VII/1

Atmospheric transport and chemistry lecture

I. Introduction

II. Fundamental concepts in atmospheric dynamics: Brewer-Dobson circulation and waves

III. Radiative transfer, heating and vertical transport

IV. Stratospheric ozone chemistry

V. The tropical tropopause

VI. Climate gases

VII. Solar variability

1 The sun

2 Solar radiation changes, climate & ozone

3 Solar particles and the middle atmosphere

VII/2

Solar irradiance provides energy to the earth system

Turco 1997

SW heatingUV/Vis/NIR

LW coolingThermal IR

VII/3

Solar irradiance at TOA: near UV/Vis/IR

Weber et al., 1998, Weber 1999

Skupin et al., 2005

05-MAR-2004

Ca II

H

VII/4

MgII h and k emission

Fraunhofer lines:wing: absorption originating

in the photosphere (T~6000K)

core: emission, originating in the chromophere/transition region

Rottmann et al., 2005

VII/5

Mg II index chromospheric activity index from GOME

UV solar activity proxy from core-to-wing ratio of Mg II line

insensitive to optical degradation

linearly correlates well with UV and EUV wavelength variations down to 30 nm (Viereck et al. 2001)

VII/6

Solar UV irradiance variability

Mg II index is a suitable proxy for modelling solar UV and EUV variability (Viereck et al. 2001)

suitable proxy for modelling UV irradiance in climate models and for TSI reconstruction (Fröhlich et al. 2004)

VII/7

Origin of solar irradiance variability

variations in received solar UV irradiance are caused by the emergence and decay of active regions as they transit the solar disk.

Active regions contain enhanced:

UV brightness (photospheric faculae and chromspheric plages)

localized enhanced magnetic fields

Solar UV/vis radiation originates

upper photosphere

chromosphere

transition region

Fox, 2004

VII/8

origin of solar irradiance variability

H continuum image (white light)

H line center emission

VII/9

VII/10

The magnetic flux at the solar surface also varies quasi-periodicallyover the 11-year solar cycle.

MaximumMaximumMaximumMaximum

Magnetic fluxMagnetic flux MinimumMinimum

X-raysX-rays

The short-wave radiation varies strongly throughthe activity cycle: from a factor 2 in the UV (<100nm) up to a factor 100 in X-rays.

The solar activity cycle

VII/11

solar irradiance variability

Largest variations in UV

Small variation in visible and NIR (not well known)

Lean, 1994

VII/12

UV variation from solar minimum (1996) to maximum (1992)

UV variation below 400 nm linearly correlates with MgII index (280 nm)

(Rottmann, 2000

UARS/SOLSTICE

VII/13

Total solar irradiance from space („solar constant“)

CGD, NCARPMOD TSI

0.1%

Froehlich, priv. comm.

VII/14

„solar constant“

TSI composite time series from satellite observations

Froehlich, priv. communication

VII/15

Modelled TSI contribution

UV (<400 nm) contributes 8% to TSI

60% of TSI variability comes from the UV (<400 nm)

Lean et al. (1997) estimated abt. 30% contribution from 200-400 nm varibility to that of TSI (from SOLSTICE observations)

Krivova et al. 2006Krivova et al. 2006

500 nm50 nm 100 nm

≈60%

≈8%

VII/16

Contribution to TSI variability

Lean et al., 1997

VII/17

Solar indices

Various solar indices show variation with the 11 year solar cycle and 27 d solar rotation (full disc)

UV brightening competing with sunspot darkening (VIS)

Mg index starts in 1978F10.8 since the early 1900sSunspots counts since 1700s

122 nm

VII/18

Correlation among indices

Sunspot AreaSunspot Area 10.7cm Radio Flux10.7cm Radio Flux GOES X-Ray FlaresGOES X-Ray Flares

Climax Cosmic-Ray FluxClimax Cosmic-Ray FluxGeomagnetic aa indexGeomagnetic aa indexTotal IrradianceTotal Irradiance

