Search

Space weather describes the way in which the Sun, and conditions in space more generally, impact human activity and technology both in space and on the ground. It is now well understood that space weather represents a significant threat to infrastructure resilience, and is a source of risk that is wide-ranging in its impact and the pathways by which this impact may occur. Although space weather is growing rapidly as a field, work rigorously assessing the overall economic cost of space weather appears to be in its infancy. Here, we provide an initial literature review to gather and assess the quality of any published assessments of space weather impacts and socioeconomic studies. Generally speaking, there is a good volume of scientific peer-reviewed literature detailing the likelihood and statistics of different types of space weather phenomena. These phenomena all typically exhibit "power-law" behavior in their severity. The literature on documented impacts is not as extensive, with many case studies, but few statistical studies. The literature on the economic impacts of space weather is rather sparse and not as well developed when compared to the other sections, most probably due to the somewhat limited data that are available from end-users. The major risk is attached to power distribution systems and there is disagreement as to the severity of the technological footprint. This strongly controls the economic impact. Consequently, urgent work is required to better quantify the risk of future space weather events.

An accurate understanding of space weather socioeconomic impact is fundamental to the development of appropriate operational services, forecasting capabilities, and mitigation strategies. One way to approach this problem is by developing physics‐based models and frameworks that can lead to a bottom‐up estimate of risk and likely impact. Here we describe the development of a new framework to assess the economic impact of space weather on power distribution networks and the supply of electricity. In particular, we focus on the phenomenon of the geomagnetic substorm, which is relatively localized in time and space, and occurs multiple times with varying severity during a geomagnetic storm. The framework uses the AE index to characterize substorm severity, and the impact of the substorm is modulated by the resilience of the power grid and the nature of available forecast. Possible scenarios for substorm sequences during a 1‐in‐10‐, a 1‐in‐30‐, and a 1‐in‐100‐year geomagnetic storm events are generated based on the 2003, 1989, and 1859 geomagnetic storms. Economic impact, including international spill over, can then be calculated using standard techniques, based on the duration and the geographical footprint of the power outage. Illustrative calculations are made for the European sector, for a variety of forecast and resilience scenarios. However, currently available data are highly regionally inhomogeneous, frustrating attempts to define an overall global economic impact at the present time.

Space weather describes the way in which the Sun, and conditions in space more generally, impact human activity and technology both in space and on the ground. It is now well understood that space weather represents a significant threat to infrastructure resilience, and is a source of risk that is wide-ranging in its impact and the pathways by which this impact may occur. Although space weather is growing rapidly as a field, work rigorously assessing the overall economic cost of space weather appears to be in its infancy. Here, we provide an initial literature review to gather and assess the quality of any published assessments of space weather impacts and socioeconomic studies. Generally speaking, there is a good volume of scientific peer-reviewed literature detailing the likelihood and statistics of different types of space weather phenomena. These phenomena all typically exhibit "power-law" behavior in their severity. The literature on documented impacts is not as extensive, with many case studies, but few statistical studies. The literature on the economic impacts of space weather is rather sparse and not as well developed when compared to the other sections, most probably due to the somewhat limited data that are available from end-users. The major risk is attached to power distribution systems and there is disagreement as to the severity of the technological footprint. This strongly controls the economic impact. Consequently, urgent work is required to better quantify the risk of future space weather events.

Heliophysics is a new discipline that studies of the effect of the Sun on the Solar System and spans a number of existing scientific domains—solar physics, heliospheric physics, and magnetospheric and ionospheric physics. In order to build a virtual observatory for heliophysics we have to find ways to conduct searches that span the domains and track the evolution of phenomena in 4 dimensions as they propagate through interplanetary space. To facilitate this it will be necessary to improve the quality of the metadata that are used in the search and to describe the observations. We describe some of the issues and how these can be addressed.

This paper presents a morphological analysis of the active region NOAA AR 484 as well as its intensity and magnetic field variations associated with flare occurrences. The active region is tracked during a one solar rotation with the automated technique used in Solar Feature Catalogue (SFC). The location and intensity parameters of region AR484 were extracted from 1 minute cadence Hα solar images from the Big Bear observatory (BBSO), SOHO/EIT images in Fe XII, 195 A and the SOHO/MDI magnetograms. During the whole period of tracking from October, 19 until November, 11, 2003 the AR484 produced many flares of different significance including a few X-class flares. We investigate the total AR intensity variations in each band leading to a flare production and compare these with the magnetic field changes before and during a flare for five flares of different significance. Based on this comparison the key parameters defining the region activity in a flare production are found that include the resulting, or excess, flux and the ratio between areas covered by negative and positive pixels. These parameters can be used for a preliminary pre-flare classification of active regions in addition to other classifiers associated with a magnetic field.

