Fig 10 - uploaded by Timothy Kenneth Yeoman
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The FAC estimate per unit Pedersen conductance B · ( × v) (µA m −2 S −1 ) obtained from the map potential contours for the scans starting at (a) 10:57 UT, (b) 11:06 UT, (c) 11:10 UT, and (d) 11:25 UT. The FAC direction is defined according to the SuperDARN coordinate convention, where z is radially out of the ionosphere. Negative vorticity (into the ionosphere) corresponds to a positive FAC component (red), and positive vorticity (out of the ionosphere) corresponds to a negative FAC component (blue).
Source publication
We examine the
large-scale ultraviolet aurora and convection responses to a series of flux
transfer events that immediately followed a sharp and isolated southward
turning of the IMF. During the interval of interest, SuperDARN was monitoring
the plasma convection in the dayside northern ionosphere, while the VIS Earth
Camera and the Far Ul-traviole...
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Citations
... To facilitate the study of FACs, previous studies commonly assumed that variations in ionospheric conductance were insignificant and could be ignored (Chisham et al., 2009;Freeman et al., 1990;McWilliams et al., 2001;Sofko et al., 1995). These studies also proposed that vorticities can be a reliable proxy or diagnostic for FACs. ...
... They found that upward FACs in the postnoon sector corresponded to the bright aurora, while downward FACs were located on both sides of the bright auroral region. McWilliams et al. (2001) also employed this approximation and expanded the vorticity map to cover the entire polar region. They discovered that the distribution of FACs was consistent with the dayside current wedge in the footprint of the dayside magnetic reconnection region. ...
... Previous studies relied on using vorticities as a proxy for FACs due to the lack of direct observations of conductances (Chisham et al., 2009;Freeman et al., 1990;McWilliams et al., 2001;Sofko et al., 1995). However, the validity of using vorticities as a proxy for FACs is debatable as the required approximation of uniform conductances is often a poor assumption (Amm et al., 2005;Green et al., 2006;Kosch et al., 2001). ...
Studies commonly assumed that variations in ionospheric conductance were insignificant and proposed that vorticities can be a reliable proxy or diagnostic for ionospheric field‐aligned currents (FACs). We propose a complete method for measuring FACs using data from the Super Dual Auroral Radar Network radar and the Defense Meteorological Satellite Program. In our method, the FACs are determined by three terms. The first term is referred to as magnetospheric‐origin FACs, while the second and third terms are known as ionospheric‐origin FACs. This method incorporates height‐integrated conductances based on observational data, thereby addressing the limitation of assuming uniform conductances. Different from previous works, we can calculate FACs at a low altitude of 250 km and obtain high‐resolution measurements within observable areas. Another advantage of this method lies in its ability to directly calculate and analyze the impact of ionospheric vorticity and conductance on FACs. We apply this method to obtain FACs in the Northern Hemisphere from 2010 to 2016 and analyze the distributions of height‐integrated conductances and total FACs. Our analysis reveals that the average FACs clearly exhibit the large‐scale R1 and R2 FAC systems. We conduct statistical analysis on magnetospheric‐origin FACs and ionospheric‐origin FACs. Our findings show that within the auroral oval, ionospheric‐origin FACs reach a comparable level to magnetospheric‐origin FACs. However, ionospheric‐origin FACs are significantly minor and almost negligible in other regions. This implies that height‐integrated conductance gradients and vorticities play equally significant roles within the auroral oval, whereas vorticities dominate in other regions.
... In this paper, we follow on from work on the underlying probability distributions of Birkeland current densities. Super Dual Auroral Radar Network (SuperDARN) data have been used to obtain ionospheric vorticities which are closely related to Birkeland currents (Chisham et al., 2009;McWilliams et al., 2001;Sofko et al., 1995). These data were used by Chisham and Freeman (2010) to show that the distributions of vorticity magnitude had more kurtosis than normally-distributed quantities (they were leptokurtic). ...
