sup -6} bubbles/n) detection efficiency of the then available gel detectors. Detectors with {approx}100 times higher efficiency per centimeter of thickness are now available. At the high bubble densities expected in the new detectors, the spatial distribution of the bubbles must be measured by a line integral technique such as x-ray transmission. This avoids the need for optically transparent detectors, allowing much higher densities of superheated drops, smaller drop diameters, and detector thicknesses of several centimeters. It now appears that high-resolution images of NIF and LMJ target plasmas at neutron yields {>=}10{sup 13} may be possible using high efficiency gel bubble detectors.

Fisher, R. K. [General Atomics, P.O. Box 85608, San Diego, California 92186-5608 (United States)

2006-10-15

121

A multidimensional theory for electron trapping by a plasma wake generated in the bubble regime  

Microsoft Academic Search

We present a theory for electron self-injection in nonlinear, multidimensional plasma waves excited by a short laser pulse in the bubble regime or by a short electron beam in the blowout regime. In these regimes, which are typical for electron acceleration in the last impressive experiments, the laser radiation pressure or the electron beam charge pushes out plasma electrons from

I. Kostyukov; E. Nerush; A. Pukhov; V. Seredov

2010-01-01

122

Electrical and spectroscopic characterization of underwater plasma discharge inside rising gas bubbles  

Microsoft Academic Search

The generation of high-energetic species in plasma by discharge in liquids makes it suitable for applications such as water treatment. Effective reduction of input power and an increase in the process efficiency can be achieved by externally generated gas bubbles introduced in the liquid. Pulsed discharge in nitrogen, helium and argon bubbles in between a pin-to-plate electrode system submerged in

Patrick Vanraes; Anton Nikiforov; Christophe Leys

2012-01-01

123

X-ray imaging of an X-pinch plasma with a bubble compound refractive lens  

Microsoft Academic Search

We present diagnostic images taken of an X-pinch plasma x-ray source driven by the XP pulser (100 ns, 500 kA) at Cornell University using an x-ray bubble compound refractive lens. The lens consists of a 200 ?m inside diameter glass capillary that contains about 100 biconcave microlenses formed by a string of bubbles in epoxy. A precise system for lens

C. K. Gary; S. A. Pikuz; M. D. Mitchell; K. M. Chandler; T. A. Shelkovenko; D. A. Hammer; Yu. I. Dudchik

2004-01-01

124

X-ray imaging of an X-pinch plasma with a bubble compound refractive lens  

Microsoft Academic Search

We present diagnostic images taken of an X-pinch plasma x-ray source driven by the XP pulser (100 ns, 500 kA) at Cornell University using an x-ray bubble compound refractive lens. The lens consists of a 200 mum inside diameter glass capillary that contains about 100 biconcave microlenses formed by a string of bubbles in epoxy. A precise system for lens

C. K. Gary; S. A. Pikuz; M. D. Mitchell; K. M. Chandler; T. A. Shelkovenko; D. A. Hammer; Yu. I. Dudchik

2004-01-01

125

Internal conditions of a bubble containing radio-frequency plasma in water  

Microsoft Academic Search

We analyzed the gas generated by a radio-frequency plasma in water and found that the ratio of oxygen to hydrogen in it was approximately 0.7-11%. Numerical simulations of the chemical reactions occurring inside and outside the bubble with increasing energy supply in the concentric volume in it were carried out. Thermal conduction and diffusion occurring inside and outside the bubble,

Shinobu Mukasa; Shinfuku Nomura; Hiromichi Toyota; Tsunehiro Maehara; Hiroshi Yamashita

2011-01-01

126

Electron self-injection into an evolving plasma bubble: Quasi-monoenergetic laser-plasma acceleration in the blowout regime  

NASA Astrophysics Data System (ADS)

An electron density bubble driven in a rarefied uniform plasma by a slowly evolving laser pulse goes through periods of adiabatically slow expansions and contractions. Bubble expansion causes robust self-injection of initially quiescent plasma electrons, whereas stabilization and contraction terminate self-injection thus limiting injected charge; concomitant phase space rotation reduces the bunch energy spread. In regimes relevant to experiments with hundred terawatt- to petawatt-class lasers, bubble dynamics and, hence, the self-injection process are governed primarily by the driver evolution. Collective transverse fields of the trapped electron bunch reduce the accelerating gradient and slow down phase space rotation. Bubble expansion followed by stabilization and contraction suppresses the low-energy background and creates a collimated quasi-monoenergetic electron bunch long before dephasing. Nonlinear evolution of the laser pulse (spot size oscillations, self-compression, and front steepening) can also cause continuous self-injection, resulting in a large dark current, degrading the electron beam quality.

Kalmykov, S. Y.; Beck, A.; Yi, S. A.; Khudik, V. N.; Downer, M. C.; Lefebvre, E.; Shadwick, B. A.; Umstadter, D. P.

2011-05-01

127

Equatorial heating and hemispheric decoupling effects on inner magnetospheric core plasma evolution  

SciTech Connect

The authors have extended their previous semikinetic study of early stage plasmasphere refilling with perpendicular ion heating by removing the restriction that the northern and southern boundaries are identical and incorporating a generalized transport description for the electrons. This allows investigation of the effects of electron heating and a more realistic calculation of electric fields produced by ion and electron temperature anisotropies. The combination of perpendicular ion heating and parallel electron heating leads to an equatorial electrostatic potential peak, which tends to shield and decouple ion flows in the northern and southern hemispheres. Unequal ionospheric upflows in the northern and southern hemispheres lead to the development of distinctly asymmetric densities and other bulk parameters. At t=5 hour after the initiation of refilling with different source densities (N{sub north} = 100 cm{sup {minus}3}, N{sub south} = 50 cm{sup {minus}3}), the maximum potential drops of the northern and southern hemispheres are 0.5 and 1.3 V, respectively. At this time the minimum ion densities are 11 and 7 cm{sup {minus}3} for the northern and southern hemispheres. DE 1 observations of asymmetric density profiles by Olsen may be consistent with these predictions. Termination of particle heating causes the reduction of equatorial potential and allows interhemispheric coupling. When the inflows from the ionospheres are reduced (as may occur after sunset), decreases in plasma density near the ionospheric regions are observed while the heated trapped ion population at the equator persists. 42 refs., 12 figs.

Lin, J.; Horwitz, J.L.; Wilson, G.R. [Univ. of Alabama, Huntsville, AL (United States)] [and others

1994-04-01

128

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

129

Modelling chemical reactions in dc plasma inside oxygen bubbles in water  

NASA Astrophysics Data System (ADS)

Plasmas generated inside oxygen bubbles in water have been developed for water purification. Zero-dimensional numerical simulations were used to investigate the chemical reactions in plasmas driven by dc voltage. The numerical and experimental results of the concentrations of hydrogen peroxide and ozone in the solution were compared with a discharge current between 1 and 7 mA. Upon increasing the water vapour concentration inside bubbles, we saw from the numerical results that the concentration of hydrogen peroxide increased with discharge current, whereas the concentration of ozone decreased. This finding agreed with the experimental results. With an increase in the discharge current, the heat flux from the plasma to the solution increased, and a large amount of water was probably vaporized into the bubbles.

Takeuchi, N.; Ishii, Y.; Yasuoka, K.

2012-02-01

130

Design of a compact coaxial magnetized plasma gun for magnetic bubble expansion experiments  

Microsoft Academic Search

Summary form only given. We will discuss the design of a compact coaxial magnetized plasma gun and its associated hardware systems in detail. The plasma gun is used for experimental studies of magnetic bubble expansion into a lower pressure background plasma, as a model for extragalactic radio lobes. The gun is powered by a 120 muF, 10 kV ignitron-switched capacitor

Yue Zhang; A. G. Lynn; S. C. Hsu; Hui Li; Wei Liu; M. Gilmore; C. Watts

2009-01-01

131

Plasma pressure in Mercury's equatorial magnetosphere derived from MESSENGER Magnetometer observations  

NASA Astrophysics Data System (ADS)

Since insertion of the MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) spacecraft into orbit around Mercury on 18 March 2011, the probe's Magnetometer has routinely observed localized reductions of the magnetic field magnitude below the level predicted by a planetary dipole model corrected for magnetospheric magnetic fields. These magnetic depressions are observed on almost every orbit, and the latitude at which they are observed is local-time dependent. The depression signatures are indicators of the presence of enhanced plasma pressures, which inflate the magnetic field locally to maintain pressure balance, thus lowering the magnetic flux density. Mapping the magnetic depressions in local time and latitude provides insight into the plasma distribution near the planet, which complements that provided by MESSENGER's Fast Imaging Plasma Spectrometer. The spatial distribution shows that magnetic depressions are concentrated in two distinct regions, one near the equator on the nightside and another at high latitudes principally on the dayside. Here we focus on the nightside, equatorial pressure signatures, which we attribute to the magnetotail plasma sheet. The plasma-sheet pressures extend from dusk to dawn and are offset northward from the planetary geographic equator by about 10 in latitude, commensurate with the offset of the planetary dipole. The pressures associated with the plasma-sheet depressions range from 0.1 to 3 nPa and are systematically higher at dawn than at dusk. Proton gradient-curvature and convection drift in Mercury's dipole magnetic field with a dawn-to-dusk electric field result in low drift velocities near dawn, leading to systematically higher densities and pressures at dawn than at dusk, consistent with the observations.

Korth, Haje; Anderson, Brian J.; Raines, Jim M.; Slavin, James A.; Zurbuchen, Thomas H.; Johnson, Catherine L.; Purucker, Michael E.; Winslow, Reka M.; Solomon, Sean C.; McNutt, Ralph L., Jr.

2011-11-01

132

An empirical model of the drift velocity of equatorial plasma depletions  

NASA Astrophysics Data System (ADS)

The Far-Ultraviolet Imager on the IMAGE spacecraft (IMAGE-FUV) has been used to observe O+plasma depletions in the post-sunset equatorial ionosphere. Small-scale density irregularities associated with such depletions are believed to adversely affect trans-ionospheric radio signals such as GPS. Prediction of the motion of these plasma depletions is a necessary component of the ability to forecast the occurrence of such radio signal interference. An automated method has recently been developed to identify and track the position and zonal drift velocity of these depletions. Here we use this method to create a large database of the zonal drift velocities of these depletions. We present an empirical model based on these observations that describes the observed drift velocities as a function of both local time and magnetic latitude, which is essential to represent their behavior. A comparison of the observed drift velocities with zonal winds from both an empirical model (Horizontal Wind Model; HWM07) and a first-principles model (the TIEGCM) reveals that the plasma depletions' drift velocities have a latitudinal gradient that cannot be explained solely by the F-region dynamo in the post-sunset period, at least by these climatological models. This suggests that these plasma depletions may not simply drift with the background F-region plasma. It has previously been suggested that vertical polarization electric fields associated with the plasma depletions are responsible for their zonal drifts exceeding the background flow, which may explain the previously-observed discrepancy in the drift velocities and the discrepancy in their gradients reported here.

England, S. L.; Immel, T. J.

2012-12-01

133

Generation of intense ultrashort midinfrared pulses by laser-plasma interaction in the bubble regime  

NASA Astrophysics Data System (ADS)

As an intense laser pulse propagates through an underdense plasma, the strong ponderomotive force pushes away the electrons and produces a trailing plasma bubble. In the meantime the pulse itself undergoes extreme nonlinear evolution that results in strong spectral broadening toward the long-wavelength side. By experiment we demonstrate that this process can be utilized to generate ultrashort midinfrared pulses with an energy three orders of magnitude larger than that produced by crystal-based nonlinear optics. The infrared pulse is encapsulated in the bubble before exiting the plasma, hence is not absorbed by the plasma. The process is analyzed experimentally with laser-plasma tomographic measurements and numerically with three-dimensional particle-in-cell simulation. Good agreement is found between theoretical estimation, numerical simulation, and experimental results.

Pai, C.-H.; Chang, Y.-Y.; Ha, L.-C.; Xie, Z.-H.; Lin, M.-W.; Lin, J.-M.; Chen, Y.-M.; Tsaur, G.; Chu, H.-H.; Chen, S.-H.; Lin, J.-Y.; Wang, J.; Chen, S.-Y.

2010-12-01

134

Cluster observations of kinetic structures and electron acceleration within a dynamic plasma bubble  

NASA Astrophysics Data System (ADS)

Fast plasma flows are believed to play important roles in transporting mass, momentum and energy in the magnetotail during active periods, such as the magnetospheric substorms. In this paper, we present Cluster observations of a plasma-depleted flux tube, i.e., a plasma bubble associated with fast plasma flow before the onset of a substorm in the near-Earth tail around X= -18RE. The bubble is bounded by both sharp leading (?bz/?x<0) and trailing (?bz/?x>0) edges. The two edges are thin current layers (~ ion inertial length) that carry not only intense perpendicular current but also field-aligned current. The leading edge is a dipolarization front (DF) within a slow plasma flow, while the trailing edge is embedded in a super-Alfvnic convective ion jet. The electron jet speed exceeds the ion flow speed thus producing a large tangential current at the trailing edge. The electron drift is primarily given by the EB drift. Interestingly, the trailing edge moves faster than the leading edge, which causes shrinking of the bubble and local flux pileup inside the bubble. This resulted in a further intensification of Bz, or a secondary dipolarization. Both the leading and trailing edges are tangential discontinuities that confine the electrons inside the bubble. Strong electron acceleration occurred corresponding to the secondary dipolarization, with perpendicular fluxes dominating the field-aligned fluxes. We suggest that betatron acceleration is responsible for the electron energization. Whistler waves and lower hybrid drift waves were identified inside the bubble. Their generation mechanisms and potential roles in electron dynamics are discussed.

Zhou, Meng; Deng, Xiaohua; Ashour-Abdalla, Maha; Walker, Raymod J.; Pang, Ye; Tang, Chaoling; Huang, Shiyong; El-Alaoui, Mostafa; Yuan, Zhigang; Li, Huimin

2013-04-01

135

East-west plasma bubble irregularity motion determined from spaced VHF polarimeters: Velocity shear in the zonal F-region bulk plasma motion  

NASA Astrophysics Data System (ADS)

VHF electronic polarimeters were used to monitor Faraday rotation angle and amplitude of geostationary satellite (GOES-3) beacon signals, simultaneously at two stations, Cachoeira Paulista and Sao Jose dos Campos, separated by 110km exactly in the magnetic East-West direction in Brazil. The analysis of the data for a few months in 1981-82 period shows TEC fluctuations correlated with range type spread F events in the local ionograms and amplitude scintillation in the satellite beacon signals, thereby identifying themselves as eastward propagating plasma bubbles, and structures within them, in the equatorial ionosphere. The nighttime variation pattern in these velocities is in excellent agreement with those of the eastward bulk plasma motion measured by Jicamarca radar, the irregularity patch movement obtained from closely spaced antennas over Natal, the eastward airglow patch velocities determined from all-sky 6300 A images over Ascension Island, and the thermospheric zonal winds measured by Fabry-Perot interferometer over Kwajalein Atoll. There exist, however, significant differences in the values of the eastward velocities for these different cases.

Abdu, M. A.; Kantor, I. J.; Batista, I. S.; Depaula, E. R.

1983-05-01

136

Supra-bubble regime for laser acceleration of coldelectron beams in tenuous plasma  

SciTech Connect

Relativistic electrons can be accelerated by an ultraintense laser pulse in the "supra-bubble" regime, that is, in the blow-out regime ahead of the plasma bubble (as opposed to the conventional method, when particles remain inside the bubble). The acceleration is caused by the ponderomotive force of the pulse, via the so-called snow-plow mechanism. The maximum energy gain, ?? ~ ?g a, is attained when the particle Lorentz factor ? is initially about ?g/a, where ?g is the pulse group speed Lorentz factor, and a is the laser parameter, proportional to the laser field amplitude. The scheme operates at a ? ?g, yielding ?? of up to that via wakefield acceleration for the same plasma and laser parameters, ?? ~ ?2g. The interaction length is shorter than that for the wake field mechanism but grows with the particle energy, hindering acceleration in multiple stages.

V.I. Geyko, I.Y. Dodin, and N.J. Fisch G.M. Fraiman

2009-01-18

137

Using Monoenergetic Proton Radiography to Probe Magnetic Reconnection of Laser-Generated Plasma Bubbles  

NASA Astrophysics Data System (ADS)

The magnetic topology changes due to reconnection of laser-generated magnetic fields, which can affect energy transport inside hohlraums and around inertial confinement fusion (ICF) capsule implosions. To probe and better understand this effect, a series of experiments were conducted in which the interaction of azimuthal magnetic fields surrounding laser-produced plasma bubbles was imaged using face-on monoenergetic proton radiography. The timing of the interaction beams with respect to each other and to the backlighter was varied to provide snapshots of the reconnection both during and after the laser-foil interaction. Images and quantitative field-mapping demonstrate a change in magnetic topology during the bubble interaction. Future work will entail side-on radiography of interacting plasma bubbles to probe for Hall fields associated with fast magnetic reconnection. This work was performed at the LLE NLUF, and was supported in part by the US DOE, LLNL, and LLE.

Rosenberg, M.; Li, C.; Seguin, F. H.; Frenje, J.; Manuel, M.; Petrasso, R.; Stoeckl, C.; Glebov, V.; Kilkenny, J.; Nikroo, A.

2011-11-01

138

Equatorial F-Region Zonal Plasma Drifts Over Jicamarca During Quiet and Disturbed Conditions  

NASA Astrophysics Data System (ADS)

F-region zonal plasma drifts are important low latitude ionospheric parameters. We use extensive incoherent scatter observations obtained at the Jicamarca Radio Observatory between 1970 and 2003 to study the characteristics of equatorial zonal plasma drifts near the F-region peak. We present initially the results of a local time, season, and solar flux dependent quiet zonal drift model which uses Bernstein polynomials as base functions. These results indicate that over Jicamarca the dependence of the nighttime eastward drift is stronger during equinox and December solstice than during June solstice. We also present the results of the first detailed study of the effect of geomagnetic activity on the zonal drifts. Our results indicate that the zonal disturbance drifts are predominantly westward with the largest values near midnight. In the post-midnight sector, these perturbation drifts are strongly solar flux dependent. The Jicamarca zonal disturbance drifts are largely accounted for by disturbance dynamo electric fields with a dominant time delay of 3-15 hours. The effects of disturbance dynamo electric field with longer time constant are restricted to the late night sector and are largest near solar maximum

Fejer, B. G.; de Souza, J.; Santos, A. S.; Costa Pereira, E.

2004-12-01

139

Remote sensing of possible plasma density bubbles in the inner Jovian dayside magnetosphere  

NASA Astrophysics Data System (ADS)

During the 2001 Cassini encounter with Jupiter, the Radio and Plasma Wave Science (RPWS) instrument detected fine spectral and temporal structure with broadband kilometric radiation. Applying known electron cyclotron harmonic radiation models, this microstructure is interpreted as originating from a plasma density depletion or bubble at the edge of the Io torus. The microstructure became very complicated at the event beginning and end (formation of broadband bursty structures), and this is interpreted as originating from high-frequency (3-4 s period) density waves or fingers found at the edge of the larger density bubble. Such high-frequency structure at the edges of plasma bubbles is reminiscent of small-scale structure associated with terrestrial spread-F density irregularities. We suggest that the narrow extended fingers, observed on a convex portion of the Io torus surface, result from the interchange instability that is shredding the outer edges of the plasma bubble. A similar set of circumstances occurring on a larger scale may explain the emission of Jovian radio bull's-eye emission observed previously by Ulysses.

Farrell, W. M.; Kaiser, M. L.; Kurth, W. S.; Desch, M. D.; Gurnett, D. A.; Hospodarsky, G. B.; MacDowall, R. J.

2004-09-01

140

Latitudinal extension of equatorial scintillations measured with a network of GPS receivers  

Microsoft Academic Search

A latitudinally-spaced network of GPS receivers extending within Colombia, Peru and Chile has served to provide a measurement of the latitudinal extension of scintillations and TEC depletions associated with equatorial plasma bubbles. These observations were obtained with five Leica GPS receivers managed by Boston College and five additional receivers that are operated by other institutions. The BC receivers are controlled

C. Valladares; R. Sheehan; S. Basu; M. Hagan

2003-01-01

141

Coordinated study of equatorial scintillation and in situ and radar observations of nighttime F region irregularities  

Microsoft Academic Search

A coordinated set of Atmospheric Explorer E (AE-E) satellite in situ, VHF radar backscatter, and scintillation measurements performed during 1977 over a common ionospheric volume is used to study the relationship between the plasma depletions or bubbles, the extended 3-m irregularity structures known as plumes, and bursts of scintillation activity or patches in the nighttime equatorial F region. The implications

Santimay Basu; J. P. McClure; J. Aarons

1980-01-01

142

On the spatial relationship of 1-meter equatorial irregularities and depletions in total electron contents  

NASA Astrophysics Data System (ADS)

A radar experiment was conducted at Kwajalein Atoll, Marshall Islands to investigate the spatial relationship of 1 m equatorial spread-F irregularities to total electron content (TEC) depletion. A high-power radar was operated (1) in a backscatter scan mode to spatially map the distribution of 1 m irregularities, and (2) in a dual-frequency, satellite-track mode to obtain the longitudinal TEC variations. Using the radar data, we show that radar backscatter 'plumes' found in the disturbed, nighttime equatorial ionosphere are longitudinally coincident with TEC depletions. We suggest that the TEC depletions are probably due to the presence of plasma bubbles in the equatorial F layer.

Tsunoda, R. T.

1980-02-01

143

Modification of equatorial ionospheric electric fields during some major magnetic storms  

NASA Astrophysics Data System (ADS)

Geomagnetic field measurements at equatorial and off-equatorial low latitude stations have been used, in recent years, to study the variations in the daytime equatorial ionospheric electric fields caused by prompt penetration of a magnetospheric electric field into the low latitude ionosphere during periods of undershielding or overshielding. Changes in the daytime equatorial ionospheric electric fields produced by disturbance dynamo effects may also contribute to the observed magnetic field variations. However, at nighttime, due to low electrical conductivity of the ionosphere, changes in the equatorial ionospheric electric field are not expected to contribute significantly to the residual geomagnetic variations after removal of ring current contributions. On some magnetically disturbed days when ground observations have yielded significant negative excursions of the residual magnetic field variations at nighttime, magnetic field measurements made by CHAMP satellite around the dip equator close to the longitude region of the ground obsevations, have shown some unexpected results. An important consequence of variation in the post-sunset equatorial ionospheric electric field due to magnetic activity and the resultant change in the height of the equatorial F layer, is either suppression or enhancement of the growth of equatorial plasma bubbles and associated equatorial spread F irregularities. Observations of ionospheric scintillations caused by these irregularities have also been used to obtain information about changes in the equatorial ionospheric electric fields during some major magnetic storms.

Bhattacharyya, Archana; Alex, S.; Luehr, Hermann; Stolle, Claudia; Tiwari, Diwakar

144

3-D effects in magnetic reconnection of laser-produced plasma bubbles  

NASA Astrophysics Data System (ADS)

Recent experiments have observed magnetic reconnection in high-energy-density, laser-produced plasma bubbles. It is of great interest to extend previous 2-D simulations [1] to understand the full 3-D evolution of the bubbles. This 3-D evolution, studied by PIC simulations, includes the 3-D spherical expansion of the bubbles and 3-D geometry of the interaction, including the formation of isolated magnetic nulls and null-null lines. In cylindrical 3-D geometry, we study the dynamics of long-wavelength kink instabilities and short-wavelength lower-hybrid instabilities in the return currents, over a range of parameters characteristic of the experiments. Observational signatures of 3-D dynamics in the experiments will be discussed.[4pt] [1] W. Fox, A. Bhattacharjee, K. Germaschewski, Phys. Rev. Lett. 106, 215003 (2011).

Fox, W.; Mollica, F.; Bhattacharjee, A.; Germaschewski, K.

2011-11-01

145

Accelerated thinning of the near-Earth plasma sheet caused by a bubble-blob pair  

NASA Astrophysics Data System (ADS)

In the late stage of a substorm growth phase, the magnetic field in the near-Earth region is highly stretched. We assume that such conditions can lead to violation of the frozen-in-flux condition, allowing transfer of plasma from one flux tube to another and creating a plasma blob tailward of a plasma bubble. In this letter we present results of a simulation where we artificially impose a bubble-blob pair by introducing a disturbance in PV5/3 in the near-Earth plasma sheet. In the subsequent evolution, as calculated by the equilibrium version of the Rice Convection Model (RCM-E), the bubble surges earthward and the blob moves tailward, while the magnetic field between them weakens and the localized cross-tail current density increases. We speculate that, at substorm onset, there could be a positive feedback in which the breakdown of the frozen-in condition would increasingly make the current sheet thinner until magnetic reconnection occurs.

Yang, J.; Wolf, R. A.; Toffoletto, F. R.

2011-01-01

146

Relation of zonal plasma drift and wind in the equatorial F region as derived from CHAMP observations  

NASA Astrophysics Data System (ADS)

In this paper we estimate zonal plasma drift in the equatorial ionospheric F region without counting on ion drift meters. From June 2001 to June 2004 zonal plasma drift velocity is estimated from electron, neutral, and magnetic field observations of Challenging Mini-satellite Payload (CHAMP) in the 09:00-20:00 LT sector. The estimated velocities are validated against ion drift measurements by the Republic of China Satellite-1/Ionospheric Plasma and Electrodynamics Instrument (ROCSAT-1/IPEI) during the same period. The correlation between the CHAMP (altitude ~ 400 km) estimates and ROCSAT-1 (altitude ~ 600 km) observations is reasonably high (R ? 0.8). The slope of the linear regression is close to unity. However, the maximum westward drift and the westward-to-eastward reversal occur earlier for CHAMP estimates than for ROCSAT-1 measurements. In the equatorial F region both zonal wind and plasma drift have the same direction. Both generate vertical currents but with opposite signs. The wind effect (F region wind dynamo) is generally larger in magnitude than the plasma drift effect (Pedersen current generated by vertical E field), thus determining the direction of the F region vertical current.

Park, J.; Lhr, H.

2013-06-01

147

Experimental study of plasma bubble expansion as a model for extragalactic radio lobes  

NASA Astrophysics Data System (ADS)

Recent work in plasma astrophysics has suggested that magnetic energy features prominently in the large-scale evolution of active galaxies. The Plasma Bubble Expansion Experiment (PBEX) at UNM will conduct laboratory experiments to address outstanding nonlinear plasma physics issues related to how magnetic energy and helicity carried by extra-galactic jets interacts with the intergalactic medium to form extra-galactic radio lobe structures. A newly-built pulsed coaxial gun will form and inject magnetized plasma bubbles into a lower pressure weakly-magnetized background plasma formed by the helicon and/or hot cathode source in HELCAT, a 4 m long and 50 cm diameter linear plasma device. Plasma properties can be adjusted such that important dimensionless parameters are relevant to the astrophysical context. Ideal MHD simulations of the experiment have indicated the strong possibility of MHD shocks appearing. This poster will provide an overview of the physics goals, experimental design/status, and coordinated theory/modeling of PBEX.

Hsu, Scott; Lynn, Alan G.; Zhang, Yue; Liu, Wei; Li, Hui; Watts, Christopher; Gilmore, Mark

2008-04-01

148

Analytic model of electron self-injection in a plasma wakefield accelerator in the strongly nonlinear bubble regime  

NASA Astrophysics Data System (ADS)

We study self-injection into a plasma wakefield accelerator in the blowout (or bubble) regime, where the bubble evolves due to background density inhomogeneities. To explore trapping, we generalize an analytic model for the wakefields inside the bubble [1] to derive expressions for the fields outside. With this extended model, we show that a return current in the bubble sheath layer plays an important role in determining the trapped electron trajectories. We explore an injection mechanism where bubble growth due to a background density downramp causes reduction of the electron Hamiltonian in the co-moving frame, trapping the particle in the dynamically deepening potential well [2]. Model calculations agree quantitatively with PIC simulations on the bubble expansion rate required for trapping, as well as the range of impact parameters for which electrons are trapped. This is an improvement over our previous work [3] using a simplified spherical bubble model, which ignored the fields outside of the bubble and hence overestimated the expansion rate required for trapping. [4pt] [1] W. Lu et al., Phys. Plasmas 13, 056709 (2006).[0pt] [2] S. Kalmykov et al., Phys. Rev. Lett 103, 135004 (2009).[0pt] [3] S.A. Yi et al., Plasma Phys. Contr. Fus. 53, 014012 (2011).

Yi, Sunghwan; Khudik, Vladimir; Shvets, Gennady

2012-10-01

149

Evolution of self-injected quasi-monoenergetic electron beams in a plasma bubble  

NASA Astrophysics Data System (ADS)

The evolution of electron beam injection and acceleration in the bubble regime of a laser wakefield is studied experimentally. When a 50 TW, 35 fs laser pulse is focused to a spot size of 22 ?m (FWHM) in a tenuous 1-cm-long helium gas jet, well-collimated (a few milliradians) electron beams with energies in the sub-GeV level are produced. Multiple electron bunches are observed when the laser-plasma channel (i.e., interaction length) is long (<1 cm). However, only one bunch is generated when the channel is short (2 mm). These experimental results confirm the evolution scenarios of the electron bunches observed in 3D PIC simulations [refer to the publications: [6] N. Hafz et al., Nat. Photon. 2 (2008) 571 and [7] S. Kalmykov et al., Phys. Rev. Lett. 103 (2009) 135004], which suggested that multiple electron injections are a characteristic process for a long acceleration length and an evolving plasma bubble.

Hafz, Nasr A. M.; Lee, Seong Ku; Jeong, Tae Moon; Lee, Jongmin

2011-05-01

150

SEARCHING FOR QUARK - GLUON PLASMA (QGP) BUBBLE EFFECTS AT RHIC / LHC.  

SciTech Connect

Since the early eighties, we have shared with Leon Van Hove the view that if a QGP were produced in high energy heavy ion colliders that its hadronization products would likely come from small localized in phase space bubbles of plasma. In previous papers we have discussed the case where one to at most a few separated bubbles were produced. In this paper we develop a model based on HIJING to which we added a ring of adjoining multi bubble production, which we believe is a higher cross-section process which dominates the near central rapidity region. We have performed simulations which were designed to be tested by the expected first to become available suitable test data, namely the forthcoming RHIC STAR detector data on 65Gev/n Au colliding with 65 Gev/n Au. We took into account background effects and resonance effects so that a direct comparison with the data, and detailed test of these ideas could be made in the near future. Subsequently 100 Gev/n Au on 100 Gev/n Au forthcoming data can be tested, and of course these techniques, suitably modified by experience can be applied to it and eventually to LHC. We concluded that two charged particle correlations versus the azimuthal angle {Delta}{phi}; vs the opening angle, and vs psuedorapidity {eta}, can detect important bubble signals in the expected background, with statistical significances of 5 - 20{sigma}, provided the reasonably conservative assumptions we have made for bubble production occur. We also predicted charge fluctuation suppressions which increase with the bubble signal, and range from {approx} 5% to 27% in the simulations performed. We demonstrated reasonably that in our model, these charge suppression effects would not significantly be affected by resonances.

LINDENBAUM,S.J.; LONGACRE,R.S.; KRAMER,M.

2003-03-01

151

Design of a Compact Coaxial Magnetized Plasma Gun for Magnetic Bubble Expansion Experiments  

NASA Astrophysics Data System (ADS)

We will discuss the design of a compact coaxial magnetized plasma gun and its associated hardware systems in detail. The plasma gun will be used for experimental studies of magnetic bubble expansion into a lower pressure background plasma, as a model for extragalactic radio lobes. The gun is powered by an ignitron-switched capacitor bank. High-pressure gas will be puffed into an annular gap between inner and outer coaxial electrodes. An applied high voltage ionizes the gas and creates a radial current sheet. The 100kA discharge current generates toroidal flux; poloidal flux is provided by using an external bias magnet. The axial JxB force ejects plasma out of the gun. If the JxB force exceeds the magnetic tension of the poloidal flux by a sufficient amount then a detached magnetized plasma will be formed. The poster will discuss the plasma bubble formation system including the power system, gas valve control system, bias flux power system, and the magnetic probe diagnostic in detail. Experimental data will be provided.

Zhang, Yue; Lynn, Alan G.; Hsu, Scott C.; Li, Hui; Liu, Wei; Gilmore, Mark; Watts, Christopher

2008-11-01

152

A new inversion method of plasma density distribution of plasmasphere in the geomagnetic equatorial plane from IMAGE data  

NASA Astrophysics Data System (ADS)

The plasma density distribution of plasmasphere in the geomagnetic equatorial plane can help us study the magnetosphere like plasmasphere, ionosphere and their kinetics. In this paper, we introduce a new inversion method, GE-ART, to calculate the plasma density distribution in the geomagnetic equatorial plane from the Extreme Ultraviolet (EUV) data of IMAGE satellite under the assumption that the plasma density is constant along each geomagnetic field line. The new GE-ART algorithm was derived from the traditional Algebraic Reconstruction Techniques (ART) in Computed Tomography (CT) which was different from the several existing methods. In this new method, each value of the EUV image data was back-projected evenly to the geomagnetic field lines intersected by this EUV sight. A 3-D inversion matrix was produced by the contributions of all the voxels contained in the plasmasphere covered by the EUV sensor. That is, we considered that each value of the EUV image data was relative to the plasma densities of all the voxels passed through by the corresponding EUV radiation, which is the biggest difference to all the existing inversion methods. Finally, the GE-ART algorithm was evaluated by the real EUV data from the IMAGE satellite.

