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At least 163 records · Page 9
All sourcesNASA NTRSDOE OSTI
DOE OSTI2025

Data-Driven Clustering and Classification of Outage Patterns with Insights into their Links to Extreme Events

At a global level extreme events have increased in both scale and impact. These events have the potential to affect the electrical grid infrastructure and cause a wide range of outages, which can lead to a disruption in daily patterns, cost millions of dollars and also the loss of life. Currently, to track these outage events there have been various approaches developed ranging from regional to national level quantifications for what defines an outage. However, this variation in methods can potentially lead to subjective decision-making and a lack of proper management in relation to the event. While previous work has made strides in determining spatio-temporal patterns, minimal attention has been given to the type and number of outages an area may be exposed to. The differences in incurred cost and the overall severity of an event between a transformer box malfunction and a hurricane are drastic, and by finding historical signals, we can allow for more efficient management, potentially saving lives and millions of dollars. Here, we leverage unsupervised machine learning techniques to delineate outage patterns among 22 counties within the United States and find that there are clear, segregated clusters (0.93 silhouette) of data which are related by event behavior and underlying cause. This finding will allow for energy stakeholders, policy makers, and researchers to gain a deeper understanding of the extent and severity of historic events and to better prepare for electrical grid infrastructure planning and management.

Koob, Benjamin [ORNL]↗
NASA NTRS1973

Solar cosmic ray micro-events

To study small discrete solar particle events, it has proven useful to define a special class such that the proton flux at energies greater than 20 MeV exceed 0.0001 protons/sq cm-sec-sr-MeV. These increases are termed microevents. An arbitrary upper limit is placed at 2 X 0.02 protons/sq cm-sec-sr-MeV. By demanding a measurable flux above 20 MeV, a better separation from corotating events is achieved and onset times can in general be determined more precisely. Over an observing period extending from May 1967 through December 1971, approximately 105 events were observed. There are several different sources of these small events. Some are produced by moderate to large solar flares near the east limb or by solar flares on the nonvisible disk of the sun. Others are produced by generally minor solar activity: typically in 1N flare, a group of type 3 radio bursts and a well defined X-ray burst. A significant number of this latter type are accompanied by type 2 radio emission. A small sample of the micro-events can be classified as scatter-free events. For these the distance traveled by the particles before their initial detection at earth is on the order of 1.5 AU and observed rise and decay times are much less than normal. Examples of these general types of micro-events and their solar association are discussed.

Mcdonald, F. B.↗
NASA NTRS1974

Skylab short-lived event alert program

During the three manned Skylab missions, the Center for Short-Lived Phenomena (CSLP) reported a total of 39 significant events to the Johnson Space Center (JSC) as part of the Skylab Short-Lived Event Alert Program. The telegraphed daily status reports included the names and locations of the events, the track number and revolution number during which the event could be observed, the time (GMT) to within plus or minus 2 sec when Skylab was closest to the event area, and the light condition (daylight or darkness) at that time and place. The messages sent to JSC during the Skylab 4 mission also included information pertaining to ground-truth studies and observations being conducted on the events. Photographic priorities were assigned for each event.

Citron, R. A.↗
NASA NTRS1975

Relative abundance of proton to helium nuclei in solar cosmic ray events

A statistical study of the relative abundance of proton to alpha particles at equal energy per nucleon has been carried out on the basis of some hundred solar particle events in the energy range 6-20 MeV/nuc. A small qualitative effect of the coronal propagation has been found for events associated with solar flares away from the observer 'preferred connection region' (20-80 deg W from the central meridian). The variation of the relative abundance of the proton to alpha particle at ejection is analyzed using events for which the coronal transport is minimum. It is found that micro events characterized by small proton intensity, little or no scattering in interplanetary medium and little or no trapping in the corona has an abundance of He-4 of 5-30% relative to proton. Those events frequently display a very high He-3 abundance from 30 to 150% relatively to He-4. For larger particle events, the alpha abundance decreases following a relation which is not valid for flare-associated events that accelerate particles to relativistic energies.

