Directed Network of Substorms Using SuperMAG Ground‐Based Magnetometer Data

Orr, Lauren; Chapman, Sandra C.; Gjerloev, J. W.

doi:10.1029/2019gl082824

Cited by 11 publications

(21 citation statements)

References 32 publications

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“…The network has been constructed by identifying connections using the canonical cross-correlation (CCC) lag at which the CCC between each pair of magnetometers is at its peak so that each connection has an associated lag, τ c . The magnitude of the lag ∣ τ c ∣ indicates whether connections within a given community are formed rapidly (zero CCC lag i.e., τ c = 0 (gray)) or whether they are associated with propagation and/or expansion (non-zero CCC lags from 1 to 15 min (blue-red)) 27 , see “Methods,” “Calculating the direct network.”…”

Section: Resultsmentioning

confidence: 99%

“…The details of the underpinning methodology for forming the raw network are detailed in refs. 27 , 34 and we summarize it here. The magnetometers are the nodes of the network and a pair of nodes are connected (have an edge between them) if the CCC 46 of their vector magnetic field perturbation time series exceeds a station and event-specific threshold.…”

Section: Methodsmentioning

confidence: 99%

“…Importantly, to recover the full dynamics that occurs on multiple timescales, the CCC at all time lags is needed. Orr et al 27 pioneered this approach, obtaining the first directed networks for the response to substorms seen in the full SuperMAG data set. Including time-lagged correlations means that a magnetometer pair, which were not connected to the network (i.e., correlated above the threshold) at zero lag may be connected at non-zero time lag.…”

Section: Methodsmentioning

confidence: 99%

“…In ref. 27 , we recently made the first application of directed networks to the set of 100+ ground-based magnetometers collated by SuperMAG, which allowed us to test these ideas on a large set of isolated substorm events. To objectively test the hypothesized large-scale SCW models, we used the raw network properties to resolve timings of propagation/expansion of the current wedge within and between three predefined spatial regions and found timings of a consistent sequence in which the classic SCW forms.…”

Section: Introductionmentioning

confidence: 99%

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Network community structure of substorms using SuperMAG magnetometers

et al. 2021

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Geomagnetic substorms are a global magnetospheric reconfiguration, during which energy is abruptly transported to the ionosphere. Central to this are the auroral electrojets, large-scale ionospheric currents that are part of a larger three-dimensional system, the substorm current wedge. Many, often conflicting, magnetospheric reconfiguration scenarios have been proposed to describe the substorm current wedge evolution and structure. SuperMAG is a worldwide collaboration providing easy access to ground based magnetometer data. Here we show application of techniques from network science to analyze data from 137 SuperMAG ground-based magnetometers. We calculate a time-varying directed network and perform community detection on the network, identifying locally dense groups of connections. Analysis of 41 substorms exhibit robust structural change from many small, uncorrelated current systems before substorm onset, to a large spatially-extended coherent system, approximately 10 minutes after onset. We interpret this as strong indication that the auroral electrojet system during substorm expansions is inherently a large-scale phenomenon and is not solely due to many meso-scale wedgelets.

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Section: Resultsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Network community structure of substorms using SuperMAG magnetometers

et al. 2021

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“…More recently, using data from the WIC and SI12 instruments on IMAGE, Walach et al (2017) found that the brightening of the electron auroral oval expanded toward the dawn and dusk sectors 10–40 minutes after substorm onset, during the substorm expansion phase, covering 12 hours of MLT. In contrast, by applying directed network analysis to ground magnetometer data, Orr et al (2019) found that magnetic perturbations associated with substorm activity and loosely linked to the auroral bulge expanded westward toward the dusk MLT sectors after substorm onset before expanding dawnward at a later time. We found that the average rate of expansion of the region of contracting OCB toward the dawn and dusk directions was |0.2| and |0.3| MLT/minutes, respectively, corresponding to approximately 1.1 km/s at 65° latitude, in agreement with these earlier studies of the expansion of the auroral brightness and westward and eastward moving surges.…”