... The relationship between aurora and Birkeland current has been investigated parametrically , and there is a lack of correspondence on the dusk side between field-aligned currents and the auroral oval, which may lend credence to the idea that this is being driven by some asymmetry in the relationship between current and charge carriers. Conversely, McWilliams et al. (2001) used SuperDARN vorticity to calculate the quantity J ‖ /Σ P and found that using this method, upward field-aligned current was colocated with aurora from the Polar Visible Imaging System (VIS) in the post-noon sector. Chisham et al. (2007) presented Figure 10c from McWilliams et al. (2001) alongside data from Polar VIS and the Polar Ultraviolet Imager (UVI) in their Figure 11, demonstrating a correspondence between upward current and aurora on both sides of the polar cap. ...
... Conversely, McWilliams et al. (2001) used SuperDARN vorticity to calculate the quantity J ‖ /Σ P and found that using this method, upward field-aligned current was colocated with aurora from the Polar Visible Imaging System (VIS) in the post-noon sector. Chisham et al. (2007) presented Figure 10c from McWilliams et al. (2001) alongside data from Polar VIS and the Polar Ultraviolet Imager (UVI) in their Figure 11, demonstrating a correspondence between upward current and aurora on both sides of the polar cap. As far as we are aware, these studies are the only published comparisons between the system-scale positions of field-aligned currents and aurora. ...
We examine the statistical distribution of large‐scale Birkeland currents measured by the Active Magnetosphere and Planetary Electrodynamics Response Experiment in four unique categories of geomagnetic activity for the first time: quiet times, storm times, quiet‐time substorms, and storm‐time substorms. A novel method is employed to sort data into one of these four categories, and the categorizations are provided for future research. The mean current density is largest during substorms and its standard deviation is largest during geomagnetic storms. Current densities which are above a low threshold are more likely during substorms, but extreme currents are far more likely during geomagnetic storms, consistent with a paradigm in which geomagnetic storms represent periods of enhanced variability over quiet times. We demonstrate that extreme currents are most likely to flow within the Region 2 current during geomagnetic storms. This is unexpected in a paradigm of the current systems in which Region 1 current is generally larger.
... We postulate the reason for the mismatch between the SED and CPCP evolution is due to the southward IMF turning. Studies suggest that the adjustment in convection to IMF turnings occurred in the dayside cusp first and then propagates toward the nightside over a period of ∼10 min Etemadi et al., 1988;Khan & Cowley, 1999;Lockwood & Cowley, 1999;Lockwood et al., 1986;Saunders et al., 1992;Todd et al., 1988), and the adjustment in total takes from 12 to 30 min before a new steady state pattern is established (Hairston & Heelis, 1995;McWilliams et al., 2000McWilliams et al., , 2001Ruohoniemi & Greenwald, 1998). In the following section, we analyze a geospace plume event under a prolonged steady IMF condition to investigate the impact of plumes on the integrated global reconnection rate. ...
The role a geospace plume in influencing the efficiency of magnetopause reconnection is an open question with two contrasting theories being debated. A local‐control theory suggests that a plume decreases both local and global reconnection rates, whereas a global‐control theory argues that the global reconnection rate is controlled by the solar wind rather than local physics. Observationally, limited numbers of point measurements from spacecraft cannot reveal whether a local change affects the global reconnection. A distributed observatory is hence needed to assess the validity of the two theories. We use THEMIS and Los Alamos National Laboratory spacecraft to identify the occurrence of a geospace plume and its contact with the magnetopause. Global evolution and morphology of the plume is traced using GPS measurements. SuperDARN is then used to monitor the distribution and the strength of dayside reconnection. Two storm‐time geospace plume events are examined and show that as the plume contacts the magnetopause, the efficiency of reconnection decreases at the contact longitude. The amount of local decrease is 81% and 68% for the two events, and both values are consistent with the mass loading effect of the plume if the plume's atomic mass is ∼4 amu. Reconnection in the surrounding is enhanced, and when the solar wind driving is stable, little variation is seen in the cross polar cap potential. This study illuminates a pathway to resolve the role of cold dense plasma on solar wind‐magnetosphere coupling, and the observations suggest that plumes redistribute magnetopause reconnection activity without changing the global strength substantially.
