stratospheric no y studies with the slimcat 3d ctm
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Stratospheric NO y Studies with the SLIMCAT 3D CTM. Wuhu Feng , Stewart Davies, Jeff Evans and Martyn Chipperfield School of the Environment, University of Leeds, Leeds, UK. Studies of NO 3 Chemistry Comparison with balloon and aircraft NOy data

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stratospheric no y studies with the slimcat 3d ctm
Stratospheric NOy Studies with the SLIMCAT 3D CTM

Wuhu Feng, Stewart Davies, Jeff Evans and Martyn Chipperfield

School of the Environment, University of Leeds, Leeds, UK

  • Studies of NO3 Chemistry
  • Comparison with balloon and aircraft NOy data
  • Improved Arctic 2002/03 Winter ozone loss
  • Coupled microphysical model (DLAPSE/SLIMCAT)
  • Long-term NO2 trends


Bhaswar Sen, Geoff Toon (NASA JPL)

and all TOPOZ and VINTERSOL scientists

slimcat 3d ctm

3D Off-line Chemical Transport model

  • Horizontal winds and T from analyses (ECMWF, UKMO)
  • - vertical coordinate
  • Tracer Transport

Default advection Scheme: Prather 2nd order moment scheme

Vertical motion: CCM or MIDRAD radiation scheme

  • Detailed Chemical Scheme:

41 chemical species;

123 gas phase chemical reactions;

32 photolysis reactions

~9 heterogeneous reactions on liquid sulphate aerosols and solid PSCs

Chipperfield M. P., JGR 104, 1781-1805, 1999

stratospheric no 3 chemistry
Stratospheric NO3 Chemistry

NO3 has very simple chemistry in the stratosphere:

NO2 + O3NO3 + O2 (1)

NO3 + h NO2 + O

NO3 + h NO + O2

NO3 + NO2 + M N2O5 + O2 (2)

At night in the low-mid stratosphere NO3 can still be in steady state:

[NO3] = k1[NO2][O3]/(k3[NO2][M]) = k1[O3]/(k3[M])

 Nighttime [NO3] determined solely by O3 and T (no dependence on NOy!)

testing of no 3 chemistry from balloon observations
Testing of NO3 Chemistry from Balloon Observations

SALOMON Balloon observations

J.B. Renard et al (CNRS, Orleans)

Nighttime (moonlight) observations of NO3, NO2 and O3.




Model underestimates observed NO3, but steady-state a very good approximation 15-40 km.

(Not a problem due to O3 which agrees well).

comparison of 6 salomon flights with slimcat
Comparison of 6 SALOMON flights with SLIMCAT


Model underestimates NO3 at high T

k for

O3 + NO2

Can derive best fit for k1:

k1 = 6 x 10-13 exp(-2740/T)

compared to JPL:

k1 = 1.2 x 10-13 exp(-2450/T)


Renard et al., J. Atmos Chem (submitted)

polar ozone loss
Polar Ozone loss
  • To quantify and understand the degree of chemical ozone loss in the Arctic stratosphere is an important issue

But current models can’t give a satisfactory of the observed ozone loss based on the fact that models can not reproduce the observed ozone.

  • Transport problem (Different Cly and NOy in a given model lead to significant difference in chemical process).
  • Chemistry process
  • Radiative transfer process
  • Microphysics process
  • Complex interaction between theses processes
ozone hole
Ozone Hole
  • SLIMCAT reproduce the O3 column
  • Also show POAM PSC and MKIV location
mk iv interferometer measurements
MK IV Interferometer Measurements
  • Fourier Transform Infra-Red (FTIR) Spectrometer
  • By Jet Propulsion Laboratory in 1984
  • Remote-sensing by solar absorption spectrometry
  • Provides stratosphere gases including NOy

Trajectory of the MkIV payload from Esrange across Finland and into Russia on December 16, 2002

no y n 2 o correlation
NOy-N2O Correlation



  • Model captures denitrification/renitrification signal well
no y partitioning
NOy Partitioning
  • Model Captures major features of NOy species distribution
  • NO2 is poor in the lower stratosphere
clono 2 and clo
ClONO2 and ClO

The model overestimate ClONO2 due to underestimate the chlorine activation!

no y ratios
NOy Ratios
  • HNO3 and N2O5, ClONO3 overestimate, NO2 poor below 25Km
m55 geophysica aircraft
M55 Geophysica Aircraft

comparison with aircraft data cold region
Comparison with Aircraft data (Cold region)
  • Different radiation transfer process result in different descent
  • Good simulation of NOy for the cold region (T< 195K)
comparison with aircraft data t 200k
Comparison with aircraft data (T>200K)

SLIMCAT model overestimate denitrification due to equilibrium scheme

comparison with o3 sondes
Comparison with O3 sondes

SLIMCAT model (2.8 x 2.8) with CCM radiation scheme can successfully reproduce observed O3 in the polar region and midlatitude.

Large O3 depletion occurred by the end of March.

ozone loss
Ozone loss
  • Different local ozone loss and polar ozone loss
  • CTM with MIDRAD radiation scheme lead to less O3 loss
fully coupled microphysical model for denitrification
Fully Coupled Microphysical Model for Denitrification

A Lagrangian particle sedimentation model (DLAPSE, Carslaw, Mann et al.) has now been fully integrated with SLIMCAT code.

Example 3D results for 19/12/2002 505K

Modelled HNO3 decrease in good agreement with MIPAS

(see EU MAPSCORE Project)

studies of long term no 2 trend
Studies of Long-term NO2 trend
  • Two runs:
  • 1989 – 2003. ECMWF (ERA40/operational) winds. 7.5o x 7.5o x 20 levels (0-60km).
  • (1) Time-dependent source gases (CFCs, CH3Br, CH4, N2O etc from WMO [2003])
  • (2) As (1) but with fixed N2O after 1990.
3d ctm v lauder no 2 observations
3D CTM v Lauder NO2 Observations

Run 311 – with observed surface N2O trend.

Run 313 – As 311 but with constant surface N2O after 1990.

observed 1 1981 9 2003 modelled 1 1989 6 2003 lauder trends
Observed (1/1981- 9/2003) + Modelled (1/1989-6/2003) Lauder Trends

Trend model: linear trend, QBO, solar cycle, ENSO, offset annual cycle (K. Kreher, NIWA)

Trend values in %/decade

Model (with N2O trend)

Model (without N2O trend)


NOy, N2O should not show am/pm difference !

NO3 Chemistry
  • Night-time NO3 is independence on any other NOy species. The assumption of model steady state NO3 is good although model underestimates the observed NO3
  • Comparison with MK4 Balloon and aircraft data:
  • Model Captures denitrification/renitrification signal and major features of NOy species distribution well, but poor NO2 simulation in the LS;

SLIMCAT can simulate the observed low NOy well in the cold region, but overestimate denitrification at high T due to the equilibrium scheme

  • Improved Poalr Ozone loss

Different radiation scheme result in different transport and ozone loss

  • High resolution simulation gives better NOy partitioning
  • Coupled microphysical model (DLAPSE/SLIMCAT)

Successful denitrification compared with MIPAS

  • Long-term NO2 trend

Model captures the observed increase NO2 trend,positive N2O give a negative NOy

future work
Future work
  • Rerun SLIMCAT model using chemical species from Reprobus CTM as initialisation.
  • Comparison with MIPAS data (NOy..) for 2002/03 winter.
  • Intercomparison with other CTMs.