scholarly journals Analysis of the PKT correction for direct CO<sub>2</sub> flux measurements over the ocean

2013 ◽  
Vol 13 (10) ◽  
pp. 28279-28308 ◽  
Author(s):  
S. Landwehr ◽  
S. D. Miller ◽  
M. J. Smith ◽  
E. S. Saltzman ◽  
B. Ward
Keyword(s):  
Heat Flux ◽  
Water Vapour ◽  
Latent Heat ◽  
Latent Heat Flux ◽  
Co2 Flux ◽  
Density Fluctuations ◽  
Sensor Data ◽  
Co2 Fluxes ◽  
Open Path ◽  
Order Of Magnitude

Abstract. Eddy covariance measurements of air–sea CO2 fluxes can be affected by cross-sensitivities of the CO2 measurement to water vapour, resulting in order-of-magnitude biases. Well established causes for these biases are (i) cross-sensitivity of the broadband non-dispersive infrared sensors due to band-broadening and spectral overlap (commercial sensors typically correct for this) and (ii) the effect of air density fluctuations (removed by determining the CO2 mixing ratio respective to dry air). However, another bias related to water vapour fluctuations has recently been observed with open-path sensors, and was attributed to sea salt build-up and water films on sensor optics. Two very different approaches have been used to deal with these water vapour-related biases. Miller et al. (2010) employed a membrane drier to physically eliminate 97% of the water vapour fluctuations in the sample air before it enters the gas analyser. Prytherch et al. (2010a) on the other hand, employed the empirical (Peter K. Taylor, PKT) post-processing correction to correct open-path sensor data. In this paper, we test these methods side by side using data from the Surface Ocean Aerosol Production (SOAP) experiment in the Southern Ocean. The air–sea CO2 flux was directly measured with four closed-path analysers, two of which were positioned down-stream of a membrane dryer. The CO2 fluxes from the two dried gas analysers matched each other and were in general agreement with common parametrisations. The flux estimates from the un-dried sensors agreed with the dried sensors only during periods with low latent heat flux (&amp;leq; 7 W m−2). When latent heat flux was higher, CO2 flux estimates from the un-dried sensors exhibited large scatter and an order-of magnitude bias. We applied the PKT correction to the flux data from the un-dried analysers and found that it did not remove the bias when compared to the data from the dried gas analyser. Our detailed analysis of the correction algorithm reveals that this method is not valid for the correction of CO2 fluxes.

scholarly journals Analysis of the PKT correction for direct CO<sub>2</sub> flux measurements over the ocean

2014 ◽  
Vol 14 (7) ◽  
pp. 3361-3372 ◽  
Author(s):  
S. Landwehr ◽  
S. D. Miller ◽  
M. J. Smith ◽  
E. S. Saltzman ◽  
B. Ward
Keyword(s):  
Heat Flux ◽  
Water Vapour ◽  
Latent Heat ◽  
Latent Heat Flux ◽  
Co2 Flux ◽  
Sensor Data ◽  
Closed Path ◽  
Co2 Fluxes ◽  
Open Path ◽  
Order Of Magnitude

Abstract. Eddy covariance measurements of air–sea CO2 fluxes can be affected by cross-sensitivities of the CO2 measurement to water vapour, resulting in order-of-magnitude biases. Well-established causes for these biases are (i) cross-sensitivity of the broadband non-dispersive infrared sensors due to band-broadening and spectral overlap (commercial sensors typically correct for this) and (ii) the effect of air density fluctuations (removed by determining the dry air CO2 mixing ratio). Another bias related to water vapour fluctuations has recently been observed with open-path sensors, attributed to sea salt build-up and water films on sensor optics. Two very different approaches have been used to deal with these water vapour-related biases. Miller et al. (2010) employed a membrane drier to physically eliminate 97% of the water vapour fluctuations in the sample air before it entered a closed-path gas analyser. Prytherch et al. (2010a) employed the empirical (Peter K. Taylor, PKT) post-processing correction to correct open-path sensor data. In this paper, we test these methods side by side using data from the Surface Ocean Aerosol Production (SOAP) experiment in the Southern Ocean. The air–sea CO2 flux was directly measured with four closed-path analysers, two of which were positioned down-stream of a membrane dryer. The CO2 fluxes from the two dried gas analysers matched each other and were in general agreement with common parameterisations. The flux estimates from the un-dried sensors agreed with the dried sensors only during periods with low latent heat flux (&amp;leq;7 W m−2). When latent heat flux was higher, CO2 flux estimates from the un-dried sensors exhibited large scatter and an order-of-magnitude bias. Applying the PKT correction to the flux data from the un-dried analysers did not remove the bias when compared to the data from the dried gas analyser. The results of this study demonstrate the validity of measuring CO2 fluxes using a pre-dried air stream and show that the PKT correction is not valid for the correction of CO2 fluxes.

