Geomagnetism Program Research Plan, 2020–2024

Circular 1469

U.S. Department of the Interior

U.S. Geological Survey
Cover. Powerlines on a sunrise (Photograph by Vladyslav Starohylov, Dreamstime.com LLC, 

purchased license).
Geomagnetism Program Research Plan, 

2020–2024

By Jeffrey J. Love, Anna Kelbert, Benjamin S. Murphy, E. Joshua Rigler, and 

Kristen A. Lewis

Circular 1469

U.S. Department of the Interior

U.S. Geological Survey
U.S. Department of the Interior

DAVID BERNHARDT, Secretary

U.S. Geological Survey

James F. Reilly II, Director

U.S. Geological Survey, Reston, Virginia: 2020

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Suggested citation:

Love, J.J., Kelbert, A., Murphy, B.S., Rigler, E.J., and Lewis, K.A., 2020, Geomagnetism Program research plan, 

2020–2024: U.S. Geological Survey Circular 1469, 19 p., https://doi.org/10.3133/cir1469.

ISSN 2330-5703 (online)
iii

Preface

This circular presents a research plan for the U.S. Geological Survey Geomagnetism Program. 

The report was written at the request of the Senior Advisor for Earthquake and Geologic Hazards 

and the Director of the Geologic Hazards Science Center.
iv

Acknowledgments

The authors thank M.S. Ashman, P.A. Bedrosian, K.A. Hartley, G.P. Hayes, T.M. Larson, 

J. McCarthy, H.J. Singer, J.L. Slate, and A.M. Tocci for reviewing a draft manuscript.
v

Contents

Preface ...........................................................................................................................................................iii

Acknowledgments........................................................................................................................................iv

Abstract...........................................................................................................................................................1

Directives and Priorities ...............................................................................................................................1

Background.....................................................................................................................................................2

Program Roles and Capabilities ..................................................................................................................4

Data Context ..........................................................................................................................................4

Project 1. Historical Magnetic Superstorms ....................................................................................6

Project 2. Geomagnetic Field Mapping .............................................................................................6

Project 3. Earth-Conductivity Modeling ............................................................................................8

Project 4. National Impedance Map ..................................................................................................8

Project 5. Geoelectric-Field Mapping .............................................................................................10

Project 6. Statistical Maps of Geoelectric Hazards ......................................................................11

Project 7. Electromagnetic-Pulse Hazard Analysis ......................................................................12

Project 8. Gap Analyses and Operational Support ........................................................................13

External Collaborative Projects ........................................................................................................14

Community Leadership................................................................................................................................14

Some Conditional Aspirations ...................................................................................................................14

References Cited..........................................................................................................................................15

Figures

1. Schematic diagram showing a current (J0) of increasing intensity over time in 

the space environment above the Earth’s surface .................................................................3

2. Schematic depiction of physical processes related to estimation of storm-time 

geoelectric fields ..........................................................................................................................4

3. Map of USGS and NRCan (Natural Resources, Canada) 

geomagnetic-observatory locations and U.S. and Canadian magnetotelluric 

(MT) survey sites ..........................................................................................................................5

4. Latitude-weighted disturbance time series from the Watheroo, Australia (WAT, 

gray), Apia, Samoa (API, yellow), Vassouras, Brazil (VSS, green), and San 

Fernando, Spain (SFS, pink) observatories, and the DstWAVS (WAT, API, VSS, 

SFS) time series (black) from 00:30 (GMT, Greenwich Mean Time) May 13 to 

02:30 May 17, 1921 (Love and others, 2019a). nT, nanotesla ..................................................7

5. Snapshots of the North American distribution of spherical elementary 

current-system-interpolated horizontal magnetic-field vectors during the 2015 

St. Patrick's Day magnetic storm (Rigler and others, 2019). nT, nanotesla .........................7

6. A synthesized CONUS electrical-conductivity model at a depth of 30 kilometers 

obtained from the inversion of EarthScope impedance tensors (Kelbert and 

others, 2019) ...................................................................................................................................9
vi

7. Maps showing the amplitude and polarization imparted by magnetotelluric 

impedances to the induced geoelectric field for a given geomagnetic field 

A, as a function of the azimuthal direction (declination) of the geomagnetic 

field, and B, as a function of the azimuthal direction of the induced geoelectric 

field, each for variational periods of 10, 100, and 1,000 seconds (smallest to 

largest ovals) ...............................................................................................................................10

8. Snapshot from the NOAA-USGS time-dependent mapping project, which is 

similar to the map presented by NOAA in real time ..............................................................11

9. Once-per-century extreme magnetic-storm-event predictions of 

transmission-line voltage (Lucas and others, 2020): high and low hazards are 

yellow and purple, respectively ...............................................................................................12

10. Comparison of A, 1-minute north-south Bx geomagnetic-disturbance time 

series recorded at the Ottawa, Canada (red, OTT) and Fredericksburg, Virginia 

(blue, FRD) observatories during the Halloween storm of October 29–31, 2003 

(Balch and others 2004), and B, the difference between the OTT and FRD 

time series....................................................................................................................................13
vii

Abbreviations and Acronyms

AFRL Air Force Research Laboratory

AGU American Geophysical Union

CONUS conterminous United States

DC direct current

DOE U.S. Department of Energy

DOI U.S. Department of the Interior

Dst storm-time disturbance

EMAC Electromagnetic Advisory Committee

EMIW Electromagnetic Induction Workshops

EMP electromagnetic pulse

EMPRAD Electromagnetic Pulse Research and Development working group

EO Executive Order for Coordinating National Resilience to 

Electromagnetic Pulses

FERC Federal Energy Regulatory Commission

GEM Geospace Environment Modeling program

GIC geomagnetically induced current

GMT Greenwich Mean Time

HAO High Altitude Observatory

IAGA International Association of Geomagnetism and Aeronomy

IEC International Electrotechnical Commission

IGY International Geophysical Year

INTERMAGNET International Real-time Magnetic Observatory Network

IRIS Incorporated Research Institutions for Seismology

km kilometer

LANL Los Alamos National Laboratory

ModEM Modular system for ElectroMagnetic inversion software

NASA National Aeronautics and Space Administration

NCAR National Center for Atmospheric Research

NERC North American Electric Reliability Corporation

NGA National Geospatial-Intelligence Agency

NOAA National Oceanic and Atmospheric Administration

NRCan Natural Resources, Canada

NSF National Science Foundation

NSO National Solar Observatory
viii

NSTC National Science and Technology Council

NSWSAP National Space Weather Strategy and Action Plan

nT nanotesla

PROSWIFT Promoting Research and Observations of Space Weather to Improve the 

Forecasting of Tomorrow Act

SECS spherical elementary current system

SWORM Space Weather Operations, Research, and Mitigation working group

SWPCSpace Weather Prediction Center

3D Three-dimensional

U.S. United States

USGS U.S. Geological Survey

V volt
Geomagnetism Program Research Plan, 2020–2024

By Jeffrey J. Love, Anna Kelbert, Benjamin S. Murphy, E. Joshua Rigler, and Kristen A. Lewis

