topics in space weather lecture 11 the upper atmosphere
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Topics in Space WeatherTopics in Space Weather
Lecture 11
The Upper Atmosphere
Topics in Space WeatherTopics in Space Weather
Lecture 11
The Upper Atmosphere
Robert R. Meier
School of Computational SciencesGeorge Mason University
rmeier@gmu.edu
CSI 76915 November 2005
2
Remaining Lectures
• Lecture 11 – November 15– Upper Atmosphere
• Lecture 12 – November 22– Ionosphere– Geomagnetic storms
• Lecture 13 – November 29– Geomagnetic storms & magnetosphere
connection– Aurora and Airglow
• Lecture 14 – December 6– Effects on Technological Systems– John Goodman will give last lecture
3
Topics - Lecture 11
• Sun as a star
• Solar effects on the atmosphere
• Upper atmospheric processes
• Temperature
• Density and composition
• Winds
surface
particles and magnetic fields
SUN EARTH
Sun-Earth SystemSun-Earth System:: Energy Coupling Energy Coupling
photons
core
convection zoneradiative zone
surface atmosphere
magnetosphere
sunspotplage
coronal mass ejection
bow shock
plasmasphere
not to scale
solar wind
heliosphereatmosphere
5
SOLAR - TERRESTRIAL SOLAR - TERRESTRIAL ENERGY SOURCESENERGY SOURCES
Source Energy Solar Cycle Deposition (Wm-2) Change (Wm-2) Altitude
Solar RadiationSolar Radiation• total 1366 1.2 surface• UV 200-300 nm 15.4 0.17 10-80 km• VUV 0-200 nm 0.15 0.15 50-500 km
ParticlesParticles• electron aurora III 0.06 90-120 km• solar protons 0.002 30-90 km• galactic cosmic rays 0.0000007 0-90 km Peak Joule Heating (strong storm)Peak Joule Heating (strong storm)• E=180 mVm-1 0.4 90-200 km
Solar WindSolar Wind 0.0006 above 500 km
6
Sun as a StarSun as a Star
SPEC
TRU
M
SPEC
TRU
M
VAR
IAB
ILIT
YVA
RIA
BIL
ITY
TOTA
L TO
TAL
IRR
AD
IAN
CE
IRR
AD
IAN
CE
VAR
IAB
ILIT
YVA
RIA
BIL
ITY
8magnetic fields have different effects on radiation at different wavelengths
sunspot
faculae
UV radiation varies more than visible radiation because UV faculae are brighter
The Sun’s Radiation SpectrumThe Sun’s Radiation Spectrum
EUV Radiation is Emitted from the Sun’s EUV Radiation is Emitted from the Sun’s Outer Atmosphere: Outer Atmosphere: Chromosphere, CoronaEUV spectrum:
>1500 lines5 continua
emission line temperatures vary over 2 orders of
magnitude
19960304 20000502EIT
304Å
0.0
8MK
284Å
2M
K
quiet Sun
He+ 304
quiet Sun
750K Exospheric Temperature 1300Kflares and
27-day rotations superimposed on
11-year cycles
Warren et al., 2001
GOES
SOLAR IRRADIANCE VARIABILITY MECHANISMSSOLAR IRRADIANCE VARIABILITY MECHANISMS
SOLAR ROTATION SOLAR ACTIVITY CYCLE
11
Ap
spacecraft drag
critical frequency
solar EUV photon energy
solar wind kinetic energy
corona
chromosphere heliosphere
16 JAN 03
Sun and Thermosphere-IonosphereSun and Thermosphere-Ionosphere
400 km
quiet Sun
response to EUV photons
response to particles, plasma, fields
NRLMSIS:500 km
temperature
neutral density
electron density
nemax=1.24×104fo2
NAVSPACECOMsolar wind
energy
EUV Radiation is Emitted from the Sun’s EUV Radiation is Emitted from the Sun’s Outer Atmosphere: Outer Atmosphere: Chromosphere, Corona
EUV spectrum: >1500 lines5 continua
emission line temperatures vary over 2 orders of
magnitude
19960304 20000502EIT
304Å
0.0
8MK
284Å
2M
K
quiet Sun
304
quiet Sun
Primary EUV Sources of Upper Atmosphere Heating: ch chromospheric cr coronal ch+cr mixed
Roble, 1987
750K Exospheric Temperature 1300K
Solar Cycle EUV Spectrum Variability
He II “304” He II “304” Å Irradiance VariabilityÅ Irradiance Variability
11-year cycle
27-day rotation
episodic flaring
SEM “304”Å5 min irradiance
NRLEUV HFG EUVACSOLAR2000
particlecontamination
model
SOHO/
TIMED/
SOHO EIT 195ÅSolar EUV Radiation Alters Ionosphere Solar EUV Radiation Alters Ionosphere