scholarly journals Measuring turbulent CO<sub>2</sub> fluxes with a closed-path gas analyzer in a marine environment

2018 ◽  
Vol 11 (9) ◽  
pp. 5335-5350 ◽  
Author(s):  
Martti Honkanen ◽  
Juha-Pekka Tuovinen ◽  
Tuomas Laurila ◽  
Timo Mäkelä ◽  
Juha Hatakka ◽  
...  
Keyword(s):  
Heat Flux ◽  
Water Vapor ◽  
Latent Heat ◽  
Latent Heat Flux ◽  
Flux Measurement ◽  
Sea Spray ◽  
Closed Path ◽  
Co2 Fluxes ◽  
Gas Analyzer ◽  
Virtual Impactor

Abstract. In this study, we introduce new observations of sea–air fluxes of carbon dioxide using the eddy covariance method. The measurements took place at the Utö Atmospheric and Marine Research Station on the island of Utö in the Baltic Sea in July–October 2017. The flux measurement system is based on a closed-path infrared gas analyzer (LI-7000, LI-COR) requiring only occasional maintenance, making the station capable of continuous monitoring. However, such infrared gas analyzers are prone to significant water vapor interference in a marine environment, where CO2 fluxes are small. Two LI-7000 analyzers were run in parallel to test the effect of a sample air drier which dampens water vapor fluctuations and a virtual impactor, included to remove liquid sea spray, both of which were attached to the sample air tubing of one of the analyzers. The systems showed closely similar (R2=0.99) sea–air CO2 fluxes when the latent heat flux was low, which proved that neither the drier nor the virtual impactor perturbed the CO2 flux measurement. However, the undried measurement had a positive bias that increased with increasing latent heat flux, suggesting water vapor interference. For both systems, cospectral densities between vertical wind speed and CO2 molar fraction were distributed within the expected frequency range, with a moderate attenuation of high-frequency fluctuations. While the setup equipped with a drier and a virtual impactor generated a slightly higher flux loss, we opt for this alternative for its reduced water vapor cross-sensitivity and better protection against sea spray. The integral turbulence characteristics were found to agree with the universal stability dependence observed over land. Nonstationary conditions caused unphysical results, which resulted in a high percentage (65 %) of discarded measurements. After removing the nonstationary cases, the direction of the sea–air CO2 fluxes was in good accordance with independently measured CO2 partial pressure difference between the sea and the atmosphere. Atmospheric CO2 concentration changes larger than 2 ppm during a 30 min averaging period were found to be associated with the nonstationarity of CO2 fluxes.

scholarly journals Latent heat flux measurements over complex terrain by airborne water vapour and wind lidars

2011 ◽  
Vol 137 (S1) ◽  
pp. 190-203 ◽  
Author(s):  
Christoph Kiemle ◽  
Martin Wirth ◽  
Andreas Fix ◽  
Stephan Rahm ◽  
Ulrich Corsmeier ◽  
...  
Keyword(s):  
Heat Flux ◽  
Water Vapour ◽  
Latent Heat ◽  
Latent Heat Flux ◽  
Complex Terrain ◽  
Flux Measurements

scholarly journals Measuring turbulent CO<sub>2</sub> fluxes with a closed-path gas analyzer in marine environment

