A NITRIC OXIDE A NITRIC OXIDE PHOTOMETER FOR ASIMPHOTOMETER FOR ASIM

P.J. Espy, Norwegian University of Science and Technology P.J. Espy, Norwegian University of Science and Technology (NTNU), Norway(NTNU), Norway

T. Neubert, Danish National Space Centre, DenmarkT. Neubert, Danish National Space Centre, Denmark

N. Ostgaard, University of Bergen, NorwayN. Ostgaard, University of Bergen, Norway

OUTLINEOUTLINE

Importance of TLE produced Importance of TLE produced NOx NOx

Production mechanismsProduction mechanisms ObservationsObservations

Importance of TLE Produced NOxImportance of TLE Produced NOx Produced in-situ in stratosphere and mesosphereProduced in-situ in stratosphere and mesosphere

Primary reactions:Primary reactions:

NO + ONO + O33 NO NO22 + O + O22 NONO22 + O + O NO + O NO + O22

Represents a Represents a catalyticcatalytic loss of ozone (Net: O loss of ozone (Net: O33 + O + O 2O 2O2)2)

A possible mechanism influencing upper stratospheric OA possible mechanism influencing upper stratospheric O33 recovery recovery

Eventually forms NEventually forms N22OO55 which converts to HNO which converts to HNO33 This reacts with stratospheric aerosolsThis reacts with stratospheric aerosols Participates in ozone chemistryParticipates in ozone chemistry Descends and precipitates out contributing to rain acidificationDescends and precipitates out contributing to rain acidification

Reacts with other IPCC climate change factors (e.g. sulphate aerosols)Reacts with other IPCC climate change factors (e.g. sulphate aerosols)

DIFFICULTIESDIFFICULTIES

It is unknown whether TLE produce NOIt is unknown whether TLE produce NO If NO is created, then how can it be detectedIf NO is created, then how can it be detected

Some proposed production mechanisms produce Some proposed production mechanisms produce NONO**

resulting radiation may be observedresulting radiation may be observed Other proposed mechanisms produce ground Other proposed mechanisms produce ground

state NOstate NO can be observed to fluoresce in sunlight can be observed to fluoresce in sunlight

Can it be observed within the limitations of Can it be observed within the limitations of the ISSthe ISS

NO Shock-Wave Production NO Shock-Wave Production

Zel’dovitch-Zel’dovitch- Shock wave dissociates NShock wave dissociates N22 & O & O22 @ T ~ 30,000K @ T ~ 30,000K N and O recombine to form NON and O recombine to form NO Shock wave expands and rapidly cools to T~2000KShock wave expands and rapidly cools to T~2000K NO “freezes out” with significant NONO “freezes out” with significant NO** that radiates that radiates Primary mechanism for tropospheric lightningPrimary mechanism for tropospheric lightning

but unknown if shocks are produced by TLEbut unknown if shocks are produced by TLE

High-Altitude Rocket Shocks High-Altitude Rocket Shocks NO NO

Ts=5000K Ts=12000K

Rocket shock wave creates excited NO that radiates. Emission falls off rapidly with altitude

MODELLED TLE PRODUCTION MODELLED TLE PRODUCTION OF NOOF NO

Liu and Pasko, GRL 2007

Production of N2(A) state

in TLE streamers

Chemical production of NO

Some NO* production and

detectable radiation

““Auroral” Production of NOxAuroral” Production of NOx

2

2

2

2

2

2

ONONO

ONON

NNOO

O

O

N

O

O

N

e

ONOODNSNDN

ODN

N

NOe

2

2

42

2

2

)()()(

)(

But the NO is produced in the ground state

Only observed in resonance fluorescence or absorption

Electron impact of every species leads to NO+

Which subsequently recombines to form NO

Observed Nitric Oxide Observed Nitric Oxide SpectraSpectra

95 km Tangent Height•Spectrum dominated by NO fluorescence

182 km Tangent Height•N+, O+, and N2 Vegard-Kaplan

emissions contribute

Auroral enhancement of NO fluorescing in the dayglow: A proxy for TLE produced NO

UV ALBEDO/SCREENINGUV ALBEDO/SCREENING

ASIM photometer channel

UV absorption screens lower atmosphere while allowing mesospheric TLE produced NO to be observed

ASIM VIEW FROM SPACEASIM VIEW FROM SPACE

160km tangent height

Screening height ~60 km

Wide field-of-view photometer 220-240 nm on ISS, observing -15° to +5° about the limb

ASIM OBSERVATION OF TLE ASIM OBSERVATION OF TLE NONO

Observe NO produced by TLE

in the mesosphere

Either direct NO- radiance (dark).

Or

Solar fluorescence of enhanced NO

CONCLUSIONSCONCLUSIONS

Important but challenging measurement to makeImportant but challenging measurement to make

UV observations of NO- UV observations of NO- band radiance, 220-240 nm from enhanced [NO]

Wavelength range avoids contaminating emissions Wavelength range avoids contaminating emissions and utilizes atmospheric absorption to screen and utilizes atmospheric absorption to screen lower atmospherelower atmosphere

Either direct radiation or solar resonance Either direct radiation or solar resonance fluorescence of high-altitude NOfluorescence of high-altitude NO