... There is also an ion-drag force that acts in the equatorward direction over a short timescale, associated with southward ion motion due to the expanding convection pattern, for an interval on the order of tens of minutes. The latter of these is associated with an equatorward moving adiaroic boundary (e.g., Chen et al., 2016;McWilliams et al., 2001), that is, the expanding and contracting polar cap in response to the opening and closing of magnetic flux (Siscoe & Huang, 1985). We show in Figure 7 that there is indeed some equatorward flowing plasma during the substorm growth phase. ...
Two‐dimensional thermospheric wind fields, at both E and F region altitudes within a common vertical volume, were made using a Scanning Doppler Imager (SDI) at Poker Flat, Alaska, during a substorm event. Coinciding with these observations were F region plasma velocity measurements from the Super Dual Auroral Radar Network (SuperDARN) and estimations of the total downward and upward field‐aligned current density from the Active Magnetosphere and Planetary Electrodynamics Response Experiment (AMPERE). This combination of instruments gives an excellent opportunity to examine the spatial characteristics of high‐latitude ionosphere‐thermosphere coupling and how a process which is triggered in the magnetosphere (the substorm) affects that coupling at different altitudes. We find that during the substorm growth phase, the F region thermospheric winds respond readily to an expanding ionospheric plasma convection pattern, while the E region winds appear to take a much longer period of time. The differing response timescales of the E and F region winds are likely due to differences in neutral density at those altitudes, resulting in E region neutrals being much more “sluggish” with regard to ion drag. We also observe increases in the F region neutral temperature, associated with neutral winds accelerating during both substorm growth and recovery phases.
... An example of multi-instrument study of cusp precipitation can be found in Lorentzen et al. (2007), who combined observations from the European Incoherent Scatter (EISCAT) Svalbard Radar, optical instruments from the Kjell Henriksen Observatory, a DMSP satellite and a rocket experiment to explain a pulsating dayside aurora event by pulsed lobe reconnection driven by IMF with positive B z and strongly negative B y . Coherent scatter radars can also provide information on the cusp dynamics by providing information on the plasma horizontal convection; the SuperDARN radar network has proven useful for such studies (e.g., McWilliams et al., 2001). ...
Particle precipitation is a central aspect of space weather, as it strongly couples the magnetosphere and the ionosphere and can be responsible for radio signal disruption at high latitudes. We present the first hybrid-Vlasov simulations of proton precipitation in the polar cusps. We use two runs from the Vlasiator model to compare cusp proton precipitation fluxes during southward and northward interplanetary magnetic field (IMF) driving. The simulations reproduce well-known features of cusp precipitation, such as a reverse dispersion of precipitating proton energies, with proton energies increasing with increasing geomagnetic latitude under northward IMF driving, and a nonreversed dispersion under southward IMF driving. The cusp is also found more polewards in the northward IMF simulation than in the southward IMF simulation. In addition, we find that the bursty precipitation during southward IMF driving is associated with the transit of flux transfer events in the vicinity of the cusp. In the northward IMF simulation, dual lobe reconnection takes place. As a consequence, in addition to the high-latitude precipitation spot associated with the lobe reconnection from the same hemisphere, we observe lower-latitude precipitating protons which originate from the opposite hemisphere's lobe reconnection site. The proton velocity distribution functions along the newly closed dayside magnetic field lines exhibit multiple proton beams travelling parallel and antiparallel to the magnetic field direction, which is consistent with previously reported observations with the Cluster spacecraft. In both runs, clear electromagnetic ion cyclotron waves are generated in the cusps and might further increase the calculated precipitating fluxes by scattering protons to the loss cone in the low-altitude cusp. Global kinetic simulations can improve the understanding of space weather by providing a detailed physical description of the entire near-Earth space and its internal couplings.
