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Space weather. Mladen Martinis Theoretical Physics Division Rudjer Boskovic Institute Zagreb, Croatia. 1st International Congress of CAPNIR-Opatija 2006. Space weather refers to the phenomena taking place in the
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Space weather Mladen Martinis Theoretical Physics Division Rudjer Boskovic Institute Zagreb, Croatia 1st International Congress of CAPNIR-Opatija 2006
Space weather refers to the phenomena taking place in the Sun-Earth environment. It is connected with the violent transfers of matter and electromagnetic energy from the Sun to the Earth. Basically all the energy that reaches the Earth comes from the Sun. The Sun provide all the energy needed to maintain life on Earth. This huge nuclear engine drives also the Earth's weather.
Outline Solar activity Solar spectrum UV radiation Earth's atmosphere Ozone
Activity of the Sun Eλ= hc/λ Planck's law Wien's law E = mc2
The solar cycle The Sun follows an 11-year activity cycle. One indicator of solar activity is the number of sunspots. This chart shows that the Sun was near its peak level or “solar maximum” at late 2000 or early 2001.
This image is taken through a filter centered on a spectral line of Hydrogen that forms above the surface of the Sun Interesting new features seen on this image are filaments, dark string-like structures visible on the disk, and prominences, bright structures extending outward over the limb Physically, filaments and prominences are one and the same, namely condensations of cooler gas high up in the solar atmosphere. Filaments/Prominences Prominences Filament
Some filaments and prominences can reach impressive sizes, and remain visible very far above the solar disk. The prominence on the picture extends some 200000 km above the solar surface Prominences
The Solar Corona Surface: 5000 o C • The corona is the area just above the surface. While the surface is about 5,000o Celsius, the temperature in the corona reaches about 2 million degrees Celsius. • What causes this rapid increase in tempera-ture is still one of the big mysteries in solar physics. Corona: 2,000,000 o C The black circle divides two images.
The Sun’s Magnetic Field • The Sun is strongly affected by magnetic forces. • The redarrows show open magnetic field lines emerging from the poles. • The grayarrowsrepresent solar wind particles which carry field lines with it. • The bright active regions have closed magnetic field lines (orange).
The solar spectrum By and large, the spectrum of the Sun resembles closely a blackbody.
Why measure solar UV light? • Solar Physics, i.e. the mechanisms responsible for the workings of and changes in the Sun. • The Earth's Upper Atmosphere, i.e. changes resulting from the UV light absorption in the stratosphere, mesosphere, and thermosphere. • The Earth's Climate, e.g. changes in tropospheric temperatures. The sun is the primary driving force behind the Earth's climate. Both the sun itself and the climate are changing and evolving consistent with known physical laws. However, due to the very complicated nature of these laws, predictions of their overall effects are uncertain. To understand and properly model the evolution of the state of the upper atmosphere or climate systems, it is necessary to know the spectral distribution of solar light and the energies and fluxes of incoming particles.
Earth's upperatmosphere • Solar UV light is primarily responsible for both creation and destruction of ozone in the earth's stratosphere and mesosphere. • Ozone is the molecular form of oxygen which shields the Earth's surface from solar UVB radiation through their absorption. • The same process also causes the temperature in the stratosphere to be higher than in the upper troposphere. • Stratospheric ozone densities are known to vary with the 11 year solar cycle. Solar variability over the solar cycle causes expansion and contraction of the outward extension of the Earth's atmosphere into space.
Earth'sclimate • The connection of solar UV light and its variability to climate change is controversial among scientists. Recent measurements of the sun's total irradiance show that it varied by about 0.1% during the recent 11 year solar cycle. • Computational models indicate that this level of variation is insufficient to significantly modulate the climate. • However, the models do not include subtle feedback mechanisms (e.g. enhanced cloud formation) which could magnify the impact of this tiny variation. It is also possible that changes in the Earth's upper atmosphere induced by solar UV light could similarly affect the surface climate. • Yet, skeptics point out that the energy per unit volume stored in the tropopause (the boundary between the troposphere and the stratosphere) is 100 times greater than in the upper atmosphere indicating that such causality is unlikely. • Numerous correlations between solar activity and climatic events have been claimed in the past, many of which were abandoned when their statistical significance could not be convincingly established. • A dramatic example of a connection which remains credible occurred during the extended seventeenth century period known as the Little Ice Age which was characterized by Earth surface temperatures much colder than normal and which coincided with a very unusual period of low solar activity and no sunspots known as the Maunder Minimum.
Variations in the solar EUV (10-120 nm) and UV (120-400 nm) spectral irradiance is known to affect Earth's atmosphere,especially its upper layers. Longerterm,they also may influence terrestrial climate.
Ozone layer formation The ozone layer is located 50 kilometers above the ground. Most of the solar ultraviolet light is absorbed by the ozone molecules, which temporarily break up when the ultraviolet light photons collide with them. + IR O O2 O3 UV O2 O + O2→ O3 + IR O2 + UV → O + O O2 UV O O3 O3 + UV → O2 + O
Changes in the sun's ultraviolet light affects the ozone layer and the energy input into the upper atmosphere. As the upper atmosphere is heated, it expands into space causing increased friction for satellites.
UV and sunspot cycles • The amount of UV from the Sun ( specifically UVB) changes during the sunspot cycle. • At sunspot maximum, there is 0.1 % more UV-B radiation than at minimum. Scientists have detected this sunspot cycle-effect in a 2% change in ozone concentrations. • The difference in total ozone between maximum and minimum conditions during the sunspot cycle were estimated using yearly averages of total ozone. • For solar cycle 21, 1.16% and 1.26% for solar cycle 22, a larger difference of 3.8% and 4.1% were found. • The corresponding variation in UVB at 300 nm, using Beer's law, is 4-10% with maxima occurring during the minimum of the solar cycle.
