Showing papers on "Space weather published in 1997"

Monitoring of global ionospheric irregularities using the Worldwide GPS Network

Abstract: A prototype system has been developed to monitor the instantaneous global distribution of ionospheric irregularities, using the worldwide network of Globa Positioning System (GPS) receivers. Case studies in this pape indicate that GPS receiver loss of lock of signal tracking may be associated with strong phase fluctuations. It is shown that a network-based GPS monitoring system will enable us to study the generation and evolution of ionospheric irregularities continuously around the globe under various solar and geophysical conditions, which is particularly suitable for studies of ionospheric storms, and for space weather research and applications.

The Sun's Variable Radiation and Its Relevance For Earth

Abstract: ▪ Abstract To what extent are changes in the Earth's global environment linked with fluctuations in its primary energy source, the radiation from a variable star, the Sun? A firm scientific basis for policy making with regard to anthropogenic greenhouse warming of climate and chlorofluorocarbon depletion of ozone requires a reliable answer to this question. Reduction of the vulnerability of spacecraft operations and communications to space weather necessitates knowledge of solar induced variability in Earth's upper atmosphere. Toward these goals, solar radiation monitoring and studies of solar variability mechanisms facilitate an understanding of the sources and amplitudes of the Sun's changing radiation. Interdisciplinary studies that link these changes with a wide array of terrestrial phenomena over the longer time scales of global change and the shorter time scales of space weather address the relevance of solar radiation variability for Earth. However, although numerous associations are apparent betwe...

Equatorial scintillation and systems support

Abstract: The need to nowcast and forecast scintillation for the support of operational systems has been recently identified by the interagency National Space Weather Program. This issue is addressed in the present paper in the context of nighttime irregularities in the equatorial ionosphere that cause intense amplitude and phase scintillations of satellite signals in the VHF/UHF range of frequencies and impact satellite communication, Global Positioning System navigation, and radar systems. Multistation and multifrequency satellite scintillation observations have been used to show that even though equatorial scintillations vary in accordance with the solar cycle, the extreme day-to-day variability of unknown origin modulates the scintillation occurrence during all phases of the solar cycle. It is shown that although equatorial scintillation events often show correlation with magnetic activity, the major component of scintillation is observed during magnetically quiet periods. In view of the day-to-day variability of the occurrence and intensity of scintillating regions, their latitude extent, and their zonal motion, a regional specification and short-term forecast system based on real-time measurements has been developed. This system, named the Scintillation Network Decision Aid, consists of two latitudinally dispersed stations, each of which uses spaced antenna scintillation receiving systems to monitor 250-MHz transmissions from two longitudinally separated geostationary satellites. The scintillation index and zonal irregularity drift are processed on-line and are retrieved by a remote operator on the Internet. At the operator terminal the data are combined with an empirical plasma bubble model to generate three-dimensional maps of irregularity structures and two-dimensional outage maps for the region.

Recurrent geomagnetic storms and relativistic electron enhancements in the outer magnetosphere: ISTP coordinated measurements

Abstract: New, coordinated measurements from the International Solar-Terrestrial Physics (ISTP) constellation of spacecraft are presented to show the causes and effects of recurrent geomagnetic activity during recent solar minimum conditions. It is found using WIND and POLAR data that even for modest geomagnetic storms, relativistic electron fluxes are strongly and rapidly enhanced within the outer radiation zone of the Earth's magnetosphere. Solar wind data are utilized to identify the drivers of magnetospheric acceleration processes. Yohkoh solar soft X-ray data are also used to identify the solar coronal holes that produce the high-speed solar wind streams which, in turn, cause the recurrent geomagnetic activity. It is concluded that even during extremely quiet solar conditions (sunspot minimum) there are discernible coronal holes and resultant solar wind streams which can produce intense magnetospheric particle acceleration. As a practical consequence of this Sun-Earth connection, it is noted that a long-lasting E>1MeV electron event in late March 1996 appears to have contributed significantly to a major spacecraft (Anik E1) operational failure.

