Minnesota 1973 Atmospheric Boundary Layer Experiment
Purpose: To make measurements of 1) the vertical fluxes of momentum and heat and 2) profiles of wind velocity and temperature within the planetary boundary layer.
Location: Northwestern Minnesota. (48°34 N latitude and 96°51 1W longitude; elevation 255 m above sea level)
When: September 10-17, 1973.
Number of Tests: 11
Nature of Experiment: A full-scale measurement program over flat, smooth terrain to measure turbulent fluxes at multiple levels from a 32-m tower and a tethered balloon. The meteorological conditions were fully developed stationary convective periods, with mixing depths to approximately 2300 m. Meteorological measurements included, mean profiles of winds and temperatures, and fluctuations of three wind components and temperatures. The measurements were obtained through a combination of tower, tethered balloon, and slow-ascent Rawinsondes. We especially thank Yutaka Izumi of the Air Force Geophysical Laboratory who provided the original Minnesota 1973 rawinsonde data so that it could be added to the data set.
NARRATIVE DESCRIPTION OF EXPERIMENT AND DATA
Site
A full-scale planetary boundary layer field experiment was conducted in northwestern Minnesota in the late summer of 1973 (Izumi and Caughey, 1976; Readings, Haugen and Kaimal, 1974). The site was at the middle of the southern edge of an extremely flat, square-mile section of farm land about 3 km east of Donaldson 48°34" N latitude and 96°51" 1W longitude; elevation 255 m above sea level). The surface cover was wheat stubble and narrowed soil. The fetch was undisturbed for 10 km to the north in the wind direction used for observations.
Measurements
The data from the surface to 32 m were collected from a tower, and those from 61 to 1220 m were collected from a 330-cu-m kite balloon. A second 4-m tower was located 40 m away from the main tower and supported one level of turbulence instrumentation. The specific measurements, elevations, methods, and observation schedules are listed below:
MEASUREMENTS |
LOCATION |
METHODS |
FREQUENCY |
Mean wind speed and wind direction |
At 1, 2, 4, 8, 16, and 32m 5 levels from 61 to 1220m |
Two-axis sonic anemometers MRU turbulence probe (magneflux vane and cup) |
Continuous for 11 afternoon periods |
Mean temperatures |
At 0.5, 1, 2, 4, 8, 16, and 32m 5 levels from 61 to 1220m |
Quartz thermometers
Platinum wire resistance thermometers |
Continuous for 11 afternoon periods |
Fluctuating wind components (U,V,W) and temperature |
At 4 and 32m on main tower and 4m on adjacent mast At 5 levels from 61 to 1220m |
Three-axis sonic anemometers
Hot wire inclinometers, Eight cup polystyrene rotor, Platinum wire thermometer |
Continuous for 11 afternoon periods |
Pressure, temperature, relative humidity, and wind speed |
To 3km |
Slow-ascent rawinsonde |
Every 2-hr day and evening, and 3- to 4-hr at night |
The tower winds and temperatures were sampled once per second and the tower and balloon turbulence instruments were sampled 10 times per second. Drag plate measurements were reportedly attempted but their success is not known and not reported.
Data
Eleven 75-minute runs were documented by Izumi and Caughey (1976) and are contained in this archive. The reported results did not contain the slow ascent rawinsonde data, however, and these have been added in this archive using original data provided by Izumi. These runs span the period from early to late afternoon, although data were collected through the nocturnal transition. The nocturnal transition data were not analyzed or reported by Izumi and Caughey and are not part of the data archive at this time; however, they are the subject of a journal article by Caughey.
Wyngaard and Kaimal (1979). The archived data consist of the data tables reported by Izumi and Caughey (1976) and the added rawinsonde data. The data tables for each run include:
1) summary statistics including: friction velocity, surface heat flux, scaling temperature, Monin-Obukhov length, mixing height, convective velocity scale
2) profiles of temperature, wind speed and direction, velocity component and temperature standard deviations and momentum and heat fluxes.
The unpublished rawinsonde values were checked as part of the archiving process. The raw rawinsonde data were used to recompute the wind profiles. This was accomplished using a rawinsonde computer program at the Hanford Meteorological Station. Reasonable agreement occurred between the outputs of this program and the reduced data listings for most of the profiles. The following lists the exceptions that were found. Ascension numbers 36, 40, and 58 had wind speeds that seemed too high and ascension numbers 17, 18. 26, 54, and 57 had wind speeds that seemed too low. Also ascension number 17 wind directions did not agree. All the profiles of temperature and relative humidity were checked and appeared to be correctly derived. Some of the discrepancies noted may be the result of using different recording intervals. The failure to duplicate certain profiles does not mean they are incorrect, but that these identified profiles should be used with caution. The archived data includes both the raw and reduced data listings.
