scholarly journals Estimates of magnetotail reconnection rate based on IMAGE FUV and EISCAT measurements

2005 ◽  
Vol 23 (1) ◽  
pp. 123-134 ◽  
Author(s):  
N. Østgaard ◽  
J. Moen ◽  
S. B. Mende ◽  
H. U. Frey ◽  
T. J. Immel ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Solar Wind ◽  
Electric Field ◽  
Field Line ◽  
Oscillation Mode ◽  
Closed Field ◽  
Reconnection Rate ◽  
Magnetospheric Convection ◽  
Closed Field Line ◽  
Magnetotail Reconnection

Abstract. Dayside merging between the interplanetary and terrestrial magnetic fields couples the solar wind electric field to the Earth's magnetosphere, increases the magnetospheric convection and results in efficient transport of solar wind energy into the magnetosphere. Subsequent reconnection of the lobe magnetic field in the magnetotail transports energy into the closed magnetic field region. Combining global imaging and ground-based radar measurements, we estimate the reconnection rate in the magnetotail during two days of an EISCAT campaign in November-December 2000. Global images from the IMAGE FUV system guide us to identify ionospheric signatures of the open-closed field line boundary observed by the two EISCAT radars in Tromsø (VHF) and on Svalbard (ESR). Continuous radar and optical monitoring of the open-closed field line boundary is used to determine the location, orientation and velocity of the open-closed boundary and the ion flow velocity perpendicular to this boundary. The magnetotail reconnection electric field is found to be a bursty process that oscillates between 0mV/m and 1mV/m with ~10-15min periods. These ULF oscillations are mainly due to the motion of the open-closed boundary. In situ measurements earthward of the reconnection site in the magnetotail by Geotail show similar oscillations in the duskward electric field. We also find that bursts of increased magnetotail reconnection do not necessarily have any associated auroral signatures. Finally, we find that the reconnection rate correlates poorly with the solar wind electric field. This indicates that the magnetotail reconnection is not directly driven, but is an internal magnetospheric process. Estimates of a coupling efficiency between the solar wind electric field and magnetotail reconnection only seem to be relevant as averages over long time intervals. The oscillation mode at 1mHz corresponds to the internal cavity mode with additional lower frequencies, 0.5 and 0.8mHz, that might be modulated by solar wind pressure variations.

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 Dependence of the open-closed field line boundary in Saturn's ionosphere on both the IMF and solar wind dynamic pressure: comparison with the UV auroral oval observed by the HST

2008 ◽  
Vol 26 (1) ◽  
pp. 159-166 ◽  
Author(s):  
E. S. Belenkaya ◽  
S. W. H. Cowley ◽  
S. V. Badman ◽  
M. S. Blokhina ◽  
V.V. Kalegaev
Keyword(s):  
Magnetic Field ◽  
Solar Wind ◽  
Field Line ◽  
Open Field ◽  
Dynamic Pressure ◽  
Auroral Oval ◽  
Closed Field ◽  
Field Region ◽  
Closed Field Line ◽  
The Imf

Abstract. We model the open magnetic field region in Saturn's southern polar ionosphere during two compression regions observed by the Cassini spacecraft upstream of Saturn in January 2004, and compare these with the auroral ovals observed simultaneously in ultraviolet images obtained by the Hubble Space Telescope. The modelling employs the paraboloid model of Saturn's magnetospheric magnetic field, whose parameters are varied according to the observed values of both the solar wind dynamic pressure and the interplanetary magnetic field (IMF) vector. It is shown that the open field area responds strongly to the IMF vector for both expanded and compressed magnetic models, corresponding to low and high dynamic pressure, respectively. It is also shown that the computed open field region agrees with the poleward boundary of the auroras as well as or better than those derived previously from a model in which only the variation of the IMF vector was taken into account. The results again support the hypothesis that the auroral oval at Saturn is associated with the open-closed field line boundary and hence with the solar wind interaction.

scholarly journals Local time extent of magnetopause reconnection using space–ground coordination

