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 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.

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.

Scanning 10-W Water Vapor DIAL for the Investigation of Atmospheric Turbulence and Land-Atmosphere Feedback

2021 ◽  
Author(s):  
Andreas Behrendt ◽  
Florian Spaeth ◽  
Volker Wulfmeyer
Keyword(s):  
Heat Flux ◽  
Water Vapor ◽  
Latent Heat ◽  
Atmospheric Turbulence ◽  
Latent Heat Flux ◽  
Climate Models ◽  
Weather Forecast ◽  
Surface Characteristics ◽  
Scanning System ◽  
Forecast Models

&lt;p&gt;We will present recent measurements made with the water vapor differential absorption lidar (DIAL) of University of Hohenheim (UHOH). This scanning system has been developed in recent years for the investigation of atmospheric turbulence and land-atmosphere feedback processes.&lt;/p&gt;&lt;p&gt;The lidar is housed in a mobile trailer and participated in recent years in a number of national and international field campaigns. We will present examples of vertical pointing and scanning measurements, especially close to the canopy. The water vapor gradients in the surface layer are related to the latent heat flux. Thus, with such low-elevation scans, the latent heat flux distribution over different surface characteristics can be monitored, which is important to verify and improve both numerical weather forecast models and climate models.&lt;/p&gt;&lt;p&gt;The transmitter of the UHOH DIAL consists of a diode-pumped Nd:YAG laser which pumps a Ti:sapphire laser. The output power of this laser is up to 10 W. Two injection seeders are used to switch pulse-to-pulse between the online and offline signals. These signals are then either directly sent into the atmosphere or coupled into a fiber and guided to a transmitting telescope which is attached to the scanner unit. The receiving telescope has a primary mirror with a dimeter of 80 cm. The backscatter signals are recorded shot to shot and are typically averaged over 0.1 to 1 s.&lt;/p&gt;

scholarly journals Latent Heat Flux Profiles from Collocated Airborne Water Vapor and Wind Lidars during IHOP_2002

2007 ◽  
Vol 24 (4) ◽  
pp. 627-639 ◽  
Author(s):  
C. Kiemle ◽  
G. Ehret ◽  
A. Fix ◽  
M. Wirth ◽  
G. Poberaj ◽  
...  
Keyword(s):  
Heat Flux ◽  
Water Vapor ◽  
Latent Heat ◽  
Latent Heat Flux ◽  
Deep Convection ◽  
Minor Role ◽  
Flux Divergence ◽  
Convective Boundary ◽  
Budget Analysis ◽  
Wind Lidar

Abstract Latent heat flux profiles in the convective boundary layer (CBL) are obtained for the first time with the combination of the Deutsches Zentrum für Luft- und Raumfahrt (DLR) water vapor differential absorption lidar (DIAL) and the NOAA high resolution Doppler wind lidar (HRDL). Both instruments were integrated nadir viewing on board the DLR Falcon research aircraft during the International H2O Project (IHOP_2002) over the U.S. Southern Great Plains. Flux profiles from 300 to 2500 m AGL are computed from high spatial resolution (150 m horizontal and vertical) two-dimensional water vapor and vertical velocity lidar cross sections using the eddy covariance technique. Three flight segments on 7 June 2002 between 1000 and 1300 LT over western Oklahoma and southwestern Kansas are analyzed. On two segments with strong convection, the latent heat flux peaks at (700 ± 200) W m−2 in the entrainment zone and decreases linearly to (200 ± 100) W m−2 in the lower CBL. A water vapor budget analysis reveals that this flux divergence [(0.9 ± 0.4) g kg−1 h−1] plus the advection (0.3 g kg−1 h−1) are nearly balanced by substantial CBL drying [(1.5 ± 0.2) g kg−1 h−1] observed by airborne and surface in situ instruments, within the limits of the overall budget rms error of 0.5 g kg−1 h−1. Entrainment of dry air from aloft and net upward humidity transport caused the CBL drying and finally inhibited the initiation of deep convection. All cospectra show significant contributions to the flux between 1- and 10-km wavelength, with peaks between 2 and 6 km, originating from large eddies. The main flux uncertainty is due to low sampling (55% rmse at mid-CBL), while instrument noise (15%) and systematic errors (7%) play a minor role. The combination of a water vapor and a wind lidar on an aircraft appears as an attractive new tool that allows measuring latent heat flux profiles from a single overflight of the investigated area.