Panel achieves consensus prediction of solar cycle 23

Abstract: In September 1996, a panel of experts on solar cycle prediction techniques met in Boulder, Colorado, to survey forecasts of solar and geomagnetic activity and to arrive at a consensus on how the solar cycle will develop. After two weeks of deliberation, the panel of 12 scientists (from Australia, Germany, the United Kingdom, and the United States) agreed that a large amplitude solar cycle with a smoothed sunspot maximum of approximately 160 is probable near the turn of the century. The amplitude of the predicted cycle is comparable to that of the previous two solar cycles (see Figure 1). Our ability to predict solar and geomagnetic activity is crucial to many technologies, including the operation of low-Earth orbiting satellites, electric power transmission grids, geophysical exploration, and highfrequency radio communications and radars. Because the scale height of Earth's upper atmosphere (and thus the drag on satellites in low Earth orbit) depends on the levels of short-wavelength solar radiation and geomagnetic activity, we need to know the profile and magnitude of the next solar and geomagnetic cycle in order to plan for reboosting the Hubble Space Telescope and assembling the International Space Station.

Geomagnetic storm forecasts and the power industry

Abstract: There is a well-recognized link between solar activity, geomagnetic disturbances, and disruptions to man-made systems such as power grids, satellites, communications, and defense systems. As technology evolves, these systems become more susceptible to magnetic disturbances than their counterparts of previous solar cycles. Analysis suggests that these vulnerabilities will continue and perhaps even increase as these systems continue to evolve. Geomagnetic disturbances can cause geomagnetically induced currents (GIC) to flow through the power system, entering and exiting the many grounding points on a transmission network. This is generally of most concern at the latitudes of the northern United States, Canada, and Scandinavia, for example, but regions much farther south are also affected during intense magnetic storms.

Strides made in understanding space weather at Earth

Abstract: Disturbances on the Sun can produce dramatic effects in the space environment surrounding the Earth. Energetic particle effects become more intense and pose a hazard to astronauts and damage spacecraft electronics; satellite lifetimes are shortened by increased atmospheric drag, and communications and navigation are disrupted by the changing plasma environment. “Space weather” has become the modern idiom for these effects, and periods of high activity are called geomagnetic storms. During a storm the ionosphere can be severely altered. A typical episode may reveal either a large decrease (negative phase) or increase (positive phase) in the normal daily peak ion density (NmF2) or total electron content (TEC). These changes in ion density are sometimes called ionospheric storms, and often persist for more than a day after a period of high geomagnetic activity.

Solar Power Satellites: A Space Energy System for Earth

Abstract: Solar power satellites could make an important contribution to meeting the world`s energy needs. The technical feasibility of gathering solar energy in space and transmitting it to Earth has been considered and studied over the last thirty years. This book discusses the use of space power options based on wireless power transmission (WPT) and this technology`s contribution to reducing dependence on fossil and nuclear fuels. (UK)

System and method for geomagnetic and ionospheric forecasting

Abstract: A system and method forecast geomagnetic events and resulting currents from ground and space weather data, including solar wind velocity data and interplanetary magnetic field data. The system has a processor including a first prediction generator for predicting a midnight equatorial boundary (MEB) value; a second prediction generator for predicting a polar cap potential (PCP) value from the ground and space weather data; an AL and AU prediction generator for predicting AL and AU values; a pseudo Kp value generator for generating a pseudo Kp related value; an electric field pattern generator for determining electric field patterns from the pseudo Kp value, the PCP value, and the ground and space weather data; a conductivity generator for determining conductivity values from the ground and space weather data and the pseudo Kp value; and an adaptive feedback generator for adaptively generating the geomagnetic parameters from the conductivity values, the electric field values, and the predicted AL and AU values. The geomagnetic forecasting system and method forecast geomagnetic parameters and events such as the occurrence of magnetic storms and substorms and their effects on ionospheric currents using ground and space-based measurements.

