Geomagnetically Induced Currents from the Sun to the Power Grid E-Book
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- Herausgeber: John Wiley & Sons
- Kategorie: Wissenschaft und neue Technologien
- Serie: Geophysical Monograph Series
- Sprache: Englisch
An introduction to geomagnetic storms and the hazards they pose at the Earth's surface Geomagnetic storms are a type of space weather event that can create Geomagnetically Induced Currents (GICs) which, once they reach Earth's surface, can interfere with power grids and transport infrastructure. Understanding the characteristics and impacts of GICs requires scientific insights from solar physics, magnetospheric physics, aeronomy, and ionospheric physics, as well as geophysics and power engineering. Geomagnetically Induced Currents from the Sun to the Power Grid is a practical introduction for researchers and practitioners that provides tools and techniques from across these disciplines. Volume highlights include: * Analysis of causes of geomagnetic storms that create GICs * Data and methods used to analyze and forecast GIC hazard * GIC impacts on the infrastructure of the bulk power system * Analysis techniques used in different areas of GIC research * New methods to validate and predict GICs in transmission systems
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Table of Contents
Cover
CONTRIBUTORS
PREFACE
Part I: Space Weather
1 An Introduction to Geomagnetically Induced Currents
1.1. INTRODUCTION
1.2. THE SPACE WEATHER CHAIN
1.3. GEOMAGNETICALLY INDUCED CURRENTS
1.4. EXTREME EVENTS
1.5. CONCLUDING REMARKS
ACKNOWLEDGMENTS
REFERENCES
2 Interpolating Geomagnetic Observations: Techniques and Comparisons
2.1. INTRODUCTION
2.2. SYNTHETIC GEOMAGNETIC DISTURBANCE OVER NORTH AMERICA
2.3. INTERPOLATION METHODOLOGIES AND RESULTS
2.4. DISCUSSION AND RECOMMENDATIONS
ACKNOWLEDGMENTS
APPENDIX: 2D VECTOR CORRELATIONS
REFERENCES
3 Magnetohydrodynamic Models of B and Their Use in GIC Estimates
3.1. THEORY AND MODELS
3.2. VALIDITY OF MHD AT EARTH
3.3. MHD AND GICs
3.4. THE FUTURE OF MHD AND GICs
REFERENCES
4 Empirical Modeling of the Geomagnetic Field for GIC Predictions
4.1. INTRODUCTION
4.2. EMPIRICAL MODEL STRENGTHS AND WEAKNESSES
4.3. EXAMPLES FROM THREE EVENTS
4.4. IMPROVING PREDICTION OF HIGHER FREQUENCY VARIATIONS
4.5. IMPROVING PREDICTIONS OF SUBSTORM PERTURBATIONS
4.6. SUMMARY
ACKNOWLEDGMENTS, SAMPLES, AND DATA
REFERENCES
5 Geoelectric Field Generation by Field‐Aligned Currents
5.1. INTRODUCTION
5.2. A MODEL OF GEOELECTRIC FIELD GENERATION
5.3. GROUND SIGNATURE OF A LOCALIZED FAC
5.4. RELATION TO PREVIOUS MODELS
5.5. COMPARISON TO THE BIOT–SAVART APPROACH
5.6. CONCLUSIONS
APPENDIX: REFLECTION FROM A VERTICALLY‐STRUCTURED GROUND PROFILE
ACKNOWLEDGMENTS
REFERENCES
Part II: Geomagnetic Induction
6 Empirical Estimation of Natural Geoelectric Hazards
6.1. INTRODUCTION
6.2. DEFINING THE HAZARD
6.3. INDUCTION IN THE CONDUCTING EARTH
6.4. A LOOK AT SOME DATA
6.5. GEOELECTRIC TIME SERIES
6.6. 100‐YEAR AND 1989 HAZARD MAPS
6.7. DISCUSSION
ACKNOWLEDGMENTS
REFERENCES
7 The Magnetotelluric Method and Its Application to Understanding Geomagnetically Induced Currents
7.1. INTRODUCTION
7.2. THE MAGNETOTELLURIC METHOD
7.3. MT FUNDAMENTAL PRINCIPLES
7.4. DATA ACQUISITION
7.5. DATA PROCESSING AND INVERSION
7.6. RESISTIVITY MODEL INTERPRETATION
7.7. CONCLUSIONS
ACKNOWLEDGMENTS
REFERENCES
8 The First 3D Conductivity Model of the Contiguous United States: Reflections on Geologic Structure and Application to Induction Hazards
8.1. INTRODUCTION
8.2. ELECTROMAGNETIC METHODS IN GEOPHYSICS
8.3. MAGNETOTELLURICS AND GEOELECTRIC FIELD ESTIMATION
8.4. MAGNETOTELLURIC DATA IN THE CONTIGUOUS UNITED STATES
8.5. 3D ELECTRICAL CONDUCTIVITY MODELS OF THE CONTIGUOUS UNITED STATES
8.6. DEEP STRUCTURE: GLOBAL ELECTRICAL CONDUCTIVITY MODEL
8.7. MERGED 3D CONDUCTIVITY MODEL OF CONTIGUOUS UNITED STATES
8.8. NORTH AMERICAN GEOLOGY REFLECTED IN THE MODEL
8.9. UTILITY FOR INDUCTION HAZARDS RESEARCH AND OPERATIONS
8.10. CONCLUSIONS
ACKNOWLEDGMENTS
REFERENCES
9 A Data‐Driven Approach to Estimating Geoelectric Fields: Comparison, Validation, and Discussion of Geomagnetic Hazard Assessment Within Common Physiographic Zones
9.1. INTRODUCTION
9.2. INDUCTION
9.3. DATA
9.4. 1‐D CONDUCTIVITY MODELS AND PHYSIOGRAPHIC ZONES
9.5. METHODS
9.6. RESULTS