- Bastille Day 2000 solar eruption
pre-flare
flare
Meier et al., GRL, 2001
ionosphericelectron density
response
X-ray and EUV
irradiancevariation
TRACE
NRL SAMI2 model(Huber and Joyce)
15
Availability of Solar XR, EUV & UV Data
• Solar Extreme Ultraviolet (SEE) data from NASA/TIMED satellite– http://lasp.colorado.edu/see/
• Solar Radiation and Climate Experiment (SORCE)– http://lasp.colorado.edu/sorce/
• Solar EUV model (EUV81) [Hinteregger et al., Geophys. Res. Lett. 8, 1147-1150, 1981]– Can be found at SEE website, along with other
models (click on Data-General information and other data-Solar Irradiance Models)
16
Solar Effects on the Solar Effects on the AtmosphereAtmosphere
GLOBAL CHANGE
SPACE WEATHER
EUV FUV MUVRADIATION
Solar Energy Solar Energy DepositionDeposition
Atmospheric Atmospheric StructureStructure
18
Radiative energy deposition follows Beer’s Law
Change in solar flux
n = # absorbers/cc = absorption cross
section
Integrating,
dF n F dz
F
F+dF
dz’
z
n(z ')dz '
F(z) F( ) e
19
Optical Depth
• Definition
• For several species– i = N2, O2, O
• Altitude of unit optical depth: F(z)= F() e-1 – Solve (z) = 1 for z (See slide 16)
z
(z) n(z ')dz '
i ii z
(z) n (z ')dz '
20
Column Density
• If const.,
• Vertical Column Density
number of atoms/molecules in a 1 cm2 column above altitude z
z
(z) n(z ')dz ' N(z)
z
N(z) n(z ')dz '
21
Slant path optical depth
Assume plane parallel atmosphere– H << earth radius– Away from terminator
s = z / cos and
(s) = (z) / cos solar zenith angle
What happens at the terminator ( = 90o)?
(z)
0(s)
z
F()
s
22
Large solar zenith angles• Allowing for earth curvature and isothermal atmosphere,
then:
(s) = (z) Ch(x, )
– X = (Re + z)/H– Re = earth radius– H = scale height– Ch(x, ) = Chapman function
where + > 90o and - < 90o
• Must do numerical integration along slant path from Sun:– If not isothermal– If accounting for oblate spheroid shape of Earth
2
2xcos χ 0.50.521 xcos χ
Ch(x, χ) π x sinχ e 1 ± erf2 2
*
* From Rishbeth and Garriott, Intro. To Iono. Phys.
23
Solar Energy in the Upper Atmosphere
ENERGETIC SUNLIGHT AND PARTICLES
EXCITATION
IONIZATION DISSOCIATION
ION CHEMISTRY NEUTRALCHEMISTRY
COLLISIONALDEACTIVATION
PHOTOELECTRONS
ELECTRON HEATING ION HEATING NEUTRAL HEATING
SPECTRALEMISSIONS
24
Atmospheric Absorption Processes
• Ionization– O2 + h O2
+ + e*, …
• Dissociation– N2 + h N + N, …
• Excitation– O + h O*
• O* O + h ’ radiation• O* + X O + X quenching or deactivation
• Dissociative ionization – excitation– N2 + h N+* + N + e, …
...
25
Energy Thresholds for Processes*
Species Dissociation
(Å)
Dissociation
(eV)
Ionization
(Å)
Ionization
(eV)
H
He
O
O2
N2
NO
2423.7
1270.4
1910
5.11
9.76
6.49
911.75
504.27
910.44
1027.8
796
1340
13.6
24.58
13.62
12.06
15.57
9.25
* From Heubner et al., Astrophys. Space Sci., 195, 1-294, 1992
Useful relationship: E(eV) x (Å) = 12397
26
N2 Absorption Cross Section*
* Pl. Space Sci. 31, 597, 1983
27
O2 Absorption Cross Section*
* Pl. Space Sci. 31, 597, 1983
28R. Conway and Brendan McLaughlin, personal communication
SOLAR CYCLE CHANGES IN EUV RADIATION SOLAR CYCLE CHANGES IN EUV RADIATION IMPACT UPPER ATMOSPHERE IMPACT UPPER ATMOSPHERE TEMPERATURE and DENSITYTEMPERATURE and DENSITY
Solar Cycle Changes Solar Cycle Changes at 700 km:at 700 km:
Neutral Temperature:Neutral Temperature: 2 times2 times
Neutral Density:Neutral Density: 50 times50 times
Electron Density:Electron Density: 10 times10 times
30
Atmospheric Processes
Described by Thermospheric Global Circulation Models
(GCMs)
31
GCM Physics: Upper AtmosphereGeoff Crowley
Atmospheric & Space Technology Research Associates (ASTRA)
11118 Quail PassSan Antonio, TX 78249
210-691-0432
Objective:
What’s required to build a GCM?
