A direct carbon budgeting approach to study CO2 sources and sinks

ICDC7Broomfield, 25-30 September 2005

C. Crevoisier1

E. Gloor1, J. Sarmiento1, L. Horowitz2, S. Malyshev2, E. Shevliakova2, C. Sweeney3, A.

Andrews3, P. Tans3

•Aircraft measurements:

•Determining the location, the intensity and the evolution in time of the sink of carbon in the northern hemisphere remains one of the main issues in carbon cycle study.

•Huge amount of measurements of CO2 by aircraft and tall towers will soon be available at many locations across the United States, in the framework of the North American Carbon Plan.

•This should allow the design of new estimation methods, possibly avoiding the use of a priori information.

Direct carbon budgeting approach and test of the network.

Introduction

Measurements up to 8 km once per week.

19 sites + 3 new sites (2006).

Let’s put a ‘box’ over the region where we want to estimate surface fluxes.

Direct carbon budgeting approach

surface CO2

fluxes

In

Out

Exchanges with the upper atmosphere

(convection, advection)

h dC/dt = (Fhin-Fh

out) - Fvertical+ Fsurf

Observations aircrafts + towers.

€

ρ r

u χ

€

rn

Following the existing network, we chose:

•h=8km.

•box over the US + South Canada.

?

Carbon mass budget

Simulations of atmospheric CO2

dC/dt

Fsurf

2

0

-4

-2

MOZART

atmospheric transport/chemistry model

NCEP (2º2º, 29 levels)

CO2

air/land fluxesmonthly fossil fuel emissions air/sea fluxes

CASA modelGFDL, J. Dunne[Blasing et al. 2004]

dC/dt = (Fhin-Fh

out) - Fvertical+ Fsurf

From these simulations, we can compute each term of the carbon mass budget.

(GtC

.mon

th-1)

what we want to retrieve…

[Horowitz et al. 2003]

[Randerson et al. 1997]

month

Horizontal Fluxes: Advection

dC/dt = (Fhin-Fh

out) - Fvertical + Fsurf

e.g.: November

+-

+

-

Evolution of the horizontal fluxes along the edges of the box: income and outcome pathways.

In Out

InOut

Center: NCEP winds

Horizontal Fluxes: Advection

dC/dt = (Fhin-Fh

out) - Fvertical + Fsurf

e.g.: November

-

+

-

Evolution of the horizontal fluxes along the edges of the box: income and outcome pathways.

Out

In

Center: NCEP winds

Monthly variation (sum along the edges)

Fhin-Fh

out

dC/dt

Fsurf

2

0

-4

-2(GtC

.mon

th-1)

month

Vertical fluxes: convection (and advection) at h=8 km

Convection fluxes summer - h=8km

dC/dt = (Fhin-Fh

out) - Fvertical + Fsurf

Fhin-Fh

out

dC/dt

Fsurf

Monthly variation

convection

vertical advection

2

0

-4

-2

month(k

gC.m

-2.s

-1)

At h=8 km, the vertical fluxes are small but the lower the altitude, the higher the convection flux.

Vertical fluxes: convection (and advection) at h=8 km

8 km

5 km

700m

Convection fluxes summer - h=8km

Monthly convection flux at different levels

dC/dt = (Fhin-Fh

out) - Fvertical + Fsurf

Fhin-Fh

out

dC/dt

Fsurf

Monthly variation

convection

vertical advection

2

0

-4

-2

0

-0.2

-0.6

-0.4

(GtC

.mon

th-1)

month(k

gC.m

-2.s

-1)

Study of the Observation Network

From CO2 simulated at 19 sites, we infer CO2 in the whole US.

Use of a geostatistical interpolation technique: kriging.

Study of the Observation Network

From CO2 simulated at 19 sites, we infer CO2 in the whole US.

Use of a geostatistical interpolation technique: kriging.

Monthly mean error on CO2 mixing ration (integrated content 0-8 km)

(ppm

v)

Error on CO2 mixing ratio after interpolationWinds

Surface fluxes

Example: Error in July

The corresponding error on flux estimation is 19.3 %.

1

0

-1

1.5

0

-1.5

(ppm

v)

(kgC

.m-2.y

r-1)

The error on flux estimation is reduced to 8.3 %.

Network design

A way to reduce the interpolation error: adding a few stations…

e.g.: one more station in NW [55N;110W]

1

0

-1

1

0

-1

Monthly error on CO2 mixing ratio - August

Planned network + 1 station

(ppm

v)

Extending the method to higher spatial (0.5°) and temporal (hourly) resolutions.

Conclusions and perspectives

•The main target is the convection. Some ways to estimate it:

With a few more stations in NW and SW, we should be able to have an accurate description of CO2 in the US.

•Estimated surface fluxes = biospheric fluxes + fossil fuel emissions.

Using other tracers (O3, APO~O2+1.1xCO2, SF6, others?).

CO2 from satellite (measurements in the mid to high troposphere) to fix the top of the box.

•A direct budgeting approach seems possible with the high density measurements … at least on simulations!

use of other tracers to separate both contribution (14CO2).

Applying the method in restricted regions where no convection.

Estimation of the errors (interpolation, convection, etc).