9.7. EXAMINING AN ARRAY OF IMPEDANCES IN MINNESOTA
9.8. IMPLICATIONS FOR GEOHAZARD ASSESSMENT
ACKNOWLEDGMENTS
REFERENCES
Part III: Power System Impacts
10 An Overview of Modeling Geomagnetic Disturbancesin Power Systems
10.1. INTRODUCTION
10.2. MAJOR POWER SYSTEM COMPONENTS
10.3. TRANSFORMER: A CLOSER LOOK
10.4. GIC CALCULATIONS: DC ANALYSIS
10.5. REACTIVE POWER LOSSES AND VOLTAGE STABILITY: AC ANALYSIS
10.6. DYNAMIC ELECTRIC FIELDS
10.7. CONCLUDING REMARKS
ACKNOWLEDGMENTS, SAMPLES, AND DATA
APPENDIX
REFERENCES
11 Geomagnetically Induced Currents from ExtremeSpace Weather Events
11.1. INTRODUCTION
11.2. EXTREME GEOMAGNETIC STORMS
11.3. EXTREME STORM DEFINITIONSFOR GIC STUDIES
11.4. OCCURRENCE RATE FOR EXTREME GMDs
11.5. GIC IMPACTS TO INFRASTRUCTURE
11.6. CONCLUSIONS
ACKNOWLEDGMENTS
REFERENCES
12 The Challenge Posed by Space Weather to Electric Power Reliability: Evidence from the New York Electric Power Grid
12.1. INTRODUCTION
12.2. THE GEOMAGNETIC DATA EMPLOYED IN THIS STUDY
12.3. AN OVERVIEW OF THE POWER GRID AND THE VALUE OF ELECTRIC POWER RELIABILITY
12.4. THE NEW YORK ELECTRIC POWER SYSTEM
12.5. SYSTEM ALERTS AND RESERVE PICK‐UPS
12.6. GICS AND RELIABILITY ACTIONS IN NYISO: IS THERE A RELATIONSHIP?
12.7. GEOMAGNETIC ACTIVITY AND THE PREDICTED PROBABILITY OF A RPSA
12.8. CONCLUSION
ACKNOWLEDGMENTS
REFERENCES
13 Mitigating Power System Response to GICs in Known Networks
13.1. INTRODUCTION
13.2. BACKGROUND ON GMD RESPONSE PROCEDURES
13.3. GIC MODELING
13.4. POWER FLOW SOLUTION INCLUDING GICs
13.5. GENERATION REDISPATCH THROUGH RELIABILITY‐BASED OPF
13.6. GMD MITIGATION THROUGH TRANSMISSION LINE SWITCHING
13.7. GMD MITIGATION THROUGH BLOCKING DEVICES
13.8. FUTURE WORK
ACKNOWLEDGMENTS
REFERENCES
Index
End User License Agreement
List of Tables
Chapter 2
Table 2.1 Names, Abbreviations, and Locations of All Synthetic Magnetic Obser...
Chapter 4
Table 4.1 Magnetometer Station Names and Locations.
Chapter 7
Table 7.1 Units Used in Electromagnetism.
Chapter 8
Table 8.1 Inductive Electromagnetic (EM) Methods for Constraining Subsurface ...
Table 8.2 Regional 3D Electrical Conductivity Models in the Contiguous United...
Table 8.3 Details on Inversion Configurations and Model Performance for Regio...
Table 8.4 Regional 3D Electrical Conductivity Models used in the CONUS Compil...
Chapter 11
Table 11.1 Historical and Recent Large Geomagnetic Storms.
Chapter 12
Table 12.1 Descriptive Statistics for the GIC Proxy, 1 January 2002 to 31 Dec...
Table 12.2 Approximate Peak Load and Capacity within NYISO in 2002.
Table 12.3 Estimation Results.
Table 12.4 Out‐of‐Sample Predicted Probabilities.
List of Illustrations
Chapter 1
Figure 1.1 Technological infrastructure affected by space weather events at ...
Figure 1.2 The basic principle for the generation of GICs: variations of the...
Figure 1.3 Depiction of electromagnetic signal penetration at different peri...
Figure 1.4 EarthScope USArray MT status map across the lower‐48 U.S. The sta...
Figure 1.5 Geomagnetic latitude distributions comprising 12 extreme events t...
Chapter 2
Figure 2.1 Simulated “St. Patrick’s Day” geomagnetic storm horizontal vector...
Figure 2.2 Snapshots of the North American distribution of simulated horizon...
Figure 2.3 Snapshots of the North American distribution of nearest neighbor‐...
Figure 2.4 Comparison of synthetic truth and nearest neighbor‐interpolated v...
Figure 2.5 Delaunay tessellation for the set of geomagnetic observatory coor...
Figure 2.6 Snapshots of the North American distribution of TRI‐interpolated ...
Figure 2.7 Comparison of synthetic truth and triangle barycentric‐interpolat...
Figure 2.8 Snapshots of the North American distribution of Gaussian Process ...
Figure 2.9 Comparison of synthetic truth and Gaussian Process Regression‐int...
Figure 2.10 Snapshots of the North American distribution of spherical cap ha...
Figure 2.11 Comparison of synthetic truth and spherical cap harmonic analysi...
Figure 2.12 Divergence‐free spherical elementary current (SEC). Vector
S
poi...
Figure 2.13 Distribution of spherical elementary current (SEC) poles used fo...
Figure 2.14 Snapshots of the North American distribution of spherical elemen...
Figure 2.15 Comparison of synthetic truth and spherical elementary current s...
Chapter 3
Figure 3.1 MHD pressure (contours) and magnetic field (white lines) from a B...
