BOREAS TF-03 NSA-OBS Tower Flux, Meteorological, and Soil Temperature Data. Summary The BOREAS TF-03 team collected tower flux, surface meterological, and soil temperature data at the BOREAS NSA-OBS site continuously from the March 1994 through October 1996. The data are available in tabular ASCII files. Table of Contents * 1 Data Set Overview * 2 Investigator(s) * 3 Theory of Measurements * 4 Equipment * 5 Data Acquisition Methods * 6 Observations * 7 Data Description * 8 Data Organization * 9 Data Manipulations * 10 Errors * 11 Notes * 12 Application of the Data Set * 13 Future Modifications and Plans * 14 Software * 15 Data Access * 16 Output Products and Availability * 17 References * 18 Glossary of Terms * 19 List of Acronyms * 20 Document Information 1. Data Set Overview 1.1 Data Set Identification BOREAS TF-03 NSA-OBS Tower Flux, Meteorological, and Soil Temperature Data 1.2 Data Set Introduction Continuous eddy-correlation flux measurements of sensible heat, latent heat, CO2, and momentum fluxes were made at the BOReal Ecosystem-Atmosphere Study (BOREAS) Northern Study Area (NSA) Old Black Spruce (OBS) site from March 1994 to October 1996. 1.3 Objective/Purpose The principal objective was to determine directly the net ecosystem exchange of CO2 and the surface energy budget over diurnal, seasonal, and annual time scales and to couple these observations with a comprehensive characterization of the physical environment (Photosynthetically Active Radiation (PAR), soil temperature, etc.). In addition, CO2 and water vapor concentration throughout the forest column were measured. This suite of long-term measurements should provide information to assess the effect of seasons and seasonal changes on the carbon balance of the forest. Determination of the boundary layer CO2 concentration anomaly can also be determined, and thus the effect of the forest on the boundary layer CO2 concentration can be studied. 1.4 Summary of Parameters Latent heat flux, sensible heat flux, carbon dioxide flux, momentum flux, CO2 profile, water vapor profile, air temperature profile, net radiation, incident Photosynthetic Photon Flux Density (PPFD), reflected PPFD, below-canopy PPFD, wind speed and direction, soil temperature, precipitation amount. 1.5 Discussion Eddy-correlation flux measurements for CO2 and H2O were made at the northern black spruce site from the late summer of 1993 through the fall of 1996. The principal objective was to directly determine the net ecosystem exchange of CO2, and the surface energy budget over diurnal, seasonal and annual time scales and to couple these observations with a comprehensive characterization of the physical environment (PAR, soil temperature, etc.). A low-power automated array was installed to measure eddy fluxes and forest column content of CO2, sensible heat, and water vapor; soil temperatures and moisture; and incident and intercepted PAR. The system was operated continuously from installation in September 1993 to October 1994 (with some gaps). Additionally, measurements of the flux of CO2 from the soil were made during the summer of 1994 using an array of automated open chambers. Among other things, these long-term measurements should allow assessment of the importance of winter respiration and assimilation during transitional periods to the annual carbon balance of the boreal forest. 1.6 Related Data Sets Tower flux measurements made at other sites: BOREAS TF-09 NSA OJP Tower Flux, Meteorological, and Soil Temperature Data BOREAS TF-09 SSA OBS Tower Flux, Meteorological, and Soil Temperature Data BOREAS TF-10 NSA Fen and YJP Flux, Meteorological, and Soil Temperature Data Other measurements made at the NSA-OBS site: BOREAS TGB-01 NSA CH4 and CO2 Chamber Flux Data BOREAS TE-06 Forest Biophysical Measurements BOREAS TE-09 NSA Photosynthetic Response Data 2. Investigator(s) 2.1 Investigator(s) Name and Title Wofsy, S.C., M.L. Goulden, B.C. Daube, J.W. Munger, Song-Miao Fan, D.J. Sutton, D.J., A. Bazzaz Harvard University Cambridge, MA 2.2 Title of Investigation Eddy Correlation Flux Measurements of CO2 for BOREAS 2.3 Contact Information Contact 1 --------- Dr. Doug Sutton Cambridge, MA (617) 496-4571 djs@io.harvard.edu Contact 2 --------- Dr. Mike Goulden Earth System Science University of California Irvine, CA (714) 824-1983 (714) 824-3256 (fax) mgoulden@uci.edu Contact 3 --------- Steven