Section: Discussionmentioning

confidence: 99%

Examining Local Time Variations in the Gains and Losses of Open Magnetic Flux During Substorms

et al. 2020

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The open magnetic flux content of the magnetosphere varies during substorms as a result of dayside and nightside reconnection. The open flux can be calculated from the area of the polar cap, delineated by the open-closed field line boundary (OCB). This study presents a superposed epoch analysis of the location of the OCB and the change in the magnetic flux content in individual nightside MLT sectors during substorm growth, expansion, and recovery phases. Far ultraviolet (FUV) observations from the IMAGE satellite are used to derive a proxy of the OCB location.In the hour prior to substorm onset, the total nightside flux content increases by up to 0.12 GWb on average, resulting in an equatorward expansion of the OCB. Following substorm onset, the OCB contracts toward the pole as the open magnetic flux content decreases by up to 0.14 GWb on average, but the rate of decrease of the total nightside open flux content differs by 5-66% between the three IMAGE far ultraviolet instruments. The OCB does not contract poleward uniformly in all nightside magnetic local time (MLT) sectors after substorm onset. Close to the substorm onset MLT sector, the OCB contracts immediately following substorm onset; however, the OCB in more dawnward and duskward MLT sectors continues to expand equatorward for up to 120 minutes after substorm onset. Despite the continued increase in flux in these sectors after substorm onset, the total nightside flux content decreases immediately at substorm onset, indicating that the nightside reconnection rate exceeds the dayside rate following substorm onset.Plain Language Summary Earth's magnetic field shields us from the steady stream of particles originating from the Sun, which carry the Sun's magnetic field. At Earth, the solar magnetic field can break open our magnetic field and allow energy to build up inside Earth's magnetic field. This energy can be explosively released during substorms. The auroral oval is a ring of aurora around the magnetic poles which varies in size, shape, and brightness during substorms. As energy is building in the magnetic field, the auroral oval expands. As the energy is released, it contracts. Using satellite images of the auroral oval, we show that prior to substorm onset, the nightside auroral oval expands toward the equator. At substorm onset, the auroral oval also rapidly moves poleward. The poleward motion initially occurs in a localized region as the rest of the nightside oval continues to expand. The poleward motion then spreads eastward and westward around the entire nightside oval over the following 20-120 minutes. Our results show that although most of the auroral oval continues to expand equatorward after substorm onset, the total area of the auroral oval decreases resulting in an overall net decrease in the energy stored in the Earth's magnetic field.

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Global dynamical network of the spatially correlated Pc2 wave response for the 2015 St. Patrick's Day storm

Chaudhry

Chapman

Gjerloev³

et al. 2022

Preprint

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We show the global dynamics of spatial cross-correlation of Pc2 wave activity can track the evolution of the 2015 St. Patrick's Day geomagnetic storm for an 8 hour time window around onset. The global spatially coherent response is tracked by forming a dynamical network from 1 second data using the full set of 100+ ground-based magnetometer stations collated by SuperMAG and Intermagnet. The pattern of spatial coherence is then captured by a few network parameters which in turn track the evolution of the storm. At onset IMF B z>0 and Pc2 power increases, we find a global response with stations being correlated over both local and global distances. Following onset, whilst B z>0, the network response is confined to the day-side. When IMF B z<0, there is a strong local response at high latitudes, consistent with the onset of polar cap convection driven by day-side reconnection. The spatially coherent response as revealed by the network grows and is maximal when both SME and SMR peak, consistent with an active electrojet and ring-current. Throughout the storm there is a coherent response both in stations located along lines of constant geomagnetic longitude, between hemispheres, and across magnetic local time. The network does not simply track the average Pc2 wave power, however is characterized by network parameters which track the evolution of the storm. This is a first study to parameterize global Pc2 wave correlation and offers the possibility of statistical studies across multiple events to detailed comparison with, and validation of, space weather models.

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Directed Network of Substorms Using SuperMAG Ground‐Based Magnetometer Data

Cited by 11 publications

References 32 publications

Network community structure of substorms using SuperMAG magnetometers

Network community structure of substorms using SuperMAG magnetometers

Examining Local Time Variations in the Gains and Losses of Open Magnetic Flux During Substorms

Global dynamical network of the spatially correlated Pc2 wave response for the 2015 St. Patrick's Day storm

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