International audience; This paper presents the techniques developed for the automated detection of filaments on Meudon Halpha spectroheliograms, and, by extension, on any full-disk Halpha Sun observations. Some cleaning processes are first applied to the images to correct them from defects characteristic of the instrument. Indeed, these defects may lead to spurious detections. From the cleaned images, filament areas are then segmented using a region growing method which efficiently returns the full extent of these dark areas. The filaments are finally described by means of their pruned skeleton. This representation allows one to compare the automatically segmented filaments with those manually recorded for Meudon Synoptic Maps. The very good agreement observed on a representative set of images confirms that this method can effectively be used in the frame of the EGSO (European Grid of Solar Observations) project in order to produce a reliable catalog dedicated to solar features.

Space weather phenomena can effect many areas of commercial airline operations including avionics, communications and GPS navigation systems. Of particular importance at present is the recently introduced EU legislation requiring the monitoring of aircrew radiation exposure, including any variations at aircraft altitudes due to solar activity. With the introduction of new ultra-long-haul “over-the-pole” routes, “more-electric” aircraft in the future, and the increasing use of satellites in the operation, the need for a better understanding of the space weather impacts on future airline operations becomes all the more compelling. This paper will present the various space weather effects, some provisional results of an ongoing 3-year study to monitor cosmic radiation in aircraft, and conclude by summarising some of the identified key operational issues, which must be addressed, with the help of the science community, if the airlines want to benefit from the availability of space weather services.

We describe the RESIK (REntgenovsky Spektrometr s Izognutymi Kristalami) instrument, consisting of two double-channel X-ray spectrometers, designed to observe solar active region and flare plasmas. RESIK is one of the instruments making up the scientific payload of the Russian CORONAS-F solar mission. The uncollimated spectrometer uses two silicon and two quartz bent crystals observing flare, active region and coronal spectra in four wavelength bands with a resolving power (λ/Δ λ) of ∼1000. The wavelength coverage, 3.3–6.1 A, includes emission lines of Si, S, Cl, Ar, and K and in the third diffraction order, the wavelength range includes He-like Fe lines (1.85 A) and Ni lines (1.55 A) with dielectronic satellites, emitted during intense, hot flares. The instrument is believed to be the best calibrated space-borne crystal spectrometer flown to date. The spectrometer dynamically adjusts the data gathering intervals from 1 s to 5 minutes, depending on the level of solar X-ray emission at the time of observation. The principal aims of RESIK are the measurements of relative and absolute element abundances in the emitting plasma and the temperature distribution of plasma (differential emission measure) over the temperature interval 3 and 50 MK. This paper summarizes the scientific objectives of RESIK and describes the design, characteristics, and performance of the instrument.

The collaborative project involving the Mullard Space Science Laboratory (MSSL), Virgin Atlantic Airways (VAA), the UK Civil Aviation Authority (CAA) and the UK National Physical Laboratory (NPL) has been performing tissue-equivalent proportional counter measurements of cosmic ray doses in commercial aircraft since January 2000. In that time data have been recorded on over 700 flights, including over 150 flights with Air New Zealand (ANZ). This substantial set of data from the southern hemisphere is an ideal complement to the London-based measurements performed primarily on VAA flights. Although some ANZ data remains to be analysed, dose information from 111 flights has been compared with the CARI and EPCARD computer codes. Overall, the agreement between the measurements and EPCARD was excellent (within 1% for the total ambient dose equivalent), and the difference in the total effective doses predicted by EPCARD and CARI was

