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USGS2026

Remote compositional analyses of space-weathered lunar maria

Visible-to-shortwave infrared (VSWIR) reflectance spectroscopy has revolutionized our understanding of planetary surface compositions. However, space-weathering processes on airless bodies complicate quantitative compositional analyses. Here, we present a framework to isolate the signatures of space weathering in VSWIR spectra of lunar maria by leveraging radiative transfer modeling under the assumptions that (i) a space-weathered target can be expressed as a mixture of fresh and fully space-weathered components and (ii) remaining signatures can be modeled by including agglutinates as an end-member component. We first validate this approach against laboratory spectra of space-weathered Apollo mare soils of known mineral compositions using a probabilistic Markov Chain Monte Carlo implementation of the Hapke radiative transfer model. Second, we illustrate how this approach can be applied to orbital Moon Mineralogy Mapper data. The proposed space-weathering correction workflow for lunar maria could be expanded to other lunar lithologies and applied to existing and future data sets.

Planetary Science Journal↗

USGS2011

The USGS geomagnetism program and its role in space weather monitoring

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.

Space Weather↗

USGS2012

Solar thematic maps for space weather operations

Thematic maps are arrays of labels, or "themes", associated with discrete locations in space and time. Borrowing heavily from the terrestrial remote sensing discipline, a numerical technique based on Bayes' theorem captures operational expertise in the form of trained theme statistics, then uses this to automatically assign labels to solar image pixels. Ultimately, regular thematic maps of the solar corona will be generated from high-cadence, high-resolution SUVI images, the solar ultraviolet imager slated to fly on NOAA's next-generation GOES-R series of satellites starting ~2016. These thematic maps will not only provide quicker, more consistent synoptic views of the sun for space weather forecasters, but digital thematic pixel masks (e.g., coronal hole, active region, flare, etc.), necessary for a new generation of operational solar data products, will be generated. This paper presents the mathematical underpinnings of our thematic mapper, as well as some practical algorithmic considerations. Then, using images from the Solar Dynamics Observatory (SDO) Advanced Imaging Array (AIA) as test data, it presents results from validation experiments designed to ascertain the robustness of the technique with respect to differing expert opinions and changing solar conditions.

Space Weather↗

USGS2020

Magnetic field variations in Alaska: Recording space weather events on seismic stations in Alaska

Seismometers are highly sensitive instruments to not only ground motion but also many other nonseismic noise sources (e.g., temperature, pressure, and magnetic field variations). We show that the Alaska component of the Transportable Array is particularly susceptible to recording magnetic storms and other space weather events because the sensors used in this network are unshielded and magnetic flux variations are stronger at higher latitudes. We also show that vertical‐component seismic records across Alaska are directly recording magnetic field variations between 40 and 800 s period as opposed to actual ground motion during geomagnetic events with sensitivities ranging from 0.004 to 0.48    ( m / s 2 ) / T "> 0.48 ( m / s 2 ) / T 0.48 (m/s2)/T ⁠ . These sensitivities were found on a day where the root mean square variation in the magnetic field was 225 nT. Using a method developed by Forbriger (2007 , his section 3.1), we show that improving vertical seismic resolution of an unshielded sensor by as much as 10 dB in the 100–400 s period band using magnetic data from a collocated three‐component magnetometer is possible. However, due to large spatial variations in Earth’s magnetic field, this methodology becomes increasingly ineffective as the distance between the seismometer and magnetometer increases (no more than 200 km separation). A potential solution to this issue may be to incorporate relatively low‐cost magnetometers as an additional environmental data stream at high‐latitude seismic stations. We demonstrate that the Bartington Mag‐690 sensors currently deployed at Global Seismographic Network sites are not only acceptable for performing corrections to seismic data, but are also capable of recording many magnetic field signals with similar signal‐to‐noise ratios, in the 20–1000 s period band, as the observatory grade magnetometers operated by the U.S. Geological Survey Geomagnetism Program. This approach would densify magnetic field observations and could also contribute to space weather monitoring by supplementing highly calibrated magnetometers with additional sensors.

Alaska↗

USGS2013

Report of geomagnetic pulsation indices for space weather applications

The phenomenon of ultra-low frequency geomagnetic pulsations was first observed in the ground-based measurements of the 1859 Carrington Event and has been studied for over 100 years. Pulsation frequency is considered to be “ultra” low when it is lower than the natural frequencies of the plasma, such as the ion gyrofrequency. Ultra-low frequency pulsations are considered a source of noise in some geophysical analysis techniques, such as aeromagnetic surveys and transient electromagnetics, so it is critical to develop near real-time space weather products to monitor these geomagnetic pulsations. The proper spectral analysis of magnetometer data, such as using wavelet analysis techniques, can also be important to Geomagnetically Induced Current risk assessment.

