Ionosphere- Thermosphere

Transcription

1 Ionosphere- Thermosphere Jan J Sojka Center for Atmospheric and Space Sciences Utah State University, Logan, Utah PART I: Local I/T processes (relevance for Homework Assignments) PART II: Terrestrial I/T system (relevance for Laboratory Tasks) Heliophysics Summer School V: Boulder, Colorado 27 July to 3 August, 2011

2 Material adopted from the following authors. HSS lecture notes prepared by Professor Tim Fuller- Rowell (volume 1 HSS text book) Robert Schunk and Andrew Nagy: their text Ionospheres, a Cambridge press Atmospheric and Space Science Series book.

3 Neutral Atmospheres All ionospheres exist in an atmosphere. The thermosphere- ionosphere forms the neutral to plasma interface between planets with atmospheres and space. The composizon of the ionosphere is governed by the atmosphere and the ionizing radiazon. The atmospheric dynamics influences the ionosphere.

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5 ALTITUDE (km) H O 2 He N 2 O LATITUDE = 45 o LOCAL TIME = 15: DENSITY (cm -3 ) The Terrestrial Thermospheric composizon: the basis for the ionosphere

6 Altitude (km) km 102 km 94 km Mauersberger et al. (1968) Kasprzak et al. (1968) DeVries et al. (1970) n(ar) /n(n ) ( relative scale ) 2 Lower atmosphere has turbulent mixing which leads to constant composizon. Above the turbopause the neutral species are in their own hydrostazc equilibrium.

7 ALTITUDE (km) n(o) / n(o 2 ) AT 120 km K cm 2 s x x x 10 6 N 2 90 LOCAL PHOTOCHEMICAL EQUILIBRIUM O O CONCENTRATION (cm ) In the terrestrial upper atmosphere atomic oxygen is produced. Atomic oxygen is associated with its own chemistry reaczons.

8 Altitude (km) NO O 2 O CO CO Number Density (cm-3) N 2 MARS, it also has an atmosphere! Atomic oxygen is also present, as is a lot of carbon dioxide.

9 Ionospheres Ionospheres exist in a neutral gas. The relazve plasma to neutral density is variable. The dayzme plasma is produced by solar EUV so` X- ray ionizazon. The ionosphere is electrically coupled to the magnetosphere. The terrestrial ionospheres natural coordinate system is the Earths magnezc field.

10 ALTITUDE (km) He +, H + PROTONOSPHERE F2 o + IONOSPHERE F1 E D O 2 +,N 2 +,NO ELECTRON DENSITY (cm -3 )

11 O+ F2 Layer Above the peak it is in diffusive equilibrium with its plasma scale height. Below the peak chemistry dominates, but molecular composizon creates a large range of chemical reaczons and temperature dependencies. ALTITUDE (km) chemical equilibrium diffusive equilibrium ELECTRON DENSITY (cm -3 )

12 ym F2 EQUIVALENT PARABOLIC LAYER fof2 hmf2 Height E-F VALLEY E-F REGION fof1 E LAYER ho foe hme Plasma Frequency Nomenclature and simple mathemazcal funczons for the ionosphere.

13 Z P Z P (a) T n T i T ns SMIN SMAX T 4 (b) n T i T ns T e TEMPERATURE ( K) T e HEIGHT (km) HEIGHT (km) A natural coordinate for the atmosphere is the pressure level!

14 CO 2 + H + Altitude (km) NO + O Number Density (cm -3 ) O MARS has an ionosphere! The ionosphere is dominated by the molecular ion O2+, that on the Earth would be called the E- region.

15 PhotoionizaZon The Solar EUV irradiance is key. Only recently has the short wavelength component become rouznely observable. Proxy indices are less than sazsfactory! NASA: satellites TIMED(SEE) and SDO(EVE) have provided high resoluzon spectral and now temporal informazon about EUV irradiance variability.