Robust techniques are developed to put the Hα and Ca K line full-disk images taken at the Meudon Observatory into a standardised form of a `virtual solar image'. The techniques include limb fitting, removal of geometrical distortion, centre position and size standardisation and intensity normalisation. The limb fitting starts with an initial estimate of the solar centre using raw 12-bit image data and then applies a Canny edge-detection routine. Candidate edge points for the limb are selected using a histogram based method and the chosen points fitted to a quadratic function by minimising the algebraic distance using SVD. The five parameters of the ellipse fitting the limb are extracted from the quadratic function. These parameters are used to define an affine transformation that transforms the image shape into a circle. Transformed images are generated using the nearest neighbour, bilinear or bicubic interpolation. Intensity renormalisation is also required because of a limb darkening and other non-radial intensity variations. It is achieved by fitting a background function in polar coordinates to a set of sample points having the median intensities and by standardising the average brightness. Representative examples of intermediate and final processed results are presented in addition to the algorithms developed. The research was done for the European Grid of Solar Observations (EGSO) project.

A recent EC directive has called for all member states to introduce legislation covering the assessment and restriction of air crew exposure to cosmic radiation. In the UK the Civil Aviation Authority, in conjunction with the Department of the Environment. Transport and the Regions issued guidelines suggesting the use of a predictive code such as CARI for this purpose. In order to validate the use of calculated route doses, an extensive programme of measurements is being carried out on long haul routes in conjunction with Virgin Atlantic Airways, using a prototype HAWK TEPC developed by Far West Technology. This programme began in January 2000 and by the end of February 2001 had resulted in the accumulation of data from 74 flights. In this paper the instrument design is discussed, together with the calibration programme. An overview of the in-flight results is also presented, including comparisons between measurements and calculations, which indicates that CARI under-predicts the route doses by approximately 20%.

We have investigated problems concerning the discrepancy between estimates of absolute calcium abundances (A Ca ) in solar flares as derived from soft X-ray high resolution spectra as obtained from Yohkoh and Solar Maximum Mission ( SMM ) Bragg spectrometers. The analysis of these spectra allows for determination of absolute calcium abundance since both Ca xix resonance line and neighbouring continuum are reliably measured in these experiments. The abundance determinations are possible by means of fitting the synthetic spectra to the observed ones. In previous work, we attributed part (around 50%) of the observed disagreement to a possible instrumental problem in Yohkoh . In the present research, we consider in more details possible causes of the other part of the discrepancy. We first investigate whether the estimates of (A Ca ) depend substantially on the extension of the observed short wavelength wing of the Ca xix resonance line. This problem is important in the case of the analysis of Yohkoh spectra, since the extension of the spectrum towards the short wavelengths depends on the position of the flare along North—South direction on the Sun. After verifying the robustness of results of the spectral fitting technique, we have considered possible physical scenario which may cause the observed discrepancy. The hypothesis tested was that the Ca abundance in flares is correlated with brightness in the source — namely that it is a few times higher in the centre of the source (flaring kernel) than outside. We have found that postulated model may account for a part of the noted discrepancy as the SMM spectrometer has been equipped with the 6 × 6 arcmin collimator and no collimator has been used on Yohkoh .

The analysis of X-ray solar flare spectra obtained by the Bent Crystal Spectrometer on board the Solar Maximum Mission satellite is presented. The ratio of the Ca XIX resonance line intensity to the nearby continuum is used to measure the calcium abundance relative to hydrogen (ACa). A description of the spectroscopic method of determining the absolute calcium abundance is given. Possible instrumental and solar effects that might influence the abundance estimates are evaluated. Over 5000 spectra from more than 100 flares are analyzed. We find a flare-to-flare variation for ACa that is not correlated with flare size, Hα importance, or with several other flare characteristics. For flares observed from two active regions, the observed value of ACa increases as a function of time. The average for all flares is ACa = (5.77 ± 1.41) × 10-6. A discussion of investigated correlations of derived ACa values with several flare characteristics is presented.

High-resolution microwave observations of several flares performed with the Westerbork Synthesis Radio Telescope (WRST) on 3 and 4 July 1993 are compared with Yohkoh observations in the soft and hard X-ray domain. Only for one flare, among the six analyzed, was the hard X-ray spectrum between 20 and 200 keV available from the Wide Bragg Spectrometer, supplying the energy spectrum of non-thermal particles responsible for this radiation and for the radio emission. A complete model of this flare is derived which accounts for all available observations in the X-ray and radio wavelengths.