... The ionospheric signatures include poleward-moving auroral forms (PMAFs), channels of flows moving anti-sunward across the openclosed field line boundary (e.g., Southwood, 1985), and cusp precipitation Smith, 1989, 1994;Smith et al., 1992). Radar studies have shown that the flows can differ considerably in size, varying from tens of kilometers (Oksavik et al., , 2005 to hundreds of kilometers (Goertz et al., 1985;Pinnock et al., 1993Pinnock et al., , 1995Provan and Yeoman, 1999;Thorolfsson et al., 2000;McWilliams et al., 2000bMcWilliams et al., , 2001 or thousands of kilometers (Provan et al., 1998;Nishitani et al., 1999;Provan and Yeoman, 1999). A similarly broad distribution has been found for PMAFs (e.g., Sandholt et al., 1986Sandholt et al., , 1990Lockwood et al., , 1990Milan et al., 2000Milan et al., , 2016 and the cusp (Crooker et al., 1991;Newell and Meng, 1994;Newell et al., 2007). ...
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.
... [e.g., Southwood, 1985], and cusp precipitation [Lockwood andSmith, 1989, 1994;Smith et al., 122 1992]. Radar studies have shown that the flows can differ considerably in size, varying from tens of 123 km [Oksavik et al., 2004[Oksavik et al., , 2005, to hundreds of km [Goertz et al., 1985;Pinnock et al., 1993Pinnock et al., , 1995124 Provan and Yeoman, 1999; Thorolfsson et al., 2000;McWilliams et al., 2001aMcWilliams et al., , 2001b, and to 125 thousands of km [Provan et al., 1998;Nishitani et al., 1999;Provan and Yeoman, 1999]. A 126 similarly broad distribution has been found for PMAFs [e.g. ...
Magnetic reconnection X-lines can vary considerably in length. At the Earth's magnetopause, the length generally corresponds to the extent in local time. The extent has been probed by multi-spacecraft crossing the magnetopause, but the estimates have large uncertainties because of the assumption of a continuous X-line between spacecraft and the lack of information beyond areas of spacecraft coverage. The extent has also been inferred by radars as fast ionospheric flows moving anti-sunward across the open-closed field line boundary, but whether a particular ionospheric flow results from reconnection needs to be confirmed. To achieve a reliable interpretation, we compare X-line extents probed by multi-spacecraft and radars for three conjunction events. We find that when reconnection is active at only one spacecraft, only the ionosphere conjugate to this spacecraft shows a channel of fast anti-sunward flow. When reconnection is active at two spacecraft and the spacecraft are separated by 1Re, the ionosphere conjugate to both spacecraft shows a channel of fast anti-sunward flow. The consistency allows us to determine the X-line extent by measuring the ionospheric flows. The flow extent is 520, 572, and 1260km, corresponding to an X-line extent of 4, 5, and 11Re. This strongly indicates that both spatially patchy (a few Re) and spatially continuous and extended reconnection (>10Re) are possible forms of 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 X-line extent are discussed.
... An example of ionospheric convection measured by three SuperDARN high latitude radars (the Hankasalmi radar at 62.32 N 26.61 E, the Pykkvibaer radar at 63.77 N 20.54 W, and the Stokkseyri radar at 63.86 N 22.02 W, all with fields-of-view extending from magnetic latitudes~65 towards the north pole) is presented in Fig. 6a. These data are taken from McWilliams et al. (2001), and show the high latitude ionospheric response to high latitude dayside magnetopause processes. Similarly, data from Grocott et al. (2011) is shown in Fig. 6b, presenting measured ionospheric convection from SuperDARN mid-latitude radars (the Falkland Islands radar at 51.8 S 59.0 W and the Blackstone radar at 37.1 N 78.0 W, with fields-of-view extending from magnetic latitudes~50 -~80 ). ...
