The BOREAS Information System
Airborne Fluxes and Meteorology (AFM)


AFM-2: Airborne Investigation of Biosphere -- Atmosphere Interactions Over the Boreal Forest


P.I.(s): Robert D. Kelly -- University of Wyoming
Co-I(s): Donald H. Lenschow -- National Center for Atmospheric Research (NCAR)

Objectives: To characterize the fluxes of momentum, sensible and latent heat and carbon dioxide over the boreal forest, using the Wyoming King Air (FK) and NCAR Electra (AFM-3) (FE). Variations in these fluxes as related to time of day, season, weather, soil and vegetation type and maturity (e.g., new growth vs. old growth forests), surface features and location within the boreal forest zone (e.g. southern vs. northern edge) were investigated. The objective is to determine the suitability and reliability of these factors as predictors of the fluxes.
Crucial to this is the question of variability as a function of scale; namely, how are the scales and magnitudes of the flux variations related to the scales and types of surface variations? Flux variations are also generated by variability in cloudiness. Patchy low-level cumuliform and stratiform clouds are common in this region, and a fundamental question being investigated is how the transient variations induced by cloudiness can be distinguished from those induced by surface variations. These issues are part of a more general problem being addressed when characterizing fluxes over particular regions of interest: describing and estimating errors in flux measurements, and developing measurement strategies appropriate for characterizing fluxes over inhomogeneous surfaces.

AFM-2 Pictures

The University of Wyoming King Air

AFM-2 Data Sets

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    AFM-2 BOREAS Operations in 1994


    Objectives:
    The primary objectives were to use the University of Wyoming King Air research aircraft for measurement of fluxes, profiles, and budgets of sensible heat, latent heat, and carbon dioxide in the boundary layer over the BOREAS experiment areas. Analyses are focused in several areas, including:

    1. comparison of King Air flux measurements with those from the other 3 flux aircraft (Twin Otter, Electra, Long-EZ) and from the surface tower
    2. studies of the scales of boundary layer processes, including the fluxes, by means of spectral analysis and conditional sampling
    3. footprint analysis in coordination with similar studies for the Twin Otter
    4. the effects of seasonal changes, vegetation types, and clouds and smoke on the various fluxes
    5. error analysis of the flux values


    Type of Data/Instrumentation:
    The King Air flux measurements were obtained with the eddy covariance method, using the following instruments:

    1. a boom-mounted gust probe with a laser-ring inertial navigation system and accelerometers for 3-D wind and gust components
    2. a fast-response temperature probe (modified at UW from original design by Friehe et al.)
    3. a LICOR 6262 infrared spectrometer for fast-response measurement of water vapor and carbon dioxide concentrations.
    Other measurements include up- and down-welling total and infrared radiation, as well as all the other "standard" dynamic and thermodynamic atmospheric variables.


    Places and Times of Measurement:
    The King Air was flown over both the northern and southern study areas of BOREAS in each of the three intensive field campaigns of 1994, logging 90 hours of research flight time during 29 flights (47 specific missions). Nearly all the flights were in the period 0900-1400 local time. Missions using the majority of King Air flight time were:

    1. horizontal passes at various heights along a 120-km transect across the southern study area
    2. single-level passes on multiple, parallel lines above 32x32 km areas in both study areas
    3. low-level transects between the two study areas
    4. wing-to-wing intercomparison runs with other flux aircraft


    Known Problems and Caveats:
    The spectra for carbon dioxide concentration show lower SNR values than those for vertical velocity, temperature, and water vapor, with correspondingly greater scatter in the carbon dioxide fluxes. The radiation measurements are probably not appropriate for estimates of net radiation.

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    Last Updated: October 20, 1997