Li, Liang; Chen, Zhiqiang; Xu, Ronglan; Huang, Ya

2011-12-01

153

Bubble formation in NiCr splat on aluminum substrate during plasma spray: Surface chemistry effect  

NASA Astrophysics Data System (ADS)

NiCr single splats were plasma-sprayed on aluminum substrates which were modified by thermal treatments over a range of specific temperatures. It was observed that the splat morphologies changed from highly fingered splats to disk splats with increasing thermal treatment temperature. In addition, the density of the bubble pores which formed at the underside of NiCr splats significantly reduced with an increase of substrate temperature. X-ray photoelectron spectroscopy was used to examine the variation of surface chemistry with thermal treatment. The release of water from the dehydration of an oxyhydroxide layer, which was found to form on the substrate surface, was strongly correlated with the splat morphology and bubble formation at the splat underside. It is proposed that the water desorption from the substrate surface causes turbulence in the spreading process of the splat and the bubble formation at the splat underside, which leads to the splashing of the splat. Preheating or heating the substrate during spraying can partly remove the water prior to spraying, thereby greatly improving the contact between the splats and the substrate which enhanced the formation of a disk splat and significantly reduced the bubble formation at the splat underside.

Tran, A. T. T.; Hyland, M. M.

2009-08-01

154

Formation and ascent of nonisothermal ionospheric and chromospheric bubbles  

SciTech Connect

The influences of nonisothermicity on the dynamics of ionospheric and chromospheric bubbles is discussed. The possibility of the existence in the ionosphere of a recombination-thermal instability, arising from the temperature dependence of the coefficient of charge exchange between molecules and atomic ions, is shown, and its influence on the formation and evolution of equatorial bubbles is analyzed. It is shown that the formation and dynamics of bubbles may depend on recombination processes and gravity, while plasma heating (predominantly by vertical electric fields) leads to the deepening and preservation of bubbles as they move to greater altitudes. The hypothesis is advanced that the formation of bubbles may be connected with the ascent of clumps of molecules in ionospheric tornados.

Genkin, L.G.; Erukhimov, L.M.; Myasnikov, E.N.; Shvarts, M.M.

1987-11-01

155

Supra-bubble regime for laser acceleration of cold electron beams in tenuous plasma  

SciTech Connect

Relativistic electrons can be accelerated by an ultraintense laser pulse in the 'supra-bubble' regime, that is, in the blow-out regime ahead of the plasma bubble (as opposed to the conventional method, when particles remain inside the bubble). The acceleration is caused by the ponderomotive force of the pulse, via the so-called snow-plow mechanism. The maximum energy gain, DELTAgammaapproxgamma{sub g}a, is attained when the particle Lorentz factor gamma is initially about gamma{sub g}/a, where gamma{sub g} is the pulse group speed Lorentz factor, and a is the laser parameter, proportional to the laser field amplitude. The scheme operates at a < or approx. gamma{sub g}, yielding DELTAgamma of up to that via wakefield acceleration for the same plasma and laser parameters, DELTAgammaapproxgamma{sub g}{sup 2}. The interaction length is shorter than that for the wakefield mechanism but grows with the particle energy, hindering acceleration in multiple stages.

Geyko, V. I.; Dodin, I. Y.; Fisch, N. J. [Department of Astrophysical Sciences, Princeton University, Princeton, New Jersey 08544 (United States); Fraiman, G. M. [Institute of Applied Physics, RAS, 46 Ulyanov Street, Nizhny Novgorod 603950 (Russian Federation)

2010-02-15

156

Equatorial ionosphere responses to two magnetic storms of moderate intensity from conjugate point observations in Brazil  

NASA Astrophysics Data System (ADS)

Equatorial ionospheric responses during two magnetic storms of moderate intensity are investigated, for the first time, by conjugate point observations in Brazil. The study focuses on storm-induced changes in the evening prereversal vertical drift, thermospheric trans-equatorial winds, spread F/plasma bubble irregularity development, electron density/plasma frequency heights, the EIA strength, and zonal plasma drifts. It is based on data obtained from five Digisondes operated in Brazil, three of them being part of a conjugate point equatorial experiment (COPEX) involving a dip equatorial and two magnetic conjugate sites at 12. The other two were operated at the equatorial ionization anomaly (EIA) trough and crest locations at nearby magnetic meridians. The results bring out, and clarify, many outstanding aspects of the strong influence of storm time electric fields on the equatorial ionosphere at different phases of the two long lasting storm sequences. During both storms prompt penetration electric fields dominated the ionospheric response features as compared to the disturbance wind dynamo effects that were not very conspicuous. An under-shielding (over-shielding) electric field occurring in the evening hours causes enhancement (suppression) of the prereversal vertical drift and post sunset spread F/plasma bubble generation. The same electric fields cause post sunset EIA enhancement and suppression, respectively. Post sunset (post midnight) spread F can develop from under-shielding (over-shielding) electric fields, while it can be disrupted by over-shielding (under-shielding) electric field. Trans-equatorial winds are found to be ineffective to stabilize the post sunset F region against the destabilizing effect of strong prereversal vertical drift. Storm time westward plasma drifts are found to be driven by prompt penetration eastward electric fields (through their effect of inducing vertical Hall electric fields), rather than by a disturbance westward thermospheric wind during these storms.

Abdu, M. A.; Batista, I. S.; Bertoni, F.; Reinisch, B. W.; Kherani, E. A.; Sobral, J. H. A.

2012-05-01

157

The growth and decay of equatorial backscatter plumes  

NASA Astrophysics Data System (ADS)

During the past three years, a series of rocket experiments from the Kwajalein Atoll, Marshall Islands, were conducted to investigate the character of intense, scintillation-producing irregularities that occur in the nighttime equatorial ionosphere. Because the source mechanism of equatorial irregularities, believed to be the Rayleigh-Taylor instability, is analogous to that which generates plasma-density striations in a nuclear-induced environment, there is considerable interest in the underlying physics that controls the characteristics of these irregularities. A primary objective of ALTAIR investigations of equatorial irregularities is to seek an understanding of the underlying physics by establishing the relationship between meter-scale irregularities (detected by ALTAIR), and the large-scale plasma-density depletions (or 'bubbles') that contain the kilometer-scale, scintillation-producing irregularities. We describe the time evolution of backscatter 'plumes' produced by one meter equatorial field-aligned irregularities. Using ALTAIR, a fully steerable backscatter radar, to repeatedly map selected plumes, we characterize the dynamic behavior of plumes in terms of growth and a decay phase. Most of the observed characteristics are found to be consistent with equatorial-irregularity generation predicted by current theories of Rayleigh-Taylor and gradient-drift instabilities. However, other characteristics have been found that suggest key roles played by the eastward neutral wind and by altitude-modulation of the bottomside F layer in establishing the initial conditions for plume growth.

Tsunoda, R. T.

1980-02-01

158

Analysis of the electromagnetic fields and electron acceleration in the bubble regime of the laser-plasma interaction  

SciTech Connect

An analytical model for the electromagnetic fields in the bubble regime of the interaction of ultrahigh-intensity laser with plasma is given. The two-dimensional model is based on the results of particle-in-cell simulation and includes the bubble front region. It is used to consider the generation of dense ultrashort quasimonoenergetic high-energy electron bunches. The resulting bunch parameters agree fairly well with those from the simulation.

Xie Baisong; Wu Haicheng; Wang Hongyu; Wang Naiyan; Yu, M. Y. [Key Laboratory of Beam Technology and Materials Modification of Ministry of Education, Beijing Normal University, Beijing 100875 (China); Institute of Low Energy Nuclear Physics, Beijing Normal University, Beijing 100875 (China); Department of Physics, Anshan Normal University, Anshan 114007 (China); Key Laboratory of Beam Technology and Materials Modification of Ministry of Education, Beijing Normal University, Beijing 100875 (China); Institute of Low Energy Nuclear Physics, Beijing Normal University, Beijing 100875 (China); Institut fuer Theoretische Physik I, Ruhr-Universitaet Bochum, D-44780 Bochum (Germany); Institute for Fusion Theory and Simulation, Zhejiang University, Hangzhou 310027 (China)

2007-07-15

159

Comment on 'Phenomenological theory of laser-plasma interaction in 'bubble' regime''[Phys. Plasmas 11, 5256 (2004)  

SciTech Connect

A reliable analytical expression for the maximum energy (gamma{sub max}) of the accelerated electrons in the bubble regime is derived. The presented equation is more consistent than the previous equation derived by Kostyukov et al. [Phys. Plasmas 11, 5256 (2004)]. The (gamma{sub max}) derived by I. Kostyukov et al. was two time larger than gamma{sub max} observed in the particle in the cell (PIC) simulations. This new equation explains the monoenergetic electron energy more accurately in the relativistic regime and is in consistence with the observed PIC simulations.

Rahmatollahpur, Sh. [Material School, 55515-196 Bonab (Iran, Islamic Republic of)

2010-05-15

160

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

161

Equatorial vertical plasma drift velocities and electron densities inferred from ground-based ionosonde measurements during low solar activity  

NASA Astrophysics Data System (ADS)

Average values of ionosonde hmF2 data acquired from an African equatorial station have been used to determine vertical plasma drift (Vz) measurements during period of low solar activity. Pre-noon peak was around 1000 h LT for all seasons. The peak daytime F2 drift is higher during the equinoctial months with an average of 18.1 m/s than the solsticial months (14.7 m/s). At nighttime, Vz is characterized first by upward enhancement around 1900 h LT with a range of 0.3-8.0 m/s, then by a downward reversal. The highest enhancement was recorded in December solstice and start earliest during the March equinox. The peak reversal values are 13.3, 10.7, 9.0 and 4.2 m/s for December Solstice, September Equinox, March Equinox and June Solstice respectively. The observed simultaneous post-sunset rise in hmF2 and in vertical EB drift together with a sharp drop in NmF2 at all season infer that electrons moving away from the equator are at a region of low recombination loss rate. The abrupt faster drift of the plasma away from the equator as indicated by the pre-reversal enhancement (PRE) in upward plasma drift is responsible for the sharp drop in NmF2 immediately after sunset. Some past results were also confirmed in this work.

Adebesin, B. O.; Adeniyi, J. O.; Adimula, I. A.; Reinisch, B. W.

2013-05-01

162

In situ measurement of nighttime plasma density irregularities over an equatorial station Trivandrum  

NASA Astrophysics Data System (ADS)

A rocket-borne Langmuir probe was flown from an equatorial station Trivandrum (8.5N, 76.9E) during nighttime to study the nature of electron density irregularities present in the E region. Irregularities were observed over a large-scale size range (few kilometers to 1 m) in regions of both positive and negative electron density gradients. Amplitudes of irregularities were in the range of 0.01% to 15%. In addition to these, irregularities with scale sizes as small as 13 cm were also detected in 97-104 km altitude region. Spectral indices of irregularities in large-scale (few kilometers > ? > 50 m), medium-scale (50 m > ? > 10 m), and small-scale (10 m > ? > 1 m) size ranges were -1.7 0.1, -2.2 0.4, and -2.7 0.5, respectively. A wind-driven gradient drift instability (GDI) is invoked as the mechanism for irregularities observed in positive gradient regions. The power spectrum of irregularities showed an unusual behavior in 102 1.4 km altitude region, where an almost flat spectrum was observed for the scale size range of 15-120 m. The only other nighttime rocket measurement of irregularities over an equatorial station reported so far in the literature highlighted the presence of irregularities in regions of negative electron density gradients and ascribed these to the electric field driven GDI but did not discuss the mechanism of generation of irregularities with comparable strengths in the positive gradient regions observed in the same flight. Also the present electron density profile did not show sharp layers as reported earlier.

Sinha, H. S. S.; Pandey, R.; Misra, R. N.

2010-11-01

163

Particle energization in the course of plasma-sheet bubble injection: results of RCM-E simulations  

NASA Astrophysics Data System (ADS)

To investigate the particle energization at geosynchronous orbit during the substorm expansion phase, we present simulation results of an idealized bubble injection by using the Rice Convection Model with self-calculated equilibrated magnetic field model (RCM-E). The bubble is initiated in the near-Earth plasma sheet at X=-15 RE with severely depleted entropy parameter PV5/3 following a substorm growth phase. The simulation confirms the well-established particle injection features, including prominent dispersionless particle flux enhancement for energetic protons (>100keV) near midnight geosynchronous orbit and dispersive flux enhancement around the dusk sector. We find that dispersionless flux enhancement coincides with the magnetic field dipolarization well inside the plasma-sheet bubble and the injection boundary is overlapped with the earthward shape of the bubble. We suggest that the particles are accelerated as the magnetic field dipolarizes remarkably, which is caused by the large flux tube content reduction inside the bubble. We also find that this mechanism is more effective for higher energy particles near the transition region.

Yang, J.; Toffoletto, F.; Wolf, R. A.; Sazykin, S.

2010-12-01

164

Insights in the laser-induced breakdown spectroscopy signal generation underwater using dual pulse excitation Part I: Vapor bubble, shockwaves and plasma  

NASA Astrophysics Data System (ADS)

Plasma and vapor bubble formation and evolution after a nanosecond laser pulse delivered to aluminum targets inside water were studied by fast photography. This technique was also applied to monitor the plasma produced by a second laser pulse and for different interpulse delays. The bubble growth was evident only after 3 ?s from the first laser pulse and the bubble shape changed during expansion and collapse cycles. The evolution and propagation of the initial shockwave and its reflections both from the back sample surface and cell walls were detected by Schlieren photography. The primary plasma develops in two phases: violent particle expulsion and ionization during the first ?s, followed by slow plasma growth from the ablation crater into the evolving vapor bubble. The shape of the secondary plasma strongly depends on the inner bubble pressure whereas the particle expulsion into the expanded bubble is much less evident. Both the primary and secondary plasma have similar duration of about 30 ?s. Detection efficiency of the secondary plasma is much reduced by light refraction at the curved bubble-water interface, which behaves as a negative lens; this leads to an apparent reduction of the plasma dimensions. Defocusing power of the bubble lens increases with its expansion due to the lowering of the vapor's refraction index with respect to that of the surrounding liquid (Lazic et al., 2012 [1]). Smell's reflections of secondary plasma radiation at the expanded bubble wall redistribute the detected intensity on a wavelength-dependent way and allow gathering of the emission also from the external plasma layer that otherwise, would not enter into the optical system.

Lazic, V.; Laserna, J. J.; Jovicevic, S.

2013-04-01

165

Equatorial zonal plasma drifts measured by the C/NOFS satellite during the 2008-2011 solar minimum  

NASA Astrophysics Data System (ADS)

We use the measurements by the Vector Electric Field Investigation (VEFI) on board the Communication/Navigation Outage Forecasting System (C/NOFS) satellite to study the local time and seasonal- and longitudinal-dependent climatology of equatorial F region zonal plasma drifts during 2008-2011. These drifts are essentially westward during the day and eastward at night. Over Jicamarca Radio Observatory, the satellite measurements are in good agreement with incoherent scatter radar drifts. Our data show strong longitudinal variations, particularly in the South American sector during the solstices. The equinoctial data exhibit short-lived and largely enhanced westward drifts near sunrise and wave-4 structures from the early afternoon to late night equinoctial periods. The nighttime eastward drifts are largest near the western American sector at all seasons. The June solstice postmidnight eastward drifts decrease sharply at longitudes of about 310 and have much smaller values in the entire Eastern Hemisphere. We also briefly discuss the relationship between the longitude-dependent vertical and zonal plasma drifts.

Fejer, Bela G.; Tracy, Brian D.; Pfaff, Robert F.

2013-06-01

166

The bubble to jetting transition mechanism of plasmas in NaNO3 solutions sustained by pulsed power  

NASA Astrophysics Data System (ADS)

Plasmas in NaNO3 solutions sustained by pulsed power with Ton = 10-500 s are studied. With an applied voltage equal to or lower than 100 V, the bubble mode is observed. In this mode, bubbles, a few hundred ?m in diameter, are formed and detached continuously at the electrode surface because of the buoyant force. An increase in the applied voltage to 125 V results in a bubble to jetting transition. When this transition occurs, bubbles with diameters smaller than 100 m are formed and are rapidly jetted away continuously. The examination of various conditions shows that the transition occurs when the power and energy input simultaneously exceed critical values 4.4 10-3 6 10-4 J and 45 5 W, respectively, within Ton. Given the electrode surface area, this critical power is equivalent to a heat flux of 229 25 MW m-2, which is close to the heat flux required, 223 MW m-2, for the occurrence of explosive vaporization reported in the literature. Such an observation strongly supports the hypothesis that the bubble to jetting transition is induced by the electrothermal effect.

Hsieh, An-hsuan; Chang, Hung-wen; Hsu, Cheng-che

2012-10-01

167

Nature of axial tail instability and bubble-blob formation in near-Earth plasma sheet  

NASA Astrophysics Data System (ADS)

ABSTRACTPrevious global magnetohydrodynamic (MHD) simulations of substorm events have identified the dynamic presence of an axial tail instability that is uniform in the dawn-dusk direction in the near-Earth plasma sheet. The axial tail instability is found to be a major cause of the initial growing MHD force imbalance on closed field lines prior to the subsequent magnetic reconnection and substorm expansion onset processes. In this work, energy principle analysis indicates that a two-dimensional thin current sheet configuration in the magnetotail is typically stable to the axial mode within the framework of ideal MHD model. However, linear resistive MHD calculations find axial tail instabilities on closed field lines in the generalized Harris sheet configurations. The properties of these instabilities are similar to the axial tail modes observed in the global MHD simulations. The axial tail mode is unstable in regimes of low Lundquist number and regions with small normal component of magnetic field. Such resistive axial tail instability would by many researchers be considered as tearing instability in a two-dimensional tail configuration. Unlike the conventional tearing mode of Harris sheet, the linear axial tail instability does not involve any reconnection process. Instead, the nature of the mode is dominantly a slippage process among neighboring flux tubes as facilitated by resistive dissipation. A natural consequence of the axial tail instability is shown to be the formation of bubble-blob pairs in the pressure and entropy profiles in the near-Earth plasma sheet.

Zhu, P.; Raeder, J.; Hegna, C. C.; Sovinec, C. R.

2013-02-01

168

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

NASA Astrophysics Data System (ADS)

We derive and employ an algorithm for the three-dimensional fluid treatment of ionospheric plasma, including the complete set of electromagnetic fields. Traditionally, simulations of ionospheric plasma instabilities assume electrostatic physics and/or simplify the problem in two dimensions while the dynamics along the Earth's magnetic field lines are neglected. Explored are the 3-D electric and magnetic fields resulting from current divergence, current flows, and Alfvn waves associated with low-latitude plasma irregularity dynamics. We investigate both dynamic and static electromagnetic properties. For the first time, we present simulations of the Alfvnic dynamics that map electric fields along the Earth's magnetic field lines. We also find that 1-D theory can significantly overestimate 3-D ambipolar electric fields.

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

2013-06-01

169

On seeding equatorial spread F: Parallel or transverse transport?  

NASA Astrophysics Data System (ADS)

There is considerable current interest in how the spawning of equatorial plasma bubbles (EPBs) is affected by the nature of the plasma-seeding process. The process most likely involves an atmospheric gravity-wave and coupling of its wind perturbations to the plasma in the bottomside of the F layer. Neutral-ion coupling can occur either via transverse transport (TT) perpendicular to geomagnetic field (B?) lines, or via parallel transport (PT) along B?. Whether TT or PT is responsible is important, because each involves different physics, which could lead to substantial differences in EPB development. The general consensus, until recently, was that TT controlled both seeding and the EPB growth process. Evidence, however, has appeared in the literature, which seemingly supports the notion that PT is playing a role in the plasma-seeding process. In this paper, a clarification of the physics is presented, which show that TT is, in fact, the dominant seeding process.

Tsunoda, Roland T.

2013-10-01

170

An equatorial scintillation model  

Microsoft Academic Search

Radiowave scintillation in the presence of natural and\\/or high altitude nuclear disturbances has the potential to disrupt numerous transionospheric radio and radar systems. This report develops a model characterizing the plasma density irregularities that produce scintillation in the naturally disturbed equatorial F layer. The model has been incorporated into Program WBMOD along with subroutines for computing both link geometry and

E. J. Fremouw; R. E. Robins

1985-01-01

171

Lightning-induced lower-hybrid turbulence and trapped Extremely Low Frequency (ELF) electromagnetic waves observed in deep equatorial plasma density depletions during intense magnetic storms  

Microsoft Academic Search

During the early phase of the intense magnetic storm of 7-11 November 2004, the DEMETER satellite encountered large-scale equatorial plasma density depletions with density decreases of two or three orders of magnitude. Wave measurements carried out inside these depletions show the occurrence of broadband and localized lower-hybrid turbulence triggered by whistlers propagating from thunderstorm lightning occurring below the orbit path.

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

2008-01-01

172

On the height variation of the equatorial F region vertical plasma drifts  

Microsoft Academic Search

The authors have used improved incoherent scatter radar measurements at the Jicamarca Radio Observatory to study the height variation of the F region vertical plasma drift velocity (driven by the zonal electric field) during moderately quiet conditions. Preliminary results indicate a nearly linear change of the vertical drift velocity with altitude between 200 and 700 km, but with considerable day-to-day

J. E. Pingree; B.G. Fejer

1987-01-01

173

Plasma density irregularities in the equatorial D-region produced by neutral turbulence  

NASA Astrophysics Data System (ADS)

Plasma density irregularities in the D-region are studied in a large-scale size range (1-300 m) during the daytime. The amplitude of these irregularities ranges from a few percent for small-scale sizes (under 15 m) to 10-15 percent for larger-scale sizes (15-300 m). Spectra of all the daytime irregularities clearly exhibit a change in the spectral index at a scale corresponding to a few tens of meters. Turbulence parameters, namely the vertical turbulent velocity, the energy dissipation rate, the eddy diffusion coefficient, the bouyancy scale, and the Kolmogorov microscale are derived. The spectral index of the irregularities in the inertial subrange is found to be very close to -5/3, indicating that these irregularities are produced by the neutral turbulence mechanism. These irregularities are distinctly different, in their appearance and extent, from the irregularities produced by plasma instabilities such as cross-field and two-stream instabilities.

Sinha, H. S. S.

1992-01-01

174

Nature of Axial Tail Instability and Bubble-Blob Formation in Near-Earth Plasma Sheet*  

NASA Astrophysics Data System (ADS)

Previous global MHD simulations of substorm events have identified the dynamic presence of an axial tail instability with dawn-dusk symmetry in the near-Earth plasma sheet as a major cause of the initial loss of MHD equilibrium on closed field lines prior to the subsequent magnetic reconnection and substorm expansion onset processes [Raeder et al. 2010; Siscoe et al. 2009]. In this work, energy principle analysis indicates that a two-dimensional thin current sheet configuration in the magnetotail is typically stable to the axial mode within the framework of ideal MHD model. Linear resistive MHD calculations find axial tail instabilities on closed field lines in the generalized Harris sheet configurations. The properties of these instabilities are similar to the axial tail modes observed in the global MHD simulations. The axial tail mode is unstable in regimes of low Lundquist number and regions with small normal component of magnetic field. Mode growth and structure show both similarities and differences in comparison to the linear resistive tearing mode of a one-dimensional Harris sheet. Unlike the conventional tearing mode of Harris sheet, the linear axial tail instability does not involve any reconnection process. Instead, the nature of the mode is dominantly an interchange or slippage process among neighboring flux tubes as facilitated by dissipations such as resistivity. The formation of bubble-blob pairs in pressure and entropy distributions in the near-Earth plasma sheet is shown to be a natural component as well as consequence of this axial instability process. *Supported by NSF grants AGS-0902360 and PHY-0821899. REFERENCES: Raeder, J., P. Zhu, Y. Ge, and G. Siscoe (2010), Open Geospace General Circulation Model simulation of a substorm: Axial tail instability and ballooning mode preceding substorm onset, J. Geophys. Res., 115, A00I16, doi:10.1029/2010JA015876. Siscoe, G. L., M. M. Kuznetsova, and J. Raeder (2009), Search for an onset mechanism that operates for both CMEs and substorms, Ann. Geophys., 27, 31413146.

Zhu, P.; Raeder, J.; Hegna, C. C.; Sovinec, C. R.

2011-12-01

175

Optical signature of shear in the zonal plasma flow along with a tilted structure associated with equatorial spread F during a space weather event  

NASA Astrophysics Data System (ADS)

Optical signature for shear in the zonal plasma flow is obtained along with a tilted plasma plume structure in VHF radar map during a space weather event on 11 February 2004 (AP=28). A multi-wavelength photometer with a narrow spectral band-width and a narrow field-of-view was operated from Gadanki (13.5N, 79.2E, dip lat 6.3N) to measure airglow emissions emanating from two different altitude regions in a bi-directional mode corresponding to zenith and 45 elevation along the eastward direction. The identifiable features in the 630.0 nm airglow emission that originates from the base of the F region moved westward, while similar features in the 777.4 nm airglow emission, that originates from a region around the peak of the F layer, moved eastward. This indicates a shear in the zonal plasma flow. Simultaneous measurements of equatorial plasma irregularity structures using a VHF radar reveal the presence of a C-shaped plume structure during the period of the sheared flow. The plausible linkage between the space weather event and the shear in the zonal plasma flow is discussed. The implicit evidences for the alteration in the E region dynamo in the presence of the space weather event are shown. This investigation highlights the importance of magnetosphere-ionosphere-thermosphere coupling in addressing the equatorial spread F process comprehensively.

Sekar, R.; Chakrabarty, D.; Pallamraju, D.

2012-02-01

176

On the exclusion of intracluster plasma from active galactic nuclei-blown bubbles  

NASA Astrophysics Data System (ADS)

Simple arguments suggest that magnetic fields should be aligned tangentially to the surface of an AGN-blown bubble. If this is the case, charged particles from the fully ionized intracluster medium (ICM) will be prevented, ordinarily, from crossing the boundary by the Lorentz force. However, recent observations indicate that thermal material may occupy up to 50 per cent of the volume of some bubbles. Given the effect of the Lorentz force, the thermal content must then be attributed to one, or a combination, of the following processes: (i) the entrainment of thermal gas into the active galactic nuclei (AGN) outflow that inflated the bubble; (ii) rapid diffusion across the magnetic field lines at the ICM/bubble interface; (iii) magnetic reconnection events which transfer thermal material across the ICM/bubble boundary. Unless the AGN outflow behaves as a magnetic tower jet, entrainment may be significant and could explain the observed thermal content of bubbles. Alternatively, the cross-field diffusion coefficient required for the ICM to fill a typical bubble is ~1016cm2s-1, which is anomalously high compared to predictions from turbulent diffusion models. Finally, the mass transfer rate due to magnetic reconnection is uncertain, but significant for plausible reconnection rates. We conclude that entrainment into the outflow and mass transfer due to magnetic reconnection events are probably the most significant sources of thermal content in AGN-blown bubbles.

Pope, Edward C. D.

2010-05-01

177

On the height variation of the equatorial F region vertical plasma drifts  

SciTech Connect

The authors have used improved incoherent scatter radar measurements at the Jicamarca Radio Observatory to study the height variation of the F region vertical plasma drift velocity (driven by the zonal electric field) during moderately quiet conditions. Preliminary results indicate a nearly linear change of the vertical drift velocity with altitude between 200 and 700 km, but with considerable day-to-day variations in the value of the slope. On the average, the velocity gradients are positive in the late night and morning periods and negative during the afternoon and evening hours. Simultaneous vertical and zonal drift measurements confirm that the measured height variation of the vertical drift is consistent with the existence of a curl free electric field in the low latitude ionosphere. The time dependence of the Jicamarca vertical drifts extrapolated to higher altitudes closely resembles the diurnal variation of the drift component due to the zonal electric field observed at F region heights over Arecibo.

Pingree, J.E.; Fejer, B.G. (Cornell Univ., Ithaca, NY (United States))

1987-05-01

178

Field and plasma periodicities in Saturn's equatorial middle magnetosphere: Links between the asymmetric ring current and plasma circulation  

NASA Astrophysics Data System (ADS)

Superimposed on the predominantly dipolar field of Saturn's middle magnetosphere (here taken as between 5 and 10 RS) are perturbations of a few nT amplitude that vary with the SKR periodicity. Andrews and coworkers (2008) have determined that averages of the perturbations of the radial and azimuthal field components vary roughly sinusoidally and in quadrature, with the radial component leading. Thus these two components of the magnetic perturbations can be represented as an approximately uniform field rotating in the sense of Saturn's rotation (Espinosa et al., 2003). This perturbation field is referred to by Southwood and Kivelson (2007) as the cam field. Andrews et al. (2008) show that perturbation of the theta component, (theta is colatitude) is also nearly sinusoidal and in-phase with the radial perturbations. It follows that near the equator variations of the field magnitude are also in phase with the radial perturbations. Provan et al. (2009) and Khurana et al. (2009) have attributed the periodicity of the field magnitude to an asymmetric ring current. Saturn's asymmetric ring current is not fixed in local time,as it is at Earth, but rotates quasi-rigidly at the SKR period. A distributed, rotating field-aligned current (FAC) system must develop between regions with an excess of or a dearth of azimuthal current but, because those FACs spread over a large spatial region, the associated current density will be smaller than the current density of the more localized cam current system. Thus, it is the electrons associated with the latter currents that are likely to drive the periodically modulated SKR signals. The ring current of the middle magnetosphere is dominated by inertial currents carried by the thermal plasma (Sergis et al., 2010), but the variation of azimuthal current may arise either from density variations or variations of plasma beta. In either case, the current pattern must drive a circulation of the plasma in the middle magnetosphere. [A circulating plasma pattern in the inner magnetosphere at distances less than 5 RS has been described by Gurnett et al. (2007) but has not yet been related to the analysis of this talk.] Because of the local time asymmetry of the magnetosphere, the flows and some of the magnetic perturbations are expected to increase in magnitude when the outward flow sector rotates into the post dusk magnetosphere, a phenomenon possibly related to the recurrent energization of plasma in the midnight-to-dawn quadrant of Saturn's magnetosphere described by Mitchell et al (2009). In this talk we expand on the description of this abstract and analyze the consequences for plasma circulation of the rotating asymmetry in field and particles in Saturn's middle magnetosphere.

Kivelson, Margaret; Southwood, David

179

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

180

Equatorial Guinea.  

PubMed

Equatorial Guinea is situated on the Gulf of Guinea along the west African coast between Cameroon and Gabon. The people are predominantly of Bantu origin. The country's ties with Spain are significant; in 1959, it became the Spanish Equatorial region ruled by Spain's commissioner general. Recent political developments in Equatorial Guinea include the formation of the Democratic Party for Equatorial Guinea in July of 1987 and the formation of a 60-member unicameral Chamber of Representatives of the People in 1983. Concerning the population, 83% of the people are Catholic and the official language is Spanish. Poverty and serious health, education and sanitary problems exist. There is no adequate hospital and few trained physicians, no dentists, and no opticians. Malaria is endemic and immunization for yellow fever is required for entrance into the country. The water is not potable and many visitors to the country bring bottled water. The tropical climate of Equatorial Guinea provides the climate for the country's largest exports and source of economy; cacao, wood and coffee. Although the country, as a whole, has progressed towards developing a participatory political system, there are still problems of governmental corruption in the face of grave health and welfare conditions. In recent years, the country has received assistance from the World Bank and the United States to aid in its development. PMID:12177983

1989-03-01

181

Magnetic activity linked generation of nighttime equatorial spread F irregularities  

NASA Astrophysics Data System (ADS)

Results derived from a statistical study of the generation of equatorial spread F (ESF) irregularities as a result of magnetic activity based on spaced receiver ionospheric scintillation data recorded at a dip equatorial station is reported here. For a study of this nature it is essential to establish whether the observed scintillations are caused by freshly generated irregularities or by irregularities generated earlier, which later drift onto the signal path. It has been observed in the past that the maximum cross-correlation between the spaced receiver signals is significantly less than 1 during the initial phase of development of ESF irregularities due to the presence of perturbation electric fields associated with the Rayleigh-Taylor (R-T) instability that produces equatorial plasma bubbles (EPBs), whereas in the later phase, when these perturbation electric fields die down, the correlation between the two signals increases rapidly. This feature is used in the present study to identify freshly generated ESF irregularities associated with EPBs using spaced receiver scintillation data. Magnetically disturbed days are chosen by using three hourly geomagnetic activity index ap, daily index Ap, and also AE index to study the cases of prompt penetration of high-latitude electric field to the equatorial ionosphere. Disturbed time statistical occurrence pattern of freshly generated irregularities shows seasonal variation for all three types of magnetic disturbances: disturbance dynamo, prompt penetration, combination of disturbance dynamo and prompt penetration. However, it is found that fresh generation of the irregularities due to magnetic activity is most likely to occur around midnight hours in all seasons. Suppression of generation of irregularities immediately after sunset due to inhibition of the growth of the R-T instability on the bottomside of the equatorial F region is clearly seen in vernal equinox (March and April) and solstice months but is not observed for autumnal equinox (September and October).

Kakad, B.; Jeeva, K.; Nair, K. U.; Bhattacharyya, A.

2007-07-01

182

Solar Trans-equatorial Activity  

NASA Astrophysics Data System (ADS)

We have found that solar flares in NOAA active region (AR) 10696 were often associated with large-scale trans-equatorial activities. These trans-equatorial activities appeared to be very common and manifest themselves through i) the formation and eruption of trans-equatorial loops (TELs), ii) the formation and eruption of trans-equatorial filaments (TEFs), and iii) the trans-equatorial brightening (TEB) in the chromosphere. It is determined that the TEF was formed following episodic plasma ejecta from flares occurring in the AR. The TEF eruption was associated with a trans-equatorial flare. All flares in the AR that were accompanied by trans-equatorial activities were associated with halo coronal mass ejections (CMEs). It was noticed that one or several major flares in the AR were followed by an increase of brightness and nonpotentiality of a TEL. These coupled events had a lifetime of more than 12 hours. In addition their associated halo CMEs always had a positive acceleration, indicating prolonged magnetic reconnections in the outer corona at high altitudes.

