Impact of Solar Activity on Space Weather

1. Solar Activity as a Driver of the Space Weather • I. Dorotovič, Slovak Central Observatory, Hurbanovo, Slovakia • Space Weather (SpW): • describes the conditions in the interplanetary space that affect Earth and its technological systems. • is greatly influenced by the solar activity. • SpW can be defined as (US National Space Weather Programme):"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." • A variety of physical phenomena are associated with SpW.

2. The Sun is the main driver of space weather. Sudden ejections of plasma and magnetic field structures from the Sun's atmosphere called coronal mass ejections (CMEs) together with sudden bursts of radiation termed solar flares, all cause space weather effects at the Earth.

3. The main causes of space weather: • Solar Activity and the Solar Wind • The Earth's Magnetosphere: • Geomagnetic Storms and Substorms • Radiation Belts • Galactic Cosmic Rays, Solar Protons • and their entry into the Magnetosphere • Meteoroids and Space Debris

4. Solar Activity and the Solar Wind: The Sun is not a quiet place, but one that exhibits sudden releases of energy. • Indicators of the solar variability: • Sunspots-have been observed since ancient times. The number of sunspots and the level of solaractivity vary in a periodic manner – the 11 year solar cycle. • The solar cycle was discovered by Heinrich Schwabe in 1843 from observations of the sunspot number as a function of time. • Sunspot number or Wolf number (Rudolf Wolf, 1849) is a quantity which measures the number of sunspots and groups of sunspots present on the surface of the Sun. G. Galilei, 1612

5. also known as the International sunspot number, relative sunspot number, or Zürich number. This sunspot number is defined as R = k (10 g + f ), where g is the number of sunspot groups, f is the total number of spots, and k is a constant for the obser- vatory related to the sensitivity of the observing equipment. Sunspot Index Data Center (SIDC), Royal Observatory of Brussels, Belgium

6. The Maunder minimum is the name given to the period roughly from 1645to 1715, when sunspots became exceedingly rare, as noted by solar observers of the time. During one 30-year period within the Maunder Minimum, for example, astronomers observed only about 50 sunspots, as opposed to a more typical 40,000–50,000 spots.

7. A solar flareis a sudden, • localized and explosive • release of energy in the solar • atmospherethat occur in • active regions near sunspots. • This energy is released as • particle acceleration, plasma • heating and dramatically • enhanced radiation. • They are usually most easily seen in H-alpha and X-rays (sometimes in the photosphere as white-light flares also). • They may last for a minute to several hours. • Coronal Mass Ejections (CMEs) • A CME is a large cloud of magnetised • coronal plasma which is injected into the • interplanetary medium, sometimes in • association with a solar flare. CMEs are • best observed using a space coronagraph • (with occulting disk).

8. CMEs eject a large amount of material into the • solar wind- a persistent flow of ionised solar plasma and a remnant of the solar magnetic field which spreads out in the interplanetary space in a spiral pattern. The solar wind is always present, but it does not always flow at the same speed, „slow“ speed is about 400 km.s-1, • high speed level is 800 km.s-1 and even more. • Another indicator of the level of solar activity is also the flux of • radio emission from the Sun at a wavelength of 10.7 cm (2.8 GHz • frequency). This flux has been measured daily since 1947. It is an important indicator of solar activity because it tends to follow the changes in the solar ultraviolet radiation that influence the Earth's upper atmosphere and ionosphere. • etc.

9. All forms of solar activity are believed to be driven by energy release from the solar magnetic field. This movie is made up of three different images and provides a journey through the Sun's atmosphere. The first image shows the photosphere - the Sun's visible surface. The second image was taken using a H-alpha filter and shows the chromosphere. The third image shows the million degree solar coronaobserved in X-rays.

10. Predicting the behavior of a sunspot cycle: A number of techniques are used to predict the amplitude of a cycle during the time near and before sunspot minimum. Relationships have been found between the size of the next cycle maximum and the length of the previous cycle, the level of activity at sunspot minimum, and the size of the previous cycle. Among the most reliable techniques are those that use the measurements of changes in the Earth's magnetic field:the level of geomagnetic activity near the time of solar activity minimum has been shown to be a reliable indicator for the amplitude of the following solar activity maximum. The prediction is fairly reliable once the cycle is well underway (about 3 years after the minimum in sunspot number). Prior to that time the predictions are less reliable but nonetheless equally as important. Planning for satellite orbits and space missions often require knowledge of solar activity levels years in advance.

