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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