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 CO 2 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 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: C fit = a 1 + a 2 t + a 3 cos(2πt)+a 4 sin(2πt)+a 5 cos(4πt)+a 6 sin(4πt) Residuals: C resid = C – C fit 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 AsiaEuropeAmerica

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 2-7Plateau Rosa: TM5_eur, level 3-8 Obs

Amplitude vs phase Mt Cimone, CMN, 2165mPlateau Rosa, PRS, 3480m Sonnblick, SNB, 3106m Zugspitze/Schneefernerhaus, ZGP, 2960m

Flux towers: Tapajos, Brazil Mean diurnal CO 2 concentration, JJAMean CO 2 flux, JJA

Distribution of diurnal amplitude (JJA) Tapajos, BrazilBoreas, Canada

Synoptic variation in amplitude: Boreas Jul 24Aug 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 FraserdaleMace Head Neuglobsow Tapajos Amplitude normalised by mean amplitude across 12 months

Conclusions Valuable dataset for comparing modelled CO 2 with in- situ records To realistically sample most sites, probably need better than 2x2 o 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 CO 2 routinely used in inversions

Overview paper 1 Diurnal cycle only Probable target journal: Global Biogeochemical Cycles Almost complete, sec is possible addition Revised DEHM to be included, LMDZ fluxes now available Submission by end of May?