Soft X-ray observations by SMM and other spacecraft have shown that the abundance of certain elements in solar corona varies from flare to flare. In this study, observations made by the Yohkoh Bragg Crystal Spectrometer (BCS) in helium-like Ca XIX have been analysed, and Ca abundance determined for 177 flares observed during the first four years of the mission (1991–1995). The average abundance of Ca relative to H for all flares is 〈ACa〉 = (3.64±0.39) × 10−6. As with an earlier study of SMM data, the abundance is found to be enhanced compared to the photosphere ((2.24±0.10) × 10−6), and with only minor variation from flare to flare. However, the absolute value and range of values determined by this study is smaller than in the previous study; these differences are discussed.

A knowledge of the relative timing of the hard X-ray burst and emission in soft X-rays is helpful in deciding between a number of theoretical models that describe the mechanism of a solar flare. Here we continue a study of this relationship using observations from the Yohkoh Bragg Crystal Spectrometer and Hard X-ray Telescope, together with supporting observations from the CGRO Batse experiment. The enhanced capabilities of the instruments onboard Yohkoh have made it possible to study the problem in a way that was not previously possible. A study of the timing, intensity and evolution of the soft X-ray blue-wing shows that there is no simple relationship between hard and soft X-ray emissions; strong blue-wings sometimes result from relatively weak hard X-ray bursts; the burst responsible for the blue wing need not be the first or most intense burst associated with the flare; the blue-wing is found to follow very closely after the hard X-ray burst. We also discuss timing issues and why other researchers may have reached different conclusions on this matter.

Solar active-region temperatures have been determined from the full-Sun spectra of helium-like sulphur (Sxv) observed by the Bragg Crystal Spectrometer on board theYohkoh satellite. The average temperature deduced from Sxv is demonstrated to vary with the solar activity level: A temperature of 2.5 × 106 K is derived from the spectra taken during low solar activity, similar to the general corona, while 4 × 106 K is obtained during a higher activity phase. For the latter, the high-temperature tail of the differential emission measure of active regions is found most likely due to the superposition of numerous flare-like events (micro/nano-flares).

Yohkoh observations of an impulsive solar flare which occurred on 16 December, 1991 are presented. This flare was a GOES M2.7 class event with a simple morphology indicative of a single flaring loop. X-ray images were taken with the Hard X-ray Telescope (HXT) and soft X-ray spectra were obtained with the Bragg Crystal Spectrometer (BCS) on board the satellite. The spectrometer observations were made at high sensivity from the earliest stages of the flare, are continued throughout the rise and decay phases, and indicate extremely strong blueshifts, which account for the majority of emission in Caxix during the initial phase of the flare. The data are compared with observations from other space and ground-based instruments. A balance calculation is performed which indicates that the energy contained in non-thermal electrons is sufficient to explain the high temperature plasma which fills the loop. The cooling of this plasma by thermal conduction is independently verified in a manner which indicates that the loop filling factor is close to 100%. The production of ‘superhot’ plasma in impulsive events is shown to differ in detail from the morphology and mechanisms appropriate for more gradual events.

International audience; Heliophysics is a new research field that explores the Sun-Solar System Connection; it requires the joint exploitation of solar, heliospheric, magnetospheric and ionospheric observations.HELIO, the Heliophysics Integrated Observatory, will facilitate this study by creating an integrated e-Infrastructure that has no equivalent anywhere else. It will be a key component of a worldwide effort to integrate heliophysics data and will coordinate closely with international organizations to exploit synergies with complementary domains.HELIO was proposed under a Research Infrastructure call in the Capacities Programme of the European Commission's 7th Framework Programme (FP7). The project was selected for negotiation in January 2009; following a successful conclusion to these, the project started on 1 June 2009 and will last for 36 months.

Observations of two flares, an M 2.2 event on 16 December, 1991 and the precursor to an X1 flare on 15 November, 1991 are presented. Spectra obtained with the Bragg Crystal Spectrometer (BCS) are compared with data from the Hard and Soft X-ray Telescopes (HXT, SXT) and the Wide Band Spectrometer (WBS) on the satellite. For both events the creation of upflowing plasma is detected. While the first event seems to conform well to the chromospheric evaporation model for high temperature plasma production, the behaviour for the second event is more complex.

