scholarly journals Detailed dayside auroral morphology as a function of local time for southeast IMF orientation: implications for solar wind-magnetosphere coupling

2004 ◽  
Vol 22 (10) ◽  
pp. 3537-3560 ◽  
Author(s):  
P. E. Sandholt ◽  
C. J. Farrugia ◽  
W. F. Denig
Keyword(s):  
Solar Wind ◽  
Local Time ◽  
High Latitude ◽  
Specific Activity ◽  
Moderate Intensity ◽  
Auroral Activity ◽  
Activity Intensity ◽  
Subsolar Point ◽  
Field Lines ◽  
Ground Magnetic

Abstract. In two case studies we elaborate on spatial and temporal structures of the dayside aurora within 08:00-16:00 magnetic local time (MLT) and discuss the relationship of this structure to solar wind-magnetosphere interconnection topology and the different stages of evolution of open field lines in the Dungey convection cycle. The detailed 2-D auroral morphology is obtained from continuous ground observations at Ny Ålesund (76° magnetic latitude (MLAT)), Svalbard during two days when the interplanetary magnetic field (IMF) is directed southeast (By>0; Bz<0). The auroral activity consists of the successive activations of the following forms: (i) latitudinally separated, sunward moving, arcs/bands of dayside boundary plasma sheet (BPS) origin, in the prenoon (08:00-11:00 MLT) and postnoon (12:00-16:00 MLT) sectors, within 70-75° MLAT, (ii) poleward moving auroral forms (PMAFs) emanating from the pre- and postnoon brightening events, and (iii) a specific activity appearing in the 07:00-10:00 MLT/75-80° MLAT during the prevailing IMF By>0 conditions. The pre- and postnoon activations are separated by a region of strongly attenuated auroral activity/intensity within the 11:00-12:00 MLT sector, often referred to as the midday gap aurora. The latter aurora is attributed to the presence of component reconnection at the subsolar magnetopause where the stagnant magnetosheath flow lead to field-aligned currents (FACs) which are of only moderate intensity. The much more active and intense aurorae in the prenoon (07:00-11:00 MLT) and postnoon (12:00-16:00 MLT) sectors originate in magnetopause reconnection events that are initiated well away from the subsolar point. The high-latitude auroral activity in the prenoon sector (feature iii) is found to be accompanied by a convection channel at the polar cap boundary. The associated ground magnetic deflection (DPY) is a Svalgaard-Mansurov effect. The convection channel is attributed to effective momentum transfer from the solar wind-magnetosphere dynamo in the high-latitude boundary layer (HBL), on the downstream side of the cusp.

scholarly journals High-latitude HF Doppler observations of ULF waves: 2. Waves with small spatial scale sizes

1999 ◽  
Vol 17 (7) ◽  
pp. 868-876 ◽  
Author(s):  
D. M. Wright ◽  
T. K. Yeoman
Keyword(s):  
High Latitude ◽  
Radar Data ◽  
Mhd Waves ◽  
Ulf Waves ◽  
Vhf Radar ◽  
Magnetic Signature ◽  
High Latitude Ionosphere ◽  
Field Lines ◽  
Ground Magnetic ◽  
The Waves

Abstract. The DOPE (Doppler Pulsation Experiment) HF Doppler sounder located near Tromsø, Norway (geographic: 69.6°N 19.2°E; L = 6.3) is deployed to observe signatures, in the high-latitude ionosphere, of magnetospheric ULF waves. A type of wave has been identified which exhibits no simultaneous ground magnetic signature. They can be subdivided into two classes which occur in the dawn and dusk local time sectors respectively. They generally have frequencies greater than the resonance fundamentals of local field lines. It is suggested that these may be the signatures of high-m ULF waves where the ground magnetic signature has been strongly attenuated as a result of the scale size of the waves. The dawn population demonstrate similarities to a type of magnetospheric wave known as giant (Pg) pulsations which tend to be resonant at higher harmonics on magnetic field lines. In contrast, the waves occurring in the dusk sector are believed to be related to the storm-time Pc5s previously reported in VHF radar data. Dst measurements support these observations by indicating that the dawn and dusk classes of waves occur respectively during geomagnetically quiet and more active intervals.Key words. Ionosphere (auroral ionosphere; ionosphere-magnetosphere interactions) · Magnetospheric physics (MHD waves and instabilities)

scholarly journals Momentum transfer at the high-latitude magnetopause and boundary layers

2008 ◽  
Vol 26 (8) ◽  
pp. 2449-2458
Author(s):  
E. J. Lund ◽  
C. J. Farrugia ◽  
P. E. Sandholt
Keyword(s):  
Solar Wind ◽  
Momentum Transfer ◽  
Boundary Layers ◽  
Open Field ◽  
High Latitude ◽  
Hall Current ◽  
Space Physics ◽  
Flow Channel ◽  
Field Lines ◽  
Multiple Spacecraft

Abstract. How and where momentum is transferred from the solar wind to the magnetosphere and ionosphere is one of the key problems of space physics. Much of this transfer occurs through direct reconnection on the dayside, particularly when the IMF is southward. However, momentum transfer also occurs at higher latitudes via Alfvén waves on old open field lines, even for southward IMF. This momentum is transferred to the ionosphere via field-aligned currents (FACs), and the flow channel associated with these FACs produces a Hall current which causes magnetic variations at high latitude (the Svalgaard-Mansurov effect). We show examples where such momentum transfer is observed with multiple spacecraft and ground-based instruments.

