Overview

Measurements of surface sensible heat flux, momentum flux, wind components, and virtual temperature.

Data Details

• X (column 1) is a component of wind cm/s plus toward north.
• Y (column 2) is a component of wind cm/s plus toward east.
• Z (column 3) is a component of wind cm/s plus up.
• T (column 4) is sonic virtual temperature in degrees C*100.
• hh:mm:ss is data collection time in UTC.

Data Quality

The Argonne National Laboratory sonic anemometer measurements are visually inspected weekly for data outliers or instrument problems. The final dataset sent to the DAP will have all outliers or problematic data removed using automated and visual processes, including minimum/maximum checks, in a similar process used for Atmospheric Radiation Measurement (ARM) program eddy correlation (ECOR) data.

Uncertainty

The uncertainties of the basic sonic anemometer measurements are taken to be the accuracy of the individual measurements as specified by the instrument manufacturer. Based on historical experience with this measurement technique, flux measurement uncertainty is +/- 10 percent, although the uncertainty can be much greater during stable atmospheric conditions when turbulence intensity and atmospheric gradients are small and advection from beyond the normal fetch can occur. In particular, the Physics Site-12 tower's sonic anemometer measurements can have greater uncertainty when the wind blows through the tower structure.

Constraints

During stable atmospheric conditions, turbulence intensity and atmospheric gradients often are small, approaching or exceeding the measurement resolution of sonic anemometers. Under these conditions, advection from beyond the normal fetch also can occur, making interpretation of the fluxes difficult. Notably, the Physics Site-12 tower sonic anemometer measurements can be affected when the wind blows through the tower structure. Some unusual biases in the vertical velocities measured at the Physics Site-12 tower with west wind conditions also have not been adequately explained.