BOREAS TF-09 SSA-OBS Tower Flux, Meteorological, and Soil Temperature Data Summary The BOREAS TF-09 team collected energy, carbon dioxide and water vapor flux data at the BOREAS SSA-OBS site during the growing season of 1994 and most of the year for 1996. From the winter of 1995 to 1996, soil temperature data were also collected and provided. 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-09 SSA-OBS Tower Flux, Meteorological, and Soil Temperature Data 1.2 Data Set Introduction This data set includes heat, carbon dioxide, and water vapor fluxes measured by eddy covariance (EC) and meteorological data all measured from the Boreal Ecosystem-Atmosphere Study (BOREAS) Southern Study Area (SSA)-Old Black Spruce (OBS) tower. Soil heat flux and soil temperature profiles are also included. Through the winter of 1995 to 1996, soil temperature data were collected, these data are stored in separate files. 1.3 Objective/Purpose The objectives of this study were to measure and model the CO2 exchanges of boreal black spruce forest to determine whether the soils and vegetation are significant global sinks for atmospheric CO2. Stand CO2 fluxes were measured using EC and the CO2 concentration profile was also measured to allow estimation of the atmospheric storage of CO2 within the canopy. These measurements will be used to verify scaling up procedures from leaf level measurements and may be scaled up to regional scales. 1.4 Summary of Parameters and Variables Latent heat flux, sensible heat flux, carbon dioxide flux, soil heat flux, momentum flux, CO2 profile, water vapor profile, air temperature profile, net radiation, incident and reflected Photosynthetic Photon Flux Density (PPFD), incident and reflected solar radiation, wind speed and direction, friction velocity, soil temperatures, precipitation amount, vapor pressures. 1.5 Discussion The tower at the SSA-OBS site (53.99° N, 105.312° W) was equipped with a CO2, water vapor, and sensible heat flux measuring EC system and a weather station to measure flux driving environmental variables. CO2 concentration profiles and soil temperatures at various depths were also measured, as was soil heat flux. The EC system at the top of the tower consisted of a Solent 3-D sonic anemometer and LI-COR LI-6262 closed-path infrared gas analyzer (IRGA). The anemometer was placed 2.6 m above the top platform (25.8 m) on a vertical pole on the SW corner of the tower. The air was ducted by tube from close to the anemometer to the LI- 6262. The data were collected and processed in 'real time' to provide near- continuous measurements. Profiles of CO2 and H2O vapor concentrations were continuously monitored. In 1994, five heights were measured; in 1996, measurements were made at eight heights through the canopy. These measurements were made using an IRGA (LI-COR 6262) fitted with time-switched solenoid valves. The sample heights for 1994 were at 1.5, 3, 6, 12, and 26 meters, corresponding to one-eighth, one-fourth, one-half, one, and two times the canopy height. In 1996, the samples were collected at eight heights above the ground at approximately 0.5, 1.5, 3.5, 6.5, 9.5, 12.5, 18, and 26 meters. Air was drawn continuously through the sample pipes at each of the heights, and each line was sampled in turn. In 1994 each line was sampled for 3 minutes of every 15 minutes; in 1996, each line was sampled for 1 minute every 10 minutes. Data from the beginning of each period were discarded to allow for flushing of the short tube between the solenoids and the analyzer. In 1994, the first minute of data was discarded; in 1996, the first 20 seconds were discarded. At the top of the tower, a simple weather station was set up to measure the following environmental variables: net radiation, PPFD, shortwave solar radiation, temperature, relative humidity, vapor pressure, wind speed and direction, and rainfall. In 1996, a second weather station, comprising a ventilated psychrometer and net radiometer, was set up at 2 m height above the ground. Soil temperatures were measured at four locations at 0.05, 0.1, 0.2, and 0.5 meters depth, using differential thermocouples referenced to thermistors at 1 meter. Soil heat flux was measured using seven soil heat flux plates, buried about 7 cm below the surface. 