(Equations, numerical techniques, parameterizations, boundary conditions, input specifications, validation with data)
32
Important Inputs to the Thermosphere – Ionosphere System
Solar UV Input
Upper Atmosphere (Thermosphere – Ionosphere)
Tides and Gravity Waves
E-fields Particles?
Neutral density temperature wind electron density
33
Simplified Physics of Upper Atmosphere
Composition
Temperature
Winds
E-fields
Electron Density
Diffusion Coeffs
Boundary Conds
Chemistry
Joule Heating Particle Heating
Solar EUV Chemical HeatingTides
Gravity Waves
Solar EUV
34
The leap-frog method is employed with vertical thermal conductivity treated implicitly to second order accuracy. This leads to a tridiagonal scheme requiring boundary conditions at the top and bottom of the domain as implied by the differential equation. Advection is treated implicitly to fourth order in the horizontal, second order in the vertical
Energy equation
ppp
e
p
i
po
s
c
Q
Hc
RTTV
c
aT
c
aT
sK
H
1
scp
ge
t
T
Molecular conduction radiation advection adiab. heating
Many terms
35
NEUTRAL GAS HEATING
36
Continuity equation
RSdz
dV
dz
dezK
dz
deL
T
T
m
m
dz
de
dt
d zz125.0
0
N
1z
2
molecular diffusion eddy diffusion Horiz. advection
Vert. adv.
Production
Recombination
i is the mass mixing ratio for species i: i = I(z) / I(z), where is the mass density
The leap-frog method is employed leading to a tridiagonal scheme requiring boundary conditions at the top and bottom of the domain.
37
Example: Nitrogen Chemistry (Simplified)
Each species equation includes horizontal and vertical advection, photo-chemical production and loss, and vertical molecular and eddy diffusion.
38
Neutral Species
The model includes 15 separate neutral species, not counting some excited states which are also tracked.
CO2, O, N2, CO, O2, O3, H, H2, H2O, HO2,
N, NO, NO2, Ar, and He.
Ionized Species
The model includes 7 ion species
O+, N+, CO2+, O2
+, N2+, NO+, and H+
with ionization primarily from solar EUV and x-ray. The ions are assumed to be in photochemical equilibrium with one another and the free electrons.
39
Momentum equations
Zonal velocity
Meridional velocity
The Leap frog method is employed with vertical molecular viscosity treated implicitly to second order accuracy. Since the zonal and meridional momentum equations are coupled through Coriolis and off-diagonal ion drag terms, the system reduces to a diagonal block matrix scheme, where (2 x 2) matrices and two component vectors are used at each level. Boundary conditions for the zonal (u) and meridional ( v) wind components are needed at the top and bottom of the model.