Wang, Jingxiu; Zhang, Yuzong; Zhou, Guiping; Harra, Louise K.; Williams, David R.; Jiang, Yunchun

2007-08-01

183

Electron temperature variations in developing plasma bubbles - rocket observations from brazil  

Microsoft Academic Search

In-situ measurements of the height variation of the ionospheric electron density and electron temperature were made on 18-th December, 1995 at 2117 hrs (LT) from the equatorial station Alcantara (2,31S;44,4W) in Brazil, with a rocket-borne Langmuir probe. The main objective of the measurement was to study the height variation of the ionospheric electron density and electron temperature under ionospheric conditions

P. Muralikrishna

2004-01-01

184

Electron temperature variations in developing plasma bubbles rocket observations from Brazil  

Microsoft Academic Search

In situ measurements of the height variation of the ionospheric electron density and electron temperature were made on 18th December, 1995 at 2117h (LT) from the equatorial station Alcantara (2.31S; 44.4W) in Brazil, with a rocket-borne Langmuir probe. The main objective of the measurement was to study the height variation of the ionospheric electron density and electron temperature under ionospheric

P. Muralikrishna

2006-01-01

185

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

186

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

187

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

188

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

189

Time evolution and dynamics of equatorial backscatter plumes. I - Growth phase  

NASA Astrophysics Data System (ADS)

The growth of equatorial VHF backscatter plumes, which can be used to study the development of small-scale F region irregularities as well as plasma bubbles, is analyzed on the basis of radar measurements. The development of selected plumes was monitored by the use of the ALTAIR fully steerable backscatter radar located in the Kwajalein Atoll, Marshall Islands. Three examples of the growth-phase characteristics of backscatter plumes are presented which illustrate the generation of the plumes in the bottomside of the F layer about the time of F layer sunset. Observations are found to be generally consistent with equatorial irregularity generation as predicted by the Rayleigh-Taylor and gradient drift instabilities, however an east-west asymmetry in backscatter strength found in the bottomside F layer suggests the importance of the eastward neutral wind and altitude modulation of the bottomside F layer in establishing the initial conditions for plume growth.

Tsunoda, R. T.

1981-01-01

190

An equatorial scintillation model  

NASA Astrophysics Data System (ADS)

Radiowave scintillation in the presence of natural and/or high altitude nuclear disturbances has the potential to disrupt numerous transionospheric radio and radar systems. This report develops a model characterizing the plasma density irregularities that produce scintillation in the naturally disturbed equatorial F layer. The model has been incorporated into Program WBMOD along with subroutines for computing both link geometry and scintillation indices, the latter by means of phase screen diffraction theory. The model is based on similarly extensive analysis of Wideband data from two equatorial stations. It describes irregularities at an effective height of 350 km that are isotropic across the geomagnetic field and elongated by a factor of 50 along the field and whose one dimensional spatial power spectrum obeys a single regime power law with a (negative) spectral index of 1.5. The height-integrated spectral strength of the irregularities is modeled as a function of solar epoch (sunspot number), the angle between the sunset terminator and the geomagnetic field line through the equatorial F layer point in question (a measure of seasonal and longitudinal variation), time after E-layer sunset on that field line, and the F-layer magnetic apex latitude of the point. The report also highlights a factor missing from complete characterization of the joint seasonal/longitudinal variation of scintillation, thought to depend upon thermospheric neutral winds.

Fremouw, E. J.; Robins, R. E.

1985-09-01

191

Electron Self-Injection into an Evolving Plasma Bubble: The Way to a Dark Current Free GeV-Scale Laser Accelerator  

SciTech Connect

A time-varying electron density bubble created by the radiation pressure of a tightly focused petawatt laser pulse traps electrons of ambient rarefied plasma and accelerates them to a GeV energy over a few-cm distance. Expansion of the bubble caused by the shape variation of the self-guided pulse is the primary cause of electron self-injection in strongly rarefied plasmas (n{sub e{approx}}10{sup 17} cm{sup -3}). Stabilization and contraction of the bubble extinguishes the injection. After the bubble stabilization, longitudinal non-uniformity of the accelerating gradient results in a rapid phase space rotation that produces a quasi-monoenergetic bunch well before the de-phasing limit. Combination of reduced and fully self-consistent (first-principle) 3-D PIC simulations complemented with the Hamiltonian diagnostics of electron phase space shows that the bubble dynamics and the self-injection process are governed primarily by the driver evolution; collective transverse fields of the trapped electron bunch reduce the accelerating gradient, slow down phase space rotation, and result in a formation of monoenergetic electron beam with higher energy than test-particle modeling predicts.

Kalmykov, S. Y.; Shadwick, B. A. [Department of Physics and Astronomy, University of Nebraska-Lincoln, Lincoln, NE 68588-0299 (United States); Beck, A.; Lefebvre, E. [CEA, DAM, DIF, Bruyeres-le-Chatel, 91297 Arpajon Cedex (France); Yi, S. A.; Khudik, V.; Downer, M. C. [Department of Physics, C1500, University of Texas at Austin, Austin, TX 78712 (United States)

2010-11-04

192

Electron Self-Injection into an Evolving Plasma Bubble: The Way to a Dark Current Free GeV-Scale Laser Accelerator  

NASA Astrophysics Data System (ADS)

A time-varying electron density bubble created by the radiation pressure of a tightly focused petawatt laser pulse traps electrons of ambient rarefied plasma and accelerates them to a GeV energy over a few-cm distance. Expansion of the bubble caused by the shape variation of the self-guided pulse is the primary cause of electron self-injection in strongly rarefied plasmas (ne~1017 cm-3). Stabilization and contraction of the bubble extinguishes the injection. After the bubble stabilization, longitudinal non-uniformity of the accelerating gradient results in a rapid phase space rotation that produces a quasi-monoenergetic bunch well before the de-phasing limit. Combination of reduced and fully self-consistent (first-principle) 3-D PIC simulations complemented with the Hamiltonian diagnostics of electron phase space shows that the bubble dynamics and the self-injection process are governed primarily by the driver evolution; collective transverse fields of the trapped electron bunch reduce the accelerating gradient, slow down phase space rotation, and result in a formation of monoenergetic electron beam with higher energy than test-particle modeling predicts.

Kalmykov, S. Y.; Beck, A.; Yi, S. A.; Khudik, V.; Shadwick, B. A.; Lefebvre, E.; Downer, M. C.

2010-11-01

193

Geomagnetic storm effects in equatorial ionization anomaly and equatorial spread-F over a low latitude station  

Microsoft Academic Search

Equatorial spread-F and Equatorial Ionization Anomaly EIA are very important geophysical phenomena These two important processes are very much associated with the geomagnetic disturbances geomagnetic storms of varying magnitude Equatorial belt of strong spread-F extends right through the Appleton anomaly crest latitudes during high sunspot years Intense scintillations do occur in presence of the plasma density irregularities that are associated

S. Sharma; H. Chandra; H. S. S. Sinha

2006-01-01

194

Dark-current-free petawatt laser-driven wakefield accelerator based on electron self-injection into an expanding plasma bubble  

NASA Astrophysics Data System (ADS)

A dark-current-free plasma accelerator driven by a short (<=150 fs) self-guided petawatt laser pulse is proposed. The accelerator uses two plasma layers, one of which, short and dense, acts as a thin nonlinear lens. It is followed by a long rarefied plasma (~1017 electrons cm-3) in which background electrons are trapped and accelerated by a nonlinear laser wakefield. The pulse overfocused by the plasma lens diffracts in low-density plasma as in vacuum and drives in its wake a rapidly expanding electron density bubble. The expanding bubble effectively traps initially quiescent electrons. The trapped charge given by quasi-cylindrical three-dimensional particle-in-cell (PIC) simulations (using the CALDER-Circ code) is ~1.3 nC. When laser diffraction saturates and self-guiding begins, the bubble transforms into a bucket of a weakly nonlinear non-broken plasma wave. Self-injection thus never resumes, and the structure remains free of dark current. The CALDER-Circ modelling predicts a few ? mm mrad normalized transverse emittance of electron beam accelerated in the first wake bucket. Test-particle modelling of electron acceleration over 9 cm (using the quasistatic PIC code WAKE) sets the upper limit of energy gain 2.6 GeV with ~2% relative spread.

Kalmykov, S. Y.; Yi, S. A.; Beck, A.; Lifschitz, A. F.; Davoine, X.; Lefebvre, E.; Khudik, V.; Shvets, G.; Downer, M. C.

2011-01-01

195

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

196

O the Hierarchy of Processes Contributing to Equatorial Spread F  

Microsoft Academic Search

Unstable plasma stratification in the twilight equatorial F region ionosphere is subject to plasma instabilities known collectively as equatorial spread F. Small-scale irregularities in electron density give rise to coherent VHF and UHF radio scatter during spread F while in situ spacecraft detect intermediate- and large-scale plasma structures. We present data from observations made over three years at the Jicamarca

David Lee Hysell

1992-01-01

197

On the hierarchy of processes contributing to equatorial spread F  

Microsoft Academic Search

Unstable plasma stratification in the twilight equatorial F region ionosphere is subject to plasma instabilities known collectively as equatorial spread F. Small-scale irregularities in electron density give rise to coherent VHF and UHF radio scatter during spread F while in situ spacecraft detect intermediate- and large-scale plasma structures. We present data from observations made over three years at the Jicamarca

David Lee Hysell

1992-01-01

198

Evidence of Localized and Anisotropic Irregularity Growth Associated With Equatorial Spread-F Plasma Depletions Observed by the San Marco Satellite Electric Field Instrument  

NASA Astrophysics Data System (ADS)

Irregularities in equatorial spread-F develop from a variety of plasma instabilities, for which the Rayleigh-Taylor mechanism is the most dominant at scales of tens of kilometers and longer. Shorter scale waves also contribute to the spectra, and develop from drift wave instabilities, turbulent cascades, and other processes. In situ observations permit in-depth understanding of both the evolving irregularity spectra and the instability processes at work. Important observable parameters include the vector spectral distributions, the local DC electric field, and the local plasma density and associated gradients. In situ electric field measurements provide detailed knowledge of both the irregularities and their wavevector directions since the wave electric field is parallel to the k-vector in an electrostatic wave. Although the San Marco data set is very limited in bandwidth, its measurements nonetheless contribute to our knowledge of spread-F irregularities. We present filter bank data that provide evidence for non-uniform short scale (10's of meter and shorter) wave growth associated with the walls of plasma depletions. In addition, by filtering the DC electric field components, we also show evidence of km-scale irregularities that are highly anisotropic and relate them to the driving DC electric fields within the depletion region. The results are used to help elucidate our current understanding of spread-F instabilities.

Pfaff, R. F.; Liebrecht, C.; Freudenreich, H.; Heelis, R.; Coley, R.

2004-05-01

199

Bubble Tray  

NSDL National Science Digital Library

Bubble Tray from the Exploratorium is an activity about surface tension and constructive or destructive interference observed in soap bubbles. The site provides a soap bubble recipe and suggests common supplies like a coat hanger and pizza pan to produce large, long lasting bubbles. An explanation of the physics involved and other methods of making large bubbles are also supplied. This activity is part of Exploratorium's Science Snacks series.

2006-07-16

200

Influence of conductivity on the generation of a radio frequency plasma surrounded by bubbles in water  

Microsoft Academic Search

A radio frequency plasma was generated and maintained in water over a wide range of water conductivities (0.2-7000 mS m-1). The conductivity of water was changed by adding NaCl to it. The size of the plasma increased with conductivity. Although the intensity of the OH(A-X) line monotonically decreased with increasing conductivity, the generation of hydrogen peroxide and the degradation of

T. Maehara; S. Honda; C. Inokuchi; M. Kuramoto; S. Mukasa; H. Toyota; S. Nomura; A. Kawashima

2011-01-01

201

Development of a passive VHF radar system using software-defined radio for equatorial plasma instability studies  

NASA Astrophysics Data System (ADS)

In this paper, a bistatic passive radar receiver system named "Coherent-scatter Atmospheric Passive Radar Imager (CAPRI)" is described. It is primarily designed to study the dynamics of the upper atmosphere by utilizing "transmitters of opportunity" as the RF target illuminators. CAPRI is constructed using the open source software-defined radio toolkit, GNU Radio, to meet the signal processing requirements in combination with the open source hardware, Universal Software Radio Peripheral 2, for data acquisition. The resultant system is highly flexible, and we present the details of the design as well as a performance analysis. CAPRI will be deployed in Peru, near the magnetic equator, for long-term operations in the area. FM stations near Lima, Peru, will be utilized with the targets of interest being the equatorial electrojet and the spread F. The results will then be compared to the Jicamarca Unattended Long-term investigations of the Ionosphere and Atmosphere (JULIA) radar data, and CAPRI will be used to improve the simultaneous time and spatial coverage in the region in a more cost-effective manner.

Tuysuz, B.; Urbina, J.; Lind, F. D.

2013-07-01

202

Characterizing the 10 November 2004 storm-time middle-latitude plasma bubble event in Southeast Asia using multi-instrument observations  

Microsoft Academic Search

The development and dynamics of ionospheric plasma bubble (PB) irregularity during the super storm of 711 November 2004 are investigated using the data from a multi-instrument network operated in Southeast Asia. Analysis of fluctuations in Global Positioning System total electron content (GPS TEC), ionosonde, GPS scintillation, and in situ satellite density data indicates a series of intense PB-associated irregularities at

Guozhu Li; Baiqi Ning; Biqiang Zhao; Libo Liu; Weixing Wan; Feng Ding; J. S. Xu; J. Y. Liu; K. Yumoto

2009-01-01

203

Characterizing the 10 November 2004 storm-time middle-latitude plasma bubble event in Southeast Asia using multi-instrument observations  

Microsoft Academic Search

The development and dynamics of ionospheric plasma bubble (PB) irregularity during the super storm of 7-11 November 2004 are investigated using the data from a multi-instrument network operated in Southeast Asia. Analysis of fluctuations in Global Positioning System total electron content (GPS TEC), ionosonde, GPS scintillation, and in situ satellite density data indicates a series of intense PB-associated irregularities at

Guozhu Li; Baiqi Ning; Biqiang Zhao; Libo Liu; Weixing Wan; Feng Ding; J. S. Xu; J. Y. Liu; K. Yumoto

2009-01-01

204

Influence of conductivity on the generation of a radio frequency plasma surrounded by bubbles in water  

NASA Astrophysics Data System (ADS)

A radio frequency plasma was generated and maintained in water over a wide range of water conductivities (0.2-7000 mS m-1). The conductivity of water was changed by adding NaCl to it. The size of the plasma increased with conductivity. Although the intensity of the OH(A-X) line monotonically decreased with increasing conductivity, the generation of hydrogen peroxide and the degradation of methylene blue suggested that the number of generated OH radicals decreased with increasing conductivity in the range 0.2-80 mS m-1 and increased in the range 80-7000 mS m-1. Ultraviolet irradiation was found to enhance the degradation of methylene blue not only in pure water but also in high-conductivity water (sime5000 mS m-1).

Maehara, T.; Honda, S.; Inokuchi, C.; Kuramoto, M.; Mukasa, S.; Toyota, H.; Nomura, S.; Kawashima, A.

2011-06-01

205

Growth and decay of a post-sunset equatorial anomaly at low latitudes: Control of EB, neutral winds and daytime electrojet strength  

NASA Astrophysics Data System (ADS)

Analyzing the 2 months ionospheric electron content (IEC) data acquired during a high solar activity period from a network of a stations whose sub-ionospheric points at 420 km were located within 1 of 84 meridian and covering a latitude belt of 3 21N (magnetic), it has been shown that following sunset a fresh equatorial anomaly develops in continuation to the decaying daytime equatorial anomaly (DEA) in the low latitude belt. The occurrence of this post-sunset equatorial anomaly (PEA) is although a regular phenomenon but large day-to-day variations are seen in its strength (crest to trough ratio) and the latitude extent, PEA develops fully within 2 3 h of sunset and then decays. During its development crest of anomaly clearly shows a pole-ward movement and during decay it shows substantial equator-ward movement. While the trough of PEA is always seen over the magnetic equator, the crest of fully developed anomaly may be seen to lie at latitudes anywhere between 12N and 21N magnetic or more on different days. Thus the development and decay of PEA produce large latitudinal disturbance of F-region plasma in the lower latitude belt in the post-sunset hours and the occurrence of various low latitude phenomenon observed in IEC, e.g. post-sunset IEC decreases at equatorial latitudes, post-sunset IEC enhancements at 12N or higher latitudes, pre-midnight IEC enhancements at equatorial latitudes, etc., have been attributed to the systematic development and decay of PEA. Also, the occurrence and development of PEA has been found to play an important role in the onset of equatorial plasma bubble associated ionospheric irregularities and their latitudinal growth. The equatorial ionization anomaly (EIA) is primarily caused by the ExB drifts whereas meridional winds in association with EB drifts also seems to play some role in determining the crest of PEA.

Dabas, R. S.; Singh, Lakha; Garg, S. C.; Das, Rupesh M.; Sharma, Kavita; Vohra, V. K.

2006-09-01

206

Global characteristics of the cold plasma in the equatorial plasmapause region as deduced from the geos 1 mutual impedance probe  

SciTech Connect

Thermal plasma parameters derived by the muntal impedance experiment on GEOS are described. The experiment is well suited to the measurement of the electron density and temperature of the outer plasmasphere (when kT/sub e//N/sub e/<1.6 eV/cm/sup 3/). This investigation of the whole set of data supplied by GEOS 1 (4plasma trough. In the plasmasphere, we observe profiles with N/sub e/proportionalL/sup -4/, while T/sub e/ stands around 10,000 /sup 0/K or less. The intermediate region, situated next to the plasmasphere and above it, is always present in the day sector, where the ionospheric source plays a leading part. In that zone, the plasma parameters, poorly known up to now, exhibit N/sub e/ values approx.2 to 20 cm/sup -3/, together with T/sub e/ values of 20,000 /sup 0/K on the average, dispersed over a 5,000 to 100,000 /sup 0/K range during disturbances. In the night sector, the intermediate region is seen only during the recovery phase. The region of depleted density is observed at the higher L values in the night and morning MTL sectors. There, plasmas out of Maxwellian equilibrium are seen under disturbed conditions. The dynamic response of the thermal plasma parameters to temporal variations of the a/sub m/ index of magnetic activity follows a known scenario as concerns N/sub e/, making apparent a night-to-day, MTL dependent time delay. As concerns T/sub e/, the dynamical study reveals striking features, such as the persistance of the T/sub e/ modifications into the dusk sector, the interpretation of which remains to be clarified.

Decreu, P.M.E.; Beghin, C.; Parrot, M.

1982-02-01

207

Soap Bubbles  

NSDL National Science Digital Library

Learners explore three-dimensional geometric frames including cubes and tetrahedrons, as they create bubble wands with pipe cleaners and drinking straws. Then they investigate how soap film flows into a state of minimum energy when they lift the wand up from the bubble solution. Learners also see how light reflection and interference create shimmering colors in the bubbles.

Exploratorium, The

2011-12-07

208

Dynamics of equatorial F region irregularities from spaced receiver scintillation observations  

Microsoft Academic Search

Spaced receiver observations of amplitude scintillations on a 244 MHz signal, at an equatorial station, have been used to study random temporal changes associated with the scintillation-producing irregularities and the variability of their motion. The computed drift of the scintillation pattern shows the presence of velocity structures associated with equatorial bubbles in the early phase of their development. On magnetically

A. Bhattacharyya; S. Basu; K. M. Groves; C. E. Valladares; R. Sheehan

2001-01-01

209

Equatorial ionospheric irregularities produced by the Brazilian ionospheric modification experiment (BIME)  

SciTech Connect

On two separate evenings in September 1982, rockets were launched into the bottomside equatorial F{sub 2} region off the coast of Natal, Brazil, to inject chemicals, consisting of mainly H{sub 2}O and CO{sub 2}, to create a hole in ionization. The chemicals were injected near the height where the density gradient was steepest, and at a time when the F{sub 2} region was rising rapidly to see whether plasma bubble irregularities could be generated from instabilities triggered by the ionization hole. On both occasions, hole-induced depletions in total electron content (TEC) of more than 10{sup 16} el/m{sup 2} were observed over horizontal distances of at least 60 km from the chemical injection point. The eastward drifts of these artificial depletions were observed by the time difference in the TEC features observed at various TEC monitoring stations, and from the changing range of oblique ionosonde echoes observed by an ionosonde located 300 km magnetically east of the chemical release point. Their subsequent evolution into plasma bubble irregularities was demonstrated from the observations of spread F echoes, strong amplitude scintillation, and TEC depletion at distances of from 300 to 500 km eastward of the release points. The fact that similar behavior of the ionosphere was observed during the evenings of both rocket chemical releases, and on no other nights of the campaign, is strong evidence of successful artificial generation of bubble irregularities by chemical injection into the bottomside F{sub 2} region.

Klobuchar, J.A. (Air Force Geophysics Lab., Hanscom Air Force Base, MA (USA)); Abdu, M.A. (Instituto de Pesquisas Espaciais, Sao Jose dos Campos (Brazil))

1989-03-01

210

Bubble and bubble cloud dynamics  

NASA Astrophysics Data System (ADS)

Cavitation bubbles are formed from small air bubbles, so-called nuclei, with the surrounding pressure reduction caused by the flow, and then, the bubbles shrink and collapse with the surrounding pressure rise. Such volumetric changes of bubbles are calculated in detail and it is found that they are significantly influenced by the internal phenomena, such as thermal diffusion, mist formation due to a homogeneous condensation, mass diffusion between vapor and noncondensable gas, heat and mass transfer through the bubble wall. The structure in cavitating flow interacts with the cavitation bubbles, and those bubbles form a cloud cavitation. It is well known that cloud cavitation is one of the most destructive forms. The behavior of bubble clouds is simulated numerically. An inward propagating shock wave is formed during the collapse of the bubble cloud, and the shock wave and its precursor are focused at the cloud center area. These phenomena associate high frequency pressure oscillations and violent bubble collapses. Those bubble collapses emit high pressure peaks, which are several hundreds times larger than that of a single bubble collapse. .

Matsumoto, Yoichiro

2000-07-01

211

Bubble Puzzles  

NASA Astrophysics Data System (ADS)

Bubbles are fascinating. With their ubiquitous occurrence in a multitude of fluid systems bubbles occupy a very important place in contemporary science and technology. In many applications, bubble control is crucial. I will demonstrate that bubble nucleation at surfaces, which always has been associated with randomness, can be perfectly controlled both in space and time. This new technique allows to quantitatively study bubble-bubble and bubble-surface interaction and reveals a shielding effect in bubble clusters [1]. -- In a second example for the importance of bubble control I will discuss their disturbing effect in piezo-acoustic ink-jet printing: I will show how bubbles are entrained, grow by rectified diffusion, and finally seriously disturb the jetting process by counteracting the pressure build-up at the nozzle [2]. [1] N. Bremond, M. Arora, C. D. Ohl, and D. Lohse, Phys. Rev. Lett. 96, 224501 (2006). [2] J. de Jong, H. Reinten, M. van den Berg, H. Wijshoff, M. Versluis, G. de Bruin, and D. Lohse, J. Acoust. Soc. Am., (August 2006).

Lohse, Detlef

2006-11-01

212

Big Bubbles  

NSDL National Science Digital Library

How do you measure a bubble when it's floating? You can't really, but in this activity, learners can measure the diameter of the ring of suds a bubble leaves on a flat surface. The fun is blowing up the bubbles as big as possible with a straw. Then comes the measuring. This activity can be used to connect science and math, and makes a great rainy day or indoor lunch activity.

Science, Lawrence H.

2010-01-01

213

Magnetic Bubble Materials.  

National Technical Information Service (NTIS)

The Czochralski growth of defect-free, non-magnetic garnet crystals and the preparation of epitaxial magnetic bubble garnet films by liquid phase epitaxy (LPE) and arc-plasma spraying (APS) were investigated. Two garnet systems, Eu-Yb-Y and Sm-Y, were ide...

J. T. Cheng J. W. Moody M. C. Willson R. M. Sandfort R. W. Shaw

1973-01-01

214

Magnetic Bubbles  

NASA Astrophysics Data System (ADS)

Bubbles in liquids driven by a sound field are used in many disciplines: for example bubbles clean surfaces in ultrasonic water bathes, they catalyze unique chemical reactions in sonochemistry, and under special conditions even create light. However, conventional bubbles have a major limitation when placed in an acoustic field: it is extremely hard to control their position. Here we present a new type of bubble that has permanent magnetization originating from a shell of self-assembled nanoparticles, so that magnetic fields can be used to control the bubble's position independently. We will report on the recipe and the experiment to study bubble oscillations in weak magnetic fields. The magnetic susceptibility of the bubbles is proportional to their surface area,?=(93x10-6m)r^2, where r is the radius. Also they are compressible in moderate acoustic fields and induce a microstreaming flow with a toroidal vortex at the upper pole of the bubble. Similar microstreaming flows have been used to transport and rupture cells at small scales. Thus we envision applications in manipulation of biological materials and in microfluidic devices using acoustic and magnetic forces.

Zhao, Xue; Quinto-Su, Pedro; Ohl, Claus-Dieter

2008-11-01

215

Recent results from CHAMP plasma parameter and magnetic field observations  

NASA Astrophysics Data System (ADS)

The multi-year data base of magnetic field and ionospheric measurements from the CHAMP satellite contains an enormous potential to investigate the behaviour and the origin of currents in the F region. Very prominent phenomena are the post-sunset equatorial plasma irregularities (commonly known as "bubbles", or "Equatorial Spread-F" (ESF)) which cause also signatures in the total magnetic field due to diamagnetic currents. The continuous magnetic observations, available at a 1Hz rate, have allowed for the compilation of a comprehensive climatology of the magnetic signatures due to ESF. It reveals a distinct seasonal/longitudinal (S/L) distribution, and the occurrence rate reduces considerably with decreasing solar flux. The (S/L) distribution of bubbles has been found to correlate very well, up to 90 percent, with the pre-reversal enhancement vertical plasma drift peak. This provides strong evidence for the close relation between these phenomena. Since the amplitude of the diamagnetic effect depends on the ambient magnetic field strength and on the background electron density, the global distribution shows also slight differences to the ESF climatology based on plasma depletions. Although electron density readings are only available every 15s, CHAMP data suggest that the plasma irregularities are less structured at places where the ambient magnetic field is strong (e.g. East Asia, Indonesia). In these regions the bubble statistic based on magnetic signatures is systematically lower than that from plasma measurements.

Stolle, Claudia; Luehr, Hermann; Park, Jaeheung; Xiong, Chao; Fejer, B. G.

216

Effect of solar variability on transionospheric radio wave propagation in the equatorial region  

Microsoft Academic Search

Growth of plasma instabilities in the post-sunset equatorial ionospheric F region gives rise to irregularities known by the generic name: equatorial spread F (ESF), which scatter incident VHF or higher frequency radio waves to produce scintillations on trans-ionospheric radio waves. Changes in large scale (> 10 km) electron density distribution in the equatorial and low latitude ionosphere due to electrodynamic

A. Bhattacharyya; B. Engavale; D. Tiwari; S. Bose

2006-01-01

217

Bubble, Bubble, Toil and Trouble.  

ERIC Educational Resources Information Center

|Bubbles are a fun way to introduce the concepts of surface tension, intermolecular forces, and the use of surfactants. Presents two activities in which students add chemicals to liquid dishwashing detergent with water in order to create longer lasting bubbles. (ASK)|

Journal of Chemical Education, 2001

2001-01-01

218

Strong post-midnight Equatorial Ionospheric Anomaly and Equatorial spread F Observations during magnetically quiet period  

NASA Astrophysics Data System (ADS)

Post sunset equatorial ionospheric irregularities, especially during magnetically active periods, have been a subject of many studies. The most prominent irregularities often observed right after sunset are the resurgence of the equatorial ionospheric anomaly (EIA) and equatorial spread F (ESF). It is well understood and documented that pre-reversal enhancement, due to the ionospheric conductivity gradient at the dusk, is one of the prime triggering mechanisms for the post-sunset irregularities in the equatorial region. However, less attention has been given to the equatorial irregularities (EIA and ESF) that often occur in post-midnight, especially during magnetically quiet periods. It has been suggested that the primary process responsible for the dramatic post-midnight ESF during magnetically active periods is the change in magnitude and direction of the usual equatorial electric field. Earlier studies speculated that during magnetically active post-midnight periods the change in electric field direction from westward to eastward for a short intervals cause an upward E B drift, resulting in increased h'F and decreased electron densities at the magnetic equator. Individual scans of Jicamarca vertical drift also often observe significant upward drift during post-midnight periods. We present a case of post-midnight strong equatorial ionospheric anomaly during a magnetically quiet (Kp < 3) period using TOPEX altimeter TEC data. Simultaneously, the ionosonde station at S.J. Campos (23.2S, 45.9W; dip lat. 17.6S) observed strong ESF and unusual h'F height rise during post-midnight period, where TOPEX detected strong EIA. At the same time ROCSAT-1 and DMSP satellites also clearly show existence of EIA during post-midnight period at their orbiting altitude. The former satellite also detected post-midnight in situ density irregularities (such as bubbles) at the same time as strong EIA and ESF. The questions here are what triggers these post-midnight equatorial ionospheric irregularities? Are these post-midnight EIAs related to dusk side pre-reversal EIA? If so, what causes the post-midnight ESF and bubble formation? If, as suggested before, the electric field shifted direction from westward to eastward during post-midnight period, how does this happen and what is the physics behind this direction shift?

Moldwin, M. B.; Yizengaw, E.; Sahai, Y.

2008-12-01

219

Nonlinear evolution of equatorial spread F. 1. On the role of plasma instabilities and spatial resonance associated with gravity wave seeding  

Microsoft Academic Search

We have used a computer simulation to study properties of large-scale equatorial F region irregularities produced by gravity waves by separating such different processes as the spatial resonance effect and the Rayleigh-Taylor instability. Our purpose is to show their relative importance in the production of strong ionization perturbations. When a gravity wave propagates perpendicular to the magnetic field, it generates

Chao-Song Huang

1996-01-01

220

Modelling and observations of the equatorial ionosphere  

Microsoft Academic Search

The equatorial ionosphere experiences one of the most severe forms of a geophysical plasma instability - a phenomenon known as spread F. An observational campaign was organized to bring a complement of diagnostic instruments to two sites in the western Pacific sector (Kwajalein Atoll in the Marshall Islands and Wake Island) for a period of coordinated optical and radio measurements

Michael Mendillo

1990-01-01

221

The Coud Equatorials  

NASA Astrophysics Data System (ADS)

Between 1884 and 1892, no fewer than seven coud equatorials were installed in France, Algeria and Austria. Invented by Maurice Loewy, these equatorials allowed the observer to sit comfortably in a closed room, with all the controls and readings at hand. However they were expensive, they required two flat mirrors, which were a source of concern because of their thermal distortion, and their mechanics was complex and delicate, so that they did not succeed in replacing the conventional equatorials in spite of their advantages. Only two are preserved, in Lyons and in Algiers. We describe in detail these instruments, their history and their use.

Lequeux, James

2011-11-01

222

Soap Bubbles  

NSDL National Science Digital Library

This fun activity from PBS uses simple household items to explore the different shapes a soap bubble can take. It also contains a poll so that visitors can report their results and compare them with those of other visitors.

2010-07-09

223

Digisonde spread F and GPS phase fluctuations in the equatorial ionosphere during solar maximum  

NASA Astrophysics Data System (ADS)

The Jicamarca (11.95S, 76.87W) digisonde and the Arequipa (16.47S, 71.49W) GPS receiver observed the equatorial F region irregularities on the western South America from April 1999 to March 2000. The spread F measured by the digisonde were classified into four types, and the GPS phase fluctuations derived from the temporal variation of total electron content were divided into three levels to represent the irregularity strength. The observation shows that the occurrences of all four types of spread F are higher in the D months (January, February, November, and December) than in the E months (March, April, September, and October). For the GPS phase fluctuations, both seasonal and nighttime variations show that the occurrences of strong level irregularities are higher than moderate level irregularities in the E months, but the situation is reversed in the D months. Moreover, the occurrence sequences of four types of spread F and three levels of GPS phase fluctuations all can be explained by the E B drift variations and the generalized Rayleigh-Taylor instability. For the comparisons between the GPS phase fluctuations and the digisonde spread F/plasma bubbles, results show that the GPS phase fluctuations can represent the appearances of the digisonde spread F, and the strong level of GPS phase fluctuations are associated with the occurrence of topside plasma bubbles. These results imply that the greater GPS phase fluctuation is related to the larger altitudinal range distribution of irregularities.

Chen, W. S.; Lee, C. C.; Liu, J. Y.; Chu, F. D.; Reinisch, B. W.

2006-12-01

224

An average image of proton plasma pressure and of current systems in the equatorial plane derived from AMPTE\\/CCE-CHEM measurements  

Microsoft Academic Search

The present study attempts to visualize the global equatorial current systems and the proton pressure in the near-Earth magnetosphere based on AMPTE\\/CCE-CHEM measured proton distributions, which were sorted by the AE index (``quiet'': AE<100nT, ``active'': 100nT

Paola De Michelis; Ioannis A. Daglis; Giuseppe Consolini

1999-01-01

225

Tiny Bubbles  

NSDL National Science Digital Library

In this activity, which can be performed as a demonstration by the teacher or by the students themselves, carbon dioxide is generated in a fish tank using sodium bicarbonate and vinegar. The students can observe as the accumulating carbon dioxide extinguishes candles of different heights, marking rising levels of CO2 in the tank. They can also blow soap bubbles (which contain air) into the tank and observe them floating on the denser CO2 at first, then sinking as the gas diffuses through the soap film that forms the bubbles.

Dolphin, Glenn

226

On the occurrence of equatorial F-region irregularities during solar minimum using radio occultation measurements  

NASA Astrophysics Data System (ADS)

The technique of radio occultation (RO) is demonstrated to be a powerful tool for studying equatorial F-region irregularities (EFIs) associated with equatorial plasma bubbles. The extensive 4.9 year RO dataset of the Constellation Observing System for Meteorology, Ionosphere and Climate (COSMIC) satellites was employed in this study and contains EFI observations under a wide variety of solar and geomagnetic conditions. From an analysis of the EFI occurrence dependence on season/longitude, it is found that the EFI occurrence statistics largely match those reported previously, with the exception of an equinoctial EFI occurrence maximum in the American sector that is absent from previous studies. It is revealed that this maximum is due to enhanced EFI occurrence near the South Atlantic anomaly, where EFIs are expected to be suppressed by particle precipitation. An investigation into the solar activity dependence of the EFI occurrence characteristics revealed significant increases in the range of local times and latitudes with solar activity for most longitude sectors and seasons. Finally, the EFI suppression and enhancement effects of storm-time electric fields are also investigated using the COSMIC data.