Abstract

The Geomagnetism Program of the U.S. Geological 

Survey (USGS) monitors geomagnetic field variation through 

operation of a network of observatories across the United 

States and its territories, and it pursues scientific research 

needed to estimate and assess geomagnetic and geoelectric 

hazards. Over the next five years (2020–2024 inclusive) and 

in support of national and agency priorities, Geomagnetism 

Program research scientists plan to pursue an integrated 

set of research projects broadly encompassing empirical 

estimation and mapping of geomagnetic disturbance, 

modeling of solid-Earth conductivity structure and surface 

impedance, and mapping of magnetic-storm-induced 

geoelectric fields. Analyses are empirically based, relying 

on measured time series as well as statistical and numerical 

modeling of geomagnetic-monitoring data from ground-based 

observatories and surface-impedance tensors acquired during 

magnetotelluric surveys. The plan describes augmentation 

and development of the Geomagnetism Program's existing 

research portfolio, assuming present funding levels and 

staffing numbers. Because the projects are interdependent, 

they cannot be straightforwardly prioritized. They will all 

be pursued as resources and time permit; additional funding 

and staffing would enable the projects to be broadened and 

more rapidly completed. Where appropriate and subject 

to budgetary constraints and staffing numbers, research on 

specific projects might be accelerated or even judiciously 

expanded—some opportunities for expansion are discussed 

in this plan. Results will provide realistic illumination of 

the nature of the ground-level expression of space-weather 

disturbance, a subject of particular importance for projects 

focused on evaluating the vulnerability of electric-power-grid 

systems. This plan does not cover Geomagnetism Program 

operations, which are primarily concerned with the operation 

of magnetic observatories and, now, magnetotelluric surveys, 

although the context of such observatories and surveys is 

discussed. The research element of the program provides 

guidance for the expansion of program operations and research 

projects. In addition to the research projects summarized 

here, program scientists continue to provide leadership to the 

national and international geomagnetic, magnetotelluric, and 

space-weather communities.

Directives and Priorities

The National Space Weather Strategy and Action 

Plan (NSWSAP) of the National Science and Technology 

Council (NSTC, 2019) directs the U.S. Department of 

the Interior (DOI), and, by proxy, the Geomagnetism 

Program of the U.S. Geological Survey (USGS), to work 

in collaboration with other agencies to enhance national 

protection by refining space-weather benchmarks (NSTC, 

2019, Their Objective 1.1) and modeling the effects of space 

weather (Objective 1.3), in order to support assessing the 

vulnerability of critical infrastructure (Objective 1.2) and 

assessing the cost of space weather (Objective 1.4). The 

program is directed, in collaboration with other agencies, to 

contribute to the development of improved space-weather 

forecasts by supporting fundamental research (Objective 2.3), 

enhancing modeling techniques and the development of 

models (Objective 2.5), and releasing historical datasets 

(Objective 2.6). Furthermore, program research should 

inform operational priorities within the NSWSAP, including 

identifying baseline-observation capabilities (Objective 2.1), 

ensuring the continued operation and possible expansion 

of observation capabilities (Objective 2.2), identifying new 

and enhanced measurement methods (Objective 2.4), and 

enhancing accessibility to operational data (Objective 2.8).

Under the Executive Order for Coordinating National 

Resilience to Electromagnetic Pulses (White House, 

March 26, 2019, 13865, Section 5c), the DOI is directed to 

pursue research, development, deployment, and operational 

capabilities that enhance understanding of variations of the 

Earth’s magnetic field associated with electromagnetic pulses 

(EMPs), both natural and anthropogenic.

The research projects of the USGS Geomagnetism 

Program are consistent with the DOI (2018) strategic plan 

for providing science to safeguard communities from natural 

hazards. The program's work is also consistent with the USGS 

Natural Hazards Science Strategy for enhancing observations 

(Holmes and others, 2013, their Goal 1), pursuing fundamental 

understanding (Goal 2), improving hazard assessments 

(Goal 3), and providing situational awareness (Goal 4).

Under an act before Congress (as of August 2020, HR 

5260) known as Promoting Research and Observations of 

Space Weather to Improve the Forecasting of Tomorrow 

(PROSWIFT), the DOI is noted as being responsible for 

magnetometer operations and for developing “crustal 
2 Geomagnetism Program Research Plan, 2020–2024

conductivity models to assess and mitigate risks from 

space-weather-induced electric ground currents.” Under 

PROSWIFT, the USGS (along with other agencies) is directed 

to transition space-weather-research findings, models, and 

capabilities, as appropriate, to the National Oceanic and 

Atmospheric Administration (NOAA) and the Department of 

Defense (DOD).

Background

Magnetic storms are hazardous to the activities and 

technological infrastructure of modern society. This fact 

was dramatically demonstrated in March of 1989 when 

a rare magnetic superstorm (Allen and others, 1989) 

damaged satellites and interfered with their operation, and 

disrupted geophysical surveys and over-the-horizon radio 

communication. This storm caused the collapse of the 

Hydro-Québec electric power grid in Canada (Bolduc, 2002), 

damaged a high-voltage transformer at a nuclear-power plant 

in Salem, New Jersey (Barnes and others, 1991; Rossi, 1990), 

and, more generally, was responsible for over 200 significant 

anomalies in North American power-grid transmission 

networks (North American Electric Reliability Corporation 

(NERC), 1990). The cost of the March 1989 storm for the 

Canadian economy has been estimated to have been between 

$3 and $6 billion (in 1989 Canadian dollars) (Government of 

Canada, 2002; Riswadkar and Dobbins, 2010). Reflective of 

the rise of the global economy and an increased reliance on 

technology, should another Québec-like event occur today, 

a worldwide economic impact of $2.4 to $3.4 trillion could 

be expected, equivalent to a global loss in gross domestic 

product of 3.9 to 5.6 percent (Schulte in den Bäumen and 

others, 2014).

Longer ago, the great magnetic storm of May 1921 (for 

example, Hapgood, 2019; Love and others, 2019b) disrupted 

radio communication and telegraph and telephone systems 

around the world, and, notably, caused fires in telegraph 

stations used by New York State and City railroad companies. 