SPIDR on the Web: Space Physics Interactive Data Resource on‐line analysis tool

Abstract: The National Geophysical Data Center's innovative Space Physics Interactive Data Resource (SPIDR) is a multidisciplinary on-line system to search, browse, and access space weather and environmental data sets over the Internet. SPIDR is a tool for the online user to select data or imagery by date and geographical location and deliver an image to the user over the World Wide Web. Currently, Defense Meteorological Satellite Program (DMSP) satellite imagery, geomagnetic variations, ionospheric vertical incidence databases, and NOAA Goestationary Operational Environmental Satellites (GOES) space environment monitor data can be accessed by SPIDR. DMSP visible, infrared, and microwave imagery displays aurora, city lights, fires, lightning strikes, and cloud coverage. Ionospheric and geomagnetic data, as well as GOES X ray, energetic particle, and the magnetic field at the spacecraft, can be plotted from interactive menus. Solar and geomagnetic indices can be generated as plots for comparison. The Web user selects the month and year from pull-down menus and clicks the worldwide map in the region of interest. Worldwide contour maps of maximum electron density can also be generated from a global model of the ionosphere.

Identification of the solar source for the 18 october 1995 magnetic cloud

Abstract: It is necessary to identify signatures of solar sources in order to improve predictions of solar-caused geomagnetic activity. This is not a straightforward task as the relationship is not well understood. We apply an algorithm, derived from numerical simulations to identify the solar source of an interplanetary event that was observed by the WIND spacecraft on October 18, 1995 and was followed by a geomagnetic storm. No specific geomagnetic activity had been predicted at Space Weather Operations (SWO) in Boulder, CO, on the basis of earlier solar observations. The algorithm is used to estimate the time and location of the expected solar source of this interplanetary event. A review of solar observations prior to the WIND observations showed that solar activity precursors could be identified. A long-duration-event was seen by GOES in soft X-rays at the same time as a type IV burst was observed in metric radio wavelengths, and a rearrangement of fields was observed by the soft X-ray telescope on the Yohkoh satellite. This suggests that the algorithm is useful for post facto identification of solar sources, and that such combinations of solar activity should be further investigated for use in geomagnetic forecasting.

Particle Acceleration in Geospace and its Association with Solar Events

Abstract: Particle acceleration is a prominent feature of the geomagnetic storm, which is the prime dynamic process in Geospace – the near-Earth space environment Magnetic storms have their origin in solar events, which are transient disturbances of the solar atmosphere and radiation that propagates as variations of the solar wind fields and particles through interplanetary space to the Earth's orbit During magnetic storms, ions of both solar wind origin and terrestrial origin are accelerated and form an energetic ring current in the inner magnetosphere This current has global geomagnetic effects, which have both physical and technical implications Recently, it has been shown that large magnetic storms, which exhibit an unusually energized ionospheric plasma component, are closely associated with coronal mass ejections (CMEs) This implies a cause/effect chain connecting solar events through CMEs and the solar wind with the acceleration of terrestrial ion populations which eventually constitute the main source of global geomagnetic disturbances Here we present spacecraft observations related to storm-time particle acceleration and assess the observations within the framework of causes and effects of solar-terrestrial relationships

Workshop focuses on space weather's impact on electric power

Abstract: The National Space Weather Program (NSWP) defines space weather as the “conditions on the sun and in the solar wind, magnetosphere, ionosphere, and thermosphere that can influence the performance and reliability of space-borne and ground-based technological systems and can endanger human life or health.” It further observes that “Adverse conditions in the space environment can disrupt satellite operations, communications, navigation, and electric power distribution grids and lead to a variety of socioeconomic losses [NSWP, 1996]. While the NSWP clearly involves many areas of basic research, it also includes, by definition, an applied aspect. If the program is to have an impact on space weather's adverse effects on technological systems, the scientific community must learn to understand the real problems that users have. Conversely, users must learn what types of information may become available. Practical solutions to the problems space weather poses depend on a continuing dialogue between both communities.