The equatorial region of the Earth's ionosphere is one of the most complex ionospheric regions due to its interactions, instabilities, and several unresolved questions regarding its dynamics, electrodynamics, and physical processes. The equatorial ionosphere overall spans three continents with the longest region being that over the African continent. Satellite observations have demonstrated that very large differences exist in the formation of ionospheric irregularities over the African sector compared with other longitudinal sectors. This may be a consequence of the symmetric shape of the magnetic equator over the continent and the lack of variability in latitude. In this paper, we propose a science campaign to equip the African sector of the magnetic equator with ground-based instruments, specifically magnetometers and radars. The network of radars proposed is similar in style and technique to the high-latitude SuperDARN radar network, while the magnetometers will form an array along the equatorial belt. These two proposed space physics instruments will be used to study this region of the equatorial ionosphere over a long interval of time, at least one solar cycle. The deployment of an array of magnetometers (AfrequaMA) and a radar network (AfrequaRN) in the African sector of the magnetic equator is jointly called the Africa Equatorial Magnetometer Array and Radar Network (AfrequaMARN), which will provide simultaneous observations of both electric and magnetic variations over the African sector. We also examine the possible science questions such a magnetometer array and radar network would be able to address, both individually and in conjunction with other space-based and ground-based instrumentation. The proposed projects will clearly improve our understanding of the dynamics of the equatorial ionosphere and our understanding of its role in balancing the large-scale ionospheric current system, and will contribute to our ability to adequately model ionospheric and plasmaspheric densities. It will also enhance our understanding of global ionospheric processes, which will improve the space weather capabilities of the African and international space science communities.
... Between 57°and 75°MLAT, with peak power at 65.9°, X-rays were observed [Foat et al., 1998]. The UV morphology is associated with the auroral oval [McWilliams et al., 2001]. It was demonstrated that the maximum intensity of NO + ions is situated around 65°MLAT at altitudes of 100-160 km and is strongly correlated with the aurora activity [Solomon et al., 1999]. ...
This study presents a geophysicochemical model of an ionospheric auroral gyroscope. The gyroscopic effect occurs due to the electromagnetic interaction in Earth's polar regions between two types of vertical cavity auroras: the herpolhodic cone (proton cavity aurora), operating in the cusp polar region, and two polhodic cones (an electronic cone and a protonic cone), operating in the aurora region. The ratio between the angular speeds of the herpolhodic and polhodic cones is established by the angle between Earth's rotational axis and the geomagnetic dipole axis. We have developed a theory of the ionospheric auroral gyroscope as a kinematic part of the terrestrial magnetosphere and ionosphere that enables a unified explanation of important macroscopic phenomena that occur at this level. Accordingly, we have explained the oval shape of the polar auroras, Schumann resonances, geomagnetic micropulsation excitation, and the structuring of Earth's areas of radiation. The terrestrial gravitomagnetic field and dark matter are implicated in the initiation and behavior of the auroral ionospheric gyroscope, both of which provide stability and accuracy. Viewed in a wider context, the ionospheric auroral gyroscope theory could offer a way to experimentally investigate dark matter on Earth. Furthermore, it may have a potential value as a predictive tool, providing information about the large earthquakes and Earth's phenomena.
... (2) Describing the duration of the restructuring process. Some research indicates delays ranging from 12 to 30 min from the time the transition reaches the ionosphere for the convection pattern to reconfigure [Hairston and Heelis, 1995;Ruohoniemi and Greenwald, 1998;McWilliams et al., 2000McWilliams et al., , 2001. Huang et al. [2000] reported that it took 10-20 min after the initial convection response for the convection pattern to fully reconfigure to a steady state pattern. ...
Reconfiguration of the convection pattern associated with a sudden
transition in the north/south component of the IMF from stable positive
to stable negative values is investigated for two events using both
magnetometer and SuperDARN data. The IMF transition impinges upon the
magnetosphere near the 10 MLT sector; perturbations are clearly seen on
the dayside at the time of onset and on the nightside with a ˜10 min
delay from onset. This implies a dayside-to-nightside progression of the
ionospheric response observed in the magnetic perturbations and
SuperDARN velocities, contrary to the globally simultaneous response
reported in the literature for a number of other events. The foci of the
dawnside convection cells are shown to shift from near midnight toward
the dayside, reaching a final location between 06 MLT and 08 MLT within
14-18 min of onset. The location of the duskside convection cell
remains in the early afternoon sector both prior to and after the
transition for both events. Once the convection foci reach a final
location, the overall convection pattern enhances.