1.6 Related Data Sets BOREAS TF-05 SSA-OJP Tower Flux, Meteorological, and Soil Temperature Data BOREAS TF-03 NSA-OBS Tower Flux, Meteorological, and Soil Temperature Data BOREAS TF-04 SSA-YJP Tower Flux, Meteorological, and Soil Temperature Data BOREAS TF-11 SSA Fen Tower Flux, Meteorological, and Soil Temperature Data BOREAS TF-09 SSA-OBS Branch Level Flux Data 2. Investigator(s) 2.1 Investigator(s) Name and Title Prof. Paul G. Jarvis and Dr. John B. Moncrieff Institute of Ecology and Resource Management University of Edinburgh UK 2.2 Title of Investigation The CO2 Exchanges of Boreal Black Spruce Forest 2.3 Contact Information Contact 1 --------- Mr. Jonathan M. Massheder Institute of Ecology and Resource Management University of Edinburgh Edinburgh UK +131 650 8746 +131 662 0478 (fax) J.Massheder@ed.ac.uk Contact 2 --------- Dr. John B. Moncrieff Institute of Ecology and Resource Management University of Edinburgh Edinburgh UK +131 650 5402 +131 662 0478 (fax) J.Moncrieff@ed.ac.uk Contact 3 --------- Mr. Mark B. Rayment Institute of Ecology and Resource Management University of Edinburgh Edinburgh UK +131 650 5423 +131 662 0478 (fax) M.Rayment@ed.ac.uk Contact 4 --------- K. Fred Huemmrich University of Maryland NASA GSFC (University of Maryland) Greenbelt, MD (301) 286-4862 (301) 286-0239 (fax) Karl.Huemmrich@gsfc.nasa.gov 3. Theory of Measurements The net carbon uptake of a forest depends on the assimilation of carbon dioxide by photosynthesis and on carbon dioxide emissions resulting from respiratory processes. Carbon dioxide assimilation depends on the species, age, and physiological activity of the trees. Emission depends on the respiratory cost of maintenance and growth, production of litter, and turnover of organic matter in the soil. Influencing both these processes are soil, climate, and weather. During the day, carbon dioxide will generally be taken up by the stand by photosynthesis, while at night carbon dioxide is lost from the stand. A conservation of mass equation gives: Fc = Fa + Fs + Fr + Fg + DS where Fc is the net flux of carbon dioxide into (or out of) the stand from the air above, Fa is the canopy assimilation (or at-night respiration), Fs is stem respiration, Fr is root respiration, Fg is soil respiration, and DS is storage of carbon dioxide in the air of the stand. With EC, the carbon dioxide flux is measured through a plane above the stand (Fc), and with the carbon dioxide concentration profile the change in storage (DS) can be estimated. The flux measurements were calculated using EC and corrections were applied to the covariances to correct for density effects (Webb et al., 1980). Coordinate rotation of the wind vector components ensured that the flux calculated was perpendicular with respect to local streamlines, and transfer functions (Moore 1986; Philip, 1963) were used to correct for inadequate frequency response. 4. Equipment 4.1 Sensor/Instrument Description. 4.1.1 Collection Environment Measurements were collected from late May through mid-September 1994 and early April through late November of 1996. Over that time period, temperature conditions from below freezing to over 30 °C were experienced. 4.1.2 Source/Platform Above-canopy measurements were made from a 23-meter double scaffold walk-up tower. The anemometer used in the EC measurements was a Solent 3-D research ultrasonic anemometer. The Solent outputs three orthogonal wind velocity components and the speed of sound from which air temperature may be derived at 21 Hz. To measure CO2 and water vapor concentrations, a LI-COR LI-6262 closed-path IRGA was used. Air 5 cm from the center of the sonic anemometer's path was ducted down a 32-m Dekabon tube (aluminum tube with PVC coating and polyethylene lining) of 6-mm internal diameter (i.d.). The airflow down the tube was controlled by a Tylan FC2900B mass flow controller at 6 dm3 min-1, which resulted in pressure in the LI-6262's sample cell typically 7 kPa less than atmospheric. The analog-to-digital (A/D) converter in the Solent was used to sample the analog output from the LI-6262 at 11 Hz. The linear outputs of the LI-6262 were used, which allowed utilization of the LI-6262's processor to correct for sample cell pressure and for CO2 band broadening and dilution caused by water vapor. The fully processed CO2 output of the LI-6262 is at 5 Hz and for H2O at 3 Hz. The combined wind velocity and IRGA outputs were then transmitted from the Solent serially and received by a notebook PC, where the fluxes were