Toward forecasting space weather in the heliosphere

Abstract: We cross correlate years of solar wind ion plasma speed and entropy observations at various sites throughout the heliosphere to determine the conditions under which one spacecraft can be successfully used as a monitor for other spacecraft. Peak correlation coefficients occur when two spacecraft lie radially aligned, although coefficients are generally enhanced during an ∼2– to 3-month period surrounding alignment. Within the inner heliosphere, the prevalence of corotating solar wind streams can enable useful predictions even when the monitoring spacecraft lies on the other side of the Sun. Similarly, observations at Earth can be useful in predicting conditions in the outer heliosphere to the orbit of Jupiter or even Saturn during periods of near-radial alignment. Observations at Earth cannot be used to successfully predict conditions beyond this distance without considering steepening on the leading edge of streams or stream interactions.

Solar wind magnetosphere coupling: Predicted and modeled with intelligent hybrid systems

Abstract: The solar wind-magnetosphere coupling is described as a mapping of the solar-solar wind state (input) to the magnetosphere-ionosphere state (output). The input-state is defined by solar wind parameters and the output-state is defined by geomagnetic disturbance indices. Most often are the geomagnetic disturbance indices D st and AE used. However, a new family of geomagnetic disturbance indices, CO, SO and EO, have been constructed which even might be able to describe the cusp and dayside magnetosphere. As mapper, a multi-layer backpropagation network, an Elman neural network and a radial basis function neural network, were used. Predictions of solar wind parameters and geomagnetic indices D st and AE are presented. The mapper represents a coupling function. It was found that the coupling function, learned by the neural networks, was more accurate than predefined theoretical coupling functions. In the case of modeling, it is therefore very important to explain the mapper and the trained neural network. Several methods are available: By extracting rules and decision trees from neural networks. By studying the prediction accuracy for different combinations of solar wind input parameters and for different coupling functions. By comparison with well-known mathematical methods. Integrating both data-driven and theory-driven methods into intelligent hybrid systems further improves the scientific method of studying the solar wind-magnetosphere coupling. Lund Space Weather Model is such a hybrid system. IHSs are also capable of mapping simultaneous multi-satellite observations. Such a mapping is therefore also suggested to improve the understanding of the solar wind-magnetosphere coupling.

Space weather, SuperDARN and the Tasmanian tiger

Abstract: The plasma environment extending from the solar surface through interplanetary space to the outermost reaches of the Earth’s atmosphere and magnetic field is dynamic, often disturbed, and capable of harming humans and damaging manmade systems. Disturbances in this environment have been identified as space weather disturbances. At the present time there is growing interest in monitoring and predicting space weather disturbances. In this paper we present some of the difficulties involved in achieving this goal by comparing the processes that drive tropospheric-weather systems with those that drive space-weather systems in the upper atmosphere and ionosphere. The former are driven by pressure gradients which result from processes that heat and cool the atmosphere. The latter are driven by electric fields that result from interactions between the streams of ionised gases emerging from the Sun (solar wind) and the Earth’s magnetosphere. Although the dimensions of the Earth’s magnetosphere are vastly greater than those of tropospheric weather systems, the global space-weather response to changes in the solar wind is much more rapid than the response of tropospheric-weather systems to changing conditions. We shall demonstrate the rapid evolution of space-weather systems in the upper atmosphere through measurements with a global network of radars known as SuperDARN. We shall also describe how the SuperDARN network is evolving, including a newly funded Australian component known as the Tasman International Geospace Environmental Radar (TIGER).

The forecasting of intense geomagnetic storms

Abstract: Resumen en: Intense geomagnetic storms are produced by the arrival at the magnetopause of solar wind carrying a magnetic field with a large southward component last...

