ASEN 5335 Aerospace Environments -- The Sun & Intro to Earth’s Upper Atmosphere1 PARTICLE RADIATION The Sun is constantly emitting streams of charged particles, the solar wind, in all outward directions. Solar wind particles, primarily protons and electrons, travel at an average speed of ~450km/s, with a density of 5 particles per cubic centimeter. The speed and density of the solar wind, and its variability, can increase markedly during periods of solar activity, and this causes some of the most significant operational impacts.

ASEN 5335 Aerospace Environments -- The Sun & Intro to Earth’s Upper Atmosphere2 Coronal hole & uni-polar magnetic field Solar wind di-polar magnetic field

ASEN 5335 Aerospace Environments -- The Sun & Intro to Earth’s Upper Atmosphere3

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6 Joint ESA-NASA Launch: 6 October 1990 Orbit: Elliptical Heliocentric Instruments Ulysses is equipped with a comprehensive range of scientific instruments to detect and measure solar wind ions and electrons, magnetic fields, energetic particles, cosmic rays, natural radio and plasma waves, cosmic dust, interstellar neutral gas, solar X-rays and cosmic gamma-ray bursts. The Ulysses Mission Mission History Ulysses was launched by the Space Shuttle Discovery on 6 October, It headed out to Jupiter, arriving in February 1992 for a gravity-assist maneuver that swung the craft into its unique solar polar orbit. This highly elliptical operational orbit takes the spacecraft from Jupiter's orbit to within ~1.4 AU from the Sun and back out again, with a period of 6.2 years. Around each perihelion, Ulysses performs passes of the Sun's poles. The first two sets of polar passes were completed in 1994/1995 and 2000/2001. # Aphelion SP Pass Perihelion NP Pass *Note: the polar passes each last between 3 and 4.3 months. The dates given here are for when Ulysses is at the maximal heliocentric latitude in the middle of each pass.

ASEN 5335 Aerospace Environments -- The Sun & Intro to Earth’s Upper Atmosphere7 Plot of Ulysses's third solar orbit, with the orbit of the Earth and Jupiter also indicated. The regions over the Sun's poles (above 70° heliographic latitude) covered in the third set of polar passes are marked in yellow. The Ulysses orbit is viewed here from a perspective of 15° above the ecliptic plane, with the Earth and Jupiter orbits also indicated.

SWOOPS = (Solar Wind Observations Over the Poles of the Sun).

ASEN 5335 Aerospace Environments -- The Sun & Intro to Earth’s Upper Atmosphere9 Sunspots are areas of intense magnetic fields. Viewed at the surface of the sun, they appear darker as they are cooler than the surrounding solar surface - about 4000 o C compared to the surface (6000 o C). 4. FEATURES OF THE SOLAR ATMOSPHERE: SUNSPOTS video

ASEN 5335 Aerospace Environments -- The Sun & Intro to Earth’s Upper Atmosphere10 The video below depicts regions of negative (black) qnd positive (white) magnetic polarity (like a magnet). SUNSPOTS ARE REGIONS OF INTENSE MAGNETIC FIELDS Sunspots are darker and cooler because the intense magnetic fields impede upward convection, i.e., transfer of heat from the interior.

ASEN 5335 Aerospace Environments -- The Sun & Intro to Earth’s Upper Atmosphere11 Why are closed magnetic structures in the corona bright, but are dark in the photosphere (i.e., sunspots)? The intense magnetic fields associated with sunspots act as a valve and choke off heat and energy flowing outward from the convection zone, and are thus cooler than their surroundings In the corona, the closed magnetic loops are filled with higher-density energized plasma, and thus appears bright (in x-ray) compared to its surroundings.

ASEN 5335 Aerospace Environments -- The Sun & Intro to Earth’s Upper Atmosphere12 SUNSPOT BUTTERFLY PLOT – 11 year cycle Magnetic Polarity Plot – 22 year cycle

ASEN 5335 Aerospace Environments -- The Sun & Intro to Earth’s Upper Atmosphere13 5. THE SOLAR CYCLE The number of sunspots (‘Zurich’ or ‘Wolf’ sunspot number) on the solar disk varies with a period of about 11 years, a phenomenon known as the solar (or sunspot) cycle. Sunspot Number in recent centuries Maunder Minimum

Sunspot Number in Recent Centuries Maunder Minimum In the middle of the 17th century temperatures dropped so low that the Baltic sea and the Thames River froze over regularly. The ice on the Thames in London was so thick that people organized winter festivals with skating parties and carnivals on the river. One of these festivals on the Thames was painted by the Dutch painter Abraham Hondius in December Skating on the Thames even occurred in July!

ASEN 5335 Aerospace Environments -- The Sun & Intro to Earth’s Upper Atmosphere15 Johann Rudolph Wolf ( ), Director, Zurich Observatory Wolf (or Zurich) Sunspot Number = 10 x no. of groups + total count of individual spots A weighted average over a network of observatories is used, since the count depends on observer interpretation and experience; depends on local weather conditions; and sunspots evolve and vary with solar longitude

ASEN 5335 Aerospace Environments -- The Sun & Intro to Earth’s Upper Atmosphere16

ASEN 5335 Aerospace Environments -- The Sun & Intro to Earth’s Upper Atmosphere17

ASEN 5335 Aerospace Environments -- The Sun & Intro to Earth’s Upper Atmosphere18 GRANULES

ASEN 5335 Aerospace Environments -- The Sun & Intro to Earth’s Upper Atmosphere19 H , 6563 Å CHROMOSPHERIC FILAMENTS & PLAGES Filaments are the dark, ribbon-like features seen in H  light against the brighter solar disk. Filaments are elongated blobs of plasma supported by relatively strong magnetic fields. When seen on the disk the suspended gas absorbs more photospheric energy than it gives off along the line of sight, and thus it appears dark. Plages are hot, bright regions of the chromosphere, often over sunspot regions, and are often sources of enhanced 2800 MHz (10.7 cm) radio flux

ASEN 5335 Aerospace Environments -- The Sun & Intro to Earth’s Upper Atmosphere20 Filaments are referred to as prominences when they are present on the limb of the Sun, and appear as bright structures against the darkness of space. Prominences are variously described as surges, sprays or loops. SOLAR PROMINENCES

ASEN 5335 Aerospace Environments -- The Sun & Intro to Earth’s Upper Atmosphere21 SOLAR FLARES Flares and Coronal mass ejections (CMEs) are different aspects of solar activity that are not necessarily related. - Flares produce energetic photons and particles. - CMEs consist of low-energy plasma. CMEs and flares are very important sources of dynamical phenomena in the space environment. The triggering mechanisms for CMEs and flares, and the particle acceleration mechanisms, are not understood beyond a rudimentary level. However, this knowledge is essential for development of predictive capabilities.