SPECIAL INFORMATION
Some unique aspects of the Minnesota 1973 data are the high vertical spatial density of comparable turbulence measurements in the surface layer and extending to a height of 1220 m in the mixed layer. Profile and turbulence measurements above 32 m were obtained utilizing the balloon-borne instruments and techniques developed by the Meteorological Research Unit (MRU) of the British Meteorological Office, Royal Air Force, Cardington, England (Readings and Butler, 1972). The comparability of the tower and balloon-borne instruments and measurements was established before the Minnesota 1973 experiment by Readings and Butler (1972) and Haugen et al. (1975). In addition, comparability tests were made before each field run during the experiment. These comparisons and the Minnesota experiment have an added significance in that they establish a basis for comparability to a significant body of data generated by the MRU over many years in the United Kingdom.
DIGITAL FILE DESCRIPTION
The archived Minnesota 1973 data are in six (6) files. The six files follows a data archival format developed by Battelle, Pacific Northwest Laboratories for the U.S. Environmental Protectin Agency. The archival format was designed to make the results of extensive field tests readily accessible for model testing, development, and verification efforts.
Minnesota 1973 Digital Data Files:
M73File1.txt (1KB) – Headings for Files 2-6.
M73File2.txt (40KB) – November 1986 report documenting the production and format of the 1973 Minnesota data archive files.
M73File3.txt (5KB) – Listing and definition of data variables
M73File4.txt (2KB) – Brief summary of conditions occurring during the eleven sampling periods.
M73File5.txt (159KB) – Main listing of all data.
M73File6.txt (1KB) - Listing of original names for the six(6) data files.
REFERENCES
The original Minnesota 1973 data for the 11 reported runs and a detailed description of the experiment are contained in the report by Izumi and Caughey (1976) and the paper by Readings, Haugen and Kaimal (1974). The data for the nocturnal transition period were transferred to and analyzed and reported by Caughey, Wyngaard and Kaimal (1979).
A list of the reports and papers mentioned above for the Minnesota 1973 data follows:
Caughey, S. J., J. C. Wyngaard and J. C. Kaimal (1979): Turbulence in the Evolving Stable Boundary Layer. J. Atmos. Sci., 36:1041-1052.
Haugen, D. A., J. C. Kaimal, C. J. Readings and R. Rayment (1975): A Comparison of Balloon-Borne and Tower-Mounted Instrumentation for Probing the Atmospheric Boundary Layer. J. Appl. Meteor., 14:540-545.
Izumi, Y., and J. S. Caughey. Minnesota (1976) (1.1MB): Atmospheric Boundary Layer Experiment Data Report (1976): AFCRL-TR-76-0038, Environmental Research Papers No. 547, Meteorology Laboratory, Project 7655, Air Force Cambridge Research Laboratories, Hanscom AFB, Massachusetts.
Readings, C. J., and H. E. Butler (1972): Turbulence from a Captive Balloon. Meteorological Magazine, 101:286-298.
Readings, C. J., D. A. Haugen and J. C. Kaimal (1974a): The 1973 Minnesota Atmospheric Boundary Layer Experiment. Weather, 29:309-312.
Readings, C. J., D. A. Haugen and J. C. Kaimal (1974b) (132KB): The 1973 Minnesota Atmospheric Boundary-Layer Study. Meteorological Office Boundary Layer Research Branch Turbulence & Diffusion Note, MET.O.14, T.D.N. No. 45. January 1974, 12 pages.
Additional references for these data are:
Caughey, S. J., and S. G. Palmer (1979): Some Aspects of Turbulence Structure Through the Depth of the Convective Boundary Layer. Quart. J. R. Meteorol. Soc., 105:811-827.
Kaimal, J. C., J. C. Wyngaard, D. A. Haugen, O. R. Cote, Y. Izumi, S. J.
Caughey and C. J. Readings (1976): Turbulence Structure in the Convective Boundary Layer. J. Atmos. Sci., 33:2152-2169.
Kaimal, J. C. (1978): Horizontal Velocity Spectra in an Unstable Surface Layer.
J. Atmos. Sci., 35:18-24.
Wyngaard, J. C. (1975): Modeling the Planetary Boundary Layer - Extension to the Stable Case. Boundary Layer Meteorology, 9:441-460.