RUSSIAN JOURNAL OF EARTH SCIENCES VOL. 10, ES3005, doi:10.2205/2007ES000247, 2008
Solar geoeffective phenomena: Impact on the near-Earth space and the opportunity to forecastV. N. Ishkov Institute of Terrestrial Magnetism, Ionosphere, and Radiowave Propagation, Russian Academy of Sciences, Troitsk, Moscow Region, RussiaContents
Abstract[1] The solar research of the last decade has left no doubt that geoeffective phenomena on the Sun, which dynamically affect the state of near-Earth space (NES) are extremely large flare events and coronal holes. We attribute to the class of flare phenomena solar flares with a complete spectrum of dynamic manifestations of the mass motion and radiation in all ranges of the electromagnetic spectrum as well as solar filament eruptions with all accompanying phenomena. The possibility to predict geoeffective solar phenomena and their effects on NES is based on the analysis of correlations: emergence of new magnetic fluxes in the solar atmosphere, their physical characteristics, and the character of their interaction with the already present magnetic field; time distribution of large flares within active regions; temporal and spatial distribution of solar filament eruptions; formation, distribution, and evolution of solar coronal holes (CH). The agents causing NES disturbances are transient structures: coronal mass ejections, which result from active processes in flares and filament eruptions; high-speed flows of solar plasma following a shock wave from large solar flares and solar filament eruptions or outflowing from regions with an open magnetic configuration. Prediction for the beginning of NES disturbances and of their duration is possible for a period from 1 to 5 days and for coronal holes for a period of one solar revolution (27.3 days). This makes possible planning various technological, biological, and medical experiments together with protective measures for the team and instruments of space laboratories. Introduction[2] The beginning of the space era became a new step in the study of the Earth in a broad sense, from its interiors up to the interface with the heliosphere, by ground-based as well as spaceborne instruments. The integration of observations from the Earth and space within the framework of the International Geophysical Year (1957-1958) gave a stimulus to all science such that its development follows just the path of comparison and consideration of measurements from space and from the ground. The ever increasing rate of space exploration has set a problem of assessment and prediction of the NES environment state and in any given region of the heliosphere. [3] In this paper we mean for near-Earth space the region beginning from heights 50-60 km above the Earth and extending to distances of tens of Earth radii up to the interface with the heliosphere; in the heliosphere, the material that fills it is still connected to our planet, not with the Sun or any other celestial body. It is clear that in this region we deal mainly with natural plasma. [4] For "space weather'' we mean the state of the upper Earth's atmosphere (mesosphere, thermosphere), magnetosphere, ionosphere, all layers of near-Earth space in any given time interval. By present it has been understood that the main effect on near-Earth space is exerted by the Sun and by geoeffective phenomena in its atmosphere. However, the events of the last decade have given examples of an appreciable effect of other factors, both heliospheric (asteroid and comet hazards) and galactic: galactic cosmic rays and ultrahard X-ray bursts from nonstationary galactic objects (the event of 27 December 2004). [5] A vivid example of the asteroid and comet hazards was vividly demonstrated by the fall of fragments of Comet Shoemaker-Levy 9 on Jupiter in November 2001; it showed that such an event, though infrequent, is however quite real. This is confirmed by the discovery of giant craters (ring structures) on the Earth's surface; these craters were formed by impacts of rather large ( < 1 km) asteroids or fragments of comets. The comprehension of this risk has resulted in the creation of Near-Earth Asteroid Tracking Service, which follows significant Solar System objects passing in the immediate proximity from the Earth (asteroids, comets). The list of such potentially hazardous objects is regularly published on the Web page http://www.spaceweather.com/. [6] Flows of galactic cosmic-ray particles arrive to the Earth from all directions of space. They consist of nuclei of chemical elements from hydrogen to uranium in proportions that approximately match the average element abundances in the Universe. At present the main presumed sources of galactic cosmic rays are supernova explosions. In the heliosphere at the Earth's orbit the energy spectrum of particles in these flows has a sharp peak at energies 0.5-1 GeV; the exact peak position depends on the state of the interplanetary magnetic field of the Solar System; in its turn, the latter is determined by the solar activity level. The flux of galactic cosmic ray particles changes in antiphase with solar activity variations [Panasyuk et al., 2006]. Cyclicity of Solar Activity
[8] All this puts in question the correctness of using the retrieved part of the series in the majority of applications. In other words, to study the effect of solar activity on various long-term processes, one can use only the reliable series of Wolf numbers (1849-2006), from the middle of cycle 9 to cycle 23 of solar activity. The small statistics of reliable solar cycles (14) and absence of a physical model of a solar cycle development puts so far insuperable barriers to the reliability of solar cycle prediction prior to its beginning. However, the situation changes with the beginning of a new cycle: after 18-24 months of its development, it is already possible to determine its height, the epoch of its maximum, and probable duration of the current solar cycle. For the last two cycles the most successful prediction of the solar cycle development its beginning was done by the Waldmeier method and by the method of solar cycle sets similarity proposed by the author [Ishkov, 2003, 2005]. Table 1 lists the characteristics of all "numbered'' solar cycles.
