October 9, 2008 EVE Workshop 2008 Scott Bailey and Justin Yonker

Nitric Oxide and the Solar Soft X-ray Irradiance

Scott M. Bailey and Justin Yonker

Virginia Tech

October 9, 2008 EVE Workshop 2008 Scott Bailey and Justin Yonker

Production of Nitric Oxide

NO is primarily created through the reaction of excited atomic nitrogen with molecular oxygen:

N(2D) + O2 → NO + O

A major source of excited atomic nitrogen is energetic electron impact with molecular nitrogen:

e* + N2 → N(2D) + N + e*

Destruction of Nitric Oxide

NO is primarily destroyed through the reaction with ground state atomic nitrogen:NO + N(4S) → N2 + O

NO is also destroyed through photodissociation:NO + hν → N(4S) + O

Note that this reaction is doubly effective since it creates a ground state N atom which can also destroy NO.

The effective lifetime of an NO molecule is about 1 day under sunlit conditions.

October 9, 2008 EVE Workshop 2008 Scott Bailey and Justin Yonker

Abundance of NO is Very Sensitive to Solar 2‐7 nm Irradiance

October 9, 2008 EVE Workshop 2008 Scott Bailey and Justin Yonker

Comparison of SNOE and SEE 0 – 7nm Irradiance as of 2005

Average of F107 and 81day average F10.7

Irradian

ce (m

W m

‐2)

SNOE

SEE

October 9, 2008 EVE Workshop 2008 Scott Bailey and Justin Yonker

Comparison of SNOE and SEE 0 – 7nm Irradiance Today

October 9, 2008 EVE Workshop 2008 Scott Bailey and Justin Yonker

Comparison of SNOE and SEE 0 – 7nm Irradiance Today

October 9, 2008 EVE Workshop 2008 Scott Bailey and Justin Yonker

A one-dimensional chemical model reproduced observed equatorial altitude profiles

Model Incorporates:• Solar soft X-ray irradiance, λ < 20 nm, measured by SNOE• Relevant photochemistry, 35 reactions• Vertical diffusion• MSIS neutral atmosphere, GLOW energetic electron transport code

SNOE ObservationsModel Predictions

March 1998 September 2000

October 9, 2008 EVE Workshop 2008 Scott Bailey and Justin Yonker

SNOE ObservationsModel Predictions

The agreement was good near the NO peak at 106km, but the model underestimated the NO density at high altitudes.

October 9, 2008 EVE Workshop 2008 Scott Bailey and Justin Yonker

Reaction k(cm^3/s) Source 106 km % diff

150 km % diff

Herron (1999) -32 12

Richards (2004) 4 15

Herron (1999) fit to Fell (1990)

15 -17

Gamallo et al (2006) -4 4

NET CHANGE = Δ 1 = -17 14

ONOODN +→+ 22 )(

ONNOSN +→+ 24 )(

OSNODN +→+ )()( 42

ONOOSN +→+ 24 )(

28.12 )68.130exp(1035.4 TTx ⋅−

)260exp(1065.1 12 Tx −−

)/185exp(107.9 12 Tx −−

TTx ⋅−− )3270exp(105.1 14

The NO Model has been Updated to Include New Lab and Other Results

Diffusion coefficients have been updated:

Eddy Diffusion: Vlasov (2007) finds values of zmax=110 and kmax=1e7 using the triple exponential , five-parameter fit of Shimazaki (1972).

Molecular Diffusion:Collision integrals of Wright et al (2005) enable first principles determination. Our results reduce the previous value (Banks and Kokarts, 1973) by a factor of 3.

October 9, 2008 EVE Workshop 2008 Scott Bailey and Justin Yonker

Observed and Modeled NO at 106 km

October 9, 2008 EVE Workshop 2008 Scott Bailey and Justin Yonker

Observed and Modeled NO at 150 km