www.csiro.au

TransCom continuous experiment – overview and diurnal results

Rachel Law, Wouter Peters, Christian Rödenbeck and TC-continuous modellers

Outline – experiment overview

1. Background / Aim

2. Fluxes

3. Sites

4. Models

5. Output files

6. General features of output

Background

Continuous CO2 contains flux information that is not captured in inversions using monthly mean data

Pallas, Finland

Cape Grim, Australia

Fluxes

1. SiB biosphere fluxes

Hourly

Daily

Monthly

2. CASA biosphere fluxes

3 hourly

Monthly

3. Fossil - 1998

4. Ocean (Takahashi-02)

5. SF6

6. Radon

Sites – ‘allsite.list’

280 locations: modellers chose how to sample e.g. nearest grid-point or interpolate. Land and ocean point requested for coastal sites

Sites – ‘contsite.list’

100 locations:

Tracer concentration output for all model levels to 500 hPa

Met variables: u, v, pressure for all levels to 500 hPa

Trace gas flux, surface pressure, cloud cover, boundary layer height

Models

Output files

Submitted files for 2002 and 2003 (models run from 2000)

all.MODEL.INSTITUTION.yyyy.nc – contains trace gas concentration for 9 tracers at 280 sites. Also latitude, longitude, level, land arrays

tracer.MODEL.INSTITUTION.yyyy.nc – one file for each tracer, all levels to 500 hPa, 100 sites. Also tracer flux.

met.MODEL.INSTITUTION.yyyy.nc – met data

Processed files

SITE.MODEL.INSTITUTION.yyyy.nc – all the data for a single site for each model. Currently for 50 sites.

Things to watch out for …1. Check where model has sampled: lat, lon, land/ocean

2. Check level – in ‘all’ file some models always sampled surface layer, most chose levels above the surface for sites with altitude > ~100m

3. Profile information useful because removes altitude choice

4. Flux information very useful – confirms whether models sampling similar conditions

5. Some models were unable to submit all the data: IFS – 3 hourly output; DEHM – subset of tracers COMET – only ‘all’ files

6. Many models have been revised since their original submission to fix bugs or add missing data

Outline – diurnal results

1. Observations

2. Model data processing

3. Summer diurnal cycle

4. Case studies

5. Vertical resolution

6. Seasonal cycle of diurnal amplitude

7. Conclusions and paper

Observations

Data processing• 3 tracers : CASA (3hr), Taka02, fossil98

• Fit with trend and harmonics: Cfit = a1 + a2t + a3cos(2πt)+a4sin(2πt)+a5cos(4πt)+a6sin(4πt)

• Residuals: Cresid = C – Cfit

• Sum residuals : CASA+Taka02+fossil98

• For each month, average residuals by hour of day to give mean diurnal cycle

• Average June, July, August; calculate amplitude as max concentration – min concentration

• NB daily diurnal amplitude calculated at fixed time of day (may be <= max-min conc for that day)

Summer diurnal amplitude (JJA)

Black cross – models

Red dot – observations

Sites plotted by continent and latitude

Large range – models span observed

Sampling location contributes e.g. high altitude sites

Asia Europe America

Case studies: 1. Mikawa-Ichinomiya

Colour and line style indicate flux magnitude

Zero (blue), small (cyan), moderate (green), large (red) biosphere flux

Small (solid), large (dash) fossil flux

Mean summer diurnal cycle

Black, obs; colours, models

Which level represents high altitude sites?

Mt Cimone: LMDZ level 2-7 Plateau Rosa: TM5_eur, level 3-8

Obs

Obs

Amplitude vs phase

Mt Cimone, CMN, 2165m Plateau Rosa, PRS, 3480m

Sonnblick, SNB, 3106m Zugspitze/Schneefernerhaus, ZGP, 2960m

Flux towers: Tapajos, Brazil

Mean diurnal CO2 concentration, JJA Mean CO2 flux, JJA

Distribution of diurnal amplitude (JJA)

Tapajos, Brazil Boreas, Canada

Synoptic variation in amplitude: Boreas

Jul 24 Aug 18

Is model vertical resolution important?

Concentration to flux ratio at 7 surface sites

Ptp diurnal amplitude concentration divided by CASA flux amplitude plus fossil flux

Most models give similar ratio

Small influence from vertical resolution

Some variation across sites e.g. TPJ vs FRD

Seasonal cycle of diurnal amplitude

Fraserdale Mace Head

Neuglobsow Tapajos

Amplitude normalised by mean amplitude across 12 months

Conclusions

• Valuable dataset for comparing modelled CO2 with in-situ records

• To realistically sample most sites, probably need better than 2x2o resolution

• Moderate to high altitude sites remain a challenge

• For the diurnal cycle most models show similar strengths and weaknesses compared to observations

• Seasonal and synoptic changes in diurnal amplitude show some model skill

• More detailed analysis required before observed diurnal cycle of CO2 routinely used in inversions

Overview paper 1

• Diurnal cycle only

• Probable target journal: Global Biogeochemical Cycles

• Almost complete, sec 5.1.2 is possible addition

• Revised DEHM to be included, LMDZ fluxes now available

• Submission by end of May?