Steve Oncley

Project Scientist II
TIIMES - EOL
BEACHON & BGS

Contact Information:
PO Box 3000, Boulder, CO 80307-3000
Office: FL1-2069
Telephone: 303-497-8757
Email: oncley@ucar.edu
Home Page | Integrated Surface Flux System

Project Summary:

Horizontal Advection of Carbon Dioxide

My TIIMES research has been focused on understanding horizontal advection of carbon dioxide in forest canopies, which is thought to be a significant process controlling the Net Ecosystem Exchange (NEE) of carbon. This research has been a collaboration with Jielun Sun (MMM/TIIMES), Russ Monson (University of Colorado, Biology), and others. Because there exist very few data sets that investigate this problem, we are carrying out a series of experiments at the University of Colorado's Ameriflux site on Niwot Ridge, CO, in collaboration with Prof. Russ Monson:

Click on picture to view the entire figure.

 

A few of the many photos from the NIWOT07 Field Experiment.
Additional photos

 

• 2002 (Niwot02): EOL (then ATD) set up three towers of the Integrated Surface Flux Facility (ISFF) at 75m spacing to augment the in-canopy measurements being made by CU and the US Geological Survey. We also developed, with NCAR/Biogeosciences support, the "Hydra" system to sample air from multiple locations. Each tower thus had CO2 concentration and wind information to calculate advection. These measurements showed that horizontal advection
  was significant, though suggested that advection was largest near the local water drainage, Como Creek. They also suggested that nocturnal drainage flows were quite shallow, and perhaps maximum in the lowest meter (trunk
  space).

• 2004 (CME04): EOL again deployed ISFF, now on three towers that extended above the canopy and were 150m apart to span Como Creek. Hydra also was deployed across Como Creek, with inlets as low as 0.25m. CME04 also was the first deployment of EOL's Adaptive Sensor Array (ASA), which measured soil temperature at 72 locations to determine average CO2 respiration. Analysis of these data is continuing, but it is obvious that at least some advection of carbon occurs at very local spatial scales.

• 2006/2007 (Niwot07): EOL deployed, for the first time, the TRAnsect Measurement (TRAM) system (also developed with TIIMES support) along a 110m-long path crossing Como Creek both in the trunk space and in the middle of the canopy space. Hydra and ASA were deployed along this transect and will be used to anchor the TRAM measurements. These observations will be used to determine the physical dimensions and magnitude of sub-canopy advection, but initial results indicate that flow with a cross section of only 20m does occur, coincident with Como Creek. This research also is supported by a grant from NSF/Biocomplexity (with CU).

• The TRAM track will be moved in 2007/2008 to investigate variations in CO2 concentration that have been observed between the long-term CU and USGS towers that may be associated with a change in canopy density.

Pressure fluctuations in the roughness sublayer

Click on picture to view the entire figure.

 

Keith Romberg, Steve Oncley, Jielun Sun at the CHATS Field Site.
Additional photos

Click on picture to view the entire figure.

 

A few of the many photos from the NIWOT07 Field Experiment.
Additional photos

As part of the CHATS experiment, TIIMES/BEACHON supported the development of a fast-response barometer, capable of measuring turbulent fluctuations of pressure, p'. There have been few measurements of p' in the atmosphere and fewer still in the roughness sublayer (where form drag is important) due to the difficulty of finding a pressure port that doesn't add dynamic pressure errors. For CHATS, we borrowed quad-disk probes (QDP) patented and manufactured by NOAA/ETL and tested two commercial designs in the EOL wind tunnel. A simple modification to the less expensive commercial QDP appeared
to perform nearly as well as the NOAA probes. We also operated two different transducer systems to determine the quality of the measurements. Data analysis is just beginning, though indications are that both systems operated as expected. Experience with these sensors will guide the design of several more pressure sensors that will be deployed as part of the Advective Horizontal Array of Turbulence Study (AHATS) in Summer 2008. This research is in collaboration with William Massman (US Forest Service, Rocky Mountain Research Station).

TIIMES External Collaborators:

Rick Han, University of Colorado
William Massman, United States Forest Service (USFS) - Rocky Mountain Research Station
Russell Monson, University of Colorado

Publications:

Sun, J., S. P. Burns, A. C. Delaney, S. P. Oncley, A. A. Turnipseed, B. B. Stephens, D. H. Lenschow, M. A. LeMone, R. K. Monson, D. E. Anderson, 2007: CO2 Transport over Complex Terrain. Agric. For. Meteorol., 145, 1-21, doi: 10.1016/j.agrformet.2007.02.007.

Chen, F., K. W. Manning, M. A. LeMone, S. B. Trier, J. G. Alfieri, R. Roberts, M. Tewari, D. Niyogi, T. W. Horst, S. P. Oncley, J. B. Basara, P. D. Blanken, 2007: Description and evaluation of the characteristics of the NCAR high-resolution land data assimilation system. J. Appl. Meteor. Climat., 46, 694-713, doi: 10.1175/JAM2463.1.