Figure 3.2 Ionospheric electrodynamics in terms of field‐aligned currents (c...
Figure 3.3 Correlation between MHD predictions (vertical axes) of CPCP (left...
Figure 3.4 Machine identification of FACs from the LFM model using coarse (l...
Figure 3.5 Contributions of different current density categories to the tota...
Figure 3.6 Similar to the bottom frame of Figure 3.5, but for a higher latit...
Figure 3.7 An illustration of the data‐model comparisons leveraged in the SW...
Figure 3.8 Median
dB
/
dt
prediction errors of different MHD and empirical mod...
Chapter 4
Figure 4.1 Empirical model prediction for 27–28 May 2017. The solar wind and...
Figure 4.2 Empirical model prediction for 16 July 2017. The solar wind and I...
Figure 4.3 Empirical model prediction for 3 August 2017. The solar wind and ...
Figure 4.4 The SWPC/SWMF numerical model prediction for 3 August 2017, 21:56...
Figure 4.5 Maps of geomagnetic perturbations for a clock angle of 270° ± 90°...
Chapter 5
Figure 5.1 Cartoon illustration of the domain and coordinate system of the m...
Figure 5.2 Two‐dimensional profile of (a) the ionospherically‐incident local...
Figure 5.3 Two‐dimensional profile of (a) the ionospherically‐incident local...
Figure 5.4 Spatial distribution of the ionospheric FACs and the resultant ge...
Figure 5.5 Comparison of peak geoelectric field magnitudes as a function of ...
Figure 5.6 Frequency dependence of largest geoelectric field for all top‐lay...
Figure 5.7 Spatial distribution of geoelectric fields for FACs that include ...
Figure 5.8 Geoelectric fields associated with a self‐closing coaxial FAC. (a...
Chapter 6
Figure 6.1 Time series of 1‐min resolution (a) north
B
x
(
t
) (black) and east
Figure 6.2 Apparent resistivities,
(yellow),
(blue),
(red),
(green),...
Figure 6.3 Time series of 1‐min resolution (a and c) north
E
x
(
t
) and east
E
y
Figure 6.4 Maps of horizontal‐component geoelectric field vectors
E
h
(
t
,
x
,
y
Figure 6.5 Maps showing (a) 100‐year geoelectric exceedance amplitudes at th...
Chapter 7
Figure 7.1 (a) Vector combinations used in the impedance tensor when vertica...
Figure 7.2 Schematic of typical MT station installation geometry. (left) Two...
Figure 7.3 A two‐day recording of raw, uncalibrated MT time series data from...
Figure 7.4 (a) Example of MT data with error bars. Only the
Z
xy
(light gray)...
Figure 7.5 Example of a 3D resistivity model created from MT inversion with ...
Chapter 8
Figure 8.1 Locations of all magnetotelluric sites currently at IRIS EMTF dat...
Figure 8.2 3D electrical conductivity variations in Earth’s mantle beneath N...
Figure 8.3 Relative locations of six regional models in the central and east...
Figure 8.4 First‐order geologic provinces within the CONUS adapted from Reed...
Figure 8.5 Electrical resistivity model at upper‐crustal (3 km) depth. Label...
Figure 8.6 Electrical resistivity model at mid‐crustal (15 km) depth. Geolog...
Figure 8.7 Electrical resistivity model at lower‐crustal (30 km) depth. Geol...
Figure 8.8 Electrical resistivity model predominantly within the mantle lith...
Figure 8.9 Two alternative workflows for estimation of gridded (geo‐)electri...
Chapter 9
Figure 9.1 Maps showing the locations of the magnetic observatories (availab...
Figure 9.2 Real (left panels, upper lines; right panels, lower lines) and im...
Figure 9.3 Real (left panels, upper lines; right panels, lower lines) and im...
Figure 9.4 Full time series for geomagnetic fields observed at the Brandon (...
Figure 9.5 Discrete real (top panels, upper lines; bottom panels, lower line...
Figure 9.6 Discrete real (left panels, upper lines; right panels, lower line...
Figure 9.7 Full time series for geomagnetic fields at the Fredericksburg (FR...
Figure 9.8 1D Resistivity model for SU‐1, indicating a one‐dimensional condu...
Figure 9.9 1D Resistivity model for PT‐1, indicating a one‐dimensional condu...
Figure 9.10 Validation geoelectric field estimations showing a comparison be...
Figure 9.11 Time series for geomagnetic fields at the Brandon (BRD) magnetic...
Figure 9.12 Power spectra derived from estimated geoelectric fields during t...
Figure 9.13 Time series for geomagnetic fields at the Fredericksburg (FRD) m...
Figure 9.14 Power spectra derived from estimated geoelectric fields during t...
Figure 9.15 Estimations of the electric field Ex (top) and Ey (bottom) for E...
Figure 9.16 Map showing the location of NRCan Brandon (BRD) magnetic observa...
Figure 9.17 (a) Full time series for the x‐component (northing) of the geoma...
Chapter 10
Figure 10.1 Basic structure of a power grid reproduced from DOE (2015).
Figure 10.2 Transmission substation illustration. (A) Primary Side. 1. Incom...
Figure 10.3 Transformer winding connections.
Figure 10.4 Differences between isolation transformer (left column) and auto...
Figure 10.5 Simple power system and its three phase, DC representation for G...
Figure 10.6 GIC analysis form, with the electric field input dialog.
Figure 10.7 Four‐bus test case with GICs visualized for a 1 V/km Eastward el...
Figure 10.8 Forty‐bus test system.
Figure 10.9 Transformer input and estimated data for DC analysis.
Figure 10.10 DC current calculation options for transformers.
Figure 10.11 GIC analysis results.
Figure 10.12 Options for selecting “Areas” to include their (i) GMD‐induced ...