calculated by the EddySol software. All CO2 concentration data were logged on a Campbell Scientific CR10 logger, which also controlled the sample line switching three-way solenoid valves through a customized control circuit. Sample pipes were of 5-mm-i.d. nylon tubing; CO2 adsorption/desorption was not considered a problem since all pipes were continuously purged to exhaust while not being sampled to the IRGA. Sample points consisted of a gauze mosquito cover, an inverted funnel water trap and a fine particulate filter. Sampling to the LI-COR 6252 IRGA was carried out via a Charles Austin dymax pump, downstream of which was a needle valve and flow meter, restricting flow to 0.5 dm3 min-1. The downstream end of the IRGA was left open to the atmosphere, ensuring operation at atmospheric pressure. The entire apparatus was housed off the ground, within an enclosed, but ventilated, metal box. Weather station: Campbell 21x data loggers with AM416 multiplexors were used to log output from the sensors listed below. Variable Sensor ============================================================== Net radiation 2 x Radiation Energy Balance System (REBS) Q6 net radiometers Low-level net radiation REBS Q6 net radiometers Total solar radiation Kipp solarimeter, LI-COR pyranometer PPFD LI-COR quantum sensor Relative humidity Campbell Skye humidity probe Wind direction Vector Instruments windvane Wind speed Vector Instruments cup anemometer Air temperature DeltaT ventilated psychrometer Wet bulb temperature DeltaT ventilated psychrometer Soil temperatures Probe developed at Edinburgh University Soil heat flux 7 x REBS heat flux plates Precipitation DeltaT tipping bucket rain gauge, resolution 0.2 mm 4.1.3 Source/Platform Mission Objectives The objective was to measure CO2, water vapor, and sensible heat fluxes and related environmental variables over a black spruce stand at the southern edge of the boreal forest. 4.1.4 Key Variables EC: CO2 and water vapor fluxes, sensible heat, latent heat fluxes, air temperature, and wind speed in nominal x, y, and z planes. Supporting meteorological variables: net radiation, PPFD, air temperature, wet bulb temperature, total solar radiation, wind direction, wind speed, soil temperatures, CO2, and water vapor concentration profiles. 4.1.5 Principles of Operation The Solent anemometer uses pulses of ultrasound to measure windspeed. The forward and reverse transit times for a pulse of ultrasound, between two transducers, gives the speed of sound and the wind speed (sound travels faster with a following wind). The 3-D sonic has three pairs of transducers arranged in nonparallel axes, allowing the 3-D components of the wind velocity to be derived. The LI-COR LI-6262 IRGAs are closed path instruments with reference and sample cells with an infrared source at one end and a detector at the other. Different gases absorb infrared of different frequencies and filters are used to select a narrow band that corresponds to an absorption band of the gas of interest. The LI-6252 measures only CO2 while the LI-6262 measures CO2 and H2O concentration. A gas of known concentration is passed through a reference cell, and the gas whose concentration is to be measured is passed through the sample cell. The amount of infrared reaching the detector in each cell is a function of the gas concentration in the cell. The difference in voltage produced by the detectors of the reference and sample cells is then a function of the difference in concentration of the gas in the cells. Other sensors were common meteorological sensors used in a standard fashion. For principles of operations of these sensors, please see a relevant textbook, e.g., Pearcy et al. (1991). 4.1.6 Sensor/Instrument Measurement Geometry The closed-path EC system was placed on an upright pole at the south west corner of the top of the flux tower. The southwest corner was chosen because a tramway system was set up at the northern end of the tower, and the main fetch at the site is from the west. Because the equipment was 3 m above the top of the tower on a pole, the tower would cause very little disturbance to the wind, whatever its direction. Therefore, EC measurements would not be especially invalidated by any wind direction with respect to the tower; however, the access trail to the site is to the east, and any production of CO2 by people or vehicles on the trail may affect