Solar Outputs, the Variations and their effects on Earth M. Lockwood Space Science and Technology Department, Rutherford Appleton Laboratory, Chilton, UK and Department of Physics and Astronomy, Southampton University, Southampton, UK

DRAFT

SAAS Lecture Course Davos, Switzerland March 2004

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1. Introduction to the Sun and the solar activity cycle The Sun is the source of the energy that powers our climate systems and allows life on Earth. It also provides particles, and the energy with which to accelerate them, which bombard the Earth: these have a variety of effects on both natural phenomena and man-made systems. At the same time, the Sun provides magnetic field which spreads throughout the heliosphere, and which shields Earth from energetic particles generated by supernova explosions. Table 1 lists some details of the Sun. Table 1.1. The Characteristics of the Sun (SI units) 6.9599 × 108 m = 109.3RE (an Earth radius, 1RE = 6.37× 106 m)

Solar radius, Rs (radius of the visible disk, the photosphere) Solar mass, ms

1.989 × 1030 kg = 3.33 × 105 mE (an Earth mass, mE = 5.97 × 1024 kg) 6.087 × 1018 m2 (1.19 × 104 × that of Earth) 1.412 × 1027 m3 (1.304 × 106 × that of Earth) 4.57 × 109 yr 3.846 × 1026 W 1.414 × 1022 W 5770 K

Surface area Volume Age Luminosity Power lost in solar wind Surface temperature Surface density

2.07 × 10-5 kg m-3 (1.6×10-4× the density of air at Earth’s surface) 70% H, 28% He, 2% (C, N, O, ...)

Surface composition (by mass) Central temperature Central density

1.56 × 107 K 1.50× 105 kg m-3 (8 × density of gold) 35% H, 63% He, 2% (C, N, O, ...)

Central composition by mass Mean density

1.40 × 103 kg m-3 (0.25× the mean density of Earth) 1.50 × 1011 m = 1AU = 215 Rs 0.532°

Mean distance from Earth, dES Mean angle subtended by a solar diameter at Earth = 2tan-1(Rs/dES) Mean solid angle subtended by a solar disk at Earth = π(Rs/dES)2 Surface gravity

6.7635 × 10-5 sr 274 m s-2 (27× the gravity at Earth’s surface) 6.18 × 105 m s-1 25.5 days (frequency, f = 460 nHz) 27 days 34 days (frequency, f = 340 nHz) 109 kg s-1

Escape velocity at surface Equatorial rotation period (w.r.t. fixed stars) Equatorial rotation period (w.r.t. Earth) Polar rotation period (w.r.t. fixed stars) Mass loss rate Inclination of equator w.r.t. ecliptic

7°

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The visible solar surface is called the photosphere, which lies at an average heliocentric distance r = Rs. The regions below the photosphere are not directly observable and our knowledge of them comes from application of the helioseismology technique, from numerical models and, now that we understand more about their mass and oscillations, from neutrinos which can escape the interior without interacting. At the centre of the Sun lies the core (0 < r < 0.25 Rs) where the high pressure and temperature cause the thermonuclear reactions which power the sun. The energy is then passed, mainly by the diffusion of gamma rays and X-rays, through the radiative zone (0.25 Rs < r