BOREAS HYD-05 Bear Trap Creek and Namekus Lake Winter Surface Flux Data Summary The BOREAS HYD-05 team collected tower flux, surface meteorological, and surface temperature data on a frozen lake (Namekus Lake) and in a mature jack pine forest in the Beartrap Creek watershed. Both sites were located in the BOREAS SSA. The objective of this study was to characterize the winter energy and water vapor fluxes, as well as related properties (such as snow density, depth, temperature, and melt) for forested and nonforested areas of the boreal forest. Data were collected on Namekus Lake in the winters of 1994 and 1996, and at Beartrap Creek in the winter of 1994 only. 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 HYD-05 Winter Surface Fluxes 1.2 Data Set Introduction Surface flux, meteorological, and temperature data were collected on the frozen surface of Namekus Lake and in a mature, slightly open, jack pine stand (Pinus banksia) in the Beartrap Creek catchment. Both sites are in the Prince Albert National Park (PANP) in the BOReal Ecosystem-Atmosphere Study (BOREAS) Southern Study Area (SSA). Data were collected on Namekus Lake in the winters of 1994 and 1996 and at Beartrap Creek in the winter of 1994 only. 1.3 Objective/Purpose The objective of this study was to characterize the winter energy and water vapor fluxes, as well as related properties (such as snow density, depth, temperature, and melt) for forested and nonforested areas of the boreal forest. 1.4 Summary of Parameters and Variables Latent heat flux, sensible heat flux, net radiation, humidity, wind speed and direction, air temperature, incident and reflected shortwave radiation, and surface temperature data were collected. 1.5 Discussion A comparison of a surface meteorology and energy balance of a snow-covered lake and an adjacent forest area was made. There were small, but measurable, contrasts in the temperature and wind speed measured over the lake and forest (the lake was cooler and windier), but it is the comparison of the energy balance of the forest and the open snow surface that is dramatic: the mean net radiation flux was into the forest canopy but out of the snow-covered lake. Similarly, when the forest canopy was clear of snow, the sensible heat flux was of different sign (and magnitude) over the forest and lake. When the forest canopy was snow- covered the partition of the sensible and latent heat fluxes was different again, exhibiting a large upward latent heat flux and a compensating downward sensible heat flux. 1.6 Related Data Sets Tower flux measurements made in the winter at other sites: BOREAS TF-01 SSA OA Tower Flux, Meteorological, and Soil Temperature Data BOREAS TF-03 NSA OBS Tower Flux, Meteorological, and Soil Temperature Data BOREAS TF-09 SSA OBS Tower Flux, Meteorological, and Soil Temperature Data Other measurements made at the HYD-05 sites: BOREAS HYD-03 Snow Measurements 2. Investigator(s) 2.1 Investigator(s) Name and Title Richard Harding Institute of Hydrology 2.2 Title of Investigation The Regional Representation of the Energy and Moisture Fluxes from Snow Covered Areas in the BOREAS Experiment 2.3 Contact Information Contact 1 --------- Richard Harding Institute of Hydrology Crowmarsh Gifford Wallingford Oxfordshire United Kingdom 44 1491 838800 44 1491 832256 (fax) R.Harding@unixa.nerc-wallingford.ac.uk Contact 2 ------------- 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 This study collected data to contrast the winter energy and water vapor fluxes for forested and nonforested areas of the boreal forest. The long, cold winter characteristic of the boreal forest causes cessation of growth for 5 to 7 months of the year and is the most distinguishing feature of this biome. The components of the energy balance, which determine the net energy supply to the canopy and the snow surface, are small during this winter period - with direct effects on biological activity. Most of the components of the energy balance: the radiation flux (solar and thermal), sensible heat flux (turbulent transfer of heat from the surface to the atmosphere), latent heat flux (evaporative cooling or warming upon condensation), and to a lesser degree the soil heat flux, are strongly influenced by the presence and depth of snow cover and its interaction with vegetation. Snow reflects most incident solar radiation and hence dramatically reduces the net radiative energy input. However, when the snow covers a forest canopy, the multiple reflections within the canopy scatter rather than reflect the majority of incident radiation, and the albedo remains low (Harding and Pomeroy, 1996; van de Hulst, 1957; Oke, 1978). 