Wofsy Harvard University Cambridge, MA (617) 495-4566 (617) 495-9837 (fax) scw@io.harvard.edu Contact 4 ------------- K. Fred Huemmrich University of Maryland NASA GSFC Greenbelt, MD (301) 286-4862 (301) 286-0239 (fax) Karl.Huemmrich@gsfc.nasa.gov 3. Theory of Measurements Most investigations of forest CO2 exchange have relied on models to extrapolate short-term gas-exchange measurements made with small chambers. This approach has contributed greatly to understanding, but uncertainties are inevitable when small-scale observations are aggregated to whole ecosystems, and short-term data to annual balances. An alternative approach, used here, was to use the eddy covariance technique over a complete growing season to directly measure the net exchange of CO2 between the atmosphere and a patch of forest several hectares in size. 4. Equipment 4.1 Sensor/Instrument Description 4.1.1 Collection Environment The measurements were made at a remote (50 km from the nearest town and 5 km from the nearest road), old (70-90 years) black spruce site. The coverage was relatively homogeneous, and the trees were approximately 10 m tall. The ground cover was primarily feather moss mixed with some lower-level areas of sphagnum bog. The data were collected continuously through several years; therefore the full range of boreal weather conditions was experienced including temperature ranges between 30 and -40 degrees C. 4.1.2 Source/Platform The instruments were supported on a 31-m-tall Rohn 25-G triangular cross section communications tower. Summary of Eddy Correlation System used by Harvard: Vertical and horizontal velocity sensor 3-axis ATI sonic with Kaimel probe Temperature sensor ATI virtual temperature Moisture sensor LiCor 6262 Infrared Gas Analyzer (IRGA) CO2 sensor LiCor 6262 IRGA Sensor height above ground 29 m Sampling rate 4 Hz Vertical wind speed ATI sonic anemometer Horizontal wind speed ATI sonic anemometer Met One spinning cup Wind direction ATI sonic anemometer Met One sensor Temperature ATI sonic anemometer CO2 LiCor 6262 H2O LiCor 6262 Inlet Filter Gelman Zeflour 3 µm pores, 4 x 50 mm diameter Tubing 0.64" ID high-density polyethylene 50 meters long (replaced May 1996 with PFA Teflon) Pumps KNF Neuberger K022 ANA pumps Data logger Campbell Scientific CR10 Pressure and flow controllers MKS Instruments 4.1.3 Source/Platform Mission Objectives The tower was erected to support instruments above the forest canopy to collect flux data at NSA-OBS. 4.1.4 Key Variables Eddy-correlation measurements of latent heat flux, sensible heat flux, CO2 flux, and momentum flux. Profiles of CO2, water vapor, and air temperature. Incident, reflected, and below-canopy PPFD. Wind speed and direction, soil temperature, precipitation. 4.1.5 Principles of Operation Sonic Anemometer: Three-dimensional orthogonal wind velocities (u, v, and w) and virtual temperature (Tv) were measured with a sonic anemometer (Applied Technology, Boulder, CO). The path length between transducers was 0.15 m. The sensor software corrected for transducer shadowing effects (see Kaimal et al., 1990). Virtual temperature heat flux was converted to sensible heat flux using algorithms described by Kaimal and Gaynor (1991) and Schotanus et al. (1983). Infrared Absorption Spectrometer: Water vapor and CO2 concentrations were measured with an open-path infrared absorption spectrometer. 4.1.6 Sensor/Instrument Measurement Geometry The sonic anemometer was located at a height of 29-m on a 31-m triangular- cross- section radio tower (Rohn 25-G). The tubing inlet for the air sample was located 0.5-m below the sonic anemometer. The LiCor sensors were placed in a climate- controlled hut 20-m northeast of the tower. The air was drawn down the tower at 18 standard liters per minute. The air was passed through a thermostated block to stabilize the temperature and drawn through the LiCor at 4 standard liters per minute. Pressure was controlled in the cell of the LiCor at 53 kPa. Air temperature profiles were measured at 27.0 m, 8.2 m, and 1.15 m above ground level. Relative humidity was measured at 27.0 m. Wind speed and direction were measured at 29.6 m. The sonic anemometer was mounted at 29 m. Under-canopy PPFD sensor arrays were placed at ground level. Soil temperature probes were placed at depths of 1 cm, 5 cm, 10 cm, 20 cm, 50 cm, and 100 cm. Soil heat flux plates were at depths