the CO2 fluxes measured if the wind is from the east. Also, in the making of the access trail extensive damage was caused to the muskeg, with many trees being felled; hence, photosynthesis over this area will be uncharacteristically lower and respiration similarly high. Sample points for the CO2 concentration measurements for 1994 were at 1.5, 3, 6, 12, and 26 meters, corresponding to one-eighth, one-fourth, one-half, one, and approximately two times the canopy height. In 1996 the samples were collected at eight heights above the ground at 0.52, 1.66, 3.36, 6.44, 9.6, 12.66, 17.74, and 27.42 meters. The weather station was set up on the eastern side at the top of the tower at 24 m about 2.6 m horizontally from the EC system. The rain gauge was located on top of the tower which was the place that offered the least obstruction. Two net radiometers were mounted on the south side of the tower at a height of 16 m extending 3 m from the tower. This position offered more symmetry of the effect of the tower on upward and downward fluxes than if the radiometers were placed at the top of the tower. Two solarimeters (CM3, Kipp & Zonen) were also mounted on these booms, measuring incoming and reflected solar radiation. The low-level EC system and weather station were set up approximately 30 m to the west of the main tower. A net radiometer was positioned below the canopy, at a height of 2 m above the ground. In 1994, the soil temperature probe was located about 10 m from the southwest corner of the tower. In 1996, four soil temperature probes were installed, two to the northeast and two to the southeast of the tower. Two soil heat flux plates were placed within 5 m of each probe. 4.1.7 Manufacturer of Sensor/Instrument Solent sonic anemometer: Gill Instruments Limited Solent House Cannon Street Lymington, Hampshire SO41 9BR UK Campbell CA27s sonic anemometer: Skye Humidity probe: Campbell Scientific P.O. Box 551 Logan, UT 84321 USA LI-COR LI-6262 and LI-6252 IRGAs Pyranometer, quantum sensor: LI-COR P.O. Box 4425/4421 Superior Street Lincoln, NE 68504 USA Advanced Systems E009a IRGA: Advanced Systems Inc. Okayama City, Japan Delta-T psychrometers and rain gauge: Delta-T Devices ltd. 128 Low Rd., Burwell, Cambs CB5 0EJ UK Soil heat flux plate Net radiometer: REBS P.O. Box 15512 Seattle, WA 98115-0512 Elmer NJ 08318 USA Wind vane, cup anemometer: Vector Instruments 115 Marsh Road Rhyl Clwyd LL18 2AB UK Rain gauge: Cassella Regent House Britannia Walk London N1 7ND UK 21x, CR10 Data logging system: Campbell Scientific P.O. Box 551, Logan, UT 84321 USA A/D card: Strawberry Tree Inc. 160 S. Wolfe Rd. Sunnyvale, CA 94086 USA Dekabon tubing: J.P. Deane & Co. Ltd., 91, Ormonde Crescent Glasgow. G44 3SW UK Mass flow controller: Tylan General Swindon UK 4.2 Calibration 4.2.1 Specifications LI-6262, closed-path EC system: The output linearization of this instrument is calibrated by the manufacturer and was last performed in July 1993. The field calibration fixes the lower and upper ends of the linearization function and is carried out by passing CO2 and water vapor free air through the reference cell (the instrument is used in the absolute mode) and setting the CO2 and water vapor channels to zero. The upper point is set by passing dry air of known CO2 or of known water vapor concentration through the sample cell and adjusting the appropriate channel to read the correct value. CO2 standard gases were cross-referenced to the BOREAS primary standards, and a LI-COR LI-610 dewpoint generator was used to produce air of known water vapor density. Solent anemometers: These instruments have stable calibrations, and factory values were used. The calibrations have been tested in Edinburgh University's wind tunnel and were found satisfactory. LI-6262 CO2 concentration profile system: The IRGA was calibrated at the outset. The air from the uppermost height was the same air that had been through the EC LI-6262 IRGA, and the analyzer was calibrated whenever the difference between the two IRGAs was more then a couple of ppm. No corrections were applied to compensate water vapor cross- sensitivity. Radiometers: One of the radiometers was purchased new from the manufacturers: the calibration factor supplied with it was assumed to be accurate, and it was used as a standard against which the second one was calibrated in July 1993. Quantum sensor: This was calibrated against another quantum sensor that is kept as a standard and is not used the field. This calibration was performed in 1993. Cup anemometer: The cup anemometer was calibrated in the wind tunnel at Edinburgh University. Humidity probe: The Skye temperature and humidity probe was calibrated in July 1993 by enclosing it in flasks containing salt solutions of known equilibrium water vapor pressures as supplied by Campbell. Psychrometer: 1994: The psychrometer was calibrated in July 1993. 