4. Equipment 4.1 Sensor/Instrument Description 4.1.1 Collection Environment There were two sites in this study. The first site was a mature, slightly open, jack pine stand (Pinus banksia) in the Beartrap Creek catchment. The fetch was level and reasonably uniform for at least 100 m. The pine canopy was 16-22 m in height with a sparse understory of deciduous bushes. The winter "leaf" (branch and needle) area index of this stand was 2.2, and the canopy cover of sky was 82% measured with a LI-COR LAI-2000 Canopy Density meter (Gower and Norman, 1991). The second site was on the snow-covered frozen surface of Namekus Lake, 10 km southeast of the jack pine stand. The surface was quite smooth (snow over ice), and the fetch exceeded 700 m. Data were collected at both sites during winter periods, experiencing temperatures as low as -37 °C on the lake to a high of 18 °C over the forest. 4.1.2 Source/Platform The Beartrap Creek site was equipped with a 26-m meteorological tower from which measurements were taken of shortwave radiation (downward and reflected) and net all-wave radiation above and below the canopy, along with vertical profiles of temperature, humidity, snow particle flux, and wind speed through the canopy. A "Hydra" eddy correlation system was also operated from the top of the tower for direct measurement of sensible and latent heat fluxes (Shuttleworth et al., 1988). Hydra was developed at the Institute of Hydrology. It consists of a vertical component sonic anemometer, a fine wire thermocouple thermometer, an infrared absorption hydrometer, and a fast response cup anemometer. A second eddy correlation system measuring only sensible heat flux was operated from the tower. This consisted of a "solent" sonic anemometer (Gill Instruments Ltd., Lymington, U.K.), a fine wire thermocouple, and a Campbell Scientific CR21 with software similar to that described by Shuttleworth et al. (1988). The net all-wave radiation above the canopy was measured with two instruments, both on short (~2 m) booms at the top of the tower; a Middleton radiometer and a Radiation Energy Balance Systems (REBS), Seattle, Washington) Q*5. Below the canopy, shortwave and net all-wave radiation were measured with "Delta 7" tube radiometers (Delta-T Devices Ltd., Cambridge, U.K.). These tubes (almost 1 meter in length) average the speckled light found beneath the canopy (Szeicz et al,. 1964). The Namekus Lake site was equipped with a 3-m mast with instruments to measure the two shortwave components of the radiation balance, the all-wave net radiation, temperature, humidity, snow particle flux, and wind speed (at 1, 2, and 3 m) above the snow surface. A second Hydra was operated to provide fluxes of heat and water vapor. Nipher-shielded snow gauges under the forest canopy and in a nearby open area provided weekly snowfall and snow interception. Weekly snow surveys, both underneath the forest canopy and on the lake, were undertaken to give average snow depth and the water equivalent of the pack. 4.1.3 Source/Platform Mission Objectives Towers were established to support the measurement of tower flux, surface meteorological, and surface temperature data on a frozen lake (Namekus Lake) and in a mature jack pine forest (Beartrap Creek). 4.1.4 Key Variables Latent heat flux, sensible heat flux, net radiation, humidity, wind speed and direction, air temperature, incident and reflected shortwave radiation, and surface temperature data were collected. 4.1.5 Principles of Operation The Hydra, based on the eddy correlation technique, consists of sensors and real- time and offline computers. It is a complete instrumentation system, designed specifically to provide routine measurements of the surface energy fluxes with minimum supervision. 4.1.6 Sensor/Instrument Measurement Geometry Beartrap Creek site: At the top of a 26-m meteorological tower: Hydra eddy correlation system and a Solent sonic anemometer. On short (~2 m) booms at the top of the tower: a Middleton radiometer and a REBS Q*5. Below the canopy: Delta 7 tube radiometers. Namekus Lake site: A 3-m mast with a Hydra eddy correlation system and instruments to measure the two shortwave components of the radiation balance, the all-wave net radiation, temperature, humidity, snow particle flux, and wind speed (at 1, 2, and 3 m) above the snow surface. The Hydra has to be set up so that the sonic anemometer is at right angles to the local stream lines of the flow. Nipher-shielded snow gauges under the forest canopy and in a nearby open area. 4.1.7 Manufacturer of Sensor/Instrument Hydra eddy correlation system: Developed at the Institute of Hydrology Hydra consists of a vertical component sonic anemometer, a fine wire thermocouple thermometer, an infrared absorption hydrometer, and a fast response cup anemometer. Solent sonic anemometer: Gill Instruments Limited Solent House Cannon Street Lymington, Hampshire SO41 9BR UK Campbell Scientific CR21: Campbell Scientific P.O. Box 551 Logan, UT 84321 USA REBS Q*5: Radiation Energy Balance Systems P.O. Box 15512 Seattle, WA 98115-0512 USA Delta 7 tube radiometers: Delta-T Devices Ltd. 128 Low Rd, Burwell, Cambs CB5 .0EJ UK 4.2 Calibration 4.2.1 Specifications A constant check of the Hydra's performance is made on a 24-hour basis by checking that the sum of sensible and latent heat fluxes is equivalent to the available energy for this same period. +/-10% is considered good, although +/- 20% is quite common, especially when weather conditions are changeable. If errors become consistent or if a failure occurs, a spare set of sensors and electronics is carried with each Hydra, which is designed to accept changeover in the field easily. 