Carter, B. A.; Zhang, K.; Norman, R.; Kumar, V. V.; Kumar, Sushil

2013-02-01

227

Modeling the Direct Penetration of Electric Fields to the Equatorial Ionosphere  

NASA Astrophysics Data System (ADS)

The interplanetary electric field has been observed to penetrate directly to the equatorial region where it affects the generation of plasma bubbles which, in turn, cause the scintillation of transionospheric electromagnetic signals. We use the approach of Nopper and Caravillano [1978] to model the effect of the Region I and Region II currents on the global electric field. We find, consistent with observations, the well-known shielding of the equatorial region by Region II currents. Numerically, two approaches are taken. The first approach is to solve N-squared simultaneous linear algebraic equations for each of the grid points. The second approach is to use the Multigrid technique, which allows a rapid convergence of the SOR (successive over- relaxation) iterations. The advantage of the algebraic approach is accuracy, while the advantage of the second approach is speed. Further comparisons between these two approaches will be made. Effects of the magnetic dipole tilt relative to the polar cap, the presence of a sub storm current wedge, the saturation of the transpolar potential, and seasonal effects will be discussed . Nopper R.W. and R. L. Carovillano, Geophys. Res. Ltrs., 5, 699, 1978.

Rothwell, P. L.; Jasperse, J. R.; Burke, W. J.; Grossbard, N. J.; Huang, C.

2004-05-01

228

Imaging equatorial spread F irregularities with the So Lus coherent backscatter radar interferometer  

NASA Astrophysics Data System (ADS)

We present new results of a study of the interferometric coherent backscatter radar imaging technique applied to So Lus observations made on the night of 1 December 2005. The range-time-intensity (RTI) map of the observations shows echoes occurring near theF region peak and topside heights followed by echoing layers confined to bottomside F region heights. Analyses of the measurements made on this night allowed us to investigate the ability of the So Lus radar interferometer to provide information about the morphology of the scattering structures responsible for different types of equatorial spread Fechoing layers. Results show that topside echoes were produced by a vertically elongated, horizontally narrow scattering channel of irregularities associated with a large-scale plasma depletion ("bubble") as evidenced by colocated GPS scintillation measurements. Bottomside echoes were caused by structured, eastward drifting scattering regions with limited vertical development. Bottom-type echoes, on the other hand, were detected at heights below the minimum altitude of the bottomside echoes and were caused by an undifferentiated scattering region. Our imaging results are discussed in light of current equatorial spreadFtheories and previous higher-resolution imaging observations made at the Jicamarca Radio Observatory.

Rodrigues, F. S.; Moraes, A. O.; de Paula, E. R.

2012-04-01

229

Dawn Sector Plasma Density Observations from DMSP  

NASA Astrophysics Data System (ADS)

Before the launch of the Communication/Navigation Outage Forecasting System (C/NOFS) spacecraft, equatorial plasma bubbles (EPBs) were generally regarded as a post-sunset phenomenon. However, solar minimum observations from the first two years of the C/NOFS mission reveal a very different picture of equatorial dynamics. The planar Langmuir probe (PLP) on the C/NOFS satellite has detected very few irregularities after sunset. Most plasma turbulence was observed after midnight and at dawn at all C/NOFS altitudes and longitudes. These results suggested that a study of the Defense Meteorological Satellite Program (DMSP) dawn sector plasma density measurements might be useful to determine if this shift is typical of solar minimum conditions or the result of this unusually quiet span of solar activity. DMSP observations indicate that equatorial dynamics in the dawn sector are quite different from those of the evening side. For DMSP F17 in 2008 and 2009 the occurrence rates of plasma depletions in the dawn sector were highest around the June and December solstices and extremely low near the March and September equinoxes. For previous solar minimum years 1996 and 1997, dawn sector measurements from F13 exhibited significantly lower rates of occurrence but similar distribution patterns by season and longitude. A preliminary analysis suggests that the low levels of solar EUV flux and reduced electric fields during 2008-2009 established very favorable conditions for the development of post-midnight irregularities.

Gentile, L. C.; Burke, W. J.; Roddy, P. A.; Retterer, J. M.

2010-12-01

230

Forecasting Equatorial Scintillation Activity in Real-time  

NASA Astrophysics Data System (ADS)

It is well-known that the generation of equatorial, F-region plasma density irregularities, via the Generalized Rayleigh-Taylor instability mechanism is critically dependent on the magnitude of the pre-reversal enhancement (PRE) in upward ExB drift velocity after sunset. These plasma density "bubbles" that are generated after sunset lead to the "scintillation" of trans-ionospheric radio wave signals that pass through these bubbles and is commonly referred to as "scintillation activity". Communication and Navigation systems can be severely disrupted by these plasma density irregularities. A measure of scintillation activity is given by the "S4 Index" and a network of Air Force, ground-based UHF and L-band receivers measuring the S4 Index is called the SCIntillation Network Decision Aid (SCINDA) network. This paper describes a technique for automatically forecasting, in real-time, the occurrence or non-occurrence of scintillation activity that relies on real-time data from a ground-based ionospheric sounder at or near the geomagnetic equator. After sunset, the height-rise with time of the bottom-side of the F-layer reflects the magnitude of the upward ExB drift velocity. The value of the ionospheric parameter, h'f (the virtual height of the bottom-side F-layer) at 1930 LT reflects the integrated ExB drift effect on lifting the F-layer to an altitude where the Rayleigh-Taylor instability mechanism becomes important. Incorporating observed h'f values from the Jicamarca, Peru digital sounder at 1930 LT and relating these values to the Total Hourly S4 Index (THS4) observed by the UHF receiver at the Ancon, Peru SCINDA site, it is found that a "threshold" in h'f exists below which, THS4 < 1 (no scintillation activity) and above which THS4 > 1 (scintillation activity). Examples of Jicamarca sounder observations and h'f values prior to the onset of scintillation activity are given. We present results that describe how the threshold value of h'f changes with solar cycle activity and how these results have been incorporated into a real-time capability for automatically forecasting scintillation activity that is available on Google Earth to all interested parties.

Redmon, R.; Anderson, D.; Caton, R. G.; Bullett, T. W.

2008-12-01

231

Tiny Bubbles.  

ERIC Educational Resources Information Center

|A simple oxygen-collecting device (easily constructed from glass jars and a lid) can show bubbles released by water plants during photosynthesis. Suggestions are given for: (1) testing the collected gas; (2) using various carbon dioxide sources; and (3) measuring respiration. (DH)|

Kim, Hy

1985-01-01

232

Occurrence of equatorial F region irregularities: Evidence for tropospheric seeding  

NASA Astrophysics Data System (ADS)

We present a new gap-free version of the seasonal and longitudinal (s/1) variations of PEFI, the equatorial F region irregularity (EFI) occurrence probability, based on data from the AE-E spacecraft. The agreement of this and three earlier partial PEFI patterns verifies all four. We reinterpret another earlier gap-ridden pattern, that of DRSF, a topside ionogram index of average darkening by range spread F. We compare it with PEFI and, using ionosonde radio science considerations, we conclude that DRSF=PEFI times a factor depending on the average number of topside plasma bubbles visible to the ionosonde. The s/1 variations of DRSF thus imply s/1 variations in the average spacing of bubbles, whose seeds have an occurrence probability pattern Pseed. For discussion we assume PEFI=PinstPseed, where Pinst is the pattern of F region instability. The PEFI pattern, which is by definition independent of seed and/or bubble spacing, is far too complex to be explained by the dominant paradigm, that of changes in Pinst by simple changes in the F region altitude and/or north-south asymmetry. We examine evidence behind this dominance, and find it unconvincing. Both the asymmetry and sunset-node/altitude hypotheses of 1984 and 1985, respectively, seem to be partly based on misunderstood data, and their features appear displaced in time and space from those of our repeatable PEFI pattern. In contrast, if Pseed variations influence the PEFI pattern and depend on thermospheric gravity waves from tropospheric convection near the dip equator, then the seasonal maxima (minima) of PEFI could be explained, since they all occur above relatively warm (cold) surface features, where convection is maximal (minimal). Also, the hypothesis of the dominance of the Pseed term could explain an unusual December/January PEFI maximum in the deep, wide, normal Pacific minimum in the one data set obtained in El Nio years. Based on the experiments we consider, we predict that the s/l variations of Pseed will be found to be similar to those of PEFI, and largely to explain them. Finally, we find reasons, based on the similarity of the DRSF variations to s/l patterns of the average scintillation index, for not using, as is commonly done, such scintillation patterns as substitutes for PEFI or Pinst patterns.

McClure, J. P.; Singh, S.; Bamgboye, D. K.; Johnson, F. S.; Kil, Hyosub

1998-12-01

233

Behavior of laser-induced cavitation bubbles in liquid nitrogen  

NASA Astrophysics Data System (ADS)

Initial behavior and the subsequent motion of a bubble in liquid nitrogen are investigated experimentally using high-speed photography. A bubble is generated by focusing a pulsed ruby laser into liquid nitrogen at 78.0 K, changing the ambient pressures up to 253.2 kPa which corresponds to the applied pressure (or overpressure), ?p, being 147.1 kPa. When the energy level of the laser beam at the focus exceeds an irradiance threshold, for instance 5.41011 W/cm2 for ?p=4.9 kPa, the optical breakdown occurs in the liquid nitrogen, followed by a series of high-speed phenomena such as plasma formation, shock wave emission, and vapor bubble generation. It is found that during a very short period after the plasma formation a bubble grows nonspherically reflecting from the plasma shape, but the bubble volume itself varies with time in the same way for all cases performed in the present experiment. The liquid inertia is a dominant factor affecting the bubble growth, while the thermal effect becomes remarkable during the bubble collapse, resulting in the retardation of the bubble motion. The characteristic behavior of a laser-induced cavitation bubble in liquid nitrogen is significantly influenced by the phase change of vapor at the bubble surface as well as by the vapor pressure inside the bubble. Immediately after the bubble rebound, instabilities are amplified over the bubble surface similar to those caused in the water case.

Tomita, Y.; Tsubota, M.; Nagane, K.; An-Naka, N.

2000-11-01

234

Empirical models of storm time equatorial zonal electric fields  

Microsoft Academic Search

Ionospheric plasma drifts often show highly complex and variable signatures during geomagnetically active periods due to the effects of different disturbance processes. We describe initially a methodology for the study of storm time dependent ionospheric electric fields. We present empirical models of equatorial disturbance zonal electric fields obtained using extensive F region vertical plasma drift measurements from the Jicamarca Observatory

Ludger Scherliess

1997-01-01

235

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.

236

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

237

Layers in the equatorial mesosphere, motions and aerosol: rocket and radar measurements during EQUIS II  

Microsoft Academic Search

The NASA EQUIS II (Equatorial Ionosphere Studies) campaign was conducted in August\\/September 2004 at U.S. Army Kwajalein Atoll\\/Reagan Test Site on Roi-Namur, Marshall Islands (9N, 168E). The LEMMA (Layers in the Equatorial Mesosphere, Motions and Aerosol) program was devoted to neutral and plasma density fluctuations in the equatorial mesosphere and lower thermosphere. One objective was to detect layers of small

G. A. Lehmacher; C. L. Croskey; J. D. Mitchell; M. Friedrich; K. Torkar; F.-J. Lbken; M. Rapp; E. Kudeki

2005-01-01

238

Equatorial Electrojet Observations in the African Continent  

NASA Astrophysics Data System (ADS)

Although Satellite observations in the African sector show unique equatorial ionospheric structures that can severely impact navigation and communication systems, the study of ionospheric disturbances in this region is difficult due to the lack of ground-based instruments. This has created a gap in global understanding of the physics behind the evolution and formation of plasma irregularities in the equatorial region, which imposes limitations on ionospheric density modeling efforts. Therefore, in order to have a more complete global understanding of equatorial ionosphere motion, the international space science community has begun to develop an observational infrastructure in the African sector. This includes the deployment of a number of arrays of small instruments, including the AMBER magnetometer array, through the International Heliophysical Year (IHY) cooperative program with the United Nations Basic Space Science (UNBSS) program. Two AMBER magnetometers have been deployed successfully at Adigrat (~6N magnetic) in Ethiopia and at Medea in Algeria (28N magnetic), and became fully operational on 03 August 2008. The remaining two AMBER magnetometers will be deployed soon in Cameroon and Namibia. One of the prime scientific objectives of AMBER is to understand the processes governing electrodynamics of the equatorial ionosphere as a function of latitude, local time, magnetic activity, and season in the African region. The most credible driving mechanism of ionospheric plasma (E B drift) can be estimated using two magnetometers, one right at the equator and the other about 6 off the equator. Therefore, using the AMBER magnetometer at Adigrat and the INTERMAGNET magnetometer located at Addis Ababa (0.9N magnetic) in Ethiopia, the equatorial electrojet (E B drift) activities in that longitudinal sector of the African continent is estimated. The paper also presents the comparison between the estimated vertical drift and the drift values obtained from the vector electric field instrument observation onboard the C/NOFS satellite. The evolution of equatorial ionospheric irregularities will also be presented using data from the growing number of ground- and space-based (on Low-Earth-Orbit (LEO) satellites) GPS receivers in the African region.

Yizengaw, E.; Moldwin, M. B.; Mebrahtu, A.; Damtie, B.; Pfaff, R.; Zesta, E.

2008-12-01

239

Penetration of ELF currents and electromagnetic fields into the Earth's equatorial ionosphere  

Microsoft Academic Search

The penetration of extremely low frequency (ELF) transient electromagnetic fields and associated currents in the Earth's equatorial E-region plasma is studied theoretically and numerically. In the low-frequency regime, the plasma dynamics of the E-region is characterized by helicon waves since the ions are viscously coupled to neutrals while the electrons remain mobile. For typical equatorial E-region parameters, the plasma is

B. Eliasson; K. Papadopoulos

2009-01-01

240

The Local Bubble: an update  

NASA Astrophysics Data System (ADS)

Our view of the the Sun's near neighbourhood in space, the "Local Bubble" region, has changed dramatically over the past decade. The interstellar gas inside this rarefied Cavity is character-ized by a surprisingly wide range of temperatures (100K -1,000,000K), densities, and diffuse structures that are all contained within a 150pc diameter region of space whose fragmented neutral boundary has recently been mapped in 3-D. Rather surprisingly, doubts have even been cast on whether the Local Bubble cavity is filled with a hot million degree emitting gas and, much to the bewilderment of many astrophysicists, we still do not know which physical processes are responsible for the observed ionization state of the local interstellar plasma. This short talk will discuss the latest observational results from several recent studies of the Local Bubble region and how current theoretical models seem at odds with empirical evidence.

Welsh, Barry

241

ALTAIR radar study of equatorial spread F  

NASA Astrophysics Data System (ADS)

The results of research on equatorial spread-F (ESF) phenomena obtained by using two backscatter radars, ALTAIR and TRADEX, are summarized. The radar measurements were made in support of three rocket campaigns conducted from the Kwajalein Atoll during the summers of 1977 through 1979. Backscatter data from ESF irregularities and incoherent-scatter (IS) data from thermal plasma fluctuations were used to show that the structuring of the equatorial F-region plasma is initiated by large-scale (tens to a few hundred kilometers in the east-west direction) plasma-density modulations in the bottomside F layer. The modulation, best described by wavelike altitude variations in constant electron-density contours, appears to be imposed on the bottomside F layer around E-region sunset by a yet-to--be-identified source (although atmospheric gravity waves are a likely candidate). The amplification of the wavelike modulation, in the form of upwellings from the crests of the modulation, is consistent with the amplification expected from the collisional Rayleigh-Taylor instability. Once the upwellings begin to grow in altitude extent, the west walls become unstable via the gradient-drift instability, driven by an eastward neutral wind blowing through the walls of the upwellings. The enhanced structuring of the west wall at low F-region altitudes is made possible by the presence of a velocity shear in eastward plasma drift.

Tsunoda, R. T.

1981-02-01

242

Equatorial spread F effects on an HF path: Doppler spread, spatial coherence, and frequency coherence  

Microsoft Academic Search

In August 1990 we participated in the Equatorial Ionospheric Studies sounding rocket campaign near Kwajalein Atoll in the equatorial Pacific region. The campaign included measurements of plasma density using rocket probes and coherent and incoherent scatter radar. During the campaign we fielded high-frequency ionospheric sounders over a bistatic path between Maloelap Atoll and Bikini Atoll in the Marshall Islands. The

T. Joseph Fitzgerald; Paul E. Argo; Robert C. Carlos

1999-01-01

243

Diagnosing temperature change inside sonoluminescing bubbles by calculating line spectra.  

PubMed

With the numerical calculation of the spectrum of single bubble sonoluminescence, we find that when the maximum temperature inside a dimly luminescing bubble is relatively low, the spectral lines are prominent. As the maximum temperature of the bubble increases, the line spectrum from the bright bubble weakens or even fades away relative to the background continuum. The calculations in this paper effectively interpret the observed phenomena, indicating that the calculated results, which are closely related to the spectrum profile, such as temperature and pressure, should be reliable. The present calculation tends to negate the existence of a hot plasma core inside a sonoluminescing bubble. PMID:19905449

An, Yu; Li, Chaohui

2009-10-28

244

Study of equinoctial asymmetry in the Equatorial Spread F (ESF) irregularities over Indian region using multi-instrument observations in the descending phase of solar cycle 23  

NASA Astrophysics Data System (ADS)

In this paper, we present the results of a morphological study of Equatorial Spread F (ESF) irregularities over Indian region based mainly on observations of (1) amplitude scintillations on GPS L-band signal and Rate of TEC Index (ROTI) obtained using a network of GPS receivers and (2) amplitude scintillations on a VHF signal using spaced receivers at Tirunelveli, an equatorial station. Occurrence of both amplitude scintillations on the GPS L1 signal and occurrence of significant ROTI recorded at several stations has been investigated. The latitudinal extent of L-band scintillations shows that their strength is weak over the dip equator but stronger over Equatorial Ionization Anomaly (EIA) region, preferentially during vernal equinox. We find an equinoctial asymmetry in both the occurrence of scintillations and ROTI wherein their occurrence is greater in the vernal equinox than in the autumn equinox. Attempts have been made to understand the asymmetry in latitudinal extent using maximum cross-correlation (CI) of intensity fluctuations obtained from the VHF spaced receivers observations. The observations suggest that occurrence of CI less than 0.5 is more in the vernal equinox than in the autumn equinox suggesting that the maximum height of the Equatorial Plasma Bubbles (EPBs) during vernal equinox may be higher than that during autumn equinox. TIMED/GUVI retrieved peak electron density during the same period also indicates that background electron density is higher and more symmetric during vernal equinox than autumn equinox. Hence, our results suggest that background electron density may be playing a vital role in creating the equinoctial asymmetry.

Sripathi, S.; Kakad, B.; Bhattacharyya, A.

2011-11-01

245

Modelling and observations of the equatorial ionosphere  

NASA Astrophysics Data System (ADS)

The equatorial ionosphere experiences one of the most severe forms of a geophysical plasma instability - a phenomenon known as spread F. An observational campaign was organized to bring a complement of diagnostic instruments to two sites in the western Pacific sector (Kwajalein Atoll in the Marshall Islands and Wake Island) for a period of coordinated optical and radio measurements of spread F phenomena in August 1988. All-sky optical imaging observations were conducted from 2 to 16 August in conjunction with ALTAIR radar observations on Kwajalein. Preliminary review of the data sets obtained identified at least five case study events for detailed investigation.

Mendillo, Michael

1990-10-01

246

Onset conditions for equatorial spread F determined during EQUIS II  

Microsoft Academic Search

An investigation into the dynamics and layer structure of the postsunset ionosphere prior to the onset of equatorial spread F (ESF) took place during the NASA EQUIS II campaign on Kwajalein Atoll on August 7 and 15, 2004. On both nights, an instrumented rocket measured plasma number density and vector electric fields to an apogee of about 450 km. Two

D. L. Hysell; M. F. Larsen; C. M. Swenson; A. Barjatya; T. F. Wheeler; M. F. Sarango; R. F. Woodman; J. L. Chau

2005-01-01

247

Steepened structures in equatorial spread F: 1. New observations  

Microsoft Academic Search

Sounding rocket data from the 1990 CRRES\\/EQUIS equatorial spread F campaign on Kwajalein Atoll are presented. Two Terrier Malamute sounding rockets were launched into active spread F conditions on July 30 and August 2, respectively, and achieved apogee slightly below 500 km, just above the F peak. Plasma frequency probes aboard both rockets showed that the unstable nighttime F region

D.L. Hysell; M. C. Kelley; W.E. Swartz; R. F. Pfaff; C. M. Swenson

1994-01-01

248

Steepened structures in equatorial spread F. 1: New observations  

Microsoft Academic Search

Sounding rocket data from the 1990 Combined Release and Radiation Effects Satellite (CRRES)\\/EQUIS equatorial spread F campaign on Kwajalein Atoll are presented. Two Terrier Malamute sounding rockets were launched into active spread F conditions on July 30 and August 2, respectively, and achieved apogee slightly below 500 km, just above the F peak. Plasma frequency probes aboard both rockets showed

D. L. Hysell; M. C. Kelley; W. E. Swartz; R. F. Pfaff; C. M. Swenson

1994-01-01

249

Steepened structures in equatorial spread F: 2. Theory  

Microsoft Academic Search

This paper investigates the properties of a one-dimensional fluid model of plasma convection in the equatorial F region ionosphere. The model equations are similar in form to Burgers equation except for additional higher-order spatial derivatives. Like Burgers equation, solutions to the model have the form of propagating, shocklike structures. Numerical simulations of the model closely resemble the steepened structures observed

D.L. Hysell; C. E. Seyler; M. C. Kelley

1994-01-01

250

Interferometer studies of equatorial F region irregularities and drifts  

Microsoft Academic Search

A radar interferometer technique developed at Jicamarca, Peru and first used to study electrojet irregularities has now been used successfully to study plasma turbulence in the equatorial F region. First results have shown that the most turbulent echoes appear to come from a region that extends for tens of kilometers in altitude but for only a kilometer or less in

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

1981-01-01

251

Off-equatorial circular orbits in magnetic fields of compact objects  

NASA Astrophysics Data System (ADS)

We present results of investigation of the off-equatorial circular orbits existence in the vicinity of neutron stars, Schwarzschild black holes with plasma ring, and near Kerr-Newman black holes and naked singularities.

Stuchlk, Zden?k; Kov?, Ji?; Karas, Vladimr

2009-04-01

252

Scintillations Associated with Bottomside Sinusoidal Irregularities in the Equatorial F Region.  

National Technical Information Service (NTIS)

A new category of equatorial F region plasma irregularities characterized by nearly sinusoidal wave forms in the ion number density N sub i was observed by the Atmosphere Explorer satellites. Multisatellite scintillation observations made at Huancayo, Per...

S. Basu S. Basu C. E. Valladares A. DasGupta H. E. Whitney

1986-01-01

253

Buoyant bubbles in a cooling intracluster medium. I. Hydrodynamic bubbles  

NASA Astrophysics Data System (ADS)

Aims:Over the past several years, numerous examples of X-ray cavities coincident with radio sources have been observed in so-called cool core clusters of galaxies. Motivated by these observations, we explore the evolution and the effect of cavities on a cooling intracluster medium (ICM) numerically, adding relevant physics step by step. Methods: In this paper we present a first set of hydrodynamical, high resolution (10243 effective grid elements), three-dimensional simulations, together with two-dimensional test cases. The simulations follow the evolution of radio cavities, modeled as bubbles filled by relativistic plasma, in the cluster atmosphere, while the ICM is subject to cooling. Results: We find that the bubble rise retards the development of a cooling flow by inducing motions in the ICM, which repeatedly displace the material in the core. Even bubbles initially set significantly far from the cluster center affect the cooling flow, although much later than the beginning of the simulation. The effect is, however, modest: the cooling time is increased by at most only 25%. As expected, the overall evolution of pure hydrodynamic bubbles is at odds with observations, showing that some additional physics has to be considered to match the data.

Gardini, A.

2007-03-01

254

Observations of the Day to Night transition of Equatorial Ionization Anomaly  

NASA Astrophysics Data System (ADS)

The Equatorial Fountain creates global scale ionospheric density enhancements on both sides of the magnetic equator in the Earth's sub-tropical regions which is the well known Equatorial Ionization Anomaly or EIA. It is understood that this phenomena result from thermospheric winds interacting with ionospheric plasma. We examine aspects of this process by comparing the equatorial upward plasma drifts of the fountain to the observed plasma distribution in the Equatorial Anomaly. We focus on the development of the density structures from the day period into the nighttime with particular focus on the pre-reversal enhancement of the vertical plasma drifts on the EIA. We examine if this relatively brief enhancement in vertical drift velocity can be traced to significant plasma transport into the night time Equatorial Anomaly and examine the important seasonal and longitudinal differences. The density observations of the Equatorial Anomaly are deduced from the GUVI instrument on NASA's TIMED spacecraft. This instrument records radiance data at 135.6nm that results from recombination of Oxygen ions and can be used as a proxy for plasma density. GUVI's high altitude limb scans are used to study both the dayside and night side Equatorial Anomaly as a function of local time, season and longitude. Plasma drifts from ROCSAT-1 observations as presented by Fejer etal, JGR 2008 are used for the vertical drifts. Further comparisons of the Equatorial Anomaly density structure as a function of season are made with the NRL Horizontal Neutral Wind model to discuss the driving sources from the EIA. This paper presents the data analysis techniques to produce observations of the EIA at all local times from GUVI as well as the comparisons of GUVI data with plasma drifts and neutral wind models.

Swenson, C. M.; Burr, S.; Shankar, J.; Paxton, L.; Christensen, A.

2008-12-01

255

Low-voltage pulsed plasma discharges inside water using a bubble self-generating parallel plate electrode with a porous ceramic  

NASA Astrophysics Data System (ADS)

Characteristics of pulsed bubbles discharges in water were investigated using parallel punched plate electrodes with a porous thin ceramic plate inserted between two metal plates. The micro-bubbles were generated just beneath the porous ceramic plate by flowing gas through it. The transition from spiky dielectric barrier discharges to pulsed glow discharges enables efficient bubble discharges at a relatively low voltage of 1.8 ~ 4.0 kV of the 5 kHz square-waves with a pulse-width of about 750 ns. With 80% Ar and 20% O2 mixture gas at 4.0 kV, the 50 mg/l Indigo Carmine aqueous solution was efficiently decolorized within about 3 min.

Muradia, Sonia; Nagatsu, Masaaki

2013-04-01

256

Global characterization of the equatorial ionospheric anomaly with data from the global ultraviolet imager  

NASA Astrophysics Data System (ADS)

The Equatorial Anomaly (EA) is host to the highest ionospheric densities in the Earth's atmosphere. Disturbances within the EA result in plasma density depletions and large density gradients. In this dissertation we present a method for measuring EA morphology using nighttime 135.6 nm radiance observed by the Global Ultraviolet Imager (GUVI) on-board the Thermosphere Ionosphere Mesosphere Energetics and Dynamics (TIMED) spacecraft. The method uses the singular value decomposition to estimate an along-track intensity profile as TIMED passes over the EA. The method is unique in that it removes intensity depletions due to equatorial plasma bubbles (EPBs) from the estimated intensity profile. Thus, the profiles reflect plasma distribution in response to equatorial E x B drifts and neutral winds. A set of metrics including crest maximum intensity (CM) and crest latitude (CL) is extracted from the intensity profiles. EPBs are also detected. By using these metrics, extensive observations of EA and EPB morphology show that EA morphology can be well characterized by data taken from the 2030-2130 MLT range. Further, this dissertation identifies crest symmetry in intensity and latitude as an indicator of both EA and EPB morphology. For all longitudes, the crest-to-trough ratio (CTR) is shown to be well correlated with the EPB rate. While the CTR may drop with solar flux, EPB levels do not. Thus, the absolute CTR, is less an indicator than the change in the CTR, as a function of longitude for a given season and solar flux. One significant exception to this correlation is observed in the Pacific sector during the June solstice. In this case the EPB rate is high despite a low CTR. In order to estimate global EA morphology for all night local times, the data, are used to train empirical models of the CMS and CLS. Our results indicate that EA enhancement is well correlated with F10.7 cm solar flux, especially during equinox. In terms of seasonal dependence we find that at equinox, north and south crest latitude symmetry occurs before 2300 MLT except in the African-Indian sector where CSL?CNL . Before 2300 MIT during the June solstice, CNM?CSM andCNL?C SL while the reverse is true during the December solstice. We also study the driver-response relationship between the equatorial zonal electric field and the EA. This is done by comparing the vertical plasma drift velocity as predicted by the Scherliess and Fejer empirical model with our EA crest models. Comparing the maximum CM (MaxCM) and maximum CL (MaxCL) observed in a crest with the maximum vertical drift of the prereversal enhancement (MaxVD), we find that the equinox EA response time as a function of longitude is 2.5 to 5 hours in the north crest and 2 to 3.25 hours in the south crest. During the solstices minimum response times were observed at under 1 hour. The magnitude of MaxCM is coarsely correlated with MaxVD. During equinox MaxCL is well correlated with MaxVD.

Henderson, Sidney B., II

257

Physics of the Equatorial Atmosphere.  

National Technical Information Service (NTIS)

A School on 'Physics of the Equatorial Atmosphere' was held at the Abdus Salam International Center for Theoretical Physics from September 24 through October 5, 2001. The School was aimed primarily at advanced graduate students and young postdoctoral scie...

K. Hamilton L. Gray

2003-01-01

258

The Colorado Equatorial Sundial  

NASA Astrophysics Data System (ADS)

The University of Colorado received from Mr. and Mrs. J. H. Tippit in 1995 a large equatorial sundial in memory of one of their sons, John Garrey Tippit, who graduated from the University of Colorado and was killed in a construction accident in 1969. The sundial is installed in the quadrangle in front of our main Norlin Library. The sundial is made of a large slab of Colorado rose-red granite, mined a few miles from Boulder. It is approximately 185 cm in diameter and 16 cm thick. The gnomon is a steel rod 7.6 cm in diameter and 205 cm in total length. The total mass, estimated from the average densities of granite and steel, is about 1400 kg, and this large mass made it impossible to make slight adjustments to the setup after installation. The sundial carries the motto "Knowledge and time abide in the same place". The sundial can be read to an accuracy of about one minute. We are making a large number of checks of the time; after allowing for the longitude and the equation of time the residuals are up to about three minutes, depending on whether one is using the winter or summer side and on whether it is morning or afternoon. We intend to analyze the errors after we have made checks for about a year.

Garstang, R. H.

1996-05-01

259

ORIGIN OF THE FERMI BUBBLE  

SciTech Connect

Fermi has discovered two giant gamma-ray-emitting bubbles that extend nearly 10 kpc in diameter north and south of the Galactic center. The existence of the bubbles was first evidenced in X-rays detected by ROSAT and later WMAP detected an excess of radio signals at the location of the gamma-ray bubbles. We propose that periodic star capture processes by the galactic supermassive black hole, Sgr A*, with a capture rate 3 x 10{sup -5} yr{sup -1} and energy release {approx}3 x 10{sup 52} erg per capture can produce very hot plasma {approx}10 keV with a wind velocity {approx}10{sup 8} cm s{sup -1} injected into the halo and heat up the halo gas to {approx}1 keV, which produces thermal X-rays. The periodic injection of hot plasma can produce shocks in the halo and accelerate electrons to {approx}TeV, which produce radio emission via synchrotron radiation and gamma rays via inverse Compton scattering with the relic and the galactic soft photons.

Cheng, K.-S.; Chernyshov, D. O.; Dogiel, V. A. [Department of Physics, University of Hong Kong, Pokfulam Road, Hong Kong (China); Ko, C.-M.; Ip, W.-H. [Institute of Astronomy, National Central University, Chung-Li 32054, Taiwan (China)

2011-04-10

260

Echo effect in a liquid containing gas bubbles  

Microsoft Academic Search

Acoustic echo is considered for a liquid containing gas bubbles, which is analogous to cyclotron echo in plasma. An analytical calculation is performed on the parameters of the entire series of echo pulses for the case where standing-wave pulses are generated. The addition of a small number of randomly distributed gas bubbles to a liquid substantially alters the dispersion behavior

Kotelnikov

1984-01-01

261

Radio Bubbles in Clusters of Galaxies  

SciTech Connect

We extend our earlier work on cluster cores with distinct radio bubbles, adding more active bubbles, i.e. those with GHz radio emission, to our sample, and also investigating ''ghost bubbles'', i.e. those without GHz radio emission. We have determined k, which is the ratio of the total particle energy to that of the electrons radiating between 10MHz and 10GHz. Constraints on the ages of the active bubbles confirm that the ratio of the energy factor, k, to the volume filling factor, f lies within the range 1 {approx}< k/f {approx}< 1000. In the assumption that there is pressure equilibrium between the radio-emitting plasma and the surrounding thermal X-ray gas, none of the radio lobes has equipartition between the relativistic particles and the magnetic field. A Monte-Carlo simulation of the data led to the conclusion that there are not enough bubbles present in the current sample to be able to determine the shape of the population. An analysis of the ghost bubbles in our sample showed that on the whole they have higher upper limits on k/f than the active bubbles, especially when compared to those in the same cluster. A study of the Brightest 55 cluster sample shows that 17, possibly 20, clusters required some form of heating as they have a short central cooling time, t{sub cool} {approx}< 3 Gyr, and a large central temperature drop, T{sub centre}/T{sub outer} < 1/2. Of these between 12 (70 per cent) and 15 (75 per cent), contain bubbles. This indicates that the duty cycle of bubbles is large in such clusters and that they can play a major role in the heating process.