2019 ◽  
Vol 37 (2) ◽  
pp. 215-234 ◽  
Author(s):  
Ying Zou ◽  
Brian M. Walsh ◽  
Yukitoshi Nishimura ◽  
Vassilis Angelopoulos ◽  
J. Michael Ruohoniemi ◽  
...  
Keyword(s):  
Field Line ◽  
Local Time ◽  
Maximum Flow ◽  
Closed Field ◽  
Full Width ◽  
Half Maximum ◽  
Reconnection Rate ◽  
Lack Of Information ◽  
Closed Field Line ◽  
Multiple Spacecraft

Abstract. Magnetic reconnection can vary considerably in spatial extent. At the Earth's magnetopause, the extent generally corresponds to the extent in local time. The extent has been probed by multiple spacecraft crossing the magnetopause, but the estimates have large uncertainties because of the assumption of spatially continuous reconnection activity between spacecraft and the lack of information beyond areas of spacecraft coverage. The limitations can be overcome by using radars examining ionospheric flows moving anti-sunward across the open–closed field line boundary. We therefore infer the extents of reconnection using coordinated observations of multiple spacecraft and radars for three conjunction events. We find that when reconnection jets occur at only one spacecraft, only the ionosphere conjugate to this spacecraft shows a channel of fast anti-sunward flow. When reconnection jets occur at two spacecraft and the spacecraft are separated by < 1 Re, the ionosphere conjugate to both spacecraft shows a channel of fast anti-sunward flow. The consistency allows us to determine the reconnection jet extent by measuring the ionospheric flows. The full-width-at-half-maximum flow extent is 200, 432, and 1320 km, corresponding to a reconnection jet extent of 2, 4, and 11 Re. Considering that reconnection jets emanate from reconnections with a high reconnection rate, the result indicates that both spatially patchy (a few Re) and spatially continuous and extended reconnections (> 10 Re) are possible forms of active reconnection at the magnetopause. Interestingly, the extended reconnection develops from a localized patch via spreading across local time. Potential effects of IMF Bx and By on the reconnection extent are discussed.

Effects of the interplanetary magnetic field on the location of the open-closed field line boundary

2016 ◽  
Vol 121 (7) ◽  
pp. 6341-6352 ◽  
Author(s):  
C. Wang ◽  
J. Y. Wang ◽  
R. E. Lopez ◽  
L. Q. Zhang ◽  
B. B. Tang ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Interplanetary Magnetic Field ◽  
Field Line ◽  
Closed Field ◽  
Closed Field Line

scholarly journals IMF dependence of Saturn's auroras: modelling study of HST and Cassini data from 12–15 February 2008

2010 ◽  
Vol 28 (8) ◽  
pp. 1559-1570 ◽  
Author(s):  
E. S. Belenkaya ◽  
I. I. Alexeev ◽  
M. S. Blokhina ◽  
E. J. Bunce ◽  
S. W. H. Cowley ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Field Line ◽  
Hubble Space Telescope ◽  
Auroral Oval ◽  
Closed Field ◽  
Propagation Delays ◽  
Magnetic Field Model ◽  
Closed Field Line ◽  
Orbit Insertion ◽  
The Imf

Abstract. To gain better understanding of auroral processes in Saturn's magnetosphere, we compare ultraviolet (UV) auroral images obtained by the Hubble Space Telescope (HST) with the position of the open-closed field line boundary in the ionosphere calculated using a magnetic field model that employs Cassini measurements of the interplanetary magnetic field (IMF) as input. Following earlier related studies of pre-orbit insertion data from January 2004 when Cassini was located ~ 1300 Saturn radii away from the planet, here we investigate the interval 12–15 February 2008, when UV images of Saturn's southern dayside aurora were obtained by the HST while the Cassini spacecraft measured the IMF in the solar wind just upstream of the dayside bow shock. This configuration thus provides an opportunity, unique to date, to determine the IMF impinging on Saturn's magnetosphere during imaging observations, without the need to take account of extended and uncertain interplanetary propagation delays. The paraboloid model of Saturn's magnetosphere is then employed to calculate the magnetospheric magnetic field structure and ionospheric open-closed field line boundary for averaged IMF vectors that correspond, with appropriate response delays, to four HST images. We show that the IMF-dependent open field region calculated from the model agrees reasonably well with the area lying poleward of the UV emissions, thus supporting the view that the poleward boundary of Saturn's auroral oval in the dayside ionosphere lies adjacent to the open-closed field line boundary.