4.2.1.1 Tolerance Not known. 4.2.2 Frequency of Calibration The Hydra is calibrated typically once a year if it is not overseas for longer than this. 4.2.3 Other Calibration Information Not known. 5. Data Acquisition Methods None given. 6. Observations 6.1 Data Notes None given. 6.2 Field Notes None given. 7. Data Description 7.1 Spatial Characteristics 7.1.1 Spatial Coverage All data were collected at two sites in PANP in the BOREAS SSA. The North American Datum 1983 (NAD83) coordinates of these sites were: Site Latitude Longitude -------------- ----------- ------------ Beartrap Creek 53.84779° N 106.17090° W Namekus Lake 53.83101° N 106.04127° W 7.1.2 Spatial Coverage Map Not available. 7.1.3 Spatial Resolution The data represent point source measurements taken at the given locations. The location and size of the footprint from which the measurements were made varied with ambient meteorological conditions. At the Beartrap Creek site, the fetch was level and reasonably uniform for at least 100 m. At the Namekus Lake site the surface was quite smooth (snow over ice) during data collection, and the fetch exceeded 700 m. 7.1.4 Projection Not applicable. 7.1.5 Grid Description Not applicable. 7.2 Temporal Characteristics 7.2.1 Temporal Coverage For the Beartrap Creek site, measurements are available from 03-Feb to 17-Apr- 1994. For the Namekus Lake site, measurements are available from 10-Feb to 28- Mar-1994 and 17-Mar to 07-Apr-1996. 7.2.2 Temporal Coverage Map All data were collected at the Beartrap Creek and Namekus Lake sites. 7.2.3 Temporal Resolution Data values are reported hourly. 7.3 Data Characteristics Data characteristics are defined in the companion data definition file (h5flxd.def). 7.4 Sample Data Record Sample data format shown in the companion data definition file (h5flxd.def). 8. Data Organization 8.1 Data Granularity The Bear Trap Creek and Namekus Lake Winter Surface Flux Data are contained in separate datasets. 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 (h5flxd.def). 9. Data Manipulations 9.1 Formulae See Shuttleworth et al. (1988) for a description of formulas used in the Hydra data processing. 9.1.1 Derivation Techniques and Algorithms None given. 9.2 Data Processing Sequence 9.2.1 Processing Steps See Shuttleworth et al. (1988) for a description of the Hydra data processing. BORIS staff processed these data by: 1) Reviewing the initial data files and loading them online for BOREAS team access. 2) Designing relational database tables to inventory and store the data. 3) Loading the data into the relational database tables. 4) Working with the team to document the dataset. 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 None given. 9.4 Graphs and Plots None. 10. Errors 10.1 Sources of Error Factors contributing to instrument errors include signal-to-noise ratio, height of the instrument, and sensor separation. Non-steady conditions and surface inhomogeneities are sources of natural variability. 10.2 Quality Assessment At the Namekus Lake site, the sum of the turbulent fluxes agrees reasonably with the input net radiation. At the Beartrap Creek site, the net radiation was measured by two completely separate systems, which agreed to within 10 W m-2, and the sensible heat fluxes were measured by two systems, and again the agreement was within a few watts per square meter. Finally, measurement of the latent heat flux using eddy correlation is strongly supported by measurements from the weighted tree, which gave a continuous output of the weight of the snow on the forest canopy (the weighted tree data were not submitted to BORIS, contact the investigator for these data). 10.2.1 Data Validation by Source Over the Namekus Lake, the sum of the turbulent fluxes agrees reasonably with the input net radiation (particularly considering the small size of the fluxes). Unfortunately, neither snowmelt nor ground (ice) heat fluxes were measured at this site; but the energy closure, neglecting these, suggests they were small. However, there appears to be an imbalance between the sensible and latent heat fluxes and the radiation input in the forest; the energy from net radiation and downward sensible heat flux could not provide sufficient energy to supply the high observed evaporation. Measurements of ground heat flux are typically 2 W m-2 and so could not provide this energy. It seems unlikely that the flux measurements were seriously in error: the net radiation was measured by two completely separate systems, which agreed to within 10 W m-2. The sensible heat fluxes were again measured by two systems, and again the agreement was within a few watts per square meter. Finally, measurement of the latent heat flux using eddy correlation is strongly supported by measurements from the weighted tree. It is possible that there was some strong horizontal advection at this site (with the localized radiation measurements being unrepresentative of the "footprint" of the measurements of the turbulent fluxes), or there is also the possibility of some large change of heat storage within the trunk space. 