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Solar Activity as a Driver of the Space Weather

• I. Dorotovic, 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.

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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.
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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

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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
  solar activity 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
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• 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
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The Maunder minimum is the name given to the
period roughly from 1645 to 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 40,00050,000 spots.
7

• A solar flare is a sudden,
• localized and explosive
• release of energy in the solar
• atmosphere that 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).

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• 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.

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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 corona observed in
X-rays.
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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.
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Geomagnetic activity indicates large amplitude
for sunspot cycle 24, higher than in the
previous cycle and with a peak smoothed
sunspot number of 16025 (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/cy
cle24/2006AGU.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).
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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.
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• 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

Solanki, 2007
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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 flare particles 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.
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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 called
co-rotating interaction regions induces
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.
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As a consequence, the distance of the
magnetopause from the Earth is only about 10
Earth's radii (RE6400 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.

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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 500 km 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 Earths 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.
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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.
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Meteoroids and Space Debris
24
Space Weather and Earths 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 Earths
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).
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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 Earths 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
Earths 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.
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• Changes in the Sun and changes
• in Earth's orbit affect the amount
• of energy that reaches the Earth.
• Through time, the shape of
• Earths 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

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).
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• 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.

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• 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.ne
  t/
• 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.

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SEIS Data Catalogue Browser (with data preview).
SEIS Monitoring Tool - Virtual Monitoring Panel.
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SPACE WEATHER DATA ground-based instruments
satellites SOHO, ACE, TRACE, GOES, CLUSTER,
WIND, GEOTAIL, ... REFERENCE
LINKS http//www.wikipedia.org/ http//www.windo
ws.ucar.edu http//esa-spaceweather.net/ http//ww
w.spaceweather.com/ http//soho.esac.esa.int/ or
http//sohowww.nascom.nasa.gov/ http//www.sec.noa
a.gov/index.html or http//www.sec.noaa.gov/today.
html http//bass2000.obspm.fr/home.php?langen ...
and many other links