 |
| Titel |
Estimating a Lagrangian Length Scale using CO2 Measurements in Two Plant Canopies |
| VerfasserIn |
Shannon Brown, Jon Warland, Ralf Staebler, Eduardo Santos, Claudia Wagner-Riddle, Paul Bartlett |
| Konferenz |
EGU General Assembly 2011
|
| Medientyp |
Artikel
|
| Sprache |
Englisch
|
| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 13 (2011) |
| Datensatznummer |
250050919
|
|
|
|
|
|
| Zusammenfassung |
| Studies of trace gas fluxes have advanced the understanding of bulk interactions between the
atmosphere and ecosystems. Micrometeorological instrumentation is currently unable to
resolve vertical scalar sources and sinks within plant canopies. Analytical Lagrangian
equations capable of predicting concentration profiles from known source distributions
provide the opportunity to calculate source/sink distributions through inverted forms of these
equations. Previous studies have shown that the inverse equations generally produce
reasonable source profiles in a variety of canopies. However, the inverse equations can be
unstable and give erratic results. Uncertainty concerning estimates of the essentially
immeasurable Lagrangian length scale (LL), a key input to describe the transport of the
scalars, compromises the source predictions. Most parameterizations of LL are based on
measurements of the Eulerian length scale. Recent research indicates that a possible cause of
error is the inability of the LL profiles to capture scalar movement in decoupled flow
situations.
The present study seeks to investigate LL in plant canopies by using field measurements
to constrain the Warland and Thurtell (2000) analytical Lagrangian equation. Measurements
of two sources, the net CO2 flux and soil CO2 flux, along with in-canopy profiles of CO2
concentrations taken in a corn field and mixed forest near Toronto, Ontario, Canada, provided
the information required to solve for LL. The inversion to solve for LL is also highly
unstable. A test of the inversion with wind tunnel data of turbulence statistics, a known heat
source, and temperature profiles from Coppin et al. (1986) shows that the parameter
estimation routine is capable of closely estimating the measured Eulerian length scale.
Inversions using the field data only produces erratic and nonsensical length scale profiles,
which suggests that the flow in the canopy may not be captured by the length scale
alone. Results contrasting the parameter estimations from both canopies will be
presented. |
|
|
|
|
|
|