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The 2005 Nocturnal Boundary Layer Experiment The CO2 side of it. Starring Caroline Bain, Françoise Guichard Frédéric Baup, Laurent Kergoat, Yacouba Traore and Chris ‘Bekham’ Taylor with data from C. Lloyd, F. Lavenu, F. Timouck, V. Le Dantec P de Rosnay E Mougin , P Hiernaux and others. - PowerPoint PPT Presentation
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The 2005 Nocturnal Boundary Layer Experiment
The CO2 side of it.
Starring Caroline Bain, Françoise GuichardFrédéric Baup, Laurent Kergoat, Yacouba Traore and Chris ‘Bekham’ Taylor
with data from C. Lloyd, F. Lavenu, F. Timouck, V. Le DantecP de Rosnay E Mougin , P Hiernaux and others
Objectives
1) Obtain large scale surface fluxes of CO2
2) Document near surface atmosphere (mixing, monsoon flux, low level jet)
Method used in Brasil, Canada.
Method : on calm night, no wind, no turbulence, no vertical mixingCO2 from the surface accumulates in the first meters of air.
Using the atmosphere as a giant ‘cuvette’
How : mass balance of CO2 from CO2 vertical profiles during the same night
Material
Balloon
PTU sonde
Vaisala sonde plugged to the PTUdata radio-transmitted
Protocole : as many profiles as possible
Results
about 100 profiles from 7/08 to 22/08
a few nights suitable for CO2
(too windy, squall line arriving, technical failures)
CO2 data processed as of April 2006 :
14/0815/0817/08 CO2 Golden day18/08
Inversions, CO2, wind (jet)very consistent
Large accumulation over night
17/08/2006
Surface Flux = 5.1 mol/m2/s
u* around 0.01
120 km
MODIS NDVI. Orange = « bare » soil
16 08 2005 2h45 25.5 mm Kobou
120 km
14/08F=2.0
15/08F=4.6
18/08F=3.7
Conclusions
Vaisala carbocap+radio : great ! (Agoufou world record 700m)
Confirms 2004 high fluxes : order of 4-5 mol/m2/s
2005 = windy. Typical scenario : Jet starts, increases (speed and depth)see typical night og August 11th
On windy nights, shear driven turbulence creates ‘leaks’ of the ‘cuvette’.How much ? Sometime LLJ strong enough to mix the air completely. u* and richardson number filtering/parameterizing ?
Links with Low Level Jet : Is it a barrier for CO2 ? (some say yesour feeling is hum… interesting …)Would L.E.S help ? We’d like to try some.Some more processing to be done, and writing.
Perspectives 2006
No more night-time fluxes (habana !)
Field trip in Benin, Mali, (july/september).
Objective : try day-time Boundary Layer budgets
method : measure height of boudary layer + [CO2], T, Rv in the CBL.
Benin : Zi from profiler, UHF etc… [CO2] from kite (?)Mali : Zi from balloon (2.5 km !). Might be last balloon campaign