3D CTM Study of Polar and Mid-Latitude Ozone Depletion and Climate Change

Updated 3D CTM SLIMCAT (Recent improvements to the model)

Polar Ozone Loss (2004/05 Arctic winter compared with previous winters)

Mid-Latitudes Ozone change (Sensitivity Experiments of BrO Chemistry)

Conclusions

Wuhu Feng and Martyn ChipperfieldSchool of Earth and Environment,University of Leeds, U.K.

Acknowledgments Supported by NERC and SCOUT-O3 projects

SLIMCAT/TOMCAT 3D CTM• Off-line chemical transport model [Chipperfield, JGR, 1999]

• Extends to surface using hybrid - levels (SLIMCAT version). Variable horizontal/vertical resolution.

• Horizontal winds and temperatures from analyses (e.g. UKMO, ECMWF (ERA-40 or operational)).

• Vertical motion from diagnosed heating rates or divergence.

• Tropospheric physics: convection, PBL mixing etc.

• Chemistry: ‘Full’ stratospheric chemistry scheme (41 species, 160 reactions) with heterogeneous chemistry on liquid/solid aerosols/PSCs and an equilibrium denitrification scheme.

NAT-based denitrification scheme included.

http://www.env.leeds.ac.uk/slimcat

Updated 3D CTM: Arctic Ozone loss versus VPSC

Chipperfield et al.(GRL, 2005)

• Linear relationship between ozone loss and PSC volume;• First successful CTM simulation of seasonal O3 column loss and reproduces the past climate sensitivity of Arctic ozone depletion on T.

New T42 run

Obs

Old T15 runNew T15 run

Record-Observed Arctic Ozone Loss in 04/05 Winter

Quirin Schiermeier (Nature,2005)

The Largest Arctic ozone losses observed in 2004/2005

Cold Meteorological Conditions in 2004/2005 Arctic Winter

• Large Area of PSC formation as result of very low temperatures.

PSC AreaMinimum Temperature

Unusual polar vortex in 2004/2005 Arctic winter

Largest Polar Vortex since late January in 2004/2005 Arctic winter.

Comparison of SLIMCAT runs for past 11 years (ECMWF analyses)

456K 493K

• Largest NAT PSC area from late January in 2004/5• Largest Ice PSC area since late January in 2004/2005 Arctic winter.

Large PSC Occurrence in 2004/2005 Arctic Winter

456K 493K

Comparison with O3 sonde data

• Model gives a good simulation of O3, except overestimates the observations 300-100 hPa.

• Large O3 depletion between 400-650K with the largest ozone loss ~450K.

Ny-Alesund 79oN 12oE

1000

100

10

O3 (mPa)

O3 (vmr) O3 loss

400

450

500550

The

ta

700

350

300

Pre

ssur

e

Comparison with O3 sonde data

SLIMCAT reproduces the increase in December ozone and also reproduces the large decline of ozone mixing ratio from January to the mid-March.

Chemical loss

Passive O3

O3 Loss at 456K

Partial Column O3 Loss

Near-record large O3 loss in 2004/2005 Fast deactivation in March than 99/00

CTM BrO problem

Stratospheric bromine supplied by decomposition of VSL (very short lived) organics not considered in most global models as well as tropospheric BrO (Salawitch et al., GRL, 2005)

(Salawitch et al., GRL, 2005)

BrO Experiment

Multi-annual T15 run from 01/01/1977 Forced by ECMWF analyses

(ERA40+Operational) Exp336: Basic SLIMCAT run with new Bry EXP337:as EXP336 but with fixed halogen EXP338:as EXP336 but without the extra

bromine species (about 6 pptv less Bry)

Model captures the observed year-to-year variability Low Tropical column O3, and too large O3 in the mid and higher

latitude

Long-term Column Ozone Comparison (1978-2004)

Anomaly Mid-lat column ozone comparison

Model reproduce the observed decrease of mid-latitude column ozone, but large discrepancy occurred in 1988 and 1993.

Large effect of BrO chemistry in the mid-latitude ozone change

Basic RunBasic Run

Fixed Halogen

Fixed Halogen

35N-60N 60S-35S

Conclusions

• Updated New SLIMCAT CTM now gives a good simulation of seasonal O3 column loss

• Near-record Arctic ozone loss in 2004/2005 due to much more chlorine activation occurring on the largest surface areas of polar stratospheric clouds (PSCs) inside the polar vortex at very low temperatures, • However, less chlorine activation on PSCs in March 2005 than 2000 slowed down further chemical ozone loss in the late spring.

• Stratospheric bromine supplied by decomposition of VSL has been added in SLIMCAT and has important effect on mid-latitude ozone trends.