Figure 10.13 Relationship between transformer reactive power losses and GICs...
Figure 10.14 (a) Transformer core types in PowerWorld Simulator. (b) Enterin...
Figure 10.15 Default
K
factor settings (can be modified).
Figure 10.16 (a) Bus voltages of the 40‐bus case without a GMD. (b) Bus volt...
Figure 10.17 Comparison between measured and simulated GIC (using 1D conduct...
Chapter 11
Figure 11.1 Composite image from the SOHO image gallery of the 14 July 2000 ...
Figure 11.2 Horizontal component of the magnetic field measured in Ottawa, C...
Figure 11.3 The time‐derivative of the horizontal component of the magnetic ...
Chapter 12
Figure 12.1 The basic structure of the electric power system.
Figure 12.2 NYISO's geographic footprint.
Figure 12.3 NYISO's high voltage transmission system.
Figure 12.4 A GIC proxy, the day‐ahead reference price in NYISO, and the rea...
Figure 12.5 A receiver operating characteristic curve for the within‐sample ...
Figure 12.6 The GIC proxy and the geomagnetically induced predicted incremen...
Chapter 13
Figure 13.1 The line selection process in each step of the iterative line sw...
Figure 13.2 Reducing the computational complexity of the iterative line swit...
Figure 13.3 GIC‐saturated loss in the individual transformers before and aft...
Figure 13.4 Multi‐action line switching framework. (a) Assigning the actions...
Figure 13.5 Impact of the proposed line switching on the GIC‐saturated loss ...
Guide
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CONTRIBUTORS
Christopher BalchSpace Weather Prediction Center, National Oceanic and Atmospheric Administration, Boulder, CO, USA
Paul A. BedrosianGeology, Geophysics, and Geochemistry Science Center, United States Geological Survey, Denver, CO, USA;Crustal Geophysics, United States Geological Survey, Denver, CO, USA
Stephen W. CuttlerDepartment of Geophysics, Colorado School of Mines, Golden, CO, USA
Robyn A. D. FioriGeomagnetic Laboratory, Canadian Hazards Information Service, Natural Resources Canada, Ottawa, Ontario, Canada
Kevin F. ForbesThe Busch School of Business and Department of Economics, The Catholic University of America, Washington, DC, USA
Maryam KazerooniDepartment of Electrical and Computer Engineering, University of Illinois at Urbana‐Champaign, Urbana, IL, USA
Anna KelbertGeomagnetism Program, United States Geological Survey, Denver, CO, USA;College of Earth, Ocean, and Atmospheric Sciences, Oregon State University, Corvallis, OR, USA
Jeffrey J. LoveGeomagnetism Program, United States Geological Survey, Denver, CO, USA
Greg M. LucasGeomagnetism Program, United States Geological Survey, Denver, CO, USA
Esteban Bowles‐MartinezCollege of Earth, Ocean, and Atmospheric Sciences, Oregon State University, Corvallis, OR, USA
Benjamin S. MurphyCollege of Earth, Ocean, and Atmospheric Sciences, Oregon State University, Corvallis, OR, USA
Chigomezyo M. NgwiraDepartment of Physics, The Catholic University of America, Washington, DC, USA;Goddard Space Flight Center, Space Weather Laboratory, National Aeronautics and Space Administration, Greenbelt, MD, USA
Thomas J. OverbyeDepartment of Electrical and Computer Engineering, Texas A&M University, College Station, TX, USA
Antti A. PulkkinenGoddard Space Flight Center, Space Weather Laboratory, National Aeronautics and Space Administration, Greenbelt, MA, USA
E. Joshua RiglerGeomagnetism Program, United States Geological Survey, Golden, CO, USA
Adam SchultzCollege of Earth, Ocean, and Atmospheric Sciences, Oregon State University, Corvallis, OR, USA
Komal S. ShetyeDepartment of Electrical and Computer Engineering, Texas A&M University, College Station, TX, USA
O. C. St. CyrGoddard Space Flight Center, National Aeronautics and Space Administration, Greenbelt, MD, USA
D. R. WeimerBradley Department of Electrical and Computer Engineering and Center for Space Science and Engineering Research, Virginia Tech, Blacksburg, VA, USA;National Institute of Aerospace, Hampton, Virginia, USA
Daniel Welling
University of Texas at Arlington Physics Department, Arlington, TX, USA
Michael WiltbergerHigh Altitude Observatory, National Center for Atmospheric Research, Boulder, CO, USA
L. M. WinterLos Alamos National Laboratory, Los Alamos, NM, USA
J. R. WoodroffeSpace Science and Applications, Los Alamos National Laboratory, Los Alamos, NM, USA
PREFACE
When beginning work in the study of Geomagnetically Induced Currents (GICs), one of the most common difficulties experienced by a researcher is in overcoming, and eventually embracing, the interdisciplinary nature of the field. To understand the GIC process from start to end, we must understand a little bit of solar physics, space weather, geophysics, and power engineering – fields with completely different applications, expertise, and language. At a typical university, these disciplines are often in different departments, and likely in completely different schools. Overcoming disciplinary barriers takes a willingness to leave behind the high degree of specialization that the academic path requires and become a novice in at least one new field. This is daunting for most of us.
GIC research is also highly applied. Because of the potential for extreme GICs to damage critical power grid infrastructure, there is a great deal of societal importance. New research may have a significant effect on industry and government. This real‐world relevance is often what draws us to the field, but means that there are also practical considerations. Given the wide range of backgrounds and priorities among participants in the field, it is no wonder that there are sometimes disagreements, but also great potential for cross‐pollination of ideas and information.