Geoeffective Solar Phenomena[10] The solar studies of the last decade have left no doubt that geoeffective phenomena on the Sun that completely determine the state of near-Earth space are extremely large flare events and coronal holes. The class of flare phenomena includes:
[11] Solar flares take place in active regions with sunspot groups and without them; they represent a response of the solar atmosphere to a fast energy release, which results in a sharp local heating of all layers of the solar atmosphere accompanied by generation of powerful radiation in a broad band of the electromagnetic spectrum, from g-ray quanta to kilometer radio waves as well as by flows of electrons, protons, and heavy nuclei. Solar filaments are clouds of dense and cooler (than the surrounding medium) plasma, which take in the magnetic field of the solar atmosphere the form of structures extended along the polarity reversal line. The mean sizes of solar filaments: length is 50 megameters (Mm), width is several megameters, and height above the visible surface of the Sun (photosphere) is 10 Mm. Solar filament eruptions observed with a high resolution have an appearance of a two-ribbon flare with a slowly growing intensity before the maximum ( > 1 hour) and a long timescale of the intensity decline ( > 3 hours). In the great majority of cases the phenomenon takes place outside active regions, in weak magnetic fields ( < 50 G)
![]() [14] Using the observations of emerging magnetic fluxes (EMF), we can summarize phenomena after which the flare activity increases [Ishkov, 1998]:
[15] The time interval in which the major part of large- and
medium-importance flares is implemented in an active region is
called period of flare energy release. Depending on the degree of
development of an active region, characteristics of its magnetic
field, and power of the new EMF, this period can take from 16 to
80 hours, on the average 55 [16] The prediction of solar filament eruptions is more difficult: only direct observations of an EMF in weak magnetic fields can give a possibility to predict them. EMF interacts with the background magnetic field and can emerge only to regions of the neutral line of the axial magnetic-field component.
