Seasonal and interplanetary magnetic field dependence of the field-aligned currents for both Northern and Southern Hemispheres

Green, D. L.; Waters, C. L.; Anderson, B. J.; Korth, H.

doi:10.5194/angeo-27-1701-2009

Cited by 71 publications

(115 citation statements)

References 48 publications

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“…Overall, our Swarm FAC patterns are consistent with previous results which are based on different data sets (e.g., Weimer, 2001;Christiansen et al, 2002;Papitashvili et al, 2002;Wang et al, 2005Wang et al, , 2008bAnderson et al, 2008;Green et al, 2009;He et al, 2012). The main purpose of the presented FAC patterns is to provide the framework for interpreting the auroral Hall currents derived at the same time.…”

Section: Dependence Of Facs On Season and Imfsupporting

confidence: 78%

Global characteristics of auroral Hall currents derived from the Swarm constellation: dependences on season and IMF orientation

Huang¹,

Lühr

Wang³

2017

Ann. Geophys.

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Abstract. On the basis of field-aligned currents (FACs) and Hall currents derived from high-resolution magnetic field data of the Swarm constellation, the average characteristics of these two current systems in the auroral regions are comprehensively investigated by statistical methods. This is the first study considering both current types determined simultaneously by the same spacecraft in both hemispheres. The FAC distribution, derived from the novel Swarm dualspacecraft approach, reveals the well-known features of Region 1 (R1) and Region 2 (R2) FACs. At high latitudes, Region 0 (R0) FACs appear on the dayside. Their flow direction, up or down, depends on the orientation of the interplanetary magnetic field (IMF) B y component. Of particular interest is the distribution of auroral Hall currents. The prominent auroral electrojets are found to be closely controlled by the solar wind input, but we find no dependence of their intensity on the IMF B y orientation. The eastward electrojet is about 1.5 times stronger in local summer than in winter. Conversely, the westward electrojet shows less dependence on season. As to higher latitudes, part of the electrojet current is closed over the polar cap. Here the seasonal variation of conductivity mainly controls the current density. During local summer of the Northern Hemisphere, there is a clear channeling of return currents over the polar cap. For positive (negative) IMF B y a dominant eastward (westward) Hall current circuit is formed from the afternoon (morning) electrojet towards the dawn side (dusk side) polar cap return current. The direction of polar cap Hall currents in the noon sector depends directly on the orientation of the IMF B y . This is true for both signs of the IMF B z component. Comparable Hall current distributions can be observed in the Southern Hemisphere but for opposite IMF B y signs. Around the midnight sector the westward substorm electrojet is dominating. As expected, it is highly dependent on magnetic activity, but it shows only little response to season and IMF B y polarity. An important finding is that all the IMF B y dependences of FACs and Hall currents practically disappear in the dark winter hemisphere.

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Section: Dependence Of Facs On Season and Imfsupporting

confidence: 78%

Global characteristics of auroral Hall currents derived from the Swarm constellation: dependences on season and IMF orientation

Huang¹,

Lühr

Wang³

2017

Ann. Geophys.

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“…For example, the influence of the IMF B y , which governs the direction of high-latitude flows arising from magnetopause reconnection, on the configuration of the dayside Birkeland currents is consistent with previous studies conducted in the Northern Hemisphere. The effect of the sign of IMF B y on the Birkeland current topology is reversed in the Southern Hemisphere due to the anti-symmetry of the reconnection site with respect to the noon-midnight meridian (Green et al, 2009). For southward IMF, the Birkeland current distributions derived from Iridium data do not show significant currents poleward of 80 • MLAT, whereas some previous results show statistically significant NBZ-sense currents for all IMF orientations.…”

Section: Introductionmentioning

confidence: 68%

“…The Birkeland currents are affected primarily by the Pedersen conductance, P , and Green et al (2009) have shown that the current densities on the dayside are markedly reduced during the winter months when the conductance due to solar EUV is generally lower. The solar EUV influence on P can be expressed in terms of the solar zenith angle as (Rasmussen et al, 1988):…”