Some of these differences will be apparent in this book. The book is presented in three parts – Space Weather, Geomagnetic Induction, and Power System Impacts. Each section is curated by an editor in the particular subfield, with authors invited from among the leading experts in the field. We have endeavored to include a range of expertise and backgrounds, and each of the authors has provided a perspective on their topic aimed at experts in adjacent fields. This book would not exist without the hard work of these authors, for which we are extremely grateful and humbled that they would join us in this effort. We hope that the result is a practical, interdisciplinary introduction to a full range of topics relevant to the GIC problem.
We hope that you, as a reader of this book, find it useful as a bridge to a new discipline within the broad range of GIC topics, or perhaps even find something new within your own specialty.
Jennifer L. GannonAndrei SwidinskyZhonghua Xu
Part ISpace Weather
1An Introduction to Geomagnetically Induced Currents
Chigomezyo M. Ngwira1,2,3 and Antti A. Pulkkinen2
1 Department of Physics, The Catholic University of America, Washington, DC, USA
2 Goddard Space Flight Center, Space Weather Laboratory, National Aeronautics and Space Administration, Greenbelt, MD, USA
3 Now at Atmospheric and Space Technology Research Associates, Louisville, CO, USA
ABSTRACT
Earth‐directed space weather is a serious concern that is recognized as one of the top priority problems in today’s society. Space weather‐driven geomagnetically induced currents (GICs) can disrupt operation of extended electrically conducting technological systems. This threat to strategic technological assets, like power grids, oil and gas pipelines, and communication networks, has rekindled interest in extreme space weather. To improve national preparedness, it is critical that we understand the physical processes related to extreme events in order to address key national and international objectives. This paper serves to provide a basic introduction to space weather and GICs, and highlights some of the major science challenges the GIC community continues to face.
Key Points
Geomagnetically induced currents (GICs) is a space weather‐driven phenomena.
It is a threat to strategic technological assets, such as power grids, oil and gas pipelines, and communication networks.
This paper serves to provide basic introduction on space weather and GICs, and the major science challenges the GIC community continues to face.
1.1. INTRODUCTION
Space weather is a serious natural threat to national security, and is recognized as one of the top priority problems today. The term “space weather” generally refers to dynamic conditions on the Sun, in the solar wind, and in the near‐Earth space environment that can influence the performance of man‐made technology, and can also affect human health and activities. Space weather is a multi‐faceted phenomenon, thus the scientific community is faced with a challenge to better understand this natural hazard in order to enhance preparedness.
Geomagnetically induced currents (GICs), a space weather‐driven phenomena, have received increased international policy, science, industry, and public interest. GICs flowing on ground‐based electrically conducting systems can disrupt operation of critical infrastructure such as power grids, pipelines, telecommunication cables, and railway systems (e.g., Barlow, 1849; Davidson, 1940; Boteler and Jansen van Beek, 1999; Molinski et al., 2000; Pirjola, 2000; Pulkkinen et al., 2001; Eroshenko et al., 2010, and references therein). The majority of community efforts focus on extreme forms of space weather which not only have severe impact on our technology and human space travel, but also challenge our understanding of the space weather phenomena.
Scientific investigations are critical for understanding the basic physics and predicting the potential impact of extreme space weather. Public opinions on the topic of extreme space weather include wide ranging views. This chapter provides a high‐level summary of space weather and GICs. While some of the topics touched on cover a broad range of space weather domains, the discussions are oriented/biased towards the geophysical facet of GICs. For more insight on specific GIC aspects, the reader is urged to consult other sections of this volume.
1.2. THE SPACE WEATHER CHAIN
The Sun is the primary source of all space weather in the heliosphere. Sudden, violent eruptions of solar material from the Sun’s atmosphere (the corona) called coronal mass ejections (CMEs), mark the beginning of major space weather events that eventually produce geomagnetic storms (disturbances) in the Earth’s upper atmosphere. The Sun’s activity is closely governed by the solar activity cycle, which has an average length of about 11 years. The cycle is defined by the number of visible active sunspots on the solar surface.
During solar maximum period when solar activity is high, the Sun can launch multiple CMEs towards Earth per day. A CME can be perceived as a cloud of plasma with the solar magnetic field known as the interplanetary magnetic field (IMF) embedded within it. Upon arriving at Earth, CMEs interact with the magnetosphere, a low‐density partially ionized region around the upper atmosphere dominated by Earth’s magnetic field. This interaction then triggers geomagnetic disturbances (GMDs) that lead to violent global magnetic field variations.
Orientation of the IMF varies with time and is important for interaction between the solar wind and the magnetosphere. Historically, the most intense disturbances have been recorded when the IMF Bz component, which is parallel to the solar rotation axis is oppositely directed to the Earth’s magnetic field, a condition often referred to as a southward or negative IMF. Under southward condition, the coupling between the solar wind and the magnetosphere is enhanced and the transfer of CME plasma, momentum, and energy into the near‐Earth space environment is increased. This enhanced energy flow stimulates a chain of complex processes within the magnetosphere–ionosphere (M–I) coupled system that regulate phenomena such as storm enhanced density, ionospheric irregularities, substorms, GICs, and auroral displays at high‐latitude locations. In addition to these effects, space weather can also compromise the integrity and performance of our technology (Lanzerotti, 2001). Figure 1.1 highlights some of the key technological assets affected by space weather. Per the purpose of this book, we now focus our discussions exclusively on GICs that occur at the end of the space weather chain.
Figure 1.1 Technological infrastructure affected by space weather events at the Earth.
Source: Courtesy of NASA: https://www.nasa.gov/mission_pages/rbsp/science/rbsp‐spaceweather.html.
