Polar Cap O + Ion Outflow and Its Impact on Magnetospheric Dynamics

2021 ◽  
pp. 83-114
Author(s):  
Binzheng Zhang ◽  
Oliver J. Brambles
Keyword(s):  
Polar Cap ◽  
Ion Outflow ◽  
Magnetospheric Dynamics

Nightside auroral zone and polar cap ion outflow as a function of substorm size and phase

2004 ◽  
Vol 109 (A2) ◽  
Author(s):  
G. R. Wilson ◽  
D. M. Ober ◽  
G. A. Germany ◽  
E. J. Lund
Keyword(s):  
Auroral Zone ◽  
Polar Cap ◽  
Ion Outflow

scholarly journals Storm-time related mass density anomalies in the polar cap as observed by CHAMP

2010 ◽  
Vol 28 (1) ◽  
pp. 165-180 ◽  
Author(s):  
R. Liu ◽  
H. Lühr ◽  
S.-Y. Ma
Keyword(s):  
Magnetic Field ◽  
Geomagnetic Storms ◽  
Mass Density ◽  
Small Scale ◽  
Polar Cap ◽  
Ion Outflow ◽  
The North ◽  
Scale Field ◽  
Density Enhancement ◽  
The Magnetic Field

Abstract. Strong and localized thermospheric mass density events are observed in the polar cap region by the CHAMP satellites at about 400 km altitude during geomagnetic storms. During the 4 years considered (2002–2005) 29 storms with Dst<−100 nT occurred, in 90% of them polar cap density anomalies were detected. Based on the altogether 56 anomaly events a statistical analysis was performed. The anomalies are of medium scale (500–1500 km) and seem to have a short dwell-time (<1.5 h) in the polar cap. The relative density enhancement is found to range around 2 in both hemispheres. The peak density is in the Northern Hemisphere by a factor of 1.4 larger than in the southern. Also the number of detected events in the north is twice as large as that in the south (37 vs. 19). Mass density anomalies in the polar cap occur under all interplanetary magnetic field (IMF) directions. Numerous strong anomalies have been detected in positive and negative IMF Bz conditions when the magnetic field strength is above 5 nT. Rather few events occurred for small |Bz| (<5 nT) or for positive Bz combined with vanishing By. Some of the density anomalies are accompanied by intensive small-scale field-aligned currents (FACs). But about as many show no relation to FACs. If FACs are present there, the current density is believed to be correlated with the strength of the IMF Bz. Although this paper concentrates on the presentation of the observations, we show for one event that the ion outflow mechanism could be responsible for the mass density anomalies in the polar cap.

scholarly journals Solar wind influence on the oxygen content of ion outflow in the high-altitude polar cap during solar minimum conditions

2001 ◽  
Vol 106 (A4) ◽  
pp. 6067-6084 ◽  
Author(s):  
H. A. Elliott ◽  
R. H. Comfort ◽  
P. D. Craven ◽  
M. O. Chandler ◽  
T. E. Moore
Keyword(s):  
Solar Wind ◽  
High Altitude ◽  
Oxygen Content ◽  
Solar Minimum ◽  
Polar Cap ◽  
Ion Outflow ◽  
Wind Influence

scholarly journals Observational Consequences of Polar Cap Theories

1981 ◽  
Vol 95 ◽  
pp. 99-102
Author(s):  
Andrew F. Cheng
Keyword(s):  
Magnetic Field ◽  
Temporal Modulation ◽  
Polar Cap ◽  
Ion Outflow ◽  
X Ray ◽  
Surface Magnetic Field ◽  
Polar Caps ◽  
Temperature Oscillations ◽  
Field Lines ◽  
Positive Ion

Possible observational consequences are outlined for pulsar models with positive ion outflow at the polar caps together with e+-e− pair production discharge there. A characteristic thermal x-ray luminosity is maintained by discharge heating in regions of positive current outflow. A decrease in polar cap thermal x-ray emission may occur during radio nulls. Two mechanisms are identified which can yield temporal modulation of the outflowing ion and e+-e− plasmas, and which may lead to modulation of coherent radio emission on observed microstructure timescales. These are: (1) polar cap temperature oscillations which occur preferentially in pulsars of low surface magnetic field, and (2) the tendency of sparks to migrate toward the convex side of the magnetic field lines.

scholarly journals Transients in oxygen outflow above the polar cap as observed by the Cluster spacecraft

2008 ◽  
Vol 26 (11) ◽  
pp. 3365-3373 ◽  
Author(s):  
H. Nilsson ◽  
M. Waara ◽  
O. Marghitu ◽  
M. Yamauchi ◽  
R. Lundin ◽  
...  
Keyword(s):  
High Altitude ◽  
Time Scale ◽  
Ion Beams ◽  
Limiting Factor ◽  
Time Interval ◽  
Polar Cap ◽  
Ion Outflow ◽  
Oxygen Ion ◽  
Typical Time ◽  
Temporal Structures