The Carrington event of 1859 was, by some measures, the 

most intense magnetic storm ever recorded (for example, 

Tsurutani and others, 2003; Cliver and Dietrich, 2013); it also 

disrupted telegraph systems around the world and caused 

fires at telegraph stations. Should a storm of similar intensity 

occur today, technological systems around the world might 

be adversely affected. Under some scenarios, the future 

occurrence of a rare “perfect magnetic storm” might have a 

widespread impact, possibly including the widespread collapse 

of electric-power networks. Such a potential event, sometimes 

described as being “high-impact, low-frequency,” could 

have deleterious consequences for the economy and national 

security (for example, NERC and U.S. Department of Energy 

(DOE), 2010). While acknowledging that economic impact 

can be difficult to predict (Eastwood and others 2017), some 

estimates place the economic cost of such a perfect storm for 

the United States at $0.6 to 2.6 trillion, with recovery taking 

years (National Research Council, 2008; Lloyd's, 2013).

Qualitatively, the physical connection between magnetic 

storms and the interference they can cause to power-grid 

systems is well understood, and the basic concepts are 

illustrated in figures 1 and 2. Briefly, geomagnetic disturbance 

induces geoelectric fields in the Earth's conducting interior. 

Surface geoelectric fields can drive geomagnetically induced 

currents (GICs) in power grids through their grounding 

connections (for example, Molinski, 2002; Piccinelli and 

Krausmann, 2014). Two factors affect the nature of surface 

geoelectric fields (Thomson and others, 2009; Love and 

others, 2014; Kelbert, 2020a). First, storm-induced electric 

currents in the ionosphere and magnetosphere, driven by 

the dynamic action of the Sun and its solar wind, generate 

ground-level geomagnetic disturbances that can be both 

temporally and spatially complicated. Indeed, predicting 

storm-time geomagnetic disturbance remains a challenging 

goal of space-weather modeling projects (for example, 

National Research Council, 2013; Pulkkinen and others, 

2017). Second, the geologic structure of the solid Earth is 

complicated, and therefore surface electromagnetic impedance 

is complicated as well. All this means that storm-induced 

geomagnetic fields are both highly time dependent, and their 

amplitude and polarization can have a high degree of localized 

geographic granularity.

During an intense magnetic storm, geoelectric-field 

intensities of 1 volt per kilometer (V/km) are common in many 

places on the Earth's surface; over relatively resistive geologic 

formations, field intensities can exceed 10 V/km. This might 

seem rather modest at first, but given that power-grid lines 

are often more than 100 km in length, integrated voltage can 

possibly exceed 1000 V. Assuming a line resistance of, for 

example, 1 ohm, GICs of hundreds of amps over a minute 

or more can be realized. For a power grid designed for 

alternating current at a frequency of (typically) 60 Hz, such 

a GIC is effectively a direct current (DC). This can cause 

havoc, tripping relays and causing operational instability (for 

example, Kappenman, 2003; Piccinelli and Krausmann, 2014). 

Indeed, this is what brought down the Hydro-Québec system 

in 1989 (for example, Boteler, 2001; Bolduc, 2002). Prolonged 

periods of DC current can damage high-voltage transformers 

(Girgis and Vedante, 2012), and if they need to be replaced, 

restoration of service will be delayed.

An analogous hazard would be an EMP generated by a 

high-altitude nuclear explosion (for example, Dupont, 2004; 

Rivera and others, 2016; Gombosi and others, 2017). The 

low-frequency part of an EMP, referred to as E3, resembles 

the impulsive disturbance realized during some magnetic 

storms, although it has a somewhat shorter period band from 

about 1 to 1,000 seconds. Like storms, an E3 interacts with 

the Earth's surface impedance to induce geoelectric fields 

that could interfere with grounded power-grid systems. A hint 

of the destructive potential of EMP weapons came during 

the U.S. Starfish Prime test of July 9, 1962, above Johnston 
Background 3

Island in the Pacific Ocean: 1,350 km away from ground zero, 

burglar alarms were tripped in Honolulu, Hawaii (Glasstone 

and Dolan, 1977), and local street lights went black (Vittitoe, 

1989). Soviet test 184 (also designated K3) on October 22, 

1962, caused fires, destroyed power supplies, and blew fuses 

on a long communication-cable system beneath ground zero 

(Greetsai and others, 1998). The proliferation of nuclear 

weapons and the fundamental dependence of modern society 

on electricity and electronic technology have motivated recent 

evaluations of the risk posed by a hostile EMP explosion for 

national and international security (for example, Graham and 

others, 2008; Popik and others, 2017).

Low conductivity High conductivity

J0

E E

J1

Space current of

increasing intensity 

J1 E J1

Geomagnetic field B0

Generated by

space current

Figure 1. Schematic diagram showing a current (J0) of increasing intensity over time in the space environment above the Earth’s 

surface. This current generates a geomagnetic field (B0) that is also increasing in intensity over time. This geomagnetic field, in turn, 

induces geoelectric fields (E) in the Earth, generally of high (low) amplitude within rock of low conductivity (high conductivity). These 

geoelectric fields then drive electric currents (J1) that flow from the Earth through ground connections at transformer substations and 

across high-voltage transmission lines (for example, Pirjola, 2002).
4 Geomagnetism Program Research Plan, 2020–2024

Program Roles and Capabilities

In support of national priorities for developing and 

providing information and services in the National interest, the 

USGS Geomagnetism Program monitors geomagnetic-field 

variation through the operation of a network of observatories 

across the U.S. and its territories (Love and Finn, 2011), 

and it pursues scientific research needed to estimate and 

assess geomagnetic and geoelectric hazards. Recent omnibus 

appropriations legislation has expanded Geomagnetism 

Program responsibilities to ensure the completion of a 

magnetotelluric survey across the conterminous U.S. 

(CONUS). The program's research element is small: two 

scientists are assigned full-time research, and one scientist is 

categorized as equipment development grade, and, as such, 

he concentrates on operational product development; in 

addition, the program benefits from occasional 2-year-term, 

postdoctoral fellows. The program is headquartered in the 

Geologic Hazards Science Center in Golden, Colorado, along 

with national and international earthquake programs and the 

national landslides program. Program scientists collaborate 

with the USGS Geology, Geophysics, and Geochemistry 

Science Center located nearby at the Denver Federal Center. 

Program scientists collaborate with colleagues from allied 

government agencies and academia and increasingly from the 

commercial sector.

