Earth’s Atmosphere
with focus on the upper atmosphere – above 100km
(Thermosphere and Ionosphere)
Gang Lu
High Latitude Observatory
National Center for Atmospheric Research
High Altitude Observatory (HAO) – National Center for Atmospheric Research (NCAR)
2007 Summer School for REU
The National Center for Atmospheric Research is operated by the University Corporation for Atmospheric Research
under sponsorship of the National Science Foundation. An Equal Opportunity/Affirmative Action Employer.
Outline
• Atmospheric Layers
• The Thermosphere & Ionosphere
• Electrodynamical Processes in the Ionosphere
• Storm Impacts on the Upper Atmosphere
• Homework Problems
Atmosphere Layers
The Thermosphere
Atmospheric Distribution
under Hydrostatic Equilibrium
Pressure gradient:
z is altitude
g(z) is the acceleration of gravity
 is mass density
dp
  g (z ) 
dz
For perfect gas approximation:
p  nkT 

M
nT
k = Boltzmann’s constant
M = mean mass of the molecules
Combining the above 2 equations yields:
dp
gM
dz

dz  
p
kT
H
H
kT
is the scale height
Mg
If H does not vary with altitude z:
z  z0
p ( z )  p ( z0 ) exp(
)
H
Atmospheric Density Distribution
If T, M, and g are not functions of z:
 z  z0 
n( z )  n( z0 ) exp 
H 

Mixed atmosphere (below ~100 km):
kT
H
Mg
M is the mean molecular
weight of atmospheric gases
Diffusively separating atmosphere (above ~100 km):

kT
Hi 
mi g
mi is the molecular weight of
individual species
Each species has its own scale height.

Column Density
Column Density: the number of molecules per unit area
in a column above z0:
N(z0 ) 


z0
n(z)dz
Total Electron Content:

TEC  z0 ne ( z ) dz
1 TEC Unit = 1012 electron/cm2
If H is independent of altitude:
 z  z0 
N ( z0 )  z0 n( z0 ) exp
dz   Hn( z0 )

H 

 Hn( z0 )

z0
 z  z0 
exp
H 

Ionospheric Regions
Ionospheric Regions
Solar Min and Max Distributions
Ionospheric Regions
Day and Night Distributions
Sources of Ionization
Solar EUV and X-rays
Galactic Cosmic Rays
Courtesy of Scot Elkington
Altitude Attenuation of Solar Irradiance
Thermosphere
Mesosphere
Stratosphere
Troposphere
Ionization Rate (cm-3 sec-1)
Solar Minimum
Solar Maximum
Courtesy of Stan Solomon
Principal Chemical Processes
in the Thermosphere and Ionosphere
Photoionization:
hu + O [ O+ + ehu + O2 [ O2+ + ehu + N2 [ N2+ + eCollisional Ionization:
e- + O [ O+ + 2eCharge Exchange:
H + O+ [ H+ + O
O 2 + O + [ O 2+ + O
N2 + O+ [ N2+ + O
Conversion:
N2+ + O [ NO+ + O
N2 + O+ [ NO+ + O
Recombination:
O + O + N2 [ O2 + N2
Dissociative Recombination:
O2+ + e- [ O + O
N2+ + e- [ N + N
NO+ + e- [ N + O
Radiative Recombination:
O+ + e- [ hu + O
Thermospheric Compositions
Ionospheric Compositions
Electrodynamic Processes
In the Ionospere
Ionospheric Currents
Horizontal Current:

 
J  N e e(Vi  Ve )
 

 P E  Hb  E
Pedersen
Current
Hall
Current
where P = height integrated
Pedersen conductivity
H = height integrated
Hall conductivity

 
E  V  B
Ionospheric Currents
Horizontal Current:
JH
 


J  P E  H b  E
JP
Field-aligned Current:

j||    J
 

   ( P E   H b  E )
Region 1 currents
Region 2 currents
Distributions of Ionospheric Currents
Energy Transfer to the Ionosphere
Poynting’s Theorem:
 
 EB
 B
0E   
0

  J  E    


t  20
2 
 0 
2
where
0E 2
2
2
B2 V 2

 1
2
2 0 c
For static conditions, the Poynting’s theorem reduces to:
 
 
 EB
  J  E
  


 0 
 
J  E  0, magnetic energy
J  E  0, mechanical energy
mechanical or thermal energy
magnetic energy
Energy Transfer to the Ionosphere
Horizontal Current:
 


J  P E  H b  E
Electromagnetic Energy Dissipation:
(Ohm’s Law)
  
 

J  E  P E  H b  E  E   p E 2


Joule heating
When neutral wind is neglected:

 
E  V  B


  
  
