scholarly journals Relation between substorm characteristics and rapid temporal variations of the ground magnetic field

2006 ◽  
Vol 24 (2) ◽  
pp. 725-733 ◽  
Author(s):  
A. Viljanen ◽  
E. I. Tanskanen ◽  
A. Pulkkinen
Keyword(s):  
Magnetic Field ◽  
Time Derivative ◽  
Sunspot Cycle ◽  
Temporal Variations ◽  
Field Vector ◽  
Geomagnetically Induced Currents ◽  
Horizontal Magnetic Field ◽  
Auroral Substorm ◽  
Induced Currents ◽  
Ground Magnetic

Abstract. Auroral substorms are one of the major causes of large geomagnetically induced currents (GIC) in technological systems. This study deals with different phases of the auroral substorm concerning their severity from the GIC viewpoint. Our database consists of 833 substorms observed by the IMAGE magnetometer network in 1997 (around sunspot minimum) and 1999 (rising phase of the sunspot cycle), divided into two classes according to the Dst index: non-storm (Dst>-40 nT, 696 events) and storm-time ones (Dst<-40 nT, 137 events). The key quantity concerning GIC is the time derivative of the horizontal magnetic field vector (dH/dt) whose largest values during substorms occur most probably at about 5 min after the onset at stations with CGM latitude less than 72 deg. When looking at the median time of the occurrence of the maximum dH/dt after the expansion onset, it increases as a function of latitude from about 15 min at CGM lat=56 deg to about 45 min at CGM lat=75 deg for non-storm substorms. For storm-time events, these times are about 5 min longer. Based on calculated ionospheric equivalent currents, large dH/dt occur mostly during the substorm onset when the amplitude of the westward electrojet increases rapidly.

scholarly journals Characteristics of variations in the ground magnetic field during substorms at mid latitudes

2009 ◽  
Vol 27 (9) ◽  
pp. 3421-3428 ◽  
Author(s):  
K. L. Turnbull ◽  
J. A. Wild ◽  
F. Honary ◽  
A. W. P. Thomson ◽  
A. J. McKay
Keyword(s):  
Magnetic Field ◽  
Transmission Lines ◽  
Power Transmission ◽  
Time Derivative ◽  
High Time Resolution ◽  
Power Transmission Lines ◽  
Geomagnetically Induced Currents ◽  
Horizontal Magnetic Field ◽  
Ground Magnetic ◽  
The Uk

Abstract. Substorms are known to cause geomagnetically induced currents (GIC) in power transmission lines through variations in the ground magnetic field. An improved knowledge and understanding of how the different phases of substorms affect the ground magnetic field will ultimately help to better understand how GIC arise. Although usually associated with high latitude power transmission networks, GIC potentially pose a risk to mid latitude networks such as the UK's National Grid. Using a list of substorm expansion phase onsets derived from auroral observations by the IMAGE-FUV satellite, this study examines 553 individual onsets. In order to cover mid latitudes, ground magnetometer data from the UK Sub-Auroral Magnetometer Network (SAMNET) are exploited. These high time resolution (5 s) data are used to study the ground magnetic field for an hour after onset, in particular the time derivative of the horizontal magnetic field, H. The data covers the period from 2000 to 2003 (just after solar maximum). Results are compared with a previous study of magnetic field variations at higher latitudes, using data with a much lower (1 min) cadence during substorms identified from geomagnetic indices during a period just after solar minimum.

scholarly journals Induced currents due to 3D ground conductivity play a major role in the interpretation of geomagnetic variations

2020 ◽  
Vol 38 (5) ◽  
pp. 983-998
Author(s):  
Liisa Juusola ◽  
Heikki Vanhamäki ◽  
Ari Viljanen ◽  
Maxim Smirnov
Keyword(s):  
Magnetic Field ◽  
Electric Fields ◽  
Time Derivative ◽  
Three Dimensional ◽  
Geomagnetically Induced Currents ◽  
Ionospheric Currents ◽  
Geomagnetic Variations ◽  
Near Surface ◽  
Induced Currents ◽  
Telluric Currents