Dunn, Robert J.H.; Fabian, A.C.; /Cambridge U., Inst. of Astron.; Taylor, G.B.; /NRAO, Socorro /KIPAC, Menlo Park

2005-12-14

262

Radio bubbles in clusters of galaxies  

NASA Astrophysics Data System (ADS)

We extend our earlier work on cluster cores with distinct radio bubbles, adding more active bubbles, i.e. those with GHz radio emission, to our sample and also investigating `ghost bubbles', i.e. those without GHz radio emission. We have determined k, which is the ratio of the total particle energy to that of the electrons radiating between 10 MHz and 10 GHz. Constraints on the ages of the active bubbles confirm that the ratio of the energy factor, k, to the volume filling factor, f, lies within the range 1 <~k/f<~ 1000. On the assumption that there is pressure equilibrium between the radio-emitting plasma and the surrounding thermal X-ray gas, none of the radio lobes has equipartition between the relativistic particles and the magnetic field. A Monte Carlo simulation of the data led to the conclusion that there are not enough bubbles present in the current sample to be able to determine the shape of the population. An analysis of the ghost bubbles in our sample showed that on the whole they have higher upper limits on k/f than the active bubbles, especially when compared with those in the same cluster. A study of the Brightest 55 (B55) cluster sample shows that 17, possibly 20, clusters required some form of heating as they have a short central cooling time, tcool<= 3Gyr, and a large central temperature drop, Tcentre/Touter < 1/2. Of these, between 12 (70 per cent) and 15 (75 per cent) contain bubbles. This indicates that the duty cycle of bubbles is large in such clusters and that they can play a major role in the heating process.

Dunn, R. J. H.; Fabian, A. C.; Taylor, G. B.

2005-12-01

263

Acoustical observation of bubble oscillations induced by bubble popping  

NASA Astrophysics Data System (ADS)

Acoustic measurements of aqueous foams show three distinct radiation mechanisms that contribute to the sound pressure field: oscillations of a bubble surface that precede popping due to the instability of thin liquid film, impulsive radiation due to bursts of bubbles, and oscillations from neighboring bubbles excited by a burst bubble. The movies captured by a fast camera confirm that the bubbles adjacent to a breaking bubble oscillate under the influence of the pressure generated by the burst bubble. The spectra of resulting transient sounds fall in the range of 2-8kHz and those from bubble oscillations correlate well with the bubble size.

Ding, Junqi; Tsaur, Felicia W.; Lips, Alex; Akay, Adnan

2007-04-01

264

Acoustical observation of bubble oscillations induced by bubble popping.  

PubMed

Acoustic measurements of aqueous foams show three distinct radiation mechanisms that contribute to the sound pressure field: oscillations of a bubble surface that precede popping due to the instability of thin liquid film, impulsive radiation due to bursts of bubbles, and oscillations from neighboring bubbles excited by a burst bubble. The movies captured by a fast camera confirm that the bubbles adjacent to a breaking bubble oscillate under the influence of the pressure generated by the burst bubble. The spectra of resulting transient sounds fall in the range of 2-8 kHz and those from bubble oscillations correlate well with the bubble size. PMID:17500901

Ding, Junqi; Tsaur, Felicia W; Lips, Alex; Akay, Adnan

2007-04-03

265

Magnetic Bubble Expansion as an Experimental Model for Extra-Galactic Radio Lobes  

NASA Astrophysics Data System (ADS)

The Plasma Bubble Expansion Experiment (PBEX) is conducting laboratory experiments to address outstanding nonlinear plasma physics issues related to how magnetic energy and helicity carried by extra-galactic jets interacts with the intergalactic medium to form radio lobe structures. Experiments are being conducted in the 4 meter long, 50 cm diameter HELCAT linear plasma device at UNM. A pulsed magnetized coaxial gun (10 kV, 100 kA, 2 mWb) forms and injects magnetized plasma bubbles perpendicularly into a lower pressure weakly magnetized background plasma formed by a helicon and/or hot cathode source in HELCAT. Ideal MHD simulations show that an MHD shock develops ahead of the bubble as it propagates, and that the bubble develops asymmetries due to the background field [1]. Experimental data from plasma bubble injection into a background plasma, particularly magnetic probe measurements, will be discussed. [4pt] [1] W. Liu et al., Phys. Plasmas 15, 072905 (2008).

Lynn, Alan; Zhang, Yue; Hsu, Scott

2010-11-01

266

Measurement of pressure and density inside a single sonoluminescing bubble.  

PubMed

The average pressure inside a sonoluminescing bubble in sulfuric acid has been determined by two independent techniques: (1) plasma diagnostics applied to Ar atom emission lines, and (2) light scattering measurements of bubble radius vs time. For dimly luminescing bubbles, both methods yield intracavity pressures approximately 1500 bar. Upon stronger acoustic driving of the bubble, the sonoluminescence intensity increases 10,000-fold, spectral lines are no longer resolved, and radius vs time measurements yield internal pressures > 3700 bar. Implications for a hot inner core are discussed. PMID:16803173

Flannigan, David J; Hopkins, Stephen D; Camara, Carlos G; Putterman, Seth J; Suslick, Kenneth S

2006-05-22

267

Microfluidic bubble logic.  

PubMed

We demonstrate universal computation in an all-fluidic two-phase microfluidic system. Nonlinearity is introduced into an otherwise linear, reversible, low-Reynolds number flow via bubble-to-bubble hydrodynamic interactions. A bubble traveling in a channel represents a bit, providing us with the capability to simultaneously transport materials and perform logical control operations. We demonstrate bubble logic AND/OR/NOT gates, a toggle flip-flop, a ripple counter, timing restoration, a ring oscillator, and an electro-bubble modulator. These show the nonlinearity, gain, bistability, synchronization, cascadability, feedback, and programmability required for scalable universal computation. With increasing complexity in large-scale microfluidic processors, bubble logic provides an on-chip process control mechanism integrating chemistry and computation. PMID:17289994

Prakash, Manu; Gershenfeld, Neil

2007-02-01

268

Development of bubble tester  

NASA Astrophysics Data System (ADS)

A Bubble Tester is developed to do the measurements of bubble classes for optical elements. The tester is composed of illumination system,refractor slot, imaging system,CCD,computer controller and data processor,3D workshop and ground base. The light from the illumination system is refracted by the bubbles and inclosures in the optical elements, the imaging system captured the light and imaged the image to CCD and computer captured the image and did data processing to get the dimension, quantity and distribution of the bubbles and enclosures. The tester can measure bubbles with ?0.05~?5mm in diameter and the accuracy is 5%.The tester can measure bubbles and enclosures of optical elements and welding line of the optics according to GB 7661-87.

Yang, Wenzhi; Jing, Hongwei; Wu, Shibin; Cao, Xuedong

2009-05-01

269

Solar Wind Effects on Plasma Density Depletions: C/NOFS Results with Related Observations from DMSP  

NASA Astrophysics Data System (ADS)

Before C/NOFS, the prevailing wisdom was that equatorial plasma bubbles (EPBs) were primarily a post-sunset phenomenon. Changes in the ionosphere after sunset create conditions favorable for instability formation as polarization electric fields increase near the terminator. Plasma irregularities that develop in the bottomside of the F-layer grow into large depletions that rise rapidly into the topside ionosphere. By two hours in local time after sunset the initial upward drift of the ionosphere reverses suppressing further development of instabilities. Tsunodas [1985] seasonal-longitudinal model predicted that EPB rates should peak near times when the equatorial declination and the dusk terminator are closely aligned. Under these conditions E-layer conductance vanishes at both ends of flux tubes simultaneously, allowing EPBs to grow most rapidly. We validated this model during the recent solar maximum. In this unusual solar minimum, however, C/NOFS has encountered very few post-sunset depletions. They commonly appear between local midnight and dawn. We trace the energy flow from the Sun to the Earth to demonstrate that C/NOFS measurements are providing key insights into the dynamics of the Ionosphere-Thermosphere system. Results suggest that systematic effects of solar wind / IMF on dynamics of equatorial plasmas and electric fields may allow long-term alerts about impending ionospheric disturbances that lead to scintillation activity. Reference: Tsunoda, R. T. (1985), J. Geophys. Res., 90, 447.

Burke, W. J.; Gentile, L. C.; Roddy, P. A.; Retterer, J. M.; Wilson, G. R.; de La Beaujardiere, O.; Su, Y.

2010-12-01

270

Bubble-Containing Foods  

Microsoft Academic Search

The presence of bubbles in a number of food products, such as bread, champagne, ice cream and beer, has dominated our perception\\u000a of product quality. Novel bubble-containing products occupy a greater proportion of supermarket shelf space. The inclusion\\u000a of bubbles in foods permits the creation of very novel structures while offering lighter alternatives in terms of calories.\\u000a Manufacturers generally find

K. Niranjan; S. F. J. Silva

271

Physics of bubble oscillations  

NASA Astrophysics Data System (ADS)

Bubbles in liquids, soft and squeezy objects made of gas and vapour, yet so strong as to destroy any material and so mysterious as at times turning into tiny light bulbs, are the topic of the present report. Bubbles respond to pressure forces and reveal their full potential when periodically driven by sound waves. The basic equations for nonlinear bubble oscillation in sound fields are given, together with a survey of typical solutions. A bubble in a liquid can be considered as a representative example from nonlinear dynamical systems theory with its resonances, multiple attractors with their basins, bifurcations to chaos and not yet fully describable behaviour due to infinite complexity. Three stability conditions are treated for stable trapping of bubbles in standing sound fields: positional, spherical and diffusional stability. Chemical reactions may become important in that respect, when reacting gases fill the bubble, but the chemistry of bubbles is just touched upon and is beyond the scope of the present report. Bubble collapse, the runaway shrinking of a bubble, is presented in its current state of knowledge. Pressures and temperatures that are reached at this occasion are discussed, as well as the light emission in the form of short flashes. Aspherical bubble collapse, as for instance enforced by boundaries nearby, mitigates most of the phenomena encountered in spherical collapse, but introduces a new effect: jet formation, the self-piercing of a bubble with a high velocity liquid jet. Examples of this phenomenon are given from light induced bubbles. Two oscillating bubbles attract or repel each other, depending on their oscillations and their distance. Upon approaching, attraction may change to repulsion and vice versa. When being close, they also shoot self-piercing jets at each other. Systems of bubbles are treated as they appear after shock wave passage through a liquid and with their branched filaments that they attain in standing sound fields. The N-bubble problem is formulated in the spirit of the n-body problem of astrophysics, but with more complicated interaction forces. Simulations are compared with three-dimensional bubble dynamics obtained by stereoscopic high speed digital videography.

Lauterborn, Werner; Kurz, Thomas

2010-10-01

272

Bubbles: Using Controls  

NSDL National Science Digital Library

In this experiment, learners use JOY liquid detergent and glycerin to make the largest bubble they can that lasts 15 seconds. They blow the bubbles in a Teaching Tank, a narrow tank that is commercially available, which allows them to easily measure and monitor the bubbles. Results are collected and graphed by learners. Questions and teaching notes are included to encourage learners to consider what the multiple variables are, and what the effects of sugar, corn syrup, or other sweeteners are on their bubbles.

Products, American E.

2000-01-01

273

Spherical and non-spherical bubbles in cosmological phase transitions  

NASA Astrophysics Data System (ADS)

The cosmological remnants of a first-order phase transition generally depend on the perturbations that the walls of expanding bubbles originate in the plasma. Several of the formation mechanisms occur when bubbles collide and lose their spherical symmetry. However, spherical bubbles are often considered in the literature, in particular for the calculation of gravitational waves. We study the steady state motion of bubble walls for different bubble symmetries. Using the bag equation of state, we discuss the propagation of phase transition fronts as detonations and subsonic or supersonic deflagrations. We consider the cases of spherical, cylindrical and planar walls, and compare the energy transferred to bulk motions of the relativistic fluid. We find that the different wall geometries give similar perturbations of the plasma. For the case of planar walls, we obtain analytical expressions for the kinetic energy in the bulk motions. As an application, we discuss the generation of gravitational waves.

Leitao, Leonardo; Mgevand, Ariel

2011-03-01

274

Equatorial zonal circulations: Historical perspectives  

NASA Astrophysics Data System (ADS)

The changing perceptions on zonal circulations in the equatorial belt are traced for (a) stratospheric wind regimes, and (b) vertical-zonal circulation cells in the troposphere. (a) Observations from the Krakatoa eruption 1883 and Berson's 1908 expedition to East Africa, along with later soundings over Batavia (Jakarta) led to the notion of Krakatoa easterlies around 30 km (10 mb) and Berson westerlies around 20 km (50 mb). Prompted by contrary observations since the late 1950s, this dogma was replaced by the notion of easterlies alternating with westerlies in the equatorial stratosphere at a rhythm of about 26 months. (b) Stimulated by Bjerknes postulate of a Walker circulation along the Pacific Equator, a multitude of such cells have been hypothesized at other longitudes, in part from zonal contrasts of temperature and cloudiness. Essential for the diagnosis of equatorial zonal circulation cells is the continuity following the flow between the centers of ascending and subsiding motion. Evaluation of the recent NCEP-NCAR and ECMWF Reanalysis upper-air datasets reveals equatorial zonal circulation cells over the Pacific all year round, over the Atlantic only in boreal winter, and over the Indian Ocean only in autumn, all being seasons and oceanic longitudes with strong zonal flow in the lower troposphere.

Hastenrath, Stefan

2007-04-01

275

Storm time dependence of equatorial disturbance dynamo zonal electric fields  

Microsoft Academic Search

We use Jicamarca radar observations of F region vertical plasma drifts and auroral electrojet indices during 1968-1988 to study the characteristics and temporal evolution of equatorial disturbance dynamo zonal electric fields. These electric fields result from the dynamo action of storm time winds and\\/or thermospheric composition changes driven by enhanced energy deposition into the high-latitude ionosphere during geomagnetically active conditions.

Ludger Scherliess

1997-01-01

276

Evaporation, Boiling and Bubbles  

ERIC Educational Resources Information Center

|Evaporation and boiling are both terms applied to the change of a liquid to the vapour/gaseous state. This article argues that it is the formation of bubbles of vapour within the liquid that most clearly differentiates boiling from evaporation although only a minority of chemistry textbooks seems to mention bubble formation in this context. The

Goodwin, Alan

2012-01-01

277

Let Them Blow Bubbles.  

ERIC Educational Resources Information Center

|Describes a series of activities and demonstrations involving the science of soap bubbles. Starts with a recipe for bubble solution and gives instructions for several activities on topics such as density, interference colors, optics, static electricity, and galaxy formation. Contains some background information to help explain some of the

Korenic, Eileen

1988-01-01

278

Constrained Vapor Bubble Experiment  

Microsoft Academic Search

Microgravity experiments on the Constrained Vapor Bubble Heat Exchanger, CVB, are being developed for the International Space Station. In particular, we present results of a precursory experimental and theoretical study of the vertical Constrained Vapor Bubble in the Earth's environment. A novel non-isothermal experimental setup was designed and built to study the transport processes in an ethanol\\/quartz vertical CVB system.

Shripad Gokhale; Joel Plawsky; Peter C. Wayner Jr.; Ling Zheng; Ying-Xi Wang

2002-01-01

279

The Vacuum Bubble Nucleation  

SciTech Connect

We study the nucleation of a vacuum bubble via the vacuum-to-vacuum tunneling transition in curved spacetime. We consider Coleman-de Luccia's semiclassical approximation at zero temperature in pure Einstein theory of gravity and the theory with nonminimal coupling. We discuss the dynamics of a nucleated vacuum bubble.

Lee, Bum-Hoon [Department of Physics and Center for Quantum Spacetime, Sogang University Seoul 121-742 (Korea, Republic of); Lee, Wonwoo [Center for Quantum Spacetime, Sogang University, Seoul 121-742 (Korea, Republic of)

2009-07-10

280

Let Them Blow Bubbles.  

ERIC Educational Resources Information Center

Describes a series of activities and demonstrations involving the science of soap bubbles. Starts with a recipe for bubble solution and gives instructions for several activities on topics such as density, interference colors, optics, static electricity, and galaxy formation. Contains some background information to help explain some of the effects.

Korenic, Eileen

1988-01-01

281

Seasonal Dependence of Equatorial Electrodynamic Effects During Stratospheric Warming Periods  

NASA Astrophysics Data System (ADS)

Sudden stratospheric warming (SSW) events are known to give rise to large global equatorial electrodynamic perturbations. These effects have been studied mostly during December solstices. We study the equatorial electrodynamic response to SSW events during December solstice winter and equinoctial periods using Jicamarca vertical plasma drifts and equatorial electrojet current densities derived from CHAMP satellite measurements. During December solstice, our data typically show largely enhanced morning upward drifts and eastward electrojet currents along with afternoon downward drifts and westward currents. This perturbation pattern occurs near new and full moons and shifts to later local times with increasing lunar age. On the other hand, the morning and early afternoon upward drifts and eastward currents are enhanced during equinoctial warmings following new and full moons, but there are no noticeable decreases in the afternoon drifts and electrojet currents. This pattern also shifts to later local times with increasing lunar age. Arctic and Antarctic warming equinoctial warming events seem to give rise to nearly identical equatorial electrodynamic perturbation patterns. The CHAMP satellite data show that solstice and equinoctial SSW perturbations occur first in the western hemisphere. The satellite data also show strong two-day wave activity that generally occurs before and during both solstice and equinoctial warming events.

Olson, M. E.; Fejer, B. G.; Stolle, C.; Luhr, H.

2010-12-01

282

Global Characteristics of the Equatorial Anomaly of the low Latitude Ionosphere Observed by IMAGE\\/FUV  

Microsoft Academic Search

The Equatorial Anomaly (EA) of the low latitude ionosphere has been studied extensively since its discovery by Nanba and Maeda (1939) and Appleton (1946). The EA is produced basically by the uplift of the F-layer plasma at the magnetic equator by zonal electric fields, which subsequently enhances the density of the plasma at the base of field lines on both

E. Sagawa; T. J. Immel; H. U. Frey; S. B. Mende

2003-01-01

283

Effects of magnetic storm phases on f-layer irregularities from auroral to equatorial latitudes. Quarterly report, 1 January-31 March 1993  

SciTech Connect

Equatorial ionospheric irregularities in the F layer have been the subject of intensive experimental and theoretical investigations during recent years. The class of irregularities which continues to receive much attention is characterized by large scale plasma depletions, generally referred to as ionospheric plumes and bubbles. The F-region nightglow emissions arising from recombination processes can be used to observe the dynamics of transequatorial ionospheric plasma bubbles and smaller scale plasma irregularities. In a collaborative project between the Center for Space Physics of Boston University and the Brazilian Institute for Space Research (INPE), an all-sky imaging system was operated at Cachoeira Paulista (22.7 deg S, 45.0 deg W, dip latitude 15.8 deg S), between March 1987 and October 1991. In addition to the imager, photometer and VHF polarimeter observations were conducted at Cachoeira Paulista with ionospheric soundings carried out at C. Paulista and Fortaleza, the latter at 3.9 deg S. 38.4 deg W, dip latitude 3.7 deg S. A VHF electronic polarimeter is in operation at C. Paulista. This long series of 01 630.0 nm imaging observations has permitted determination that when there are extended plumes, the altitudes affected over the magnetic equator often exceed 1500 km and probably exceed 2500 km at times, the maximum projection that can be seen from Cachoeira Paulista. This holds true even during years of low solar flux. For this longitude, the observed seasonal variation of the airglow depletions shows a maximum from October through March and a very low occurrence of airglow depletions from April through September.

Aarons, J.; Mendillo, M.

1993-03-31

284

Hydrodynamical similarities between bubble column and bubbly pipe flow  

Microsoft Academic Search

The hydrodynamical similarities between the bubbly flow in a bubble column and in a pipe with vertical upward liquid flow are investigated. The system concerns air\\/water bubbly flow in a vertical cylinder of 14.9 cm inner diameter. Measurements of the radial distribution of the liquid velocity, gas fraction and the bubble velocity and size are performed using laser Doppler anemometry

Robert F. Mudde; Takayuki Saito

2001-01-01

285

Bubble core field modification by residual electrons inside the bubble  

SciTech Connect

Bubble core field modification due to the nondepleted electrons present inside the bubble is investigated theoretically. These residual electrons induce charge and current densities that can induce the bubble core field modification as well as the bubble shape change. It is found that the electrons entering into the bubble move backward at almost light speed and would weaken the transverse bubble fields. This reduces the ratio of longitudinal to transverse radius of the bubble. For the longitudinal bubble field, two effects compensate with each other because of their competition between the enhancement by the shortening of bubble shape and the reduction by the residual electrons. Therefore the longitudinal field is hardly changeable. As a comparison we perform particle-in-cell simulations and it is found that the results from theoretical consideration are consistent with simulation results. Implication of the modification of fields on bubble electron acceleration is also discussed briefly.

Wu Haicheng [College of Nuclear Science and Technology, Beijing Normal University, Beijing 100875 (China); Center for Applied Physics and Technology, Peking University, Beijing 100084 (China); Xie Baisong; Zhao Xueyan [College of Nuclear Science and Technology, Beijing Normal University, Beijing 100875 (China); Zhang Shan [College of Nuclear Science and Technology, Beijing Normal University, Beijing 100875 (China); Department of Mathematics and Physics, Shijiazhuang Railway Institute, Shijiazhuang 050043 (China); Hong Xueren [College of Nuclear Science and Technology, Beijing Normal University, Beijing 100875 (China); College of Physics and Electronic Engineering, Northwest Normal University, Lanzhou 730070 (China); Liu Mingping [School of Information Engineering, Nanchang University, Nanchang 330031 (China)

2010-11-15

286

Bubbles slowing down economic growth  

Microsoft Academic Search

To analyze the effects of bubbles on economic growth, we study a three-period life overlapping generations economy with accumulation of physical and human capital, using an extension of Azariadis and Drazen (1990). We characterize the balanced growth paths and the local dynamics both in the model without bubbles and with bubbles. Tirole (1985)'s study of bubbles is extended to the

Philippe MICHEL

1992-01-01

287

Bubble generation during transformer overload  

Microsoft Academic Search

Bubble generation in transformers has been demonstrated under certain overload conditions. The release of large quantities of bubbles would pose a dielectric breakdown hazard. A bubble prediction model developed under EPRI Project 1289-4 attempts to predict the bubble evolution temperature under different overload conditions. This report details a verification study undertaken to confirm the validity of the above model using

Oommen

1990-01-01

288

Speculations on Nonlinear Speculative Bubbles  

Microsoft Academic Search

This paper reviews a variety of issues related to speculative bubbles, especially those involving nonlinear dynamics. Models of irrational bubbles, rational bubbles, and bubbles arising from heterogeneous agents with varying degrees of knowledge or rationality are examined. The latter are shown to be prone to nonlinear dynamics with catastrophic discontinuities, chaos, and other forms of complex phenomena. Empirical evidence regarding

J. Barkley Rosser

1997-01-01

289

The stable bubble test.  

PubMed

Idiopathic Respiratory Distress Syndrome (I.R.D.S.) occurs mainly in preterm babies (Halliday and McClure, 1976). The cause of the condition is a deficiency of surfactant in the fetal lung. (Avery and Mead, 1959). The condition, if untreated, is associated with high fetal mortality. A simple test, The Bubble Stability Test, which can predict the possibility of I.R.D.S. occuring is now in use in the University Teaching Hospital, Lusaka. An analysis of the use of the Bubble Stability Test in fifty cases is presented. In our series a positive Bubble Stability Test accurately predicted fetal lung maturity. PMID:878632

O'Dowd, M J; Chikamata, D M

290

Gravity-driven bubbly flows  

Microsoft Academic Search

? Abstract Gravity-driven bubbly flows are a specific class of flows, where all action is provided by gravity. An industrial example,is formed,by the so-called bubble column: a vertical cylinder filled with liquid through,which,bubbles,flow that are introduced at the bottom of the cylinder. On the bubble scale, gravity gives rise to buoyancy of individual bubbles. On larger scales, gravity acts on

Robert F. Mudde

2005-01-01

291

Magnetic Bubble Materials.  

National Technical Information Service (NTIS)

The intent of the study was to define those physical properties of magnetic bubble materials which need to be characterized, to investigate the known methods for making these characterization, and, finally, to recommend those characterization procedures w...

J. W. Moody R. M. Sandfort R. W. Shaw

1972-01-01

292

What's in a Bubble?  

ERIC Educational Resources Information Center

|Describes a unit on detergents and bubbles that establishes an interest in the properties of materials and focuses on active learning involving both hands- and minds-on learning rather than passive learning. (ASK)|

Saunderson, Megan

2000-01-01

293

Bubble Domain Structures.  

National Technical Information Service (NTIS)

The patent application provides a film of nickel/iron alloy evaporated onto a substrate at an angle of from 45 degrees to 80 degrees, and having bubble domains formed therein by an applied magnetic field.

I. Puchalska-Hibner

1974-01-01

294

Interplay Between the Equatorial Geophysical Processes  

NASA Astrophysics Data System (ADS)

r_sridharanspl@yahoo.com With the sun as the main driving force, the Equatorial Ionosphere- thermosphere system supports a variety of Geophysical phenomena, essentially controlled by the neutral dynamical and electro dynamical processes that are peculiar to this region. All the neutral atmospheric parameters and the ionospheric parameters show a large variability like the diurnal, seasonal semi annual, annual, solar activity and those that are geomagnetic activity dependent. In addition, there is interplay between the ionized and the neutral atmospheric constituents. They manifest themselves as the Equatorial Electrojet (EEJ), Equatorial Ionization Anomaly (EIA), Equatorial Spread F (ESF), Equatorial Temperature and Wind Anomaly (ETWA). Recent studies have revealed that these phenomena, though apparently might show up as independent ones, are in reality interlinked. The interplay between these equatorial processes forms the theme for the present talk.

Sridharan, R.

2006-11-01

295

Dependence of the equatorial anomaly and of equatorial spread F on the maximum prereversal E B drift velocity measured at solar maximum  

NASA Astrophysics Data System (ADS)

The relation of equatorial bubbles to the equatorial anomaly is important because scintillation that is most disruptive to transionospheric RF propagation occurs when it passes through the intersection of the two. However, measurement of the relation between the two and of the electric field from which both arise is difficult because of large separations in space and time. This first attempt to perform these measurements employs a latitudinal array of ionospheric sounders spanning 0 to 40 dip latitude (DLAT) in the Western American sector. Measured on each day of a solar maximum year are the following: (1) the maximum electron density of the postsunset equatorial anomaly, Ne, at 16 and at 20.3 DLAT at 2100 LT, the time when the anomaly crest is at its maximum latitude; (2) equatorial spread F (ESF), detected by the occurrence of macroscopic bubbles and of bottomside spread F (BSSF), the latter recorded at levels of none, weak and strong; (3) Kp averaged over the 6 hours before sunset. Ne and ESF are considered functions of the maximum prereversal F layer drift E B drift velocity measured by the Jicamarca incoherent scatter radar also during solar maximum and at the same longitude. Parameters are averaged over two levels of Kp for the three seasons, the E months (March, April, September, and October), D months (November-February), and J months (May-August) to yield the following results: (1) Ne measured at 16, at 20.3 DLAT or at the anomaly crest are linearly dependent on maximum E B drift velocity. (2) Occurrence of each level of ESF increases with Ne approximately linearly during the E and J months but not during the D months. (3) ESF occurrence is dependent on and increases approximately linearly with maximum E B drift velocity during the E and J months. During the D months this dependence is absent. Except for the D months, these results indicate that scintillation increases with maximum prereversal E B drift velocity: at L-band at the bubble-anomaly intersection because bubble occurrence increases, Ne increases, and the latitudinal extent of the anomaly increases; and at VHF/UHF near the equator because the occurrence of strong BSSF increases.

Whalen, J. A.

2003-05-01

296

Colloquium: Soap bubble clusters  

NASA Astrophysics Data System (ADS)

Soap bubble clusters and froths model biological cells, metallurgical structures, magnetic domains, liquid crystals, fire-extinguishing foams, bread, cushions, and many other materials and structures. Despite the simplicity of the governing principle of energy or area minimization, the underlying mathematical theory is deep and still not understood, even for rather simple, finite clusters. Only with the advent of geometric measure theory could mathematics treat surfaces which might have unprescribed singularities and topological complexities. In 1884, Schwarz gave a rigorous mathematical proof that a single round soap bubble provides the least-area way to enclose a given volume of air. Similarly, the familiar double bubble provides the absolute least-area way to enclose and separate the two given volumes of air, although the proof did not come until 2000 and has an interesting story, as this Colloquium explains in some detail. Whether a triple soap bubble provides the least-area way to enclose and separate three given volumes of air remains an open conjecture today. Even planar bubble clusters remain mysterious. In about 200 B.C. Zenodorus essentially proved that a circle provides the least-perimeter way to enclose a single given area. The planar double and triple bubbles were proved minimizing recently. The status of the planar four-bubble remains open today. In most spaces other than Euclidean space, even the best single bubble remains unproven. One exception is Gauss space, which is of much interest to probabilists and should be more familiar to physicists. General isoperimetric problems of minimizing area for given volume occur throughout mathematics and play an important role in differential geometry and analysis, including Perelmans proof of the Poincar conjecture.

Morgan, Frank

2007-07-01

297

Interacting two-dimensional bubbles and droplets in a yield-stress fluid  

NASA Astrophysics Data System (ADS)

We study the buoyancy-driven motion of two-dimensional bubbles and droplets in a Bingham fluid using a regularization method. The finite-element computations are carried out using the method of level sets to track the interface. We find that multiple bubbles and droplets can move in a body force field under conditions where a single bubble or droplet with the same physical properties would be unable to overcome the integrated yield stress and would be trapped. The finite yielded region around a single bubble or droplet in a Bingham fluid causes a backflow, resulting in unyielded ``ears'' that rotate and exchange material points with the yielded fluid to maintain a fixed position on the equatorial plane as the bubble rises or the droplet falls. The backflow flattens the tail of the trailing bubble or droplet in a pair and, at a sufficiently high level of interfacial tension, causes a splitting of the tail and the creation of a cusp. Three bubbles in a triangular configuration interact in a manner that is qualitatively predictable by considering pair interactions. Despite important differences in detail, the general shape evolution of bubbles and droplets in a Bingham fluid is similar to that in a Newtonian liquid when time scales are considered on a comparable basis.

Singh, John P.; Denn, Morton M.

2008-04-01

298

Local bubble distribution in bubbly turbulent Taylor-Couette flow  

NASA Astrophysics Data System (ADS)

In turbulent Taylor-Couette flow, the injection of bubbles reduces the global drag on the cylinder surfaces. The previous bubbly turbulent drag reduction measurements in TC flow were mainly based on the global torque, which is not sufficient to understand the mechanism of bubbly drag reduction. One of the key issues is the actual bubble distribution inside the TC gap. Using optical fibers placed inside the TC gap, we scanned the local bubble distribution in the radial direction. An extension of this technique is a four-point optical fiber probe, which enables to retrieve the bubble velocity vector and aspect ratio.

Narezo, Daniela; van Gils, Dennis; Sun, Chao; Lohse, Detlef

2010-11-01

299

Evidence for hydrogen generation in laser- or spark-induced cavitation bubbles  

NASA Astrophysics Data System (ADS)

The growing use of focused lasers or electric sparks to generate cavitation bubbles raises concerns about the possible alteration of gas content during the initiation process and its effect on bubble dynamics. We provide experimental evidence that hydrogen molecules are produced for such plasma-induced bubbles. We performed spectral analysis of the light emitted by the plasma and monitored the dissolved hydrogen concentration in water. The mass of dissolved hydrogen was found proportional to the potential energy of the rebound bubble for both laser and spark methods. Nevertheless, hydrogen concentration was found 2.7 times larger with the spark.

Sato, Takehiko; Tinguely, Marc; Oizumi, Masanobu; Farhat, Mohamed

2013-02-01

300

Statistical equilibrium of bubble oscillations in dilute bubbly flows  

PubMed Central

The problem of predicting the moments of the distribution of bubble radius in bubbly flows is considered. The particular case where bubble oscillations occur due to a rapid (impulsive or step change) change in pressure is analyzed, and it is mathematically shown that in this case, inviscid bubble oscillations reach a stationary statistical equilibrium, whereby phase cancellations among bubbles with different sizes lead to time-invariant values of the statistics. It is also shown that at statistical equilibrium, moments of the bubble radius may be computed using the period-averaged bubble radius in place of the instantaneous one. For sufficiently broad distributions of bubble equilibrium (or initial) radius, it is demonstrated that bubble statistics reach equilibrium on a time scale that is fast compared to physical damping of bubble oscillations due to viscosity, heat transfer, and liquid compressibility. The period-averaged bubble radius may then be used to predict the slow changes in the moments caused by the damping. A benefit is that period averaging gives a much smoother integrand, and accurate statistics can be obtained by tracking as few as five bubbles from the broad distribution. The period-averaged formula may therefore prove useful in reducing computational effort in models of dilute bubbly flow wherein bubbles are forced by shock waves or other rapid pressure changes, for which, at present, the strong effects caused by a distribution in bubble size can only be accurately predicted by tracking thousands of bubbles. Some challenges associated with extending the results to more general (nonimpulsive) forcing and strong two-way coupled bubbly flows are briefly discussed.

Colonius, Tim; Hagmeijer, Rob; Ando, Keita; Brennen, Christopher E.

2008-01-01

301

Bubble bursting mediated aerosols  

NASA Astrophysics Data System (ADS)

Wave breaking over the ocean in the surf zone is responsible for a substantial amount of atmospheric aerosols production. The objects mediating their formation are bubbles entrained below breaking waves, and bursting at the sea surface. We describe the mechanisms by which the liquid shell constitutive of a bubble ultimately results into small drops, also called film drops. A bubble bursts when a hole nucleates through the liquid shell. The hole grows at the Culick velocity balancing inertia with surface tension and is bordered by a rim collecting the shell liquid. This initially smooth toroidal rim corrugates when the centripetal acceleration caused by the recession motion is strong enough to trigger a Rayleigh-Taylor destabilization. Ligaments then emerge from corrugations crests and resolve by a Plateau-Rayleigh mechanism into droplets. The final myst properties are thus solely determined by the shell geometry at the bursting onset. It depends on the ratio of the bubble radius to the capillary length, and on the slow gravity drainage of the liquid on which are superimposed rearrangements due to the marginal regeneration at the bubble foot. Our findings will be discussed in connexion with know facts in that context.

