Amazon, tropical forest
Regional estimates of surface CO2 exchange rates using atmospheric boundary layer budgeting techniques above tropical forest near Manaus, Brazil were made in comparisons with simultaneous measurements from two eddy covariance towers below (Lloyd et al., 2007).
The study area was located within a Biological Reserve of the Instituto Nacional de Pesquisas da Amazonia (INPA), consisting of tropical forest canopy of on average 30 to 40 m height but with occasional emergent trees to 50 m.
During the period 7–21 July 2001, profiles of CO2 from 100 m to 3000 m above ground level were obtained on 14 occasions. Profiles were typically made either at around 10:00 h Local Time, LT, (morning conditions) or 16:00 h LT (afternoon conditions).
Morning flights were timed to coincide with the early period of convective growth, during which respired CO2 trapped within the forest canopy overnight was anticipated to have just been mixed into the growing ABL (Lloyd et al., 1996). Afternoon flights coincided with the time at which the sensible heat flux from the rainforest canopy into the ABL was approaching zero.
In all cases, flights were made between two eddy covariance flux measurement towers (“C14” and “K34”) situated about 11 km from each other. Measurement flights were conducted as part of the Cooperative LBA Airborne Regional Experiment (LBA-CLAIRE 2001) using a Bandeirante aircraft (Embraer EMB 145) equipped with a system designed for the accurate and continuous profiling of atmospheric CO2 concentrations (Lloyd et al., 2002) using an LICOR 6251 infrared gas analyzer (IRGA).
Air flow through the analyzer was at a rate of 1.7 to 2.5×10−5 m ³ s−1, depending on the ambient pressure. The pressure of the IRGA cell was continuously monitored using a Vaisala PTB 100 A pressure transmitter connected via a polyurethane tube to the output port of the sample cell. The analogue Vaisala output was passed back to the LICOR 6251 for pressure corrections according to the customized software.
The LICOR pressure corrected CO2 mole fractions and the raw barometer output were logged at 1 Hz frequency with a Campbell CR21X laptop computer combination. The IRGA was recalibrated regularly during each flight, typically at every 250 m elevation increments using span gases of approximately 340 and 380 μmol mol−1. Also connected to the data logger with a 1 Hz acquisition time was instrumentation to measure humidity and temperature (model HMP35D, Vaisala, Helsinki, Finland), mounted on the port wing close to the gas inlet tubes (directly in the airstream) and a second barometer giving the cabin pressure.
Continuous-profile data were reprocessed off-line to take into account the inability of the IRGA software to correct for changes in atmospheric pressure on the raw output signal.
Variables & Instruments
- Profiles of CO2 - infrared gas analyzer IRGA (LI6251)
- Mass fow - high precision mass fow controller 1179A53CS1BVS140
- Air pressure - pressure transmitter PTB101B, Vaisala
- Air temperature and humidity - temperature-humidity-sensor HMP35D and HMP45D, Vaisala
- CO2 mole fractions - datalogger CR21X, Campbell Scientific & laptop
Beck, V., Chen, H., Gerbig, C., Bergamaschi, P., Bruhwiler, L., Houweling, S., Rockmann, T., Kolle, O., Steinbach, J., Koch, T., Sapart, C. J., van der Veen, C., Frankenberg, C., Andreae, M. O., Artaxo, P., Longo, K. M., Wofsy, S. C. (2012). Methane airborne measurements and comparison to global models during BARCA. JOURNAL OF GEOPHYSICAL RESEARCH-ATMOSPHERES, 117: D15310. doi:10.1029/2011JD017345
Chen, H., Winderlich, J., Gerbig, C., Höfer, A., Rella, C. W., Crosson, E. R., Van Pelt, A. D., Steinbach, J., Kolle, O., Beck, V., Daube, B. C., Gottlieb, E. W., Chow, V. Y., Santoni, G. W., Wofsy, S. C. (2010). High-accuracy continuous airborne measurements of greenhouse gases (CO2 and CH4) using the cavity ring-down spectroscopy (CRDS) technique. Atmospheric Measurement Techniques, 3(2), 375-386.
Kuhn, U., Ganzeveld, L., Thielmann, A., Dindorf, T., Schebeske, G., Welling, M., Sciare, J., Roberts, G., Meixner, F. X., Kesselmeier, J., Lelieveld, J., Kolle, O., Ciccioli, P., Lloyd, J., Trentmann, J., Artaxo, P., Andreae, M. O. (2010). Impact of Manaus City on the Amazon Green Ocean atmosphere: ozone production, precursor sensitivity and aerosol load. Atmospheric Chemistry and Physics, 10(19), 9251-9282. doi:10.5194/acp-10-9251-2010.
Lloyd, J., Kolle, O., Fritsch, H., De Freitas, S. R., Dias, M., Artaxo, P., Nobre, A. D., De Araujo, A. C., Kruijt, B., Sogacheva, L., Fisch, G., Thielmann, A., Kuhn, U., Andreae, M. O. (2007). An airborne regional carbon balance for Central Amazonia. Biogeosciences, 4(5), 759-768.