11. Geomagnetic activity indicates large amplitude for sunspot cycle 24, higher than in the previous cycle and with a peak smoothed sunspot number of 160±25 (Hathaway and Wilson, 2006). The two components of the smoothed geomagnetic Inter-Hourly Variability (IHV) index. The solar activity component (IHVR) is pro-portional to the sunspot number and directly reflects the solar activity cycle. The interplanetary component (IHVI) is the remaining signal [David H. Hathaway & Robert M. Wilson, NASA/National Space Science & Technology Center, Huntsville, AL http://science.nasa.gov/headlines/y2006/images/cycle24/2006AGU.ppt].

12. Determination of the size of the next sunspot cycle using a combination of several techniques that weights the different predictions by their reliability [Hathaway, Wilson, and Reichmann J. Geophys. Res.104, 22,375 (1999)].

13. The heliosphere is a bubble in space produced by the solar wind. Although electri- cally neutral atoms from inter-stellar space can penetrate this bubble, virtually all of the material in the heliosphere originates from the Sun itself. The solar wind streams off of the Sun in all directions at speeds of several hundred km/s near the Earth. At some distance from the Sun, well beyond the orbit of Pluto, this supersonic wind must slow down to meet the gases in the interstellar medium. It must first pass through a shock, the termination shock, to become subsonic. The outer surface of the heliosphere (where the heliosphere meets the interstellar medium) is called the heliopause.

14. SpW effects of solar activity: • The Sun is very active on all length- • and time-scales. • Sunspots themselves produce only • minor effects on solar emission. • Total Solar Irradiance (TSI) – is • measured by instruments on • satellites since 1978.TSI describes • the radiant energy emitted by the • Sun over all wavelengths that falls • each second on 1 square meter • outside the Earth's atmosphere • a quantity proportional to the • "solar constant". Variations of a few • tenths of a percent are common, • usually associated with the passage • of sunspots across the solar disk. • Flares contribute to the TSI as well. • The solar cycle variation of TSI is • on the order of 0.1% [top panel]. [Solanki, 2007]

15. Chromospheric flares - the magnetic activity that accompanies the sunspots can during flares produce dramatic changes in the ultraviolet and soft x-ray emission levels. These changes over the solar cycle have important consequences for the Earth's upper atmosphere. Mechanism: a solar flare dramatically enhances the amount of UV- radiation reaching the Earth. This leads to expansion of the upper parts of the Earth's atmosphere which is an important space weather effect for spacecraft (S/C) operators controlling satellites in low Earth orbit. The atmosphere is suddenly more dense than expected at their orbit. This leads to atmospheric drag and may reduce the S/C lifetime if appropriate corrections cannot be made. Accelerated flareparticles are able to escape into interplanetary space where they can propagate, be re-accelerated and finally reach the terrestrial orbit where they may cause damage to delicate satellite optics, solar arrays, and electronics (SEU - single event upset, charging effects, etc.). In extreme cases, these particles may also pose a threat to astronauts for example onboard the orbiting International Space Station. Also aircrew flying frequently at high altitude and on long flights might receive a radiation dose equivalent to several chest X-rays due to the arrival at the Earth of energetic flare particles.

16. CMEs - typically disrupt helmet streamers in the solar corona and eject a large amount of material into the solar wind. CMEs propagate out in the solar wind, where they may encounter the Earth and influence geomagnetic activity - CMEs create disturbances in the background solar wind which can lead to geomagnetic storms when they reach the Earth between 2 and 6 days after leaving the Sun. CMEs are often (but not always) accompanied by prominence eruptions, where the cool, dense prominence material also erupts outward. The CMEs are transient disturbances and take place at random intervals. These disturbances are superimposed over a background solar wind. Different parts travel faster than others. As a result alternating regions of dense particles and fields and less dense regions are formed. The passage of these regions calledco-rotating interaction regionsinduces geomagnetic activity through variations of the solar wind pressure and magnetic field orientation at the Earth's magnetopause. All these SpW effects are a significant hazard to space missions.