1.3. GEOMAGNETICALLY INDUCED CURRENTS
Overall the GIC problem can be categorized by a two‐step approach (Pirjola, 2000, 2002a). In step 1, the geophysical facet involving the estimation of the geoelectric field based on M‐I currents and the ground conductivity is considered. Step 1 is fundamentally a science piece and the connection to space weather phenomenon. In step 2 (“engineering piece”) the current flowing on the system is calculated based on the estimated geoelectric field and detailed information about the particular ground system (e.g., Lehtinen and Pirjola, 1985; Molinski et al., 2000; Pirjola, 2000). In other words, the magnitude of GICs flowing through a network is generally determined by a combination of the horizontal surface geoelectric field, the geology, and elements of a given network (e.g., Molinski et al., 2000; Pirjola, 2000). We now briefly examine each of these three components.
1.3.1. The Geoelectric Field
The ground geoelectric field is the actual link to space weather through M‐I processes. The primary feature of geomagnetic storms that pertains to GICs is the variation of electric currents in the M‐I mode. Intense time‐varying magnetosphere and ionosphere currents lead to rapid fluctuation of the geomagnetic field on the ground. Faraday’s law of induction is the basic principle related to the flow of GICs on ground networks: a changing magnetic field induces an electric field through geomagnetic induction in the earth. In turn this electric field is responsible for currents that flow on ground conductors, such as power grids, according to Ohm’s law J = σE, where J is the current density, σ is the conductivity, and E is the electric field. The key processes for the creation and flow of GICs are illustrated in Figure 1.2.
Figure 1.2 The basic principle for the generation of GICs: variations of the ionospheric currents (I(t)) generate an electric field (E(t)) through geomagnetic induction in the earth. This electric field then drives GICs on ground conductors. Also shown are actual GIC recordings from the Finnish natural gas pipeline. Image credit Wikipedia.
Mathematically, Faraday’s law of induction can be expressed as:
Hence, the observed induced surface geoelectric field depends only on geomagnetic field variations and electromagnetic induction in the earth determined by the local geology (e.g., Pirjola, 1982). It follows, therefore, that this induced geoelectric field is completely independent of any technological system but is determined by M‐I currents that are a function of space weather conditions and the ground conductivity, as discussed before.
To calculate the geoelectric field, a simple but illustrative 1‐dimensional (1‐D) model that assumes a plane wave propagating vertically downwards and a uniform half‐space earth with conductivity σ is traditionally used (Cagniard, 1953; Pirjola, 1982). The fields are all presumed to be horizontally uniform to simplify the modeling. Adopting a single frequency ω, then the geoelectric field Ex and Ey components can be deduced in terms of the perpendicular geomagnetic field component By and Bx as:
where μ0 is permeability of free space, whereas the layer of air between the ground and the ionosphere is taken to have zero conductivity to limit significant attenuation of external electromagnetic fields. Since Equation (1.2) outlines the basis for deriving the Earth’s conductivity using geoelectric and geomagnetic field measurements recorded at the surface, it is considered as the “basic equation of magnetotellurics.”
1.3.2. Ground Conductivity
The Earth’s geology is another key ingredient in the geomagnetic induction process. Penetration of the geomagnetic field into the Earth’s crust is determined by the ground conductivity and frequency of the geomagnetic field variations. That is to say, the rate of attenuation of the induced electric field is dependent on the vertical distribution of the resistivity of the ground, and the period considered. Upper layers generate stronger influences at short periods, and deeper layers are more bearing at long periods, as depicted in Figure 1.3. It should be noted that the geomagnetic induction process is not fully discussed in the present paper. Here, we mostly emphasize the different conductivity models used for GIC applications. However, Part 2 of this volume is dedicated to discussions on geomagnetic induction.
Figure 1.3 Depiction of electromagnetic signal penetration at different periods. Long‐period signals penetrate deeper into the underground than short periods.
Source: Adopted with modification: http://userpage.fu‐berlin.de/mtag/MT‐principles.html.
The “plane wave” approach described above is a firmly‐established and simplest procedure for calculating GICs (see e.g., Pirjola, 2002a; Viljanen et al., 2006; Ngwira et al., 2008; Liu et al., 2009; da Silva Barbosa et al., 2015; Pulkkinen et al., 2015). This approach has also been applied to extreme events with much success (Wik et al., 2009; Pulkkinen et al., 2012; Ngwira et al., 2013, 2015). Historically, the most widely used ground structure has been the 1‐D layered conductivity (where σ is depth dependent) applied to specific or given location (e.g., Boteler and Pirjola, 1998; Viljanen et al., 2006; Pulkkinen et al., 2007; Ngwira et al., 2008; Fernberg, 2012; Zhang et al., 2012). In the United Kingdom, however, past studies have calculated GICs flowing on the high‐voltage transmission system using the “thin‐sheet” approximation (Beamish et al., 2002; McKay, 2003; Thomson et al., 2005; Beggan, 2015). The thin‐sheet approach uses a spatially varying conductance on a 2‐D surface covering the region of interest, combined with a 1‐D layered conductivity of upper lithosphere conductance (McKay, 2003). Thus, a thin‐sheet model incorporates the effect of lateral conductivity variations on redistribution of regional currents induced elsewhere (e.g., oceans or shelf seas).
Several recent studies emphasize the use of 3‐D conductivity that more accurately represent the true 3‐D earth response (e.g., Love, 2012; Bonner IV and Schultz, 2017; Kelbert et al., 2017, and references therein). Unfortunately, these 3‐D conductivity models are not readily available in many areas, thus their application is quite limited. In the United States, data from magnetotelluric (MT) campaigns such as EarthScope USArray MT program (http://ds.iris.edu/spud/emtf) are improving the conductivity models (e.g., Schultz, 2009). So far, nearly 60% of the continental United States has already been covered [Adam Schultz, personal communication]. In Figure 1.4 is a map showing the locations and current status of the NSF‐funded EarthScope USArray MT project.
