Geology topics
Publications and source records attributed to Jeffrey J. Love.
A magnetic observatory is a specially designed ground-based facility that supports time-series measurement of the Earth’s magnetic field. Observatory data record a superposition of time-dependent signals related to a fantastic diversity of physical processes in the Earth’s core, mantle, lithosphere, ocean, ionosphere, magnetosphere, and, even, the Sun and solar wind.
Recent studies have led to speculation that solar‐terrestrial interaction, measured by sunspot number and geomagnetic activity, has played an important role in global temperature change over the past century or so. We treat this possibility as an hypothesis for testing. We examine the statistical significance of cross‐correlations between sunspot number, geomagnetic activity, and global surface temperature for the years 1868–2008, solar cycles 11–23. The data contain substantial autocorrelation and nonstationarity, properties that are incompatible with standard measures of cross‐correlational significance, but which can be largely removed by averaging over solar cycles and first‐difference detrending. Treated data show an expected statistically‐significant correlation between sunspot number and geomagnetic activity, Pearson p < 10 −4 , but correlations between global temperature and sunspot number (geomagnetic activity) are not significant, p = 0.9954, ( p = 0.8171). In other words, straightforward analysis does not support widely‐cited suggestions that these data record a prominent role for solar‐terrestrial interaction in global climate change. With respect to the sunspot‐number, geomagnetic‐activity, and global‐temperature data, three alternative hypotheses remain difficult to reject: (1) the role of solar‐terrestrial interaction in recent climate change is contained wholly in long‐term trends and not in any shorter‐term secular variation, or, (2) an anthropogenic signal is hiding correlation between solar‐terrestrial variables and global temperature, or, (3) the null hypothesis, recent climate change has not been influenced by solar‐terrestrial interaction.
Analysis is made of the geomagnetic-activity aa index and its source K -index data from groups of ground-based observatories in Britain, and Australia, 1868.0–2009.0, solar cycles 11–23. The K data show persistent biases, especially for high (low) K -activity levels at British (Australian) observatories. From examination of multiple subsets of the K data we infer that the biases are not predominantly the result of changes in observatory location, localized induced magnetotelluric currents, changes in magnetometer technology, or the modernization of K -value estimation methods. Instead, the biases appear to be artifacts of the latitude-dependent scaling used to assign K values to particular local levels of geomagnetic activity. The biases are not effectively removed by weighting factors used to estimate aa . We show that long-term averages of the aa index, such as annual averages, are dominated by medium-level geomagnetic activity levels having K values of 3 and 4.
Magnetic storms result from the dynamic interaction of the solar wind with the coupled magnetospheric-ionospheric system. Large storms represent a potential hazard for the activities and infrastructure of a modern, technologically based society [Baker et al., 2008]; they can cause the loss of radio communications, reduce the accuracy of global positioning systems, damage satellite electronics and affect satellite operations, increase pipeline corrosion, and induce voltage surges in electric power grids, causing blackouts. So while space weather starts with the Sun and is driven by the solar wind, it is on, or just above, the surface of the Earth that the practical effects of space weather are realized. Therefore, ground-based sensor networks, including magnetic observatories [Love, 2008], play an important role in space weather monitoring.
W e produce a 1-min time resolution storm-time disturbance index, the USGS Dst, called Dst 8507-4 SM . This index is based on minute resolution horizontal magnetic field intensity from low-latitude observatories in Honolulu, Kakioka, San Juan and Hermanus, for the years 1985–2007. The method used to produce the index uses a combination of time- and frequency-domain techniques, which more clearly identifies and excises solar-quiet variation from the horizontal intensity time series of an individual station than the strictly time-domain method used in the Kyoto Dst index. The USGS 1-min Dst is compared against the Kyoto Dst, Kyoto Sym-H, and the USGS 1-h Dst ( Dst 5807-4 SH ). In a time series comparison, Sym-H is found to produce more extreme values during both sudden impulses and main phase maximum deviation, possibly due to the latitude of its contributing observatories. Both Kyoto indices are shown to have a peak in their distributions below zero, while the USGS indices have a peak near zero. The USGS 1-min Dst is shown to have the higher time resolution benefits of Sym-H, while using the more typical low-latitude observatories of Kyoto Dst.