Numerical simulation study of sea spray’s effect on tropical cyclone——a case study of typhoon “Megi”

2021 ◽  
Author(s):  
Jialin Zhang ◽  
Wenqing Zhang ◽  
Haofeng Xia ◽  
Changlong Guan
Keyword(s):  
Numerical Simulation ◽  
Heat Flux ◽  
Tropical Cyclone ◽  
Latent Heat ◽  
Latent Heat Flux ◽  
Momentum Flux ◽  
Sensible Heat Flux ◽  
Sea Spray ◽  
Sensible Heat ◽  
Thermodynamic Effects

&lt;p&gt;Sea spray has important influence on the evolution of tropical cyclone. The influence of sea spray in the numerical simulation and prediction of tropical cyclones is not ignorable. In order to explore the kinetic and thermodynamic effects of sea spray on tropical cyclone, the drag coefficient C&lt;sub&gt;D &lt;/sub&gt;and the enthalpy transfer coefficient C&lt;sub&gt;K&lt;/sub&gt; with sea spray&amp;#8217;s effects were included in the coupled ocean-atmosphere-wave-sediment transport modeling system (COAWST). The numerical results show that, the effect of sea spray can effectively improve the simulation results of tropical cyclone path. When only the kinetic effect of sea spray is considered, the momentum flux at the surface of sea is little affected, and the upward sensible heat flux and latent heat flux are slightly increased. When kinetic and thermodynamic effects of sea spray is considered at the same time, the momentum flux is slightly increased, the upward sensible heat flux is increased, and the latent heat flux is significantly increased, the intensity of tropical cyclone is significantly enhanced, mainly due to the thermodynamic effect . Considering the kinetic and thermodynamic effects of sea spray at the same time is more effective than considering the kinetic effects of sea spray in improving the intensity simulation of tropical cyclone.&lt;/p&gt;

Land-Atmosphere Interactions

Geography ◽  
2020 ◽  
Author(s):  
Geoffrey M. Henebry ◽  
Nathan J. Moore ◽  
Jiquan Chen
Keyword(s):  
Heat Flux ◽  
Water Vapor ◽  
Solar Radiation ◽  
Latent Heat ◽  
Latent Heat Flux ◽  
Land Surface ◽  
Longwave Radiation ◽  
Coupled Processes ◽  
Shortwave Radiation ◽  
Ground Heat Flux

Land-atmosphere interactions encompass a multitude of processes that link the land surface with the atmospheric boundary layer. Interactions are bidirectional, include energy and material exchanges, and can include feedbacks that can amplify or attenuate coupled processes. Shortwave radiation drives most of the biogeophysical processes at the land surface. Photosynthetically active radiation (PAR) is the subset of shortwave radiation (400–700 nanometers) and is critical for most life on the planet. Thermal infrared is the more energetic subset of terrestrial radiation that results primarily from interactions of solar radiation with the land surface. Microwaves are an important subset of terrestrial radiation that facilitate monitoring both atmosphere and land surface. Net radiation is the energy left over after accounting for incoming direct and indirect solar radiation less outgoing solar radiation reflected by the surface, plus incoming longwave radiation (from water vapor and other gases in the atmosphere and terrestrial materials within view of the surface), less outgoing longwave radiation from the land surface. This radiation remaining at an “ideal surface” can be simply partitioned into energy transferred into the surface (ground heat flux) plus energy transferred to heat the atmosphere above the surface (sensible heat flux) plus energy transferred via evapotranspiration (latent heat flux) to moisten the atmosphere. Additionally, objects on the surface can absorb radiation and later radiate this stored heat. Photosynthesis uses only a small portion of incident energy. Precipitation on the surface may (1) return to the atmosphere as water vapor (latent heat flux), (2) move as liquid laterally to another surface point (runoff), (3) move as liquid below the surface (drainage), (4) be retained at or below the surface, including in the soil (storage), (5) be transported away, if frozen, from the surface by wind (advection), or combinations of these. Material exchanges between surface and atmosphere include mineral dust, organic particles, biota, and biological materials such as pollen, seeds, combustion products, volcanic ash and ejecta, trace gas emissions, and anthropogenic emissions from stationary and mobile sources. Interactions between the land surface and lower portion of the atmosphere at various time scales from seconds to centuries are influenced by the amount and type of incident sunlight, radiative characteristics of the materials at the surface, amount of moisture at and below the surface, vegetation amount and type, soils and substrate, vertical structures at the surface that affect wind, land cover type and arrangement, atmospheric constituents, and recent weather. Here we focus on interactions moving from land to the atmosphere.

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.

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