Lhuissier, Henri; Villermaux, Emmanuel

2009-11-01

302

Central Equatorial Pacific Experiment (CEPEX)  

SciTech Connect

The Earth's climate has varied significantly in the past, yet climate records reveal that in the tropics, sea surface temperatures seem to have been remarkably stable, varying by less than a few degrees Celsius over geologic time. Today, the large warm pool of the western Pacific shows similar characteristics. Its surface temperature always exceeds 27[degree]C, but never 31[degree]C. Heightened interest in this observation has been stimulated by questions of global climate change and the exploration of stabilizing climate feedback processes. Efforts to understand the observed weak sensitivity of tropical sea surface temperatures to climate forcing has led to a number of competing ideas about the nature of this apparent thermostat. Although there remains disagreement on the processes that regulate tropical sea surface temperature, most agree that further progress in resolving these differences requires comprehensive field observations of three-dimensional water vapor concentrations, solar and infrared radiative fluxes, surface fluxes of heat and water vapor, and cloud microphysical properties. This document describes the Central Equatorial Pacific Experiment (CEPEX) plan to collect such observations over the central equatorial Pacific Ocean during March of 1993.

Not Available

1993-01-01

303

IONOSPHERIC EQUATORIAL ANOMALY STUDIES DURING SOLAR STORMS  

Microsoft Academic Search

The ionosphere is the major error source in GNSS receivers. Models for single frequency time delay correction do not work at low geomagnetic latitude regions (20), where the ionosphere has a peculiar behavior, known as the Ionospheric Equatorial Anomaly. In order to study the global behavior of the Ionospheric Equatorial Anomaly, dynamic maps based on IONEX data have been generated.

Alexandre B. V. Oliveira; F. Walter

304

VLSI intelligent magnetic bubble memories  

SciTech Connect

This thesis presents a systematic exploration of VLSI possibilities for intelligent magnetic bubble memories in which back-end processors and memory elements could be incorporated in bubble VLSI chips. To provide the basis of system designs on bubble chips, a comprehensive library of magnetic bubble logic components was established, with emphasis on standardization in terms of dimensions and I/O to facilitate the chip composition task. These components were designed in current-access perforated-sheet configuration and fabricated on magnetic garnet wafers supporting 2-..mu..m bubbles. Operating margins were studied on 8-..mu..m period devices at 1 MHz by using a high speed magneto-optical sampling camera system. Bubble-to-bubble interaction force was found very reliable in producing successful logic operation with 12% bias field margins equal to 80% of the bubble propagation margin and about 60% of the free bubble bias field margin. An 8.5% overlapped bias margin was obtained for all of the logic components. The established library of bubble logic components was used to design intelligent bubble memories that support string-pattern matching and associative-searching functions. The intrinsic features of bubble logic technology were examined to indicate opportunities for VLSI bubble logic systems on memory chips.

Hwang, J.P.

1985-01-01

305

Effect of bubble deformation on the properties of bubbly flows  

NASA Astrophysics Data System (ADS)

Direct numerical simulations of the motion of 27 three-dimensional deformable buoyant bubbles in periodic domains are presented. The full Navier Stokes equations are solved by a parallelized finite-difference/front-tracking method that allows a deformable interface between the bubbles and the suspending fluid and the inclusion of surface tension. The Etvs number is taken as equal to 5, so that the bubbles are ellipsoidal, and the Galileo number is 900, so that the rise Reynolds number of a single bubble in an unbounded flow is about 26. Three values of the void fraction have been investigated: 2%, 6% and 12%. At 6%, a change in the behaviour of the bubbles is observed. The bubbles are initially dispersed homogeneously throughout the flow field and their average rise Reynolds number is 23. After the bubbles have risen by about 90 bubble diameters, they form a vertical stream and accelerate. The microstructure of the bubble suspension is analysed and an explanation is proposed for the formation of these streams. The results for the ellipsoidal bubbles are compared to the results for nearly spherical bubbles, for which the Etvs number is 1 and the Galileo number is 900. The dispersion of the bubbles and the velocity fluctuations in the liquid phase are analysed.

Bunner, Bernard; Tryggvason, Grtar

2003-11-01

306

Study of electron trapping by a transversely ellipsoidal bubble in the laser wake-field acceleration  

NASA Astrophysics Data System (ADS)

We present electron trapping in an ellipsoidal bubble which is not well explained by the spherical bubble model by [Kostyukov et al., Phys. Rev. Lett. 103, 175003 (2009)]. The formation of an ellipsoidal bubble, which is elongated transversely, frequently occurs when the spot size of the laser pulse is large compared to the plasma wavelength. First, we introduce the relation between the bubble size and the field slope inside the bubble in longitudinal and transverse directions. Then, we provide an ellipsoidal model of the bubble potential and investigate the electron trapping condition by numerical integration of the equations of motion. We found that the ellipsoidal model gives a significantly less restrictive trapping condition than that of the spherical bubble model. The trapping condition is compared with three-dimensional particle-in-cell simulations and the electron trajectory in test potential simulations.

Cho, Myung-Hoon; Kim, Young-Kuk; Hur, Min Sup

2013-09-01

307

Maintenance of Equatorial Superrotation in Titan's Atmosphere  

NASA Astrophysics Data System (ADS)

The long-standing problem of the existence of equatorial superrotation in a rotating planetary atmosphere has been solved. Various momentum force terms that could drive the equatorial superrotation are examined. In general, it is found that: (i) the pumping by thermal tides is the only dominant momentum source for the equatorial superrotation; (ii) a small planetary rotation rate is not crucial for the existence of an equatorial superrotation; (iii) it is unlikely that the eddy horizontal momentum transfer in a slowly rotating atmosphere such as Venus' is against its gradient, though this remains an open question; (iv) upward momentum flux by Hadley circulation below the jet center of an equatorial superrotation is a momentum sink, which will impede rather than assist the formation of the equatorial superrotation. Each of ten terms in the averaged zonal momentum equation is evaluated analytically. The analytic forms of the approach explicitly show how an equatorial superrotation of a planetary atmosphere is dependent on various external and internal parameters, including: (i) Sun-planet distance, (ii) radius of planet, (iii) rotation rate, (iv) inclination of the equatorial plane, (v) gravity, (vi) atmospheric scale height, (vii) atmospheric buoyancy frequency, (viii) frictional drag, (ix) albedo, and (x) the pressure level at which the deposition of the solar radiation occurs. When the general solution is applied to Titan's atmosphere, the results are: (i) no solution is found for Titan's stratospheric equatorial superrotation at 1-mb level; (ii) however, if the main absorption layer of the solar radiation in Titan's atmosphere is lifted from 1 mb ( 185 km) to above 0.15 mb ( 270 km) level, a stable equatorial superrotation of >86 m/s can be maintained near the solstice. Two momentum sinks for Titan's superrotation are frictional drag force and meridional advection of wind shear by horizontal branches of the Hadley circulation.

Zhu, X.

2004-12-01

308

Bubble Nucleation in Supersaturated Fluids.  

National Technical Information Service (NTIS)

An understanding of the physics of bubble formation is of importance in such diversified endeavors as propeller design, fluid flow, undersea medicine, and the brewing of beer. While the properties of preformed bubbles are well understood, relatively littl...

T. D. Kunkle

1979-01-01

309

Resent Status of ITER Equatorial Launcher Development  

SciTech Connect

The ITER equatorial launcher is divided into a front shield and a port plug. The front shield is composed of fourteen blanket shield modules so as to form three openings for the injection of mm-wave beams into plasma. Twenty-four waveguide transmission lines, internal shields, cooling pipes and so on are installed in the port plug. The transmission lines consist of the corrugated waveguides, miter bends and the free space propagation region utilizing two mirrors in front of the waveguide outlet. The analysis of mm-wave beam propagation in the region shows that the transmission efficiency more than 99.5% is attained. The high power experiments of the launcher mock-up have been carried out and the measured field patterns at each mirror and the outlet of the launcher are agreed with the calculations. It is concluded that the transmission line components in the launcher mock-up are fabricated as designed and the present mm-wave design in the launcher is feasible.

Takahashi, K.; Kajiwara, K.; Kasugai, A.; Oda, Y.; Kobayashi, N.; Sakamoto, K. [Japan Atomic Energy Agency, 801-1, Naka Ibaraki, 311-0193 (Japan)

2009-11-26

310

Resent Status of ITER Equatorial Launcher Development  

NASA Astrophysics Data System (ADS)

The ITER equatorial launcher is divided into a front shield and a port plug. The front shield is composed of fourteen blanket shield modules so as to form three openings for the injection of mm-wave beams into plasma. Twenty-four waveguide transmission lines, internal shields, cooling pipes and so on are installed in the port plug. The transmission lines consist of the corrugated waveguides, miter bends and the free space propagation region utilizing two mirrors in front of the waveguide outlet. The analysis of mm-wave beam propagation in the region shows that the transmission efficiency more than 99.5% is attained. The high power experiments of the launcher mock-up have been carried out and the measured field patterns at each mirror and the outlet of the launcher are agreed with the calculations. It is concluded that the transmission line components in the launcher mock-up are fabricated as designed and the present mm-wave design in the launcher is feasible.

Takahashi, K.; Kajiwara, K.; Kasugai, A.; Oda, Y.; Kobayashi, N.; Sakamoto, K.

2009-11-01

311

The trouble with the Local Bubble  

NASA Astrophysics Data System (ADS)

The model of a Local Hot Bubble has been widely accepted as providing a framework that can explain the ubiquitous presence of the soft X-ray background diffuse emission. We summarize the current knowledge on this local interstellar region, paying particular reference to observations that sample emission from the presumed local million degree K hot plasma. However, we have listed numerous observations that are seemingly in conflict with the concept of a hot Local Bubble. In particular, the discovery of solar wind charge exchange that can generate an appreciable soft X-ray background signal within the heliosphere, has led to a re-assessment of the generally accepted model that requires a hot local plasma. In order to explain the majority of observations of the local plasma, we forward two new speculative models that describe the physical state of the local interstellar gas. One possible scenario is similar to the present widely accepted model of the Local Hot Bubble, except that it accounts for only 50% of the soft X-ray emission currently detected in the galactic plane, has a lower thermal pressure than previously thought, and its hot plasma is not as hot as previously believed. Although such a model can solve several difficulties with the traditional hot Local Bubble model, a heating mechanism for the dimmer and cooler gas remains to be found. The second possible explanation is that of the Hot Top model, in which the Local Cavity is an old supernova remnant in which no (or very little) million degree local plasma is presently required. Instead, the cavity is now thought to be filled with partially ionized cloudlets of temperature 7000 K that are surrounded by lower density envelopes of photo-ionized gas of temperature 20,000 K. Although this new scenario provides a natural explanation for many of the observations that were in conflict with the Local Hot Bubble model, we cannot (as yet) provide a satisfactory explanation or the emission levels observed in the B and Be ultra-soft X-ray bands.

Welsh, Barry Y.; Shelton, Robin L.

2009-09-01

312

Bubble formation via multidrop impacts  

Microsoft Academic Search

Gas bubbles are often generated when droplets impact a liquid-air interface. For the impact of single droplets, a critical impact velocity must be exceeded for air to be entrained in the form of bubbles. Here we establish that bubbles can be generated at much lower velocities provided that two or more drops impact the liquid-air interface within a sufficiently short

Alexander G. Bick; William D. Ristenpart; Ernst A. van Nierop; Howard A. Stone

2010-01-01

313

Bubbly jets in stagnant water  

Microsoft Academic Search

Airwater bubbly jets are studied experimentally in a relatively large water tank with a gas volume fraction, Co, of up to 80% and nozzle Reynolds number, Re, ranging from 3500 to 17,700. Measurements of bubble properties and mean axial water velocity are obtained and two groups of experiments are identified, one with relatively uniform bubble sizes and another with large

David Z. Zhu; Nallamuthu Rajaratnam

2008-01-01

314

Dependence on zenith angle of the strength of 3-meter equatorial electrojet irregularities  

Microsoft Academic Search

Radar measurements in Peru were used to deduce the zenith angle dependence of the scattering cross section of plasma irregularities generated by instabilities in the equatorial electrojet. The irregularities probed by the 50 MHz Jicamarca radar had a wavelength of 3m. The cross section for the type 2 irregularities was isotopic in the plane perpendicular to the magnetic field, while

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

1980-01-01

315

Modelling and observations of the equatorial ionosphere. Rept. for 1 Oct 87-30 Sep 88  

Microsoft Academic Search

The equatorial ionosphere experiences one of the most severe forms of a geophysical plasma instability - a phenomenon known as spread F. An observational campaign was organized to bring a complement of diagnostic instruments to two sites in the western Pacific sector (Kwajalein Atoll in the Marshall Islands and Wake Island) for a period of coordinated optical and radio measurements

Mendillo

1990-01-01

316

First incoherent-scatter measurements of the equatorial E layer obtained with the ALTAIR radar  

Microsoft Academic Search

We describe the first incoherent-scatter (IS) radar measurements made of the daytime E layer at equatorial latitudes. Using ALTAIR, a steerable IS radar located in the Kwajalein Atoll, we not only show that the E-layer profiles are consistent with those obtained in situ by rockets, we present the first direct evidence of a latitudinal gradient in plasma density in the

Roland T. Tsunoda

1995-01-01

317

Nonplanar mhd model for solar flare-generated disturbances in the heliospheric equatorial plane  

Microsoft Academic Search

An analysis, with a representative (canonical) example of solar-flare-generated equatorial disturbances, is presented for the temporal and spatial changes in the solar wind plasma and magnetic field environment between the Sun and one astronomical unit (AU). Our objective is to search for first order global consequences rather than to make a parametric study. The analysis - an extension of earlier

S. T. Wu; M. Dryer; S. M. Han

1983-01-01

318

Lunar-dependent equatorial ionospheric electrodynamic effects during sudden stratospheric warmings  

Microsoft Academic Search

We have used plasma drift and magnetic field measurements during the 2001-2009 December solstices to study, for the first time, the longitudinal dependence of equatorial ionospheric electrodynamic perturbations during sudden stratospheric warmings. Jicamarca radar measurements during these events show large dayside downward drift (westward electric field) perturbations followed by large morning upward and afternoon downward drifts that systematically shift to

M. E. Olson; C. Stolle; H. Lhr; L. P. Goncharenko; K. Yumoto; T. Nagatsuma

2010-01-01

319

Radar imaging of equatorial F region irregularities with maximum entropy interferometry  

Microsoft Academic Search

Radar interferometry with multiple collinear antenna baselines has been performed at Jicarnarca, near Lima, Per6, and high-resolution images of plasma irregularities in equatorial spread F have been constructed from the data. The images represent the brightness distribution of the radar backscatter, which is the Fourier transform of the visibility or spatial cross correlation of the scattered radar signal on the

D. L. Hysell

1996-01-01

320

Geomagnetic storm effects in equatorial ionization anomaly and equatorial spread-F over a low latitude station  

NASA Astrophysics Data System (ADS)

Equatorial spread-F and Equatorial Ionization Anomaly EIA are very important geophysical phenomena These two important processes are very much associated with the geomagnetic disturbances geomagnetic storms of varying magnitude Equatorial belt of strong spread-F extends right through the Appleton anomaly crest latitudes during high sunspot years Intense scintillations do occur in presence of the plasma density irregularities that are associated with the spread-F these may disrupt trans-ionospheric radio communication Steep rise of the F-layer in the post sun set period and strong ionization anomaly that develops subsequently associated with the equatorial spread -F In view of the important effects on radio communications it is important therefore to study the effects of the geomagnetic storm on ionization anomaly and on the occurrence of spread-F Data over Ahmedabad 23 1 oN 72 4 oE dip 33 and at Kodaikanal 10 2 oN 77 5 oE dip 5 are analyzed for the study of geomagnetic storm effects of high medium and low solar activity periods Ionospheric data for more than 120 geomagnetic storms covering different solar epochs 1989-1991 1994-1996 and for the 1999-2001 of varying magnitude have been analyzed A total of about 60 storms Dst - 50 nT of different strength occurred during the period of 1999-2001 only About 55 of storms were found to develop through a multi-step growth in the ring current that is a multi-step decrease in Dst in the main phase of the storms About 35 magnetic storms were linked with magnetic clouds About 60 of intense and

Sharma, S.; Chandra, H.; Sinha, H. S. S.

321

Bubbles generated from wind-steepened breaking waves: 1. Bubble plume bubbles  

Microsoft Academic Search

Measurements of bubble plumes from paddle-amplified, wind stress breaking waves were made in a large wind-wave channel during the LUMINY experiment in fresh (but not clean) water. Bubble plumes exhibited considerable variability with respect to dynamics, bubble size distribution, and physical extent. A classification scheme was developed, and time- and size-resolved bubble population distributions were calculated for each plume class.

Ira Leifer; Gerrit de Leeuw

2006-01-01

322

Bubble Chamber Site  

NSDL National Science Digital Library

This substantial site features a large number of photos of bubble chamber (BC) tracks, many with a discussion of the physics. There is a description of how the BC works and also useful tutorial on reading BC pictures. The high quality of the images and the explanations of the events that are shown make this site especially valuable.

2008-06-11

323

The Liberal Arts Bubble  

ERIC Educational Resources Information Center

|The author expresses his doubt that the general higher education bubble will burst anytime soon. Although tuition, student housing, and book costs have all increased substantially, he believes it is still likely that the federal government will continue to pour billions into higher education, largely because Americans have been persuaded that it

Agresto, John

2011-01-01

324

Bubbles and steam electricity  

Microsoft Academic Search

Abstract In 1840, Lord Armstrong was the first to study the electrical charge produced as steam escaped from boilers, the phenomenon called steam electricity. In 1969, interest in steam electricity was renewed because of explosions caused by the ignition of chemical vapors during the washing of ship tanks with steam jets. Steam electricity is proposed explained by the bubbles nucleated

T. V. Prevenslik

325

Magnetic Bubble Materials.  

National Technical Information Service (NTIS)

The object of this project is to establish a reliable supply of high quality magnetic bubble materials to support the device work of various Department of Defense agencies. This work encompasses bulk, non-magnetic garnet crystal growth (for use as substra...

J. W. Moody R. J. Janowiecki R. M. Sandfort R. W. Shaw

1973-01-01

326

Magnetic Bubble Materials.  

National Technical Information Service (NTIS)

The object of this project was to establish a reliable supply of high quality magnetic bubble materials to support the device work of various Department of Defense Agencies. Bulk, single crystals of Gd3Ga5O12 were grown by the Czochralski method. Crystals...

J. W. Moody R. M. Sandfort R. W. Shaw

1972-01-01

327

Magnetic bubble computer systems  

Microsoft Academic Search

The purpose of this paper is to extend the work presented earlier on the methods for performing logic on magnetic bubble chips, and to illustrate these techniques by presenting the outline of a design for a general-purpose digital computer.

R. C. Minnick; P. T. Bailey; R. M. Sandfort; W. L. Semon

1972-01-01

328

EQUATORIAL SUPERROTATION ON TIDALLY LOCKED EXOPLANETS  

SciTech Connect

The increasing richness of exoplanet observations has motivated a variety of three-dimensional (3D) atmospheric circulation models of these planets. Under strongly irradiated conditions, models of tidally locked, short-period planets (both hot Jupiters and terrestrial planets) tend to exhibit a circulation dominated by a fast eastward, or 'superrotating', jet stream at the equator. When the radiative and advection timescales are comparable, this phenomenon can cause the hottest regions to be displaced eastward from the substellar point by tens of degrees longitude. Such an offset has been subsequently observed on HD 189733b, supporting the possibility of equatorial jets on short-period exoplanets. Despite its relevance, however, the dynamical mechanisms responsible for generating the equatorial superrotation in such models have not been identified. Here, we show that the equatorial jet results from the interaction of the mean flow with standing Rossby waves induced by the day-night thermal forcing. The strong longitudinal variations in radiative heating-namely intense dayside heating and nightside cooling-trigger the formation of standing, planetary-scale equatorial Rossby and Kelvin waves. The Rossby waves develop phase tilts that pump eastward momentum from high latitudes to the equator, thereby inducing equatorial superrotation. We present an analytic theory demonstrating this mechanism and explore its properties in a hierarchy of one-layer (shallow-water) calculations and fully 3D models. The wave-mean-flow interaction produces an equatorial jet whose latitudinal width is comparable to that of the Rossby waves, namely the equatorial Rossby deformation radius modified by radiative and frictional effects. For conditions typical of synchronously rotating hot Jupiters, this length is comparable to a planetary radius, explaining the broad scale of the equatorial jet obtained in most hot-Jupiter models. Our theory illuminates the dependence of the equatorial jet speed on forcing amplitude, strength of friction, and other parameters, as well as the conditions under which jets can form at all.

Showman, Adam P. [Department of Planetary Sciences and Lunar and Planetary Laboratory, University of Arizona, 1629 University Blvd., Tucson, AZ 85721 (United States); Polvani, Lorenzo M., E-mail: showman@lpl.arizona.edu [Department of Applied Physics and Applied Mathematics, Columbia University, New York, NY (United States)

2011-09-01

329

Signature of anisotropic bubble collisions  

SciTech Connect

Our universe may have formed via bubble nucleation in an eternally inflating background. Furthermore, the background may have a compact dimension--the modulus of which tunnels out of a metastable minimum during bubble nucleation--which subsequently grows to become one of our three large spatial dimensions. When in this scenario our bubble universe collides with other ones like it, the collision geometry is constrained by the reduced symmetry of the tunneling instanton. While the regions affected by such bubble collisions still appear (to leading order) as disks in an observer's sky, the centers of these disks all lie on a single great circle, providing a distinct signature of anisotropic bubble nucleation.

Salem, Michael P. [Institute of Cosmology, Department of Physics and Astronomy, Tufts University, Medford, Massachusetts 02155 (United States)

2010-09-15

330

When sound slows down bubbles  

NASA Astrophysics Data System (ADS)

We report experimental observations that a bubble rising in water in the presence of a sound field is significantly slowed down, even at moderate acoustic pressures. We measure the mean rise velocity of bubbles under various acoustic forcings and show this effect occurs if the noise spectrum matches or overlaps bubble resonance. We render surface oscillations and translational movements of bubbles using high speed video imaging and thereby identify Faraday waves on the bubble wall as the cause for the velocity reduction. The associated mechanisms are discussed in terms of induced forces.

Dangla, Rmi; Poulain, Cdric

2010-04-01

331

On the modelling of equatorial waves  

NASA Astrophysics Data System (ADS)

The present theory of geophysical waves that either raise or lower the equatorial thermocline, based on the reduced-gravity shallow-water equations on the ?-plane, ignores vertical variations of the flow. In particular, the vertical structure of the Equatorial Undercurrent is absent. As a remedy we propose a simple approach by modeling this geophysical process as a wave-current interaction in the f-plane approximation, the underlying current being of positive constant vorticity. The explicit dispersion relation allows us to conclude that, despite its simplicity, the proposed model captures to a reasonable extent essential features of equatorial waves.

Constantin, A.

2012-03-01

332

Vertical cloud structure of Jupiter's equatorial plumes  

NASA Astrophysics Data System (ADS)

A model for the vertical cloud structure of Jupiter's Equatorial Plumes is deduced based on an analysis of Voyager images of the equatorial region in the 6190- methane band and the 6000- continuum, and ground-based 8900- methane band images of Jupiter. A computer code that represents scattering and absorption from aerosol and gas layers was applied to a hierarchy of increasingly complex model aerosol structures to match the observations in the three wavelengths. The observations are consistent with a model for the vertical cloud structure of the equatorial region that consists of four aerosol layers.

Stoker, C. R.; Hord, C.

1985-12-01

333

Altair - An incoherent scatter radar for equatorial spread F studies  

Microsoft Academic Search

The paper reports preliminary results on 1-m equatorial spread F irregularities obtained with a high-power VHF backscatter radar located at equatorial latitudes. The field experiment was conducted at Kwajalein Atoll, Marshall Islands, during August 1977. The examples, which include both incoherent scatter measurements and backscatter from equatorial spread F irregularities, illustrate the usefulness of a fully steerable radar for equatorial

R. T. Tsunoda; M. J. Baron; J. Owen; D. M. Towle

1979-01-01

334

Altair: an incoherent scatter radar for equatorial spread F studies  

Microsoft Academic Search

We report preliminary results on l-m equatorial spread F irregularities obtained with a high-power VHF backscatter radar located at equatorial latitudes. The field experiment was conducted at Kwajalein Atoll, Marshall Islands, during August 1977. The examples, which include both incoherent scatter measurements and backscatter from equatorial spread F irregularities, illustrate the usefulness of a fully steerable radar for equatorial spread

R. T. Tsunoda; M. J. Baron; J. Owen; D. M. Towle

1979-01-01

335

On the hierarchy of processes contributing to equatorial spread F  

SciTech Connect

Unstable plasma stratification in the twilight equatorial F region ionosphere is subject to plasma instabilities known collectively as equatorial spread F. Small-scale irregularities in electron density give rise to coherent VHF and UHF radio scatter during spread F while in situ spacecraft detect intermediate- and large-scale plasma structures. The authors present data from observations made over three years at the Jicamarca Radio Observatory and from the summer 1990 CRRES/EQUIS campaign which involved the Cornell 50 MHz radar interferometer (CUPRI) and the Altair UHF radar at Kwajalein, MI. Radar findings are correlated with spread F data from sounding rockets launched during the EQUIS project and from the Atmospheric Explorer E satellite. A review of fundamental fluid theory for the ionospheric interchange instability emphasizes dissipative and non-local effects that restrict linear instability to intermediate-scale wavelengths. A nonlinear fluid theory incorporating three wave interactions extends the range of instability to transitional and small scales, and renormalization group analysis offers a way to evaluate enhanced transport due to these nonlinearly excited modes. At large scales, circumstantial evidence suggests that internal gravity waves seed plasma upwellings and initiate topside spread F. Density and electric field spectra measured by the spread F sounding rockets exhibit inertial-convective and inertial-diffusive subranges. A model of quasi one-dimensional plasma turbulence reproduces the spectral indices and breaking scales observed by the rockets. Density power spectra from 30 AE-E orbits also possess convective and diffusive subranges, but their characteristic scale sizes are about 10 times larger than the rocket's. One-dimensional rocket and satellite power spectra combine to form a two-dimensional spectral model of F region irregularities which predicts VHF radar scattering cross-sections.

Hysell, D.L,.

1992-01-01

336

Nonplanar MHD model for solar flare-generated disturbances in the heliospheric equatorial plane  

Microsoft Academic Search

An analysis, with a representative (canonical) example of solar-flare-generated equatorial disturbances, is made for the temporal and spatial changes in the solar wind plasma and magnetic field environment between the sun and 1 AU. The goal is to search for first-order global consequences rather than to make a parametric study. The analysis treats all three plasma velocity and magnetic field

S. T. Wu; M. Dryer; S. M. Han

1983-01-01

337

Numerical simulations of equatorial spread F using ALTAIR incoherent backscatter measured electron density profiles from the 17 July 1979 DNA Kwajalein campaign  

NASA Astrophysics Data System (ADS)

Using electron density profiles measured by the ALTAIR radar on 17 July 1979, we have performed global large scale size numerical simulations of the nonlinear evolution of the collisional Rayleigh-Taylor instability in the equatorial ionosphere. The ALTAIR profiles were taken approximately four and one-half hours prior to the onset of equatorial spread F. Using 5% amplitude sinusoidal initial perturbations in our numerical simulations, we find fully developed spread F bubbles (plumes) on time scales of approximately one-half hour for both small (8 km) and large (200 km) horizontal scale lengths.

Zalesak, S. T.; Ossakow, S. L.

1980-12-01

338

Downward Mapping of Equatorial Ionospheric Electric Fields.  

National Technical Information Service (NTIS)

The problem of downward mapping of equatorial ionospheric electric fields is studied in two dimensions. Numerical solutions are shown and are compared with the corresponding ones for high latitudes. It is found that ionospheric electric fields can map dow...

W. D. Gonzalez S. L. G. Dutra A. L. C. Gonzalez A. E. C. Pereira

1985-01-01

339

ALTAIR Radar Study of Equatorial Spread F.  

National Technical Information Service (NTIS)

The results of research on equatorial spread-F (ESF) phenomena obtained by using two backscatter radars, ALTAIR and TRADEX, are summarized. The radar measurements were made in support of three rocket campaigns conducted from the Kwajalein Atoll during the...

R. T. Tsunoda

1981-01-01

340

Longitudinal variations of the equatorial electojet  

NASA Astrophysics Data System (ADS)

We have utilized a three dimensional electrostatic potential model to explain the longitudinal variations of the equatorial electrojet. The model runs were constrained by net H component magnetic field measurements from three equatorial stations, namely, Huancayo (Peru) 12.05 S, 284.67 E; Addis Ababa (Ethiopia) 9.8 N, 38.8 E; Tirunelveli (India) 8.42 N, 77.48 E. The model runs were done in an iterative fashion until the computed and measured H component magnetic field values come into a close agreement. The physical mechanisms for the longitudinal variations of the equatorial electrojet were inferred by comparing and contrasting the resulting computed vertical polarization electric field (which drives the equatorial electrojet), and zonal current density profiles for the three stations mentioned above.

Shume, Esayas

341

A statistical study of Pc 1-2 magnetic pulsations in the equatorial magnetosphere 1. Equatorial occurrence distributions  

SciTech Connect

A study of AMPTE CCE magnetic field data covering the frequency range 0.1-4.0 Hz using all data obtained during the first complete local time precession of the satellite orbit major axis (7,500 hours of observations) has been made to evaluate the occurrence of transverse, narrowband Pc 1-2 emissions, identified as electromagnetic ion cyclotron (EMIC) waves, in the equatorial magnetosphere from L = 3.5 to L = 9 at all local times. A set of example events illustrates the pattern of Pc 1-2 occurrence: events occur primarily for L > 7, and a radial separation of several R{sub E} between low (<6) and high L(>6) pulsations is observed. Statistically, the highest concentration of events occurred near apogee in the afternoon. The L>6 and L,6 event populations appear to be radially separated in the morning but merge together in the afternoon. The authors construct a normalized occurrence distribution throughout the equatorial plane from L = 3.5 to L = 9 of Pc 1-2 with peak to peak amplitudes greater than 0.8 nT. The occurrence distribution exhibits a number of properties: for L > 7, Pc 1-2 occur at any given place in the early afternoon (1200-1500 MLT) with 10-20% probability and in the morning (0300-0900 MLT) with {approx} 3% probability; the L = 6-7 local time distribution reproduces results obtained previously from data at geostationary orbit; L < 5 events occur with a probability of {le}1% and a relatively uniform local time distribution. The predominance of L > 7 events implies that plasma sheet ion develop sufficient temperature anisotropy to generate EMIC waves on a routine basis in their drift from the nightside to the dayside and that plasma sheet ions on open drift paths rather than ring current ions on closed drift paths present the greatest source of equatorially generated EMIC waves.

Anderson, B.J.; Erlandson, R.E.; Zanetti, L.J. (John Hopkins Univ., Laurel, MD (United States))

1992-03-01

342

Substorm currents in the equatorial magnetotail  

SciTech Connect

The authors have determined characteristics of magnetospheric equatorial currents during substorms from the vector magnetic field data acquired with the GOES 5 and GOES 6 satellites, separated about 1.9 hours in MLT in geosynchronous orbit. These data have been used to determine the local time (azimuthal) and radial variation of the equatorial current. The divergence of the equatorial current was computed from these variations, and systems of field-aligned currents were deduced. During the growth phase to the maximum phase of the taillike reconfiguration of the near-Earth magnetic field, a positive divergence (away from the equatorial plane) of the westward equatorial current occurs in the late evening to premidnight MLT sector, and a negative divergence (away from the equatorial plane) occurs in the late evening to premidnight MLT sector, and a negative divergence (away from the equatorial plane) occurs in the premidnight to early morning MLT sector. This flow direction pattern is the same as that of the region 2 field-aligned current system. The authors have also determined the presence of a radial current that flows toward the earth in the late evening to premidnight sector and flows away from the Earth in the midnight to morning sector. The intensity of the radial currents increases before the expansion phase. Consequently, the patterns of field-aligned currents associated with various substorm phases are the superposition of currents driven by multiple sources with different temporal variations. They have identified at least three different but related sources of field-aligned currents during the growth and expansion phases. These sources are related to the divergence of the westward flowing equatorial current and to distributions of pressure and magnetic field gradients that evolve in the magnetotail. When combined, these complicated systems support the basic region 1 to region 2 field-aligned current flow pattern. 22 refs., 12 figs., 1 tab.

Iijima, T.; Watanabe, M. [Univ. of Tokyo (Japan); Potemra, T.A.; Zanetti, L.J. [John Hopkins Univ., Laurel, MD (United States); Kan, J.R.; Akasofu, S.I. [Univ. of Alaska, Anchorage, AK (United States)

1993-10-01

343

North-south aligned equatorial airglow depletions  

Microsoft Academic Search

A new instrument for all-sky spectrophotometric imaging of aurora and airglow has been installed in the Air Force Geophysics Laboratory's Airborne Ionospheric Observatory. Initial observations of equatorial and near-equatorial 6300-A O I airglow show the existence of north-south aligned regions of airglow depletion. These dark bands often extend more than 1200 km in the north-south direction and 50-200 km in

E. J. Weber; J. Buchau; R. H. Eather; S. B. Mende

1978-01-01

344

Cavitation Bubble in Shear Flow  

NASA Astrophysics Data System (ADS)

In the orifice of liquid injectors at high pressure, cavitation occurs behind the sharp corners, where a strong pressure drop is present due to quick change in the flow direction. In addition, a high level of shear is present inside the boundary layer. Therefore, it is important to understand the influence of the shear on the cavitation. In this study, the deformation of a cavitation bubble in shear and extensional flows is numerically investigated. The Navier-Stokes equations are solved to observe the three-dimensional behavior of the bubble as it grows and collapses. During the collapse phase of the bubble, two re-entrant jets are observed on two sides of the bubble due to interaction of the bubble with the background flow. Re-entrant jets with enough strength could breakup the bubble into smaller bubbles. Post processing of the results is done to cast the disturbance by the bubble on the liquid velocity field in terms of spherical harmonics. It is found that a quadrupole moment is created in addition to the monopole source. As the bubble collapses regions of high vorticity are created near the bubble interface.