Single event upset (SEU) rates in orbit have been measured for the ROSAT satellite Wide Field Camera's (WFC) Command and Data Handling System (CDHS) memory. The WFC was launched as part of the German/UK/USA ROSAT satellite mission on the 1st of June 1990. In over 600 days of operation 40 SEUs were detected. Most appear to be associated with the South Atlantic Anomaly. Agreement between predicted and measured rates is discussed. Problems associated with such analysis are highlighted including the need for more relevant test data for electronic devices used in orbit. Detection technique is described along with several features of the WFC operations, CDHS software and construction which directly relate to SEUs. No incidences of multiple bit upsets were detected.

The Japanese Yohkoh satellite is now in orbit observing the sun with a set of x-ray imagers and x-ray and gamma-ray spectrometers. The data from this successful mission provide new information on solar flares and the sun's corona. This paper discusses the Yohkoh observations and presents a sample of the first scientific results from the mission.

A one-dimensional position sensitive proportional counter has been developed. It incorporates a wedge-and-wedge cathode as the position sensitive element, which operates by measuring the charge induced from a nearby anode wire. The detector is sealed and contains a Xe-Ar-CO 2 gas mixture. Tests of a number of detectors of this type are described. Position resolutions of ∼350 μm are demonstrated, as well as good energy resolution and gain characteristics. These detectors will form part of a soft X-ray spectrometer on board Solar-A, a solar studies satellite to be launched in 1991.

Following a successful launch on 1990 June 1, the ROSAT spacecraft and its payload, consisting of an X-ray and an EUV telescope, underwent two months of in-orbit calibration and detailed performance checks. A preliminary observation of a small section of the sky, carried out over July 11-16 (the mini-survey) showed all ROSAT systems to be functioning well and has allowed predictions to be made on the ultimate productivity of both ROSAT all-sky surveys. An analysis of the mini-survey data from the UK Wide Field Camera, has revealed 35 EUV sources, including several white dwarf stars, a variety of active cool stars and several other objects. In all, 23 sources have probable optical counterparts

All of the SOLAR-A telemetry data will be reformatted before distribution to the analysis computers and the various users. This paper gives an overview of the files which will be created and the format and organization which the files will use. The organization has been chosen to be efficient in space, to ease access to the data, and to allow for the data to be transportable to different machines. An observing log file will be created automatically using the reformatted data files as the input. It will be possible to perform searches with the observing log to list cases where instruments are in certain modes and/or seeing certain signal levels.

A generalized method of calculating the distribution of the emission measure with temperature (DEM) for optically thin plasma has been developed. The method simultaneously uses line flux ratios in addition to line fluxes. When a ratio of lines from the same element is used, the resulting DEM is independent of this element's abundance. The method has been applied to derive the absolute abundances of iron in solar flares from X-ray spectra recorded by the Bent Crystal Spectrometer on SMM. The iron abundances have been found to vary between flares. The calcium abundances have also been calculated using the same method and are found to be in close agreement with the values derived from the line-to-continuum technique (Lemen et al., 1990 and Sylwester et al., 1990). The variation of iron and calcium abundances is compared. A correction to the ionization balance for iron is proposed.

A Bragg Crystal spectrometer is one of the instruments on the Solar-A mission. Using bent crystals, the spectrometer will observe the resonance line complexes of the H-like Fe XXVI, and He-like Fe XXV and Ca XIX ions with a sensitivity 5 to 10 times that of the SMM Bent Crystal Spectrometer. It will also study the lower temperature lines of He-like S XV. The improved sensitivity will allow observations much earlier in the impulsive phase of flares than has previously been possible. The new observations should help to answer questions about plasma heating and dynamics. As well as providing information on line profiles and shifts, the selected spectral lines will also provide electron temperature and emission measure estimates over a range from 5 to 50 MK. The onboard microprocessor will permit spectral resolution to be traded against time resolution during an observation.

The Yohkoh spacecraft was launched on 30 August, 1991 by the Japanese Institute of Space and Astronautical Science. The instruments, which include hard and soft X-ray imaging telescopes, a Bragg spectrometer and wide band full sun spectrometers, (which cover the energy range 2 kev to 10 MeV), were described. Results obtained from these instruments were presented with special emphasis on data from the soft X-ray telescope which views the Sun in the 0.2 – 3 keV range with an angular resolution of 2.5 arc sec. Videos made from SXT datas were also presented at the meeting.