Van Hollebeke, M. A. I.↗
NASA NTRS1976

The speeds of coronal mass ejection events

Results are presented for a systematic study of ejection speeds for the mass-ejection events observed with the white-light coronagraph aboard Skylab. At least 66 such events (most of them not associated with flares) were observed during the Skylab mission. Direct measurements of the displacements of the leading edges of the observed disturbances yield ejection speeds ranging from less than 100 to greater than 1200 km/s, with the average being close to 470 (+ or - 50) km/s; seventy percent of the events are found to have speeds exceeding the escape velocity at 6 solar radii. It is shown that the speeds are loosely correlated with the type of H-alpha activity associated with the mass ejections and that events associated with flares usually have speeds greater than those of events associated with eruptive prominences. Despite their poor quality, statistics indicate that the fastest mass-ejection events tend to produce type II-IV burst pairs, while single type II or type IV bursts tend to be associated with events of intermediate speed.

Gosling, J. T.↗
NASA NTRS1978

SAS 3 observations of two X-ray transient events with precursors

SAS 3 has observed two unusual fast transient X-ray events from different sources, one lasting about 150 s and one, approximately 1500 s. Both events were preceded by precursor pulses which lasted a few seconds and which rose and fell in less than 0.4 s. The precursors were separated from the 'main' events by several seconds, during which no X-rays were detected. There are similarities between the two main events and X-ray bursts in both their temporal and spectral evolution. The spectra of the main events started out much softer than the spectra of the precursors, became harder as they approached maximum intensity, and softened as they decayed. In the 1500-s event, X-rays with energies greater than 10 keV were delayed by about 80 s compared with 1.5-6-keV X-rays. A blackbody fit to the spectral data of the main event of approximately 1500-s duration gives a maximum temperature of 29 million K and a radius for the emitting region of at least about 9 km (at a distance of 10 kpc); this is similar to the temperature and sizes found for several X-ray burst sources.

Hoffman, J. A.↗
NASA NTRS1980

A survey of He-3 enriched events between 1974 and 1978

In five years of observations between 1974 and 1978, at least 17 He-3 enriched events have been identified in the energy range 2 to 13 MeV/nucleon, with He-3/He-4 ratios ranging from less than 0.1 to greater than 4. The scarcity of H-2 in He-3 events found by other workers is confirmed in this data. Flattening of He-3 spectra relative to He-4 is identified in several of the events. Many but not all of the sampled events are found to have small H-1/He-4 ratios. A sum of the sampled events shows not only Fe enrichments but abundances enhanced relative to oxygen of all heavier elements. No substantial depletion of carbon is identified. A dependence of the enhancements in He-3 events on atomic number like that found in other Fe-enriched solar cosmic ray events suggests a common mechanism producing the enhancements.

Mcguire, R. E.↗
NASA NTRS1983

A statistical study of large electric field events in the earth's magnetotail

A statistical study of large electric field events, measured on ISEE 1 at geocentric distances of 3 to 23 earth radii, has been performed in order to determine the occurrence frequency and spatial distribution of such events. Large electric fields were seen at all altitudes, with the lowest altitude events occurring on auroral field lines and the higher altitude events occurring on the high latitude boundary of the plasma sheet. The largest events had amplitudes that were approximately proportional to the square root of the local magnetic field strength, in agreement with expectations of a simple mapping model. The apparent concentration of big field events near local midnight is caused, at least in part, by a nonuniform frequency of satellite crossings through the plasma sheet boundary as a function of local time. Thus, the spatial distribution and amplitudes of the large field events are not inconsistent with the mapping of low-altitude electrostatic shocks to the plasma sheet boundary along equipotential magnetic field lines.

Levin, S.↗
NASA NTRS1985

Solar source regions of 3HE-rich particle events

Hydrogen alpha X-ray, and metric and kilometric radio data to examine the solar sources of energetic 3He-rich particle events observed near earth in association with impulsive 2 to 100 keV electron events were applied. Each 3He/electron event is associated with a kilometric type 3 burst belonging to a family of such bursts characterized by similar interplanetary propagation paths from the same solar active region. The 3He/electron events correlate very well with the interplanetary low frequency radio brightnesses of these events, but progressively worse with signatures from regions closer to the Sun. When H alpha brightnings can be associated with 3He/electron events, they have onsets coinciding to within 1 min of that of the associated metric type 3 burst but are often too small to be reported. The data are consistent with the earlier idea that many type 3 bursts, the 3He/electron events, are due to particle acceleration in the corona, well above the associated H alpha and X-ray flares.

