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M. J. Heikinheimo
,
G. W. Thurtell
, and
G. E. Kidd

Abstract

A fast response C02 and water vapor (H2O) analyzer was developed in this study for the measurement of atmospheric turbulence fluctuations and, in conjunction with a fast response anemometer, transport of these entities. High speed and high resolution detection of C02 and H2O was accomplished simultaneously for the same air sample with open path IR absorption techniques. The miniature size sensor features a once folded 12.5 cm pathlength. The sensor structure and sampling technique provided direct compensation for undesirable factors (e.g., dust) affecting transmission of IR-radiation in the optical path and for the changes in source intensity and detector response due to sensor temperature fluctuations.

The rms-noise level of the C02 and H2O outputs corresponded to 0.3 ppm and 0.02 g m−2 fluctuations respectively, when absorbing gases were removed from the path. Spectral analysis showed that the noise was well below the signal level for both gases within the frequency range from 0.002 to 5 Hz. In comparison with the commercially available Lyman-α hygrometer the H2O output noise level of the IR-sensor was a factor of two larger, but the simultaneously measured signal spectra and also the latent heat flux values obtained with the two sensors in the field were practically identical. The IR-sensor produced C02 flux values that were comparable to those reported in the literature.

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E. Raschke
,
J. Meywerk
,
K. Warrach
,
U. Andrea
,
S. Bergström
,
F. Beyrich
,
F. Bosveld
,
K. Bumke
,
C. Fortelius
,
L. P. Graham
,
S.-E. Gryning
,
S. Halldin
,
L. Hasse
,
M. Heikinheimo
,
H.-J. Isemer
,
D. Jacob
,
I. Jauja
,
K.-G. Karlsson
,
S. Keevallik
,
J. Koistinen
,
A. van Lammeren
,
U. Lass
,
J. Launianen
,
A. Lehmann
,
B. Liljebladh
,
M. Lobmeyr
,
W. Matthäus
,
T. Mengelkamp
,
D. B. Michelson
,
J. Napiórkowski
,
A. Omstedt
,
J. Piechura
,
B. Rockel
,
F. Rubel
,
E. Ruprecht
,
A.-S. Smedman
, and
A. Stigebrandt

The Baltic Sea Experiment (BALTEX) is one of the five continental-scale experiments of the Global Energy and Water Cycle Experiment (GEWEX). More than 50 research groups from 14 European countries are participating in this project to measure and model the energy and water cycle over the large drainage basin of the Baltic Sea in northern Europe. BALTEX aims to provide a better understanding of the processes of the climate system and to improve and to validate the water cycle in regional numerical models for weather forecasting and climate studies. A major effort is undertaken to couple interactively the atmosphere with the vegetated continental surfaces and the Baltic Sea including its sea ice. The intensive observational and modeling phase BRIDGE, which is a contribution to the Coordinated Enhanced Observing Period of GEWEX, will provide enhanced datasets for the period October 1999–February 2002 to validate numerical models and satellite products. Major achievements have been obtained in an improved understanding of related exchange processes. For the first time an interactive atmosphere–ocean–land surface model for the Baltic Sea was tested. This paper reports on major activities and some results.

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