Figure 1.4 EarthScope USArray MT status map across the lower‐48 U.S. The stations are spaced in an approximate 70 km grid. http://www.usarray.org/researchers/obs/magnetotelluric.
With the development of 3‐D ground models, one challenge is to pinpoint exactly when and where the 1‐D case fails and the 3‐D case becomes necessary for GIC purposes. This is partly due to the data limitation mentioned before but with more 3‐D models becoming available, the picture is beginning to change. Take for instance the recent Mid‐Atlantic region case study by Love et al. (2018). They estimate that geoelectric fields calculated from 3‐D conductivity models could be a few orders of magnitude larger than the fields estimated from 1‐D models. If indeed the 1‐D models under‐estimate the induced fields (the order of magnitude might vary), then this could raise significant concern for power system operators in affected regions. However, the actual impact of such fields on any system is a matter requiring more detailed analysis that consider all sides of the problem, including the coupling of space weather processes to the grid.
1.3.3. Engineering Considerations
Generally, information about the geoelectric field produced on the ground during GMD events is acquired as described above. Once this information is obtained, determining the level of GICs flowing through a given node for any ground system is relatively straightforward. The GIC can be calculated by considering the geoelectric field to be uniform in the near vicinity of the network using the expression
where a and b are the network coefficients specific to each network node depending only on the resistance and geometrical composition of a system (Viljanen and Pirjola, 1994). This is a purely engineering task that requires a full description of the system under consideration, which is beyond the scope of this paper. Nevertheless, readers can turn to Lehtinen and Pirjola (1985) or Viljanen and Pirjola (1994), and more recently Boteler (2014), for more information concerning this procedure. In addition, Part 3 of this volume contains several discussions on GICs and the power system.
1.4. EXTREME EVENTS
While mild and moderate space weather is fairly “common,” relatively speaking, it is often the extreme events that gather the most attention because they are “infrequent” but pose the highest risk. A truly extreme and rare space weather event could have produced large GICs that can seriously disrupt technology. Policy makers, the general public, industry, and the science community are all interested to know “how bad can space weather really get?” Recent policy action at the White House level in terms of development of the National Space Weather Strategy and National Space Weather Action Plan (SWAP) has sparked renewed interest on this topic (National Science and Technology Council, 2015a,b). It is worth noting at this point that goal 1 of the SWAP calls for extracting information about extreme 1‐in‐100 year geoelectric fields and theoretical maximums. While GICs are not the only space weather hazard highlighted in these policies, the phenomenon does play an important role in them. In this section, a general view of GICs, extreme events, and impact are covered.
1.4.1. General View of GIC Studies
Space weather is a global phenomenon, however, most notable effects tend to occur locally, that is, isolated area, as is the case for GICs. For this reason, many GIC studies focus on specific regions or networks. Nevertheless, there are several examples of studies that have a wider scope and provide a global snapshot of events (e.g., Pulkkinen et al., 2012; Ngwira et al., 2013, 2015; Fiori et al., 2014; Kataoka and Ngwira, 2016; Carter et al., 2016; Moldwin and Tsu, 2017; de Villiers et al., 2017; Barbosa et al., 2017; Oliveira et al., 2018, and references therein).
The largest number of GIC studies have come from high‐latitude regions because of the proximity to the auroral zone (Pirjola, 1982; Lehtinen and Pirjola, 1985; Viljanen and Pirjola, 1994; Boteler et al., 1998; Boteler, 2001; Pulkkinen et al., 2001; Pirjola, 2002b,c; Pulkkinen et al., 2003; Trichtchenko and Boteler, 2004; Thomson et al., 2005; Viljanen et al., 2006; Wintoft, 2005; Wik et al., 2009; Myllys et al., 2014; Beggan, 2015; Ngwira et al., 2018a, and references therein). The most interesting feature about the auroral zone is associated with auroral electrojet current flowing in the ionosphere. During storms, this current system can be strongly intensified mostly by magnetospheric substorms, thereby causing large GICs on the ground.
For many years, it was believed that GICs were a high‐latitude phenomena, thus mid‐low latitudes were generally not regarded to be susceptible to adverse impact by GICs. But this picture changed after evidence in South Africa revealed that GICs may have contributed significantly to the failure of several transformers (see reports by Koen, 2002; Gaunt and Coetzee, 2007). Since then, the GIC community has experienced a major growth in the number of studies focusing on mid‐latitude locations such as, Australia, China, France, Greece, Hungary, Ireland, Japan, New Zealand, South Africa, Spain, and the United States (Kappenman, 2006; Bernhardi et al., 2008; Ngwira et al., 2008, 2009; Watari et al., 2009; Turnbull et al., 2009; Liu et al., 2009; Ngwira et al., 2011; Love, 2012; Torta et al., 2012; Zois, 2013; Marshall et al., 2013; Lotz and Cilliers, 2014; Fujii et al., 2015; Blake et al., 2016; Matandirotya et al., 2016; Lotz and Danskin, 2017; Kelly et al., 2017; Love et al., 2018, and references therein).