of 1 cm, 5 cm, and 10 cm. 4.1.7 Manufacturer of Sensor/Instrument Sonic anemometer: Applied Technologies, 6395 Gunpark, Boulder, CO. CO2 and H2O sensor: LiCor, P.O. Box 4425, Lincoln, NE. Data logging systems: Campbell Scientific Instruments, P.O. Box 551, Logan, UT 84321 and others. Pressure and Flow Control: MKS Instruments, Andover, MA. 4.2 Calibration 4.2.1 Specifications Sonic anemometer: Supplied by the manufacturer. Instrument zeros and maintenance performed at least twice per year. CO2 sensor: Calibrated every 3 hours by standard addition of 4% CO2 at 40 and 80 standard milliliters per minute for 2 minutes 15-m below the sample inlet on tower. Zero datum for the LiCor IRGA was achieved by passing sample air through a column of soda lime for 2 minutes. H2O sensor: Calibrated every few months using a LiCor dew point generator. Calibration was checked by comparison with a Vaisala probe on the tower. Zero information was recorded every 3 hours by passing sample air through a column of magnesium perchlorate for 2 minutes. CO2 concentration calibration: Used an independent LiCor 6262 IGA and two span gases (~340 ppm and ~420 ppm). These gas samples are traceable to the 1993 Scripps-World Meteorological Organization (WMO) standard. Calibrations were done every 3 hours by passing each of the gases through the LiCor IGA at 1.25 standard liters per minute for 2 minutes. Zero information was achieved by the same method as that used for the the eddy CO2-sensor. 4.2.1.1 Tolerance Not known. 4.2.2 Frequency of Calibration Sonic anemometer: Instrument zeros and maintenance performed at least twice per year. CO2 sensor: Calibrated every 3 hours by standard addition of 4% CO2 at 40 and 80 standard milliliters per minute for 2 minutes 15-m below the sample inlet on tower. H2O sensor: Calibrated every few months using LiCor dew point generator. Zero information is recorded every 3 hours by passing sample air through a column of magnesium perchlorate for 2 minutes. CO2 concentration calibration: Calibrations are done every 3 hours by passing each of the gas samples through the LiCor at 1.25 standard liters per minute for 2 minutes. 4.2.3 Other Calibration Information Not known. 5. Data Acquisition Methods Data for flux measurements were continuously recorded at 4 Hz while other parameters were recorded at 0.5 Hz. The data were stored on a PC and collected twice per week. The delay time between the wind speed and concentration measurement was calculated at 5.5 seconds. The time constant for response time of the instrument to a change in the mixing ratio of the air sample was determined to be 0.6 seconds for CO2 and 1.25 seconds for H2O. The difference in time was due to adsorption of H2O to the tubing. The response-time corrections typically were 5 to 10% during the day and 15 to 25% at night. An averaging time of 30 minutes was used and a linear least-squares regression was used to detrend the flux data. 6. Observations 6.1 Data Notes None available. 6.2 Field Notes Notable data gaps occurred in May 1994, when an error was introduced into the data acquisition code; August 1994, when the sonic anemometer was damaged twice by lightning; fall 1994, when the generator failed repeatedly; June 1995, when computer disks failed twice; and November 1995, when the sonic anemometer failed with the onset of cold temperatures. 7. Data Description 7.1 Spatial Characteristics 7.1.1 Spatial Coverage All data were collected at the BOREAS NSA OBS site. The site is located at latitude 55.88007° N, longitude 98.48139° W, and elevation of 259 m. 7.1.2 Spatial Coverage Map Not applicable. 7.1.3 Spatial Resolution The data represent point source measurements taken at the given location. The location and size of the footprint from which the measurements were made varied with ambient meteorological conditions. 7.1.4 Projection Not applicable. 7.1.5 Grid Description Not applicable. 7.2 Temporal Characteristics 7.2.1 Temporal Coverage Measurements are available from 16-Mar-1994 through 31-Oct-1996. Valid measurements are available 72% of the time. Notable gaps occurred in May 1994, August 1994, fall 1994, June 1995, and November 1995. 