When neutral wind is included: E  E '  ( E  U  B )  (V  U )  B
plasma drift
velocity
neutral wind
velocity
Comparison of Energy Inputs From the Sun to the Earth
Source
Energy Input
(W/m2)
Deposition
Altitude (km)
1368
16
0.1
0.003
Surface
0-50 km
50-120 km
100-500 km
0.002
0.001-0.006
0.003-0.03
0.000007
30-90 km
100-130 km
70-130 km
0-90 km
0.000014~0.14
100-500 km
Solar Radiation
Total irradiance
UV 200-300nm
UV 120-200nm
EUV
Particles
Solar Energetic Protons
Magnetosph. Protons
Magnetosph. Electrons
Galactic Cosmic Rays
Joule Heating
E = 1~100 mV/m
Solar wind
Kinetic 1/2v3
Electromagnetic ExB/0
0.0003
0.00003
Solar and Magnetospheric Energy Budget
Solar irradiance: 1017 W (with 0.1% variability)
Solar wind kinetic power: 1013~1014 W
Magnetospheric power: 1011~1013 W
Auroral precipitation: 109~1011 W
Joule heating rate: 1010~1012 W
Ring current injection: 1010~1012 W
Plasma sheet heating: ~1011 W
Plasmoid ejections: 1010~1011 W
Power consumed by US: ~8x1011 W
 Energy input to the magnetosphere: 1016~1018 Joules
 Energy released by a typical CME: 1024 Joules
 Mass input into the magnetosphere: 105~106 kg
 Mass released by typical CME: 2~5x1012 kg
Solar Flare Effects
on the thermosphere and Ionosphere
Electron Density at ~110 km During Flare on 9/7/2005
1730UT Flare onset 1740UT
1750UT
3x105
cm-3
1720UT
1810UT
1820UT
1830UT
1x103
3x105
cm-3
1800UT
1850UT
1900UT
1910UT
3x105
cm-3
1840UT
1x103
1x103
Neutral Temperature Change at ~350 km During Flare
1730UT Flare onset 1740UT
1750UT
100
oK
1720UT
1810UT
1820UT
1830UT
100
oK
1800UT
0
1910UT
2000UT
2200UT
100
oK
1850UT
0
0
Solar Energetic Proton Effects
on the Upper Atmosphere
% Change of Electron Density due to SEPs
Northern Polar Cap
October 27 – November 5, 2003
Southern Polar Cap
October 27 – November 5, 2003
Changes of NOX (NO+NO2) and Ozone due to SEPs
Northern Polar Cap
Southern Polar Cap
NOX
NOX
O3
O3
October 27 – December 31, 2003
October 27 – December 31, 2003
Effects of Magnetospheric Energy Inpout
on the Upper Atmosphere
TIEGCM Difference TEC Maps During Storm
1600UT
1700UT
1730UT
1800UT
8
0
-8
1830UT
1900UT
1930UT
2000UT
8
0
-8
2030UT
2100UT
2130UT
2230UT
8
0
-8
TIEGCM Difference O/N2 Ratio During Storm
1600UT
1700UT
1730UT
1800UT
0.5
0
-0.5
1830UT
1900UT
1930UT
2000UT
0.5
0
2030UT
2100UT
2130UT
2230UT
-0.5
0.5
0
-0.5
Neutral Temperature Change at ~350 km During Storm
1620UT
1630UT
1640UT
300
Kelven
1610UT
1730UT
1750UT
1820UT
300
Kelven
1710UT
0
1940UT
2100UT
2130UT
300
Kelven
1900UT
0
0
Neutral Temperature Change at ~350km
100
300
DTN OK
During Storm on Sep. 10
DTN OK
During Flare on Sep. 7
0
0
Homework Assignment
Homework Problem 1:
(a) Name the layers 1 to 4
(b) Identify the curves A, B,
C and D
Homework Problem 2:
If the neutral temperature at
300 km is increases from
1300 oK to 1500 oK during a
solar flare event, will the
neutral number density at
300 km increase or
decrease? Assuming the
thermosphere is mainly
composed of atomic oxygen.
Homework Problem 3:
When neutral wind is neglected, Joule heating QJH is simply
expressed as:
QJH   p E
2
Rewrite the full expression for Joule heating in the reference frame

of neutral wind U. Do neutral winds contribute positively or
negatively to Joule heating?

'
   
(Hint: replacing E with E , where E  E  U  B )
'
Dipole Magnetic Field
Distorted Magnetic Field
Magnetic Reconnection &
Circulation
x
Noon-Midnight Meridional Plane
Magnetospheric
Topology & Plasma
Convection
Solar
wind
Flow lines
60°
Noon
Open-Closed
Boundary
Dawn
Midnight
Equatorial Plane
Magnetopause
High-Latitude
Ionosphere
Dusk