USGS Geomagnetism Program scientists have a diverse 

mix of expertise in geology, solid-Earth geophysics, space 

physics, and data science. In recent years, this expertise 

has been utilized in the pursuit of an influential portfolio of 

research projects: analysis of historical magnetic superstorms, 

empirical mapping of storm-caused geomagnetic disturbance, 

inverse modeling of solid-Earth electrical-conductivity 

structure, analysis of its surface expression as impedance, and 

empirical mapping of storm-induced and EMP geoelectric 

fields. In the coming years, the program's research portfolio is 

expected to expand slightly to include analysis of the ground 

response to EMP. Program research results inform utility 

companies in vulnerability evaluations of electric-power 

grid systems mandated by regulatory agencies, and, more 

generally, they provide realistic illumination on the nature of 

the ground effects of space-weather disturbance.

Data Context

USGS Geomagnetism Program research scientists rely 

on time series acquired by magnetometers at ground-based 

stations (fig. 3). Program research complements program 

operational responsibilities for its network of 14 magnetic 

observatories, 6 of which are in CONUS (Love and Finn, 

2011). Additionally, and of relevance to the emphasis of 

this research plan, geoelectric time series are being acquired 

at the Boulder magnetic observatory (Blum and others, 

2017). Program observatories provide a baseline observation 

capability (NSTC, 2019, Objective 2.1) that needs to be 

sustained (Objective 2.2) and even enhanced (Holmes and 

others, 2013, Goal 1).

Some Geomagnetism Program observatories have been 

in operation for over a century, providing long time-series 

recordings of magnetic storms, quasi-diurnal solar-quiet 

tides, and slow secular geomagnetic variation generated 

in the Earth's core. The program's oldest data, time series 

acquired by analog variometers, are of high accuracy (a few 

nTs; nT, nanotesla) and useful for identifying general features 

of magnetic storms, but these data have a resolution of 

only 1 hour. Electronic fluxgate magnetometers, a standard 

instrument for measuring magnetic field variation over time 

(for example, Primdahl 1979), and digital acquisition systems 

have been operated at the observatories since the 1980s, and 

since then the program's basic data product has been 1-minute 

Input-signal

time series

Output-signal

time series 

Convolution

through a filter

Geomagnetic

variation

Geoelectric

field

Figure 2. Schematic depiction of physical processes related to estimation of storm-time geoelectric fields. As with formal concepts 

from time-series analysis, in which an input signal is convolved with a filter function to produce an output signal, geomagnetic 

disturbance generated by the Sun and solar wind is filtered through an impedance tensor that is itself a function of the conductivity 

structure of the Earth. The resulting geoelectric field is a geophysical quantity that directly interferes with the operation of 

electric-power grids.
USGS Geomagnetic ObservatoriesNRCan Geomagnetic ObservatoriesEarthScope USArray MT SitesNASA MTArray MT SitesUSGS MT SitesLithprobe MT SitesOther MT Sites

EXPLANATION

MEXICO

UNITED STATES

CANADA

Base from Natural Earth

0 200 400 600 800 KILOMETERS0 200 400 600 800 MILES

120° W 110° W 100° W 90° W 80° W 

40° N

50° N

30° N

Figure 3. Map of USGS and NRCan (Natural Resources, Canada) geomagnetic-observatory locations and U.S. and Canadian magnetotelluric (MTof the magnetotelluric impedance tensors are available through IRIS; additional data (also shown here) are in the process of being archived. Omniblegislation for fiscal year 2020 has provided funds to the USGS for continuation of EarthScope-protocol magnetotelluric-data acquisition in the soutsouth-central United States.
6 Geomagnetism Program Research Plan, 2020–2024

time series; 1-second resolution data have been acquired 

at the observatories since the early 2010s. The program's 

1-minute and 1-second data are transmitted from all the 

observatories to program headquarters in Golden, Colorado, 

within minutes of acquisition, they are then made available 

to users, both in-house and to external partner agencies. 

The program's observatory operations are coordinated with 

those in other countries through the International Real-time 

Magnetic Observatory Network (INTERMAGNET, 

https://www.intermagnet.org), a global consortium of magnetic 

observatory institutes (for example, Love and Chulliat, 2013).

Geomagnetism Program research scientists also 

use magnetotelluric impedance tensors constructed from 

data acquired during surveys across North America and 

especially CONUS. In summary, (for example, Chave 

and Jones, 2012; Unsworth, 2007) at a given geographic 

site, simultaneous time-series measurements are made of 

natural-geomagnetic and geoelectric-field variation. The 

empirical relationship between these measurements is a 

transfer function equivalent to an impedance tensor divided 

by permeability. Magnetotelluric impedance tensors, 

constructed from data across a distribution of sites as part 

of a survey (for example, Egbert, 2007a), can be inverted 

for models of the internal conductivity structure of the Earth 

(for example, Kelbert and others, 2019). For purposes of 

geoelectric-hazard analysis, the combination of impedance 

tensors and time series (from observatories or models) can 

be used to estimate geoelectric-field variation (for example, 

Kelbert and others, 2017). Across CONUS, many impedance 

tensors (Schultz and others, 2006–2018; Schultz, 2010) used 

by the program were acquired by the EarthScope project of 

the National Science Foundation (NSF) (Williams and others, 

2010); these tensors have a site spacing of about 70 km and 

a useful acquisition-period band from about 10 seconds to 

10,000 seconds. Other tensors, such as from Florida and 

northern Arkansas, are derived from data collected by the 

U.S. Geological Survey in accordance with EarthScope 

protocol; still other tensors are collected as parts of other 

projects and often under different protocols.

In support of priorities for releasing new datasets 

(NSTC, 2019, Objective 2.6), enhancing the accessibility and 

sharing of observational data (Objective 2.8), and enhancing 

observations (Holmes and others, 2013, Goal 1), the USGS 

Geomagnetism Program is leading a project for compiling 

new and historical magnetotelluric impedance tensors (Kelbert 

and others, 2018; Kelbert, 2020b). These tensors are archived 

in a database (http://ds.iris.edu/spud/emtf) hosted by the 

Incorporated Research Institutions for Seismology (IRIS). 

The work includes checking and, in some cases, repairing 

historical functions. Compilation of historical impedance 

tensors, such as those acquired by the Lithoprobe Program 

of the Canadian Natural Sciences and Engineering Research 

Council, is a high priority. Work on this project has involved, 

and will continue to involve, collaboration with Oregon State 

University and IRIS. Results will provide input to the national 

impedance map (Project 4. National Impedance Map) and 

the project on EMP (Project 7. Electromagnetic-Pulse Hazard 

Analysis). Fiscal Year 2020 appropriated funds will support 

continuation of the magnetotelluric survey across the southern 

CONUS sector not completed by EarthScope.