Kahler, S. W.↗
NASA NTRS1983

Solar He-3-rich events observed on ISEE-3

A scan has been made of ISEE-3 data for all events with He-3/He-4 between 0.20 and 1.3 MeV/nucl. The 67 events found show some evidence of 27-day recurrence. Larger events show both velocity dispersion and magneic field-aligned arrival from the solar direction. At least one third of the events are preceded by increases in about 300 keV electrons, although several larger events show no electron increases. Spike events also exist suggesting nearly scatter-free propagation of He-3 from well-connected events.

Reames, D. V.↗
NASA NTRS1985

A comparison of solar helium-3-rich events with type II bursts and coronal mass ejections

The acceleration process for energetic particles in He-3-rich events and for particles in normal-abundance events are compared. A list of 66 He-3-rich events observed with the Goddard Space Flight Center particle detector on ISEE 3 is presented, and it is shown that these events are not statistically associated with either of the two common signatures of normal-abundance events, metric type II and coronal mass ejections. This result indicates that enhanced abundance events may be produced only in the impulsive phases of flares, while normal abundance events are produced in subsequent flare shock waves.

Kahler, S.↗
NASA NTRS1986

The identification of solar He-3-rich events and the study of particle acceleration at the sun

Kilometric radio observations are to associate type III radio bursts with solar He-3-rich events and to identify and study the sources of those events at the sun and the transport of the particles outward toward earth. The events exhibit an impulsive behavior that earns them a natural role in the event classification scheme based upon the time scale of the particle acceleration process. Multiple He-3-rich events are observed frequently from a single active region where they provide a convenient signature to test theories of particle storage and transport. These multiple events act as impulsive probes of the condition of the interplanetary medium. Their profiles contrast with the source-acceleration-induced profiles of the long-duration events from the same active region that are interspersed among them.

Reames, D. V.↗
NASA NTRS1987

Characteristics of solar coronal source regions producing He-3-rich particle events

H-alpha, X-ray, and kilometric radio data are used to examine solar coronal activity associated with energetic He-3-rich particle events observed near earth. The basis of the study is the 12 He-3-rich events observed in association with impulsive 2-100 keV electron events reported by Reames et al. (1985). In three or four events, associated H-alpha or X-ray flares were found, and in two events even the metric type III bursts were weak or absent. The measured low energy electron spectra for these events show no evidence of a flattening due to Coulomb collisional losses. These results and several other recent findings are consistent with the idea that the He-3/electron events are due to particle acceleration in the corona well above the associated H-alpha and X-ray flares.

Kahler, S. W.↗
NASA NTRS1988

X-ray and radio properties of solar (He-3) rich events

Radio and X-ray properties of solar flares associated with a new sample of individual (He-3) rich solar particle events are examined. Given the association between kilometric type III bursts and (He-3) rich events, the timing of the radio events is used to identify the related X-ray increases. The X-ray events exhibit a rich variety, from the standpoint of both intensity and complexity. Examination of the events shows statistically significant anticorrelations between the He-3/He-4 ratio and the intensity of the event as measured at kilometric wavelengths and in hard and soft X-rays; larger He-3/He-4 ratios occur in smaller flares. The result suggests that a coupling may exist between the preheating phase and the acceleration phase of these events or that mixing occurs between an enriched particle population accelerated within the compact flare and a normal population accelerated by a shock propagating away from an intense flare.

Reames, D. V.↗
NASA NTRS1988

Late Eocene impact events recorded in deep-sea sediments

Raup and Sepkoski proposed that mass extinctions have occurred every 26 Myr during the last 250 Myr. In order to explain this 26 Myr periodicity, it was proposed that the mass extinctions were caused by periodic increases in cometary impacts. One method to test this hypothesis is to determine if there were periodic increases in impact events (based on crater ages) that correlate with mass extinctions. A way to test the hypothesis that mass extinctions were caused by periodic increases in impact cratering is to look for evidence of impact events in deep-sea deposits. This method allows direct observation of the temporal relationship between impact events and extinctions as recorded in the sedimentary record. There is evidence in the deep-sea record for two (possibly three) impact events in the late Eocene. The younger event, represented by the North American microtektite layer, is not associated with an Ir anomaly. The older event, defined by the cpx spherule layer, is associated with an Ir anomaly. However, neither of the two impact events recorded in late Eocene deposits appears to be associated with an unusual number of extinctions. Thus there is little evidence in the deep-sea record for an impact-related mass extinction in the late Eocene.