IMP 8, WIND and INTERBALL observations of the solar wind

Abstract: The IMP 8 spacecraft, which was launched in October 1973, provides a baseline of 23 years of plasma data showing the time-variability of the solar wind. The time scales of periodic solar wind variability range from the solar cycle length of 11 years, to the unexpected 1.3-year variation also seen in the outer heliosphere, down to variations associated with the synodic solar rotation period of 27 days. All of these variations can affect the behavior of Earth's magnetosphere, as is clearly demonstrated by the presence of a 1.3-year period in the ap index of geomagnetic activity. Although recent work has suggested the presence of periodic variations in solar wind flux due to solar oscillations, such oscillations are not major contributors to the IMP 8 plasma frequency spectra. However, nonperiodic variations are an important contributor to the solar wind's impact on Earth, especially since they are superimposed on the longer-term periodic features. Various IMP observations are presented, showing solar wind variability on the time scales discussed. In addition, caveats are made about known anomalies in the IMP data, such as the one-year period in the elevation (north-south) flow angle. Some comparisons with data from the WIND, spacecraft, launched in November 1994, and the INTERBALL-1 spacecraft, launched in August 1995, demonstrate that the solar wind is spatially, as well as temporally variable, and that work remains to be done to quantify this variability.

Solar disturbances and correlated geospace responses: Relativistic magnetospheric electron acceleration

Abstract: The role of high-speed solar wind streams in driving relativistic electron acceleration within the earth's magnetosphere is discussed based on International Solar-Terrestrial Physics (ISTP) Observatory and related spacecraft observations. A 'recirculation' mechanism for electron acceleration and redistribution was invoked. Recently, an increase in the number of coronal mass ejections (CMEs) and related 'magnetic clouds' was seen at 1 AU. As these CME/cloud systems interact with the earth's magnetosphere, they are able to produce rapid enhancements in the magnetospheric electron population. The relativistic electron signatures observed by the POLAR, SAMPEX, and other spacecraft during recent magnetic cloud events, especially January 1997 and May 1997, were compared and contrasted. In these cases, there were large solar wind and IMF changes during the cloud passages and very rapid energetic electron acceleration was observed. The relative geoeffectiveness of these events is examined and 'space weather' predicatability is assessed.

A Career in the Solar Wind

Abstract: This is a personal history of the author's experiences, starting with the earliest direct measurements of the solar wind and continuing through later experiments to investigate the physics of the solar wind and its interaction with comets.

Satellites, scientists track storm from Sun to surface

Abstract: On January 6, the Sun spat a coronal mass ejection (CME) into the solar wind and toward Earth; by January 10, a cloud of charged particles buffeted the face of the planet. It was, by several accounts, a run-of-the-mill space weather event. But the scientific work surrounding the storm was anything but run-of-the-mill. For the first time, space physicists observed and recorded a space weather event from start to finish, from solar surface to earthly impact. Researchers are calling it the first true success story of the four-year-old International Solar Terrestrial Physics program (ISTP), which includes NASA's WIND and POLAR spacecraft; the joint Solar and Heliospheric Observatory (SOHO) mission of NASA and the European Space Agency; the joint Geotail mission of NASA and Japan's Institute of Space and Aeronautical Science; and Russia's Interball satellites.

Real-Time GPS network facilitates geophysical studies

Abstract: The Global Positioning System (GPS) is being widely used to monitor lithospheric processes with millimeter precision, which it achieves by correcting for signal delays induced by the ionosphere [Ho et al., 1996] and atmosphere [Businger et al., 1996]. Alternatively, uncorrected GPS data can be used to estimate properties of the ionosphere and atmosphere important to meteorology, climate, and space weather.

LASCO Data Dazzle Chapman Conference

Abstract: Research on coronal mass ejections (CMEs)—giant bubbles of magnetized gas blown into the heliosphere by the Sun (Figure 1)—has entered a time of dramatic growth. The large angle spectrometric coronagraph (LASCO) on the recently launched Solar and Heliospheric Observatory (SOHO) spacecraft has revealed unexpected aspects of the beautiful and puzzling CME phenomenon (see Figure 1), which was recently shown to be a key element for space weather. Studies of LASCO and other SOHO data combined with Yohkoh Soft X Ray Telescope observations are certain to provide new insight on how CMEs are initiated at the Sun. Concurrently, analyses of in situ plasma and field data from the Wind and Ulysses spacecraft are elucidating the structure of CMEs in the interplanetary (IP) medium.

