image credit: nasa response of the earth’s environment to solar radiative forcing ingrid cnossen...
TRANSCRIPT
Image credit: NASA
Response of the Earth’s environment to solar radiative forcing
Ingrid CnossenBritish Antarctic Survey
OutlineThis lecture• Intro to atmosphere structure and processes• Absorption of solar radiation• Atmosphere composition• Energy balance• Ionization• Conductivity• Low latitude currentsNext lecture• Effects of variations in solar radiative forcing (examples)• High-latitude currents• Coupling to magnetosphere
Vertical structure of the atmosphere
D layer
F2 layer
F1 layer
E layer Thermosphere
Mesosphere
StratosphereTroposphere
2 3 4 5 6 7400
350
300
250
200
150
100
50
00 200 400 600 800 1000
Electron density (log10 cm-3)
Temperature (K)
Hei
ght (
km)
Low High
Air density
scale height
Absorption of solar radiation
Balance between
• Intensity of incoming solar radiation
• Atmosphere density
Atmospheric absorption cross-sections
From Cnossen et al. (2007)
X-ray EUV FUV middle UV near UV
What happens with absorbed solar energy?
Photo-ionization
Fast electron
(photo-electron)
Slow ion (He+)
He atom
EUV photon
Photo-dissociation
Excitation
Chemical reactions Heating Radiative loss (cooling)
EUV photon
Transformation of radiative energy
From Fomichev (JASTP, 2009)
LTE radiative processes
non-LTE radiative processes
non-LTE chemical processes
non-LTE kinetic processes
LTE = local thermodynamic equilibrium
10
Energy Thresholds for Processes
Species Dissociation(Å)
Dissociation(eV)
Ionization(Å)
Ionization(eV)
HHeOO2
N2
NO
2423.71270.41910
5.119.766.49
911.75504.27910.441027.8
7961340
13.624.5813.6212.0615.579.25
From Heubner et al., Astrophys. Space Sci., 195, 1-294, 1992
Neutral atmosphere composition
O
H
He
Ar
O2
N2
Important minor species:
NO (nitric oxide)
CO2 (carbon dioxide)
O3 (ozone)
turbopause (balance between molecular and eddy diffusion)
heterosphere
homosphere
Absorption of solar radiation within the atmosphere
Image credit: John Emmert/NRL
Energy balance in the atmosphere
zonal mean absorbed solar radiation
zonal mean outgoing infrared radiation
From Mlynczak (2000)
planetary balance
Winds in the thermosphere
Radiative energy terms in the middle atmosphere
From Fomichev (JASTP, 2009)
IR = infrared coolingCP = chemical heatingSol = solar heating
LTE
non-LTE
Radiative energy terms in the middle atmosphere
From Fomichev (JASTP, 2009)
IR = infrared coolingCP = chemical heatingSol = solar heating
LTE
non-LTE
What latitude?
Middle atmosphere radiative heating and cooling
solar heating infrared cooling
From Fomichev (JASTP, 2009)
LTE
non-LTE
O3
O2 (>205 nm)
O2 (<205 nm)
CO2
H2O
CO2
H2O (>18.5 μm)
O3
CH4
H2O (<18.5 μm)
Thermosphere heating and cooling rates (solar min)
total neutral heating
collisions with ions/electrons
exothermic chemical reactions
Joule heating
auroral particle precipitation
O2 absorption
O3 absorption
O recombination
quenching of O(1D)
total neutral cooling
molecular thermal conduction eddy thermal
conduction
NO 5.3 μm emission
CO2 15 μm emission atomic oxygen cooling
Roble et al. (1987)
Photochemistry in the upper atmosphere
From Richards (JGR, 2011)
Ionosphere composition
Major species: O2+, NO+, and O+
Molecular ions dominate < ~150 km; approximate photo-chemical equilibrium
O+ dominant > ~200 km
Conductivity of the ionosphere
𝑁_𝑒
Solar quiet (Sq) current system
Winds drive currents
Currents perturb the magnetic field
Observations from l’Aquila
Summary
Solar activity affects… Heating and cooling processes throughout the
atmosphere Pressure gradients and winds Composition Ionization Conductivity Currents in the ionosphere
These processes also interact with each other!