In general, low‐latitude geomagnetic variations tend to be relatively smaller than those experienced at mid‐ and high‐latitudes, thus the region has largely been overlooked and is the least studied area in terms of GICs. One of the earliest studies on low‐latitude networks was conducted in Brazil by Trivedi et al. (2007). However, on examining the March 1989 and October 2003 extreme geomagnetic storms, Pulkkinen et al. (2012) first showed that induced surface geoelectric fields can be strongly amplified at the magnetic equator, thus could pose a higher threat to power systems at low‐latitudes than at mid‐latitudes. Then, Ngwira et al. (2013) extended study of extreme storms not only confirmed the findings by Pulkkinen et al. (2012), but also associated the effect to amplification of equatorial electrojet (EEJ) current by high‐latitude penetration electric fields. Penetration electric fields are attributed to sudden changes in the strength of field‐aligned currents, which are required for shielding the inner magnetosphere and the low‐mid‐latitude ionosphere from the dawn–dusk magnetospheric convection electric field (Fejer et al., 2007; Maruyama and Nakamura, 2007). After the extended study of extreme storms, Carter et al. (2015) investigated the potential effects of interplanetary shocks on the equatorial region and further demonstrated that their magnetic signature was amplified by the EEJ. Partly due to the investigation by Pulkkinen et al. (2012), we have witnessed an increased interest in GICs at low‐latitudes during the last 5 years (e.g., Liu et al., 2014; da Silva Barbosa et al., 2015; Barbosa et al., 2015; Adebesin et al., 2016; Moldwin and Tsu, 2017; Oliveira et al., 2018, and references therein).
1.4.2. Extreme GICs
In the past three decades, the space weather field has observed significant progress that has strengthened insight on the central processes driving GICs. However, rare but extremely intense geomagnetic storms continue to challenge our understanding of space weather (Kataoka and Ngwira, 2016; Pulkkinen et al., 2017; Ngwira and Pulkkinen, 2018; Tsurutani et al., 2018; Ngwira et al., 2018b). As noted in our introduction, scientific investigations are critical for raising awareness and predicting the impact of extreme space weather.
The space weather community is well aware that during extreme geomagnetic storms, intense high‐latitude currents can expand into the mid‐latitudes (e.g., Kappenman, 2005; Ngwira et al., 2013, 2014). However, understanding how deep into the lower latitudes the high‐latitude ionospheric currents can extend is still a challenge. Figure 1.5 shows global maximum geomagnetic field dB/dt distribution computed from ground magnetometer recordings. The distribution in this figure comprises of data from 12 from historical extreme geomagnetic storms that occurred between the years 1989 and 2005 (see report by Ngwira et al., 2013). Firstly, the figure clearly illustrates the impact of extreme storms on geomagnetic field perturbations at the geomagnetic equator, as seen by the amplified response near zero geomagnetic latitude. Secondly, the dark gray dashed lines mark the geomagnetic latitude boundary (GLB) location, a dynamic transition zone between high‐ and mid‐latitudes, while the thick solid curve is the sixth order polynomial fit.
Figure 1.5 Geomagnetic latitude distributions comprising 12 extreme events that occurred between 1989 and 2005. Plot shows the maximum time derivative of the horizontal magnetic field, dB/dt, at specific ground sites represented by the “*” symbol.
Source: Image credit Ngwira et al. (2013). Reproduced with permission of John Wiley and Sons.
The GLB is crucial because it identifies the latitude band where dB/dt (or the geoelectric field) experience roughly an order of magnitude drop/jump, and hence helps to define locations most exposed to the GIC hazard. Some investigators have determined the GLB location to be around 50–55°. geomagnetic latitude (e.g., Thomson et al., 2011; Pulkkinen et al., 2012; Ngwira et al., 2013). However, Ngwira et al. (2014) suggest that under extremely strong space weather conditions (“Carrington‐type” event), the GLB location can be substantially displaced deeper (∼40° geomagnetic latitude) into the lower latitudes. Such a location is much lower than previously determined for observed extreme geomagnetic storms, including the March 1989 and the October 2003 Halloween storm.
1.4.3. Impact
Reducing the Nation’s vulnerability to space weather is identified as a national priority, and GICs are also identified as the top threat (National Science and Technology Council, 2015b). The telegraph system was the first technology to report disruption (1847) by space weather‐driven GICs (Barlow, 1849). But perhaps in todays society, the power grid is the most critical infrastructure affected by GICs due to the wide‐spread demand for electrical power. The first reported disruption on power grids was in 1940 (Davidson, 1940; McNish, 1940).
However, the most widely known impact of space weather on any system is the collapse of the Hydro‐Quebec power network grid in Canada during the 13 March 1989 superstorm. Intense GICs produced during the superstorm triggered a complete blackout of the entire Hydro‐Quebec network in a relatively short time interval (Boteler, 2001; Bolduc, 2002, and references therein). It is believed that after a large substorm, system stability was lost thereby cutting off main load points from a major generation source (see Bolduc, 2002, for a more detailed discussion). During the same March 1989 event, a generator step‐up power transformer was damaged in New Jersey, USA.
Other, more recent but perhaps not well‐known GIC impacts on power grids include, failure of a high‐voltage power transmission system in Sweden (e.g., Pulkkinen et al., 2005; Wik et al., 2009), and possible transformer damages in South Africa (Gaunt and Coetzee, 2007). These two event are both associated with the “Halloween storm” of October 2003. GICs affect a wide range of technologies, as noted above. An extensive record of GIC impact on different systems within the last 80 years was recently compiled by Ngwira and Pulkkinen (2018).
1.5. CONCLUDING REMARKS
Space weather is an interesting but complex phenomenon. One of the top priorities of the science community today is extending our current understanding of the space weather phenomena. Extreme events in particular not only challenge our understanding of the physics of this phenomena, but can also cause deleterious effects. With several on‐going national and international efforts, our awareness of the problem is growing, thus could help to resolve outstanding challenges. More detailed discussion on specific areas of the GIC problem are provided in different chapters of this volume.
ACKNOWLEDGMENTS
We thank Peter Schuck at NASA Goddard Space flight Center and the two anonymous reviewers for assisting this effort. The discussion presented in this chapter relies on the data collected at magnetic observatories. The authors thank the national institutes that support their operation and INTERMAGNET for promoting high standards of magnetic observatory practice (www.intermagnet.org). Research effort at The Catholic University of America (CUA) was supported via NASA Grants NNG11PL10A 670.135 and NNG11PL10A 670.157 to CUA/IACS.
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