2018 ◽  
Author(s):  
Martti Honkanen ◽  
Juha-Pekka Tuovinen ◽  
Tuomas Laurila ◽  
Timo Mäkelä ◽  
Juha Hatakka ◽  
...  
Keyword(s):  
Heat Flux ◽  
Water Vapor ◽  
Latent Heat ◽  
Latent Heat Flux ◽  
Flux Measurement ◽  
Sea Spray ◽  
Closed Path ◽  
Co2 Fluxes ◽  
Gas Analyzer ◽  
Virtual Impactor

Abstract. Sea-air fluxes of carbon dioxide (CO2) were measured using the eddy covariance method at a new station established on the Utö Island in the Baltic Sea. The flux measurement system is based on a closed-path infrared gas analyzer (LI-7000, LI-COR) requiring only occasional maintenance, so the station is capable of continuous monitoring. However, such infrared gas analyzers are prone to significant water vapor interference in a marine environment, where CO2 fluxes are small. In July–October 2017, two LI-7000 analyzers were run in parallel to test the effect of a sample air drier which dampens water vapor fluctuations, and a virtual impactor, included to remove liquid sea spray, both of which were attached to the sample air tubing of one of the analyzers. The systems showed closely similar (R2 = 0.99) sea-air CO2 fluxes when the latent heat flux was low, which proved that neither the drier nor the virtual impactor perturbed the CO2 flux measurement. However, the undried measurement had a positive bias that increased with increasing latent heat flux, suggesting water vapor interference. For both systems, cospectral densities between vertical wind speed and CO2 were distributed within the expected frequency range, with a moderate attenuation of high frequency fluctuations. While the setup equipped with a drier and a virtual impactor generated a slightly higher flux loss, we opt for this alternative for its reduced water vapor cross-sensitivity and better protection against sea spray. The integral turbulence characteristics were found to agree with the universal stability dependence observed over land. Non-stationary flow conditions caused unphysical results, which resulted in a high percentage (up to 63 %) of discarded measurements. After removing the non-stationary cases, the direction of the sea-air CO2 fluxes was in good accordance with the measured CO2 partial pressure difference between the sea and the atmosphere. Atmospheric CO2 concentration changes larger than 2 ppm during a 30 min averaging period were found to be associated with the non-stationarity of CO2 fluxes. The Utö Atmospheric and Marine Research Station continues to monitor the regional CO2 exchange between the sea and the atmosphere, utilizing the results of this work.

Sensible and latent heat flux in the tropical Pacific from satellite multi-sensor data

2004 ◽  
Vol 90 (2) ◽  
pp. 166-177 ◽  
Author(s):  
Young-Heon Jo ◽  
Xiao-Hai Yan ◽  
Jiayi Pan ◽  
W.Timothy Liu ◽  
Ming-Xia He
Keyword(s):  
Heat Flux ◽  
Latent Heat ◽  
Latent Heat Flux ◽  
Tropical Pacific ◽  
Sensor Data ◽  
The Tropical Pacific

scholarly journals Diurnal cycle of short-term fluctuations of integrated water vapour above Switzerland

2019 ◽  
Vol 19 (19) ◽  
pp. 12083-12090
Author(s):  
Klemens Hocke ◽  
Leonie Bernet ◽  
Jonas Hagen ◽  
Axel Murk ◽  
Matthias Renker ◽  
...  
Keyword(s):  
Heat Flux ◽  
Standard Deviation ◽  
Water Vapour ◽  
Latent Heat ◽  
Latent Heat Flux ◽  
Diurnal Cycle ◽  
Short Term ◽  
Filtering Method ◽  
Integrated Water Vapour ◽  
Band Pass