Space Weather Physics, Prediction and classification of solar wind structures and geomagnetic activity using artificial neural networks.

Abstract: This thesis concerns the application of artificial neural network techniques to space weather physics. The networks applied include multi-layer error-backpropagation, radial basis function, and self-organized maps. Different parts in the solar-terrestrial chain are analysed with the emphasis on developing methods for real time predictions of geomagnetic activity. The neural networks are general models which utilize learning algorithms to adjust the free parameters of the models based on data samples. The models used here rely heavily on observations of solar magnetic fields, measurements of solar wind plasma and magnetic fields, and indices of geomagnetic activity. The thesis consists of an introductory part followed by 5 papers. The introduction describes part of the solar-terrestrial physics that is relevant to the papers and includes a summary of the applied neural networks used. Papers I and II describe the application of multi-layer error-backpropagation networks to the solar wind-magnetosphere coupling, where the geomagnetic activity is described by the Dst index. It is shown that real time predictions of the Dst index can be made one hour in advance. Papers III and IV examine the possibility to predict the daily average solar wind velocity from solar magnetic field observations. The model consists of a potential field model describing the solar coronal magnetic fields and a radial basis function neural network for the mapping from the corona to the solar wind. Paper V considers the analysis of hourly average solar wind structures at 1 AU using self-organizing maps. It is found that it is possible to identify specific solar wind events on the self-organized maps that are associated to geomagnetic storms occurring several hours later. (Less)

Space Weather Physics: Dynamic Neural Network Studies of Solar Wind-Magnetosphere Coupling

Abstract: This thesis presents studies of solar wind-magnetosphere coupling using dynamic neural networks in combination with statistically correlative analysis. The primary contribution of the thesis is dynamic neural network models that can be implemented for near real-time predictions of geomagnetic storms from the solar wind alone. With acceptable accuracy, the prediction time has been extended up to 5 hours. This is of great socioeconomic significance in space weather forecasting. The secondary contribution of the thesis is the modeling of the magnetospheric dynamics, which optimizes combinations of solar wind parameters and coupling functions. The third contribution of the thesis includes the development of a C-cod of Elman recurrent network models, the development of an algorithm for pruning Elman networks and the algorithms for post network error analyses. The fourth contribution of the thesis is the exploitation of the hybrid of a time-delay network and a recurrent network by examining the role of a time-delay line in recurrent networks. This thesis consists of five chapters. Chapter 1 provides an introduction to solar-terrestrial physics. Chapter 2 is a general description of neural networks. Chapter 3 describes solar wind-magnetosphere coupling and related studies. Chapter 4 is devoted to studies of a time-dependent system, such as the solar wind-driven magnetosphere, using neural networks. Chapter 5 is a summary of the papers included in this thesis. Paper I pioneered exploitation of recurrent neural networks in prediction of geomagnetic activity and presents very accurate one hour ahead prediction of magnetic storms using only solar wind data. Paper II is a study of solar wind-magnetosphere coupling using a partially recurrent neural network to find the optimal coupling functions. The optimal coupling functions found are used to predict magnetic storms up to 5 hours with acceptable accuracy. This study was the first to present real-time one hour ahead prediction of magnetic storms using the satellite WIND real-time data. Paper III made predictions of magnetic storms up to 8 hours. It presents the appropriate combinations of solar wind parameters for predicting magnetic storms, which reveals the relative importance of solar wind parameters. It is found that a magnetic storm is formed in the magnetosphere on a timescale of about 1 hour. In this study, we exploit a time-delay recurrent network which is a hybrid of a time-delay network and an Elman recurrent network, and prove it very helpful in improving predictions. Paper IV studies solar wind-magnetosphere interaction in detail, which finds the best coupling functions for accurate prediction of geomagnetic activity based on neural network modeling, in comparison with the results from cross-correlation analyses. The algorithms for computation of confidence limits on the prediction accuracy are developed in this study. (Less)