GWU + F + u + + t
cosr
g u vu RAYK* ) tan
r
u + (f +
s
u
H
) K+ K(
s
P
eg =
t
uxIxxIxyxxuxy
EM
o
s
GWV+ F + + u z
r
g v RAYK* u) tan
r
u + (f
s
H
)K + K(
s
P
eg =
tIyyIyxxxxy
EM
o
s
Viscosity (Molecular and Eddy)
Coriolis
gravity wave drag
Pressure gradientsRayleigh friction
ion drag momentum advection
40
Upper atmospheric temperature, density and
composition
Some simplified concepts
41
78% N2
21% O2
1% other
42
Thermodynamics
• Temperature equation very difficult to solve• Even under simplified 1-D geometry, the
temperature equation is a 2nd order time-dependent PDE– See Equation 8.77 of Gombosi
• Net heating rate (Production – Loss) is positive in the thermosphere (low cooling rate)– Leads to increase in temperature with altitude– Heat conducted downward and radiated to space in the
lower thermosphere by CO2, NO, and small amount of O fine structure radiation
43
Schematic of Energy Deposition in Thermosphere
44
Bates [1959] Temperature Profile
Analytic approximation for temperature profile:
T(z) = T - (T - Tzo) e-s(z – zo)
– s = shape function » Varies with conditions» typical ~ 0.02 km-1
– Matches observations– Functional form agrees with GCM models
o
o
z
z
dTdz
s =T - T
45
Fitting Bates Temperature Profile to GCM Model
• Non-linear least squares fit– “+” are model– Lines are function
• Worst error: few % • Therefore, can use
Bates profile for simple models of the thermosphere
• Note– Some places, T ~ const.– Some places, T ~ linear
Low solar activity
High solar activity
46
Diffusion
• Eddy diffusion– Turbulent mixing/wave breaking approximated
by diffusion of small eddys
• Molecular diffusion– Each species follows its own scale height
• Turbopause– Where eddy and molecular diffusion rates are
equal– Typically ~ 105 km
• But transition is smooth over some altitude interval• Below is called the homosphere• Above is the heterosphere
47
Turbopause
Gombosi, Fig 8.3
Turbopause
Ho
mo
sp
her
eH
ete
rosp
he
re
48
• Maxwell-Boltzmann velocity distribution
• No net vertical diffusion velocity• No chemistry • Steady-state, static equilibrium
– Ignore velocities
• Chapter 8 [Gombosi]
Diffusive Equilibrium
49
Area A
(p+dp)A
pA
dw
Diffusive Equilibrium
The Gibbs-Dalton Law of partial pressures applies. For any species, force balance yields:
dw + (p+dp)A = pA
but dw = g A dz
Then
dp = - g dz = - nm g dz where p = pressure
= mass density
n = molecules cm-3
m = molecular massg = grav. acceleration
Forces balance on slab of gas in equilibrium
at altitude z
dz
z
zo
50
Combine with Ideal Gas Law
p = n k T
dp = kT dn + nk dT = - nm g dz
dividing by nkT
dn/n + dT/T + dz/H = 0
where H = kT/(mg)
If T and g constant, then
n(z) = n(zo) e-(z-zo)/H
Note-Earth is an oblate spheroid:- Equatorial Radius: 6378 km & g = 9.78 m/s2
- Polar Radius: 6357 km & g = 9.83 m/s2
- Mean Radius: 6371 km
51
Barometric Equation
From Ideal Gas Law
p = n k T
And with
n(z) = n(zo) e-(z-zo)/H
Substituting:
p(z) = p(zo) e-(z-zo)/H
This applies over small altitude intervals or at high altitudes where T is ~ constant
52
Non-isothermal Atmosphere
Diffusive equilibrium:
dn/n + dT/T + dz/H = 0
d Log n + d Log T = - dz/H
Integrating:
n(z) = n(zo) T(zo)/T(z) e-dz/H
or
p(z) = p(zo) e-dz/H
53
Multi-constituent AtmosphereTotal Pressure:
p(z) = pi
where i = N2, O2, O
Test for Diffusive Equilibrium
dpi = - ni mi g dz = - pi mi g dz / (kT)
Solving for g/(kT) for species I and j, leads to:
Integrating,
I=atomic mass of i
ji
i i j j
dpdp1 1=
mp dz m p dz
i
j
1
μi
1
μj
n T= const. = R
n TMeier et al.JGR, 106, 15519, 2001
54
Diffusive Equilibrium for TIE-GCM and MSIS: O
• Plot R for two models– TIE-GCM first
principles model– MSIS empirical model
• Solar medium conditions– June
• Models qualitatively similar for O
Meier et al.JGR, 106, 15519, 2001
55
Diffusive Equilibrium for TIE-GCM and MSIS: O2
• Important differences in O2
• Major discrepancies exist in measure-ments of O2
– After 50 years of space research, O2 remains uncertain
56
A Couple of Shortcuts
• Isothermal Scale Heights– Hi = kT/(mig)
for g(200 km)
HN2 = 0.032* T
HO2 = 0.028* T =37 km
HO = 0.0567* T
• Estimate scale height: n(z)/n(zo) = 0.1 = e-(z-zo)/H
or H = (z-zo)/loge (10)
H = (z-zo)/2.3
Altitude interval where density decreases by 10:277 km – 205 km = 72 km
H = 72 km/2.3 = 31.3 km
ON2
O2
57
Bates-Walker Model Atmosphere[Walker, J. Atmos. Sci, 22, 462, 1965]
Using the Bates T(z):
T(z) = T – (T - Tzo) e-s(z-zo))
And diffusive equilibrium: ni(z) = ni(zo) T(zo)/T(z) e-dz/Hi
And changing to geopotential altitude:
= (z-zo)(Re+ zo)/(Re+ z)
Then
where
1+
-μς(z)oi i o
T(z )n (z) = n (z ) e
T(z)
i o
e o
m g(z )1μ = s + =
R + z μkT
58
Bates-Walker Model Atmospherecont.