Open-File Report↗

USGS2018

The extreme space weather event in September 1909

We evaluate worldwide low-latitude auroral activity associated with the great magnetic storm of September 1909 for which a minimum Dst value of −595 nT has recently been determined. From auroral observations, we calculate that the equatorward boundary of the auroral oval in the 1909 event was in the range from 31°–35° invariant latitude (assuming auroral height of 400 km) to 37°–38° (800 km). These locations compare with satellite-based observations of precipitating auroral electrons down to 40° magnetic latitude for the March 1989 storm with its comparable minimum Dst value of −589 nT. According to Japanese auroral records, bluish colour started to appear first, followed by reddish colour. The colour change can be attributed to the transition from sunlit aurora to the usual low-latitude reddish aurora. Telegraph communications were disrupted at mid/low latitudes, coincidently with the storm main phase and the early recovery phase. The telegraphic disturbances were caused by geomagnetically induced currents associated with the storm-time ring current and substorm current wedge. From the calculated CME energy ─ based on the 24.75 hr separation between the flare-associated magnetic crochet and the geomagnetic storm sudden commencement and interplanetary conditions inferred from geomagnetic data ─ and consideration of the ∼−40 nT crochet amplitude, we estimated that the soft X-ray class of the 24 September 1909 flare was ≥X10. As is the case for other extreme storms, strong/sharp excursions in the horizontal component of the magnetic field observed at low-latitude magnetic stations were coincident with the observation of low-latitude aurora.

Monthly Notices of the Royal Astronomical Society↗

USGS2016

Weathering a Perfect Storm from Space

Extreme space-weather events — intense solar and geomagnetic storms — have occurred in the past: most recently in 1859, 1921 and 1989. So scientists expect that, sooner or later, another extremely intense spaceweather event will strike Earth again. Such storms have the potential to cause widespread interference with and damage to technological systems. A National Academy of Sciences study projects that an extreme space-weather event could end up costing the American economy more than $1 trillion. The question now is whether or not we will take the actions needed to avoid such expensive consequences. Let’s assume that we do. Below is an imagined scenario of how, sometime in the future, an extreme space-weather event might play out.

Earth Magazine↗

USGS2017

Real-time geomagnetic monitoring for space weather-related applications: Opportunities and challenges

An examination is made of opportunities and challenges for enhancing global, real-time geomagnetic monitoring that would be beneficial for a variety of operational projects. This enhancement in geomagnetic monitoring can be attained by expanding the geographic distribution of magnetometer stations, improving the quality of magnetometer data, increasing acquisition sampling rates, increasing the promptness of data transmission, and facilitating access to and use of the data. Progress will benefit from new partnerships to leverage existing capacities and harness multisector, cross-disciplinary, and international interests.

Space Weather↗

USGS2011

Optical maturity variation in lunar spectra as measured by Moon Mineralogy Mapper data

High spectral and spatial resolution data from the Moon Mineralogy Mapper (M3) instrument on Chandrayaan-1 are used to investigate in detail changes in the optical properties of lunar materials accompanying space weathering. Three spectral parameters were developed and used to quantify spectral effects commonly thought to be associated with increasing optical maturity: an increase in spectral slope ("reddening"), a decrease in albedo ("darkening"), and loss of spectral contrast (decrease in absorption band depth). Small regions of study were defined that sample the ejecta deposits of small fresh craters that contain relatively crystalline (immature) material that grade into local background (mature) soils. Selected craters are small enough that they can be assumed to be of constant composition and thus are useful for evaluating trends in optical maturity. Color composites were also used to identify the most immature material in a region and show that maturity trends can also be identified using regional soil trends. The high resolution M3 data are well suited to quantifying the spectral changes that accompany space weathering and are able to capture subtle spectral variations in maturity trends. However, the spectral changes that occur as a function of maturity were observed to be dependent on local composition. Given the complexity of space weathering processes, this was not unexpected but poses challenges for absolute measures of optical maturity across diverse lunar terrains. Copyright 2011 by the American Geophysical Union.

Journal of Geophysical Research E: Planets↗

USGS2019

The first 3D conductivity model of the contiguous US: Reflections on geologic structure and application to induction hazards

Estimation of ground level geoelectric fields has been identified by the National Space Weather Action Plan as a key component of assessment and mitigation of space weather impacts on critical infrastructure. Estimates of spatially and temporally variable electric fields are used to generate statistically based hazard maps and show promise toward monitoring and responding to geomagnetic disturbances in near real‐time. One approach to geoelectric field estimation is to employ three‐dimensional (3D) Earth conductivity models. These data‐constrained conductivity models are the results of regional magnetotelluric inversions based primarily on NSF’s Earthscope USArray impedances, which to date cover ~60% of the contiguous United States. Here, we present the first‐ever composite conductivity model of the contiguous United States and describe its compilation from 3D regional conductivity models, a global mantle conductivity model, offshore bathymetry, and sediment thickness data. We discuss structures within the conductivity model and how they relate to the complex geologic tapestry of the continent. Finally, we discuss the utility of this synthesis model for estimation and mitigation of geomagnetically induced currents.