![]() ![]() ![]() ![]() [18] The electromagnetic disturbances from flare events appear virtually at the instant of the process development; corpuscular and plasma disturbances from solar geoeffective phenomena (flare events, coronal holes) propagating in the heliosphere, through the solar wind, affect the magnetospheres of planets, their satellites, and comets, causing considerable deviations from the background quiet state in nearly all layers of the considered objects. The agents causing this disturbance are:
Effect on Near-Earth Space (Space Weather)[19] The full chain of disturbances from in an individual large flare event can be represented in three separate stages of the effect (http://sec.noaa.gov/NOAAscales): Electromagnetic shock[20] reaches near-Earth space at the speed of light, i.e., at the instant of the development of a solar flare. During its effect in short-wave ranges of electromagnetic radiation the flux increases by several orders of magnitude relative to the background values. For instance, in soft X rays (1-8 Å, 12.5-1 keV) the flux increase can reach four orders. As a consequence, immediately at the instant of of a flare development (timescale of the disturbance development is a few minutes after the beginning of the flare) sudden ionospheric disturbances develop in near-Earth space, causing a complete radio silence in the range of high frequencies at the dayside of the Earth; its duration reaches several hours, upsetting the radio communication with ships and airplanes. In the range of low frequencies at the dayside of the planet, errors in positioning systems of ground-based objects and satellites sharply increase and are accumulated during many hours. At present, a five-grade scale for the assessment of this kind of disturbances has been introduced: from R1 for flares with an X-ray importance of M (up to 950 events per cycle) to R5 for the most powerful flares with an X-ray importance of![]() Ejection of energetic solar particles[21] (protons, electrons, neutrons), which, reaching NES, cause solar proton events (SPE). Invasions of high-energy solar particles ( Epr>10 Å) sharply raise the level of radiation hazard to astronauts, crews and passengers of high-altitude airplanes at high latitudes, result in losses of satellites and in failures of scientific and navigation instruments on space objects, interrupt short-wave communication in subauroral regions, and provoke a sharp increase in positioning system errors. This results in serious problems in positioning of ground-based and space objects. The timescale of the SPE onset with respect to the beginning of a proton flare is a few hours, though particles with GeV energies arrive to the Earth at the speed of light. To describe SPE in near-Earth space, a five-grade scale of the protons flux assessment with energies E> 10 MeV has also been introduced: from S1 for a proton flux of 10 particles per second per steradian per square centimeter (up to 50 events per cycle) to S5 for a proton flux by four orders of magnitude greater (less than one event per cycle).Plasma shock:[22] interplanetary shocks and flows of solar plasma with enhanced density and/or speed (transient structures, high-speed solar wind flows) cause magnetic and ionospheric disturbances in near-Earth space. For disturbances of the geomagnetic field of the Earth with the intensity exceeding the threshold of magnetic storms, a five-grade system of their estimation has also been introduced: from G1 for disturbances in which at least one three-hour Kp index has reached 5 (~900 days per solar cycle) to G5 with Kp = 9 (1-5 days per cycle). It should be kept in mind that this scale estimates the intensity of a geomagnetic disturbance; it is quite possible to imagine a situation when the disturbance has an importance G1 or G2, but in fact there is no magnetic storm, and the diurnal geomagnetic index Ap is much lower than the magnetic storm threshold. Certainly, it is a problem of definition of "MAGNETIC STORM''--magnetic disturbance with a duration not shorter than 12 hours and with a mean Ap-index not lower than 27 (in western countries the threshold value is Ap = 30).[23] At present the problem of reflection of the situation in near-Earth space and estimation of its state is solved by "space weather'' services, which have been created in leading institutes and organizations all over the world (more than 40 URLs); the main ones are:
[24] Their task is to give in real time the main characteristics of phenomena determining the NES state and the indices describing the state of the magnetosphere, ionosphere, and other layers of the Earth's atmosphere. The most informative Web pages of the space weather state are granted by the Space Weather Prediction Center of the National Oceanic and Atmospheric Administration (SWPC, NOAA, USA) (http://www.swpc.noaa.gov/). Prediction of Geoeffective Solar Phenomena and the State of Near-Earth Space[25] Here we mean for the prediction of geoeffective solar phenomena a combination of all kinds of forecasts aiming to the calculation of the development of processes and phenomena taking place in the solar atmosphere and directly influencing the magnetic and radiation conditions in near-Earth space in the given time intervals. Time intervals for which the forecast is possible are determined by the characteristics of physical processes of emergence of new magnetic fluxes in the solar atmosphere, the character of their interaction with the already present magnetic field as well as regularities in the appearance and evolution of solar structures, such as solar flare events and coronal holes. The prediction of disturbances in near-Earth space directly depends on a successful, reliable forecast of solar geoeffective phenomena, such as large flare events and coronal holes. The observational data for the determination of the evolutionary and flare state of the Sun are stored at http://www.swpc.noaa.gov/Data/.
[26] The observational data on the interplanetary medium are presented on the Web page http://www.swpc.noaa.gov/Data/.