17. The Earth's Magnetosphere – Geomagnetic Storms and Substorms: The Earth's magnetic field is like a dipole magnet only close to the surface. Within the Earth's magnetosphere are found cold plasma from the Earth's ionosphere, hot plasma from the Sun's outer atmosphere, and even hotter plasma accelerated to great speeds which "rains" on our upper atmosphere causing aurora in both the northern and southern hemispheres. Solar wind and the interplanetary magnetic field (IMF) modify the form of the magneto- sphere, by pushing it in the dayside and creating a long magnetotail in the nightside.

18. As a consequence, the distance of the magnetopause from the Earth is only about 10 Earth's radii (RE=6400 km) in the dayside, while the tail is more than 10 times longer. The Earth's magnetic environment at times connects into the IMF and experiences a magnetic storm, a disturbance of the magnetic field observable all around the globe, lasting a few days and adding appre- ciably to the Earth's trapped plasma. The storm is accompanied by large bright auroral substorms, often extending well beyond the auroral zone. When the plasma sheet is disturbed, accelerated particles move along the Earth's magnetic field and bombard the upper atmosphere around the poles in the auroral ovals causing auroras, eventualy power system shortcuts, etc. Geomagnetic induced currents may cause also corrosion of pipelines.

19. At low-altitude limit, magnetosphere ends at the ionosphere. Because of the Sun 's UV radiation, Earth 's upper atmosphere is partly (0.1% or less) ionized plasma at altitudes of 70-1100 km. This region, ionosphere, is coupled to both the magnetosphere and the neutral atmosphere. It is of great practical importance because of its effect on radio waves. Ionization appears at layers: D (75 and 95km), E (95 and 150km) and F (150km). The topside of the ionosphere is at heights of 500km at night or 1100 km in the daytime.

20. Radiation Belts: The Earth has both an inner and outer radiation belt (Van Allen belts). The inner radiation belt extends above the equator about 1 RE = 6371 km. It is populated by very energetic protons in the 10 -100 MeV range. These particles can readily penetrate spacecraft  and on prolonged exposure they can damage instruments and be a hazard to astonauts. The outer radiation belt is a part of the plasma trapped in the magneto- sphere (e.g. ions of about 1 MeV of energy). The more numerous lower-energy particles are known as the "ring current", since they carry the current responsible for magnetic storms.

21. Galactic Cosmic Rays, Solar Protons and their entry into the Magnetosphere: Galactic cosmic rays (GCR)are high-energy charged particles that enter the solar system from the outside (originating far outside our solar system). They are composed of protons, electrons, and fully ionized nuclei of light elements.They arrive from all directions in the sky. Their flux is modulated by solar activity. Enhanced solar wind shields the solar system from these particles. Cosmic rays with extreme high energies (GeV) are energized by shock waves which expand from supernovas. The Earth’s atmosphere is coupled to the solar activity. The galactic cosmic rays increase the amount of 14C in the atmospheric CO2 and, consequently, also in vegetation. During the increased solar activity close to solar cycle maximum years, Earth is better shielded from the cosmic rays than during the minimum years, and the amount of 14C decreases. Thus the 14C content of, for example, annual rings of old trees (redwoods) may reveal something about the Sun's performance during the last few millenia.

22. Solar energetic particle Events (SEPs) or Solar Proton Events (SPE) are made up of particles with MeV energies and above. A SPE can originate from either a solar flare or the shock wave driven by a co- ronal mass ejection (CME). Flares frequently inject large amounts of energetic nuclei into space, and the composition varies from flare to flare.They move away from the Sun due to plasma heating, acceleration, and numerous other forces. The accelerated particles travel toward and away from the Sun along IMF in the solar wind. Once the propagating shock reaches Earth, the energetic proton flux can increase suddenly by as much as two orders of magnitude.

