Analysis of periods with strong and coherent advection

1
Analysis of periods with strong and coherent
advection

• Marcelo Zeri, Corinna Rebmann, Pavel Sedlak, and
  Christian Feigenwinter

2
Overview

• Advection patterns
• East
• Northwest
• Agreement with modeling results
• Reverse flow at the lee side
• CO2 accumulation at the downwind side
• Removal and gap-filling of periods with advection
• Conclusions

3
Advection at the Wetzstein site

• Three sites
• Wetzstein VA, HA
• Specific sectors for adv

Feigenwinter et al. (2008), Agr. For. Met.
4
Pattern 1 easterly winds

• VA and HA important
• High air pressure
• Low u stable stratification

Zeri, M., Rebmann, C., Sedlak, P. and
Feigenwinter, C., In preparation.
5
Pattern 2 northwesterly winds

• HA high VA negligible
• Low pressure
• High u neutral stratification

Zeri, M., Rebmann, C., Sedlak, P. and
Feigenwinter, C., In preparation.
6
Cross-ridge flows

• Cross-ridge flows gt advection
• Expected from hill flow modeling

Zeri, M., Rebmann, C., Sedlak, P. and
Feigenwinter, C., In preparation.
7
Flow over the hill

• Modeling of the sub-canopy wind speed for a
  forested hill (Finnigan and Belcher, 2004)
• Vertical profiles of the disturbance ?u induced
  by the hill

• Pressure gradient disturbing the flow
• Reverse flow at the lee side of the hill

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Reverse flow at the lee side

• Agreement with modeling work of the flow over a
  low hill
• Support the existence of sub-canopy flows

Zeri, M., Rebmann, C., Sedlak, P. and
Feigenwinter, C., In preparation.
9
Accumulation at the downwind side

• CO2 gradient at 1.5 m
• Agreement with LES modeling (Ned Patton)

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Advection versus friction velocity

• VA higher at low u
• Positive and negative outliers
• HA higher at high u
• Only positive outliers

• Advective fluxes occur constantly
• Solution removal of situations with cross-ridge
  flows
• Which wind direction sectors?

Zeri, M., Rebmann, C., Sedlak, P. and
Feigenwinter, C., In preparation.
11
Advection versus friction velocity

• VA still higher at low u same average VA
• HA lower average for high u

• Advection accounted (HA VA) 79
• Annual sum net uptake increases only for 2006
• Data removed 43

Zeri, M., Rebmann, C., Sedlak, P. and
Feigenwinter, C., In preparation.
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Conclusions

• Advection related to cross-ridge flows
• Agreement with modeling works
• Reverse flow at the lee side
• Accumulation at the downwind side
• Removal and gap-filling
• 43 of nocturnal data account for 80 of
  advection
• Higher net uptake only in 2006

13
Acknowledgements

• The field crew from the Max Planck Institute for
  Biogeochemistry
• All the ADVEX Experiment participants