7.2.2 Temporal Coverage Map All data were collected at the NSA-OBS site. 7.2.3 Temporal Resolution Data for flux measurements were continuously recorded at 4 Hz while other parameters were recorded at 0.5 Hz. The delay time between the wind speed and concentration measurement was calculated at 5.5 seconds. The time constant for response time of the instrument to a change in the mixing ratio of the air sample was determined to be 0.6 seconds for CO2 and 1.25 seconds for H2O. The difference in time was due to adsorption of H2O to the tubing. The response-time corrections typically were 5 to 10% during the day and 15 to 25% at night. An averaging time of 30 minutes was used and a linear least-squares regression was used to detrend the flux data. 7.3 Data Characteristics Data characteristics are defined in the companion data definition file (tf3tflxd.def). 7.4 Sample Data Record Sample data format shown in the companion data definition file (tf3tflxd.def). 8. Data Organization 8.1 Data Granularity All of the NSA-OBS Tower Flux, Meteorological, and Soil Temperature data are contained in one dataset. 8.2 Data Format The data file contains numerical and character fields of varying length separated by commas. The character fields are enclosed with single apostrophe marks. There are no spaces between the fields. Sample data records are shown in the companion data definition file (tf3tflxd.def). 9. Data Manipulations 9.1 Formulae None. 9.1.1 Derivation Techniques and Algorithms None. 9.2 Data Processing Sequence 9.2.1 Processing Steps BORIS staff processed these data by: 1) Reviewing the initial data files and loading them online for BOREAS team access. 2) Designing relational data base tables to inventory and store the data. 3) Loading the data into the relational data base tables. 4) Working with the team to document the data set. 5) Extracting the data into logical files. 9.2.2 Processing Changes None. 9.3 Calculations 9.3.1 Special Corrections/Adjustments The sonic anemometer developed problems with spiking occasionally, caused either by precipitation or by malfunctioning transducers. Processing code was adapted to determine the number of spikes in each interval and to recalculate the turbulent fluxes after filtering out spikes. 9.3.2 Calculated Variables None. 9.4 Graphs and Plots None. 10. Errors 10.1 Sources of Error Errors in flux measurements may be associated with wind from behind the tower, calm conditions, and the damping of high-frequency fluctuations. The sonic anemometer developed problems with spiking occasionally caused either by precipitation or by malfunctioning transducers. 10.2 Quality Assessment 10.2.1 Data Validation by Source Raw flux data were examined for errors associated with wind from behind the tower, calm conditions, and the damping of high-frequency fluctuations, and for intervals with malfunctioning instruments. These periods were excluded or the errors were corrected. 10.2.2 Confidence Level/Accuracy Judgment None given. 10.2.3 Measurement Error for Parameters None given. 10.2.4 Additional Quality Assessments None given. 10.2.5 Data Verification by Data Center Data were examined to check for spikes, values that are four standard deviations from the mean, long periods of constant values, and missing data. 11. Notes 11.1 Limitations of the Data None given. 11.2 Known Problems with the Data CO2 fluxes may be underestimated when the friction velocity is less than 0.2 m/sec. The closed-path IRGA and long sampling tube resulted in an underestimation of water vapor and CO2 flux because of the damping of high- frequency fluctuations. 11.3 Usage Guidance None given. 11.4 Other Relevant Information None given. 12. Application of the Data Set This suite of long-term measurements should provide information to assess the effect of seasons and seasonal changes on the carbon balance of the forest. Determination of the boundary layer CO2 concentration anomaly can also be determined, and thus the effect of the forest on the boundary layer CO2 concentration can be studied. 13. Future Modifications and Plans Under separate funding, flux data continued to be collected beyond 31-Oct-1996. Contact personnel at Harvard University about these data. 14. Software 14.1 Software Description None given. 14.2 Software Access None given. 15. Data Access 15.1 Contact Information Ms. Beth Nelson BOREAS Data Manager NASA GSFC Greenbelt, MD (301) 286-4005 (301) 286-0239 (fax) Elizabeth.Nelson@gsfc.nasa.gov 15.2 Data Center Identification See Section 15.1. 