Formation of Aurora Anni Leinonen and Anniina Väyrynen Ionospheric physics project work 24.4.2017

Contents Background Formation of Aurora Classification of Aurora Incidence of Aurora Forecasting of Aurora Picture 1. Auroras in Lapland [7]

Background Sunspots Places where magneticfield go through the surface of the Sun The plasma can’t go back inside the Sun at those places  radiation Place of sunspots moves with magnetic field Picture 2. Sunspots. [8]

In heliosphere and heliopause Transports the magneticfield of the Sun Solar wind Hot gas of corona Consists of ions: protons, electrons, He- nuclei and other charged particles of the Sun In heliosphere and heliopause Transports the magneticfield of the Sun At the orbit of the Earth v=400 km/h T=100 000 ⁰C B=2-4 nT

Electromagnetic radiation and particles with great amount of energy Flares and coronal mass ejections There are gas clouds in the magneticfield of the Sun: protuberances and prominences Because of flares energy of the magneticfield of the Sun is released explosively Electromagnetic radiation and particles with great amount of energy Coronal mass ejections are giant gas clouds 10 billion tons of matter Strenghten the solar wind and the transported magnetic field it Picture 3. [9]

Protects the Earth against particles of the solar wind The magnetic field of the Earth Protects the Earth against particles of the solar wind Comes from the liquid outer nucleus of the Earth Dipolic structure Solar wind prolongs a tail for the magnetic field of the Earth Picture 4. The Earth’s dipole magnetic field [2] Picture 5. Magnetosphere [2]

Formation of Aurora Dipolic form of the magnetc field of the Earth Auroral oval Dipolic form of the magnetc field of the Earth  Charged particles access the atmosphere of the Earth  circle formed areas = auroral oval Continuous band on both hemispheres Size of the auroral oval depends on the magnetic activity of the Sun Area where Auroras appears most likely Mainitse alussa, että aurinkotuuli synnyttää revontulet Alue jolla tod näk ilmenee: ESIINTYVYYS, kilpisjärvellä 75% ja utsjoella 65% (?)!! Oulussa 25% Picture 6. Auroral oval. [2]

In the atmosphere ions collide with molecules of the ionosphere Excitation of the atoms in the atmosphere and formation of the colors In the atmosphere ions collide with molecules of the ionosphere molecules become excited to higher energy level Excitation level release  Released energy can be seen as different colors of Aurora C-type: 100 km Oxygengreen Aurora Nitrogenhuman eye can’t see the spectrum of nitrogen Picture 7. The lowest energy levels of oxygen atom. [2]

D-type: A-type: B-type: E-type: 150 km Oxygenred Aurora Combination of types C and D Green Auroras shading to red at the top B-type: 70-100 km OxygenGreen Aurora Nitrogen red lower border E-type: Fast moving B-type Aurora

In addition, Hα- and Hβ- proton emissions form Auroras F-type: Sunlit Auroras Nitrogen blue and purple Auroras Resonance scattering In addition, Hα- and Hβ- proton emissions form Auroras Protons capture electron and produce excited hydrogen atom  Excitation level release  Auroras are seen Proton aurora is much weaker than electron aurora

Picture 8. Type C Aurora [2] Picture 9. Type A Aurora [2]

Picture 11. Type D Aurora [2] Picture 10. Type F Aurora [6]

Classification of Aurora Diffuse Aurora are wide spread No internal structure, matt Discrete Aurora Internal structure, bright Aurora band and Auroral arc Aurora rays Pulsating Aurora Auroras can be either quiet or active Quiet are slow, active are fast The brightness of Aurora is classified into four groups Picture 12. Auroral arc [5] Picture 13. Auroral band [5] Picture 14. Auroral rays [5]

Forecasting of Aurora Incidence of Aurora debends on activity of the Sun and the amount of the sunspots Forecasting the amount and of the Auroras and how great they look like Magnetic field of the Sun changes direction every 11th year During the maximum activity the magnetic field is messy During the decrease of the activity there are lots of holes in the corona  solar wind  more Auroras

Solar wind comes to Earth in 3 days When consirdered from the Earth, the rotation time of the Sun is 27 days Holes of corona can remain for couple rotations  the same hole can cause many Auroras Coronal mass ejections are single and therefore they can’t be forecasted Solar wind comes to Earth in 3 days From the mass ejections in the Sun, the velocity of the solar wind can be forecasted  Forecast of the time of the Auroral performance There are satellites in the L1-point, those measure the solar wind It takes 0,5-2,0 hours for the solar wind to come to the Earth The changes of the magnetic field of the Earth are reflected to the Auroras Disturbances occur at the same time Impacts are seen immediately

References [1] http://ilmatieteenlaitos.fi/tietoa-revontulista (check 23.4.2017) [2] Aikio Anita. Auroral Physics. Luentomoniste. Fysiikan laitos. Oulun yliopisto. 2017. [3] Aikio Anita. Ionospheric Physics. Luentomoniste ja luentodiat. Fysiikan laitos. Oulun Yliopisto. 2017. [4] http://www.ursa.fi/yhd/sirius/vk/vk9404/revont.html (check 23.4.2017) [5] http://www.taivaanvahti.fi/ (check 23.4.2017) [6]http://spaceweathergallery.com/ (check 23.4.2017) [7] http://nimiennalka.blogspot.fi/2014/07/kuura-vadelma-aamu-usva-ja-monet- muut.html (check 23.4.2017) [8] http://www.co2-raportti.fi/index.php?page=ilmastouutisia&news_id=2903 (check 23.4.2017) [9] http://www.tiedetuubi.fi/avaruus/entista-tarkempia-avaruussaaennusteita (check 23.4.2017)