ACCMIP simulations of Climate Change impacts on CO-tracer

transport

Ruth Doherty, Ian Mackenzie U. Edinburgh Paul Young, Oliver Wild U. Lancaster

Mieyun Lin GFDL, Michael Prather UCI,ACCMIP modellers …

ACITES York, Dec 2nd 2013

Uses of a CO-Tracer

What can a passive CO-tracer with a 50-day lifetime tell us about transport in a CCM?What are its strengths and weaknesses?Can we use this CO-tracer to create a metric of vertical overturning in the troposphere?Focus on climate change effects on transport …

First …CO tracer results from HTAP (TP1x)

Seasonal cycle of the boundary layer exchange ratio=for well-mixed source region, →0 for stable conditionsLeft column driven with ECMWF, middle NCEP/CMCRight column using GEOS or GCM dataMost models within ensemble meanModel E no convective transportModel I – high bias → too rapid exchange→low surface concentrations?

CO tracer results from HTAP for Present and Future Climates

Implemented a CO tracer for a species with a 50 day lifetime emitted as for CO over the NA, EU, EA and SA source regionTwo chemistry-climate models STOC-HADAM3 and UM-CAM both driven by the same SSTs from the HadAM3 GCMResults for 5-year (10-year) 2000s and 2100s climates

CO-Tracer results from NA

5 year (10-year) annual-average surface NA CO tracer concentrations for 2000 climateDifference in 5-year annual-average surface CO-tracer concentrations between the 2095 and 2000 climates In the future climate, less CO tracer from NA remaining at the surface especially over the Great Plains region but more over the E. and W. United States and outflow regions

And for other regions…

Similar results for the other three HTAP regionsDistinct patterns of adjacent areas of lower and higher surface CO tracer concentrations Shift in circulation within all the regions that extends across the regional boundaries between present day and futureBut only one representation of climate change….Full vertical picture

Atmospheric Chemistry & Climate Model Intercomparison Project (ACCMIP)

Another model intercomparison with a focus on climate change Only “CO-direct”- a tracer with a 50-day lifetime emitted form all CO emission sources across the globeDirect= emissions from fossil and bio fuel combustion, biomass burning, plant and soil releasePresent-day = ACChist= “2000s” ~10 years (SST climatology)Future = RCP 8.5 “2100s” ~10 years (SST climatology

Surface annual-mean CO tracer concentrations for 2000s

Like CO sources

Surface annual-mean CO_T:2100s-2000s (2000s-1990s)

Shifts in surface patterns over major source regionsSome model to model similarities (eastern USA, S EU) and some differences → some evidence of reproducibility of shiftsSignal larger than decadal variability (as in CMAM)Causes?

Surface annual-mean CO_T:2100s-2000s (2000s-1990s)

Zonal-mean CO-tracer decadal mean 2000s (top)Diff CO-tracer decadal mean 2100s-2000s (bottom)

Reasonable agreement Surface –general decreases strongest at Equator (up to 5-10 ppb), increases 10°N & 30°N (up to 2-5 ppb) UT- tropics reductions of 1-2ppb (up to 5 ppbv) – weaker Hadley circulation signal?UT- extra-tropics esp NH- enhanced STE /higher tropopause (Fang et al. 2011 JGR)

Co-tracer decadal mean 2000s 1000-900hPa average (top) and 400-200 hPa average (bottom)

Fairly similar patterns across models

Gradient co-tracer (1000-900)-(400-200) hPa 2000s (ppb)

Positive values over emission source regions and nearby outflowNegative values for outflow especially S. HemisphereSimilarish picture in 2100s (not shown)

Difference 2100s-2000s co-tracer (1000-900) hPa (top) and 400-200

hPa (bottom)

At 1000-900 hpa: mixed signal N and S of equator (global mean decreases but with N. Africa and Asia increases)At 400-200 hPa: tropical signal more uniform across hemispheres (large decreases) and large increases at N. poles (STE, higher tropopause)

Difference 2100s-2000s co-tracer gradient

(1000-900)-(400-200) hPa gradient increases over tropical land but decreases elsewhere especially northern polar latitudesTropics: co-tracer gradient strengthens over emission regions (Fang et al. suggest reduced convective mass flux)

Vertical overturning?Model name UM-CAM GISS NCAR-

CAM3.5CMAM STOC-HadAM3

           Global-mean gradient co-tracer 2000s/2100s

7.847.01

8.107.74

7.016.22

7.697.46

6.286.12

 % change fut-pres  -10.5%  -3.4%  -11.3%  -3.0%  -2.5% 30°S-0° gradient2000s/2100sChange 2100s-2000s (land)

 2.11.6-0.5 (-0.4)