A time and frequency-domain analysis is made of the effects of averaging and sampling methods used for constructing magnetic-observatory hourly data values. Using 1-min data as a proxy for continuous, geomagnetic variation, we construct synthetic hourly values of two standard types: instantaneous "spot" measurements and simple 1-h "boxcar" averages. We compare these average-sample types with others: 2-h average, Gaussian, and "brick-wall" low-frequency-pass. Hourly spot measurements provide a statistically unbiased representation of the amplitude range of geomagnetic-field variation, but as a representation of continuous field variation over time, they are significantly affected by aliasing, especially at high latitudes. The 1-h, 2-h, and Gaussian average-samples are affected by a combination of amplitude distortion and aliasing. Brick-wall values are not affected by either amplitude distortion or aliasing, but constructing them is, in an operational setting, relatively more difficult than it is for other average-sample types. It is noteworthy that 1-h average-samples, the present standard for observatory hourly data, have properties similar to Gaussian average-samples that have been optimized for a minimum residual sum of amplitude distortion and aliasing. For 1-h average-samples from medium and low-latitude observatories, the average of the combination of amplitude distortion and aliasing is less than the 5.0 nT accuracy standard established by Intermagnet for modern 1-min data. For medium and low-latitude observatories, average differences between monthly means constructed from 1-min data and monthly means constructed from any of the hourly average-sample types considered here are less than the 1.0 nT resolution of standard databases. We recommend that observatories and World Data Centers continue the standard practice of reporting simple 1-h-average hourly values.
We present 29 movie‐maps of low‐latitude horizontal‐intensity magnetic disturbance for the years 1999–2006: 28 recording magnetic storms and 1 magnetically quiescent period. The movie‐maps are derived from magnetic vector time series data collected at up to 25 ground‐based observatories. Using a technique similar to that used in the calculation of Dst , a quiet time baseline is subtracted from the time series from each observatory. The remaining disturbance time series are shown in a polar coordinate system that accommodates both Earth rotation and the universal time dependence of magnetospheric disturbance. Each magnetic storm recorded in the movie‐maps is different. While some standard interpretations about the storm time equatorial ring current appear to apply to certain moments and certain phases of some storms, the movie‐maps also show substantial variety in the local time distribution of low‐latitude magnetic disturbance, especially during storm commencements and storm main phases. All movie‐maps are available at the U.S. Geological Survey Geomagnetism Program Web site ( http://geomag.usgs.gov ).
Analysis is made of the accuracy of magnetic-observatory hourly means constructed from definitive minute data having missing values (gaps). Bootstrap sampling from different data-gap distributions is used to estimate average errors on hourly means as a function of the number of missing data. Absolute and relative error results are calculated for horizontal-intensity, declination, and vertical-component data collected at high, medium, and low magnetic latitudes. For 90% complete coverage (10% missing data), average (RMS) absolute errors on hourly means are generally less than errors permitted by Intermagnet for minute data. As a rule of thumb, the average relative error for hourly means with 10% missing minute data is approximately equal to 10% of the hourly standard deviation of the source minute data.
The thirteenth biennial International Association of Geomagnetism and Aeronomy (IAGA) Workshop on Geomagnetic Observatory Instruments, Data Acquisition and Processing was held in the United States for the first time on June 9-18, 2008. Hosted by the U.S. Geological Survey's (USGS) Geomagnetism Program, the workshop's measurement session was held at the Boulder Observatory and the scientific session was held on the campus of the Colorado School of Mines in Golden, Colorado. More than 100 participants came from 36 countries and 6 continents. Preparation for the workshop began when the USGS Geomagnetism Program agreed, at the close of the twelfth workshop in Belsk Poland in 2006, to host the next workshop. Working under the leadership of Alan Berarducci, who served as the chairman of the local organizing committee, and Tim White, who served as co-chairman, preparations began in 2007. The Boulder Observatory was extensively renovated and additional observation piers were installed. Meeting space on the Colorado School of Mines campus was arranged, and considerable planning was devoted to managing the many large and small issues that accompany an international meeting. Without the devoted efforts of both Alan and Tim, other Geomagnetism Program staff, and our partners at the Colorado School of Mines, the workshop simply would not have occurred. We express our thanks to Jill McCarthy, the USGS Central Region Geologic Hazards Team Chief Scientist; Carol A. Finn, the Group Leader of the USGS Geomagnetism Program; the USGS International Office; and Melody Francisco of the Office of Special Programs and Continuing Education of the Colorado School of Mines. We also thank the student employees that the Geomagnetism Program has had over the years and leading up to the time of the workshop. For preparation of the proceedings, thanks go to Eddie and Tim. And, finally, we thank our sponsors, the USGS, IAGA, and the Colorado School of Mines.
