%0 Book Section
%@nexthigherunit 8JMKD3MGPCW/46JKC45
%@holdercode {isadg {BR SPINPE} ibi 8JMKD3MGPCW/3DT298S}
%X Tropical forest represents significant sources/sinks for trace gases (C02, O], CH4), and the exchange of CO2 between forest and the atmosphere is an important component of the global carbon cycle because of its greenhouse effect. The secular increase of C02 concentration is reasonably well defined (Keeling and Whorf, 1994) but a full comprehension of C02 cycles for different biomes and its impact on climate and ecology is not well understood. Baldocchi et al. (1996) have addressed this issue based on the conclusions of a workshop to discuss the strategies for monitoring and modeling CO2 fluxes over terrestrial ecosystems. The diurnal cycle of atmospheric CO2 reflects the exchange of metabolic carbon between the atmosphere and the vegetation-soil system. The typical behavior of CO2 concentration shows an increase during the night, when soil emissions and respiration combine as a source of CO2 to the atmosphere and start to decrease during mid morning when atmospheric CO2 is taken up by the vegetation. The nighttime CO2 flux is positive, reversing its sign (to downward) in the early morning. Although the nighttime CO2 flux above the canopy is a sum of aIl CO2 released by the vegetation and the soil, the atmospheric stability near the canopy does not allow mixing between the rich CO2 air inside canopy and that above it. Fitzjarrald and Moore (1990) have observed some events (waves) that occur during the night in the Amazon forest and associate these events with periods ofhigher turbulent mixing between the canopy and the atmosphere, leading to increasing of values of C02 exchange. They point out that these events occur on average 5 times during the night with a time interval ranging from 25 to 60 minutes .They also noted that these events happen when the windspeed above the canopy is typicallyaround 1.8 m S.I. Grace et al. (1995) noticed that in the early morning there was a higher flux ofC02 out ofthe canopy due to the onset of turbulence. They pointed out that the onset of turbulence disrupted the stable layer at lhe crown, allowing mixing between air, wich has been accumulating CO2, and the atmosphere. They have called this phenomena the moming ventilation and it has high values of C02 flux the maximum value observed in tropical forest (at Rondônia) is +20 ?mol m-2s-l.
%E Lal, R.,
%E Kimble, J. M.,
%E Stewart, B. A.,
%T Carbon dioxide measurements in the nocturnal boundary layer over Amazonian forest
%@isbn 1-56670-485-5
%S Advance soil science
%@secondarytype PRE LI
%K climatologia, meteorologia.
%B Global climate change and tropical ecosystem
%@usergroup administrator
%@usergroup fabia
%@group DMA-INPE-MCT-BR
%@e-mailaddress fabia@cptec.inpe.br
%3 11747.pdf
%C Boca Raton
%@copyholder SID/SCD
%@secondarykey INPE-11747-PRE/7106
%F self-archiving-INPE-MCTIC-GOV-BR
%2 cptec.inpe.br/walmeida/2004/11.03.15.16.39
%@affiliation CPTEC-INPE-Cachoeira Paulista-12630-000-SP-Brasil
%@versiontype publisher
%P 391- 403
%4 cptec.inpe.br/walmeida/2004/11.03.15.16
%D 2000
%@documentstage not transferred
%V 1
%A Fisch, Gilberto,
%A Culf, A. D.,
%A Malhi, Y.,
%A Nobre, Carlos Afonso,
%A Nobre, Antonio Donato,
%@dissemination NTRSNASA; BNDEPOSITOLEGAL.
%@area MET