Evidence of nocturnal horizontal transport of CO2 at an Amazon pasture/agricultural site

Otávio Acevedo, Osvaldo Moraes, Rodrigo da SilvaUniversidade Federal de Santa Maria, Santa Maria, RS, Brazil

David Fitzjarrald, Ricardo Sakai, Matt CzikowskiAtmospheric Sciences Research Center, Albany, NY, USA

Motivation: CO2 accumulation rates observed at the Km 77 flux tower

• What is causing the strong (and shallow) peak in CO2 accumulation rate, around 2200 LST?

Hypothesis: the peak marks the arrival of the drainage flow, transporting CO2 from the forest

Km 77 tower

- Largest accumulation rates are observed when northwesterlies (from the forest, downslope) prevail;- Smallest accumulation rates for northerlies (from unforested regions)

Boundary layer CO2 profiling system (designed by Rodrigo da Silva)

The system operated for 5 nights at Km 77 (november 2003)

Wind composites

Estimating advective transport

x

CO

t

CO 2

ADV

2

U

m 00001Δ

ppm 30CO

m/s 5.0

2

x

U

ppm/h 4.5t

CO

ADV

2

What is the accumulation rate during the evening peak?

6.8 ppm/h

6.1 ppm/h

Who cares?• Estimations of the nocturnal respiration rates by the

accumulation method are affected:

zx

CO

t

CO2CO22

FU

Example: assuming a 50-m thick boundary layer and vertically homogeneous accumulation rate:

(mgCO2 m-2 s-1) Without advection With advection

Calm nights 0.21 0.17

Windy nights 0.14 0.10

Respiration rates:

Alternatively: assuming a 0.08-mg CO2 m-2 s-1 respiration rate and vertically homogeneous accumulation rate:

Boundary layer thickness:

(m) Without advection With advection

Calm nights 19.3 23.7

Windy nights 28.6 39.4

FUTURE WORK

- Go further from simple evidences;- Make a more detailed quantitative analysis