23. The micrometeoroid and space debris environment are often consi-dered together since they are fast moving pieces of matter. Behaving like projectiles, they can penetrate material easily. The energy they possess is very high and the impact can vaporise the primary particle, generate fragments and leave a crater or hole on the surface like this: The amount of damage depends on the mass of the particle and the relative velocity of the impact. Man-made space debris and natural micro-meteoroid particles can damage satellites and constitute a serious hazard to manned spaceflight. The International Space Station, with its large surface area and long planned lifetime has multi-wall design to protect it. Meteoroids and Space Debris:

24. Space Weather and Earth’s climate change An increasing number of studies indicates that variations in solar activity (SA) and space weather have a significant influence on Earth's climate. Climate is the average weather over many years. Possible mechanism: the Earth's climate depends directly on its reflectance (albedo). Galactic cosmic rays act in the Earth’s atmosphere as condensation nuclei. Enhanced solar activity shields the solar system from galactic particles. During solar minima the atmosphere is bombarded by higher amount of cosmic particles, there are more condensation nuclei, and possibility of rainfall is higher; during solar maxima should be rainfall lower. Based on the ground – based observations of the reflected radiation (Big Bear Solar Observatory, USA) and the cloud conditions as well as the modelling has been found an indirect response of the SA on the climate - the albedo was significantly higher during 1994-1995 (SA minimum) than for the more recent period covering 1999-2001 (SA maximum).

25. Earth gets all its energy from the Sun and it is the Sun's energy that keeps Earth warm. Energy of the solar radiation governs a variety of processes in the Earth’s atmo- sphere and at its surface. But the amount of energy Earth receives is not always the same. Variations of solar spectral irradiance may inluence the Earth’s climate. Scientists study tree rings like these to figure out what climates of the past were like. Each year that the tree was alive it grew another ring, making its trunk wider. The thickness of a ring depends on what the weather was like during the year in which it grew. The weather depends on the level of the solar activity.

26. Changes in the Sun and changes in Earth's orbit affect the amount of energy that reaches the Earth. Through time, the shape of Earth’s orbit becomes more or less oval (eccentricity). The eccentricity of the Earth's orbit today is 0.0167 but it varies from nearly 0 to almost 0.05 as a result of gravitational attractions between the planets. Earth wobbles as it spins (precession), and Earth's axis changes too (tilt). All these changes, over thousands of years, causes Earth's climate to change. The variation in the eccentricity of the Earth's orbit over the last 750,000 years (blue line). The orange line shows today's value for comparison. The data are from Berger and Loutre (1991).

27. Earth's climate has been changing for billions (109) of years. • It warmed and cooled many times long before humans were around. • However, today climates are warming more rapidly as natural processes are affected by modern global changes caused by humans.  Global Warming and Climate Change • http://www.gcrio.org/, www.panda.org/climate/ • Moreover, the climate system has its own internal dynamics! • It is very important to promote explanation of the space weather effects to wide public. Presentations in planetarium are the most appropriate and useful tool for this purpose.

28. SPACE WEATHER INITIATIVES AND LINKS: • - Lomnický štít Neutron Monitor: Real-time data, http://neutronmonitor.ta3.sk/ • COST 724 action, Developing the Scientific Basis for Monitoring, Modelling and • Predicting Space Weather, http://cost724.obs.ujf-grenoble.fr/ • ESA Space WeatherSite, http://esa-spaceweather.net/ • Space Environment Information System – SPENVIS, http://www.spenvis.oma.be/spenvis/intro.html • Space Environment Centre, NOAA, Boulder, USA, http://www.sec.noaa.gov/index.html • Space Weather News, http://www.spaceweather.com/ • Space Environment System Overview • Information System – SEIS, • ESA project; software tool • developed by UNINOVA, • New University of Lisbon • – CA3, Soft Computing • and Autonomous Agents • – software installed • in ESOC, Darmstadt, • Germany. • http://www2.uninova.pt/ca3/en/project_SEIS.htm

29. SEIS Data Catalogue Browser (with data preview). SEIS Monitoring Tool - Virtual Monitoring Panel.

30. SPACE WEATHER DATA: ground-based instruments + satellites: SOHO, ACE, TRACE, GOES, CLUSTER, WIND, GEOTAIL, ... REFERENCE LINKS: http://www.wikipedia.org/ http://www.windows.ucar.edu http://esa-spaceweather.net/ http://www.spaceweather.com/ http://soho.esac.esa.int/ or http://sohowww.nascom.nasa.gov/ http://www.sec.noaa.gov/index.html or http://www.sec.noaa.gov/today.html http://bass2000.obspm.fr/home.php?lang=en ... and many other links