Glass, B. P.↗
NASA NTRS1989

The role of polar stratospheric clouds on total ozone minihole events

Using seven years of data from tha SAM 2 (Stratospheric Aerosol Measurement 2) and TOMS (Total Ozone Mapping Spectrometer) instruments, along with 70 mbar temperatures extracted from an NMC analysis, the effect of the austral spring polar stratospheric clouds (PSC) on the formation of total ozone miniholes is investigated. A total ozone minihole event is designated as the rapid decrease of more than 20 DU of total ozone over a time period of a day and a spatial extent of approximately 1000 by 1000 km. The severe decrease of total ozone during these minihole events could be explained in part by PSC being formed at altitudes of 10 to 24 km and preventing scattered UV radiation from ozone below the cloud from reaching the TOMS instrument. A result of the cloud's opaqueness is that the total ozone retrieval from TOMS data would underestimate the ozone column in the vicinity of the PSC. The approach to investigate the effect of PSC on total ozone was to use SAM 2 aerosol extinction values in conjunction with NMC stratospheric temperatures to determine if PSC are present during total ozone minihole events occurring during August and September, 1979 to 1986. The minihole events during these seven years were divided into two types: type 1, where the minihole region of 24 hour darkness from regions exposed to sunlight, and type 2, where the minihole occurred 5 to 10 degrees north of the terminator. The presence of PSC in a given region was ascertained by a maximum aerosol extinction greater than .006/km occurring with a temperature less than 189 K. It is found that PSC are consistently present with type 2 minihole events. This is contrasted with PSC rarely occurring in the same vicinity of type 2 miniholes. Also observed of that type 1 minihole events have minimum total ozone values which are on the average 3 to 10 DU smaller than type 2 miniholes. It can be concluded that care must be taken when trying to deduce a dynamical explanation of minihole events near the polar terminator and the role of PSC must be accounted for in type 1 minihole formation.

Sabutis, Joseph L.↗
NASA NTRS1994

Energetic-particle abundances in impulsive solar flare events

We report on the abundances of energetic particles from impulsive solar flares, including those from a survey of 228 He-3 rich events, with He-3/He-4 is greater than 0.1, observed by the International Sun Earth Explorer (ISEE) 3 spacecraft from 1978 August through 1991 April. The rate of occurrence of these events corresponds to approximately 1000 events/yr on the solar disk at solar maximum. Thus the resonant plasma processes that enhance He-3 and heavy elements are a common occurrence in impulsive solar flares. To supply the observed fluence of He-3 in large events, the acceleration must be highly efficient and the source region must be relatively deep in the atmosphere at a density of more than 10(exp 10) atoms/cu cm. He-3/He-4 may decrease in very large impulsive events because of depletion of He-3 in the source region. The event-to-event variations in He-3/He-4, H/He-4, e/p, and Fe/C are uncorrelated in our event sample. Abundances of the elements show a pattern in which, relative to coronal composition, He-4, C, N, and O have normal abundance ratios, while Ne, Mg, and Si are enhanced by a factor approximately 2.5 and Fe by a factor approximately 7. This pattern suggests that elements are accelerated from a region of the corona with an electron temperature of approximately 3-5 MK, where elements in the first group are fully ionized (Q/A = 0.5), those in the second group have two orbital electrons (Q/A approximately 0.43), and Fe has Q/A approximately 0.28. Ions with the same gyrofrequency absorb waves of that frequency and are similarly accelerated and enhanced. Further stripping may occur after acceleration as the ions begin to interact with the streaming electrons that generated the plasma waves.

Reames, D. V.↗
NASA NTRS1998

Track Structure Model for Radial Distributions of Electron Spectra and Event Spectra from High-Energy Ions

An analytic method is described for evaluating the average radial electron spectrum and the radial and total frequency-event spectrum for high-energy ions. For high-energy ions, indirect events make important contributions to frequency-event spectra. The method used for evaluating indirect events is to fold the radial electron spectrum with measured frequency-event spectrum for photons or electrons. The contribution from direct events is treated using a spatially restricted linear energy transfer (LET). We find that high-energy heavy ions have a significantly reduced frequency-averaged final energy (yF) compared to LET, while relativistic protons have a significantly increased yF and dose-averaged lineal energy (yD) for typical site sizes used in tissue equivalent proportional counters. Such differences represent important factors in evaluating event spectra with laboratory beams, in space- flight, or in atmospheric radiation studies and in validation of radiation transport codes. The inadequacy of LET as descriptor because of deviations in values of physical quantities, such as track width, secondary electron spectrum, and yD for ions of identical LET is also discussed.

Cucinotta, F. A.↗