 4.24.9-0.7 (3.5)

 1.40.23-1.2 (-1.9)

1.52.2-0.7 (2.8)

 1.00.75-0.25 (-0.32)

15°S to 15°N2000s/2100sChange 2100s-2000s

12.011.5-0.5 (-1.8)

14.616.11.5 (5.2)

13.913.1-0.8 (-0.6)

13.113.90.8 (4.2)

12.912.90.0 (-0.2)

0°-30°N gradient2000s/2100sChange 2100s-2000s

16.916.7-0.2 (0.4)

17.618.50.9 (3.5)

16.116.20.1 (2.0)

18.219.41.2 (5.0)

15.416.30.9 (1.9)

30°N-60°N gradient2000s/2100sChange 2100s-2000s

19.117.2-1.9 (-2.1)

16.914.9-2.0 (-1.8)

18.917.6-1.3 (-1.7)

19.818.0-1.8 (-1.5)

14.314.50.2 (0.5)

60°N-90°N gradient2000s/2100sChange 2100s-2000s

9.36.0-3.3 (-3.4)

8.14.5-3.6 (-3.6)

11.910.0-1.9 (-1.9)

13.410.2-3.2 (-3.4)

8.55.9-2.6 (-2.7)

ConclusionsShifts in circulation patterns of surface CO-tracer around major emission source regionsLargest CO-tracer decreases in tropics -weaker Hadley circulation but confined areas of increased CO-tracer at the Equator also (convection scheme?)Large uniform increases in northern mid-latitudes upper troposphere and reduced LT-UT gradient Mixed gradient changes over tropics- increases over N. tropical landContributions from changes in tropopause height/STE and from changes in upwelling

Seasonal (MAM and JJA CO-T changes: 2100s-2000s (2000s-1990s)

UM-CAM, GISS similar between seasons, more increases in tropics in JJACAM 3.5 very different in tropics

Fang et al. (2011) JGR

20 year average zonal mean distribution of CO tracer (unit: ppbv) during 1981–2000 (black solid contour) and the changes of that tracer from 1981–2000 to 2081–2100 (color shaded) Blue dashed and dotted lines show the tropopause location during 1981–2000 and 2081–2100, respectivelyOnly changes significant at the 95% confidence level are shown

Vertical overturningModel name UM-CAM GISS NCAR-

CAM3.5CMAM STOC-

HadAM3Michael’s suggestion

         

1. emiss_co4*area: total over all grid boxes (kg s-1)

18819.8 19622.4

19344.5 19307.0 19327.1

           2. emiss_aco / Mass air (normalised to a 125m cell height)ratio Mair/MCO: mean (ppb day-1) 2000s/2100s

23.54 24.05

24.4424.75

23.48 23.76

23.94 24.36

24.27 24.72

           3. diff (925-325 hpa)2 co-tracer: mean of all grid cells (ppb)2000s/2100s

3.683.64

4.604.41

3.232.83

4.474.85

4.024.07

           4. mean grad co-tracer (ppb) /mean(emiss co in ppb day-1)**(days)

0.1570.151

0.1880.178

0.1370.119

0.1870.199

0.1650.173

5. diff fut-pres of 11.(day) and (%)

-0.005(-3.2%)

-0.010(-5.4%)

-0.018 (-13.2%)

+0.012(+12.4%)

+0.007(+4.3%)

           6. Fang et al. relative change in the COt gradient change but between 925hPa and 325hPa and (2nd left term)***

-2.7% -4.3% -12.5% +8.9% +2.4%

Results from ACCMIP monthly data: italics = rcp 8.5, nonitalics = acchist 2000 – 10 yearsNotes:1cmam and stoc-hadam3 are very slightly different. 2nearest model layer to 925 and 325 hpa (not much divergence between models)- need to interpolate**~3ppb/~24 ppb/day=0.14-0.19 days- 3.x hours seems not sensible. Not sure that this division tells us truly about transport between the two levels- would lifetime (50days) not come in? (checked emission field in ppb looks sensible)*** Fang et al. use lifetime and a 2 box model for the LT and FT. I’ve calculated the same relative change in the COt gradient change but between 925 - 325 hPa. (They calculate FT-LT )Message: Both methods give a similar idea about global mean changes LT-UT of (range -13% to +10/2%) but these are the combined result of different responses in tropics and high latitudes (be nice to separate tropics especially land tropics but not sure of validity)Fang Y., A. M. Fiore, L. W. Horowitz, A. Gnanadesikan, I. Held, G. Chen, G. Vechhi, H. Levy (2011) Impacts of changing transport and precipitation on pollutant distribution in a future climate, J. Geophys. Res.>, doi:10.1029/2011JD016105.