Book chapter↗

USGS2008

Monitoring the Earth's dynamic magnetic field

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.

Fact Sheet↗

USGS2019

On the intensity of the magnetic superstorm of September 1909

Analysis is made of solar observations and ground‐based magnetometer data recording space weather before and during the magnetic superstorm of 25 September 1909. From these data, it is inferred that the storm was initiated by an interplanetary coronal‐mass ejection having a mean Sun‐to‐Earth velocity of ~1,679 km/s. The commencement pressure on the magnetopause was ~32.4 nPa, sufficient to compress the subsolar magnetopause radius to ~5.9 Earth radii. Early on in the evolution of the storm, low‐latitude geomagnetic disturbance exhibited extreme longitudinal asymmetry, something that can be attributed to substorm activity extending to low latitudes. For this storm, Dst attained a minimum of −595 nT, comparable to that of the great magnetic storm of March 1989 (−589 nT; the most intense storm in terms of Dst of the space age). These results inform projects focused on understanding and mitigating the deleterious effects of extreme space‐weather events.

Space Weather↗

USGS2011

M3 spectral analysis of lunar swirls and the link between optical maturation and surface hydroxyl formation at magnetic anomalies

We examined the lunar swirls using data from the Moon Mineralogy Mapper (M 3 ). The improved spectral and spatial resolution of M 3 over previous spectral imaging data facilitates distinction of subtle spectral differences, and provides new information about the nature of these enigmatic features. We characterized spectral features of the swirls, interswirl regions (dark lanes), and surrounding terrain for each of three focus regions: Reiner Gamma, Gerasimovich, and Mare Ingenii. We used Principle Component Analysis to identify spectrally distinct surfaces at each focus region, and characterize the spectral features that distinguish them. We compared spectra from small, recent impact craters with the mature soils into which they penetrated to examine differences in maturation trends on- and off-swirl. Fresh, on-swirl crater spectra are higher albedo, exhibit a wider range in albedos and have well-preserved mafic absorption features compared with fresh off-swirl craters. Albedoand mafic absorptions are still evident in undisturbed, on-swirl surface soils, suggesting the maturation process is retarded. The spectral continuum is more concave compared with off-swirl spectra; a result of the limited spectral reddening being mostly constrained to wavelengths less than ∼1500 nm. Off-swirl spectra show very little reddening or change in continuum shape across the entire M 3 spectral range. Off-swirl spectra are dark, have attenuated absorption features, and the narrow range in off-swirl albedos suggests off-swirl regions mature rapidly. Spectral parameter maps depicting the relative OH surface abundance for each of our three swirl focus regions were created using the depth of the hydroxyl absorption feature at 2.82 μ m. For each of the studied regions, the 2.82 μ m absorption feature is significantly weaker on-swirl than off-swirl, indicating the swirls are depleted in OH relative to their surroundings. The spectral characteristics of the swirls and adjacent terrains from all three focus regions support the hypothesis that the magnetic anomalies deflect solar wind ions away from the swirls and onto off-swirl surfaces. Nanophase iron (npFe 0 ) is largely responsible for the spectral characteristics we attribute to space weathering and maturation, and is created by vaporization/deposition by micrometeorite impacts and sputtering/reduction by solar wind ions. On the swirls, the decreased proton flux slows the spectral effects of space weathering (relative to nonswirl regions) by limiting the npFe 0 production mechanism almost exclusively to micrometeoroid impact vaporization/deposition. Immediately adjacent to the swirls, maturation is accelerated by the increased flux of protons deflected from the swirls.

Journal of Geophysical Research E: Planets↗

USGS2020

Geomagnetism Program research plan, 2020–2024

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.

