scholarly journals Excitation of transient lobe cell convection and auroral arc at the cusp poleward boundary during a transition of the interplanetary magnetic field from south to north

2001 ◽  
Vol 19 (5) ◽  
pp. 487-493 ◽  
Author(s):  
P. E. Sandholt ◽  
C. J. Farrugia ◽  
S. W. H. Cowley ◽  
M. Lester ◽  
J.-C. Cerisier
Keyword(s):  
Magnetic Field ◽  
Interplanetary Magnetic Field ◽  
Large Scale ◽  
Intermediate Phase ◽  
Bright Spot ◽  
Convection Cell ◽  
Plasma Convection ◽  
Cell Pattern ◽  
Auroral Phenomena ◽  
Lobe Reconnection

Abstract. We document the activation of transient polar arcs emanating from the cusp within a 15 min long intermediate phase during the transition from a standard two-cell convection pattern, representative of a strongly southward interplanetary magnetic field (IMF), to a "reverse" two-cell pattern, representative of strongly northward IMF conditions. During the 2–3 min lifetime of the arc, its base in the cusp, appearing as a bright spot, moved eastward toward noon by ~ 300 km. As the arc moved, it left in its "wake" enhanced cusp precipitation. The polar arc is a tracer of the activation of a lobe convection cell with clockwise vorticity, intruding into the previously established large-scale distorted two-cell pattern, due to an episode of localized lobe reconnection. The lobe cell gives rise to strong flow shear (converging electric field) and an associated sheet of outflowing field-aligned current, which is manifested by the polar arc. The enhanced cusp precipitation represents, in our view, the ionospheric footprint of the lobe reconnection process.Key words. Magnetospheric physics (auroral phenomena; magnetopause, cusp, and boundary layers; plasma convection)

scholarly journals Interplanetary magnetic field control of Saturn's polar cusp aurora

2005 ◽  
Vol 23 (4) ◽  
pp. 1405-1431 ◽  
Author(s):  
E. J. Bunce ◽  
S. W. H. Cowley ◽  
S. E. Milan
Keyword(s):  
Magnetic Field ◽  
Solar Wind ◽  
Interplanetary Magnetic Field ◽  
Field Line ◽  
High Latitude ◽  
Closed Field ◽  
Vortical Flows ◽  
Dayside Magnetopause ◽  
Closed Field Line ◽  
Lobe Reconnection

Abstract. Dayside UV emissions in Saturn's polar ionosphere have been suggested to be the first observational evidence of the kronian "cusp" (Gérard et al., 2004). The emission has two distinct states. The first is a bright arc-like feature located in the pre-noon sector, and the second is a more diffuse "spot" of aurora which lies poleward of the general location of the main auroral oval, which may be related to different upstream interplanetary magnetic field (IMF) orientations. Here we take up the suggestion that these emissions correspond to the cusp. However, direct precipitation of electrons in the cusp regions is not capable of producing significant UV aurora. We have therefore investigated the possibility that the observed UV emissions are associated with reconnection occurring at the dayside magnetopause, possibly pulsed, akin to flux transfer events seen at the Earth. We devise a conceptual model of pulsed reconnection at the low-latitude dayside magnetopause for the case of northwards IMF which will give rise to pulsed twin-vortical flows in the magnetosphere and ionosphere in the vicinity of the open-closed field-line boundary, and hence to bi-polar field-aligned currents centred in the vortical flows. During intervals of high-latitude lobe reconnection for southward IMF, we also expect to have pulsed twin-vortical flows and corresponding bi-polar field-aligned currents. The vortical flows in this case, however, are displaced poleward of the open-closed field line boundary, and are reversed in sense, such that the field-aligned currents are also reversed. For both cases of northward and southward IMF we have also for the first time included the effects associated with the IMF By effect. We also include the modulation introduced by the structured nature of the solar wind and IMF at Saturn's orbit by developing "slow" and "fast" flow models corresponding to intermediate and high strength IMF respectively. We then consider the conditions under which the plasma populations appropriate to either sub-solar reconnection or high-latitude lobe reconnection can carry the currents indicated. We have estimated the field-aligned voltages required, the resulting precipitating particle energy fluxes, and the consequent auroral output. Overall our model of pulsed reconnection under conditions of northwards and southwards IMF, and for varying orientations of IMF By, is found to produce a range of UV emission intensities and geometries which is in good agreement with the data presented by Gérard et al. (2004). The recent HST-Cassini solar wind campaign provides a unique opportunity to test the theoretical ideas presented here.

scholarly journals Central polar cap convection response to short duration southward Interplanetary Magnetic Field

2000 ◽  
Vol 18 (8) ◽  
pp. 887-896 ◽  
Author(s):  
P. T. Jayachandran ◽  
J. W. MacDougall
Keyword(s):  
Magnetic Field ◽  
Interplanetary Magnetic Field ◽  
Short Duration ◽  
Initial Response ◽  
Plasma Convection ◽  
Polar Cap ◽  
Ionosphere Plasma ◽  
Rapid Transition ◽  
Convection Speed ◽  
A Chain

