Space weather. Introduction to lectures by Dr John S. Reid. Image courtesy:

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1 Space weather Introduction to lectures by Dr John S. Reid Image courtesy:

Sunspot 9393 First pass from late March to early April, 2001 See: Storms from the Sun http://books.nap.

2 Sunspot 9393 First pass from late March to early April, 2001 See: Storms from the Sun Animated gif, courtesy:

3 Satellites on 30/10/2006 Satellites Data courtesy:

4 Out there Out there EM radiation solar wind cosmic rays micrometeorites Closer to Earth radiation belts Earth s atmosphere provides enough protection for life can we exist outside it? Interplanetary magnetic field Sun

5 EM radiation from the Sun γ-rays X-rays UV Visible IR Micro-wave Radio At Earth ~1366 W m -2 Photosphere of Sun appears ~ blackbody at 5780K Total energy o/p ~10 26 W Distribution ~ follows Planck radiation law Peak wavelength is in the visible 7% UV, 44 % visible 37% near IR, 11% far IR 1% radio spectrum

distance of Moon (1 AU) = 2 1366 = 2732 W This makes

6 Flux hitting an astronaut on the Moon or around the Earth Say maximum area 2 m 1 m = 2 m 2 Flux at distance of Moon (1 AU) = = 2732 W This makes temperature control hard Challenger crew Aldrin on the Moon

Digression on space suits Space suits need to: Hamilton Sundstrand services the suggestions from class Hubble Space Telescope They operate at reduced pressure, with an

7 Digression on space suits Space suits need to: Hamilton Sundstrand services the suggestions from class Hubble Space Telescope They operate at reduced pressure, with an internal atmosphere of pure O 2 several hours of acclimatisation are necessary to remove N 2 from the blood what happens to the breathed out CO 2? how is temperature control achieved?

8 Reminder: Temperatures in K Temperature in degrees Kelvin (e.g. 300 K) usual in physics laws general conversion: e.g. 20 C 293 K e.g K 5507 C K = C Celsius Kelvin

9 Radiant energy emitted by a hot body Total radiant energy (E) emitted per m 2 of surface per second for a black body at temp T 4 E = σt, where σ is W m -2 K -4 Stefan-Boltzmann Law; σ is Stefan s constant E.g. T = 5780 K, E = 63.3 MW m -2 E.g. T = 273 K, E = 315 W m 2

10 How hot is a body left in space? Body of radius r R Radiation R from one direction Fraction a reflected Space all round Radiation spread over body by conduction and rotation Stefan-Boltzmann law tells us how hot the body will be Fraction a reflected Radiation T Radius r Space

11 Energy conservation Radiation received = radiation re-emitted Consider the body at distance Earth is from Sun incoming energy spread over a disk of area πr 2 re-radiated energy comes from area of a sphere 4πr 2 R(1 - a)πr 2 = σ T 4 4πr 2 T 4 = R(1-a)/4σ Disk area πr 2 Total area = 4πr 2 Temperature in K Temperature at 1 AU for different fractions of incident radiation reflected fraction reflected (a)

12 The further you are from Sun, the colder it is At increasing distance d from the Sun, the energy passing through 1m 2 decreases as 1/d 2 this is essentially a statement of the law of conservation of radiant energy Source Area d 2 1m 2 4m 2 9m 2 < d Energy per m 2 1/d 2

13 Example of the inverse square law in action As a formula: R d = R 1 /d 2 ; where R d is the rate energy is received at distance d E.g., the Earth at 1 AU distant from the Sun receives solar radiation at a rate of 1366 W m -2 How much radiation is received by the Venus Express probe when it is 0.6 AU from the Sun? R Venus express = R Earth /0.6 2 = 1366/0.6 2 = 3794 W m -2 Venus Express, courtesy:

How cold is the Cassini probe near Saturn? Saturn is 9.54 times distance of the Earth from the Sun (9.54 Astronomical Units) Hence the flux of energy at Saturn from the Sun is 1366/9.54 2 = 15.

14 How cold is the Cassini probe near Saturn? Saturn is 9.54 times distance of the Earth from the Sun (9.54 Astronomical Units) Hence the flux of energy at Saturn from the Sun is 1366/ = 15.0 W m -2 Average temperature of the Cassini probe as it spins around depends on its reflectivity temperature (K) Cassini probe, NASA Temperature of a probe at distance of Saturn for a range of reflectivities reflectivity

15 The electromagnetic spectrum ev: γ-rays X-rays UV Visible IR Micro-wave Radio Wavelength: 0.01 nm 30 nm 400 nm 700 nm 1000 µm 100 mm Different parts of the spectrum have different historical names Diagram shows approx wavelengths of the boundaries wavelengths determine the equipment used to transmit & receive Energy, E, comes in packets ( photons ) that depend on the wavelength (λ) through Planck s constant h packets are measured in ev ( electron volts ) > 2 ev will break some chemical bonds much of the UV and beyond is chemically damaging E = hf = c h λ f is the frequency of the radiation; c the speed of travel

16 Visible solar spectrum showing absorption lines Visible emission of the Sun Joseph Fraunhofer Solar spectrum from 500 nm to 600 nm Courtesy:

17 Broad spectrum of Sun Shorter than 200 nm there is much more radiation than a blackbody emits Where does this come from? the outer atmosphere of the Sun visible

edu/ypop/spotlight/today/ Notice the Sun doesn t appear a

18 Sun in X-ray and Extreme UV X-ray EUV Images courtesy: Notice the Sun doesn t appear a uniform hard disk soft X-ray picture on the left (0.3 to 4.5 nm) extreme UV picture on right (30.4 nm)

