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 Acknowledgments Bhaswar Sen, Geoff Toon (NASA JPL) and all TOPOZ and VINTERSOL scientists  Studies of NO 3 Chemistry  Comparison with balloon and aircraft NOy data  Improved Arctic 2002/03 Winter ozone loss  Coupled microphysical model (DLAPSE/SLIMCAT)  Long-term NO 2 trends

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 2 nd 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, , 1999

NO 3 has very simple chemistry in the stratosphere: NO 2 + O 3 NO 3 + O 2 (1) NO 3 + h  NO 2 + O NO 3 + h  NO + O 2 NO 3 + NO 2 + M N 2 O 5 + O 2 (2) At night in the low-mid stratosphere NO 3 can still be in steady state: [NO 3 ] = k 1 [NO 2 ][O 3 ]/(k 3 [NO 2 ][M]) = k 1 [O 3 ]/(k 3 [M])  Nighttime [NO 3 ] determined solely by O 3 and T (no dependence on NOy!) Stratospheric NO 3 Chemistry

SALOMON Balloon observations J.B. Renard et al (CNRS, Orleans) Nighttime (moonlight) observations of NO 3, NO 2 and O 3. O3O3 NO 3 21/1/2002 Model underestimates observed NO 3, but steady-state a very good approximation km. (Not a problem due to O 3 which agrees well). Testing of NO 3 Chemistry from Balloon Observations

NO 3 /O 3 k for O 3 + NO 2 ln(k) Model underestimates NO 3 at high T Can derive best fit for k 1 : k 1 = 6 x exp(-2740/T) compared to JPL: k 1 = 1.2 x exp(-2450/T) Renard et al., J. Atmos Chem (submitted) Comparison of 6 SALOMON flights with SLIMCAT

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. 1)Transport problem (Different Cly and NOy in a given model lead to significant difference in chemical process). 2) Chemistry process 3) Radiative transfer process 4) Microphysics process 5) Complex interaction between theses processes Polar Ozone loss

Meteorology

Ozone Hole SLIMCAT reproduce the O 3 column Also show POAM PSC and MKIV location

MK IV Interferometer Measurements Trajectory of the MkIV payload from Esrange across Finland and into Russia on December 16, Fourier Transform Infra-Red (FTIR) Spectrometer By Jet Propulsion Laboratory in 1984Jet Propulsion Laboratory Remote-sensing by solar absorption spectrometry Provides stratosphere gases including NO y

NO y -N 2 O Correlation Denitrification Renitrification Model captures denitrification/renitrification signal well

NO y Partitioning Model Captures major features of NO y species distribution NO 2 is poor in the lower stratosphere

ClONO 2 and ClO The model overestimate ClONO2 due to underestimate the chlorine activation!

NO y Ratios HNO 3 and N 2 O 5, ClONO 3 overestimate, NO 2 poor below 25Km

M55 Geophysica Aircraft

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) SLIMCAT model overestimate denitrification due to equilibrium scheme

Comparison with O3 sondes SLIMCAT model (2.8 x 2.8) with CCM radiation scheme can successfully reproduce observed O 3 in the polar region and midlatitude. Large O 3 depletion occurred by the end of March.

Ozone loss  Different local ozone loss and polar ozone loss  CTM with MIDRAD radiation scheme lead to less O 3 loss

1999/2000 Arctic winter

Example 3D results for 19/12/ K Modelled HNO 3 decrease in good agreement with MIPAS (see EU MAPSCORE Project) A Lagrangian particle sedimentation model (DLAPSE, Carslaw, Mann et al.) has now been fully integrated with SLIMCAT code. Fully Coupled Microphysical Model for Denitrification

Two runs: 1989 – ECMWF (ERA40/operational) winds. 7.5 o x 7.5 o x 20 levels (0-60km). (1) Time-dependent source gases (CFCs, CH 3 Br, CH 4, N 2 O etc from WMO [2003]) (2) As (1) but with fixed N 2 O after Studies of Long-term NO 2 trend

Run 311 – with observed surface N 2 O trend. Run 313 – As 311 but with constant surface N 2 O after D CTM v Lauder NO 2 Observations

ampmampmampm NO ± ± ± ± ± ± 2.6 NO y -5.0 ± ± ± ± 2.2 N2ON2O 3.5 ± ± 0.3 Trend model: linear trend, QBO, solar cycle, ENSO, offset annual cycle (K. Kreher, NIWA) Trend values in %/decade Obs. Model (with N 2 O trend) Model (without N 2 O trend) NO y, N 2 O should not show am/pm difference ! Observed (1/ /2003) + Modelled (1/1989-6/2003) Lauder Trends

Conclusions  NO 3 Chemistry Night-time NO 3 is independence on any other NOy species. The assumption of model steady state NO 3 is good although model underestimates the observed NO 3  Comparison with MK4 Balloon and aircraft data: Model Captures denitrification/renitrification signal and major features of NO y species distribution well, but poor NO 2 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 NO y 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  Rerun SLIMCAT model using chemical species from Reprobus CTM as initialisation.  Comparison with MIPAS data (NOy..) for 2002/03 winter.  Intercomparison with other CTMs.