We have analysed X-ray spectra of 13 solar flares as obtained by the Bent Crystal Spectrometer (BCS) on the Solar Maximum Mission. In particular, we have examined the observed ratio of T Fe/T Ca where T Fe and T Ca are the temperatures obtained from the Fexxv and Caxix spectra, respectively. In order to simplify the investigation we have analysed only flares which reach quasi-steady-state during the decay. It turned out that the observed ratios cannot be explained by a model consisting of a single, uniformly heated loop, with a constant or variable cross-sectional area. We propose that this problem may be solved by introducing some distribution of the heating function across the flaring loop. This model has been tested by detailed calculations.

The European Grid of Solar Observations (EGSO) is a Solar virtual observatory (see Hill et al., 2002). It has been funded through the 5th Framework Program of the European Community. A dozen of laboratories, mixing Solar Physics and Information Technology, in Great Britain, France, Italy and Swiss have been involved in this project during 3 years. A grid accessing several dozens of databases and archives scattered all around the world has been developped as well as a Solar Event Catalogue and a Solar Feature Catalogue. The original aspect of this work consists in the possibility not only to search through the characteristics of observations, but also search for available data corresponding to specific kinds of events. So it is now very important to be able to follow the Sun 24 hours a day in order to enrich the events database for future queries. More informations on EGSO, catalogues and user interface can be accessd through the web site: http://www.egso.org/

The Bragg crystal spectrometer (BCS) is one of four instruments forming the scientific payload of the Solar-A mission. The spectrometer employs crystals that have been curved to diffract four wavelength ranges of importance for the study of high temperature plasma produced in solar flares. The ions involved and the related wavelength ranges are Fe XXVI(1.7636/~1.8404•), Fe XXV(1.8298/~1.8942/~), Ca XIX(3.1631A3.1912/~) and SXV(D.0160/~to 5.11432/~). The important emission lines in these ranges will be observed with resolving powers (A/AA) of between 3000 and 6000. The principle of operation of the instrument is illustrated schematically in Figure 1, while the layout of the spectrometer is given in Figure 2. Solar radiation enters the four apertures (labelled 1 to 4 and with the appropriate ion designations), encounters the crystals and is diffracted to one-dimensional position sensitive proportional counter detectors which register the spectra. This arrangement allows the four spectra to be obtained simultaneously and with good time resolution. The spectrometers are between 6 and 9 times more sensitive than those flown on the Solar Maximum Mission (Acton et al. 1980, Rapley et al. 1977). An instrument microcomputer allows the flexible organisation of the spectral data for transmission. In addtion, a large queue memory is available which allows preflare data to be stored at a rate which matches that of the spacecraft's flare mode telemetry format. The scientific goals of the investigation are concerned with clarifying the connection between the impulsive release of solar flare energy and the creation of high temperature plasma in the corona. The dynamics of the plasma will be examined by studying line broadening and wavelength shifts while temperatures and emission measures will be obtained from line ratios and intensities. The comparison of these observations with the images obtained with the Solar-A hard and soft X-ray

[1] We investigate the circumstances required for aircrew and passengers to experience an increased radiation exposure rate from a solar energetic particle (SEP) event occurring during a flight. The effects of the 14 July 2000 National Oceanic and Atmospheric Administration S3 class SEP event are examined using ground-based and satellite measurements together with coincident measurements made using a tissue equivalent proportional counter (TEPC) on board a Virgin Atlantic Airways flight from London Heathrow to Hong Kong. In this paper we present the first measurements made during a SEP event using a TEPC at flight altitudes. Our results indicate that there were no increased radiation levels detected during the flight due to the SEPs, but the measurements agreed well with the CARI-6 model calculations made using a heliocentric potential value derived immediately prior to the SEP event. In addition, a prolonged increase in the >85 MeV particle flux is observed for up to 2 days after the SEP onset by the SAMPEX spacecraft at latitudes >55°.