• Gives good representation of atmosphere in diffusive equilibrium
• Basis of many atmospheric studies
• Basis of MSIS-class empirical models of the upper atmosphere– Needs to be modified for O and O2
photochemistry, which is important below ~ 200 km
59
Departures from Diffusive Equilibrium: Simplified O2 Photochemistry*
• LossO2 + h O + O j = 4.2 to 6.8 x 10-6 s-1 solar min to max
tL = j-1 = 2.4 to 1.5 x 105 s
• ProductionO + O + M O2 + M k = 2.76 x 10-34 e710/T cm6 s-1
tP = (k nO nM)-1 s
• Diffusion timetD = H2/D tD(110km) ~ 2.4 x 105 s
tD(120km) ~ 1.2. x 105 s
• Therefore O2 not in diffusive equilibrium (tL ~ tD)
* Other O2 photochemistry also involved: Gombosi, 8.8.2
60From Rees, Phys. & Chem. of Upper Atmos.
61
MSIS Class Empirical Atmospheric Models
• MSIS-class Models Are the Community Standard• Inputs: Day, Time (UT, Apparent Solar Local Time),
Location, Solar EUV Flux Proxy (F10.7 , F10.781 day
ave), Magnetic Activity (ap, Ap)
• Outputs: Composition (N2, O2, O, N, He, Ar, H, Oa), Total Mass Density, and Temperature, 0 - 1000 km
• Empirical, Analytic, Assimilative– Spherical Harmonics + Bates-Walker Altitude Profile– Interpolates Among Or Extrapolates Numerous Data Sets To
User-Specified Inputs– Nominal 1s Error 15-25 % (vs Altitude/Latitude)
• NRLMSIS 2000E supercedes MSISE-90: Automated/Web Distribution
62
MSIS Data Bases
• Data Sets Incorporated Into NRLMSIS– Satellites (Mass spectrometer [MS], EUV
absorption)– Rockets (MS, Pressure gauge, falling sphere,
grenade)– Ground-based Incoherent Scatter Radar (ISR)– Middle Atmosphere Program (MAP) Handbook
Tables– Satellite Drag, Accelerometer– Recent O2 Data: Solar Maximum Mission (SMM)
• Data Sets Yet To Be Incorporated– Upper Atmosphere Research Satellite (UARS)– NRL/DOD UV Remote Sensing: ARGOS, SSULI
63
MSIS Accessibility
• Description and downloading:– http://uap-www.nrl.navy.mil/models_web/msis/msis_home.htm– http://modelweb.gsfc.nasa.gov/models/msis.html
• MSIS 90 (earlier version)
• Reference to NRLMSIS2000– Picone, J. M., A. E. Hedin, D. P. Drob, and A. C. Aikin, J.
Geophys. Res., 107(A12), 1468 (2002)
• MSIS solar-geophysical inputs can be found at:
– ftp://ftp.ngdc.noaa.gov/STP/GEOMAGNETIC_DATA/INDICES/KP_AP/– http://www.sec.noaa.gov/today.html
64
NRLMSIS Example: March 21F10.7 = 150, Ap = 4 , Altitude = 300 km
65
NRLMSIS Example: June 21F10.7 = 150, Ap = 4, Altitude = 300 km
66
How Good are the Models?
• Compare MSIS & TIE-GCM Models
Solar-Geophysical Conditions• Summer Solstice June 19
• Solar Medium F10.7=150
• Low Geomagnetic Ap = 4• Latitudes -60 to + 60o
• Longitudes all• Altitude Range 110 – 478 km• GMT 00:00 H
• Plot Ratios of GCM/MSIS Parameters
67
Thermospheric Global Circulation Model and MSIS Empirical Model Show Major Discrepancies
Meier et al. JGR, 106, 15519, 2001
68
Upper Atmospheric Dynamics
Short Summary
(More after ionosphere and geomagnetic storm lectures)
69
Atmospheric Momentum Sources
• Solar (Heating) Tide
• Coriolis Force
• Ion Drag
• Gravity Waves
70
71
Altitude-Latitude Variation of Thermospheric Circulation from GCM Model
Quiet
Average
Storm
GeomagneticActivity
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