Little ice age 11-yr sunspot cycles
Solar activity and climate change • The most well-documented connection between solar activity and climate change is the Maunder Minimum. This was a 40-year period when extreme cold weather prevailed in Europe. It also coincided with astronomers watching the sun and not seeing many sunspots! • Scientists have examined the climate record for other signs of the connection between space weather and climate-weather changes with many surprising results.
Radiation is a common word, but in space weather studies, there are two types that differ in important ways. Matter - in the form of electrons, protons and the ions of various atoms, which travel much slower than the speed of light. Electromagnetic - In the form of X-rays, visible light, gamma rays and other forms of energy that travel at the speed of light.
This solar image is taken through a 10Å wide filter centered on the K line of Calcium ( Å). Bright, filamentary structures, most easily seen near the limb Plages
The shortwave radiation from the Sun and the Earth energy balance Energy balance: • Incoming solar insolation and outgoing radiation are equal in quantity. • Shortwave radiation from the Sun enters the surface-atmosphere system of the Earth and is ultimately returned to space as longwave radiation.
The longwave radiation of the Earth • The surface of the Earth emits 117 units of longwave radiation • The atmosphere emits 160 units of longwave energy • The total amount of energy lost to space in the global longwave radiation cascade is 70 units (surface emission 6 units + atmospheric emission 64 units.) • This is the same amount of energy that was added to the Earth's atmosphere and surface by the shortwave radiationof the Sun
Sun Facts • Solar radius = 695,990 km = 432,470 mi = 109 Earth radii • Solar mass = 1.989 1030 kg = 4.376 1030 lb = 333,000 Earth masses • Solar luminosity (energy output of the Sun) = 3.846 1033 erg/s • Surface temperature = 5770 K = 9,930º F • Surface density = 2.07 10-7 g/cm3 = 1.6 10-4 Air density • Surface composition = 70% H, 28% He, 2% (C, N, O, ...) by mass • Central temperature = 15,600,000 K = 28,000,000º F • Central density = 150 g/cm3 = 8 × Gold density • Central composition = 35% H, 63% He, 2% (C, N, O, ...) by mass • Solar age = 4.57 109 yr
Energy and the sun Hydrostatic equilibrium and ideal-gas behaviour ensure that the center of the Sun is very hot, and energy (in the form of light) is radiated from the center. The high opacity of the Sun to light determines the rate at which the energy leaks out. As we have seen, it takes a long time for photons to diffuse from center to surface. This cannot go on forever, without the Sun cooling down, or replacement for the energy that leaks away. We know that the solar system is about 4.5x109 years old (from many radioisotope abundance measurements on meteorites), and that life has existed here for at least 3x109 years. Thus the Sun must have had close to its present luminosity for billions of years.
How could the Sun convert mass-energy to radiation? Nuclear fusion: basically the liberation of mass energy stored as potential energy of the strong nuclear interaction. Would this work under the conditions known to prevail at the center of the Sun? Yes. Requires such conditions, in fact. To demonstrate these answers we need to talk a bit about the fundamental interactions of matter. ρC = 150 g cm-3 , PC = 2.1 1017 dyne cm-2 T = 15.7 106 K Mostly hydrogen .
The Solar Wind A constant stream of particles flows from the Sun’s corona, with a temperature of about a million degrees and with a velocity of about 450 km/s. The solar wind reachesout beyond Pluto'sorbit (about 5900 million kilometers).
Although sunspots themselves produce only minor effects on solar emissions, the magnetic activity that accompanies the sunspots can 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
Ultraviolet 1-400 nm; Most blocked by Earth’s atmosphere (O3 absorption) • except from 300-400 nm.
The atmosphere is a gaseous envelope that • surrounds the earth. • Electromagnetic energy from the Sun must pass • through the Earth's atmosphere to the surface, • and then back through the atmosphere to the • remote sensing instrument. • During this process, the atmosphere • –absorbs, • –scatters • –and transmits • electromagnetic energy.
ABSORBTION • The blocking characteristics of the atmosphere protect living things from • the damaging high-energy radiation from the sun. • Without the atmosphere to block most of the ultraviolet radiation, human • skin exposed to sunlight would quickly be sunburned and develop skin • cancer. For remote sensing, these blocking characteristics are • problematic. • The transmission characteristics of the earth's atmosphere vary with • wavelength. Some wavelengths are transmitted almost perfectly while • others are completely blocked. • Ranges of wavelengths transmitted well by the atmosphere • Ranges of wavelengths transmitted well by the atmosphere • are termed atmospheric windows.
Atmospheric absorption occurs when energy is lost to • constituents of the atmosphere. • • Energy absorbed by the atmosphere is subsequently • reradiated at longer wavelengths. When it is radiated at • infrared wavelengths, we sense it as heat. • • Three atmospheric gases account for most of the • atmospheric absorption of solar radiation: water vapor, • carbon dioxide, and ozone. • Of the three, water vapor is capable of the most absorption. • Water vapor absorbs electromagnetic radiation two to three • times more strongly than ozone or carbon dioxide.
Rayleigh (or molecular) Scattering which occurs when the size of the particles is smaller than the wavelength of light. Amount of scattering is inversely proportional to wavelength ^ 4 • Mie (or non-molecular) scattering occurs when there is sufficient quantity of materials with diameters .1 to 10 times the wavelength of light under consideration. • Non selective Scattering is the most problematic of the scattering processes and is found only in the lowest portions of the atmosphere.