Circular↗

USGS2013

The Anemomilos prediction methodology for Dst

This paper describes new capabilities for operational geomagnetic D isturbance s torm t ime (Dst) index forecasts. We present a data‐driven, deterministic algorithm called Anemomilos for forecasting Dst out to a maximum of 6 days for large, medium, and small storms, depending upon transit time to the Earth. This capability is used for operational satellite management and debris avoidance in Low Earth Orbit (LEO). Anemomilos has a 15 min cadence, 1 h time granularity, 144 h prediction window (+6 days), and up to 1 h latency. A new finding is that nearly all flare events above a certain irradiance threshold, occurring within a defined solar longitude/latitude region and having sufficient estimated liftoff velocity of ejected material, will produce a geoeffective Dst perturbation. Three solar observables are used for operational Dst forecasting: flare magnitude, integrated flare irradiance through time, and event location. Magnitude is a proxy for ejecta quantity or mass and, combined with speed derived from the integrated flare irradiance, represents the kinetic energy. Speed is estimated as the line‐of‐sight velocity for events within 45° radial of solar disk center. Storms resulting from high‐speed streams emanating from coronal holes are not modeled or predicted. A new result is that solar disk, not limb, observable features are used for predictive techniques. Comparisons between Anemomilos predicted and measured Dst for every hour over 25 months in three continuous time frames between 2001 (high solar activity), 2005 (low solar activity), and 2012 (rising solar activity) are shown. The Anemomilos operational algorithm was developed for a specific customer use related to thermospheric mass density forecasting. It is an operational space weather technology breakthrough using solar disk observables to predict geomagnetically effective Dst up to several days at 1 h time granularity. Real‐time forecasts are presented at http://sol.spacenvironment.net/~sam_ops/index.html?

Space Weather↗

USGS2017

Extreme geomagnetic storms: Probabilistic forecasts and their uncertainties

Extreme space weather events are low-frequency, high-risk phenomena. Estimating their rates of occurrence, as well as their associated uncertainties, is difficult. In this study, we derive statistical estimates and uncertainties for the occurrence rate of an extreme geomagnetic storm on the scale of the Carrington event (or worse) occurring within the next decade. We model the distribution of events as either a power law or lognormal distribution and use (1) Kolmogorov-Smirnov statistic to estimate goodness of fit, (2) bootstrapping to quantify the uncertainty in the estimates, and (3) likelihood ratio tests to assess whether one distribution is preferred over another. Our best estimate for the probability of another extreme geomagnetic event comparable to the Carrington event occurring within the next 10 years is 10.3% 95% confidence interval (CI) [0.9,18.7] for a power law distribution but only 3.0% 95% CI [0.6,9.0] for a lognormal distribution. However, our results depend crucially on (1) how we define an extreme event, (2) the statistical model used to describe how the events are distributed in intensity, (3) the techniques used to infer the model parameters, and (4) the data and duration used for the analysis. We test a major assumption that the data represent time stationary processes and discuss the implications. If the current trends persist, suggesting that we are entering a period of lower activity, our forecasts may represent upper limits rather than best estimates.

Space Weather↗

USGS2020

Some experiments in extreme-value statistical modeling of magnetic superstorm intensities

In support of projects for forecasting and mitigating the deleterious eﬀects of extreme space-weather storms, an examination is made of the intensities of magnetic superstorms recorded in the Dst index time series (1957-2016). Modiﬁed peak-over-threshold and solar-cycle, block-maximum sampling of the Dst time series are performed to obtain compi-lations of storm-maximum −Dstm intensity values. Lognormal, upper-limit lognormal, generalized Pareto, and generalized extreme-value model distributions are ﬁtted to the−Dstm data using a maximum-likelihood algorithm. All four candidate models provide good representations of the data. Comparisons of the statistical signiﬁcance and good-ness of ﬁts of the various models gives no clear indication as to which model is best. The statistical models are used to extrapolate to extreme-value intensities, such as would be expected (on average) to occur once per century. An upper-limit lognormal ﬁt to peak-over-threshold −Dstm data above a superstorm threshold of 283 nT gives a 100-year ex-trapolated intensity of 542 nT and a 68% conﬁdence interval (obtained by bootstrap re-sampling) of [466, 583] nT. An upper-limit lognormal ﬁt to solar-cycle, block-maximum−DstBM data gives a 9-solar-cycle (approximately 100-year) extrapolated intensity of 553 nT. The Dst data are found to be insuﬃcient for providing usefully accurate esti-mates of a statistically theoretical upper limit for magnetic storm intensity. Secular change in storm intensities is noted, as is a need for improved estimates of pre-1957 magnetic storm intensities.

Space Weather↗

USGS2016

The geomagnetic blitz of September 1941

Seventy-five years ago, on 18–19 September 1941, the Earth experienced a great magnetic storm, one of the most intense ever recorded. It arrived at a poignant moment in history, when radio and electrical technology was emerging as a central part of daily life and when much of the world was embroiled in World War II, which the United States had not yet officially entered. Auroras danced across the night sky as voltage surged in power grid lines. A radio blackout interrupted fan enjoyment of a baseball game, while another radio program was interrupted by private phone conversations. Citizens, already on edge, wondered if neon lights were some sort of antiaircraft signal. And far away in the North Atlantic, the illuminated night sky exposed an Allied convoy to German attack. These effects raised awareness within the scientific community and among the public of the societal significance of the effects that the Sun and outer space can have on the Earth—what we now call space weather .

Eos, Earth and Space Science News↗