The US geomagnetism community is supported by NASA, NOAA, USGS, NSF, DOD, and US universities. During the Decade of Geopotential Field Research, inaugurated in 1999 with the launch of the Danish satellite Ørsted on a US rocket, the US community has been involved in satellite mission development and analysis, instrument development, model development, and in the discovery and understanding of new processes with satellite magnetic signatures. The ESA Swarm mission has been a primary focus of the US community, with three US scientists on Swarm's Mission Advisory Group. Swarm will measure, for the first time, the E-W gradient of the magnetic field. One of us (T. Sabaka) is involved with the development of a Comprehensive inversion scheme as part of the SMART consortium. This effort is an outgrowth of the Comprehensive Model [1]. Swarm will also provide valuable observations for ionospheric specification and forecast. The geomagnetism group at NOAA (S. Maus, P. Alken and C. Manoj) has developed algorithms to estimate the strength of the eastward electric field (EEF). As the driver of the equatorial plasma fountain, the EEF is an important space weather parameter. ESA is considering the implementation of the EEF as a dedicated inversion chain in the Level-2 Facility. In 2006, NASA launched a minisatellite magnetometer constellation mission (ST-5) to test technologies and software. The ST-5 constellation featured the first along-track gradient measurements. NASA has also initiated efforts to study geomagnetism mission concepts after Swarm. One of the ideas under consideration is the systematic measurement of radial field gradients. Instrument development, and geomagnetic observatories, are also an integral part of the US effort. The past decade has seen significant advances in the development of a self-calibrating vector helium magnetometer, and in the automation of the US observatory network. Working in coordination with Intermagnet, the USGS Geomagnetism Program has made operational 1-second data acquisition at 13 of its magnetic observatories. The Program is also developing a realtime 1-minute and 1-hour Dst service. Within the past decade, US scientists have been leaders in the development of models that describe the global geomagnetic environment, including comprehensive models (the CM series), maps of the lithospheric field from satellite (MF-series), near surface maps of the lithospheric field (WDMAM-series), models of the thickness of the magnetic crust, the IGRF and World Magnetic Model series, ionospheric models such as the EEJM1, JVDM1, and the IRI, and data assimilation-based models (MoSST-series) that predict the future state of the geomagneic field.
High-resolution geomagnetic field data (i.e., ≤5 seconds) have recently become more commonly used by space physicists. The data permit the identification of Pi2 pulsations, having periods of 40-150 seconds and irregular waveforms. Pulsations of this type appear clearly in time series from mid- and low-latitude ground stations on the nightside at substorm onset. Therefore, with data from multiple observatories, substorm genesis and evolution can be monitored. Here we propose a new substorm index, the Wp index (Wavelet and planetary), which measures Pi2 spectral power at low-latitude. This index is derived from geomagnetic field data obtained from observatories arranged in longitude around the Earth’s circumference. Presently, data from 5 ground stations (Fürstenfeldbruck, Iznik, Urumqi, Kakioka, and Teoloyucan) are used, but future work will include data from other sites as well (Honolulu, Tucson, San Juan, Tristan da Cunha, and Ebro). Here we compare substorm occurrence estimated from the Wp index and those from the AE and ASY indices. We show that Wp index is a good indicator of substorm onset.
For centuries, navigators of the world’s oceans have been familiar with an effect of Earth’s magnetic field: It imparts a directional preference to the needle of a compass. Although in some settings magnetic orientation remains important, the modern science of geomagnetismhas emerged from its romantic nautical origins and developed into a subject of great depth and diversity. The geomagnetic field is used to explore the dynamics of Earth’s interior and its surrounding space environment, and geomagnetic data are used for geophysical mapping, mineral exploration, risk mitigation, and other practical applications. A global distribution of ground-based magnetic observatories supports those pursuits by providing accurate records of the magnetic-field direction and intensity at fixed locations and over long periods of time. Magnetic observatories were first established in the early 19th century in response to the influence of Alexander von Humboldt and Carl Friedrich Gauss. Since then, magnetic measurement has advanced significantly, progressing from simple visual readings of magnetic survey instruments to include automatic photographic measurement and modern electronic acquisition. To satisfy the needs of the scientific community, observatories are being upgraded to collect data that meet ever more stringent standards, to achieve higher acquisition frequencies, and to disseminate data in real time. To appreciate why data from magnetic observatories can be used for so many purposes, one needs only to recall that the geomagnetic field is a continuum, connecting the different parts of Earth to each other and to nearby space. Beneath our feet and above our heads, electric currents generate magnetic fields that contribute to the totality of the geomagnetic field measured at an observatory on Earth’s surface. The many physical processes that operate in each geophysical domain give rise to a complicated field that exhibits a wide variety of time-dependent behavior. In this article I review the status of the global community of magnetic observatories, show how Earth and space can be monitored for purposes of scientific understanding and practical application, and highlight the role played by magnetic observatories in the history of geomagnetism research.