15.3 Procedures for Obtaining Data Users may place requests by telephone, electronic mail, or fax. 15.4 Data Center Status/Plans These data are available from the Earth Observing System Data and Information System (EOSDIS) Oak Ridge National Laboratory (ORNL) Distributed Active Archive Center (DAAC). The BOREAS contact at ORNL is: ORNL DAAC User Services Oak Ridge National Laboratory (865) 241-3952 ornldaac@ornl.gov ornl@eos.nasa.gov 16. Output Products and Availability 16.1 Tape Products None. 16.2 Film Products None. 16.3 Other Products The data are available as tabular American Standard Code for Information Interchange (ASCII) text files. 17. References 17.1 Platform/Sensor/Instrument/Data Processing Documentation LI-COR 1991. LI-6262 CO2/H2O analyzer operating and service manual. Publ. 9003- 59, Linclon,NE. 17.2 Journal Articles and Study Reports Goulden, M.L., B.C. Daube, S.M. Fan, D.J. Sutton, A. Bazzaz, J.W. Munger, and S.C. Wofsy. 1997. Physiological responses of a black spruce forest to weather, Journal of Geophysical Research 102 (D24):28987,28996. Kaimal, J.C. and J.E. Gaynor. 1991. Another look at sonic thermometry. Boundary Layer Meteorology. 56:401-410. Kaimal, J.C., J.E. Gaynor, H.A. Zimmerman, and G.A. Zimmerman. 1990. Minimizing flow distortion errors in a sonic anemometer. Boundary Layer Meteorology. 53:103- 115. Schotanus, P., F.T.M. Nieuwstadt, and H.A.R. De Bruin. 1983. Temperature measurement with a sonic anemometer and its application to heat and moisture fluxes. Boundary-Layer Meteorology. 26: 81-93. Sellers, P. and F. Hall. 1994. Boreal Ecosystem-Atmosphere Study: Experiment Plan. Version 1994-3.0, NASA BOREAS Report (EXPLAN 94). Sellers, P. and F. Hall. 1996. Boreal Ecosystem-Atmosphere Study: Experiment Plan. Version 1996-2.0, NASA BOREAS Report (EXPLAN 96). Sellers, P. and F. Hall. 1997. BOREAS Overveiw Paper. JGR Special Issue. Sellers, P., F. Hall, and K.F. Huemmrich. 1996. Boreal Ecosystem-Atmosphere Study: 1994 Operations. NASA BOREAS Report (OPS DOC 94). Sellers, P., F. Hall, and K.F. Huemmrich. 1997. Boreal Ecosystem-Atmosphere Study: 1996 Operations. NASA BOREAS Report (OPS DOC 96). Sellers, P., F. Hall, H. Margolis, B. Kelly, D. Baldocchi, G. den Hartog, J. Cihlar, M.G. Ryan, B. Goodison, P. Crill, K.J. Ranson, D. Lettenmaier, and D.E. Wickland. 1995. The boreal ecosystem-atmosphere study (BOREAS): an overview and early results from the 1994 field year. Bulletin of the American Meteorological Society. 76(9):1549-1577. Sellers, P.J., F.G. Hall, R.D. Kelly, A. Black, D. Baldocchi, J. Berry, M. Ryan, K.J. Ranson, P.M. Crill, D.P. Lettenmaier, H. Margolis, J. Cihlar, J. Newcomer, D. Fitzjarrald, P.G. Jarvis, S.T. Gower, D. Halliwell, D. Williams, B. Goodison, D.E. Wickland, and F.E. Guertin. 1997. BOREAS in 1997: Experiment overview, scientific results, and future directions. Journal of Geophysical Research. 102(D24):28731-28770. 17.3 Archive/DBMS Usage Documentation None. 18. Glossary of Terms None. 19. List of Acronyms ASCII - American Standard Code for Information Interchange BOREAS - BOReal Ecosystem-Atmosphere Study BORIS - BOREAS Information System DAAC - Distributed Active Archive Center EOS - Earth Observing System EOSDIS - EOS Data and Information System GMT - Greenwich Mean Time GSFC - Goddard Space Flight Center IRGA - Infrared Gas Analyzer NASA - National Aeronautics and Space Administration NSA - Northern Study Area OBS - Old Black Spruce ORNL - Oak Ridge National Laboratory PANP - Prince Albert National Park PAR - Photosynthetically Active Radiation SSA - Southern Study Area PPFD - Photosynthetic Photon Flux Density URL - Uniform Resource Locator WMO - World Meteorological Organization 20. Document Information 20.1 Document Revision Date Written: 07-Jul-1995 Revised: 05-Jun-1998 20.2 Document Review Date(s) BORIS Review: 19-May-1998 Science Review: 20.3 Document ID 20.4 Citation Goulden, M. L., Daube, B. C., Fan, S. M., Sutton, D. J., Bazzaz, A., Munger, J. W., and Wofsy, S. C. (1997), Physiological responses of a black spruce forest to weather, Journal of Geophysical Research, 102 (D24):28987,28996. 20.5 Document Curator 20.6 Document URL Keywords BLACK SPRUCE TOWER FLUX METEOROLOGY SENSIBLE HEAT FLUX LATENT HEAT FLUX CARBON DIOXIDE FLUX CARBON DIOXIDE CONCENTRATION PHOTOSYNTHETIC PHOTON FLUX DENSITY PHOTOSYNTHETICALLY ACTIVE RADIATION PPFD PAR NET RADIATION AIR TEMPERATURE SOIL TEMPERATURE VAPOR PRESSURE WIND SPEED RAINFALL TF03_Flux_Met.doc 06/11/98