As it crossed the solar disk in May and June 1998, AR 8227 was tracked by TRACE, Yohkoh, SOHO, and many ground-based observatories. We have studied how the evolution of the magnetic field resulted in changes in activity in the corona. In particular, we examine how the evolving field may have led to the acceleration of electrons which emit noise storms observed by the Nangay Radio Heliograph between 30 May and 1 June 1998, in the absence of any flare. The magnetic changes were related to moving magnetic features (MMFs) in the vicinity of the leading spot and are related to the decay of this spot. Within the limits of the instrumental capabilities, the location in time and space of the radio emissions followed the changes observed in the photospheric magnetograms. We have extrapolated the photospheric magnetic field with a linear force-free approximation and find that the active region magnetic field was very close to being potential. These computations show a complex magnetic topology associated to the MMFs. The observed photospheric evolution is expected to drive magnetic reconnection in such complex magnetic topology. We therefore propose that the MMFs are at the origin of the observed metric noise-storms.

The Solar and Heliospheric Observatory (SoHO) was launched in December 1995 and because fully operational in April 1996. As well as making studies of helio-seismology, and in-situ measurements of the solar wind, it carries a compliment of instruments designed to observe the quiet Sun. The spacecraft is in a halo orbit around the Sun-Earth L1 Lagrangian point, and makes continuous observations of the Sun.

This memorandum report summarizes the data produced during the sixth year of operation by the Bragg Crystal Spectrometer (BCS) on the Yohkoh spacecraft. Each page shows the total count rate in the S XV channel of the BCS for a single day. This channel nominally observes the Sun in the wavelength range from 5.0163 - 5.1143 Angstroms. These plots are useful for identifying flare data for further analysis and for determining the data file name and tape number that contains the data.

This memorandum report summarizes the data produced during the fifth year of operation by the Bragg Crystal Spectrometer (BCS) on the Yohkoh spacecraft. Each page shows the total count rate in the S XV channel of the BCS for a single day. This channel nominally observes the Sun in the wavelength range from 5.0163 - 5.1143 A. These plots are useful for identifying flare data for further analysis and for determining the data file name and tape number that contains the data.

Mass motions of material are seen in many wavelength and at many different layers of the solar atmosphere during flares. In this paper we try to summarize observations of mass motions in the corona made in soft X-rays by crystal spectrometers on the SMM, P78−1, Hinotori and Yohkoh spacecraft. Such observations are key to our understanding of energy release and of what is happening to the hot plasma during a flare.

The Yohkoh spacecraft was launched on 30 August, 1991 by the Japanese Institute of Space and Astronautical Science. The instruments, which include hard and soft X-ray imaging telescopes, a Bragg spectrometer and wide band full sun spectrometers, are described in outline below. Results obtained from these instruments showing a number of solar flares and other activity were presented with special emphasis on data from the soft X-ray telescope.

We present early results from observations made by the UK’s imaging EUV telescope, the Wide Field Camera (WFC). This telescope is being flown aboard the West German satellite ROSAT. In conjunction with a large X-ray telescope, built by the West Germans, the WFC is conducting a survey of the whole sky. This is the first in the EUV waveband. Afterwards ROSAT will be devoted to pointed observations of specific objects. We use results from the earliest phases of the ROSAT mission to highlight the importance of WFC observations for the study of white dwarfs and related objects such as the central stars of planetary nebulae.

We discuss X-ray spectra and soft X-ray images of an M1.9 flare that occurred on 1991 November 9 near 03.2 UT. These data were obtained with instrumentation on the Japanese Yohkoh spacecraft. They cover the entire rise phase and peak flare emission, and the beginning of the decay phase. We determine the dynamics, temperature, and emission measure of the flare as inferred from the X-ray line profiles of resonance lines of Fe XXV, Ca XIX, and S XV. We discuss the morphology of the flare as inferred from the soft X-ray images. The November 9 flare is atypical in that a stronger than usual blueshifted emission component (relative to the stationary component) is observed for the resonance lines at flare onset. We discuss several methods for deconvolving the blueshifted component from the stationary component. The X-ray line profiles are consistent with predictions of numerical simulations of chromospheric evaporation. The X-ray images reveal a flare with a complicated loop geometry that is not fully understood. Many of the features in the images are moving upwards at speeds ranging from a few km/s to about 800 km/s. The blueshifted emission begins near the onset of hard X-ray emission, implying that particle acceleration and upflowing plasma have a common energy source.