Project 1. Historical Magnetic Superstorms

In support of priorities for developing space-weather 

benchmarks (NSTC, 2019, Objective 1.1), releasing 

new datasets (NSTC, 2019, Objective 2.6), and pursuing 

fundamental understanding (Holmes and others, 2013, 

Goal 2), the USGS Geomagnetism Program is leading projects 

to estimate the intensity of historical magnetic superstorms 

(for example, Love and others, 2019a, 2019b; Love, 2020) and 

the probability of their occurrence in the future (for example, 

Love and others, 2015); an example of the former is shown in 

figure 4. Estimating the intensity of storms that occurred after 

1957 is relatively straightforward—during the International 

Geophysical Year (IGY, 1957–1958), standard measures of 

storm intensity, such as Dst (storm-time disturbance), were 

developed, and observatory operations were improved, 

resulting in data of improved accuracy and continuity. Prior to 

the IGY, when there were fewer observatories, and operational 

continuity was sometimes poor, the situation is more 

challenging. A recent reconnaissance of historical records 

by program scientists suggests that useful records exist for 

the most intense storm for each solar cycle since about 1900. 

With such a compilation and physically justified statistical 

models, scientists anticipate that improved estimates can be 

made of the occurrence frequency of intense storms together 

with estimates of statistical variance (uncertainty). This project 

will augment historical datasets (NSTC, 2019, Objective 2.6) 

and inform a subproject on the evaluation of historical 

magnetic-storm effects.

Project 2. Geomagnetic Field Mapping

In support of priorities for developing space-weather 

models (NSTC, 2019, Objective 2.5) and improving hazard 

assessments (Holmes and others, 2013, Goal 3), the USGS 

Geomagnetism Program is leading a project for developing 

capabilities for real-time and retrospective mapping of 

geomagnetic-field disturbance over North America (Rigler 

and others, 2019); an example of such a map is shown in 

figure 5. This project uses data from the USGS Geomagnetism 

Program's observatory network (and that of Natural Resources, 

Canada (NRCan); Newitt and Coles, 2007). Geospatial 

interpolation is required to estimate geomagnetic-field 

disturbances at locations far from the observatories. For 

various reasons, and especially because they are physically 

realistic and interpretable, the program has identified spherical 

elementary current systems (SECS) (for example, Amm, 1997; 

Amm and Viljanen, 1999) as suitable for this interpolation—

the fields below the ionosphere and above the Earth’s surface 

are assumed to be potential (free of currents). A robust 
Program Roles and Capabilities 7

Figure 4. Latitude-weighted disturbance time series from the Watheroo, Australia (WAT, gray), Apia, Samoa (API, yellow), Vassouras, 

Brazil (VSS, green), and San Fernando, Spain (SFS, pink) observatories, and the DstWAVS (WAT, API, VSS, SFS) time series (black) from 00:30 

(GMT, Greenwich Mean Time) May 13 to 02:30 May 17, 1921 (Love and others, 2019a). nT, nanotesla.

Figure 5. Snapshots of the North American distribution of spherical elementary current-system-interpolated horizontal magnetic-field 

vectors during the 2015 St. Patrick's Day magnetic storm (Rigler and others, 2019). nT, nanotesla.
8 Geomagnetism Program Research Plan, 2020–2024

optimal-estimation algorithm enables the SECS functions to 

be fitted to observatory data, and these fits can, in turn, be 

expressed as a map of geomagnetic-field disturbance at the 

Earth's surface.

Errors associated with the geomagnetic-field maps 

need to be reduced. Most fundamentally, these errors 

could be substantially reduced with data from additional 

magnetic observatories and variometer stations across 

CONUS. Indeed, this project can help justify additional 

monitoring stations (Project 8. Gap Analyses and Operational 

Support). Geomagnetism Program scientists are working 

to combine the SECS mapping models with physics-based 

models of the ionospheric-magnetospheric system by using 

machine-learning techniques and data assimilation. Work 

on this project involves collaboration with the NOAA 

Space Weather Prediction Center (SWPC), the National 

Aeronautics and Space Administration (NASA), the U.S. Air 

Force Research Laboratory (AFRL), and the High Altitude 

Observatory (HAO) at the National Center for Atmospheric 

Research (NCAR). When combined with work on the national 

impedance map (Project 4. National Impedance Map), results 

will provide input for real-time geoelectric-field mapping 

(Project 5. Geoelectric-Field Mapping).

In support of priorities for developing space-weather 

models (NSTC, 2019, Objective 2.5), for pursuing 

fundamental understanding (Holmes and others, 2013, 

Goal 2), improving hazard assessments (Goal 3), and 

providing situational awareness (Goal 4), the USGS 

Geomagnetism Program is developing statistical methods for 

separating geomagnetic-disturbance signals from solar-quiet 

and secular signals in observatory data (Rigler, 2017) 

that can be used for the calculation of magnetic indexes 

(scalar measures of disturbance) that are widely used in the 

space-weather and terrestrial-geomagnetism communities. 

The program has developed statistical maps of geomagnetic 

disturbance (Love and others, 2016a) that, in combination 

with surface impedance values (Project 4. National Impedance 

Map), can be used for (simple) statistical estimations of 

geoelectric hazards (Love and others, 2016b). These projects 

could be further developed, for example, by characterizing the 

statistics of storm-time magnetic declination, which would be 

a product of potential interest for navigation and directional 

drilling for oil and gas.

Project 3. Earth-Conductivity Modeling

In support of priorities for pursuing fundamental 

understanding (Holmes and others, 2013, Goal 2), 

and as a basis for developing space-weather models 

(NSTC, 2019, Objective 2.5) and improving hazard 

assessments (Holmes and others, 2013, Goal 3), the USGS 

Geomagnetism Program is developing models of CONUS 

subsurface electrical-conductivity structure. Heretofore, 

three-dimensional (3D) conductivity models have been 

obtained on a regional basis (for example, Meqbel and others, 

2014; Yang and others, 2015; Murphy and Egbert, 2017) 

or globally at a substantially lower spatial resolution (for 

example, Sun and others, 2015). Initial work has involved the 

compilation of regional and global 3D conductivity models 

obtained at different resolutions; these have been combined 

into one continuous model (Kelbert and others, 2019) (fig. 6). 

Incremental updates and improvements are expected as new 

data become available. In the long term, consistent modeling 

for all of CONUS will be accomplished by the simultaneous 

modeling of thousands of magnetotelluric impedance tensors 

through the use of inverse theoretical methods (for example, 

Egbert, 2007b) and the Modular system for ElectroMagnetic 

inversion (ModEM) software (Kelbert and others, 2014), 

modified to accommodate supercomputer-memory needs and 

the spherical geometry of the Earth.