VII/19

Penetration depth of solar radiation in the atmosphere

Liou, 2002

Thuillier et al., 2004

VII/20

Solar influence on climate

Climate impact from periodic earth events

some evidence for surface T response to solar variability on time scales longer than the 11y cycle (before 1980)

solar influence

VII/21

Milankovich cycles: changes in earth orbit parameters

~41ky

~100ky

~19 and 24 ky

obliquity

excentricity

precession

Changes in earth

parametersChange in solar

insolation

VII/22

Milankovich cycles: climate impact

solar insulation anomaly

ice volume derivative

Wallace & Hobbs 2005

VII/23

Global warming & cooling

Lohmann, priv. communication

VII/24

Solar variability and climate: recent past

TSI about 0.25% lower than current values during Maunder minimum

Sunsp

ot

num

bers Maunder

mínimumDalton

mínimum

VII/25

recent trends

solarwave drivingBD circulationaerosol

ESC

Total ozone trends: mid- to high NH latitudes

Dhomse et al. (2006)

Increase in NH total ozone since mid ninetiesincrease in BD circulation strength rise of solar cycle 23return to stratospheric aerosol background conditions after

Pinatubo eruption

VII/26

Global ozone trends and solar cycle variability

WMO 2006, Chapter 3

VII/27

Global ozone trends and solar cycle variability

WMO 2006, Chapter 3

Models do not show the double peak (25 and 50 km altitude)

Possible reasons Data record too short (~2.5 solar cycles) NOx from particle (electron precipitation) leads to ozone destruction during solar minimum in middle stratosphere -> BUT:

equires „huge“ amounts of Nox Reduced ozone production (less sunlight) in middle stratosphere from enhanced ozone in the upper stratosphere Interference from QBO and other dynamical effects Lower stratospheric solar signature are probbaly from dynamical response to solar variability

VII/28

Dynamics

Δ Absorption ofsolar UV-radiation

Δ NOx / HOx

chemistry

Δ UV Δ CP

Temperature

Ozone

Coupling between solar variability and atmospheric dynamics

VII/29

Solar coupling & planetary waves & polar O3 loss

extra solar heating during solar max strengthens subtropical stratopause jet (SJ) in early winter

radiative response

Strengthening of westerlies (SJ) means reduced wave progation and reduced BD circulation /warming of tropical tropopause region in early einter

dynamical response

Deflection of planetary waves away from subtropics (towards pole) while SJ descends downwards and polewards leading to a waekening weakening of polar night jet (polar vortex) in mid- to late winter

warmer polar stratospheric temperatures with reduced polar ozone loss in late winter

chemical responseKodera and Kuroda (2002)

VII/30

U and T response to solar cycle

Change in zonal mean wind (u) in m/s and zonal mean temperature (T) in K for a cahnge of 100 sfu (F10.8 units)

From solar minimum to maximum ~120 sfu

T

u

VII/31

Solar coupling and QBO

extra solar heating during solar max strengthens subtropical stratopause jet (SJ) in early winter

radiative response

Strengthening of westerlies (SJ) means reduced wave progation and reduced BD circulation /warming of tropical tropopause region in early einter

dynamical response

Deflection of planetary waves away from subtropics (towards pole) while SJ descends downwards and polewards leading to a waekening weakening of polar night jet (polar vortex) in mid- to late winter

warmer polar stratospheric temperatures with reduced polar ozone loss in late winter

chemical response

Update from Labitzke,1987, and Labitzke and van Loon, 1988

mostly during QBO west phase

VII/32

The Quasi-Biennial Oscillation (QBO)

QBO phase defined by zonal mean wind speed (u) in the lower tropical stratosphere (define QBO phase)

Downward descent of alternating easterly and westerlies

Baldwin et al., 2001

Red: westerliesBlue: easterlies

VII/33Baldwin, et. al., 2001

Holton-Tan mechanism (1980)

QBO: coupling to the extratropics

Wind speed differences between QBO east and QBO west phase (40hPa)

Blue: wind speed difference (u) negative (more easterly)

Red: wind speed difference (u) positive (more westerly)

Holton-Tan mechanism relates mid-latitude planetary wave propagation to QBO

impacting the mean meridonal circulation