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Atmospheric Measurement Techniques An interactive open-access journal of the European Geosciences Union

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https://doi.org/10.5194/amt-2017-454
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.
Research article
01 Feb 2018
Review status
This discussion paper is a preprint. It is a manuscript under review for the journal Atmospheric Measurement Techniques (AMT).
The Polar 5 airborne measurement of turbulence and methane fluxes during the AirMeth campaigns
Jörg Hartmann1, Martin Gehrmann1, Torsten Sachs2, Katrin Kohnert2, and Stefan Metzger3,4 1Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research, Bremerhaven, Germany
2GFZ German Research Centre for Geosciences, Telegrafenberg, 14473 Potsdam, Germany
3National Ecological Observatory Network, Battelle, 1685 38th Street, Boulder, CO 80301, USA
4University of Wisconsin-Madison, Dept. of Atmospheric and Oceanic Sciences, 1225 West Dayton Street, Madison, WI 53706, USA
Abstract. Low level flights over tundra wetlands in Alaska and Canada have been conducted during the AirMeth campaigns to measure turbulent methane fluxes into the atmosphere. In this paper we describe the instrumentation and new calibration procedures for the essential pressure parameters required for turbulence sensing by an aircraft that exploit suitable regular measurement flight legs without the need for dedicated calibration patterns. We estimate the accuracy of the mean wind and the turbulence measurements. We show that airborne measurements of turbulent fluxes of methane and carbon dioxide using cavity ring down spectroscopy trace gas analysers together with established turbulence equipment achieves a relative accuracy similar to that of measurements of sensible heat flux if applied during low level flights over natural area sources. The inertial subrange of the trace gas fluctuations cannot be resolved due to insufficient high frequency precision of the analyser but since this scatter is uncorrelated with the vertical wind velocity, the covariance and thus the flux is reproduced correctly. In the covariance spectra the −7/3 drop-off in the inertial subrange can be reproduced if sufficient data are available for averaging. For convective conditions and flight legs of several tens of kilometers we estimate the flux detection limit to about 4 mg/m2/d for w'CH4', 1.4 g/m2/d for w'CO2', and 4.2 W/m2/s for the sensible heat flux.
Citation: Hartmann, J., Gehrmann, M., Sachs, T., Kohnert, K., and Metzger, S.: The Polar 5 airborne measurement of turbulence and methane fluxes during the AirMeth campaigns, Atmos. Meas. Tech. Discuss., https://doi.org/10.5194/amt-2017-454, in review, 2018.
Jörg Hartmann et al.
Jörg Hartmann et al.
Jörg Hartmann et al.

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