Dabiri, Sadegh; Sirignano, William; Joseph, Daniel

2009-11-01

345

CONTINUOUSLY SENSITIVE BUBBLE CHAMBER  

DOEpatents

A radiation detector of the bubble chamber class is described which is continuously sensitive and which does not require the complex pressure cycling equipment characteristic of prior forms of the chamber. The radiation sensitive element is a gas-saturated liquid and means are provided for establishing a thermal gradient across a region of the liquid. The gradient has a temperature range including both the saturation temperature of the liquid and more elevated temperatures. Thus a supersaturated zone is created in which ionizing radiations may give rise to visible gas bubbles indicative of the passage of the radiation through the liquid. Additional means are provided for replenishing the supply of gas-saturated liquid to maintaincontinuous sensitivity.

Good, R.H.

1959-08-18

346

Can bubbles sink ships?  

NASA Astrophysics Data System (ADS)

I investigate the interplay between the buoyancy force and the upwelling (or drag) force which act on a floating object when bubbles are rising through a body of water. Bubbles reduce the buoyant force by reducing the density of the water, but if they entrain an upwelling flow of water as they rise, they can produce a large upward drag force on the floating object. In an upwelling flow, our model ship (density=0.94 g/cm3) floats in a foam whose density is only 0.75 g/cm3. Comparing results with and without upwelling currents is an interesting demonstration and has real-world applications to ships in the ocean.

Hueschen, Michael A.

2010-02-01

347

First incoherent-scatter measurements of the equatorial E layer obtained with the ALTAIR radar  

NASA Astrophysics Data System (ADS)

We describe the first incoherent-scatter (IS) radar measurements made of the daytime E layer at equatorial latitudes. Using ALTAIR, a steerable IS radar located in the Kwajalein Atoll, we not only show that the E-layer profiles are consistent with those obtained in-situ by rockets, we present the first direct evidence of a latitudinal gradient in plasma density in the bottomside E layer that extended from 3 deg N dip latitude to beyond 6 deg N. We suggest that the gradient involves the electrodynamic transport of metallic ions, e.g., the gradient could be produced by the equatorial metallic-ion fountain or possibly by the dumping of metallic ions at the base of the E layer by the wind-shear mechanism for sporadic E. We close with a brief discussion of the implications of such a gradient on the equatorial electrojet.

Tsunoda, Roland T.

1995-04-01

348

The magnetooptic bubble display  

Microsoft Academic Search

The various factors that affect the properties of magnetooptic (M\\/O) bubble displays which use bismuth-substituted iron garnets are discussed. A composite bias magnet-ferrite drive-coil assembly is described which allows optical access to the display chip. The drive coils required 300 mW to produce an in-plane field of 30 Oe when operated at 10 kHz, and the bias field was uniform

D. E. Lacklison; G. B. Scott; A. D. Giles; J. A. Clarke; R. F. Pearson; J. L. Page

1977-01-01

349

The magnetooptic bubble display  

Microsoft Academic Search

The various factors that affect the properties of magneto-optic (M\\/O) bubble displays which use bismuth substituted iron garnets are discussed. A composite bias magnet-ferrite drive coil assembly is described which allows optical access to the display chip. The drive coils required 300 mW to produce an in-plane field of 30 Oe when operated at 10 kHz, and the bias field

D. E. LACKLISON; G. B. SCOTT; A. D. GILES; J. Clarke; R. F. PEARSON; J. L. PAGE

1977-01-01

350

On postmidnight low-latitude ionospheric irregularities during solar minimum: 1. Equatorial Atmosphere Radar and GPS-TEC observations in Indonesia  

NASA Astrophysics Data System (ADS)

Using the 47 MHz Equatorial Atmosphere Radar (EAR) in West Sumatra, Indonesia (10.36S dip latitude), it is shown that postmidnight irregularities during solar minimum are morphologically different from those detected during solar maximum and are quite similar to those observed with the middle and upper atmosphere (MU) radar in midlatitudes (29.3N dip latitude). Utilizing the rapid beam-steering capability of the EAR, the spatial structure of the postmidnight irregularities is clearly presented for the first time. It is found that they usually propagate westward and can be categorized into two types. One shows sharp upwelling plumes near local midnight, which should not be a mere passage of fossil plasma bubbles. The other has successive tilted structures which have the same orientation as medium-scale traveling ionospheric disturbances typically observed at midlatitudes. We suggest that the convergence of the equatorward thermospheric wind which is believed to be responsible for the midnight temperature maximum may be an important factor to produce a preferable condition for the upwelling plumes in the postmidnight sector. The displacement between geographic and magnetic equators may also be important for seasonal/longitudinal variation of the postmidnight irregularities.

Yokoyama, T.; Yamamoto, M.; Otsuka, Y.; Nishioka, M.; Tsugawa, T.; Watanabe, S.; Pfaff, R. F.

2011-11-01

351

Equatorial storm sudden commencements and interplanetary magnetic field  

NASA Astrophysics Data System (ADS)

Interplanetary (IP) shock signatures from interplanetary magnetic field (IMF) data gathered by the Explorer 33, 34 and 35 satellites were compared with H magnetograms associated with major sudden shock commencements (SC) from ground observatories within the equatorial electrojet belt (Huancayo, Addis Ababa and Trivandrum) during 1967-70. It is suggested that the SC in H at low latitudes are composed of two effects: one due to hydromagnetic pressure on the magnetosphere caused by the solar plasma, and the other due to the induced electric field associated with the solar wind velocity. The effect of the magnetospheric electric field is faster than the effect due to the compression of the magnetosphere by the impinging solar plasma.

Rastogi, R. G.

1980-10-01

352

Inside a collapsing bubble: sonoluminescence and the conditions during cavitation.  

PubMed

Acoustic cavitation, the growth and rapid collapse of bubbles in a liquid irradiated with ultrasound, is a unique source of energy for driving chemical reactions with sound, a process known as sonochemistry. Another consequence of acoustic cavitation is the emission of light [sonoluminescence (SL)]. Spectroscopic analyses of SL from single bubbles as well as a cloud of bubbles have revealed line and band emission, as well as an underlying continuum arising from a plasma. Application of spectrometric methods of pyrometry as well as tools of plasma diagnostics to relative line intensities, profiles, and peak positions have allowed the determination of intracavity temperatures and pressures. These studies have shown that extraordinary conditions (temperatures up to 20,000 K; pressures of several thousand bar; and heating and cooling rates of >10(12) K s(1)) are generated within an otherwise cold liquid. PMID:18393682

Suslick, Kenneth S; Flannigan, David J

2008-01-01

353

Day-to-day variability of the equatorial ionization anomaly and scintillations at dusk observed by GUVI and modeling by SAMI3  

NASA Astrophysics Data System (ADS)

The day-to-day variability in ionospheric irregularity generation giving rise to equatorial scintillation has remained an unresolved issue over many decades. We take a fresh look at the problem utilizing the global imagery provided by the Global Ultraviolet Imager (GUVI) instrument on NASA's Thermosphere, Ionosphere, Mesosphere Energetics and Dynamics satellite. GUVI has been acquiring images of 135.6-nm emission in the Earth's ionosphere-thermosphere system since 2001. These GUVI disk images at dusk have been used to identify cases where the equatorial ionization anomaly (EIA) crests lie near the magnetic equator over a relatively narrow longitude range, so that the anomaly looks collapsed. A 16-month period of GUVI data collected during evening at solar maximum is used to study the morphology of these so-called collapses, since the EIA collapse is shown to be linked to the suppression of equatorial plasma bubbles and scintillations. In particular, we look at the June solstice, during which the Atlantic and Pacific show very different climatology and EIA collapses are most frequent in the GUVI data. On the other hand, EIA collapses are a relatively rare occurrence during the equinox period when scintillations are most prevalent globally. We obtained a few dramatic examples of day-to-day variability in EIA behavior and scintillations over India. The Sami3 is Also a Model of the Ionosphere (SAMI3) model was used to investigate the conditions during the evening collapse of the anomaly in the Indian longitude sector, where measurements of total electron content (TEC) and scintillations and estimates of the daytime vertical drifts and those at dusk were available. Results from SAMI3 show that the observed collapse of the anomaly at dusk can be simulated by a reversal of the upward vertical drift in midafternoon in agreement with the drift estimates from magnetometer observations. Such reversed vertical drifts at this time of the day are generally seen during counterelectrojet events. Introduction of neutral winds into SAMI3 better approximates the dusk behavior of TEC at low-latitude stations in India. This study reveals that the longitudinally confined EIA collapse may explain some of the differences in day-to-day variability of scintillations at different locations around the globe.

Basu, Su.; Basu, S.; Huba, J.; Krall, J.; McDonald, S. E.; Makela, J. J.; Miller, E. S.; Ray, S.; Groves, K.

2009-04-01

354

Bubble column dynamics with bubble induced turbulence and dispersion  

NASA Astrophysics Data System (ADS)

The paper presents an evolution of developed mathematical model which is devoted to the description of turbulent flows of bubbly media. The model utilizes Euler-Euler approach which is expanded by k-?-SST turbulence model with additional modifications, related to the bubble induced turbulence and bubble path dispersion. Numerical code based on the proposed model was developed to perform computation of bubble column evolution. Good agreement with experimental data was obtained, and necessity of inclusion of both modifications related to the turbulent motion was shown.

Chernyshev, Alexander; Schmidt, Alexander

2013-10-01

355

Layers in the equatorial mesosphere, motions and aerosol: rocket and radar measurements during EQUIS II  

NASA Astrophysics Data System (ADS)

The NASA EQUIS II (Equatorial Ionosphere Studies) campaign was conducted in August/September 2004 at U.S. Army Kwajalein Atoll/Reagan Test Site on Roi-Namur, Marshall Islands (9N, 168E). The LEMMA (Layers in the Equatorial Mesosphere, Motions and Aerosol) program was devoted to neutral and plasma density fluctuations in the equatorial mesosphere and lower thermosphere. One objective was to detect layers of small scale structures that might be related to mesospheric VHF radar echoes observed regularly at equatorial and low latitudes. The payload carried multiple instruments from U.S. and European investigators, including an ionization gauge for the first in situ measurements of neutral turbulence fluctuations in the equatorial mesosphere. One sounding rocket and three falling spheres were launched successfully on September 20, 2004, supported by a large, steerable 422 MHz UHF radar receiving incoherent backscatter from ~85-700 km. We give an overview of the investigation and present some results including the comparison of in situ and ground based electron density measurements, neutral temperature and wind structure, and observations of neutral and electron density fluctuations.

Lehmacher, G. A.; Croskey, C. L.; Mitchell, J. D.; Friedrich, M.; Torkar, K.; Lbken, F.-J.; Rapp, M.; Kudeki, E.

2005-08-01

356

Equatorial ionospheric electrodynamics associated with high-speed solar wind streams during January-April 2007  

NASA Astrophysics Data System (ADS)

High-speed solar wind streams cause recurrent geomagnetic activity and ionospheric disturbances. In this study, we analyze the equatorial ionospheric ion drift measured by the Defense Meteorological Satellite Program (DMSP) satellites near dusk when high-speed solar wind streams with a period of 13.5 days occurred during January-April 2007. A well-defined quantitative correlation between the solar wind velocity and the equatorial ionospheric ion drift is identified for the first time. The plasma drift in the dusk equatorial ionosphere induced by high-speed solar wind streams is eastward in the zonal direction and downward in the vertical direction at the altitude of DMSP orbit (840 km) during this low solar activity period (January-April 2007). The zonal component of the equatorial ionospheric ion drift is inversely correlated with the vertical component. The ionospheric ion zonal drift varies, on average, from -40 to 40 m s-1 when the solar wind velocity varies from 300 to 700 km s-1 over a 13.5 day period, and the ion vertical drift varies from 10 to -10 m s-1. The quantitative correlations between the solar wind velocity and ionospheric ion drift and between the vertical and zonal components of the ion drift velocity are important for understanding the equatorial ionospheric electrodynamics associated with high-speed solar wind streams and for space weather prediction.

Huang, Chao-Song

2012-10-01

357

Solar Cycle Effects on Equatorial Electrojet Strength and Low Latitude Ionospheric Variability (P10)  

NASA Astrophysics Data System (ADS)

veena_iig@yahoo.co.in The most obvious indicators of the activity of a solar cycle are sunspots, flares, plages, and soon. These are intimately linked to the solar magnetic fields, heliospheric processes which exhibit complex but systematic variations. The changes in geomagnetic activity, as observed in the ground magnetic records follow systematic correspondence with the solar activity conditions. Thus the transient variations in the magnetic field get modified by differing solar conditions. Also the solar cycle influences the Earth causing changes in geomagnetic activity, the magnetosphere and the ionosphere. Daily variations in the ground magnetic field are produced by different current systems in the earths space environment flowing in the ionosphere and magnetosphere which has a strong dependence on latitude and longitude of the location. The north-south (Horizontal) configuration of the earths magnetic field over the equator is responsible for the narrow band of current system over the equatorial latitudes and is called the Equatorial electrojet (EEJ) and is a primary driver for Equatorial Ionization anomaly (EIA). Equatorial electric fields and plasma drifts play the fundamental roles on the morphology of the low latitude ionosphere and strongly vary during geomagnetically quiet and disturbed periods. Quantitative study is done to illustrate the development process of EEJ and its influence on ionospheric parameters. An attempt is also made to examine and discuss the response of the equatorial electrojet parameters to the fast varying conditions of solar wind and interplanetary parameters.

Veenadhari, B.; Alex, S.

2006-11-01

358

Effect of solar variability on transionospheric radio wave propagation in the equatorial region  

NASA Astrophysics Data System (ADS)

Growth of plasma instabilities in the post-sunset equatorial ionospheric F region gives rise to irregularities known by the generic name: equatorial spread F (ESF), which scatter incident VHF or higher frequency radio waves to produce scintillations on trans-ionospheric radio waves. Changes in large scale (> 10 km) electron density distribution in the equatorial and low latitude ionosphere due to electrodynamic effects associated with magnetic storms, influence the generation of ESF irregularities as seen in the pattern of occurrence of nighttime equatorial scintillations that may be specifically linked with magnetic activity. Besides such effects due to transient solar events, it is well known that the probability of occurrence of ionospheric scintillations caused by ESF irregularities as well as the strength of these scintillations during different phases of the solar cycle show a significant modulation of the generation and evolution of these irregularities by solar cycle related changes in the ionosphere and thermosphere. Evolution of spatial structure in the ESF irregularities determines the spatial scales that occur in the ground scintillation pattern during different phases of a scintillation event, and these spatial scales together with the dynamics of the irregularities determine the extent of degradation of transionospheric radio signals. Solar cycle effects on the structure and dynamics of ESF irregularities and hence on degradation of transionospheic radio signals during magnetically quiet periods, as also the effect of magnetic activity on the generation of ESF irregularities are discussed here on the basis of long term spaced receiver scintillation observations at an equatorial location.

Bhattacharyya, A.; Engavale, B.; Tiwari, D.; Bose, S.

359

In Search of the Big Bubble  

ERIC Educational Resources Information Center

|Freely rising air bubbles in water sometimes assume the shape of a spherical cap, a shape also known as the "big bubble". Is it possible to find some objective function involving a combination of a bubble's attributes for which the big bubble is the optimal shape? Following the basic idea of the definite integral, we define a bubble's surface as

Simoson, Andrew; Wentzky, Bethany

2011-01-01

360

Experimental investigation of laser-induced bubble dynamics near elastic/soft material in distilled water  

NASA Astrophysics Data System (ADS)

This study deals with an experimental investigation of the dynamics of laser-induced single bubble near the rigid material plate and near the elastic/soft material plate in the distilled water at room temperature under atmospheric pressure. A pulsed Nd:YAG laser was focused into the distilled water to make plasma and single bubble. The bubble repeated expanding and shrinking motion several times, and then collapsed. This behavior occurred on the sub-millisecond timescale. The solid wall near the bubble makes an asymmetric flow field. Many experiments on the behavior of laser-induced bubble near the rigid material have been reported. The bubble near the solid wall moves toward the rigid wall during its shrinking and rebounding process. The behavior of laser-induced bubble near the soft material, however, has not been well clarified. The soft material such as body tissue can deform and influence the behavior of the laser-induced bubble. Since the high peak power laser has been applied in the field of bioengineering and medical treatment, it is of great importance to clarify the effect of the soft material near the laser-induced cavitation bubble. In this research the behavior of laser-induced bubble near the elastic/soft material was visualized with schlieren method and investigated.

Nakajima, S.; Yamamoto, Y.; Ota, M.; Maeno, K.

2009-02-01

361

Equatorial electric fields during magnetically disturbed conditions. II - Implications of simultaneous auroral and equatorial measurements  

Microsoft Academic Search

Simultaneous auroral and equatorial electric field data are used along with magnetic field data to study anomalous electric field patterns during disturbed times. During some substorms, accompanied by ring current activity, the worldwide equatorial zonal electric field component reverses from the normal pattern. This is interpreted as a partial closure of high latitude field aligned currents in the dayside, low

C. A. Gonzales; M. C. Kelley; B. G. Fejer; J. F. Vickrey; R. F. Woodman

1979-01-01

362

Upper equatorial Atlantic variability during 2002 and 2005 associated with equatorial Kelvin waves  

NASA Astrophysics Data System (ADS)

On the basis of moored (35W, 0 and 23W, 0) and satellite observations, we contrast the upper equatorial Atlantic variability during 2002 with those during 2005. Inspection of the interannual boreal summer cold tongue variability revealed a warm (cold) event in 2002 (2005), with relaxed (intensified) winds in the west and the Equatorial Undercurrent (EUC) embedded in a shallower (deeper) thermocline at 23W. During both years, 2002 and 2005, equatorial Kelvin waves are present in moored observations as 20C isotherm depth anomalies and dynamic height anomalies. Basin-wide sea surface height anomalies are used to derive an equatorial Kelvin wave mode. The time evolution of this mode represents the basis for a regression analysis to investigate related oceanic variability: Compared to the exceptionally strong wave activity in 2002, equatorial Kelvin waves were generally weaker during 2005. The main effect of equatorial Kelvin waves on zonal velocity anomalies at 23W, 0 is evident well below the EUC core. Their direct influence on cold tongue sea surface temperature is small, but they are found to affect the equatorial thermocline slope. Prior to the cold tongue onset in 2002 (2005), the presence of equatorial Kelvin waves is associated with a flattened (steeper) thermocline slope that is crucial for the shallowing (deepening) of the EUC core at 23W and that might precondition the development of the warm (cold) event.

Hormann, Verena; Brandt, Peter

2009-03-01

363

Equatorial electric fields during magnetically disturbed conditions 2. Implications of simultaneous auroral and equatorial measurements  

Microsoft Academic Search

Simultaneous auroral and equatorial electric field data are used along with magnetic field data to study anomalous electric field patterns during disturbed times. During some substorms, accompanied by ring current activity, the worldwide equatorial zonal electric field component reverses from the normal pattern. This is interpreted as a partial closure of high latitude field aligned currents in the dayside, low

C.A. Gonzales; M.C. Kelley; B.G. Fejer; J.F. Vickrey; R.F. Woodman

1979-01-01

364

Bubble generation during transformer overload  

SciTech Connect

Bubble generation in transformers has been demonstrated under certain overload conditions. The release of large quantities of bubbles would pose a dielectric breakdown hazard. A bubble prediction model developed under EPRI Project 1289-4 attempts to predict the bubble evolution temperature under different overload conditions. This report details a verification study undertaken to confirm the validity of the above model using coil structures subjected to overload conditions. The test variables included moisture in paper insulation, gas content in oil, and the type of oil preservation system. Two aged coils were also tested. The results indicated that the observed bubble temperatures were close to the predicted temperatures for models with low initial gas content in the oil. The predicted temperatures were significantly lower than the observed temperatures for models with high gas content. Some explanations are provided for the anomalous behavior at high gas levels in oil. It is suggested that the dissolved gas content is not a significant factor in bubble evolution. The dominant factor in bubble evolution appears to be the water vapor pressure which must reach critical levels before bubbles can be released. Further study is needed to make a meaningful revision of the bubble prediction model. 8 refs., 13 figs., 11 tabs.

Oommen, T.V. (Westinghouse ABB Power T and D Co., Sharon, PA (USA). Materials and Mfg. Technology Dept.)

1990-03-01

365

Deep, cross-equatorial eddies  

NASA Astrophysics Data System (ADS)

The question of how deep ocean eddies can cross the equator is addressed with the aid of analytical and numerical models. We focus on the possibility that deep ocean (lens-like) eddies can cross the equator via deep cross equatorial channels on the ocean floor. We first examine the behavior of solid balls (i.e., free particles) in a meridional parabolic channel on a plane. Such balls are subject to similar topographical forcing and inertial forces that a lens is subject to, except that pressure forces and friction are absent. We examine both single isolated balls and a "cloud" of (noninteractive) balls. In general, the balls' trajectories have a chaotic character; a fraction of the cloud crosses the equator and ends up in the northern hemisphere, and a fraction is left behind. More realistic numerical experiments (with a fully nonlinear reduced-gravity isopycnic model of the Bleck and Boudra type) show similar behavior. In all cases the equator acts as an "eddy smasher" in the sense that it breaks the lens into at least two parts, one crosses the equator and ends up in the northern hemisphere, and the other is left behind. Here, however, the system is not chaotic. Despite the obvious differences between clouds of balls and eddies, there is a remarkable similarity between the percentage of balls that penetrate into the opposite hemisphere and the percentage of eddies' mass that ends up in the other hemisphere. This suggests that the geometry of the channel and the presence of the equator determine how the fluid will be partitioned among the two hemispheres.

Borisov, Sergey; Nof, Doron

366

Onset conditions for equatorial spread F determined during EQUIS II  

NASA Astrophysics Data System (ADS)

An investigation into the dynamics and layer structure of the postsunset ionosphere prior to the onset of equatorial spread F (ESF) took place during the NASA EQUIS II campaign on Kwajalein Atoll on August 7 and 15, 2004. On both nights, an instrumented rocket measured plasma number density and vector electric fields to an apogee of about 450 km. Two chemical release rockets were launched both nights to measure lower thermospheric wind profiles. The Altair UHF/VHF radar was used to monitor coherent and incoherent scatter. In both experiments, strong plasma shear flow was detected. Periodic, patchy bottom-type scattering layers were observed in the westward-drifting plasma below the shear nodes. The large-scale plasma depletions that formed later during ESF reproduced the periodic structure of the original, precursor layers. The layers were therefore predictive of the ESF that followed. We surmise that collisional shear instabilities may have given rise to large-scale plasma waves that were highlighted by the bottom- type layer structure and that preconditioned the postsunset ionosphere for ESF.

Hysell, D. L.; Larsen, M. F.; Swenson, C. M.; Barjatya, A.; Wheeler, T. F.; Sarango, M. F.; Woodman, R. F.; Chau, J. L.

2005-12-01

367

Traveling ionospheric disturbances and their relations to storm-enhanced density features and plasma density irregularities in the local evening and nighttime hours of the Halloween superstorms of 29-31 October 2003  

NASA Astrophysics Data System (ADS)

This study focuses on the local evening or nighttime hours of the Halloween superstorms. Its database, containing multi-instrument Defense Meteorological Satellite Program data plus ionosonde and magnetometer data, allowed us to investigate the various plasma density features developed and the impact of traveling ionospheric disturbances (TIDs), drift perturbations, and South Atlantic Magnetic Anomaly (SAMA) effects on them. We identified the midlatitude trough, some topside bubbles, the equatorial ionization anomaly (EIA), and some storm-enhanced density (SED) features. Results reveal that these features' underlying vertical plasma flows became enhanced (degraded) when they were in the same (opposite) direction as the field-aligned flows associated with a TID. Demonstrated with some Coupled Thermosphere-Ionosphere-Plasmasphere-simulated wind vector maps, high (low) plasma densities were maintained by equatorward (poleward) winds. We observed some descending (600 m/s) bubbles with increased temperatures (4500K), due to their fast poleward movement (1.4 km/s), structuring some nearby SED features in the SAMA region and some low-latitude plasma in the Australian sector. During the second superstorm's main phase (30 October 2003), a rising bubble with increased temperatures (5000K), due to the SAMA's energetic electrons, further depleted the EIA trough. This observation contradicts a current interpretation of this depleted EIA trough as bubble. At the time of prereversal enhancement (2300 UT on 30 October), some extremely large SED features (85 104 ions+/cm3) developed (30N geomagnetic latitude) around the symmetrical EIA over Brazil. This scenario created a symmetrical plasma density profile contradicting some current speculations on the EIA's asymmetry and its southern crest's displacement to higher latitudes over Brazil. Indeed, a SED feature appeared at higher latitudes (35S geographic latitude).

Horvath, Ildiko; Lovell, Brian C.

2010-09-01

368

Shattering a micro-bubble by an expanding bubble  

NASA Astrophysics Data System (ADS)

We investigate the interaction and fragmentation of a pulsed laser induced micro-bubble B1 by another laser induced micro-bubble B2. The high pressure field associated with the expanding B2 compresses B1, associated with an axial jet on B1 through inertia dominated Richtmyer-Meshkov surface instability. The further interplay of the penetrating jet and the pressure field of the forward flow surrounding B1 induce complicated patterns in the next re-expanding stage of B1, which leads to different spherical bubbles of different sizes at the end of the third collapsing phase of B1. The backward interaction from B1 also induces backward jetting and entanglement on B2. For two symmetric bubbles generated at the same time, a thin lubrication liquid layer can be formed between the two bubbles, which can be unstable at the large laser energy. For two bubbles formed at slight phase delay at short distance, the impact of the second expansion bubble leads to the formation of multiple jets on the collapsing bubble B1.

Chen, Yen-Hung; I, Lin

2007-07-01

369

Thin filament simulations for Earth's plasma sheet: Interchange oscillations  

NASA Astrophysics Data System (ADS)

This paper presents a quantitative theory of interchange oscillations, which occur as an earthward-moving low-entropy plasma bubble slows and eventually comes to rest. Our theoretical picture is based on an idealized situation where an ideal-MHD magnetic filament moves without friction through a stationary background that represents the plasma sheet. If the relevant region of the background plasma sheet is interchange stable, then the filament usually executes a damped oscillation about an equilibrium position, where its entropy parameter matches the local background. The oscillations are typically dramatic only if the equatorial plasma beta is greater than about one. We derive an approximate analytic formula for the oscillation period, which is not simply related to slow- or intermediate-wave travel times. For an oscillation that Panov and collaborators carefully studied using THEMIS data, our simple theory, though based on an unrealistic 2D background magnetic field, predicted an oscillation period that agrees with the observations within about 40%. The simulations suggest that the ionospheric oscillation should lag behind the magnetospheric one by between 40 and 90 degrees. Ionospheric conductance affects the damping rate, which maximizes for an auroral zone conductance 2 S. Adding a friction force acting between the filament and the background increases the decay rate of the oscillation.

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

2012-02-01

370

Vortex ring modelling of toroidal bubbles  

Microsoft Academic Search

During the collapse of a bubble near a surface, a high-speed liquid jet often forms and subsequently impacts upon the opposite\\u000a bubble surface. The jet impact transforms the originally singly-connected bubble to a toroidal bubble, and generates circulation\\u000a in the flow around it. A toroidal bubble simulation is presented by introducing a vortex ring seeded inside the bubble torus\\u000a to

Q. X. Wang; K. S. Yeo; B. C. Khoo; K. Y. Lam

2005-01-01

371

New mechanism for bubble nucleation: Classical transitions  

SciTech Connect

Given a scalar field with metastable minima, bubbles nucleate quantum mechanically. When bubbles collide, energy stored in the bubble walls is converted into kinetic energy of the field. This kinetic energy can facilitate the classical nucleation of new bubbles in minima that lie below those of the 'parent' bubbles. This process is efficient and classical, and changes the dynamics and statistics of bubble formation in models with multiple vacua, relative to that derived from quantum tunneling.

Easther, Richard [Department of Physics, Yale University, New Haven, Connecticut 06520 (United States); Giblin, John T. Jr [Department of Physics, Kenyon College, Gambier, Ohio 43022 (United States); Perimeter Institute for Theoretical Physics, 31 Caroline Street N, Waterloo, ON N2L 2Y5 (Canada); Hui Lam; Lim, Eugene A. [ISCAP and Physics Department, Columbia University, New York, 10027 (United States)

2009-12-15

372

Bubble levitation and translation under single-bubble sonoluminescence conditions.  

PubMed

Bubble levitation in an acoustic standing wave is re-examined for conditions relevant to single-bubble sonoluminescence. Unlike a previous examination [Matula et al., J. Acoust. Soc. Am. 102, 1522-1527 (1997)], the stable parameter space [Pa,R0] is accounted for in this realization. Forces such as the added mass force and drag are included, and the results are compared with a simple force balance that equates the Bjerknes force to the buoyancy force. Under normal sonoluminescence conditions, the comparison is quite favorable. A more complete accounting of the forces shows that a stably levitated bubble does undergo periodic translational motion. The asymmetries associated with translational motion are hypothesized to generate instabilities in the spherical shape of the bubble. A reduction in gravity results in reduced translational motion. It is hypothesized that such conditions may lead to increased light output from sonoluminescing bubbles. PMID:12942960

Matula, Thomas J

2003-08-01

373

Magnetic Bubble Expansion as an Experimental Model for Extra-Galactic Radio Lobes  

NASA Astrophysics Data System (ADS)

The Plasma Bubble Expansion Experiment (PBEX) has begun laboratory experiments and coordinated nonlinear MHD simulations to address outstanding nonlinear plasma physics issues related to how magnetic energy and helicity carried by extra-galactic jets interacts with the intergalactic medium to form radio lobe structures. Experiments are being conducted in the 4 meter long, 50 cm diameter HELCAT linear plasma device at UNM. A pulsed magnetized coaxial gun (10 kV, 100 kA, 2 mWb) forms and injects magnetized plasma bubbles perpendicularly into a lower pressure weakly magnetized background plasma formed by a helicon and/or hot cathode source in HELCAT. Experimental parameters can be adjusted so that important dimensionless parameters are relevant to the astrophysical context. Ideal MHD simulations show that an MHD shock develops ahead of the bubble as it propagates, and that the bubble develops asymmetries due to the background field [1]. First experimental data from plasma bubble injection into a background plasma, including magnetic probe measurements and high-speed camera imaging, will be presented. [1] W. Liu et al., Phys. Plasmas 15, 072905 (2008). Supported by NSF-AST/DOE grant AST-0613577 and LANL LDRD.

Lynn, Alan; Zhang, Yue; Hsu, Scott; Li, Hui; Liu, Wei; Gilmore, Mark; Watts, Christopher

2009-05-01

374

Radiolytic Bubble Gas Hydrogen Compositions  

SciTech Connect

Radioactive waste solids can trap bubbles containing hydrogen that may pose a flammability risk if they are disturbed and hydrogen is released. Whether a release is a problem or not depends, among other things, on the hydrogen composition of the gas. This report develops a method for estimating the hydrogen composition of trapped bubbles based on waste properties.

Hester, J.R.

2003-02-05

375

Sonoporation from Jetting Cavitation Bubbles  

Microsoft Academic Search

The fluid dynamic interaction of cavitation bubbles with adherent cells on a substrate is experimentally investigated. We find that the nonspherical collapse of bubbles near to the boundary is responsible for cell detachment. High-speed photography reveals that a wall bounded flow leads to the detachment of cells. Cells at the edge of the circular area of detachment are found to

Claus-Dieter Ohl; Manish Arora; Roy Ikink; Nico de Jong; Michel Versluis; Michael Delius; Detlef Lohse

2006-01-01

376

Dynamics in reactive bubbly flow  

Microsoft Academic Search

Multiphase flow in microfluidic channels encompasses a rich collection of phenomena of widespread interest in both fundamental and technological context. While studies on non reactive multiphase flow focus on the dynamics of bubble breakup, coalescence and stability, a reactive multiphase flow opens up a broader spectrum of dynamics, like nucleation, growth and detachment of bubbles as well as the secondary

Pavithra Sundararajan; Donald Koch; Abraham Stroock

2010-01-01

377

BUBBLES A ND C RISES  

Microsoft Academic Search

In recent financial crises a bubble, in which asset prices rise, is followed by a collapse and widespread default. Bubbles are caused by agency relationships in the banking sector. Investors use money borrowed from banks to invest in risky assets, which are relatively attractive because investors can avoid losses in low payoff states by defaulting on the loan. This risk

Franklin Allen; Douglas Gale

2000-01-01

378

A bubble domain memory cell  

Microsoft Academic Search

The present conception of a 100 M bit bubble domain digital data recorder for spacecraft applications requires the storage to be compartmentalized in cells containing a group of bubble domain chips. Arranging the memory chips in cells minimizes coil size and power by requiring only a small group of chips to be driven at any given time, and also permits

P. J. Hayes; I. J. Walker

1976-01-01

379

Bubble formation via multidrop impacts  

NASA Astrophysics Data System (ADS)

Gas bubbles are often generated when droplets impact a liquid-air interface. For the impact of single droplets, a critical impact velocity must be exceeded for air to be entrained in the form of bubbles. Here we establish that bubbles can be generated at much lower velocities provided that two or more drops impact the liquid-air interface within a sufficiently short time interval. Using high-speed imaging, we show that bubbles are entrained when a drop lands in the impact crater of a previous drop. We quantify the critical crater depth formed upon impact and the necessary time interval between drop impacts for bubble entrainment to occur. For 1 mm diameter water drops falling at 1 m/s, the critical separation time is approximately 5 ms. This critical time is consistent with a scaling analysis of the time required for an impact crater to close by capillarity.

Bick, Alexander G.; Ristenpart, William D.; van Nierop, Ernst A.; Stone, Howard A.