Relation of solar wind parameters to high-latitude magnetic pulsations

2006 ◽  
Vol 12 (1) ◽  
pp. 80-84
Author(s):  
S.N. Samsonov ◽  
◽  
I.Ya. Plotnikov ◽  
D.Y. Sibeck ◽  
Yu. Watermann ◽  
...  
Keyword(s):  
Solar Wind ◽  
High Latitude ◽  
Magnetic Pulsations ◽  
Solar Wind Parameters

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 Characteristics of solar wind control on Jovian UV auroral activity deciphered by long-term Hisaki EXCEED observations: Evidence of preconditioning of the magnetosphere?

2016 ◽  
Vol 43 (13) ◽  
pp. 6790-6798 ◽  
Author(s):  
Hajime Kita ◽  
Tomoki Kimura ◽  
Chihiro Tao ◽  
Fuminori Tsuchiya ◽  
Hiroaki Misawa ◽  
...  
Keyword(s):  
Solar Wind ◽  
Auroral Activity

scholarly journals Birkeland current effects on high‐latitude ground magnetic field perturbations

2015 ◽  
Vol 42 (18) ◽  
pp. 7248-7254 ◽  
Author(s):  
K. M. Laundal ◽  
S. E. Haaland ◽  
N. Lehtinen ◽  
J. W. Gjerloev ◽  
N. Østgaard ◽  
...  
Keyword(s):  
Magnetic Field ◽  
High Latitude ◽  
Ground Magnetic

scholarly journals Dayside auroral activity and magnetic flux transfer from the solar wind

1989 ◽  
Vol 16 (1) ◽  
pp. 33-36 ◽  
Author(s):  
M. Lockwood ◽  
P. E. Sandholt ◽  
S. W. H. Cowley
Keyword(s):  
Solar Wind ◽  
Magnetic Flux ◽  
Auroral Activity ◽  
Flux Transfer

High-latitude observations of solar wind streams and coronal holes

1976 ◽  
Vol 81 (22) ◽  
pp. 3845-3850 ◽  
Author(s):  
B. J. Rickett ◽  
D. G. Sime ◽  
N. R. Sheeley ◽  
W. R. Crockett ◽  
R. Tousey
Keyword(s):  
Solar Wind ◽  
High Latitude ◽  
Coronal Holes

scholarly journals Azimuthal magnetic fields in Saturn’s magnetosphere: effects associated with plasma sub-corotation and the magnetopause-tail current system

2003 ◽  
Vol 21 (8) ◽  
pp. 1709-1722 ◽  
Author(s):  
E. J. Bunce ◽  
S. W. H. Cowley ◽  
J. A. Wild
Keyword(s):  
Magnetic Field ◽  
Solar Wind ◽  
Magnetic Fields ◽  
Current System ◽  
Heavy Ion ◽  
Local Times ◽  
Dynamical Process ◽  
Tail Current ◽  
Field Lines ◽  
Inner Region

Abstract. We calculate the azimuthal magnetic fields expected to be present in Saturn’s magnetosphere associated with two physical effects, and compare them with the fields observed during the flybys of the two Voyager spacecraft. The first effect is associated with the magnetosphere-ionosphere coupling currents which result from the sub-corotation of the magnetospheric plasma. This is calculated from empirical models of the plasma flow and magnetic field based on Voyager data, with the effective Pedersen conductivity of Saturn’s ionosphere being treated as an essentially free parameter. This mechanism results in a ‘lagging’ field configuration at all local times. The second effect is due to the day-night asymmetric confinement of the magnetosphere by the solar wind (i.e. the magnetopause and tail current system), which we have estimated empirically by scaling a model of the Earth’s magnetosphere to Saturn. This effect produces ‘leading’ fields in the dusk magnetosphere, and ‘lagging’ fields at dawn. Our results show that the azimuthal fields observed in the inner regions can be reasonably well accounted for by plasma sub-corotation, given a value of the effective ionospheric Pedersen conductivity of ~ 1–2 mho. This statement applies to field lines mapping to the equator within ~ 8 RS (1 RS is taken to be 60 330 km) of the planet on the dayside inbound passes, where the plasma distribution is dominated by a thin equatorial heavy-ion plasma sheet, and to field lines mapping to the equator within ~ 15 RS on the dawn side outbound passes. The contributions of the magnetopause-tail currents are estimated to be much smaller than the observed fields in these regions. If, however, we assume that the azimuthal fields observed in these regions are not due to sub-corotation but to some other process, then the above effective conductivities define an upper limit, such that values above ~ 2 mho can definitely be ruled out. Outside of this inner region the spacecraft observed both ‘lagging’ and ‘leading’ fields in the post-noon dayside magnetosphere during the inbound passes, with ‘leading’ fields being observed both adjacent to the magnetopause and in the ring current region, and ‘lagging’ fields being observed between. The observed ‘lagging’ fields are consistent in magnitude with the sub-corotation effect with an effective ionospheric conductivity of ~ 1–2 mho, while the ‘leading’ fields are considerably larger than those estimated for the magnetopause-tail currents, and appear to be indicative of the presence of another dynamical process. No ‘leading’ fields were observed outside the inner region on the dawn side outbound passes, with the azimuthal fields first falling below those expected for sub-corotation, before increasing, to exceed these values at radial distances beyond ~ 15–20 RS , where the effect of the magnetopause-tail currents becomes significant. As a by-product, our investigation also indicates that modification and scaling of terrestrial magnetic field models may represent a useful approach to modelling the three-dimensional magnetic field at Saturn.Key words. Magnetospheric physics (current systems; magnetosphere-ionosphere interactions; solar wind-magnetosphere interactions)

Sign in / Sign up

Export Citation Format

Share Document