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 These data were collected while the ground was snow covered. 11.2 Known Problems with the Data There appears to be an imbalance between the sensible and latent heat fluxes and the radiation input in the forest at the Beartrap Creek site; the energy from net radiation and downward sensible heat flux could not provide sufficient energy to supply the high observed evaporation. Measurements of ground heat flux are typically 2 W m-2 and so could not provide this energy. It is possible that there was some strong horizontal advection at this site (with the localized radiation measurements being unrepresentative of the "footprint" of the measurements of the turbulent fluxes), or there is also the possibility of some large change of heat storage within the trunk space. This imbalance obviously requires further study. 11.3 Usage Guidance None given. 11.4 Other Relevant Information None given. 12. Application of the Data Set This data set is useful for studying the winter energy and water balance of both open and forested sites. 13. Future Modifications and Plans None given. 14. Software 14.1 Software Description None given. 14.2 Software Access None given. 15. Data Access 15.1 Contact for Data Center/Data Access Information These BOREAS data are available from the Earth Observing System Data and Information System (EOS-DIS) 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 15.2 Procedures for Obtaining Data BOREAS data may be obtained through the ORNL DAAC World Wide Web site at http://www-eosdis.ornl.gov/ or users may place requests for data by fax, telephone, or electronic mail. 15.3 Output Products and Availability Requested data can be provided electronically on the ORNL DAAC's anonymous FTP site or on various media including, CD-ROMs, 8-MM tapes, or diskettes. The complete set of BOREAS data CD-ROMs, entitled "Collected Data of the Boreal Ecosystem-Atmosphere Study", edited by Newcomer, J., et al., NASA, 1999, are also available. 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 Gower, S.T., and J.M. Norman. 1991. Rapid estimation of leaf area index in conifer and broad-leaf plantations. Ecology. 72: 1896-1900. Harding, R.J., and J.W. Pomeroy. 1996. The energy balance of the winter boreal landscape. Journal of Climate. 9(11): 2778-2787. Oke, T.R. 1978. Boundary Layer Climates. Methuen and Sons, pp. 110-112. Pomeroy, J.W., and K. Dion. 1996. Winter radiation extinction and reflection in a boreal pine canopy: measurements and modeling. Hydrol. Process. 10(12): 1591- 1608. 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 early results 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 (OPS DOC 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 (OPS DOC 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. 1997. BOREAS in 1997: Experiment overview, scientific results, and future directions. Journal of Geophysical Research 102(D24):28731-28769. Shuttleworth, W.J., J.H. C. Gash, C.R. Lloyd, D.D. McNeil, C.J. Moore, and J.S. Wallace. 1988. An integrated micrometeorological system for evaporation measurement. Agric. Meteor. 43: 295-317. Szeicz, G., J.L. Monteith, and J. dos Santos. 1964. A tube solimeter to measure radiation among plants. J. Appl. Ecol. 1: 169-174. Van de Hulst, H.C. 1957. Light Scattering by Small Particles. Wiley and Sons, 470 pp. 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 GSFC - Goddard Space Flight Center HYD - Hydrology NAD83 - North American Datum of 1983 NASA - National Aeronautics and Space Administration NSA - Northern Study Area OBS - Old Black Spruce ORNL - Oak Ridge National Laboratory PANP - Prince Albert National Park SSA - Southern Study Area TF - Tower Flux URL - Uniform Resource Locator 20. Document Information 20.1 Document Revision Date Written: 13-Jul-1998 Revised: 14-Sep-1998 20.2 Document Review Date(s) BORIS Review: 15-Jul-1998 Science Review: 17-Aug-1998 20.3 Document ID 20.4 Citation Data were collected by R.J. Harding. Please cite the following article when using these data: Harding, R.J., and J.W. Pomeroy. 1996. The energy balance of the winter boreal landscape. Journal of Climate. 9(11): 2778-2787. 20.5 Document Curator 20.6 Document URL Keywords TOWER FLUX METEOROLOGY SNOW WINTER SENSIBLE HEAT FLUX LATENT HEAT FLUX NET RADIATION AIR TEMPERATURE WIND SPEED SURFACE TEMPERATURE HYD05_Flux.doc 09/14/98