2010-04-01

380

Bubble dynamics in N dimensions  

NASA Astrophysics Data System (ADS)

Cavitation and bubble dynamics are central concepts in engineering, the natural sciences, and the mathematics of fluid mechanics. Due to the nonlinear nature of their dynamics, the governing equations are not fully solvable. Here, the dynamics of a spherical bubble in an N-dimensional fluid are discussed in the hope that examining bubble behavior in N dimensions will add insight to their behavior in three dimensions. Several canonical results in bubble dynamics are re-derived, including the Rayleigh collapse time, the Rayleigh-Plesset equation, and the Minnaert frequency. Recent analytical approximations to the Rayleigh collapse are discussed, and the N-dimensional generalization is used to resolve a known discrepancy. Numerical simulations are used to examine the onset of nonlinear behavior. Overall, the dynamics of bubbles are faster at higher dimensions, with nonlinear behavior occurring at lower strain. Several features are found to be unique to three dimensions, including the trend of nonlinear behavior and apparent coincidences in timescales.

Klotz, Alexander R.

2013-08-01

381

Influence of bubble size on micro-bubble drag reduction  

NASA Astrophysics Data System (ADS)

Micro-bubble drag reduction experiments were conducted in a turbulent water channel flow. Compressed nitrogen was used to force flow through a slot injector located in the plate beneath the boundary layer of the tunnel test section. Gas and bubbly mixtures were injected into a turbulent boundary layer (TBL), and the resulting friction drag was measured downstream of the injector. Injection into tap water, a surfactant solution (Triton X-100, 20 ppm), and a salt-water solution (35 ppt) yielded bubbles of average diameter 476, 322 and 254 ?m, respectively. In addition, lipid stabilized gas bubbles (44 ?m) were injected into the boundary layer. Thus, bubbles with d + values of 200 to 18 were injected. The results indicate that the measured drag reduction by micro-bubbles in a TBL is related strongly to the injected gas volumetric flow rate and the static pressure in the boundary layer, but is essentially independent of the size of the micro-bubbles over the size range tested.

Shen, Xiaochun; Ceccio, Steven L.; Perlin, Marc

2006-09-01

382

Investigation of the response time of the equatorial ionosphere in context of the equatorial electrojet and equatorial ionization anomaly  

NASA Astrophysics Data System (ADS)

Equatorial Electrojet (EEJ) and Equatorial Ionization Anomaly (EIA) are two large-scale processes in the equatorial/low latitude ionosphere, driven primarily by the eastward electric field during daytime. In the present paper we investigate the correlation between the Integrated EEJ strength (IEEJ) and the EIA parameters like the total electron content at the northern crest, location of crest in Magnetic latitude and strength of the EIA for the Indian sector. A good correlation has been observed between the IEEJ and EIA when a time delay is introduced between IEEJ and EIA parameters. This time delay is regarded as the response time of equatorial ionosphere in context of the evolution of EIA vis--vis EEJ. Further, a seasonal variation in the time delay has been observed, which is believed to be due to changes in thermospheric wind. Using the response time and the linear relationship obtained, the possibility of near-real time prediction of EIA parameters has been attempted and found that the prediction holds well during the geomagnetically quiet periods. The paper discusses these aspects in detail.

Jose, L.; Ravindran, S.; Vineeth, C.; Pant, T. K.; Alex, S.

2011-07-01

383

Digital hf radar observations of equatorial spread-F  

SciTech Connect

Modern digital ionosondes, with both direction finding and doppler capabilities can provide large scale pictures of the Spread-F irregularity regions. A morphological framework has been developed that allows interpretation of the hf radar data. A large scale irregularity structure is found to be nightward of the dusk terminator, stationary in the solar reference frame. As the plasma moves through this foehn-wall-like structure it descends, and irregularities may be generated. Localized upwellings, or bubbles, may be produced, and they drift with the background plasma. The spread-F irregularity region is found to be best characterized as a partly cloudy sky, due to the patchiness of the substructures. 13 references, 16 figures.

Argo, P.E.

1984-01-01

384

Shear flow effects at the onset of equatorial spread F  

Microsoft Academic Search

Experiments were conducted during the NASA Equatorial Ionospheric Study (EQUIS) II sounding rocket campaign on Kwajalein Atoll to investigate the dynamics and stability of the postsunset equatorial F region ionosphere prior to the onset of equatorial spread F (ESF). Experiments took place on 7 and 15 August 2004, each composed of the launch of an instrumented and two chemical release

D. L. Hysell; M. F. Larsen; C. M. Swenson; T. F. Wheeler

2006-01-01

385

Check list of the Melastomataceae of Equatorial Guinea  

Microsoft Academic Search

PARMENTIER, I. & D. GEERINCK (2003). Check list of the Melastomataceae of Equatorial Gui- nea. Anales Jard. Bot. Madrid 60(2): 331-346. A chec klist of the Melastomataceae of Equatorial Guinea is presented with 57 taxa. Three species were accepted based only on literature records, their distribution area strongly suggests their presence in Equatorial Guinea. Six species are known from Annobn,

Ingrid Parmentier; Daniel Geerinck

2003-01-01

386

Three-dimensional numerical simulations of equatorial spread F: Results and observations in the Pacific sector  

NASA Astrophysics Data System (ADS)

A three-dimensional numerical simulation of plasma density irregularities in the postsunset equatorial F region ionosphere leading to equatorial spread F (ESF) is described. The simulation evolves under realistic background conditions including bottomside plasma shear flow and vertical current. It also incorporates C/NOFS satellite data which partially specify the forcing. A combination of generalized Rayleigh-Taylor instability (GRT) and collisional shear instability (CSI) produces growing waveforms with key features that agree with C/NOFS satellite and ALTAIR radar observations in the Pacific sector, including features such as gross morphology and rates of development. The transient response of CSI is consistent with the observation of bottomside waves with wavelengths close to 30 km, whereas the steady state behavior of the combined instability can account for the 100+ km wavelength waves that predominate in the F region.

Aveiro, H. C.; Hysell, D. L.; Caton, R. G.; Groves, K. M.; Klenzing, J.; Pfaff, R. F.; Stoneback, R.; Heelis, R. A.

2012-03-01

387

Regional variations of equatorial electrojet parameters  

Microsoft Academic Search

Data from the Polar Orbital Geophysical Observatory satellites in daytime at altitudes of 400-800 km spanning all longitudes of the earth included at least 70 readings of the electrojet parameters for each longitude. Daytime averages, hourly averages of the half-width, the current intensity, and the total current of the equatorial electrojet were determined for eight sectors in 45 deg longitudinal

C. A. Onwumechili; C. E. Agu

1982-01-01

388

Country Analysis Briefs: Equatorial Guinea, January 2011.  

National Technical Information Service (NTIS)

Equatorial Guinea has become a significant oil and natural gas exporter since the discovery and development of large offshore oil reserves in the 1990s. While both oil and gas production have increased significantly over the past decade, both volumes appe...

2011-01-01

389

ECOREGIONAL ASSESSMENT EQUATORIAL PACIFIC: TERRESTRIAL COMPONENT  

Microsoft Academic Search

The main objective of the Terrestrial component of this Ecoregional Assessment is to identify priority conservation sites within the terrestrial ecosystems in the Equatorial Pacific region. With this purpose, a portfolio of sites was identified, including information available for decision makers and stake-holders for natural resources, such as biodiversity, soils, vegetation cover and others. The methodology, developed by The Nature

G. Pinos

390

Equatorial Front Between Peru and Galapagos.  

National Technical Information Service (NTIS)

The equatorial front, lying between Peru and the Galapagos, is a narrow, shallow feature separating the cold, salty waters of the Peru Current from the warmer and fresher tropical waters farther north. As one passes southward into the Peru Current, the tr...

W. S. Wooster

1969-01-01

391

Fuel system bubble dissipation device  

SciTech Connect

This patent describes a bubble dissipation device for a fuel system wherein fuel is delivered through a fuel line from a fuel tank to a fuel control with the pressure of the fuel being progressively increased by components including at least one pump stage and an ejector in advance of the pump state. The ejector an ejector casing with a wall defining an elongate tubular flow passage which forms a portion of the fuel line to have all of the fuel flow through the tubular flow passage in flowing from the fuel tank to the fuel control, a nozzle positioned entirely within the tubular flow passage and spaced from the wall to permit fuel flow. The nozzle has an inlet and an outlet with the inlet connected to the pump stage to receive fuel under pressure continuously from the pump stage, a bubble accumulation chamber adjoining and at a level above the ejector casing and operatively connected to the fuel line in advance of the ejector casing. The bubble accumulation chamber is of a size to function as a fuel reservoir and hold an air bubble containing vapor above the level of fuel therein and having an outlet adjacent the bottom thereof operatively connected to the tubular flow passage in the ejector casing at an inlet end, a bubble accumulation chamber inlet above the level of the bubble accumulation chamber outlet whereby fuel can flow through the bubble accumulation chamber from the inlet to the outlet thereof with a bubble in the fuel rising above the fuel level in the bubble accumulation chamber.

Iseman, W.J.

1987-11-03

392

Equatorial scintillation model. Technical report, 1 February 1983-30 April 1985  

Microsoft Academic Search

Radiowave scintillation in the presence of natural and\\/or high-altitude nuclear disturbances has the potential to disrupt numerous transionospheric radio and radar systems. This report develops a model characterizing the plasma-density irregularities that produce scintillation in the naturally disturbed equatorial F layer. The model is incorporated into Program WBMOD along with subroutines for computing both link geometry and scintillation indices, the

E. J. Fremouw; R. E. Robins

1985-01-01

393

Ionospheric effects of the March 13, 1989, magnetic storm at low and equatorial latitudes  

Microsoft Academic Search

The great geomagnetic storm of March 13, 1989 caused severely anomalous behavior in the equatorial and low latitude ionosphere in the Brazilian longitude sector. The ionograms over Fortaleza indicated F region upward plasma drifts exceeding 200 m s⁻¹ at 1,830 LT as compared to normal values of 40 m s⁻¹ for this epoch. Large negative phases were observed in foF2

Inez S. Batista; E.R. De Paula; M. A. Abdu; N. B. Trivedi; M. E. Greenspan

1991-01-01

394

Theory of low-scale MHD waves in the near equatorial region of the Earth plasmasphere  

Microsoft Academic Search

Study of low-scale MHD waves in the inner Earth magnetosphere was performed using the standard set of ballooning mode equations obtained naturally for finite pressure plasmas in general magnetic field geometries. Flute- and ballooning-type low-scale disturbances in the near equatorial plasmasphere where they may have maximum growth rates were studied. The ballooning mode stability condition was obtained, the wave excitation

O. S. Burdo; O. K. Cheremnykh; O. P. Verkhoglyadova

2001-01-01

395

Understanding air-gun bubble behavior  

Microsoft Academic Search

An air-gun bubble behaves approximately as a spherical bubble of an ideal gas in an infinite volume of practically incompressible water. With this simplification, the equation of bubble motion and its far-field signature is more understandable than with the more exact theory commonly cited in the literature. The terms of the equation of bubble motion are explained using elementary physics

Daniel T. Johnson

1994-01-01

396

Measuring bubble distribution with multibeam sonar  

Microsoft Academic Search

Bubbles in water are very efficient scatterers of sound. Depending upon the ratio of acoustic wavelength to bubble radius, the scattering mechanism can be Rayleigh, resonant, or geometric. The strength of the scattered signal depends strongly on this ratio. The strength of the scattered signal can be used to estimate the number of bubbles per unit volume, or bubble density,

R. Lee Culver; David Bradley

2002-01-01

397

Bubble Breakup Caused by Shape Instabilities  

Microsoft Academic Search

The breakup of a bubble is the most intriguing phenomenon in the bubble dynamics to many fluid dynamics researcher. Bubble may break up due to different kinds of mechanisms. However due to the complexity of the system, no general analytical approachis available for studying this breakup phenomenon of a bubble. Hence numerical approach is taken in our current work to

Y.-H. Su; Z. C. Feng

1998-01-01

398

Bubble Growth in Lunar Basalts  

NASA Astrophysics Data System (ADS)

Although Moon is usually said to be volatile-"free", lunar basalts are often vesicular with mm-size bubbles. The vesicular nature of the lunar basalts suggests that they contained some initial gas concentration. A recent publication estimated volatile concentrations in lunar basalts (Saal et al. 2008). This report investigates bubble growth on Moon and compares with that on Earth. Under conditions relevant to lunar basalts, bubble growth in a finite melt shell (i.e., growth of multiple regularly-spaced bubbles) is calculated following Proussevitch and Sahagian (1998) and Liu and Zhang (2000). Initial H2O content of 700 ppm (Saal et al. 2008) or lower is used and the effect of other volatiles (such as carbon dioxide, halogens, and sulfur) is ignored. H2O solubility at low pressures (Liu et al. 2005), concentration-dependent diffusivity in basalt (Zhang and Stolper 1991), and lunar basalt viscosity (Murase and McBirney 1970) are used. Because lunar atmospheric pressure is essentially zero, the confining pressure on bubbles is completely supplied by the overlying magma. Due to low H2O content in lunar basaltic melt (700 ppm H2O corresponds to a saturation pressure of 75 kPa), H2O bubbles only grow in the upper 16 m of a basalt flow or lake. A depth of 20 mm corresponds to a confining pressure of 100 Pa. Hence, vesicular lunar rocks come from very shallow depth. Some findings from the modeling are as follows. (a) Due to low confining pressure as well as low viscosity, even though volatile concentration is very low, bubble growth rate is extremely high, much higher than typical bubble growth rates in terrestrial melts. Hence, mm-size bubbles in lunar basalts are not strange. (b) Because the pertinent pressures are so low, bubble pressure due to surface tension plays a main role in lunar bubble growth, contrary to terrestrial cases. (c) Time scale to reach equilibrium bubble size increases as the confining pressure increases. References: (1) Liu Y, Zhang YX (2000) Earth Planet. Sci. Lett. 181, 251. (2) Liu Y, Zhang YX, Behrens H (2005) J. Volcanol. Geotherm. Res. 143, 219. (3) Murase T, McBirney A (1970) Science 167, 1491. (4) Proussevitch AA, Sahagian DL (1998) J. Geophys. Res. 103, 18223. (5) Saal AE, Hauri EH, Cascio ML, et al. (2008) Nature 454, 192. (6) Zhang YX, Stolper EM (1991) Nature 351, 306.

Zhang, Y.

2009-05-01

399

Equatorial aeronomy - I; Proceedings of the Sixth International Symposium on Equatorial Aeronomy, Aguadilla, PR, July 17-23, 1980  

Microsoft Academic Search

Papers on equatorial aeronomy are presented, covering the following general areas: electric fields, coupling processes, neutral atmosphere, ionospheric D- and F-regions, F-region irregularities, equatorial electrojets and their irregularities, transequatorial radio propagation, and geomagnetic fields. Specific topics covered include: (1) internal structure of the equatorial ionospheric dynamo, (2) electromagnetic interactions between high and low latitudes shown by computer simulation movies, (3)

S. Matsushita; B. Balsley; H. Rishbeth

1981-01-01

400

Internal gravity waves in the equatorial Pacific  

SciTech Connect

Mixing in the ocean surface layer is an important process in the transport of heat, momentum, and CO[sub 2] into the deep ocean, For example, the flux of heat into the cold, upwelling water in equatorial regions provides one of the major heat sources driving the ocean circulation. Direct measurements of the ocean mixed layer have provided good estimates of the bulk layer properties. However, estimates of the small-scale effects of intenial waves and related turbulence have remained ambiguous because of the difficulty in observing these processes. Until more detailed measurements become available, numerical models can provide a convenient and cost-effective way to analyze the details of the surface mixed layer. Modeling the surface layer of the equatorial Pacific Ocean is challenging because of the strong vertical current shear and density stratification common to the region. The primary zonal current is the eastward flowing Equatorial Undercurrent (EUC) centered at roughly 120 m depth, with a speed of about 1.5 ms[sup [minus]1] as shown in Figure 1. The EUC is forced by a zonal pressure gradient resulting from the westward directed surface wind stress. Above the EUC, the wind stress directly forces thee South Equatorial Current (SEC), which flows westward with a speed of about 0.5 ms[sup [minus]1]. The shear zone generated by these currents is marginally stable and exhibits a diurnal cycle of turbulence dependent on convection forced by surface cooling. In addition, surface convection forces internal gravity waves, which can transport momentum away from the surface current to deeper waters. In this report, we discuss recent modeling results for the equatorial Pacific showing the generation of convection, turbulence, and internal waves.

Skyllingstad, E.D.; Denbo, D.W. (Battelle/Marine Sciences Lab., Sequim, WA (United States))

1992-09-01

401

Internal gravity waves in the equatorial Pacific  

SciTech Connect

Mixing in the ocean surface layer is an important process in the transport of heat, momentum, and CO{sub 2} into the deep ocean, For example, the flux of heat into the cold, upwelling water in equatorial regions provides one of the major heat sources driving the ocean circulation. Direct measurements of the ocean mixed layer have provided good estimates of the bulk layer properties. However, estimates of the small-scale effects of intenial waves and related turbulence have remained ambiguous because of the difficulty in observing these processes. Until more detailed measurements become available, numerical models can provide a convenient and cost-effective way to analyze the details of the surface mixed layer. Modeling the surface layer of the equatorial Pacific Ocean is challenging because of the strong vertical current shear and density stratification common to the region. The primary zonal current is the eastward flowing Equatorial Undercurrent (EUC) centered at roughly 120 m depth, with a speed of about 1.5 ms{sup {minus}1} as shown in Figure 1. The EUC is forced by a zonal pressure gradient resulting from the westward directed surface wind stress. Above the EUC, the wind stress directly forces thee South Equatorial Current (SEC), which flows westward with a speed of about 0.5 ms{sup {minus}1}. The shear zone generated by these currents is marginally stable and exhibits a diurnal cycle of turbulence dependent on convection forced by surface cooling. In addition, surface convection forces internal gravity waves, which can transport momentum away from the surface current to deeper waters. In this report, we discuss recent modeling results for the equatorial Pacific showing the generation of convection, turbulence, and internal waves.

Skyllingstad, E.D.; Denbo, D.W. [Battelle/Marine Sciences Lab., Sequim, WA (United States)

1992-09-01

402

Self-Pulsing Regime of DC Electric Discharge in Dielectric Tube Filled With Water Containing Gas Bubble  

Microsoft Academic Search

Effective generation of biochemically active species inside a liquid can be performed by an electric discharge in small gas bubbles admixed from outside into the liquid. In such a case, active species are produced by a gas discharge plasma inside bubbles and then transported due to diffusion into the liquid. This paper presents experimental data of electric discharges in small

Yuri Akishev; Michail Grushin; Vlad Karalnik; Anton Monich; Alex Petryakov; Nikolay Trushkin

2008-01-01

403

Aspherical bubble dynamics and oscillation times  

SciTech Connect

The cavitation bubbles common in laser medicine are rarely perfectly spherical and are often located near tissue boundaries, in vessels, etc., which introduce aspherical dynamics. Here, novel features of aspherical bubble dynamics are explored by time-resolved photography and numerical simulations. The growth-collapse period of cylindrical bubbles of large aspect ratio (length:diameter {approximately}20) differs only slightly from twice the Rayleigh collapse time for a spherical bubble with an equivalent maximum volume. This fact justifies using the temporal interval between the acoustic signals emitted upon bubble creation and collapse to estimate the maximum bubble volume. As a result, hydrophone measurements can provide an estimate of the bubble size and energy even for aspherical bubbles. The change of the oscillation period of bubbles near solid walls and elastic (tissue-like) boundaries relative to that of isolated spherical bubbles is also investigated.

Vogel, A.; Noack, J. [Meizinisches Laserzentrum Luebeck (Germany); Chapyak, E.J.; Godwin, R.P. [Los Alamos National Lab., NM (United States)

1999-06-01

404

Vertical and meridional equatorial ion flows observed by CINDI during the 26 September 2011 storm  

NASA Astrophysics Data System (ADS)

equatorial ionosphere is generally shielded from outside electrical fields except during large geomagnetic storms. During these storms, the polar region electric fields can temporarily extend to the equatorial regions in what is called a penetration field. During the subsequent recovery period, a disturbance dynamo is produced with an enhanced electric field with the opposite orientation relative to the penetration field. The penetration electric field would be oriented toward the east on the dayside causing an excess upward E B motion of the equatorial ionospheric ions. The disturbance dynamo electric field would have the opposite orientation, westward on the dayside, producing an excess downward E B motion of the equatorial ionospheric ions. The moderate storm (minimum Dst = -103 nT) on 26 September 2011 is examined using ion flow data from the Coupled Ion-Neutral Dynamics Investigation (CINDI) thermal plasma instrument package on the Communication/Navigation Outage Forecast System (C/NOFS) spacecraft on the dayside and early evening local times to look for examples of these flows. Despite what should have been a large enough storm to produce penetration fields and upward flows, a detailed examination of the observed flows from this storm shows only enhanced downward flows before the storm, during the main phase, and through the recovery.

Hairston, Marc R.; Coley, W. Robin; Stoneback, Russell

2013-08-01

405

Observations and model calculations of the F3 layer in the Southeast Asian equatorial ionosphere  

NASA Astrophysics Data System (ADS)

To clarify the characteristics of the F3 layer with a focus on magnetic latitude dependence and the relationship to the equatorial anomaly, we performed statistical analysis of F3 layer occurrences using the ionosonde chain data in a magnetic meridional plane in Southeast Asia and performed model calculations. From comparison of the observational and model calculation results, it was found that the field-aligned diffusion of plasma acts to make the F3 layer prominent in the magnetic low-latitude region while acting to decrease the peak density of the F3 layer near the magnetic equator. The magnetic latitude dependence of the F3 layer formation comes not only from the meridional neutral wind effect but also from the field-aligned diffusion effect. The model calculations revealed that the F3 peak corresponds to the electron density-enhanced region associated with the equatorial anomaly. This relationship is consistent with the suggestion that the field-aligned diffusion acts to make the F3 layer prominent in the magnetic low-latitude region since the fundamental factors for generation of the equatorial anomaly are also E B drift and field-aligned downward diffusion. It is suggested that the local time and magnetic latitudinal variations of the F3 layer result from those of the electron density-enhanced region associated with the equatorial anomaly.

Uemoto, Jyunpei; Maruyama, Takashi; Ono, Takayuki; Saito, Susumu; Iizima, Masahide; Kumamoto, Atsushi

2011-03-01

406

Vapor Bubble Nucleation: A Microscopic Phenomenon  

Microsoft Academic Search

In this article, vapor bubble nucleation in liquid and the evaporation process of a liquid droplet at its superheat limit\\u000a were discussed from the viewpoint of molecular clustering (molecular cluster model for bubble nucleation). For the vapor bubble\\u000a formation, the energy barrier against bubble nucleation was estimated by the molecular interaction due to the London dispersion\\u000a force. Bubble nucleation by

Ho-Young Kwak

2004-01-01

407

Nonclassical Thermomigration of an Air Bubble  

NASA Astrophysics Data System (ADS)

We study air bubbles confined in capillaries with a temperature gradient. Classically, air bubbles move in a temperature gradient due to decreased surface tension at higher temperatures, creating a net surface traction towards the cold pole, pushing the bubble towards the hot pole for mass conservation. Here we report non-classical thermo-migration of confined air bubbles: in the presence of surfactant the bubbles can go the other way.

Michler, Dominik; Sprik, Rudolf; Schall, Peter; Bonn, Daniel

2012-02-01

408

Magnetic Bubble Traveling Wave Tube.  

National Technical Information Service (NTIS)

A device is disclosed for amplifying electromagnetic waves propagating along a meander line slow wave structure by means of magnetic cylindrical domains or bubbles which are propagating at substantially the same velocity as the RF wave in an adjacent plat...

L. J. Jasper

1978-01-01

409

SKAT Bubble Chamber Film Processing.  

National Technical Information Service (NTIS)

The technique of SKAT bubble chamber photographic image processing is briefly described. On the base of the technique 125000 images were processed in neutrino-seances and 182000 images in antineutrino seances. The analysis of geometric reconstruction of t...

D. S. Baranov L. L. Zakamskij A. A. Ivanilov

1984-01-01

410

Nambu bubbles with curvature corrections  

SciTech Connect

A finite-width correction for a two-dimensional membrane described by the Nambu action modified by the addition of the Ricci curvature scalar is studied. The particular case of a spherical bubble is considered in some detail.

Letelier, P.S. (Departamento de Matematica Aplicada, IMECC, Universidade Estadual de Campinas, 13 100 Campinas, Sao Paulo, Brazil (BR))

1990-02-15

411

Transient bubbles, bublets and breakup  

NASA Astrophysics Data System (ADS)

The non-spherical nature of the collapse of bubbles has important ramifications in many practical situations such as ultrasonic cleaning, tanning of leather, and underwater explosions. In particular the high speed liquid jet that can thread a collapsing bubble is central to the functional performance. An impressive photographic record of a liquid jet was obtained by Crum using a bubble situated in the vicinity of a platform oscillating vertically at a frequency of 60 Hz. A boundary integral method is used to model this situation and is found to closely mimic some of the observations. However, a slight variation of parameters or a change in the phase of the driving frequency can lead to dramatically different bubble behaviour, a feature also observed by Crum.

Keen, Giles; Blake, John

1999-11-01

412

Snapping shrimp make flashing bubbles.  

PubMed

Snapping shrimp produce a loud crackling noise that is intense enough to disturb underwater communication. This sound originates from the violent collapse of a large cavitation bubble generated under the tensile forces of a high-velocity water jet formed when the shrimp's snapper-claw snaps shut (Fig. 1). Here we show that a short, intense flash of light is emitted as the bubble collapses, indicating that extreme pressures and temperatures of at least 5,000 K (ref. 4) must exist inside the bubble at the point of collapse. We have dubbed this phenomenon 'shrimpoluminescence' - the first observation, to our knowledge, of this mode of light production in any animal - because of its apparent similarity to sonoluminescence, the light emission from a bubble periodically driven by ultrasound. PMID:11586346

Lohse, D; Schmitz, B; Versluis, M

2001-10-01

413

Magnetic bubble memory chip design  

Microsoft Academic Search

The choice and organization of bubble-circuit functions in the design of a magnetic bubble mass memory chip are discussed with emphasis on factors such as circuit function compatibility and performance, circuit density, and processing simplicity. A specific major-minor organized chip design is described which uses rotating field driven propagation, $-sign transfer gates, all T-bar minor loops, a nucleate generator with

PETER I. BONYHARD; J. E. GEUSIC; ANDREW H. BOBECK; Yu-Ssu Chen; PAUL C. MICHAELIS; JAMES L. SMITH

1973-01-01

414

Evolution of a Collection of Bubbles with Application to Wakes, Bubble Screens, and Cloud Noise.  

National Technical Information Service (NTIS)

Contents: Bubble Dynamics and Cavitation Inception in Non-Uniform Flow Fields; Bubble Interactions with Vortices; Cavitation Dynamics at Microscale Level; Viscous Interaction Between Bubble and Line Vortex; The Motion of a Spherical Body Below a Free Surf...

G. L. Chahine

1994-01-01

415

Holographic Description of Vacuum Bubbles  

NASA Astrophysics Data System (ADS)

We discuss a holographic description of vacuum bubbles, with possible implications for a consistent description of the multiverse. In particular, we elaborate on the recent observation by Maldacena, that the interior of AdS bubbles can be described in terms of CFT degrees of freedom living on the worldsheet of the bubble wall. We consider the scattering of bulk gravitons in the ambient parent vacuum, off the bubble wall. In the dual description, the transmission coefficient is interpreted as the probability that a graviton is absorbed by the worldsheet CFT degrees of freedom. The result is in agreement with intuitive expectations. Conformal invariance is not exact in this setup, and the leading corrections due to the IR and UV cut-offs are displayed. Aside from bulk scattering states, we find that when a bubble nucleates within a parent dS vacuum, there is a zero mode of the graviton which describes lower dimensional gravity with a finite Newton's constant. This massless graviton lives within one Hubble radius away from the bubble wall. Possible implications for a fully holographic description of the inflating multiverse are briefly discussed.

Garriga, J.

416

Lithospheric Flexural Modeling of Iapetus' Equatorial Ridge  

NASA Astrophysics Data System (ADS)

Iapetus, which is one of Saturn's ball-shaped satellites, has some unique features in the Solar System. This satellite has a mean radius of 735 km, and there is an approximately 20-kilometer-high mountain lying precisely on its equator. The mountain is known as an "equatorial ridge" since it makes Iapetus appear walnut shaped. The origin of the equatorial ridge is attributed to several hypotheses, including different endogenesis and exogenesis processes. In this work, we attempted to construct a flexural model of the equatorial ridge using elastic lithosphere theory. The equatorial ridge is treated as a linear load which exerts uniform force on Iapetus' hard shell (i.e. elastic lithosphere of Iapetus). To calculate the deflection of surface, we use the Digital Terrain Model (DTM) data of Iapetus' leading side published by Giese et al. (2008). Giese et al. also pointed out that the elastic lithospheric thickness of Iapetus must exceed 100 km to support the ridge without deflecting. However, we found possible evidence in the DTM data that implied deflection. There are two sites of surface depression on the northern side of the equatorial ridge. The few-kilometer deflection implies a thinner lithosphere than previous suggested. Assume that the thickness of elastic lithosphere is only 5% below of the radius of Iapetus, so the flat-Earth and one-plate condition could adapt to the flexure model of Iapetus. Based on analysis of the distance between a bulge and the ridge, the calculated lithospheric thickness is 6-10 km. The new result seems controversial, but the modeled surface profile is highly consistent with numerical ridge DTM profile extracted from Giese et al. (2008). Thinner lithosphere also supports the contraction model proposed by Sandwell and Schubert (2010) since the bucking harmonic degree increases. In the other hand, the transformation layer between hard shell and plastic inner core may need constraint on thermal history or crystal form of ice. In conclusion, The flexural model of Iapetus' equatorial ridge reveals the possibility of thinner hard shell, fits the surface profile, and supplies more clues to the origin of Iapetus, the interesting satellite in the Solar System.

Zheng, W.; Ip, W.-H.; Teng, L. S.

2012-04-01

417

Aerosols in equatorial Atlantic air - n-alkanes as a function of particle size  

NASA Astrophysics Data System (ADS)

The concentrations and distributions of n-alkanes in the western equatorial Atlantic, Gulf of Guinea region were determined by aerosol sampling and calculated in terms of particle size. Data were gathered in the period May-June 1977 by means of a five stage cascade impactor for large air volumes mounted on the bow of a boat. The collected gases were separated into six particle size fractions, and n-alkanes were identified by means of gas chromatography. Concentrations were found to vary from 6-13 ng/cu m, which contributes to previous findings that the tropical Atlantic has higher aerosol carbon concentrations than the tropical north Pacific Ocean. The major part of the observed aerosol mass was determined to reside in particles less than 1 micron across. It is concluded that the particles are expelled from the sea in bubbles which burst in the air.

Marty, J.-C.; Saliot, A.

1982-07-01

418

Quantitative ultrasound method to detect and monitor laser-induced cavitation bubbles.  

PubMed

An ultrasound technique to measure the spatial and temporal behavior of the laser-induced cavitation bubble is introduced. The cavitation bubbles were formed in water and in gels using a nanosecond pulsed Nd:YAG laser operating at 532 nm. A focused, single-element, 25-MHz ultrasound transducer was employed both to detect the acoustic emission generated by plasma expansion and to acoustically probe the bubble at different stages of its evolution. The arrival time of the passive acoustic emission was used to estimate the location of the cavitation bubble's origin and the time of flight of the ultrasound pulse-echo signal was used to define its spatial extent. The results of ultrasound estimations of the bubble size were compared and found to be in agreement with both the direct optical measurements of the stationary bubble and the theoretical estimates of bubble dynamics derived from the well-known Rayleigh model of a cavity collapse. The results of this study indicate that the proposed quantitative ultrasound technique, capable of detecting and accurately measuring laser-induced cavitation bubbles in water and in a tissue-like medium, could be used in various biomedical and clinical applications. PMID:18601556

Karpiouk, Andrei B; Aglyamov, Salavat R; Bourgeois, Frederic; Ben-Yakar, Adela; Emelianov, Stanislav Y

419

Regional variations of equatorial electrojet parameters  

NASA Astrophysics Data System (ADS)

Data from the Polar Orbital Geophysical Observatory satellites in daytime at altitudes of 400-800 km spanning all longitudes of the earth included at least 70 readings of the electrojet parameters for each longitude. Daytime averages, hourly averages of the half-width, the current intensity, and the total current of the equatorial electrojet were determined for eight sectors in 45 deg longitudinal increments. The total current value was found to agree well with ground station data. The sectorial mean half width values of the equatorial electrojet remained close to the mean value at 234 km, with an s.d. of 6 km. Peak current intensity regions were found at 45-90 deg and 270-315 deg at 1100, 1400, and 1500 L.T. The lowest current intensity occurred at 135-180 deg.

Onwumechili, C. A.; Agu, C. E.

1982-09-01

420

Optimal time reversal of multiphase equatorial states  

SciTech Connect

Even though the time reversal is unphysical (it corresponds to the complex conjugation of the density matrix), for some restricted set of states it can be achieved unitarily, typically when there is a common dephasing in a n-level system. However, in the presence of multiple phases (i.e., a different dephasing for each element of an orthogonal basis occurs) the time reversal is no longer physically possible. In this paper we derive the channel which optimally approaches in fidelity the time reversal of multiphase equatorial states in arbitrary (finite) dimension. We show that, in contrast to the customary case of the universal-NOT on qubits (or the universal conjugation in arbitrary dimension), the optimal phase covariant time reversal for equatorial states is a nonclassical channel, which cannot be achieved via a measurement-and-preparation procedure. Unitary realizations of the optimal time reversal channel are given with minimal ancillary dimension, exploiting the simplex structure of the optimal maps.

Buscemi, Francesco; D'Ariano, Giacomo Mauro; Macchiavello, Chiara [QUIT Group, Dipartimento di Fisica 'A. Volta', Universita di Pavia, via Bassi 6, I-27100 Pavia (Italy)

2005-12-15