image credit: nasa response of the earth’s environment to solar radiative forcing ingrid cnossen...

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!