The mission of the U.S. Geological Survey's Geomagnetism Program is to monitor the Earth's magnetic field. Using ground-based observatories, the Program provides continuous records of magnetic field variations covering long timescales; disseminates magnetic data to various governmental, academic, and private institutions; and conducts research into the nature of geomagnetic variations for purposes of scientific understanding and hazard mitigation. The program is an integral part of the U.S. Government's National Space Weather Program (NSWP), which also includes programs in the National Aeronautics and Space Administration (NASA), the Department of Defense (DOD), the National Oceanic and Atmospheric Administration (NOAA), and the National Science Foundation (NSF). The NSWP works to provide timely, accurate, and reliable space weather warnings, observations, specifications, and forecasts, and its work is important for the U.S. economy and national security. Please visit the National Geomagnetism Program?s website, http://geomag.usgs.gov, where you can learn more about the Program and the science of geomagnetism. You can find additional related information at the Intermagnet website, http://www.intermagnet.org.
We consider the nonstationary, statistical modeling of the occurrence in time of large Kp geomagnetic storms over the course of multiple solar cycles. Previous work showed that wait times between storms can be represented by an exponential density function, consistent with the realization of a Poisson process. Here we also assume a Poisson process, but to account for solar cycle modulation of storm likelihood, we assume an occurrence rate given by a parametric constant plus a simple sinusoidal function of time. Parameter estimation is accomplished using maximum likelihood, yielding good fits to the Kp data. We find that the relative phase between storms and sunspots depends on storm size. We quantify previous observations that small storms tend to occur during the declining phase of the solar cycle, while large storms tend to occur very close to solar maximum. We predict average wait time between storms and the storm occurrence rate up through the year 2018.
Magnetic indices are simple measures of magnetic activity that occurs, typically, over periods of time of less than a few hours and which is recorded by magnetometers at ground‐based observatories (Mayaud, 1980 ; Rangarajan, 1989 ; McPherron, 1995 ). The variations that indices measure have their origin in the Earth's ionosphere and magnetosphere. Some indices having been designed specifically to quantify idealized physical processes, while others function as more generic measures of magnetic activity. Indices are routinely used across the many subdisciplines in geomagnetism, including direct studies of the physics of the upper atmosphere and space, for induction studies of the Earth's crust and mantle, and for removal of disturbed‐time magnetic data in studies of the Earth's deep interior and core. Here we summarize the most commonly used magnetic indices, using data from a worldwide distribution of observatories, those shown in Figure M31 and whose sponsoring agencies are given in Table M1 .
The Geomagnetism Program of the US Geological Survey has, for over a century now, monitored the Earth's magnetic field through a network of magnetic observatories and conducted scientific analysis on the data collected. The program traces its origins to the Reorganization Act of 1843, in which Congress authorized the creation of a coastal survey agency, as part of the Treasury Department, that was responsible for, among other things, geomagnetic surveys. The 19th century saw the establishment of relatively short‐lived magnetic stations, as well as the production of declination maps for the United States and territories. With the purchase of Alaska, coastal surveys became an increasingly higher priority, and in 1889 the Coast and Geodetic Survey, with a Division of Terrestrial Magnetism, was established. The first essentially permanent geomagnetic observatories were established under the Division's leadership of Dr. Louis A. Bauer and Dr. John A. Fleming: Cheltenham Maryland Observatory was established in 1900, subsequently moved to the Fredericksburg site in 1956; Sitka Alaska Observatory was established in 1901 and that of Honolulu Hawaii in 1902. Soon after these observatories became operational, it was found that the Sitka and Honolulu magnetometers were also sensitive to local earthquakes, and so seismometers were installed at the sites. In part, because of this colocation of instruments, the magnetic and seismological programs in the Coast and Geodetic Survey were united in 1925 under the Division of Geomagnetism and Seismology. Over the years, the Geomagnetism Program has evolved in response to the needs of the United States and in response to changes in the nation's various federal agencies. In 1903 the Coast and Geodetic Survey was transferred to the newly organized Department of Commerce, and in 1970 the survey became part of the National Oceanic and Atmospheric Administration (NOAA). In 1973, the US Geological Survey of the Department of the Interior assumed responsibility for the nation's Geomagnetism and Seismology programs.