We have investigated the temporal correlation between hard X-ray bursts and the intensity of Doppler blueshifted soft X-ray spectral line emission. We find a strong correlation for many events that have intense blueshifted spectral signatures and some correlation in events with modest blueshifts. The onset of hard X-rays frequently coincides to within a few seconds with the onset of blueshifted emission. The peak intensity of blueshifted emission is frequently close in time to the peak of the hard X-ray emission. Decay rates of the blueshifted and hard X-ray emission are similar, with the decay of the blueshifted emission tending to lag behind the hard X-ray emission in some cases. There are, however, exceptions to these conclusions, and, therefore, the results should not be generalized to all flares. Most of the data for this work were obtained from instruments flown on the Japanese Yohkoh solar spacecraft.

Using data from the Bragg crystal spectrometer on the Yohkoh spacecraft we have computed measures of the total intensity, centroid position, and line width for the resonance line of Ca XIX during the rise phase and after maximum for 219 solar flares. The difference between the centroid positions early and late in each flare yields a measure of the line-of-sight velocity shift of the line centroid. We find a trend in the average value of the centroid shift with distance from Sun center suggesting radial mass motions with a characteristic velocity of 58 km s −1 . There is a correlation between the rise-phase line widths and the centroid shift

We discuss X-ray spectra and soft X-ray images of an M1.9 flare that occurred on 1992 January 5 near 13.3 UT. These data were obtained with instrumentation on the Japanese Yohkoh spacecraft. They cover the entire rise phase of the flare. To supplement these data we have ground-based magnetograms and Halpha spectroheliograms. We calculate the electron temperature and emission measure of the flare as a function of time during the early rise phase using X-ray spectral line intensities and line ratios. Using spectral line widths, line profile asymmetries, and wavelength shifts due to the Doppler effect, we calculate the dynamical properties of the flare. The time development of the morphology of the flare, as revealed by the soft X-ray images and the Halpha spectroheliograms, and the physical quantities inferred from the X-ray spectra, are compared with chromospheric evaporation models. There is an enhancement of blueshifted emission that is closely correlated with the hard X-ray bursts. Heating of one loop in the flare is consistent with a conduction-evaporation model, but heating is found in several structures that do not appear to be physically associated with each other. No standard evaporation model can adequately explain all of the observations.

This paper focuses on what can be learned about the emission measure distribution and certain atomic physics parameters from spectral lines of highly ionized ions of sulfur, calcium, and iron that appear in solar flare spectra. The particular lines chosen for analysis allow the electron temperature to be determined independently of the assumption of ionization equilibrium. An attempt is made to find emission measure models based on selected functional dependences of emission measure on temperature that reproduce the observed temperatures deduced from spectral line ratios as well as the relative intensities of resonance lines of different elements.

The helium and lithium-like X-ray transitions of Ca XVIII-XIX have been used to make an absolute measurement of the coronal calcium elemental abundance relative to hydrogen (ACa) in solar flares. Cooling phase spectra of 43 flares obtained in channel 1 of the Bent Crystal Spectrometer (BCS) on the Solar Maximum Mission have been analyzed. The abundance is determined from the intensity ratio of the Ca XIX resonance line (1S0 - 1P1) and nearby continuum. A large variation is observed in the values of the derived abundances, ranging up to a factor of 2.5 between the extreme cases. This confirms the earlier results of Sylwester, Lemen, and Mewe [1], who investigated a smaller sample of flares. In addition to the variability of ACa observed between different flares, it was suggested [1] that ACa varies during the heating phase of some flares. We neglect this phenomenon in the present work, and concentrate on the cooling phase during which ACa appears to remain constant for any individual flare. Attempts to correlate the ACa measurements with other observable features are discussed.

The VLA maps at 6-cm wavelength discussed here are generated from observations of a solar active region (NOAA 2363) on March 29 and 30, 1980. The X-ray spectroheliograms were acquired for this region in the lines of O VIII, Ne IX, Mg XI, Si XIII, S XV, and Fe XXV. It is found that the peaks of X-ray and 6-cm emission do not coincide but that the sources in the two wavelength domains tend to overlap. These facts are seen as evidence for the existence of opacity mechanisms other than thermal bremsstrahlung. To quantify this assertion, differential emission measures are computed to derive densities and temperatures. Using these and calculated force-free magnetic fields from Kitt Peak magnetograms, an assessment is made of the mechanism of gyroresonance absorption at low harmonics of the electron gyrofrequency as the source of opacity responsible for the microwave features. It is concluded that large-scale currents must be present in the active region loops to account for the bright 6-cm sources far from sunspots.