1. Evidence of nocturnal horizontal transport of CO 2 at an Amazon pasture/agricultural site Otávio Acevedo, Osvaldo Moraes, Rodrigo da Silva Universidade Federal de Santa Maria, Santa Maria, RS, Brazil David Fitzjarrald, Ricardo Sakai, Matt Czikowski Atmospheric Sciences Research Center, Albany, NY, USA

2. Motivation: CO 2 accumulation rates observed at the Km 77 flux tower What is causing the strong (and shallow) peak in CO 2 accumulation rate, around 2200 LST?

3. Hypothesis: the peak marks the arrival of the drainage flow, transporting CO 2 from the forest Km 77 tower

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

5. Boundary layer CO 2 profiling system (designed by Rodrigo da Silva)

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

8. Wind composites

9. Estimating advective transport

10. What is the accumulation rate during the evening peak? 6.8 ppm/h 6.1 ppm/h

11. Who cares? Estimations of the nocturnal respiration rates by the accumulation method are affected: Example: assuming a 50-m thick boundary layer and vertically homogeneous accumulation rate: (mgCO 2 m -2 s -1 )Without advectionWith advection Calm nights 0.210.17 Windy nights 0.140.10 Respiration rates:

12. Alternatively: assuming a 0.08-mg CO 2 m -2 s -1 respiration rate and vertically homogeneous accumulation rate: Boundary layer thickness: (m)Without advectionWith advection Calm nights 19.323.7 Windy nights 28.639.4 FUTURE WORK - Go further from simple evidences; - Make a more detailed quantitative analysis