[27] Indices and observational data on the geomagnetic field (http://www.swpc.noaa.gov/ace/):
[28] A brief description for all interested in space weather is given on the Web page http://www.spaceweather.com, on which short articles on phenomena in NES, conditions of the observations of planets, comets, and meteor showers are published. The information on near-Earth asteroids and many other interesting articles on aurora, atmospheric phenomena, etc. are also published. The prediction of solar flare events on the basis of the analysis of emerging magnetic fluxes in active regions is implemented only in the Institute of Terrestrial Magnetism, Ionosphere, and Radiowave Propagation, Russian Academy of Sciences, since 1990. It is accessible to public within the framework of the weekly review of the state of near-Earth space, which appears on Mondays since 1997 at http://www.izmiran.rssi.ru/space/solar/forecast (Russian version) and http://titan.wdcb.ru/virbo_rus/viewlast.do?Section=RBBulletin (English version). In the case of appearance in an active region of a new magnetic flux with a magnitude and ascent rate sufficient for the implementation of large flares, the Web page gives an appendix, in which the probable flare potential of the given active region is estimated. [29] The situation on the Sun in a daily mode and attempts of warning about flare events are given on the following Web pages: of the Big Bear Observatory, USA:
[30] The prediction of space weather (geomagnetic field) invoking mainly solar-wind parameters from the data of the ACE (Advanced Composition Explorer) spacecraft located at the L1 libration point (this enables to forecast geomagnetic disturbances approximately 40 min prior to their beginning). The main ones are Space Weather Prediction Center of the National Oceanic and Atmospheric Administration (SWPC, NOAA, USA) (http://www.swpc.noaa.gov/alerts/index.html) and Naval Research Laboratory (USA) (http://ppdweb.nrl.navy.mil/whatsnew/prediction/). Conclusion[31] From what was said we can conclude that prediction of the state of near-Earth space is now possible and is sufficiently exact. At the first stage, one-two days beforehand, using observations of emerging new magnetic fluxes, we predict the time interval in which, with a probability not less than 90%, large flare events will take place; their probable geoefficiency in all three space weather positions is estimated. At the second stage, during or immediately after a flare event, the prediction is updated using electromagnetic radiation as well as CME and (1) the probability of the arrival of solar high-energy particles (solar proton event) to near-Earth space, their probable maximum fluxes and duration are given (prognostic interval from 1 to 6 hours, prediction probability is about 70%); (2) the probability of a geomagnetic disturbance, its probable intensity, and duration as well as parameters of a probable ionospheric disturbance and aurora are assessed (prognostic interval from 17 hours to 5 days, probability of the forecast is not lower than 70%). [32] The third stage consists in refinement of the prediction of the geomagnetic disturbance intensity and duration involving the parameters of structures in the perturbed solar wind using SOHO data (stationary orbit at 1.5 million kilometers from the Earth). Approximately 40 min before its beginning, it is concluded whether the geomagnetic disturbance will reach the level of a magnetic storm; its magnitude, intensity, and duration are predicted (prediction probability is not lower than 80%). [33] At present the technique of prediction of large geoeffective solar flare events from observations of emerging new magnetic fluxes has passed a successful check by the operation of the Russian research satellites GRANAT, GAMMA, CORONAS-I, and CORONAS-F; this technique is successfully applied to realistic practical tasks. Acknowledgments[34] The author thanks the SOHO MDI, EIT, and LASCO teams for the opportunity to use the data of their observations for the illustration of active solar events. This work was supported by the Russian Foundation for Basic Research (project codes 07-02-13525 and 07-02-00246) as well as by Program No. 16 of the Presidium of the Russian Academy of Sciences. ReferencesIshkov, V. N. 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Index Terms: 7536 Solar Physics, Astrophysics, and Astronomy: Solar activity cycle; 7899 Space Plasma Physics: General or miscellaneous; 7974 Space Weather: Solar effects; 7984 Space Weather: Space radiation environment. ![]() Citation: 2008), Solar geoeffective phenomena: Impact on the near-Earth space and the opportunity to forecast, Russ. J. Earth Sci., 10, ES3005, doi:10.2205/2007ES000247. (Copyright 2008 by the Russian Journal of Earth SciencesPowered by TeXWeb (Win32, v.2.0). |