1996: The psychrometer were purchased new, and the manufacturer's calibration factors for the temperature sensors were assumed to be accurate. Wind vane: This was purchased new, and the manufacturer's calibration factors were used. Pyranometer: This was purchased new, and the manufacturer's calibration factors were used. 4.2.1.1 Tolerance None given. 4.2.2 Frequency of calibrations The LI-6262 was usually calibrated, every 4 to 7 days. Typical CO2 drift was 1 ppm drift in span and offset. Typical drift for the water vapor was 0.1 kPa in span and offset. 4.2.3 Other Calibration Information None given. 5. Data Acquisition Methods Closed-path EC system: Analog output from the LI-6262 IRGA (CO2 and water vapor concentrations) was digitized by the Solent anemometer at 11 Hz (which has provision for up to five analog inputs). The three wind velocity components and speed of sound at 21 Hz were added, and 20 of these records were transmitted in a packet together almost every second to a computer (PC) using a serial (RS232) link. The software (EddySol) then computed fluxes in real time, including coordinate rotation but not frequency response corrections. Corrections for the effect of water vapor density on CO2 density were carried out by the LI-6262's internal software. The Solent digitization is 11 bit with input voltage between 0 and 5 V. The LI-6262 output A/D converters were set for a 0 to 5 V range to correspond with a 300 to 500 ppm CO2 concentration range and a 0 to 25 kPa vapor pressure range. Primary data and computed fluxes were stored on hard disk. Primary data were periodically offloaded onto removable Syquest hard disk cartridges. Three Campbell Scientific 21x data loggers were employed to log the data: one for the soil temperature probes and soil heat flux plates, one for the CO2 and H2O concentration profiles and one for the rest of the weather station. The raw signal from each sensor was converted into the appropriate units in the data logger program. 6. Observations 6.1 Data Notes None 6.2 Field Notes. None 7. Data Description 7.1 Spatial Characteristics 7.1.1 Spatial Coverage All data were collected at the BOREAS SSA-OBS site. North American Datum 1983 (NAD83) coordinates for the site are latitude 53.98717° N, longitude 105.11779° W, and elevation of 628.94 m. 7.1.2 Spatial Coverage Map Not applicable. 7.1.3 Spatial Resolution The EC, CO2 concentration profile, and water vapor measurements are all point measurements but the concentrations of CO2 and water vapor and the temperature at a point are influenced by a certain area downwind, sometimes referred to as a 'footprint'. Other related terms are Wind Aligned Blob (WAB) and fetch, and their use is sometimes confused. The footprint is the roughly pear-shaped (broad end toward the measurement point) area contributing to a particular measurement and its size and shape depends on measurement height, wind speed, sensible heat flux, and surface roughness during the measurement period. The contribution to the measurement by a point upwind is a logarithmic function of distance . The theoretical footprint is infinite, but to make the concept of a footprint more useful, the footprint should be defined as the area contributing to a certain proportion of the measured quantity; e.g., 95%. The term WAB as used in BOREAS is the area contributing to measurements over the period of the field campaign; i.e., the area occupied by the footprints of many measurements. The shape of such a WAB is circular, though often with a sector discarded because either the wind rarely comes from that direction or contamination is expected from that direction. The fetch is the distance the wind travels over a certain surface type before it reaches a particular (e.g., the measurement) point. Therefore, if one is trying to make measurements pertaining to a certain vegetation type, the length of the footprint should be less than or equal to the fetch over that vegetation. As the measurement is influenced by a large area downwind (the footprint) if the wind flow and vegetation over that area are homogenous, the measurements will be representative for that area; hence, the stringent requirements for EC sites. The CO2 concentrations are point data, vertically spread below the EC system with footprints similar to that of the top EC system but smaller and complicated by the less homogenous turbulence within the canopy compared to that above. 