Abstract. Geomagnetically induced currents (GICs) are directly described by ground electric fields, but estimating them is time-consuming and requires knowledge of the ionospheric currents and the three-dimensional (3D) distribution of the electrical conductivity of the Earth. The time derivative of the horizontal component of the ground magnetic field (dH∕dt) is closely related to the electric field via Faraday's law and provides a convenient proxy for the GIC risk. However, forecasting dH∕dt still remains a challenge. We use 25 years of 10 s data from the northern European International Monitor for Auroral Geomagnetic Effects (IMAGE) magnetometer network to show that part of this problem stems from the fact that, instead of the primary ionospheric currents, the measured dH∕dt is dominated by the signature from the secondary induced telluric currents at nearly all IMAGE stations. The largest effects due to telluric currents occur at coastal sites close to high-conducting ocean water and close to near-surface conductivity anomalies. The secondary magnetic field contribution to the total field is a few tens of percent, in accordance with earlier studies. Our results have been derived using IMAGE data and are thus only valid for the stations involved. However, it is likely that the main principle also applies to other areas. Consequently, it is recommended that the field separation into internal (telluric) and external (ionospheric and magnetospheric) parts is performed whenever feasible (i.e., a dense observation network is available).

Dynamics of ionospheric and telluric currents during large events of geomagnetically induced currents

2021 ◽  
Author(s):  
Mirjam Kellinsalmi ◽  
Ari Viljanen ◽  
Liisa Juusola ◽  
Sebastian Käki
Keyword(s):  
Large Time ◽  
Time Derivative ◽  
Geomagnetically Induced Currents ◽  
Angular Variation ◽  
Horizontal Magnetic Field ◽  
Geomagnetic Variations ◽  
Induced Currents ◽  
Directional Distributions ◽  
Derivatives Of ◽  
Telluric Currents

&lt;p&gt;Geomagnetic variations are mainly produced by external currents in the ionosphere and magnetosphere, and secondarily by induced (internal/telluric) currents in the conducting Earth. Large geomagnetically induced currents (GIC) are associated with large time derivatives of the horizontal magnetic field. Recent results show that the time derivative is typically dominated by the contribution from the telluric currents. Our study aims to find measures to quantify the behaviour of external and internal currents and their time derivatives during large GIC events. Results of this study show that strong external currents have quite narrow directional distributions. Angular variation is larger for internal currents, and especially for their time derivatives. For external currents angular variation is larger at higher latitudes. Similar behaviour is not seen with internal currents.&lt;/p&gt;

scholarly journals Extreme value analysis of the time derivative of the horizontal magnetic field and computed electric field

2016 ◽  
Vol 34 (4) ◽  
pp. 485-491 ◽  
Author(s):  
Peter Wintoft ◽  
Ari Viljanen ◽  
Magnus Wik
Keyword(s):  
Magnetic Fields ◽  
Time Derivative ◽  
Extreme Value ◽  
Power Grids ◽  
Extreme Value Analysis ◽  
Geomagnetically Induced Currents ◽  
Horizontal Magnetic Field ◽  
Value Analysis ◽  
Electrical Fields ◽  
Ground Magnetic

Abstract. High-frequency ( ≈  minutes) variability of ground magnetic fields is caused by ionospheric and magnetospheric processes driven by the changing solar wind. The varying magnetic fields induce electrical fields that cause currents to flow in man-made conductors like power grids and pipelines. Under extreme conditions the geomagnetically induced currents (GIC) may be harmful to the power grids. Increasing our understanding of the extreme events is thus important for solar-terrestrial science and space weather. In this work 1-min resolution of the time derivative of measured local magnetic fields (|dBh∕dt|) and computed electrical fields (Eh), for locations in Europe, have been analysed with extreme value analysis (EVA). The EVA results in an estimate of the generalized extreme value probability distribution that is described by three parameters: location, width, and shape. The shape parameter controls the extreme behaviour. The stations cover geomagnetic latitudes from 40 to 70° N. All stations included in the study have contiguous coverage of 18 years or more with 1-min resolution data. As expected, the EVA shows that the higher latitude stations have higher probability of large |dBh∕dt| and |Eh| compared to stations further south. However, the EVA also shows that the shape of the distribution changes with magnetic latitude. The high latitudes have distributions that fall off faster to zero than the low latitudes, and upward bounded distributions can not be ruled out. The transition occurs around 59–61° N magnetic latitudes. Thus, the EVA shows that the observed series north of  ≈ 60° N have already measured values that are close to the expected maxima values, while stations south of  ≈ ° N will measure larger values in the future.

