AtmosphericAtmospheric Science Science ConferenceConference, ESA ESRIN , ESA ESRIN FrascatiFrascati, 11 May 2006, 11 May 2006

Michael Höpfner, Michael Höpfner, NielsNiels Larsen, Reinhold Larsen, Reinhold SpangSpang, , BeiBei Ping Ping LuoLuo, Jun Ma, , Jun Ma, SynneSynne H. H. SvendsenSvendsen, Stephen D. , Stephen D. EckermannEckermann, ,

Paola Paola MassoliMassoli, Francesco Cairo, Marcel , Francesco Cairo, Marcel SnelsSnels, Guido , Guido didiDonfrancescoDonfrancesco, , BjoernBjoern Knudsen, Knudsen, UtaUta BiermannBiermann, Gabriele , Gabriele

Stiller, Thomas von Stiller, Thomas von ClarmannClarmann, Herbert Fischer, Herbert Fischer

MIPAS discovers Antarctic MIPAS discovers Antarctic nitric acid nitric acid trihydratetrihydrate (NAT) (NAT)

polar stratospheric cloud beltpolar stratospheric cloud belt

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AtmosphericAtmospheric Science Science ConferenceConference, ESA ESRIN , ESA ESRIN FrascatiFrascati, 11 May 2006, 11 May 2006

•• What is the composition of solid What is the composition of solid nitric acid containing (Type 1a) nitric acid containing (Type 1a) PSCs?PSCs?

•• How do these particles nucleate?How do these particles nucleate?

QuestionsQuestions

AtmosphericAtmospheric Science Science ConferenceConference, ESA ESRIN , ESA ESRIN FrascatiFrascati, 11 May 2006, 11 May 2006

Analysis of space-borne mid-infrared limb-emission measurements during the initial PSC formation in the Antarctic stratosphere in May/June 2003.

Approach

Space borne → global view of PSC distributionMid-infrared → possibility to identify PSC composition

through spectroscopic signaturesLimb → good sensitivity to thin clouds through long optical pathEmission → visibility of PSCs also during polar night Antarctic stratosphere → ideal natural laboratory for PSC studies

MIPAS on Envisat

14.6 µm 4.15 µm

AtmosphericAtmospheric Science Science ConferenceConference, ESA ESRIN , ESA ESRIN FrascatiFrascati, 11 May 2006, 11 May 2006

MIPAS PSC observations over MIPAS PSC observations over McMurdoMcMurdo on 4 Aug 2003 on 4 Aug 2003

800 850 900 9500

200

400

600

800

1000

Tangent altitude 13.1 km 16.1 km 19.2 km

Rad

ianc

e [n

W/(c

m2 sr

cm

-1)]

Wavenumber [cm-1]

CFC-11

HNO3

CFC-12

SF6

CO2

???

AtmosphericAtmospheric Science Science ConferenceConference, ESA ESRIN , ESA ESRIN FrascatiFrascati, 11 May 2006, 11 May 2006

Spang and Remedios, 2003:

Spectral feature around 820 cm-1 attributed to NAT indirectly by HNO3-temperature relationship and occurrence temperature of the band

CRISTA PSC observations in August 1997

AtmosphericAtmospheric Science Science ConferenceConference, ESA ESRIN , ESA ESRIN FrascatiFrascati, 11 May 2006, 11 May 2006

Refractive indices

ν3(NO3-)

ν2(NO3-) ν1(NO3

-) ν2(H3O+)

AtmosphericAtmospheric Science Science ConferenceConference, ESA ESRIN , ESA ESRIN FrascatiFrascati, 11 May 2006, 11 May 2006

Bierm.98 smoothed

780 800 820 840 860 880 9000

200

400

600

800

1000Tangent altitude

13.1 km 16.1 km 19.2 km

Wavenumber [cm-1]

ν2(NO3-)

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Spectral fit to the measurement

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MIPAS measurement

AtmosphericAtmospheric Science Science ConferenceConference, ESA ESRIN , ESA ESRIN FrascatiFrascati, 11 May 2006, 11 May 2006

MIPAS measurement

ν3(NO3-)

ν3(NO3-)

ν3(NO3-)

AtmosphericAtmospheric Science Science ConferenceConference, ESA ESRIN , ESA ESRIN FrascatiFrascati, 11 May 2006, 11 May 2006

Observed positions of the ν2(NO3-)-band of NAD and NAT

AtmosphericAtmospheric Science Science ConferenceConference, ESA ESRIN , ESA ESRIN FrascatiFrascati, 11 May 2006, 11 May 2006

Search for NAT in MIPAS observationsSearch for NAT in MIPAS observations

SimulationSimulationββ--NATNATSTSSTSIceIceββ--NAT: R < 3 µmNAT: R < 3 µmββ--NAT: R > 3 µmNAT: R > 3 µm

Observation Observation

0.2 - 1 µm

2 µm

3 - 4 µm5 - 6 µm

AtmosphericAtmospheric Science Science ConferenceConference, ESA ESRIN , ESA ESRIN FrascatiFrascati, 11 May 2006, 11 May 2006

Comparison: MIPAS PSC composition Comparison: MIPAS PSC composition ↔↔ LidarLidar PSC typesPSC types

MIPAS closestmatch

MIPAS closestmatch but one

Temperature

McMurdo LidarRed: Type 1aGreen: Type 1bBlue: Type 2

Red: NATGreen: STSBlue: IceBlue-green: ?

AtmosphericAtmospheric Science Science ConferenceConference, ESA ESRIN , ESA ESRIN FrascatiFrascati, 11 May 2006, 11 May 2006

Development of PSC Types over AntarcticaDevelopment of PSC Types over Antarctica

First First NATNATafterafter~20 ~20

days!days!

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First ice observations

NAT only downwind the Antarctic Peninsula

Oscillatory ECMWF temperature contours

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Naval Research Laboratory Mountain Wave Forecast Model Naval Research Laboratory Mountain Wave Forecast Model

AtmosphericAtmospheric Science Science ConferenceConference, ESA ESRIN , ESA ESRIN FrascatiFrascati, 11 May 2006, 11 May 2006

ΔT [K]

Backward trajectoriesBackward trajectories

AtmosphericAtmospheric Science Science ConferenceConference, ESA ESRIN , ESA ESRIN FrascatiFrascati, 11 May 2006, 11 May 2006

Microphysical PSC model runsMicrophysical PSC model runsMeasurementMeasurement ModelModel

without without with with mountain wavesmountain waves

AtmosphericAtmospheric Science Science ConferenceConference, ESA ESRIN , ESA ESRIN FrascatiFrascati, 11 May 2006, 11 May 2006

SummarySummary• Spectroscopic evidence for β-NAT as constituent of Type 1a PSC

• No indication for NAD found in MIPAS PSC observations

• Detection of a NAT belt in the early Antarctic stratospheric vortex 2003: 20 days after first PSC observation

• Mountain wave activity over the Peninsula and the Ellsworth Mountains explains the sudden NAT formation

→ Trigger for subsequent frequent vortex-wide NAT observations?

→ No freezing mechanism of NAT above the ice frost point necessary to explain the observed ‘denitrification before dehydration’ in the Antarctic vortex?

Spectroscopic Evidence for NAT, STS, and ice in MIPAS infrared limb emission measurements of polar stratospheric clouds M. Höpfner, et al., Atmos. Chem. Phys., 6, 1201-1219, 2006.

MIPAS detects Antarctic stratospheric belt of NAT PSCs caused by mountain waves M. Höpfner et al., Atmos. Chem. Phys., 6, 1221-1230, 2006.

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