7.1.4 Projection None. 7.1.5 Grid Description None. 7.2 Temporal Characteristics 7.2.1 Temporal Coverage The data were collected from 24-May to 19-September-1995 and from 24-March to 29-November-1996. Soil temperatures and heat fluxes were measured from 15- November-1995 to 29-November-1996. 7.2.2 Temporal Coverage Map None. 7.2.3 Temporal Resolution The values are half hour averages except for rainfall, which is a half hour total. Soil temperatures in 1996 before 11-April-1996 are hourly averages. 7.3 Data Characteristics Data characteristics are defined in the companion data definition file (tf9tflxd.def). 7.4 Sample Data Record Sample data format shown in the companion data definition file (tf9tflxd.def). 8. Data Organization 8.1 Data Granularity All of the SSA-OBS Tower Flux, Meteorological, and Soil Temperature Data are contained in one dataset. 8.2 Data Format The data files contain 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 (tf9tflxd.def). 9. Data Manipulations 9.1 Formulae Fluctuations were calculated using an autoregressive moving average (digital filter). These fluctuations were used to calculate the covariances and variances. Coordinate rotation was a geometric transformation. The speed of sound was corrected for wind speed normal to the transducer path (Kaimal and Gaynor, 1990) with geometric transformations to allow for the nonorthogonal arrangement of transducer in the Solent anemometer. Sonic temperature was calculated from the speed of sound, and corrections to sensible heat flux calculated using sonic rather than absolute temperature were made (Schotanus et al., 1983). Corrections for nonideal response were applied (Moore, 1986; Philip, 1963). 9.1.1 Derivation Techniques and Algorithms None. 9.2 Data Processing Sequence Moving averages, variances, and covariances were calculated in real time, and coordinate rotation was applied on the half-hourly covariances and variances. Corrections for the use of sonic temperature were applied after data collection. 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 None. 9.3.2 Calculated Variables The eddy flux measurements on calm nights underestimate the surface fluxes. Inspection of the CO2 storage flux also shows that storage flux does not account for the underestimation by the CO2 eddy flux. To provide estimates of the surface fluxes of CO2, H2O, sensible heat, and latent heat fluxes, the variables FILLED_CO2_FLUX_26M, FILLED_SENSIBLE_HEAT_26M, FILLED_LATENT_HEAT_26M, and FILLED_H2O_FLUX_26M have been added to the data set. These variables are equal to the corresponding eddy flux values except on calm nights as defined below. Gaps in the eddy flux measurements have also been "filled in" by use of regression equations of eddy flux against meteorological variables. Below is the SAS (SAS Institute, NC) program that was used to calculate these variables. /**************** SAS PROGRAM ************************/ data boreas96.boris96f; merge boreas96.boris96m boreas96.amodel; by end_time; SVP = 0.611 * exp(17.27*Tskye/(Tskye+237.15)); * saturated vapour pressure * Tskye is AIR_TEMP_26M VPD = SVP - VP; * VPD is saturated vapour pressure deficit * VP is vapour pressure Rn_G = Rn - SHF; * Rn is R_NET_16M; SHF is SOIL_HEAT_FLUX_7CM if month >= 6 and month <=8 then R = exp(0.6038 + 0.0833 *Ts5cm + 0.0096 * Tskye); * Respiration else R = exp(0.2688 + 0.0874 *Ts5cm + 0.0413 * Tskye); RTa = exp(0.403+0.0875*Tskye); * Respiration as function of AIR_TEMP_26M only RTs5 = exp(0.117+0.1483*Ts5cm); * Respiration as function of SOIL_TEMP_5CM only retain Tmin -3 Topt 18 Tmax 32; P = (Tmax-Topt)/(Topt-Tmin); if Tskye > Tmin and Tskye < Tmax then At = ((Tskye - Tmin)*((Tmax-Tskye)**P)) / ((Topt-Tmin)*((Tmax-Topt)**P)); else At = 0; * At is assimilation =(CO2 flux - respiration) as * normalised function of AIR_TEMP_26M if VPD < 1.3 then Ad = 1; * Ad is assimilation as