The BOREAS Information System
P.I.(s): Donald H. Lenschow -- National Center for Atmospheric Research (NCAR); Robert D. Kelly -- University of Wyoming
Co-I(s):Steven Oncley, Ken Davis, Qing Wang, Jakob Mann, Andi Gietz, Gerhard Erhard, Christoff Kiemle, Al Cooper -- University of Wyoming
Objectives: (Same as AFM-2). To characterize the fluxes of momentum, sensible and latent heat and carbon dioxide over the boreal forest, using the Wyoming King Air (AFM-2) (FK) and NCAR Electra (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.
The NCAR Electra
Objectives:
The Electra aircraft was used to measure the fluxes of momentum, sensible and latent heat, carbon dioxide, and ozone over the entire BOREAS region to tie together measurements made in both the Southern and Northern Study Areas. It also was used to study the planetary boundary layer using both in situ and remote-sensing measurements.
Type of Data/Instrumentation:
In situ measurements of turbulent fluctuations of the three-component wind velocity, temperature, humidity, carbon dioxide and ozone were made by sensors onboard the Electra. Also measured were aerosol and cloud droplet size distributions, radiation (upward and downward-going broadband shortwave (visible), infrared, and infrared temperatures), and surface radiation at 650 and 862 nm (to calculate the Normalized Difference Vegetation Index (NDVI). Video imagery from the Electra also is available.
A water vapor Differential Absorption Infrared Lidar (DIAL) system was deployed by the Deutsche Forschungsanstalt fur Luftund Raumfahrt (DLR). This system looked downward and measured the aerosol backscatter and will be processed to produce profiles of water vapor through the boundary layer.
A special air sampler was used for the first time to measure fluxes of water and carbon dioxide, and also collected samples for analysis of turpenes.
Places and Times of Measurement:
The Electra usually flew along some portion of the "transect" between Saskatoon, Saskatchewan and a point north of Churchill, Manitoba. Most flight legs were at an altitude of 100 m above ground, however some legs were flown higher in and above the planetary boundary layer.
The Electra flew 25 missions during the three 1994 IFCs. Each flight was about 7 hours in duration and approximately centered around local noon.
Known Problems and Caveats:
There were several instrument malfunctions during this program, however most can be worked around by use of data from redundant sensors. The LiCor CO2 calibration is still somewhat uncertain, though we are using the best that is currently available.
We have seen at times significant differences (factors of 2) between most second-order statistics calculated from data collected during wing-to-wing intercomparison flights with the University of Wyoming King-Air. We are attempting to resolve these differences.
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Last Updated: October 20, 1997