Abstract. Central polar cap convection changes associated with southward turnings of the Interplanetary Magnetic Field (IMF) are studied using a chain of Canadian Advanced Digital Ionosondes (CADI) in the northern polar cap. A study of 32 short duration (~1 h) southward IMF transition events found a three stage response: (1) initial response to a southward transition is near simultaneous for the entire polar cap; (2) the peak of the convection speed (attributed to the maximum merging electric field) propagates poleward from the ionospheric footprint of the merging region; and (3) if the change in IMF is rapid enough, then a step in convection appears to start at the cusp and then propagates antisunward over the polar cap with the velocity of the maximum convection. On the nightside, a substorm onset is observed at about the time when the step increase in convection (associated with the rapid transition of IMF) arrives at the polar cap boundary.Key words: Ionosphere (plasma convection; polar ionosphere) - Magnetospheric physics (solar wind - magnetosphere interaction)

scholarly journals Plasma convection in the magnetotail lobes: statistical results from Cluster EDI measurements

2008 ◽  
Vol 26 (8) ◽  
pp. 2371-2382 ◽  
Author(s):  
S. Haaland ◽  
G. Paschmann ◽  
M. Förster ◽  
J. Quinn ◽  
R. Torbert ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Interplanetary Magnetic Field ◽  
Geomagnetic Disturbance ◽  
Plasma Convection ◽  
Data Set ◽  
Central Plasma ◽  
Strong Convection ◽  
Central Plasma Sheet ◽  
Field Lines ◽  
Convection Patterns

Abstract. A major part of the plasma in the Earth's magnetotail is populated through transport of plasma from the solar wind via the magnetotail lobes. In this paper, we present a statistical study of plasma convection in the lobes for different directions of the interplanetary magnetic field and for different geomagnetic disturbance levels. The data set used in this study consists of roughly 340 000 one-minute vector measurements of the plasma convection from the Cluster Electron Drift Instrument (EDI) obtained during the period February 2001 to June 2007. The results show that both convection magnitude and direction are largely controlled by the interplanetary magnetic field (IMF). For a southward IMF, there is a strong convection towards the central plasma sheet with convection velocities around 10 km s−1. During periods of northward IMF, the lobe convection is almost stagnant. A By dominated IMF causes a rotation of the convection patterns in the tail with an oppositely directed dawn-dusk component of the convection for the northern and southern lobe. Our results also show that there is an overall persistent duskward component, which is most likely a result of conductivity gradients in the footpoints of the magnetic field lines in the ionosphere.

About the Relation Between the Limb Effect of the Redshift on the Sun and the Large-Scale Distribution of Solar activity

1976 ◽  
Vol 71 ◽  
pp. 113-118
Author(s):  
P. Ambrož
Keyword(s):  
Magnetic Field ◽  
Solar Activity ◽  
Magnetic Fields ◽  
Interplanetary Magnetic Field ◽  
Large Scale ◽  
The Sun ◽  
Limb Effect

The measurement of the magnitude of the limb effect was homogenized in time and a recurrent period of maxima of 27.8 days was found. A relation was found between the maximum values of the limb effect of the redshift, the boundaries of polarities of the interplanetary magnetic field, the characteristic large-scale distribution of the background magnetic fields and the complex of solar activity.

scholarly journals O<sup>+</sup> transport in the dayside magnetosheath and its dependence on the IMF direction

2015 ◽  
Vol 33 (3) ◽  
pp. 301-307 ◽  
Author(s):  
R. Slapak ◽  
H. Nilsson ◽  
L. G. Westerberg ◽  
R. Larsson
Keyword(s):  
Magnetic Field ◽  
Interplanetary Magnetic Field ◽  
Ion Flux ◽  
Opposite Hemisphere ◽  
Oxygen Ions ◽  
Upper Limit ◽  
Field Lines ◽  
Lobe Reconnection ◽  
Open Magnetic Field ◽  
The Imf

Abstract. Recent studies have shown that the escape of oxygen ions (O+) into the magnetosheath along open magnetic field lines from the terrestrial cusp and mantle is significant. We present a study of how O+ transport in the dayside magnetosheath depends on the interplanetary magnetic field (IMF) direction. There are clear asymmetries in the O+ flows for southward and northward IMF. The asymmetries can be understood in terms of the different magnetic topologies that arise due to differences in the location of the reconnection site, which depends on the IMF direction. During southward IMF, most of the observed magnetosheath O+ is transported downstream. In contrast, for northward IMF we observe O+ flowing both downstream and equatorward towards the opposite hemisphere. We observe evidence of dual-lobe reconnection occasionally taking place during strong northward IMF conditions, a mechanism that may trap O+ and bring it back into the magnetosphere. Its effect on the overall escape is however small: we estimate the upper limit of trapped O+ to be 5%, a small number considering that ion flux calculations are rough estimates. The total O+ escape flux is higher by about a factor of 2 during times of southward IMF, in agreement with earlier studies of O+ cusp outflow.

Sign in / Sign up

Export Citation Format

Share Document