Ionosphere-‐Thermosphere
Jan J Sojka
Center for Atmospheric and Space Sciences Utah State University, Logan, Utah 84322
• 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
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.
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.
H O2 He N2O LATITUDE = 45o
LOCAL TIME = 15:00
470
420
370
320
270
220
170
120104 105 106 107 108 109 1010 1011
DENSITY (cm-3)
ALT
ITU
DE
(km
)
The Terrestrial Thermospheric composiZon: the basis for the ionosphere
Mauersberger et al. (1968)
Kasprzak et al. (1968)
DeVries et al. (1970)
160
140
120
100
80
60
400.01 0.1 1 10
n(Ar) /n(N ) ( relative scale )2
Alt
itu
de
(km
) 112 km102 km94 km
Lower atmosphere has turbulent mixing which leads to constant composiZon.
Above the turbopause the neutral species are in their own hydrostaZc equilibrium.
CONCENTRATION (cm )-3
140
1310
1210
1110
1010
1410
130
120
110
100
90
AL
TIT
UD
E (
km
)
80
LOCAL
PHOTOCHEMICAL
EQUILIBRIUM
n(O) / n(O2)
AT 120 kmK
cm2 s-1
N2
2O
O
1.0 4.5 x 106
0.5 9.0 x 106
2.0 2.3 x 106
In the terrestrial upper atmosphere atomic oxygen is produced.
Atomic oxygen is associated with its own chemistry reacZons.
340
300
260
220
180
140
100
Alt
itude
(km
)
102 104 106 108 1010 1012
Number Density (cm-3)
O
CO2
CONO O2
N2
MARS, it also has an atmosphere!
Atomic oxygen is also present, as is a lot of carbon dioxide.
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.
900
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100
0103 104 105 106
ELECTRON DENSITY (cm-3)
AL
TIT
UD
E (
km
)
ION
OS
PH
ER
E
PR
OT
ON
OS
PH
ER
E
F2
F1
E
D
O2+,N2
+,NO+
He+, H+
o+
103 104 105 106 107
ELECTRON DENSITY (cm-3)
200
300
400
500
600
700
800
AL
TIT
UD
E (
km
)
chemicalequilibrium
diffusive equilibrium
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.
Plasma Frequency
Hei
ght
EQUIVALENTPARABOLIC LAYER
ym F2
hmF2
foF2
E-F VALLEY
foF1
hmE
foEho
E-F REGION
E LAYER
Nomenclature and simple mathemaZcal funcZons for the ionosphere.
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4
3
2
1
0
-1
-2
-3
-4
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-6
-70 200 400 600 800 1000 1200 1400 1600 1800
500
400350
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250
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100
HE
IGH
T (k
m)
TEMPERATURE (°K)
ZP
ZP
SMAX
5
4
3
2
1
0
-1
-2
-3
-4
-5
-6
-7
400
350
300
250
200
150
120
100H
EIG
HT
(km
)
SMIN
(a)
(b)
Tn
Tn
Ti
Ti
Tns
Tns
Te
Te
A natural coordinate for the atmosphere is the pressure level!
360
320
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200
160
120
Alt
itud
e (k
m)
105104103102101
Number Density (cm-3)
O2+
H+CO2+
NO+
O+
MARS has an ionosphere!
The ionosphere is dominated by the molecular ion O2+, that on the Earth would be called the E-‐region.
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.
(a)
(b)
Solar EUV and Soft X-Ray Flux
photoionization; ion-
electron pair production photodissociation
photoelectron
escape flux
incoming
particle flux
airglow
electron heating ion heatingneutral gas heating
energy loss to the
mesosphere
transport processes ( e. g. molecular diffusion, thermal conduction)
secondary & tertiary
ionization excited species;
chemistry
!Zh
atmosphere
planetary
surface
Solar Zenith angle geometry
Tn
Ti
Te
TEMPERATURE (°K) 200 800 1400 2000 2600 3200
TEMPERATURE (°K) 400 800 1200 1600 2000 2400 2800 3200
800
720
640
560
480
400
320
240
160
HE
IGH
T (k
m)
800
700
600
500
400
300
200
120
HE
IGH
T (k
m)
Tn Ti
Te
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.
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).
The alZtude of ionizaZon depends upon the energy of the auroral parZcles
12-24-68 at 12176-26-68 at 1225
TEMPERATURE (°K) ELECTRON DENSITY ( 10 cm )x -35
ALT
ITU
DE
(km
)
400
300
200
100
00 500 1000 1500 2000 0 4 8 12 16
neeT
eTiT
iT
The auroral electrons precipitaZon leads to heaZng and density increases in the ionosphere
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.
The Earths magneZc field is a poor dipole!
But many models sZll use a dipole representaZon!
An Eastward Electric field together with the magnetic field creates an upward plasma drift.
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).
5.20
5.40
5.60
5.80
6.00
6.20 6
.00
5.80
5.80
6.00
6.40
6.206.00
5.805.60
5.405.205.0
0
5.60
6.00
800
700
600
400
300
200-24
S
-18 -12 -6 6 12 18 24
N
500
AL
TIT
UD
E (
km
)
0
DIP LATITUDE
The Appleton anomalies also known as the Equatorial anomalies.
The F-‐region densiZes are shown as Log10 Ne (cm**-‐3)
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80
70
60
50
0000
1200 MLT
1800 0600
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.
18
12
0
6-0.1
Observed ionospheric plasma dri` velociZes, over-‐layed with a corresponding 2-‐cell electric field pakern
AL
TIT
UD
E (
km
)
103
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106
100
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600
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800
a b c
104
ION DENSITY (cm )-3
The effect of the E X B induced electric field (or wind) on the ionospheric density and profile.
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.
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!
Auroral Precipitation
Joule Dissipation
Solar EUV
Plasmaspheric Downflow
Starlight & Scattered Radiation
Meteors
UV Radiation
X-rays
Very EnergeticParticlePrecipitation
F1 - RegionE - Region
Lower Thermosphere
D-RegionMesosphere
Tides andGravity Waves
80
70
60
50
12
3
4 56
78
06001800
0000
1200 MT
LABEL
CIRCULATION
PERIOD (day)
2 3 4 5 6 7 8
1.00 1.01 0.10 1.34 0.50 0.31 0.18 0.11
1
MLT
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.
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!
GEOGRAPHIC LOCAL TIME COORDINATES
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30
-30
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-90
(a) -180 -150 -90-120 -60 -30 30 60 90 120 150 180400 m/s
Z = 2.0 AVE HT = 286.3UT = 19.00
0
LA
TIT
UD
E
0
LONGITUDE
90
60
30
-30
-60
-90
(b) -180 -150 -90-120 -60 -30 30 60 90 120 150 180
0
LA
TIT
UD
E
0
LONGITUDE
Thermospheric wind field are alZtude dependent and responsive to Changes in magnetospheric energy input, STORMS.