Modeling 3D CONUS electrical conductivity 

is an important steppingstone for several of the 

other projects outlined here. It supports the National 

Impedance Map (Project 4. National Impedance Map) 

by enabling geophysically based interpolation between 

the magnetotelluric survey sites to yield high-resolution, 

gridded impedances in CONUS. The framework of 

this project will further facilitate the investigation of 

anomalous, non-plane-wave response to short-spatial-scale 

geomagnetic-field disturbance realized during storms. 

Exploration of the limitations of the plane-wave 

approximation, inherent to magnetotelluric modeling, 

are planned by using realistic ionospheric-current 

sources (Projects 2. Geomagnetic Field Mapping and 5. 

Geoelectric-Field Mapping). Outside of the Geomagnetism 

Program, insights from the geological structure that the 

models reveal (for example, Hermance, 2011) inform 

projects undertaken by the USGS Geology, Geophysics, and 

Geochemistry Science Center for the evaluation of mineral 

resources (for example, Bedrosian, 2016; Murphy and others, 

2019) and projects undertaken by the Earthquake Program 

for the evaluation of tectonic structures in areas prone to 

earthquake hazards. An important plausible extension of this 

project is consistent modeling of the conductivity structure 

of CONUS and Canada. Collaboration will be with Oregon 

State University.

Project 4. National Impedance Map

In support of priorities for developing space-weather 

models (NSTC, 2019, Objective 2.5) and improving hazard 

assessments (Holmes and others, 2013, Goal 3), the USGS 

Geomagnetism Program is mapping the surface impedance of 

CONUS—an important and high-profile product needed for 

retrospective, real-time, and prospective scenario estimation 

of geoelectric fields induced by magnetic storms and for the 

prospective estimation of geoelectric fields induced by EMP 

(White House, 2019). Synthetic analyses have already shown 

that the amplitude and polarization of induced geoelectric 
Program Roles and Capabilities 9

fields are strongly affected by the Earth's surface impedance 

(for example, McKay and Whaler, 2006; Bedrosian and 

Love, 2015).

Several variants of the National Impedance Map are 

being developed and maintained, and their utility for real-time 

geoelectric-field mapping (Project 5. Geoelectric-Field 

Mapping) and statistical-hazard mapping (Project 6. 

Statistical Maps of Geoelectric Hazards) is being evaluated 

and explored. Most straightforwardly, impedance can be 

mapped by plotting integrated quantities derived from the 

magnetotelluric tensors—for example, amplitude-polarization 

ovals (as shown in figure 7A and B), an empirical impedance 

map), apparent resistivity, or phase. Geographically dense 

estimates of surface impedance can be obtained by sampling 

impedances derived from a conductivity model (Project 3. 

Earth-Conductivity Modeling). Finally, these impedance 

maps can be interpolated on the power grids themselves 

to facilitate the calculation of line voltages and GICs. An 

important plausible extension of this project is modeling of 

CONUS-Canadian surface impedance.

Impedance maps inform needed evaluations of the 

quality of data acquired by ongoing magnetotelluric 

surveys, such as that for completing the national survey 

under EarthScope protocols. By illustrating the geographic 

complexity of impedance, the project informs gap analyses 

needed to justify additional magnetotelluric surveying 

(Project 8. Gap Analyses and Operational Support). As new 

magnetotelluric surveys are performed and new impedance 

tensors become available, the impedance map are planned 

to be periodically updated. To facilitate checking and 

reproducibility by outside investigators, version numbers, 

digital object identifiers, and metadata are planned to be used 

for reference data, models, and algorithms.

30°N

40°N

110°W 100°W 90°W 80°W

1 0 0 1 0 1 1 0 2 1 0 3 1 0 4

R esistiv it y (Ωm )

Figure 6. A synthesized CONUS electrical-conductivity model at a depth of 30 kilometers obtained from the inversion of EarthScope 

impedance tensors (Kelbert and others, 2019). Depth-dependent models of conductivity structure inform fundamental understanding of 

geologic structures. Integration of conductivity models can provide physically realistic and geographically continuous maps of surface 

impedance. Lack of structure in the south-central and southwest areas is a result of the lack of magnetotelluric data.
10 Geomagnetism Program Research Plan, 2020–2024

Project 5. Geoelectric-Field Mapping

In support of priorities for developing space-weather 

models (NSTC, 2019, Objective 2.5), transitioning 

capabilities from research to operations (Objective 2.7), 

and providing situational awareness (Holmes and others, 

2013, Goal 4), the USGS Geomagnetism Program is 

collaborating with NOAA SWPC and the University of 

Colorado to provide real-time and retrospective CONUS 

maps of geoelectric-field variation (Love and others, 2018; 

see fig. 8). This project is the result of several years of 

concentrated effort, which involves time-domain convolution 

of magnetic-field maps (Project 2. Geomagnetic Field 

Mapping) with the national impedance map (Project 4. 

National Impedance Map) (for example, Kelbert and others, 

2017, 2019). The current real-time map product uses only 

one-dimensional, depth-dependent models of surface 

impedance. Program scientists are working with NOAA 

to implement more realistic models of surface impedance, 

including geographically dense sampling of CONUS surface 

impedance derived from conductivity models.

Checks on the accuracy of the estimated geoelectric fields 

will be made by comparing them directly against measured 

data, such as those now being acquired at the USGS Boulder 

magnetic observatory (Blum and others, 2017) or those 

acquired during magnetotelluric surveys. A critical validation 

analysis will include Geomagnetism Program collaboration 

with NOAA and the power-grid industry for examination 

and comparison of modeled geoelectric-field maps as inputs 

to GIC calculations compared to real GIC measurements in 

the power grids (for example, Pulkkinen and others, 2017; 

Sun and Balch, 2019). The outcome of such validation 

exercises will, in turn, inform needed refinements of USGS 

magnetic-field and national impedance-mapping projects and 

possibly even motivate denser magnetotelluric surveys and the 

installation of additional magnetic observatories.

Max Scaling [mv/km]/[nT]

30°N

40°N

30°N

40°N

110°W 100°W 90°W 80°W

1 0 −1 1 0 0 1 0 1 1 0 2

Figure 7. Maps showing the amplitude and 

polarization imparted by magnetotelluric 

impedances to the induced geoelectric field 

for a given geomagnetic field A, as a function 

of the azimuthal direction (declination) of the 

geomagnetic field, and B, as a function of the 

azimuthal direction of the induced geoelectric 

field, each for variational periods of 10, 100, 

and 1,000 seconds (smallest to largest ovals). 