Section: Conductance Normalizationmentioning

confidence: 99%

Statistical analysis of the dependence of large-scale Birkeland currents on solar wind parameters

2010

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Abstract. The spatial distributions of large-scale fieldaligned Birkeland currents have been derived using magnetic field data obtained from the Iridium constellation of satellites from February 1999 to December 2007. From this database, we selected intervals that had at least 45% overlap in the large-scale currents between successive hours. The consistency in the current distributions is taken to indicate stability of the large-scale magnetosphere-ionosphere system to within the spatial and temporal resolution of the Iridium observations. The resulting data set of about 1500 two-hour intervals (4% of the data) was sorted first by the interplanetary magnetic field (IMF) GSM clock angle (arctan(B y /B z )) since this governs the spatial morphology of the currents. The Birkeland current densities were then corrected for variations in EUV-produced ionospheric conductance by normalizing the current densities to those occurring for 0 • dipole tilt. To determine the dependence of the currents on other solar wind variables for a given IMF clock angle, the data were then sorted sequentially by the following parameters: the solar wind electric field in the plane normal to the Earth-Sun line, E yz ; the solar wind ram pressure; and the solar wind Alfvén Mach number. The solar wind electric field is the dominant factor determining the Birkeland current intensities. The currents shift toward noon and expand equatorward with increasing solar wind electric field. The total current increases by 0.8 MA per mV m −1 increase in E yz for southward IMF, while for northward IMF it is nearly independent of the electric field, increasing by only 0.1 MA per mV m −1 increase in E yz . The dependence on solar wind pressure is comparatively modest. After correcting for the solar dynamo dependencies in intensity and distribution, the total current intensity increases with solar wind dynamic pressure by 0.4 MA/nPa for southward IMF. Normalizing the BirkeCorrespondence to: H. Korth (haje.korth@jhuapl.edu) land current densities to both the median solar wind electric field and dynamic pressure effects, we find no significant dependence of the Birkeland currents on solar wind Alfvén Mach number.

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“…Reasons for a change in the pattern of seasonal dependence for the CRB location and weakening of the summer-winter contrast after ∼ 2008 in our data are not clear. Our original thought was that the seasonal variations in the CRB location are due to a poleward shift of summer field-aligned currents (e.g., Green et al (2009) and references therein). But this effect would not explain our data for period 2 although we do not know if the FAC seasonal shifts are still in effect (recent FAC data have not been statistically investigated, to the best of our knowledge).…”

Section: Discussionmentioning

confidence: 99%

Seasonal and solar cycle variations in the ionospheric convection reversal boundary location inferred from monthly SuperDARN data sets

Koustov

Fiori

2016

Ann. Geophys.

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Abstract. Multi-year (1995Multi-year ( -2013 velocity data collected by the Super Dual Auroral Network (SuperDARN) HF radars are considered to investigate seasonal and solar cycle variations of the convection reversal boundary (CRB) location for interplanetary magnetic field (IMF) B z < 0. By considering monthly data sets we show that the CRB is at higher latitudes in summer between 1995 and 2007. The poleward shifts are on the order of 2-5 • . After 2007, the seasonal effect weakens, and the highest latitudes for the CRB start to occur during the winter time. We show that the CRB latitudes decrease with an increase of the IMF transverse component at a rate of (1-2 • )/2 nT. Because of this effect, on average, the CRB latitudes are lower during high solar activity periods with stronger IMFs. We also confirm the effect of the CRB dawn-dusk shifts related to the IMF changes in the IMF B y sign.

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Seasonal and interplanetary magnetic field dependence of the field-aligned currents for both Northern and Southern Hemispheres

Cited by 71 publications

References 48 publications

Global characteristics of auroral Hall currents derived from the Swarm constellation: dependences on season and IMF orientation

Global characteristics of auroral Hall currents derived from the Swarm constellation: dependences on season and IMF orientation

Statistical analysis of the dependence of large-scale Birkeland currents on solar wind parameters

Seasonal and solar cycle variations in the ionospheric convection reversal boundary location inferred from monthly SuperDARN data sets

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