Abstract. Oxygen ion outflow associated with the cusp and cleft give rise to persistent oxygen ion beams which can be observed over the polar cap. For high altitude spacecraft such as Cluster these beams are often observed for several hours on each occasion. This allows for a study of typical temporal structures on the time scale of minutes. We have used 3 years of data from spring, January to May of years 2001 to 2003, for a study of the oxygen number flux variation in the polar cap ion outflow. The source of these oxygen ion beams is the cusp and cleft, and variations in ionospheric upflow on time scales of around 8 min have been reported from ground based studies using incoherent scatter radar. Such upflows typically do not reach escape velocity, and further energization above the ionosphere is required for outflow to occur. Our study shows that a typical time scale between sudden number flux enhancements observed by Cluster in a geocentric distance range of 5 RE to 12 RE is 5 to 10 min. A superposed epoch study does not reveal any significant convection velocity or temperature changes around the flux enhancement events. Sudden temperature enhancements occur with a typical time interval of about 4 min, A superposed epoch study does not reveal any number flux enhancements associated with the temperature enhancements. The clear modulation of the high altitude number flux in a manner which resembles the modulation of the ionospheric upflow indicates that this is the main limiting factor determining the total outflow. The process behind transient upflow events in the ionosphere is therefore important for the total ionospheric outflow. Subsequent heating above the ionosphere appears to be common enough in the cusp/cleft region that it does not significantly modulate the oxygen ion number flux.

scholarly journals DE-1 versus Cluster spectral density observations: the effect on ion outflow above the polar cap

2015 ◽  
Vol 58 (5) ◽  
Author(s):  
Hamza A. Abudayyeh ◽  
Imad A. Barghouthi ◽  
Ghadeer Al-Sarsour ◽  
Husain Alsamamra
Keyword(s):  
Spectral Density ◽  
Diffusion Coefficients ◽  
Particle Interaction ◽  
Particle Interactions ◽  
High Altitudes ◽  
Polar Cap ◽  
Ion Outflow ◽  
Density Measurements ◽  
Velocity Diffusion

<p>Wave-particle interaction is a very important mechanism in describing the outflow of ions at high latitudes and high altitudes. Quasi-linear perpendicular velocity diffusion coefficients are used to describe the effect of wave-particle interactions, therefore it is essential to determine the correct diffusion coefficients that must be used to model the outflow of ions. In this study a Monte Carlo method is used to assess the role of different diffusion coefficients for O+ and H+ ions at high altitudes above the polar cap. Two different sets of diffusion coefficients obtained from Barghouthi [1997]; Barghouthi et al. [1998] and Nilsson et al. [2013] are used. Barghouthi [1997]; Barghouthi et al. [1998] used spectral density measurements from Dynamic Explorer 1 spacecraft (DE-1) observations to calculate the diffusion coefficients, while Nilsson et al. [2013] used spectral density measurements from the Cluster spacecraft to obtain the diffusion coefficients. It was found that diffusion coefficients from Barghouthi [1997]; Barghouthi et al. [1998] in the cusp (aurora) and central polar cap (polar wind) respectively, describe well the observations of ion outflow at altitudes lower than 5 RE, but yield unreasonably high parallel velocities and temperatures at higher altitudes. Also diffusion coefficients from Cluster spectral density measurements produce reasonable results for high altitudes and unreasonably low parallel velocities and temperatures for the low altitude region. Therefore it is suggested that a combination of these diffusion coefficients is used where the diffusion coefficients given by Barghouthi [1997]; Barghouthi et al. [1998] are used at low altitudes and the diffusion coefficients obtained from Cluster measurements are used at high altitudes.</p>

scholarly journals Seasonal and hemispheric asymmetries in the cold ion outflow source region: Swarm and CHAMP observations of F-region polar cap plasma density

2020 ◽  
Author(s):  
Spencer Mark Hatch ◽  
Stein Haaland ◽  
Karl M. Laundal ◽  
Therese Moretto Jorgensen ◽  
Andrew Yau ◽  
...  
Keyword(s):  
Plasma Density ◽  
Source Region ◽  
Polar Cap ◽  
Hemispheric Asymmetries ◽  
Ion Outflow ◽  
F Region

scholarly journals Seasonal and hemispheric asymmetries in the cold ion outflow source region: Swarm and CHAMP observations of F-region polar cap plasma density

2020 ◽  
Author(s):  
Spencer Mark Hatch ◽  
Stein Haaland ◽  
Karl M. Laundal ◽  
Therese Moretto Jorgensen ◽  
Andrew Yau ◽  
...  
Keyword(s):  
Plasma Density ◽  
Source Region ◽  
Polar Cap ◽  
Hemispheric Asymmetries ◽  
Ion Outflow ◽  
F Region

A large rotating structure around AB Doradus A at VLBI scale

2019 ◽  
Vol 15 (S354) ◽  
pp. 189-194
Author(s):  
J. B. Climent ◽  
J. C. Guirado ◽  
R. Azulay ◽  
J. M. Marcaide
Keyword(s):  
Magnetic Reconnection ◽  
Main Sequence ◽  
Complex Structure ◽  
Main Sequence Star ◽  
Polar Cap ◽  
Vlbi Observations ◽  
Rotating Structure ◽  
Source Structure ◽  
Expected Position

AbstractWe report the results of three VLBI observations of the pre-main-sequence star AB Doradus A at 8.4 GHz. With almost three years between consecutive observations, we found a complex structure at the expected position of this star for all epochs. Maps at epochs 2007 and 2010 show a double core-halo morphology while the 2013 map reveals three emission peaks with separations between 5 and 18 stellar radii. Furthermore, all maps show a clear variation of the source structure within the observing time. We consider a number of hypothesis in order to explain such observations, mainly: magnetic reconnection in loops on the polar cap, a more general loop scenario and a close companion to AB Dor A.

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