Sun in visible, IR and microwave White: 400 700

19 Sun in visible, IR and microwave White: nm IR: 1083 Nm Microwave 17 mm Images courtesy: The Sun is conspicuously uniform in visible light

20 Radio flux from the Sun Substantial sunspot dependence /SolarCycle/index.html

21 X-ray monitoring X-ray flux monitored by geostationary satellite Wavelength units are Å, where 10 Å 1 nm GOES 10 Lat 135 W GOES 12 Lat 76 W

22 Photon flux and power density Photon flux W m -2 Photon flux in photons m -2 s -1 Power density in W m -2 1W 1 J s -1 1 ev J therefore 1 J = 1/( ) ev = ev Hence 1W = ev s -1 For X-ray photons of energy 3000 ev 1 W photons s W m photons s -1 m -2

The solar wind Solar wind is a flux of plasma http://www.starhillinn.com/images/hale-bopp-2.

23 The solar wind Solar wind is a flux of plasma coming from the Sun plasma is an electrical neutral gas of positively and negatively charged particles solar wind: +ve particles are mainly protons (H + ), He nuclei (He 2+ ) and heavier element ions -ve particles are electrons trapped magnetic field, the IMF ( interplanetary magnetic field ) The solar wind has a significant impact on everyone s use of space

24 Positive ions in the solar wind The ACE probe solar wind ion composition spectrometer (SWICS) results a second instrument, an ion mass spectrometer (SWIMS), contributes Ions of elements up to Ni are measured many have no electrons at all

25 Fe + ions observed by ACE Histogram of Fe + ions in solar wind detected by ACE Fe has atomic mass ~56 Variability of Fe + ions over a period of 3 days

ACE Advanced Composition Explorer homepage http://www.srl.caltech.edu/ace/ ACE sits permanently between the Earth and Sun, about 1.

26 ACE Advanced Composition Explorer homepage ACE sits permanently between the Earth and Sun, about km from the Earth ACE orbits around the first Lagrangian point ACE has six instruments that monitor particle content, speed, density, etc. and the interplanetary magnetic field also monitors galactic cosmic rays

27 Variability of the solar wind The solar wind and related particle flux from the Sun is the most variable component of space weather The solar wind can be a hazard to man and instrumentation browse-plots/4day_plot.html

28 Output from ACE probe B z is magnetic field in 10-9 T (a unit called gamma (γ)) Phi is azimuthal angle (see next slide) Density: particles per cm 3 Speed km s -1 Temp in K

29 Coordinate systems What exactly are you measuring? There are various useful coordinate systems ACE data reports results in GSE coordinates Geocentric solar ecliptic X-direction is Earth Sun line Z direction is ecliptic north pole A magnetic field B in diagram B x, B y, B z or B, θ, ϕ Theta (θ) Earth Z B Plane of ecliptic Y To Sun X Phi (ϕ)

30 Particle density and flux Density is quoted in particles cm -3 e.g. 4 particles cm -3 Flux is quoted in particles cm -2 s -1 in 1 second all the particles in a Velocity v cylinder of length v pass through unit area if v = 500 km s cm s -1 4 particles cm -3 flux of particles cm -2 s -1 flux of particles m -2 s -1 Fluence is quoted in particles cm -2 radiation damage depends on fluence cm 3 cm 2

31 Temperature and thermal speed If particles are in thermal equilibrium with their surroundings, their average KE = thermal energy mv 2 = kt, k 2 Boltzmann's Temperature T is given by is constant, E.g. coronal proton, m = kg, v = ms -1 T = K Calculation fails if particles aren t in thermal equilibrium temperature is a concept that applies to systems in equilibrium m T v v 2 is the average square speed mv = 3k 2 JK Particles in thermal equilibrium

32 Temperature of a stream of particles Normally gas particles are spread around an average speed of zero Temperature is related to the spread of their speed, the average of v 2 relative number of particles Schematic distribution of velocities in a beam of particles of average speed relative number of particles Schematic distribution of particle velocities If the same particles are all given a speed (say 10) then their temperature stays the same The spread of v 2 about the average is the same velocity velocity

33 Solar wind temperatures V 0 Just moving a box of particles at speed v 0 doesn t change its temperature What counts is the speed of the wind particles once the average motion has been subtracted ACE s measurements show T ~ 10 5 K the spread of particle velocities of the protons is ~50 km s -1 electron temperatures are comparable to proton temperatures

Additional solar wind indicators http://www.sec.noaa.

html Dials and the auroral oval give a quick overview of

34 Additional solar wind indicators Dials and the auroral oval give a quick overview of the solar wind on the Earth dials show real-time display and history loop

35 Geostationary satellite environment Example of fluctuating environment at height of geostationary satellite K p is the planetary K index, a measure of the fluctuations in the Earth s magnetic field in range 0 to 9

36 Public prediction of K p index from ACE s solar wind data High index means high geomagnetic abnormality Tremendous aurora

Properties of Electromagnetic Radiation Chapter 5. What is light? What is a wave? Radiation carries information

Concepts: Properties of Electromagnetic Radiation Chapter 5 Electromagnetic waves Types of spectra Temperature Blackbody radiation Dual nature of radiation Atomic structure Interaction of light and matter