Generally, due to resistive rock structures, 

impedance is high over parts of the Midwest and 

the area of the Piedmont east of the Appalachians; 

conversely, impedance is low over sedimentary 

basins, such as over the state of Michigan.
Program Roles and Capabilities 11

Scenario mapping of storm-induced geoelectric fields 

that incorporate whole-Earth, physics-based modeling of 

the magnetosphere, ionosphere, and solid Earth (Projects 2. 

Geomagnetic Field Mapping, 3. Earth-Conductivity Modeling, 

and 4. National Impedance Map), will likely show that 

some places exhibit localized complexity resulting from a 

combination of geomagnetic disturbance and impedance, 

both of which are spatially complicated. Scenario mapping 

constrained by data will enable and inform the analyses 

of errors associated with the plane-wave approximation of 

magnetotellurics (Project 4. National Impedance Map), and 

it will help users to identify needs for additional and higher 

density magnetotelluric surveys (Project 8. Gap Analyses and 

Operational Support).

Results from this project will inform the electricity 

utility industry in their projects for evaluating the 

vulnerability of power-grid systems. Additional 

Geomagnetism Program projects could include real-time 

and retrospective estimation of time-varying voltages on 

CONUS power grids, similar to that done in the mid-Atlantic 

U.S. before the March 1989 storm (Lucas and others, 

2018), although an ongoing challenge is the sparsity of 

observatories used for geomagnetic-field mapping (Project 2. 

Geomagnetic Field Mapping). An important and plausible 

extension of this project is the consistent, joint mapping of 

CONUS and Canadian geoelectric fields.

Project 6. Statistical Maps of Geoelectric 

Hazards

In support of priorities for facilitating vulnerability 

assessments of critical infrastructure (NSTC, 2019, 

Objective 1.2), developing space-weather models 

(Objective 2.5), and improving hazard assessments (Holmes 

and others, 2013, Goal 3), the USGS Geomagnetism 

Program is leading a project for developing statistical maps 

of geoelectric hazard across CONUS (Lucas and others, 

2018; Love and others, 2019c; Lucas and others, 2020). This 

project uses interpolations of magnetic observatory data and 

magnetotelluric impedance tensors. In the future, the latter 

could be improved by using a geographically dense sampling 

of surface impedance (Project 4. National Impedance 

Map) derived from conductivity models (Project 3. 

Figure 8. Snapshot from the NOAA-USGS time-dependent mapping project, which is similar to the map presented by NOAA in 

real time. Shown here is an instance during the March 1989 magnetic superstorm. NOAA, National Oceanic and Atmospheric 

Administration; USGS, U.S. Geological Survey; EMTF, electromagnetic transfer function; NRCan, Natural Resources Canada; UTC, 

coordinated universal time.
12 Geomagnetism Program Research Plan, 2020–2024

Earth-Conductivity Modeling). Importantly, the geographic 

sparsity of observatories is a lesser challenge for statistical 

analyses than for time-continuous mapping (Project 5. 

Geoelectric-Field Mapping).

Hazard maps, such as shown in figure 9 as voltages on 

the national power grid, can inform vulnerability-evaluation 

projects of the NERC mandated by the Federal Energy 

Regulatory Commission (FERC) (2013). Once extreme-value 

voltage is estimated, GICs can be estimated by using 

Kirchhoff's laws, line resistances, and grid interconnectivity; 

in turn, the stress a grid would experience during a 

rare magnetic superstorm can be estimated. Recently 

initiated work includes the parameterization of maximum 

geoelectric-field intensity in terms of global indexes of 

geomagnetic disturbance, permitting retrospective estimation 

of the geoelectric hazards realized during great magnetic 

storms of the past. An important plausible extension of this 

project is consistent mapping of CONUS and Canadian 

geoelectric hazards needed to evaluate the exposure and 

vulnerability of the integrated North American power-grid 

systems. Collaboration is with the USGS Geology, 

Geophysics, and Geochemistry Science Center and the 

University of Colorado.

Project 7. Electromagnetic-Pulse Hazard 

Analysis

In support of priorities motivated by the EMP Executive 

Order 13865 (White House, 2019), the USGS Geomagnetism 

Program is examining the effects of realistic surface 

impedance on E3-induced geoelectric fields. Towards that 

end, the program uses some of the methods developed in its 

analysis of storm-induced geoelectric fields (Lucas and others, 

2018, 2020). An idealized but standard model is being used 

for estimating bomb-induced geomagnetic disturbance (Legro 

and others, 1985; International Electrotechnical Commission 

(IEC), 1996). This model is convolved with surface impedance 

(Project 4. National Impedance Map) to obtain maps of the 

E3 geoelectric field. Both time-dependent-scenario and hazard 

maps can be developed in this way.

This project will illuminate the effects of the Earth’s 3D 

conductivity structure on the E3-induced geoelectric fields—

until now, E3induction was typically considered for idealized 

one-dimensional Earth models (Commission to Assess the 

Threat to the United States (U.S.) from Electromagnetic Pulse 

(EMP) Attack, 2017). As for magnetic storms, investigation is 

needed of the non-plane-wave response to short-spatial-scale 

geomagnetic-field disturbance.

Figure 9. Once-per-century extreme magnetic-storm-event predictions of transmission-line voltage (Lucas and others, 2020): high and 

low hazards are yellow and purple, respectively. That the highest hazards are in the northern Midwest and the Piedmont east of the 

Appalachians demonstrates the important role that surface impedance plays in determining localized geoelectric hazards.
Program Roles and Capabilities 13

This project might benefit from reconnaissance 

deployments of high-frequency magnetotelluric sensors with a 

variety of spacings and orientations in a variety of geological 

settings across CONUS. Collaboration is needed among 

diverse agencies—possibly including the Los Alamos National 

Laboratory (for example, Rivera and others, 2016)—to enable 

realistic modeling. Results are likely to be influential for the 

EMP-assessment projects of the FERC (2013), Electric Power 

Research Institute (EPRI) (Horton, 2017), DOE (2017), and 

the DOD (Siebert and Witt, 2019).