16 (a) (b)

17 Solar EUV and Soft X-Ray Flux photodissociation photoionization; ionelectron pair production photoelectron escape flux incoming particle flux excited species; chemistry secondary & tertiary ionization transport processes ( e. g. molecular diffusion, thermal conduction) airglow neutral gas heating ion heating electron heating energy loss to the mesosphere

18 h! Z atmosphere planetary surface Solar Zenith angle geometry

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20 HEIGHT (km) T n T i T e TEMPERATURE ( K) HEIGHT (km) T n T i T e TEMPERATURE ( K) DayZme thermal profiles for the thermosphere and ionosphere at Millstone Hill, MA. A midlaztude locazon: le` panel 14:22 LT, right panel 02:22 LT at equinox in 1970.

21 Auroral IonizaZon The magnetosphere generates ionizazon via energezc parzcles, usually electrons. These parzcles are energized in the magnetosphere and create ionizazon and heazng in the thermosphere- ionosphere. Auroral displays are the manifestazon of this process. Ionospheric conduczvity is a dynamic resistor in the M- I electro- dynamics (MHD).

22 The alztude of ionizazon depends upon the energy of the auroral parzcles

23 at at 1225 T i T e ALTITUDE (km) T i T e n e TEMPERATURE ( K) 5-3 ELECTRON DENSITY ( x10 cm ) The auroral electrons precipitazon leads to heazng and density increases in the ionosphere

24 Electric Fields and Winds In the F- region the electric field and neutral winds can induce plasma dri`s to raise and lower the F- Layer. This modifies the plasma diffusion balance and hence density and profile shape. The ionosphere also corotates. At all laztude E X B can transport plasma perpendicular to the magnezc field line.

25 The Earths magnezc field is a poor dipole! But many models szll use a dipole representazon!

26 An Eastward Electric field together with the magnetic field creates an upward plasma drift.

27 The low laztude day Zme ionosphere is dominated by transport caused by the Eastward electric field. This results in plasma redistribuzon and the formazon of the Appleton Anomaly (equatorial anomaly).

28 ALTITUDE (km) S DIP LATITUDE N The Appleton anomalies also known as the Equatorial anomalies. The F- region densizes are shown as Log10 Ne (cm**- 3)

29 1200 MLT SchemaZc polar plot of the electric field called a 2- cell pakern. The F- region plasma E X B dri` trajectory direczons are shown by the arrows.

30 Observed ionospheric plasma dri` velocizes, over- layed with a corresponding 2- cell electric field pakern

31 ALTITUDE (km) a b c ION DENSITY (cm ) The effect of the E X B induced electric field (or wind) on the ionospheric density and profile.

32 O+ F2- layer is the dominant ionospheric layer under quiet geomagnezc condizons. However, during very disturbed geomagnezc condizons the rapid conversion of O+ into NO+ leads to a E/F1 layer becoming dominant.

33 PART- II Morphology of the ionosphere is a systems level problem. Many physics processes operate together as a system. Historically studies akempted to understand these processes individually and then assimilate their net effects. NOT A GOOD APPROACH!

34 Auroral Precipitation Joule Dissipation Solar EUV Plasmaspheric Downflow Starlight & Scattered Radiation Meteors UV Radiation X-rays F1 - Region E - Region Lower Thermosphere Very Energetic Particle Precipitation D-Region Mesosphere Tides and Gravity Waves

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36 1200 MLT MT LABEL CIRCULATION PERIOD (day) Even simple E X B is complex because there are two separate sources of E The ionosphere co- rotates, implying an E field, and then the magnetosphere s E field maps into the ionsophere and an atmospheric dynamo generated yet Another E field.

37 GEOGRAPHIC LOCAL TIME COORDINATES The F- region plasma as seen in a geographic local Zme from executes very complicated trajectories! This means that a ground based observatory at high laztudes is not monitoring the same plasma flux tube conznually, and hence the observer is not seeing the plasma evoluzon!

38 UT = Z = 2.0 AVE HT = LATITUDE (a) LONGITUDE m/s LATITUDE (b) LONGITUDE Thermospheric wind field are alztude dependent and responsive to Changes in magnetospheric energy input, STORMS.

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