Evaluating a New Deposition Velocity Module in the Noah Land-Surface Model

By Dev Niyogi

Purdue University

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The community Noah land-surface model (Noah LSM) has been modified to
couple with a photosynthesis-transpiration scheme (GEM) to estimate the deposition veloc-
ity (Vd ) for air quality studies. This new capability of the Noah-GEM model was tested
in a point version of the National Center for Atmospheric Research-High Resolution Land
Data Assimilation System (HRLDAS). Ozone Vd observations from June 1–30, 2002 over the
AmeriFlux forested site located at Niwot Ridge, Colorado, USA (40◦ 1 58 N; 105◦ 32 47 W)
were used. The model reasonably captures Vd variations for both dry and wet conditions but
has problems at nighttime. Experiments were performed to assess the sensitivity of Vd cal-
culations to surface characteristics related to vegetation and soil parameters. The results
indicated that Vd values are sensitive to accurate specifications of the leaf area index (LAI)
and a lesser extent to vegetation type, maximum stomatal resistance (Rsmax ) and soil texture
prescription. The model sensitivity to canopy resistance was noted for both daytime and
nighttime. For this forest site, neither soil textures nor soil moisture appeared to affect Vd
calculations significantly, though they affected the surface heat-flux estimation particularly
under low soil moisture conditions. Therefore, the Vd estimation in the Noah model can be
enhanced by either site-specific LAI or assimilating regional normal difference vegetation
index information for specific time periods. Results also highlighted the need to lower the
current constant Rsmax value used in Noah and other land-surface models.

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Researchers should cite this work as follows:

  • Dev Niyogi (2011), "Evaluating a New Deposition Velocity Module in the Noah Land-Surface Model ," https://mygeohub.org/resources/204.

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