Project 8. Gap Analyses and Operational 

Support

In support of priorities for ensuring baseline operational 

space-weather-observation platforms, capabilities, and 

networks (NSTC, 2019, Objective 2.2); identifying, developing, 

and testing innovative approaches to enable enhanced, 

more informative, robust, and cost-effective measurements 

(Objective 2.4) and observations (Holmes and others, 2013, 

Goal 1); the USGS Geomagnetism Program is examining the 

temporal and spatial complexity of storm-time geomagnetic 

and geoelectric disturbance. As illustrated in figure 10, the 

difference in geomagnetic disturbance recorded at distant 

but neighboring observatories can be significant. Work on 

this project can exploit the geomagnetic-disturbance maps 

(Project 2. Geomagnetic Field Mapping) and include analyses of 

geomagnetic data from the relatively dense observatory network 

in Europe. Geoelectric hazard maps (Project 6. Statistical 

Maps of Geoelectric Hazards) can also be used to identify 

potential locations for additional observatories or variometer 

stations—new stations might, for example, be installed in 

areas where geoelectric hazards are known to be high and far 

removed from existing observatory locations. The program 

plans to also examine the spatial resolution of the National 

Impedance Map (Project 4. National Impedance Map) derived 

from available magnetotelluric- survey tensors; the 70-kilometer 

survey-station spacing under EarthScope protocols might need 

to be augmented with surveys of finer scale in areas of spatially 

complex impedance. All of this will, in turn, help scientists 

to address the challenges of mapping geomagnetic (Project 2. 

Figure 10. Comparison of A, 1-minute north-south Bx geomagnetic-disturbance time series recorded at the Ottawa, Canada (red, OTT) 

and Fredericksburg, Virginia (blue, FRD) observatories during the Halloween storm of October 29–31, 2003 (Balch and others 2004), and 

B, the difference between the OTT and FRD time series. These observatories are separated by 814 kilometers.
14 Geomagnetism Program Research Plan, 2020–2024

Geomagnetic Field Mapping) and geoelectric disturbances 

(Projects 5. Geoelectric-Field Mapping and 6. Statistical Maps 

of Geoelectric Hazards).

External Collaborative Projects

USGS Geomagnetism Program scientists collaborate 

with several research groups on their projects. For example, as 

part of an ongoing collaboration with NCAR on physics-based 

modeling of the magnetospheric-ionospheric system, staff are 

developing (as of August 2020) a Biot-Savart algorithm that 

can be used to estimate ground geomagnetic-field disturbance. 

On another front, program scientists are collaborating 

with (1) the University of Texas at Arlington on numerical 

simulations of the most extreme sudden geomagnetic impulse 

theoretically possible; (2) the National Solar Observatory 

on analysis of historical records of an intense solar flare and 

solar-proton event; and (3) the USGS Geology, Geophysics, 

and Geochemistry Science Center on several projects related 

to geoelectric hazards and the modeling of solid-Earth 

conductivity structure by using magnetotelluric-survey data.

Community Leadership

The scientists of the USGS Geomagnetism Program play 

important roles in the terrestrial geomagnetic, magnetotelluric, 

and space-weather communities. They serve the Nation 

through the NSTC's Space Weather Operations, Research, and 

Mitigation (SWORM) working group and the Electromagnetic 

Pulse Research and Development (EMPRAD) working 

group, providing expertise in the ground effects of natural and 

anthropogenic electromagnetic-field disturbance. They advise 

FERC and NERC on storm-induced geoelectric hazards. They 

advise the National Geospatial-Intelligence Agency (NGA) on 

their World Magnetic Model project. They provide a liaison 

to NSF's Geospace Environment Modeling (GEM) steering 

group, and they serve on GEM's metrics-and-validation 

resource group. They serve on an advisory panel for university 

magnetometer programs and on IRIS's Electromagnetic 

Advisory Committee (EMAC). They advised NSF's EarthScope 

program on its magnetotelluric survey, and they played essential 

roles in the processing of EarthScope magnetotelluric data and 

in archiving related impedance tensors (Kelbert and others, 

2018). They have served on the Leadership Council of NSF's 

EarthCube (Kelbert, 2014; Aronson and others, 2015), as well 

as on its committees for science, technology and architecture, 

and nominations. They have organized conference sessions for 

the American Geophysical Union (AGU) and the International 

Union of Geology and Geophysics (IUGG). They have advised 

the domestic oil-and-gas industry on the use of geomagnetic 

data for directional drilling (Buchanan and others, 2013).

Internationally, USGS Geomagnetism Program 

research scientists and leadership support geomagnetic 

monitoring (Love and Finn, 2017) by providing guidance for 

INTERMAGNET. They serve on the Executive Committee 

of the International Association of Geomagnetism and 

Aeronomy (IAGA) and on the program committee of IAGA's 

Electromagnetic Induction Workshops (EMIW). Program 

scientists have a strong publication record, and notably, their 

research results have been reported in the popular press.

Some Conditional Aspirations

The preceding plan (with its eight integrated projects) 

is ambitious, and aspects of each project are currently being 

pursued (as of August 2020). Even with the present level 

of funding and staffing numbers, given the demonstrated 

productivity of USGS Geomagnetism Program scientists, 

good progress on all eight projects can be anticipated, as 

program scientists are fully occupied with their individual 

responsibilities. Given this, we can then imagine what the 

program might be able to do should increased funding and 

higher staffing numbers be realized. Most directly, progress on 

the projects might be accelerated and judiciously expanded. 

This would certainly benefit electric-utility companies with 

their projects for evaluating the vulnerability of power-grid 

systems to the deleterious effects of natural and anthropogenic 

geoelectric disturbance.

In more detail, the capability for mapping geoelectric 

fields (Project 5. Geoelectric-Field Mapping) could enable 

retrospective analyses of historical magnetic storms (Project 1. 

Historical Magnetic Superstorms) and prospective analyses of 

physics-based models (Project 2. Geomagnetic Field Mapping) 

of a potential superstorm. Scenario results would help put the 

statistical geoelectric-hazard maps (Project 6. Statistical Maps 

of Geoelectric Hazards) and the time-dependent geoelectric 

maps (Project 5. Geoelectric-Field Mapping) into perspective. 

Similarly, building on the proposed EMP analysis (Project 7. 

Electromagnetic-Pulse Hazard Analysis), physics-based 

models of source geomagnetic disturbance would help to 

put idealized EMP geoelectric maps into perspective. Any 

of these projects would benefit from additional support for 

Geomagnetism Program research, including work done 

through postdoctoral appointments.

If funding were sufficient to support new and 

additional Geomagnetism Program observatories (or 

simpler variometer stations) across CONUS and (or) new 

and additional regional magnetotelluric surveys in areas 

that the national-scale survey shows are likely to have 

high and spatially complicated geoelectric hazards, then 

scientific analyses of the new resulting data would provide 

more detailed time-dependent geoelectric maps (Project 

5. Geoelectric-Field Mapping) and more detailed regional 

geoelectric-hazard maps (Project 6. Statistical Maps of 

Geoelectric Hazards). Additional support could also enable 

the analysis of geoelectric hazards that can affect pipelines, 

railroads, and transoceanic telecommunication cables, 

each of which would be qualitatively different from hazard 

analyses for power grids.
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