Abstract. The TROpospheric WAter RAdiometer (TROWARA) continuously measures integrated water vapour (IWV) with a time resolution of 6 s at Bern in Switzerland. During summer, we often see that IWV has temporal fluctuations during daytime, while the nighttime data are without fluctuations. The data analysis is focused on the year 2010, where TROWARA has a good data quality without data gaps. We derive the spectrum of the IWV fluctuations in the period range from about 1 to 100 min. The FFT spectrum with a window size of 3 months leads to a serious underestimation of the spectral amplitudes of the fluctuations. Thus, we apply a band pass filtering method to derive the amplitudes as a function of period Tp. The amplitudes are proportional to Tp0.5. Another method is the calculation of the moving standard deviation with time window lengths from about 1 to 100 min. Here, we get similar results to those with the band pass filtering method. At all periods, the IWV fluctuations are strongest during summer, while they are smallest during winter. We derive the diurnal variation of the short-term IWV fluctuations by applying a moving standard deviation with a window length of 10 min. The daily cycle is strongest during the summer season, with standard deviations up to 0.22 mm at about 14:00 CET. The diurnal cycle disappears during wintertime. A similar seasonal behaviour is observed in the diurnal cycle of latent heat flux as provided by the Modern-Era Retrospective Analysis for Research and Applications, version 2 (MERRA-2 reanalysis) at Bern. Further, the 3 d averages of the latent heat flux and the magnitude of the short-term IWV variability show a strong correlation at Bern in 2010 (r=0.82 with a 95 % confidence interval from 0.75 to 0.87). Thus, we suggest that the diurnal cycle of short-term IWV fluctuations at Bern is mainly caused by large convective heating during daytime in summer.

scholarly journals Seasonal and Diurnal Fluxes of Radiation, Heat, Water Vapor, and Carbon Dioxide over a Suburban Area

2004 ◽  
Vol 43 (11) ◽  
pp. 1700-1710 ◽  
Author(s):  
R. Moriwaki ◽  
M. Kanda
Keyword(s):  
Carbon Dioxide ◽  
Heat Flux ◽  
Latent Heat ◽  
Latent Heat Flux ◽  
Deciduous Forest ◽  
Co2 Flux ◽  
Field Measurements ◽  
Bare Soil ◽  
Wave Radiation ◽  
Temperate Deciduous Forest

Abstract Based on 1 yr of field measurements, the diurnal, seasonal, and annual fluxes of energy and carbon dioxide (CO2) at a residential area of Tokyo, Japan, are described. The major findings are as follows. 1) The storage heat flux G in the daytime had little seasonal variation, irrespective of significant seasonal change of net all-wave radiation Rn. 2) The latent heat flux in the summer daytime was large despite the small areal fraction of natural coverage (trees and bare soil). The estimated local latent heat flux per unit natural coverage was 2 times the available energy (Rn − G), which indicates that the “oasis effect” was significant. 3) The CO2 flux was always upward throughout the year and the magnitude was larger in winter, mainly because of an increase of fossil fuel consumption. The annual total CO2 flux was 6 times the downward CO2 flux at a typical temperate deciduous forest.

scholarly journals Wavelet maxima curves of surface latent heat flux associated with two recent Greek earthquakes

2004 ◽  
Vol 4 (3) ◽  
pp. 359-374 ◽  
Author(s):  
G. Cervone ◽  
M. Kafatos ◽  
D. Napoletani ◽  
R. P. Singh
Keyword(s):  
Remote Sensing ◽  
Heat Flux ◽  
Latent Heat ◽  
Latent Heat Flux ◽  
Sensor Data ◽  
Data Mining Technique ◽  
One Dimensional ◽  
Mining Technique ◽  
Surface Latent Heat Flux ◽  
Wavelet Transformations

Abstract. Multi sensor data available through remote sensing satellites provide information about changes in the state of the oceans, land and atmosphere. Recent studies have shown anomalous changes in oceans, land, atmospheric and ionospheric parameters prior to earthquakes events. This paper introduces an innovative data mining technique to identify precursory signals associated with earthquakes. The proposed methodology is a multi strategy approach which employs one dimensional wavelet transformations to identify singularities in the data, and an analysis of the continuity of the wavelet maxima in time and space to identify the singularities associated with earthquakes. The proposed methodology has been employed using Surface Latent Heat Flux (SLHF) data to study the earthquakes which occurred on 14 August 2003 and on 1 March 2004 in Greece. A single prominent SLHF anomaly has been found about two weeks prior to each of the earthquakes.

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