Intense dB/dt variations driven by near-Earth Bursty Bulk Flows (BBFs): A case study

2021 ◽  
Author(s):  
Dong Wei ◽  
Malcolm Dunlop ◽  
Junying Yang ◽  
Xiangcheng Dong ◽  
Yiqun Yu ◽  
...  
Keyword(s):  
Large Scale ◽  
Current System ◽  
Geomagnetically Induced Currents ◽  
Inner Magnetosphere ◽  
Wide Range ◽  
Ground System ◽  
Induced Currents ◽  
Ground Magnetic ◽  
Bursty Bulk Flows

&lt;p&gt;During geomagnetically disturbed times the surface geomagnetic field often changes abruptly, producing&amp;#160;geomagnetically induced currents (GICs) in a number of ground based systems. There are, however,&amp;#160;few studies reporting GIC effects which are driven directly by bursty bulk flows (BBFs) in the inner&amp;#160;magnetosphere. In this study, we investigate the characteristics and responses of the magnetosphere-ionosphere-ground system during the 7 January 2015 storm by using a multi-point approach which combines space-borne measurements and ground magnetic observations. During the event, multiple BBFs are&amp;#160;detected in the inner magnetosphere while the magnetic footprints of both magnetospheric and ionospheric&amp;#160;satellites map to the same conjugate region surrounded by a group of magnetometer ground stations. It is&amp;#160;suggested that the observed, localized substorm currents are caused by the observed magnetospheric BBFs,&amp;#160;giving rise to intense geomagnetic perturbations. Our results provide direct evidence that the wide-range&amp;#160;of intense dB/dt&lt;strong&gt;&amp;#160;&lt;/strong&gt;(and dH/dt) variations are associated with a large-scale, substorm current system, driven&amp;#160;by multiple BBFs.&lt;/p&gt;

DIPOLE-FIELD TYPE MAGNETIC DISTURBANCES AND AURORAL ACTIVITIES

1961 ◽  
Vol 39 (2) ◽  
pp. 350-366 ◽  
Author(s):  
B. K. Bhattacharyya
Keyword(s):  
Magnetic Field ◽  
Current System ◽  
Field Vector ◽  
Maximum Magnitude ◽  
Horizontal Magnetic Field ◽  
Auroral Activity ◽  
The North ◽  
Initial Location ◽  
Sequence Relationship ◽  
Direction Of Movement

The characteristics of the magnetic field components at Agincourt have been calculated for a current system produced by an electric dipole located in the region of auroral activity near Ottawa. It is noted that, irrespective of the orientation of the dipole, the horizontal magnetic field component rotates in the clockwise and anticlockwise senses for motion of the dipole towards the east and the west respectively, when the dipole is situated in the north half of the sky as seen from the observing station.Next, the magnetograms obtained at Agincourt have been studied at those times of the night when auroral activity was recorded in the all-sky camera photographs at Springhill near Ottawa. It is noted that the horizontal magnetic field describes a loop during a particular phase of auroral activity because of its gradual growth and decay. The distributions of clockwise and anticlockwise rotations with respect to local time are found to be very similar in many respects to those of auroral motions to the east and west respectively. The sense of rotation of the loop is predominantly anticlockwise in the early part of the night and clockwise in the late hours of the night.It is found that eastward and westward orientations of the dipole are the most probable ones. The direction of movement and the initial location of the predominant auroral form in the sky are found to tally well with those of the dipole deduced from a study of the magnetograms.It seems that there is a time sequence relationship between successive phases of auroral activity and changes of characteristics of the loops described by the horizontal magnetic field vector. The area of a loop and the maximum magnitude of the field vector in the loop appear to be related to the brightness and horizontal extent of the auroral forms.

scholarly journals Evaluation of Murrell’s EKF-Based Attitude Estimation Algorithm for Exploiting Multiple Attitude Sensor Configurations

Sensors ◽  
2021 ◽  
Vol 21 (19) ◽  
pp. 6450
Author(s):  
Sharanabasaweshwara Asundi ◽  
Norman Fitz-Coy ◽  
Haniph Latchman
Keyword(s):  
Magnetic Field ◽  
Time Derivative ◽  
Estimation Algorithm ◽  
Field Vector ◽  
Attitude Estimation ◽  
Magnetic Field Vector ◽  
Sun Sensor ◽  
Satellite Attitude ◽  
Multiple Sensor ◽  
Sensor Suite