a normalised else if VPD > 5 then Ad = 0; * function of VPD else Ad = 1 -1/(5- 1.3)*(VPD - 1.3); if month =3 then qfe = 0.0002; * Quantum flux efficiency if month =4 then qfe = 0.004; if month =5 then qfe = 0.013; if month =6 then qfe = 0.027; if month =7 then qfe = 0.035; if month =8 then qfe = 0.032; if month =9 then qfe = 0.031; if month =10 then qfe = 0.011; if month =11 then qfe = 0.0006; Amax=50; theta = 0.8; Aq = ((qfe*parin+Amax) - sqrt( (qfe*parin+Amax)**2-4*theta*qfe*Amax*parin)) / 2*theta; * Light response curve, NOT normalised (parin is PPFD_26M ) Amodel=Aq*Ad*At; * Assimilation model s function of PPFD, VPD and temperature Fcmodel = -Amodel+R; * CO2_FLUX_26M model if parin = 0 then do; if Fc = . or friction < 0.35 then * friction is FRICTION_VELOCITY if R = . then if Rta = . then Fc_fill = RTs5; else Fc_fill = RTa; else Fc_fill= R; else Fc_fill = Fc; if E = . or friction < 0.35 then E_fill = 0; else E_fill = E; if LE = . or friction < 0.35 then LE_fill= 0; else LE_fill = LE; if H = . or friction < 0.35 then if shf = . then H_fill = Rn; else H_fill = Rn_G; else H_fill = H; end; else /* if parin > 0; */ do; if Fc = . then if Ts5cm = . then Fc_fill = -Amodel + RTa; else Fc_fill = Fcmodel; else Fc_fill = Fc; if LE = . then if month = 3 then if shf = . then LE_fill = 0.04 * Rn; else LE_fill = 0.04*Rn_G; else if shf = . then LE_fill = 0.30 * Rn; else LE_fill = 0.30*Rn_G; else LE_fill = LE; if E = . then E_fill = LE_fill/44.4; else E_fill = E; if H = . then if shf = . then H_fill = 0.62 *Rn; else H_fill = 0.62 * Rn_G; else H_fill = H; end; drop VPD CUMTEMP AD AT AQ AQlonly AMMAX LNAMMAX weeks2 week qfe amax theta fcres Rn_G Amodel Fcmodel R RTa RTs5 A P Tmin Topt Tmax SVP; run; /*************************************************************************/ 9.4 Graphs and Plots None. 10. Errors 10.1 Sources of Error The EC system was placed on an upright pole 3 m above the top of the tower so that the tower would cause very little disturbance to the wind, whatever its direction. Therefore, EC measurements would not be especially invalidated by any wind direction with respect to the tower; however, the access trail to the site is to the east, and any production of CO2 by people or vehicles on the trail may affect the CO2 fluxes measured if the wind is from the east. Also, in the making of the access trail, extensive damage was caused to the muskeg, with many trees being felled; hence, photosynthesis over this area will be uncharacteristically lower and respiration similarly high. The eddy flux measurements on calm nights underestimate the surface fluxes. This problem is address in the filled data columns. 10.2 Quality Assessment 10.2.1 Data Validation by Source None given. 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 See Section 10.1. 11.2 Known Problems with the Data For the 1994 data: Soil temperature at 1 m: before 1-July-1994 this was measured using a thermistor from which the signal was very noisy. On 1-July-1994 at 22:30 Greenwich Mean Time (GMT) this thermistor was replaced by a thermocouple with a much more accurate output. There was no trend in the soil temperature at 1 m before 15- June-1994 at 02:00 with a mean of 0 °C and the noisy values for this period have been replaced with 0 °C. From 1-June 02:00 GMT until 1-July-1994 20:00 GMT, the signal has been smoothed. Any true diurnal trend has been removed by this substitution, but the values are estimated to be within 0.3 °C. EC measurements: The data acquisition software missed the flux averaging times shown below. (This failure was caused by a fragmented hard disk making disk access slow.) Data were not lost, although the fluxes were not averaged at the end of the half hour, but at the end of an hour. Therefore, the missing averages (at the times shown below) have been substituted with the value calculated at the next half hour (times given as GMT): Day: 26/07/94 Times: 03:30, 05:30, 07:30, 09:30, 11:30, 13:30, 15:30, 21:30, 23:30 Day: 27/07/94 Times: 00:30 01:30 03:30 05:30 06:00 07:30 09:30 11:30 13:30 19:00 21:00 23:00 Day: 28/07/94 Times: 00:00, 01:00, 03:00, 07:00, 09:00, 12:30, 13:00, 14:30, 15:00, 15:30, 16:30, 18:30, 20:30, 22:30 Day: 29/07/94 Times: 00:30, 02:30, 04:30, 06:30, 08:30, 10:30, 12:30, 14:30, 15:00, 16:30, 18:30, 20:30, 21:00, 22:30, 23:00 Day: 30/07/94 Times: 00:30, 02:30, 03:00, 04:30 Day: 09/08/94 Times: 18:00, 22:00 Day: 10/08/94 