Magnetic field perturbations in closed-field-line systems with zero toroidal magnetic field

2004 ◽  
Vol 11 (5) ◽  
pp. 2318-2321 ◽  
Author(s):  
D. D. Ryutov ◽  
J. Kesner ◽  
M. E. Mauel
Keyword(s):  
Magnetic Field ◽  
Field Line ◽  
Toroidal Magnetic Field ◽  
Closed Field ◽  
Closed Field Line

scholarly journals The auroral and ionospheric flow signatures of dual lobe reconnection

2006 ◽  
Vol 24 (11) ◽  
pp. 3115-3129 ◽  
Author(s):  
S. M. Imber ◽  
S. E. Milan ◽  
B. Hubert
Keyword(s):  
Magnetic Field ◽  
Interplanetary Magnetic Field ◽  
Field Line ◽  
Radar Data ◽  
Auroral Oval ◽  
Closed Field ◽  
Closed Field Line ◽  
Field Lines ◽  
Lobe Reconnection ◽  
Northern And Southern Hemispheres

Abstract. We present the first substantial evidence for the occurrence of dual lobe reconnection from ionospheric flows and auroral signatures. The process of dual lobe reconnection refers to an interplanetary magnetic field line reconnecting with lobe field lines in both the northern and southern hemispheres. Two bursts of sunward plasma flow across the noon portion of the open/closed field line boundary (OCB), indicating magnetic flux closure at the dayside, were observed in SuperDARN radar data during a period of strongly northward IMF. The OCB is identified from spacecraft, radar backscatter, and auroral observations. In order for dual lobe reconnection to take place, we estimate that the interplanetary magnetic field clock angle must be within ±10° of zero (North). The total flux crossing the OCB during each burst is small (1.8% and 0.6% of the flux contained within the polar cap for the two flows). A brightening of the noon portion of the northern auroral oval was observed as the clock angle passed through zero, and is thought to be due to enhanced precipitating particle fluxes due to the occurrence of reconnection at two locations along the field line. The number of solar wind protons captured by the flux closure process was estimated to be ~2.5×1030 (4 tonnes by mass), sufficient to populate the cold, dense plasma sheet observed following this interval.

scholarly journals IMF dependence of the open-closed field line boundary in Saturn's ionosphere, and its relation to the UV auroral oval observed by the Hubble Space Telescope

2007 ◽  
Vol 25 (5) ◽  
pp. 1215-1226 ◽  
Author(s):  
E. S. Belenkaya ◽  
I. I. Alexeev ◽  
M. S. Blokhina ◽  
S. W. H. Cowley ◽  
S. V. Badman ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Field Line ◽  
Hubble Space Telescope ◽  
Auroral Oval ◽  
Field Structure ◽  
Closed Field ◽  
Space Telescope ◽  
Magnetic Field Structure ◽  
Open Field Line ◽  
Closed Field Line

Abstract. We study the dependence of Saturn's magnetospheric magnetic field structure on the interplanetary magnetic field (IMF), together with the corresponding variations of the open-closed field line boundary in the ionosphere. Specifically we investigate the interval from 8 to 30 January 2004, when UV images of Saturn's southern aurora were obtained by the Hubble Space Telescope (HST), and simultaneous interplanetary measurements were provided by the Cassini spacecraft located near the ecliptic ~0.2 AU upstream of Saturn and ~0.5 AU off the planet-Sun line towards dawn. Using the paraboloid model of Saturn's magnetosphere, we calculate the magnetospheric magnetic field structure for several values of the IMF vector representative of interplanetary compression regions. Variations in the magnetic structure lead to different shapes and areas of the open field line region in the ionosphere. Comparison with the HST auroral images shows that the area of the computed open flux region is generally comparable to that enclosed by the auroral oval, and sometimes agrees in detail with its poleward boundary, though more typically being displaced by a few degrees in the tailward direction.

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