Pico- and nano-satellites, due to their form factor and size, are limited in accommodating multiple or redundant attitude sensors. For such satellites, Murrell’s implementation of the extended Kalman filter (EKF) can be exploited to accommodate multiple sensor configurations from a set of non redundant attitude sensors. The paper describes such an implementation involving a sun sensor suite and a magnetometer as attitude sensors. The implementation exploits Murrell’s EKF to enable three sensor configurations, which can be operationally commanded, for satellite attitude estimation. Among the three attitude estimation schemes, (i) sun sensor suite and magnetometer, (ii) magnetic field vector and its time derivative and (iii) magnetic field vector, it is shown that the third configuration is better suited for attitude estimation in terms of precision and accuracy, but can consume more time to converge than the other two.

scholarly journals Induced telluric currents play a major role in the interpretation of geomagnetic variations

2020 ◽  
Author(s):  
Liisa Juusola ◽  
Heikki Vanhamäki ◽  
Ari Viljanen ◽  
Maxim Smirnov
Keyword(s):  
Magnetic Field ◽  
Electric Fields ◽  
Time Derivative ◽  
Three Dimensional ◽  
Image Data ◽  
Geomagnetically Induced Currents ◽  
Ionospheric Currents ◽  
Geomagnetic Variations ◽  
Near Surface ◽  
Telluric Currents

Abstract. Geomagnetically induced currents (GIC) are directly described by ground electric fields, but estimating them is time-consuming and requires knowledge of the ionospheric currents as well as the three-dimensional distribution of the electrical conductivity of the Earth. The time derivative of the horizontal component of the ground magnetic field (dH/dt) is closely related to the electric field via Faraday's law, and provides a convenient proxy for the GIC risk. However, forecasting dH/dt still remains a challenge. We use 25 years of 10 s data from the North European International Monitor for Auroral Geomagnetic Effects (IMAGE) magnetometer network to show that part of this problem stems from the fact that instead of the primary ionospheric currents, the measured dH/dt is dominated by the signature from the secondary induced telluric currents nearly at all IMAGE stations. The largest effects due to telluric currents occur at coastal sites close to highly-conducting ocean water and close to near-surface conductivity anomalies. The secondary magnetic field contribution to the total field is a few tens of percent, in accordance with earlier studies. Our results have been derived using IMAGE data and are thus only valid for the involved stations. However, it is likely that the main principle also applies to other areas. Consequently, it is recommended that the field separation into internal (telluric) and external (ionospheric and magnetospheric) parts is performed whenever feasible, i.e., a dense observation network is available.

scholarly journals Statistical relationships between variations of the geomagnetic field, auroral electrojet, and geomagnetically induced currents

2019 ◽  
Vol 5 (1) ◽  
pp. 48-58
Author(s):  
Андрей Воробьев ◽  
Andrey Vorobev ◽  
Вячеслав Пилипенко ◽  
Vyacheslav Pilipenko ◽  
Ярослав Сахаров ◽  
...  
Keyword(s):  
Geomagnetic Field ◽  
Extreme Values ◽  
Time Derivative ◽  
Geomagnetically Induced Currents ◽  
Ae Index ◽  
Induced Currents ◽  
Statistical Relationships ◽  
Highly Correlated ◽  
Log Normal ◽  
Field Variability

Using observations from the IMAGE magnetic observatories and the station for recording geomagnetically induced currents (GIC) in the electric transmission line in 2015, we examine relationships between geomagnetic field and GIC variations. The GIC intensity is highly correlated (R>0.7) with the field variability |dB/dt| and closely correlated with variations in the time derivatives of X and Y components. Daily variations in the mean geomagnetic field variability |dB/dt| and GIC intensity have a wide night maximum, associated with the electrojet, and a wide morning maximum, presumably caused by intense Pc5–Pi3 geomagnetic pulsations. We have constructed a regression linear model to estimate GIC from the time derivative of the geomagnetic field and AE index. Statistical distributions of the probability density of the AE index, geomagnetic field derivative, and GIC correspond to the log-normal law. The constructed distributions are used to evaluate the probabilities of extreme values of GIC and |dB/dt|.

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