Times: 04:00, 06:00, 08:00, 10:00, 12:00, 14:00, 16:00, 18:00, 20:00, 22:00, 23:30 Day: 11/08/94 Times: 00:00, 01:30, 02:00, 03:30, 04:00, 06:00, 08:00, 09:30, 10:00, ,11:30, 12:00, 14:00, 16:00, 18:00, 20:00, 21:30, 22:00, 23:30 Day: 12/08/94 Times: 00:00, 01:30, 02:00, 03:30, 04:00 Day: 29/08/94 Times: 17:30, 19:30, 21:30, 23:30 Day: 30/08/94 Times: 01:30, 03:30, 05:30, 07:30, 09:30, 11:30, 13:30, 15:00, 15:30, ,17:00, 17:30, 19:30, 21:30, 23:00, 23:30 Day: 31/08/94 Times: 01:00, 01:30, 02:00 Day: 09/09/94 Times: 02:00, 04:00, 12:00, 14:00, 16:00, 18:00, 20:00, 22:00 Day: 10/09/94 Times: 00:00, 02:00, 04:00, 06:00, 08:00, 10:00, 12:00, 14:00, 16:00, 18:00 Day: 17/09/94 Times: 06:00, 18:00, 21:30 Day: 18/09/94 Times: 01:30, 03:30, 05:30, 07:30, 09:30, 11:30, 13:30, 15:30, 17:30, ,19:30, 21:30, 23:30 Day: 19/09/94 Times: 01:30, 03:30, 05:30, 07:30 11.3 Usage Guidance None given. 11.4 Other Relevant Information None given. 12. Application of the Data Set These data are useful for the study of water, energy, and carbon exchange in a mature black spruce forest. 13. Future Modifications and Plans None. 14. Software 14.1 Software Description Some samples of code used in the analysis are shown in Section 9.3.2. 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 None. 17.2 Journal Articles and Study Reports Jarvis, P.G., J.M. Massheder, S.E. Hale, J.G. Moncrieff, M. Rayment, and S. L. Scott. 1997. Seasonal variation of carbon dioxide, water vapour and energy exchanges of a boreal black spruce forest. JGR. 102(D24):28953-28966. Kaimal, J.C. and Gaynor, J.E. 1991. Another look at sonic thermometry. Bound. Layer Meteorol. 56:401-410. Moore, C.J. 1986. Frequency response corrections for eddy correlation systems. Bound. Layer Meteorol. 37:17-35. Pearcy, R.W., J. Ehleringer, H. A. Mooney, and P.W. Rundel. 1991. Plant Physiological Ecology: Field methods and instrumentation. Chapman and Hall, London and New York. Philip, J.R. 1963. The damping of a fluctuating concentration by continuous sampling through a tube. Aust. J. Phys. 16:454-463. Scheupp, P.H., M.Y. Leclerc, J.I. Macpherson, and R.L. Desjardins, R.L. 1990. Bound. Layer Meteorol. 50:355-373. 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. Bound. Layer Meteorol. 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., 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 earlyresults from the 1994 field year. Bulletin of the American Meteorological Society. 76(9):1549-1577. Sellers, P., F. Hall, and K.F. Huemmrich. 1996. Boreal Ecosystem-Atmosphere Study: 1994 Operations. NASA BOREAS Report (OPSDOC 94). Sellers, P.and F. Hall. 1996. Boreal Ecosystem-Atmosphere Study: Experiment Plan. Version 1996-2.0, NASA BOREAS Report (EXPLAN 96). Sellers, P., F. Hall, and K.F. Huemmrich. 1997. Boreal Ecosystem-Atmosphere Study: 1996 Operations. NASA BOREAS Report (OPSDOC 96). 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, BOREAS in 1997: Experiment overview, scientific results, and future directions, Journal of Geophysical Research, 102 (D24), 28731-28769, 1997. Webb, E.K., G.I. Pearman, and R. Leuning. 1980. Correction of flux measurements density effects due to heat and water vapour transfer. Quart. J. R. Met. Soc. 106:85-100 17.3 Archive/DBMS Usage Documentation None. 18. Glossary of Terms None. 19. List of Acronyms A/D - Analog to Digital ASCII - American Standard Code for Information Interchange BOREAS - BOReal Ecosystem-Atmosphere Study BORIS - BOREAS Information System DAAC - Distributed Active Archive Center EC - Eddy Covariance EOS - Earth Observing System EOSDIS - EOS Data and Information System GMT - Greenwich Mean Time GSFC - Goddard Space Flight Center i.d. - internal diameter 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 PC - Personal Computer PPFD - Photosynthetic Photon Flux Density REBS - Radiation Energy Balance Systems SSA - Southern Study Area TF - Tower Flux URL - Uniform Resource Locator WAB - Wind Aligned Blob WMO - World Meteorological Organization 20. Document Information 20.1 Document Revision Date Written: 22-May-1998 Revised: 06-Oct-1998 20.2 Document Review Date(s) BORIS Review: 06-Oct-1998 Science Review: 20.3 Document ID 20.4 Citation P.G. Jarvis, J.M. Massheder, J.B. Moncrieff, and M.B. Rayment, Institute of Ecology and Resource Management, Edinburgh University. 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 TF09_Flux_Met.doc 10/09/98